Competition between unlimited and limited energy growth in a two-dimensional time-dependent billiard - Fregolente Mendes de Oliveira, Diego; Pöschel, Thorsten (Physics Letters A, 2013)
Some dynamical properties for a dissipative time-dependent Lorentz gas are studied. We assume that the size of the scatterers change periodically in time. We show that for some combination of the control parameters the particles come to a complete stop between the scatterers, but for some other cases, the average velocity grows unbounded. This is the first time that the unlimited energy growth is observed in a dissipative system. Finally, we study the behavior of the average velocity as a function of the number of collisions and we show that the system is scaling invariant with scaling exponents well defined. © 2013 Elsevier B.V. All rights reserved.
Keywords: Billiards; Chaos; Dissipation; Lorentz gas; Scaling

Competition for graphene: Graphynes with direction-dependent dirac cones - Malko, Daniel; Neiß, Christian; Vines, Francesc; Görling, Andreas (Physical Review Letters, 2012)
The existence of Dirac cones in the band structure of two-dimensional materials accompanied by unprecedented electronic properties is considered to be a unique feature of graphene related to its hexagonal symmetry. Here, we present other two-dimensional carbon materials, graphynes, that also possess Dirac cones according to first-principles electronic structure calculations. One of these materials, 6,6,12-graphyne, does not have hexagonal symmetry and features two self-doped nonequivalent distorted Dirac cones suggesting electronic properties even more amazing than that of graphene. © 2012 American Physical Society.

Complementary Molecular Dynamics and X-ray Reflectivity Study of an Imidazolium-Based Ionic Liquid at a Neutral Sapphire Interface - Brkljaca, Zlatko; Klimczak, Michael; Milicevic, Zoran; Weißer, Matthias; Taccardi, Nicola; Wasserscheid, Peter; Smith, David M.; Magerl, Andreas; Smith, Ana-Suncana (Journal of Physical Chemistry Letters, 2015)
Understanding the molecular-level behavior of ionic liquids (ILs) at IL–solid interfaces is of fundamental importance with respect to their application in, for example, electrochemical systems and electronic devices. Using a model system, consisting of an imidazolium-based IL ([C2Mim][NTf2]) in contact with a sapphire substrate, we have approached this problem using a complementary combination of high-resolution X-ray reflectivity measurements and atomistic molecular dynamics (MD) simulations. Our strategy enabled us to compare experimental and theoretically calculated reflectivities in a direct manner, thereby critically assessing the applicability of several force-field variants. On the other hand, using the best-matching MD description, we are able to describe the nature of the model IL–solid interface in appreciable detail. More specifically, we find that characteristic interactions between the surface hydroxyl groups and donor and acceptor sites on the IL constituents have a dominant role in inducing a multidimensional layering profile of the cations and anions.

Complex 3D structures via double imprint of hybrid structures and sacrificial mould techniques - Steinberg, Christian; Rumler, Maximilian; Manuel, Runkel A.; Papenheim, Marc; Wang, Si; Mayer, Andre; Becker, Marco; Rommel, Mathias; Scheer, Hella-Christin (Microelectronic Engineering, 2017)
The preparation of transparent complex 3D structures over large areas at low cost paves the way for numerous optical applications. We prepared nanostructures on the surface of microstructures in a negative tone photoresist by a double imprint process combined with VUV-induced surface hardening. Successful preparation of the aforementioned structures asks for a compromise between the surface hardening of the nanostructures and the replication fidelity of the microstructures. Our results show that a VUV treatment time of at least 3 s is required so that the cross-linked layer does not break-up. Adequate process parameters as well as their limiting values were identified by using high aspect ratio microstructures. The complex 3D structures were successfully replicated in UV-PDMS to provide long-term stable templates. To ensure effective separation despite of the undercuts a sacrificial mould technique is applied.
EAM Import::2019-03-13

Complex Faraday Rotation in Microstructured Magneto-optical Fiber Waveguides - Schmidt, Markus A.; Wondraczek, Lothar; Lee, Ho W.; Granzow, Nicolai; Da, Ning; Russell, Philip St. J. (Advanced Materials, 2011)
Magneto-optical glasses are of considerable current interest, primarily for applications in fiber circuitry, optical isolation, all-optical diodes, optical switching and modulation. While the benchmark materials are still crystalline, glasses offer a variety of unique advantages, such as very high rare-earth and heavy-metal solubility and, in principle, the possibility of being produced in fiber form. In comparison to conventional fiber-drawing processes, pressure-assisted melt-filling of microcapillaries or photonic crystal fibers with magneto-optical glasses offers an alternative route to creating complex waveguide architectures from unusual combinations of glasses. For instance, strongly diamagnetic tellurite or chalcogenide glasses with high refractive index can be combined with silica in an all-solid, microstructured waveguide. This promises the implementation of as-yet-unsuitable but strongly active glass candidates as fiber waveguides, for example in photonic crystal fibers.
EAM Import::2019-03-13

Complex source beam: A tool to describe highly focused vector beams analytically - Orlov, S.; Peschel, Ulf (Physical Review A, 2010)
The scalar-complex-source model is used to develop an accurate description of highly focused radially, azimuthally, linearly, and circularly polarized monochromatic vector beams. We investigate the power and full beam widths at half maximum of vigorous Maxwell equation solutions. The analytical expressions are employed to compare the vector complex source beams with the real beams produced by various high-numerical-aperture (NA) focusing systems. We find a parameter set for which the spatial extents of the analytical beams are the same as those of experimentally realized ones. We ensure the same shape of the considered beams by investigating an overlap of the complex source beams with high-NA beams. We demonstrate that the analytical expressions are good approximations for realistic highly focused beams.
EAM Import::2019-03-13

Complex velocity dependence of the coefficient of restitution of a bouncing ball - Müller, Patric; Heckel, Michael; Sack, Achim; Pöschel, Thorsten (Physical Review Letters, 2013)
We investigate the coefficient of normal restitution as a function of the impact velocity, ε(v), for inelastic spheres. We observe oscillating behavior of ε(v) which is superimposed to the known decay of the coefficient of restitution as a function of impact velocity. This remarkable effect was so far unnoticed because under normal circumstances it is screened by statistical scatter. We detected its clear signature by recording large amounts of data using an automated experiment. The new effect may be understood as an interplay between translational and vibrational degrees of freedom of the colliders. Both characteristics of the oscillation, the wavelength and the amplitude, agree quantitatively with a theoretical description of the experiment. © 2013 American Physical Society.

Composite Nanostructures of TiO2 and ZnO for Water Splitting Application: Atomic Layer Deposition Growth and Density Functional Theory Investigation - Kulmas, Marina; Paerson, Leanne; Höflich, Katja; Bashouti, Muhammad Y.; Wu, Yanlin; Göbelt, Manuela; Ristein, Jürgen; Bachmann, Julien; Meyer, Bernd; Christiansen, Silke (Advanced Functional Materials, 2016)
The commercialization of solar fuel devices requires the development of novel engineered photoelectrodes for water splitting applications which are based on redundant, cheap, and environmentally friendly materials. In the current study, a combination of titanium dioxide (TiO) and zinc oxide (ZnO) onto nanotextured silicon is utilized for a composite electrode with the aim to overcome the individual shortcomings of the respective materials. The properties of conformal coverage of TiO and ZnO layers are designed on the atomic scale by the atomic layer deposition technique. The resulting photoanode shows not only promising stability but also nine times higher photocurrents than an equivalent photoanode with a pure TiO encapsulation onto the nanostructured silicon. Density functional theory calculations indicate that segregation of TiO at the ZnO surfaces is favorable and leads to the stabilization of the ZnO layers in water environments. In conclusion, the novel designed composite material constitutes a promising base for a stable and effective photoanode for the water oxidation reaction.
Keywords: density functional theory; photoanodes; titanium dioxide; water oxidation; zinc oxide

Compressed sensing electron tomography of needle-shaped biological specimens - Potential for improved reconstruction fidelity with reduced dose - Saghi, Zineb; Divitini, Giorgio; Winter, Benjamin; Leary, Rowan; Spiecker, Erdmann; Ducati, Caterina; Midgley, Paul A. (Ultramicroscopy, 2016)
Electron tomography is an invaluable method for 3D cellular imaging. The technique is, however, limited by the specimen geometry, with a loss of resolution due to a restricted tilt range, an increase in specimen thickness with tilt, and a resultant need for subjective and time-consuming manual segmentation. Here we show that 3D reconstructions of needle-shaped biological samples exhibit isotropic resolution, facilitating improved automated segmentation and feature detection. By using scanning transmission electron tomography, with small probe convergence angles, high spatial resolution is maintained over large depths of field and across the tilt range. Moreover, the application of compressed sensing methods to the needle data demonstrates how high fidelity reconstructions may be achieved with far fewer images (and thus greatly reduced dose) than needed by conventional methods. These findings open the door to high fidelity electron tomography over critically relevant length-scales, filling an important gap between existing 3D cellular imaging techniques. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Electron tomography; Isotropic resolution; Compressed sensing; Life science

Compression moduli of foamed films of fluorinated ethylene propylene copolymers determined by nanoindentation - Zirkel, Larissa; Maier, Verena; Durst, Karsten; Münstedt, Helmut (Polymer Testing, 2011)
Nanoindentation was applied to determine the elastic moduli in the compression mode of films of fluorinated ethylene propylene copolymers (FEP) foamed by means of supercritical carbon dioxide. For this purpose, a flat punch indenter with a diameter larger than the average cell size of the foams was found to be appropriate. The dependence of the mechanical properties of the films on their cellular structure was investigated by varying material and process parameters: molar mass of the FEP, the magnitude of the pressure drop and the temperature during the foaming process. The elastic modulus showed a strong influence of the cellular structure of the films. A decrease of the molar mass of FEP as well as an increase of pressure drop and foaming temperature considerably reduced the elastic modulus of the foams generated. This lowering of the stiffness correlated with the decrease of foam density. In addition, a significant contribution of the cellular morphology and the thickness of the compact skin layers of the foams could be noted. A further reduction of the foam stiffness was achieved by a biaxial stretching of the foams, which deformed the cells into a lens shape.
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Computational Homogenisation of Material Layers with Micromorphic Mesostructure - Hirschberger, C. B.; Sukumar, N; Steinmann, Paul (Philosophical Magazine, 2008)
In this paper, a multiscale approach to capture the behavior of material layers that possess a micromorphic mesostructure is presented. To this end, we seek to obtain a macroscopic traction-separation law based on the underlying meso and microstructure. At the macro level, a cohesive interface description is used, whereas the underlying mesostructure is resolved as a micromorphic representative volume element. The micromorphic continuum theory is particularly well-suited to account for higher-order and size-dependent effects in the material layer. On considering the height of the material layer, quantities at different scales are related through averaging theorems and the Hill condition. An admissible scale-transition is guaranteed via the adoption of customized boundary conditions, which account for the deformation modes in the interface. On the basis of this theoretical framework, computational homogenization is embedded within a finite-element approach, and the capabilities of the model are demonstrated through numerical example
UnivIS-Import:2015-03-09:Pub.2008.tech.FT.FT-TM.comput_7
Keywords: Cohesive interface; Computational homogenization; Multiscale mechanics; Size effect; Thin layer

Computational Multiscale Modelling of Heterogeneous Material Layers - Hirschberger, C. B.; Ricker, S.; Steinmann, Paul; Sukumar, N (Engineering Fracture Mechanics, 2009)
A computational homogenization procedure for a material layer that possesses an underlying heterogeneous microstructure is introduced within the framework of finite deformations. The macroscopic material properties of the material layer are obtained from multiscale considerations. At the macro level, the layer is resolved as a cohesive interface situated within a continuum, and its underlying microstructure along the interface is treated as a continuous representative volume element of given height. The scales are linked via homogenization with customized hybrid boundary conditions on this representative volume element, which account for the deformation modes along the interface. A nested numerical solution scheme is adopted to link the macro and micro scales. Numerical examples successfully display the capability of the proposed approach to solve macroscopic boundary value problems with an evaluation of the constitutive properties of the material layer based on its micro-constitution.
UnivIS-Import:2015-03-09:Pub.2009.tech.FT.FT-TM.comput_6

Computational optimization and solution-processing of thick and efficient luminescent down-shifting layers for photovoltaics - Solodovnyk, Anastasiia; Kick, Christopher; Osvet, Andres; Egelhaaf, Hans-Joachim; Stern, Edda; Batentschuk, Miroslaw; Forberich, Karen; Brabec, Christoph (Physics, Simulation, and Photonic Engineering of Photovoltaic Devices V, 2016)
Luminescent down-shifting (LDS) is a simple, powerful tool for increasing the range of solar irradiance that can be efficiently utilized by photovoltaic devices. We developed an optical model to simulate the ideal optical properties (absorbance, transmittance, luminescence quantum yield, etc.) of LDS layers for solar cells. We evaluated which quantum efficiencies and which optical densities are necessary to achieve an improvement in solar cell performance. In particular we considered copper indium gallium diselenide (CIGS) devices. Our model relies on experimentally measured data for the transmission and emission spectra as well as for the external quantum efficiency (EQE) of the solar cell. By combining experimental work with this optical model, we aim to propose an environmentally friendly technology for coating thick (300-500 μm), efficient luminescent down-shifting layers. These layers consist of polyvinyl butyral (PVB) and organic UV-converting fluorescent dyes. The absorption coefficients and luminescence quantum yields of the dyes were determined both in a solution of the solvent benzyl alcohol and in the solid polymer layers. This data shows that the dyes retain luminescence quantum yields of approximately 90% after solution-processing. The produced layers were then applied to CIGS solar cells, thereby improving the EQE of the devices in the UV region. At a wavelength of 390 nm, for instance, the EQE increased from 18% to 53%. These values closely agree with the theoretically calculated ones. The proposed technology, thus, provides a pathway toward efficient, fully solutionprocessable encapsulated photovoltaic modules.
Keywords: Absorbance; EQE; Luminescence; Organic dye; Photovoltaics; Quantum yield

Conceptional design of nano-particulate ITO inks for inkjet printing of electron devices - Kölpin, Nadja; Wegener, Carsten Moritz; Teuber, Erik; Polster, Sebastian; Frey, Lothar; Roosen, Andreas (Journal of Materials Science, 2013)
This manuscript presents the conceptional design of indium tin oxide inkjet inks for the manufacture of electron devices. For this purpose, the process window of the printer used is identified and the inks are conceived to meet the requirements. The nano-particles are effectively stabilized in different dispersion media. The rheological, the wetting and the drying behavior of the inks are adapted to the inkjet process and the substrates to be coated. To assemble a field effect transistor (FET), the most suitable ink is chosen and source and drain contacts are printed. In the device, a nano-particulate ZnO layer acts as semiconducting layer and the gate electrode as well as the dielectric layer is formed by a thermally oxidized silicon wafer. The electron device assembled shows the typical FET characteristic proving its functionality. © 2012 Springer Science+Business Media New York.

Concept of a Molecular Charge Storage Dielectric Layer For Organic Thin-Film Memory Transistors - Burkhardt, Martin; Jedaa, Abdesselam; Novak, Michael; Ebel, Alexander; Voitchovsky, Kislon; Stellacci, Francesco; Hirsch, Andreas; Halik, Marcus (Advanced Materials, 2010)
(Figure Presented) A mixed self-assembled monolayer containing aliphatic and electron-accepting (C ) components is employed as an ultrathin molecular gate dielectric to facilitate reversible, nonvolatile electronic memory functionality in organic transistors at low supply voltages. By adjusting the stoichiometry of the monolayer components, the transistor and memory characteristics can be tuned. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Conduction Mechanisms and Environmental Sensitivity of Solution-Processed Silicon Nanoparticle Layers for Thin-Film Transistors - Weis, Sebastian; Körmer, Richard; Jank, Michael; Lemberger, Martin; Otto, Michael; Ryssel, Heiner; Peukert, Wolfgang; Frey, Lothar (Small, 2011)
Room-temperature, solution-processed, silicon nanoparticle thin films show significant gating with distinct hysteresis in their current–voltage characteristics. Device performance strongly depends on measurement environment and charge transport is determined by particle surfaces. Particle encapsulation with polymethyl methacrylate or Al2O3 reduces hysteresis and device sensitivity against environmental influences. Both Al2O3 coating and UV exposure during measurements alter current transport and enhance conductivity, providing evidence for surface-dominated transpor
UnivIS-Import:2015-03-09:Pub.2011.tech.IE.LEB.conduc
Keywords: silicon; nanoparticle; thin; film

Configurationally Stable Chiral Dithia-Bridged Hetero[4]helicene Radical Cation: Electronic Structure and Absolute Configuration - Gliemann, Bettina; Petrovic, Ana G.; Zolnhofer, Eva; Dral, Pavlo O.; Hampel, Frank; Breitenbruch, Georg; Schulze, Philipp; Raghavan, Vijay; Meyer, Karsten; Polavarapu, Prasad L.; Berova, Nina; Kivala, Milan (Chemistry - An Asian Journal, 2017)
A stable chiral hetero[4]helicene radical cation was synthesized and characterized by UV/Vis absorption and EPR spectroscopy, as well as X-ray crystallography. For the first time, a combination of chiroptical methods involving ECD, ORD, and VCD, supported by quantum mechanical predictions, enabled the elucidation of the absolute configuration of such open-shell helical species.
EAM Import::2019-03-13

Conformational flexibility of metalloporphyrins studied by density-functional calculations - Wölfle, Thorsten; Hieringer, Wolfgang; Görling, Andreas (Physical Chemistry Chemical Physics, 2008)
Reliable energetic data on the conformational flexibility of organic molecules are important ingredients to better understand the adsorption of such molecules on solid surfaces. Herein, the conformational flexibility of the phenyl substituents in metallo tetraphenyl porphyrins (M-TPP, M = Zn, Co) and metallo tert-butyl tetraphenyl porphyrins (M-TTBPP, M = Zn, Co) has been studied in detail for the first time using density-functional methods. For each molecule, a relaxed two-dimensional potential energy surface scan has been calculated for the two angles describing the rotation and the out-of-plane bending of the phenyl substituents. The results quantify that the molecules are rather flexible close to the energetic minimum while more extreme twisting or tilting of the phenyl substituents results in high-energy deformations of the porphyrin core from planarity due to steric repulsions of adjacent hydrogen atoms. © the Owner Societies.

Conical-shaped titania nanotubes for optimized light management in DSSCs reach back-side illumination efficiencies > 8% - So, Seulgi; Kriesch, Arian; Peschel, Ulf; Schmuki, Patrik (Journal of Materials Chemistry A, 2015)
In the present work, we introduce the anodic growth of conical shaped TiO2 nanotube arrays. These titania nanocones provide a scaffold for dye-sensitized solar cell (DSSC) structures with significantly improved photon management, providing an optimized absorption profile compared with conventional cylindrical nanotube arrays. Finite difference time domain (FDTD) modelling demonstrates a drastically changed power-absorption characteristic over the tube length. When used in a back-side illumination DSSC configuration, nanocone structures can reach over 60% higher solar cell conversion efficiency ( extgreekh) than conventional tubes. The resulting extgreekh ≈ 8% represents one of the highest reported values for Grätzel type DSSCs used under back-side illumination.
EAM Import::2019-03-13

Consecutive interlayer disassembly-reassembly during alumination of UOV zeolites: insight into the mechanism - Kasneryk, Valeryia; Opanasenko, Maksym; Shamzhy, Mariya; Musilova, Zuzana; Avadhut, Yamini; Hartmann, Martin; Cejka, Jiri (Journal of Materials Chemistry A, 2017)
Investigation of the kinetics of UOV germanosilicate alumination by X-ray diffraction, Al-27 and Si-29 MAS NMR, ICP/OES and FTIR spectroscopy showed the multi-stage mechanism of the process. The first step consists of degermanation and partial disassembly followed by Al incorporation into the UOV germanosilicate framework in the second step. The Al atoms stabilize the UOV framework by healing the defects formed after rapid hydrolysis of Ge-O-Si bonds, which was evidenced by comparison with the reference treatment of initial UOV samples with HNO3 (pH = 2). Post-synthesis alumination of UOV leads to the generation of strong Bronsted and Lewis acid sites; their ratio in aluminated UOV derivatives can be adjusted by the variation of treatment conditions. The intrinsic properties of parent UOV germanosilicates determine the textural properties of aluminated derivatives.

Contact of granular particles and the simulation of rapid flows using event-driven molecular dynamics - Pöschel, Thorsten; Brilliantov, Nikolai; Formella, Arno; Heckel, Michael; Kruelle, Christof; Müller, Patric; Salueña, Clara; Schwager, Thomas (European Journal of Environmental and Civil Engineering, 2008)
We discuss several models for granular particles commonly used in Molecular Dynamics simulations of granular materials, including spheres with linear dashpot force, viscoelastic spheres and adhesive viscoelastic spheres. Starting from the vectorial interaction forces we derive the coefficients of normal and tangential restitution as functions of the vectorial impact velocity and of the material constants. We review the methods of measurements of the coefficients of restitution and characterize the coefficient of normal restitution as a fluctuating quantity. Moreover, the scaling behavior and the influence of different force laws on the dynamical system behavior are discussed. The powerful method of event-driven Molecular Dynamics is described and the algorithmic simulation technique is explained in detail. Finally we discuss the limitations of event-driven MD.

Continuous direct melt foaming of a preceramic polymer using carbon dioxide: extrusion device and first results - Wolff, Friedrich; Münstedt, Helmut (Journal of Materials Science, 2011)
EAM Import::2019-03-13

Continuous flow synthesis of plasmonic gold patches and nearly-complete nanoshells on polystyrene core particles - Meincke, Thomas; Klupp Taylor, Robin (Particuology, 2023)
We describe the development of a T-mixer based continuous flow process for the coating of 86-500 nm diameter spherical polystyrene particles with thin gold patches by heterogeneous nucleation and growth. After establishing a suitable flow rate for good mixing and sufficiently uniform product morphology we systematically investigate the main reaction parameters. This reveals a considerable tunability of the patch morphology and, by virtue of the localized surface plasmon resonance of gold, the optical properties of the product dispersions. In order to further widen the range of nanostructures accessible by our process, a second T-mixer was added. This introduced new gold precursor, leading to further growth of the patches that were formed after the first mixer. By this approach nearly complete gold nanoshells could be produced in high yield on both small and large core particles, without the unwanted production of free-standing gold nanoparticles. Due to the pronounced optical properties of nearly complete gold nanoshells on small core particles, we could estimate from electrodynamic simulations the equivalent shell thickness to be as low as 8.6 nm. This is significantly thinner than can be routinely achieved using the standard seeded growth approach to synthesise gold nanoshells. Our results are therefore highly promising for the gram-scale synthesis of plasmon resonant nanostructures with designed optical propertie
Keywords: Continuous flow; core-shell particles; patchy particles; nucleation; diffusion limited growth

Continuous gas-phase desulfurisation using supported ionic liquid phase (SILP) materials - Kohler, Florian; Roth, Daniel; Kuhlmann, Esther; Wasserscheid, Peter; Haumann, Marco (Green Chemistry, 2010)
Supported ionic liquid phase (SILP) materials have been developed for a continuous gas cleaning process. The technology is exemplified for the desulfurisation of a model gas stream consisting of 500 ppmwtn-butyl mercaptan in n-heptane vapour to levels of mercaptan below 5 ppmwt. By varying the ionic liquid structure, acidity and loading, [C12MIM]Cl/SnCl2 (XSnCl2 = 0.50) on alumina in an ionic liquid loading of 20 vol% of the support's pore volume was identified as a particularly suitable gas sorption system. Breakthrough experiments demonstrate desulfurisation performance of up to 130 h time-on-stream, and the suitability of the system for loading/unloading cycles in a pressure and temperature swing operation mode.

Continuous Gas-Phase Hydroformylation of a Highly Diluted Technical C4 Feed using Supported Ionic Liquid Phase Catalysts - Haumann, Marco; Jakuttis, Michael; Franke, Robert; Schönweiz, Andreas; Wasserscheid, Peter (ChemCatChem, 2011)
The concept of supported ionic liquid phase (SILP) catalysis has been established in recent years by our group and others. Its application in continuous catalytic gas-phase processes provides a very attractive way to bridge the gap between homogeneous and heterogeneous catalysis. In this contribution, we extend SILP hydroformylation catalysis to reactions with a highly diluted, technical C4 feed containing 1.5 % 1-butene, 28.5 % 2-butenes, and 70 % of inert n-butane. To obtain the desired product, n-pentanal, the Rh-biphephos catalyst system was immobilized in the SILP system to allow for consecutive isomerization/hydroformylation activity. The resulting SILP catalyst material converted up to 81 % of the reactive butenes, with a residence time of 155s in the reactor. An n-pentanal selectivity greater than 92% was realized for more than 500h time-on-stream in the continuous gas-phase reaction. Post-reaction NMR studies revealed no significant loss of the phosphite ligand through ligand oxidation during the reaction.

Continuous gas-phase isopropylation of toluene and cumene using highly acidic Supported Ionic Liquid Phase (SILP) catalysts - Joni, Joni; Haumann, Marco; Wasserscheid, Peter (Applied Catalysis A-General, 2010)
Continuous gas-phase Friedel-Crafts isopropylation of toluene and cumene has been investigated using acidic Supported Ionic Liquid Phase (SILP) materials as the catalyst. Detailed kinetic studies in a multi-stage tubular reactor revealed that reactant's water content and the aromatic-to-alkene ratio are the most relevant influencing factors for the catalyst stability and selectivity in these reactions. Based on this insight, our process optimization led to the first highly stable, highly active and selective SILP-type acidic catalyst system for gas-phase aromatic alkylation. We anticipate that this concept offers great potential for more sustainable Friedel-Crafts alkylation processes.

Continuous synthesis of CuInS2 quantum dots - Akdas, Tugce; Haderlein, Michael; Walter, Johannes; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Peukert, Wolfgang (RSC Advances, 2017)
In colloidal semiconductor nanocrystal synthesis, many activities have been focused on the control over the mean particle size of the product. However, for device applications additional requirements apply, e.g. the necessity for a narrow particle size distribution (PSD). In the present work, we investigate the impact of reactor characteristics on the synthesis of CuInS2 quantum dots (QDs). Therefore, the synthesis is carried out in three different reactors, namely in a fully scalable and continuous tubular reactor, in a commercial microreactor and in a batch three-neck round-bottom flask. All reaction products from the three reactor types have the same crystal structure and inorganic composition. Slight differences in optical properties are mainly ascribed to differences in the PSD, which is confirmed by sedimentation velocity experiments. Furthermore, the necessity for using different post-processing routines coupled with our findings by analytical ultracentrifugation (AUC) hint at changes in the organic matrix surrounding the CuInS2 QDs. Our study demonstrates the massive impact of heat transfer on the synthesis and the final PSD of CuInS2 QDs synthesized via heating-up and allows us to draw conclusions on their formation.

Controlled functionalization of graphene oxide with sodium azide - Eigler, Siegfried; Hu, Yichen; Ishii, Yoshitaka; Hirsch, Andreas (Nanoscale, 2013)
We present the first example of azide functionalization on the surface of graphene oxide (GO), which preserves thermally unstable groups in GO through the mild reaction with sodium azide in solids. Experimental evidence, by N solid-state NMR and other spectroscopic methods, indicates the substitution of organosulfate with azide anions as the reaction mechanism. © 2013 The Royal Society of Chemistry.

