The Strengthening Effect of Phase Boundaries in a Severely Plastically Deformed Ti-Al Composite Wire - Marr, Tom; Freudenberger, Jens; Maier, Verena; Höppel, Heinz Werner; Göken, Mathias; Schultz, Ludwig (Metals, 2014)
An accumulative swaging and bundling technique is used to prepare composite wires made of Ti and an Al alloy. These wires show reasonable higher yield stresses than expected from the pure material flow curves. The additional strengthening in the composite is analyzed using nanoindentation measurements, tensile testings and investigations of the microstructure. In addition, these properties are analyzed in relation to the fracture surface of the mechanically tested wires. Additional strengthening due to the presence of phase boundaries could be verified. Indications for residual stresses are found that cause a global hardness gradient from the center to the wire rim. Finally, the yield stress of the wires are calculated based on local hardness measurements.
Keywords: SPD; Ti; Al; nanoindentation; mechanical properties

The surface structure matters: thermal stability of phthalic acid anchored to atomically-defined cobalt oxide films - Xu, Tao; Schwarz, Matthias; Werner, Kristin; Mohr, Susanne; Amende, Maximilian; Libuda, Jörg (Physical Chemistry Chemical Physics, 2016)
We have investigated the influence of the structure of oxide surfaces on the thermal stability of anchored phthalic acid (PA) thin films. Specifically, we have performed temperature programmed infrared reflection absorption spectroscopy (TP-IRAS) of PA films deposited by physical vapor deposition (PVD) in ultra-high vacuum (UVH) onto three well-ordered surfaces: Co3O4(111), CoO(111) and CoO(100), all grown on Ir(100). Restructuring and desorption of PA were monitored in situ by TP-IRAS. Upon annealing of PA multilayers, co-adsorbed phthalic anhydride (PAA) desorbs at 200 K and a structural transition to a flat-lying adsorption geometry occurs at 250 K, before the PA multilayer desorbs at 300 K. At temperatures up to 400 K co-adsorbed mono-carboxylates partially desorb and partially convert to bis-carboxylates. Pronounced structure dependencies are observed regarding the thermal stability of the anchored bis-carboxylate monolayers. From Co3O4(111) the anchored PA desorbs over a wide range of temperatures centered at around 540 K. Weaker binding is observed for CoO(111) with desorption temperatures centered around 490 K. The strongest binding occurs on CoO(100), where the anchored PA films are found to be perfectly stable up to 510 K, before desorption starts and centers at around 580 K. The differences in binding strength are rationalized based on the density and the accessibility of the surface Co2+ ions. The findings show that the atomic structure of the oxide surface plays an important role in the stability of organic hybrid interfaces.

The surface trans effect: Influence of axial ligands on the surface chemical bonds of adsorbed metalloporphyrins - Hieringer, Wolfgang; Flechtner, Ken; Kretschmann, Andreas; Seufert, Knud; Auswärter, Willi; Barth, Johannes V.; Görling, Andreas; Steinrück, Hans-Peter; Gottfried, Michael (Journal of the American Chemical Society, 2011)
The chemical bond between an adsorbed, laterally coordinated metal ion and a metal surface is affected by an additional axial ligand on the metal ion. This surface analogon of the trans effect was studied in detail using monolayers of various M(II)-tetraphenylporphyrins (MTTPs, M = Fe, Co, Zn) and their nitrosyl complexes on a Ag(111) surface. X-ray photoelectron spectroscopy (XPS) shows that the oxidation state of the Fe and Co (but not Zn) ions in the MTPP monolayers is reduced because of the interaction with the substrate. This partial reduction is accompanied by the appearance of new valence states in the UV photoelectron and scanning tunneling spectra (UPS and STS), revealing the covalent character of the ion-substrate bond. Subsequent coordination of nitric oxide (NO) to the metal ions (Fe, Co) reverses these surface-induced effects, resulting in an increase of the oxidation states and the disappearance of the new valence states. Removal of the NO ligands by thermal desorption restores the original spectroscopic features, indicating that the described processes are fully reversible. The NO coordination also changes the spin state and thus the magnetic properties of the metal ions. Density-functional theory (DFT) calculations on model systems provide structural and energetic data on the adsorbed molecules and the surface chemical bond. The calculations reveal that competition effects, similar to the trans effect, play a central role and lead to a mutual interference of the two axial ligands, NO and Ag, and their bonds to the metal center. These findings have important implications for sensor technology and catalysis using supported planar metal complexes, in which the activity of the metal center is sensitively influenced by the substrate. © 2011 American Chemical Society.

The Synthesis of Nanostructured Ni5P4 Films and their Use as a Non-Noble Bifunctional Electrocatalyst for Full Water Splitting - Ledendecker, Marc; Calderon, Sandra Krick; Papp, Christian; Steinrück, Hans-Peter; Antonietti, Markus; Shalom, Menny (Angewandte Chemie International Edition, 2015)
The investigation of nickel phosphide (Ni5P4) as a catalyst for the hydrogen (HER) and oxygen evolution reaction (OER) in strong acidic and alkaline environment is described. The catalyst can be grown in a 3D hierarchical structure directly on a nickel substrate, thus making it an ideal candidate for practical water splitting devices. The activity of the catalyst towards the HER, together with its high stability especially in acidic solution, makes it one of the best non-noble materials described to date. Furthermore, Ni5P4 was investigated in the OER and showed activity superior to pristine nickel or platinum. The practical relevance of Ni5P4 as a bifunctional catalyst for the overall water splitting reaction was demonstrated, with 10 mA cm(-2) achieved below 1.7 V.
Keywords: ceramics; hydrogen evolution reaction; nickel phosphides; oxygen evolution reaction; water splitting reaction

The urea method for the direct synthesis of ZnAl layered double hydroxides with nitrate as the interlayer anion - Inayat, Alexandra; Klumpp, Michael; Schwieger, Wilhelm (Applied Clay Science, 2011)
ZnAl layered double hydroxides (LDHs) with nitrate as the charge balancing anion in the interlayer space were synthesized by precipitation from homogeneous solution using urea hydrolysis. The composition of the synthesis mixture and the synthesis time were varied in order to identify the parameters, which control if nitrate or carbonate will be the interlayer anion. Especially, the addition of ammonium nitrate turned out to be an effective tool for the synthesis of nitrate containing ZnAl LDHs independent from the synthesis time. Results are mainly based on powder X-ray diffraction measurements of the obtained samples. (C) 2011 Elsevier B.V. All rights reserved.
Keywords: Layered double hydroxides; Hydrotalcite-like materials; Synthesis of nitrate form; Urea method; Precipitation from homogeneous solution; XRD pattern

Thickness and grain size dependence of the strength of copper thin films as investigated with bulge tests and nanoindentations - Merle, Benoit; Schweitzer, Elmar; Göken, Mathias (Philosophical Magazine, 2012)
Thin films have often been reported to exhibit increased strength compared to their bulk counterparts. In this study, copper films with a thickness ranging from 400 to 2400 nm were investigated via bulge testing and nanoindentation, focusing on the influence of thickness and microstructure on the mechanical properties. Bulge tests on freestanding membranes show that the yield strength follows Hall–Petch behaviour, as bulk materials do. This also holds true for films on a substrate, as long as the microstructure contains several grains in the thickness direction. The determined Hall–Petch coefficient of 0.16 MPa m-1/2 is also similar to bulk materials. Texture was found to have very limited influence on mechanical behaviour. Nanoindentation data, evaluated by the Han–Nix method, showed that the hardness of thin films is higher than that of bulk materials with the same grain size.
WW1::949

Thin membranes versus bulk substrates: Investigation of proximity effects in focused electron beam-induced processing - Walz, Marie-Madeleine; Vollnhals, Florian; Rietzler, Florian; Schirmer, Michael; Kunzmann, Andreas; Steinrück, Hans-Peter; Marbach, Hubertus (Journal of Physics D-Applied Physics, 2012)
The resolution of focused electron beam induced processing techniques is limited by electron scattering processes. General wisdom holds that using a membrane, this can be effectively improved due to a cutoff of the electron interaction volume and thus diminished proximity effects. Recently, we demonstrated that in contrast to the expectation, proximity effects can be indeed larger on a 200nm silicon nitride membrane than on the respective bulk substrate, due to charging-induced surface activation. Herein, we expand these investigations on proximity effects in electron beam-induced surface activation to other substrates and to electron beam-induced deposition followed by autocatalytic growth. © 2012 IOP Publishing Ltd.

Third-order corrections to random-phase approximation correlation energies - Heßelmann, Andreas (Journal of Chemical Physics, 2011)
Several random-phase approximation (RPA) correlation methods were compared in third order of perturbation theory. While all of the considered approaches are exact in second order of perturbation theory, it is found that their corresponding third-order correlation energy contributions strongly differ from the exact third-order correlation energy contribution due to missing interactions of the particle-particle-hole-hole type. Thus a simple correction method is derived which makes the different RPA methods also exact to third-order of perturbation theory. By studying the reaction energies of 16 chemical reactions for 21 small organic molecules and intermolecular interaction energies of 23 intermolecular complexes comprising weakly bound and hydrogen-bridged systems, it is found that the third-order correlation energy correction considerably improves the accuracy of RPA methods if compared to coupled-cluster singles doubles with perturbative triples as a reference.
EAM Import::2019-03-12

Three-dimensional and quantitative reconstruction of non-accessible internal porosity in hematite nanoreactors using 360 degrees electron tomography - Distaso, Monica; Apeleo Zubiri, Benjamin; Mohtasebi, Amirmasoud; Inayat, Alexandra; Dudak, Michal; Koci, Petr; Butz, Benjamin; Klupp Taylor, Robin; Schwieger, Wilhelm; Spiecker, Erdmann; Peukert, Wolfgang (Microporous and Mesoporous Materials, 2017)
In the current paper, mesocrystals are used as effective precursors to design nanoreactors with different kinds of enclosed porosity. The thermal treatment of hematite mesocrystalline nanoparticles is investigated as a post-processing tool for the engineering of internal organization of hierarchical structures. The porosity of starting materials and of particles thermally treated at different temperatures is investigated by transmission electron microscopy, nitrogen sorption and 360 degrees electron tomography. Virtual Capillary Condensation and Maximum Sphere Inscription are used as independent approaches for the quantitative assessment of internal porosity. The combination of experimental evidences and simulations provides a deep understanding of the internal topology of nanoreactors upon thermal treatment of mesocrystalline particles. This new design strategy may pave the way for exploring the use of the post treated mesocrystals as carriers to encapsulate materials for optoelectronic applications. (C) 2017 Elsevier Inc. All rights reserve
Keywords: Mesocrystals; Inorganic hollow nanoparticles; Compartmentalization; Encapsulation

Three-dimensional photonic crystals with an active surface: Gold film terminated opals - Ding, Boyang; Pemble, Martyn E.; Korovin, Alexander V.; Peschel, Ulf; Romanov, Sergey (Physical Review B, 2010)
A hybrid metal-dielectric photonic crystal, a thin opal slab coated by a gold film, has been designed in order to exercise additional control upon the light propagation in a photonic band-gap material using extraordinary optical transmission in the corrugated gold film. The photonic and plasmonic components of the hybrid crystal are closely linked, because the photonic crystal lattice provides a spatial template for the gold film corrugation and modifies the electromagnetic vacuum in the vicinity of the gold film. Due to coupling of light diffracted in the opal lattice to surface plasmon polaritons in the metal film, the spectra and angle diagrams of transmission in hybrid structures deviate from the linear superposition of transmission functions of both hybrid components. In particular, the selective conversion of diffraction minima, and cavity mode and thickness dependence of the surface plasmon polariton-related properties have been observed. The synergy of three resonance mechanisms behind the functionality of hybrid photonic crystals provides a uniquely broad tunability of their optical properties.
EAM Import::2019-03-12

Three-dimensional printing of a bioactive glass - Meszaros, Robert; Zhao, Rong; Travitzky, Nahum; Fey, Tobias; Greil, Peter; Wondraczek, Lothar (Glass Technology-European Journal of Glass Science and Technology Part A, 2011)
We report on three-dimensional printing and subsequent sintering of 13-93 bioactive glass as a powerful method for the fabrication of patient-specific inlays and substitutes for unloaded implants. In a multi-method study, an assessment of thermal sintering, isotropic and anisotropic shrinkage, crystallisation and microstructural evolution was performed as a prerequisite for the development of a suitable 3D-printing and sintering process. Concave and convex model geometries were then produced, and their consolidation behaviour was examined with respect to process parameters such as adequate preparation of precursor glass powders, particle size used, glass viscosity, green body preparation and sintering conditions. Almost complete densification could be achieved for sintering temperatures of 742-795 degrees C. Crystallisation was observed to involve subsequent precipitation of diopside (similar to 750 degrees C), parawollastonite (similar to 850 degrees C) and calcium phosphate (similar to 900 degrees C). A process window of 712-745 degrees C reducing to 712-730 degrees C, if crystallisation must be avoided, is suggested for sintering of 3D printed bioactive glass type 13-93.

Three-dimensional printing of SiSiC lattice truss structures - Fu, Zongwen; Schlier, Lorenz; Travitzky, Nahum; Greil, Peter (Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2013)
Silicon/silicon carbide ceramic composites were fabricated by the three-dimensional printing (3DP™) from Si/SiC/dextrin powder blends. After printing the C/Si/SiC preforms were infiltrated with a liquid silicone resin for transient shape stabilization. The green bodies were pyrolyzed at 1000. °C in nitrogen atmosphere resulting in a residue with a porosity of 41%. The porous preforms exhibit excellent infiltration behavior for liquid Si at 1500. °C in vacuum. Bending strength, fracture toughness and Young's modulus were analyzed with respect to Si volume fraction. © 2012 Elsevier B.V.
Keywords: Macrocellular lattice structure; Mechanical properties; Melt infiltration; Polymer-derived ceramics; SiSiC composites; Three-dimensional printing

Time- and temperature-dependent crosslinking behaviour of a silicone resin - Wolff, Friedrich; Kugler, Christoph; Münstedt, Helmut (Rheologica Acta, 2012)
The crosslinking behaviour of a silicone resin which is interesting from a technical point of view was investigated by means of rheology. In order to accelerate the crosslinking process, zinc acetylacetonate and aluminium acetylacetonate were applied as latent catalysts. The effect of the type of catalyst, its concentration, and the temperature on crosslinking was determined by isothermal dynamic-mechanical measurements. A radial gradient in crosslinking causes the gel point to be reached earlier at the outer edge of the sample in the rheometer. This radial gradient is averaged when measuring G′ and G''. Therefore, since the physically well-defined state of critical gelation (gel point) could not be obtained from the data, the time at which a distinct crosslinking state is reached was determined by the crossover of the moduli G′ and G''. For this distinguished point, the denotation gelation index GI is introduced. The gelation indices measured at different temperatures follow an Arrhenius-type relationship. Activation energies between 89 and 126 kJ/mol were determined. They were found to be dependent on the type of catalyst used but independent of its concentration. The activation energies of the crosslinking processes enable the calculation of the gelation index at temperatures not measured directly.
EAM Import::2019-03-12

Time-dependent deformation behavior of freestanding and SiNx-supported gold thin films investigated by bulge tests - Merle, Benoit; Cassel, Detlev; Göken, Mathias (Journal of Materials Research, 2015)
A novel strain-rate jump method was developed for the plane-strain bulge test and used to investigate the time-dependent deformation behavior of gold thin films in the thickness range 100-400 nm. The experimental method is based on an abrupt variation of the pressurization rate. The evaluated strain-rate sensitivity was found to be five times higher for films in freestanding condition (m = 0.094) than for films tested on a SiNx substrate (m = 0.020). Bulge creep tests confirmed this increased time-dependence. The observation of the surface of the freestanding films after the creep tests provided evidence of apparent grain boundary sliding taking place next to intragranular plastic deformation. The out-of-plane deformation was presumably favored by the columnar microstructure of the samples, with grains extending between both free surfaces. In the case of SiNx-supported films, grain boundary sliding was prevented by the good adhesion of gold to the SiNx substrate.

Time-dependent morphology evolution of solution-processed small molecule solar cells during solvent vapor annealing - Min, Jie; Jiao, Xuechen; Ata, Ibrahim; Osvet, Andres; Ameri, Tayebeh; Baeuerle, Peter; Ade, Harald; Brabec, Christoph (Advanced Energy Materials, 2016)
Morphological modification using solvent vapor annealing (SVA) provides a simple and widely used fabrication option for improving the power conversion efficiencies of solution-processed bulk heterojunction (BHJ) small molecule solar cells. Previous reports on SVA have shown that this strategy influences the degree of donor/acceptor phase separation and also improves molecular donor ordering. A blend composed of a dithienopyrrole containing oligothiophene as donor (named UU07) and [6,6]-phenyl-C61-butyric acid methyl ester as acceptor is investigated with respect to SVA treatment to explore the dynamics of the BHJ evolution as a function of annealing time. A systematic study of the time dependence of morphology evolution clarifies the fundamental mechanisms behind SVA and builds the structure-property relation to the related device performance. The following two-stage mechanism is identified: Initially, as SVA time increases, donor crystallinity is improved, along with enhanced domain purity resulting in improved charge transport properties and reduced recombination losses. However, further extending SVA time results in domains that are too large and a few large donor crystallites, depleting donor component in the mixed domain. Moreover, the larger domain microstructure suffers from enhanced recombination and overall lower bulk mobility. This not only reveals the importance of precisely controlling SVA time on gaining morphological control, but also provides a path toward rational optimization of device performance. Time-dependent morphology evolution of solution-processed small molecule solar cells during solvent vapor annealing is systematically and methodically investigated. This not only reveals the importance of precisely controlling SVA time on gaining morphological control, but also provides a path toward the rational optimization of device performance.
Keywords: bulk mobility; device performance; morphology evolution; solar cells; solvent vapor annealing

TiO2-WO3 Composite Nanotubes by Alloy Anodization: Growth and Enhanced Electrochromic Properties - Nah, Yoon-Chae; Ghicov, Andrei; Kim, Dam-Hee; Berger, Stefan; Schmuki, Patrik (Journal of the American Chemical Society, 2008)
The present work demonstrates that uniform and highly ordered arrays of TiO_2-WO_3 nanotubes can be grown by anodization of Ti alloys in an ethylene glycol/fluoride based electrolyte under selected electrochemical conditions. These aligned mixed oxide nanotube structures are highly suitable for enhanced electrochromic reactions; in particular we show that already small amounts of WO_3 (such as 0.2 at%) present in the tube oxide drastically improve the electrochromic properties (contrast, onset potential, cycling stability) of nanotube layer based devices.
EAM Import::2019-03-13

TiO2 Nano Test Tubes as a Self-Cleaning Platform for High-Sensitivity Immunoassays - Song, Yanyan; Schmidt-Stein, Felix; Berger, Stefan; Schmuki, Patrik (Small, 2010)
High-aspect-ratio TiO2 nanotube (TiNT) layers can be used as low-cost, low-volume arrays for fluorescence immunosensing. High sensitivity for antibodies at a concentration of 0.01 pg mL-1 is provided by the high observation length (L) of the nanotubes. The photocatalytic properties of TiO2 make the TiNT arrays reusable after a short UV treatment.
EAM Import::2019-03-13

TiO2 nanotubes and their application in dye-sensitized solar cells - Roy, Poulomi; Kim, Dam-Hee; Lee, Kiyoung; Spiecker, Erdmann; Schmuki, Patrik (Nanoscale, 2010)
The present article reviews the current status of using TiO2 nanotubes in Gratzel-type, dye-sensitized solar cells and extends the overview with the latest results and findings. Critical factors in tube geometry (length, diameter, top morphology), crystal structure (amorphous, anatase, rutile) as well as factors affecting dye loading or electron mobility are addressed. The highest solar cell efficiencies today for pure nanotube systems reach approximately 4% while for some mixed systems, around 7% has been reported. For both Systems significant room for enhancement is anticipated and some key points and strategies for improvement are outlined.

