Fracture toughness of silicon nitride thin films of different thicknesses as measured by bulge tests - Merle, Benoit; Göken, Mathias (Acta Materialia, 2011)
A bulge test setup was used to determine the fracture toughness of amorphous low-pressure chemical vapor deposited (LPCVD) silicon nitride films with various thicknesses in the range 40–108 nm. A crack-like slit was milled in the center of each free-standing film with a focused ion beam, and the membrane was deformed in the bulge test until failure occurred. The fracture toughness KIC was calculated from the pre-crack length and the stress at failure. It is shown that the membrane is in a transition state between pure plane-stress and plane-strain which, however, had a negligible influence on the measurement of the fracture toughness, because of the high brittleness of silicon nitride and its low Young's modulus over yield strength ratio. The fracture toughness KIC was found to be constant at 6.3 ± 0.4 MPa m1/2 over the whole thickness range studied, which compares well with bulk values. This means that the fracture toughness, like the Young's modulus, is a size-independent quantity for LPCVD silicon nitride. This presumably holds true for all amorphous brittle ceramic materials.
WW1::875

Free Material Optimization with Fundamental Eigenfrequency Constraints - Stingl, Michael; Kocvara, Michal; Leugering, Günter (SIAM Journal on Optimization, 2009)
The goal of this paper is to formulate and solve free material optimization problems with constraints on the smallest eigenfrequency of the optimal structure. A natural formulation of this problem as a linear semidefinite program turns out to be numerically intractable. As an alternative, we propose a new approach, which is based on a nonlinear semidefinite low-rank approximation of the semidefinite dual. We introduce an algorithm based on this approach and analyze its convergence properties. The article is concluded by numerical experiments proving the effectiveness of the new approach

Free-Standing Membranes to Study the Optical Properties of Anodic TiO2 Nanotube Layers - Cha, Gi; Schmuki, Patrik; Altomare, Marco (Chemistry - An Asian Journal, 2016)
In the present work we investigate various optical properties (such as light absorption and reflectance) of anodic TiO2 nanotube layers directly transferred as self-standing membranes onto quartz substrates. This allows investigation in a transmission geometry which provides significantly more reliable data than measurements on the metallic Ti substrate. Light transmission and reflectance measurements were carried out for layers of thickness varying from 1.8 to 50 extgreekmm, and the layers were investigated in their amorphous and crystalline forms. A series of wavelength-dependent light attenuation coefficients are extrapolated and found to match the photocurrent versus irradiation wavelength behavior. A feature specific to anodic nanotubes is that their intrinsic carbon contamination content causes a proportional sub-bandgap response. Overall, the extracted data provide a valuable basis and understanding for the design of photo-electrochemical devices based on TiO2 nanotubes. In the present work we investigate various optical properties (such as light absorption and reflectance) of anodic TiO2 nanotube layers directly transferred as self-standing membranes onto quartz substrates. This allows investigation in a transmission geometry which provides significantly more reliable data than measurements on the metallic Ti substrate. Light transmission and reflectance measurements were carried out for layers of thickness varying from 1.8 to 50 extgreekmm, and the layers were investigated in their amorphous and crystalline forms. A series of wavelength-dependent light attenuation coefficients are extrapolated and found to match the photocurrent versus irradiation wavelength behavior. A feature specific to anodic nanotubes is that their intrinsic carbon contamination content causes a proportional sub-bandgap response. Overall, the extracted data provide a valuable basis and understanding for the design of photo-electrochemical devices based on TiO2 nanotubes.
EAM Import::2019-03-14

Free Surface Lattice Boltzmann with Enhanced Bubble Model - Anderl, Daniela; Bogner, Simon; Rauh, Cornelia; Rüde, Ulrich; Delgado, Antonio (Computers & Mathematics with Applications, 2014)
This paper presents an enhancement to the free surface lattice Boltzmann method (FSLBM) for the simulation of bubbly flows including rupture and breakup of bubbles. The FSLBM uses a volume of fluid approach to reduce the problem of a liquid–gas two-phase flow to a single-phase free surface simulation. In bubbly flows compression effects leading to an increase or decrease of pressure in the suspended bubbles cannot be neglected. Therefore, the free surface simulation is augmented by a bubble model that supplies the missing information by tracking the topological changes of the free surface in the flow. The new model presented here is capable of handling the effects of bubble breakup and coalesce without causing a significant computational overhead. Thus, the enhanced bubble model extends the applicability of the FSLBM to a new range of practically relevant problems, like bubble formation and development in chemical reactors or foaming processes.
UnivIS-Import:2015-03-09:Pub.2013.tech.IMMD.lsinfs.freesu
Keywords: Lattice Boltzmann; Free surface; Volume of fluid; Interface capturing; Bubbly flow; Numerical algorithms

Friction and Dissipation in Epitaxial Graphene Films - Filleter, Tobin; Mcchesney, J. L.; Bostwick, Aaron; Rotenberg, Eli; Emtsev, K. V.; Seyller, Thomas; Horn, K.; Bennewitz, Roland (Physical Review Letters, 2009)
We have studied friction and dissipation in single and bilayer graphene films grown epitaxially on SiC. The friction on SiC is greatly reduced by a single layer of graphene and reduced by another factor of 2 on bilayer graphene. The friction contrast between single and bilayer graphene arises from a dramatic difference in electron-phonon coupling, which we discovered by means of angle-resolved photoemission spectroscopy. Bilayer graphene as a lubricant outperforms even graphite due to reduced adhesion.
EAM Import::2019-03-14

From bismuth oxide/hydroxide precursor clusters towards stable oxides: Proton transfer reactions and structural reorganization govern the stability of [Bi18 O13 (OH)10]-nitrate clusters - Walther, Markus; Zahn, Dirk (Chemical Physics Letters, 2018)
Structural relaxation and stability of a Bi18-cluster as obtained from association of [Bi6O4(OH)4](NO3)6 precursor clusters in DMSO solution is investigated from a combination of quantum chemical calculations and µs-scale molecular dynamics simulations using empirical interaction potentials. The Bi18-cluster undergoes a OH·sOH proton transfer reaction, followed by considerable structural relaxation. While the aggregation of the Bi18-cluster is induced by the dissociation of a single nitrate ion leading to [Bi6O4(OH)4](NO3)5+ as an activated precursor species that can bind two more Bi6-clusters, we find the [Bi18O13(OH)10](NO3)18-x+x species (explored for x = 1–6) rather inert against either nitrate dissociation, collision with Bi6-precursors or combinations thereof.
EAM Import::2019-03-14

From evaporation-induced self-assembly to shear-induced alignment - Srikantharajah, Rubitha; Schindler, Torben; Landwehr, Inga; Romeis, Stefan; Unruh, Tobias; Peukert, Wolfgang (Nanoscale, 2016)
The functionality of compact nanostructured thin films depends critically on the degree of order and hence on the underlying ordering mechanisms during film formation. For dip coating of rigid nanorods the counteracting mechanisms, evaporation-induced self-assembly (EISA) and shear-induced alignment (SIA) have recently been identified as competing ordering mechanisms. Here, we show how to achieve highly ordered and homogeneous thin films by controlling EISA and SIA in dip coating. Therefore we identify the influences of the process parameters including temperature, initial volume fraction and nanorod aspect ratio on evaporation-induced convective flow and externally applied shear forces and evaluate the resulting films. The impact of evaporation and shear can be distinguished by analysing film thickness, surface order and bulk order by careful in situ SAXS, Raman and SEM-based image analysis. For the first time we derive processing guidelines for the controlled application of EISA and SIA towards highly ordered thin nematic films.