Controlled In Situ PbSe Quantum Dot Growth around Single-Walled Carbon Nanotubes: A Noncovalent PbSe-SWNT Hybrid Structure - Schornbaum, Julia; Winter, Benjamin; Schießl, Stefan; Butz, Benjamin; Spiecker, Erdmann; Zaumseil, Jana (Chemistry of Materials, 2013)
We developed a simple method of synthesizing noncovalently linked hybrids of PbSe quantum dots (QDs) and single-walled carbon nanotubes (SWNTs). The PbSe QDs grow around the SWNTs without any linker molecule or chemical modification of the SWNTs. We are able to control the size and shape of the QDs attached to the SWNTs by varying the synthesis conditions and elucidate the three-dimensional (3D) morphology and atomic structure of the half-ring-shaped PbSe QDs bonded to the SWNTs using scanning transmission electron microscopy (STEM) tomography and high-resolution transmission electron microscopy (HRTEM). The PbSe QDs not only assemble on the SWNT bundles, but they actually grow around them. The growth of the PbSe QDs around SWNT sidewalls is favored over the growth of spherical particles in solution, probably due to dipole stabilization by the large pi-electron system of the SWNTs.
Keywords: hybrid material; PbSe quantum dots; single-walled carbon nanotubes; electron tomography

Controlling additive behavior to reveal an alternative morphology formation mechanism in polymer: Fullerene bulk-heterojunctions - Güldal, Nusret Sena; Berlinghof, Marvin; Kassar, Thaer; Du, Xiaoyan; Jiao, Xuechen; Meyer, Markus; Ameri, Tayebeh; Osvet, Andres; Li, Ning; Destri, Giovanni Li; Fink, Rainer; Ade, Harald; et al. (Journal of Materials Chemistry A, 2016)
One of the most employed morphology optimization methods to design better performing organic photovoltaic devices is ink formulation engineering with additives. In this work, by employing a suboptimal host solvent mixture and 1,8-diiodooctane (DIO) as a very optimal solvent for both components in poly-thieno[3,2b]thiophene-diketopyrrolopyrrole-co-thiophene (DPP-TT-T)-based bulk-heterojunctions (BHJ), an alternative, previously unknown mechanism of additive behavior on BHJ microstructure formation is presented. In situ characterization methods involving grazing incidence X-ray diffraction, white-light reflectometry, laser light scattering and photoluminescence during film drying reveal that the microstructure formation under the influence of DIO is led towards thermodynamic equilibrium during host solvent drying, and the kinetics of morphology formation (i.e. polymer crystallization, fullerene aggregation...) are controlled dominantly by the additive during its evaporation. Ex situ X-ray-based characterization methods, such as scanning transmission X-ray microspectroscopy (STXM) and resonant soft X-ray scattering (R-SoXS), additionally reveal that the microstructure of dried films favors smaller domain sizes with purer domains, smaller fullerene aggregates, bimodal polymer crystallization relative to the substrate and more face-on molecular orientation relative to the donor/acceptor interface, which at the end lead to better performing devices with power conversion efficiencies ranging from 1.25% to 4.68%.
Keywords: Engineering controlled terms: Additives; Fullerenes; Heterojunctions; Interfaces (materials); Light scattering; Microstructure; Molecular orientation; Morphology; Polymers; Solvents; Thiophene; X ray diffraction; X ray scattering Bulk heterojunction (BHJ); Characterization methods; Donor/acceptor interface; Grazing incidence X-ray diffraction; In-situ characterization; Microstructure formation; Organic photovoltaic devices; Power conversion efficiencies Engineering main heading: Polymer films

Controlling metal/oxide interactions in bifunctional nanostructured model catalysts: Pd and BaO on Al2O3/NiAl(110) - Desikusumastuti, Aine; Qin, Zhihui; Staudt, Thorsten; Happel, Markus; Lykhach, Yaroslava; Laurin, Mathias; Shaikhutdinov, Sh.; Libuda, Jörg (Surface Science, 2009)
We have investigated the structure and growth of Pd and BaO containing nanoparticles sequentially co-deposited on an ordered Al2O3/NiAl(1 1 0) by scanning tunneling microscopy (STM), and their interaction with CO and NO2 by infrared reflection absorption spectroscopy (IRAS).Ba deposition and subsequent oxidation result in BaxAl2yOx+3y nanciparticles being formed which are characterized by high particle densities and nucleation both on regular terraces and at oxide defects. In contrast, Pd interaction with the model support is weaker and preferential nucleation occurs mainly at rotational domain boundaries and to a lesser extent at anti-phase domain boundaries. For subsequent co-deposition of Pd on preformed BaxAl2yOx+3y/Al2O3/NiAl(1 1 0), Pd nucleates at the BaxAl2yOx+3y nanoparticles and covers them. The reverse deposition sequence, i.e. Subsequent Ba co-deposition and oxidation on preformed Pd/Al2O3/NiAl(1 1 0), leads to formation of small isolated BaxAl2yOx+3y nanoparticles without contact to Pd, together with large Pd crystallites modified by BaxAl2yOx+3y. The present results provide control over the degree of interaction between metal nanoparticles and oxide nanoparticles on a well-defined model catalyst and thus allow LIS to study effects related effects on the reactivity and catalytic behavior. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: Barium oxide; Palladium; Aluminium oxide; Carbon monoxide; Nitrogen dioxide; Scanning tunneling microscopy; IR reflection absorption spectroscopy

Controlling morphology and optical properties of self-catalyzed, mask-free GaN rods and nanorods by metal-organic vapor phase epitaxy - Tessarek, C.; Bashouti, M.; Heilmann, M.; Dieker, Christel; Knoke, Isabel; Spiecker, Erdmann; Christiansen, S. (Journal of Applied Physics, 2013)
A simple self-catalyzed and mask-free approach will be presented to grow GaN rods and nanorods based on the metal-organic vapor phase epitaxy technique. The growth parameter dependent adjustment of the morphology of the structures will be discussed. Rods and nanorods with diameters reaching from a few mu m down to 100 nm, heights up to 48 mu m, and densities up to 8.10(7) cm(-2) are all vertically aligned with respect to the sample surface and exhibiting a hexagonal shape with smooth sidewall facets. Optical properties of GaN nanorods were determined using cathodoluminescence. It will be shown that the optical properties can be improved just by reducing the Ga precursor flow. Furthermore, for regular hexagonal shaped rods and nanorods, whispering gallery modes with quality factors up to 500 were observed by cathodoluminescence pointing out high morphological quality of the structures. Structural investigations using transmission electron microscopy show that larger GaN nanorods (diameter > 500 nm) contain threading dislocations in the bottom part and vertical inversion domain boundaries, which separate a Ga-polar core from a N-polar shell. In contrast, small GaN nanorods (similar to 200 nm) are largely free of such extended defects. Finally, evidence for a self-catalyzed, Ga-induced vapor-liquid-solid growth will be discussed. (C) 2013 AIP Publishing LLC.

Controlling the Adsorption Kinetics via Nanostructuring: Pd Nanoparticles on TiO2 Nanotubes - Honciuc, Andrei; Laurin, Mathias; Albu, Sergiu; Sobota, Marek; Schmuki, Patrik; Libuda, Jörg (Langmuir, 2010)
Activity and selectivity of supported catalysts critically depend on transport and adsorption properties. Combining self-organized porous oxide films with different metal deposition techniques, we have prepared novel Pd/TiO2 catalysts with a new level of structural control. It is shown that these systems make it possible to tune adsorption kinetics via their nanostructure. Self-organized TiO2 nanotubular arrays (TiNTs) prepared by electrochemical methods are used as a support, on which Pd particles are deposited. Whereas physical vapor deposition (PVD) in ultrahigh vacuum (UHV) allows us to selectively grow Pd particles at the tube orifice, Pd/TiNT systems with homogeneously distributed Pd aggregates inside the tubes are available by particle precipitation (PP) from solution. Both methods also provide control over particle size and loading. Using in-situ infrared reflection absorption spectroscopy (IRAS) and molecular beam (MB) methods, we illustrate the relation between the nanostructure of the Pd/TiNT systems and their adsorption kinetics. Control over the metal nanoparticle distribution in the nanotubes leads to drastic differences in adsorption probability and saturation behavior. These differences are rationalized based on differences in surface and gas phase transport resulting from their nanostructure. The results suggest that using carefully designed metal/TiNT systems it may be possible to tailor transport processes in catalytically active materials.

Controlling the Chromaticity of Small-Molecule Light-Emitting Electrochemical Cells Based on TIPS-Pentacene - Weber, Michael; Adam, Matthias; Tykwinski, Rik; Costa, Ruben Dario (Advanced Functional Materials, 2015)
This work demonstrates a novel proof-of-concept to implement pentacene derivatives as emitters for the third generation of light-emitting electrochemical cells based on small-molecules (SM-LECs). Here, a straightforward procedure is shown to control the chromaticity of pentacene-based lighting devices by means of a photoinduced cycloaddition process of the 6,13-bis(triisopropylsilylethynyl) (TIPS)-pentacene that leads to the formation of anthracene-core dimeric species featuring a high-energy emission. Without using the procedure, SM-LECs featuring deep-red emission with Commission Internationale d'Eclairage (CIE) coordinates of x = 0.69/y = 0.31 and irradiance of 0.4 extgreekmW cm-2 are achieved. After a careful optimization of the cycloaddition process, warm white devices with CIE coordinates of x = 0.36/y = 0.38 and luminances of 10 cd m-2 are realized. Here, the mechanism of the device is explained as a host–guest system, in which the dimeric species acts as the high-energy band gap host and the low-energy bandgap TIPS-pentacene is the guest. To the best of the knowledge, this work shows the first warm white SM-LECs. Since this work is based on the archetypal TIPS-pentacene and the photoinduced cycloaddition process is well-knownfor any pentacenes, this proof-of-concept could open a new way to use these compounds for developing white lighting sources.
EAM Import::2019-03-13

Controlling the conductance of molecular junctions using proton transfer reactions: A theoretical model study - Hofmeister, Chriszandro; Coto, Pedro B.; Thoss, Michael (Journal of Chemical Physics, 2017)
The influence of an intramolecular proton transfer reaction on the conductance of a molecular junction is investigated employing a generic model, which includes the effects of the electric field of the gate and leads electrodes and the coupling to a dissipative environment. Using a quantum master equation approach it is shown that, depending on the localization of the proton, the junction exhibits a high or low current state, which can be controlled by external electric fields. Considering different regimes, which range from weak to strong hydrogen bonds in the proton transfer complex and comprise situations with high and low barriers, necessary preconditions to achieve control are analyzed. The results show that systems with a weak hydrogen bond and a significant energy barrier for the proton transfer can be used as molecular transistors or diodes.
EAM Import::2019-03-13

Controlling the diameter of aligned single-walled carbon nanotubes on quartz via catalyst reduction time - Schweiger, Manuel; Schaudig, Maximilian; Gannott, Florentina; Killian, Manuela; Bitzek, Erik; Schmuki, Patrik; Zaumseil, Jana (Carbon, 2015)
One of the main objectives of chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWCNT) is control over their diameter and type (metallic or semiconducting). Here, we investigate the evolution of iron catalyst particles on quartz substrates depending on the duration of the reduction step with hydrogen and its effect on the growth of horizontally aligned SWCNT. We find a strong dependence of catalyst particle size and size distribution on the initial iron film thickness and the reduction time at 630 °C. Initial decrease of the particle size is followed by an unexpected increase. Statistical analysis of the Raman radial breathing modes of the SWCNT over large areas gave reliable and reproducible diameter distributions that correlated directly with the catalyst particle size distributions. By changing the reduction time it was possible to reproducibly shift the average SWCNT diameter from 1.5 (±0.3) nm to 1.2 (±0.2) nm while maintaining a nanotube density of 5–6 SWCNT/ extgreekmm. In order to describe the evolution of the particle size during the reduction process at this particular temperature, we propose a model that includes the diffusion of iron into the quartz and its re-emergence.
WW1::1053
Keywords: Simulation and Modeling

Control of crack propagation by shape-topological optimization - Leugering, Günter; Sokolowski, Jan; Zochowski, Antoni (Discrete and Continuous Dynamical Systems, 2015)
An elastic body weakened by small cracks is considered in the framework of unilateral variational problems in linearized elasticity. The frictionless contact conditions are prescribed on the crack lips in two spatial dimensions, or on the crack faces in three spatial dimensions. The weak solutions of the equilibrium boundary value problem for the elasticity problem are determined by minimization of the energy functional over the cone of admissible displacements. The associated elastic energy functional evaluated for the weak solutions is considered for the purpose of control of crack propagation. The singularities of the elastic displacement field at the crack front are characterized by the shape derivatives of the elastic energy with respect to the crack shape within the Griffith theory. The first order shape derivative of the elastic energy functional with respect to the crack shape, i.e., evaluated for a deformation field supported in an open neighbourhood of one of crack tips, is called the Griffith functional. The control of the crack front in the elastic body is performed by the optimum shape design technique. The Griffith functional is minimized with respect to the shape and the location of small inclusions in the body. The inclusions are located far from the crack. In order to minimize the Griffith functional over an admissible family of inclusions, the second order directional, mixed shape-topological derivatives of the elastic energy functional are evaluated. The domain decomposition technique is applied to the shape and topological sensitivity analysis of variational inequalities. The nonlinear crack model in the framework of linear elasticity is considered in two and three spatial dimensions. The boundary value problem for the elastic displacement field takes the form of a variational inequality over the positive cone in a fractional Sobolev space. The variational inequality leads to a problem of metric projection over a polyhedric convex cone, so the concept of conical differentiability applies to shape and topological sensitivity analysis of variational inequalities under consideration.

Control over charge transfer through molecular wires by temperature and chemical structure modifications - Wielopolski, Mateusz; De Miguel Rojas, Gustavo; Van Der Pol, Cornelia; Brinkhaus, Linda; Katsukis, Georgios; Bryce, Martin; Clark, Timothy; Guldi, Dirk Michael (Acs Nano, 2010)
A series of electron donor-acceptor arrays containing π-conjugated oligofluorenes (oFL) of variable length between a zinc porphyrin (ZnP) as electron donor and fullerene (C ) as electron acceptor have been prepared by following a convergent synthesis. The electronic interactions between the electroactive species were determined by cyclic voltammetry, UV-visible, fluorescence, and femto/nanosecond transient absorption spectroscopy. Our studies clearly confirm that, although the C units are connected to the ZnP donor through π-conjugated oFL frameworks, no significant electronic interactions prevail in the ground state. Theoretical calculations predict that a long-range electron transfer occurs primarily due to a maximized π-conjugated pathway from the donor to the acceptor. Photoexcitation of ZnP-oFL -C results in transient absorption maxima at 715 and 1010 nm, which are unambiguously attributed to the photolytically generated radical ion pair state, [ZnP - oFL -C ], with lifetimes in the microsecond time regime. Temperature-dependent photophysical experiments have shown that the charge-transfer mechanism is controllable by temperature. Both charge separation and charge recombination processes give rise to a molecular wire behavior of the oFL moiety with an attenuation factor (β) of 0.097 Å . The correlation β to the connection pattern between the ZnP donor and the oFL linker revealed that even small alterations of the linker π-electron system break the homogeneous π-conjugation pattern, leading to higher values of β. © 2010 American Chemical Society.

Cooperativity and tunable excited state deactivation: Modular self-assembly of depsipeptide dendrons on a Hamilton receptor modified porphyrin platform - Gnichwitz, Jan-Frederik; Wielopolski, Mateusz; Hartnagel, Kristine; Hartnagel, Uwe; Guldi, Dirk Michael; Hirsch, Andreas (Journal of the American Chemical Society, 2008)
A series of novel supramolecular architectures were built around a tin tetraphenyl porphyrin platform 6 - functionalized by a 2-fold 1-ethyl-3-3-(3-dimethylaminopropyl)carbodiimide (EDC) promoted condensation reaction - and chiral depsipeptide dendrons of different generations 1-4. Here, implementation of a Hamilton receptor provided the necessary means to keep the constituents together via strong hydrogen bonding. Characterization of all architectures has been performed, including 4 which is the fourth generation, on the basis of NMR and photophysical methods. In particular, several titration experiments were conducted suggesting positive cooperativity, an assessment that is based on association constants that tend to be higher for the second binding step than for the first step. Importantly, molecular modeling calculations reveal a significant deaggregation of the intermolecular network of 6 during the course of the first binding step. As a consequence, an improved accessibility of the second Hamilton receptor unit in 6 emerges and, in turn, facilitates the higher association constants. The features of the equilibrium, that is, the dynamic exchange of depsipeptide dendrons 1-4 with fullerene 5, was tested in photophysical reference experiments. These steady-state and time-resolved measurements showed the tunable excited-state deactivations of these complexes upon photoexcitation. © 2008 American Chemical Society.

Coordination and metalation bifunctionality of Cu with 5,10,15,20-tetra(4- pyridyl)porphyrin: Toward a mixed-valence two-dimensional coordination network - Li, Yang; Xiao, Jie; Shubina, Tatyana; Chen, Min; Shi, Ziliang; Schmid, Martin; Steinrück, Hans-Peter; Gottfried, J. Michael; Lin, Nian (Journal of the American Chemical Society, 2012)
We investigated the coordination self-assembly and metalation reaction of Cu with 5,10,15,20-tetra(4-pyridyl)porphyrin (2HTPyP) on a Au(111) surface by means of scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. 2HTPyP was found to interact with Cu through both the peripheral pyridyl groups and the porphyrin core. Pairs of pyridyl groups from neighboring molecules coordinate Cu(0) atoms, which leads to the formation of a supramolecular metal-organic coordination network. The network formation occurs at room temperature; annealing at 450 K enhances the process. The interaction of Cu with the porphyrin core is more complex. At room temperature, formation of an initial complex Cu(0)-2HTPyP is observed. Annealing at 450 K activates an intramolecular redox reaction, by which the coordinated Cu(0) is oxidized to Cu(II) and the complex Cu(II)TPyP is formed. The coordination network consists then of Cu(II) complexes linked by Cu(0) atoms; that is, it represents a mixed-valence two-dimensional coordination network consisting of an ordered array of Cu(II) and Cu(0) centers. Above 520 K, the network degrades and the Cu atoms in the linking positions diffuse into the substrate, while the Cu(II)TPyP complexes form a close-packed structure that is stabilized by weak intermolecular interactions. Density functional theory investigations show that the reaction with Cu(0) proceeds via formation of an initial complex between metal atom and porphyrin followed by formation of Cu(II) porphyrin within the course of the reaction. The activation barrier of the rate limiting step was found to be 24-37 kcal mol depending on the method used. In addition, linear coordination of a Cu atom by two CuTPyP molecules is favorable according to gas-phase calculations. © 2012 American Chemical Society.

Coordination reactions and layer exchange processes at a buried metal-organic interface - Chen, Min; Röckert, Michael; Xiao, Jie; Drescher, Hans-Joerg; Steinrück, Hans-Peter; Lytken, Ole; Gottfried, J. Michael (Journal of Physical Chemistry C, 2014)
The reactive interface between phthalocyanine (2HPc) and a Cu(111) surface was investigated with X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption/reaction (TPD/TPR). 2HPc reacts with Cu(111) to form copper(II) phthalocyanine (CuPc). For 2HPc submonolayers, the reaction starts already below 240 K. Thin 2HPc multilayers (4 monolayers) are completely converted into CuPc at elevated temperatures (500 K). To understand how molecules can react even though they are initially not in contact with the Cu surface, TPD/TPR studies with a NiPc interlayer between Cu and 2HPc were performed. These studies reveal the operation of an exchange mechanism, by which CuPc or NiPc molecules from the first layer are replaced by 2HPc molecules from higher layers. Once a 2HPc molecule comes into contact with the Cu surface, the molecule can react with the surface, forming CuPc, which can then be replaced by another unreacted 2HPc molecule. These findings have important implications for metal-organic interfaces in organic electronic devices, in which the charge carrier injection at the electrodes depends on the electronic properties of the interface. © 2014 American Chemical Society.

CO oxidation on Pt(111) at near ambient pressures - Krick Calderon, Sandra; Grabau, Mathias; Ovari, L.; Kress, B.; Steinrück, Hans-Peter; Papp, Christian (Journal of Chemical Physics, 2016)
The oxidation of CO on Pt(111) was investigated simultaneously by near ambient pressure X-ray photoelectron spectroscopy and online gas analysis. Different CO:O reaction mixtures at total pressures of up to 1 mbar were used in continuous flow mode to obtain an understanding of the surface chemistry. By temperature-programmed and by isothermal measurements, the onset temperature of the reaction was determined for the different reactant mixtures. Highest turnover frequencies were found for the stoichiometric mixture. At elevated temperatures, the reaction becomes diffusion-limited in both temperature-programmed and isothermal measurements. In the highly active regime, no adsorbates were detected on the surface; it is therefore concluded that the catalyst surface is in a metallic state, within the detection limits of the experiment, under the applied conditions. Minor bulk impurities such as silicon were observed to influence the reaction up to total inhibition by formation of non-platinum oxides.

Correct description of the bond dissociation limit without breaking spin symmetry by a random-phase-approximation correlation functional - Heßelmann, Andreas; Görling, Andreas (Physical Review Letters, 2011)
A correlation functional that is termed exact-exchange random phase approximation (EXX-RPA) functional and is obtained with the exact frequency-dependent exchange kernel via the fluctuation-dissipation theorem is shown to correctly describe electron pair bonds in the dissociation limit without the need to resort to symmetry breaking in spin space. Because the functional also yields more accurate electronic energies for molecules in their equilibrium geometry than standard correlation functionals, it combines accuracy at equilibrium bond distances and in dissociation processes with a correct description of spin, something all commonly employed correlation functionals fail to do. The reason why the EXX-RPA correlation functional yields distinctively and qualitatively better results than RPA approaches based on Hartree-Fock and time-dependent Hartree-Fock is explained. © 2011 American Physical Society.

Correction: A star-shaped D-π-A small molecule based on a tris(2-methoxyphenyl)amine core for highly efficient solution-processed organic solar cells - Min, Jie; Luponosov, Yuriy N.; Solodukhin, Alexander N.; Kausch-Busies, Nina; Ponomarenko, Sergei A.; Ameri, Tayebeh; Brabec, Christoph (Journal of Materials Chemistry C, 2014)
Correction for 'A star-shaped D-π-A small molecule based on a tris(2-methoxyphenyl)amine core for highly efficient solution-processed organic solar cells' by Jie Min et al., J. Mater. Chem. C, 2014, 2, 7614-7620. This journal is

Correlation between product purity and process parameters for the synthesis of Cu2ZnSnS4 nanoparticles using microwave irradiation - Ahmad, Rameez; Nicholson, K. S.; Nawaz, Qaisar; Peukert, Wolfgang; Distaso, Monica (Journal of Nanoparticle Research, 2017)
Kesterites (CZT(S,Se)4) emerged as a favourable photovoltaic material, leading to solar cell efficiencies as high as 12.7%. The development of sustainable roll-to-roll printing processes that make use of Cu2ZnSnS4 (CZTS) nanoparticle inks requires the proper design of synthetic approaches and the understanding of the relation between process parameters and product purity. In the current paper, we developed this relationship by calculating a specific energy factor. A microwave-assisted synthetic method that operates at atmospheric pressure and makes use of eco-friendly solvents is established. Four solvents, i.e. ethylene glycol (EG), diethylene glycol (di-EG), triethylene glycol (tri-EG) and tetraethylene glycol (tet-EG) are compared and the temperature during the reaction is assessed by two different methods. In particular, two by-products have been identified, i.e. Cu2-x S and a hexagonal phase. We show that the variation of reaction parameters such as power irradiation, type of solvent and precursor concentration influences the nanoparticles' sizes (from 12 to 6 nm) and also the temperature-time profile of reaction which, in turn, can be related to phase purity of CZTS nanoparticles. The results suggest that the product purity scales with the specific energy factor providing a useful tool to a rational design of high-quality CZTS nanoparticles.
Keywords: Disordered CZTS; Energy conversion; Cubic CZTS; Photovoltaics; Solar cells; Green chemistry; Kesterite

Correlation of Enhanced Strength and Internal Structure for Heat-Treated Submicron Stöber Silica Particles - Romeis, Stefan; Paul, Jonas; Hanisch, Mathias; Marthala, Venkata; Hartmann, Martin; Klupp Taylor, Robin; Schmidt, Jochen; Peukert, Wolfgang (Particle & Particle Systems Characterization, 2014)
The Stöber–Fink–Bohn (SFB) method allows the synthesis of spherical silica particles over a wide size range. Owing to the complex formation mechanism, the internal structure and related mechanical properties are not well understood. Within this account, the internal structure of synthesized SFB particles is changed systematically by heat treatments. Characterization by colloid titration, infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy and the assessment of mechanical properties for single particles by in situ micromanipulation shed light on structure–property relations. Over the course of heat treatment, SFB particles become denser and owing to condensation of internal hydroxyl groups, the cross-linking of the silica network is enhanced. The observed chemical and structural changes are reflected by the mechanical properties of the particles: starting from a low Young’s modulus and hardness, clearly below the bulk properties of fused silica, both values are increasing over the course of the thermal treatment. Hardness for fused silica is approached after a treatment at 800 °C and exceeded after a treatment at 1000 °C. Young’s modulus approaches the bulk value. Furthermore, a significant plasticity is found: the sustained deformations are extremely high, and thus silica spheres with enhanced strength have been obtained by the thermal treatment.

Correlation of film morphology and defect content with the charge-carrier transport in thin-film transistors based on ZnO nanoparticles - Polster, Sebastian; Jank, Michael; Frey, Lothar (Journal of Applied Physics, 2016)
The correlation of defect content and film morphology with the charge-carrier transport in field-effect devices based on zinc oxide nanoparticles was investigated. Changes in the defect content and the morphology were realized by annealing and sintering of the nanoparticle thin films. Temperature-dependent electrical measurements reveal that the carrier transport is thermally activated for both the unsintered and sintered thin films. Reduced energetic barrier heights between the particles have been determined after sintering. Additionally, the energetic barrier heights between the particles can be reduced by increasing the drain-to-source voltage and the gate-to-source voltage. The changes in the barrier height are discussed with respect to information obtained by scanning electron microscopy and photoluminescence measurements. It is found that a reduction of surface states and a lower roughness at the interface between the particle layer and the gate dielectric lead to lower barrier heights. Both surface termination and layer morphology at the interface affect the barrier height and thus are the main criteria for mobility improvement and device optimization. (C) 2016 AIP Publishing LLC.

Correlation of spin and velocity in the homogeneous cooling state of a granular gas of rough particles - Kranz, W. T.; Brilliantov, Nikolai V.; Pöschel, Thorsten; Zippelius, A. (European Physical Journal - Special Topics, 2009)
In a granular gas of rough particles the spin of a grain is correlated with its linear velocity. We develop an analytical theory to account for these correlations and compare its predictions to numerical simulations, using Direct Simulation Monte Carlo as well as Molecular Dynamics. The system is shown to relax from an arbitrary initial state to a steady-state, which is characterized by time-independent, finite correlations of spin and linear velocity. The latter are analyzed systematically for a wide range of system parameters, including the coefficients of tangential and normal restitution as well as the moment of inertia of the particles. For most parameter values the axis of rotation and the direction of linear momentum are perpendicular like in a sliced tennis ball, while parallel orientation, like in a rifled bullet, occurs only for a small range of parameters. The limit of smooth spheres is singular: any arbitrarily small roughness unavoidably causes significant translation-rotation correlations, whereas for perfectly smooth spheres the rotational degrees of freedom are completely decoupled from the dynamic evolution of the gas. © 2009 EDP Sciences and Springer.

Correlative micro-diffraction and differential phase contrast study of mean inner potential and subtle beam-specimen interaction - Wu, Mingjian; Spiecker, Erdmann (Ultramicroscopy, 2017)
We present a correlative micro-diffraction and differential phase contrast (DPC) study within scanning transmission electron microscopy (STEM) on the determination of mean inner potential (MIP) and explain the origin of subtle beam-specimen interactions at the edge of wedge-shaped crystals using both experiment and simulation. Our measurement of MIP of Si and GaAs resulted in 12.48 ± 0.22 V and 14.15 ± 0.22 V, respectively, from directly evaluating beam refraction in micro-diffraction mode. DPC-STEM measurements gave very similar values. Fresnel fringes within the diffraction disk resulting from interaction of the highly coherent electron beam with the aperture are observed and a numerical simulation scheme is implemented to reproduce the effect of the specimen on the fringe pattern. Perfect agreement between experiment and simulation has been achieved in terms of subtle displacements of the fringes upon approaching the sample edge with the electron probe. The existence of the fringes has minor effect on the DPC-STEM signal, which is well below the noise level of our setup at practically reasonable acquisition times. We suggest the possibility to perform pseudo-contactless probing of weak potential differences in beam sensitive samples by evaluating the subtle displacements of Fresnel fringes quantitatively. <embed height="0" id="xunlei_com_thunder_helper_plugin_d462f475-c18e-46be-bd10-327458d045bd" type="application/thunder_download_plugin" width="0"></embed> <embed height="0" id="xunlei_com_thunder_helper_plugin_d462f475-c18e-46be-bd10-327458d045bd" type="application/thunder_download_plugin" width="0"></embed> <embed height="0" id="xunlei_com_thunder_helper_plugin_d462f475-c18e-46be-bd10-327458d045bd" type="application/thunder_download_plugin" width="0"></embed> <embed height="0" id="xunlei_com_thunder_helper_plugin_d462f475-c18e-46be-bd10-327458d045bd" type="application/thunder_download_plugin" width="0"></embed>
Keywords: DPC; Fresnel fringes; Mean inner potential; Micro-diffraction; STEM

Corrosion behaviour of multiwall carbon nanotube/magnesium composites in 3.5% NaCl - Turhan, Can Metehan; Li, Qianqian; Jha, Himendra; Singer, Robert; Virtanen, Sannakaisa (Electrochimica Acta, 2011)
Corrosion behaviour of multiwall carbon nanotube (MWNT) modified pure magnesium (Mg) composites (MWNT/Mg) prepared by melt stirring technique was investigated by weight loss, H2 gas collection and pH measurements, as well as electrochemical methods such as open circuit potential (OCP) monitoring, polarisation curves and electrochemical impedance spectroscopy (EIS). Results show that the corrosion rate of MWNT/Mg composites is significantly higher than the corrosion rate of pure Mg. The corrosion rate of the composites also depends on the degree of dispersion of MWNTs during melt stirring process. The role of the MWNTs in increasing the corrosion rate clearly can be attributed to their high cathodic activity. Characterization of the corrosion product layers indicates that dispersion of MWNTs in the matrix leads to a more homogeneous coverage of the surface by corrosion products, and the lowest thickness of the corrosion product layer. The corrosion product layers in all cases provide poor protection of the surface. The corrosion rate of pure Mg as well as Mg/MWNT composites significantly increases during 1-week immersion; this effect is the strongest for the composite with dispersed nanotubes and can be attributed to the increased cathodic kinetics with time.

Cost analysis of roll-to-roll fabricated ITO free single and tandem organic solar modules based on data from manufacture - Machui, Florian; Hosel, Markus; Li, Ning; Spyropoulos, Georgios; Ameri, Tayebeh; Sondergaard, Roar R.; Jorgensen, Mikkel; Scheel, Arnulf; Gaiser, Detlef; Kreul, Kilian; Lenssen, Daniel; Legros, Mathilde; et al. (Energy and Environmental Science, 2014)
We present a cost analysis based on state of the art printing and coating processes to fully encapsulated, flexible ITO- and vacuum-free polymer solar cell modules. Manufacturing data for both single junctions and tandem junctions are presented and analyzed. Within this calculation the most expensive layers and processing steps are identified. Based on large roll-to-roll coating experiments the exact material consumptions were determined. In addition to the data for the pilot scale experiment presented here, projections to medium and large scale scenarios serve as a guide to achieve cost targets of 5 €ct per W in a detailed material and cost analysis. These scenarios include the replacement of cost intensive layers, as well as process optimization steps. Furthermore, the cost structures for single and tandem devices are listed in detail and discussed. In an optimized model the material costs drop below 10 € per m which proves that OPV is a competitive alternative to established power generation technologies. This journal is © the Partner Organisations 2014.
Keywords: Engineering controlled terms: Coatings; Costs; Experiments; Manufacture; Optimization; Rolls (machine components); Solar cells Coating process; Optimized models; Pilot-scale experiments; Polymer Solar Cells; Power generation technology; Processing steps; Single junction; Tandem junction Engineering main heading: Cost accounting GEOBASE Subject Index: coating; cost-benefit analysis; numerical model; photovoltaic system; solar power

Counterion effect on the aggregation of anionic perylene dyes and the influence on carbon nanotube dispersion efficiencies - Backes, Claudia; Schunk, Torsten; Hauke, Frank; Hirsch, Andreas (Journal of Materials Chemistry, 2011)
The effect of alkali metal counterions on the aggregation behaviour of an anionic perylene dye has been investigated by absorption and emission spectroscopy. In the presence of Na aggregation is enhanced leading to a decreased surfactant capability for the dispersion of carbon nanotubes. © The Royal Society of Chemistry 2011.