TiO2 Nanotubes: Nitrogen-Ion Implantation at Low Dose Provides Noble-Metal-Free Photocatalytic H-2-Evolution Activity - Zhou, Xuemei; Häublein, Volker; Liu, Ning; Nguyen, Nhat Truong; Zolnhofer, Eva; Tsuchiya, Hiroaki; Manuela, Killian; Meyer, Karsten; Schmuki, Patrik; Frey, Lothar (Angewandte Chemie International Edition, 2016)
Low-dose nitrogen implantation induces an ion and damage profile in TiO2 nanotubes that leads to co-catalytic activity for photocatalytic H-2-evolution (without the use of any noble metal). Ion implantation with adequate parameters creates this active zone limited to the top part of the tubes. The coupling of this top layer and the underlying non-implanted part of the nanotubes additionally contributes to an efficient carrier separation and thus to a significantly enhanced H-2 generatio
Keywords: H-2 evolution; ion implantation; nitrogen; photocatalysis; TiO2 nanotubes

Titanium carbide-derived carbon as a novel support for platinum catalysts in direct methanol fuel cell application - Schlange, Alicja; Dos Santos, Antonio Rodolfo; Hasse, Benjamin; Etzold, Bastian; Kunz, Ulrich; Turek, Thomas (Journal of Power Sources, 2012)
The improvement of direct methanol fuel cells (DMFCs) requires the development of highly active catalysts. Carbide-derived carbon (CDC) is a new class of carbon materials which are produced via selective extraction of the non-carbon compounds from metal carbides. Nanoporous carbon with a surface area of 906 m2 g-1 and mean pore size of 3.4 nm was produced in consequence of chlorinating pure titanium carbide. This material was oxidatively treated to create the nucleation sites for the metal precursor. An increase of oxygen content in the carbon sample was observed after the functionalization step. The CDC material was subsequently loaded with 18.62 wt.% platinum, with an average particle size of 1.16 nm, by wet impregnation and chemical reduction. As a result, an enhanced electrochemical activity towards oxygen reduction was observed. The maximum power density of 50.16 mW cm-2 was achieved and is subsequently 18% higher than the value measured for commercial platinum catalyst (20 wt.% Pt) on activated carbon. This increase can be attributed to good catalyst dispersion, high surface area and small platinum cluster sizes, thus, confirming the potential of carbide-derived carbon supported catalysts for DMFC applications.
EAM Import::2019-03-13

T-matrix analysis of dipole waves on chains of dielectric particles - Zhuromskyy, Oleksandr; Peschel, Ulf (7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, 2013)
Loss less propagation of longitudinal magnetic-dipole waves is predicted for regular chains of rutile particles. Rigorous T-matrix simulation techniques are applied to deduce the dispersion characteristics of the dipole waves and to optimize the properties of the closing elements in the waveguide for maximum power transmission. The proposed technique can be used to optimize the interaction between light and particle ensembles.
EAM Import::2019-03-13

ToF-SIMS and XPS studies of the adsorption characteristics of a Zn-porphyrin on TiO2 - Killian, Manuela; Gnichwitz, Jan-Frederik; Hirsch, Andreas; Schmuki, Patrik; Kunze, Julia (Langmuir, 2010)
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) were used to study monolayers (ML) and thick films of porphyrin Zn-TESP (CHNO SiZn) attached to titanium dioxide (TiO) substrates via silanization. Films on ideal hydroxyl-terminated silicon (SiO) surfaces were used for comparison. ToF-SIMS and XPS spectra show that the type of adsorption varies depending on the thickness of the organic film, the preparation temperature, and the adsorption time. We show that the intensity of a molecular peak at mass 1121.5 u in ToF-SIMS can be used as a direct measure of the ratio of chemisorption/physisorption of Zn-TESP. On TiO, the amount of chemisorbed porphyrin can be increased by increasing the reaction temperature and time during the silanization process. On the SiO reference, only chemisorbed species were detected under all investigated preparation conditions. The present work thus not only gives information on the Zn-TESP linkage to TiO but provides a direct tool for generally determining the type of adsorption of monolayers. © 2009 American Chemical Society.

Topographical study of TiO2 nanostructure surface for photocatalytic hydrogen production - Cha, Gi; Lee, Kiyoung; Yoo, Jeong Eun; Killian, Manuela; Schmuki, Patrik (Electrochimica Acta, 2015)
In the present work we investigate the photocatalytic hydrogen production (water splitting) activity of different Pt loaded TiO2 nanotube layers. Therefore, we fabricate free standing membranes and fix them in four different configurations: top up (with initiation layer ``grass'' or without) and bottom up (bottom closed or open), then decorate the tubes with various amounts of Pt and measure the open-circuit photocatalytic H2 production rate. We find a strong influence of the configuration with the open top morphology showing the highest photocatalytic hydrogen production efficiency, these nanotubes yield 3.5 times more H2 than the least efficient structure (bottom closed). The work therefore provides valuable guidelines for optimizing TiO2 nanotube layers for photocatalytic applications.
EAM Import::2019-03-13

Topological derivatives for networks of elastic strings - Leugering, Günter; Sokolowski, J. (ZAMM - Zeitschrift für angewandte Mathematik und Mechanik, 2011)
We consider linear second order differential equations on metric graphs under given boundary and nodal conditions. We are interested in the problem of changing the topology of the underlying graph in that we replace a multiple node by a subgraph or concentrate a subgraph to a single node. We wish to do so in an optimal fashion. More precisely, given a cost function we may look for its sensitivity with respect to these operations in order to find an optimal topology of the graph. Thus, in essence, we are looking for the topological gradient for linear second order problems on metric graphs.

Topology optimization of a cantilevered piezoelectric energy harvester using stress norm constraints - Wein, Fabian; Kaltenbacher, Manfred; Stingl, Michael (Structural and Multidisciplinary Optimization, 2013)
Vibrational piezoelectric energy harvesters are devices which convert ambient vibrational energy into electric energy. Here we focus on the common cantilever type in which an elastic beam is sandwiched between two piezoelectric plates. In order to maximize the electric power for a given sinusoidal vibrational excitation, we perform topology optimization of the elastic beam and tip mass by means of the SIMP approach, leaving the piezoelectric plates solid. We are interested in the first and especially second resonance mode. Homogenizing the piezoelectric strain distribution is a common indirect approach increasing the electric performance. The large design space of the topology optimization approach and the linear physical model also allows the maximization of electric performance by maximizing peak bending, resulting in practically infeasible designs. To avoid such problems, we formulate dynamic piezoelectric stress constraints. The obtained result is based on a mechanism which differs significantly from the common designs reported in literature.
Keywords: Topology optimization; Energy harvester; Stress constraints

Toward combining graphene and QDs: Assembling CdTe QDs to exfoliated graphite and nanographene in water - Katsukis, Georgios; Malig, Jenny; Schulz-Drost, Christian; Leubner, Susanne; Jux, Norbert; Guldi, Dirk Michael (Acs Nano, 2012)
Herein, we report for the first time on a full-fledged investigation of water-soluble CdTe quantum dots (QD) that are immobilized onto exfoliated graphite (EG) and/or nanographene (NG). Particular emphasis was placed on a top-down preparation of stable aqueous dispersions-starting from natural graphite rather than graphene oxide-while preserving the intrinsic properties of graphene. To this end, we circumvented the harsh conditions commonly employed for the pre-exfoliation (i.e., Hummers method). First, a hydrophobic- hydrophobic/π-π stacking motif was tested between EG and pyrene, to which QDs are covalently attached (QD-pyrene). Second, we employed the combination of hydrophobic-hydrophobic/π-π stacking and electrostatic interactions to build up hierarchical structures composed of NG, positively charged pyrene (pyrene ), and negatively charged QDs. The novel nanohybrids-QD- pyrene/EG and QD/pyrene /NG-were characterized with specific emphasis on electron-transfer chemistry. In fact, both assays provide kinetic and spectroscopic evidence that support electron transfer dynamics that vary, however, between EG and NG as a reflection of the different degree of graphite exfoliation. © 2012 American Chemical Society.

Toward ionic-liquid-based model catalysis: Growth, orientation, conformation, and interaction mechanism of the [Tf2N]- anion in [BMIM][Tf2N] thin films on a well-ordered alumina surface - Sobota, Marek; Nikiforidis, Ioannis; Hieringer, Wolfgang; Paape, Natalia; Happel, Markus; Steinrück, Hans-Peter; Görling, Andreas; Wasserscheid, Peter; Laurin, Mathias; Libuda, Jörg (Langmuir, 2010)
Aiming at a better understanding of the interaction of ionic liquid (IL) thin films with oxide supports, we have performed a model study under ultrahigh vacuum (UHV) conditions. We apply infrared reflection absorption spectroscopy (IRAS) in combination with density functional theory (DFT). Thin films of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][Tf N] are grown on an atomically flat, well-ordered alumina film on NiAl(110) using a novel UHV-compatible evaporator. Time-resolved IRAS measured during the growth and subsequent thermal desorption points toward reversible molecular adsorption and desorption. There was no indication of decomposition. The vibrational bands are assigned with the help of DFT calculations. Strong relative intensity changes in individual [TfN] bands are observed in the monolayer region. This indicates pronounced orientation effects for the anion. The adsorption geometry of [TfN] is determined on the basis of a detailed comparison with DFT. The results suggest that [TfN] anions adopt a cis conformation in the submonolayer region. They adsorb in a slightly tilted orientation with respect to the surface, mainly interacting with the support via the sulfonyl groups. © 2010 American Chemical Society.

Towards a full understanding of regioisomer effects of indene-C60 bisadduct acceptors in bulk heterojunction polymer solar cells - Cao, Tiantian; Chen, Ning; Liu, Guangxin; Wan, Yingbo; Perea, Jose Dario; Xia, Yijun; Wang, Zhaowei; Song, Bo; Li, Ning; Li, Xiaohong; Zhou, Yi; Brabec, Christoph; et al. (Journal of Materials Chemistry A, 2017)
Indene-C60 bisadduct (IC60BA), which can offer a significantly higher open-circuit voltage (Voc) than monoadducts, has become the research focus as electron acceptor materials in polymer solar cells (PSCs) in recent years. However, despite its popularity, IC60BA have always been applied in PSCs as mixture of several regioisomers and the nature of this mixture has never been fully investigated and understood. Herein, for the first time, 12 major regioisomers of IC60BA were isolated and a full investigation was carried out with respect to their structure, abundance, solubility and their corresponding photovoltaic performance. The results show that the PSCs based on these regioisomeric structures present very diverse PCE and their photovoltaic performance was dramatically affected not only by the relative indene positions but also by the steric orientation of the two indene groups. Electrochemical studies further revealed that the effect of energetic disorder inside the IC60BA regioisomers on their photovoltaic performance is insignificant when applied in PSCs. However, the steric structures and solubility of the regioisomers were found to have significant impact on the morphology and bulk properties of the active layer of PSCs, which give rise to very different PCE of devices based on IC60BA regioisomers with different structures. © 2017 The Royal Society of Chemistry.
Keywords: Heterojunctions; Mixtures; Open circuit voltage; Photovoltaic effects; Polycyclic aromatic hydrocarbons; Polymer solar cells; Solubility; Bulk heterojunction; Bulk properties; Different structure; Electrochemical studies; Electron acceptor materials; Photovoltaic performance; Polymer solar cell (PSCs); Steric structure; Solar cells

Towards a molecular understanding of cation-anion interactions-Probing the electronic structure of imidazolium ionic liquids by NMR spectroscopy, X-ray photoelectron spectroscopy and theoretical calculations - Cremer, Till; Kolbeck, Claudia; Lovelock, Kevin; Paape, Natalia; Woelfel, Rene; Schulz, Peter; Wasserscheid, Peter; Weber, Henry; Thar, Jens; Kirchner, Barbara; Maier, Florian; Steinrück, Hans-Peter (Chemistry - A European Journal, 2010)
Ten [CCIm] (1-methyl-3- octylimidazolium)-based ionic liquids with anions Cl, Br , I, [NO], [BF] , [TfO], [PF], [Tf N], [PfN], and [FAP] (TfO = trifluoromethylsulfonate, TfN = bis(trifluoromethylsulfonyl) imide, PfN = bis(pentafluoroethylsulfonyl)imide, FAP = tris-(pentafluoroethyl)trifluorophosphate) and two [CC CIm] (1,2-dimethyl-3-octylimidazolium)-based ionic liquids with anions Br and [TfN] were investigated by using X-ray photoelectron spectroscopy (XPS), NMR spectroscopy and theoretical calculations. WhileH NMR spectroscopy is found to probe very specifically the strongest hydrogen-bond interaction between the hydrogen attached to the C position and the anion, a comparative XPS study provides first direct experimental evidence for cation-anion charge-transfer phenomena in ionic liquids as a function of the ionic liquid's anion. These charge-transfer effects are found to be surprisingly similar for [CCIm] and [CCC Im] salts of the same anion, which in combination with theoretical calculations leads to the conclusion that hydrogen bonding and charge transfer occur independently from each other, but are both more pronounced for small and more strongly coordinating anions, and are greatly reduced in the case of large and weakly coordinating anions. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Towards large-scale production of solution-processed organic tandem modules based on ternary composites: Design of the intermediate layer, device optimization and laser based module processing - Li, Ning; Kubis, Peter; Forberich, Karen; Ameri, Tayebeh; Krebs, Frederik C.; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2014)
We report on a novel approach including: 1. the design of an efficient intermediate layer, which facilitates the use of most high performance active materials in tandem structure and the compatibility of the tandem concept with large-scale production; 2. the concept of ternary composites based on commercially available materials, which enhances the absorption of poly(3-hexylthiophene) (P3HT) and as a result increase the PCE of the P3HT-based large-scale OPV devices; 3. laser-based module processing, which provides an excellent processing resolution and as a result can bring the power conversion efficiency (PCE) of mass-produced organic photovoltaic (OPV) devices close to the highest PCE values achieved for lab-scale solar cells through a significant increase in the geometrical fill factor. We believe that the combination of the above mentioned concepts provides a clear roadmap to push OPV towards large-scale production and commercial applications. © 2013 Elsevier B.V.
Keywords: Intermediate layer; Laser-based module processing; Optical-simulation; Organic tandem solar cells; Solution processing; Ternary composites

Towards low-cost, environmentally friendly printed chalcopyrite and kesterite solar cells - Azimi, Seyed Hamed; Hou, Yi; Brabec, Christoph (Energy and Environmental Science, 2014)
Solution-processed organic and inorganic semiconductors offer a promising path towards low-cost mass production of solar cells. Among the various material systems, solution processing of multicomponent inorganic semiconductors offers considerable promise due to their excellent electronic properties and superior photo- and thermal stability. This review surveys the recent developments of "all solution-processed" copper-indium (-gallium)-chalcogenide (CuInS, CuInSe and Cu(In, Ga)(Se, S)) chalcopyrites and copper-zinc-tin-chalcogenide (CuZnSnS and CuZnSnSe (CZTS(e))) kesterite solar cells. A brief overview further addresses some of the most critical material aspects and associated loss mechanisms in chalcopyrite and kesterite devices. Today's state-of-the-art performance as well as future challenges to achieve low-cost and environmentally friendly production is discussed. This journal is © the Partner Organisations 2014.
Keywords: Engineering controlled terms: Chalcogenides; Copper compounds; Costs; Electronic properties; Gallium Cu(In; Ga)(Se; S)2; Future challenges; Inorganic semiconductors; Mass production; Material systems; Solution-processed; Solution-processing; State-of-the-art performance Engineering main heading: Solar cells GEOBASE Subject Index: alternative energy; cost analysis; fuel cell; renewable resource; solar power

Towards optimization of crack resistance of composite materials by adjustment of fiber shapes - Prechtel, Marina; Leugering, Günter; Stingl, Michael; Steinmann, Paul (Engineering Fracture Mechanics, 2011)
We investigate the evolution and propagation of cracks in 2-d elastic domains, which are subjected to quasi-static loading scenarios. In addition to the classical variational formulation, where the standard potential energy is minimized over the cracked domain under physical conditions characterizing the behavior of the material close to the crack (e.g. non-penetration conditions), we include a 'cohesive traction term' in the energy expression. In this way we obtain a mathematically concise set of partial differential equations with non-linear boundary conditions at the crack interfaces. We perform a finite element discretization using a combination of standard continuous finite elements and so-called cohesive elements. During the simulation process cohesive elements are adaptively inserted at positions where a certain stress bound is exceeded. In our numerical studies we consider domains consisting of a matrix material with fiber inclusions. Beyond pure crack path simulation, our ultimate goal is to determine an optimal shape of the fibers resulting in a crack path that releases for a given load scenario as much energy as possible without destroying the specimen completely. We develop a corresponding optimization model and propose a solution algorithm for the same. The article is concluded by numerical results. © 2011 Elsevier Ltd.
UnivIS-Import:2015-03-09:Pub.2011.tech.FT.FT-TM.toward
Keywords: Cohesive zone modeling; Crack growth; Fiber reinforced material; Shape optimization

Towards the engineering of molecular nanostructures: Local anchoring and functionalization of porphyrins on model-templates - Ditze, Stefanie; Röckert, Michael; Buchner, Florian; Zillner, Elisabeth; Stark, Michael Werner; Steinrück, Hans-Peter; Marbach, Hubertus (Nanotechnology, 2013)
We demonstrate that Cu(111) surfaces pre-covered with a submonolayer of copper oxide or metallic nickel are suitable model-templates for the selective adsorption and/or localized functionalization of functional molecules such as different free base porphyrins and metalloporphyrins. The oxide/Cu(111) model-template is able to steer the adsorption of tetraphenylporphyrins (TPP): 2HTPP selectively adsorbs on the bare Cu areas, and for CoTPP anchoring at the rim of the copper oxide islands is found. On the Ni/Cu(111) model-template TPP molecules are pinned on the Ni areas while they are mobile on the bare Cu surface. Interestingly, adsorption of free base octaethylporphyrin on Ni/Cu(111) leads to a local functionalization, namely the metalation to NiOEP on the Ni areas. Model-template preparation and characterization by scanning tunneling microscopy is performed at room temperature. © 2013 IOP Publishing Ltd.

Towards the treatment of boundary conditions for global crack path tracking in three-dimensional brittle fracture - Jäger, Paul; Steinmann, Paul; Kuhl, Ellen (Computational Mechanics, 2009)
The aim of the present paper is a systematic elaboration of a three dimensional finite element analysis tool for discontinuous fracture in brittle solids. Brittle or quasi-brittle fracture usually occurs when a material reaches the limit of its strength and no plastic deformation has been observed prior to failure. In the present approach, this kind of failure is characterized by three sets of governing equations: (i) the elastic bulk problem and (ii) the cohesive interface problem regarding the solid deformation field and (iii) the crack tracking problem concerning the crack kinematics. This manuscript describes a unique modular tool set for the coupled set of nonlinear equations. We focus in particular on the boundary conditions for the crack tracking problem of this analysis tool. We critically discuss important implementation details: (i) the choice of crack onset boundary conditions for the additional global field, (ii) the numerical integration, (iii) the modeling of geometrically exact crack tips for cohesive fracture, and (iv) the post-processing procedure for the discontinuity visualization. The potential of the method to simulate brittle fracture is demonstrated by qualitative and quantitative comparisons with experiments from the literature as well as by common benchmark problems. © 2009 Springer-Verlag.
UnivIS-Import:2015-03-09:Pub.2009.tech.FT.FT-TM.toward_2
Keywords: Brittle fracture; Cohesive crack concept; Concrete modeling; Discontinuous failure; Interface; Visualization

Toward strain resistant flexible organic thin film transistors - Jedaa, Abdesselam; Halik, Marcus (Applied Physics Letters, 2009)
We suggest a molecular design for small molecules as polycrystalline organic semiconductors in flexible organic thin film transistor applications, providing an improved stability during substrate bending. A stable operation of alkyl-substituted sexithiophens was obtained under strain up to ±2.5%. The stability relates to the flexibility of the alkyl chain substitution, scales with their chain length, and outperforms those of pentacene devices. These findings were independent from the underlying dielectric layer.

