Influence of rheology and geometry on the teapot effect of a curtain coater - Döll, Harald; Gerlach, Daniel; Alleborn, Norbert; Delgado, Antonio (European Physical Journal - Special Topics, 2009)
The present study investigates the deflection of a liquid sheet forming at the die lip of a slide-fed curtain coater, known as 'teapot effect'. The influence of the shear-rate dependent viscosity, the geometry ofthe lip edge and the flow rate on the degree of deflection has been considered. © EDP Sciences and Springer 2009.
UnivIS-Import:2015-03-09:Pub.2009.tech.ITC.stmmec.influe_0

Influence of self-assembled monolayer dielectrics on the morphology and performance of α,ω-dihexylquaterthiophene in thin film transistors - Novak, Michael; Schmaltz, Thomas; Faber, Hendrik; Halik, Marcus (Applied Physics Letters, 2011)
Three different ultrathin hybrid dielectrics based on self-assembled monolayers (SAMs) from phosphonic acid molecules were investigated on aluminum oxide. The impact of the underlying SAMs on the semiconductor morphology and transistor device performance was studied by reducing the film thickness of the subsequently deposited extgreeka, extgreekw-dihexylquaterthiophene semiconductor to one monolayer and less. The nature of the SAM relates to the molecular orientation of submonolayer films, which is investigated by photoluminescence microscopy and atomic force microscopy. SAMs with high surface energy tend to induce a face-on growing of the semiconductor, whereas for SAMs with low surface energy an edge-on growth is favorable.
EAM Import::2019-03-14

Influence of steps on the adsorption and thermal evolution of SO2 on clean and oxygen precovered Pt surfaces - Streber, Regine; Papp, Christian; Lorenz, Michael Peter Andreas; Höfert, Oliver; Zhao, Wei; Wickert, Sandra; Darlatt, Erik; Bayer, Andreas; Denecke, Reinhard; Steinrück, Hans-Peter (Journal of Physical Chemistry C, 2010)
We investigated the adsorption and reaction of SO on clean and oxygen precovered, flat, and regularly stepped Pt surfaces, Pt(111), Pt(322), and Pt(355) by in situ high resolution X-ray photoelectron spectroscopy. Induced by the steps and/or the coadsorbed oxygen, several new SO species are observed, in addition to the two known SO species on Pt(111). On all investigated surfaces, a hit and stick mechanism is found for the adsorption, and no diffusion from terrace to step sites occurs at low temperatures. For the oxygen free stepped surfaces, a higher reactivity toward SO dissociation/disproportionation is found compared to Pt(111). On all three oxygen precovered Pt surfaces some SO is already formed directly upon SO exposure at low temperatures. Heating of this mixed O/SO layers first results in oxidation of more SO to SO, and at higher temperatures in subsequent oxidation of SO to SO, which finally decomposes above 450 K. The different reactions show a significant influence of the steps. © 2010 American Chemical Societ

Influence of substituents and functional groups on the surface composition of ionic liquids - Kolbeck, Claudia; Niedermaier, Inga; Deyko, Alexey; Lovelock, Kevin; Taccardi, Nicola; Wei, Wei; Wasserscheid, Peter; Maier, Florian; Steinrück, Hans-Peter (Chemistry - A European Journal, 2014)
We have performed a systematic study addressing the surface behavior of a variety of functionalized and non-functionalized ionic liquids (ILs). From angle-resolved X-ray photoelectron spectroscopy, detailed conclusions on the surface enrichment of the functional groups and the molecular orientation of the cations and anions is derived. The systems include imidazolium-based ILs methylated at the C2 position, a phenyl-functionalized IL, an alkoxysilane-functionalized IL, halo-functionalized ILs, thioether- functionalized ILs, and amine-functionalized ILs. The results are compared with the results for corresponding non-functionalized ILs where available. Generally, enrichment of the functional group at the surface is only observed for systems that have very weak interaction between the functional group and the ionic head groups. Scratching the surface: The surface behavior of various functionalized ionic liquids (ILs) is studied by angle-resolved X-ray photoelectron spectroscopy and conclusions on surface-enrichment effects and molecular orientation of cations and anions are derived (see figure; Im=imidazolium, Tf=trifluoromethanesulfonyl). Overall, surface enrichment is only observed for functional groups that interact weakly with the ionic head groups. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of surface tension and inner pressure on the process of fibre drawing - Luzi, Giovanni; Epple, Philipp; Scharrer, Michael; Fujimoto Meinecke, Ken; Rauh, Cornelia; Delgado, Antonio (Journal of Lightwave Technology, 2010)
The present contribution deals with thermofluidynamical features occurring during the drawing of capillaries for microstructured optical fibres. Here, the process stability depends strongly on flow and thermal processes taking place as a preform is heated and drawn in the furnace. This is the case particularly for hollow fibres for which the existence of the inner hole directly depends on material parameters such as the surface tension and the rheological properties and on process parameter such as hole internal pressure and the process temperature. A fluid-mechanics model suggested in the literature that makes use of asymptotic analysis based on small aspect ratio of the micro capillaries, has been revisited and improved recently and the leading-order equations have been then examined in some asymptotic limits by Luzi et al.. Starting from the novel class of solutions of the simplified equations of motion the present paper focuses on the effect of both surface tension and internal hole pressure since those are of essential importance during drawing. Thus, comparisons with experimental data are performed, in order to validate the analytical model developed in , which will be briefly presented here. The theoretical model gives very accurate predictions both when the internal hole is pressurized or when no pressure is applied, as long as the temperature does not reach too high values. © 2006 IEEE.
UnivIS-Import:2015-03-09:Pub.2010.tech.ITC.stmmec.influe
Keywords: Asymptotic analysis; Holey fibres; Micro structured optical fibres (MOFs); Numerical methods; Photonic crystal fibres

Influence of Tail Groups during Functionalization of ZnO Nanoparticles on Binding Enthalpies and Photoluminescence - Segets, Doris; Lin, Wei; Schmidt, Jochen; Peukert, Wolfgang; Mahler, Michael; Schindler, Torben; Unruh, Tobias; Meyer, Bernd (Langmuir, 2017)
We report on the tailoring of ZnO nanoparticle (NP) surfaces by catechol derivatives (CAT) with different functionalities: tert-butyl group (tertCAT), hydrogen (pyroCAT), aromatic ring (naphCAT), ester group (esterCAT), and nitro group (nitroCAT). The influence of electron-donating/-withdrawing properties on enthalpy of ligand binding (ΔH) was resolved and subsequently linked with optical properties. First, as confirmed by ultraviolet/visible (UV/vis) and Fourier transform infrared (FT-IR) spectroscopy results, all CAT molecules chemisorbed to ZnO NPs, independent of the distinct functionality. Interestingly, the ζ-potentials of ZnO after functionalization shifted to more negative values. Then, isothermal titration calorimetry (ITC) and a mass-based method were applied to resolve the heat release during ligand binding and the adsorption isotherm, respectively. However, both heat- and mass-based approaches alone did not fully resolve the binding enthalpy of each molecule adsorbing to the ZnO surface. This is mainly due to the fact that the Langmuir model oversimplifies the underlying adsorption mechanism, at least for some of the tested CAT molecules. Therefore, a new, fitting-free approach was developed to directly access the adsorption enthalpy per molecule during functionalization by dividing the heat release measured via ITC by the amount of bound molecules determined from the adsorption isotherm. Finally, the efficiency of quenching the visible emission caused by ligand binding was investigated by photoluminescence (PL) spectroscopy, which turned out to follow the same trend as the binding enthalpy. Thus, the functionality of ligand molecules governs the binding enthalpy to the particle surface, which in turn, at least in the current case of ZnO, is an important parameter for the quenching of visible emission. We believe that establishing such correlations is an important step toward a more general way of selecting and designing ligand molecules for surface functionalization. This allows developing strategies for tailored colloidal surfaces beyond empirically driven formulation on a case by case basi
Keywords: functionalization; nanoparticle; photoluminesence

Influence of the bridging atom on the performance of a low-bandgap bulk heterojunction solar cell - Scharber, Markus C.; Koppe, Markus; Gao, Jia; Cordella, Fabrizio; Loi, Maria A.; Denk, Patrick; Morana, Mauro; Egelhaaf, Hans-Joachim; Forberich, Karen; Dennler, Gilles; Gaudiana, Russ; Waller, Dave; et al. (Advanced Materials, 2010)
X=C or Si(Chemical equation presented)Replacing a carbon atom with silicon (see figure) on the main chain of a conjugated polythiophene gives a polysilole with higher crystallinity, improved charge transport, reduced bimolecular recombination, and reduced formation of charge-transfer complexes when blended with a fullerene derivative. Optimized bulk heterojunction solar cells using this blend give certified efficiencies of 5.2% under AMI.5 illumination. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

Influence of the counterion on the synthesis of ZnO mesocrystals under solvothermal conditions - Klupp Taylor, Robin; Distaso, Monica; Taccardi, Nicola; Wasserscheid, Peter; Peukert, Wolfgang (Chemistry - A European Journal, 2011)
Polymers and coordinating solvents have been shown to serve as templating agents to assist the precipitation of ZnO nanoparticles and address their morphology. In this work we show for the first time that a difference in the coordination strength between the polymer (poly-N-vinylpyrrolidone (PVP)) and the two Zn precursor salts (nitrate and acetate) is able to promote or suppress the formation of mesocrystalline structures and even more importantly to tune their three-dimensional organization. On the basis of FTIR and C NMR spectroscopic studies, we propose that not only the polymer (PVP) but also the solvent (DMF) play a key role as directing agents. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: NMR spectroscopy; optical properties; oriented attachment; poly-N-vinylpyrrolidone; ZnO mesocrystals

Influence of the exchange-correlation potential in methods based on time-dependent density-functional theory - Bleiziffer, Patrick; Heßelmann, Andreas; Umrigar, C. J.; Görling, Andreas (Physical Review A, 2013)
Time-dependent density-functional methods are used to compute excitation energies and, via the adiabatic-connection fluctuation-dissipation theorem, ground-state correlation energies of atoms, ions, and the H molecule at various bond lengths. Various exchange-correlation potentials v and exchange-correlation kernels f are tested. Accurate exchange-correlation potentials are found to be essential for getting accurate energies. Methods employing in the Kohn-Sham self-consistency process the exact local Kohn-Sham exchange potential while neglecting completely the correlation potential lead to better excitation and correlation energies than methods with exchange-correlation potentials within the local density approximation or the generalized gradient approximation. Taking into account the exact exchange-correlation potential and thus the exact Kohn-Sham potential further improves excitation and correlation energies. © 2013 American Physical Society.

Influence of the growth conditions of epitaxial graphene on the film topography and the electron transport properties - Weingart, S.; Bock, C.; Kunze, Ulrich; Emtsev, Konstantin; Seyller, Thomas; Ley, Lothar (Physica E-Low-Dimensional Systems & Nanostructures, 2010)
In this work we report on temperature-dependent magnetotransport measurements on epitaxial graphene grown on SiC(0 0 0 1) under different preparation conditions. We demonstrate that the temperature dependence of the charge carrier density and mobility is correlated to the annealing conditions during the graphitization process. As recently shown, SiC substrates annealed in an Ar atmosphere near atmospheric pressure exhibit continuous monolayer graphene films over 2 - 3 μ m wide and more than 50 μ m long terraces. For these films we determine a constant charge carrier density in the range from 1.4 K up to room temperature and an electron mobility exceeding 3000 cm (V s) at low temperatures. © 2009 Elsevier B.V. All rights reserved.
Keywords: Charge carrier density; Charge carrier mobility; Epitaxial graphene; Magnetotransport

Influence of the starting materials used in the crystal growth process of CZT for gamma ray radiation applications - Zheng, Qian; Crocco, Jerome; Bensalah, Hakima; Wellmann, Peter; Osvet, Andres; Künecke, Ulrike; Dierre, Fabrice; Vela, O.; Perez, J.M.; Dieguez, E. (Journal of Crystal Growth, 2013)
The influences of two different ways of crystal growth preparations by using different starting materials on the detector properties have been investigated. The characterization has been carried out in terms of structural, optical, and electrical properties of the materials grown with the vertical gradient freeze method. The distributions of Zn and In at different axial positions with different crystals have been compared by using the Induced Coupled Plasma-Mass Spectroscopy technique. The size and density of Te inclusions within the materials have been identified by Infrared Microscopy. The luminescence behaviors have been investigated by studying the defects levels. Particularly, the current-voltage characteristics and Gamma-ray Spectroscopy have been investigated by comparing the performance of detectors achieved from different axial directions of the ingots. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: Characterization; Defects; Gradient freeze technique; Semiconducting II-VI materials

Influence of upscaling accumulative roll bonding on the homogeneity and mechanical properties of AA1050A - Ruppert, Mathis; Böhm, Wolfgang; Nguyen, H.; Höppel, Heinz Werner; Merklein, Marion; Göken, Mathias (Journal of Materials Science, 2013)
Accumulative roll bonding (ARB), as a method for production of ultrafine grained materials, is frequently supposed to be easily transferable to established industrial production lines. In literature, however, common sheet dimensions used for ARB in a laboratory scale are between 20 and 100 mm in width. In order to quantify the potential of upscaling the ARB process to a technological relevant level, sheets of AA1050A with an initial sheet width of 100–450 mm were accumulative roll bonded up to 8 cycles. In this regard, three different rolling mills of distinct dimensions were used for processing of the sheet material. The influence of process parameters and the reproducibility of the process, in terms of mechanical properties and homogeneity of the sheets, were studied by means of mechanical and microstructural characterization. Both appear to be largely independent on the sheet size and the rolling mill utilized for production. Only small deviations after the first cycles could be detected, vanishing in subsequent cycles due to the features of microstructural evolution. The finally obtained results indicate a high potential for industrial application of ARB and illustrate the possibility to upscale the process to a level necessary for that purpose.
WW1::970

Influences on 3D image quality in a high-resolution X-ray laminography system - Ebensperger, T.; Rimbach, C.; Zabier, S.; Hanke, R. (Journal of Instrumentation, 2014)
Recently, we demonstrated that projective X-ray microscopy is feasible with a two-dimensional spatial resolution down to 100 nm by using laboratory nanofocus X-ray sources and a geometric magnification of up to 1000x. Based on these previous results, we developed a high-resolution X-ray laminography system which uses an optimized thin-film X-ray transmission target together with a modified electron probe micro analyzer. Unlike conventional axial computed tomography (CT), 3D laminography imaging involves a linear translation of both detector and object with respect to a stationary point source. In this contribution we present a detailed characterization of the setup concerning especially the laminographic imaging mode. The quality of the volume reconstruction is assessed by simulating an ideal setup with an analytical model including features down to 200 nm which are resolved in the setup given a high enough SNR in the projections. We further address the issue of a drop in the detector resolution under oblique X-ray illumination which is a common problem to such systems. The finite penetration depth of the X-rays into the detector pixels causes an anisotropic blurring of the detector point spread function (PSF) under oblique irradiation. We tested the influence of this blurring by calculating the illumination-dependent modulation transfer function (MTF) of the detector. Our measurements are supported by numerical simulations of the detector MTF. Both simulations and measurements show a drop in spatial resolution (20% of the MTF) from 12.5 lp/mm (irradiation perpendicular to the detector screen) down to 5.2 lp/mm (irradiation 30° oblique to the screen). Furthermore, first examples of 3D imaging of test structures and material imaging are given.
EAM Import::2019-03-13

Influencing Hardness and Wear During the Dynamic Tempered Microinjection Molding Process by Considering Isothermal Holding Time - Fischer, Christopher; Seefried, Andreas; Merle, Benoit; Göken, Mathias; Drummer, Dietmar (Polymer Engineering and Science, 2017)
For semicrystalline thermoplastic parts it is well known that increasing isothermal holding temperature can affect inner component properties, respectively, crystalline structure (e.g., morphology, degree of crystallization, crystal modification, etc.) and, therefore, resulting global component properties such as hardness and wear. Nevertheless, in literature there is no explicit focus on the effect of isothermal holding time during dynamically tempered injection molding process. In this article, semicrystalline microcomponents have been injection molded by varying isothermal holding time within the material's crystallization temperature area. As materials, POM-C, as a material with relatively high crystallization kinetic, and PA 12, as a material with medium crystallization kinetic, were used. To evaluate the effects on hardness and wear, nanoindentation measurements as well as pin-on-disc wear tests were performed. Results show that for fast crystallizing POM-C an isothermal holding step has no significant influence on inner component and resulting global component properties. For slower crystallizing PA 12, however, the morphology and the degree of crystallization could be influenced and, as a result, hardness could be increased by 21% while wear could be reduced by 30%.
UnivIS-Import:2017-07-10:Pub.2017.tech.FT.FT-KT.influe

Infrared Spectroscopy of a Wilkinson Catalyst in a Room-Temperature Ionic Liquid - Kiefer, Johannes; Obert, Katharina; Himmler, Simone; Schulz, Peter; Wasserscheid, Peter; Leipertz, Alfred (ChemPhysChem, 2008)
Homogeneous catalysis in room-temperature ionic liquids (ILs) constitutes a most interesting field of research with high potential in technical applications. As concerns the hydrogenation of unsaturated hydrocarbons, Wilkinson's compound RhCl(PPh_3)_3 represents a catalyst that provides high selectivity and activity. Herein, we demonstrate the application of infrared spectroscopy to the quantitative analysis of the Wilkinson catalyst in the IL 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]). Our study demonstrates for the first time the quantitative, accurate and reproducible determination of the concentration of a rhodium catalyst by means of IR spectroscopy and, moreover, allows the investigation of intermolecular interactions. Spectral features, located mainly in the fingerprint region of the IR spectrum, are identified revealing the influence of the dissolved catalyst on the IL's vibrational structure. In particular, the ring-bending mode of the imidazolium ring shows a frequency shift as a function of catalyst concentration, probably due to hydrogen-bond formation between the IL cation and the Rh complex. The results show the potential of IR spectroscopy both for application as a quick process control technology in catalytic processes and as a tool for better understanding of IL–catalyst interactions.
Keywords: IR spectrum Wilkinson catalyst ionic liq ethylmethylimidazolium acetate

Innovative Aluminium Lightweight Design by the Combination of Accumulative Roll Bonding and Local Intermediate Heat Treatment - Böhm, Wolfgang; Merklein, Marion; Lechner, Michael (Materials Today, 2015)
The intensifying regulations for CO2 emissions of passenger cars lead to increased efforts in the field of lightweight construction. In this context, the application of aluminium is a promising strategy. Another approach is the implementation of high strength materials to enable the reduction of the wall thickness of components and to ensure the crash performance. The manufacturing of multi-layered aluminium sheet metal with enhanced strength and nanocrystalline grain structure can be performed using the Accumulative Roll Bonding process (ARB). However, the formability of ARB processed aluminium is relatively poor. Therefore, within this paper an innovative approach to enhance the formability is presented. Key idea of the local short term intermediate heat treatment is the tailoring of the mechanical properties between two forming operations. In order to identify suitable process parameters for beneficial heat treatment, the interaction of pre-straining and heat treatment is evaluated.
EAM Import::2019-03-13

Innovative toxikologische Untersuchungsmethoden für Eisenoxidnanopartikel in der Nanomedizin - Janko, Christina; Pottler, Marina; Matuszak, Jasmin; Unterweger, Harald; Hornung, Annkathrin; Friedrich, Ralf P.; Alexiou, Christoph (Chemie Ingenieur Technik, 2017)
Superparamagnetische Eisenoxidnanopartikel (SPIONs) bieten vielfältige Anwendungsmöglichkeiten in der Medizin. Toxikologische Untersuchungen, die auf der physikochemischen Charakterisierung der Nanopartikel aufbauen, sind eine wesentliche Voraussetzung für die zukünftige Translation in die klinische Anwendung. Da Nanopartikel mit zahlreichen klassischen toxikologischen Nachweismethoden interferieren, sind Alternativmethoden notwendig. Multiparameterfärbungen für Durchflusszytometrie und Fluoreszenzmikroskopie, markierungsfreie Echtzeitanalysen, 3D-Zellkultur und Flussmodelle werden diskutiert.
EAM Import::2019-03-13

Insights in the Reaction Mechanistics: Isotopic Exchange During the Metalation of Deuterated Tetraphenyl-21,23D-porphyrin on Cu(111) - Röckert, Michael; Franke, Matthias; Tariq, Quratulain; Lungerich, Dominik; Jux, Norbert; Stark, Michael Werner; Kaftan, Andre; Ditze, Stefanie; Marbach, Hubertus; Laurin, Mathias; Libuda, Jörg; Steinrück, Hans-Peter; et al. (Journal of Physical Chemistry C, 2014)
Using temperature-programmed desorption (TPD), the self-metalation and dehydrogenation of deuterated 5,10,15,20-tetraphenyl-21,23D-porphyrin on Cu(111) has been studied, resulting in new insight into the metalation of porphyrins on surfaces. The metalation is found to proceed through the transfer of the central aminic hydrogen atoms to the Cu(111) surface and not, as suggested by gas phase calculations, through the combination of the hydrogen atoms to molecular hydrogen above the partially inserted metal center. This finding suggests that the metalation reaction could be significantly influenced by the stability of hydrogen on the substrate surface. The metalation reaction and the subsequent hydrogenation and dehydrogenation of theperiphery of the porphyrin molecule leading to hydrogen-deuterium exchange are modeled with a simple microkinetic reaction model. The model is able to d escribe the main features of the TPD spectra.

Insights into the surface composition and enrichment effects of ionic liquids and ionic liquid mixtures - Maier, Florian; Cremer, Till; Kolbeck, Claudia; Lovelock, Kevin; Paape, Natalia; Schulz, Peter; Wasserscheid, Peter; Steinrück, Hans-Peter (Physical Chemistry Chemical Physics, 2010)
A systematic study of ionic liquid surfaces by angle resolved X-ray photoelectron spectroscopy (ARXPS) is presented. By reviewing recent and presenting new results for imidazolium-based ionic liquids (ILs), we discuss the impact of chemical differences on surface composition and on surface enrichment effects. (1) For the hydrophilic ethylene glycol (EG) functionalised ILs [Me(EG)MIm][TfN], [Et(EG)MIm][TfN] and [Me(EG)MIm][TfN], which vary in the number of ethylene glycol units (from 1 to 3), we find that the surface composition of the near-surface region is in excellent agreement with the bulk composition, which is attributed to attractive interactions between the oxygen atoms on the cation to the hydrogen atoms on the imidazolium ring. (2) For [CC Im][TfN] (where n = 1-16), i.e. ILs with an alkyl chain of increasing length, an enrichment of the aliphatic carbons is observed for longer chains (n > 2), at the expense of the polar cation head groups and the anions in the first molecular layer, both of which are located approximately at the same distance from the outer surface. (3) To study the influence of the anion on the surface enrichment, we investigated ten ILs [CC Im][X] with the same cation, but very different anions [X] . In all cases, surface enrichment of the cation alkyl chains is found, with the degree of enrichment decreasing with increasing size of the anion, i.e., it is most pronounced for the smallest anions and least pronounced for the largest anions. (4) For the IL mixture [CC Im][TfN] and [CCIm][Tf N] we find a homogeneous distribution in the outermost surface region with no specific enrichment of the [CCIm] cation. © 2010 the Owner Societies.

In Situ and Analytical Transmission Electron Microscopy - Birajdar, Balaji; Spiecker, Erdmann (Imaging & Microscopy, 2012)
In situ and analytical transmission electron microscopy (TEM) has been used to investigate the mechanism of material transport during Al-induced layer exchange (ALILE) and crystallization of amorphous Si (a-Si). Significant lateral and vertical redistribution of Al was observed, yielding Al deficient dendritic cell centers surrounded by an about 10 µm wide Al excess zone containing epitaxial islands of -upAl whose number density and size decreases with increasing distance from the cell boundary.
EAM Import::2019-03-13

In situ characterization methods for evaluating microstructure formation and drying kinetics of solution-processed organic bulk-heterojunction films - Güldal, Nusret Sena; Kassar, Thaer; Berlinghof, Marvin; Unruh, Tobias; Brabec, Christoph (Journal of Materials Research, 2017)
Recently, in situ characterization methods have attracted increasing attention, especially in organic photovoltaics (OPV) field, since they provide greater insight into the mechanism of film formation, thus help to identify optimized processing conditions used to process the most efficient organic bulk-heterojunction thin films. In combination with various powerful X-ray-based characterization methods, several studies observed the morphological changes under the influence of different processing conditions. In this review, we summarize the fundamentals and implementation of X-ray-based and optical characterization methods, utilized in in situ mode and introduce the reader a better overview of the information acquired from a given technique in terms of microstructure formation in OPV. While we give a chronological development of in situ characterization methods in the field of OPV, we discuss the interplay between thermodynamics of solutions and drying kinetics of different types of organic blends. © 2017 Materials Research Society.
Keywords: Characterization; Drying; Heterojunctions; Microstructure; Thermodynamics; Thin films; Characterization methods; In-situ characterization; Microstructure formation; Optical characterization; Organic bulk heterojunctions; Organic photovoltaics; Photovoltaic; Thermodynamics of solutions; In situ processing

In situ cracking of silica beads in the SEM and TEM - Effect of particle size on structure-property correlations - Paul, Jonas; Romeis, Stefan; Mackovic, Mirza; Marthala, Venkata; Herre, Patrick; Przybilla, Thomas; Hartmann, Martin; Spiecker, Erdmann; Schmidt, Jochen; Peukert, Wolfgang (Powder Technology, 2015)
Stöber Fink Bohn (SFB) silica is a well-known colloidal system: monodisperse spherical particles are readily obtained by this wet chemical synthesis route. Despite the frequent application of SFB silica, its mechanical properties are not comprehensively understood. Within this account, size dependent mechanical properties of single SFB particles are systematically investigated using in situ SEM and TEM techniques: particle properties are addressed in the size range of 1.5 μm down to 200 nm. Both, untreated particles and heat treated particles densified at 1000 °C are investigated. Structural characterization by vibrational spectroscopy, by solid state nuclear magnetic resonance spectroscopy, by scanning electron microscopy and by focused ion beam machining allows correlating mechanical properties and the internal particle structure. For untreated particles comprised of a weakly cross-linked silica network a high degree of plasticity associated with low Young’s moduli and hardness values is found. At large strains only cracking without full fracture of the particles occurs, whereby the crack path is clearly linked to the synthesis conditions: for larger particles obtained from a multistep growth process cracks propagate along weak intraparticle interfaces and are deflected around an inner core structure. After the thermal treatment cross-linking of the silica network is significantly enhanced and Young’s moduli comparable to vitreous silica accompanied by increased hardness values are found. Only the smallest particles exhibit cracking; fracture into two or more pieces is distinguished for particles above 500 nm. It is found by SEM imaging that the relative occurrence of cracking into several pieces is increasing with size - a behaviour associated with the brittle to ductile transition of silica. By testing a large quantity of particles, statistical significance is ensured.

In situ flaw detection by IR-imaging during electron beam melting - Schwerdtfeger, Jan; Singer, Robert; Körner, Carolin (Rapid Prototyping Journal, 2012)
Purpose - The purpose of this paper is to investigate the possibility of in situ flaw detection for powder bed, beam-based additive manufacturing processes using a thermal imaging system. Design/methodology/approach - The authors compare infrared images (IR) which were taken during the generation of Ti-6Al-4V parts in a selective electron beam melting system (SEBM) with metallographic images taken from destructive material investigation. Findings - A good match is found between the IR images and the material flaws detected by metallographic techniques. Research limitations/implications - First results are presented here, mechanisms of flaw formation and transfer between build layers are not addressed in detail. Originality/value - This work has important implications for quality assurance in SEBM and rapid manufacturing in general. © Emerald Group Publishing Limited.
Keywords: Electron beam melting; Infra-red devices; Infrared imaging; Manufacturing systems; Process control

In Situ Heterogeneous Catalysis Monitoring in a Hollow-Core Photonic Crystal Fiber Microflow Reactor - Cubillas, Ana Maria; Schmidt, Matthias; Euser, Tijmen G.; Taccardi, Nicola; Unterkofler, Sarah; Russell, Philip St. John; Wasserscheid, Peter; Etzold, Bastian (Advanced Materials Interfaces, 2014)
A novel process for uniform deposition of noble-metal catalyst nanoparticles on the inner core wall of a hollow-core photonic crystal fiber is presented. The resulting continuous flow microreactor enables heterogeneous catalysis reactions on extremely low (sub- extgreekmL) sample volumes. Strikingly, the excellent single mode transmission properties of the HC-PCF are preserved after the deposition process, allowing sensitive in situ spectroscopy measurements over unprecedented length scales of up to 50 cm.

In situ high-resolution X-ray photoelectron spectroscopy – Fundamental insights in surface reactions - Steinrück, Hans-Peter; Papp, Christian (Surface Science Reports, 2013)
Since the advent of third generation synchrotron light sources optimized for providing soft X-rays up to 2 keV, X-ray photoelectron spectroscopy (XPS) has been developed to be an outstanding tool to study surface properties and surface reactions at an unprecedented level. The high resolution allows identifying various surface species, and for small molecules even the vibrational fine structure can be resolved in the XP spectra. The high photon flux reduces the required measuring time per spectrum to the domain of a few seconds or even less, which enables to follow surface processes in situ. Moreover, it also provides access to very small coverages down to below 0.1% of a monolayer, enabling the investigation of minority species or processes at defect sites. The photon energy can be adjusted according to the requirement of a particular experiment, i.e., to maximize or minimize the surface sensitivity or the photoionization cross-section of the substrate or the adsorbate. For a few instruments worldwide, a next step forward was taken by combining in situ high-resolution spectrometers with supersonic molecular beams. These beams allow to control and vary the kinetic and internal energies of the incident molecules and provide a local pressure of up to 10 mbar, which can be switched on and off in a controllable way, thus offering a well-defined time structure to study adsorption or reaction processes. Herein, we will review some specific scientific aspects which can be addressed by in situ XPS in order to demonstrate the power and potential of the method: In particular, the following topics will be addressed: (1) The sensitivity of the binding energy to adsorption sites will be analyzed, using CO on metals as example. From measurements at different temperatures, the binding energy difference between different sites can be derived, and exchange processes between different adsorbate species at step edges can be followed. (2) The vibrational fine structure of adsorbed small hydrocarbon species on metal surfaces will be analyzed in detail. We will first introduce the linear coupling model, then discuss the properties of adsorbed methyl and of a number of other small hydrocarbons, and show that the vibrational signature can be used as fingerprint for identifying surface species. (3) It is demonstrated that the binding energy of equivalent atoms in a molecule can be differentially changed by adsorption to a substrate; this sensitivity to the local environment will be discussed for adsorbed ethylene, benzene and graphene. (4) By temperature programmed XPS, the thermal evolution of adsorbed species can be followed in great detail, allowing for the identification of reaction intermediates and the determination of their stabilities. (5) The investigation of reaction kinetics by isothermal XPS measurements will be discussed; here results for the oxidation of sulfur and of CO will be presented and the corresponding activation energies of the rate limiting steps will be determined. © 2013 Elsevier B.V.