From Flat Surfaces to Nanoparticles: In Situ Studies of the Reactivity of Model Catalysts - Papp, Christian (Catalysis Letters, 2017)
This perspective summarizes results of in situ adsorption and reaction experiments on graphene-supported nanoparticles: the particular aim is to point out similarities and differences between studies on ``traditional'' single crystal studies and the more complex, more realistic nanoparticles. It is shown that the use of quantitative X-ray photoelectron spectroscopy allows for gaining a detailed insight even into these complex systems, thereby facilitating a further step into bridging the materials gap from fundamental science to applied sciences. The use of graphene as a substrate gives intriguing new possibilities, as the template effect of graphene can lead to a very narrow size distribution of the clusters, while graphene itself is chemically innocent, thereby making side processes such as spill over and reverse spill over less likely. The systems discussed range from extremely well studied systems such as the adsorption and reaction of CO on a Pt(111) surface, to stepped surfaces and finally to nanocluster arrays supported on a graphene support. Also, the important chemistry of sulfur, being a strong catalyst poison, on such systems will be discussed. While the adsorption behavior on nanoclusters is strongly reminiscent of the adsorption on stepped surfaces, a strong increase in the reactivity of nanoparticles systems is found.
EAM Import::2019-03-14

From oligomers towards a racemic crystal: molecular simulation of DL-norleucine crystal nucleation from solution - Ectors, Philipp; Duchstein, Patrick; Zahn, Dirk (Crystengcomm, 2015)
We elucidate the evolution of forming nuclei leading towards a racemic molecular crystal by means of computer simulation. Our simulations start with the association of individual D- and L-norleucine molecules and subsequent formation of aggregates and thus provide molecular scale insights into the early stages of nucleation from (octanol) solution. During aggregate evolution from micelles to bilayers and eventually nanoparticles comprising staggered bilayers we identified a step-wise increase in molecular ordering. While the key structural motifs in the early aggregates are given by hydrogen bonded dimers, after association of 150 molecules a solid–solid phase transition leads to ordering of the hydrogen-bonded network in favour of the final crystal structure. This secondary nucleation event seems to be of key importance for changing the initially random arrangement of D and L enantiomers in the small (<150 molecules) aggregates to an ordered arrangement, that is alternating -D-D- and -L-L-alignments within the staggered bilayers of the molecular crystal.
EAM Import::2019-03-14

From White to Red: Electric-Field Dependent Chromaticity of Light-Emitting Electrochemical Cells based on Archetypal Porphyrins - Weber, Michael; Wittmann, Judith; Burger, Alexandra; Malcioglu, Osman; Segarra-Marti, Javier; Hirsch, Andreas; Coto, Pedro B.; Bockstedte, Michel; Costa, Ruben D. (Advanced Functional Materials, 2016)
The differences in the electroluminescence (EL) of red-emitting free-base (H2TPP) and Zn-metalated (ZnTPP) archetypal porphyrins are rationalized in light-emitting electrochemical cells by means of an electric-field dependent effect, leading to whitish and reddish devices, respectively. Although H2TPP shows superior electrochemical and photophysical features compared to ZnTPP, devices prepared with ZnTPP surprisingly stand out with a deep-red EL similar to its photoluminescence (PL), while H2TPP devices feature unexpected whitish EL. Standard arguments such as degradation, device architecture, device mechanism, and changes in the nature of the emitting excited states are discarded. Based on electrochemical impedance spectroscopy and first-principles electronic structure methods, we provide evidence that the EL originates from two H2TPP regioisomers, in which the inner ring H atoms are placed in collinear and vicinal configurations. The combination of their optical features provides an explanation for both the high- and low-energy EL features. Here, the emitting excited state nature is ascribed to the Q bands, since the Soret excited states remain high in energy. This contrasts to what is traditionally postulated in reports focused on H2TPP lighting devices. Hence, this work provides a new explanation for the nature of the high-energy EL band of H2TPP that might inspire future works focused on white-emitting molecular-based devices.
Keywords: collinear and vicinal regioisomers; electric-field dependent chromaticity; light-emitting electrochemical cells; tetraphenyl porphyrin; thin-film white-emitting sources

Front side illuminated dye-sensitized solar cells using anodic TiO2 mesoporous layers grown on FTO-glass - Lee, Kiyoung; Kim, Dam-Hee; Berger, Stefan; Kirchgeorg, Robin; Schmuki, Patrik (Electrochemistry Communications, 2012)
In the present work, we investigate the performance of anodic, self-organized TiO2 mesoporous structures (TMSs) in dye-sensitized solar cells (DSSCs) under front-side illumination conditions. In order to fabricate structures usable in a front-side (FS) configuration, TMSs were formed on FTO glass by a full anodic conversion of evaporated Ti films on the glass substrate in a glycerol/K2HPO4 electrolyte at 180 °C. The resulting mesoporous layers can be assembled to FS dye sensitized solar cells which show a thickness of only 3 extgreekmm and a remarkable efficiency of 4.34%. This is significantly higher than, for example, anodic TiO2 nanotubes of the same length even after efficiency enhancing TiCl4 treatments (3.01%). The best efficiency value for TMS-based DSSCs that we currently reached is for a 7 extgreekmm thick TMS layer, this is ≈6.82% which is highly promising for further improvements.
EAM Import::2019-03-14

Fullerene Van der Waals Oligomers as Electron Traps - Shubina, Tatyana; Sharapa, Dmitry; Schubert, Christina; Zahn, Dirk; Halik, Marcus; Keller, Paul A.; Pyne, Stephen G.; Jennepalli, Sreenu; Guldi, Dirk Michael; Clark, Timothy (Journal of the American Chemical Society, 2014)
Density functional theory calculations indicate that van der Waals fullerene dimers and larger oligomers can form interstitial electron traps in which the electrons are even more strongly bound than in isolated fullerene radical anions. The fullerenes behave like "super atoms", and the interstitial electron traps represent one-electron intermolecular σ-bonds. Spectroelectrochemical measurements on a bis-fullerene-substituted peptide provide experimental support. The proposed deep electron traps are relevant for all organic electronics applications in which non-covalently linked fullerenes in van der Waals contact with one another serve as n-type semiconductors.

Full wafer microlens replication by UV imprint lithography - Schmitt, Holger; Rommel, Matthias; Bauer, Anton; Frey, Lothar; Bich, Andreas; Eisner, Martin; Voelkel, Reinhard; Hornung, Michael (Microelectronic Engineering, 2010)
The fabrication of microlenses is of great interest for several applications in the field of optics like wafer level cameras, homogenization of light, and coupling of light into glass fibers. Especially for low-cost optical products, microlenses have to be fabricated with a high throughput at an adequate quality. One way to fulfil these requirements is the patterning of microlenses by UV imprint lithography (UV-IL). Within this work, microlenses were replicated into the UV curing material PAK-01 by step and stamp UV-IL on silicon substrates with a diameter of 150 mm. The resulting substrates were used as masters to cast PDMS templates. These PDMS templates can be used for high throughput full wafer UV-IL. Additionally, quartz substrates with a diameter of 100 mm were patterned which could be directly used as so called “optowafers”. Master and patterned microlenses were inspected by scanning electron microscopy and with a white light profilometer. The results clearly demonstrate the excellent quality of the replication process and the capability of UV-IL to pattern microlenses on full wafer level for high throughput applications.

Fully Patterned Low-Voltage Transparent Metal Oxide Transistors Deposited Solely by Chemical Spray Pyrolysis - Faber, Hendrik; Butz, Benjamin; Dieker, Christel; Spiecker, Erdmann; Halik, Marcus (Advanced Functional Materials, 2013)
All-inorganic transparent thin-film transistors deposited solely by the solution processing method of spray pyrolysis are reported. Different precursor materials are employed to create conducting and semiconducting species of ZnO acting as electrodes and active channel material, respectively, as well as zirconium oxide as gate dielectric layer. Additionally, a simple stencil mask system provides sufficient resolution to realize the necessary geometric patterns. As a result, fully functional low-voltage n-type transistors with a mobility of 0.18 cm2 V−1 s−1 can be demonstrated via a technique that bears the potential for upscaling. A detailed microscopic evaluation of the channel region by electron diffraction, high-resolution and analytical TEM confirms the layer stacking and provides detailed information on the chemical composition and nanocrystalline nature of the individual layers.

Fully printed organic tandem solar cells using solution-processed silver nanowires and opaque silver as charge collecting electrodes - Guo, Fei; Li, Ning; Radmilovic, Vuk V.; Radmilovic, Velimir R.; Turbiez, Mathieu; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (Energy and Environmental Science, 2015)
We report in this work efficient, fully printed tandem organic solar cells (OSCs) using solution-processed silver as the reflective bottom electrode and silver nanowires as the transparent top electrode. Employing two different band-gap photoactive materials with complementary absorption, the tandem OSCs are fully printed under ambient conditions without the use of indium tin oxide and vacuum-based deposition. The fully printed tandem devices achieve power conversion efficiencies of 5.81% (on glass) and 4.85% (on flexible substrate) without open circuit voltage (Voc) losses. These results represent an important progress towards the realization of low-cost tandem OSCs by demonstrating the possibility of printing efficient organic tandem devices under ambient conditions onto production relevant carrier substrates.