Towards tunable graphene/phthalocyanine-PPV hybrid systems - Malig, Jenny; Jux, Norbert; Kießling, Daniel; Cid, Juan-Jose; Vazquez, Purificacion; Torres, Tomas; Guldi, Dirk Michael (Angewandte Chemie International Edition, 2011)
Exfoliation of graphite was achieved using a zinc phthalocyanine oligomer that is also an electron donor. The resulting functionalized graphene material was investigated by Raman and electron spectroscopy and was trialed in a photoelectrochemical cell. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Towards wafer-size graphene layers by atmospheric pressure graphitization of silicon carbide - Emtsev, Konstantin; Bostwick, A.; Horn, Karsten; Jobst, Johannes; Kellogg, Gary L.; Ley, Lothar; McChesney, J.; Ohta, T.; Reshanov, Sergey; Röhrl, Jonas; Rotenberg, E.; Schmid, A.; et al. (Nature Materials, 2009)
Graphene, a single monolayer of graphite, has recently attracted considerable interest owing to its novel magneto-transport properties, high carrier mobility and ballistic transport up to room temperature. It has the potential for technological applications as a successor of silicon in the post Moore's law era, as a single-molecule gas sensor, in spintronics, in quantum computing or as a terahertz oscillator. For such applications, uniform ordered growth of graphene on an insulating substrate is necessary. The growth of graphene on insulating silicon carbide (SiC) surfaces by high-temperature annealing in vacuum was previously proposed to open a route for large-scale production of graphene-based devices. However, vacuum decomposition of SiC yields graphene layers with small grains (30-200 nm; refs 14-16). Here, we show that the ex situ graphitization of Si-terminated SiC(0001) in an argon atmosphere of about 1 bar produces monolayer graphene films with much larger domain sizes than previously attainable. Raman spectroscopy and Hall measurements confirm the improved quality of the films thus obtained. High electronic mobilities were found, which reach =2,000 cm 2 V 1 s 1 at T=27 K. The new growth process introduced here establishes a method for the synthesis of graphene films on a technologically viable basis.
UnivIS-Import:2015-04-14:Pub.2009.nat.dphy.IAP.LAP.towwar

Toward well-defined metal-polymer interfaces: Temperature-controlled suppression of subsurface diffusion and reaction at the calcium/poly(3- Hexylthiophene) interface - Bebensee, Fabian; Schmid, Martin; Steinrück, Hans-Peter; Campbell, C. T.; Gottfried, Michael (Journal of the American Chemical Society, 2010)
The thickness of the reaction zone at the interface between calcium and regioregular poly(3-hexylthiophene), which is one of the best performing metal/polymer combinations in photovoltaic devices, depends critically on the temperature of the polymer during the initial phase of metal deposition. It is shown that deposition at 130 K reduces the thickness of the reaction zone, an effect that also persists after warming to room temperature. © 2010 American Chemical Society.

Toxicity of Mitoxantrone-loaded Superparamagnetic Iron Oxide Nanoparticles in a HT-29 Tumour Spheroid Model - Hornung, Annkathrin; Poettler, Marina; Friedrich, Ralf P.; Weigel, Bianca; Dürr, Stephan; Zaloga, Jan; Cicha, Iwona; Alexiou, Christoph; Janko, Christina (Anticancer Research, 2016)
Cancer research is commonly carried out in two-dimensional (2D) cell cultures, which poorly reflect in vivo settings where the growing tumours are exposed to mechanical forces and biochemical gradients. In this study we established a HF-29 colon carcinoma tumor spheroid model to investigate the effect of free mitoxantrone (MTO) and its nanoparticle-bound form (SPION(MTO)) under 3D cell culture conditions.Tumour spheroids were generated by seeding HT-29 colon carcinoma cells on agarose-coated cell culture wells. Growth of the spheroids was monitored daily by transmission microscopy upon treatment with free MTO, SPION(MTO) or unloaded SPION.Unloaded SPION did not affect the spheroid size compared to untreated controls, while both free MTO and SPION(MTO) inhibited growth of the spheroids in a dose- and time-dependent manner. In comparison to free MTO, the effect of SPION(MTO) on spheroid growth was slightly delayed. Further analyses are necessary to investigate if MTO infiltrates spheroids in its nanoparticle-bound form or whether it is released from SPION before infiltration.
EVALuna2:20010

Transfer of Individual Micro- and Nanoparticles for High-Precision 3D Analysis Using 360° Electron Tomography - Przybilla, Thomas; Apeleo Zubiri, Benjamin; Maria Beltran, Ana; Butz, Benjamin; Machoke, Albert; Inayat, Alexandra; Distaso, Monica; Peukert, Wolfgang; Schwieger, Wilhelm; Spiecker, Erdmann (Small Methods, 2017)
A versatile approach is demonstrated, providing a general routine for an extensive and advanced 3D characterization of individually selected micro- and nanoparticles, enabling the combination of complementary and scale-bridging techniques. Quintessential to the method is the transfer of individual particles onto tailored tips using a conventional scanning electron microscope equipped with a suitable micromanipulator. The method enables a damage- and contamination-free preparation of freestanding particles. This is of significant importance for applications addressing the measurement of structural, physical, and chemical properties of specifically selected particles, such as 360° electron tomography, atom probe tomography, nano X-ray tomography, or optical near-field measurements. In this context, the method is demonstrated for 360° electron tomography of micro-/macroporous zeolite particles with sizes in the micrometer range and mesoporous alpha-hematite nanoparticles exhibiting sizes of 50–100 nm, including detailed pre- and post-characterization on the nanoscal
Keywords: 360 degrees electron tomography; dual-beam SEM/FIB; micromanipulation; pick and place; sample preparation

Transformation of porous glasses into MCM-41 containing geometric bodies - Uhlig, Hans; Gimpel, Marie-Luise; Inayat, Alexandra; Glaeser, Roger; Schwieger, Wilhelm; Einicke, Wolf-Dietrich; Enke, Dirk (Microporous and Mesoporous Materials, 2013)
During the transformation the primary pore walls were found to swell into the initial pore space, which is caused by bulk density differences between the non-porous glass walls and the template containing MCM-41 material. A pore volume above 1.0 cm(3)/g and pore diameters above 60 nm were found to be prerequirements for a pseudomorphic transformation of the porous glasses into MCM-41. Furthermore, a complete transformation was only possible for glasses exhibiting sufficiently high surface area, which was not the case for very large pore diameters of around 390 nm. (C) 2013 Elsevier Inc. All rights reserved.
Keywords: Pseudomorphic transformation; Controlled pore glass; Porous glass; Hierarchy; MCM-41

Transmission electron microscopy and time resolved optical spectroscopy study of the electronic and structural interactions of ZnO nanorods with bovine serum albumin - Klaumünzer, Martin; Weichsel, Ulrike; Mackovic, Mirza; Spiecker, Erdmann; Peukert, Wolfgang; Kryschi, Carola; Spiecker, Erdmann; Mackovic, Mirza (Journal of Physical Chemistry B, 2013)
The adsorption behavior and electronic interactions of bovine serum albumin (BSA) with ZnO nanorod surfaces were investigated using high-resolution transmission electron microscopy as well as stationary and time-resolved optical spectroscopy techniques. Transmission electron microscopy shows that ZnO nanorod surfaces are surrounded by a homogeneous amorphous BSA film with thicknesses between ∼2.5 and 5.0 nm. The electronic structure and adsorption geometry of BSA were examined using high-angle annular dark field scanning transmission electron microscopy combined with electron energy loss spectroscopy. The adsorption process was observed to result into an unfolded conformation of BSA becoming predominantly bound in the side-on orientation at the ZnO surface. This adsorption mode of the BSA molecules allows for a strong interaction with surface states of the ZnO nanorods. This is obvious from its efficient quenching of the defect-center photoluminescence of ZnO. Complementary information of electronic interactions across the ZnO nanorod interface was obtained from femtosecond transient absorption spectroscopy experiments. The rise dynamics of the measured transients revealed altered hole trapping dynamics and, thus, indicated to heterogeneous charge transfer as emerging from adsorbed BSA molecules to defect centers of the ZnO interface. © 2013 American Chemical Society.

Transparent antifouling material for improved operative field visibility in endoscopy - Sunny, Steffi; Cheng, George; Daniel, Daniel; Lo, Peter; Ochoa, Sebastian; Howell, Caitlin; Vogel, Nicolas; Majid, Adnan; Aizenberg, Joanna (Proceedings of the National Academy of Sciences of the United States of America, 2016)
Camera-guided instruments, such as endoscopes, have become an essential component of contemporary medicine. The 15-20 million endoscopies performed every year in the United States alone demonstrate the tremendous impact of this technology. However, doctors heavily rely on the visual feedback provided by the endoscope camera, which is routinely compromised when body fluids and fogging occlude the lens, requiring lengthy cleaning procedures that include irrigation, tissue rubbing, suction, and even temporary removal of the endoscope for external cleaning. Bronchoscopies are especially affected because they are performed on delicate tissue, in high-humidity environments with exposure to extremely adhesive biological fluids such as mucus and blood. Here, we present a repellent, liquid-infused coating on an endoscope lens capable of preventing vision loss after repeated submersions in blood and mucus. The material properties of the coating, including conformability, mechanical adhesion, transparency, oil type, and biocompatibility, were optimized in comprehensive in vitro and ex vivo studies. Extensive bronchoscopy procedures performed in vivo on porcine lungs showed significantly reduced fouling, resulting in either unnecessary or 10-15 times shorter and less intensive lens clearing procedures compared with an untreated endoscope. We believe that the material developed in this study opens up opportunities in the design of next-generation endoscopes that will improve visual field, display unprecedented antibacterial and antifouling properties, reduce the duration of the procedure, and enable visualization of currently unreachable parts of the body, thus offering enormous potential for disease diagnosis and treatment.
Keywords: Antifouling materials; Biopsy; Endoscopy; Surface wetting

Transparent Self-Ordered Niobium-Oxide Nanochannel Layers Formed on Conducting Glass by Total Anodization of Thin Metal Films in Glycerol/Phosphate Electrolyte - Barredo-Damas, Sergio; Lee, Kiyoung; Kirchgeorg, Robin; Sanchez-Tovar, Rita; Schmuki, Patrik (ECS Electrochemistry Letters, 2013)
In the present work, we show the feasibility to grow highly ordered anodic Nb2O5 nanochannel structures from a thin Nb-layer on conducting glass (fluorine doped tin oxide, FTO). This is achieved using a glycerol-phosphate electrolyte at 180◦C and a suitable anodization voltage that allows a rapid and complete conversion of the entire metallic layer into a transparent oxide layer of an extremely well defined directional nature with 20–30 nm wide open vertical channels. These layers can be used, either in the amorphous state or after thermal crystallization, for efficient reversible electrochromic switching devices.
EAM Import::2019-03-13

Transport properties of high-quality epitaxial graphene on 6H-SiC(0001) - Jobst, Johannes; Waldmann, Daniel; Speck, Florian; Hirner, R.; Maude, Duncan; Seyller, Thomas; Weber, Heiko B. (Solid State Communications, 2011)
We have extensively studied the electronic properties of epitaxial graphene grown on the Si face of a 6H silicon carbide substrate by thermal decomposition in an argon atmosphere. Using e-beam lithography, large van der Pauw structures as well as Hall bars were patterned. Their size ranged from millimeters down to submicrometer-sized Hall bars, the latter entirely placed on atomically flat substrate terraces. We found reproducible electronic properties, independent of the sample size and orientation, over a broad temperature range. A comparison of the mobility values indicated no enhanced scattering at the macroscopic step edges of the SiC substrate and due to adsorbed molecules. However, the strong coupling to the substrate results in an elevated charge carrier density n and a reduced mobility mu compared to exfoliated graphene. If n is decreased the mobility rises substantially (up to 29 000 cm(2)/V s at 25 K), and Shubnikov-de Haas oscillations and the graphene-like quantum Hall effect become visible. This leads to the conclusion that the electrons in epitaxial graphene have the same quasi-relativistic properties previously shown in exfoliated graphene and expected from theory. (C) 2011 Elsevier Ltd. All rights reserved.

Transport properties of single TiO2 nanotubes - Stiller, Markus; Barzola-Quiquia, Jose; Lorite, Israel; Esquinazi, Pablo; Kirchgeorg, Robin; Albu, Sergiu; Schmuki, Patrik (Applied Physics Letters, 2013)
We investigated the electric transport properties of single TiO2 nanotubes separated from an anodic titania nanotube array. The temperature dependence of the resistance measured with the conventional four point method of all investigated samples show a Mott variable range hopping behavior. The results obtained with two contacts indicate the existence of a potential barrier between the Cr/Au contacts and samples surfaces, which influence is clearly observable at temperatures <150 K. Impedance spectroscopy in the frequency range of 40 Hz to 1 MHz carried out at room temperature indicates that the electronic transport of these polycrystalline tubes is dominated by the grain cores.
EAM Import::2019-03-13

Treatment Efficiency of Free and Nanoparticle-Loaded Mitoxantrone for Magnetic Drug Targeting in Multicellular Tumor Spheroids - Hornung, Annkathrin; Poettler, Marina; Friedrich, Ralf P.; Zaloga, Jan; Unterweger, Harald; Lyer, Stefan; Nowak, Johannes; Odenbach, Stefan; Alexiou, Christoph; Janko, Christina (Molecules, 2015)
Major problems of cancer treatment using systemic chemotherapy are severe side effects. Magnetic drug targeting (MDT) employing superparamagnetic iron oxide nanoparticles (SPION) loaded with chemotherapeutic agents may overcome this dilemma by increasing drug accumulation in the tumor and reducing toxic side effects in the healthy tissue. For translation of nanomedicine from bench to bedside, nanoparticle-mediated effects have to be studied carefully. In this study, we compare the effect of SPION, unloaded or loaded with the cytotoxic drug mitoxantrone (MTO) with the effect of free MTO, on the viability and proliferation of HT-29 cells within three-dimensional multicellular tumor spheroids. Fluorescence microscopy and flow cytometry showed that both free MTO, as well as SPION-loaded MTO (SPION(MTO)) are able to penetrate into tumor spheroids and thereby kill tumor cells, whereas unloaded SPION did not affect cellular viability. Since SPION(MTO) has herewith proven its effectivity also in complex multicellular tumor structures with its surrounding microenvironment, we conclude that it is a promising candidate for further use in magnetic drug targeting in vivo.
EVALuna2:19979

Triazole bridges as versatile linkers in electron donor-acceptor conjugates - De Miguel Rojas, Gustavo; Wielopolski, Mateusz; Schuster, David I.; Fazio, Michael A.; Lee, Olivia P.; Haley, Christopher K.; Ortiz, Angy L.; Echegoyen, Luis; Clark, Timothy; Guldi, Dirk Michael (Journal of the American Chemical Society, 2011)
Aromatic triazoles have been frequently used as π-conjugated linkers in intramolecular electron transfer processes. To gain a deeper understanding of the electron-mediating function of triazoles, we have synthesized a family of new triazole-based electron donor-acceptor conjugates. We have connected zinc(II)porphyrins and fullerenes through a central triazole moiety-(ZnP-Tri-C )-each with a single change in their connection through the linker. An extensive photophysical and computational investigation reveals that the electron transfer dynamics-charge separation and charge recombination-in the different ZnP-Tri-C conjugates reflect a significant influence of the connectivity at the triazole linker. Except for the m4m-ZnP-Tri-C 17, the conjugates exhibit through-bond photoinduced electron transfer with varying rate constants. Since the through-bond distance is nearly the same for all the synthesized ZnP-Tri-C conjugates, the variation in charge separation and charge recombination dynamics is mainly associated with the electronic properties of the conjugates, including orbital energies, electron affinity, and the energies of the excited states. The changes of the electronic couplings are, in turn, a consequence of the different connectivity patterns at the triazole moieties. © 2011 American Chemical Society.

Triethynylmethanol Derivatives: Stable Acetylenic Building Blocks for Surface Chemistry - Prenzel, Dominik; Sander, Tim; Gebhardt, Julian; Soni, Himadriben; Hampel, Frank; Görling, Andreas; Maier, Sabine; Tykwinski, Rik (Chemistry - A European Journal, 2017)
The synthesis of non-conjugated, carbon-rich building blocks is described, based on a basic scaffold of triethynylmethanol (TEtM). The substitution of the ethynyl groups can be easily varied (including R3Si, H, Br), and this allows structural tuning for stabilization, synthetic derivatization, and adsorption on Ag(111) or Au(111). X-ray crystallography helps to explain the surprising stability of the selected derivatives in the solid state, and an unusual form of hydrogen bonding is identified from these analyses. Preliminary efforts to achieve surface-based reactions on Ag(111) and Au(111) are outlined experimentally and computationally.
Keywords: alkynes; carbon allotropes; graphdiyne; graphyne; surface chemistry

Trion Electroluminescence from Semiconducting Carbon Nanotubes - Jakubka, Florian; Grimm, Stefan; Zakharko, Yuriy; Gannott, Florentina; Zaumseil, Jana (ACS nano, 2014)
Near-infrared emission from semiconducting single-walled carbon nanotubes (SWNTs) usually results from radiative relaxation of excitons. By binding an additional electron or hole through chemical or electrochemical doping, charged three-body excitons, so-called trions, are created that emit light at lower energies. The energy difference is large enough to observe weak trion photoluminescence from doped SWNTs even at room temperature. Here, we demonstrate strong trion electroluminescence from electrolyte-gated, light-emitting SWNT transistors with three different polymer-sorted carbon nanotube species, namely, (6,5), (7,5) and (10,5). The red-shifted trion emission is equal to or even stronger than the exciton emission, which is attributed to the high charge carrier density in the transistor channel. The possibility of trions as a radiative relaxation pathway for triplets and dark excitons that are formed in large numbers by electron-hole recombination is discussed. The ratio of trion to exciton emission can be tuned by the applied voltages, enabling voltage-controlled near-infrared light sources with narrow line widths that are solution-processable and operate at low voltages (<3 V).
EAM Import::2019-03-13

Triphenylamine-Based Push-Pull Molecule for Photovoltaic Applications: From Synthesis to Ultrafast Device Photophysics - Kozlov, Oleg V.; Liu, Xiaomeng; Luponosov, Yuriy N.; Solodukhin, Alexander N.; Toropynina, Victoria Y.; Min, Jie; Buzin, Mikhail I.; Peregudova, Svetlana M.; Brabec, Christoph; Ponomarenko, Sergei A.; Pshenichnikov, Maxim S. (Journal of Physical Chemistry C, 2017)
Small push-pull molecules attract much attention as prospective donor materials for organic solar cells (OSCs). By chemical engineering, it is possible to combine a number of attractive properties such as broad absorption, efficient charge separation, and vacuum and solution processabilities in a single molecule. Here we report the synthesis and early time photophysics of such a molecule, TPA-2T-DCV-Me, based on the triphenylamine (TPA) donor core and dicyanovinyl (DCV) acceptor end group connected by a thiophene bridge. Using time-resolved photoinduced absorption and photoluminescence, we demonstrate that in blends with [70]PCBM the molecule works both as an electron donor and hole acceptor, thereby allowing for two independent channels of charge generation. The charge-generation process is followed by the recombination of interfacial charge transfer states that takes place on the subnanosecond time scale as revealed by time-resolved photoluminescence and nongeminate recombination as follows from the OSC performance. Our findings demonstrate the potential of TPA-DCV-based molecules as donor materials for both solution-processed and vacuum-deposited OSCs. (Figure Presented). © 2017 American Chemical Society.
Keywords: Charge transfer; Molecules; Organic solar cells; Photoluminescence; Solar cells; Vacuum applications; Charge separations; Independent channels; Interfacial charge transfer; Photoinduced absorption; Photovoltaic applications; Push-pull molecules; Subnanosecond time scale; Time-resolved photoluminescence; Synthesis (chemical)

Tunable conduction type of solution-processed germanium nanoparticle based field effect transistors and their inverter integration - Peukert, Wolfgang; Meric, Zeynep; Mehringer, Christian; Jank, Michael; Frey, Lothar; Karpstein, Nicolas (Physical Chemistry Chemical Physics, 2015)
In this work we demonstrate the fabrication of germanium nanoparticle (NP) based electronics. The whole process chain from the nanoparticle production up to the point of inverter integration is covered. Ge NPs with a mean diameter of 33 nm and a geometric standard deviation of 1.19 are synthesized in the gas phase by thermal decomposition of GeH4 precursor in a seeded growth process. Dispersions of these particles in ethanol are employed to fabricate thin particulate films (60 to 120 nm in thickness) on substrates with a pre-patterned interdigitated aluminum electrode structure. The effect of temperature treatment, polymethyl methacrylate encapsulation and alumina coating by plasma-assisted atomic layer deposition (employing various temperatures) on the performance of these layers as thin film transistors (TFTs) is investigated. This coating combined with thermal annealing delivers ambipolar TFTs which show an Ion/Ioff ratio in the range of 102. We report fabrication of n-type, p-type or ambipolar Ge NP TFTs at maximum temperatures of 450 °C. For the first time, a circuit using two ambipolar TFTs is demonstrated to function as a NOT gate with an inverter gain of up to 4 which can be operated at room temperature in ambient ai
Keywords: nanoparticle; electronic; thermal; decomposition; growth; particulate; film