In situ investigation of two-step nucleation and growth of CdS nanoparticles from solution - Schiener, Andreas; Magerl, Andreas; Krach, A.; Seifert, Soenke; Steinrück, Hans-Georg; Zagorac, Jelena; Zahn, D.; Weihrich, R. (Nanoscale, 2015)
We report on a combined ultra-fast in situ SAXS and WAXS study along a free-jet providing insight into the evolution of the morphology and crystalline structure of CdS quantum dots in the very early stage of nucleation between 100 μs and 2.5 ms with a time resolution down to 10 μs. Accessing this yet unexplored time regime provides direct evidence of a two-step mechanism via formation of prenucleation clusters followed by nanoparticle nucleation from coalescing precursors. Using ab initio calculations, the latter species is identified as Cd13S4(SH)18 clusters, the stability of which results from a compact surface and inner structure.

In-situ investigation on the deformation and damage behaviour of diamond-like carbon coated thin films under uniaxial loading - Schaufler, Jens; Durst, Karsten; Massler, Orlaw; Göken, Mathias (Thin Solid Films, 2009)
In the present work, the failure behaviour of diamond-like carbon (DLC) coatings on thin steel substrate under uniaxial tensile loading is analyzed in-situ in scanning electron microscopy as well as ex-situ using focused ion beam cross section and transmission electron microscopy. Aim of the work is to find correlations between the failure behaviour of the coating system, the adhesion and the stress–strain behaviour of a DLC coating system under tensile loadings conditions. Therefore thin amorphous DLC films were coated onto thin stainless steel foils using a plasma assisted chemical vapour deposition technique. It is found from the in-situ investigations that at increasing strains cracks were formed in the coating, with decreasing spacing at higher strains. By comparing uncoated steels foils with coated systems the stress–strain behaviour of a DLC coating was determined. The DLC coating, although already strongly cracked, bears loads up to a total strain of 15%. Cross section analyses with a focused ion beam and microscopy techniques supported these investigations. During straining the formation of two deformation bands adjacent to the Cr adhesion layer was observed. This deformation bands also indicate a high interfacial adhesion.
WW1::811

In situ mechanical quenching of nanoscale silica spheres in the transmission electron microscope - Mackovic, Mirza; Niekiel, Florian; Wondraczek, Lothar; Bitzek, Erik; Spiecker, Erdmann (Scripta Materialia, 2016)
A novel approach for in situ mechanical quenching experiments of nanoscale silica spheres inside the transmission electron microscope is presented. Electron irradiation is used to mimic temperature by mediating plastic flow. Quenching under load is achieved by switching-off the electron beam. This is employed in different loading scenarios. Complementary finite element method simulations underline a change of Young's modulus, which strongly depends on the interplay of electron irradiation and mechanical load. We attribute the reduction in Young's modulus to compression-induced structural anisotropy which is frozen-in by rapid quenching and propose a model on how structural anisotropy develops in nanoscale silic
Keywords: Amorphous materials; Compression test; In situ mechanical testing; Silica glass; Transmission electron microscopy

In situ micro-cantilever tests to study fracture properties of NiAl single crystals - Iqbal, Farasat; Ast, Johannes; Göken, Mathias; Durst, Karsten (Acta Materialia, 2012)
In situ micro-cantilever tests were carried out to determine the anisotropic fracture toughness of NiAl single crystals. Notched micro-cantilever beams with a beam length of 8 extgreekmm, 1.5 extgreekmm thickness and 1.8 extgreekmm width were milled in so-called ``hard'' and ``soft'' orientations of NiAl using a focused ion beam. These cantilevers were loaded in situ with the help of a cantilever-based nanoindenter mounted inside a scanning electron microscope. A fracture toughness of 3.52 ± 0.29 MPa m1/2 was obtained for the ``soft'' orientation and 5.12 ± 0.50 MPa m1/2 for the ``hard'' orientation, which is in good agreement with literature values on the fracture toughness of macroscopic NiAl specimens. Furthermore, nanoindentations were performed for studying the size effects occurring at small length scales for both orientations. The applicability of the small sample geometries for testing the fracture toughness is finally discussed in terms of size effects in the flow stress of the material due to dislocation nucleation and strain gradients at the crack tip.
WW1::933

In situ monitoring of the acetylene decomposition and gas temperature at reaction conditions for the deposition of carbon nanotubes using linear Raman scattering - Reinhold Lopez, Karla; Bräuer, Andreas; Popovska, Nadejda; Leipertz, Alfred (Optics Express, 2010)
To understand the reaction mechanisms taking place by growing carbon nanotubes via the catalytic chemical vapor deposition process, a strategy to monitor in situ the gas phase at reaction conditions was developed applying linear Raman spectroscopy. The simultaneous determination of the gas temperature and composition was possible by a new strategy of the evaluation of the Raman spectra. In agreement to the well-known exothermic decomposition of acetylene, a gas temperature increase was quantified when acetylene was added to the incident flow. Information about exhaust gas recirculation and location of the maximal acetylene conversion was derived from the composition measurements.

In Situ Raman Mapping of Charge Carrier Distribution in Electrolyte-Gated Carbon Nanotube Network Field-Effect Transistors - Zaumseil, Jana; Jakubka, Florian; Wang, Ming; Gannott, Florentina (Journal of Physical Chemistry C, 2013)
Solution-processed networks of purely semiconducting single-walled carbon nanotubes (s-SWNTs) can be used to create high-mobility field-effect transistors (FETs) for flexible electronics. In order to optimize network alignment and density, an understanding of carrier distribution within the FET channel is necessary. Here, we used confocal Raman microscopy to investigate charge accumulation and doping in electrolyte-gated FETs with asymmetric layers of only (7,5) nanotubes, that were selected by dispersion in poly(9,9-dioctylfluorene). The nanotube FETs exhibited hole mobilities of up to 7.5 cm2 V–1 s–1 and on/off ratios of 105. All Raman modes decreased in intensity with hole accumulation. The G′-peak and D-peak shifted linearly with negative gate voltages to higher wavenumbers. Using the G′-peak shift, the charge carrier distribution in an operating FET was mapped at different gate and source-drain voltages with high spatial resolution ( 300 nm) and over large areas. With this simple technique, we were able to visualize directly how the assignment of source and drain electrodes determined channel pinch-off and the onset of the saturation regime in FETs with nonuniform carbon nanotube distributions along the channel. In situ Raman mapping could also be applied to other semiconductors that show significant changes in their Raman spectra with doping.
EAM Import::2019-03-13

In situ spectroscopy of ligand exchange reactions at the surface of colloidal gold and silver nanoparticles. - Peukert, Wolfgang; Dinkel, Rebecca; Braunschweig, Björn (Journal of Physics: Condensed Matter, 2017)
Gold and silver nanoparticles with their tunable optical and electronic properties are of great interest for a wide range of applications. Often the ligands at the surface of the nanoparticles have to be exchanged in a second step after particle formation in order to obtain a desired surface functionalization. For many techniques, this process is not accessible in situ. In this review, we present second-harmonic scattering (SHS) as an inherently surface sensitive and label-free optical technique to probe the ligand exchange at the surface of colloidal gold and silver nanoparticles in situ and in real time. First, a brief introduction to SHS and basic features of the SHS of nanoparticles are given. After that, we demonstrate how the SHS intensity decrease can be correlated to the thiol coverage which allows for the determination of the Gibbs free energy of adsorption and the surface coverage.
Keywords: nanoparticle; property; second; harmonic; scattering

In situ STXM investigations of pentacene-based OFETs during operation - Hub, Christian; Burkhardt, Martin; Halik, Marcus; Tzvetkov, G.; Fink, Rainer (Journal of Materials Chemistry, 2010)
Ultrathin pentacene-based organic field-effect transistors (OFETs) on commercially available silicon nitride membranes suitable for transmission X-ray experiments are demonstrated. The devices produced by high-vacuum deposition show excellent electronic performance ( = 0.6 cm V s, I = 10). STXM-experiments recorded with the PolLux microspectroscope correlate structural and electronic properties at highest spatial and spectral resolution while the OFET is operated. Local NEXAFS spectra are used to analyze the different orientations of the pentacene nanocrystals. Spectral changes due to modifications in the electronic structure during OFET operation can hardly be detected with the current setup. © The Royal Society of Chemistry 2010.

In Situ Surface Characterization of Polydisperse Colloidal Particles by Second Harmonic Generation - Schürer, Benedikt; Peukert, Wolfgang (Particulate Science and Technology, 2010)
Optical second harmonic generation (SHG) has a high potential for studying surface properties of colloidal particles in situ with a high temporal resolution. In the past the SHG technique has been applied successfully to determine the surface potential of colloidal particles and emulsion droplets and to study adsorption processes at the interface of solid and liquid particles. However, in previous studies mainly monodisperse particles were used. Here we demonstrate that it is also possible to study adsorption processes on polydisperse particle systems with SHG by comparing in situ adsorption measurements on monodisperse and on polydisperse mixtures of polystyrene (PS) particles. In addition, the results suggest that SHG is also applicable for surface characterization of polydisperse samples at high particle concentrations, where absorption and scattering of the particles is dominant.

In-situ tensile testing of crystalline diamond coatings using Raman spectroscopy - Ahmed, Furqan; Durst, Karsten; Rosiwal, Stefan; Fandrey, Jan; Schaufler, Jens; Göken, Mathias (Surface & Coatings Technology, 2009)
In the present work, the fracture behaviour of crystalline diamond thin films on titanium substrate has been studied under uniaxial in-situ tensile loading in Micro-Raman spectroscopy. Thin crystalline diamond films were deposited onto thin titanium foils using a hot filament chemical vapour deposition technique. The in-situ investigations in Raman spectroscope indicated that the internal stresses, which were compressive at the beginning, can be reduced by the application of tensile load. At higher strain values, when internal stresses were of tensile nature, cracks were formed in the coating with reduced crack spacing at higher strains and also the tensile stress stayed constant during cracking. Cross-section analyses, across tensile cracks, with a focused ion beam microscopy showed that the crack starts from the surface of the coating, then propagates into the interlayer, stops at the surface of the metallic substrate and opens up on further straining without delamination. This cracking behaviour indicates a good adhesion of the coating to the substrat

In-situ thermal activation of carbide-derived carbon - Schmirler, Martina; Glenk, Friedrich; Etzold, Bastian (Carbon, 2011)
Microporous carbons attract high interest due to their application as a medium for gas storage, catalyst support or electrode material in lithium ion batteries or supercapacitors. Carbide-derived carbons (CDC) produced by halogenation of carbides exhibit a narrow pore size distribution and a tunable pore and microstructure by choosing the appropriate carbide precursor and chlorination temperature. However, the pore volume is limited by the amount of metal in the carbide structure, and the variation of pore size by varying the process conditions is not possible for all carbides. With an in-situ thermal activation in CO_2 parallel to the chlorination, the porosity of the CDC materials can be further increased. This improved carbide-derived carbon process also allows producing novel pore structures which vary in the meso- to micropore ratio from the outside to the center of the particle. Thereby also the boarder case of shell-like carbon structures showing different pore size distributions in the shells can be produced. For this in-situ activation and chlorination of carbides the influence of the processing, the concentration of CO_2 and activation time on the pore structure of CDC was studied.
EAM Import::2019-03-13

In situ ultrasonic diagnostic of zeolite X crystallization with novel (hierarchical) morphology from coal fly ash - Musyoka, Nicholas M.; Petrik, Leslie F.; Hums, Eric; Baser, Hasan-Hüseyin; Schwieger, Wilhelm (Ultrasonics, 2014)
In this paper the applicability of an in situ ultrasonic diagnostic technique in understanding the formation process of zeolite X with a novel morphology was demonstrated. The complexity of the starting fly ash feedstock demands independent studies of the formation process for each type of zeolite since it is not known whether the crystallization mechanism will always follow the expected reaction pathway. The hierarchical zeolite X was noted to follow a solution phase-mediated crystallization mechanism which differs from earlier studies of the zeolite A formation process from unaged, clear solution extracted from fused fly ash. The use of the in situ ultrasonic monitoring system provided sufficient data points which enabled closer estimation of the time of transition from the nucleation to the crystal growth step. In order to evaluate the effect of temperature on the resulting in situ attenuation signal, synthesis at three higher temperatures (80, 90 and 94 degrees C) was investigated. It was shown, by the shift of the US-attenuation signal, that faster crystallization occurred when higher temperatures were applied. The novel hierarchical zeolite X was comprised of intergrown disc-like platelets. It was further observed that there was preferential growth of the disc-shaped platelets of zeolite X crystals in one dimension as the synthesis temperature was increased, allowing tailoring of the hierarchical morphology. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: In situ ultrasonic; Hierarchical zeolite X; Fly ash

In situ ultrasonic monitoring of zeolite A crystallization from coal fly ash - Baser, Hasan-Hüseyin; Schwieger, Wilhelm; Hums, Eric; Musyoka, Nicholas M.; Petrik, Leslie F. (Catalysis Today, 2012)
In this study, high phase purity of zeolite A was prepared from coal fly ash precursors. The molar regime of both the clear solution extract and unseparated fly ash slurry was adjusted to achieve the right composition for zeolite A crystallization. The formation process for zeolite A from coal fly ash precursors was monitored in detail using an in situ ultrasonic system and was complemented by use of ex situ techniques such as XRD, FTIR, SEM and FTIR. The findings from both the in situ ultrasonic monitoring process and ex situ techniques clearly contributed significantly in unmasking the formation process of zeolite A from coal fly ash compared to previous studies reported in the literature. The study also enriches the existing body of literature by deeply investigating the gel-solution-crystal interactions starting from this complex feedstock. Comparable ultrasonic signals were generated when both clear and unseparated fly ash based precursor solutions were used during the zeolite synthesis process. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: In situ; Ultrasound; Coal fly ash; Zeolite A; Mechanism; Ageing process

In-Situ X-ray Diffraction Analysis of the Recrystallization Process in Cu2ZnSnS4 Nano Particles Synthesized by Hot-Injection - Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Azimi, Hamed; Hou, Yi; Peukert, Wolfgang; Brabec, Christoph; Hock, Rainer (Thin Solid Films, 2015)
Kesterite Cu2ZnSnS4 (CZTS) is a promisingmaterial for thin film solar cell applications. The biggest advantages of this compound lie in the abundance and non-toxicity of the contained elements. Low temperature hot injection synthesis can provide an economic way to produce CZTS nanoparticles for application in solution processed solar cells. Powder X-ray diffraction (PXRD) measurements on the as-synthesised particles suggest that the crystal structure is cubic and can be best described as sphalerite-like. This means that the cations in the CZTS are statistically distributed on the cation sites of the crystal lattice rather than well-ordered like in the tetragonal kesterite structure. An in-situ PXRD measurement while annealing the particles up to 550 °C revealed a recrystallization process that transforms the structure from cubic to tetragonal meaning an ordering of the cations.
EAM Import::2019-03-13

Instantaneous healing of micro-fractures during coseismic slip: Evidence from microstructure and Ti in quartz geochemistry within an exhumed pseudotachylyte-bearing fault in tonalite - Bestmann, Michel; Pennacchioni, Giorgio; Mostefaoui, Smail; Göken, Mathias; de Wall, Helga (Lithos, 2016)
Exhumed faults within the tonalitic Adamello pluton (Southern Alps) were seismic at depth as indicated by the presence of pseudotachylytes (solidified friction-induced melts). During cooling of tonalite, early-formed joints were first exploited by localized ductile shear zones associated with deposition of quartz veins (at similar to 500 degrees C), and later by pseudotachylyte-bearing cataclastic faults (at similar to 250-300 degrees C ambient temperature). Adjacent to pseudotachylytes, quartz of the host tonalite shows pervasive thin (1-10 mu m wide) healed micro-fractures and ultra-fine (1-2 mu m grain size) recrystallized aggregates along micro-shear zones. Under cathodoluminescence (CL) the healed micro-fractures have a darker gray shade than the host "magmatic" quartz that reflects a change in Ti concentrations ( [Ti]) as indicated by NanoSIMS measurements. [Ti] vary from 35-55 ppm in the CL-lighter host quartz to 10-13 ppm along the CL-darker healed micro-fractures. These [Ti] were inherited by the ultra-fine recrystallized aggregates that overprinted both the magmatic quartz and the healed micro-fractures during the high temperature transient related to frictional seismic slip. Based on Ti-in-quartz thermometry, we infer that micro-fracture healing occurred at higher temperatures than the ambient temperatures of faulting (250-300 degrees C at 0.2 GPa), for which [Ti] <1 ppm would be expected. Micro-fracture healing can be ascribed to the stage of seismic slip of faults on the basis of the observation that: (i) they are absent in the host rock surrounding high-T quartz veins un-exploited by faults; and (ii) they locally occur at the tip of pseudotachylyte injection veins filling new fractures developed during the propagation of the earthquake rupture. The relatively high [Ti] of micro-fractures are therefore interpreted to reflect quartz healing by a fluid overheated during the initial stages of frictional seismic slip and escaping from fault surface through the damage zone. This suggests that, in the presence of fluids, thermal pressurization of the fault did not occur and did not prevent frictional melting. The small-scale microstructures and geochemistry of quartz in the wall of the studied paleo-seismic fault record a complex deformational history, referable to the short-lived (on the order of 10(4) s) thermal anomaly induced by frictional seismic slip, that includes both micro-fracture healing and recrystallization. This microstructural assemblage of the natural exhumed fault provides a key for understanding the mechanics of an earthquake source. (c) 2016 Elsevier B.V. All rights reserved.
Keywords: Titanium in quartz; Cathodoluminescence; Quartz deformation; Pseudotachylyte; NanoSIMS; Micro-fracturing

Integrated molecular, morphological and interfacial engineering towards highly efficient and stable solution-processed small molecule solar cells - Min, Jie; Luponosov, Yuriy N.; Gasparini, Nicola; Xue, Lingwei; Drozdov, Fedor V.; Peregudova, Svetlana M.; Dmitryakov, Petr V.; Gerasimov, Kirill L.; Anokhin, Denis V.; Zhang, Zhi-Guo; Ameri, Tayebeh; Chvalun, Sergei N.; et al. (Journal of Materials Chemistry A, 2015)
The synthesis of a series of A-π-D-π-A oligomers bearing coplanar electron-donating dithieno[3,2-b:2′,3′-d]silole (DTS) unit linked through bithiophene π-bridges with the electron-withdrawing alkyldicyanovinyl (alkyl-DCV) groups is described. This study demonstrates a systematic investigation of structure-property relationships in this type of oligomer and shows obvious benefits of alkyl-DCV groups as compared to the commonly used DCV ones, in terms of elaboration of high performance organic solar cells (OSCs). Considerable efforts have been made to improve the power conversion efficiency (PCE) of oligomer-based OSCs by diverse strategies including fine-tuning of the oligomer properties via variation of their terminal and central alkyl chains, blend morphology control via solvent vapor annealing (SVA) treatment, and surface modification via interfacial engineering. These efforts allowed achieving PCEs of up to 6.4% for DTS(Oct)-(2T-DCV-Me) blended with PCBM. Further morphological investigations demonstrated that the usage of SVA treatment indeed effectively results in increased absorption and ordering of the BHJ composite, with the only exception for the most soluble oligomer DTS(Oct)-(2T-DCV-Hex). Besides, a detailed study analyzed the charge transport properties and recombination loss mechanisms for these oligomers. This study not only revealed the importance of integrated alkyl chain engineering on gaining morphological control for high performance OSCs, but also exhibited a clear correlation between molecular ordering and charge carrier mobility respective to carrier dynamics. These results outline a detailed strategy towards a rather complete characterization and optimization methodology for organic photovoltaic devices, thereby paving the way for researchers to easily find the performance parameters adapted for widespread applications.
Keywords: Engineering controlled terms: Cell engineering; Oligomers; Surface treatment; Varactors Electronwithdrawing; Morphological control; Optimization methodology; Organic photovoltaic devices; Performance parameters; Power conversion efficiencies; Solvent-vapor annealing; Structure property relationships Engineering main heading: Solar cells

Integrated proteomic and metabolomic analysis to assess the effects of pure and benzo[a]pyrene-loaded carbon black particles on energy metabolism and motility in the human endothelial cell line EA.hy926 - Pink, Mario; Verma, Nisha; Rettenmeier, Albert W.; Schmitz-Spanke, Simone (Archives of Toxicology, 2014)
Epidemiological studies suggest that environmental exposure to airborne particulate matter may promote cardiovascular diseases; however, it is not clear whether this observation actually reflects exposure to nanosized particles in the environment. In the present study, the human endothelial cell line EA.hy926 was exposed to pure carbon black and, to mimic exposure to diesel exhaust, carbon black loaded with benzo[a]pyrene to ascertain effects of these particles on the cell proteome and metabolom. Particular emphasis was laid on an extended exposure period (14 days) and a low particle concentration (100 ng/mL). While ROS production essentially remained unaffected, exposure of the cells to the particles resulted in a significantly enhanced cell proliferation. Evaluation of the obtained proteomic and phosphoproteomic data revealed modulations of proteins involved in catalytic processes and cytoskeleton maintenance. The bioinformatic evaluation of the data revealed the possible involvement of the transcription factor peroxisome proliferator-activated receptor gamma. The further analysis of the cytoskeleton indicated changes of the cell motility, which is in agreement with an observed increase in the cellular migration and invasion, and macroscopic changes of the cytoskeleton of the exposed cells.
EVALuna2:9704

Integrated X-ray photoelectron spectroscopy and DFT characterization of benzene adsorption on Pt(111), Pt(355) and Pt(322) surfaces - Zhang, Renqin; Hensley, Alyssa J.; Mcewen, Jean-Sabin; Wickert, Sandra; Darlatt, Erik; Fischer, Kristina; Schöppke, Matthias; Denecke, Reinhard; Streber, Regine; Lorenz, Michael Peter Andreas; Papp, Christian; Steinrück, Hans-Peter (Physical Chemistry Chemical Physics, 2013)
We systematically investigate the adsorption of benzene on Pt(111), Pt(355) and Pt(322) surfaces by high-resolution X-ray photoelectron spectroscopy (XPS) and first-principle calculations based on density functional theory (DFT), including van der Waals corrections. By comparing the adsorption energies at 1/9, 1/16 and 1/25 ML on Pt(111), we find significant lateral interactions exist between the benzene molecules at 1/9 ML. The adsorption behavior on Pt(355) and Pt(322) is very different. While on Pt(355) a step species is clearly identified in the C 1s spectra at low coverages followed by occupation of a terrace species at high coverages, no evidence for a step species is found on Pt(322). These different adsorption sites are confirmed by extensive DFT calculations, where the most favorable adsorption configurations on Pt(355) and Pt(322) are also found to vary: a highly distorted across the step molecule is found on Pt(355) while a less distorted configuration adjacent to the step molecule is deduced for Pt(322). The theoretically proposed C 1s core level binding energy shifts between these most favorable configurations and the terrace species are found to correlate well with experiment: for Pt(355), two adsorbate states are found, separated by ∼0.4 eV in XPS and 0.3 eV in the calculations, in contrast to only one state on Pt(322). © 2013 the Owner Societies.

Integrating metalloporphycenes into p-type NiO-based dye-sensitized solar cells - Feihl, Sebastian; Costa, Ruben D.; Brenner, Wolfgang; Margraf, Johannes; Casillas Pacheco, Ruben; Langmar, Oliver; Browa, Anne; Shubina, Tatyana; Jux, Norbert; Guldi, Dirk Michael; Clark, Timothy (Chemical Communications, 2014)
In the current work, we have explored a novel synthetic route towards metalated porphycenes and their use in p-type NiO-based dye-sensitized solar cells. Particular emphasis is placed on the influence that the relative positioning of the anchoring group exerts on the DSSC performance.

Integration of plasmonic Ag nanoparticles as a back reflector in ultra-thin Cu(In,Ga)Se2 solar cells - Yin, Guanchao; Steigert, Alexander; Andrae, Patrick; Göbelt, Manuela; Latzel, Michael; Manley, Phillip; Lauermann, Iver; Christiansen, Silke; Schmid, Martina (Applied Surface Science, 2015)
Integration of plasmonic Ag nanoparticles as a back reflector in ultra-thin Cu(In,Ga)Se (CIGSe) solar cells is investigated. X-ray photoelectron spectroscopy results show that Ag nanoparticles underneath a Sn:InO back contact could not be thermally passivated even at a low substrate temperature of 440 °C during CIGSe deposition. It is shown that a 50 nm thick AlO film prepared by atomic layer deposition is able to block the diffusion of Ag, clearing the thermal obstacle in utilizing Ag nanoparticles as a back reflector in ultra-thin CIGSe solar cells. Via 3-D finite element optical simulation, it is proved that the Ag nanoparticles show the potential to contribute the effective absorption in CIGSe solar cells.
Keywords: Ag nanoparticles; Al2O3 film; Atomic layer deposition; Thermal stability; Ultra-thin Cu(In; Ga)Se2 solar cells

Intense red photoluminescence from Mn2+-doped (Na+; Zn2+) sulfophosphate glasses and glass ceramics as LED converters - Da, Ning; Peng, Mingying; Krolikowski, Sebastian; Wondraczek, Lothar (Optics Express, 2010)
We report on intense red fluorescence from Mn2+-doped sulfophosphate glasses and glass ceramics of the type ZnO-Na_2O-SO_3-P_2O5. As a hypothesis, controlled internal crystallization of as-melted glasses is achieved on the basis of thermally-induced bimodal separation of an SO_3-rich phase. Crystal formation is then confined to the relict structure of phase separation. The whole synthesis procedure is performed in air at łeq 800 °C. Electron spin resonance and Raman spectroscopy indicate that Mn2+ species are incorporated on Zn2+ sites with increasingly ionic character for increasing concentration. Correspondingly, in the glasses, increasing MnO content results in decreasing network polymerization. Stable glasses and continuously increasing emission intensity are observed for relatively high dopant concentration of up to 3 mol.%. Recrystallization of the glass results in strongly increasing emission intensity. Dynamic emission spectroscopy reveals only on type of emission centers in the glassy material, whereas three different centers are observed in the glass ceramic. These are attributed to octahedrally coordinated Mn2+ in the residual glass phase and in crystalline phosphate and sulfate lattices, respectively. Relatively low crystal field strength results in almost ideal red emission, peaking around 625 nm. Excitation bands lie in the blue-to-green spectral range and exhibit strong overlap. The optimum excitation range matches the emission properties of GaN- and InGaN-based light emitting devices.
EAM Import::2019-03-13

Intensification of heat transfer in catalytic reactors by additively manufactured periodic open cellular structures (POCS) - Busse, Corinna; Freund, Hannsjörg; Schwieger, Wilhelm (Chemical Engineering and Processing, 2018)
Cellular structures are considered as alternative catalyst carrier with high potential for process intensification of catalytic reactors due to their remarkable combination of beneficial properties: high specific surface area, low pressure drop and adjustable heat transfer properties. In this contribution, the potential for heat transfer intensification of a new generation of cellular structures, so-called periodic open cellular structures (POCS), is investigated. These structures are produced via additive manufacturing which provides two major advantages. First, highly regular structures can be obtained with perfect reproducibility, which makes them ideal model systems for systematic investigations. Second, the design flexibility of the manufacturing techniques enables an innovative approach for structure optimization. Such optimization, however, requires a detailed understanding of the geometry-transport interaction. In this regard, the first advantage is exploited here to examine in detail the influence of each relevant property of the structure (material, morphology, wall coupling) on the heat transfer. These findings, along with newly derived correlations, enlarge the toolbox for the design of POCS for catalytic applications. Furthermore, POCS can now be designed and optimized a priori according to the needs of the given application. This adds a new degree of freedom to the process intensification approach regarding equipment optimization.
Keywords: Catalyst support; Heat transfer; Additive manufacturing; Metal foam; Periodic open cellular structures

Interacting waves on chains of split-ring resonators in the presence of retardation - Lomanets, Vadym; Zhuromskyy, Oleksandr; Onishchukov, Georgy; Sydoruk, Oleksiy; Tatartschuk, Eugen; Shamonina, E.; Leuchs, Gerd; Peschel, Ulf (Applied Physics Letters, 2010)
Wave propagation is studied experimentally in a one-dimensional periodic chain of magnetically coupled split-ring resonators with a spacing of about one tenth of the resonant wavelength. Retardation leads to a strong interaction between magnetoinductive and free-space waves. Two kinds of guided modes are observed: a slow backward wave which propagates far outside the light cone, and a fast forward wave close to the light cone. The two merge in a region of zero group velocity. The results are relevant for all one- and two-dimensional periodic systems interacting with waves of the surrounding space.
EAM Import::2019-03-13

Interaction between silver nanowires and CO on a stepped platinum surface - Streber, Regine; Tränkenschuh, Barbara; Schöck, Johannes; Papp, Christian; Steinrück, Hans-Peter; Mcewen, J. -S.; Gaspard, P.; Denecke, Reinhard (Journal of Chemical Physics, 2009)
We studied the interplay between Ag decoration of a stepped Pt(355) surface and CO adsorption by in situ high-resolution x-ray photoelectron spectroscopy. Varying amounts of Ag deposited at 300 K initially lead to a row-by-row growth starting from the lower Pt step edges. Such decoration of the step sites results in a change in the CO adsorption behavior. An apparent blocking of step sites for low CO coverages is attributed to a change in the electronic structure, resulting in a C 1s binding energy of CO at step sites being equal to that for CO at terrace on-top sites in the presence of Ag. Higher CO coverages induce the formation of embedded Ag clusters within the upper terraces, thus freeing up a part of the original Pt step sites for CO adsorption, as was derived by a comparison to density functional theory calculations in the corresponding surface models. © 2009 American Institute of Physics.