Fully Solution-Processed Small Molecule Semitransparent Solar Cells: Optimization of Transparent Cathode Architecture and Four Absorbing Layers - Min, Jie; Bronnbauer, Carina; Zhang, Zhi-Guo; Cui, Chaohua; Luponosov, Yuriy N.; Ata, Ibrahim; Schweizer, Peter; Przybilla, Thomas; Guo, Fei; Ameri, Tayebeh; Forberich, Karen; Spiecker, Erdmann; et al. (Advanced Functional Materials, 2016)
Semitransparent solar cells (SSCs) can open photovoltaic applications in many commercial areas, such as power-generating windows and building integrated photovoltaics. This study successfully demonstrates solution-processed small molecule SSCs with a conventional configuration for the presently tested material systems, namely BDTT-S-TR:PCBM, N(Ph-2T-DCN-Et):PCBM, SMPV1:PCBM, and UU07:PCBM. The top transparent cathode coated through solution processes employs a highly transparent silver nanowire as electrode together with a combination interface bilayer of zinc oxide nanoparticles (ZnO) and a perylene diimide derivative (PDINO). This ZnO/PDINO bilayer not only serves as an effective cathode buffer layer but also acts as a protective film on top of the active layer. With this integrated contribution, this study achieves a power conversion efficiency (PCE) of 3.62% for fully solution-processed SSCs based on BDTT-S-TR system. Furthermore, the other three systems with various colors exhibited the PCEs close to 3% as expected from simulations, demonstrate the practicality and versatility of this printed semitransparent device architecture for small molecule systems. This work amplifies the potential of small molecule solar cells for window integration.
Keywords: building integrated photovoltaics; interface bilayer; power conversion efficiency; semitransparent solar cells; small molecule

Fully Solution-Processing Route toward Highly Transparent Polymer Solar Cells - Guo, Fei; Kubis, Peter; Stubhan, Tobias; Li, Ning; Baran, Derya; Przybilla, Thomas; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (ACS Applied Materials and Interfaces, 2014)
We report highly transparent polymer solar cells using metallic silver nanowires (AgNWs) as both the electron- and hole-collecting electrodes. The entire stack of the devices is processed from solution using a doctor blading technique. A thin layer of zinc oxide nanoparticles is introduced between photoactive layer and top AgNW electrode which plays decisive roles in device functionality: it serves as a mechanical foundation which allows the solution-deposition of top AgNWs, and more importantly it facilitates charge carriers extraction due to the better energy level alignment and the formation of ohmic contacts between the active layer/ZnO and ZnO/AgNWs. The resulting semitransparent polymer:fullerene solar cells showed a power conversion efficiency of 2.9%, which is 72% of the efficiency of an opaque reference device. Moreover, an average transmittance of 41% in the wavelength range of 400-800 nm is achieved, which is of particular interest for applications in transparent architectures.
Keywords: semitransparent polymer solar cells; fully solution processing; OPV; ITO-free

Functional Interfaces in Pure and Blended Oxide Nanoparticle Networks: Recombination versus Separation of Photogenerated Charges - Siedl, Nicolas; Elser, Michael J.; Bernardi, Johannes; Diwald, Oliver (Journal of Physical Chemistry C, 2009)
Solvent-mediated particle aggregation was employed to produce nanoparticle networks containing a high abundance of functional interfaces. Using electron paramagnetic resonance spectroscopy (EPR), we experimentally observed that the intentional attachment of vapor-grown ZrO_2 nanocrystals to TiO_2 particle surfaces yields networks of intermixed nanoparticles with substantially improved charge separation properties. The superior performance holds also in comparison to homogeneous ZrO_2 and TiO_2 nanoparticle networks that exhibit a higher charge recombination loss in comparison to powders of unconnected nanocrystals.
EAM Import::2019-03-14

Functionalization of graphene by electrophilic alkylation of reduced graphite - Englert, Jan; Knirsch, Kathrin; Dotzer, Christoph; Butz, Benjamin; Hauke, Frank; Hirsch, Andreas; Spiecker, Erdmann (Chemical Communications, 2012)
The reaction of Na/K-reduced graphite with hexyliodide represents a new, versatile and mild approach to synthesize alkylated graphene derivatives, which were characterized by a combination of Raman spectroscopy, TEM and TGA/MS analysis. © The Royal Society of Chemistry 2012.

Functionalization of oxide surfaces through reaction with 1,3-dialkylimidazolium ionic liquids - Schernich, Stefan; Laurin, Mathias; Lykhach, Yaroslava; Steinrück, Hans-Peter; Tsud, Nataliya; Skala, Tomas; Prince, Kevin C.; Taccardi, Nicola; Matolin, Vladimir; Wasserscheid, Peter; Libuda, Jörg (Journal of Physical Chemistry Letters, 2013)
Practical applications of ionic liquids (ILs) often involve IL/oxide interfaces, but little is known regarding their interfacial chemistry. The unusual physicochemical properties of ILs, including their exceptionally low vapor pressure, provide access to such interfaces using a surface science approach in ultrahigh vacuum (UHV). We have applied synchrotron radiation photoelectron spectroscopy (SR-PES) to the study of a thin film of the ionic liquid [CCIm][TfN] prepared in situ in UHV on ordered stoichiometric CeO(111) and partially reduced CeO . On the partially reduced surface, we mostly observe decomposition of the anion. On the stoichiometric CeO(111) surface, however, a layer of surface-anchored organic products with high thermal stability is formed upon reaction of the cation. The suggested acid-base reaction pathway may provide well-defined functionalized IL/solid interfaces on basic oxides. © 2012 American Chemical Society.

Functionalization of Silver Nanowires Surface using Ag-C Bonds in a Sequential Reductive Method - Bashouti, Muhammad Y.; Resch, Sebastian; Ristein, Jürgen; Mackovic, Mirza; Spiecker, Erdmann; Waldvogel, Siegfried. R.; Christiansen, Silke. H. (ACS Applied Materials and Interfaces, 2015)
Silver nanowires (Ag-NW) assembled in interdigitated webs have shown an applicative potential as transparent and conducting electrodes. However, upon integration in practical device designs, the presence of silver oxide, which instantaneously forms on the Ag-NW surfaces in ambient conditions, is unwanted. Here, we report on the functionalization of Ag-NWs with 4-nitrophenyl moieties through A-C bonds using a versatile two step reduction process, i.e., ascorbate reduction combined electrografting. We show that 40% of the Ag atop sites were terminated and provide high surface stability toward oxidation for more than 2 months while keeping the same intrinsic conductivity as in bulk silver.
Keywords: silver nanowires; transparent electrodes; Ag-C bonds; electrografting; XPS; surface functionalization

Functionalized Porphyrins on an Atomically Defined Oxide Surface: Anchoring and Coverage-Dependent Reorientation of MCTPP on Co3O4(111) - Werner, Kristin; Mohr, Susanne; Schwarz, Matthias; Xu, Tao; Amende, Maximilian; Döpper, Tibor; Görling, Andreas; Libuda, Jörg (Journal of Physical Chemistry Letters, 2016)
We have studied the adsorption of tetraphenylporphyrin (2HTPP) and its carboxylated counterpart mono-para-carboxyphenyltriphenylporphyrin (MCTPP) on an atomically defined CoO(111) film under ultrahigh vacuum (UHV) conditions. Using time-resolved infrared reflection absorption spectroscopy (TR-IRAS), we show that 2HTPP adsorbs molecularly in a flat-lying orientation, whereas MCTPP binds to the surface via formation of a chelating bidentate carboxylate upon deposition at 400 K. Combining TR-IRAS and density-functional theory (DFT), we determine the molecular tilting angle as a function of coverage. We show that the MCTPP adsorption geometry changes from a nearly flat-lying orientation (tilting angle <30°) at low coverage to a nearly perfectly upright-standing orientation (tilting angle of approximately 80°) in the full monolayer.