Counterions control the self-assembly of structurally persistent micelles: Theoretical prediction and experimental observation of stabilization by sodium ions - Jäger, Christof; Hirsch, Andreas; Schade, Boris; Böttcher, Christoph; Clark, Timothy (Chemistry - A European Journal, 2009)
We show by molecular-dynamics (MD) simulations and cryotransmission electron microscopy (cryo-TEM) experiments that the size and form of structurally persistent micelles formed by the T-shaped amphiphile 1 are controlled by the counterions. The two techniques reveal that the micelles are specifically stabilized by sodium counterions relative to po-tassium ions. Both the simulations and the cryo-TEM experiments suggest that the micelles are stabilized by strongly conserved hydrated contact ion pairs with sodium counterions but not with potassium ions. We suggest that the TEM is observing local high density due to hydrated carboxylate/sodium ion pairs at the surface of the micelle. A high concentration of such structures is found in MD simulations with sodium counterions, but not with potassium. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

Counting electrons on supported nanoparticles - Lykhach, Yaroslava; Kozlov, Sergey M.; Skala, Tomas; Tovt, Andrii; Stetsovych, Vitalii; Tsud, Nataliya; Dvorak, Filip; Johanek, Viktor; Neitzel, Armin; Myslivecek, Josef; Fabris, Stefano; Matolin, Vladimir; et al. (Nature Materials, 2016)
Electronic interactions between metal nanoparticles and oxide supports control the functionality of nanomaterials, for example, the stability, the activity and the selectivity of catalysts(1-5). Such interactions involve electron transfer across the metal/support interface. In this work we quantify this charge transfer on a well-defined platinum/ceria catalyst at particle sizes relevant for heterogeneous catalysis. Combining synchrotron-radiation photoelectron spectroscopy, scanning tunnelling microscopy and density functional calculations we show that the charge transfer per Pt atom is largest for Pt particles of around 50 atoms. Here, approximately one electron is transferred per ten Pt atoms from the nanoparticle to the support. For larger particles, the charge transfer reaches its intrinsic limit set by the support. For smaller particles, charge transfer is partially suppressed by nucleation at defects. These mechanistic and quantitative insights into charge transfer will help to make better use of particle size effects and electronic metal-support interactions in metal/oxide nanomaterials.

Coupled relaxation processes in a glass forming ZrTiNiCuBe liquid - Yang, Fan; Unruh, Tobias; Meyer, Andreas (EPL - Europhysics Letters, 2014)
We studied liquid Zr46.5Ti18.2Cu7.5Ni10Be27.5 in the temperature range from 1060 K to 1255 K using a combination of quasielastic neutron scattering and newly developed electrostatic levitation. We show that not only the microscopic incoherent and coherent relaxation times, and the derived mean self-diffusion coefficient of Ni/Cu/Ti, but also the macroscopic melt viscosity exhibit very similar temperature dependences. Thus, independent of the experimental time/length scales and the different natures of the relaxation times, the Maxwell relation of linear viscoelasticity holds, as a result of highly coupled structural relaxation processes in the melt. Copyright (C) EPLA, 2014

COUPLED THERMALLY GENERAL IMPERFECT AND MECHANICALLY COHERENT ENERGETIC INTERFACES SUBJECT TO IN-PLANE DEGRADATION - Esmaeili, Ali; Steinmann, Paul; Javili, Ali (Journal of Mechanics of Materials and Structures, 2017)
To date, the effects of interface in-plane damage on the thermomechanical response of a thermally general imperfect (GI) and mechanically coherent energetic interface are not taken into account. A thermally GI interface allows for a discontinuity in temperature as well as in the normal heat flux across the interface. A mechanically coherent energetic interface permits a discontinuity in the normal traction but not in the displacement field across the interface. The temperature of a thermally GI interface is a degree of freedom and is computed using a material parameter known as the sensitivity. The current work is the continuation of the model developed by Esmaeili et al. (2016a) where a degrading highly conductive (HC) and mechanically coherent energetic interface is considered. An HC interface only allows for the jump in normal heat flux and not the jump in temperature across the interface. In this contribution, a thermodynamically consistent theory for thermally GI and mechanically coherent energetic interfaces subject to in-plane degradation is developed. A computational framework to model this class of interfaces using the finite element method is established. In particular, the influence of the interface in-plane degradation on the sensitivity is captured. To this end, the equations governing a fully nonlinear transient problem are given. They are solved using the finite element method. The results are illustrated through a series of three-dimensional numerical examples for various interfacial parameters. In particular, a comparison is made between the results of the intact and the degraded thermally GI interface formulation.

Coupling multibody dynamics and computational fluid dynamics on 8192 processor cores - Götz, Jan; Iglberger, Klaus; Feichtinger, Christian; Donath, Stefan; Rüde, Ulrich (Parallel Computing, 2010)
This paper describes a method for the fully resolved simulation of particle laden flows. For this purpose, we discuss the parallelization of large scale coupled fluid structure interaction with up to 37 million geometrically modeled moving objects incorporated in the flow. The simulation is performed using a 3D lattice Boltzmann solver for the fluid flow and a so-called rigid body physics engine for the treatment of the objects. The numerical algorithms and the parallelization are discussed in detail. Furthermore, performance results are presented for test cases on up to 8192 processor cores running on an SGI Altix supercomputer. The approach enables a detailed simulation of large scale particulate flows that are relevant for many industrial applications. © 2010 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2010.tech.IMMD.lsinfs.coupli
Keywords: Fast frictional dynamics algorithm; Fluid structure interaction; Lattice Boltzmann method; Massively parallel simulation; Rigid body dynamics

Coupling of discrete element model (DEM) with computational fluid mechanics (CFD): A validation study - Iqbal, Naveed; Rauh, Cornelia (Applied Mathematics and Computation, 2016)
A numerical model is developed in the framework of OpenFOAM; an open source computational fluid dynamics (CFD) simulation code to simulate particle laden dense flows. The model uses discrete element method (DEM) for the discrete/particle phase and computational fluid dynamics approach (CFD) for the fluid/continuum phase. In current study, validation of the model is done in two steps. In first step the drag model is validated by comparing the results of settling velocity of spherical particle. In second step, spout fluidization test cases with different operating conditions are simulated and results of numerical simulation of spout-fluidized bed are compared against experimental and simulation results reported in literature. The isosurface plots of solid volume fraction show a good qualitative prediction of different flow regimes. The particle velocity profiles in the vertical direction for different test cases corresponding to different flow regimes are plotted and compared with the literature data. The predictions of the model are in good agreement with the experimental and numerical results reported in the literature.
UnivIS-Import:2016-06-01:Pub.2016.tech.ITC.stmmec.coupli
Keywords: CFD-DEM; Eulerian-Lagrangian; Fluidization; Jet flows; Spout fluidization

Covalent bulk functionalization of graphene - Englert, Jan; Dotzer, Christoph; Yang, Guang; Schmid, Martin; Papp, Christian; Gottfried, Michael; Steinrück, Hans-Peter; Spiecker, Erdmann; Hauke, Frank; Hirsch, Andreas; Hauke, Frank; Spiecker, Erdmann (Nature Chemistry, 2011)
Graphene, a truly two-dimensional and fully π-conjugated honeycomb carbon network, is currently evolving into the most promising successor to silicon in micro- and nanoelectronic applications. However, its wider application is impeded by the difficulties in opening a bandgap in its gapless band-structure, as well as the lack of processability in the resultant intrinscially insoluble material. Covalent chemical modification of the π-electron system is capable of addressing both of these issues through the introduction of variable chemical decoration. Although there has been significant research activity in the field of functionalized graphene, most work to date has focused on the use of graphene oxide. In this Article, we report on the first wet chemical bulk functionalization route beginning with pristine graphite that does not require initial oxidative damage of the graphene basal planes. Through effective reductive activation, covalent functionalization of the charged graphene is achieved by organic diazonium salts. Functionalization was observed spectroscopically, and successfully prevents reaggregation while providing solubility in common organic media. © 2011 Macmillan Publishers Limited. All rights reserved.

Covalent Immobilization of Imidazolium Cations Inside a Silica Support: Palladium-Catalyzed Olefin Hydrogenation - Wang, Lei; Shylesh, Sankaranarayanapillai; Dehe, Daniel; Philippi, Thomas; Doerr, Gunder; Seifert, Andreas; Zhou, Zhou; Hartmann, Martin; Klupp Taylor, Robin; Jia, Mingjun; Ernst, Stefan; Thiel, Werner R. (ChemCatChem, 2012)
Mesoporous organosilica materials with different contents of bistrialkoxysilyl imidazolium salts in the framework were synthesized by a one-step synthesis. Textural characterization of the materials confirmed that the morphology and surface properties of the imidazolium-bridged organosilicas depended critically on the amount of organic groups in the framework, whereas solid-state NMR characterization showed that the imidazolium fragments were integrated covalently into the framework. Further reaction of these materials with Pd(OAc)(2), followed by reduction with NaBH4 yielded palladium nanoparticles stabilized in the mesoporous organosilicas. The stabilizing effect of the imidazolium cations and the mesostructure contributed to the high activity, selectivity, and stability of the palladium nanoparticles and allowed olefin hydrogenation under mild reaction conditions.
Keywords: heterogeneous catalysis; hydrogenation; immobilization; organic-inorganic hybrid composites; palladium

Coverage- and Temperature-Dependent Metalation and Dehydrogenation of Tetraphenylporphyrin on Cu(111) - Röckert, Michael; Franke, Matthias; Tariq, Quratulain; Ditze, Stefanie; Stark, Michael Werner; Uffinger, Patrick; Wechsler, Daniel; Singh, Upendra; Xiao, Jie; Marbach, Hubertus; Steinrück, Hans-Peter; Lytken, Ole (Chemistry - A European Journal, 2014)
Using temperature-programmed desorption, supported by X-ray photoelectron spectroscopy and scanning tunneling microscopy, a comprehensive overview of the main reactions of 5,10,15,20-tetraphenyl-21H,23H-porphyrin (2HTPP) on Cu(111) as a function of coverage and temperature is obtained. Three reactions were identified: metalation with Cu substrate atoms, stepwise partial dehydrogenation, and finally complete dehydrogenation. At low coverage the reactions are independent of coverage, but at higher coverage metalation becomes faster and partial dehydrogenation slower. This behavior is explained by a weaker interaction between the iminic nitrogen atoms and the Cu(111) surface in the high-coverage checkerboard structure, leading to faster metalation, and the stabilizing effect of T-type interactions in the [Cu(TPP)] islands formed at high coverage after metalation, leading to slower dehydrogenation. Based on the amount of hydrogen released and the appearance in STM, a structure of the partially dehydrogenated molecule is suggested.

Coverage-Dependent Anchoring of 4,4 '-Biphenyl Dicarboxylic Acid to CoO(111) Thin Films - Mohr, Susanne; Schmitt, Tobias; Döpper, Tibor; Xiang, Feifei; Schwarz, Matthias; Görling, Andreas; Schneider, M. Alexander; Libuda, Jörg (Langmuir, 2017)
We investigated the adsorption behavior of 4,4'-biphenhyl dicarboxylic acid (BDA) on well-ordered CoO(111) films grown on Ir(100) as a function of coverage and temperature using time-resolved and temperature programmed infrared reflection absorption spectroscopy (TR-IRAS, TP-IRAS) in combination with density functional theory (DFT) and scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. To compare the binding behavior of BDA as a function of the oxide film thickness, three different CoO(111) film thicknesses were explored: films of about 20 bilayers (BLs) (approximately 5 nm), 2 BLs, and 1 BL. The two carboxylic acid groups of BDA offer two potential anchoring points to the oxide surface. At 150 K, intact BDA adsorbs on 20 BL thick oxide films in planar geometry with the phenyl rings aligned parallel to the surface. With decreasing oxide film thickness, we observe an increasing tendency for deprotonation and the formation of flat-lying BDA molecules anchored as dicarboxylates. After saturation of the first monolayer, intact BDA multilayers grow with molecules aligned parallel to the surface. The BDA multilayer desorbs at around 360 K. Completely different growth behavior is observed if BDA is deposited above the multilayer desorption temperature. Initially, doubly deprotonated dicarboxylates are formed by adopting a flat-lying,orientation. With increasing exposure, however, the adsorbate layer transforms into upright standing monocarboxylates. A sharp OH stretching band (3584 cm(-1)) and a blue-shifted CO stretching band (1759 cm(-1)) indicate weakly interacting apical carboxylic acid groups at the vacuum interface. The anchored monocarboxylate phase slowly desorbs in a temperature range of up to 470 K. At higher temperature, a flat-lying doubly deprotonated BDA is formed, which desorbs and decomposes in a temperature range of up to 600 K.

Coverage dependent disorder-order transition of 2H-tetraphenylporphyrin on Cu(111) - Stark, Michael Werner; Ditze, Stefanie; Drost, Martin; Buchner, Florian; Steinrück, Hans-Peter; Marbach, Hubertus (Langmuir, 2013)
In this study, we investigate the peculiar coverage dependent supramolecular arrangement of 2H-tetraphenylporhpyrin (2HTPP) on Cu(111) with scanning tunneling microscopy at room-temperature. At low coverage, "slow" diffusion of individual 2HTPP molecules along the close-packed atomic rows of the substrate is observed, and no supramolecular ordering occurs. However, at higher coverage, the formation of ordered, checkerboard-like domains is found, with two molecules per unit cell at different distances from the surface. This behavior is attributed to a complex interplay of site specific molecule-substrate interaction, mainly the strong interaction between the iminic N atoms and Cu substrate atoms, with intermolecular T-type and π-π interactions. © 2013 American Chemical Society.

Crack healing induced electrical and mechanical properties recovery in a Ti2SnC ceramic - Li, Shibo; Bei, Guoping; Chen, Xiaodong; Zhang, Linquan; Zhou, Yang; Mackovic, Mirza; Spiecker, Erdmann; Greil, Peter (Journal of the European Ceramic Society, 2016)
Ceramics are able to heal cracks and flaws by triggering local sintering (internal cracks) or oxidation reaction (surface cracks) which may induce the recovery of mechanical strength. Crack healing in ceramics, however, is limited to micro-sized cracks and requires elevated temperatures (above 1000°C) and long time periods even up to 100h. In this work we report on accelerated crack healing of a TiSnC ceramic which is capable to repair thermal shock induced cracks at a relatively low temperature of 800°C within only 1h. After healing treatment both the low flexural strength and electrical conductivity measured on the damaged material after quenching were almost fully recovered. Furthermore, TiSnC exhibits repeatable healing capability which offers a high potential for developing durable ceramics with prolonged lifetime under harsh thermal conditions.
Keywords: Carbides; Microstructure; Electrical conductivity; Mechanical properties; Electron microscopy

Creation of storage centers in CsBr: Eu2+ needle image plates by vacuum ultraviolet radiation - Weidner, Martina; Batentschuk, Miroslaw; Osvet, Andres; Winnacker, Albrecht; Tahon, J. P.; Leblans, P. (Journal of Applied Physics, 2009)
In this study, the photostimulated luminescence of the CsBr:Eu2+ needle image plates (NIPS) after vacuum ultraviolet (VUV) irradiation and their photoluminescence under VUV and UV excitation were investigated. It was shown that the photostimulable storage centers arise almost exclusively due to irradiation of the CsBr:Eu NIPs in the spectral lines of creation of the 4p55s anion excitons, and not in the region of interband transitions of CsBr. The explanation of the results is based mainly on the radiative and nonradiative decay of the self-localized e+Br_2- excitons.

Crowding of receptors induces ring-like adhesions in model membranes - Schmidt, Daniel; Bihr, Timo; Fenz, Susanne; Merkel, Rudolf; Seifert, Udo; Sengupta, Kheya; Smith, Ana-Suncana (Biochimica Et Biophysica Acta-Molecular Cell Research, 2015)
The dynamics of formation of macromolecular structures in adherent membranes is a key to a number of cellular processes. However, the interplay between protein reaction kinetics, diffusion and the morphology of the growing domains, governed by membrane mediated interactions, is still poorly understood. Here we show, experimentally and in simulations, that a rich phase diagram emerges from the competition between binding, cooperativity, molecular crowding and membrane spreading. In the cellular context, the spontaneously-occurring organization of adhesion domains in ring-like morphologies is particularly interesting. These are stabilized by the crowding of bulky proteins, and the membrane-transmitted correlations between bonds. Depending on the density of the receptors, this phase may be circumvented, and instead, the adhesions may grow homogeneously in the contact zone between two membranes. If the development of adhesion occurs simultaneously with membrane spreading, much higher accumulation of binders can be achieved depending on the velocity of spreading. The mechanisms identified here, in the context of our mimetic model, may shed light on the structuring of adhesions in the contact zones between two living cells. This article is part of a Special Issue entitled: Mechanobiology. (C) 2015 Elsevier B.V. All rights reserved.
Keywords: Cell adhesion; Immunological synapse; Adhesion dynamics; Membrane transmitted correlations; Ligand-receptor bonds; Crowding effects; Membrane fluctuations; Diffusion-reaction systems

Cryogenic optical localization provides 3D protein structure data with Angstrom resolution - Weisenburger, Siegfried; Boening, Daniel; Schomburg, Benjamin; Giller, Karin; Becker, Stefan; Griesinger, Christian; Sandoghdar, Vahid (Nature methods, 2017)
We introduce Cryogenic Optical Localization in 3D (COLD), a method to localize multiple fluorescent sites within a single small protein with Angstrom resolution. We demonstrate COLD by determining the conformational state of the cytosolic Per-ARNT-Sim domain from the histidine kinase CitA of Geobacillus thermodenitrificans and resolving the four biotin sites of streptavidin. COLD provides quantitative 3D information about small- to medium-sized biomolecules on the Angstrom scale and complements other techniques in structural biology.
EAM Import::2019-03-13

Crystal Shape Engineering of Silicon Nanoparticles in a Thermal Aerosol Reactor - Koermer, Richard; Butz, Benjamin; Spiecker, Erdmann; Peukert, Wolfgang (Crystal Growth & Design, 2012)
In this work, the capability of gas phase synthesis for crystal shape engineering of silicon nanoparticles (SiNP) in a hot wall reactor is demonstrated. Therefore, the necessary boundary conditions for the formation of monodisperse spherical SiNP as well as octahedral shaped particles from silane pyrolysis are systematically deduced. The different shapes of the SiNP are ascribed to different growth regimes (reaction limitation, diffusion limitation) depending on the global process parameters. Single crystalline, defect-free, spherical particles with a mean diameter of 30 nm (geometric standard deviation below 1.1) and octahedra with a mean edge length of about 100 nm could be obtained solely by process parameter adjustment. Particle size and shape as well as crystallinity were characterized by scanning electron microscopy and X-ray diffraction. The inner structure and faceting of the particles was analyzed in detail by high resolution transmission electron microscopy. A model which elucidates the orientation relation between inner silicon structure and the particle shape is derived for the octahedra.

Current annealing and electrical breakdown of epitaxial graphene - Hertel, Stefan; Kißlinger, Ferdinand; Jobst, Johannes; Waldmann, Daniel; Krieger, Michael; Weber, Heiko B. (Applied Physics Letters, 2011)
We report on epitaxial graphene on silicon carbide at high current densities. We observe two distinguished regimes, and a final breakdown. First for low current densities the conductance is enhanced due to desorption of adsorbates. Second with increasing bias the sample locally starts to glow and is strongly heated. The silicon carbide material decomposes, graphitic material is formed and thus additional current paths are created. The graphene layer breaks down, which is, however, not visible in high bias data. The final breakdown is a self-amplifying process resulting in a locally destroyed sample but surprisingly with better conductance than the original sample. © 2011 American Institute of Physics.
UnivIS-Import:2015-04-14:Pub.2011.nat.dphy.IAP.LAP.curren

Current dependent formation of PEDOT inverse nanotube arrays - Kowalski, Damian; Albu, Sergiu; Schmuki, Patrik (RSC Advances, 2013)
PEDOT nanostructures with distinct patterns can be formed by means of electrodeposition in titania nanotubes. The deposition process critically depends on the current protocol, leading to selective filling of the inner and/or outer space of the tubes. The approach allows for synthesis of vertically aligned PEDOT–titania composites or polymer nanostructures in the form of PEDOT inverse-nanotube-arrays and PEDOT nanopore-arrays.
EAM Import::2019-03-13

Current noise in single-molecule junctions induced by electronic-vibrational coupling - Schinabeck, Christian; Härtle, Rainer; Weber, Heiko B.; Thoss, Michael (Physical Review B, 2014)
The influence of multiple vibrational modes on current fluctuations in electron transport through single molecule junctions is investigated. Our analysis is based on a generic model of a molecular junction, which comprises a single electronic state on the molecular bridge coupled to multiple vibrational modes and fermionic leads, and employs a master equation approach. The results reveal that in molecular junctions with multiple vibrational modes, already weak to moderate electronic-vibrational coupling may result in high noise levels, especially at the onset of resonant transport, in accordance with the experimental findings of Secker et al. [Phys. Rev. Lett. 106, 136807 (2011)]. The underlying mechanisms are analyzed in some detail.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.LAP.curren

Curvature estimation from a volume-of-fluid indicator function for the simulation of surface tension and wetting with a free-surface lattice Boltzmann method - Bogner, Simon; Rüde, Ulrich; Harting, Jens (Physical Review E, 2016)
The free surface lattice Boltzmann method (FSLBM) is a combination of the hydrodynamic lattice Boltzmann method with a volume-of-fluid (VOF) interface capturing technique for the simulation of incompressible free surface flows. Capillary effects are modeled by extracting the curvature of the interface from the VOF indicator function and imposing a pressure jump at the free boundary. However, obtaining accurate curvature estimates from a VOF description can introduce significant errors. This article reports numerical results for three different surface tension models in standard test cases and compares the according errors in the velocity field (spurious currents). Furthermore, the FSLBM is shown to be suited to simulate wetting effects at solid boundaries. To this end, a new method is developed to represent wetting boundary conditions in a least-squares curvature reconstruction technique. The main limitations of the current FSLBM are analyzed and are found to be caused by its simplified advection scheme. Possible improvements are suggested.

Cyano-Functionalized Triarylamines on Au(111): Competing Intermolecular versus Molecule/Substrate Interactions - Gottardi, Stefano; Muller, Kathrin; Moreno-Lopez, Juan Carlos; Yildirim, Handan; Meinhardt, Ute; Kivala, Milan; Kara, Abdelkader; Stohr, Meike (Advanced Materials Interfaces, 2014)
The self-assembly of cyano-substituted triarylamine derivatives on Au(111) is studied with scanning tunneling microscopy and density functional theory calculations. Two different phases, each stabilized by at least two different cyano bonding motifs are observed. In the first phase, each molecule is involved in dipolar coupling and hydrogen bonding, while in the second phase, dipolar coupling, hydrogen bonding and metal-ligand interactions are present. Interestingly, the metal–ligand bond is already observed for deposition of the molecules with the sample kept at room temperature leaving the herringbone reconstruction unaffected. It is proposed that for establishing this bond, the Au atoms are slightly displaced out of the surface to bind to the cyano ligands. Despite the intact herringbone reconstruction, the Au substrate is found to considerably interact with the cyano ligands affecting the conformation and adsorption geometry, as well as leading to correlation effects on the molecular orientation.
EAM Import::2019-03-13

Cyano-Functionalized Triarylamines on Coinage Metal Surfaces: Interplay of Intermolecular and Molecule-Substrate Interactions - Muller, Kathrin; Moreno-Lopez, Juan Carlos; Gottardi, Stefano; Meinhardt, Ute; Yildirim, Handan; Kara, Abdelkader; Kivala, Milan; Stohr, Meike (Chemistry - A European Journal, 2016)
The self-assembly of cyano-functionalized triarylamine derivatives on Cu(111), Ag(111) and Au(111) was studied by means of scanning tunnelling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy and density functional theory calculations. Different bonding motifs, such as antiparallel dipolar coupling, hydrogen bonding and metal coordination, were observed. Whereas on Ag(111) only one hexagonally close-packed pattern stabilized by hydrogen bonding is observed, on Au(111) two different partially porous phases are present at submonolayer coverage, stabilized by dipolar coupling, hydrogen bonding and metal coordination. In contrast to the self-assembly on Ag(111) and Au(111), for which large islands are formed, on Cu(111), only small patches of hexagonally close-packed networks stabilized by metal coordination and areas of disordered molecules are found. The significant variety in the molecular self-assembly of the cyano-functionalized triarylamine derivatives on these coinage metal surfaces is explained by differences in molecular mobility and the subtle interplay between intermolecular and molecule-substrate interactions.
EAM Import::2019-03-13

Cyclic organization of stable periodic and chaotic pulsations in Hartley’s oscillator - Gallas, Jason A.; Gallas, Jason; Freire, J. G. (Chaos Solitons & Fractals, 2014)
A recent conjecture in this Journal, concerning the existence of spiral stability phases in Hartley’s oscillator, is corroborated amply. We report numerically computed stability phase diagrams indicating precisely where spirals of periodicity and chaos may be found in several control planes of the system. In addition, we describe some remarkable parameter loops in control space which allow one to trace identical dynamical behaviors by tuning totally independent parameters.

Cyclic thiouronium ionic liquids: Physicochemical properties and their electronic structure probed by X-ray induced photoelectron spectroscopy - Taccardi, Nicola; Niedermaier, Inga; Maier, Florian; Steinrück, Hans-Peter; Wasserscheid, Peter (Chemistry - A European Journal, 2012)
Radiography of a structure skeleton: Cyclic thiouronium ionic liquids have been synthesized and characterized in such a way that the straightforward introduction of three different alkyl substituents at the cation has been realized. X-ray induced photoelectron spectroscopy studies indicated a significant electronic contribution of the free electrons at the sulfur to stabilize the cationic charge, leading to structures with peculiar physicochemical properties (see figure). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Deciphering the Role of Impurities in Methylammonium Iodide and Their Impact on the Performance of Perovskite Solar Cells - Levchuk, Ievgen; Hou, Yi; Gruber, Marco; Brandl, Marco; Herre, Patrick; Tang, Xiaofeng; Högl, Florian; Batentschuk, Miroslaw; Osvet, Andres; Hock, Rainer; Peukert, Wolfgang; Tykwinski, Rik; et al. (Advanced Materials Interfaces, 2016)
Solution-based perovskite solar cell fabrication typically involves rather complex processing sequences to yield highest performance. While most studies concentrate on the exploration of processing conditions, the purity levels of common perovskite precursor solutions have been investigated and a number of impurities that are critically important toward controlling the crystallization of perovskites are found. In this study, an in-depth chemical study of the possible impurities formed during CHNHI preparation is presented and their relevance on solar cell processing is revealed. A primary consideration is the chemical transformation of hypophosphorous acid, which plays the role of the stabilizer for HI. The detrimental role of the impurities is best demonstrated by comparing perovskite solar cell devices fabricated from impurity-free precursors versus precursors containing different concentrations of impurities. Most interestingly, it is revealed that a certain concentration of impurities is detrimental to the growth of large-grained crystals. PbHPO nanoparticles, which are formed after hypophosphorous acid transformation, actually cause crystal domain growth through serving as a nucleation center. This study gives valuable insight into the rate determining steps of perovskite crystal growth and further provides the basis for developing reliable and reproducible high-performance recipes for perovskite solar cell processing.
Keywords: Grain size; Impurities; Perovskites; Seed growth; Solar cells

Decomposition of Acetic Acid on Model Pt/CeO2 Catalysts: The Effect of Surface Crowding - Neitzel, Armin; Lykhach, Yaroslava; Johanek, Viktor; Tsud, Nataliya; Skala, Tomas; Prince, Kevin C.; Matolin, Vladimir; Libuda, Jörg (Journal of Physical Chemistry C, 2015)
Adsorption and decomposition of acetic acid were studied by means of synchrotron radiation photoelectron spectroscopy, resonant photoemission spectroscopy, and temperature-programmed desorption on Pt/CeO2(111) model catalysts prepared on Cu(111). Reference experiments under identical conditions were performed on stoichiometric CeO2(111), partially reduced CeO2-x, and oxygen pre-exposed O/Pt/CeO2(111)/Cu(111). The principal species formed on all samples during adsorption of acetic acid at 150 K were acetate and molecularly adsorbed acetic acid. On the basis of the differences in the splitting between the methyl and carboxyl/carboxylate groups in the C 1s spectra, we identified the adsorption sites for acetate and molecularly adsorbed acetic acid on Pt/CeO2. During annealing, we detected an increase in the concentration of acetate on CeO2(111) support exclusively in the presence of supported Pt particles. The effect is caused by the decomposition of molecularly adsorbed acetic acid on Pt particles followed by spillover of acetate to CeO2(111) support. The following surface crowding by acetate on CeO2(111) support alters the decomposition mechanism of acetate with respect to the Pt-free CeO2(111). In particular, the formation of ketene and acetone was largely eliminated on Pt/CeO2. We assume that the surface crowding by acetate triggers a switch in the adsorption geometry of acetate from the bidentate to the monodentate configuration. The acetates in both adsorption geometries were identified according to the different splitting between the methyl and carboxylate groups in the C 1s spectra. Decomposition of acetate did not leave behind any surface carbon on Pt-free CeO2. In contrast, carbonaceous residues were found on CeO2-x, and Pt/CeO2. The carbon residues were oxidatively removed above 500 K only from Pt/CeO2.