Tunable dual-mode photoluminescence from nanocrystalline Eu-doped Li2ZnSiO4 glass ceramic phosphors - Gao, Guojun; Reibstein, Sindy; Peng, Mingying; Wondraczek, Lothar (Journal of Materials Chemistry, 2011)
We report on tunable photoluminescence from mixed-valence Eu-doped nanocrystalline Li_2ZnSiO_4 glass ceramics. After preparation of the precursor glass in air, gradual reduction of Eu^3+ to Eu2+ occurs intrinsically during thermal annealing and precipitation of crystalline Li_2ZnSiO_4. Dual-mode photoemission can be generated for exciting at a wavelength of about 360 nm. The resulting colour of luminescence, ranging from orange/red to blue, can be controlled by adjusting the annealing temperature and, hence, the degree of crystallization: with increasing annealing temperature, the ratio of luminescence intensities related to Eu3+ and Eu2+ species, respectively, varies as a result of increasing degree of Eu3+-reduction as well as distinct changes in the optical scattering behaviour of the obtained glass ceramic. At the same time, the bandwidth of Eu2+-related photoemission increases from 87 to 154 nm. The underlying mechanisms of photoemission and energy transfer from Eu2+ to Eu3+ are discussed on the basis of dynamic emission spectroscopy and structural considerations, and a description of the internal reduction process is given.
EAM Import::2019-03-13

Tungsten doping of Ta3N5-nanotubes for band gap narrowing and enhanced photoelectrochemical water splitting efficiency - Grigorescu, Sabina Georgiana; Bärhausen, Benedikt; Wang, Lei; Mazare, Anca Valentina; Yoo, Jeong Eun; Hahn, Robert; Schmuki, Patrik (Electrochemistry Communications, 2015)
Ordered W-doped Ta2O5 nanotube arrays were grown by self-organizing electrochemical anodization of TaW alloys with different tungsten concentrations and by a suitable high temperature ammonia treatment, fully converted to W:Ta3N5 tubular structures. A main effect found is that W doping can decrease the band gap from 2 eV (bare Ta3N5) down to 1.75 eV. Ta3N5 nanotubes grown on 0.5 at.% W alloy and modified with Co(OH)x as co-catalyst show 33% higher photocurrents in photoelectrochemical (PEC) water splitting than pure Ta3N5.
EAM Import::2019-03-13

Tuning Charge Transfer Energetics in Reaction Center Mimics via Th-Functionalization of Fullerenes - Guldi, Dirk Michael; Ohkubo, Kei; Hauke, Frank; Hauke, Frank; Hirsch, Andreas; Spänig, Fabian; Fukuzumi, Shunichi; Kovács, Christian (Journal of the American Chemical Society, 2009)
We have introduced an approach of mono- and hexakis-adducts of C-60 involving a T-h-symmetrical addition pattern, where up to 12 ferrocene or 10 ferrocene and one porphyrin units are linked flexibly to C-60 with the objective to systematically raise the energy of the radical ion pair state. A detailed electrochemical and photophysical investigation has shed light onto charge transfer events that depend largely on (i) the functionalization pattern of C-60, (ii) the donor strength of the donor, (iii) the excited-state energy of the predominant chromophore, and (iv) the solvent polarity. Considering (i)-(iv), the presence of the porphyrins is key to providing sufficient driving forces for affording spatially separated radical ion pair states. An ideal scenario, that is, testing ZnP-C-60-(Fc)(10) (19) in benzonitrile and DMF, allows storing nearly 1.7 eV in a nanosecond lived radical ion pair state. In this context, the flexible linkage, powering a through space charge transfer, prevents, however, stabilization of the radical ion pair state beyond nanoseconds.

Tuning conversion efficiency in metallo endohedral fullerene-based organic photovoltaic devices - Ross, Russel B.; Cardona, Claudia M.; Swain, Francis B.; Guldi, Dirk Michael; Sankaranarayanan, Shankara Gayathri; Van Keuren, Edward; Holloway, Brian C.; Drees, Martin (Advanced Functional Materials, 2009)
Here the influence that l-(3-hexoxycarbonyl)propyl-l-phenyl-[6,6]-Lu N@C, LuN@C-PCBH, a novel acceptor material, has on active layer morphology and the performance of organic photovoltaic (OPV) devices using this material is reported. Polymer/fullerene blend films with poly(3-hexylthiophene), P3HT, donor material and Lu N@C-PCBH acceptor material are studied using absorption spectroscopy, grazing incident X-ray diffraction and photocurrent spectra of photovoltaic devices. Due to a smaller molecular orbital offset the OPV devices built with LuN@C-PCBH display increased open circuit voltage over empty cage fullerene acceptors. The photovoltaic performance of these metallo endohedral fullerene blend films is found to be highly impacted by the fullerene loading. The results indicate that the optimized blend ratio in a P3HT matrix differs from a molecular equivalent of an optimized P3HT/ [6,6]-phenyl-C-butyric methyl ester, C-PCBM, active layer, and this is related to the physical differences of the C fullerene. The influence that active layer annealing has on the OPV performance is further evaluated. Through properly matching the film processing and the donor/acceptor ratio, devices with power conversion efficiency greater than 4% are demonstrated. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tuning Elasticity of Open-Cell Solid Foams and Bone Scaffolds via Randomized Vertex Connectivity - Nachtrab, Susan; Kapfer, Sebastian; Rietzel, Dominik; Drummer, Dietmar; Madadi, Mahyar; Arns, Christoph; Kraynik, Andrew M.; Schröder-Turk, Gerd; Mecke, Klaus (Advanced Engineering Materials, 2012)
Tuning mechanical properties of and fluid flow through open-cell solid structures is a challenge for material science, in particular for the design of porous structures used as artificial bone scaffolds in tissue engineering. We present a method to tune the effective elastic properties of custom-designed open-cell solid foams and bone scaffold geometries by almost an order of magnitude while approximately preserving the pore space geometry and hence fluid transport properties. This strong response is achieved by a change of topology and node coordination of a network-like geometry underlying the scaffold design. Each node of a four-coordinated network is disconnected with probability p into two two-coordinated nodes, yielding network geometries that change continuously from foam- or network-like cellular structures to entangled fiber bundles. We demonstrate that increasing p leads to a strong, approximately exponential decay of mechanical stiffness while leaving the pore space geometry largely unchanged. This result is obtained by both voxel-based finite element methods and compression experiments on laser sintered models. The physical effects of randomizing network topology suggest a new design paradigm for solid foams, with adjustable mechanical properties. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
UnivIS-Import:2015-03-09:Pub.2012.tech.FT.FT-KT.tuning

Tuning of charge carrier density of ZnO nanoparticle films by oxygen plasma treatment - Walther, Sabine; Polster, Sebastian; Jank, M. P. M.; Thiem, H.; Ryssel, Heiner; Frey, Lothar (Advanced Powder Technology, 2011)
In this work, the charge carrier density of ZnO nanoparticle films was modified after deposition and annealing by an oxygen plasma treatment. The respective films were utilized as active layers in thin film transistors. For a discussion of the plasma–surface interaction on the molecular level, the electrical behavior of the layers was investigated which in general is highly sensitive to low level variations in defect or doping densities. A treatment with remote oxygen plasma at 400 W for 10 s led to a shift of the turn-on voltage from -12 to 4 V and a reduction of the off-current by more than two orders of magnitude. A model for the influence of oxygen species adsorbed to ZnO nanoparticle surfaces on electrical characteristics of ZnO nanoparticle thin film transistors is introduced.
Keywords: Plasma treatment; Printed electronics; TFT; ZnO

Tuning the molecular order of C60-based self-assembled monolayers in field-effect transistors - Schmaltz, Thomas; Khassanov, Artöm; Steinrück, Hans-Peter; Magerl, Andreas; Hirsch, Andreas; Halik, Marcus (Nanoscale, 2014)
The control of order in organic semiconductor systems is crucial to achieve desired properties in electronic devices. We have studied the order in fullerene functionalized self-assembled monolayers by mixing the active molecules with supporting alkyl phosphonic acids of different chain length. By adjusting the length of the molecules, structural modifications of the alignment of the C60 head groups within the SAM can be tuned in a controlled way. These changes on the sub-nanometre scale were analysed by grazing incidence X-ray diffraction and X-ray reflectivity. To study the electron transport properties across these layers, self-assembled monolayer field-effect transistors (SAMFETs) were fabricated containing only the single fullerene monolayer as semiconductor. Electrical measurements revealed that a high 2D crystalline order is not the only important aspect. If the fullerene head groups are too confined by the supporting alkyl phosphonic acid molecules, defects in the crystalline C60 film, such as grain boundaries, start to strongly limit the charge transport properties. By close interpretation of the results of structural investigations and correlating them to the results of electrical characterization, an optimum chain length of the supporting alkyl phosphonic acids in the range of C10 was determined. With this study we show that minor changes in the order on the sub-nanometre scale, can strongly influence electronic properties of functional self-assembled monolayers.

Tuning the Molecular Order of C60 Functionalized Phosphonic Acid Monolayers - Rumpel, Armin; Novak, Michael; Walter, Johannes; Braunschweig, Björn; Halik, Marcus; Peukert, Wolfgang (Langmuir, 2011)
Mixed self-assembled monolayers (SAM) of alkyl phosphonic acids and C60 functionalized octadecyl phosphonic acids (C60C18–PA) are deposited on alumina substrates from solution and are shown to form wellordered structures with an insulating layer of alkyl chains and a semiconducting layer that comprises mainly C60. Such an ordered structure is a necessity for the application of SAMs in organic transistors but is difficult to obtain since C60C18–PA without additional support do self-assemble in dense packaging but not in a well-ordered fashion. To avoid disordering of the SAM and to gain a better control of the interfacial properties we have investigated the stabilizing effects of fluorinated dodecyl phosphonic acids (FC12–PA) on the C60C18–PA monolayer. Vibrational sum-frequency (SFG) spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, and electrical measurements were applied to study the mixed monolayers. Here, we make use of the differently labeled PA to determine surface coverages and molecular properties of the two species independently. Adsorption of FC12–PA gives rise to vibrational bands at 1344 cm-1 and 1376 cm-1 in SFG spectra, while a pronounced vibrational band centered at 1465 cm-1 is attributable to C60 vibrations. The coexistence of the bands is indicative for the presence of a mixed monolayer that is composed of both molecular species. Furthermore, a pronounced maximum in SFG intensity of the C60 band is observed for SAMs, which are deposited from solutions with  75% C60C18–PA and  25% FC12–PA. The intensity maximum originates from successful stabilization of C60 modified C60C18–PA by FC12–PA and a significantly improved molecular order. Conclusions from SFG spectra are corroborated by electric measurements that show best performance at these concentrations. Our results provide new information on the morphology and composition of C60 modified SAMs and establish a route to fabricate well-defined layers for molecular scale organic electronics.
Keywords: Thickness; Nonlinear optics; Layers; Monolayers

Tuning the Reactivity of a Cu/ZnO Nanocatalyst via Gas Phase Pressure - Martinez-Suarez, Luis; Frenzel, Johannes; Marx, Dominik; Meyer, Bernd (Physical Review Letters, 2013)
By calculation of a thermodynamic phase diagram we provide an atomistic understanding of the morphological changes in ZnO-supported Cu nanocatalysts, which are subject to strong metal-support interactions, in response to the redox properties of the surrounding gas phase, i.e., depending on temperature and pressure. The reactivity, and thus the strong metal-support interactions, of this catalyst is traced back to a redox-state dependent occupation of delocalized ZnO substrate bands and localized Cu cluster states at the Fermi level. It is shown that at the conditions of industrial methanol synthesis complex electronic charge transfer processes across the metal-support interface, driven by morphological and electronic changes, explain the enhanced catalytic reactivity toward CO2.
EAM Import::2019-03-13

Tuning the reorganization energy of electron transfer in supramolecular ensembles - metalloporphyrin, oligophenylenevinylenes, and fullerene - and the impact on electron transfer kinetics - Stangel, Christina; Schubert, Christina; Kuhri, Susanne; Rotas, Georgios; Margraf, Johannes; Regulska, Elzbieta; Clark, Timothy; Torres, Tomas; Tagmatarchis, Nikos; Coutsolelos, Athanassios G.; Guldi, Dirk Michael (Nanoscale, 2015)
Oligo(p-phenylenevinylene) (oPPV) wires of various lengths featuring pyridyls at one terminal and C-60 moieties at the other, have been used as molecular building blocks in combination with porphyrins to construct a novel class of electron donor-acceptor architectures. These architectures, which are based on non-covalent, directional interactions between the zinc centers of the porphyrins and the pyridyls, have been characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. Complementary physico-chemical assays focused on the interactions between electron donors and acceptors in the ground and excited states. No appreciable electron interactions were noted in the ground state, which was being probed by electrochemistry, absorption spectroscopy, etc.; the electron acceptors are sufficiently decoupled from the electron donors. In the excited state, a different picture evolved. In particular, steady-state and time-resolved fluorescence and transient absorption measurements revealed substantial electron donor-acceptor interactions. These led, upon photoexcitation of the porphyrins, to tunable intramolecular electron-transfer processes, that is, the oxidation of porphyrin and the reduction of C-60. In this regard, the largest impact stems from a rather strong distance dependence of the total reorganization energy in stark contrast to the distance independence seen for covalently linked conjugates.

Tuning the Selectivity of Photocatalytic Synthetic Reactions Using Modified TiO2 Nanotubes - Tripathy, Jyotsna; Lee, Kiyoung; Schmuki, Patrik (Angewandte Chemie International Edition, 2014)
Differently modified TiO2 nanotubes were used to achieve a drastic change in the selectivity of a photocatalytic reaction. For the photocatalytic oxidation of toluene, depending on the electronic properties of TiO2 (anatase, rutile, Ru-doped), a strong change in the main reaction product (namely benzoic acid versus benzaldehyde) can be achieved, and certain undesired reaction pathways can be completely shut down.
EAM Import::2019-03-13

Tuning the size and the optical properties of ZnO mesocrystals synthesized under solvothermal conditions - Distaso, Monica; Segets, Doris; Wernet, Ruth; Peukert, Wolfgang; Klupp Taylor, Robin (Nanoscale, 2012)
Mesocrystals are a promising class of nanomaterials enabling new optical and mechanical properties due to their three dimensional organization of primary crystallites sharing a common crystallographic orientation. In the present article, the influence of process parameters such as temperature profile and stirring on the primary and secondary size of ZnO mesocrystals synthesized under solvothermal conditions has been investigated. In general, small but noticeable lattice strain is introduced to the particles during the synthesis process. Additionally, with increasing mass transport the fusion of primary crystallites due to coarsening is enhanced. A closer analysis revealed an influence of the polymer chain length on the final particle structure throughout different hierarchical levels. Based on our findings a reaction mechanism with nucleation and growth taking place embedded in poly-N-vinylpyrrolidone (PVP), followed by a polymer-mediated step of oriented aggregation and subsequent coarsening is proposed. In consequence, the careful control throughout all hierarchical levels of particle synthesis allows fine-tuning of the optical properties of ZnO mesocrystals which show a high UV absorption and minimal scattering in the visible region. © 2012 The Royal Society of Chemistry.

Two-ball problem revisited: Limitations of event-driven modeling - Müller, Patric; Pöschel, Thorsten (Physical Review E, 2011)
The main precondition of simulating systems of hard particles by means of event-driven modeling is the assumption of instantaneous collisions. The aim of this paper is to quantify the deviation of event-driven modeling from the solution of Newton's equation of motion using a paradigmatic example: If a tennis ball is held above a basketball with their centers vertically aligned, and the balls are released to collide with the floor, the tennis ball may rebound at a surprisingly high speed. We show in this article that the simple textbook explanation of this effect is an oversimplification, even for the limit of perfectly elastic particles. Instead, there may occur a rather complex scenario including multiple collisions which may lead to a very different final velocity as compared with the velocity resulting from the oversimplified model. © 2011 American Physical Society.

Two computational models for simulating the tumbling motion of elongated particles in fluids - Bartuschat, Dominik; Fischermeier, Ellen; Gustavsson, Katarina; Rüde, Ulrich (Computers & Fluids, 2016)
Suspensions with fiber-like particles in the low Reynolds number regime are modeled by two different approaches that both use a Lagrangian representation of individual particles. The first method is the well established formulation based on Stokes flow that is formulated as integral equations. It uses a slender body approximation for the fibers to represent the interaction between them directly without explicitly computing the flow field. The second is a new technique using the 3D lattice Boltzmann method on parallel supercomputers. Here the flow computation is coupled to a computational model of the dynamics of rigid bodies using fluid-structure interaction techniques. Both methods can be applied to simulate fibers in fluid flow. They are carefully validated and compared against each other, exposing systematically their strengths and weaknesses regarding their accuracy, the computational cost, and possible model extensions. (C) 2015 Elsevier Ltd. All rights reserved.
UnivIS-Import:2015-04-14:Pub.2015.tech.IMMD.lsinfs.twocom_7
Keywords: Fluid–particle interaction; Tumbling fibers; Slender body formulation; Lattice Boltzmann method

Two-dimensional airflow modeling underpredicts the wind velocity over dunes - Michelsen, Britt; Strobl, Severin; Ribeiro Parteli, Eric Josef; Pöschel, Thorsten (Scientific Reports, 2015)
We investigate the average turbulent wind field over a barchan dune by means of Computational Fluid Dynamics. We find that the fractional speed-up ratio of the wind velocity over the three-dimensional barchan shape differs from the one obtained from two-dimensional calculations of the airflow over the longitudinal cut along the dune's symmetry axis - that is, over the equivalent transverse dune of same size. This finding suggests that the modeling of the airflow over the central slice of barchan dunes is insufficient for the purpose of the quantitative description of barchan dune dynamics as three-dimensional flow effects cannot be neglected.

Two intertwined facets of adherent membranes: membrane roughness and correlations between ligand-receptors bonds - Reister, Ellen; Bihr, Timo; Seifert, Udo; Smith, Ana-Suncana (New Journal of Physics, 2011)
We study equilibrium fluctuations of adherent membranes by means of Langevin simulations in the case when the interaction of the membrane with the substrate is twofold: a non-specific homogeneous harmonic potential is placed at large distances, whereas discrete ligand-receptor interactions occur at short distances from the flat substrate. We analyze the correlations between neighboring ligand-receptor bonds in a regime of relatively strong membrane fluctuations. By comparison with the random distribution of bonds, we find that the correlations between the bonds are always positive, suggesting spontaneous formation of domains. The equilibrium roughness of the membrane is then determined by fluctuations in the number density of bonds within the domains. Furthermore, we show that the excess number of bonds arising due to correlations and the instantaneous roughness of the membrane both follow master curves that depend only on the instantaneous bond density and not on the intrinsic binding strength of the ligand-receptor pair. The master curves show identical trends, further corroborating the link between membrane roughness and bond correlations.
Keywords: SUPPORTED MEMBRANES; GIANT VESICLES; ADHESION; DIFFUSION; DYNAMICS; MOLECULES; SURFACE; MODELS; CELLS

Two-scale elastic parameter identification from noisy macroscopic data - Schmidt, Ulrike; Steinmann, Paul; Mergheim, Julia (Archive of Applied Mechanics, 2015)
A two-scale parameter identification procedure to identify microscopic elastic parameters from macroscopic data is introduced and thoroughly analyzed. The macroscopic material behavior of microscopically linear elastic heterogeneous materials is described by means of numerical homogenization. The microscopic material parameters are assumed to be unknown and are identified from noisy macroscopic displacement data. Various examples of microscopically heterogeneous materials—with regularly distributed pores, particles, or layers—are considered, and their parameters are identified from different macroscopic experiments by means of a gradient-based optimization procedure. The reliability of the identified parameters is analyzed by their standard deviations and correlation matrices. It was found that the two-scale parameter identification works well for cellular materials, but has to be designed carefully for layered materials. If the homogenized macroscopic material behavior can be described by less material parameters than the microscopic material behavior, as, e.g., for regularly distributed particles, the identification of all microscopic parameters from macroscopic experiments is not possible.