Interaction of Ester-Functionalized Ionic Liquids with Atomically-Defined Cobalt Oxides Surfaces: Adsorption, Reaction and Thermal Stability - Xu, Tao; Wähler, Tobias; Vecchietti, Julia; Bonivardi, Adrian; Bauer, Tanja; Schwegler, Johannes; Schulz, Peter; Wasserscheid, Peter; Libuda, Jörg (ChemPhysChem, 2017)
Hybrid materials consisting of ionic liquid (ILs) films on supported oxides hold a great potential for applications in electronic and energy materials. In this work, we have performed surface science model studies scrutinizing the interaction of ester-functionalized ILs with atomically defined Co3O4(111) and CoO(100) surfaces. Both supports are prepared under ultra-high vacuum (UHV) conditions in form of thin films on Ir(100) single crystals. Subsequently, thin films of three ILs, 3-butyl-1-methyl imidazolium bis(trifluoromethyl-sulfonyl) imide ([BMIM][NTf2]), 3-(4-methoxyl-4-oxobutyl)-1-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([MBMIM][NTf2]), and 3-(4-isopropoxy-4-oxobutyl)-1-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([IPBMIM][NTf2]), were deposited on these surfaces by physical vapor deposition (PVD). Time-resolved and temperature-programmed infrared reflection absorption spectroscopy (TR-IRAS, TP-IRAS) were applied to monitor insitu the adsorption, film growth, and thermally induced desorption. By TP-IRAS, we determined the multilayer desorption temperature of [BMIM][NTf2] (360 +/- 5K), [MBMIM][NTf2] (380K) and [IPBMIM][NTf2] (380K). Upon deposition below the multilayer desorption temperature, all three ILs physisorb on both cobalt oxide surfaces. However, strong orientation effects are observed in the first monolayer, where the [NTf2](-) ion interacts with the surface through the SO2 groups and the CF3 groups point towards the vacuum. For the two functionalized ILs, the [MBMIM](+) and [IPBMIM](+) interact with the surface Co2+ ions of both surfaces via the CO group of their ester function. A very different behavior is found, if the ILs are deposited above the multilayer desorption temperature (400K). While for [BMIM][NTf2] and [MBMIM][NTf2] a molecularly adsorbed monolayer film is formed, [IPBMIM][NTf2] undergoes a chemical transformation on the CoO(100) surface. Here, the ester group is cleaved and the cation is chemically linked to the surface by formation of a surface carboxylate. The IL-derived species in the monolayer desorb at temperatures around 500 to 550K.
Keywords: chemical anchoring; cobalt oxide; ionic liquids; IRAS; thermal stability

Interaction of highly focused vector beams with a metal knife-edge - Marchenko, P.; Orlov, S.; Huber, C.; Banzer, Peter; Quabis, Susanne; Peschel, Ulf; Leuchs, Gerd (Optics Express, 2011)
We investigate the interaction of highly focused linearly polarized optical beams with a metal knife-edge both theoretically and experimentally. A high numerical aperture objective focusses beams of various wavelengths onto samples of different sub-wavelength thicknesses made of several opaque and pure materials. The standard evaluation of the experimental data shows material and sample dependent spatial shifts of the reconstructed intensity distribution, where the orientation of the electric field with respect to the edge plays an important role. A deeper understanding of the interaction between the knife-edge and the incoming highly focused beam is gained in our theoretical model by considering eigenmodes of the metal-insulator-metal structure. We achieve good qualitative agreement of our numerical simulations with the experimental findings.
EAM Import::2019-03-13

Interaction of light with hematite hierarchical structures: Experiments and simulations - Distaso, Monica; Zhuromskyy, Oleksandr; Seemann, Benjamin; Pflug, Lukas; Mackovic, Mirza; Encina, Ezequiel Roberto; Klupp Taylor, Robin; Müller, Rolf; Leugering, Günter; Spiecker, Erdmann; Peschel, Ulf; Peukert, Wolfgang (Journal of Quantitative Spectroscopy & Radiative Transfer, 2017)
Mesocrystalline particles have been recognized as a class of multifunctional materials with potential applications in different fields. However, the internal organization of nanocomposite mesocrystals and its influence on the final properties have not yet been investigated. In this paper, a novel strategy based on electrodynamic simulations is developed to shed light on how the internal structure of mesocrystals influences their optical properties. In a first instance, a unified design protocol is reported for the fabrication of hematite/PVP particles with different morphologies such as pseudo-cubes, rods-like and apple-like structures and controlled particle size distributions. The optical properties of hematite/PVP mesocrystals are effectively simulated by taking their aggregate and nanocomposite structure into consideration. The superposition T-Matrix approach accounts for the aggregate nature of mesocrystalline particles and validate the effective medium approximation used in the framework of the Mie theory and electromagnetic simulation such as Finite Element Method. The approach described in our paper provides the framework to understand and predict the optical properties of mesocrystals and more general, of hierarchical nanostructured particles.
Keywords: Effective medium approximation; FEM; Maxwell-Garnett theory; Mesocrystals; Scattering; T-Matrix

Interaction of NO2 with Model NSR Catalysts: Metal-Oxide Interaction Controls Initial NOx Storage Mechanism - Desikusumastuti, Aine; Staudt, Thorsten; Qin, Zhihui; Happel, Markus; Laurin, Mathias; Lykhach, Yaroslava; Shaikhutdinov, Shamil; Rohr, Friedemann; Libuda, Jörg (ChemPhysChem, 2008)
Using scanning tunneling microscopy (STM), molecular-beam (MB) methods and time-resolved infrared reflection absorption spectroscopy (TR-IRAS), we investigate the mechanism of initial NO, uptake on a model nitrogen storage and reduction (NSR) catalyst. The model system is prepared by co-deposition of Pd metal particles and Ba-containing oxide particles onto an ordered alumina film on NiAl(110). We show that the metal-oxide interaction between the active noble metal particles and the No, storage compound in NSR model catalysts plays an important; role in the reaction mechanism. We suggest that strong interaction facilitates reverse spillover of activated oxygen species from the NOx storage compound to the metal. This process leads to partial oxidation of the metal nanoparticles and simultaneous stabilization of the surface nitrite intermediate.
Keywords: heterogeneous catalysis; IR spectroscopy; model catalysts; molecular beams; reaction mechanisms

Interactions Between the Room-Temperature Ionic Liquid [C(2)C(1)Im][OTf] and Pd(111), Well-Ordered Al2O3, and Supported Pd Model Catalysts from IR Spectroscopy - Schernich, Stefan; Kostyshyn, Dmytro; Wagner, Valentin; Taccardi, Nicola; Laurin, Mathias; Wasserscheid, Peter; Libuda, Jörg (Journal of Physical Chemistry C, 2014)
The interactions between ionic liquids and their supports determine many of their applications. The adsorption of the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [C2C1Im][OTf] on Pd(111), ordered Al2O3/NiAl(110), and Pd nanoparticles supported on Al2O3/NiAl(110) was investigated under ultrahigh vacuum (UHV) conditions using time-resolved infrared reflection absorption spectroscopy (TR-IRAS). On Pd, the [OTf]- anion stands up with its CF3 group directed toward the vacuum, whereas the anion is less clearly oriented on the oxide. We also find that strong interactions of the IL with the Pd result in migration of the IL from the oxide to the metal nanoparticles.

Interactions of imidazolium-based ionic liquids with oxide surfaces controlled by alkyl chain functionalization - Schernich, Stefan; Laurin, Mathias; Lykhach, Yaroslava; Tsud, Nataliya; Sobota, Marek; Skala, Tomas; Prince, Kevin C.; Taccardi, Nicola; Wagner, Valentin; Steinrück, Hans-Peter; Matolin, Vladimir; Wasserscheid, Peter; et al. (ChemPhysChem, 2013)
From a different angle: Thin films of functionalized ionic liquids are deposited on cerium oxides following a surface science approach. The functionalization of the alkyl chain changes its orientation with respect to the surface plane from normal to parallel. This then leads to a different surface chemistry at higher temperatures. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interface Chemistry and Molecular Bonding of Functional Ethoxysilane-Based Self-Assembled Monolayers on Magnesium Surfaces - Killian, Manuela; Seiler, Steffen; Wagener, Victoria; Hahn, Robert; Ebensperger, Christina; Meyer, Bernd; Schmuki, Patrik (ACS Applied Materials and Interfaces, 2015)
The modification of magnesium implants with functional organic molecules is important for increasing the biological acceptance and for reducing the corrosion rate of the implant. In this work, we evaluated by a combined experimental and theoretical approach the adsorption strength and geometry of a functional self-assembled monolayer (SAM) of hydrolyzed (3-aminopropyl)triethoxysilane (APTES) molecules on a model magnesium implant surface. In time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS), only a minor amount of reverse attachment was observed. Substrate–O–Si signals could be detected, as well as other characteristic APTES fragments. The stability of the SAM upon heating in UHV was investigated additionally. Density-functional theory (DFT) calculations were used to explore the preferred binding mode and the most favorable binding configuration of the hydrolyzed APTES molecules on the hydroxylated magnesium substrate. Attachment of the molecules via hydrogen bonding or covalent bond formation via single or multiple condensation reactions were considered. The impact of the experimental conditions and the water concentration in the solvent on the thermodynamic stability of possible APTES binding modes is analyzed as a function of the water chemical potential of the environment. Finally, the influence of van der Waals contributions to the adsorption energy will be discussed.
Keywords: DFT calculations; magnesium; self-assembled monolayer; silane coupling; ToF-SIMS

Interface Controls Spontaneous Crystallization in Thin Films of the Ionic Liquid [C2C1Im][OTf] on Atomically Clean Pd(111) - Schernich, Stefan; Wagner, Valentin; Taccardi, Nicola; Wasserscheid, Peter; Laurin, Mathias; Libuda, Jörg (Langmuir, 2014)
A total of 5-30 monolayer thick films of the ionic liquid (IL) [C2C1Im][OTf] were vaporized in vacuo onto an atomically clean Pd(111) single crystal surface at 220 K. Time- and temperature-resolved infrared reflection-absorption spectroscopy reveals growth, interactions with the metallic support, and the macroscopic phase behavior of the layer. At 220 K, the IL layer first grows in the form of a glassy phase. Crystallization of the IL was witnessed above a critical thickness of about 10 monolayers. On the basis of the known bulk crystal structure of the IL, we suggest the formation of well-oriented checkerboard-like crystalline film structures on the surface. The preferential orientation manifested by the crystal phase with regard to the macroscopic metallic surface is attributed to strong interactions between anionic headgroups and the metal.

Interface Design to Improve the Performance and Stability of Solution-Processed Small-Molecule Conventional Solar Cells - Min, Jie; Luponosov, Yuriy N.; Zhang, Zhi-Guo; Ponomarenko, Sergei A.; Ameri, Tayebeh; Li, Yongfang; Brabec, Christoph (Advanced Energy Materials, 2014)
A systematic study on the effect of various cathode buffer layers on the performance and stability of solution-processed small-molecule organic solar cells (SMOSCs) based on tris[4-[5-(1,1-dicyanobut-1-en-2-yl)-2,2-bithiophen-5-yl]phenyl]amine (N(Ph-2T-DCN-Et)3):6,6-phenyl-C71-butyric acid methyl ester (N(Ph-2T-DCN-Et)3:PC70BM) is presented. The power conversion efficiency (PCE) in these systems can be significantly improved from approximately 4% to 5.16% by inserting a metal oxide (ZnO) layer between the active layer and the Al cathode instead of an air-sensitive Ba or Ca layer. However, the low work-function Al cathode is susceptible to chemical oxidation in the atmosphere. Here, an amine group functionalized fullerene complex (DMAPA-C60) is inserted as a cathode buffer layer to successfully modify the interface towards ZnO/Ag and active layer/Ag functionality. For devices with ZnO/DMAPA-C60/Ag and DMAPA-C60/Ag cathodes the PCEs are improved from 2.75% to 4.31% and to 5.40%, respectively, compared to a ZnO/Ag device. Recombination mechanisms and stability aspects of devices with various cathodes are also investigated. The significant improvement in device performance and stability and the simplicity of fabrication by solution processing suggest this DMAPA-C60-based interface as a promising and practical pathway for developing efficient, stable, and roll-to-roll processable SMOSCs.
Keywords: Engineering controlled terms: Buffer layers; Butyric acid; Convergence of numerical methods; Conversion efficiency; Electrodes; Fullerenes; Molecules; Optical waveguides; Silver; Solar cells; Stability; Zinc oxide Cathode buffer layers; Conventional structures; Fullerene complexes; Power conversion efficiencies; Recombination mechanisms; Small-molecule organic solar cells; Solution-processing; Stability of solutions Engineering main heading: Cathodes

Interface Engineering in High-Performance Low-Voltage Organic Thin-Film Transistors Based on 2,7-Dialkyl-[1]benzothieno[3,2-b][1]benzothiophenes - Amin, Atefeh Y.; Reuter, Knud; Meyer-Friedrichsen, Timo; Halik, Marcus (Langmuir, 2011)
We investigated two different (2,7-dialkyl-[1]benzothieno[3,2-b][1]benzothiophenes; Cn–BTBT–Cn, where n = 12 or 13) semiconductors in low-voltage operating thin-film transistors. By choosing functional molecules in nanoscaled hybrid dielectric layers, we were able to tune the surface energy and improve device characteristics, such as leakage current and hysteresis. The dipolar nature of the self-assembled molecules led to a shift in the threshold voltage. All devices exhibited high charge carrier mobilities of 0.6–7.0 cm2 V–1 s–1. The thin-film morphology of BTBT was studied by means of atomic force microscopy (AFM), presented a dependency upon the surface energy of the self-assembled monolayer (SAM) hybrid dielectrics but not upon the device performance. The use of C13–BTBT–C13 on hybrid dielectrics of AlOx and a F15C18–phosphonic acid monolayer led to devices with a hole mobility of 1.9 cm2 V–1 s–1 at 3 V, on/off ratio of 105, small device–device variation of mobility, and a threshold voltage of only −0.9 V, thus providing excellent characteristics for further integration.

Interface Engineering of Molecular Charge Storage Dielectric Layers for Organic Thin-Film Memory Transistors - Khassanov, Artöm; Schmaltz, Thomas; Steinrück, Hans-Peter; Magerl, Andreas; Hirsch, Andreas; Halik, Marcus (Advanced Materials Interfaces, 2014)
Mixed self-assembled monolayers of C60-functionalized and different long-chained insulating phosphonic acids provide molecular scale non-volatile memory dielectrics for low-voltage organic thin-film transistors. The memory retention depends on the insulation of the C60 moiety and can be improved by embedding into the insulating SAM matrix and covering by corresponding insulating molecules.

Interface Engineering of Perovskite Hybrid Solar Cells with Solution-Processed Perylene–Diimide Heterojunctions toward High Performance - Min, Jie; Zhang, Zhi-Guo; Hou, Yi; Ramírez Quiroz, César Omar; Przybilla, Thomas; Bronnbauer, Carina; Guo, Fei; Forberich, Karen; Azimi, Seyed Hamed; Ameri, Tayebeh; Spiecker, Erdmann; Li, Yongfang; et al. (Chemistry of Materials, 2015)
Perovskite hybrid solar cells (pero-HSCs) were demonstrated to be among the most promising candidates within the emerging photovoltaic materials with respect to their power conversion efficiency (PCE) and inexpensive fabrication. Further PCE enhancement mainly relies on minimizing the interface losses via interface engineering and the quality of the perovskite film. Here, we demonstrate that the PCEs of pero-HSCs are significantly increased to 14.0% by incorporation of a solution-processed perylene–diimide (PDINO) as cathode interface layer between the [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) layer and the top Ag electrode. Notably, for PDINO-based devices, prominent PCEs over 13% are achieved within a wide range of the PDINO thicknesses (5–24 nm). Without the PDINO layer, the best PCE of the reference PCBM/Ag device was only 10.0%. The PCBM/PDINO/Ag devices also outperformed the PCBM/ZnO/Ag devices (11.3%) with the well-established zinc oxide (ZnO) cathode interface layer. This enhanced performance is due to the formation of a highly qualitative contact between PDINO and the top Ag electrode, leading to reduced series resistance (Rs) and enhanced shunt resistance (Rsh) values. This study opens the door for the integration of a new class of easily-accessible, solution-processed high-performance interfacial materials for pero-HSCs.

Interface formation between calcium and electron-irradiated poly(3-hexylthiophene) - Bebensee, Fabian; Zhu, Junfa; Baricuatro, J. H.; Farmer, Jason A.; Bai, Yun; Steinrück, Hans-Peter; Campbell, C. T.; Gottfried, Michael (Langmuir, 2010)
The adsorption of Ca on electron-irradiated poly(3-hexylthiophene) (P3HT) surfaces at 300 K (E = 100 eV) has been studied by adsorption microcalorimetry, atomic beam/surface scattering, X-ray photoelectron spectroscopy (XPS), and low-energy He ion scattering spectroscopy (LEIS). The results are compared to previous studies of Ca adsorption on pristine P3HT. The major structural effect of electron irradiation is a substantial increase in the fraction of unsaturated carbon atoms, probably a result of electron-induced hydrogen abstraction from the hexyl chains and formation of new C=C double bonds. No loss of sulfur was observed. The combined XPS, LEIS, and calorimetry data indicate that the reaction and growth behavior of Ca on P3HT surfaces is not significantly affected by this electron damage, apart from an increased sticking probability at low coverages. The sticking probability of Ca on the irradiated P3HT is initially 0.63, compared to 0.36 on the pristine surface. It increases with coverage, approaching unity between 4 and 5 ML. The heat of adsorption stays nearly constant at 405 kJ/mol up to a coverage of 0.6 ML, which is ascribed to Ca diffusing below the surface and forming CaS clusters by abstraction of sulfur from the thiophene rings, based on XPS and LEIS data. The heat of adsorption then decreases gradually until it reaches the heat of sublimation of bulk Ca, 178 kJ/mol, by 4 ML; this is attributed to the formation of 3D Ca islands on top of the polymer, which eventually coalesce into a continuous Ca film by 11 ML. The heat of reaction versus coverage and the ultimate depth up to which the Ca atoms react with the polymer thiophene groups (∼3 nm) are nearly independent of electron damage, except for a difference in the heat of adsorption below 0.1 ML associated with defects or impurities. The increase in initial sticking probability caused by electron damage is attributed to stronger bonding of Ca adatoms to unsaturated versus saturated hydrocarbons. These very weakly held Ca adatoms are transient precursors to the two reactions which dominate the measured heat of adsorption (reaction with thiophene units and Ca cluster formation), but they can also desorb in this three-path kinetic competition. Mass spectrometer data show that these precursors have longer surface residence times on the electron-damaged surface. © 2010 American Chemical Society.

Interface materials for organic solar cells - Steim, Roland; Kogler, F. Rene; Brabec, Christoph (Journal of Materials Chemistry, 2010)
The progress in the development and understanding of interfacial materials for organic photovoltaics (OPV) is reviewed. The proper choice of interface materials is a must for highly efficient and stable OPV devices and has become a significant part of the OPV research today. Interface materials are either non-conducting, semiconducting or conducting layers which not only provide selective contacts for carriers of one sort, but can also determine the polarity of OPV devices, affect the open-circuit voltage, and act as optical spacers or protective layers. In this review both inorganic and organic interface materials are discussed with respect to their function in the OPV device. © 2010 The Royal Society of Chemistry.

Interface of Ionic Liquids and Carbon: Ultrathin [C1C1Im][Tf2N] Films on Graphite and Graphene - Rietzler, Florian; Nagengast, Jens; Steinrück, Hans-Peter; Maier, Florian (Journal of Physical Chemistry C, 2015)
We investigated the initial adsorption behavior and growth of thin films of ionic liquid (IL) [CCIm][TfN] on highly ordered pyrolytic graphite (HOPG) and on a full and a fractional graphene layer on Ni(111). We found that the initial adsorption behavior and growth strongly depended on the underlying substrate. On HOPG, the IL forms an initial wetting layer with a coverage of 0.5 ML and anions and cations next to each other in direct contact with the substrate. On a complete graphene layer on Ni(111), the wetting layer has twice the thickness with alternately oriented ion pairs next to each other. On top of these wetting layers, further IL growth occurs in 3D islands, with the island formation being less pronounced on the graphene layer. On the fractional graphene layer on Ni(111), initial IL adsorption preferentially occurs on bare Ni surface areas, with anions on top of cations, followed by 3D island growth on both the bare and the graphene-covered surface regions.

Interface properties and physicochemical characterization of the low-temperature molten salt Li/K/Cs acetate - Deyko, Alexey; Bajus, Stephanie; Rietzler, Florian; Bösmann, Andreas; Wasserscheid, Peter; Steinrück, Hans-Peter; Maier, Florian (Journal of Physical Chemistry C, 2013)
The surface of macroscopic films of the ternary molten salt mixture Li KCs[OAc] has been investigated by angle-resolved X-ray photoelectron spectroscopy (XPS) as a function of temperature. With increasing temperature a preferential depletion of K is observed by ∼40%. From temperature programmed desorption we find that the onset for the cation desorption follows the order Cs, K, and Li, with activation energies of 125, 148, and 157 kJ mol, respectively; the corresponding value for the [OAc] anion is 147 kJ mol, which is, within the margin of error, identical to the average of the value found for the cations. Ultrathin films of the molten salt deposited on a Au(111) surface by physical vapor deposition show preferential enrichment of Cs, in line with the lower activation energy and thus higher desorption rate of Cs[OAc] from the ternary mixture. Angle-resolved XPS of the molten salt/gold interface demonstrates that the first molten salt monolayer grows in a layer-by-layer growth, followed by three-dimensional island growth at higher coverages. © 2013 American Chemical Society.

Interfaces of ionic liquids and transition metal surfaces - Adsorption, growth, and thermal reactions of ultrathin [C 1C 1Im] [Tf 2N] films on metallic and oxidised Ni(111) surfaces - Cremer, Till; Wibmer, Leonie; Krick Calderon, Sandra; Deyko, Alexey; Maier, Florian; Steinrück, Hans-Peter (Physical Chemistry Chemical Physics, 2012)
Ultrathin films of the ionic liquid 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([C C Im][Tf N]) were deposited on differently terminated Ni(111) single crystal surfaces. The initial wetting behaviour, the growth characteristics, the molecular arrangement at the interface, and thermal reactivity were investigated using angle-resolved X-ray photoelectron spectroscopy (ARXPS). On clean Ni(111), the initial growth occurs in a layer-by-layer mode. At submonolayer coverages up to at least 0.40 ML, a preferential arrangement of the IL ions in a bilayer structure, with the imidazolium cations in contact with the Ni surface atoms and the anions on top of the cation, is deduced. For higher coverages, a transition to a checkerboard-type arrangement occurs, which is most likely due to repulsive dipole-dipole interactions in the first layer. An overall preference for a checkerboard-type adsorption behaviour, i.e., anions and cations adsorbing next to each other, is found on the oxygen-precovered O(√3×√3)R30°Ni(111) surface. The thermal stability of adsorbed IL layers on Ni(111) and on a fully oxidised Ni(111) surface was studied by heating the layers to elevated temperatures. For clean Ni(111) reversible adsorption takes place. For the oxidised surface, however, only cation-related moieties desorb, starting at ∼450 K, while anion-related signals remain on the surface up to much higher temperatures. © 2012 the Owner Societies.

Interfacial arrangement and phase transitions of PNiPAm microgels with different crosslinking densities - Rey, Marcel; Hou, Xunan; Tang, Jo Sing; Vogel, Nicolas (Soft Matter, 2017)
Microgels are colloidal hydrogel particles that exhibit a pronounced softness, which arises from the swollen nature of the constituent polymer network. This softness leads to a substantial deformability of such particles at liquid interfaces, which, in turn translates into a complex phase behaviour that can exhibit a phase transition between a non-close packed and a close packed arrangement. Here, we explore how the degree of swellability and deformability - and therefore the softness of the particles - affects the phase behaviour of microgels at the air/water interface upon compression. We use precipitation polymerization to synthesize poly(N-isopropylacrylamide) microgels with similar hydrodynamic radii in the collapsed state and systematically vary the degree of swellability by changing the crosslinking density. We spread these microgels onto the air/water interface of a Langmuir trough and characterize their interfacial properties by surface pressure - area isotherms. Furthermore, we continuously transfer the interfacial microgel monolayer during compression onto a solid substrate, thus encoding the complete phase diagram of the microgels with increasing particle density as a function of the position on the solid substrate. We investigate the microgel arrangement by atomic force microscopy and scanning electron microscopy and use image analysis to extract quantitative information on the interparticle distance and degree of order. We find that the phase transition is very sensitive to the crosslinking density and occurs at much lower surface pressures for less deformable particles. The softest microgels do not undergo any phase transition. Instead, the system exhibits pronounced local conformation changes around point defects with local five- and sevenfold symmetries, indicating that the geometry of the assembled structure effectively controls the local pressure experienced by the microgels.

Interfacial behavior of thin ionic liquid films on mica - Deyko, Alexey; Cremer, Till; Rietzler, Florian; Perkin, Susan; Crowhurst, Lorna; Welton, Tom; Steinrück, Hans-Peter; Maier, Florian (Journal of Physical Chemistry C, 2013)
Ultrathin films of two imidazolium-based ionic liquids (ILs), [C CIm][TfN] (=1-methyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and [CCIm][Tf N] (=1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) were deposited on mica surfaces by physical vapor deposition in ultrahigh vacuum. Using angle-resolved X-ray photoelectron spectroscopy (ARXPS), the initial wetting behavior, the growth characteristics, and the molecular arrangement of the ions at the interface were investigated. The measurements were performed on freshly air-cleaved mica surfaces with different carbon precoverages. ARXPS clearly reveals that the initial IL adsorption behavior strongly depends on the amount of preadsorbed carbon: On clean mica, 3D growth (complete dewetting) occurs, whereas on a fully carbon covered surface, initially a complete 2D wetting layer forms, followed by 3D growth. © 2013 American Chemical Society.

Interfacial charge transfer in functionalized multi-walled carbon nanotube@TiO2 nanofibres - Saha, Avishek; Moya, Alicia; Kahnt, Axel; Iglesias, Daniel; Marchesan, Silvia; Wannemacher, Reinhold; Prato, Maurizio; Vilatela, Juan J.; Guldi, Dirk Michael (Nanoscale, 2017)
A new insight into photoinduced charge transfer processes across carbon nanotube@TiO2 interfaces has been gained based on experimental details from transient absorption spectroscopy. We show that photoinduced, interfacial hole transfer to carboxylic acid-functionalized multiwalled carbon nanotubes (oxMWCNTs) from TiO2 results in hole-doped oxMWCNTs and reduced TiO2. The latter is inferred from femto- and nanosecond transient absorption spectroscopy performed with oxMWCNT@TiO2 dispersions and complemented with investigations using methyl viologen and N,N,N',N'-tetramethyl-p-phenylenediamine as an electron scavenger and a hole scavenger, respectively. The results of ultraviolet photoemission spectroscopy (UPS) of the compounds corroborate the findings, highlighting the strong coupling between oxMWCNTs and TiO2 in these hybrids.
EAM Import::2019-03-13

Interfacial energy estimation in a precipitation reaction using the flatness based control of the moment trajectories - Vassilev, Vassil; Gröschel, Michael; Schmid, Hans-Joachim; Peukert, Wolfgang; Leugering, Günter (Chemical Engineering Science, 2010)
In this paper, we consider a model for precipitation experiments based on the population balance equation. The study revealed a high sensitivity of the system with respect to the modeling of intrinsic parameters, motivating a comprehensive validation of the estimates. In the forward simulation the impact of the influencing parameters including surface energy, nucleus size and distribution is investigated. Subsequently we construct a simplified model of the precipitation process in such a way that it is orbitally flat in terms of control theory, which enables the inverse calculation of the parameters. The numerical results of the inverse simulation for the interfacial energy have been compared to a physical model. The possibility of solving the inverse problem provides a promising way of estimating hardly measurable quantities for more complex molecules.

Interfacial interactions of iron(II) tetrapyrrole complexes on Au(111) - Schmid, Martin; Zirzlmeier, Johannes; Steinrück, Hans-Peter; Gottfried, J. Michael (Journal of Physical Chemistry C, 2011)
The electronic structure of monolayers of iron(II) phthalocyanine (FePc), iron(II) octaethylporphyrin (FeOEP), and iron(II) tetraphenylporphyrin (FeTPP), adsorbed on Au(111), was examined with X-ray and UV photoelectron spectroscopy (XPS/UPS). Comparison of the Fe 2p signals of FePc multilayers and monolayers revealed an additional component in the monolayer signal with a binding energy characteristic of Fe(0). This component accounts for ∼20% of the integral Fe 2p intensity, in agreement with previous observations on cobalt porphyrins on Au(111). The partial modification of the Fe 2p states suggests a laterally inhomogeneous interaction of the adsorbed molecules with the metal surface and is possibly related to the complex, reconstructed Au(111) surface morphology. Similar results obtained for FeTPP and FeOEP monolayers indicate that this effect is independent from the structure of the peripheral substituents on the core porphin moiety. The UP spectra of FePc and FeTPP monolayers show further indications for a substrate-molecule interaction mediated by the central Fe atom. In addition, FePc, FeTPP, and 2HTPP monolayers lead to a complete depopulation of the Shockley surface state of the clean Au(111) surface. © 2011 American Chemical Society.

Interfacing strong electron acceptors with single wall carbon nanotubes - Oelsner, Christian; Schmidt, Cordula; Hauke, Frank; Prato, Maurizio; Hirsch, Andreas; Guldi, Dirk Michael; Hauke, Frank (Journal of the American Chemical Society, 2011)
The complementary use of steady-state and time-resolved spectroscopy in combination with electrochemistry and microscopy are indicative of mutual interactions between semiconducting SWNTs and a water-soluble strong electron acceptor, i.e., perylenediimide. Significant is the stability and the strong electronic coupling of the perylenediimide/SWNT electron donor-acceptor hybrids. Several spectroscopic and spectroelectrochemical techniques, i.e., Raman, absorption, and fluorescence, confirmed that distinct ground- and excited-state interactions occur and that kinetically and spectroscopically well characterized radical ion pair states form within a few picoseconds. © 2011 American Chemical Society.