Functional nickel complexes of N-heterocyclic carbene ligands in pre-organized and supported thin film materials - Wang, Xinjiao; Sobota, Marek; Kohler, Florian; Morain, Bruno; Melcher, Berthold Ulrich; Laurin, Mathias; Wasserscheid, Peter; Libuda, Jörg; Meyer, Karsten (Journal of Materials Chemistry, 2012)
Nickel(ii) complexes with double alkyl chain functionalized N-heterocyclic carbene (NHC) ligands, [NiCl (C MIM) ] and [NiCl (C C IM) ], where C MIM = 1-dodecyl-3-methylimidazolin-2-ylidene (1) and C C IM = 1,3-didodecylimidazolin-2-ylidene (2), have been prepared and fully characterized by H NMR, C NMR, and CHN elemental analyses. Furthermore, we have developed a system, in which double long alkyl chain derivatized Ni-NHC complexes are dissolved in the related ionic liquid crystalline 1,3-didodecylimidazolium tetrafluoroborate, [C C IM][BF ], to form pre-organized structures for enhanced reactivity. Remarkably, differential scanning calorimetry, polarized optical microscopy, and temperature-programmed IR reflection absorption spectroscopy performed on a mixture of 10 wt% Ni complexes in [C C IM][BF ] demonstrate that this system retains an ionic liquid crystalline phase; even after immobilization onto a silica-100 support with pore filling α = 1. © 2012 The Royal Society of Chemistry.

Functional Plasmonic Nanocircuits with Low Insertion and Propagation Losses - Kriesch, Arian; Burgos, Stanley P.; Ploss, Daniel; Pfeifer, Hannes; Atwater, Harry A.; Peschel, Ulf (Nano Letters, 2013)
We experimentally demonstrate plasmonic nanocircuits operating as subdiffraction directional couplers optically excited with high efficiency from free-space using optical Yagi-Uda style antennas at extgreekl0 = 1550 nm. The optical Yagi-Uda style antennas are designed to feed channel plasmon waveguides with high efficiency (45% in coupling, 60% total emission), narrow angular directivity (<40°), and low insertion loss. SPP channel waveguides exhibit propagation lengths as large as 34 extgreekmm with adiabatically tuned confinement and are integrated with ultracompact (5 × 10 extgreekmm2), highly dispersive directional couplers, which enable 30 dB discrimination over extgreekDl = 200 nm with only 0.3 dB device loss.
EAM Import::2019-03-14

Fundamental consolidation mechanisms during selective beam melting of powders - Körner, Carolin; Bauereiß, Andreas; Attar, Elham (Modelling and Simulation in Materials Science and Engineering, 2013)
During powder based additive manufacturing processes, a component is realized layer upon layer by the selective melting of powder layers with a laser or an electron beam. The density of the consolidated material, the minimal spatial resolution as well as the surface roughness of the resulting components are complex functions of the material and process parameters. So far, the interplay between these parameters is only partially understood. In this paper, the successive assembling in layers is investigated with a recently described 2D-lattice Boltzmann model, which considers individual powder particles. This numerical approach makes several physical phenomena accessible, which cannot be described in a standard continuum picture, e.g. the interplay between capillary effects, wetting conditions and the local stochastic powder configuration. In addition, the model takes into account the influence of the surface topology of the previous consolidated layer on the subsequent powder layer. The influence of the beam power, beam velocity and layer thickness on the formation and quality of simple walls is investigated. The simulation results are compared with experimental findings during selective electron beam melting. The comparison shows that our model, although 2D, is able to predict the main characteristics of the experimental observations. In addition, the numerical simulation elucidates the fundamental mechanisms responsible for the phenomena that are observed during selective beam melting. © 2013 IOP Publishing Ltd.

Fundamental Measure Theory for Inhomogeneous Fluids of Nonspherical Hard Particles - Hansen-Goos, Hendrik; Mecke, Klaus (Physical Review Letters, 2009)
Using the Gauss-Bonnet theorem we deconvolute exactly the Mayer f-function for arbitrarily shaped convex hard bodies in a series of tensorial weight functions, each depending only on the shape of a single particle. This geometric result allows the derivation of a free energy density functional for inhomogeneous hard-body fluids which reduces to Rosenfeld's fundamental measure theory [Phys. Rev. Lett. 63, 980 (1989)] when applied to hard spheres. The functional captures the isotropic-nematic transition for the hard-spherocylinder fluid in contrast with previous attempts. Comparing with data from Monte Carlo simulations for hard spherocylinders in contact with a planar hard wall, we show that the new functional also improves upon previous functionals in the description of inhomogeneous isotropic fluids.

Fundamental measure theory for non-spherical hard particles: predicting liquid crystal properties from the particle shape - Wittmann, Rene; Marechal, Mattheus; Mecke, Klaus (Journal of Physics: Condensed Matter, 2016)
Density functional theory (DFT) for hard bodies provides a theoretical description of the effect of particle shape on inhomogeneous fluids. We present improvements of the DFT framework fundamental measure theory (FMT) for hard bodies and validate these improvements for hard spherocylinders. To keep the paper self-contained, we first discuss the recent advances in FMT for hard bodies that lead to the introduction of fundamental mixed measure theory (FMMT) in our previous paper (2015 Europhys. Lett. 109 26003). Subsequently, we provide an efficient semi-empirical alternative to FMMT and show that the phase diagram for spherocylinders is described with similar accuracy in both versions of the theory. Finally, we present a semi-empirical modification of FMMT whose predictions for the phase diagram for spherocylinders are in excellent quantitative agreement with computer simulation results.
Keywords: non-spherical particles; colloids; liquid crystals; continuum theory

Fundamental measure theory for smectic phases: Scaling behavior and higher order terms - Wittmann, Rene; Marechal, Mattheus; Mecke, Klaus (Journal of Chemical Physics, 2014)
The recent extension of Rosenfeld's fundamental measure theory to anisotropic hard particles predicts nematic order of rod-like particles. Our analytic study of different aligned shapes provides new insights into the structure of this density functional, which is basically founded on experience with hard spheres. We combine scaling arguments with dimensional crossover and motivate a modified expression, which enables an appropriate description of smectic layering. We calculate the nematic-smectic-A transition of monodisperse hard spherocylinders with and without orientational degrees of freedom and present the equation of state and phase diagram including these two liquid crystalline phases in good agreement with simulations. We also find improved results related to the isotropic-nematic interface. We discuss the quality of empirical corrections and the convergence towards an exact second virial coefficient, including higher order terms. (C) 2014 AIP Publishing LLC.

Fundamental mixed measure theory for non-spherical colloids - Wittmann, Rene; Marechal, Mattheus; Mecke, Klaus (EPL - Europhysics Letters, 2015)
Accurate predictions for the collective behavior of non-spherical colloids and nano-particles can guide the search for novel self-assembled materials. We derive a new type of density functional theory for mixtures of arbitrarily shaped convex hard bodies using integral geometry's translative integral formula and a scaling argument. Our fundamental mixed measure theory is exact in the low-density limit and does not require truncation or empirical parameters unlike previous functionals. Quantitatively correct results for hard spherocylinders validate our general approach. In particular, we present the phase diagram, including a qualitatively and quantitatively accurate smectic phase, and the isotropic-nematic interfacial tension. Copyright (C) EPLA, 2015

Fundamental theoretical and practical investigations of the polymorph formation of small amphiphilic molecules, their co-crystals and salts - Martin, Thomas; Niemietz, Paul; Greim, Dominik; Ectors, Philipp; Senker, Juergen; Zahn, Dirk; Breu, Josef (Zeitschrift für Kristallographie, 2017)
The amphiphilic nature of benzoic acid, benzoates and benzamide causes an unexpected rich polymorphism. Featuring rather rigid and small molecular structures these compounds are ideal model systems for gaining a more fundamental understanding of molecular polymorphism by systematic and concerted investigations. The hydrophilic head allows for hydrogen bonding while the phenyl moiety gives rise to various extgreekp-stacking modes. Variations of hydrogen bonding versus extgreekp-stacking modes give rise to four polymorphs of benzamide. The central synthon in all phases is a dimer where hydrophilic units form double hydrogen bonds. As suggested by MD simulations of the nucleation process, variations of the crystallization conditions trigger whether the first self-assembly occurs via the hydrophilic head or the hydrophophic tail groups. Based on NMR crystallographic investigations for the co-crystallization of benzamide with benzoic acid, we observed yet another variation of the balance of the two dominating intermolecular interactions leading to the formation of a 1:1 co-crystal. The average crystal structure resembles the packing motive of pure benzoic acid with alternating ribbons of homogenous benzamide and benzoic acid dimers. For alkali-benzoate salts a coordination dilemma arises that is of general importance for many active pharmaceutical ingredients (APIs). A 1:1 stoichiometry requires condensation of coordination polyhedra of small inorganic cations which in turn causes steric stress that varies with the relative volumes of cation and anion. Interestingly, one way of resolving the dilemma is microphase separation which is directly related to the amphiphilic character of benzoate.
EAM Import::2019-03-14