Two similar near-infrared (IR) absorbing benzannulated AZA-bodipy dyes as near-ir sensitizers for ternary solar cells - Min, Jie; Ameri, Tayebeh; Gresser, Roland; Lorenz-Rothe, Melanie; Baran, Derya; Troeger, Anna; Sgobba, Vito; Leo, Karl; Riede, Moritz; Guldi, Dirk Michael; Brabec, Christoph (ACS Applied Materials and Interfaces, 2013)
Ternary composite inverted organic solar cells based on poly(3-hexylthiophen-2,5-diyl) (P3HT) and phenyl-C-butyric acid methyl ester (PCBM) blended with two different near-infrared absorbing benzannulated aza-BODIPY dyes, difluoro-bora-bis-(1-phenyl-indoyl)-azamethine (1) or difluoro-bora-bis-(1-(5-methylthiophen)-indoyl)-azamethine (2), were constructed and characterized. The amount of these two aza-BODIPY dyes, within the P3HT and PCBM matrix, was systematically varied, and the characteristics of the respective devices were recorded. Although the addition of both aza-BODIPY dyes enhanced the absorption of the blends, only the addition of 1 improved the overall power conversion efficiency (PCE) in the near-infrared (IR) region. The present work paves the way for the integration of near-infrared absorbing aza-BODIPY derivatives as sensitizers in ternary composite solar cells. © 2013 American Chemical Society.

Two-Step Nucleation Rather than Self-Poisoning: An Unexpected Mechanism of Asymmetrical Molecular Crystal Growth - Ectors, Philipp; Anwar, Jamshed; Zahn, Dirk (Crystal Growth & Design, 2015)
The identification of two step nucleation mechanisms considerably extended our understanding of crystal nucleation. Here, we report an analogous observation of a two-step mechanism but in 2-D for deposition of molecules to a growing crystal face. Using molecular dynamics simulations connected with the Kawska-Zahn approach, extgreeka-resorcinol precipitation from the vapor is treated at the low driving force regime. Growth at the faster growing (01̅1̅) face reveals the deposition of molecules to form a disordered liquid-like layer. Strikingly, this apparently divergent (nonepitaxial) molecular arrangement does not represent self-poisoning which would lower the growth rate of the (01̅1̅) face. On the contrary, more favorable attachment energy along with a disorder–order transition, akin to a two-step nucleation observed in 3-D systems, leads to growth rates that are about 20 times faster than the more standard mode association of molecules at the (011) face where the molecules readily align according to the crystal lattice.
EAM Import::2019-03-13

Ultrafast Charge Transfer between Light Absorber and Co3O4 Water Oxidation Catalyst across Molecular Wires Embedded in Silica Membrane - Edri, Eran; Cooper, Jason K.; Sharp, Ian D.; Guldi, Dirk Michael; Frei, Heinz (Journal of the American Chemical Society, 2017)
The mechanism of visible light-induced hole transfer from a molecular light absorber, in the form of a free-base porphyrin, coupled to a Co3O4 nanoparticle catalyst for water oxidation by a molecular wire (p-oligo(phenylenevinylene) featuring three aryl units) is investigated by transient absorption spectroscopy. The wires are covalently anchored on the Co3O4 surface and embedded in a dense, yet ultrathin (2 nm), silica layer that separates light absorber and catalyst. The porphyrin is electrostatically adsorbed on the silica surface, and aqueous colloidal solutions of the core-shell particles are used for transient optical measurements. Pulsed optical excitation of the porphyrin results in rapid injection of the photogenerated hole onto the molecular wire and concurrent formation of reduced light absorber in less than 1 picosecond (ps). Ultrafast charge separation was monitored by transient absorption of the wire radical cation, which is given by bands in the 500 to 600 nm region and at 1130 nm, while formation of reduced porphyrin was characterized by absorption at 700 nm. Forward transfer of the hole to Co3O4 catalyst proceeds in 255 ± 23 ps. Ultrafast transfer of positive charge from the molecular assembly to a metal oxide nanoparticle catalyst for water oxidation is unprecedented. Holes on Co3O4 recombined with electrons of the reduced sensitizer with biphasic kinetics on a much longer time scale of ten to several hundred nanoseconds. The unusually efficient hole transfer coupling of a molecular light absorber with an Earth-abundant metal oxide catalyst by silica-embedded p-oligo(phenylenevinylene) offers an approach for integrated artificial photosystems featuring product separation on the nanoscale.
EAM Import::2019-03-13

Ultrafast Growth of Highly Ordered Anodic TiO 2 Nanotubes in Lactic Acid Electrolytes - So, Seulgi; Lee, Kiyoung; Schmuki, Patrik (Journal of the American Chemical Society, 2012)
In the present work, we show that fully functional self-organized TiO2 nanotube layers can be electrochemically grown with an unprecedented growth rate if lactic acid (LA) is used as an additive during anodization. The main effect of LA addition is that it allows performing nanotube growth at significantly higher anodization voltage than in the LA free case, and this without dielectric oxide breakdown (``burning''). As a result, for example, 15 extgreekmm tube thick nanotube layers, suitable for a use in dye-sensitized solar cells (DSSCs) can be grown in 45 s and 7 extgreekmm tubes suitable for water splitting can be grown in 25 s.
EAM Import::2019-03-13

Ultrafast x-ray photoelectron spectroscopy in the microsecond time domain - Höfert, Oliver; Gleichweit, Christoph; Steinrück, Hans-Peter; Papp, Christian (Review of Scientific Instruments, 2013)
We introduce a new approach for ultrafast in situ high-resolution X-ray photoelectron spectroscopy (XPS) to study surface processes and reaction kinetics on the microsecond timescale. The main idea is to follow the intensity at a fixed binding energy using a commercial 7 channeltron electron analyzer with a modified signal processing setup. This concept allows for flexible switching between measuring conventional XP spectra and ultrafast XPS. The experimental modifications are described in detail. As an example, we present measurements for the adsorption and desorption of CO on Pt(111), performed at the synchrotron radiation facility BESSY II, with a time resolution of 500 μs. Due to the ultrafast measurements, we are able to follow adsorption and desorption in situ at pressures of 2 × 10 mbar and temperatures up to 500 K. The data are consistently analyzed using a simple model in line with data obtained with conventional fast XPS at temperatures below 460 K. Technically, our new approach allows measurement on even shorter timescales, down to 20 μs. © 2013 AIP Publishing LLC.

Ultrafine-grained AA6014/AA5754 laminates produced by accumulative roll bonding (ARB) - Hausöl, Tina; Höppel, Heinz Werner; Göken, Mathias (Materialwissenschaft und Werkstofftechnik, 2012)
Laminates with alternating AA6014 and AA5754 layers are produced by accumulative roll bonding (ARB). Depending on the number of ARB cycles the microstructure and the mechanical properties are investigated. The microstructure is characterized by scanning electron microscopy and correlated to the local mechanical properties determined by nanoindentation experiments. The overall properties are derived by tensile testing. The ultrafine-grained microstructure and the local mechanical properties alter with the layer composition. With increasing number of ARB cycles a much higher grain refinement is achieved within the AA5754 layers than in the AA6014 layers. The hardness of the individual layers develops similarly. On the macroscopic scale it is shown that the laminates are unifying the desired properties of the materials involved: high strength by a simultaneous suppression of the Portevin-Le Châtelier effect, typically occurring in the AA5754 alloy.
WW1::950

Ultrafine-grained austenitic stainless steels X4CrNi18-12 and X8CrMnNi19-6-3 produced by accumulative roll bonding - Ruppert, Mathis; Freund, Lisa; Wenzl, Thomas; Höppel, Heinz Werner; Göken, Mathias (Metals, 2015)
Austenitic stainless steels X4CrNi18-12 and X8CrMnNi19-6-3 were processed by accumulative roll bonding (ARB). Both materials show an extremely high yield strength of 1.25 GPa accompanied by a satisfactory elongation to failure of up to 14% and a positive strain rate sensitivity after two ARB cycles. The strain-hardening rate of the austenitic steels reveals a stabilization of the stress-strain behavior during tensile testing. Especially for X8CrMnNi19-6-3, which has an elevated manganese content of 6.7 wt.%, necking is prevented up to comparatively high plastic strains. Microstructural investigations showed that the microstructure is separated into ultrafine-grained channel like areas and relatively larger grains where pronounced nano-twinning and martensite formation is observed.
WW1::1039

Ultra-Low Concentration Monitoring of Catalytic Reactions in Photonic Crystal Fiber - Cubillas, Ana Maria; Schmidt, Matthias; Scharrer, Michael; Euser, Tijmen G.; Etzold, Bastian; Taccardi, Nicola; Wasserscheid, Peter; Russell, Philip St. John (Chemistry - A European Journal, 2012)
Photonic crystal fibers as microreactors: Photonic crystal fibers can be used as microreactors (see figure). As an example, the illustration shows the difference in size between a 10cm cuvette (left), and a photonic crystal fiber (right; not to scale).

Ultra-Low-Temperature Water-Gas Shift Catalysis using Supported Ionic Liquid Phase (SILP) Materials - Werner, Sebastian; Szesni, Normen; Kaiser, Melanie; Fischer, Richard; Haumann, Marco; Wasserscheid, Peter (ChemCatChem, 2010)
SILP inside the eye of your mind: A new class of water–gas shift catalyst system that outperforms commercial shift catalysts under ultra-low-temperature real gas conditions (T<160 °C) has been developed. The new catalysts consist of [RuCl2(CO)32] dissolved in a chloride ionic liquid and dispersed on a porous basic support using the SILP approach. Its robustness and recyclability make it highly attractive for industrial hydrogen production.

Unconstrained and Cauchy-Born-constrained atomistic systems: deformational and configurational mechanics - Steinmann, Paul; Ricker, Sarah; Aifantis, Elias (Archive of Applied Mechanics, 2011)
In this contribution, the deformational and configurational mechanics of (elastic) discrete atomistic systems in relation to their continuum counterparts are considered for the quasi-static case. Thereby, we firstly investigate the basic unconstrained case in the sense of lattice statics as a reference. Based on these results, we consider two Cauchy-Born-type constraints that (locally) describe the change of the position of atoms (between the material and the spatial configuration) in terms of either a linear or a quadratic map, respectively. Insertion of these kinematic constraints into the variation of the total potential energy of the unconstrained case renders eventually Cauchy-Born-type definitions for atomistic stresses and hyperstresses, for both deformational and configurational cases. In the continuum limit, these are the relevant continuum stresses and hyperstresses contributing to the local force balances of first- (classical) and second-order (non-classical) gradient continua (here first- and second-order gradient refers to the highest gradient of the deformation map characterizing the kinematics). It is emphasized that the atomistic and the Cauchy-Born-type configurational quantities represent novel and unexpected contributions. Among other things, they may be useful in assessing the singular or non-singular character of deformation fields at crack tips and comparing numerical estimates resulting from atomistic simulations with analytical predictions resulting from solutions of related boundary value problems for gradient continua. © 2010 Springer-Verlag.
UnivIS-Import:2015-03-09:Pub.2011.tech.FT.FT-TM.deform
Keywords: Cauchy-Born constraint; Configurational mechanics; Gradient continua; Homogenization

Unconventional optical Tamm states in metal-terminated three-dimensional photonic crystals - Korovin, Alexander V.; Romanov, Sergei G. (Physical Review B, 2016)
Unconventional optical Tamm surface states have been demonstrated in transmission and reflectance spectra of three-dimensional opal photonic crystals coated by thin metal films. These states appear in registry with diffraction resonances and localize the electromagnetic energy in asymmetric resonators formed by stacks of lattice planes and metal semishells. Tamm defect states provide the bypass for light at the edges of the Bragg diffraction resonances and thus reduce the diffraction efficiency. Despite the hidden nature of this effect, its magnitude is comparable to the extraordinary transmission associated with the surface-plasmon polaritons that are simultaneously excited at the surfaces of the corrugated metal films.
EAM Import::2019-03-12

Uncovering Molecular Processes in Crystal Nucleation and Growth by Using Molecular Simulation - Anwar, Jamshed; Zahn, Dirk (Angewandte Chemie International Edition, 2011)
Exploring nucleation processes by molecular simulation provides a mechanistic understanding at the atomic level and also enables kinetic and thermodynamic quantities to be estimated. However, whilst the potential for modeling crystal nucleation and growth processes is immense, there are specific technical challenges to modeling. In general, rare events, such as nucleation cannot be simulated using a direct ``brute force'' molecular dynamics approach. The limited time and length scales that are accessible by conventional molecular dynamics simulations have inspired a number of advances to tackle problems that were considered outside the scope of molecular simulation. While general insights and features could be explored from efficient generic models, new methods paved the way to realistic crystal nucleation scenarios. The association of single ions in solvent environments, the mechanisms of motif formation, ripening reactions, and the self-organization of nanocrystals can now be investigated at the molecular level. The analysis of interactions with growth-controlling additives gives a new understanding of functionalized nanocrystals and the precipitation of composite materials.
EAM Import::2019-03-12

Understanding the correlation and balance between the miscibility and optoelectronic properties of polymer-fullerene solar cells - Zhang, Chaohong; Langner, Stefan; Mumyatov, Alexander V.; Anokhin, Denis V.; Min, Jie; Perea, Jose Dario; Gerasimov, Kirill L.; Osvet, Andres; Ivanov, Dimitri A.; Troshin, Pavel; Li, Ning; Brabec, Christoph (Journal of Materials Chemistry A, 2017)
Organic photovoltaics is one of the most promising technologies for sustainable green energy supply. Because of their high electron affinity and superior electron-transporting ability, fullerene-based materials are deemed as very strong electron-accepting components in organic solar cells. However, the most widely used fullerene-based acceptors, such as phenyl-C61-butyric acid methyl ester, exhibit limited microstructural stability and unsatisfactory thermal stability owing to their insufficient compatibility with organic donors. Here, we in-depth investigate the carrier dynamics along with structural evolution and analyze the acceptor loadings in optimized bulk-heterojunction (BHJ) solar cells as a function of the polymer-fullerene miscibility. The polymer-fullerene miscibility has more influential effects than the crystallinity of single components on the optimized acceptor:donor ratio in polymer-fullerene solar cells. The findings demonstrated in this work suggest that the balance between the miscibility of BHJ composites and their optoelectronic properties has to be carefully considered for future development and optimization of OPV solar cells based on BHJ composites. Miscibility is proposed in addition to crystallinity as a further design criterion for long lived and efficient solar cells. © 2017 The Royal Society of Chemistry.
Keywords: Engineering controlled terms: Butyric acidElectron affinityFullerenesHeterojunctionsOrganic solar cellsPolymer solar cellsPolymersSolubility Bulk heterojunction (BHJ)Electron transportingHigh electron affinitiesInfluential effectsMicrostructural stabilityOptoelectronic propertiesOrganic photovoltaicsStructural evolution Engineering main heading: Solar cells

Understanding the Extremely Low Fracture Toughness of Freestanding Gold Thin Films by In-situ Bulge Testing in an AFM - Preiß, Eva; Merle, Benoit; Göken, Mathias (Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2017)
The fracture toughness of freestanding gold films with thicknesses between 60 nm and 320 nm was determined by bulge testing to be around 2 MPa m1/2. This surprisingly low value confirms the trend also observed for other metals that thin films exhibit only a fraction of the bulk fracture toughness. In order to understand this behavior, the fracture process of freestanding gold films with a crack introduced by focused ion beam (FIB) milling was observed in-situ in an atomic force microscope (AFM). AFM scans of the crack tip region show stable crack growth mainly along grain boundaries. Plastic deformation is localized in a narrow corridor in front of the crack tip. A large plastic zone, as one would typically expect under plane stress, is not observed. Instead, strong local necking is evidenced. We conclude that the spatial confinement of the plastic deformation is the primary reason for the low fracture toughness of metallic thin film
Keywords: Fracture toughness; Thickness effect; Thin films; Bulge testing; Atomic force microscopy; Gold

Unexpected Michael Additions on the Way to 2.3,8.9-Dibenzanthanthrenes with Interesting Structural Properties - Reus, Christian; Lechner, Marc; Schulze, Matthias; Lungerich, Dominik; Diner, Colin; Gruber, Marco; Stryker, Jeffrey M.; Hampel, Frank; Jux, Norbert; Tykwinski, Rik (Chemistry - A European Journal, 2016)
The synthesis and properties of a new polycyclic aromatic hydrocarbon containing eight annulated rings and based on the anthanthrene core is described. An unexpected, nucleophile-dependent Michael addition to a dibenzanthanthrene-1,7-dione is found, giving a product with three triisopropylsilylacetylene units and a remarkable solid-state structure (as determined by X-ray crystallography).
EAM Import::2019-03-12

Unified Design Strategies for Particulate Products - Peukert, Wolfgang; Segets, Doris; Pflug, Lukas; Leugering, Günter (Academic Press Inc., 2015)
Unit operations and product design are the two most important pillars of chemical engineering. Product design is the formation, formulation, handling, manufacturing, and characterization of complex multiphase products with specific properties and is thus at the core of mesoscale science and engineering. The applications define the required product properties which cover both classical fields of process technology in the chemical industry as well as new emerging fields of electronics, energy and environmental technologies, life sciences, materials science and engineering, nanotechnology, and photonic technologies highlighting the broad relevance of mesoscale science. Unifying principles of product design are proposed which are widely applicable to many different kinds of products including solid, liquid, and even gaseous particles. Results from the Erlangen Cluster of Excellence "Engineering of Advanced Materials" show that the joint venture of chemical engineering with materials science in concert with the basic sciences opens new prospects for all involved disciplines. In particular, chemical and biochemical engineering expands through particle technologies also in physics-related fields of technology such as electronics, photonics, or 3D printing. Rigorous mathematical optimization methods based on predictive models for products, structures, and processes catalyze new possibilities for true design of particulate products which is at the core of mesoscale science and technolog
Keywords: Bottom up; Hierarchical systems; Multiscale; Optimization; Product design; Structure formation; Top down; Unifying principles

Unified model for singlet fission within a non-conjugated covalent pentacene dimer - Basel, Bettina; Zirzlmeier, Johannes; Hetzer, Constantin; Phelan, Brian T.; Krzyaniak, Matthew D.; Seelam, Rajagopala Reddy; Brana Coto, Pedro; Horwitz, Noah E.; Young, Ryan M.; White, Fraser J.; Hampel, Frank; Clark, Timothy; et al. (Nature Communications, 2017)
When molecular dimers, crystalline films or molecular aggregates absorb a photon to produce a singlet exciton, spin-allowed singlet fission may produce two triplet excitons that can be used to generate two electron-hole pairs, leading to a predicted similar to 50% enhancement in maximum solar cell performance. The singlet fission mechanism is still not well understood. Here we report on the use of time-resolved optical and electron paramagnetic resonance spectroscopy to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer. We observe the key intermediates in the singlet fission process, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons. Using these combined data, we develop a single kinetic model that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures.

Universal structure motifs in biominerals: a lesson from nature for the efficient design of bioinspired functional materials - Harris, Joseph; Böhm, Corinna; Wolf, Stephan (Interface Focus, 2017)
Biominerals are typically indispensable structures for their host organism in which they serve varying functions, such as mechanical support and protection, mineral storage, detoxification site, or as a sensor or optical guide. In this perspective article, we highlight the occurrence of both structural diversity and uniformity within these biogenic ceramics. For the first time, we demonstrate that the universality-diversity paradigm, which was initially introduced for proteins by Buehler et al. (Cranford & Buehler 2012 Biomateriomics; Cranford et al. 2013 Adv. Mater. 25, 802-824 (doi:10.1002/adma.201202553); Ackbarow & Buehler 2008 J. Comput. Theor. Nanosci. 5, 1193-1204 (doi:10.1166/jctn.2008.001); Buehler & Yung 2009 Nat. Mater. 8, 175-188 (doi:10.1038/nmat2387)), is also valid in the realm of biomineralization. A nanogranular composite structure is shared by most biominerals which rests on a common, non-classical crystal growth mechanism. The nanogranular composite structure affects various properties of the macroscale biogenic ceramic, a phenomenon we attribute to emergence. Emergence, in turn, is typical for hierarchically organized materials. This is a clear call to renew comparative studies of even distantly related biomineralizing organisms to identify further universal design motifs and their associated emergent properties. Such universal motifs with emergent macro-scale properties may represent an unparalleled toolbox for the efficient design of bioinspired functional materials.
EAM Import::2019-03-12

Unveiling the Mechanism of Water Partial Dissociation on Ru(0001) - Maier, Sabine; Stass, Ingeborg; Cerda, Jorge I.; Salmeron, Miquel (Physical Review Letters, 2014)
We have studied the mechanism of the partial dissociation of water on Ru(0001) by high resolution scanning tunneling microscopy (STM). The thermal evolution of water at submonolayer coverage has been tracked in the 110-145 K temperature range to identify the precursor structures for the partial dissociation. These were found to consist of hexagons arranged in thin stripes aligned along the close packed Ru [2 (11) over bar0] directions. The partially dissociated phase, on the other hand, contains a mixture of H2O and OH hexagons arranged into wider stripes and rotated by 30 degrees with respect to the intact water stripes. The atomic structure of both types of stripes is determined with the aid of density functional theory and STM simulations, providing insights into the partial dissociation reaction path. The reaction is found to be exothermic by around 0.4 eV and initiating at the edges of the intact water stripes. Hydrogen atoms, from water dissociation or already present at the surface, are found to play an important role in the kinetics of the reactions.