Inter-membrane adhesion mediated by mobile linkers: Effect of receptor shortage - Fenz, Susanne F.; Smith, Ana-Suncana; Merkel, Rudolf; Sengupta, Kheya (Soft Matter, 2011)
Giant unilamellar vesicles (GUVs) adhering to supported bilayers were used as a model system to mimic ligand-receptor mediated cell-cell adhesion. We present the effect of varying the concentration of receptors (neutravidin on the bilayer) and ligands (biotin on the vesicle) on GUV adhesion and the organization of receptors in the adhesion zone. At high concentrations of both ligands and receptors, the adhesion is strong, all the available membrane is adhered and receptors are accumulated under the adhered membrane up to the geometrical limit of close packing. At low concentrations of receptors (<0.5%), and an arbitrary concentration of ligands (>= 0.1%), adhesion does not proceed to completion: the membrane is only partially bound and parts of it still fluctuate. The receptors tend to accumulate under the adhered membrane but the filling is partial. Receptors get jammed and form clusters with fractal like shapes along the rim of the adhered vesicle in such a way that the annular cluster prevents further filling of the adhesion disc. We characterize the filling in terms of a compaction factor and the final concentration. Interestingly, the closing of the ring of jammed clusters switches the interior of the adhesion disc from one thermodynamic ensemble to another. In the new ensemble the receptors sealed within the adhesion disc are mobile but their number is fixed. Under such conditions, the usually strong neutravidin/biotin bond is weak. The incomplete adhesion state can be attributed to a combination of the effects of diffusion, jamming and the competition of enthalpy and entropy on bond formation. The formation of jammed receptor clusters reported here represents a new mechanism that influences membrane adhesion.
Keywords: INTERFERENCE CONTRAST MICROSCOPY; CELL-ADHESION; VESICLE ADHESION; DYNAMICS; SURFACE; BOND; STREPTAVIDIN; GLYCOPROTEIN; TRANSITION; DIFFUSION

Interplay between Solution Processing and Electronic Structure in Metal-Free Organic Magnets Based on a TEMPO Pentacene Derivative - Arantes, C.; Chernick, Erin; Gruber, Marco; Rocco, M. L. M.; Chasse, T.; Tykwinski, Rik; Casu, M. B. (Journal of Physical Chemistry C, 2016)
We have used X-ray photoelectron spectroscopy (XPS) to describe the electronic structure of two newly synthesized derivatives of the 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) carrying the 2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO) radical as a substituent. XPS results underline the existing interplay between electronic structure and preparation methods. Our observations suggest a strong influence of the film processing on the shakeup satellite intensities of the N 1s core level spectra. Preparation methods, by tuning the different degree of intermolecular screening, may be use as a tool to influence the properties and the behavior of these materials as thin films, including their local magnetic-exchange coupling.
EAM Import::2019-03-13

Interplay between the metal- support interaction and stability in Pt/ Co3O4(111) model catalysts - Lykhach, Yaroslava; Faisal, Firas; Skala, Tomas; Neitzel, Armin; Tsud, Nataliya; Vorokhta, Mykhailo; Dvorak, Filip; Beranova, Klara; Kosto, Yuliia; Prince, Kevin C.; Matolin, Vladimir; Libuda, Jörg (Journal of Materials Chemistry A, 2018)
The interplay between the metal-support interaction and stability with respect to sintering has been investigated for Pt nanoparticles supported on well-ordered Co3O4(111)/Ir(100) films in UHV and under oxidizing conditions by means of synchrotron radiation photoelectron spectroscopy (SRPES) and near ambient pressure X-ray photoelectron spectroscopy (NAP XPS). The electronic metal-support interaction between Pt and Co3O4(111) associated with charge transfer results in partial reduction of Co3O4(111) yielding partially oxidized Pt+ species at the interface. The stability of the supported Pt particles is coupled with the oxidation state of Pt+ species, which can be reduced or oxidized depending on the Pt coverage and reactive environment. Annealing of Pt/Co3O4(111)/Ir(100) in UHV triggers the reduction of Pt+ species. At higher temperature, reverse spillover of oxygen to the Pt nanoparticles is accompanied by reduction of Co3O4(111). Under these conditions, the oxidation state of Pt+ species depends strongly on Pt coverage. Thus, at low Pt coverage (0.3 ML Pt), Pt+ is converted to Pt4+, at intermediate coverage (1.3 ML Pt), Pt+ remains stable, and at high Pt coverage (1.93 ML), Pt+ is reduced to Pt-0. Sintering of Pt particles is associated with the reduction of the Pt+ species. This process is prevented under oxidizing conditions due to the formation of an interfacial oxide PtOx. The formation of an interfacial PtOx is observed at 300 K under exposure to 1 x 10(-6) mbar O-2 at Pt coverages below 1.3 ML. Using NAP XPS, we observe the formation of an interfacial PtOx at high Pt coverage (2.0 ML) in an oxygen atmosphere (1 mbar) at 300 K while the formation of surface PtOx is kinetically hindered and occurs above 550 K only.

Interplay of Internal Structure and Interfaces on the Emitting Properties of Hybrid ZnO Hierarchical Particles - Distaso, Monica; Bertoni, Giovanni; Todisco, Stefano; Marras, Sergio; Gallo, Vito; Manna, Liberato; Peukert, Wolfgang (ACS Applied Materials and Interfaces, 2017)
The design of hybrid organic/inorganic nanostructures with controlled assembly drives the development of materials with new or improved properties and superior performances. In this paper, the surface and internal structure of hybrid ZnO poly-N-vinylpyrrolidone (ZnO/PVP) mesocrystals are investigated in detail and correlated with their emitting properties. A photoluminescence study at room temperature reveals that the as-synthesized particles show a remarkable ultraviolet (UV) emission, whereas an emission from defects in the visible region is not observed. On the other hand, a visible emission is achieved upon calcination of the hybrid ZnO/PVP particles in air, and its intensity is found to increase with the calcination temperature and, in some cases, to overwhelm the UV emission. A molecular description is proposed for the absence of a visible emission from defects in the as-synthesized ZnO/PVP mesocrystals on the basis of Fourier transform infrared (FTIR) and solid-state (13)C NMR (SSNMR) spectroscopy. An in-depth electron microscopy study sheds light on the internal organization of mesocrystals and reveals the formation of nanoreactors, that is, particles with enclosed porosity, upon thermal treatment.
Keywords: structure-function relationship; nanoreactors; postprocessing; coordination; nanocomposites; mesocrystals

Intricate routes to chaos in the Mackey-Glass delayed feedback system - Gallas, Jason A.; Gallas, Jason; Junges, Leandro (Physics Letters A, 2012)
We describe some remarkable continuous deformations which create and destroy peaks in periodic oscillations of the Mackey–Glass equation, a paradigmatic example of a delayed feedback system. Peak creation and destruction results in richer bifurcation diagrams which, in addition to the familiar branches arising from period-doubling and peak-adding bifurcations, may also display arbitrary combinations of doubling and adding, leading to highly complex mosaics of stability domains in control parameter space. In addition, we show that the onset of higher dimensionality does not alter the prevailing dynamics instantaneously and, remarkably, even may have no effect at all, a result that cannot be predicted analytically with standard methods.

Intrinsic and extrinsic size effects in the deformation of amorphous CuZr/nanocrystalline Cu nanolaminates - Guo, Wei; Jaegle, Eric; Yao, Jiahao; Maier, Verena; Korte, Sandra; Schneider, Jochen M.; Raabe, Dierk (Acta Materialia, 2014)
Introducing a soft crystalline phase into an amorphous alloy can promote the compound's ductility. Here we synthesized multilayered nanolaminates consisting of alternating amorphous Cu54Zr46 and nanocrystalline Cu layers. The Cu layer thickness was systematically varied in different samples. Mechanical loading was imposed by nanoindentation and micropillar compression. Increasing the Cu layer thickness from 10 to 100 am led to a transition from sharp, cross-phase shear banding to gradual bending and co-deformation of the two layer types (amorphous/nanocrystalline). Specimens with a sequence of 100 nm amorphous Cu54Zr46 and 50 nm Cu layers show a compressive flow stress of 2.57 +/- 0.21 GPa, matching the strength of pure CuZr metallic glass, hence exceeding the linear rule of mixtures. In pillar compression, 40% strain without fracture was achieved by the suppression of percolative shear band propagation. The results show that inserting a ductile nanocrystalline phase into a metallic glass prevents catastrophic shear banding. The mechanical response of such nanolaminates can be tuned by adjusting the layer thickness. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keywords: Nanolaminates; Metallic glass; Nanotwins; Shear band

Intrinsic Au Decoration of Growing TiO2 Nanotubes and Formation of a High-Efficiency Photocatalyst for H2 Production - Lee, Kiyoung; Hahn, Robert; Altomare, Marco; Selli, Elena; Schmuki, Patrik (Advanced Materials, 2013)
Electrochemical anodization of low-concentration (0.02–0.2 at% Au) TiAu alloys in a fluoride electrolyte leads to self-organized TiO2 nanotubes that show a controllable, regular in situ decoration with elemental Au nanoclusters of ≈5 nm in diameter. The degree of self-decoration can be adjusted by the Au concentration in the alloy and the anodization time. Such Au particle decorated tubes show a high activity for photocatalytic H2 production from ethanol solutions.
EAM Import::2019-03-13

Introducing a New Potential Figure of Merit for Evaluating Microstructure Stability in Photovoltaic Polymer-Fullerene Blends - Perea, Jose Dario; Langner, Stefan; Salvador, Michael Filipe; Sanchez-Lengeling, Benjamin; Li, Ning; Zhang, Chaohong; Jarvas, Gabor; Kontos, Janos; Dallos, Andras; Aspuru-Guzik, Alan; Brabec, Christoph (Journal of Physical Chemistry C, 2017)
A theoretical understanding of the microstructure of organic semiconducting polymers and blends is vital to further advance the optoelectronic device performance of organic electronics. We outline the theoretical framework of a combined numerical approach based on polymeric solution theory to study the microstructure of polymer:small molecule blends. We feed the results of ab initio density functional theory quantum chemistry calculations into an artificial neural network for the determination of solubility parameters. These solubility parameters are used to calculate Flory-Huggings intermolecular parameters. We further show that the theoretical values are in line with experimentally determined data. On the basis of the Flory-Huggings parameters, we establish a figure of merit as a relative metric for assessing the phase diagrams of organic semiconducting blends in thin films. This is demonstrated for polymer:fullerene blend films on the basis of the prototypical polymers poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3-di(2-octyldodecyl)-2,2,5,2;5,2-quaterthiophen-5,5-diyl)] (PffBT4T-2OD). After confirming the applicability of our model with a broader range of materials and differences in molecular weight, we suggest that this combined model should be able to inform design criteria and processing guidelines for existing and new high performance semiconducting blends for organic electronics applications with ideal and stable solid state morphology. (Graph Presented). © 2017 American Chemical Society.
Keywords: BlendingCalculationsDensity functional theoryFullerenesMicrostructureNeural networksOptoelectronic devicesOrganic polymersPolymer filmsPolymersQuantum chemistrySemiconducting filmsSemiconducting polymersSolubility

Inverted, Environmentally Stable Perovskite Solar Cell with a Novel Low-Cost and Water-Free PEDOT Hole-Extraction Layer - Hou, Yi; Zhang, Hong; Chen, Wei; Chen, Shi; Ramírez Quiroz, César Omar; Azimi, Seyed Hamed; Osvet, Andres; Matt, Gebhard; Zeira, Eitan; Seuring, Jan; Kausch-Busies, Nina; Loevenich, Wilfried; et al. (Advanced Energy Materials, 2015)
A power conversion efficiency of 11.8% is demonstrated for planar perovskite solar cell based on acid water-free poly(3,4-ethylenedioxythiophene) (PEDOT) as the hole-transporting layer. This efficiency is further improved to 14.2% using a pH neutralized PEDOT, which reduces the sub-gap defects at the surface of perovskite. All the active layers reported are solution-processed at temperatures below 140 °C making it compatible with roll-to-roll production.
Keywords: low-temperature processing; perovskite solar cells; stabilities; water-free poly(3; 4-ethylenedioxythiophene)

Inverted organic solar cells using a solution processed aluminum-doped zinc oxide buffer layer - Stubhan, Tobias; Oh, Hyunchul; Pinna, Luigi; Krantz, Johannes; Litzov, Ivan; Brabec, Christoph (Organic Electronics, 2011)
In this article, we demonstrate a route to solve one of the big challenges in the large scale printing process of organic solar cells, which is the reliable deposition of very thin layers. Especially materials for electron (EIL) and hole injection layers (HIL) (except poly(3,4-ethylene dioxythiophene): (polystyrene sulfonic acid) (PEDOT:PSS)) have a low conductivity and therefore require thin films with only a few tens of nanometers thickness to keep the serial resistance under control. To overcome this limitation, we investigated inverted polymer solar cells with an active layer comprising a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-butyric acid methyl ester (PCBM) with solution processed aluminum-doped zinc oxide (AZO) EIL. Devices with AZO and intrinsic zinc oxide (i-ZnO) EIL show comparable efficiency at low layer thicknesses of around 30 nm. The conductivity of the doped zinc oxide is found to be three orders of magnitude higher than for the i-ZnO reference. Therefore the buffer layer thickness can be enhanced significantly to more than 100 nm without hampering the solar cell performance, while devices with 100 nm i-ZnO films already suffer from increased series resistance and reduced efficiency. © 2011 Elsevier B.V. All rights reserved.
Keywords: Al doped ZnO; Electron injection layer; Inverted structure; Polymer solar cell; Solution processing; Zinc oxide nanoparticles

"Inverted'' porphyrins: a distorted adsorption geometry of free-base porphyrins on Cu(111) - Lepper, Michael; Köbl, Julia; Schmitt, Tobias; Gurrath, Martin; De Siervo, Abner; Schneider, M. Alexander; Steinrück, Hans-Peter; Meyer, Bernd; Marbach, Hubertus; Hieringer, Wolfgang (Chemical Communications, 2017)
Based on density functional theory calculations combined with experimental results, we report and discuss an extremely distorted, "inverted'' adsorption geometry of free-base tetraphenylporphyrin on Cu(111). The current findings yield new insights into a wellstudied system, shedding light on the peculiar molecule-substrate interaction and the resulting intramolecular conformation.

Investigating H-2 Sorption in a Fluorinated Metal-Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering - Forrest, Katherine A.; Pham, Tony; Georgiev, Peter A.; Pinzan, Florian; Cioce, Christian R.; Unruh, Tobias; Eckert, Juergen; Space, Brian (Langmuir, 2015)
Simulations of H-2 sorption were performed in a metal organic framework (MOF) consisting of Zn2+ ions coordinated to 1,2,4-triazole and tetrafluoroterephthalate ligands (denoted [Zn(trz)(tftph)] in this work). The simulated H-2 Sorption isotherms reported in this work are consistent with the experimental data for the state points considered. The experimental H-2 isosteric heat of adsorption (Q(st)) values for this MOP are approximately 8.0 KJ mol(-1) for the considered loading range, which is in the proximity of those determined from simulation. The experimental inelastic neutron scattering (INS) spectra for H-2 in [Zn(trz)(tftph)] reveal at least two peaks that occur at low energies, which corresponds to high barriers to rotation for the respective sites. The most favorable sorption site in the MOF was identified from the simulations as sorption in the vicinity of a metal coordinated H2O molecule, an exposed fluorine atom, and a carboxylate oxygen atom in a confined region in the framework. Secondary sorption was observed between the fluorine atoms of adjacent tetrafluoroterephthalate ligands. The H-2 molecule at the primary sorption site in [Zn(trz)(tftph)] exhibits a rotational barrier that exceeds that for most neutral MOFs with open-metal sites according to an empirical phenomenological model, and this was further validated by calculating the rotational potential energy surface for H-2 at this site.

Investigation of interphase effects in silica-polystyrene nanocomposites based on a hybrid molecular-dynamics-finite-element simulation framework - Pfaller, Sebastian; Possart, Gunnar; Steinmann, Paul; Rahimi, Mohammad; Müller-Plathe, Florian; Böhm, Michael C. (Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2016)
A recently developed hybrid method is employed to study the mechanical behavior of silica-polystyrene nanocomposites (NCs) under uniaxial elongation. The hybrid method couples a particle domain to a continuum domain. The region of physical interest, i.e., the interphase around a nanoparticle (NP), is treated at molecular resolution, while the surrounding elastic continuum is handled with a finite-element approach. In the present paper we analyze the polymer behavior in the neighborhood of one or two nanoparticle(s) at molecular resolution. The coarse-grained hybrid method allows us to simulate a large polymer matrix region surrounding the nanoparticles. We consider NCs with dilute concentration of NPs embedded in an atactic polystyrene matrix formed by 300 chains with 200 monomer beads. The overall orientation of polymer segments relative to the deformation direction is determined in the neighborhood of the nanoparticle to investigate the polymer response to this perturbation. Calculations of strainlike quantities give insight into the deformation behavior of a system with two NPs and show that the applied strain and the nanoparticle distance have significant influence on the deformation behavior. Finally, we investigate to what extent a continuum-based description may account for the specific effects occurring in the interphase between the polymer matrix and the NPs.
EAM Import::2019-03-13

Investigation of proximity effects in electron microscopy and lithography - Walz, Marie-Madeleine; Vollnhals, Florian; Rietzler, Florian; Schirmer, Michael; Steinrück, Hans-Peter; Marbach, Hubertus (Applied Physics Letters, 2012)
A fundamental challenge in lithographic and microscopic techniques employing focused electron beams are so-called proximity effects due to unintended electron emission and scattering in the sample. Herein, we apply a method that allows for visualizing electron induced surface modifications on a SiN substrate covered with a thin native oxide layer by means of iron deposits. Conventional wisdom holds that by using thin membranes proximity effects can be effectively reduced. We demonstrate that, contrary to the expectation, these can be indeed larger on a 200 nm SiN-membrane than on the respective bulk substrate due to charging effects. © 2012 American Institute of Physics.

Investigation of the size-property relationship in CuInS2 quantum dots - Akdas, Tugce; Walter, Johannes; Segets, Doris; Distaso, Monica; Winter, Benjamin; Birajdar, Balaji; Spiecker, Erdmann; Peukert, Wolfgang (Nanoscale, 2015)
In this work we investigated fundamental properties of CuInS2 quantum dots in dependence of the particle size distribution (PSD). Size-selective precipitation (SSP) with acetone as poor solvent was performed as an adequate post-processing step. Our results provide deep insight into the correlation between particle size and various optical characteristics as bandgap energy, absorption and emission features and the broadness of the emission signal. These structure-property relationships are only achieved due to the unique combination of different analytical techniques. Our study reveals that the removal of 10 wt% of smallest particles from the feed results in an enhancement of the emission signal. This improvement is ascribed to a decreased quenching of the emission in larger particles. Our results reveal the impact of PSDs on the properties and the performance of an ensemble of multicomponent QDs and anticipate the high potential of controlling PSDs by well-developed post-processing.

Investigation of the thermal stability of the carbon framework of graphene oxide - Eigler, Siegfried; Grimm, Stefan; Hirsch, Andreas (Chemistry - A European Journal, 2014)
In this study, we use our recently prepared graphene oxide (GO) with an almost intact σ-framework of carbon atoms (ai-GO) to probe the thermal stability of the carbon framework for the first time. Ai-GO exhibits few defects because CO formation is prevented during synthesis. Ai-GO was thermally treated before chemical reduction and the resulting defect density in graphene was subsequently determined by statistical Raman microscopy. Surprisingly, the carbon framework of ai-GO is stable in thin films up to 100°C. Furthermore, we find evidence for an increase in the quality of ai-GO upon annealing at 50°C before reduction. The carbon framework of GO prepared according to the popular Hummers' method (GO-c) appears to be less stable and decomposition starts at 50°C, which is qualitatively indicated by CO-trapping experiments in μm-thin films. Information about the stability of GO is important for storing, processing, and using GO in many applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation on the tribological-mechanical behavior of amorphous carbon coatings by load-scanning tests - Hetzner, Harald; Schaufler, Jens; Pejic, Goran; Tremmel, Stephan; Durst, Karsten; Wartzack, Sandro (Materialwissenschaft und Werkstofftechnik, 2012)
Amorphous carbon coatings have a beneficial tribological behaviour since they provide low friction even under dry sliding conditions and at the same time they offer a good wear protection. Under high loads, the applicability of state-of-the-art amorphous carbon coatings is limited by mechanical failure. However, there is still little knowledge concerning the precise failure mechanisms under application-oriented conditions. In the present study, cylindrical specimens of a cold work tool steel were coated with two commercial amorphous carbon coating systems: a WCC coating with an a-C:H:W top layer and a DLC coating which architecture is based on that of the WCC coating, but contains an additional a-C:H top layer. The coated specimens were tested on a load-scanning test rig in dry sliding contact against uncoated specimens of the same steel substrate. In the tests, the specimens were loaded with a normal force in the range of 13 and 350 N, corresponding to a maximum contact pressure of 1 to 3 GPa. The number of load cycles was varied between 1 and 60. Firstly, the load-dependent friction behaviour was monitored. Secondly, the tests were stopped at different total cycle numbers allowing for an evaluation of the progress of wear and damage by scanning electron microscopy. For both coating systems, adhesive pick-up of counter body steel was observed prior to mechanical failure. Whilst the WCC coating system showed first indications of local failure after several load cycles and at contact pressures exceeding 2 GPa, the DLC coating system showed catastrophic failure on a global scale only after few load cycles and over the whole investigated load range.
EAM Import::2019-03-13

Investigations on the growth of bismuth oxido clusters and the nucleation to give metastable bismuth oxide modifications - Weber, Marcus; Schlesinger, Maik; Walther, Markus; Zahn, Dirk; Schalley, Christoph A.; Mehring, Michael (Zeitschrift für Kristallographie, 2017)
Investigations on bismuth oxido clusters are focused on the nucleation and growth processes towards large cluster motifs and their stability in the gas phase, which has been studied by electrospray ionization mass spectrometry (ESI-MS), molecular dynamics (MD) simulations and X-ray scattering experiments evaluated by pair distribution function (PDF) analysis. The formation of metastable bismuth(III) oxides was obtained by hydrolysis of polynuclear bismuth oxido clusters and subsequent thermal treatment under non-equilibrium conditions. Temperature dependent PXRD and Raman spectroscopic experiments gave insight into the formation process of metastable extgreekb-Bi2O3 starting from the amorphous hydrolysis products as-obtained from polynuclear bismuth oxido clusters. Furthermore, PXRD as well as energy-dispersive X-ray (EDX) spectroscopy confirmed the formation of several new ternary bismuth(III) rich oxides such as Bi14O20(MO4) (M=S, Se) as-obtained by hydrolysis of bismuth oxido clusters in the presence of diverse additives.
EAM Import::2019-03-13

In vivo performance of selective electron beam-melted Ti-6Al-4V structures - Ponader, Sabine; von Wilmowsky, Cornelius; Widenmayer, Martin; Lutz, Rainer; Heinl, Peter; Körner, Carolin; Singer, Robert; Nkenke, Emeka; Neukam, Friedrich Wilhelm; Schlegel, Karl (Journal of Biomedical Materials Research Part A, 2010)
Highly porous titanium structures are widely used for maxillofacial and orthopedic surgery because of their excellent mechanical properties similar to those of human bone and their facilitation of bone ingrowth. In contrast to common methods, the generation of porous titanium products by selective electron beam melting (SEBM), an additive manufacturing technology, overcomes difficulties concerning the extreme chemical affinity of liquid titanium to atmospheric gases which consequently leads to strongly reduced ductility of the metal. The purpose of this study was to assess the suitability of a smooth compact and a porous Ti-6Al-4V structure directly produced by the SEBM process as scaffolds for bone formation. SEBM-processed titanium implants were placed into defects in the frontal skull of 15 domestic pigs. To evaluate the direct contact between bone and implant surfaces and to assess the ingrowth of osseous tissue into the porous structure, microradiographs and histomorphometric analyses were performed 14, 30, and 60 days after surgery. Bone ingrowth increased significantly during the period of this study. After 14 days the most outer regions of the implants were already filled with newly formed bone tissue (around 14%). After 30 days the bone volume inside the implants reached almost 30% and after 60 days abundant bone formation inside the implants attained 46%. During the study only scarce bone-implant contact was found around all implants, which did not exceed 9% around compact specimens and 6% around porous specimens after 60 days. This work demonstrates that highly porous titanium implants with excellent interconnectivity manufactured using the SEBM method are suitable scaffolds for bone ingrowth. This technique is a good candidate for orthopedic and maxillofacial applications. © 2009 Wiley Periodicals, Inc.
Keywords: Bone ingrowth; Bone regeneration; Porous structures; Selective electron beam melting (SEBM); Titanium alloys

Iodine-Pseudohalogen Ionic Liquid-Based Electrolytes for Quasi-Solid-State Dye-Sensitized Solar Cells - Lennert, Annkatrin; Sternberg, Michelle; Meyer, Karsten; Costa, Ruben Dario; Guldi, Dirk Michael (ACS Applied Materials and Interfaces, 2017)
In the current work, novel symmetrically alkyl-substituted imidazolium-based ionic liquids have been synthesized featuring either iodide (I-) or selenocyanate (SeCN-) as counteranions. Physicochemical assays based on spectroscopy and electrochemistry techniques have been performed to identify the best ionic liquid for application as electrolytes in quasi-solid-state dye-sensitized solar cells (qssDSSC). The latter were mixed with additives such as 4-tert-butylpyridine (4tbpy) and guanidinium thiocyanate (GuSCN) to optimize electrode surface coverage, ionic diffusion, and dye regeneration. In addition, we demonstrate that electrolytes containing a mixture of I2 and (SeCN)2 enhance the open-circuit voltage of the final quasi-solid-state device by up to 70 mV. As such, iodine-pseudohalogen electrolytes reveal in qssDSSCs a good balance between dye regeneration and hole transport and, in turn, enhance the overall solar energy conversion efficiency by 70% with respect to reference qssDSSCs with iodine-based electrolytes. Finally, devices with the iodine-pseudohalogen electrolyte show a 1000 h stable efficiency of 7-8% under outdoor temperature operation conditions and 1 sun illumination.
EAM Import::2019-03-13

Ionic liquid based model catalysis: Interaction of [BMIM][Tf2N] with Pd nanoparticles supported on an ordered alumina film - Sobota, Marek; Schmid, Martin; Happel, Markus; Amende, Maximilian; Maier, Florian; Steinrück, Hans-Peter; Paape, Natalia; Wasserscheid, Peter; Laurin, Mathias; Gottfried, Michael; Libuda, Jörg (Physical Chemistry Chemical Physics, 2010)
Towards a better understanding of novel catalytic materials consisting of supported noble metal catalysts modified by an ionic liquid (IL) film, we have performed a study under ultrahigh-vacuum (UHV) conditions. The model surface consists of Pd nanoparticles grown in UHV on an ordered alumina film on NiAl(110). Thin films of the room temperature IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][TfN] are deposited onto this surface by means of physical vapor deposition (PVD). The interaction of the IL with clean and CO-covered Pd/AlO/NiAl(110) at 300 K and the thermal behavior of the deposited IL films on Pd/AlO /NiAl(110) are investigated by time-resolved infrared reflection absorption spectroscopy (TR-IRAS) and X-ray photoelectron spectroscopy (XPS). At 300 K, the IL adsorbs molecularly both onto the Pd particles and onto the alumina. The IR spectra suggest that the [TfN] anions interact with Pd sites preferentially via the sulfonyl groups. CO pre-adsorbed on the Pd particles is partially displaced by the IL, even at 300 K, and only the part of CO adsorbed onto hollow sites on (111) facets of the Pd particles remains in place. Upon heating to temperatures higher than the desorption temperature of the IL (>400 K), molecular desorption of the IL competes with decomposition. The decomposition products, atomic species and small fragments, remain preferentially adsorbed onto the Pd nanoparticles and strongly modify their surface properties. Most of the decomposition products originate from the [BMIM] cations, whereas the [TfN] anions desorb for the most part. © 2010 the Owner Societies.

Ionic Liquid-Modified Electrocatalysts: The Interaction of [C1C2Im][OTf] with Pt(1 1 1) and its Influence on Methanol Oxidation Studied by Electrochemical IR Spectroscopy - Brummel, Olaf; Faisal, Firas; Bauer, Tanja; Pohako-Esko, Kaija; Wasserscheid, Peter; Libuda, Jörg (Electrochimica Acta, 2016)
Ionic liquids (ILs) have recently been proposed as modifying agents to tune the selectivity and the activity of electrocatalysts. In order to explore the origin of IL-induced effects on electrocatalytic reactions, we have investigated (i) the interaction of [CCIm][OTf]-water mixtures with Pt(1 1 1) single crystal electrodes and (ii) the influence of [CCIm][OTf] on methanol oxidation in acidic aqueous solution using cyclic voltammetry (CV) and electrochemical IR spectroscopy. We show that [CCIm][OTf] interacts strongly with the Pt(1 1 1) surface in the potential range from -0.2 V to 0.65 V, leading to partial blocking of the surface, partial suppression of hydrogen adsorption, and partial suppression of OH formation. The interaction of the IL with Pt occurs in this potential range via specific adsorption of the [OTf] anions which bind to Pt(1 1 1) via the SO group in a tilted adsorption geometry. The adsorption process is largely reversible as a function of the electrode potential, but shows a complex kinetics and becomes very slow at high IL coverage. Also, [CCIm][OTf] has a strong effect on the electro-oxidation of methanol in acidic solution. Adsorption of [OTf] leads to partial blocking of the indirect oxidation pathway to CO. The onset potential for CO oxidation is found to be shifted to more positive values indicating hindered access of HO to the electrode surface. CO and the [CCIm][OTf] form a mixed co-adsorption layer which is characterized by a strongly red-shifted CO stretching band. The effect is assigned to an IL-induced ligand effect in the mixed adsorbate layer and suggests that the direct modification of active centers by surface-bound IL species plays an important role in IL-modified electrocatalytic materials.
Keywords: carbon monoxide; electrochemical IR spectroscopy; Ionic liquids; methanol oxidation; platinum

Ionic-Liquid-Modified Hybrid Materials Prepared by Physical Vapor Codeposition: Cobalt and Cobalt Oxide Nanoparticles in [C(1)C(2)Im][OTf] Monitored by In Situ IR Spectroscopy - Mehl, Sascha; Bauer, Tanja; Brummel, Olaf; Pohako-Esko, Kaija; Schulz, Peter; Wasserscheid, Peter; Libuda, Jörg (Langmuir, 2016)
The synthesis of ionic-liquid-modified nanomaterials has, attracted much attention recently. In this study we explore the potential to prepare such systems in an ultraclean fashion by physical vapor codeposition (PVCD). We codeposit metallic cobalt and the room-temperature ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [C(1)C(2)Im][OTf] simultaneously onto a Pd(111) surface at 100 K. This process is performed under ultrahigh-vacuum (UHV) conditions in the presence of CO, or in the presence of O-2 and CO. We use time-resolved (TR) and temperature-programmed (TP) infrared reflection absorption spectroscopy (IRAS) to investigate the formation and stability of the IL-modified Co deposits in situ during the PVD-based synthesis. CO is used as a probe molecule to monitor the growth. After initial growth of flat Co films on Pd(111), multilayers of Co nanoparticles (NPs) are formed. Characteristic shifts and intensity changes are observed in the vibrational bands of both CO and the IL, which originate from the electric field at the IL/Co interface (Stark effect) and from specific adsorption of the [OTf](-) anion. These observations indicate that the Co aggregates are stabilized by mixed adsorbate shells consisting of CO and [OTf](-). The CO coverage on the Co particle decreases with increasing temperature, but some CO is preserved up to the desorption temperature of the IL (370 K). Further, the IL shell suppresses the oxidation of the Co NPs if oxygen is introduced in the PVCD process. Only chemisorbed oxygen is formed at oxygen partial pressures that swiftly lead to formation of Co3O4 in the absence of the IL (5 X 10(-6) mbar O-2). This chemisorbed oxygen is found to destabilize the CO ligand shell. The oxidation of Co is not suppressed if IL and Co are deposited sequentially under otherwise identical conditions. In this case we observe the formation of fully oxidized cobalt oxide particles.