Decorating polyelectrolyte wrapped SWNTs with CdTe quantum dots for solar energy conversion - Leubner, Susanne; Katsukis, Georgios; Guldi, Dirk Michael (Faraday Discussions, 2012)
We report herein on the development of a synthetic route towards SWNT/polyelectrolyte/QD nanohybrids. On one hand, negatively charged thioglycolic acid capped CdTe QDs were prepared via an aqueous solution based synthesis. On the other hand, SWNTs were coated with a positively charged polyelectrolyte. By virtue of electrostatic interactions between QDs and SWNTs, SWNT/polyelectrolyte/QD nanohybrids were realized, whose formation was corroborated by thorough spectroscopic and microscopic investigations. Of particular relevance are changes of the QD related emission - quantum yields and lifetimes - upon their integration into the nanohybrids. The latter is indicative for electronic communication between both the photo- and redoxactive constituents, namely QDs and SWNTs, whose nature is electron transfer. © 2012 The Royal Society of Chemistry.

Decoration of TiO2 nanotube layers with WO3 nanocrystals for high-electrochromic activity - Benoit, A.; Paramasivam, Indhumati; Nah, Yoon-Chae; Roy, Poulomi; Schmuki, Patrik (Electrochemistry Communications, 2009)
We report a simple approach to decorate ordered TiO_2 nanotube (TiNT) layers with tungsten trioxide nanocrystallites by the controlled hydrolysis of a WCl6 precursor. These WO_3 nanocrystallites, when formed, are amorphous, but can be annealed to a monoclinic crystal structure. The WO_3 crystallites on the TiO_2 nanotube skeleton are electrochemically active, and hence ion insertion reactions are possible. As a result, the decorated nanotube layers show remarkable enhancement of the electrochromic properties. In particular, a significantly lower threshold voltage and an increased electrochromic contrast can be achieved compared with unloaded (neat) TiO_2 nanotube layers.
EAM Import::2019-03-13

Deep-ultraviolet to mid-infrared supercontinuum generated in solid-core ZBLAN photonic crystal fibre - Jiang, Xin; Joly, Nicolas; Finger, Martin A.; Babic, Fehim; Wong, Gordon Kwan Leung; Travers, John C.; Russell, Philip St. John (Nature Photonics, 2015)
Silica-based photonic crystal fibre has proven highly successful for supercontinuum generation, with smooth and flat spectral power densities. However, fused silica glass suffers from strong material absorption in the mid-infrared (>2,500 nm), as well as ultraviolet-related optical damage (solarization), which limits performance and lifetime in the ultraviolet (<380 nm). Supercontinuum generation in silica photonic crystal fibre is therefore only possible between these limits. A number of alternative glasses have been used to extend the mid-infrared performance, including chalcogenides, fluorides and heavy-metal oxides, but none has extended the ultraviolet performance. Here, we describe the successful fabrication (using the stack-and-draw technique) of a ZBLAN photonic crystal fibre with a high air-filling fraction, a small solid core, nanoscale features and near-perfect structure. We also report its use in the generation of ultrabroadband, long-term stable, supercontinua spanning more than three octaves in the spectral range 200-2,500 nm.

Defects in oxygen-depleted titanate nanostructures - Vittadini, Andrea; Schirmer, Michael; Walz, Marie-Madeleine; Vollnhals, Florian; Lukasczyk, Thomas; Steinrück, Hans-Peter; Marbach, Hubertus; Riss, Alexander; Elser, Michael J.; Schürer, Benedikt; Diwald, Oliver (Langmuir, 2012)
The identification of defects and their controlled generation in titanate nanostructures is a key to their successful application in photoelectronic devices. We comprehensively explored the effect of vacuum annealing on morphology and composition of Na Ti O nanowires and protonated H Ti O nanoscrolls using a combination of scanning electron microscopy, Auger and Fourier-transform infrared (FT-IR) spectroscopy, as well as ab initio density functional theory (DFT) calculations. The observation that H Ti O nanoscrolls are more susceptible to electronic reduction and annealing-induced n-type doping than Na Ti O nanowires is attributed to the position of the conduction band minimum. It is close to the vacuum level and, thus, favors the Fermi level-induced compensation of donor states by cation vacancies. In agreement with theoretical predictions that suggest similar formation energies for oxygen and sodium vacancies, we experimentally observed the annealing induced depletion of sodium from the surface of the nanowires. © 2012 American Chemical Society.

Deformation behavior of nanocrystalline titania particles accessed by complementary in situ electron microscopy techniques - Herre, Patrick; Romeis, Stefan; Mackovic, Mirza; Przybilla, Thomas; Paul, Jonas; Schwenger, Jan; Torun, Boray; Grundmaier, Guido; Spiecker, Erdmann; Peukert, Wolfgang (Journal of the American Ceramic Society, 2017)
The mechanical behavior of nanostructured spherical submicrometer titania parti- cles was studied by in situ uniaxial compression experiments in the scanning and transmission electron microscope (SEM and TEM). Mesoporous and amorphous titania particles were prepared by a wet chemical sol-gel approach. To obtain nanocrystalline (nc) single-phase anatase and rutile particles the amorphous parti- cles were cryst allized by high-temperature annealing. For each sample the defor- mation behavior of at least 50 particles was investigated by in situ compression experiments in the SEM. In all cases an elastic – predominantly plastic deforma- tion behavior accompanied by crack initiation at exceptionally high engineering strain values of several percent were observed. Crack propagation presumably along grain boundaries and a Weibull distributed fracture stress was shown for all nc particles. Complementary in situ TEM experiment s and ex situ analysis of focused ion beam prepared particle cross-sections were carried out to identify the underlying deformati on mechanisms. Grain rotations and grain sliding are observed for nc anatase particles during in situ compr ession and are further identi- fied to be linked to a densification of the mesoporous particle structure. Our dedi- cated prepar ation and quanti tative in situ characterization methodology provides an excellent basis for a better understanding of the mechanical behavior of advanced ceramics.
Keywords: mechanical properties; nanoparticles; scanning electron microscopy; titanium oxide; transmission electron microscopy

Deformation of Platonic foam cells: Effect on growth rate - Evans, Myfanwy; Zirkelbach, Johannes; Schröder-Turk, Gerd; Kraynik, Andrew M.; Mecke, Klaus (Physical Review E, 2012)
The diffusive growth rate of a polyhedral cell in dry three-dimensional foams depends on details of shape beyond cell topology, in contrast to the situation in two dimensions, where, by von Neumann's law, the growth rate depends only on the number of cell edges. We analyze the dependence of the instantaneous growth rate on the shape of single foam cells surrounded by uniform pressure; this is accomplished by supporting the cell with films connected to a wire frame and inducing cell distortions by deforming the wire frame. We consider three foam cells with a very simple topology; these are the Platonic foam cells, which satisfy Plateau's laws and are based on the trivalent Platonic solids (tetrahedron, cube, and dodecahedron). The Surface Evolver is used to model cell deformations induced through extension, compression, shear, and torsion of the wire frames. The growth rate depends on the deformation mode and frame size and can increase or decrease with increasing cell distortion. The cells have negative growth rates, in general, but dodecahedral cells subjected to torsion in small wire frames can have positive growth rates. The deformation of cubic cells is demonstrated experimentally.

Dehydrogenation mechanism of liquid organic hydrogen carriers: Dodecahydro-N-ethylcarbazole on Pd(111) - Amende, Maximilian; Schernich, Stefan; Sobota, Marek; Nikiforidis, Ioannis; Hieringer, Wolfgang; Assenbaum, Daniel; Gleichweit, Christoph; Drescher, Hans-Jörg; Papp, Christian; Steinrück, Hans-Peter; Görling, Andreas; Wasserscheid, Peter; et al. (Chemistry - A European Journal, 2013)
Dodecahydro-N-ethylcarbazole (H-NEC) has been proposed as a potential liquid organic hydrogen carrier (LOHC) for chemical energy storage, as it combines both favourable physicochemical and thermodynamic properties. The design of optimised dehydrogenation catalysts for LOHC technology requires a detailed understanding of the reaction pathways and the microkinetics. Here, we investigate the dehydrogenation mechanism of H-NEC on Pd(111) by using a surface-science approach under ultrahigh vacuum conditions. By combining infrared reflection-absorption spectroscopy, density functional theory calculations and X-ray photoelectron spectroscopy, surface intermediates and their stability are identified. We show that H-NEC adsorbs molecularly up to 173 K. Above this temperature (223 K), activation of C-H bonds is observed within the five-membered ring. Rapid dehydrogenation occurs to octahydro-N-ethylcarbazole (H-NEC), which is identified as a stable surface intermediate at 223 K. Above 273 K, further dehydrogenation of H -NEC proceeds within the six-membered rings. Starting from clean Pd(111), C-N bond scission, an undesired side reaction, is observed above 350 K. By complementing surface spectroscopy, we present a temperature-programmed molecular beam experiment, which permits direct observation of dehydrogenation products in the gas phase during continuous dosing of the LOHC. We identify H-NEC as the main product desorbing from Pd(111). The onset temperature for H-NEC desorption is 330 K, the maximum reaction rate is reached around 550 K. The fact that preferential desorption of H -NEC is observed even above the temperature threshold for H -NEC dehydrogenation on the clean surface is attributed to the presence of surface dehydrogenation and decomposition products during continuous reactant exposure. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dehydrogenation of Ammonia on Ru(0001) by Electronic Excitations - Maier, Sabine; Stass, Ingeborg; Feng, Xiaofeng; Sisto, Aaron; Zayak, Alexey; Neaton, Jeffrey B.; Salmeron, Miquel (Journal of Physical Chemistry C, 2015)
We study the mechanism leading to the breaking of the N-H bonds in ammonia on Ru(0001) by means of scanning tunneling microscopy (STM). Our results support a model where injection of electrons or holes into antibonding (LUMO) and bonding (HOMO) orbitals of the molecule is far more effective than thermal excitations for molecular dissociation. We also found that a critical electric field between tip and surface is necessary to shape the tunneling barrier to obtain efficient rates of electrons from the tip or surface. First principle DFT calculations allow us to explain the observations and show that the applied electric field cannot by itself account for the observed dissociation. Since electron injection is the process governing photo- and electrochemical reactions, our STM study provides a detailed view of the reaction mechanism at the single molecular level in these nonthermal reactions.

Dehydrogenation of Dodecahydro-N-ethylcarbazole on Pd/Al2O3 Model Catalysts - Sobota, Marek; Nikiforidis, Ioannis; Amende, Maximilian; Sanmartίn Zanón, Beatriz; Staudt, Thorsten; Höfert, Oliver; Lykhach, Yaroslava; Papp, Christian; Hieringer, Wolfgang; Laurin, Mathias; Assenbaum, Daniel; Wasserscheid, Peter; et al. (Chemistry - A European Journal, 2011)
To elucidate the dehydrogenation mechanism of dodecahydro-N-ethylcarbazole (H-12-NEC) on supported Pd catalysts, we have performed a model study under ultra high vacuum (UHV) conditions. H-12-NEC and its final dehydrogenation product, N-ethylcarbazole (NEC), were deposited by physical vapor deposition (PVD) at temperatures between 120 K and 520 K onto a supported model catalyst, which consisted of Pd nanoparticles grown on a well-ordered alumina film on NiAl(110). Adsorption and thermally induced surface reactions were followed by infrared reflection absorption spectroscopy (IRAS) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) in combination with density functional theory (DFT) calculations. It was shown that, at 120 K, H-12-NEC adsorbs molecularly both on the Al2O3/NiAl(110) support and on the Pd particles. Initial activation of the molecule occurs through C-H bond scission at the 8a- and 9a-positions of the carbazole skeleton at temperatures above 170 K. Dehydrogenation successively proceeds with increasing temperature. Around 350 K, breakage of one C-N bond occurs accompanied by further dehydrogenation of the carbon skeleton. The decomposition intermediates reside on the surface up to 500 K. At higher temperatures, further decay to small fragments and atomic species is observed. These species block most of the absorption sites on the Pd particles, but can be oxidatively removed by heating in oxygen at 600 K, fully restoring the original adsorption properties of the model catalyst.
Keywords: density functional calculations; IR spectroscopy; liquid organic hydrogen carriers; photo-electron spectroscopy; supported catalysts

Dehydrogenation of dodecahydro-N-ethylcarbazole on Pt(111) - Gleichweit, Christoph; Amende, Maximilian; Schernich, Stefan; Zhao, Wei; Lorenz, Michael Peter Andreas; Höfert, Oliver; Brückner, Nicole; Wasserscheid, Peter; Libuda, Jörg; Steinrück, Hans-Peter; Papp, Christian (Chemsuschem, 2013)
Sloshing hydrogen: Liquid organic hydrogen carriers are high-boiling organic molecules, which can be reversibly hydrogenated and dehydrogenated in catalytic processes and are, therefore, a promising chemical hydrogen storage material. One of the promising candidates is the pair N-ethylcarbazole/perhydro- N-ethylcarbazole (NEC/H-NEC). The dehydrogenation and possible side reactions on a Pt(111) surface are evaluated in unprecedented detail. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dehydrogenation of Liquid Organic Hydrogen Carriers on Supported Pd Model Catalysts: Carbon Incorporation Under Operation Conditions - Schuster, Ralf; Waidhas, Fabian; Bertram, Manon; Runge, Henning; Geile, Simon; Shayduk, Roman; Abuin, Manuel; Vonk, Vedran; Noei, Heshmat; Lykhach, Yaroslava; Bertram, Florian; Stierle, Andreas; et al. (Catalysis Letters, 2018)
Liquid organic hydrogen carriers (LOHCs) have great potential as a hydrogen storage medium needed for a future sustainable energy system. Dehydrogenation of LOHCs requires a catalyst, such as supported Pd nanoparticles. Under reaction conditions, hydrogen and carbon may diffuse into the bulk of supported Pd catalyst particles and affect their activity and selectivity. The detailed understanding of this process is critical for the use of LOHCs in future hydrogen storage technologies. In this work, we studied these processes in-situ on a Pd model catalyst using high-energy grazing incidence X-ray diffraction. Pd nanoparticles were evaporated in ultra-high vacuum on a polished alpha-Al2O3(0001) substrate. The particles, with an initial average size of 3.4 nm, were investigated at elevated temperature during their interaction with H-2 and methylcyclohexane (MCH) representing a model LOHC. The interaction with H-2 was studied in-situ at partial pressures up to 1 bar and temperatures between 300 and 500 K. At 300 K, the Pd nanoparticles (NPs) show a transition from alpha-PdH to beta-PdH as a function of the H-2 pressure. The transition occurs gradually, which is attributed to the heterogeneity of the NP system. The hydrogen uptake in beta-PdHx at 300 K and 1 bar is estimated to be X-H 0.37 +/- 0.03 indicating that the miscibility gap is narrowed for the nanoparticular system. With increasing temperature, X-H decreases until no beta-PdH phase is formed anymore at 500 K. At the same temperature, we studied the interaction of the Pd/sapphire model catalyst with MCH, both in the presence and in the absence of H-2. In the absence of H-2, carbon is formed and diffuses into the bulk yielding PdCx with a C concentration of around x 0.05 +/- 0.01. In the presence of H-2 in the gas phase, bulk carbon formation in the Pd/sapphire model catalyst is completely suppressed. These results show that Pd nanoparticles act as an adequate catalyst for the dehydrogenation of MCH.[GRAPHICS].
Keywords: Liquid organic hydrogen carrier; Dehydrogenation; Carbon; XRD; Nanoparticles

Dehydrogenation of the Liquid Organic Hydrogen Carrier System Indole/Indoline/Octahydroindole on Pt(111) - Bachmann, Philipp; Schwarz, Matthias; Steinhauer, Johann; Späth, Florian; Düll, Fabian; Bauer, Udo; Nascimento Silva, Thais; Mohr, Susanne; Hohner, Chantal; Scheuermeyer, Marlene; Wasserscheid, Peter; Libuda, Jörg; et al. (Journal of Physical Chemistry C, 2018)
Indole derivatives are considered as promising liquid organic hydrogen carriers for renewable energy storage. Using X-ray photoelectron spectroscopy, temperature-programmed desorption, and infrared reflection absorption spectroscopy, we investigated low-temperature adsorption and dehydrogenation during heating of indole, indoline, and octahydroindole on Pt(111). For all three molecules, we find deprotonation of the NH bond above 270 K, accompanied with dehydrogenation of indoline and octahydroindole via an indole intermediate, resulting in an indolide species above 300 K. For octahydroindole, we also find a side reaction yielding small amounts of a pi-allyl species between 170 and 450 K. Above 450 K, decomposition of the remaining indolide species takes place.

Delamination and Dissolution of Titanate Nanowires: A Combined Structure and in Situ Second Harmonic Generation Study - Schürer, Benedikt; Elser, Michael J.; Sternig, Andreas; Peukert, Wolfgang; Diwald, Oliver (Journal of Physical Chemistry C, 2011)
Mechanistic insights into shape and structure transformation of metal oxide nanostructures are critical to our understanding of how synthesis parameters and chemical environment affect their properties. Na2Ti3O7 nanowires, which are composed of titanate nanosheets and which contain sodium ions in the interlayer region, are thermodynamically unstable in acid solutions. At room temperature nanosheet delamination along the nanowire length axis leads to coiled-up nanoscrolls. At 373 K, a dissolution and TiO2 recrystallization process gives rise to colloidal anatase nanoparticles. The impact of temperature on different reaction pathways is attributed to differences in the energy barriers associated with the two transformation channels. We comprehensively investigated these reactions with X-ray diffraction and electron microscopy and for the first time tracked processes at the solid–liquid interface such as nanosheet delamination by time-resolved second harmonic generation (SHG) measurements. The applicability of the SHG method for in situ studies which address the transformation of layered nanostructures in aqueous solution even at high electrolyte concentrations is demonstrated.

Delamination of graphite in a high pressure homogenizer - Nacken, Thomas; Damm, Cornelia; Walter, Johannes; Rüger, Andreas; Peukert, Wolfgang (RSC Advances, 2015)
A scalable industrial method for graphene and Few-Layer-Graphene (FLG) production by graphite delamination in N-methylpyrrolidone and water-surfactant mixtures using a high pressure homogenizer is presented. This paper is focused on processing conditions and extensive subsequent analysis of the delaminated products by a combination of analytical ultracentrifugation, UV/Vis and statistical Raman spectroscopies including co-localization with atomic force microscopy. In this way quantitative processing-structure-property correlations showing how suspension properties and processing parameters governing yield, quality and lateral dimension of the produced graphene are obtained. It is found that a high pressure homogenizer can be used to obtain sufficiently high concentrated FLG suspensions with low defect concentration.

DEM simulation of particles of complex shapes using the multisphere method: Application for additive manufacturing - Ribeiro Parteli, Eric Josef (AIP Conference Proceedings, 2013)
Additive manufacturing constitutes a promising production technology with potential application in a broad range of industrial areas. In this type of manufacturing process, objects are created from powder particles by adding layers of material upon one another through selectively melting particles from the powder bed. However, understanding the mechanical behavior of the powder during manufacturing as a function of material properties and particle shape is an essential pre-requisite for optimizing the production process. Here we develop a numerical tool for modeling the dynamics of powder particles during additive manufacturing based on force-based simulations by means of the Discrete Element Method (DEM). An existing DEM software (LIGGGHTS) is extended in order to study the transport of powder particles of complex geometric shapes through accounting for the boundary conditions inherent to the manufacturing proces
Keywords: additive manufacturing; DEM simulation; granular materials; multisphere method

Dendritic architectures with positively charged cores and negatively charged shells - Schunk, Torsten; Hirsch, Andreas (European Journal of Organic Chemistry, 2012)
A new family of dipolar ionic dendrimers that consist of a cationic pyridinium core surrounded by a negatively charged shell of carboxylic acids was successfully synthesized and characterized. Both spherical architectures and examples of amphiphiles with a dipolar head group were synthesized. Studies of the aggregation behaviour in aqueous solution by determining the cmc values were performed. This new type of dipolar core-shell dendrons can be considered as molecular architectures that contain a positively charged nucleus covalently incorporated within a negatively charged shell. Dipolar ionic dendrimers that consist of dendronized pyridinium units surrounded by a shell of carboxylic acids are a new family of dendritic architectures in which opposite charges are organized within specific areas of one macromolecule. They can be considered as molecular architectures that contain a positively charged nucleus covalently incorporated within a negatively charged shell. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dendritic porphyrin-fullerene conjugates: Efficient light-harvesting and charge-transfer events - Schlundt, Sebastian; Kuzmanich, Gregory; De Miguel Rojas, Gustavo; Kovács, Christian; Garcia-Garibay, Miguel A.; Guldi, Dirk Michael; Hirsch, Andreas; et al. (Chemistry - A European Journal, 2009)
A novel dendritic C-HP(ZnP) (P = porphyrin) conjugate gives rise to the successful mimicry of the primary events in photosynthesis, that is, light harvesting, unidirectional energy transfer, charge transfer, and charge-shift reactions. Owing, however, to the flexibility of the linkers that connect the Q, HP, and ZnP units, the outcome depends strongly on the rigidity/viscosity of the environment. In an agar matrix or Triton X-100, timeresolved transient absorption spectroscopic analysis and fluorescence-lifetime measurements confirm the following sequence. Initially, light harvesting is seen by the peripheral C-H P-*(ZnP) conjugate. Once photoexcited, a unidirectional energy transfer funnels the singlet excited-state energy to HP to form C-*(HP)-(ZnP), which powers an intramolecular charge transfer that oxidizes the photoexcited HP and reduces the adjacent C species. In the correspondingly formed (C)'(HP) -(ZnP) conjugate, an intramolecular charge-shift reaction generates (C)-HP-(ZnP) , in which the radical cation resides on one of the three ZnP moieties, and for which lifetimes of up to 460 ns are found. On the other hand, investigations in organic media (i.e., toluene, THF, and benzonitrile) reveal a short cut, that is, the peripheral ZnP unit reacts directly with C to form (C)H P-(ZnP) . Substantial configurational rearrangements-placing ZnP and C in proximity to each other-are, however, necessary to ensure the required through space interactions (i.e., close approach). Consequently, the lifetime of (C)'"-H P(ZnP) is as short as 100 ps in benzonitrile. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA,.

Dendronizing and metalating trans-2 C60 tetraaryl porphyrins - A versatile approach toward water-soluble donor-acceptor conjugates - Ruppert, Michaela; Spänig, Fabian; Wielopolski, Mateusz; Jäger, Christof; Bauer, Walter; Clark, Timothy; Hirsch, Andreas; Guldi, Dirk Michael (Chemistry - A European Journal, 2010)
We have realized for the first time a series of truly water-soluble and tightly coupled porphyrin/C electron-donor-acceptor conjugates in which the charge separation and charge recombination dynamics are controlled by modifying the nature of the dendrimer and/or the choice of the central metal atom. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA. Weinheim.

Densest Local Structures of Uniaxial Ellipsoids - Schaller, Fabian; Weigel, Robert; Kapfer, Sebastian (Physical Review X, 2016)
Connecting the collective behavior of disordered systems with local structure on the particle scale is an important challenge, for example, in granular and glassy systems. Compounding complexity, in many scientific and industrial applications, particles are polydisperse, aspherical, or even of varying shape. Here, we investigate a generalization of the classical kissing problem in order to understand the local building blocks of packings of aspherical grains. We numerically determine the densest local structures of uniaxial ellipsoids by minimizing the Set Voronoi cell volume around a given particle. Depending on the particle aspect ratio, different local structures are observed and classified by symmetry and Voronoi coordination number. In extended disordered packings of frictionless particles, knowledge of the densest structures allows us to rescale the Voronoi volume distributions onto the single-parameter family of k-Gamma distributions. Moreover, we find that approximate icosahedral clusters are found in random packings, while the optimal local structures for more aspherical particles are not formed.
EAM Import::2019-03-13

Densification of Silica Spheres: A New Pathway to Nano-Dimensioned Zeolite-Based Catalysts - Machoke, Albert; Apeleo Zubiri, Benjamin; Leonhardt, Rainer; Marthala, Venkata; Schmiele, Martin; Unruh, Tobias; Hartmann, Martin; Spiecker, Erdmann; Schwieger, Wilhelm (Chemistry - A European Journal, 2017)
Nanosized materials are expected to play a unique role in the development of future catalytic processes. Herein, pre-prepared and geometrically well-defined amorphous silica spheres are densified into silica-rich zeolites with nanosized dimensions. After the densification, the obtained nanosized zeolites exhibit the same spherical morphology like the starting precursor but characterized by a drastically reduced size, higher density, and high crystallinity. The phase transformation into crystalline zeolite material and the densification effect are achieved through a well-controlled steam-assisted treatment of the larger precursor particles so that the transformation process proceeds always towards the center of the spheres, just like a shrinking process. Furthermore, this procedure is applicable also to commercially available silica particles, as well as aluminum-containing systems (precursors) leading to acidic nano-catalysts with improved catalytic performance.
Keywords: catalytic cracking; crystallization; heterogeneous catalysis; nanoparticles; silica-rich zeolites

Density and surface tension of ionic liquids - Kolbeck, Claudia; Lehmann, Julia; Lovelock, Kevin; Cremer, Till; Paape, Natalia; Wasserscheid, Peter; Fröba, Andreas Paul; Maier, Florian; Steinrück, Hans-Peter (Journal of Physical Chemistry B, 2010)
We measured the density and surface tension of 9 bis[(trifluoromethyl) sulfonyl]imide ([Tf N] )-based and 12 1-methyl-3- octylimidazolium ([C C Im] )-based ionic liquids (ILs) with the vibrating tube and the pendant drop method, respectively. This comprehensive set of ILs was chosen to probe the influence of the cations and anions on density and surface tension. When the alkyl chain length in the [C C Im][Tf N] series (n) 1, 2, 4, 6, 8, 10, 12) is increased, a decrease in density is observed. The surface tension initially also decreases but reaches a plateau for alkyl chain lengths greater than n) 8. Functionalizing the alkyl chains with ethylene glycol groups results in a higher density as well as a higher surface tension. For the dependence of density and surface tension on the chemical nature of the anion, relations are only found for subgroups of the studied ILs. Density and surface tension values are discussed with respect to intermolecular interactions and surface composition as determined by angle-resolved X-ray photoelectron spectroscopy (ARXPS). The absence of nonvolatile surface-active contaminants was proven by ARXPS. © 2010 American Chemical Society.

Density functional calculations and IR reflection absorption spectroscopy on the interaction of SO2 with oxide-supported Pd nanoparticles - Luckas, Nicola; Vines Solana, Francesc; Happel, Markus; Desikusumastuti, Aine; Libuda, Jörg; Görling, Andreas (Journal of Physical Chemistry C, 2010)
A systematic study on the interaction of sulfur dioxide (SO) on BaO-supported Pd nanoparticles has been carried out using suitable models and state-of-the-art density functional (DF) calculations. Detailed information concerning the structure and energetics of the different conformations of adsorbed SO is provided as a function of coverage together with calculated infrared reflection absorption spectroscopy (IRAS) spectra. SO may adsorb on Pd(111) in several conformations, some active, η-SO and η-S , and others inactive in IRAS, η-SO O. SO is found to attach stronger to Pd nanoparticle edges and corners, a fact intimately related to catalyst poisoning by site blocking. On Pd nanoparticles, SO is found to preferably adopt adsorption conformations that depend on the specific region on the nanoparticle, thus adding site specificity to vibrational recognition. Molecular beam experiments and IRAS have been performed on a single-crystal-based Pd/BaAlO/NiAl(110) model NO storage and reduction catalyst and its individual components. SO formation on the oxide components, evolution of a SO multilayer, and adsorption of SO on BaO or Pd nanoparticles is linked to DF calculations. The effect of cation intermixing in the oxide support and overlap of absorption bands on the unequivocal discrimination of signals are discussed. © 2010 American Chemical Society.

Density-functional theory with orbital- dependent functionals: Exact-exchange Kohn-Sham and density-functional response methods - Görling, Andreas; Ipatov, Andrey; Götz, Andreas; Heßelmann, Andreas (Zeitschrift für Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics, 2010)
Kohn-Sham methods with orbital-dependent exchange-correlation functionals, in particular exact-exchange methods, are discussed. The numerical stability of optimized-effective-potential methods to construct the exchange-correlation potential in the case of orbital-dependent energy functionals is considered. A numerically stable exact-exchange Kohn-Sham method is briefly presented. A new ansatz for time-dependent density-functional methods in the response regime is considered and an exact-exchange time-dependent density-functional method based on it is discussed and it is demonstrated that this methods is able to treat qualitatively correctly charge- transfer excitations. © by Oldenbourg Wissenschaftsverlag, München.