Unzipping carbon nanotubes: A peeling method for the formation of graphene nanoribbons - Hirsch, Andreas (Angewandte Chemie International Edition, 2009)
Zipper examined: Elegant unzipping procedures result in the clean opening of multiwalled carbon nanotubes, leading to graphene nanoribbons (see scheme). Since graphene exhibits outstanding electronic properties, this method may be important in the development of modern nanoelectronic applications. © 2009 Wiley-VCH Verlag GmbH & Co. KCaA.

Up-conversion semiconducting MoO 3:Yb/Er nanocomposites as buffer layer in organic solar cells - Wang, Hao; Stubhan, Tobias; Osvet, Andres; Litzov, Ivan; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2012)
The spectral sensitivity of organic solar cells can be sensitized in the near-IR and IR by incorporating Yb/Er-doped MoO up-conversion nanocomposites. Poly-3-hexyl thiophene (P3HT) and [6,6] phenyl C butyric acid methyl ester (PC BM) were chosen for the active layer. Yb/Er-doped MoO nanoparticles with dual functionality were solution processed as charge selective interface layer. On the one hand, the electrical functionality of MoO as hole extraction layer is demonstrated. On the other hand, up-conversion emission from Yb sensitized Er dopants in the MoO nanoparticles is observed. Since the photocurrent generated from up-conversion with 975 nm excitation was found to be in competition with photocurrent contributions from a charge transfer complex absorbing also in the near IR, up-conversion from a Yb/Er doped MoO layer within an organic solar cell is proven spectroscopically and demonstrated by analyzing the photocurrent response of the Yb/Er doped cell and the undoped cell to the excitation intensity. The concept to integrate up-conversion functionality into metal oxide (MOx) based charge extraction layer suggests a promising and practical pathway for improving the near IR and IR sensitivity of thin film solar cells. © 2012 Elsevier B.V.
Keywords: Interface layer; Organic solar cell; Solution-processable; Up-conversion semiconducting MoO 3

Upper bound on the Edwards entropy in frictional monodisperse hard-sphere packings - Schröter, Matthias; Baranau, Vasili; Zhao, Song-Chuan; Scheel, Mario; Tallarek, Ulrich (Soft Matter, 2016)
We extend the Widom particle insertion method [B. Widom, J. Chem. Phys., 1963, 39, 2808-2812] to determine an upper bound s on the Edwards entropy in frictional hard-sphere packings. s corresponds to the logarithm of the number of mechanically stable configurations for a given volume fraction and boundary conditions. To accomplish this, we extend the method for estimating the particle insertion probability through the pore-size distribution in frictionless packings [V. Baranau, et al., Soft Matter, 2013, 9, 3361-3372] to the case of frictional particles. We use computer-generated and experimentally obtained three-dimensional sphere packings with volume fractions φ in the range 0.551-0.65. We find that s has a maximum in the vicinity of the Random Loose Packing Limit φ = 0.55 and decreases then monotonically with increasing φ to reach a minimum at φ = 0.65. Further on, s does not distinguish between real mechanical stability and packings in close proximity to mechanical stable configurations. The probability to find a given number of contacts for a particle inserted in a large enough pore does not depend on φ, but it decreases strongly with the contact number.

Uranium(III) complexes with bulky aryloxide ligands featuring metal-arene interactions and their reactivity toward nitrous oxide - Franke, Sebastian; Tran, Ba L.; Heinemann, Frank Wilhelm; Hieringer, Wolfgang; Mindiola, Daniel J.; Meyer, Karsten (Inorganic Chemistry, 2013)
We report the synthesis and use of an easy-to-prepare, bulky, and robust aryloxide ligand starting from inexpensive precursor materials. Based on this aryloxide ligand, two reactive, coordinatively unsaturated U(III) complexes were prepared that are masked by a metal-arene interaction via δ-backbonding. Depending on solvent and uranium starting material, both a tetrahydrofuran (THF)-bound and Lewis-base-free U(III) precursor can easily be prepared on the multigram scale. The reaction of these trivalent uranium species with nitrous oxide, NO, was studied and an X-ray diffraction (XRD) study on single crystals of the product revealed the formation of a five-coordinate U(V) oxo complex with two different molecular geometries, namely, square pyramidal and trigonal bipyramidal. © 2013 American Chemical Society.

Use of Anodic TiO2 Nanotube Layers as Mesoporous Scaffolds for Fabricating CH3NH3Pbl3 Perovskite-Based Solid-State Solar Cells - Salazar, Raul; Altomare, Marco; Lee, Kiyoung; Tripathy, Jyotsna; Kirchgeorg, Robin; Nguyen, Nhat Truong; Mokhtar, Mohamed; Alshehri, Abdelmohsen; Al-Thabaiti, Shaeel A.; Schmuki, Patrik (ChemElectroChem, 2015)
We optimize the deposition of CH3NH3PbI3 perovskite into mesoporous electrodes consisting of anodic TiO2 nanotube layers. By a simple spin-coating approach, complete filling of the tube scaffolds is obtained, which leads to interdigitated perovskite structures in conformal contact with the TiO2 tube counterparts. Such assemblies can be used as solid-state solar cells in a hole-transporting-material-free configuration, that is, the tube scaffold serves as electron collector and blocking layer, while the perovskite acts as visible-light absorber and hole-transporting material. We show that the complete filling of the tube scaffold with the perovskite is essential to improve the solar cell efficiency.
EAM Import::2019-03-12

Using carbon nanodots as inexpensive and environmentally friendly sensitizers in mesoscopic solar cells - Margraf, Johannes; Lodermeyer, Fabian; Strauß, Volker; Haines, Philipp; Walter, Johannes; Peukert, Wolfgang; Costa, Ruben Dario; Clark, Timothy; Guldi, Dirk Michael (Nanoscale Horizons, 2016)
We discuss the use of carbon nanodots (CNDs) as sensitizers in mesoscopic solar cells. The CNDs are synthesized using a one-step, bottom-up microwave approach with citric acid, urea, and formic acid as precursors in aqueous media. Their light-harvesting capabilities can be tuned by adjusting the synthetic parameters. Comprehensive spectroscopic and theoretical studies allow us to rationalize the nature of their absorption features. Promising power conversion efficiencies ( extgreekh) of 0.24% can be achieved from these cheap and eco-friendly sensitizers by optimizing the solar-cell assembly process. Interestingly, we found that extending the light absorption towards longer wavelengths does not necessarily improve the performance of the solar cells, since the longer-wavelength absorption features hardly contribute to the cells' photo-action spectra, so that the overall power conversion efficiency is actually worse. The origin of the lower performance is corroborated in transient absorption spectroscopy and photovoltage decay measurements. Our work points, on one hand, to the limits of as-synthesized CNDs as photosensitizers and, on the other hand, to possible improvements.

Using LIGGGHTS for performing DEM simulations of particles of complex shapes with the multisphere method - Ribeiro Parteli, Eric Josef (the 6th International Conference on Discrete Element Methods, 2013)
The multisphere method is commonly used as an approximation for modeling particles of complex geometric shapes in DEM simulations. However, typically the mass and moment of inertia of the resulting sphere clumps are incorrectly computed as a result of the (artifactual) contribution of the sphere-sphere overlaps. We adapted the current public release of LIGGGHTS in order to perform DEM simulations of rigid bodies using the mass and moment of inertia of the particles as obtained through an analytical (exact) metho

Using Supercritical Carbon Dioxide for Physical Foaming of Advanced Polymer Materials - Wolff, Friederich; Zirkel, Larissa; Sarah, Betzold; Jakob, Matthias; Verena, Maier; Nachtrab, Frank; Ceron Nicolat, Bruno; Fey, Tobias; Münstädt, Helmut (International Polymer Processing, 2011)
Foams from high performance polymers find more and more interest. The processes to generate them can be difficult, however. It is shown how physical foaming with CO2 can be used as a first step to assess the potentials of such materials. For investigations of such kind an autoclave on a laboratory scale which allows pressure variations up to 300 bars and temperatures up to 300 degrees C was set up. The samples are saturated with supercritical carbon dioxide (s.c. CO2) which acts as a foaming agent. Depending on the process and material parameters different foam characteristics and cell morphologies were obtained and characterised. The potential of this method is demonstrated for two different classes of advanced polymer materials, thermoplastic fluoropolymers (PEP), and a silicone resin. In the case of the fluoropolymer, previously prepared films were foamed and the effects of various process parameters on the foam characteristics were investigated. Besides the general potential of foams from fluoropolymers, they are candidates for polymeric piezoelectric materials with a relatively high temperature stability. Silicone polymers possess some properties superior to common organic polymers. First results on the foaming behaviour of a silicone resin are presented.

Vacuum Surface Science Meets Heterogeneous Catalysis: Dehydrogenation of a Liquid Organic Hydrogen Carrier in the Liquid State - Matsuda, Takashi; Taccardi, Nicola; Schwegler, Johannes; Wasserscheid, Peter; Steinrück, Hans-Peter; Maier, Florian (ChemPhysChem, 2015)
Ultrahigh vacuum (UHV) surface science techniques are used to study the heterogeneous catalytic dehydrogenation of a liquid organic hydrogen carrier in its liquid state close to the conditions of real catalysis. For this purpose, perhydrocarbazole (PH), otherwise volatile under UHV, is covalently linked as functional group to an imidazolium cation, forming a non-volatile ionic liquid (IL). The catalysed dehydrogenation of the PH unit as a function of temperature is investigated for a Pt foil covered by a macroscopically thick PH-IL film and for Pd particles suspended in the PH-IL film, and for PH-IL on Au as inert support. X-ray photoelectron spectroscopy and thermal desorption spectroscopy allows us to follow in situ the catalysed transition of perhydrocarbazole to carbazole at technical reaction temperatures. The data demonstrate the crucial role of the Pt and Pd catalysts in order to shift the dehydrogenation temperature below the critical temperature of thermal decomposition.
Keywords: heterogeneous catalysis; ionic liquids; liquid organic hydrogen carrier; surface science; x-ray photoelectron spectroscopy

Velocity distribution of a homogeneously driven two-dimensional granular gas - Scholz, Christian; Pöschel, Thorsten (Physical Review Letters, 2017)
The theory of homogeneously driven granular gases of hard particles predicts that the stationary state is characterized by a velocity distribution function with overpopulated high-energy tails as compared to the exponential decay valid for molecular gases. While this fundamental theoretical result was confirmed by numerous numerical simulations, an experimental confirmation is still missing. Using self-rotating active granular particles, we find a power-law decay of the velocity distribution whose exponent agrees well with the theoretic prediction.

Verification of Surface Tension in the Parallel Free Surface Lattice Boltzmann Method in waLBerla - Donath, Stefan; Mecke, Klaus; Rabha, Swapna; Buwa, Vivek; Rüde, Ulrich (Computers & Fluids, 2011)
The free surface lattice Boltzmann method in the parallel software framework waLBerla solves a wide range of two-phase flow scenarios efficiently by neglecting the gas flow and only taking the gas pressure into account. To obtain a good parallel efficiency, an extensive algorithm computes the curvature needed to calculate the surface tension pressure by using only a restricted set of neighboring data, reducing the communication effort. This, however, is assumed to be the main limitation of the accuracy of the surface tension computation. Nevertheless, this work shows that this method is able to simulate typical two-phase applications accurately enough. It is validated by comparing the evolution of capillary waves to analytical solution, and checking the agreement of a rising bubble's velocity with experiments. The results show that the method differs less than 10% from theory in the micro-scale, and lies well within the confidence interval of experimental measurements. © 2010 Elsevier Ltd.
UnivIS-Import:2015-04-14:Pub.2011.tech.IMMD.lsinfs.verifi_4
Keywords: Bubbly flows; Lattice Boltzmann method; Massively parallel; Surface tension

Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer - Heilmann, Martin; Munshi, A. Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T.; van Helvoort, Antonius T. J.; Yang, Jianfeng; Latzel, Michael; Hoffmann, Bjoern; Conibeer, Gavin; Weman, Helge; et al. (Nano Letters, 2016)
The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts.
Keywords: GaN; GaN-on-Si; graphene; MOVPE; nanorods

Very Facile Polarity Umpolung and Noncovalent Functionalization of Inorganic Nanoparticles: A Tool Kit for Supramolecular Materials Chemistry - Zeininger, Lukas; Petzi, Stefanie; Schönamsgruber, Jörg; Portilla Berlanga, Luis; Halik, Marcus; Hirsch, Andreas (Chemistry - A European Journal, 2015)
The facile assembly of shell-by-shell (SbS)-coated nanoparticles [TiO2 -PAC16 ]@shell 1-7 (PAC16 = hexadecylphosphonic acid), which are soluble in water and can be isolated as stable solids, is reported. In these functional architectures, an umpolung of dispersibility (organic apolar versus water) was accomplished by the noncovalent binding of ligands 1-7 to titania nanoparticles [TiO2 -PAC16 ] containing a first covalent coating with PAC16. Ligands 1-7 are amphiphilic and form the outer second shell of [TiO2 -PAC16 ]@shell 1-7. The tailor-designed dendritic building blocks 3-5 contain negative and positive charges in the same molecule, and ligands 6 and 7 contain a perylenetetracarboxylic acid dimide (PDI) core (6/7) as a photoactive reporter component. In the redox and photoactive system [TiO2 -PAC16 ]@shell 7, electronic communication between the inorganic core to the PDI ligands was observed.

Vibrational instabilities in resonant electron transport through single-molecule junctions - Härtle, Rainer; Thoss, Michael (Physical Review B, 2011)
We analyze various limits of vibrationally coupled resonant electron transport in single-molecule junctions. Based on a master equation approach, we discuss analytic and numerical results for junctions under a high bias voltage or weak electronic-vibrational coupling. It is shown that in these limits, the vibrational excitation of the molecular bridge increases indefinitely, i.e., the junction exhibits a vibrational instability. Moreover, our analysis provides analytic results for the vibrational distribution function and reveals that these vibrational instabilities are related to electron-hole pair creation processes. © 2011 American Physical Society.
UnivIS-Import:2015-03-09:Pub.2011.nat.dphy.ITP.ppem.vibrat

Vibrationally coupled electron transport in single-molecule junctions: The importance of electron-hole pair creation processes - Haertle, R.; Peskin, U.; Thoss, Michael (physica status solidi (b), 2013)
Vibrationally coupled electron transport through single-molecule junctions is considered. Reviewing our recent theoretical work, we show that electron-hole pair creation processes represent a key to understand the vibrational excitation characteristic of a single-molecule contact. Moreover, these processes can lead to a number of interesting transport phenomena such as, for example, negative differential resistance, rectification, mode-selective vibrational excitation, and a pronounced temperature dependence of the electrical current. Thus, electron-hole pair creation processes are crucial to elucidate the basic mechanisms of vibrationally coupled electron transport through a single-molecule contact, despite the fact that these processes do not directly contribute to the electrical current that is flowing through the junction. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.ITP.ppem.vibrat_4
Keywords: Electron-hole pair creation; Electronic-vibrational coupling; Molecular electronics; Nonequilibrium Greens-function theory; Vibrationally coupled electron transport

Vibrationally dependent electron-electron interactions in resonant electron transport through single-molecule junctions - Erpenbeck, André; Haertle, R.; Bockstedte, Michel Georg; Thoss, Michael (Physical Review B, 2016)
We investigate the role of electronic-vibrational coupling in resonant electron transport through single-molecule junctions, taking into account that the corresponding coupling strengths may depend on the charge and excitation state of the molecular bridge. Within an effective-model Hamiltonian approach for a molecule with multiple electronic states, this requires to extend the commonly used model and include vibrationally dependent electron-electron interaction. We use Born-Markov master equation methods and consider selected models to exemplify the effect of the additional interaction on the transport characteristics of a single-molecule junction. In particular, we show that it has a significant influence on local cooling and heating mechanisms, it may result in negative differential resistance, and it may cause pronounced asymmetries in the conductance map of a single-molecule junction.
UnivIS-Import:2017-12-18:Pub.2016.nat.dphy.ITP.ppem.vibrat

Vibrationally induced decoherence in single-molecule junctions - Härtle, Rainer; Thoss, Michael; et al. (Physical Review B, 2013)
We investigate the interplay of quantum interference effects and electronic-vibrational coupling in electron transport through single-molecule junctions, employing a nonequilibrium Green's function approach. Our findings show that inelastic processes lead, in general, to a quenching of quantum interference effects. This quenching is more pronounced for increasing bias voltages and levels of vibrational excitation. As a result of this vibrationally induced decoherence, vibrational signatures in the transport characteristics of a molecular contact may strongly deviate from a simple Franck-Condon picture. This includes signatures in both the resonant and the nonresonant transport regimes. Moreover, it is shown that local cooling by electron-hole pair creation processes can influence the transport characteristics profoundly, giving rise to a significant temperature dependence of the electrical current. © 2013 American Physical Society.
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.ITP.ppem.vibrat

Vibrational sum-frequency generation at protein modified air–water interfaces: Effects of molecular structure and surface charging - Engelhardt, Kathrin; Peukert, Wolfgang; Braunschweig, Björn (Current Opinion in Colloid & Interface Science, 2014)
Protein and surfactant modified air–water interfaces are an important model system for colloid science as many applications for example aqueous foams in food products rely on our knowledge and ability to tune molecular structures at these interfaces. That is because interfaces are a fundamental building block in the hierarchical structure of foam, where in fact the molecular level can determine properties on larger length scales. For that reason it is of great importance to increase our ability to study air–water interfaces with molecular level probes and to obtain not only information on coverage but also direct information on interfacial composition, molecular order, orientations as well as information on the charged state of an interface. Vibrational sum-frequency generation (SFG) is a powerful tool that can help to address these issues and is inherently surface sensitive. In this contribution we will review recent developments in the use of SFG for studies of biomolecules at aqueous interfaces and discuss current issues with the interpretation of SFG spectra from electrified interfaces. In order to guide interpretations from interface spectroscopy we invoke the use of complementary methods such as ellipsometry and zetapotential measurements of bulk molecules.
Keywords: Surfactants; Interface spectroscopy; Foam; Sum-frequency generation; Proteins

Vinyl spacers - Tuning electron transfer through fluorene-based molecular wires - Wielopolski, Mateusz; Santos, José; Illescas, Beatriz M.; Ortiz, Alejandro; Insuasty, Braulio; Bauer, Thilo; Clark, Timothy; Guldi, Dirk Michael; Martín, Nazario (Energy and Environmental Science, 2011)
Rigid and soluble electron donor-acceptor conjugates (3 and 11) that combine π-extended tetrathiafulvalene (exTTF) as an electron donor and C as an electron acceptor have been synthesized using oligo-vinylfluorene (oFV) linkers to connect the electroactive entities. Fluorescence and transient absorption measurements confirm that light-induced excitation induces charge-transfer reactions over distances of 28 in THF. The incorporation of vinylene spacers into oligofluorene molecular wires has been shown both experimentally and theoretically to improve the charge-transfer features significantly to give a β value of 0.075 ± 0.001 . Enhanced π-conjugation caused by higher orbital overlap is responsible for this trend. © 2011 The Royal Society of Chemistry.