Funktionelle Beschichtungen in der Nanotechnologie - Ein Kooperationsprojekt Schule-Hochschule. - Heinzerling, Peter; Dräger, Gerald; Kometz, Andreas; Preiß, Eva (Praxis der Naturwissenschaften - Chemie in der Schule, 2015)
Es werden Experimente zur Funktionalisierung von Oberflächen vorgestellt. Neben der Beschichtung kommt es auch zu chemischen Reaktionen an der Oberfläche, was zu veränderten Eigenschaften führ
Keywords: Schule; Experiment; Beschichtung; Chemieunterricht; Kunststoff; Nanochemie; Partikel; Projekt; Nanotechnologie; Hochschule; Kooperation; Deutschland

Gaining further insight into the effects of thermal annealing and solvent vapor annealing on time morphological development and degradation in small molecule solar cells - Min, Jie; Güldal, Nusret Sena; Guo, Jie; Fang, Chao; Jiao, Xuechen; Hu, Huawei; Heumüller, Thomas; Ade, Harald; Brabec, Christoph (Journal of Materials Chemistry A, 2017)
Numerous articles on thermal annealing (TA) and solvent vapor annealing (SVA) treatments have shown that both strategies effectively improve bulk morphology, reduce carrier recombination and thus improve photovoltaic performance of bulk heterojunction (BHJ) organic solar cells (OSCs). In previous work, we found that both TA and SVA treated devices based on a blend composed of a 3-ethyl-2-thioxothiazolidin-4-one containing molecule as donor (named DRCN5T) and [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) as acceptor show the similar photovoltaic performance, but their bulk microstructures are difference. Here employing in situ photoluminescence (PL) setup and X-ray scattering technologies, we found that the early stages of SVA remarkably affect the surface of film, and in contrast TA affects the whole bulk. Meanwhile, a plurality of experimental results all further confirm the different thermodynamics and kinetics of morphology evolution processed either by TA treatment or SVA treatment. Importantly, it was found that the SVA-treated film showed the increased photo-degradation in devices as compared to the TA-treated layer, resulting from obvious bulk morphology changes under illumination over 500 hours. The aim is to provide comprehensive insight into the influence of TA and SVA on time morphological evolution and degradation in OSCs. © 2017 The Royal Society of Chemistry.
Keywords: Annealing Butyric acid Heterojunctions Molecules Morphology Organic solar cells Solar power generation Thermodynamics X ray scattering

Gallium-rich Pd-Ga phases as supported liquid metal catalysts - Taccardi, Nicola; Grabau, Mathias; Debuschewitz, Jonas; Distaso, Monica; Brandl, Marco; Hock, Rainer; Maier, Florian; Papp, Christian; Erhard, Jannis; Neiß, Christian; Peukert, Wolfgang; Görling, Andreas; et al. (Nature chemistry, 2017)
A strategy to develop improved catalysts is to create systems that merge the advantages of heterogeneous and molecular catalysis. One such system involves supported liquid-phase catalysts, which feature a molecularly defined, catalytically active liquid film/droplet layer adsorbed on a porous solid support. In the past decade, this concept has also been extended to supported ionic liquid-phase catalysts. Here we develop this idea further and describe supported catalytically active liquid metal solutions (SCALMS). We report a liquid mixture of gallium and palladium deposited on porous glass that forms an active catalyst for alkane dehydrogenation that is resistant to coke formation and is thus highly stable. X-ray diffraction and X-ray photoelectron spectroscopy, supported by theoretical calculations, confirm the liquid state of the catalytic phase under the reaction conditions. Unlike traditional heterogeneous catalysts, the supported liquid metal reported here is highly dynamic and catalysis does not proceed at the surface of the metal nanoparticles, but presumably at homogeneously distributed metal atoms at the surface of a liquid metallic phas

Gas-Phase Hydroformylation of Propene over Silica-Supported PPh3-Modified Rhodium Catalysts - Kim, Taejin; Celik, Fuat E.; Hanna, David G.; Shylesh, S.; Werner, Sebastian; Bell, Alexis T. (Topics in Catalysis, 2011)
Heterogeneous rhodium catalysts supported on SiO_2 were modified with PPh_3 for the gas-phase hydroformylation of propene to produce n- and isobutanal. High selectivity to aldehydes was achieved, with no propane or alcohols formed. Investigation of the effects of reaction temperature, reactant partial pressures, total pressure, and PPh_3/Rh ratio suggested that the supported catalyst behaved similarly to the homogeneous catalyst. In particular, the supported catalyst showed similar activation energies and partial and total pressure dependences of the reaction rates to those observed in homogeneous, liquidphase reactions. The first order dependence of the hydroformylation rate on the partial pressures of propene, CO, and H_2 individually led to a cubic dependence of butanal formation on total pressure for equimolar reactant mixtures. High regioselectivity with a typical n/i ratio of 14 was achieved.
EAM Import::2019-03-13

Gas-phase oxycarbonylation of methanol for the synthesis of dimethyl carbonate using copper-based Supported Ionic Liquid Phase (SILP) catalysts - Schneider, Martin; Haumann, Marco; Stricker, Marion; Sundermeyer, Jörg; Wasserscheid, Peter (Journal of Catalysis, 2014)
Catalyst systems for the gas-phase oxycarbonylation of methanol often suffer from low catalyst activities and strong catalyst deactivation. In this work, the continuous gas-phase oxycarbonylation of methanol was realized by using Supported Ionic Liquid-Phase (SILP) catalysts. Copper(I) bromide dissolved in various ionic liquids and dispersed on Polymer-Based Spherical Activated Carbon (PBSAC) as supporting material was found to be an active catalyst. The poor activity and stability of copper halide catalysts reported in literature was substantially increased by the presence of ionic liquids. In particular, trioctylmethylammonium bromide in combination with a basic salt additive increased the activity of the CuBr catalyst and led to comparatively stable SILP catalyst operation reaching a total turnover number of 600 over 50 h time-on-stream.

Gas phase synthesis of anisotropic silicon germanium hybrid nanoparticles - Mehringer, Christian; Wagner, Richard; Jakuttis, Thomas; Butz, Benjamin; Spiecker, Erdmann; Peukert, Wolfgang (Journal of Aerosol Science, 2014)
We demonstrate the capability of hot wall reactor gas phase synthesis to produce germanium (Ge) on silicon (Si) anisotropic particles. A two stage reactor setup is used to produce silicon nanoparticles (SiNPs) of 29.6 nm in diameter with a very narrow size distribution and to deposit Ge on them. The gaseous precursors are monosilane (SiH4) and monogermane (GeH4). In a SEM study Ge patch formation on the SiNPs due to Stranski–Krastanov growth is observed. The patch size as well as the number of patches per SiNP is dependent on the process temperature and the GeH4 partial pressure. By varying these parameters it is possible to synthesize Janus-like particles with only one e.g. facetted Ge patch per SiNP, as well as patchy particles carrying an average of four to eight patches. HRTEM analysis shows, that the Ge grows epitaxial and crystalline on the surface of the SiNPs. From geometric phase analysis (GPA) the termination of inserted (220) half planes corresponding to misfit dislocations can be deduced, indicating a largely relaxed lattice in the Ge patches. A continuous tilt of the (111) lattice planes in the Si core below a Ge patch indicates that elastic deformation also contributes to the strain relaxation.