Derivation of the dispersion energy as an explicit density- and exchange-hole functional - Heßelmann, Andreas (Journal of Chemical Physics, 2009)
Through some simple derivations, it is shown that the nonexpanded dispersion interaction energy between two molecules can entirely be written in terms of the densities and the exchange-holes of the monomers. Thus the suspicion of Becke and Johnson [J. Chem. Phys. 122, 154104 (2005) ] that the dispersion energy might be related to fluctuating dipoles produced by the electrons and their accompanying exchange-holes is confirmed. However, it will be shown that the current asymptotic result for the dispersion energy is different from the Becke–Johnson model. Some preliminary results for the polarizabilities and dispersion coefficients of a few atoms and small molecules demonstrate that the approach described in this work might be useful to estimate response properties and long-range correlation energies of molecular systems in general.
EAM Import::2019-03-13

Desiccator Volume: A Vital Yet Ignored Parameter in CaCO3 Crystallization by the Ammonium Carbonate Diffusion Method - Harris, Joseph; Wolf, Stephan (Minerals, 2017)
Employing the widely used ammonium carbonate diffusion method, we demonstrate that altering an extrinsic parameter—desiccator size—which is rarely detailed in publications, can alter the route of crystallization. Hexagonally packed assemblies of spherical magnesium-calcium carbonate particles or spherulitic aragonitic particles can be selectively prepared from the same initial reaction solution by simply changing the internal volume of the desiccator, thereby changing the rate of carbonate addition and consequently precursor formation. This demonstrates that it is not merely the quantity of an additive which can control particle morphogenesis and phase selectivity, but control of other often ignored parameters are vital to ensure adequate reproducibility.
EAM Import::2019-03-13

Design and Additive Manufacturing of 3D Phononic Band Gap Structures Based on Gradient Based Optimization - Wormser, Maximilian; Wein, Fabian; Stingl, Michael; Körner, Carolin (Materials, 2017)
We present a novel approach for gradient based maximization of phononic band gaps. The approach is a geometry projection method combining parametric shape optimization with density based topology optimization. By this approach, we obtain, in a two dimension setting, cellular structures exhibiting relative and normalized band gaps of more than 8 and 1.6, respectively. The controlling parameter is the minimal strut size, which also corresponds with the obtained stiffness of the structure. The resulting design principle is manually interpreted into a three dimensional structure from which cellular metal samples are fabricated by selective electron beam melting. Frequency response diagrams experimentally verify the numerically determined phononic band gaps of the structures. The resulting structures have band gaps down to the audible frequency range, qualifying the structures for an application in noise isolation.
Keywords: phononic band gap; additive manufacturing; selective electron beam melting; cellular materials; metamaterials; topology optimization; parametric shape optimization; gradient based optimization

Designing Squaraines to Control Charge Injection and Recombination Processes in NiO-based Dye-Sensitized Solar Cells - Langmar, Oliver; Saccone, Davide; Amat, Anna; Fantacci, Simona; Viscardi, Guido; Barolo, Claudia; Costa, Ruben Dario; Guldi, Dirk Michael (ChemSusChem, 2017)
Herein, the synthesis of a new family of squaraines (SQs) and their application in p-type dye-sensitized solar cells (DSSCs) is presented. In particular, two sets of SQs were designed featuring either two or four anchoring carboxylic groups combined with either oxygen or dicyanovinyl central groups. The SQs were characterized by using a joint theoretical, photophysical, and electrochemical approach. Importantly, the presence of different central groups forces a frozen cis (dicyanovinyl group) or a trans (oxygen group) SQ conformation. Based on the latter, the current work enables a direct comparison between cis and trans isomers as well as the impact of a different number of anchors. Considering their electron-accepting and light-harvesting character, they were tested in NiO-based DSSCs. Photocurrent-voltage, incident photon-to-current conversion efficiency (IPCE), and electrochemical impedance spectroscopy measurements were performed. By virtue of their different symmetry, stereochemistry, and number of carboxylic groups, altered adsorption behavior onto NiO electrodes as well as diverse charge injection and charge recombination dynamics were noted under operation conditions. SQs with four linkers in a frozen cis isomerism show the best charge collection properties among the investigated SQs, providing a valuable guideline for the molecular design of future SQs for p-type DSSCs. In addition, we assembled tandem DSSCs featuring SQ/NiO photocathodes and N719/TiO2 photoanodes. The IPCE of the resulting tandem DSSCs implies light harvesting throughout most of the visible part of the solar spectrum owing to the complementary absorption features of SQ and N719.
EAM Import::2019-03-13

Designing ternary blend bulk heterojunction solar cells with reduced carrier recombination and a fill factor of 77% - Gasparini, Nicola; Jiao, Xuechen; Heumüller, Thomas; Baran, Derya; Matt, Gebhard; Fladischer, Stefanie; Spiecker, Erdmann; Ade, Harald; Brabec, Christoph; Ameri, Tayebeh (Nature Energy, 2016)
In recent years the concept of ternary blend bulk heterojunction (BHJ) solar cells based on organic semiconductors has been widely used to achieve a better match to the solar irradiance spectrum, and power conversion effciencies beyond 10% have been reported. However, the fill factor of organic solar cells is still limited by the competition between recombination and extraction of free charges. Here, we design advanced material composites leading to a high fill factor of 77% in ternary blends, thus demonstrating how the recombination thresholds can be overcome. Extending beyond the typical sensitization concept, we add a highly ordered polymer that, in addition to enhanced absorption, overcomes limits predicted by classical recombination models. An effective charge transfer from the disordered host system onto the highly ordered sensitizer effectively avoids traps of the host matrix and features an almost ideal recombination behaviour.

Design of Auxetic Structures via Mathematical Optimization - Schwerdtfeger, Jan; Wein, Fabian; Leugering, Günter; Singer, Robert; Körner, Carolin; Stingl, Michael; Schury, F. (Advanced Materials, 2011)
The optimization and manufacturing of an auxetic structure is presented. An inverse homogenization method is used to obtain the optimized geometry shown in the figure. The resulting structure is then produced using selective electron beam melting. The numerically predicted properties are experimentally verifie

Design of graded materials by particle reinforcement during accumulative roll bonding - Schmidt, Christian; Ruppert, Mathis; Höppel, Heinz Werner; Nachtrab, Frank; Dietrich, Anja; Hanke, Randolf; Göken, Mathias (Advanced Engineering Materials, 2012)
Graded distributions of copper particles in ultrafine-grained aluminium sheets are produced by accumulative roll bonding and particle reinforcement. The metallic copper particles are sprayed on the sheet surfaces under variation of spray distance and/or relative velocity of the spray gun to the sheet. Therewith, the particle content could be varied by a factor of three. After solutionizing, the successful gradation is clearly proven by tensile tests showing a steady and monotonous gradient along the rolling direction. By a systematic analysis of the spraying process, the particle content profile is calculated. Accuracy of the calculation is confirmed by electrical resistivity measurements. The presented method enables the production of tailored sheets by graded particle reinforcement. The graded sheets are also used for basic investigation of materials properties along graded compositions.
WW1::920

Design of low band gap small molecules with alkyldicyanovinyl acceptor and different donor groups for efficient bulk heterojunction organic solar cells - Luponosov, Yuriy N.; Min, Jie; Solodukhin, Alexander N.; Chvalun, Sergei N.; Ameri, Tayebeh; Brabec, Christoph; Ponomarenko, Sergey A. (2015 Organic Photovoltaics XVI, 2015)
A library of low band gap small molecules with alkyldicyanovinyl acceptor and triphenylamine, tris(2-methoxyphenyl)amine or dithienosilole donor groups linked through (oligo)thiophene conjugated spacers was designed and successfully synthesized. Systematic variations of the alkyl chain length and the number of conjugated thiophene rings in the molecules allowed to elucidate the structure-properties relationships for their solubility, absorption spectra, phase behavior, morphology and structure in thin films, as well as photovoltaic properties. Bulk heterojunction organic solar cells prepared from these molecules as donors and PCBM[70] as acceptor by solution processing showed power conversion efficiency up to 5.4-6.4%.
Keywords: bulk heterojunction; dicyanovinyl; dithienosilole; donor-acceptor oligomers; oligothiophenes; Organic photovoltaics; solution processing; triphenylamine

Detailed Analysis of the Growth Kinetics of ZnO Nanorods in Methanol - Voigt, Michael; Klaumünzer, Martin; Thiem, Heiko; Peukert, Wolfgang (Journal of Physical Chemistry C, 2010)
The growth kinetics of ZnO nanorods in methanol is studied by a combination of scanning and high-resolution transmission electron microscopy and X-ray diffraction analysis. In the early stage of growth oriented attachment of 2−3 spheroidal crystallites to rod-like structures occurs. Later, rods of up to 90 nm in length with a hexagonal cross-section up to 18 nm in diameter form by ripening. Our main finding is that the growth follows a power law as a function of the ripening time with exponents of 0.32 to 0.39 for the length and 0.17 to 0.21 for the diameter. In contrast to previous studies on the growth of ZnO rods in alcohols our results indicate that the growth is dominated by anisotropic Ostwald ripening that is limited by volume diffusion.

Detailed Investigation of the Mechanism of Rh-Diphosphite Supported Ionic Liquid Phase (SILP)-Catalyzed 1-Butene Hydroformylation in the Gas Phase via Combined Kinetic and Density Functional Theory (DFT) Modeling Studies - Walter, Simon; Spohr, Hanna; Franke, Robert; Hieringer, Wolfgang; Wasserscheid, Peter; Haumann, Marco (ACS Catalysis, 2017)
A detailed kinetic investigation of the gas-phase continuous hydroformylation of 1-butene has been carried out. The supported ionic liquid phase (SILP) catalyst was based on a Rh-diphosphite, the ionic liquid [EMIM][NTf2), and silica support material. Based on the established Wilkinson mechanism, the hyperbolic rate expressions were used to fit the experimental results. While the hydroformylation could be modeled with high accuracy, the hydrogenation and isomerization trends could not be reproduced by the given rate expressions. An alternative reaction mechanism was developed and allowed an excellent fit of experimental data by the new reaction rate expressions. Initial steps of the mechanism were studied using density functional theory (DFT) calculations.
Keywords: hydroformylation; hydrogenation; isomerization; supported ionic liquid phase (SILP); kinetic modeling; density functional theory (DFT)

Detailed investigations of ZnO photoelectrodes preparation for dye sensitized solar cells - Marczak, Renata; Werner, Fabian; Ahmad, Rameez; Lobaz, Volodymyr; Guldi, Dirk Michael; Peukert, Wolfgang (Langmuir, 2011)
Wurtzite ZnO hexagonal nanopyramids were successfully synthesized in the liquid phase from homogeneous methanolic solutions of zinc acetate and tetramethylammonium hydroxide at an excess of zinc ions. The formation and properties of the nanocrystals were examined as a function of synthesis conditions. No significant influence of the [Zn ]/[OH ] ratio was noticed on the final particle size, in spite of increased amounts of OH ions, which tend to accelerate the particle nucleation and growth. Nevertheless, the reactant concentration ratio influences the surface properties of the ZnO nanocrystals. Mesoporous ZnO films were prepared by doctor blading ethanolic pastes containing ZnO nanoparticles and ethyl cellulose onto FTO conductive glass substrate followed by calcination. Additionally, the influence of a plasticizer (triacetin)-used during the paste preparation-on the film quality was investigated. A higher content of ZnO nanoparticles and plasticizer in the pastes improved the film quality. Four different temperatures (i.e., 400, 425, 450, and 475 °C) were used for the film calcination and their influence on the structural properties of the films was characterized. In principle, increasing the calcination temperature goes hand in hand with an increase of particle size, as well as the pore diameter and reduction of the surface area. Suitable mesoporous films were employed as photoanodes in dye sensitized solar cells (DSSCs). In order to assess the effect of the varied parameters on complete DSSC devices-using cis-diisothiocyanato-bis(2,2′- bipyridyl-4,4′-dicarboxylato) ruthenium(II)bis(tetrabutylammonium (N719) as a sensitizer-incident photon to current efficiency (IPCE) and current voltage measurements were carried out. The IPCE measurements confirmed photoinduced electron injection from the dye, reaching IPCE values up to 76%. Furthermore, current-voltage characteristics of complete cells emphasized the importance of the proper preparation methods and temperatures. These features are important assets for the preparation of nanocrystalline ZnO based photoelectrodes and for improving the DSSC performance. © 2011 American Chemical Society.

Detailed kinetic investigations on the selective oxidation of biomass to formic acid (OxFA process) using model substrates and real biomass - Albert, Jakob; Reichert, Jenny (ACS Sustainable Chemistry & Engineering, 2017)
A detailed kinetic analysis of the selective catalytic oxidation of different biogenic model substrates to formic acid (OxFA process) is presented using two different polyoxometalate catalysts, HPA-2 (H5PV2Mo10O40) and HPA-5 (H8PV5Mo7O40). By using high oxygen pressures (30-60 bar) and temperatures of 80-90 °C in aqueous solution, we were able to investigate the rate-determining substrate oxidation step catalyzed by the oxidized form of the polyoxometalates (POMs) by keeping the concentration of the catalytic active species constant. Under these conditions, kinetic parameters like effective reaction order and reaction rate constants could be determined by the differential method for model substrates like glucose, fructose, sorbitol, and gluconic acid. Furthermore, kinetic experiments using the two different catalysts showed a different behavior for various functionalities within the carbon framework of the substrate with the tendency of higher reaction rates with the HPA-5 catalyst. This effect was more pronounced for disaccharides like cellobiose and sucrose than for monosaccharides. Finally, a detailed kinetic study for water-insoluble biomasses like beech and spruce wood showed differences in formic acid (FA) formation and product selectivities depending on the composition of the wood in terms of their ratios of lignin, cellulose, and hemicellulose.

Detailed kinetic study of cumene isopropylation in a liquid-liquid biphasic system using acidic chloroaluminate ionic liquids. - Joni, Joni; Schmitt, Daniel; Schulz, Peter; Lotz, T. J.; Wasserscheid, Peter (Journal of Catalysis, 2008)
A kinetic study of cumene isopropylation has been carried out using the acidic ionic liq. 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl)/AlCl3 (molar ratio 1:2) as the catalyst phase in a semi-batch liq.-liq. biphasic reaction system. Kinetic models representing the alkylation reaction network have been established based on reaction temp. and propylene partial pressure variations. By comparing the results of the kinetic models with the measured concns. in the liq. org. phase, the importance of the different product solubilities in the acidic ionic liq. became evident. Correction of the product concns. in the org. phase based on a COSMO-RS calcn. of the relative product solubilities in the acidic ionic liq. [EMIM][Al2Cl7] gave a remarkably good prediction of the reaction kinetics by the kinetic model. These findings demonstrate the suitability of COSMO-RS to predict the relative solubilities of different arom. compds. in highly reactive catalytic systems. [on SciFinder(R)]
Keywords: cumene isopropylation kinetics biphasic system acidic chloroaluminate ionic liq

Determination of solubility parameters for organic semiconductor formulations - Machui, Florian; Abbott, Steven; Waller, David; Koppe, Markus; Brabec, Christoph (Macromolecular Chemistry and Physics, 2011)
The concept of Hansen solubility parameters (HSP) is applied to organic semiconductors in order to determine and predict their solubility behavior, which is essential for the design of functional and environmentally friendly ink formulations for organic photovoltaics. Two different conjugated polymers, one semicrystalline and one dominantly amorphous, and one fullerene derivative are selected as prototype candidates to evaluate the applicability of the HSP concept for organic semiconductors. The method for determining the solubility parameters is described and the quality of the HSP fits as well as their suitability for designing of organic electronic inks are discussed in detail. The applicability of Hansen solubility parameters in designing organic semiconductor ink formulations is analyzed by determining and predicting the solubility behavior of three different organic semiconductors. A large number of solvents are studied and temperature-dependent solubility is examined to enhance the practical relevance of this work. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: conjugated polymers; fullerenes; Hansen solubility parameters (HSP); ink formulations; organic photovoltaics

Determination of the effective refractive index of nanoparticulate ITO layers - Baum, Marcus; Alexeev, Ilya; Latzel, Michael; Christiansen, Silke; Schmidt, Michael (Optics Express, 2013)
Nanoparticles of transparent conducting oxides, such as indium tin oxide, can be used in printing techniques to generate functional layers for various optoelectronic devices. Since these deposition methods do not create fully consolidated films, the optical properties of such layers are expected to be notably different from those of the bulk material and should be characterized on their own. In this work we present a way to measure the effective refractive index of a particulate ITO layer by refraction of light. The obtained data points are used to identify an accurate layer model for spectroscopic ellipsometry. In this way the complex refractive index of the particle layer is determined in a wide spectral range from ultra violet to near infrared.
Keywords: ITO; refractive index; effective; ellipsometry

Determination of the interfacial strength and fracture toughness of a-C:H coatings by in-situ microcantilever bending - Schaufler, Jens; Schmid, Christoph; Durst, Karsten; Göken, Mathias (Thin Solid Films, 2012)
The interfacial fracture strength and toughness of two hydrogenated amorphous carbon coatings (a-C:H) with Cr-adhesion layers on steel substrate have been determined directly by in-situ deformation tests using microcantilever bending experiments. The coating conditions for the two systems were essentially the same, only slight differences have been introduced in the adhesion layer. These changes resulted in a totally different delamination behavior, from excellent to poor adhesion. The well adherent interface between the adhesion layer and the a-C:H has a fracture strength and toughness value close to the a-C:H coating itself. For bulk a-C:H a bending strength close to the theoretical strength was found, indicating that the tested volume was defect free. Changing the process conditions reduced the bending strength by 40%, leading to strong delamination and a catastrophic behavior during Rockwell C testing. An interfacial fracture toughness value of 2.18 MPa m0.5 was found for the well adherent coating, exceeding even that of pure a-C:H.
WW1::921

Determination of the Lateral Dimension of Graphene Oxide Nanosheets Using Analytical Ultracentrifugation - Walter, Johannes; Nacken, Thomas; Damm, Cornelia; Thajudeen, Thaseem; Eigler, Siegfried; Peukert, Wolfgang (Small, 2014)
In this paper, a method to determine the lateral dimensions of 2D nanosheets directly in suspension by analytical ultracentrifugation (AUC) is shown. The basis for this study is a well-characterized and stable dispersion of graphene oxide (GO) monolayers in water. A methodology is developed to correlate the sedimentation coefficient distribution measured by AUC with the lateral size distribution of the 2D GO nanosheets obtained from atomic force microscopy (AFM). A very high accuracy can be obtained by virtue of counting several thousand sheets, thereby minimizing any coating effects or statistical uncertainties. The AFM statistics are further used to fit the lateral size distribution obtained from the AUC to determine the unknown hydrodynamic sheet thickness or density. It is found that AUC can derive nanosheet diameter distributions with a relative error of the mean sheet diameter of just 0.25% as compared to the AFM analysis for 90 mass% of the particles in the distribution. The standard deviation of the size-dependent error for the total distribution is found to be 3.25%. Based on these considerations, an expression is given to calculate the cut size of 2D nanosheets in preparative centrifugation experiments.

Determination of the length and diameter of nanorods by a combination of analytical ultracentrifugation and scanning mobility particle sizer - Thajudeen, Thaseem; Walter, Johannes; Srikantharajah, Rubitha; Lübbert, Christian; Peukert, Wolfgang (Nanoscale Horizons, 2017)
A combination of orthogonal measurement techniques is utilized in this study to predict the average lengths and diameters of colloidal nanorods. Sedimentation coefficient distributions and electrical mobility distributions obtained from analytical ultracentrifugation and a scanning mobility particle sizer, respectively, are used for the hydrodynamic correlation. The method is validated theoretically and application to Au and ZnO nanorod samples is shown. The results demonstrate that the combination of both measurement techniques is an excellent method for the two-dimensional characterization of nanorods.

Determination of the strain-rate sensitivity of ultrafine-grained materials by spherical nanoindentation - Feldner, Patrick; Merle, Benoit; Göken, Mathias (Journal of Materials Research, 2017)
The strain-rate sensitivity of the flow stress represents a crucial parameter for characterizing the deformation kinetics of a material. In this work a new method was developed and validated for determining the local strain-rate sensitivity of the flow stress at different plastic strains. The approach is based on spherical nanoindentation strain-rate jump tests during one deformation experiment. In the case of ultrafine-grained Al and ultrafine-grained Cu good agreement between this technique and macroscopic compression tests has been achieved. In contrast to this, individual spherical nanoindentation experiments at constant strain-rates resulted in unrealistically high strain-rate sensitivities for both materials because of drift influences. Microstructural investigations of the residual spherical imprints on ultrafine-grained Al and ultrafine-grained Cu revealed significant differences regarding the deformation structure. For ultrafine-grained Cu considerably less activity of grain boundary sliding has been observed compared to ultrafinegrained A

Determination of the two-dimensional distributions of gold nanorods by multiwavelength analytical ultracentrifugation - Wawra, Simon; Pflug, Lukas; Thajudeen, Thaseem; Kryschi, Carola; Stingl, Michael; Peukert, Wolfgang (Nature Communications, 2018)
Properties of nanoparticles are influenced by various parameters like size, shape or composition. Comprehensive high throughput characterization techniques are urgently needed to improve synthesis, scale up to production and make way for new applications of multidimensional particulate systems. In this study, we present a method for measuring two-dimensional size distributions of plasmonic nanorods in a single experiment. Analytical ultracentrifuge equipped with a multiwavelength extinction detector is used to record the optical and sedimentation properties of gold nanorods simultaneously. A combination of sedimentation and extinction properties, both depending on diameter and length of the dispersed nanorods, is used to measure two-dimensional distributions of gold nanorod samples. The length, diameter, aspect ratio, volume, surface and cross-sectional distributions can be readily obtained from these results. As the technique can be extended to other non-spherical plasmonic particles and can be used for determining relative amounts of particles of different shapes it provides complete and quantitative insights into particulate systems.
EAM Import::2019-03-13

Determining the specific surface area of ceramic foams: The tetrakaidecahedra model revisited - Inayat, Amer; Freund, Hannsjoerg; Zeiser, Thomas; Schwieger, Wilhelm; Freund, Hannsjörg (Chemical Engineering Science, 2011)
Silicon carbide foams were characterized with respect to their specific surface area as well as their morphological parameters including strut diameter, window diameter and open porosities. Image analysis, computed tomography, He-pycnometry and mercury intrusion were used for characterization purposes. State-of-the-artcorrelations (based on different geometrical models for foam structures) for the estimation of the specific surface area were applied and evaluated. Based on the tetrakaidecahedron geometry and different strut morphologies of the foams, new correlations for the specific surface area were developed and successfully validated by comparison with both, own and external experimental data. With the new correlations it is possible to estimate the specific surface area of ceramic foams by using only two measured parameters, namely the window diameter and the open porosity. (C) 2010 Elsevier Ltd. All rights reserved.
Keywords: Foam; Catalyst support; Strut morphology; Specific surface area; Tetrakaidecahedra model; Correlation

Development and characterization of magnetic iron oxide nanoparticles with a cisplatin-bearing polymer coating for targeted drug delivery - Unterweger, Harald; Tietze, Rainer; Janko, Christina; Zaloga, Jan; Lyer, Stefan; Dürr, Stephan; Taccardi, Nicola; Goudouri, Ourania Menti; Hoppe, Alexander; Eberbeck, Dietmar; Schubert, Dirk W.; Boccaccini, Aldo R.; et al. (International Journal of Nanomedicine, 2014)
A highly selective and efficient cancer therapy can be achieved using magnetically directed superparamagnetic iron oxide nanoparticles (SPIONs) bearing a sufficient amount of the therapeutic agent. In this project, SPIONs with a dextran and cisplatin-bearing hyaluronic acid coating were successfully synthesized as a novel cisplatin drug delivery system. Transmission electron microscopy images as well as X-ray diffraction analysis showed that the individual magnetite particles were around 4.5 nm in size and monocrystalline. The small crystallite sizes led to the superparamagnetic behavior of the particles, which was exemplified in their magnetization curves, acquired using superconducting quantum interference device measurements. Hyaluronic acid was bound to the initially dextran-coated SPIONs by esterification. The resulting amide bond linkage was verified using Fourier transform infrared spectroscopy. The additional polymer layer increased the vehicle size from 22 nm to 56 nm, with a hyaluronic acid to dextran to magnetite weight ratio of 51:29:20. A maximum payload of 330 μg cisplatin/mL nanoparticle suspension was achieved, thus the particle size was further increased to around 77 nm with a zeta potential of -45 mV. No signs of particle precipitation were observed over a period of at least 8 weeks. Analysis of drug-release kinetics using the dialysis tube method revealed that these were driven by inverse ligand substitution and diffusion through the polymer shell as well as enzymatic degradation of hyaluronic acid. The biological activity of the particles was investigated in a nonadherent Jurkat cell line using flow cytometry. Further, cell viability and proliferation was examined in an adherent PC-3 cell line using xCELLigence analysis. Both tests demonstrated that particles without cisplatin were biocompatible with these cells, whereas particles with the drug induced apoptosis in a dose-dependent manner, with secondary necrosis after prolonged incubation. In conclusion, combination of dextran-coated SPIONs with hyaluronic acid and cisplatin represents a promising approach for magnetic drug targeting in the treatment of cancer.

Development of a new pressure drop correlation for open-cell foams based completely on theoretical grounds: Taking into account strut shape and geometric tortuosity - Inayat, Amer; Klumpp, Michael; Lämmermann, Markus; Freund, Hannsjörg; Schwieger, Wilhelm (Chemical Engineering Journal, 2016)
Owing to their outstanding geometry and material related properties, open-cell foams as structured packing in reactors, columns or heat exchangers offer clear advantages over their traditional counterparts. For the reliable and efficient design of such systems, an accurate knowledge or prediction of the pressure drop is of fundamental importance, as it plays an important economic role in situations involving high space velocities (high Reynolds numbers). The state-of-the-art pressure drop correlations for open-cell foams are not predictive as they tend to show large deviations from measured data. These deviations are observed mainly due to empirical coefficients in the correlations that have been fitted to a particular data set, but without theoretical meaning these coefficients cannot be extrapolated to other foam structures. In addition, the incorporation of inappropriate definitions (originating from misinterpretation or negligence of important aspects) of the structural and geometrical parameters of foams can also induce a considerable error. In this paper, using the notion of geometric tortuosity and starting from the basic Hagen-Poiseuille equation, a generalized pressure drop correlation for open-cell foams is developed which is based completely on theoretical grounds. The correlation is validated for a wide range of open porosities, pore sizes and materials and its applicability for different working fluids is demonstrated. Furthermore, the definitions of structural and geometrical parameters (as mentioned, these are crucial for pressure drop correlations but are sometimes misinterpreted or neglected) of open-cell foams are reviewed. A consensus on these definitions and their incorporation into the pressure drop correlations is proposed. Consequently, with the proposed correlation, pressure drop in open-cell foams can be predicted by knowing only two structural parameters: the open porosity and the window diameter.
Keywords: Correlation; Foam; Porosity; Pressure drop; Tetrakaidecahedron model; Tortuosity

Development of an optimal filter substrate for the identification of small microplastic particles in food by micro-Raman spectroscopy - Oßmann, Barbara; Sarau, George; Schmitt, Sebastian W.; Holtmannspoetter, Heinrich; Christiansen, Silke H.; Dicke, Wilhelm (Analytical and Bioanalytical Chemistry, 2017)
When analysing microplastics in food, due to toxicological reasons it is important to achieve clear identification of particles down to a size of at least 1 extgreekmm. One reliable, optical analytical technique allowing this is micro-Raman spectroscopy. After isolation of particles via filtration, analysis is typically performed directly on the filter surface. In order to obtain high qualitative Raman spectra, the material of the membrane filters should not show any interference in terms of background and Raman signals during spectrum acquisition. To facilitate the usage of automatic particle detection, membrane filters should also show specific optical properties. In this work, beside eight different, commercially available membrane filters, three newly designed metal-coated polycarbonate membrane filters were tested to fulfil these requirements. We found that aluminium-coated polycarbonate membrane filters had ideal characteristics as a substrate for micro-Raman spectroscopy. Its spectrum shows no or minimal interference with particle spectra, depending on the laser wavelength. Furthermore, automatic particle detection can be applied when analysing the filter surface under dark-field illumination. With this new membrane filter, analytics free of interference of microplastics down to a size of 1 extgreekmm becomes possible. Thus, an important size class of these contaminants can now be visualized and spectrally identified.
EAM Import::2019-03-13

Development of a Supported Ionic Liquid Phase (SILP) Catalyst for Slurry-Phase Friedel-Crafts Alkylations of Cumene - Joni, Joni; Haumann, Marco; Wasserscheid, Peter (dvanced Synthesis & Catalysis, 2009)
A supported ionic liquid phase (SILP) catalyst material has been developed based on a silica support coated with an acidic chloroaluminate ionic liquid. Compared to the results in a liquid-liquid biphasic reaction these materials showed in the isopropylation of cumene a clearly different selectivity which was found to be related to a reduction of the ionic liquid's acidity by the untreated silica support. By pretreating the support with a defined amount of ionic liquid for neutralization and removal of surface hydroxy groups, a well defined, very active and also very selective SILP catalyst for slurry phase Friedel–Crafts alkylation was obtained.