Ionic Liquids for Electrolyte-Gating of ZnO Field-Effect Transistors - Thiemann, Stefan; Sachnov, Swetlana; Porscha, S.; Wasserscheid, Peter; Zaumseil, Jana (Journal of Physical Chemistry A, 2012)
We investigate the influence of the chemical structure of a range of imidazolium-based ionic liquids (IL) on their properties as electrolytes and the device characteristics of electrolyte-gated field-effects transistors (FETs) based on spray-deposited polycrystalline zinc oxide (ZnO). We find a decrease of electron field-effect mobility that correlates with the capacitance of the ionic liquids and not only with the size of the IL-cation. The device stability depends significantly on testing conditions. While they are reasonably stable in nitrogen, ZnO-FETs degrade rapidly in ambient air due to absorption of water by the IL and the resulting ZnO surface reactions. Replacement of the most acidic hydrogen atom of the imidazolium cation and surface passivation of ZnO with hexamethyldisilazane improve environmental stability.

Ionic liquid silver salt complexes for propene/propane separation - Agel, Friederike; Pitsch, Fee; Krull, Florian Felix; Schulz, Peter; Wessling, Matthias; Melin, Thomas; Wasserscheid, Peter (Physical Chemistry Chemical Physics, 2010)
Properties of the room-temperature liquid complex salt [Ag(propene)x][Tf2N] have been studied to probe its suitability for acting as active separation layer in immobilised liquid membrane (ILM) concepts for propane/propene separation. The pressure/temperature range of complex formation has been determined and the thermal properties of Ag[Tf2N] and [Ag(propene)x][Tf2N] have been studied by DSC (differential scanning calorimetry) and TGA (thermogravimetric analysis) measurements. Pressure dependent measurements of solubility and diffusivity showed that the observed membrane selectivity is dominated by the solubility selectivity. The self-diffusion coefficient of propene is always smaller compared to propane as propene is temporarily bound to the silver ion in the [Ag(propene)x][Tf2N] ionic liquid.

Ionic Liquids in Catalysis - Wasserscheid, Peter; Steinrück, Hans-Peter (Catalysis Letters, 2015)
Ionic liquids (ILs), salts with melting points below 100 °C, represent a fascinating class of liquid materials typically characterized by an extremely low vapor pressure. Besides their application as new solvents or as electrolytes for electrochemical purposes, there are two important concepts of using ILs in catalysis: Liquid–liquid biphasic catalysis and IL thin film catalysis. Liquid–liquid biphasic catalysis enables either a very efficient manner to apply catalytic ILs, e.g. in Friedel–Crafts reactions, or to apply ionic transition metal catalyst solutions. In both cases, phase separation after reaction allows an easy separation of reaction products and catalyst re-use. One problem of liquid–liquid biphasic catalysis is mass transfer limitation. If the chemical reaction is much faster than the liquid–liquid mass transfer the latter limits the overall reaction rate. This problem is overcome in IL thin film catalysis where diffusion pathways and thus the characteristic time of diffusion are short. Here, Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL) are the two most important concepts. In both, a high surface area solid substrate is covered with a thin IL film, which contains either a homogeneously dissolved transition metal complex for SILP, or which modifies catalytically active surface sites at the support for SCILL. In each concept, interface phenomena play a very important role: These may concern the interface of an IL phase with an organic phase in the case of liquid–liquid biphasic catalysis. For IL thin film catalysis, the interfaces of the IL with the gas phase and with catalytic nanoparticles and/or support materials are of critical importance. It has recently been demonstrated that these interfaces and also the bulk of ILs can be investigated in great detail using surface science studies, which greatly contributed to the fundamental understanding of the catalytic properties of ILs and supported IL materials. Exemplary results concerning the IL/vacuum or IL/gas interface, the solubility and surface enrichment of dissolved metal complexes, the IL/support interface and the in situ monitoring of chemical reactions in ILs are presented.
Keywords: Heterogeneous catalysis; Catalysis; Homogeneous catalysis; Green chemistry; Evaporation; Methodology and Phenomena; XPS; Spectroscopy and General Characterisation; Ionic liquids; Preparation and Materials

Ionic Liquids in Chemical Engineering - Werner, Sebastian; Haumann, Marco; Wasserscheid, Peter (Annual Review of Chemical and Biomolecular Engineering, 2010)
The development of engineering applications with ionic liquids stretches back to the mid-1990s when the first examples of continuous catalytic processes using ionic liquids and the first studies of ionic liquid–based extractions were published. Ever since, the use of ionic liquids has seen tremendous progress in many fields of chemistry and engineering, and the first commercial applications have been reported. The main driver for ionic liquid engineering applications is to make practical use of their unique property profiles, which are the result of a complex interplay of coulombic, hydrogen bonding and van der Waals interactions. Remarkably, many ionic liquid properties can be tuned in a wide range by structural modifications at their cation and anion. This review highlights specific examples of ionic liquid applications in catalysis and in separation technologies. Additionally, the application of ionic liquids as working fluids in process machines is introduced.

Ionic liquids in electrocatalysis - Zhang, Guirong; Etzold, Bastian (Journal of Energy Chemistry, 2016)
The performance of an electrocatalyst, which is needed e.g. for key energy conversion reactions such as hydrogen evolution, oxygen reduction or CO2 reduction, is determined not only by the inherent structure of active sites but also by the properties of the interfacial structures at catalytic surfaces. Ionic liquids (ILs), as a unique class of metal salts with melting point below 100 °C, present themselves as ideal modulators for manipulations of the interfacial structures. Due to their excellent properties such as good chemical stability, high ionic conductivity, wide electrochemical windows and tunable solvent properties the performance of electrocatalysts can be substantially improved through ILs. In the current minireview, we highlight the critical role of the IL phase at the microenvironments created by the IL, the liquid electrolyte, catalytic nanoparticles and/or support materials, by detailing the promotional effect of IL in electrocatalysis as reaction media, binders, and surface modifiers. Updated exemplary applications of IL in electrocatalysis are given and moreover, the latest developments of IL modified electrocatalysts following the ``Solid Catalyst with Ionic Liquid Layer (SCILL)'' concept are presented.
EAM Import::2019-03-12

Ionic Liquids in Refinery Desulfurization: Comparison between Biphasic and Supported Ionic Liquid Phase Suspension Processes - Kuhlmann, Esther; Haumann, Marco; Jess, Andreas; Seeberger, Andreas; Wasserscheid, Peter (Chemsuschem, 2009)
The desulfurization of fuel compounds in the presence of ionic liquids is reported. For this purpose, the desulfurization efficiency of a variety of imidazolium phosphate ionic liquids has been tested. Dibenzothiophene/dodecane and butylmercaptan/decane mixtures were used as model systems. Single-stage extractions reduced the sulfur content from 500ppm to 200ppm. In multistage extractions the sulfur content could be lowered to less than 10ppm within seven stages. Regeneration of the ionic liquid was achieved by distillation or re-extraction procedures. Supported ionic liquid phase (SILP) materials, obtained by dispersing the ionic liquid as a thin film on highly porous silica, exhibited a significantly higher extraction performance owing to their larger surface areas, reducing the sulfur content to less than 100ppm in one stage. Multistage extraction with these SILP materials reduced the sulfur level to 50ppm in the second stage. The SILP technology offers very efficient utilization of ionic liquids and circumvents mass transport limitations because of the small film thickness and large surface area, and allows application of the simple packed-bed column extraction technique.

Ion speciation driving chirality transfer in imidazolium-based camphorsulfonate ionic liquid solutions - Huang, Mian-Mian; Schneiders, Karola; Schulz, Peter; Wasserscheid, Peter; Weingaertner, Hermann (Physical Chemistry Chemical Physics, 2011)
The underlying principle of the chirality transfer in imidazolium-based camphorsulfonate ionic liquids is rationalized by linking catalytic results from the hydrogenation of [N-(3′-oxobutyl)-N-methylimidazolium] [(+)-camphorsulfonate] to [N-(3′-hydroxybutyl)-N-methylimidazolium] [(+)-camphorsulfonate] in tetrahydrofuran with electrolyte theory by the help of dielectric relaxation spectroscopy. Using this approach we are able to explain why the maximum of the enantiomeric excess of the hydrogenation reaction in tetrahydrofuran is found at a medium concentration of 0.15 mol L-1, whereas it declines at both, lower and higher concentrations. Dielectric spectra in the concentration range between 0.05 and 1.0 mol L-1 reveal a solute mode due to dipolar ion pairs and larger dipolar ion clusters. They verify that at very low concentrations the ionic liquid ions are fully solvated with an increasing tendency to form neutral ion pairs with increasing concentration. Already at 0.025 mol L-1 the degree of dissociation reaches a minimum reflecting a maximum of neutral ion pair formation. With increasing ionic liquid concentration ordered ion clusters are formed by two and more ion pairs. At high concentrations these clusters collapse by dilution in the excess ionic liquid and the defined ion contact necessary for the chirality transfer is lost to a great extent.

Isaac Goldhirsch: a pioneer of granular matter theory - Pöschel, Thorsten; Wolf, Dietrich E. (Granular Matter, 2012)
About 20 years ago, Isaac Goldhirsch was one of the first to recognize that granular matter, behaving neither as a normal fluid nor as a normal solid, was not only an exotic terra incognita for basic science, but is paradigmatic for a whole class of complex systems with irreversible interactions. This field became his passion at a time when he was already a very successful, internationally renowned theoretical physicist. Certainly this helped to establish granular matter theory as a lively new branch of science. The very existence of a prominent new scientific journal ``Granular Matter'', entirely devoted to this field speaks for itself.

Isolating the effect of residual stresses on coating wear by a mechanical stress relaxation technique - Vierneusel, Bernd; Benker, Lisa; Tremmel, Stephan; Göken, Mathias; Merle, Benoit (Thin Solid Films, 2017)
Residual stresses play an essential role for the tribological performance of sputtered coatings since compressive residual stresses yield positive effects on wear resistance. As deposition induced residual stresses are always related to the coating microstructure, a combination of different effects is typically assessed if coatings are validated by tribological testing. Therefore, the real effect of residual stresses on the tribological performance of coatings is not entirely clear. The study aims to examine this issue by isolating the residual stress effect from the microstructural impact by mechanical relaxation of the coating after the deposition process. For this purpose, MoS2 coated substrates are mechanically pre-stretched during the coating process and relaxed again afterwards in order to reduce the coating's macroscopic residual stresses. Other samples, which are not pre-stretched but coated inside the same process with identical distance to the target, serve as a reference material. The proper function of the relaxation technique is demonstrated by applying a recently developed method for residual stress measurement, namely the “Focused Ion Beam – Digital Image Correlation” method. Both samples, the relaxed and as-deposited one, were subjected to a tribological pin-on-disk test. The results show that at high compressive residual stress levels, only mild wear at the upper surface inside the contact area occurs. In contrast, at low compressive residual stress levels, wear results from an abrasive material removal inside the contact track but most significantly from additional coating detachments outside the contact area. The observations can be related, firstly, to a superimposition of harmful bending stresses and beneficial compressive residual stresses beneath the contact area and, secondly, to a stress relaxation effect taking place only inside the tribological contact zone. In summary, owing to the developed stress relaxation technique, a microstructurally independent effect of residual stresses on wear resistance of sputtered MoS2-coatings has been prove
Keywords: Residual stress; Wear; MoS2; Sputtering; Relaxation

ITO-Free and Fully Solution-Processed Semitransparent Organic Solar Cells with High Fill Factors - Guo, Fei; Zhu, Xiangdong; Forberich, Karen; Krantz, Johannes; Stubhan, Tobias; Salinas Batallas, Michael; Halik, Marcus; Spallek, Stefanie; Butz, Benjamin; Spiecker, Erdmann; Ameri, Tayebeh; Li, Ning; et al. (Advanced Energy Materials, 2013)
Organic photovoltaic (OPV) solar cells that can be simply processed from solution are in the focus of the academic and industrial community because of their enormous potential to reduce cost. One big challenge in developing a fully solution-processed OPV technology is the design of a well-performing electrode system, allowing the replacement of ITO. Several solution-processed electrode systems were already discussed, but none of them could match the performance of ITO. Here, we report efficient ITO-free and fully solution-processed semitransparent inverted organic solar cells based on silver nanowire (AgNW) electrodes. To demonstrate the potential of these AgNW electrodes, they were employed as both the bottom and top electrodes. Record devices achieved fill factors as high as 63.0%, which is comparable to ITO based reference devices. These results provide important progress for fully printed organic solar cells and indicate that ITO-free, transparent as well as non-transparent organic solar cells can indeed be fully solution-processed without losses. Indium tin oxide (ITO)-free and fully solution-processed organic solar cells are demonstrated by employing AgNW as both the bottom and top electrodes, in conjunction with Al-ZnO and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) as charge extraction layers. Devices with electrical fill factor (FF) up to 63.0% and fully retained open circuit voltage (V) are achieved, indicating that superior optoelectronic and film quality properties of the two interlayers are perfectly compatible to AgNW electrodes. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Jammed spheres: Minkowski tensors reveal onset of local crystallinity - Kapfer, Sebastian; Mickel, Walter; Mecke, Klaus; Schröder-Turk, Gerd (Physical Review E, 2012)
The local structure of disordered jammed packings of monodisperse spheres without friction, generated by the Lubachevsky-Stillinger algorithm, is studied for packing fractions above and below 64%. The structural similarity of the particle environments to fcc or hcp crystalline packings (local crystallinity) is quantified by order metrics based on rank-four Minkowski tensors. We find a critical packing fraction phi(c) approximate to 0.649, distinctly higher than previously reported values for the contested random close packing limit. At phi(c), the probability of finding local crystalline configurations first becomes finite and, for larger packing fractions, increases by several orders of magnitude. This provides quantitative evidence of an abrupt onset of local crystallinity at phi(c). We demonstrate that the identification of local crystallinity by the frequently used local bond-orientational order metric q(6) produces false positives and thus conceals the abrupt onset of local crystallinity. Since the critical packing fraction is significantly above results from mean-field analysis of the mechanical contacts for frictionless spheres, it is suggested that dynamic arrest due to isostaticity and the alleged geometric phase transition in the Edwards framework may be disconnected phenomena.

Jet printing of colloidal solutions - Numerical modeling and experimental verification of the influence of ink and surface parameters on droplet spreading - Schneider, Olga; Epple, Philipp; Teuber, E.; Meyer, Bernhard; Jank, M. P. M.; Rauh, Cornelia; Delgado, Antonio (Advanced Powder Technology, 2011)
Ink jet printing of functional materials promises an efficient route for the manufacturing of future low cost and large-area electronics applications. The effect of capillary flow of thin liquid films, the control of droplet spreading by suitably influencing the wetting properties of surfaces, the rheology of the ink and the process design play a relevant role in improvement of ink jet printed patterns. This work presents the experimentally based numerical study of the shape of single ink jetted droplets controlled by homogeneous contact angle distributions. The dynamics of the fluid on the substrate surface is treated in the frame of the lubrication theory using the concept of a precursor film and modeling the equilibrium contact angle by a disjoining pressure. The model describes the spreading of axisymmetric droplets considering different material and process parameter configurations. It is shown that the spreading process can be modeled separately from the drying process within a certain range of contact angles.
EAM Import::2019-03-12

Junction formation and current transport mechanisms in hybrid n-Si/PEDOT:PSS solar cells - Jaeckle, Sara; Mattiza, Matthias; Liebhaber, Martin; Broenstrup, Gerald; Rommel, Mathias; Lips, Klaus; Christiansen, Silke (Scientific Reports, 2015)
We investigated hybrid inorganic-organic solar cells combining monocrystalline n-type silicon (n-Si) and a highly conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS). The build-in potential, photo- and dark saturation current at this hybrid interface are monitored for varying n-Si doping concentrations. We corroborate that a high build-in potential forms at the hybrid junction leading to strong inversion of the n-Si surface. By extracting work function and valence band edge of the polymer from ultraviolet photoelectron spectroscopy, a band diagram of the hybrid n-Si/PEDOT:PSS heterojunction is presented. The current-voltage characteristics were analyzed using Schottky and abrupt pn-junction models. The magnitude as well as the dependence of dark saturation current on n-Si doping concentration proves that the transport is governed by diffusion of minority charge carriers in the n-Si and not by thermionic emission of majorities over a Schottky barrier. This leads to a comprehensive explanation of the high observed open-circuit voltages of up to 634 mV connected to high conversion efficiency of almost 14%, even for simple planar device structures without antireflection coating or optimized contacts. The presented work clearly shows that PEDOT:PSS forms a hybrid heterojunction with n-Si behaving similar to a conventional pn-junction and not, like commonly assumed, a Schottky junction.
EAM Import::2019-03-12

Keeping argon under a graphene lid - Argon intercalation between graphene and nickel(111) - Steinrück, Hans-Peter; Bauer, Udo; Gotterbarm, Karin; Späth, Florian; Papp, Christian; Höfert, Oliver; Gleichweit, Christoph; Amende, Maximilian (Surface Science, 2016)
We report on the intercalation of graphene grown on a Ni(111) crystal with argon. Argon is implanted in the Ni(111) crystal by ion bombardment before graphene growth, and diffuses to the surface during the growth of graphene at elevated temperatures. Graphene acts as an atomically thin barrier and keeps the argon underneath. We investigated this system with high resolution X-ray photoelectron spectroscopy. From our experiments we determined the mean quantities of argon under graphene. From our analysis, a simple model to determine the pressure under the graphene layer is presented. In our measurements, we find an increased thermal stability of the intercalated graphene as compared to non-intercalated graphene on Ni(111).
Keywords: Graphene; Intercalation; Nickel; XPS

Key factors for an improved lithium ion storage capacity of anodic TiO2 nanotubes - Kirchgeorg, Robin; Kallert, Max; Liu, Ning; Hahn, Robert; Killian, Manuela; Schmuki, Patrik (Electrochimica Acta, 2016)
In the present work we investigate key factors that influence the Li-storage capacity of anodically grown self-organized TiO2 nanotube layers. First, the influence of both tube length and top morphology are investigated regarding the rate performance of the nanotube layers. Then, factors such as the presence of initiation (grass) layers and the influence of the double walled morphology of conventional TiO2 nanotube layers are elaborated. At high C-rates a grass layer even shows a beneficial contribution, mainly by adding to the double layer capacitance. The presence of a double wall morphology and the associated carbon contamination lead to a lower intercalation ability. Two different approaches are taken to eliminate the inner carbon-rich layer: Cathodic polarization and tube formation in DMSO based electrolytes. This results in an enhancement of the areal capacity by 17% and 33% compared to unmodified tube layers for the two approaches.
EAM Import::2019-03-12

Key Oxidation Parameters that Influence Photo-Induced Properties and Applications of Anodic Titanium Oxides - Piazza, Valerio; Mazare, Anca Valentina; Diamanti, Maria Vittoria; Pedeferri, Mariapia; Schmuki, Patrik (Journal of The Electrochemical Society, 2016)
In the present work we investigate compact anodic oxides formed on titanium by a broad range of anodizing parameters (electrolyte, applied voltage, substrate pre-treatment) and their influence on the performance of such oxides in photocurrent response and photocatalytic properties (photodegradation of AO7). In general, crystallinity and ion inclusion from the electrolyte are crucial. As-grown compact layers of partial crystallinity show increased efficiencies in both applications; interestingly, phosphate ions have a detrimental effect, whereas sulfate ions do not. After thermal annealing (crystallization) the photoresponse significantly increases: except for a crystallization of the anodic layer, annealing causes a rutile oxide layer growth at the oxide/metal interface - this is found to additionally affect the photoresponse. Results overall demonstrate that higher anodization voltage, exclusion of phosphates from the electrolyte, substrate pre-treatment and annealing are of major importance for achieving an enhanced photoresponse on compact anodic layers.
EAM Import::2019-03-12

Kinetic passivation of steps with sulfur and CO/S site exchange processes on stepped Pt surfaces - Streber, Regine; Papp, Christian; Lorenz, Michael Peter Andreas; Bayer, Andreas; Denecke, Reinhard; Steinrück, Hans-Peter (Chemical Physics Letters, 2008)
We studied the influence of preadsorbed sulfur on the adsorption of CO on Pt(3 5 5) and Pt(3 2 2) by in situ X-ray photoelectron spectroscopy. At low temperatures, no adsorption of CO at steps is found, indicating a passivation by sulfur. Upon heating, population of step sites with CO occurs. This behavior is attributed to a kinetic passivation of the steps by sulfur at low temperatures, which is lifted upon heating. The characteristic transition temperatures of 185 K for Pt(3 5 5) and 240 K for Pt(3 2 2) are significantly different, due to a higher activation barrier for the CO/S site exchange process for Pt(3 2 2). © 2007 Elsevier B.V. All rights reserved.

Kinetics of the sulfur oxidation on palladium: A combined in situ x-ray photoelectron spectroscopy and density-functional study - Gotterbarm, Karin; Luckas, Nicola; Höfert, Oliver; Lorenz, Michael Peter Andreas; Streber, Regine; Papp, Christian; Vines, Francesc; Steinrück, Hans-Peter; Görling, Andreas (Journal of Chemical Physics, 2012)
We studied the reaction kinetics of sulfur oxidation on the Pd(100) surface by in situ high resolution x-ray photoelectron spectroscopy and ab initio density functional calculations. Isothermal oxidation experiments were performed between 400 and 500 K for small amounts (∼0.02 ML) of preadsorbed sulfur, with oxygen in large excess. The main stable reaction intermediate found on the surface is SO , with SO and SO being only present in minor amounts. Density-functional calculations depict a reaction energy profile, which explains the sequential formation of SO , SO , and eventually SO , also highlighting that the in-plane formation of SO from S and O adatoms is the rate limiting step. From the experiments we determined the activation energy of the rate limiting step to be 85 6 kJ mol by Arrhenius analysis, matching the calculated endothermicity of the SO formation. © 2012 American Institute of Physics.

Kinetic Study of the Asymmetric Hydrogenation of Methyl Acetoacetate in the Presence of a Ruthenium Binaphthophosphepine Complex - Öchsner, Eva; Etzold, Bastian; Junge, Kathrin; Beller, Matthias; Wasserscheid, Peter (dvanced Synthesis & Catalysis, 2009)
The asymmetric hydrogenation of methyl acetoacetate (MAA) in methanol using dibromobis(S)-4-phenyl-4,5-dihydro-3H-dinaphtho[2,1-c: 1′,2′-e]phosphepine-ruthenium was studied in detail. For the determination of the reaction network, data from kinetic experiments were compared to different possible reaction networks using the kinetic software Presto Kinetics. The simulation was optimised to describe the reaction accurately with a minimal set of process parameters and reaction equations. For the best model the reaction orders, collision factors and activation energy of all reaction steps were determined. Additionally, the influence of reaction temperature and hydrogen pressure on the enantiomeric excess (ee) of the reaction was studied. It was found that high reaction temperatures and high hydrogen pressures result in increasing enantioselectivities.

KOH-promoted Pt/Al2O3 catalysts for water gas shift and methanol steam reforming: An operando DRIFTS-MS study - Kaftan, Andre; Kusche, Matthias Manfred; Laurin, Mathias; Wasserscheid, Peter; Libuda, Jörg (Applied Catalysis B-Environmental, 2017)
The performance of KOH-modified Pt/AlO catalysts has been investigated under the conditions of the water-gas shift (WGS) reaction and methanol steam reforming (MSR) with diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) coupled with online quadrupole mass spectrometry (QMS). We demonstrate that both the activity and the selectivity are enhanced in comparison to the uncoated catalyst by applying a thin coating of KOH. By means of IR spectroscopy, we were able to follow the formation of surface species on two different types of catalysts. During reaction, primarily formates are observed on the uncoated catalyst while a film of hydroxides and carbonates is observed on the KOH-coated sample. Additionally, the vibrational bands of CO adsorbed on Pt suggest a strong modification of the electronic structure of the Pt particles by K-coadsorption, leading to a weakening C[sbnd]O bond and a strengthening of the Pt[sbnd]C bond. As a result, we observe an increased selectivity to CO on the KOH modified system.
Keywords: Infrared spectroscopy; Methanol steam reforming; Online mass spectrometry; Platinum; Water-gas shift

Laboratory x-ray microscopy using a reflection target system and geometric magnification - Stahlhut, P.; Ebensperger, T.; Zabler, S.; Hanke, R. (Journal of Physics: Conference Series, 2013)
This paper describes a laboratory X-ray microscopy setup, based on geometric magnification. The setup uses a sharp metal tip as a reflection target and a highly focused electron beam of a scanning electron microscope. Here we will describe the structuring process for these metal targets. To demonstrate the capabilities of our system, we show radiographs of test structures corresponding to resolutions below 100nm. There are abilities for 3D imaging in later updates of the system. Further we discuss the first imaging examples for high- and low-absorbing samples.
EAM Import::2019-03-12

Langmuir-schaefer films for aligned carbon nanotubes functionalized with a conjugate polymer and photoelectrochemical response enhancement - Sgobba, Vito; Giancane, Gabriele; Cannoletta, Donato; Operamolla, Alessandra; Omar, Omar Hassan; Farinola, Gianluca M.; Guldi, Dirk Michael; Valli, Ludovico (ACS Applied Materials and Interfaces, 2014)
Single-walled carbon nanotubes (SWCNTs) were suspended in 1,2-dichloroethane by noncovalent functionalization with a low-band-gap conjugated polymer 1 alternating dialkoxyphenylene-bisthiophene units with benzo[c][2,1,3]thiadiazole monomeric units. The suspended 1/SWCNT blend was transferred onto different solid substrates by the Langmuir-Schaefer deposition method, resulting in films with a high percentage of aligned nanotubes. Photoelectrochemical characterization of 1/SWCNT thin films on indium-tin oxide showed the benefits of SWCNT alignment for photoconversion efficiency. © 2013 American Chemical Society.

Lanthanum implantation for threshold voltage control in metal/high-k devices - Fet, A.; Haeublein, V.; Bauer, A. J.; Ryssel, Heiner; Frey, Lothar (Microelectronic Engineering, 2009)
In this paper the tuning of the n-metal effective work function by implantation of lanthanum is demonstrated. The effect of implantation and thermal annealing on the device flat-band voltage is presented. It is shown that lanthanum doping of the gate stack produces a negative shift of the flat-band voltage of -0.53 V for a lanthanum does of 5 × 1014 cm-2, after the device undergoes S/D anneal conditions. The results are discussed within the framework of a phenomenological dipole model and compared with other results
Keywords: High-k; Implantation; Lanthanum; Threshold voltage

Large area slot-die coated organic solar cells on flexible substrates with non-halogenated solution formulations - Machui, Florian; Lucera, Luca; Spyropoulos, Georgios; Cordero, Johann; Ali, Abid Shaukat; Kubis, Peter; Ameri, Tayebeh; Voigt, Monika; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2014)
The transfer from lab scale to industrial application is one of the challenges for organic photovoltaics. For this, non halogenated formulations are a decisive need for the upscaling process, as are roll-to-toll (R2R) compatible methods. Devices processed with o-xylene using slot-die coating as a sheet-to-sheet technique show a reduced efficiency on a larger scale compared to lab scale solar cells. By using a mixture of high and low volatile solvents which selectively dissolve one component, the film homogeneity and the efficiency is dramatically improved. The slot-die coated active layers for solar cells processed from non-halogenated solvents show device efficiencies above 3% on flexible substrates.
Keywords: Film homogeneity; Flexible substrates; Ink formulation; Organic photovoltaics; Slot-die coating; Solvent

Large di- and heptafullerene poh electrolytes composed of C60 building blocks having a highly symmetrical hexakisaddition pattern - Witte, Patrick; Hörmann, Frank; Hirsch, Andreas (Chemistry - A European Journal, 2009)
We report here on the synthesis of three new prototypes (types IIII) of very large fullerene-based polyelectrolytes which can carry up to 60 charges on their periphery. All fullerene moieties incorporated in these macromolecular structures have an octahedral hexakisaddition pattern. Dumbbell-shaped icosacarboxylate 5 (type I), which can accumulate up to twenty negative charges, is very soluble in methanol as well as in neutral and basic water. On the other hand, Janus dumbbell 13 (type II) contains both positively and negatively chargeable fullerene building blocks and is very soluble in acidic and basic media. How-ever, in the region of the isoelectric point at pH 6.0-6.5 it precipitates as a pale orange solid due to pronounced intermolecular Coulomb interactions. Giant heptafullerene 15 (type III) can store up to 60 positive charges in its periphery and is the largest molecular polyelectrolyte with defined three-dimensional structure. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

Large-scale rigid body simulations - Iglberger, Klaus; Rüde, Ulrich (Multibody System Dynamics, 2010)
For decades, rigid body dynamics has been used in several active research fields to simulate the behavior of completely undeformable, rigid bodies. Due to the focus of the simulations to either high physical accuracy or real time environments, the state-of-the-art algorithms cannot be used in excess of several thousand to several ten thousand rigid bodies. Either the complexity of the algorithmswould result in infeasible runtimes, or the simulation could no longer satisfy the real time aspects. In this paper, we present a novel approach for massively parallel rigid body dynamics simulations. The presented algorithm enables rigid body simulations of more than one billion interacting rigid bodies on massively parallel supercomputers.We describe in detail the setup of large-scale rigid body simulations, the parallel rigid body algorithm and its communication infrastructure, and analyze the performance of the parallel algorithm by means of a particular simulation scenario.
UnivIS-Import:2015-03-09:Pub.2010.tech.IMMD.lsinfs.larges

Large Scale Simulations of Realistic Flow Problems - Iglberger, Klaus; Götz, Jan; Donath, Stefan; Feichtinger, Christian; Rüde, Ulrich (Innovatives Supercomputing in Deutschland : inSiDE, 2009)
The simulation of many realistic engineering problems requires enormous computing power to cope with the complexity of the simulated scenarios. Especially fluid simulations are amongst the most compute intense engineering applications. In this article we present the state of the art of two currently studied engineering problems in the field of fluid simulation: the simulation of particulate flows and the simulation of free surface flows for the optimization of low temperature fuel cells. For the simulation of fluids there exist several methods. Our simulations are based on the Lattice Boltzmann Method (LBM) [5], a mesoscopic simulation approach that is very well suited for the simulation of complex geometries (as required for both problems) and that can be efficiently implemented for the purpose of large scale simulations. The basic approach of LBM is the discretization of the computational domain by a finite number of fixed lattice nodes that contain information about the fluid particles at a specific position at a certain time step. Our C++ library for LBM simulations is the waLBerla framework [2], a software package specifically designed for large scale LBM simulations for various CFD applications.
UnivIS-Import:2015-03-09:Pub.2009.tech.IMMD.lsinfs.larges_8