Gas phase temperature measurements in the liquid and particle regime of a flame spray pyrolysis process using O2-based pure rotational coherent anti-Stokes Raman scattering - Peukert, Wolfgang; Engel, Sascha; Kögler, Andreas; Gao, Yi; Kilian, Daniel; Voigt, Michael; Seeger, Thomas; Leipertz, Alfred (Applied Optics, 2012)
For the production of oxide nanoparticles at a commercial scale, flame spray processes are frequently used where mostly oxygen is fed to the flame if high combustion temperatures and thus small primary particle sizes are desired. To improve the understanding of these complex processes in situ, noninvasive optical measurement techniques were applied to characterize the extremely turbulent and unsteady combustion field at those positions where the particles are formed from precursor containing organic solvent droplets. This particle-forming regime was identified by laser-induced breakdown detection. The gas phase temperatures in the surrounding of droplets and particles were measured with O2 -based pure rotational coherent anti-Stokes Raman scattering (CARS). Pure rotational CARS measurements benefit from a polarization filtering technique that is essential in particle and droplet environments for acquiring CARS spectra suitable for temperature fitting. Due to different signal disturbing processes only the minority of the collected signals could be used for temperature evaluation. The selection of these suitable signals is one of the major problems to be solved for a reliable evaluation process. Applying these filtering and signal selection steps temperature measurements have successfully been conducted. Time-resolved, single-pulse measurements exhibit temperatures between near-room and combustion temperatures due to the strongly fluctuating and flickering behavior of the particle-generating flame. The mean flame temperatures determined from the single-pulse data are decreasing with increasing particle concentrations. They indicate the dissipation of large amounts of energy from the surrounding gas phase in the presence of particles.
Keywords: oxyide; nanoparticle; optical; noninvasive; droplet; combustion; raman; scattering

Gated Epitaxial Graphene Devices - Waldmann, Daniel; Jobst, Johannes; Speck, Florian; Seyller, Thomas; Krieger, Michael; Weber, Heiko B. (Materials Science Forum, 2012)
A bottom gate scheme is presented to tune the charge density of epitaxial graphene via a gate voltage while leaving the surface open for further manipulation or investigation. Depending on the doping concentration of the buried gate layer, the temperature and illumination, the bottom gate structure can be operated in two regimes with distinct capacitances. A model is proposed, which quantitatively describes the gate operation. The model is verified by a control experiment with an illuminated gate structure using UV light. Using UV illumination the Schottky capacitor (SC) regime, which provides improved gate efficiency, can be used even at low temperatures. © (2012) Trans Tech Publications.
UnivIS-Import:2015-04-14:Pub.2012.nat.dphy.IAP.LAP.gatede
Keywords: Bottom gate; Buried gate; Epitaxial graphene

Gateless patterning of epitaxial graphene by local intercalation - Sorger, Christian; Hertel, Stefan; Jobst, Johannes; Steiner, Christian; Meil, Katharina; Ullmann, Konrad; Albert, A.; Wang, Yabin; Krieger, Michael; Ristein, Jürgen; Maier, Sabine; Weber, Heiko B. (Nanotechnology, 2015)
We present a technique to pattern the charge density of a large-area epitaxial graphene sheet locally without using metallic gates. Instead, local intercalation of the graphene-substrate interface can selectively be established in the vicinity of graphene edges or prede fined voids. It provides changes of the work function of several hundred meV, corresponding to a conversion from n-type to p-type charge carriers. This assignment is supported by photoelectron spectroscopy, scanning tunneling microscopy, scanning electron microscopy and Hall effect measurements. The technique introduces materials contrast to a graphene sheet in a variety of geometries and thus allows for novel experiments and novel functionalities.
UnivIS-Import:2015-04-14:Pub.2015.nat.dphy.IAP.LAP.gatele
Keywords: Graphene; Intercalation; Patterning

Gate oxide reliability at the nanoscale evaluated by combining conductive atomic force microscopy and constant voltage stress - Erlbacher, Tobias; Yanev, Vasil C.; Rommel, Mathias; Bauer, Anton; Frey, Lothar (Journal of Vacuum Science & Technology B: Microelectronics Processing and Phenomena, 2011)
The gate oxide integrity of different thin films (silicon dioxide, silicon nitride, and hafnium oxide) was analyzed by constant voltage stress (CVS) at the nanoscale using conductive atomic force microscopy (cAFM) with the probe tip directly in contact to the dielectric layer. The results were evaluated assuming a Weibull failure distribution for the dielectrics under voltage stress, and a good fit was obtained for the measurement data. This indicates that CVS measurements at the nanoscale can be applied for inline characterization of as-deposited dielectrics without the need for gate electrodes. In addition, time-to-breakdown extracted from the CVS using cAFM was compared to data retrieved from CVS measurements using conventional current-voltage measurements on samples with gate electrodes. In particular, area scaling of CVS data over eight orders of magnitude using cAFM was performed for the first time. The evaluation indicates a decent match between macroscopic and nanoscale CVS measurements for the hafnium oxide and silicon dioxide samples. In contrast, significant discrepancies are evident for the silicon nitride samples, which may be related to charge trapping effect

Generalized Brillouin diagrams for evanescent waves in metamaterials with interelement coupling - Tatartschuk, Eugen; Radkovskaya, A.; Shamonina, E.; Solymar, L. (Physical Review B, 2010)
A graphical representation for two-dimensional periodic structures is introduced that provides the full information contained in the dispersion equation: not only for the pass band but for the neighboring stop bands as well. It is a seamless natural extension of Brillouin diagrams obtained by adding eight new zones which incorporate the properties of evanescent waves. The accuracy of the infinite lattice approximation is tested both by simulations and experiments using magnetoinductive waves. For waves propagating in one direction and evanescent in the other direction, the results of the three different methods are shown to be in good agreement. The versatility of the new representation and its applicability to the design of near-field manipulating metamaterials is discussed.
EAM Import::2019-03-13

Generalized enhancement of charge injection in bottom contact/top gate polymer field-effect transistors with single-walled carbon nanotubes - Wang, Ming; Jakubka, Florian; Gannott, Florentina; Schweiger, Manuel; Zaumseil, Jana (Organic Electronics, 2014)
We investigate the influence of small amounts of dispersed single-walled carbon nanotubes (SWNTs) on the contact resistance and device characteristics of bottom contact/top gate polymer field-effect transistors (FETs). Five conjugated polymers representing different classes of polymer semiconductors with different HOMO/LUMO levels are employed, namely, polythiophenes (P3HT), polyphenylenevinylenes (MDMO-PPV), polyfluorenes (F8T2), naphthalene-bis(dicarboximide) bithiophene copolymers (P(NDI2OD-T2)), and diketopyrrolo-pyrrole-bithiophene copolymers (DPPT-TT). In all cases the presence of dispersed SWNTs reduces non-ohmic contact resistance and lowers threshold and onset voltages for charge transport. In some cases inherent ambipolar charge transport in conjugated polymers (F8T2 and P(NDI2OD-T2)) is revealed. The concentration of the SWNTs within the semiconducting layer remains below the percolation limit and thus the apparent mobilities and on/off ratios are still determined by the polymer and independent of the specific type of the carbon nanotubes (metallic or semiconducting). The degree of enhancement depends both on the energy level offset between the injecting gold electrode and the HOMO/LUMO level (i.e., Schottky barrier) and the charge carrier mobility of the respective polymer. The simplicity of this injection enhancement method and its broad applicability make it a step toward high performance polymer transistors without injection limitations.
EAM Import::2019-03-13

Generation and subwavelength focusing of longitudinal magnetic fields in a metallized fiber tip - Ploss, Daniel; Kriesch, Arian; Pfeifer, Hannes; Banzer, Peter; Peschel, Ulf (Optics Express, 2014)
We demonstrate experimentally and numerically that in fiber tips as they are used in NSOMs azimuthally polarized electrical fields (|Eazi|2 / |Etot|2 ≈55% ± 5% for extgreekl0= 1550 nm), respectively subwavelength confined (FWHM ≈450 nm ≈ extgreekl0/3.5) magnetic fields, are generated for a certain tip aperture diameter (d = 1.4 extgreekmm). We attribute the generation of this field distribution in metal-coated fiber tips to symmetry breaking in the bend and subsequent plasmonic mode filtering in the truncated conical taper.
EAM Import::2019-03-13

Generation of clean iron nanocrystals on an ultra-thin SiO x film on Si(001) - Walz, Marie-Madeleine; Vollnhals, Florian; Schirmer, Michael; Steinrück, Hans-Peter; Marbach, Hubertus (Physical Chemistry Chemical Physics, 2011)
Upon exposure to Fe(CO) , the formation of pure cubic Fe nanocrystals with dimensions up to ∼75 nm is reported on ultra-thin SiO films (thickness ≈ 0.5 nm) on Si(001), which have been prepared in situ under UHV conditions. The active centers for initial decomposition of Fe(CO) resulting in the growth of the Fe clusters are proposed to be SiO sites. After nucleation at these sites, further crystal growth is observed due to autocatalytic dissociation of Fe(CO) at room temperature. The density of the Fe clusters can be increased by irradiating the surface with a focused electron beam (15 keV) prior to gas exposure. The formation of the active SiO sites upon electron irradiation is attributed to oxygen desorption via the Knotek-Feibelman mechanism. © 2011 the Owner Societies.