Virial Coefficients and Equations of State for Hard Polyhedron Fluids - Irrgang, M. Eric; Engel, Michael; Schultz, Andrew J.; Kofke, David A.; Glotzer, Sharon C. (Langmuir, 2017)
Hard polyhedra are a natural extension of the hard sphere model for simple fluids, but there is no general scheme for predicting the effect of shape on thermodynamic properties, even in moderate-density fluids. Only the second virial coefficient is known analytically for general convex shapes, so higher-order equations of state have been elusive. Here we investigate high-precision state functions in the fluid phase of 14 representative polyhedra with different assembly behaviors. We discuss historic efforts in analytically approximating virial coefficients up to B4 and numerically evaluating them to B8. Using virial coefficients as inputs, we show the convergence properties for four equations of state for hard convex bodies. In particular, the exponential approximant of Barlow et al. (J. Chem. Phys. 2012, 137, 204102) is found to be useful up to the first ordering transition for most polyhedra. The convergence behavior we explore can guide choices in expending additional resources for improved estimates. Fluids of arbitrary hard convex bodies are too complicated to be described in a general way at high densities, so the high-precision state data we provide can serve as a reference for future work in calculating state data or as a basis for thermodynamic integration.
EAM Import::2019-03-12

Viscoelastic properties of a silicone resin during crosslinking - Wolff, Friedrich; Kugler, Christoph; Münstedt, Helmut (Rheologica Acta, 2011)
Viscoelastic properties of a silicone resin crosslinked at various extents were characterised by means of rheology. The influence of temperature on the viscoelastic properties of the material as-delivered and in a state pre-crosslinked approximately to the gel point has been investigated by dynamic-mechanical measurements. While the glass transition temperature is increased by the crosslinking, no changes of the free volume fraction at Tg and its thermal expansion coefficient were observed. Taking the different glass transition temperatures into account, it could be shown that the corresponding WLF-parameters are the same. Themolar mass and, hence, the viscosity of the material can be increased by a heat treatment. The dependence of the zero shear-rate viscosity on the weight average molar mass indicates that the existence of entanglements of the polymer molecules is not very probable.
EAM Import::2019-03-12

Viscosity and Softening Behavior of Alkali Zinc Sulfophosphate Glasses - Da, Ning; Krolikowski, Sebastian; Nielsen, Karsten H.; Kaschta, Joachim; Wondraczek, Lothar (Journal of the American Ceramic Society, 2010)
We report on the softening properties and viscosity of glasses from the system ZnO–Na_2O–SO_3–P_2O5 for low-temperature sealing applications. Up to a ratio of network-forming ions PO_43-:SO_42- of about 2:1, a gradual substitution of P_2O5 by SO_3 results in decreasing glass transition and softening temperatures. At the same time, decreasing kinetic fragility is observed, noteworthy even for decreasing the total amount of network former from 44 at.% to 39 at.%. Thermomechanical and calorimetric analyses reveal a distinct SO_42–promoted relaxation phenomenon at temperatures significantly below the macroscopic glass transition temperature, which is interpreted as a result of the formation of an increasingly interconnected assembly of SO_42- and PO_43- units with increasing SO_3 content.
EAM Import::2019-03-12

Viscosity, Interfacial Tension, Density, and Refractive Index of Ionic Liquids [EMIM][MeSO3], [EMIM][MeOHPO2], [EMIM][OcSO(4)], and [BBIM][NTf2] in Dependence on Temperature at Atmospheric Pressure - Hasse, Benjamin; Lehmann, Julia; Assenbaum, Daniel; Wasserscheid, Peter; Leipertz, Alfred; Fröba, Andreas Paul (Journal of Chemical and Engineering Data, 2009)
This work represents a continuation of former investigations, where viscosity, interfacial tension, density, and refractive index of ionic liquids (ILs) [EMIM][EtSO4] (1-ethyl-3-methylimidazolium ethylsulfate), [EMIM][NTf2] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), [EMIM][N(CN)(2)] (1-ethyl-3-methylimidazolium dicyanamide), and [OMA][NTf2)] (trioctylmethylammonium bis(trifluoromethylsulfonyl)imide) were studied. Here, the ILs [EMIM][MeSO3] (1-ethyl-3-methylimidazolium methanesulfonate), [EMIM][MeOHPO2] (1-ethyl-3-methylimidazolium methylphosphonate), [EMIM][OcSO(4)] (1-ethyl-3-methylimidazolium octylsulfate), and [BBIM][NTf2] (1-butyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide) were investigated again both by conventional techniques and by surface light scattering (SLS). An Abbe refractometer was used for the measurement of the refractive index in the range of (283.15 to 313.15) K with an expanded uncertainty (k = 2) of about 0.0005. The density was measured between (273.15 and 313.15) K with a vibrating tube densimeter and an expanded uncertainty (k = 2) of about 0.02%. The interfacial tension was obtained from the pendant drop technique at a temperature of 293.15 K with an expanded uncertainty (k = 2) of 1%. On the basis of this datum and the temperature dependence of density, the interfacial tension for all relevant temperatures was estimated via an appropriate prediction model. For the ILs studied within this work, at a first-order approximation, the quantity directly accessible by SLS was the ratio of dynamic viscosity to surface tension. Combining the results from SLS with values for density and interfacial tension from conventional methods, the dynamic viscosity could be obtained from (273.15 to 333.15) K with an estimated expanded uncertainty (k = 2) of less than 3%. Besides a comparison with the literature, the major aim of this work was to point out the influence of variations of the anion on thermophysical properties of [EMIM](+)-based ILs. In addition, the effect of different cations was studied in ILs with the [NTf2](-) anion. ILs with equal cations and similar anions can still exhibit different properties, which is interpreted with relevant molecular interactions.

Visible-light-induced photocatalysis using self-organized TiO 2 nanotubes decorated with AgBr deposits - Shrestha, Nabeen Kumar; Yang, Mingjun; Paramasivam, Indhumati; Schmuki, Patrik (Semiconductor Science and Technology, 2011)
Self-organized TiO2 nanotubes formed anodically in fluoride ion containing electrolyte were loaded with AgBr clusters from a precipitation reaction bath. The photoactivities of these nanotubes for decomposition of an azo dye were investigated under visible light irradiation and compared with those of the N-doped self-organized TiO2 nanotubes and neat TiO2 nanotubes. Compared with the N-doped nanotubes, the AgBr-loaded nanotubes demonstrate a significantly higher visible-light-driven photocatalytic activity—even higher than for neat nanotubes irradiated with UV light.
EAM Import::2019-03-12

Visible light photo response from N-doped anodic niobium oxide after annealing in ammonia atmosphere - Ruff, T.; Hahn, Robert; Killian, M. S.; Asoh, H.; Ono, S.; Schmuki, Patrik (Electrochimica Acta, 2012)
Niobium oxide films with a thickness of approximately 165 nm were prepared by electrochemical anodization. These anodic oxide layers were then treated in an ammonia atmosphere at different temperatures and durations, and characterized with XRD, XPS, ToF-SIMS and photoelectrochemical methods. Under optimized conditions nitrogen doping of the niobium oxide films takes place, resulting in a distinct photo response in the visible range of light.
EAM Import::2019-03-13

Visible-Light-Triggered Drug Release from TiO2 Nanotube Arrays: A Controllable Antibacterial Platform - Xu, Jingwen; Zhou, Xuemei; Gao, Zhida; Song, Yan-Yan; Schmuki, Patrik (Angewandte Chemie International Edition, 2016)
In this work, we use a double-layered stack of TiO2 nanotubes (TiNTs) to construct a visible-light-triggered drug delivery system. The key for visible light drug release is a hydrophobic cap on the nanotubes containing Au nanoparticles (AuNPs). The AuNPs allow for a photocatalytic scission of the hydrophobic chain under visible light. To demonstrate this principle, we loaded ampicillin (AMP) into the lower part of the TiO2 nanotube stack, triggered visible-light-induced release, and carried out antibacterial studies. The release from the platform becomes most controllable if the drug is silane-grafted in the hydrophilic bottom layer for drug storage. Thus, visible light photocatalysis can also determine the release kinetics of the active drug from the nanotube wall.
EAM Import::2019-03-12

Visualization of defect densities in reduced graphene oxide - Eigler, Siegfried; Dotzer, Christoph; Hirsch, Andreas (Carbon, 2012)
Efficiently reducible graphene oxide (GO) was obtained, even if a high degree of functionalization is present. Graphite with few defects was used as starting material and oxidized according to Hummer's method. An extremely high I /I ratio for rGO of 2.8 (532 nm) was observed in the Raman spectrum as a consequence of the lower defect density in GO. It was also possible to demonstrate the impact of local defects on the structure in rGO by local laser exposure experiments on single graphene oxide flakes. Raman spectroscopy can visualize the laser impact by I /I ratio measurements. © 2012 Elsevier Ltd. All rights reserved.

Visualizing Single-Cell Secretion Dynamics with Single-Protein Sensitivity - McDonald, Matthew; Gemeinhardt, André; König, Katharina; Piliarik, Marek; Schaffer, Stefanie; Völkl, Simon; Aigner, Michael; Mackensen, Andreas; Sandoghdar, Vahid (Nano Letters, 2017)
Cellular secretion of proteins into the extracellular environment is an essential mediator of critical biological mechanisms, including cell-to-cell communication, immunological response, targeted delivery, and differentiation. Here, we report a novel methodology that allows for the real-time detection and imaging of single unlabeled proteins that are secreted from individual living cells. This is accomplished via interferometric detection of scattered light (iSCAT) and is demonstrated with Laz388 cells, an Epstein-Barr virus (EBV)-transformed B cell line. We find that single Laz388 cells actively secrete IgG antibodies at a rate of the order of 100 molecules per second. Intriguingly, we also find that other proteins and particles spanning ca. 100 kDa-1 MDa are secreted from the Laz388 cells in tandem with IgG antibody release, likely arising from EBV-related viral proteins. The technique is general and, as we show, can also be applied to studying the lysate of a single cell. Our results establish label-free iSCAT imaging as a powerful tool for studying the real-time exchange between cells and their immediate environment with single-protein sensitivity.
EVALuna2:25781

Voltage-Induced Payload Release and Wettability Control on TiO2 and TiO2 Nanotubes - Song, Yanyan; Roy, Poulomi; Paramasivam, Indhumati; Schmuki, Patrik (Angewandte Chemie International Edition, 2010)
Please release me: Hydrocarbon monolayers attached to a TiO_2 surface can be cut by electrochemical means, thus allowing active molecules or proteins to be released from the TiO_2 surface (see picture). Requirements are suitable electronic properties of TiO_2 combined with a voltage to cause Schottky barrier breakdown; valence band holes are then sufficiently reactive to generate OH. radicals.
EAM Import::2019-03-12

WaLBerla: Exploiting Massively Parallel Systems for Lattice Boltzmann Simulations - Feichtinger, Christian; Götz, Jan; Donath, Stefan; Iglberger, Klaus; Rüde, Ulrich (Parallel Computing. Numerics, Applications, and Trends., 2009)
In this chapter, a software concept for massively parallel computational fluid dynamics (CFD) applications is introduced. The focus thereby lies on the parallelization, which is based on a domain partitioning scheme named patch concept. This concept also enables a seamless specialization of the partitions to different application features as well as the possibility for further optimization such as memory reduction. It is discussed in detail how our design ensures an efficient and flexible implementation. The suitability and efficiency of this concept is demonstrated and evaluated with the waLBerla project, which aims at the development of an efficient massively parallel lattice Boltzmann framework providing the necessary features for several CFD applications. To discuss the suitability of the parallelization for massively parallel usage, various test scenarios have been investigated on different architectures. These tests include serial, weak and strong scaling experiments up to 810 cores and up to a domain size of 15303 lattice cells. © 2009 Springer London.
UnivIS-Import:2015-04-16:Pub.2009.tech.IMMD.lsinfs.walber_1

WaLBerla: HPC software design for computational engineering simulations - Feichtinger, Christian; Donath, Stefan; Köstler, Harald; Götz, Jan; Rüde, Ulrich (Journal of Computational Science, 2011)
WaLBerla (Widely applicable Lattice-Boltzmann from Erlangen) is a massively parallel software framework supporting a wide range of physical phenomena. This article describes the software designs realizing the major goal of the framework, a good balance between expandability and scalable, highly optimized, hardware-dependent, special purpose kernels. To demonstrate our designs, we discuss the coupling of our Lattice-Boltzmann fluid flow solver and a method for fluid structure interaction. Additionally, we show a software design for heterogeneous computations on GPU and CPU utilizing optimized kernels. Finally, we estimate the software quality of the framework on the basis of software quality factors. © 2011 Elsevier B.V.
UnivIS-Import:2015-03-09:Pub.2011.tech.IMMD.lsinfs.walber_6
Keywords: Lattice-Boltzmann method; MPI; Software Engineering; Software Quality

waLBerla: Optimization for Itanium-based Systems with Thousands of Processors - Donath, Stefan; Götz, Jan; Feichtinger, Christian; Iglberger, Klaus; Rüde, Ulrich (High Performance Computing in Science and Engineering Garching-Munich 2009, 2010)
Performance optimization is an issue at different levels, in particular for computing and communication intensive codes like free surface lattice Boltzmann. This method is used to simulate liquid-gas flow phenomena such as bubbly flows and foams. Due to a special treatment of the gas phase, an aggregation of bubble volume data is necessary in every time step. In order to accomplish efficient parallel scaling, the all-to-all communication schemes used up to now had to be replaced with more sophisticated patterns that work in a local vicinity. With this approach, scaling could be improved such that simulation runs on up to 9152 processor cores are possible with more than 90% efficiency. Due to the computation of surface tension effects, this method is also computational intensive. Therefore, also optimization of single core performance plays a tremendous role. The characteristics of the Itanium processor require programming techniques that assist the compiler in efficient code vectorization, especially for complex C++ codes like the waLBerla framework. An approach using variable length arrays shows promising results.
UnivIS-Import:2015-04-16:Pub.2010.tech.IMMD.lsinfs.walber

Wasserstoff, chemisch gespeichert - Papp, Christian; Wasserscheid, Peter; Libuda, Jörg; Steinrück, Hans-Peter (Nachrichten aus der Chemie, 2014)
Ein Ansatz, Energie chemisch zu speichern, sind flüssige organische Wasserstoffträger. Die Oberflächenforschung leistet Beiträge zum mechanistischen Verständnis der katalytischen Wasserstofffreisetzung und zieht Schlussfolgerungen für die praktische Anwendung solcher Techniken.

Water Chemistry on Model Ceria and Pt/Ceria Catalysts - Lykhach, Yaroslava; Johanek, Viktor; Aleksandrov, Hristiyan A.; Kozlov, Sergey M.; Happel, Markus; Skala, Tomas; St Petkov, Petko; Tsud, Nataliya; Vayssilov, Georgi N.; Prince, Kevin C.; Neyman, Konstantin M.; Matolin, Vladimir; et al. (Journal of Physical Chemistry C, 2012)
We have studied the interaction of water with stoichiometric CeO2(111)/Cu(111), partially reduced CeO2-x/Cu(111), and Pt/CeO2/Cu(111) model catalysts by means of synchrotron-radiation photoelectron spectroscopy (SRPES), resonant photoemission spectroscopy (RPES) at the Ce 4d edge, infrared reflection absorption spectroscopy (IRAS), and density functional (DF) calculations. The principal species formed during adsorption of water at 160 K on CeO2(111) films is chemisorbed molecular water. On the surface of CeO2-x water partially dissociates yielding hydroxyl groups. By use of core-level PES, differentiation between chemisorbed water and hydroxyl groups is complicated by the overlap of the corresponding spectral features. Nevertheless, we determined three characteristic indicators for OH groups on ceria: (i) the presence of 1 pi and 3 sigma states in valence band (VB) PES; (ii) an increase of the binding energy (BE) separation between the O 1s spectral components of lattice oxygen and OH/H2O; (iii) an increase of the amplitude of the Ce3+ resonance in RPES. Chemisorbed water desorbs below 400 K and hydroxyl groups vanish at 500 K. The most favorable configurations of chemisorbed water and hydroxyl groups have been investigated by DF calculations. Both CeO2(111) and CeO2-x involve strongly tilted H2O and OH species which complicate their detection by IRAS. On Pt/CeO2, water adsorbs molecularly at 160 K but undergoes partial dissociation during annealing. The dissociation of water is accompanied by spillover of hydrogen to ceria and formation of hydroxyl groups between 180 and 250 K. Above 250 K, decomposition of hydroxyl groups and reverse spillover of hydrogen from ceria to Pt occurs, followed by desorption of molecular water.

Water on Atomically-Defined Cobalt Oxide Surfaces Studied by Temperature-Programmed IR Reflection Absorption Spectroscopy and Steady State Isotopic Exchange - Schwarz, Matthias; Mohr, Susanne; Hohner, Chantal; Werner, Kristin; Xu, Tao; Libuda, Jörg (Journal of Physical Chemistry C, 2018)
In this work, we investigate the interaction of water with three different atomically defined cobalt oxide surfaces under ultrahigh vacuum (UHV) conditions using time-resolved and temperature-programmed infrared reflection–absorption spectroscopy (TR-IRAS, TP-IRAS) in combination with isotopic exchange experiments. The three surfaces, CoO(100), CoO(111), and Co3O4(111), are prepared in form of well-ordered films on Ir(100). Very different behavior is observed on the three surfaces, both with respect to D2O adsorption and desorption. On CoO(100), water adsorbs molecularly. It forms extended ice clusters even at low adsorption temperature (200 K) and which desorb molecularly at 200 K (Ea,des ∼ 60 kJ·mol–1). A very small amount of defect sites is observed at which D2O dissociates and forms strongly bound OD groups. On CoO(111), the interaction with ordered facets is very weak and no adsorption occurs at these sites at 200 K. The CoO(111) films expose, however, a higher density of defects as compared to the CoO(100) films, at which D2O dissociates and forms strongly bound OD species with desorption temperatures of 455 ± 10 and 620 ± 10 K, respectively. In contrast to the above cases, water interacts strongly with the Co3O4(111) surface. At 200 K, D2O dissociates readily and forms a partially dissociated (D2O)n(OD)m network. With increasing temperature, the (D2O)n(OD)m network breaks up into (D2O)n(OD)m clusters the size of which decreases with increasing temperature. Desorption of molecular D2O occurs over a broad temperature range from 210 to 470 K (Ea,des ∼ 60 to ∼ 140 kJ·mol–1). Above 470 K, only isolated OD species reside on the surface which desorb at 540 ± 20 K. Isotopic exchange experiments with D2O and H2O on Co3O4(111) show that isotopic scrambling in the (D2O)n(OD)m clusters is slow in comparison to exchange with the gas phase and that the clusters are composed of distinct species that show different exchange rates with the gas phase. The structure-dependent differences regarding the interaction with D2O are rationalized in terms of the surface termination and coordination environment of the surface ions on the three different surfaces.
EAM Import::2019-03-12

Waveguide Bragg gratings in Ormocer hybrid polymers - Frey, Lothar; Förthner, Michael; Hellmann, Ralf; Rommel, Matthias; Girschikofsky, Maiko Girschikofsky (Optics Express, 2016)
We report on the fabrication of Bragg gratings within rib-type waveguides of previously UV-cured inorganic-organic Ormocer hybrid polymers by applying the interferometric phase mask technique in conjunction with deep-UV laser radiation. The fabrication process as well as the influence of the applied laser fluence and the length of the Bragg grating on the characteristics of the Bragg grating's transmission and reflection spectra are discussed and compared to numerical simulations and calculations. Depending on the applied laser fluence and the chosen grating length, waveguide Bragg gratings with strong reflectivities of up to 98% and narrow bandwidths of down to 120 pm have been achieved. (C) 2016 Optical Society of America

Wavelength Dependent Haze of Transparent Glass-Particle Filled Poly(Methyl Methacrylate) Composites - Wildner, Wolfgang; Drummer, Dietmar (ISRN Optics, 2014)
Glass particles as filler were incorporated in a poly(methyl methacrylate) matrix. The refractive indexes of both materials match at a wavelength of about 400 nm. The effect of particle volume fraction on the light transmittance and light scattering (haze) in dependence of the refractive index difference was studied. The curve shape of the haze in dependence of the wavelength is comparable to that of the refractive index difference, but the base line of the haze increases with the filling grade. This indicates that there are other scattering or absorbing mechanisms, like defects in the filler binding.
UnivIS-Import:2015-03-09:Pub.2014.tech.FT.FT-KT.wavele

Waves in metamaterials - Solymar, Laszlo; Shamonina, Ekaterina (Waves in Metamaterials, 2009)
Metamaterials is a young subject born in the 21st century. It is concerned with artificial materials which can have electrical and magnetic properties difficult or impossible to find in nature. The building blocks in most cases are resonant elements much smaller than the wavelength of the electromagnetic wave. The book offers a comprehensive treatment of all aspects of research in this field at a level that should appeal to final year undergraduates in physics or in electrical and electronic engineering. The mathematics is kept at a minimum; the aim is to explain the physics in simple terms and enumerate the major advances. It can be profitably read by graduate and post-graduate students in order to find out what has been done in the field outside their speciality, and by experts who may gain new insight about the inter-relationship of the physical phenomena involved.
EAM Import::2019-03-12

Wet Chemical Synthesis of Graphene - Eigler, Siegfried; Enzelberger-Heim, Michael; Grimm, Stefan; Hofmann, Philipp; Kroener, Wolfgang; Geworski, Andreas; Dotzer, Christoph; Röckert, Michael; Xiao, Jie; Papp, Christian; Lytken, Ole; Steinrück, Hans-Peter; et al. (Advanced Materials, 2013)
A suitable technology for the preparation of graphene based on versatile wet chemistry is presented for the first time. The protocol allows the wet chemical synthesis of graphene from a new form of graphene oxide that consists of an intact hexagonal extgreeks-framework of C-atoms. Thus, it can be easily reduced to graphene that is no longer dominated by defects.