Laser-assisted Property Gradients in Multi-layered Aluminum - Böhm, Wolfgang; Merklein, Marion (Physics Procedia, 2014)
The Accumulative Roll Bonding (ARB) process enables manufacturing of multi-layered aluminum sheet metals with outstanding mechanical properties. However, a significant increase in strength is accompanied by a reduced ductility. Besides, delamination effects can occur during forming operations. Therefore, property gradients will be applied by short-term laser heat treatment according to the Tailored Heat Treated Blanks technology to enhance the formability and to enable the production of components. These gradients can be realized across the plane and in thickness direction of a blank. In this paper, property gradients in thickness direction are applied to multi-layered aluminum sheet metal with nanocrystalline grain structure produced in the ARB process. Furthermore, the effect of different process parameters on the shape of the heat affected zone is presented. The property gradients are characterized using micro hardness tests. Finally, the enhancement of the formability is proven using air bending tests.
EAM Import::2019-03-12

Laser melting of nanoparticulate transparent conductive oxide thin films - Baum, Marcus; Polster, Sebastian; Jank, Michael; Alexeev, Ilya; Frey, Lothar; Schmidt, Michael (Journal of Laser Micro Nanoengineering, 2013)
Layers of ZnO nanoparticles with thicknesses of about 40 nm were prepared on silicon sub-strates. The layers were irradiated by single pulses of a 248 nm excimer laser, which proofed suita-ble for consolidation and significant densification of the particle layers under ambient conditions. Experiments as well as simulations have confirmed that the application of a SiO2 particle layer be-tween the substrate and the ZnO particle layer can be used to hamper heat transfer towards the sub-strate. Thusthe ZnO layer can be thermally insulated from the substrate while heating the ZnO up to its extremelyhigh melting point. Consequently, such a layer stack could enable the application of consolidated particle layers on temperature-sensitive carrier substrates such as polymer foils which are to be used in low-cost mass production of devices like displays or solar cells.
UnivIS-Import:2015-03-09:Pub.2013.tech.IE.LEB.laserm
Keywords: Conducting layers; Laser melting; Nanoparticles; Transparent; ZnO

Lattice Boltzmann simulations of the bead-spring microswimmer with a responsive stroke-from an individual to swarms - Pickl, Kristina; Pande, Jayant; Köstler, Harald; Rüde, Ulrich; Smith, Ana-Suncana (Journal of Physics: Condensed Matter, 2017)
Propulsion at low Reynolds numbers is often studied by defining artificial microswimmers which exhibit a particular stroke. The disadvantage of such an approach is that the stroke does not adjust to the environment, in particular the fluid flow, which can diminish the effect of hydrodynamic interactions. To overcome this limitation, we simulate a microswimmer consisting of three beads connected by springs and dampers, using the self-developed waLBerla and pe framework based on the lattice Boltzmann method and the discrete element method. In our approach, the swimming stroke of a swimmer emerges as a balance of the drag, the driving and the elastic internal forces. We validate the simulations by comparing the obtained swimming velocity to the velocity found analytically using a perturbative method where the bead oscillations are taken to be small. Including higher-order terms in the hydrodynamic interactions between the beads improves the agreement to the simulations in parts of the parameter space. Encouraged by the agreement between the theory and the simulations and aided by the massively parallel capabilities of the waLBerla-pe framework, we simulate more than ten thousand such swimmers together, thus presenting the first fully resolved simulations of large swarms with active responsive components.
Keywords: microswimming; three-sphere swimmer; lattice Boltzmann method; many-swimmer swarms; perturbation theory; Rotne-Prager theory

Layer architecture and fatigue life of ultrafine-grained laminated metal composites consisting of different aluminum alloys - Kümmel, Frank; Höppel, Heinz Werner; Göken, Mathias (Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2017)
The influence of the layer architecture on the fatigue properties of ultrafine-grained laminated metal composites is studied. Composites with different stacking sequences of the aluminum alloys AA1050, AA5005, and AA2024 were produced by accumulative roll bonding and characterized by microstructural analysis and nanoindentation experiments. The fatigue properties were determined by 3-point bending tests performed on a vibraphore testing machine. Subsequently, the crack path was analyzed using a scanning electron microscope. It was observed that the fatigue crack bifurcates close to the interface if the hardness difference between both materials is high. The crack then spreads parallel to the interface within the softer material. This crack branching is more pronounced at high stress amplitudes caused by a significant accumulation of plastic deformation in front of the interface. Consequently, at high stress amplitudes the fatigue lives are significantly higher for composites with a high hardness difference between the layers. At low stress amplitudes, at which crack initiation is the dominating fatigue mechanism, the material of the outer layer mainly determines the fatigue lives. Composites with the same outer layer, but different interlayers, show very similar high cycle fatigue lives. Thus, by an appropriate layer architecture ultrafine-grained laminated metal composites with significantly enhanced fatigue properties can be designed.
Keywords: Accumulative Roll Bonding (ARB); Ultrafine-grained (UFG) laminated metal composites (LMCs); Fatigue life; Fatigue crack path

Layer-by-Layer Assemblies of Catechol-Functionalized TiO2 Nanoparticles and Porphyrins through Electrostatic Interactions - Burger, Alexandra; Costa, Ruben Dario; Lobaz, Volodymyr; Peukert, Wolfgang; Hirsch, Andreas; Guldi, Dirk Michael (Chemistry - A European Journal, 2015)
In the current work, we present the successful functionalization and stabilization of P-25 TiO2 nanoparticles by means of N1,N7-bis(3-(4-tert-butyl-pyridium-methyl)phenyl)-4-(3-(3-(4-tert-butyl-pyridinium-methyl)phenylamino)-3-oxopropyl)-4-(3,4-dihydroxybenzamido)heptanediamide tribromide (1). The design of the latter is aimed at nanoparticle functionalization and stabilization with organic building blocks. On one hand, 1 features a catechol anchor to enable its covalent grafting onto the TiO2 surface, and on the other hand, positively charged pyridine groups at its periphery to prevent TiO2 agglomeration through electrostatic repulsion. The success of functionalization and stabilization was corroborated by thermogravimetric analysis, dynamic light-scattering, and zeta potential measurements. As a complement to this, the formation of layer-by-layer assemblies, which are governed by electrostatic interactions, by alternate deposition of functionalized TiO2 nanoparticles and two negatively charged porphyrin derivatives, that is, 5,10,15,20-(phenoxyacetic acid)-porphyrin (2) and 5,10,15,20-(4-(2-ethoxycarbonyl)-4-(2-phenoxyacetamido)heptanedioic acid)-porphyrin (3), is documented. To this end, the layer-by-layer deposition is monitored by UV/Vis spectroscopy, scanning electron microscopy, ellipsometry, and profilometry techniques. The resulting assemblies are utilized for the construction and testing of novel solar cells. From stable and repeatable photocurrents generated during several ön-offc̈ycles of illumination, we derive monochromatic incident photo-to-current conversion efficiencies of around 3 \

Layer-by-Layer Oxidation for Decreasing the Size of Detonation Nanodiamond - Etzold, Bastian; Neitzel, Ioannis; Kett, Manfred; Strobl, Florian; Mochalin, Vadym N.; Gogotsi, Yury (Chemistry of Materials, 2014)
Diamond nanoparticles attract much attention as they combine outstanding mechanical properties with biocompatibility and are available in large quantities. Control and tunability of the particle size is very important for any nanomaterial. Although oxidation can burn carbon and lead to a particle size decrease, this technique could not be successfully employed for nanodiamond size reduction on the nanoscale. In this work, two commercial nanodiamond powders are used to demonstrate separation of the oxidation reaction into two steps (i) the oxygen chemisorption and (ii) the CO and/or CO2 desorption. This allows for an effective control of the oxidation process. In situ thermogravimetric analysis suggests that the oxidation is thermodynamically rather than kinetically controlled, and that the carbon burn off can be adjusted by repeating chemisorption/desorption steps to remove carbon layer after layer. Small-angle X-ray scattering (SAXS) characterization of the diamond nanoparticles showed a continuous size decrease from 5.2 to 4.8 nm during 15 layer-by-layer (LbL) oxidation cycles, in contrast to average particle size increase observed in the case of continuous oxidation in air. In accordance with the size decrease after LbL oxidation, the specific surface area (SSA) of the nanopowders increased.
EAM Import::2019-03-12

Leakage current and defect characterization of p+n-source/drain diodes - Roll, Guntrade; Goldbach, Matthias; Frey, Lothar (Microelectronics Reliability, 2011)
A good control of the transient enhanced dopant diffusion is needed for MOSFET scaling down to the sub 50 nm regime. Carbon ion implant is known to significantly suppress the transient enhanced boron diffusion. However, carbon implantation is also reported to increase diode leakage current. This paper investigates the impact of ion implantation and annealing conditions during source/drain extension formation on leakage current behavior of boron/phosphorous diodes of PFET transistors. Analyzing the leakage current it is difficult to distinguish between the influence of the increased electric field due to the reduced diffusion and possible additional trap centers in the space charge region. This distinction can be made by electrical characterization, as shown in this paper. The leakage current mechanism is found to be trap assisted tunneling with phonon interaction. The corresponding trap energy within the band gap is 0.58 ± 0.10 eV. The carbon concentration in the space charge region measured by SIMS is below the detection limit. Also in electrical measurements, which are more sensitive, no significant influence of carbon related traps is observed. The leakage current is increased by the application of a Flash Anneal additionally to a Rapid Thermal Anneal for recrystallization of the silicon substrate.

Life time evaluation of PDMS stamps for UV-enhanced substrate conformal imprint lithography - Schmitt, H.; Duempelmann, P.; Fader, Robert; Rommel, Mathias; Bauer, A. J.; Frey, Lothar; Brehm, Markus; Kraft, Andreas (Microelectronic Engineering, 2012)
UV-enhanced substrate conformal imprint lithography (UV-SCIL) is a large area nano patterning technique which has the potential to find its way into industrial application. A promising application for UV-SCIL exists in the field of high brightness LEDs. Here, a surface patterning can increase the external quantum efficiency and therefore the light output of LEDs significantly. But, before UV-SCIL can be introduced as patterning technique into industrial application, process relevant parameters like the interaction between the PDMS stamp and the UV-curing material as well as the overall life time of PDMS stamps have to be evaluated. Within this work, stamps from different PDMS material compositions with a diameter of 150 mm were fabricated. These stamps were used to perform UV-SCIL with the epoxy based resist Katiobond OM VE 110707 from DELO Industrial Adhesives and it was found that the final resist layer thickness strongly depends on the PDMS material composition, the number of imprints, and the time between two subsequent imprints. This can be explained by diffusion of one or several components of the UV-curing material into the stamps, which influences the life time of the PDMS stamps. With the actual optimum PDMS material composition, 500 UV-SCIL imprints could be successfully performed without any visible degradation. © 2012 Elsevier B.V. All rights reserved.
Keywords: Life time; PDMS stamp; SCIL; Substrate conformal imprint lithography; UV-SCIL

Ligand-assisted thickness tailoring of highly luminescent colloidal CH3NH3PbX3 (X = Br and I) perovskite nanoplatelets - Levchuk, Ievgen; Herre, Patrick; Brandl, Marco; Osvet, Andres; Hock, Rainer; Peukert, Wolfgang; Schweizer, Peter; Spiecker, Erdmann; Batentschuk, Miroslaw; Brabec, Christoph (Chemical Communications, 2017)
Quantum size-confined CHNHPbX (X = Br and I) perovskite nanoplatelets with remarkably high photoluminescence quantum yield (up to 90%) were synthesized by ligand-assisted re-precipitation. Thickness-tunability was realized by varying the oleylamine and oleic acid ligand ratio. This method allows tailoring the nanoplatelet thickness by adjusting the number of unit cell monolayers. Broadly tunable emission wavelengths (450-730 nm) are achieved via the pronounced quantum size effect without anion-halide mixing.

Ligand Effects at Ionic Liquid-Modified Interfaces: Coadsorption of [C(2)C(1)lm][OTf] and CO on Pd(111) - Bauer, Tanja; Mehl, Sascha; Brummel, Olaf; Pohako-Esko, Kaija; Wasserscheid, Peter; Libuda, Jörg (Journal of Physical Chemistry C, 2016)
Thin films of ionic liquids (ILs) can be used to tune the activity and selectivity of heterogeneous catalysts and electrocatalysts (solid catalysts with IL layer, SCILL). In several cases it has been found that these IL layers have a strong beneficial effect on the selectivity. To explore the molecular origin of this phenomenon, we have performed a model study on ultrahigh-vacuum conditions. We have investigated the coadsorption of CO and the room-temperature IL [CCIm][OTf] (1-ethyl-3-methylimidazolium trifluoromethanesulfonate) on Pd(111) by time-resolved infrared reflection-absorption spectroscopy, temperature-programmed reflection absorption spectroscopy, and temperature-programmed desorption. We find that the [OTf] anion adsorbs specifically to the Pd(111) surface via the SO group, thereby adopting a well-defined orientation with the molecular axis oriented perpendicular to the surface. At higher IL coverage, unspecific but oriented adsorption occurs, before the orientation is successively lost in the multilayer region. Upon coadsorption of [CCIm][OTf] on a CO-saturated Pd(111) surface at 300 K (θ = 0.5) a well-defined coadsorption layer is formed without any loss of adsorbed CO and with very similar CO site occupation. In the coadsorption layer [OTf] is specifically adsorbed between the CO with a molecular orientation perpendicular to the surface. Thus, a dense and homogeneous coadsorption layer is formed in which Pd surface atoms are simultaneously coordinated to both CO and [OTf] ions. From this compressed layer, CO desorbs with peak temperature at 410 K (heating rate, 3.3 K/s). Above this temperature, a low-coverage coadsorption phase of CO and surface-adsorbed IL resides, with little influence of the IL on the CO desorption temperature (peak temperature, 470 K). Coadsorption of the IL gives rise to a pronounced red shift of the CO stretching frequency in the order of 50 cm. The effect originates from the electrostatic interfacial field (Stark effect) generated by the coadsorbed IL and, at high coverage, possibly from additional short-range interactions. The results show that ILs form dense and well-defined mixed phases with strongly adsorbing reactants such as CO, in which a specifically adsorbed carpet of IL anions directly modifies the active surface sites by ligand-like effects.

Ligand Effects in SCILL Model Systems: Site-Specific Interactions with Pt and Pd Nanoparticles - Sobota, Marek; Happel, Markus; Amende, Maximilian; Paape, Natalia; Wasserscheid, Peter; Laurin, Mathias; Libuda, Jörg (Advanced Materials, 2011)
Ionic liquids (ILs), such as [BMIM][Tf_2N], on well-defined SCILL model catalysts are able to replace weakly adsorbed CO. On Pt, on-top CO remains adsorbed under the ionic liquid layer, but its IR signal red-shifts by over 30 cm-1. IL–adsorbate interactions are mediated by the noble metal and similar to ligands.

Ligand effects on the surface composition of Rh-containing ionic liquid solutions used in hydroformylation catalysis - Kolbeck, Claudia; Paape, Natalia; Cremer, Till; Schulz, Peter; Maier, Florian; Steinrück, Hans-Peter; Wasserscheid, Peter (Chemistry - A European Journal, 2010)
The chemical surface composition of Rh-containing ionic liquid solutions has been studied by angle-resolved X-ray photoelectron spectroscopy (ARXPS). Rh-tppts complexes of high relevance for multiphase hydroformylation catalysis showed remarkable surface activity, whereas non-tppts containing systems showed Rh depleting from the surface (tppts=tris(3-sodium sulfonatophenyl)phosphine). © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Light-Emitting Electrochemical Cells Based on Hybrid Lead Halide Perovskite Nanoparticles - Aygueler, Meltem F.; Weber, Michael; Puscher, Bianka; Medina, Dana D.; Docampo, Pablo; Costa, Ruben Dario (Journal of Physical Chemistry C, 2015)
Methylammonium lead bromide (MAPbBr3) perovskite nanoparticles (NPs) have been recently proposed as a new material for light-emitting diodes, as well as a new paradigm to elucidate the operational mechanism in perovskite solar cells. Here, we have expanded the synthesis concept to fabricate NPs based on formamidinium lead bromide (FAPbBr3). Importantly, we have demonstrated that the photophysical features of this novel material can be easily tuned by exchanging the organic cation, achieving lower radiative bimolecular recombination rate for FAPbBr3 NPs. Additionally, we report for the first time light-emitting electrochemical cells (LECs) based on perovskite NPs by an easily up-scalable spray-coating technique. Stable luminance of 1–2 cd/m2 at low driving currents was achieved for both types of materials. Overall, this work opens a new avenue of research into the field of organic–inorganic metal halide nanoparticles bearing different alkyl ammonium groups and their application in the developing field of thin-film lighting devices.
EAM Import::2019-03-12

Light harvesting enhancement upon incorporating alloy structured CdSeXTe1−X quantum dots in DPP:PC61BM bulk heterojunction solar cells - Soltani, Rezvan; Katbab, Ali Asghar; Schaumberger, Kerstin; Gasparini, Nicola; Brabec, Christoph; Rechberger, Stefanie; Spiecker, Erdmann; Alabau, Antoni Gimeno; Ruland, Andres; Saha, Avishek; Guldi, Dirk Michael; Sgobba, Vito; et al. (Journal of Materials Chemistry C, 2017)
Hybrid solar cells based on the pDPP5T-2 electron donating polymer, [6,6]-phenyl-C-butyric acid methyl ester (PCBM) and cadmium selenide telluride (CdSeTe) quantum dots (QDs) are fabricated and their photovoltaic performance and optoelectronic properties are investigated as a function of QD loading. The power conversion efficiency (PCE) of hybrid solar cells is improved up to 5.11% for the device containing 4 wt% of QDs which is mainly due to the enhancement in short circuit current density (J) resulting from increased light harvesting. A full-fledged study is performed on the microstructure, charge transfer/transport and recombination mechanisms of our ternary hybrid solar cells by employing various advanced techniques. The transmission electron microscopy (TEM) results reveal the non-agglomerated and uniform distribution of the CdSeTe QDs within the pDPP5T-2:PCBM host matrix at low QD concentrations. Transient absorption spectroscopy (TAS) showed a slower charge carrier recombination rate due to the introduction of QDs into the photoactive layer. It can be attributed to the more efficient exciton dissociation in ternary systems. These findings are consistent with the photovoltaic properties of the device.
Keywords: Engineering controlled terms: Absorption spectroscopy; Butyric acid; Cadmium compounds; Cadmium telluride; Charge transfer; Heterojunctions; High resolution transmission electron microscopy; Nanocrystals; Polymer solar cells; Semiconductor quantum dots; Solar power generation; Transmission electron microscopy Bulk heterojunction solar cells; Charge carrier recombination; Light harvesting enhancement; Optoelectronic properties; Photovoltaic performance; Power conversion efficiencies; Recombination mechanisms; Transient absorption spectroscopies Engineering main heading: Solar cells

Light scattering and optical performance of glass-particle filled matrices with similar refractive index - Wildner, Wolfgang; Drummer, Dietmar (Journal of Composite Materials, 2018)
EAM Import::2019-03-12

Light scattering of glass-particle filled matrices with similar refractive index - Wildner, Wolfgang; Drummer, Dietmar (Journal of Composite Materials, 2018)
If fillers can be added to transparent materials without losing transparency, then advantages like enhanced mechanical and thermal properties can be integrated. The investigated specimens consist of glass particles and refractive index oil as a model for transparent matrices with a very similar refractive index. Their optical properties and resulting limitations are described. Potential uses are also demonstrated by application-oriented optical testing. Besides a standard spectrometer, additional spectrometer setups were used. These include a diffuse as well as a collimated illumination and different sample positioning. Furthermore, the scattered light intensity was measured at different angles. This analysis reveals that composites with smaller particles transmit more light directly. In contrast, standard spectrometers indicate an increasing direct transmittance of composites with larger particles. They collect significant amounts of scattered light and, therefore, are not suitable for transmission measurements of such composites. The different positioning shows that all specimens exhibit very little scattering when placed directly on a diffuse light source. With a greater distance between specimen and light source, the scattering increases strongly. To display the composites' optical appearance, the light-dark-contrast of the diffuse white light source photographed behind the composite was analyzed. Both long and short distances between composite and light source lead to a precise image of the light source. Nevertheless, the white light source appears in the color of the wavelength with matching refractive indices at long distances.
Keywords: light scattering; Glass particles; optical compound

Limitations of mathematical modelling and numerical simulation of industrial and laboratory high-pressure processes - Rauh, Cornelia; Delgado, Antonio (High Pressure Research, 2011)
High pressures up to several hundreds of MPa are utilised in a wide range of applications in chemical engineering, bioengineering, and food engineering, aiming at selective control of (bio-)chemical reactions. Non-uniformity of process conditions may threaten the safety and quality of the resulting products as the process conditions such as pressure, temperature, and treatment history are crucial for the course of (bio-)chemical reactions. Therefore, thermofluid dynamical phenomena during the high-pressure process have to be examined, and tools to predict process uniformity and to optimise the processes have to be developed. Recently, mathematical models and numerical simulations of laboratory and industrial scale high-pressure processes have been set up and validated by experimental results. This contribution deals with the assumption of the modelling that relevant (bio-)chemical compounds are ideally dissolved or diluted particles in a continuum flow. By considering the definition of the continuum hypothesis regarding the minimum particle population in a distinct volume, limitations of this modelling and simulation are addressed. © 2011 Taylor & Francis.
UnivIS-Import:2015-03-09:Pub.2011.tech.ITC.stmmec.limita
Keywords: continuum particle-loaded flow; mathematical modelling; numerical simulation; process non-uniformity

Limits of Applicability of the Voronoi Tessellation Determined by Centers of Cell Nuclei to Epithelium Morphology - Kaliman, Sara; Jayachandran, Christina; Rehfeldt, Florian; Smith, Ana-Suncana (Frontiers in Physiology, 2016)
It is well accepted that cells in the tissue can be regarded as tiles tessellating space. A number of approaches were developed to find an appropriate mathematical description of such cell tiling. A particularly useful approach is the so called Voronoi tessellation, built from centers of mass of the cell nuclei (CMVT), which is commonly used for estimating the morphology of cells in epithelial tissues. However, a study providing a statistically sound analysis of this method's accuracy is not available in the literature. We addressed this issue here by comparing a number of morphological measures of the cells, including area, perimeter, and elongation obtained from such a tessellation with identical measures extracted from direct imaging acquired by staining the cell membranes. After analyzing the shapes of 15,000 MDCK II epithelial cells under several conditions, we find that CMVT reasonably well reproduces many of the morphological properties of the tissue with an error that is between 10 and 15%. Moreover, cross-correlations between different morphological measures are reproduced qualitatively correctly by this method. However, all of the properties including the cell perimeters, number of neighbors, and anisotropy measures often suffer from systematic or size dependent errors. These discrepancies originate from the polygonal nature of the tessellation which sets the limits of the applicability of CMVT.
Keywords: epithelial tissue morphology; Voronoi tessellation; fluorescence microscopy; nuclei segmentation; image analysis; MDCK; cross-correlations; cell shape

Linear magnetoresistance in mosaic-like bilayer graphene - Kißlinger, Ferdinand; Ott, Christian; Heide, Christian; Kampert, Erik; Butz, Benjamin; Spiecker, Erdmann; Shallcross, Sam; Weber, Heiko B. (Nature Physics, 2015)
The magnetoresistance of conductors usually has a quadratic dependence on magnetic field(1), however, examples exist of non-saturating linear behaviour in diverse materials(2-6). Assigning a specific microscopic mechanism to this unusual phenomenon is obscured by the co-occurrence and interplay of doping, mobility fluctuations and a polycrystalline structure(7,8). Bilayer graphene has virtually no doping fluctuations, yet provides a built-in mosaic tiling due to the dense network of partial dislocations(9,10). We present magnetotransport measurements of epitaxial bilayer graphene that exhibits a strong and reproducible linear magnetoresistance that persists to B = 62 T at and above room temperature, decorated by quantum interference effects at low temperatures. Partial dislocations thus have a profound impact on the transport properties in bilayer graphene, a system that is frequently assumed to be dislocation-free. It further provides a clear and tractable model system for studying the unusual properties of mosaic conductors.

Linking photo- and redoxactive phthalocyanines covalently to graphene - Ragoussi, Maria-Eleni; Malig, Jenny; Katsukis, Georgios; Butz, Benjamin; Spiecker, Erdmann; De La Torre, Gema; Torres, Tomas; Guldi, Dirk Michael (Angewandte Chemie International Edition, 2012)
"Green" graphene: For the first time, the covalent attachment of a light-harvesting and electron-donating phthalocyanine to the basal plane of few-layer graphene is reported (see picture). Physicochemical characterizations reveal an ultrafast charge separation from the photoexcited phthalocyanine to few-layer graphene followed by a slower charge recombination. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Liquid Crystalline Phase Formation in Suspensions of Solid Trimyristin Nanoparticles - Gehrer, Simone; Schmiele, Martin; Westermann, Martin; Steiniger, Frank; Unruh, Tobias (Journal of Physical Chemistry B, 2014)
The presence of liquid crystalline phases in suspensions of solid lipid nanoparticles can increase the risk of their gelling upon administration through fine needles. Here we study the formation of liquid crystalline phases in aqueous suspensions of platelet-like shaped solid lipid nanoparticles. A native lecithin-stabilized trimyristin (20 wt %) suspension was investigated at different dilution levels by small-angle X-ray scattering (SAXS) and visual inspection of their birefringence between two crossed polarizers. For trimyristin concentrations phi(MMM) < 6 wt %, the dispersed platelets are well separated from each other whereas they start to self-assemble into stacked lamellae for 6 wt % <= phi(MMM) < 12 wt %. For phi(MMM) >= 12 wt %, the SAXS patterns become increasingly anisotropic, which is a signature of an evolving formation of a preferred orientation of the platelets on a microscopic scale. Simultaneously, the suspensions become birefringent, which proves the existence of an anisotropic liquid crystalline phase formed in the still low viscous liquid suspensions. Spatially resolved SAXS scans and polarization microscopy indicate rather small domains in the (sub)micrometer size range in the nematic liquid crystalline phase and the presence of birefringent droplets (tactoids). The observed critical concentrations for the formation of stacks and the liquid crystalline phase are significantly higher as for equivalent suspensions prepared from triglycerides with longer chains. This can be explained with the lower aspect ratio of trimyristin platelets. Special emphasis is put on the isotropic-liquid crystalline phase transition as a function of the ionic strength of the dispersion medium and phi(MMM). Higher salt concentrations allow shifting of the phase transition to higher trimyristin concentrations. This can be attributed to a partial screening of the repulsive forces between the platelets, which allows higher packing densities within the platelet stacks and of remaining isolated platelets.

Liquid filtration of nanoparticles through track-etched membrane filters under unfavorable and different ionic strength conditions: Experiments and modeling - Peukert, Wolfgang; Segets, Doris; Süß, Sebastian; Chen, Sheng-Chieh; Pui, David; Lee, Handol (Journal of Membrane Science, 2017)
Nanoparticle deposition experiments under unfavorable conditions were conducted experimentally and theoretically. The 0.2 and 0.4 µm rated track-etched membrane filters were challenged with 60, 100, 147, 220, 350 and 494 nm polystyrene latex (PSL) particles with different ionic strengths ranging from 0.005 to 0.05 M. The capillary tube model, with replacing the viscosity of air to water, was used to estimate the initial efficiency, or the transport efficiency of the particles to the filter surface, which was corrected in a second step by allowing the detachment of the nanoparticles according to the sum of adhesive and hydrodynamic torques. The adhesive torques were derived from surface interactions accessed by the extended DLVO theory. Calculation results showed that the adhesive torque of a particle located in the calculated primary minimum was slightly larger than the hydrodynamic torque, resulting in particle deposition. However, experimental data clearly indicated that detachment occurred. This could only be explained by the presence of additional hydration forces, leading to a larger separation which became relevant at high ionic strengths. By including hydration into our theoretical framework, experiment and theory were in very good agreement under all different ionic strength conditions. The findings allow a basic understanding of surface interactions between nanoparticles and membranes in micro- and ultra-filtration applications for drinking water production, wastewater treatment and particle free water production in industries.
Keywords: Adhesive and hydrodynamic torque; Derjaguin-Landau-Verwey-Overbeek (DLVO) theory; Microfiltration; Short range hydration effects; Track-etched polycarbonate membrane filter

Liquid-Liquid Biphasic, Platinum-Catalyzed Hydrosilylation of Allyl Chloride with Trichlorosilane using an Ionic Liquid Catalyst Phase in a Continuous Loop Reactor - Hofmann, Norbert; Bauer, Andreas; Frey, Thomas; Auer, Marco; Stanjek, Volker; Schulz, Peter; Taccardi, Nicola; Wasserscheid, Peter (dvanced Synthesis & Catalysis, 2008)
The platinum-catalyzed hydrosilylation of allyl chloride with trichlorosilane was investigated in an ionic liquid-organic biphasic reaction mode. After an ionic liquid screening and repetitive batch mode experiments, the process was realized in a continuous mode using a loop reactor concept with integrated continuous separation and recycling of the ionic liquid catalyst phase. The continuous reactor could be operated for 48h at constant activity and selectivity without addition of platinum indicating that platinum leaching into the product phase was far below 1ppm. Enhanced selectivity for the product trichloro(3-chloropropyl)silane (compared to the state-of-the art) and the possibility to use simple platinum tetrachloride (PtCl_4) as platinum source are further attractive features of this new ionic liquid-based process concept.

Liquid organic hydrogen carriers (LOHCs): Toward a hydrogen-free hydrogen economy - Preuster, Patrick; Papp, Christian; Wasserscheid, Peter (Accounts of Chemical Research, 2017)
The need to drastically reduce CO2 emissions will lead to the transformation of our current, carbon-based energy system to a more sustainable, renewable-based one. In this process, hydrogen will gain increasing importance as secondary energy vector. Energy storage requirements on the TWh scale (to bridge extended times of low wind and sun harvest) and global logistics of renewable energy equivalents will create additional driving forces toward a future hydrogen economy. However, the nature of hydrogen requires dedicated infrastructures, and this has prevented so far the introduction of elemental hydrogen into the energy sector to a large extent. Recent scientific and technological progress in handling hydrogen in chemically bound form as liquid organic hydrogen carrier (LOHC) supports the technological vision that a future hydrogen economy may work without handling large amounts of elemental hydrogen. LOHC systems are composed of pairs of hydrogen-lean and hydrogen-rich organic compounds that store hydrogen by repeated catalytic hydrogenation and dehydrogenation cycles. While hydrogen handling in the form of LOHCs allows for using the existing infrastructure for fuels, it also builds on the existing public confidence in dealing with liquid energy carriers. In contrast to hydrogen storage by hydrogenation of gases, such as CO2 or N2, hydrogen release from LOHC systems produces pure hydrogen after condensation of the high-boiling carrier compounds. This Account highlights the current state-of-the-art in hydrogen storage using LOHC systems. It first introduces fundamental aspects of a future hydrogen economy and derives therefrom requirements for suitable LOHC compounds. Molecular structures that have been successfully applied in the literature are presented, and their property profiles are discussed. Fundamental and applied aspects of the involved hydrogenation and dehydrogenation catalysis are discussed, characteristic differences for the catalytic conversion of pure hydrocarbon and nitrogen-containing LOHC compounds are derived from the literature, and attractive future research directions are highlighted. Finally, applications of the LOHC technology are presented. This part covers stationary energy storage (on-grid and off-grid), hydrogen logistics, and on-board hydrogen production for mobile applications. Technology readiness of these fields is very different. For stationary energy storage systems, the feasibility of the LOHC technology has been recently proven in commercial demonstrators, and cost aspects will decide on their further commercial success. For other highly attractive options, such as, hydrogen delivery to hydrogen filling stations or direct-LOHC-fuel cell applications, significant efforts in fundamental and applied research are still needed and, hopefully, encouraged by this Account.