Dewetted Au films form a highly active photocatalytic system on TiO2 nanotube-stumps - Yoo, Jeong Eun; Lee, Kiyoung; Schmuki, Patrik (Electrochemistry Communications, 2013)
Highly ordered TiO2 nanotube stump-[TiO2 NS]-layers, prepared by anodization of Ti in HF/H3PO4 solutions, were used as a substrate for a thermal dewetting of Au thin films. Depending on the initial Au sputter-deposited layer thickness, various sizes and densities of gold nanoparticles [Aunp] could be obtained on the TiO2 NS. Under certain conditions, very homogeneously distributed Aunp (with diameters in the range of 2–15 nm) can be generated. Such Aunp/TiO2 NS combinations show a high efficiency for H2 production from H2O/EtOH solutions. A maximum H2 production efficiency could be obtained from a 2 nm thick Au layer (57.03 extgreekml H2 for 9 h) that was dewetted to ≈ 28,000 particles/ extgreekmm2 with individual particle diameters of ≈ 5 nm.
EAM Import::2019-03-13

Dicyclohexylmethane as a Liquid Organic Hydrogen Carrier: A Model Study on the Dehydrogenation Mechanism over Pd(111) - Amende, Maximilian; Gleichweit, Christoph; Xu, Tao; Höfert, Oliver; Koch, Marcus; Wasserscheid, Peter; Steinrück, Hans-Peter; Papp, Christian; Libuda, Jörg (Catalysis Letters, 2016)
Abstract: We have studied the dehydrogenation of the liquid organic hydrogen carrier (LOHC) dicyclohexylmethane (DCHM) to diphenylmethane (DPM) and its side reactions on a Pd(111) single crystal surface. The adsorption and thermal evolution of both DPM and DCHM was measured in situ in ultrahigh vacuum (UHV) using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (HR-XPS). We found that after deposition at 170 K, the hydrogen-lean DPM undergoes C-H bond scission at the methylene bridge at 200 K and, starting at 360 K, complete dehydrogenation of the phenyl rings occurs. Above 600 K, atomic carbon incorporates into the Pd bulk. For the hydrogen-rich DCHM, the first stable dehydrogenation intermediate, a double π-allylic species, forms already at 190 K. Until 340 K, further dehydrogenation of the phenyl rings and of the methylene bridge occurs, yielding the same intermediate that is formed upon heating of DPM to this temperature, that is, DPM dehydrogenated at the methylene bridge. The onset for the complete dehydrogenation of this intermediate occurs at a much higher temperature than after adsorption of DPM. This behavior is mainly attributed to coadsorbed hydrogen from DCHM dehydrogenation. The results are discussed in comparison to our previous study of DPM and DCHM on Pt(111) revealing strong material dependencies. Graphical Abstract: [Figure not available: see fulltext.]
Keywords: Liquid organic hydrogen carrier; Model catalysis; X-ray photoelectron spectroscopy

Die Energiewende. Eine didaktische Herausforderung? - Heinzerling, Peter; Kometz, Andreas (Praxis der Naturwissenschaften - Chemie in der Schule, 2014)
Ausgehend von Daten und Fakten zur Energiewende werden die fächerübergreifenden Aspekte des Themas abgehandelt. Daran schließt sich eine experimentelles Konzept mit physikalischen und chemischen Experimenten an. Abschließend wird herausgestellt, dass die Energiewende keine besondere Herausforderung für den naturwissenschaftlichen Unterricht beinhaltet. Die eigentliche Herausforderung liegt im gesellschaftlichen und ökonomischen Bereich (Verlag).
Keywords: Experiment; Fachdidaktik; Biologieunterricht; Chemieunterricht; Wasserstoff; Fächerübergreifender Unterricht; Geografieunterricht; Energieversorgung; Erneuerbare Energie; Physikunterricht; Windenergie; Energiepolitik; Sozialwissenschaftlicher Unterricht; Klimaschutz; Deutschland

Die Helmholtz-Energie-Allianz "Energieeffiziente Chemische Mehrphasenprozesse" - Hampel, Uwe; Dittmeyer, Roland; Patyk, Andreas; Wetzel, Thomas; Lange, Ruediger; Freund, Hannsjörg; Schwieger, Wilhelm; Gruenewald, Marcus; Schlueter, Michael; Petasch, Uwe (Chemie Ingenieur Technik, 2013)
Energieeffizienz ist ein wesentlicher Baustein nachhaltigen Wirtschaftens und unabdingbare Voraussetzung zur Erreichung aktueller klimapolitischer Ziele. Die von der Helmholtz-Gemeinschaft Deutscher Forschungszentren geförderte Energie-Allianz chemische Mehrphasenprozessebündelt Kompetenzen und Forschungsaktivitäten im Bereich der chemischen Verfahrenstechnik mit dem Ziel der Weiterentwicklung von Entwurfs- und Auslegungsmethoden, numerischen und experimentellen Techniken sowie neuer Messeverfahren zur Effizienzsteigerung chemischer Mehrphasenprozesse.
EAM Import::2019-03-13

Diels-Alder Cycloaddition of Tetraphenylcyclopentadienone and 1,3,5-Hexatriynes - Sale, Anna Chiara; Murray, Adrian H.; Prenzel, Dominik; Hampel, Frank; De Luca, Lidia; Tykwinski, Rik (European Journal of Organic Chemistry, 2016)
Diels–Alder cycloaddition reactions of 1,3,5-hexatriynes with tetraphenylcyclopentadienone have been performed, and mainly gave 1,2-diethynyl-3,4,5,6-tetraphenylbenzene derivatives as products. The Diels–Alder reactions were optimized under conventional heating and microwave irradiation conditions, and showed good selectivity towards the central carbon–carbon triple bond of the triyne. Empirical evidence suggests that the selectivity of the reaction is governed predominantly by the steric demands of the end-groups of the triyne. Several of the Diels–Alder products could be further elaborated by a sequence of desilylation and oxidative homocoupling to provide dimeric products. The homocoupling reaction was optimized by Pd catalysis. The X-ray crystallographic analysis of two derivatives is reported.
EAM Import::2019-03-13

Different storage conditions influence biocompatibility and physicochemical properties of iron oxide nanoparticles - Zaloga, Jan; Janko, Christina; Agarwal, Rohit; Nowak, Johannes; Müller, Robert; Boccaccini, Aldo R.; Lee, Geoffrey; Odenbach, Stefan; Lyer, Stefan; Alexiou, Christoph (International Journal of Molecular Sciences, 2015)
Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted increasing attention in many biomedical fields. In magnetic drug targeting SPIONs are injected into a tumour supplying artery and accumulated inside the tumour with a magnet. The effectiveness of this therapy is thus dependent on magnetic properties, stability and biocompatibility of the particles. A good knowledge of the effect of storage conditions on those parameters is of utmost importance for the translation of the therapy concept into the clinic and for reproducibility in preclinical studies. Here, core shell SPIONs with a hybrid coating consisting of lauric acid and albumin were stored at different temperatures from 4 to 45 °C over twelve weeks and periodically tested for their physicochemical properties over time. Surprisingly, even at the highest storage temperature we did not observe denaturation of the protein or colloidal instability. However, the saturation magnetisation decreased by maximally 28.8% with clear correlation to time and storage temperature. Furthermore, the biocompatibility was clearly affected, as cellular uptake of the SPIONs into human T-lymphoma cells was crucially dependent on the storage conditions. Taken together, the results show that the particle properties undergo significant changes over time depending on the way they are stored.
Keywords: Colloidal stability; Iron oxide biocompatibility; Iron oxide nanoparticles; Magnetic drug targeting; Magnetite maghemite biocompatibility; Nanomedicine; Nanoparticle stability

Diffusion of Gold Nanoparticles in Inverse Opals Probed by Heterodyne Dynamic Light Scattering - Giraudet, Cédric; Knoll, Matthias; Galvan, Yaraset; Süß, Sebastian; Segets, Doris; Vogel, Nicolas; Rausch, Michael Heinrich; Fröba, Andreas Paul (Transport in Porous Media, 2020)
The diffusive behavior of nanoparticles inside porous materials is attracting a lot of interest in the context of understanding, modeling, and optimization of many technical processes. A very powerful technique for characterizing the diffusive behavior of particles in free media is dynamic light scattering (DLS). The applicability of the method in porous media is considered, however, to be rather difficult due to the presence of multiple sources of scattering. In contrast to most of the previous approaches, the DLS method was applied without ensuring matching refractive indices of solvent and porous matrix in the present study. To test the capabilities of the method, the diffusion of spherical gold nanoparticles within the interconnected, periodic nanopores of inverse opals was analyzed. Despite the complexity of this system, which involves many interfaces and different refractive indices, a clear signal related to the motion of particles inside the porous media was obtained. As expected, the diffusive process inside the porous sample slowed down compared to the particle diffusion in free media. The obtained effective diffusion coefficients were found to be wave vector-dependent. They increased linearly with increasing spatial extension of the probed particle concentration fluctuations. On average, the slowing-down factor measured in this work agrees within combined uncertainties with literature data.
CRIS-Team WoS Importer:2019-11-26
Keywords: Particle diffusion; Gold nanoparticles; Inverse opals; Heterodyne dynamic light scattering; Confinement

Diffusion of gold nanoparticles in porous silica monoliths determined by dynamic light scattering - Wu, Wenchang; Cui, Junwei; Sultan, Umair; Gromotka, Lukas; Malgaretti, Paolo; Damm, Cornelia; Harting, Jens; Vogel, Nicolas; Peukert, Wolfgang; Inayat, Alexandra; Fröba, Andreas Paul (Journal of Colloid and Interface Science, 2023)
Hypothesis: The applicability of the dynamic light scattering method for the determination of particle diffusivity under confinement without applying refractive index matching was not adequately explored so far. The confinement effect on particle diffusion in a porous material which is relevant for particle chromatography has also not yet been fully characterized. Experiments: Dynamic light scattering experiments were performed for unimodal dispersions of 11-mercaptoundecanoic acid-capped gold nanoparticles. Diffusion coefficients of gold nanoparticles in porous silica monoliths were determined without limiting refractive index matching fluids. Comparative experiments were also performed with the same nanoparticles and porous silica monolith but applying refractive index matching. Findings: Two distinct diffusivities could be determined inside the porous silica monolith, both smaller than that in free media, showing a slowing-down of the diffusion processes of nanoparticles under confinement. While the larger diffusivity can be related to the slightly slowed-down diffusion of particles in the bulk of the pores and in the necks connecting individual pores, the smaller diffusivity might be related to the diffusion of particles near the pore walls. It shows that the dynamic light scattering method with a heterodyne detection scheme can be used as a reliable and competitive tool for determining particle diffusion under confinement.
CRIS-Team Scopus Importer:2023-03-29
Keywords: Confinement; Diffusion; Dynamic light scattering; Gold nanoparticles; Porous material

Diffusion, rotation, and surface chemical bond of individual 2 H-tetraphenylporphyrin molecules on Cu(111) - Buchner, Florian; Xiao, Jie; Zillner, Elisabeth; Chen, Min; Röckert, Michael; Ditze, Stefanie; Stark, Michael Werner; Steinrück, Hans-Peter; Gottfried, Michael; Marbach, Hubertus (Journal of Physical Chemistry C, 2011)
We address the dynamic behavior and the surface chemical bond of 2H-tetraphenylporphyrin (2HTPP) on Cu(111) around room temperature by variable-temperature scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) in ultrahigh vacuum. Between 280 and 345 K, the molecules predominantly display unidirectional diffusion along one of the three densely packed substrate 〈110〉 directions, which is attributed to a high site selectivity of the adsorbate-substrate bond. Above 305 K, the diffusion direction is found to change occasionally by ±120°. The activation barriers for the unidirectional diffusion and for rotation of the diffusion direction are determined to 0.71 ± 0.08 and 1.28 ± 0.12 eV, respectively. XPS shows that the iminic nitrogen atoms of 2HTPP interact strongly with the Cu surface. It is postulated that the local bonding situation is similar as in the initial complex (sitting-atop complex), which has previously been observed during the surface-confined in situ metalation of porphyrins. © 2011 American Chemical Society.

Dimerization of ethene in a fluidized bed reactor using Ni-based Supported Ionic Liquid Phase (SILP) catalysts - Kohler, Florian; Gärtner, Konstantin; Hager, Veit; Haumann, Marco; Sternberg, Michelle; Wang, Xinjiao; Szesni, Normen; Meyer, Karsten; Wasserscheid, Peter (Catalysis: Science and Technology, 2014)
The complexes [(mall)Ni(dppanis)][SbF6] (mall = methallyl, dppanis = (2-methoxyphenyl)diphenylphosphine) 1, [(mall)Ni(PPh3OC10)][SbF6] (PPh3OC10 = (2-decyloxyphenyl)diphenylphosphine) 2, and [(mall)Ni(PPh3OdiMePh)][SbF6] (PPh3OdiMePh = (2-(2,6-dimethylphenoxy)phenyl)diphenylphosphine) 3 were immobilized as Supported Ionic Liquid Phase (SILP) catalysts and applied for the tandem dimerization/isomerization of ethylene to 2-butene in a fluidized bed reactor. The better heat removal in the fluidized bed improves the catalyst stability and allows for a more detailed investigation of the deactivation mechanism. Based on kinetic studies, a second order deactivation mechanism is proposed, in which two nickel complexes dimerize if the supply of ethene is insufficient.

Direct Detection of a Persistent Carbonyloxyl Radical in the Gas Phase - Poad, Berwyck L. J.; Kirk, Benjamin B.; Hettiarachchi, Pramesh I.; Trevitt, Adam J.; Blanksby, Stephen J.; Clark, Timothy (Angewandte Chemie International Edition, 2013)
Long lived: Carbonyloxyl radicals (RCO2.) are reactive intermediates that play key roles in initiating polymerization reactions. This reactivity also makes their direct observation difficult. For the first time a persistent organic RCO2. radical is detected in the gas phase, its extraordinary longevity is attributed to the high barrier towards fragmentation owing to the endothermicity of the decarboxylation products.

Direct in situ transmission electron microscopy observation of Al push up during early stages of the Al-induced layer exchange - Birajdar, Balaji; Antesberger, T.; Butz, Benjamin; Stutzmann, Martin; Spiecker, Erdmann (Scripta Materialia, 2012)
The mechanism of Al transport during Al-induced layer exchange and crystallization of amorphous Si (a-Si) has been investigated by in situ and analytical transmission electron microscopy. Significant grain boundary realignment and coarsening of Al grains close to the Si crystallization growth front as well as push up of excess Al into the a-Si layer at distances even a few micrometers away from the crystallization front were observed. Stress-mediated diffusion of Al is postulated to explain the experimental observations. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keywords: Thin films; Solar cells; Crystallization; Analytical electron microscopy; Diffusion

Directional noncovalent interactions: Repulsion and dispersion - Elkerdawy, Ahmed; Murray, Jane S.; Politzer, Peter; Bleiziffer, Patrick; Heßelmann, Andreas; Görling, Andreas; Clark, Timothy (Journal of Chemical Theory and Computation, 2013)
The interaction energies between an argon atom and the dihalogens Br , BrCl, and BrF have been investigated using frozen core CCSD(T)(fc)/aug-cc-pVQZ calculations as reference values for other levels of theory. The potential-energy hypersurfaces show two types of minima: (1) collinear with the dihalogen bond and (2) in a bridging position. The former represent the most stable minima for these systems, and their binding energies decrease in the order Br > Cl > F. Isotropic atom-atom potentials cannot reproduce this binding pattern. Of the other levels of theory, CCSD(T)(fc)/aug-cc-pVTZ reproduces the reference data very well, as does MP2(fc)/aug-cc-pVDZ, which performs better than MP2 with the larger basis sets (aug-cc-pVQZ and aug-cc-pvTZ). B3LYP-D3 and M06-2X reproduce the binding patterns moderately well despite the former using an isotropic dispersion potential correction. B3LYP-D3(bj) performs even better. The success of the B3LYP-D3 methods is because polar flattening of the halogens allows the argon atom to approach more closely in the direction collinear with the bond, so that the sum of dispersion potential and repulsion is still negative at shorter distances than normally possible and the minimum is deeper at the van der Waals distance. Core polarization functions in the basis set and including the core orbitals in the CCSD(T)(full) calculations lead to a uniform decrease of approximately 20% in the magnitudes of the calculated interaction energies. The EXXRPA+@EXX (exact exchange random phase approximation) orbital-dependent density functional also gives interaction energies that correlate well with the highest level of theory but are approximately 10% low. The newly developed EXXRPA+@dRPA functional represents a systematic improvement on EXXRPA+@EXX. © 2013 American Chemical Society.

Direct laser writing of μ-chips based on hybrid C-Au-Ag nanoparticles for express analysis of hazardous and biological substances - Bashouti, M. Y.; Manshina, Alina; Povolotckaia, Anastasia; Povolotskiy, Alexey; Kireev, A.; Petrov, Yuri; Mackovic, Mirza; Spiecker, Erdmann; Koshevoy, Igor; Tunik, Sergey; Christiansen, Silke (Lab on A Chip, 2015)
Micro-chips based on organic–inorganic hybrid nanoparticles (NPs) composed of nanoalloys of gold (Au) and silver (Ag) embedded in an amorphous carbonaceous matrix (C–Au–Ag NPs) were prepared directly on a substrate by the laser-induced deposition (for short: LID) method. The C–Au–Ag NPs show a unique plasmon resonance which enhances Raman scattering of analytes, making the extgreekm-chips suitable to detect ultra-low-volumes (10-12 liter) and concentrations (10-9 M) of bio-agents and a hazardous compound. These micro-chips constitute a novel, flexible solid-state device that can be used for applications in point-of-care diagnostics, consumer electronics, homeland security and environmental monitoring.
EAM Import::2019-03-13

Direct numerical simulation of water–ethanol flows in a T-mixer - Schikarski, Tobias; Peukert, Wolfgang; Avila, Marc (Chemical Engineering Journal, 2017)
The efficient mixing of fluids is key in many applications, such as chemical reactions and nanoparticle precipitation. Detailed experimental measurements of the mixing dynamics are however difficult to obtain, and so predictive numerical tools are helpful in designing and optimizing many processes. If two different fluids are considered, the viscosity and density of the mixture depend often nonlinearly on the composition, which makes the modeling of the mixing process particularly challenging. Hence water-water mixtures in simple geometries such as T-mixers have been intensively investigated, but little is known about the dynamics of more complex mixtures, especially in the turbulent regime. We here present a numerical method allowing the accurate simulation of two-fluid mixtures. Using a high-performance implementation of this method we perform direct numerical simulations resolving the spatial and temporal dynamics of water-ethanol flows for Reynolds numbers from 100 to 2000. The flows states encountered during turbulence transition and their mixing properties are discussed in detail and compared to water-water mixtures.
Keywords: Mixing; T-mixer; Direct numerical simulation; Miscible fluids; Water–ethanol; Transition to turbulence; Turbulent flows

Direct observation of dislocation formation and plastic anisotropy in Nb2AlC MAX phase using in situ nanomechanics in transmission electron microscopy - Kabiri, Yoones; Schrenker, Nadine; Müller, Julian; Mackovic, Mirza; Spiecker, Erdmann (Scripta Materialia, 2017)
We report on the direct observation of nucleation and propagation of basal plane dislocations in Nb2AlC, a member of MAX phases, using nanomechanical testing inside a transmission electron microscope. Different loading directions with respect to the basal plane resulted in completely different plastic response due to the pronounced anisotropy of the layered crystal. Discrete dislocation activities were correlated to distinct events in the force-displacement curves. In situ observations together with post-mortem contrast analyses of deformed regions show no indication of cross-slip or entanglement of dislocations during the indentations.
Keywords: Transmission electron microscopy (TEM); Nanoindentation; Dislocation nucleation; Mechanical properties; MAX phases

Direct observation of electron-beam-induced densification and hardening of silica nanoballs by in situ transmission electron microscopy and finite element method simulations - Mackovic, Mirza; Niekiel, Florian; Wondraczek, Lothar; Spiecker, Erdmann (Acta Materialia, 2014)
We report on the use of in situ transmission electron microscopy techniques and finite element method simulations to study the influence of electron beam irradiation on the deformation behavior and mechanical properties of nanoscale amorphous silica balls. We show that, on the nanometer scale, electron beam irradiation of silica results in athermal densification and simultaneous material hardening. It is demonstrated how the amount of densification can be controlled via the irradiation dose, using specific beam current densities inside a transmission electron microscope. The electron-beam-induced densification is interpreted as the direct reason for the observed hardening effect. Finite element method simulations are used to model the mechanical response of the silica balls, confirming that the intrinsic properties (such as the Young's modulus) of amorphous silica can be tailored with the electron beam on the nanoscale. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keywords: Amorphous silica; Electron-beam-induced densification; Mechanical testing; In situ TEM; FEM

Direct oxidation of benzene to phenol over hierarchical ZSM-5 zeolites prepared by sequential post synthesis modification - Shahid, Ameen; Lopez Orozco, Sofia; Marthala, Venkata; Hartmann, Martin; Schwieger, Wilhelm (Microporous and Mesoporous Materials, 2017)
Hierarchical zeolites were prepared by post synthesis treatments of commercial ZSM-5 zeolite (Sit Al = 13) involving alkali treatment, acid treatment, steam treatment, combination of acid-alkali treatments, and combination of steam-acid-alkali treatments. Various characterization techniques were employed to investigate the influence of each post synthesis treatment step on the structure, composition, porosity, acidity and iron species of the samples. The catalytic activity and selectivity of the post modified samples were also measured in the direct oxidation of benzene to phenol using nitrous oxide as an oxidising agent. The combination of steam-acid-alkali treatments of ZSM-5 zeolite exhibiting low Si/Al ratio lead to significant high level of mesoporosity with considerable preserved amount of microporosity that was not possible to achieve by the other treatment methods outlined above. ESR results reveal the homogeneous distribution of iron species when commercial MFI zeolite containing low amount of iron was steam treated. The modified iron species were not significantly altered by subsequent acid and alkali treatments, while the alkali treatment heals the destructed part of the zeolite that was produced by steam and acid treatments. These modifications in the pore structure and iron species led to excellent catalytic performance in the direct oxidation of benzene to phenol using nitrous oxide. (C) 2016 Elsevier Inc. All rights reserved.
Keywords: Hierarchical zeolite; Post synthesis modification; Direct oxidation of benzene; Iron species

Direct relations between morphology and transport in Boolean models - Scholz, Christian; Klatt, Michael; Mecke, Klaus; Wirner, Frank; Hirneise, Daniel; Schröder-Turk, Gerd; Bechinger, Clemens (Physical Review E, 2015)
We study the relation of permeability and morphology for porous structures composed of randomly placed overlapping circular or elliptical grains, so-called Boolean models. Microfluidic experiments and lattice Boltzmann simulations allowus to evaluate a power-lawrelation between theEuler characteristic of the conducting phase and its permeability. Moreover, this relation is so far only directly applicable to structures composed of overlapping grains where the grain density is known a priori. We develop a generalization to arbitrary structures modeled by Boolean models and characterized by Minkowski functionals. This generalization works well for the permeability of the void phase in systems with overlapping grains, but systematic deviations are found if the grain phase is transporting the fluid. In the latter case our analysis reveals a significant dependence on the spatial discretization of the porous structure, in particular the occurrence of single isolated pixels. To link the results to percolation theory we performed Monte Carlo simulations of the Euler characteristic of the open cluster, which reveals different regimes of applicability for our permeability-morphology relations close to and far away from the percolation threshold.

Discontinuous spirals of stable periodic oscillations - Sack, Achim; Freire, J. G.; Lindberg, Erik; Pöschel, Thorsten; Gallas, Jason (Scientific Reports, 2013)
We report the experimental discovery of a remarkable organization of the set of self-generated periodic oscillations in the parameter space of a nonlinear electronic circuit. When control parameters are suitably tuned, the wave pattern complexity of the periodic oscillations is found to increase orderly without bound. Such complex patterns emerge forming self-similar discontinuous phases that combine in an artful way to produce large discontinuous spirals of stability. This unanticipated discrete accumulation of stability phases was detected experimentally and numerically in a Duffing-like proxy specially designed to bypass noisy spectra conspicuously present in driven oscillators. Discontinuous spirals organize the dynamics over extended parameter intervals around a focal point. They are useful to optimize locking into desired oscillatory modes and to control complex systems. The organization of oscillations into discontinuous spirals is expected to be generic for a class of nonlinear oscillators.

Disentangling the effects of nanoscale structural variations on the light emission wavelength of single nano-emitters: InGaN/GaN multiquantum well nano-LEDs for a case study - Sarau, George; Heilmann, Martin; Latzel, Michael; Christiansen, Silke (Nanoscale, 2014)
The scattering in the light emission wavelength of semiconductor nano-emitters assigned to nanoscale variations in strain, thickness, and composition is critical in current and novel nanotechnologies from highly efficient light sources to photovoltaics. Here, we present a correlated experimental and theoretical study of single nanorod light emitting diodes (nano-LEDs) based on InGaN/GaN multiquantum wells to separate the contributions of these intrinsic fluctuations. Cathodoluminescence measurements show that nano-LEDs with identical strain states probed by non-resonant micro-Raman spectroscopy can radiate light at different wavelengths. The deviations in the measured optical transitions agree very well with band profile calculations for quantum well thicknesses of 2.07-2.72 nm and In fractions of 17.5-19.5% tightly enclosing the growth values. The nanorod surface roughness controls the appearance of surface optical phonon modes with direct implications on the design of phonon assisted nano-LED devices. This work establishes a new, simple, and powerful methodology for fundamental understanding as well as quantitative analysis of the strain - light emission relationship and surface-related phenomena in the emerging field of nano-emitters.
EAM Import::2019-03-13

Dislocations in bilayer graphene - Butz, Benjamin; Dolle, Christian; Niekiel, Florian; Weber, Konstantin; Waldmann, Daniel; Weber, Heiko B.; Meyer, Bernd; Spiecker, Erdmann; Spiecker, Erdmann (Nature, 2014)
Dislocations represent one of the most fascinating and fundamental concepts in materials science. Most importantly, dislocations are the main carriers of plastic deformation in crystalline materials. Furthermore, they can strongly affect the local electronic and optical properties of semiconductors and ionic crystals. In materials with small dimensions, they experience extensive image forces, which attract them to the surface to release strain energy. However, in layered crystals such as graphite, dislocation movement is mainly restricted to the basal plane. Thus, the dislocations cannot escape, enabling their confinement in crystals as thin as only two monolayers. To explore the nature of dislocations under such extreme boundary conditions, the material of choice is bilayer graphene, the thinnest possible quasi-two-dimensional crystal in which such linear defects can be confined. Homogeneous and robust graphene membranes derived from high-quality epitaxial graphene on silicon carbide provide an ideal platform for their investigation. Here we report the direct observation of basal-plane dislocations in freestanding bilayer graphene using transmission electron microscopy and their detailed investigation by diffraction contrast analysis and atomistic simulations. Our investigation reveals two striking size effects. First, the absence of stacking-fault energy, a unique property of bilayer graphene, leads to a characteristic dislocation pattern that corresponds to an alternating ABAC change of the stacking order. Second, our experiments in combination with atomistic simulations reveal a pronounced buckling of the bilayer graphene membrane that results directly from accommodation of strain. In fact, the buckling changes the strain state of the bilayer graphene and is of key importance for its electronic properties. Our findings will contribute to the understanding of dislocations and of their role in the structural, mechanical and electronic properties of bilayer and few-layer graphene. © 2014 Macmillan Publishers Limited. All rights reserved.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.LAP.disloc

Disordered spherical bead packs are anisotropic - Schröder-Turk, Gerd; Mickel, Walter; Schröter, Matthias; Delaney, Gary; Saadatfar, Mohammad; Senden, T.J.; Mecke, Klaus; Aste, T. (EPL - Europhysics Letters, 2010)
Investigating how tightly objects pack space is a long-standing problem, with relevance for many disciplines from discrete mathematics to the theory of glasses. Here we report on the fundamental yet so far overlooked geometric property that disordered mono-disperse spherical bead packs have significant local structural anisotropy manifest in the shape of the free space associated with each bead. Jammed disordered packings from several types of experiments and simulations reveal very similar values of the cell anisotropy, showing a linear decrease with packing fraction. Strong deviations from this trend are observed for unjammed configurations and for partially crystalline packings above 64%. These findings suggest an inherent geometrical reason why, in disordered packings, anisotropic shapes can fill space more efficiently than spheres, and have implications for packing effects in non-spherical liquid crystals, foams and structural glasses.