Generation of clean iron structures by electron-beam-induced deposition and selective catalytic decomposition of iron pentacarbonyl on Rh(110) - Lukasczyk, Thomas; Schirmer, Michael; Steinrück, Hans-Peter; Marbach, Hubertus (Langmuir, 2009)
We explore the electron-beam-induced deposition (EBID) of iron pentacarbonyl, Fe(CO)5, in ultrahigh vacuum (UHV) on clean and modified Rh(110) surfaces by scanning electron microscopy (SEM), scanning Auger microscopy (SAM), and local Auger electron spectroscopy (AES). In EBID a highly focused electron beam is used to locally decompose the iron pentacarbonyl precursor molecules with the goal to generate pure iron nanostructures. It is demonstrated that the selectivity of the process strongly depends on the surface properties. On a perfect, clean Rh(110) surface almost no selectivity is observed; i.e., deposition of Fe is found on irradiated and nonirradiated surface regions due to catalytic decomposition of the Fe(CO)5. However, on a structurally nonperfect Rh(110) surface and on a Tiprecovered Rh(110) surface high selectivity is found; i.e., Fe deposits are primarily formed in irradiated regions. The role of catalytic and autocatalytic growth of iron on clean Rh respective iron deposits is discussed. The purity of the Fe deposits was always very high (>88%). It is demonstrated that the deposited Fe structures can be selectively oxidized to iron oxide by exposure to oxygen. Furthermore, attempts to write Fe line deposits were also successful, and line diameters smaller than 25 nm could be achieved. © 2009 American Chemical Society.

Generation of void-like structures during hot-hydrogen etching of Si substrates for 3C-SiC epitaxy - Hens, Philip; Mueller, J.; Fahlbusch, Lars; Spiecker, E.; Wellmann, Peter; Spiecker, Erdmann (Materials Science Forum, 2011)
A new type of void-like structure has been identified in thin 3C-SiC heteroepitaxial layers grown on silicon substrates. Similar surface structures can be found in micrographs published in the literature but have not been addressed so far. We propose a mechanism which explains the formation of these "type II voids" as result of hot-hydrogen etching. Type II voids seem to act as nucleation sites for the well-known faceted voids formed beneath the 3C-SiC layer during seeding (type I voids). Suppression of type II voids by appropriate high temperature cleaning steps therefore reduces the overall density of detrimental type I void
Keywords: Silicon Carbide; 3C-SiC; Heteroepitaxy; Crystal growth; Voids

Generic principles of crack-healing ceramics - Greil, Peter (Journal of Advanced Ceramics, 2012)
Ceramic materials able to heal manufacture or damage induced microstructure defects might trigger a change in paradigm for design and application of load bearing ceramics. This work reviews thermodynamic and kinetic aspects governing the regeneration of solid contact able to transfer stress between disrupted crack surfaces in ceramics. Major crack healing processes include perturbation of crack-like pores followed by sintering of isolated pores, as well as reaction with an environmental atmosphere and filling of the crack space with an oxidation product. Since thermally activated solid state reactions require elevated temperatures which may exceed 1000 °C, processes able to trigger crack healing at lower temperatures are of particular interest for transferring into engineering applications. Generic principles of microstructure modifications able to facilitate crack repair at lower temperatures will be considered: (i) acceleration of material transport by grain boundary decoration and grain size reduction, and (ii) reduction of thermal activation barrier by repair filler activation. Examples demonstrating crack healing capability include oxidation reaction of low energy bonded intercalation metal from nano-laminate MAX phases and catalyzed surface nitridation of polymer derived ceramics containing repair fillers.
EAM Import::2019-03-13

Genotoxicity of Superparamagnetic Iron Oxide Nanoparticles in Granulosa Cells - Poettler, Marina; Staicu, Andreas; Zaloga, Jan; Unterweger, Harald; Weigel, Bianca; Schreiber, Eveline; Hofmann, Simone; Wiest, Irmi; Jeschke, Udo; Alexiou, Christoph; Janko, Christina (International Journal of Molecular Sciences, 2015)
Nanoparticles that are aimed at targeting cancer cells, but sparing healthy tissue provide an attractive platform of implementation for hyperthermia or as carriers of chemotherapeutics. According to the literature, diverse effects of nanoparticles relating to mammalian reproductive tissue are described. To address the impact of nanoparticles on cyto- and genotoxicity concerning the reproductive system, we examined the effect of superparamagnetic iron oxide nanoparticles (SPIONs) on granulosa cells, which are very important for ovarian function and female fertility. Human granulosa cells (HLG-5) were treated with SPIONs, either coated with lauric acid (SEONLA) only, or additionally with a protein corona of bovine serum albumin (BSA; SEON(LA-BSA)), or with dextran (SEON(DEX)). Both micronuclei testing and the detection of ?H2A.X revealed no genotoxic effects of SEON(LA-BSA), SEON(DEX) or SEON(LA). Thus, it was demonstrated that different coatings of SPIONs improve biocompatibility, especially in terms of genotoxicity towards cells of the reproductive system.
EVALuna2:19986

Geometry: The leading parameter for the Poisson's ratio of bending-dominated cellular solids - Mitschke, Holger; Schury, Fabian; Mecke, Klaus; Wein, Fabian; Stingl, Michael; Schroder-Turk, Gerd E. (International Journal of Solids and Structures, 2016)
Control over the deformation behaviour that a cellular structure shows in response to imposed external forces is a requirement for the effective design of mechanical metamaterials, in particular those with negative Poisson's ratio. This article sheds light on the old question of the relationship between geometric microstructure and mechanical response, by comparison of the deformation properties of bar-and-joint frameworks with those of their realisation as a cellular solid made from linear-elastic material. For ordered planar tessellation models, we find a classification in terms of the number of degrees of freedom of the framework model: first, in cases where the geometry uniquely prescribes a single deformation mode of the framework model, the mechanical deformation and Poisson's ratio of the linearly-elastic cellular solid closely follow those of the unique deformation mode; the result is a bending-dominated deformation with negligible dependence of the effective Poisson's ratio on the underlying material's Poisson's ratio and small values of the effective Young's modulus. Second, in the case of rigid structures or when geometric degeneracy prevents the bending-dominated deformation mode, the effective Poisson's ratio is material-dependent and the Young's modulus (E) over tilde (cs) large. All analysed structures of this type have positive values of the Poisson's ratio and large values of (E) over tilde (cs). Third, in the case, where the framework has multiple deformation modes, geometry alone does not suffice to determine the mechanical deformation. These results clarify the relationship between mechanical properties of a linear-elastic cellular solid and its corresponding bar-and-joint framework abstraction. They also raise the question if, in essence, auxetic behaviour is restricted to the geometry-guided class of bending-dominated structures corresponding to unique mechanisms, with inherently low values of the Young's modulus. (C) 2016 Elsevier Ltd. All rights reserved.
Keywords: Cellular structures; Homogenisation; Floppy frameworks; Auxeticity; Mechanical metamaterial

Germanium-silicon alloy and core-shell nanocrystals by gas phase synthesis - Mehringer, Christian; Kloner, Christian; Butz, Benjamin; Winter, Benjamin; Spiecker, Erdmann; Peukert, Wolfgang (Nanoscale, 2015)
In this work we present a novel route to synthesize well defined germanium-silicon alloy (GexSi1-x) and core-shell nanocrystals (NCs) employing monosilane (SiH4) and monogermane (GeH4) as precursors in a continuously operated two-stage hot-wall aerosol reactor setup. The first hot-wall reactor stage (HWR I) is used to produce silicon (Si) seed particles from SiH4 pyrolysis in Argon (Ar). The resulting seeding aerosol is fed into the second reactor stage (HWR II) and a mixture of SiH4 and GeH4 is added. The ratio of the precursors in the feed, their partial pressures, the synthesis temperature in HWR II and the overall pressure are varied depending on the desired morphology and composition. Alloy particle production is achieved in the heterogeneous surface reaction regime, meaning that germanium (Ge) and Si are deposited on the seed surface simultaneously. The NCs can be synthesized with any desired composition, whilst maintaining a mean diameter around 30 nm with a geometric standard deviation (GSD) around 1.25. The absorption behavior and the related fundamental optical band gap energy in dependence on the alloy composition are exemplarily presented. They prove the possibility to tailor NC properties for electronical and opto-electronical applications. In the homogeneous gas phase reaction regime facetted Ge-Si core-shell structures are accessible. The Ge deposition on the seeds precedes the Si deposition due to different gas phase reaction kinetics of the precursors. The Si layer grows epitaxially on the Ge core and is around 5 nm thick.