Liquid Organic Hydrogen Carriers: Surface Science Studies of Carbazole Derivatives - Papp, Christian; Wasserscheid, Peter; Libuda, Jörg; Steinrück, Hans-Peter (Chemical Record, 2014)
We review recent results towards a molecular understanding of the adsorption and dehydrogenation of carbazole-derived liquid organic hydrogen carriers on platinum and palladium single crystals and on Al2O3-supported Pt and Pd nanoparticles. By combining synchrotron-based high-resolution X-ray photoelectron spectroscopy, infrared reflection-absorption spectroscopy, advanced molecular beam methods and temperature-programmed desorption spectroscopy, detailed insights into the reaction mechanism are obtained. On Pt(111), dehydrogenation of perhydro-N-ethylcarbazole, H-12-NEC, starts with activation of the hydrogen atoms at the pyrrole unit, yielding H-8-NEC as the first stable reaction intermediate at approximate to 340K, followed by further dehydrogenation to NEC at approximate to 380K. Above 390K, dealkylation starts, yielding carbazole as an undesired byproduct. On small supported Pt particles, the dealkylation sets in at lower temperatures, due to the higher reactivity of low-coordinated sites, while on larger particles with (111) facets a reactivity as on the flat surface is observed. Carbazole derivatives with ethyl, propyl and butyl chains show an overall very similar reactivity, both on Pt(111) and on Pt nanoparticles. When comparing the dealkylation behavior of H-12-NEC on Pt(111) and Pt nanoparticles to that on Pd(111) and Pd nanoparticles, we find a higher reactivity for the Pd systems.
Keywords: dehydrogenation; liquid organic hydrogen carriers; platinum; renewable resources; surface chemistry

Liquid silver tris(perfluoroethyl)trifluorophosphate salts as new media for propene/propane separation - Pliquett, Daniel; Schulz, Peter; Heinemann, Frank Wilhelm; Bause, Angela; Wasserscheid, Peter (Physical Chemistry Chemical Physics, 2016)
A series of silver tris(perfluoroethyl) trifluorophosphate (Ag[FAP]) complexes with various ligands (acetonitrile ACN, chloroacetonitrile Cl-ACN, acrylonitrile acryl-CN, pyridine py, ethylenediamine en and propene C3H6) have been synthesized starting from Ag[NO3] and K[FAP] using three different routes. Physicochemical properties as well as crystal structures ([Ag(ACN)(2/4)][FAP], [Ag(py) 2][FAP]) were determined and the suitability of such Ag salts for propene/propane separation processes was investigated. The investigated silver complexes exhibit either low melting points or form liquid complexes when contacted with gaseous propene at 30 degrees C. This makes them promising separation materials for both liquid membranes and absorber fluids due to their high silver content and significant propene capacity. Single (iGSC) and mixed (NMR) gas solubilities as well as diffusion coefficients (PFG-NMR) of propene and propane were determined to predict the theoretical selectivity of solubility, membrane selectivity, capacity and transport properties of the silver salts according to the solution diffusion model. A strong influence of the number and type of ligands on chemical complexation, physicochemical properties and separation performance has been observed.

Liquid/solid interface of ultrathin ionic liquid films: [C 1C1Im][Tf2N] and [C8C 1Im][Tf2N] on Au(111) - Cremer, Till; Stark, Michael Werner; Deyko, Alexey; Steinrück, Hans-Peter; Maier, Florian (Langmuir, 2011)
Ultrathin films of two imidazolium-based ionic liquids (IL), [C CIm][TfN] (= 1,3-dimethylimidazolium bis(trifluoromethyl)imide) and [CCIm][TfN] (= 1-methyl-3-octylimidazolium bis(trifluoromethyl)imide) were prepared on a Au(111) single-crystal surface by physical vapor deposition in ultrahigh vacuum. The adsorption behavior, orientation, and growth were monitored via angle-resolved X-ray photoelectron spectroscopy (ARXPS). Coverage-dependent chemical shifts of the IL-derived core levels indicate that for both ILs the first layer is formed from anions and cations directly in contact with the Au surface in a checkerboard arrangement and that for [CC Im][TfN] a reorientation of the alkyl chain with increasing coverage is found. For both ILs, geometry models of the first adsorption layer are proposed. For higher coverages, both ILs grow in a layer-by-layer fashion up to thicknesses of at least 9 nm (>10 ML). Moreover, beam damage effects are discussed, which are mainly related to the decomposition of [TfN] anions directly adsorbed at the gold surface. © 2011 American Chemical Society.

Lithographically patterned silicon nanowire arrays for matrix free LDI-TOF/MS analysis of lipids - Muck, Alexander; Stelzner, Thomas; Huebner, Uwe; Christiansen, Silke; Svatos, Ales (Lab on A Chip, 2010)
Silicon nanowire arrays were patterned onto silicon chips by a combination of lithography and chemical vapor deposition using the vapor-liquid-solid growth method. Thus, highly reproducible sample deposition zones were obtained that were used for laser desorption ionization (LDI) mass spectrometric analysis of lipidic species with lithium salts as dopants. Using a conventional UV laser (337 nm), hydrocarbons and numerous lipids (triglycerides, diglycerides, wax esters) could be effectively lithiated yielding [M + Li]+ ions. Upon doping with lithium hydroxide the SiNW arrays yielded high signal-to-noise ratios with low limits of detection (e.g. 750 pg tripalmitin on target with S/N 5) and efficient ionization for a range of fatty acids (FA), mono-, di- and triglycerides and hydrocarbons (HC), in the form of [FA - H + 2Li]+, [mono- or diglyceride - H_2O + Li]+, or [triglyceride + Li]+ and [HC + Li]+, respectively. It is expected that these chips will find a broad range of applications in the analysis of natural compounds and food control.
EAM Import::2019-03-12

Loading pentapod deca(organo)[60]fullerenes with electron donors: From photophysics to photoelectrochemical bilayers - Matsuo, Yutaka; Ichiki, Takahiko; Radhakrishnan, Shankara Gayathri; Guldi, Dirk Michael; Nakamura, Eiichi (Journal of the American Chemical Society, 2010)
A pentapod deca(aryl)[60]fullerene, C (C H CO H) (C H Fc) Me (4; Fc = ferrocenyl), bearing five carboxylic acid and five ferrocenyl groups was synthesized through top and bottom functionalization of [60]fullerene by means of copper-mediated penta-addition reactions. For electrochemical measurements (i.e., E = 0.08 V, five-electron oxidation of the ferrocenyl groups; E = -1.89 and -2.28 V for the fullerene part vs Fc/Fc ), we used an ester-protected compound, C (C H CO Et) (C H Fc) Me (2), and 4 was probed by performing femtosecond flash photolysis experiments in a variety of organic solvents. Importantly, the formation of a radical ion pair state was corroborated with lifetimes of up to 333 ps in toluene. In complementary studies, penta(carboxylic acid)-penta(ferrocenyl) compound 4 was deposited on indium-tin oxide (ITO) electrodes with a surface coverage (i.e., 0.14 nmol/cm ) that corresponded to a unique bilayer structure. Decisive for the bilayer motif is the presence of five ferrocenyl groups, which are assembled with a merry-go-round-shaped arrangement on the [60]fullerene. The novel 4/ITO photoelectrode gave rise to a cathodic photocurrent with a 12% quantum yield in the presence of methyl viologen, whereas an anodic photocurrent was generated in the presence of ascorbic acid for a C (C H CO H) (C H ) Me (5)/ITO photoelectrode. Photophysical investigations revealed that the difference in photocurrent, that is, cathodic versus anodic photocurrents, is related to the nature of the excited state feature in 4 (i.e., charge separated state) and 5 (i.e., triplet excited state). The unique molecular architecture of 4, in combination with its remarkable donor-acceptor properties, validates the use of the pentapod deca(aryl)[60]fullerene in photoelectrochemically active molecular devices. © 2010 American Chemical Society.

Local exact exchange potentials within the all-electron FLAPW method and a comparison with pseudopotential results - Betzinger, Markus; Friedrich, Christoph; Bluegel, Stefan; Görling, Andreas (Physical Review B, 2011)
We present a general numerical approach to construct local Kohn-Sham potentials from orbital-dependent functionals within the all-electron full-potential linearized augmented-plane-wave (FLAPW) method, in which core and valence electrons are treated on an equal footing. As a practical example, we present a treatment of the orbital-dependent exact-exchange (EXX) energy and potential. A formulation in terms of a mixed product basis, which is constructed from products of LAPW basis functions, enables a solution of the optimized-effective-potential (OEP) equation with standard numerical algebraic tools and without shape approximations for the resulting potential. We find that the mixed product and LAPW basis sets must be properly balanced to obtain smooth and converged EXX potentials without spurious oscillations. The construction and convergence of the exchange potential are analyzed in detail for diamond. Our all-electron results for C, Si, SiC, Ge, and GaAs semiconductors as well as Ne and Ar noble-gas solids are in very favorable agreement with plane-wave pseudopotential calculations. This confirms the adequacy of the pseudopotential approximation in the context of the EXX-OEP formalism and clarifies a previous contradiction between FLAPW and pseudopotential results. © 2011 American Physical Society.

Localized growth of carbon nanotubes via lithographic fabrication of metallic deposits - TU, Fan; Drost, Martin; Szenti, Imre; Kiss, Janos; Konya, Zoltan; Marbach, Hubertus (Beilstein Journal of Nanotechnology, 2017)
We report on the fabrication of carbon nanotubes (CNTs) at predefined positions and controlled morphology, for example, as individual nanotubes or as CNT forests. Electron beam induced deposition (EBID) with subsequent autocatalytic growth (AG) was applied to lithographically produce catalytically active seeds for the localized growth of CNTs via chemical vapor deposition (CVD). With the precursor Fe(CO)5 we were able to fabricate clean iron deposits via EBID and AG. After the proof-of-principle that these Fe deposits indeed act as seeds for the growth of CNTs, the influence of significant EBID/AG parameters on the deposit shape and finally the yield and morphology of the grown CNTs was investigated in detail. Based on these results, the parameters could be optimized such that EBID point matrixes (6 × 6) were fabricated on a silica surface whereby at each predefined site only one CNT was produced. Furthermore, the localized fabrication of CNT forests was targeted and successfully achieved on an Al2O3 layer on a silicon sample. A peculiar lift-up of the Fe seed structures as was observed and the mechanism was discussed. Finally, a proof-of-principle was presented showing that EBID deposits from the precursor Co(CO)3NO are also very effective catalysts for the CNT growth. Even though the metal content (Co) of the latter is reduced in comparison to the Fe deposits, effective CNT growth was observed for the Co-containing deposits at lower CVD temperatures than for the corresponding Fe deposits.
EAM Import::2019-03-12

Localized Parallel Algorithm for Bubble Coalescence in Free Surface Lattice-Boltzmann Method - Donath, Stefan; Feichtinger, Christian; Pohl, Thomas; Götz, Jan; Rüde, Ulrich (Euro-Par 2009, 2009)
The lattice Boltzmann method is a popular method from computational fluid dynamics. An extension of this method handling liquid flows with free surfaces can be used to simulate bubbly flows. It is based on a volume-of-fluids approach and an explicit tracking of the interface, including a reconstruction of the curvature to model surface tension. When this algorithm is parallelized, complicated data exchange is required, in particular when bubbles extend across several subdomains and when topological changes occur through coalescence of bubbles. In a previous implementation this was handled by using all-to-all MPI communication in each time step, restricting the scalability of the simulations to a moderate parallelism on a small number of processors. In this paper, a new parallel bubble merge algorithm will be introduced that communicates updates of the bubble status only locally in a restricted neighborhood. This results in better scalability and is suitable for massive parallelism. The algorithm has been implemented in the lattice Boltzmann software framework waLBerla, resulting in parallel efficiency of 90% on up to 4080 cores. © 2009 Springer.
UnivIS-Import:2015-04-16:Pub.2009.tech.IMMD.lsinfs.locali

(untitled)
In particulate soft matter systems the average number of contacts extitZ of a particle is an important predictor of the mechanical properties of the system. Using x-ray tomography, we analyze packings of frictional, oblate ellipsoids of various aspect ratios α, prepared at different global volume fractions ϕ extitg

Local temperature measurement in TEM by parallel beam electron diffraction - Niekiel, Florian; Kraschewski, Simon; Müller, Julian; Butz, Benjamin; Spiecker, Erdmann (Ultramicroscopy, 2017)
With the recent advances in instrumentation pushing the limits of in situ transmission electron microscopy, the question of local sample temperature comes into focus again. In this work the applicability of parallel beam electron diffraction to locally measure and monitor the sample temperature in TEM is assessed, with applications for in situ heating experiments in mind. With Au nanoparticles applied to the sample surface, temperature is measured in the range from RT to 890°C by evaluating the change in scattering angle upon thermal expansion. Repeated measurements at constant temperature reveal a statistical precision of the method as good as 2.8K. The applicability to locally measure the temperature is demonstrated mapping the temperature gradient across a heating chip. Owing to instantaneous response of thermal expansion to temperature changes, the method is well suited for monitoring even quick temperature changes, as demonstrated by quenching experiments. In order to enable extensive in situ studies, an evaluation method capable of processing large datasets with high precision is developed. Beam parallelity is identified as crucial experimental prerequisite and a routine is established, optimizing the microscope alignment in terms of beam parallelity. Apart from establishing a procedure for local temperature measurement, the present work demonstrates the unique capabilities of MEMS-based in situ heating equipment.
Keywords: Beam parallelity; In situ microscopy; Metallic nanoparticles; Microscope alignment; Temperature measurement; Transmission electron microscopy

Local work function measurements of epitaxial graphene - Filleter, Tobin; Emtsev, Konstantin; Seyller, Thomas; Bennewitz, Roland (Applied Physics Letters, 2008)
The work function difference between single layer and bilayer graphene grown epitaxially on 6H-SiC(0001) has been determined to be 135±9 meV by means of the Kelvin probe force microscopy. Bilayer films are found to increase the work function as compared to single layer films. This method allows an unambiguous distinction between interface layer, single layer, and bilayer graphene. In combination with high-resolution topographic imaging, the complex step structure of epitaxial graphene on SiC can be resolved with respect to substrate and graphene layer steps.
EAM Import::2019-03-12

LOHC - Von der Forschung in die Schule. - Heinzerling, Peter; Kometz, Andreas (Praxis der Naturwissenschaften - Chemie in der Schule, 2014)
Es wird ein Versuch zur Herstellung von Wasserstoff aus Perhydro-N-ethylcarbazol (H12NEC) mit schulischen Mitteln vorgestellt (Original übernommen).
Keywords: Experiment; Chemieunterricht; Elektrochemie; Wasserstoff; Energiespeicherung; Energieversorgung; Erneuerbare Energie; Katalyse; Energiepolitik; Deutschland

LOHC – von der Forschung in die Schule (Update) - Heinzerling, Peter; Kometz, Andreas (Praxis der Naturwissenschaften - Chemie in der Schule, 2016)
Es wird ein Versuch zur Herstellung von Wassrstoff aus dem chemischen Energiespeicher H18-Marlothern SH (H18DBT) mit schulischen Mitteln vorgestellt.
Keywords: Liquid Organic Hydrogen Carrier (LOHC); Katalyse; Einmalspritzen

Long-alkyl-chain-derivatized imidazolium salts and ionic liquid crystals with tailor-made properties - Wang, Xinjiao; Sternberg, Michelle; Kohler, Florian; Melcher, Berthold Ulrich; Wasserscheid, Peter; Meyer, Karsten (RSC Advances, 2014)
A series of new 1,3-dialkylimidazolium salts with the general formula [CCIM][A] (for n = 12; A = PF, OTf, NTf; for n = 10, 14, 16, and 18; A = BF, ClO) has been synthesized. The [CCIM][A] salts are ionic liquids at room temperature, whereas all [CCIM][BF] and [CCIM][ClO] (n = 10, 14, 16, 18) salts demonstrate a liquid crystalline phase at elevated temperatures that have a large mesophase window, which varies from 10 to 80 °C with increasing alkyl chain length. In particular, [CCIM][BF] shows liquid crystalline behavior at room temperature and therefore is potentially suitable for application as a pre-organized reaction medium in synthesis and catalysis. Viscosity studies of [CC IM][BF] and the corresponding perchlorate salt demonstrate strong non-Newtonian viscosity behavior for the liquid crystalline state of these ionic liquids. © 2014 The Royal Society of Chemistry.

Long-distance laser propulsion and deformation- monitoring of cells in optofluidic photonic crystal fiber - Unterkofler, Sarah; Garbos, Martin K.; Euser, Tijmen G.; Russell, Philip St. John (Journal of Biophotonics, 2013)
We introduce a unique method for laser-propelling individual cells over distances of 10s of cm through stationary liquid in a microfluidic channel. This is achieved by using liquid-filled hollow-core photonic crystal fiber (HC-PCF). HC-PCF provides low-loss light guidance in a well-defined single mode, resulting in highly uniform optical trapping and propulsive forces in the core which at the same time acts as a microfluidic channel. Cells are trapped laterally at the center of the core, typically several microns away from the glass interface, which eliminates adherence effects and external perturbations. During propagation, the velocity of the cells is conveniently monitored using a non-imaging Doppler velocimetry technique. Dynamic changes in velocity at constant optical powers up to 350 mW indicate stress-induced changes in the shape of the cells, which is confirmed by bright-field microscopy. Our results suggest that HC-PCF will be useful as a new tool for the study of single-cell biomechanics.
EAM Import::2019-03-12

Long-range energy transport in single supramolecular nanofibres at room temperature - Haedler, Andreas T.; Kreger, Klaus; Issac, Abey; Wittmann, Bernd; Kivala, Milan; Hammer, Natalie; Koehler, Juergen; Schmidt, Hans-Werner; Hildner, Richard (Nature, 2015)
Efficient transport of excitation energy over long distances is a key process in light-harvesting systems, as well as in molecular electronics. However, in synthetic disordered organic materials, the exciton diffusion length is typically only around 10 nanometres (refs 4, 5), or about 50 nanometres in exceptional cases, a distance that is largely determined by the probability laws of incoherent exciton hopping. Only for highly ordered organic systems has the transport of excitation energy over macroscopic distances been reported–for example, for triplet excitons in anthracene single crystals at room temperature, as well as along single polydiacetylene chains embedded in their monomer crystalline matrix at cryogenic temperatures (at 10 kelvin, or -263 degrees Celsius). For supramolecular nanostructures, uniaxial long-range transport has not been demonstrated at room temperature. Here we show that individual self-assembled nanofibres with molecular-scale diameter efficiently transport singlet excitons at ambient conditions over more than four micrometres, a distance that is limited only by the fibre length. Our data suggest that this remarkable long-range transport is predominantly coherent. Such coherent long-range transport is achieved by one-dimensional self-assembly of supramolecular building blocks, based on carbonyl-bridged triarylamines, into well defined H-type aggregates (in which individual monomers are aligned cofacially) with substantial electronic interactions. These findings may facilitate the development of organic nanophotonic devices and quantum information technology.
EAM Import::2019-03-12

Lossless propagation of magnetic dipole excitations on chains of dielectric particles with high refractive index - Zhuromskyy, Oleksandr; Peschel, Ulf (Physical Review B, 2014)
Lossless propagation of longitudinal magnetic dipole waves along chains of high-index subwavelength particles is predicted for a narrow frequency range around the magnetic Mie resonance of the individual particles. Mathematical analogies between dipole and magnetoinductive waves are used to reduce back-reflections thus improving the power transfer efficiency of respective particle waveguides. The proposed technique can be used to optimize the propagation of even more complex particle-based configurations.
EAM Import::2019-03-12

Low-Lying Electronic Excited States of Pentacene Oligomers: A Comparative Electronic Structure Study in the Context of Singlet Fission - Brana Coto, Pedro; Sharifzadeh, Sahar; Neaton, Jeffrey B.; Thoss, Michael (Journal of Chemical Theory and Computation, 2015)
The lowest-lying electronic excited states of pentacene and its oligomers are investigated using accurate multireference wave function methods (CASPT2/CASSCF) and the many-body Greens’s function approach (GW/BSE). The results obtained for dimers and trimers of different geometry reveal a complex electronic structure, which includes locally excited, charge transfer, and multiexciton states. For singlets of single-excitation character, both approaches yield excitation energies that are in good overall quantitative agreement. While the multiexciton states are located relatively high in energy in all systems investigated, charge transfer states exist in close proximity to the lowest-lying absorbing states. The implications of the results for the mechanisms of singlet fission in pentacene are discussed.

Low melting Li/K/Cs acetate salt mixtures as new ionic media for catalytic applications - first physico-chemical characterization - Bajus, Stephanie; Deyko, Alexey; Bösmann, Andreas; Maier, Florian; Steinrück, Hans-Peter; Wasserscheid, Peter (Dalton Transactions, 2012)
In order to expand the temperature limits of Supported Ionic Liquid Phase (SILP) or Solid Catalyst with Ionic Liquid Layer (SCILL) systems to higher operation temperatures, the mixture of lithium acetate, potassium acetate, and caesium acetate (molar ratio of 0.2/0.275/0.525) has been studied in detail. Physico-chemical properties of the bulk melt are reported together with stability data of the modern salt on various solid support materials showing attractive properties for many potential high temperature applications. © 2012 The Royal Society of Chemistry.

Low-temperature and hysteresis-free electron-transporting layers for efficient, regular, and planar structure perovskite solar cells - Hou, Yi; Ramírez Quiroz, César Omar; Scheiner, Simon; Chen, Wei; Stubhan, Tobias; Hirsch, Andreas; Halik, Marcus; Brabec, Christoph (Advanced Energy Materials, 2015)
With the aim of fully utilizing the low processing temperatures of perovskite solar cells, significant progress in replacing high temperature processed TiO by various low-temperature solution processed electron transporting layers (LT-ETLs) was recently reported. Here, recent progress in the development of LT-ETLs for regular planar structure perovskite solar cells, which is essential for achieving high efficiency in parallel to avoiding hysteresis, is reviewed. In addition, the application of a novel hysteresis-free LT-ETLs for regular planar perovskite solar cells in our laboratory is briefly discussed. By incorporating a low temperature processed WOnanoparticular layer in combination with a mixed fullerene functionalized self-assembled monolayers (SAMs), a regular, planar structure, and hysteresis-free perovskite solar cell with a maximum efficiency of almost 15% can be fabricated. Recent progress in the development of low temperature processed electron-transporting layers for regular planar structure perovskite solar cells is reviewed. Moreover, the application of a novel mixed self-assembled monolayers in hysteresis-free perovskite solar cells is briefly discussed. The as-fabricated perovskite solar cells show a maximum efficiency of almost 15%.
Keywords: electron-transporting layers; hysteresis-free solar cells; low-temperature solution processed; perovskite solar cells

Low-temperature ballistic transport in nanoscale epitaxial graphene cross junctions - Weingart, S.; Bock, C.; Kunze, Ulrich; Speck, Florian; Seyller, Thomas; Ley, Lothar (Applied Physics Letters, 2009)
We report on the observation of inertial-ballistic transport in nanoscale cross junctions fabricated from epitaxial graphene grown on SiC(0001). Ballistic transport is indicated by a negative bend resistance of R ≈-170 ω, which is measured in a nonlocal, four-terminal configuration at 4.2 and which vanishes as the temperature is increased above 80 K. © 2009 American Institute of Physics.

Low-temperature binding of NO adsorbed on MIL-100(Al)-A case study for the application of high resolution pulsed EPR methods and DFT calculations - Mendt, Matthias; Barth, Benjamin; Hartmann, Martin; Poeppl, Andreas (Journal of Chemical Physics, 2017)
The low-temperature binding of nitric oxide (NO) in the metal-organic framework MIL-100(Al) has been investigated by pulsed electron nuclear double resonance and hyperfine sublevel correlation spectroscopy. Three NO adsorption species have been identified. Among them, one species has been verified experimentally to bind directly to an Al-27 atom and all its relevant N-14 and Al-27 hyperfine interaction parameters have been determined spectroscopically. Those parameters fit well to the calculated ones of a theoretical cluster model, which was derived by density functional theory (DFT) in the present work and describes the low temperature binding of NO to the regular coordinatively unsaturated Al3+ site of the MIL-100(Al) structure. As a result, the Lewis acidity of that site has been characterized using the NO molecule as an electron paramagnetic resonance active probe. The DFT derived wave function analysis revealed a bent end-on coordination of the NO molecule adsorbed at that site which is almost purely ionic and has a weak binding energy. The calculated flat potential energy surface of this species indicates the ability of the NO molecule to freely rotate at intermediate temperatures while it is still binding to the Al3+ site. For the other two NO adsorption species, no structural models could be derived, but one of them is indicated to be adsorbed at the organic part of the metal-organic framework. Hyperfine interactions with protons, weakly coupled to the observed NO adsorption species, have also been measured by pulsed electron paramagnetic resonance and found to be consistent with their attribution to protons of the MIL-100(Al) benzenetricarboxylate ligand molecules. Published by AIP Publishing.

Low temperature formation of CuIn1 - xGaxSe2solar cell absorbers by all printed multiple species nanoparticulate Se + Cu-In + Cu-Ga precursors - Möckel, Stefan; Wernicke, Tobias; Arzig, Matthias; Köder, Philipp; Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Peukert, Wolfgang; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2015)
In this work an all nanoparticulate precursor for application in Cu(InGa)Sesolar cell absorbers is presented. Binary Cu-In nanoparticles, Cu-Ga powder and elemental Se nanoparticles were mixed in dispersion and deposited on Mo-coated substrates. Research was focused on Cu(InGa)Selayer formation kinetics, phase composition characterised by differential scanning calorimetry and in-situ X-ray diffraction (XRD). Furthermore phase composition and morphology were studied by ex-situ XRD, Raman spectroscopy and scanning electron microscopy. The results revealed a fast consumption of the precursor and the formation of CuInSebelow 340 °C. Binary secondary phases were not observed at any temperature.
Keywords: Low-temperature; Copper indium gallium diselenide; Chalcopyrite; Nanoparticulate precursors; In-situ X-ray diffraction; Bimetallic nanoparticles

Low temperature solid-state wetting and formation of nanowelds in silver nanowires - Radmilovic, Vuk V.; Göbelt, Manuela; Ophus, Colin; Christiansen, S. H.; Spiecker, Erdmann; Radmilovic, Velimir R. (Nanotechnology, 2017)
This article focuses on the microscopic mechanism of thermally induced nanoweld formation between silver nanowires(AgNWs)which is a key process for improving electrical conductivity in NW networks employed for transparent electrodes. Focused ion beam sectioning and transmission electron microscopy were applied in order to elucidate the atomic structure of a welded NW including measurement of the wetting contact angle and characterization of defect structure with atomic accuracy, which provides fundamental information on the welding mechanism. Crystal lattice strain, obtained by direct evaluation of atomic column displacements in high resolution scanning transmission electron microscopy images, was shown to be non-uniform among the five twin segments of the AgNW pentagonal structure. It was found that the pentagonal cross-sectional morphology of AgNWs has a dominant effect on the formation of nanowelds by controlling initial wetting as well as diffusion of Ag atoms between the NWs. Due to complete solid-state wetting, at an angle of ∼4.8°, the welding process starts with homoepitaxial nucleation of an initial Ag layer on (100)surface facets, considered to have an infinitely large radius of curvature. However, the strong driving force for this process due to the Gibbs–Thomson effect, requires the NW contact to occur through the corner of the pentagonal cross-section of the second NW providing a small radius of curvature. After the initial layer is formed, the welded zone continues to grow and extends out epitaxially to the neighboring twin segments.
Keywords: silver nanowires (AgNWs); aluminum-doped zinc oxide (AZO); nanoweld formation; solid-state wetting; nanowire sintering

Low-temperature solution-processed memory transistors based on zinc oxide nanoparticles - Faber, Hendrik; Burkhardt, Martin; Jedaa, Abdesselam; Kälblein, D.; Klauk, Hagen; Halik, Marcus (Advanced Materials, 2009)
We report on thin!film transistors based on ZnO nanoparticles processed from solution and with a maximum temperature of 100 °C. Electron mobilities up to 2.5 cm²V−1s−1 are obtained, and top-gate TFTs show non-volatile memory properties with a large, stable hysteresis and a memory ratio of 105. Memory TFTs operate in ambient, have good shelf-life (>6 months), and useful endurance properties.

Low-Voltage Organic Field Effect Transistors with a 2-Tridecyl[1]benzothieno[3,2- b ][1]benzothiophene Semiconductor Layer - Amin, Atefeh Y.; Khassanov, Artöm; Reuter, Knud; Meyer-Friedrichsen, Timo; Halik, Marcus (Journal of the American Chemical Society, 2012)
An asymmetric n-alkyl substitution pattern was realized in 2-tridecyl[1]benzothieno[3,2-b][1]benzothiophene (C13-BTBT) in order to improve the charge transport properties in organic thin-film transistors. We obtained large hole mobilities up to 17.2 cm2/(V·s) in low-voltage operating devices. The large mobility is related to densely packed layers of the BTBT π-systems at the channel interface dedicated to the substitution motif and confirmed by X-ray reflectivity measurements. The devices exhibit promising stability in continuous operation for several hours in ambient air.