Disorder-Induced Open-Circuit Voltage Losses in Organic Solar Cells during Photoinduced Burn-In - Heumueller, Thomas; Burke, Timothy M.; Mateker, William R.; Sachs-Quintana, Isaac T.; Vandewal, Koen; Brabec, Christoph; Mcgehee, Michael D. (Advanced Energy Materials, 2015)
The photoinduced open-circuit voltage (Voc) loss commonly observed in bulk heterojunction organic solar cells made from amorphous polymers is investigated. It is observed that the total charge carrier density and, importantly, the recombination dynamics are unchanged by photoinduced burn-in. Charge extraction is used to monitor changes in the density of states (DOS) during degradation of the solar cells, and a broadening over time is observed. It is proposed that the Voc losses observed during burn-in are caused by a redistribution of charge carriers in a broader DOS. The temperature and light intensity dependence of the Voc losses can be described with an analytical model that contains the amount of disorder broadening in a Gaussian DOS as the only fit parameter. Finally, the Voc loss in solar cells made from amorphous and crystalline polymers is compared and an increased stability observed in crystalline polymer solar cells is investigated. It is found that solar cells made from crystalline materials have a considerably higher charge carrier density than those with amorphous materials. The effects of a DOS broadening upon aging are suppressed in solar cells with crystalline materials due to their higher carrier density, making crystalline materials more stable against Voc losses during burn-in.
Keywords: charge carrier densities; disorders; morphology; organic photovoltaics; solar cells; stabilities

Dissipation of Energy by Dry Granular Matter in a Rotating Cylinder - Sack, Achim; Pöschel, Thorsten (Scientific Reports, 2016)
We study experimentally the dissipation of energy in a rotating cylinder which is partially filled by granular material. We consider the range of angular velocity corresponding to continous and stationary flow of the granulate. In this regime, the stationary state depends on the angular velocity and on the filling mass. For a wide interval of filling levels we find a universal behavior of the driving torque required to sustain the stationary state as a function of the angular velocity. The result may be of relevance to industrial applications, e.g. to understand the power consumption of ball mills or rotary kilns and also for damping applications where mechanical energy has to be dissipated in a controlled wa

Dissociation of water on atomically-defined cobalt oxide nanoislands on Pt(111) and its effect on the adsorption of CO - Wähler, Tobias; Hohner, Chantal; Sun, Zhaozong; Schuster, Ralf; Rodriguez-Fernandez, Jonathan; Lauristen, Jeppe Vang; Libuda, Jörg (Journal of Materials Research, 2019)
We have investigated the adsorption and dissociation of water and its co-adsorption with CO on atomically defined cobalt oxide nanoislands on Pt(111). The CoO islands were prepared under ultrahigh vacuum (UHV) conditions by reactive deposition of Co metal in oxygen atmosphere. The island structure was characterized by scanning tunneling microscopy (STM), showing that the nanoislands consist of a CoO bilayer and are regularly shaped with island edges that are mainly terminated by Co2+ ions. D2O was dosed in UHV onto the CoO islands on Pt(111) after pre-saturation with CO. D2O dissociation was monitored in situ by isothermal and temperature programmed infrared reflection absorption spectroscopy (IRAS). Isotopic exchange experiments were performed with H2O, D2O, and D-2 O-18 to elucidate the nature of the hydroxyl groups. Three principal types of OD species are identified: (i) isolated OD at the edges of the CoO islands (Co-OeD), (ii) OD groups within larger hydroxylated areas on the CoO islands (Co-OcD), and (iii) isolated OD groups on the CoO terraces (Co-OtD). At 400 K, water adsorbs dissociatively on the CoO islands and forms isolated hydroxyl species (Co-OeD) at the island edges only. At room temperature (300 K), the coverage of hydroxyl groups increases rapidly, in line with the water-assisted hydroxylation reaction suggested previously. Adsorption experiments with D-2 O-18 suggest that two equivalent groups are formed from one water molecule after dissociation at island edges, leading to the formation of larger hydroxylated areas on the CoO islands (Co-OcD) and, in addition, isolated OD species on the CoO terraces (Co-OtD). While the initial step of D2O dissociation is facile, the formation of larger hydroxylated areas is a slow and irreversible process. At 200 K, the formation of hydroxylated areas is accompanied by the co-adsorption of molecular water. The hydroxyl groups on the CoO islands are shown to interact with the CO preadsorbed on the CoO/Pt(111) model system. In particular, we observe a new CO species, stabilized by OD groups on the CoO islands, which adsorbs much stronger than CO on the OD-free CoO surface.
CRIS-Team WoS Importer:2019-03-01

Dissociative Adsorption of Benzoic Acid on Well-Ordered Cobalt Oxide Surfaces: Role of the Protons - Schwarz, Matthias; Hohner, Chantal; Mohr, Susanne; Libuda, Jörg (Journal of Physical Chemistry C, 2017)
We performed a surface science model study to reveal the role of the protons which are released upon linking of organic molecules to oxide surfaces via carboxylic acid anchor groups. Specifically, we studied the adsorption, dissociation, and thermal stability of deuterated benzoic acid (C6H5COOD, dl-BA) on three different atomically defined cobalt oxide surfaces, namely, (i) Co3O4(111), (ii) CoO(111), and (iii) CoO(100). All surfaces were prepared in the form of thin films grown on Ir(100). dl-BA was deposited at 300 K via physical vapor deposition (PVD). The interfacial chemistry and film formation was monitored in situ by isothermal time-resolved infrared reflection absorption spectroscopy (TR-IRAS) under ultrahigh vacuum (UHV) conditions. For all three surfaces, we monitored the surface carboxylate and the surface hydroxyl groups as a function of coverage. The thermal stability of the films was probed by temperature-programmed IRAS (TP-IRAS). The comparison between the three surfaces reveals pronounced structure sensitivity. (i) On Co3O4(111), dl-BA binds via a chelating and symmetric carboxylate, strongly tilted with respect to the substrate. The surface hydroxyl groups give rise to a broad vibrational band indicating their involvement in hydrogen bonds. The coadsorbate layer is stable up to 400 K. Above this temperature, hydroxyl desorbs as water, leading to oxygen depletion most likely, followed by decomposition of the benzoate between 420 and 560 K, leaving behind aromatic residues on the surface. (ii) On the oxygen-terminated CoO(111) surface, dl-BA forms of a slightly distorted and slightly tilted bridging carboxylate. Similar as on Co3O4(111), the surface hydroxyl groups form hydrogen bonds. The film is stable up to 420 K. At higher temperature, the surface benzoates decompose slowly over a large temperature range partly, most likely via CO, release and formation of aromatic residues. The surface hydroxyl groups are stable up to higher temperatures (480 K) as compared to Co3O4(111). (iii) On CoO(100) a completely different behavior is observed. The surface benzoate forms a well-defined mixed coadsorbate layer with free surface hydroxyl groups, which are not involved in hydrogen bonds. The orientation of the carboxylate is strongly coverage dependent. At low coverage, the benzoate is tilted with respect to the surface, whereas a fully perpendicular orientation is adopted at high coverage. This film shows the lowest thermal stability. Above 345 K the surface benzoate and protons of the nearby hydroxyl group recombine, leading to desorption of intact dl-BA. Only a small amount of surface benzoate remains, an effect that we mostly attribute to defect sites.

Distribution of chaos and periodic spikes in a three-cell population model of cancer - Gallas, Jason; Gallas, Michelle R.; Gallas, Marcia R. (European Physical Journal - Special Topics, 2014)
We study complex oscillations generated by the de Pillis-Radunskaya model of cancer growth, a model including interactions between tumor cells, healthy cells, and activated immune system cells. We report a wide-ranging systematic numerical classification of the oscillatory states and of their relative abundance. The dynamical states of the cell populations are characterized here by two independent and complementary types of stability diagrams: Lyapunov and isospike diagrams. The model is found to display stability phases organized regularly in old and new ways: Apart from the familiar spirals of stability, it displays exceptionally long zig-zag networks and intermixed cascades of two- and three-doubling flanked stability islands previously detected only in feedback systems with delay. In addition, we also characterize the interplay between continuous spike-adding and spike-doubling mechanisms responsible for the unbounded complexification of periodic wave patterns. This article is dedicated to Prof. Hans Jürgen Herrmann on the occasion of his 60th birthday.

Dithiafulvenyl-Extended N-Heterotriangulenes and Their Interaction with C60: Cooperative Fluorescence - Gliemann, Bettina; Strauß, Volker; Hitzenberger, Jakob; Dral, Pavlo O.; Hampel, Frank; Gisselbrecht, Jean-Paul; Drewello, Thomas; Thiel, Walter; Guldi, Dirk Michael; Kivala, Milan (Chemistry - A European Journal, 2017)
We describe the synthesis as well as the electronic and photophysical characterization of novel N-heterotriangulene derivatives decorated with methoxycarbonyl- and methyl-sulfanyl-substituted dithiafulvenyl moieties. The association of these electron-rich compounds with fullerene C60 as electron acceptor was investigated by means of photophysical, voltammetric, and mass spectrometric methods and rationalized by DFT calculations. Importantly, light-induced interactions between the dithiafulvene-substituted N-heterotriangulene bearing methoxycarbonyl substituents with C60 leads to cooperative fluorescence. Quantitative Job plot analyses by means of fluorescence spectroscopy and voltammetry confirm a 1:1 association with binding constants in the order of 104 m-1. Supportive results for the supramolecular assembly of both N-heterotriangulenes with C60 were obtained by ESI mass spectrometric investigations in the gas phase.
EAM Import::2019-03-13

DNA-Dye-Conjugates: Conformations and Spectra of Fluorescence Probes - Beierlein, Frank; Paradas Palomo, Miguel; Sharapa, Dmitry; Zozulia, Oleksii; Mokhir, Andriy; Clark, Timothy (Plos One, 2016)
Extensive molecular-dynamics (MD) simulations have been used to investigate DNA-dye and DNA-photosensitizer conjugates, which act as reactants in templated reactions leading to the generation of fluorescent products in the presence of specific desoxyribonucleic acid sequences (targets). Such reactions are potentially suitable for detecting target nucleic acids in live cells by fluorescence microscopy or flow cytometry. The simulations show how the attached dyes/photosensitizers influence DNA structure and reveal the relative orientations of the chromophores with respect to each other. Our results will help to optimize the reactants for the templated reactions, especially length and structure of the spacers used to link reporter dyes or photosensitizers to the oligonucleotides responsible for target recognition. Furthermore, we demonstrate that the structural ensembles obtained from the simulations can be used to calculate steady-state UV-vis absorption and emission spectra. We also show how important quantities describing the quenching of the reporter dye via fluorescence resonance energy transfer (FRET) can be calculated from the simulation data, and we compare these for different relative chromophore geometries.

Donor- and/or Acceptor-Substituted Expanded Radialenes: Theory, Synthesis, and Properties - Ramsaywack, Sharwatie; Karaca, Sila; Gholami, Mojtaba; Murray, Adrian H.; Hampel, Frank; Mcdonald, Robert; Elmaci, Nuran; Luethi, Hans Peter; Tykwinski, Rik (Journal of Organic Chemistry, 2014)
The synthesis of donor- (D) and/or acceptor (A)-expanded [4]radialenes has been developed on the basis of readily available dibromoolefin (7), tetraethynylethene (10 and 20), and vinyl triflate (12) building blocks. The successful formation of D/A radialenes relies especially on (1) effective use of a series alkynyl protecting groups, (2) Sonogashira cross-coupling reactions, and (3) the development of ring closing reactions to form the desired macrocyclic products. The expanded [4]radialene products have been investigated by spectroscopic (UV-vis absorption and emission) and quantum chemical computational methods (density functional theory and time dependent DFT). The combined use of theory and experiment provides a basis to evaluate the extent of D/A interactions via the cross-conjugated radialene framework as well as an interpretation of the origin of D/A interactions at an orbital level.
EAM Import::2019-03-13

Dopant profiles in silicon created by MeV hydrogen implantation: Influence of annealing parameters - Laven, Johannes; Hans Joachim, Schulze; Häublein, Volker; Niedernostheide, Franz Josef; Ryssel, Heiner; Frey, Lothar (Physica Status Solidi (C) Current Topics in Solid State Physics, 2011)
Dopant profiles created by MeV proton implantation in float zone and Czochralski silicon are examined with spreading resistance probe measurements after annealing in the temperature range of 300–500 °C. For the description of the profile shape, two species are used, one being the implanted and mobile hydrogen and the other being an immobile irradiation induced point defect complex. The diffusion of the implanted hydrogen through the radiation damaged layer is found to be of great relevance for the resulting depth distribution of the hydrogen related donors. An effective diffusion coefficient is given for implantation into float zone silicon. Furthermore, the profile shape varies significantly with the annealing temperature. It is proposed that two donor species are generated which each exhibit a different thermal stability, and that these two species have individual depth distributions. Profiles created in Czochralski silicon seem to be additionally affected by an enhanced generation of oxygen thermal donor species.

Doped polycyclic aromatic hydrocarbons as building blocks for nanoelectronics: a theoretical study - Dral, Pavlo; Kivala, Milan; Clark, Timothy (Journal of Organic Chemistry, 2013)
Density functional theory (DFT) and semiempirical UHF natural orbital configuration interaction (UNO-CI) calculations are used to investigate the effect of heteroatom substitution at the central position of a model polycyclic aromatic hydrocarbon. The effects of the substitution on structure, strain, electronic and spectral properties, and aromaticity of the compounds are discussed.

Doppler velocimetry on microparticles trapped and propelled by laser light in liquid-filled photonic crystal fiber - Garbos, M. K.; Euser, T. G.; Schmidt, O. A.; Unterkofler, S.; Russell, Philip St. John (Optics Letters, 2011)
Laser Doppler velocimetry is used to measure very accurately the velocity and position of a microparticle propelled and guided by laser light in liquid-filled photonic crystal fiber. Periodic variations in particle velocity are observed that correlate closely with modal beating between the two lowest order guided fiber modes.
EAM Import::2019-03-13

Dose-Dependent Response to 3-Nitrobenzanthrone Exposure in Human Urothelial Cancer Cells - Pink, Mario; Verma, Nisha; Zerries, Anna; Schmitz-Spanke, Simone (Chemical Research in Toxicology, 2017)
A product of incomplete combustion of diesel fuel, 3-nitrobenzanthrone (3-NBA), has been classified as a cancer-causing substance. It first gained attention as a potential urinary bladder carcinogen due to the presence of its metabolite in urine and formation of DNA adducts. The aim of the present study was to characterize the dose-response relationship of 3-NBA in human urothelial cancer cell line (RT4) exposed to concentrations ranging from 0.0003 ?M (environmentally relevant) to 80 ?M by utilizing toxicological and metabolomic approaches. We observed that the RT4 cells were capable of bioactivation of 3-NBA within 30 min of exposure. Activity measurements of various enzymes involved in the conversion of 3-NBA in RT4 cells demonstrated NAD(P)H:quinone oxidoreductase (NQO1) as the main contributor for its bioactivation. Moreover, cytotoxicity assessment exhibited an initiation of adaptive mechanisms at low dosages, which diminished at higher doses, indicating that the capacity of these mechanisms no longer suffices, resulting in increased levels of intracellular reactive oxygen species, reduced proliferation, and hyperpolarisation of the mitochondrial membrane. To characterize the underlying mechanisms of this cellular response, the metabolism of 3-NBA and metabolomic changes in the cells were analyzed. The metabolomic analysis of the cells (0.0003, 0.01, 0.08, 10, and 80 ?M 3-NBA) showed elevated levels of various antioxidants at low concentrations of 3-NBA. However, at higher exposure concentrations, it appeared that the cells reprogrammed their metabolism to maintain the cell homeostasis via activation of pentose phosphate pathway (PPP).
EVALuna2:9762

Dual analyzer system for surface analysis dedicated for angle-resolved photoelectron spectroscopy at liquid surfaces and interfaces - Niedermaier, Inga; Kolbeck, Claudia; Steinrück, Hans-Peter; Maier, Florian (Review of Scientific Instruments, 2016)
The investigation of liquid surfaces and interfaces with the powerful toolbox of ultra-high vacuum (UHV)-based surface science techniques generally has to overcome the issue of liquid evaporation within the vacuum system. In the last decade, however, new classes of liquids with negligible vapor pressure at room temperature-in particular, ionic liquids (ILs)-have emerged for surface science studies. It has been demonstrated that particularly angle-resolved X-ray Photoelectron Spectroscopy (ARXPS) allows for investigating phenomena that occur at gas-liquid and liquid-solid interfaces on the molecular level. The results are not only relevant for IL systems but also for liquids in general. In all of these previous ARXPS studies, the sample holder had to be tilted in order to change the polar detection angle of emitted photoelectrons, which restricted the liquid systems to very thin viscous IL films coating a flat solid support. We now report on the concept and realization of a new and unique laboratory "Dual Analyzer System for Surface Analysis (DASSA)" which enables fast ARXPS, UV photoelectron spectroscopy, imaging XPS, and low-energy ion scattering at the horizontal surface plane of macroscopically thick non-volatile liquid samples. It comprises a UHV chamber equipped with two electron analyzers mounted for simultaneous measurements in 0 degrees and 80 degrees emission relative to the surface normal. The performance of DASSA on a first macroscopic liquid system will be demonstrated. (C) 2016 AIP Publishing LLC.

Dual-mode photoluminescence from Mn2+-doped Li,Zn aluminosilicate glass ceramics - Gao, Guojun; Reibstein, Sindy; Peng, Mingying; Wondraczek, Lothar (Physics and Chemistry of Glasses-European Journal of Glass Science and Technology Part B, 2011)
We report on the photoluminescence (PL) of Mn2+-doped (Li+, Zn2+) aluminosilicate glasses and glass ceramics. Glass ceramics are fabricated by controlled crystallization of as-melted precursor glasses. X-ray diffraction (XRD), electron spin resonance (ESR) and PL analyses indicate precipitation of Li4-2(x+y)ZnxMnySiO4, with relatively low x and y values during the earlier phase of crystallization and x->1 in the later phase. During the crystallization process, Mn2+ ions, octahedrally coordinated in the precursor glass, partially precipitate on tetrahedral Zn2+ sites. This gives rise to the simultaneous occurrence of green and red luminescence, respectively, due to spin-allowed 4T1(G)->6A1(S) and spin-forbidden 4T1g(G)->6A1g(S) in IVMn2+ and VIMn2+. Accordingly, the amount of IVMn2+ species, the ratio of IVMn2+/VIMn2+ and, hence, the ratio between green and red photoemission bands can be controlled by the temperature at which the glass ceramics are produced. FWHM of the resulting emission spectrum can be increased from about 100000 to about 50000 cm-1. In parallel, as a result of multiple scattering, emission intensity appears to generally increase with increasing degree of crystallization.
EAM Import::2019-03-13

Dynamically reconfigurable fibre optical spanner - Kolb, Thorsten; Albert, Sahradha; Haug, Michael; Whyte, Graeme (Lab on A Chip, 2014)
In this paper we describe a pneumatically actuated fibre-optic spanner integrated into a microfluidic Lab-on-a-Chip device for the controlled trapping and rotation of living cells. The dynamic nature of the system allows interactive control over the rotation speed with the same optical power. The use of a multi-layer device makes it possible to rotate a cell both in the imaging plane and also in a perpendicular plane allowing tomographic imaging of the trapped living cell. The integrated device allows easy operation and by combining it with high-resolution confocal microscopy we show for the first time that the pattern of rotation can give information regarding the sub-cellular composition of a rotated cell.
EAM Import::2019-03-13

Dynamical properties for the problem of a particle in an electric field of wave packet: Low velocity and relativistic approach - Fregolente Mendes de Oliveira, Diego; Leonel, Edson D. (Physics Letters A, 2012)
We study some dynamical properties for the problem of a charged particle in an electric field considering both the low velocity and relativistic cases. The dynamics for both approaches is described in terms of a two-dimensional and nonlinear mapping. The structure of the phase spaces is mixed and we introduce a hole in the chaotic sea to let the particles to escape. By changing the size of the hole we show that the survival probability decays exponentially for both cases. Additionally, we show for the relativistic dynamics, that the introduction of dissipation changes the mixed phase space and attractors appear. We study the parameter space by using the Lyapunov exponent and the average energy over the orbit and show that the system has a very rich structure with infinite family of self-similar shrimp shaped embedded in a chaotic region. © 2012 Elsevier B.V.
Keywords: Chaos; Parameter space; Shrimps; Survival probability

Dynamical regimes and stability of circular granular ratchets - Müller, Patric; Gallas, Jason; Pöschel, Thorsten (Scientific Reports, 2017)
Ratchets are simple mechanical devices which combine spatial asymmetry and nonequilibrium to produce counterintuitive transport of particles. The operation and properties of linear ratchets have already been extensively explored. However, very little is known about circular granular ratchets, startling devices able to convert vertical vibrations into rotations of the device. Here, we report results of systematic numerical investigations of the operational characteristics of circular granular ratchets. Several distinct behaviors are identified and explained in terms of the inner flow fields of the ratchet. All dynamical regimes found are robust and should not be difficult to observe in laboratory experiments.

Dynamical Simulation of Electron Transfer Processes in Alkanethiolate Self-Assembled Monolayers at the Au(111) Surface - Prucker, Veronika; Rubio-Pons, Oscar; Bockstedte, Michel Georg; Wang, Haobin; Brana Coto, Pedro; Thoss, Michael (Journal of Physical Chemistry C, 2013)
Electron transfer is investigated in a series of self-assembled monolayers (SAMs) consisting of nitrile-substituted short chain alkanethiolate molecules adsorbed at the Au(111) surface. Using first-principles methods and a model electron transfer Hamiltonian, we analyze the main factors controlling, at the molecular level, the electron injection times from donor states localized at the tail group of the SAM into the Au(111) substrate. We show that the donor-acceptor electronic couplings depend significantly on the orbital symmetry of the donor state and the length of the aliphatic spacer chain of the SAM. The dependence on the donor state symmetry and on the molecular structure of the linker can be used to control the electron injection times even in situations where the energy separation between the donor states is smaller than their width. © 2013 American Chemical Society.
UnivIS-Import:2015-04-14:Pub.2013.nat.dphy.ITP.ppem.dynami

Dynamical states in driven colloidal liquid crystals - Fischermeier, Ellen; Marechal, Mattheus; Mecke, Klaus (Journal of Chemical Physics, 2014)
We study a model colloidal liquid crystal consisting of hard spherocylinders under the influence of an external aligning potential by Langevin dynamics simulation. The external field that rotates in a plane acts on the orientation of the individual particles and induces a variety of collective nonequilibrium states. We characterize these states by the time-resolved orientational distribution of the particles and explain their origin using the single particle behavior. By varying the external driving frequency and the packing fraction of the spherocylinders we construct the dynamical state diagram. (C) 2014 AIP Publishing LLC.

Dynamic capillary phenomena using Incompressible SPH - Nair, Prapanch; Pöschel, Thorsten (Chemical Engineering Science, 2017)
Grid based fluid simulation methods are not able to solve complex non-linear dynamics like the rupture of a dynamic liquid bridge between freely colliding solids–an exemplary scenario of capillary forces competing with inertial forces in engineering applications–using a monolithic formulation for the solid and liquid phases present. We introduce a new Incompressible Smoothed Particle Hydrodynamics method for simulating three dimensional fluid-solid interaction flows with capillary (wetting and surface tension) effects at free surfaces. This meshless approach presents significant advantages over grid based approaches in terms of being monolithic and in handling interaction with free solids. The method is validated for accuracy and stability in dynamic scenarios involving surface tension and wetting. We then present three dimensional simulations of crown forming instability following the splash of a liquid drop, and the rupture of a liquid bridge between two colliding solid spheres, to show the method’s advantages in the study of dynamic micromechanical phenomena involving capillary flows.

Dynamic control of higher-order modes in hollow-core photonic crystal fibers - Euser, Tijmen; Whyte, Graeme; Scharrer, Michael; Chen, J. S. Y.; Abdolvand, Amir; Nold, J.; Kaminski, C. F.; Russell, Philip St. John (Optics Express, 2008)
We present a versatile method for selective mode coupling into higher-order modes of photonic crystal fibers, using holograms electronically generated by a spatial light modulator. The method enables non-mechanical and completely repeatable changes in the coupling conditions. We have excited higher order modes up to LP31 in hollow-core photonic crystal fibers. The reproducibility of the coupling allows direct comparison of the losses of different guided modes in both hollow-core bandgap and kagome-lattice photonic crystal fibers. Our results are also relevant to applications in which the intensity distribution of the light inside the fiber is important, such as particle- or atom-guidance.
EAM Import::2019-03-13

Dynamic equilibria in supported ionic liquid phase (SILP) catalysis: in situ IR spectroscopy identifies [Ru(CO)xCly]n species in water gas shift catalysis - Bauer, Tanja; Stepic, Robert; Wolf, Patrick; Kollhoff, Fabian; Karawacka, Weronica; Wick, Christian; Haumann, Marco; Wasserscheid, Peter; Smith, David M.; Smith, Ana-Suncana; Libuda, Jörg (Catalysis: Science and Technology, 2018)
Ru-based supported ionic liquid phase (SILP) systems efficiently catalyze the low-temperature water-gas shift reaction (WGSR). While previous studies suggest that Ru-carbonyl species play an important role in the mechanism, detailed knowledge on the catalytically active species is still missing. To identify these carbonyl complexes, we apply in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in combination with density functional theory (DFT). Investigations of an as-prepared [R(CO)3Cl2]2/ [C4C1C1Im]Cl/Al2O3 catalyst indicate splitting of the dimer induced by Cl−. Subsequently, an equilibrium between several [R(CO)xCly]n species is established, in which the IL serves as an effectively infinite Cl− reservoir. We find that the major species in the system freshly-prepared from [R(CO)3Cl2]2 is indeed [R(CO)3Cl3]−. A smaller amount of [R(CO)2Cl3]− and chloride-rich species [R(CO)2Cl4]2− or [RuCOCl4]2− are also found in the SILP. Similar Ru-carbonyl species are observed during carbonylation of RuCl3/ [C4C1C1Im]Cl/Al2O3, another potential WGSR catalyst. The response of [Ru(CO)3Cl2]2/[C4C1C1Im]Cl/Al2O3 to heating and/or CO dosing was probed in situ and the results confirm the presence of the equilibrium proposed above.
Keywords: SILP catalysis; in situ IR spectroscopy; [Ru(CO)xCly]n species

Dynamic nanoindentation of articular porcine cartilage - Franke, O.; Göken, Mathias; Meyers, M. A.; Durst, Karsten; Hodge, A. M. (Materials Science and Engineering C, 2011)
Articular cartilage is a poroelastic (biphasic) material with a complex deformation behavior, which can be considered elastic–viscoelastic. In this article, articular porcine cartilage is tested in vitro using dynamic nanoindentation and is analyzed using the frequency domain. The testing and data analysis are presented as a function of the strain rate and frequency, which allows for the results to be compared for various load amplitudes over the same frequency range. In addition, a new approach to correct the contact area during dynamic nanoindentation is presented and the effects of sample freezing on the mechanical properties are also discussed.
WW1::870

Dynamic processes in biological membrane mimics revealed by quasielastic neutron scattering. - Lautner, Lisa; Pluhackova, Kristyna; Barth, Nicolai; Seydel, Tilo; Lohstroh, Wiebke; Böckmann, Rainer; Unruh, Tobias (Chemistry and physics of lipids, 2017)
Neutron scattering is a powerful tool to study relaxation processes in biological membrane mimics in space and time. Combining different inelastic and quasielastic neutron scattering techniques, a large dynamic range can be covered: from atomic to mesoscopic lengths and from femto- to some hundreds of nanoseconds in time. This allows studies on e.g. the diffusion of lipids, the membrane undulation motions, the dispersion of sound waves in membranes as well as the mutual interactions of membrane constituents such as lipids, proteins, and additives. In particular, neutron scattering provides a quite direct experimental approach to the inter-atomic and inter-molecular potentials on length and time scales which are perfectly accessible by molecular dynamics (MD) simulations. Neutron scattering experiments may thus substantially support the further refinement of biomolecular force fields for MD simulations by supplying structural and dynamical information with high spatial and temporal resolution. In turn, MD simulations support the interpretation of neutron scattering data. The combination of both, neutron scattering experiments and MD simulations, yields an unprecedented insight into the molecular interactions governing the structure and dynamics of biological membranes. This review provides an overview of the molecular dynamics in biological membrane mimics as revealed by neutron scattering. It focuses on the latest findings such as the fundamental molecular mechanism of lateral lipid diffusion as well as the influence of additives and proteins on the short-time dynamics of lipids. Special emphasis is placed on the comparison of recent neutron scattering and MD simulation data with respect to molecular membrane dynamics on the pico- to nanosecond time scale.

Dynamic range multiwavelength particle characterization using analytical ultracentrifugation. - Peukert, Wolfgang; Walter, Johannes (Nanoscale, 2016)
We demonstrate how a sophisticated data analysis methodology enables us to perform multiwavelength evaluations of dynamic rotor speed gradient experiments obtained by analytical ultracentrifugation equipped with a multiwavelength detector. Our data evaluation tool HDR-MULTIFIT allows for the accurate analysis of sedimentation coefficient distributions which can be converted to particle size distributions. By means of multiwavelength evaluation, species dependent extinction spectra can be determined even for complex mixtures. Moreover, optical and hydrodynamic properties can be correlated for spherical particles of known optical properties applying multiwavelength evaluation and Mie's theory leading to a significant increase in the dynamic range of the experiment. We provide the theoretical background about the operation principle of our methodology and compare the performance of the multiwavelength analysis to the conventional single wavelength analysis as it is applied in turbidity analysis. We validate our technique using NIST traceable reference particles and show that our technique is universally applicable to materials of known and unknown optical properties, thus clearly extending the possibilities of particle analysis.
Keywords: muliwavelength; ultracentrifugation; sedimentation; particle

DynamO: A free O(N) general event-driven molecular dynamics simulator - Bannerman, Marcus; Lue, Leo; Sargant, R. (Journal of Computational Chemistry, 2011)
Molecular dynamics algorithms for systems of particles interacting through discrete or "hard" potentials are fundamentally different to the methods for continuous or "soft" potential systems. Although many software packages have been developed for continuous potential systems, software for discrete potential systems based on event-driven algorithms are relatively scarce and specialized. We present DynamO, a general event-driven simulation package, which displays the optimal O(N) asymptotic scaling of the computational cost with the number of particles N, rather than the O(N log N) scaling found in most standard algorithms. DynamO provides reference implementations of the best available event-driven algorithms. These techniques allow the rapid simulation of both complex and large (>10 particles) systems for long times. The performance of the program is benchmarked for elastic hard sphere systems, homogeneous cooling and sheared inelastic hard spheres, and equilibrium Lennard-Jones fluids. This software and its documentation are distributed under the GNU General Public license and can be freely downloaded from. Copyright © 2011 Wiley Periodicals, Inc.
Keywords: discontinuous potentials; event-driven simulation; hard spheres; molecular dynamics; square-well potential

Early Stages of Oriented Attachment: Formation of Twin ZnO Nanorods under Microwave Irradiation - Distaso, Monica; Mackovic, Mirza; Spiecker, Erdmann; Peukert, Wolfgang (Chemistry - A European Journal, 2012)
Let’s become twins! Early stages of formation of twin ZnO nanorods under microwave irradiation have been studied. The coupling of facets with the same polarity was triggered by the rough surface and the defect-rich microstructure of the constituent ZnO building blocks. Oriented attachment was found to be the underlying mechanism of the twinning process (see scheme).