Wet chemistry of graphene - Malig, Jenny; Englert, Jan; Hirsch, Andreas; Guldi, Dirk Michael (Electrochemical Society Interface, 2011)
A variety of sophisticated approaches have been established to obtain stable dispersions of graphene. The use of graphite as starting material for the top-down preparation of graphene offers a cost-efficient and environmentally-friendly alternative to low-dimensional nanocarbon. When in van der Waals contact, graphene sheets are subjected to very efficient π-π stacking interactions, minimizing the surface energy. An alternative approach to stabilize graphene sheets in solution is ultrasonic treatment in organic solvents. The use of amphiphilic π-systems increases the driving force and renders the exfoliation process more dominant in terms of monolayer graphene. Functionalization is certainly a crucial step not only for stabilizing the graphene sheets, but also for harvesting the material's full potential by tuning electron-donor and electron acceptor systems in solution-based processes.

Wettability of Low Weight Borides by Commercial Aluminum Alloys − A Basis for Metal Matrix Composite Fabrication - Plötz, Steven; Nowak, Rafal; Lohmüller, Andreas; Sobzcak, Natalia; Singer, Robert (Advanced Engineering Materials, 2016)
Boron compounds are promising candidates for reinforcement of metals because of their high strength and stiffness at low specific weight. For composite fabrication the wetting behavior is important. Isothermal wetting of BC, AlB, CaB, MgB, and TiB by liquid pure aluminum (99.5%) and the alloy AlSi10MgMn is studied at 700 °C for 15 min in vacuum using the dispensed drop method. No wetting occurs during testing for all substrates. The contact angles remain constant for CaB, MgB, and TiB, while for AlB and BC substrates a continuous decrease in contact angle value with time is observed.

What is the effective impact of the explosive orbital growth in discrete-time one-dimensional polynomial dynamical systems? - Gallas, Jason; Brison, Owen J. (Physica A-Statistical Mechanics and Its Applications, 2014)
We study the distribution of periodic orbits in one-dimensional two-parameter maps. Specifically, we report an exact expression to quantify the growth of the number of periodic orbits for discrete-time dynamical systems governed by polynomial equations of motion of arbitrary degree. In addition, we compute high-resolution phase diagrams for quartic and for both normal forms of cubic dynamics and show that their stability phases emerge all distributed in a similar way, preserving a characteristic invariant ordering. Such coincidences are remarkable since our exact expression shows the total number of orbits of these systems to differ dramatically by more than several millions, even for quite low periods. All this seems to indicate that, surprisingly, the total number and the distribution of stable phases is not significantly affected by the specific nature of the nonlinearity present in the equations of motion.

When Fewer Photons Do More: A Comparative O2 Photoadsorption Study on Vapor-Deposited TiO2 and ZrO2 Nanocrystal Ensembles - Siedl, Nicolas; Elser, Michael J.; Halwax, Erich; Bernardi, Johannes; Diwald, Oliver (Journal of Physical Chemistry C, 2009)
The charge separation properties of TiO_2 and ZrO_2 nanocrystal powders which were produced by metal organic chemical vapor phase deposition were compared by means of O_2 photoadsorption. Prior to the UV excitation experiments, we carefully explored the structure and morphology as well as the spectroscopic properties of the dehydroxylated nanoparticles in controlled gas atmospheres using UV diffuse reflectance, FT-IR, and electron paramagnetic resonance spectroscopy. On the basis of this information, we utilized the photogeneration of surface-adsorbed O_2- radicals and their detection by EPR spectroscopy to quantify the concentration of separated charges and to relate these figures to the number of oxide particles that were exposed to known numbers of UV photons with defined energies. The results presented in this study reveal that upon band-gap excitation, ZrO_2 nanoparticles are by 2 orders of magnitude more efficient in oxygen-assisted charge separation than TiO_2. The dramatically diminished charge separation yield in TiO_2 is attributed to the existence of deep trap states which persistently stabilize paramagnetic holes and at the same time act as recombination centers. Their absence in ZrO_2 nanocrystals gives rise to a comparable performance in terms of photoadsorbed O_2 and essentially compensates for the significantly wider optical band gap in relation to TiO_2.
EAM Import::2019-03-12

WO3/TiO2 Nanotubes with Strongly Enhanced Photocatalytic Activity - Paramasivam, Indhumati; Nah, Yoon-Chae; Das, Chittaranjan; Shrestha, Nabeen Kumar; Schmuki, Patrik (Chemistry - A European Journal, 2010)
Mixed oxide photocatalysts: WO_3- containing TiO_2 nanotubes were prepared by self-organizing electrochemical anodization of TiW alloys (Ti 0.2 W see figure, and Ti 9 W). It is shown that a content of only 0.2 at % WO_3 with respect to the titania nanotubes leads to a very significant increase of the photocatalytic reaction rate compared not only to pure anatase TiO_2 nanotubes, but also in comparison with any other modified TiO_2 nanotube system reported up to now.
EAM Import::2019-03-12

X-ray based methods for non-destructive testing and material characterization - Hanke, Randolf; Fuchs, Theobald; Uhlmann, Norman (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2008)
The increasing complexity and miniaturization in the field of new materials as well as in micro-production requires in the same way improvements and technical advances in the field of micro-NDT to provide better quality data and more detailed knowledge about the internal structures of micro-components. Therefore, non-destructive methods like radioscopy, ultrasound, optical or thermal imaging increasingly gain in importance with respect to ongoing product and material development in the different phases like material characterization, production control or module reliability testing. Because of the manifold different application fields, i.e., certain physical NDT methods applied to material inspection, characterization or reliability testing, this contribution will focus on the radioscopic-based methods related to their most important applications. Today, in modern industrial quality control, X-ray transmission is used in two different ways: • Two-dimensional radioscopic transmission imaging (projection technique), usually applied to inline inspection tasks in application fields like lightweight material production, electronic component soldering or food production. • Computed tomography (CT) for generation of three-dimensional data, representing spatial information and density distribution of objects. CT application fields are on the one hand the understanding of production process failure or component and module inspection (completeness) and on the other hand the dimensional measuring of hidden geometrical outlines (metrology). This paper demonstrates the methods including technical set-ups (X-ray source and detector), imaging and reconstruction results and the methods for high speed and high-resolution volume data generation and evaluation.
EAM Import::2019-03-12

X-ray dynamic defectoscopy utilizing digital image correlation - Jandejsek, Ivan; Nachtrab, Frank; Uhlmann, Norman; Vavrik, Daniel (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2010)
This paper presents the utilization of the image processing technique known as digital image correlation for X-ray dynamic defectoscopy purpose. Digital image correlation is a non-contact technique (optical or X-ray) that provides full-field and high resolution measurement of deformation fields within an object subjected to loading. In this case it was used for crack detection in a bar specimen subjected to tension loading.
EAM Import::2019-03-12

X-ray induced photocatalysis on TiO2 and TiO2 nanotubes: Degradation of organics and drug release - Schmidt-Stein, F.; Gnichwitz, Jan-Frederik; Salonen, J.; Hahn, Robert; Hirsch, Andreas; Schmuki, Patrik; et al. (Electrochemistry Communications, 2009)
The photocatalytic activity of titanium dioxide under X-ray radiation is of great interest for biomedical applications. In the present work we explore the use of compact TiO layers and TiO nanotubes for X-ray induced photocatalysis, in particular the degradation of organics and monolayer chain scission for drug release. The radiation was done with a conventional X-ray source and doses up to 50 × 10 J/kg. The results show the feasibility of X-ray catalysis on TiO and X-ray induced monolayer chain scission by the release of surface attached Zn-porphyrin molecules. Furthermore, a higher efficiency for anatase films and nanotubes is obtained than for amorphous morphologies. © 2009 Elsevier B.V. All rights reserved.

Zeolite/aluminum composite adsorbents for application in adsorption refrigeration - Bauer, J.; Herrmann, R.; Mittelbach, W.; Schwieger, Wilhelm; et al. (International Journal of Energy Research, 2009)
Thermally driven adsorption refrigerators, which transform available low-temperature waste heat (from processes, engines, solar radiation, district heat) into useful cooling energy, are a very promising and green technology to reduce the demand for primary energy. To improve their refrigeration performance, new zeolite/aluminum composite adsorbents with optimized sorption and heat transfer properties were prepared following the partial support transformation technique. A direct and binderless contact between the closed zeolite layer and the metal could be established which enables best thermal diffusivity. It is shown by measurements of thermal sorption capacities and kinetics on planar samples and on coated heat exchangers that this causes best sorption performance combined with high mechanical stability.
EAM Import::2019-03-12

Zeolite-Coated Porous Arrays: A Novel Strategy for Enzyme Encapsulation - Marthala, Venkata; Friedrich, Mona; Zhou, Zhou; Distaso, Monica; Reuß, Stephanie; Al-Thabaiti, Shaeel A.; Peukert, Wolfgang; Schwieger, Wilhelm; Hartmann, Martin (Advanced Functional Materials, 2015)
Zeolite Beta-coated stainless steel supports with gradient porosity are employed as filter-panels for lipase encapsulation. Enzyme encapsulation on the stainless steel porous discs is achieved via vacuum infiltration. Subsequently, two lipase-encapsulated zeolite Beta-coated stainless steel discs are attached using an adhesive. The zeolite Beta layer on the stainless steel discs largely prevents lipase leaching in comparison to the stainless steel discs without a zeolite layer. The activity of the lipase-encapsulated, attached zeolite Beta-coated stainless steel porous discs depends on the thickness of the zeolite Beta layer. It is shown that the biocatalytic performance of the lipase-encapsulated, attached zeolite Beta-coated stainless steel supports with a zeolite Beta layer thickness of ≈0.7–1 μm is better than the lipase-encapsulated, attached zeolite Beta-coated stainless steel supports with a zeolite Beta layer thickness of ≈2–3 μm in the lipase-catalyzed transesterification of vinyl propionate with 1-butanol using n-hexane as solvent.

Zeolitic Materials with Hierarchical Porous Structures - Lopez Orozco, Sofia; Inayat, Amer; Schwab, Andreas; Selvam, Thangaraj; Schwieger, Wilhelm (Advanced Materials, 2011)
During the past several years, different kinds of hierarchical structured zeolitic materials have been synthesized due to their highly attractive properties, such as superior mass/heat transfer characteristics, lower restriction of the diffusion of reactants in the mesopores, and low pressure drop. Our contribution provides general information regarding types and preparation methods of hierarchical zeolitic materials and their relative advantages and disadvantages. Thereafter, recent advances in the preparation and characterization of hierarchical zeolitic structures within the crystallites by post-synthetic treatment methods, such as dealumination or desilication; and structured devices by in situ and ex situ zeolite coatings on open-cellular ceramic foams as (non-reactive as well as reactive) supports are highlighted. Specific advantages of using hierarchical zeolitic catalysts/structures in selected catalytic reactions, such as benzene to phenol (BTOP) and methanol to olefins (MTO) are presented.

Zig-zag networks of self-excited periodic oscillations in a tunnel diode and a fiber-ring laser - Francke, Ricardo; Pöschel, Thorsten; Gallas, Jason (Physical Review E, 2013)
We report numerical evidence showing that periodic oscillations can produce unexpected and wide-ranging zig-zag parameter networks embedded in chaos in the control space of nonlinear systems. Such networks interconnect shrimplike windows of stable oscillations and are illustrated here for a tunnel diode, for an erbium-doped fiber-ring laser, and for the Hénon map, a proxy of certain CO lasers. Networks in maps can be studied without the need for solving differential equations. Tuning parameters along zig-zag networks allows one to continuously modify wave patterns without changing their chaotic or periodic nature. In addition, we report convenient parameter ranges where such networks can be detected experimentally. © 2013 American Physical Society.

Zinc oxide scaffolds on MgO nanocubes - Stankic, Slavica; Sternig, Andreas; Finocchi, Fabio; Bernardi, Johannes; Diwald, Oliver (Nanotechnology, 2010)
Powders of isolated and well-dispersed oxide nanocubes are promising components for photoelectronic applications that benefit from tunable optical properties, surface reactivity and the ease of realization of their controlled assembly. Here, we demonstrate that combustion of zinc and magnesium metal vapors at reduced pressures followed by subsequent vacuum annealing of the resulting nanoparticle powders yields single-crystalline ZnxMg1 - xO nanocubes of exceptional regular cubic shape and edge lengths below 25 nm. In line with ab initio calculations, which predict preferential Zn2 + segregation into low coordinated surface elements of the MgO nanocubes, we track the occupation of edge sites by chains of Zn2 + –O2 - units through their spectroscopic signatures. As a method to generate composite nanostructures with controlled spatial distribution of the chemical components, the annealing induced ion segregation can be extended to other well-dispersed metastable nanoparticles. We expect that the energy of segregation mainly depends on the site coordination number, which can promote controlled demixing within the nanoparticles
EAM Import::2019-03-12

ZnO Nanoparticle Formation from the Molecular Precursor [MeZnOtBu]4 by Ozone Treatment in Ionic Liquids: in-situ Vibrational Spectroscopy in an Ultrahigh Vacuum Environment - Bauer, Tanja; Voggenreiter, Markus; Xu, Tao; Wähler, Tobias; Agel, Friederike; Pohako-Esko, Kaija; Schulz, Peter; Döpper, Tibor; Görling, Andreas; Polarz, Sebastian; Wasserscheid, Peter; Libuda, Jörg (Zeitschrift für Anorganische und Allgemeine Chemie, 2017)
As reported previously, novel ZnO nanostructures can be grown by oxidation of [MeZnOtBu]“building blocks” with Oin ionic liquids (ILs). In this study, we have explored the role of the IL during ZnO formation by in-situ infrared reflection absorption spectroscopy (IRAS) in ultrahigh vacuum (UHV). [MeZnOtBu]and [CCIm][OTf] were (co-)deposited as thin films by physical vapor deposition (PVD) onto Au(111), separately or simultaneously. The IR spectrum of [MeZnOtBu]was analyzed between 300 and 4000 cmbased on calculated spectra from density-functional theory (DFT). Spectral changes in the IL-related bands during the thermal treatment of [MeZnOtBu]in [CCIm][OTf] indicate the loss of the precursor ligands and the interaction of the IL with the growing ZnO aggregates. The films were treated with ozone (10mbar) in UHV and the spectral changes were monitored in-situ by IRAS. Slow ozonolysis of [CCIm][OTf] is observed. Spectroscopically we identify the primary ozonide formed by addition of Oto [CCIm]and suggest a reaction mechanism, which leads to a biuret derivative. Upon ozone treatment of mixed [MeZnOtBu]/[CCIm][OTf] films, ZnO aggregates are formed at the IL/vacuum interface. Ozonolysis of [CCIm][OTf] is suppressed. Upon annealing to 320 K, further ZnO aggregates are formed, leading to enclosure of [CCIm][OTf] in the ZnO film. At 380 K the IL is released from the mixed film. The pure [CCIm][OTf] desorbs at 420 K, leaving behind the ZnO phase.
Keywords: Ionic liquid; Ozone; IR spectroscopy; ZnO nanoparticles; Surface science

ZnO superstructures via oriented aggregation initiated in a block copolymer melt - Klaumünzer, Martin; Distaso, Monica; Hübner, Jakob; Mackovic, Mirza; Spiecker, Erdmann; Kryschi, Carola; Peukert, Wolfgang (Crystengcomm, 2014)
A fast and simple one pot synthesis of ZnO nano- and microparticles initiated and driven by an amino block copolymer O,O′-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol (Jeffamine®) is reported. The specific building mechanism of ZnO mesocrystals is investigated in detail using electron microscopy and diffraction methods. Mesocrystals with a complex superstructure are formed as a result of a consecutive and oriented multiple stage aggregation process: first a 0D → 1D aggregation process is observed, then a 1D → 3D aggregation process occurs in which secondary particles form cones and multiple cone symmetries. Dots, rods, cones, and multiple cones have been isolated within a time resolved study which clearly supports the growth model. To control the morphology of the product particles, the influence of relevant synthesis parameters including stirring and sonication of the intermediate were investigated. Extensive surface characterization of the resulting mesocrystals is presented using infrared and photoluminescence spectroscopies as well as thermogravimetric analysis. Even after multiple washing steps, the particles exhibit a Jeffamine® coated surface that allows for easy dispersion in both polar and nonpolar solvents. The obtained mesocrystals efficiently scatter in the whole range of visible light. © 2014 The Royal Society of Chemistry.

π-Conjugation and End Group Effects in Long Cumulenes: Raman Spectroscopy and DFT Calculations - Tommasini, Matteo; Milani, Alberto; Fazzi, Daniele; Lucotti, Andrea; Castiglioni, Chiara; Januszewski, Johanna; Wendinger, Dominik; Tykwinski, Rik (Journal of Physical Chemistry C, 2014)
We have investigated the structure and spectroscopic properties of cumulenic carbon chains, focusing on the peculiar extgreekp-conjugation properties and end-group effects that influence their behavior. With support from Density Functional Theory (DFT) calculations, we have analyzed the IR and Raman spectra of cumulenes characterized by different end-capping groups and we have related them to the bond length alternation (BLA) pattern and local spectroscopic parameters associated with the CC bonds along the sp-carbon chain. For cumulenes we observe a breakdown of the correlation existing in polyynes among frequencies, Raman intensities of the R line (longitudinal CC stretching modes), and BLA. While the low line frequency and equalized CC bonds would indicate the ``metallic'' character of cumulenic species, we obtain an unusually strong Raman intensity, which is typical of bond-alternated (semiconductive) structures. DFT calculations reveal that this is a consequence of extgreekp-electron conjugation, which markedly extends from the sp-carbon chain to the aryl rings belonging to the end groups. These findings suggest the existence of a strong electronic, vibrational and structural coupling between sp-carbon chains and sp2-carbon species, which could play a key role in nanostructured sp/sp2-hybrid carbon materials (e.g., linear carbon chains coupled to graphene domains). Within this context, Raman spectroscopy is a valuable tool for the detailed characterization of the molecular properties of this kind of materials.
EAM Import::2019-03-14

σ-Holes, π-Holes and Electrostatically-Driven Interactions - Murray, Jane S.; Lane, Pat; Clark, Timothy; Riley, Kevin E.; Politzer, Peter (Journal of Molecular Modeling, 2012)
A positive extgreekp-hole is a region of positive electrostatic potential that is perpendicular to a portion of a molecular framework. It is the counterpart of a extgreeks-hole, which is along the extension of a covalent bond to an atom. Both extgreeks-holes and extgreekp-holes become more positive (a) in going from the lighter to the heavier atoms in a given Group of the periodic table, and (b) as the remainder of the molecule is more electronwithdrawing. Positive extgreeks- and extgreekp-holes can interact in a highly directional manner with negative sites, e.g., the lone pairs of Lewis bases. In this work, the complexes of 13 extgreekp-holecontaining molecules with the nitrogen lone pairs of HCN and NH3 have been characterized computationally using the MP2, M06-2X and B3PW91 procedures. While the electrostatic interaction is a major driving force in extgreekp-hole bonding, a gradation is found from weakly noncovalent to considerably stronger with possible indications of some degree of coordinate covalency.
EAM Import::2019-03-14