Low-Voltage p- and n-Type Organic Self-Assembled Monolayer Field Effect Transistors - Novak, Michael; Ebel, Alexander; Meyer-Friedrichsen, Timo; Jedaa, Abdesselam; Vieweg, Benito; Yang, Guang; Voitchovsky, Kislon; Stellacci, Francesco; Spiecker, Erdmann; Hirsch, Andreas; Halik, Marcus (Nano Letters, 2011)
We report on p- and n-type organic self-assembled monolayer field effect transistors. On the base of quaterthiophene and fullerene units, multifunctional molecules were synthesized, which have the ability to self-assemble and provide multifunctional monolayers. The self-assembly approach, based on phosphonic acids, is very robust and allows the fabrication of functional devices even on larger areas. The p- and n-type transistor devices with only one molecular active layer were demonstrated for transistor channel lengths up to 10 μm. The monolayer composition is proven by electrical experiments and by high-resolution transmission electron microscopy, electron energy loss spectroscopy, XPS, and AFM experiments. Because of the molecular design and the contribution of isolating alkyl chains to the hybrid dielectric, our devices operate at low supply voltages (-4 V to +4 V), which is a key requirement for practical use and simplifies the integration in standard applications. The monolayer devices operate in ambient air and show hole and electron mobilities of 10 cm/(V s) and 10 cm/(V s) respectively. In particular the n-type operation of self- assembled monolayer transistors has not been reported before. Hereby, structure-property relations of the SAMs have been studied. Furthermore an approach to protect the sensitive C from immediate degradation within the molecular design is provided. © 2011 American Chemical Society.

Low-Voltage Self-Assembled Monolayer Field-Effect Transistors on Flexible Substrates - Schmaltz, Thomas; Amin, Atefeh Y.; Khassanov, Artöm; Meyer-Friedrichsen, Timo; Steinrück, Hans-Georg; Magerl, Andreas; Segura, Juan Jose; Voitchovsky, Kislon; Stellacci, Francesco; Halik, Marcus (Advanced Materials, 2013)
Self-assembled monolayer field-effect transistors (SAMFETs) of BTBT functionalized phosphonic acids are fabricated. The molecular design enables device operation with charge carrier mobilities up to 10 cm V s and for the first time SAMFETs which operate on rough, flexible PEN substrates even under mechanical substrate bending. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Luminescence of Mn2+ ions in Tb3Al5O12 garnet - Zorenko, Yu; Gorbenko, V.; Voznyak, Taras; Batentschuk, Miroslaw; Osvet, Andres; Winnacker, Albrecht (Journal of Luminescence, 2010)
The paper is dedicated to investigation of the Mn2+ luminescence in Tb_3Al5O12 (TbAG) garnet, as well as the processes of excitation energy transfer between host cations (Tb3+ ions) and activators (Mn2+ and Mn2+–Ce3+ pair ions) in single crystalline films of TbAG:Mn and TbAG:Mn,Ce garnets which can be considered as promising luminescent materials for conversion of LED's radiation. Due to the effective energy transfer between TbAG host and activator, Mn2+ ions in TbAG possess the bright orange luminescence in the bands peaked at 595 nm with a lifetime of 0.64 ms which are caused by the ^4T1i̊ghtarrow6A1 radiative transitions. The simultaneous process of energy transfer is realized in TbAG:Mn,Ce: (i) from Tb3+ to Mn2+ ions; (ii) from Tb3+ cations to Ce3+ ions and then partly to Mn2+ ions through Tb3+ ion sublattice and Ce–Mn dipole–dipole interaction.
Keywords: Single crystalline films; TbAG; Energy transfer; Mn2+ and Ce3+ dopants; Luminescence

Luminescence properties and energy transfer processes in YAG:Yb,Er single crystalline films - Zorenko, Yu; Gorbenko, V.; Savchyn, V.; Batentschuk, Miroslaw; Osvet, Andres; Brabec, Christoph (Radiation Measurements, 2013)
The paper is dedicated to the study of the optical properties of YAG:Yb,Er single-crystalline films (SCF) grown by liquid phase epitaxy. The absorption, cathodoluminescence and time-resolved photoluminescence spectra and photoluminescence decay curves were measured for the SCFs with different doping levels of Er (from 0.6 to 4.2 at.%) and Yb (from 0.1 to 0.6 at.%). The spectra, excited by synchrotron radiation in the fundamental absorption range of the YAG and in the intraionic absorption bands of both dopants, reveal energy transfer from the YAG host to the Er and Yb ions and between these ions. © 2013 Elsevier Ltd. All rights reserved.
Keywords: Er 3+ and Yb3+ dopants; Liquid phase epitaxy; Luminescence; Single crystalline films; YAG

Luminescent properties and energy transfer processes in YAG:Er single crystalline films - Zorenko, Yu.; Gorbenko, V.; Zorenko, T.; Savchyn, V.; Batentschuk, Miroslaw; Osvet, Andres; Brabec, Christoph (Journal of Luminescence, 2014)
The paper is dedicated to studying the optical properties of YAG:Er single crystalline films (SCF) grown by liquid phase epitaxy. The absorption, cathodoluminescence and photoluminescence spectra were measured for the YAG:Er SCFs with different doping levels of Er from 0.735 to 6.6 at%. The luminescence spectra and luminescence excitation spectra under synchrotron radiation excitation in the fundamental absorption range of the YAG and in the intrinsic f-d absorption bands of Er ions reveal the peculiarities of energy transfer from the YAG host to the Er ions. © 2014 Elsevier B.V.
Keywords: Liquid phase epitaxy; Luminescence; Single crystalline films; YAG

Macro- and nanomechanical properties and strain rate sensitivity of accumulative roll bonded and equal channel angular pressed ultrafine-grained materials - Boehner, Andreas; Maier, Verena; Durst, Karsten; Höppel, Heinz Werner; Göken, Mathias (Advanced Engineering Materials, 2011)
Several processes of severe plastic deformation are suitable for the production of materials with ultrafine-grained microstructures which are known to exhibit high strength and often good ductility as well as strain rate sensitive behavior. The most promising ones are equal channel angular pressing (ECAP) for bulk material and accumulative roll bonding (ARB) for the production of sheet material. In order to evaluate the influence of the process on these mechanical properties and the strain rate sensitivity, tensile tests, and nanoindentation tests were performed on material produced up to similar effective plastic strains of extgreekeARB = 6.4 and extgreekeECAP = 6.3. It could be shown that the macroscopic strength is slightly higher for ARB than for ECAP material and vice versa in nanoindentation. Independent of the testing method, the strain rate sensitivities and activation volumes are similar for both materials. Thus, both processes performed up to similar effective plastic strains lead to comparable improvements in the mechanical properties. Additionally it could be shown, that this comparison allows the identification of the dominant deformation mechanism which is responsible for the observed strain rate sensitivity.
WW1::886

Macro-cellular silicon carbide reactors for nonstationary combustion under piston engine-like conditions - Schlier, Lorenz; Zhang, Wei; Travitzky, Nahum; Greil, Peter; Cypris, Jochen; Weclas, Miroslaw (International Journal of Applied Ceramic Technology, 2011)
Strut lattice structures of reaction-bonded silicon infiltrated silicon carbide ceramics (RB-SiSiC) for air-fuel mixture formation and for nonstationary lean-burn under pressure applications were fabricated. The lattice design with a high porosity >80% was shaped by indirect three-dimensional printing. It was shown that pre-ignition processes in the porous reactor are much faster than in a free combustion, especially at lower temperatures. Interaction of high velocity diesel jets with cylindrical strut ligaments of the SiSiC lattice structure offers a new possibility for quick and efficient fuel distribution (multi-jet splitting) in space. © 2010 The American Ceramic Society.

Macrokinetic effects in perhydro-N-ethylcarbazole dehydrogenation and H2 productivity optimization by using egg-shell catalysts - Peters, Willi; Seidel, Alexander; Herzog, Stefan; Bösmann, Andreas; Schwieger, Wilhelm; Wasserscheid, Peter (Energy and Environmental Science, 2015)
This contribution deals with pore diffusion influences on the dehydrogenation kinetics of perhydro-N-ethylcarbazole (H12-NEC). The reaction is of high interest in the context of hydrogen storage in the N-ethylcarbazole (NEC)/perhydro-N-ethylcarbazole (H12-NEC) Liquid Organic Hydrogen Carrier (LOHC) system. The hydrogen content of H12-NEC is 5.8 wt% and total dehydrogenation releases for each mL of H12-NEC more than 600 mL of H-2. Further optimization of H12-NEC dehydrogenation catalysis requires a better understanding of the role of mass transfer effects. Pore diffusion effects have been studied by preparing egg-shell catalysts (Pt/gamma-alumina layer on alpha-alumina core) of different active layer thicknesses (24 -88 mu m). It has been found that even at very thin catalyst layers (24 mu m) the kinetic regime is limited to 235 degrees C, thus pore diffusion effects the dehydrogenation in almost all commercial catalysts strongly.

Macroscale adhesion of gecko setae reflects nanoscale differences in subsurface composition - Loskill, Peter; Puthoff, Jonathan; Wilkinson, Matt; Mecke, Klaus; Jacobs, Karin; Autumn, Kellar (Journal of the Royal Society Interface, 2013)
Surface energies are commonly used to determine the adhesion forces between materials. However, the component of surface energy derived from long-range forces, such as van der Waals forces, depends on the material's structure below the outermost atomic layers. Previous theoretical results and indirect experimental evidence suggest that the van der Waals energies of subsurface layers will influence interfacial adhesion forces. We discovered that nanometre-scale differences in the oxide layer thickness of silicon wafers result in significant macroscale differences in the adhesion of isolated gecko setal arrays. Si/SiO2 bilayer materials exhibited stronger adhesion when the SiO2 layer is thin (approx. 2 nm). To further explore how layered materials influence adhesion, we functionalized similar substrates with an octadecyltrichlorosilane monolayer and again identified a significant influence of the SiO2 layer thickness on adhesion. Our theoretical calculations describe how variation in the SiO2 layer thickness produces differences in the van der Waals interaction potential, and these differences are reflected in the adhesion mechanics. Setal arrays used as tribological probes provide the first empirical evidence that the 'subsurface energy' of inhomogeneous materials influences the macroscopic surface forces.
Keywords: van der Waals forces; gecko adhesion; surface energy

Magic number colloidal clusters as minimum free energy structures - Wang, Junwei; Mbah Chrameh, Fru; Przybilla, Thomas; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Engel, Michael; Vogel, Nicolas (Nature Communications, 2018)
Clusters in systems as diverse as metal atoms, virus proteins, noble gases, and nucleons have properties that depend sensitively on the number of constituent particles. Certain numbers are termed ‘magic’ because they grant the system with closed shells and exceptional stability. To this point, magic number clusters have been exclusively found with attractive interactions as present between atoms. Here we show that magic number clusters exist in a confined soft matter system with negligible interactions. Colloidal particles in an emulsion droplet spontaneously organize into a series of clusters with precisely defined shell structures. Crucially, free energy calculations demonstrate that colloidal clusters with magic numbers possess higher thermodynamic stability than those off magic numbers. A complex kinetic pathway is responsible for the efficiency of this system in finding its minimum free energy configuration. Targeting similar magic number states is a strategy towards unique configurations in finite self-organizing systems across the scale

Magnetically Guided Titania Nanotubes for Site-Selective Photocatalysis and Drug Release - Shrestha, Nabeen Kumar; Macák, Jan; Schmidt-Stein, F.; Hahn, Robert; Mierke, Claudia; Fabry, Ben; Schmuki, Patrik (Angewandte Chemie, 2008)
Quick release: The spatial and temporal delivery of active molecules (dyes or drugs) can be precisely controlled by the photocatalytic activity of TiO_2 nanotubes (see picture). The cleavage of the link between the active molecule and the nanotubes, which are filled with magnetic Fe_3O_4 nanoparticles, occurs by photoinduced chain scission under UV light; the load can be released before photodegradation by action of photogenerated radicals can occur.

Magnetic microgels for drug targeting applications: Physical–chemical properties and cytotoxicity evaluation - Turcu, Rodica; Craciunescu, Izabell; Garamus, Vasil M.; Janko, Christina; Lyer, Stefan; Tietze, Rainer; Alexiou, Christoph; Vekas, Ladislau (Journal of Magnetism and Magnetic Materials, 2014)
Magnetoresponsive microgels with high saturation magnetization values have been obtained by a strategy based on the miniemulsion method using high colloidal stability organic carrier ferrofluid as primary material. Hydrophobic nanoparticles Fe3O4/oleic acid are densely packed into well-defined spherical nanoparticle clusters coated with polymers with sizes in the range 40–350 nm. Physical– chemical characteristics of magnetic microgels were investigated by TEM, SAXS, XPS and VSM measurements with the focus on the structure–properties relationship. The impact of magnetic microgels loaded with anticancer drug mitoxantrone (MTO) on the non-adherent human T cell leukemia loaded MTO penetrate into cells and both induce apoptosis and later secondary necrosis in a time- and dose dependent manner. In contrast, microgels without MTO are not cytotoxic in the corresponding concentrations. Our results show that MTO-loaded microgels are promising structures for application in magnetic drug targeting.
EAM Import::2019-03-12

Magnetic nanoparticle-based drug delivery for cancer therapy - Tietze, Rainer; Zaloga, Jan; Unterweger, Harald; Lyer, Stefan; Friedrich, Ralf P.; Janko, Christina; Pöttler, Marina; Dürr, Stephan; Alexiou, Christoph (Biochemical and Biophysical Research Communications, 2015)
Nanoparticles have belonged to various fields of biomedical research for quite some time. A promising site-directed application in the field of nanomedicine is drug targeting using magnetic nanoparticles which are directed at the target tissue by means of an external magnetic field. Materials most commonly used for magnetic drug delivery contain metal or metal oxide nanoparticles, such as superparamagnetic iron oxide nanoparticles (SPIONs). SPIONs consist of an iron oxide core, often coated with organic materials such as fatty acids, polysaccharides or polymers to improve colloidal stability and to prevent separation into particles and carrier medium [1]. In general, magnetite and maghemite particles are those most commonly used in medicine and are, as a rule, well-tolerated. The magnetic properties of SPIONs allow the remote control of their accumulation by means of an external magnetic field. Conjugation of SPIONs with drugs, in combination with an external magnetic field to target the nanoparticles (so-called "magnetic drug targeting", MDT), has additionally emerged as a promising strategy of drug delivery. Magnetic nanoparticle-based drug delivery is a sophisticated overall concept and a multitude of magnetic delivery vehicles have been developed. Targeting mechanism-exploiting, tumor-specific attributes are becoming more and more sophisticated. The same is true for controlled-release strategies for the diseased site. As it is nearly impossible to record every magnetic nanoparticle system developed so far, this review summarizes interesting approaches which have recently emerged in the field of targeted drug delivery for cancer therapy based on magnetic nanoparticles.
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Magnetotransport properties of iron microwires fabricated by focused electron beam induced autocatalytic growth - Porrati, F.; Sachser, R.; Walz, Marie-Madeleine; Vollnhals, Florian; Steinrück, Hans-Peter; Marbach, Hubertus; Huth, M. (Journal of Physics D-Applied Physics, 2011)
We have prepared iron microwires in a combination of focused electron beam induced deposition and autocatalytic growth from the iron pentacarbonyl, Fe(CO), precursor gas under ultra-high vacuum conditions. The electrical transport properties of the microwires were investigated and it was found that the temperature dependence of the longitudinal resistivity (ρ) shows a typical metallic behaviour with a room temperature value of about 88 νΩ cm. In order to investigate the magnetotransport properties we have measured the isothermal Hall-resistivities in the range between 4.2 and 260 K. From these measurements, positive values for the ordinary and the anomalous Hall coefficients were derived. The relation between anomalous Hall resistivity (ρ) and longitudinal resistivity is quadratic, , revealing an intrinsic origin of the anomalous Hall effect. Finally, at low temperature in the transversal geometry a negative magnetoresistance of about 0.2% was measured. © 2011 IOP Publishing Ltd.

Manifold angles, the concept of self-similarity, and angle-enhanced bifurcation diagrams - Gallas, Jason; Beims, Marcus W. (Scientific Reports, 2016)
Chaos and regularity are routinely discriminated by using Lyapunov exponents distilled from the norm of orthogonalized Lyapunov vectors, propagated during the temporal evolution of the dynamics. Such exponents are mean-field-like averages that, for each degree of freedom, squeeze the whole temporal evolution complexity into just a single number. However, Lyapunov vectors also contain a step-by-step record of what exactly happens with the angles between stable and unstable manifolds during the whole evolution, a big-data information permanently erased by repeated orthogonalizations. Here, we study changes of angles between invariant subspaces as observed during temporal evolution of Hénon (tm) s system. Such angles are calculated numerically and analytically and used to characterize self-similarity of a chaotic attractor. In addition, we show how standard tools of dynamical systems may be angle-enhanced by dressing them with informations not difficult to extract. Such angle-enhanced tools reveal unexpected and practical facts that are described in detail. For instance, we present a video showing an angle-enhanced bifurcation diagram that exposes from several perspectives the complex geometrical features underlying the attractors. We believe such findings to be generic for extended classes of systems.

Manufacturing, characterization, and application of nanoimprinted metallic probe demonstrators for electrical scanning probe microscopy - Jambreck, J. D.; Yanev, V.; Schmitt, H.; Rommel, Mathias; Bauer, A. J.; Frey, Lothar (Microelectronic Engineering, 2011)
For electrical scanning probe microscopy (SPM) techniques, tips with low electrical resistance nearly not being affected by probe wear out are desirable. High aspect ratio metal tips can fulfill these requirements. Nanoimprinted metallic probe demonstrators were manufactured on metal coated cantilevers by using UV nanoimprint lithography with a UV-curing resist containing silver particles, focused ion beam processing, and a micro-manipulator. The probes manufactured in this manner were electrically characterized, used in a SPM system for measurements, and compared with conventional probes. SPM experiments were performed in scanning capacitance microscopy mode (SCM), tunneling atomic force microscopy mode (TUNA), and topography atomic force microscopy mode. The demonstrator probes show a resistance which is lower than that of diamond coated probes and higher than that of metal coated probes. For the demonstrators, SCM maps with higher signal-to-noise ratio compared with standard probes were obtained. TUNA maps and local TUNA I-V-curves showed comparable results for Pt/Ir coated probes and the demonstrator probes. In topography mode the demonstrator tips show higher resolution than diamond coated tips and than silicon tips with a thicker Pt/Ir coating and lower resolution than silicon tips with a thin Pt/Ir coating.
Keywords: FIB; Metal tip; Nanoimprint lithography; Scanning probe microscopy; SCM; TUNA

Mapping Charge-Carrier Density across the p-n Junction in Ambipolar Carbon-Nanotube Networks by Raman Microscopy - Grimm, Stefan; Jakubka, Florian; Schießl, Stefan; Gannott, Florentina; Zaumseil, Jana (Advanced Materials, 2014)
In situ confocal Raman microscopy is used to map the recombination zone (induced p-n junction) in an ambipolar carbon-nanotube-network transistor with high spatial resolution. The shift of the 2D mode (G' mode) depending on hole and electron accumulation serves as a measure for the local charge-carrier density and provides complementary information about charge transport and recombination in ambipolar transistors.
EAM Import::2019-03-12

Maßgeschneiderte partikelverstärkte Verbundwerkstoffe und Werkstoffverbunde hergestellt durch den akkumulativen Walzprozess (ARB) - Schmidt, Christian; Höppel, Heinz Werner; Göken, Mathias (Tagungsband zum 18. Symposium Verbundwerkstoffe, 2011)
Der akkumulative Walzprozess (ARB) bietet die Möglichkeit ultrafeinkörnige Blechwerkstoffe mit interessanten mechanischen Eigenschaften herzustellen. Durch die kontrollierte Einbringung stabilisierter Nanopartikel während des ARB-Prozesses wurde im Rahmen dieser Arbeit gezeigt, dass der ARB-Prozess auch hervorragend dafür geeignet ist, UFG-Verbundwerkstoffe herzustellen und Eigenschaften maßzuschneidern. Bereits ein sehr geringer Anteil keramischer Nanopartikel von 0,1 vol.-% führt durch zusätzliche, lokale plastische Verformung einerseits zu beschleunigter Kornfeinung, wodurch die hohen spezifischen Festigkeiten ultrafeinkörniger Werkstoffe bereits nach zwei statt acht Walzzyklen erreicht werden können. Andererseits kann gegenüber der reinen UFG-Struktur eine zusätzliche Festigkeitssteigerung erzielt werden.
EAM Import::2019-03-12

Massive conformational changes during thermally induced self-metalation of 2H-tetrakis-(3,5-di-tert-butyl)-phenylporphyrin on Cu(111) - Stark, Michael Werner; Ditze, Stefanie; Lepper, Michael; Zhang, Liang; Schlott, Hannah; Buchner, Florian; Röckert, Michael; Chen, Min; Lytken, Ole; Steinrück, Hans-Peter; Marbach, Hubertus (Chemical Communications, 2014)
Based on a combined scanning tunnelling microscopy and X-ray photoelectron spectroscopy study we present detailed insights into pronounced changes of long-range order and intramolecular conformation during the self-metalation of 2H-5,10,15,20-tetrakis-(3,5-di-tert-butyl)-phenylporphyrin (2HTTBPP) to CuTTBPP on Cu(111). Upon metalation, the porphyrin literally ``pops up'' from the surface, due to a drastically reduced molecule–substrate interaction.

Massively parallel granular flow simulations with non-spherical particles - Iglberger, Klaus; Rüde, Ulrich (Computer Science - Research and Development, 2010)
Although granular materials have always been an important part of our everyday life, their characteristics and behavior is still only rudimentally understood. Therefore the numerical simulation has gained an increasing importance to gain deeper insight into the properties of granular media. One simulation approach is rigid body dynamics. In contrast to particle-based approaches, it fully resolves the granular particles as geometric objects and incorporates frictional contact dynamics. However, due to its complexity and the lack of large-scale parallelization, rigid body dynamics so far could not be used for very large simulation scenarios. In this paper we demonstrate massively parallel granular media simulations by means of a parallel rigid body dynamics algorithm. We will validate the algorithm for granular gas simulations and prove its scalability on up to 131∈072 processor cores. Additionally, we will show several parallel granular material simulations both with spherical and non-spherical granular particles. © 2010 Springer-Verlag.
UnivIS-Import:2015-03-09:Pub.2010.tech.IMMD.lsinfs.massiv
Keywords: Granular media; Large-scale; Massively parallel; MPI; Parallel algorithms; Parallel frameworks; Parallelization; Rigid body dynamics

Massively Parallel Rigid Body Dynamics Simulations - Iglberger, Klaus; Rüde, Ulrich (Computer Science - Research and Development, 2009)
For decades, rigid body dynamics has been used in several active research fields to simulate the behavior of completely undeformable, rigid bodies. Due to the focus of the simulations to either high physical accuracy or real time environments, the state-of-the-art algorithms cannot be used in excess of several thousand rigid bodies. Either the complexity of the algorithms would result in infeasible runtimes, or the simulation could no longer satisfy the real time aspects. In this paper we present a novel approach for large-scale rigid body dynamics simulations. The presented algorithm enables for the first time rigid body simulations of several million rigid bodies. We describe in detail the parallel rigid body algorithm and its necessary extensions for a large-scale MPI parallelization and analyze the parallel algorithm by means of a particular simulation scenario. © 2009 Springer-Verlag.
UnivIS-Import:2015-03-09:Pub.2009.tech.IMMD.lsinfs.massiv_3
Keywords: Large-scale; Massively parallel; MPI; Parallel algorithms; Parallel frameworks; Parallel programming; Parallelization; Rigid body dynamics

Material optimization in transverse electromagnetic scattering applications - Semmler, Johannes; Pflug, Lukas; Stingl, Michael (SIAM Journal on Scientific Computing, 2018)
A class of algorithms for the solution of discrete material optimization problems in electromagnetic applications is discussed. The idea behind the algorithm is similar to that of the sequential programming. However, in each major iteration a model is established on the basis of an appropriately parametrized material tensor. The resulting nonlinear parametrization is treated on the level of the sub-problem, for which, globally optimal solutions can be computed due to the block separability of the model. Although global optimization of non-convex design problems is generally prohibitive, a well chosen combination of analytic solutions along with standard global optimization techniques leads to a very efficient algorithm for most relevant material parametrizations. A global convergence result for the overall algorithm is established. The effectiveness of the approach in terms of both computation time and solution quality is demonstrated by numerical examples, including the optimal design of cloaking layers for a nano-particle and the identification of multiple materials with different optical properties in a matrix.
Keywords: Discrete optimization; Global optimization; Electromagnetic scattering; Inverse problems; Helmholtz equation; Optical properties; Material optimization; Sequential programming

Materials Integration for Printed Zinc Oxide Thin-Film Transistors: Engineering of a Fully-Printed Semiconductor/Contact Scheme - Liu, XinXin; Wegener, Carsten Moritz; Polster, Sebastian; Jank, Michael; Roosen, Andreas; Frey, Lothar (Journal of Display Technology, 2016)
We report for the first time on the impact of a printed indium tin oxide (ITO) layer inserted between a printed silver conductor and solution processed zinc oxide (ZnO) leading to an optimized semiconductor/contact scheme for full print integration. Introducing the ITO interlayer, the contact resistance is reduced by two orders of magnitude. Nanoparticle thin-film transistors (TFTs) in this Ag/ITO contact configuration show improved saturation mobility of 0.53 cm(2) . V-1 . s(-1) with respect to 0.08 cm(2) . V-1 . s(-1) without ITO interlayer. The contact improvement can be attributed to either an increased charge carrier concentration or a reduction of band offsets at the ZnO/electrode interface.
Keywords: Contact resistance; indium-tin-oxide; thin-film transistors (TFTs); zinc oxide (ZnO)

Matrix effects in the C 1s photoabsorption spectra of condensed naphthalene - Schmidt, Norman Anja; Wenzel, Jan; Dreuw, Andreas; Fink, Rainer; Hieringer, Wolfgang (Journal of Chemical Physics, 2016)
High-resolution C 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of naphthalene are investigated. By comparing the spectral signatures of condensed naphthalene molecules with those of naphthalene in the gas phase, we are able to unambiguously identify spectral features which are affected by the intermolecular interactions in the condensed phase. With the help of calculations using time-dependent density-functional theory and the second-order algebraic-diagrammatic construction scheme for the polarization propagator, resonances in the relevant energy range can be assigned to valence and Rydberg-like excitations. Thus, we obtain a more detailed identification of NEXAFS resonances beyond the present literature.
EAM Import::2019-03-12

Matrix-Valued L1-Optimal Controls in the Coefficients of linear elliptic problems - Kogut, Peter I.; Leugering, Günter (Zeitschrift für Analysis und ihre Anwendungen, 2013)
We consider optimal control problems for linear degenerate elliptic equations with mixed boundary conditions. In particular, we take the matrix-valued coeffcients A(x) of such systems as controls in L1(;RN(N+1) 2 ). One of the important features of the admissible controls is the fact that eigenvalues of the coeffcient matrices may vanish in Equations of this type may exhibit non-uniqueness of weak solutions. Using the concept of convergence in variable spaces and following the direct method in the Calculus of variations, we establish the solvability of this optimal control problem in the class of weak admissible solutions. © European Mathematical Society.
Keywords: Degenerate elliptic equations; control in coefficients; weighted Sobolev spaces; Lavrentieff phenomenon; direct method in the Calculus of Variations

Maximizing Photoluminescence Extraction in Silicon Photonic Crystal Slabs - Mahdavi, Ali; Sarau, George; Xavier, Jolly; Paraiso, Taofiq K.; Christiansen, Silke; Vollmer, Frank (Scientific Reports, 2016)
Photonic crystal modes can be tailored for increasing light matter interactions and light extraction efficiencies. These PhC properties have been explored for improving the device performance of LEDs, solar cells and precision biosensors. Tuning the extended band structure of 2D PhC provides a means for increasing light extraction throughout a planar device. This requires careful design and fabrication of PhC with a desirable mode structure overlapping with the spectral region of emission. We show a method for predicting and maximizing light extraction from 2D photonic crystal slabs, exemplified by maximizing silicon photoluminescence (PL). Systematically varying the lattice constant and filling factor, we predict the increases in PL intensity from band structure calculations and confirm predictions in micro-PL experiments. With the near optimal design parameters of PhC, we demonstrate more than 500-fold increase in PL intensity, measured near band edge of silicon at room temperature, an enhancement by an order of magnitude more than what has been reported.
EAM Import::2019-03-12

Maximum Noble-Metal Efficiency in Catalytic Materials: Atomically Dispersed Surface Platinum - Bruix, Albert; Lykhach, Yaroslava; Matolinova, Iva; Neitzel, Armin; Skala, Tomas; Tsud, Nataliya; Vorokhta, Mykhailo; Stetsovych, Vitalii; Sevcikova, Klara; Myslivecek, Josef; Fiala, Roman; Vaclavu, Michal; et al. (Angewandte Chemie International Edition, 2014)
Platinum is the most versatile element in catalysis, but it is rare and its high price limits large-scale applications, for example in fuel-cell technology. Still, conventional catalysts use only a small fraction of the Pt content, that is, those atoms located at the catalyst's surface. To maximize the noble-metal efficiency, the precious metal should be atomically dispersed and exclusively located within the outermost surface layer of the material. Such atomically dispersed Pt surface species can indeed be prepared with exceptionally high stability. Using DFT calculations we identify a specific structural element, a ceria "nanopocket", which binds Pt2+ so strongly that it withstands sintering and bulk diffusion. On model catalysts we experimentally confirm the theoretically predicted stability, and on real Pt-CeO2 nanocomposites showing high Pt efficiency in fuel-cell catalysis we also identify these anchoring sites.
Keywords: ceria nanoparticles; density functional calculations; heterogeneous catalysis; model catalyst; platinum

Mean-intercept anisotropy analysis of porous media. I. Analytic formulae for anisotropic Boolean models - Klatt, Michael A.; Schroder-Turk, Gerd E.; Mecke, Klaus (Medical Physics, 2017)
Purpose Structure-property relations, which relate the shape of the microstructure to physical properties such as transport or mechanical properties, need sensitive measures of structure. What are suitable fabric tensors that quantify the shape of anisotropic heterogeneous materials? The mean intercept length is among the most commonly used characteristics of anisotropy in porous media, for example, of trabecular bone in medical physics. Methods We analyze the orientation-biased Boolean model, a versatile stochastic model that represents microstructures as overlapping grains with an orientation bias towards a preferred direction. This model is an extension of the isotropic Boolean model, which has been shown to truthfully reproduce multi-functional properties of isotropic porous media. We explain the close relationship between the concept of intersections with test lines to the elaborate mathematical theory of queues, and how explicit results from the latter can be directly applied to characterize microstructures. Results In this series of two papers, we provide analytic formulas for the anisotropic Boolean model and demonstrate often overlooked conceptual shortcomings of this approach. Queuing theory is used to derive simple and illustrative formulas for the mean intercept length. It separates into an intensity-dependent and an orientation-dependent factor. The global average of the mean intercept length can be expressed by local characteristics of a single grain alone. Conclusions We thus identify which shape information about the random process the mean intercept length contains. The connection between global and local quantities helps to interpret observations and provides insights into the possibilities and limitations of the analysis. In the second paper of this series, we discuss, based on the findings in this paper, short-comings of the mean intercept analysis for (bone-)microstructure characterization. We will suggest alternative and better defined sensitive anisotropy measures from integral geometry.
EAM Import::2019-03-12