Effective Ligand Engineering of the Cu2ZnSnS4 Nanocrystal Surface for Increasing Hole Transport Efficiency in Perovskite Solar Cells - Khanzada, Laraib Sarfraz; Levchuk, Ievgen; Hou, Yi; Azimi, Seyed Hamed; Osvet, Andres; Ahmad, Rameez; Brandl, Marco; Herre, Patrick; Distaso, Monica; Hock, Rainer; Peukert, Wolfgang; Batentschuk, Miroslaw; et al. (Advanced Functional Materials, 2016)
Effective engineering of surface ligands in semiconductor nanocrystals can facilitate the electronic interaction between the individual nanocrystals, making them promising for low-cost optoelectronic applications. Here, the use of high purity CuZnSnS (CZTS) nanocrystals as the photoactive layer and hole-transporting material is reported in low-temperature solution-processed solar cells. The high purity CZTS nanocrystals are prepared by engineering the surface ligands of CZTS nanocrystals, capped originally with the long-chain organic ligand oleylamine. After ligand removal, CZTS nanocrystals show substantial improvement in photoconductivity and mobility, displaying also an appreciable photoresponse in a simple heterojunction solar cell architecture. More notably, CZTS nanocrystals exhibit excellent hole-transporting properties as interface layer in perovskite solar cells, yielding power conversion efficiency (PCE) of 15.4% with excellent fill factor (FF) of 81%. These findings underscore the importance of removing undesired surface ligands in nanocrystalline optoelectronic devices, and demonstrate the great potential of CZTS nanocrystals as both active and passive material for the realization of low-cost efficient solar cells.
Keywords: CZTS solar cells; HTM; Inorganic nanocrystals; Ligand exchange; Perovskite

Effective Ligand Passivation of Cu2O Nanoparticles through Solid-State Treatment with Mercaptopropionic Acid - Azimi, Seyed Hamed; Kuhri, Susanne; Osvet, Andres; Matt, Gebhard; Khanzada, Laraib Sarfraz; Lemmer, Mario; Luechinger, Norman A.; Larsson, Mats I.; Zeira, Eitan; Guldi, Dirk Michael; Brabec, Christoph (Journal of the American Chemical Society, 2014)
In colloidal nanoparticle (NPs) devices, trap state densities at their surface exert a profound impact on the rate of charge carrier recombination and, consequently, on the deterioration of the device performance. Here, we report on the successful application of a ligand exchange strategy to effectively passivate the surface of cuprite (Cu2O) NPs. Cu2O NPs were prepared by means of a novel synthetic route based on flame spray pyrolysis. FTIR, XRD, XPS, and HRTEM measurements corroborate the formation of cubic cuprite Cu2O nanocrystals, excluding the possible presence of undesired CuO or Cu phases. Most importantly, steady-state emission and transient absorption assays document that surface passivation results in substantial changes in the intensity of emissive excitonic states-centered at copper and oxygen vacancies-and in the lifetime of excitons near the band edge. To shed light onto ultrafast processes in Cu2O nanocrystals additional pump probe experiments on the femtosecond and nanosecond time scales were carried out. Two discernible species were observed: on one hand, an ultrafast component ( ps) that relates to the excitons; on the other hand, a long-lived component ( μs) that originates from the defects/trap states.
Keywords: Engineering controlled terms: Nanocrystals; Spray pyrolysis Charge carrier recombination; Colloidal nanoparticles; Ligand passivation; Mercaptopropionic acid; Pump-probe experiments; Steady-state emissions; Surface passivation; Transient absorption Engineering main heading: Excitons EMTREE drug terms: 3 mercaptopropionic acid; copper; copper nanoparticle; nanocrystal; oxygen EMTREE medical terms: article; assay; infrared spectroscopy; pyrolysis; solid; steady state; surface property; transient absorption assay; transmission electron microscopy; X ray photoelectron spectroscopy

Effective n-octane isomerization under exceptionally mild conditions using a novel class of superacidic ionic liquids - Meyer, Carolin; Wasserscheid, Peter (Chemical Communications, 2010)
Superacidic chloroaluminate ionic liquids of the general formula [cation]Cl/AlCl(3)[X(AlCl(3)) > 0.5] + H(2)SO(4) effectively isomerize n-octane to form branched liquid hydrocarbon isomers. Due to the highly acidic character of the ionic liquid the reaction proceeds under extremely mild conditions in a liquid-liquid biphasic reaction mode leading to a minimum of undesired cracking side-reactions.

Effective work function tuning in high-κ dielectric metal-oxide-semiconductor stacks by fluorine and lanthanide doping - Fet, A.; Haeublein, V.; Bauer, A. J.; Ryssel, Heiner; Frey, Lothar (Applied Physics Letters, 2010)
In this letter, an ion implantation approach to engineer the effective work function is discussed and an empirical model to explain the mechanisms of work function change is proposed. It is shown that by doping a TiN/HfSiOx stack with La and F, a silicon conduction band edge and valence band edge metal effective work function of 3.8 and 5.4 eV, respectively, can be achieved. The empirical correlation of the achieved effective work function to the electronegativity of the dopant element is explained.
EAM Import::2019-03-14
Keywords: conduction bands; doping; electronegativity; fluorine; hafniumcompounds; high-k dielectric thin films; ion implantation; lanthanum; MISstructures; titanium compounds; valence bands; work function

Effect of acid treatment on the chemical composition and the structure of Egyptian diatomite - Alyosef, Hallah Ahmad; Ibrahim, Suzan; Welscher, Julia; Inayat, Alexandra; Eilert, Andre; Denecke, Reinhard; Schwieger, Wilhelm; Muenster, Tom; Kloess, Gert; Einicke, Wolf-Dietrich; Enke, Dirk (International Journal of Mineral Processing, 2014)
In this study Egyptian diatomaceous earth from Kasr El-Sagha locality in El Fayium province, Egypt was used. A highly purified diatomite has been prepared successfully by using a two stage process. In the first stage, samples of Egyptian diatomite were subjected to several mechanical techniques (attrition scrubbing and hydrocyclone classification) to remove most of the accompanied gangue minerals like inorganic carbonate, silica sand, and clay. The fraction with a particle size of -45 mu m was then submitted to a thermo-chemical treatment. This second stage started with a calcination of the diatomite samples at 1023 K for 1 h. Three modified forms of diatomite were then prepared by hot acidification of the calcined diatomite samples with aqua regia (5 M HCl + 5 M HNO3), 5 M sulphuric acid or 5 M hydrochloric acid. The refined products were characterized by X-ray diffraction, X-ray fluorescence, low temperature nitrogen adsorption, mercury intrusion and scanning electron microscopy. Silica materials with high purity (>96 wt.% SiO2) and an accessible and interconnected mesopore structure could be obtained. Additionally, all samples displayed a large amount of macropores of about 1 mu m diameter and a broad distribution of larger interstitial macropores. The treatment with hydrochloric acid led to products with a specific surface area between 120 and 150 m(2) g(-1) and 63 wt.% of amorphous phase. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Diatomite; Acid modification; Purity; Pore structure of amorphous biogenic; silica products

Effect of a Local Laser Heat Treatment on the Formability of Multi-layered 6000 Series Aluminum Alloys - Merklein, Marion; Herrmann, Jürgen (Physics Procedia, 2016)
The production of multi-layered aluminum alloys using the Accumulative Roll Bonding Process (ARB) is an auspicious possibility to fabricate nanostructured sheet material with enhanced mechanical properties. The increased strength qualifies these semi-finished products for lightweight applications in automotive industry. However, the ARB process also leads to a reduced ductility of the ultra-fine grained material. Furthermore, failure mechanisms like delamination can occur during forming operations. A local short term laser heat treatment according to the Tailor Heat Treated Blanks technology can be applied in order to enhance the formability and prevent failure. Multi-layered sheets of the aluminum alloy AA6014 were produced in a warm rolling process. The mechanical properties as well as the bond strength are investigated within this contribution using tensile tests and T-peel tests. The material characterization is carried out in dependency of the heat treatment temperature. Air bending tests in combination with a local laser heat treatment are used in order to investigate the formability of the multi-layered aluminum sheets.
EAM Import::2019-03-14

Effect of anisotropies on the magnetization dynamics - Gallas, Jason; Perez, Laura M.; Bragard, Jean; Mancini, Hector; Cabanas, Ana M.; Suarez, Omar J.; Laroze, David (Networks and Heterogeneous Media, 2015)
We report a systematic investigation of the magnetic anisotropy effects observed in the deterministic spin dynamics of a magnetic particle in the presence of a time-dependent magnetic field. The system is modeled by the Landau-Lifshitz-Gilbert equation and the magnetic field consists of two terms, a constant term and a term involving a harmonic time modulation. We consider a general quadratic anisotropic energy with three different preferential axes. The dynamical behavior of the system is represented in Lyapunov phase diagrams, and by calculating bifurcation diagrams, Poincaré sections and Fourier spectra. We find an intricate distribution of shrimp-shaped regular island embedded in wide chaotic phases. Anisotropy effects are found to play a key role in defining the symmetries of regular and chaotic stability phases.

Effect of body deformability on microswimming - Pande, Jayant; Merchant, Laura; Krueger, Timm; Harting, Jens; Smith, Ana-Suncana (Soft Matter, 2017)
In this work we consider the following question: given a mechanical microswimming mechanism, does increased deformability of the swimmer body hinder or promote the motility of the swimmer? To answer this we run immersed-boundary-lattice-Boltzmann simulations of a microswimmer composed of deformable beads connected with springs. We find that the same deformations in the beads can result in different effects on the swimming velocity, namely an enhancement or a reduction, depending on the other parameters. To understand this we determine analytically the velocity of the swimmer, starting from the forces driving the motion and assuming that the deformations in the beads are known as functions of time and are much smaller than the beads themselves. We find that to the lowest order, only the driving frequency mode of the surface deformations contributes to the swimming velocity, and comparison to the simulations shows that both the velocity-promoting and velocity-hindering effects of bead deformability are reproduced correctly by the theory in the limit of small bead deformations. For the case of active deformations we show that there are critical values of the spring constant - which for a general swimmer corresponds to its main elastic degree of freedom - which decide whether the body deformability is beneficial for motion or not.
Keywords: LOW-REYNOLDS-NUMBER; LATTICE BOLTZMANN; SWIMMER; CILIA; PARTICLES; DYNAMICS; MOTORS; FLUIDS; SIMULATIONS; EFFICIENT

Effect of dimensionality on the spectra of hybrid plasmonic-photonic crystals - Romanova, Alexandra; Korovin, A. V.; Romanov, Sergey (Physics of the Solid State, 2013)
Based on colloidal crystals of various dimensionality, hybrid metal-dielectric plasmonic-photonic heterocrystals have been prepared. It has been shown that the spectra of optical transmission of heterocrystals are mostly controlled by the sum of contributions of composing plasmonic and photonic crystals. At the same time, there are a number of phenomena caused by the mutual effect of heterostructure components, which lead to a deviation of observed optical properties from the linear superposition of responses of these crystals. In particular, it has been found that the anomalous transmission controlled by the plasmonic crystal decreases with increasing the dimensionality of the photonic crystal attached to it. At the same time, light reflection on a metallized surface changes light diffraction in photonic crystals and leads to Fabry-Perot oscillation amplification. It has been assumed that an intermediate layer is formed, in which Bloch modes of the photonic crystal and surface plasmon-polaritons of the plasmonic crystal are hybridized.
EAM Import::2019-03-14

Effect of elastic anisotropy on strain relief and residual stress determination in cubic systems by FIB-DIC experiments - Krottenthaler, Markus; Benker, Lisa; Mughal, M. Z.; Sebastiani, Marco; Durst, Karsten; Göken, Mathias (Materials & Design, 2016)
Focused Ion Beam milling and Digital Image Correlation analysis (FIB-DIC) method has been shown to offer an effective measure of residual stresses in coatings and bulk materials. In the present work the effect of elastic anisotropy on the residual stress interpretation from FIB-DIC measurements is studied for single crystals with cubic symmetry. Crystal orientation-dependent, elastically anisotropic 3D finite element models of the double slot milling geometry were developed and verified against FIB-DIC measurements performed on in situ four point bent samples of nanocrystalline nickel and single crystal CMSX-6 alloy. A discussion is presented of the limitations of the simplified assumptions vs full anisotropic modelling. (C) 2016 Elsevier Ltd. All rights reserved.
Keywords: Focused ion beam milling assisted digital image correlation; Residual stress; Elastic anisotropy; Finite element modelling; Four point bending

Effect of excess silicate on the structure formation and textural properties of MTS materials - Inayat, Alexandra; Kuhnt, Andreas; Schwieger, Wilhelm; Einicke, Wolf-Dietrich; Kullmann, Jens; Enke, Dirk (Journal of Porous Materials, 2011)
The synthesis of micellar templated silica (MTS) materials has been conducted with different SiO2/CTAB molar ratios for two different cetyltrimethylammoniumbromide (CTAB) concentrations of 0.02 and 0.07 M to examine the structure formation for cubic (SBA-1) as well as for hexagonal (SBA-3) surfactant arrangement in acidic reaction medium with increasing silicate excess. Reaction products were analyzed with X-ray diffraction, N-2 physisorption and TG-MS. It was found that an increase of the silicate concentration leads to the formation of additional silica gel in the resulting MTS material, which causes not only a decrease of specific surface area and pore volume, but also of the mesopore diameter. The latter effect is explained by a proposed embedding theory. Furthermore, with increasing silicate content in the synthesis mixture a phase transformation from hexagonal to cubic pore arrangement was found for the CTAB concentration of 0.07 M and the maximum SiO2/CTAB molar ratio for ordered pore arrangement has been determined.
Keywords: Micellar templated silica (MTS); Silicate excess; SBA-1; SBA-3; Pore arrangement; Textural properties

Effect of interlayer anions on [NiFe]-LDH nanosheet water oxidation activity - Hunter, B. M.; Hieringer, Wolfgang; Winkler, J. R.; Gray, H. B.; Mueller, A. M. (Energy and Environmental Science, 2016)
We synthesized nickel–iron layered double hydroxide ([NiFe]-LDH) nanosheets with different interlayer anions to probe their role in water oxidation catalysis. In alkaline electrolyte in ambient air, carbonate rapidly replaced other interlayer anions and catalytic activity was highest. Electrocatalytic water oxidation in virtually carbonate-free alkaline electrolyte revealed that activity was a function of anion basicity. Our [NiFe]-LDH nanosheets, prepared by pulsed laser ablation in liquids, were regenerated in carbonate-containing aqueous KOH. Anion binding motifs were assessed by X-ray photoelectron spectroscopy in combination with density functional theory calculations, suggesting that nitrite species bound to edge-site Fe in the precatalyst correlated with higher water oxidation activity.
EAM Import::2019-03-14

Effect of nonadiabatic electronic-vibrational interactions on the transport properties of single-molecule junctions - Erpenbeck, André; Haertle, R.; Thoss, Michael (Physical Review B, 2015)
The interaction between electronic and vibrational degrees of freedom in single-molecule junctions may result from the dependence of the electronic energies or the electronic states of the molecular bridge on the nuclear displacement. The latter mechanism leads to a direct coupling between different electronic states and is referred to as nonadiabatic electronic-vibrational coupling. Employing a perturbative nonequilibrium Green’s function approach, we study the influence of nonadiabatic electronic-vibrational coupling in model molecular junctions. Thereby, we distinguish between systems with well-separated and quasidegenerate electronic levels. The results show that the nonadiabatic electronic-vibrational interaction can have a significant influence on the transport properties. The underlying mechanisms, in particular the difference between nonadiabatic and adiabatic electronic-vibrational couplings, are analyzed in some detail.

Effect of particle shape on the efficiency of granular dampers - Pourtavakoli, Hamzeh; Ribeiro Parteli, Eric Josef; Pöschel, Thorsten (New Journal of Physics, 2016)
By means of particle-based numerical simulations using the discrete element method, we address the question of how the performance of granular dampers is affected by the shape of the granular particles. In consistence with previous experiments performed with nearly spherical particles we find that independently of the particles‘ shape, the granular system is characterized by a gas-like regime for small amplitudes of the container’s oscillation and by a collect-and-collide regime for large amplitude forcing. Both regimes are separated by an optimal operation mode—the critical amplitude of the damping oscillation for which the energy dissipation is maximal—which is independent of the particle shape for given conditions of particle mass, material properties and number of particles. However, in the gas-like regime, we find that spherical particles lead to more efficient energy dissipation compared to complex shaped particles of the same mass. In this regime, a dependence on the damper’s efficiency on the particle shape is found.

Effect of polymer molecular weight and solution parameters on selective dispersion of single-walled carbon nanotubes - Jakubka, Florian; Schießl, Stefan; Martin, Sebastian; Englert, Jan; Hauke, Frank; Hirsch, Andreas; Zaumseil, Jana (ACS Macro Letters, 2012)
The selective dispersion of single-walled carbon nanotube species (n,m) with conjugated polymers such as poly(9,9-dioctylfluorene) (PFO) and poly(9,9-dioctylfluorene-cobenzothiadiazole) (F8BT) in organic solvents depends not only on the type of solvent but also on the molecular weight of the polymer. We find an increasing amount of nanotubes and altered selectivities for dispersions with higher molecular weight polymers. Including the effects of different aromatic solvents, we propose that solution viscosity is one of the factors influencing the apparent selectivity by changing the reaggregation rate of the single-walled carbon nanotubes (SWNT). The type of solvent, polymer molecular weight, concentration, and viscosity should thus be taken into account when screening for new polymers for selective SWNT dispersion. © 2012 American Chemical Society.

Effect of polymer species and concentration on the production of mefenamic acid nanoparticles by media milling - Peukert, Wolfgang; Ito, A; Konnerth, Christoph-Günther; Schmidt, Jochen (European Journal of Pharmaceutics and Biopharmaceutics, 2016)
The effect of four structurally different polymer species (hydroxypropylcellulose, polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymer and polyvinyl alcohol) on the production of mefenamic acid nanoparticles during media milling has been studied. It was found that product particle sizes are strongly determined by the type of polymeric stabiliser as well as by its concentration at constant process conditions. With respect to small product particle sizes an optimum excipient concentration was identified and adjusted for colloidal stability of the drug nanosuspensions. Furthermore, it was found that overdosing of excipients must be omitted to suppress ripening due to enhanced solubilisation phenomena. Hence, the smallest product particle sizes were obtained using a polymeric stabiliser which exhibits a high affinity to the model drug compound and a low solubilisation capacity. Affinities of each polymer species to mefenamic acid and corresponding surface concentrations were determined using straightforward and simple viscosity measurements of the supernatant. A relationship between polymer affinity, solubilisation capacity and limiting product particle size has been observed, which supports the hypothesis that final product particle sizes are rather determined by the solid-liquid equilibrium than by pure mechanical fracture.
Keywords: Active pharmaceutical ingredient; Formulation; Media milling; Mefenamic acid; Nanosuspension; Ripening; Solubilisation; Solubility; Surface concentration

Effect of rapid thermal annealing on barrier height and 1/f noise of Ni/GaN Schottky barrier diodes - Kumar, Ashutosh; Latzel, Michael; Christiansen, Silke; Kumar, V.; Singh, R. (Applied Physics Letters, 2015)
Current-voltage (as a function of temperature), capacitance-voltage, and 1/f noise characteristics of Ni/GaN Schottky barrier diodes (SBDs) as function of rapid thermal annealing (RTA) are studied. It is found that RTA treatments of SBDs at 450 °C for 60 s resulted in a significant improvement of ideality factor and Schottky barrier height: the ideality factor decreased from 1.79 to 1.12 and the barrier height increased from 0.94 to 1.13 eV. The spectral power density of current fluctuations in the diode subjected to RTA at 450 °C is found to be two orders of magnitude lower as compared to the as-deposited diode. Improved diode characteristics and decreased 1/f noise in RTA treated (450 °C/60 s) diode are attributed to reduced level of barrier inhomogeneities at the metal-semiconductor interface and explained within the framework of the spatial inhomogeneity model.
EAM Import::2019-03-14

Effect of Structure and Disorder on the Charge Transport in Defined Self-Assembled Monolayers of Organic Semiconductors - Schmaltz, Thomas; Gothe, Bastian; Krause, Andreas; Leitherer, Susanne; Steinrück, Hans-Georg; Thoss, Michael; Clark, Timothy; Halik, Marcus (Acs Nano, 2017)
Self-assembled monolayer field-effect transistors (SAMFETs) are not only a promising type of organic electronic device but also allow detailed analyses of structure-property correlations. The influence of the morphology on the charge transport is particularly pronounced, due to the confined monolayer of 2D- extgreekp-stacked organic semiconductor molecules. The morphology, in turn, is governed by relatively weak van-der-Waals interactions and is thus prone to dynamic structural fluctuations. Accordingly, combining electronic and physical characterization and time-averaged X-ray analyses with the dynamic information available at atomic resolution from simulations allows us to characterize self-assembled monolayer (SAM) based devices in great detail. For this purpose, we have constructed transistors based on SAMs of two molecules that consist of the organic p-type semiconductor benzothieno[3,2-b][1]benzothiophene (BTBT), linked to a C11 or C12 alkylphosphonic acid. Both molecules form ordered SAMs; however, our experiments show that the size of the crystalline domains and the charge-transport properties vary considerably in the two systems. These findings were confirmed by molecular dynamics (MD) simulations and semiempirical molecular-orbital electronic-structure calculations, performed on snapshots from the MD simulations at different times, revealing, in atomistic detail, how the charge transport in organic semiconductors is influenced and limited by dynamic disorder.

Effect of thermal annealing on the mechanical properties of low-emissivity physical vapor deposited multilayer-coatings for architectural applications - Meszaros, Robert; Merle, Benoit; Wild, Michael; Durst, Karsten; Göken, Mathias; Wondraczek, Lothar (Thin Solid Films, 2012)
Low-emissivity (low-E) coatings comprising a stack of multiple physical vapor deposited metallic and dielectric layers play an important role in energy management of modern buildings. The production process of such architectural glazings often requires that the coatings withstand a short-term thermal load of up to 700 °C. Here, we report on thermally-induced variations in the mechanical properties of representative large-area magnetron-sputtered low-E stacks on glass, developed specifically for high temperature stability. Coatings are investigated before and after heat treatment by bulge testing, curvature analyses using Stoney's equation, and nanoindentation. For as-deposited coatings, an in-plane residual compressive stress about 48 MPa and Young's modulus of 120 GPa are found, depending on the type of substrate. Short-term exposure to up to 700 °C converts this situation to in-plane residual tensile stress of > 400 MPa, while Young's modulus decreases to about 105 GPa. These changes in the residual stress state are explained on the basis of structural, topological and dimensional changes in the coating stack. They identified as one of the primary factors governing temperature-resistance of low-E coatings.
WW1::923

Effect of the structure and morphology of natural, synthetic and post-processed graphites on their dispersibility and electronic properties - Kozhemyakina, Nina; Eigler, Siegfried; Inayat, Alexandra; Schwieger, Wilhelm; Hirsch, Andreas; Dinnebier, Robert E. (Fullerenes Nanotubes and Carbon Nanostructures, 2013)
Twenty-two different graphite grades of the families natural, synthetic, intercalated, expanded, amorphous, and turbostratic graphite, as well as platelets and activated carbon, were analyzed on their dispersibility in N-methylpyrrolidone, cyclohexylpyrrolidone and water-sodium cholate solution. They were characterized for their properties (grain size, density, purity, surface area, pH in water) and morphology. Thermogravimetric analysis, Raman spectroscopy studies, and electrical conductivity measurements were also used. XRPD followed by a Rietveld refinement provided information on the amounts of the rhombohedral (3R) and hexagonal (2H) phases for the crystalline part of the material and the interlayer distances. The properties of graphites favoring better dispersibility are: small grain size and bulk density, neutral pH in water. The electrical conductivity in inversely proportional to the Raman D-band intensity and is highest for the graphites with shortest interlayer spacing. The D-, G- and 2D-bands in the Raman spectra of graphites are in an exponential relation. © 2013 Copyright Taylor and Francis Group, LLC.

Effects of Alkyl Terminal Chains on Morphology, Charge Generation, Transport, and Recombination Mechanisms in Solution-Processed Small Molecule Bulk Heterojunction Solar Cells - Min, Jie; Luponosov, Yuriy N.; Gasparini, Nicola; Richter, Moses; Bakirov, Artem V.; Shcherbina, Maxim A.; Chvalun, Sergei N.; Grodd, Linda; Grigorian, Souren; Ameri, Tayebeh; Ponomarenko, Sergei A.; Brabec, Christoph (Advanced Energy Materials, 2015)
Length of the terminal alkyl chains at dicyanovinyl (DCV) groups of two dithienosilole (DTS) containing small molecules (DTS(Oct)2-(2T-DCV-Me)2 and DTS(Oct)2-(2T-DCV-Hex)2) is investigated to evaluate how this affects the molecular solubility and blend morphology as well as their performance in bulk heterojunction organic solar cells (OSCs). While the DTS(Oct)2-(2T-DCV-Me)2 (a solubility of 5 mg mL-1) system exhibits both high short circuit current density (J sc) and high fill factor, the DTS(Oct)2-(2T-DCV-Hex)2 (a solubility of 24 mg mL-1) system in contrast suffers from a poor blend morphology as examined by atomic force morphology and grazing incidence X-ray scattering measurements, which limit the photovoltaic properties. The charge generation, transport, and recombination dynamics associated with the limited device performance are investigated for both systems. Nongeminate recombination losses in DTS(Oct)2-(2T-DCV-Hex)2 system are demonstrated to be significant by combining space charge limited current analysis and light intensity dependence of current-voltage characteristics in combination with photogenerated charge carrier extraction by linearly increasing voltage and transient photovoltage measurements. DTS(Oct)2-(2T-DCV-Me)2 in contrast performs nearly ideal with no evidence of nongeminate recombination, space charge effects, or mobility limitation. These results demonstrate the importance of alkyl chain engineering for solution-processed OSCs based on small molecules as an essential design tool to overcome transport limitations.
Keywords: blend morphology; molecular solubility; organic solar cells; recombination dynamics; transport limitations

Effects of bridging atom and π-bridge length on physical and photovoltaic properties of A-π-D-π-A oligomers for solution-processed organic solar cells - Luponosov, Yuriy N.; Min, Jie; Bakirov, Artem V.; Dmitryakov, Petr V.; Chvalun, Sergei N.; Peregudova, Svetlana M.; Ameri, Tayebeh; Brabec, Christoph; Ponomarenko, Sergei A. (Dyes and Pigments, 2015)
Synthesis of novel acceptor-donor-acceptor oligomers with electron-withdrawing alkyldicyanovinyl groups linked through an oligothiophene π-bridge with either dithienosilole or cyclopentadithiophene electron donor units is described. Changing the bridgehead atom from carbon to silicon in the central donor unit leads to a significant change in optical, thermal and structural properties of the oligomers. In addition, elongation of the oligothiophene π-bridge in the oligomers increases energies of HOMO and LUMO levels and leads to an unexpected hypsochromic shift of their absorption spectrum, because extension of the conjugation length cannot compensate a decrease of the intramolecular charge transfer between the dithienosilole and dicyanovinyl units. Although these minor changes in the chemical structures have a pronounced impact on the morphologies of their blends with PC70BM, the optimized solution-processed organic solar cells based on these small molecules demonstrate similar power conversion efficiencies.
EAM Import::2019-03-14
Keywords: Alkyldicyanovinyl groups; Dithienosilole; Donor-acceptor oligomers; Effect of heteroatom substitution; Oligothiophenes; Organic solar cells

Effects of deposited Pt particles on the reducibility of CeO2(111) - Bruix, Albert; Migani, Annapaola; Vayssilov, Georgi N.; Neyman, Konstantin M.; Libuda, Jörg; Illas, Francesc (Physical Chemistry Chemical Physics, 2011)
The interaction of Pt particles with the regular CeO2(111) surface has been studied using Pt-8 clusters as representative examples. The atomic and electronic structure of the resulting model systems have been obtained through periodic spin-polarized density functional calculations using the PW91 exchange-correlation potential corrected with the inclusion of a Hubbard U parameter. The focus is on the effect of the metal-support interaction on the surface reducibility of ceria. Several initial geometries and orientations of Pt-8 with respect to the ceria substrate have been explored. It has been found that deposition of Pt-8 over the ceria surface results in spontaneous oxidation of the supported particle with a concomitant reduction of up to two Ce4+ cations to Ce3+. Oxygen vacancy formation on the CeO2(111) surface and oxygen spillover to the adsorbed particle have also been considered. The presence of the supported Pt-8 particles has a rather small effect (similar to 0.2 eV) on the O vacancy formation energy. However, it is predicted that the spillover of atomic oxygen from the substrate to the metal particle greatly facilitates the formation of oxygen vacancies: the calculated energy required to transfer an oxygen atom from the CeO2(111) surface to the supported Pt-8 particle is only 1.00 eV, i.e. considerably smaller than 2.25 eV necessary to form an oxygen vacancy on the bare regular ceria surface. This strongly suggests that the propensity of ceria systems to store and release oxygen is directly affected by the presence of supported Pt particles.

Effects of electron-withdrawing group and electron-donating core combinations on physical properties and photovoltaic performance in D-π-A star-shaped small molecules - Luponosov, Yuriy N.; Min, Jie; Solodukhin, Alexander N.; Kozlov, Oleg V.; Obrezkova, Marina A.; Peregudova, Svetlana M.; Ameri, Tayebeh; Chvalun, Sergei N.; Pshenichnikov, Maxim S.; Brabec, Christoph; Ponomarenko, Sergei A. (Organic Electronics, 2016)
The first representatives of star-shaped molecules having 3-alkylrhodanine (alkyl-Rh) electron-withdrawing groups, linked through bithiophene π-spacer with electron-donating either triphenylamine (TPA) or tris(2-methoxyphenyl)amine (m-TPA) core were synthesized. The physical properties and photovoltaic performance of these novel molecules with 3-ethylrhodanine groups were comprehensively studied and compared to their full analogs having dicyanovinyl (DCV) units as the other type of well-known and frequently used acceptor groups. On one hand, the former demonstrate several advantages such as higher solubility and better photovoltaic performance in bulk-heterojunction (BHJ) organics solar cells (OSCs) as compared to the latter. Nevertheless, the former have slightly lower optical/electrochemical bandgaps and higher thermooxidation stability. On the other hand, molecules of both series based on m-TPA core along with higher solubility and higher position of HOMO energy levels have more pronounced tendency to crystalize as compared to the TPA-based molecules. Detailed investigation of the structure-property relationships for these series of molecules revealed that donor and acceptor unit combinations influence both charge generation and charge transport/recombination properties, as demonstrated by the ultrafast photoinduced absorption spectroscopy, space charge limited current measurements and transient photovoltage technique. These results give more insight how to fine-tune and predict physical properties and photovoltaic performance of small molecules having either alkyl-Rh or DCV units in their chemical structures and thus providing a molecular design guideline for the next generation of high-performance photovoltaic materials.
EAM Import::2019-03-14
Keywords: 3-Ethylrhodanine; Dicyanovinyl; Organic solar cells; Star-shaped molecules; Triphenylamine; Ultrafast charge separation