Germanium substrate loss during thermal processing - Kaiser, R. J.; Koffel, S.; Pichler, Peter; Bauer, A. J.; Amon, B.; Frey, Lothar; Ryssel, Heiner (Microelectronic Engineering, 2011)
Germanium layers are very attractive for future semiconductor devices due to their high carrier mobility. To form pn-junctions in such devices, ion implantation followed by an annealing step is the most feasible way. Several previous studies reported severe surface degradation during annealing of germanium without a capping layer. The observed deteriorations are, e.g., heavy surface roughness or even loss of bulk material. To study the loss of germanium, samples with patterned silicon dioxide layer were annealed at temperatures between 500 and 600 °C in different atmospheres. The chosen atmospheres were selected to be nominally inert (N2, Ar, or vacuum). Yet, the samples showed rates of substrate loss, e.g., up to 3 nm/min at 600 °C in Ar atmosphere. The resulting rates of substrate loss can be approximately described by Arrhenius laws with an activation energy of 2.08 + 0.21 eV in the case of Ar. Direct evaporation of germanium or germanium dioxide can be excluded because of the low vapor pressures reported in the literature. As mechanism, we propose the evaporation of germanium monoxide formed with residual oxidants such as oxygen or water vapor in the atmosphere used for processing. Rough calculations exhibit that a desorption rate of about 10-8 mol GeO per min is required in our experiments to achieve the maximum rate of substrate loss in argon at 600 °C. Results for the different atmospheres will be compared.
Keywords: Annealing; Doping profiles; Elemental semiconductors; Germanium; Thermal etching

Giant Faraday rotation in single- and multilayer graphene - Crassee, Iris; Levallois, Julien; Walter, Andrew L.; Ostler, Markus; Bostwick, Aaron; Rotenberg, Eli; Seyller, Thomas; Van Der Marel, Dirk; Kuzmenko, Alexey B. (Nature Physics, 2010)
The rotation of the polarization of light after passing a medium in a magnetic field, discovered by Faraday, is an optical analogue of the Hall effect, which combines sensitivity to the carrier type with access to a broad energy range. Up to now the thinnest structures showing the Faraday rotation were several-nanometre-thick two-dimensional electron gases. As the rotation angle is proportional to the distance travelled by the light, an intriguing issue is the scale of this effect in two-dimensional atomic crystals or films—the ultimately thin objects in condensed matter physics. Here we demonstrate that a single atomic layer of carbon—graphene—turns the polarization by several degrees in modest magnetic fields. Such a strong rotation is due to the resonances originating from the cyclotron effect in the classical regime and the inter-Landau-level transitions in the quantum regime. Combined with the possibility of ambipolar doping, this opens pathways to use graphene in fast tunable ultrathin infrared magneto-optical devices.
EAM Import::2019-03-13

Giant Rashba Splitting in CH3NH3PbBr3 Organic-Inorganic Perovskite - Niesner, Daniel; Wilhelm, Max; Levchuk, Ievgen; Osvet, Andres; Shrestha, Shreetu; Batentschuk, Miroslaw; Brabec, Christoph; Fauster, Thomas (Physical Review Letters, 2016)
As they combine decent mobilities with extremely long carrier lifetimes, organic-inorganic perovskites open a whole new field in optoelectronics. Measurements of their underlying electronic structure, however, are still lacking. Using angle-resolved photoelectron spectroscopy, we measure the valence band dispersion of single-crystal CH3NH3PbBr3. The dispersion of the highest energy band is extracted applying a modified leading edge method, which accounts for the particular density of states of organic-inorganic perovskites. The surface Brillouin zone is consistent with bulk-terminated surfaces both in the low-temperature orthorhombic and the high-temperature cubic phase. In the low-temperature phase, we find a ring-shaped valence band maximum with a radius of 0.043 Å-1, centered around a 0.16 eV deep local minimum in the dispersion of the valence band at the high-symmetry point. Intense circular dichroism is observed. This dispersion is the result of strong spin-orbit coupling. Spin-orbit coupling is also present in the room-temperature phase. The coupling strength is one of the largest ones reported so far.

Global and local strain rate sensitivity of bimodal Al-laminates produced by accumulative roll bonding - Ruppert, Mathis; Schunk, Christopher; Hausmann, Daniel; Höppel, Heinz Werner; Göken, Mathias (Acta Materialia, 2016)
Laminated metallic composites of 5 mm thickness, with a bimodal grain size distribution and alternating layers of commercial purity aluminum (Al99.5) and high purity aluminum (Al99.999) were successfully processed by accumulative roll bonding at room temperature up to 8 cycles. With increasing number of ARB cycles the layers of commercial purity aluminum become ultrafine-grained, whereas the grain size in the high purity aluminum remains clearly above 1 extgreekmm. The mechanical properties of the laminates were investigated by compression testing with strain rate jumps and by nanoindentation using continuous stiffness method and nanoindentation strain rate jump tests. Thereby the strain rate sensitivity was determined both globally, proving the bulk laminate material, and locally, proving the single layers of the laminate. It was found that the local strain rate sensitivity of the ultrafine-grained Al99.5-layers is increasing up to 4 ARB cycles, while the local strain rate sensitivity of the coarse grained Al99.999-layers remains rather constant independently of the number of cycles. In contrast to that, the global strain rate sensitivity of the bulk laminate increases up to 8 cycles without saturation. Thermally activated annihilation of dislocations at the grain boundaries and interfaces between the coarse grained and ultrafine-grained layers is proposed in order to interpret the findings.
WW1::1056
Keywords: Nanomaterials

Global structure of periodicity hubs in Lyapunov phase diagrams of dissipative flows - Gallas, Jason; Vitolo, Renato; Glendinning, Paul (Physical Review E, 2011)
Infinite cascades of periodicity hubs were predicted and very recently observed experimentally to organize stable oscillations of some dissipative flows. Here we describe the global mechanism underlying the genesis and organization of networks of periodicity hubs in control parameter space of a simple prototypical flow, namely a Rössler’s oscillator. We show that spirals associated with periodicity hubs emerge and accumulate at the folding of certain fractal-like sheaves of Shilnikov homoclinic bifurcations of a common saddle-focus equilibrium. The specific organization of hub networks is found to depend strongly on the interaction between the homoclinic orbits and the global structure of the underlying attractor.

Gluing ionic liquids to oxide surfaces: Chemical anchoring of functionalized ionic liquids by vapor deposition onto cobalt(II) oxide // Gluing Ionic Liquids to Oxide Surfaces: Chemical Anchoring of Functionalized Ionic Liquids by Vapor Deposition onto Cobalt(II) Oxide - Xu, Tao; Wähler, Tobias; Vecchietti, Ph. D. Maria Julia; Bauer, Tanja; Schwegler, Johannes; Schulz, Peter; Wasserscheid, Peter; Libuda, Jörg (Angewandte Chemie, 2017)
Ionic liquids (IL) hold a great potential as novel electrolytes for applications in electronic materials and energy technology. The functionality of ILs in these applications relies on their interface to semiconducting nanomaterials. Therefore, methods to control the chemistry and structure of this interface are the key to assemble new IL-based electronic and electrochemical materials. Here, we present a new method to prepare a chemically well-defined interface between an oxide and an IL film. An imidazolium-based IL, which is carrying an ester group, is deposited onto cobalt oxide surface by evaporation. The IL binds covalently to the surface by thermally activated cleavage of the ester group and formation of a bridging carboxylate. The anchoring reaction shows high structure sensitivity, which implies that the IL film can be ``glued'' selectively specific oxide surfaces.
EAM Import::2019-03-13

Gold film-terminated 3-dimensional photonic crystals - Ding, B.; Pemble, M. E.; Korovin, A. V.; Peschel, Ulf; Romanov, Sergey (Applied Physics A-Materials Science & Processing, 2011)
Hybrid metal-dielectric photonic crystals assembled from an opal film coated by a gold film are designed in order to realize optical spectra that emanate from mixing Bloch modes in the opal and surface plasmon polaritons in corrugated gold films. The photonic crystal provides a spatial template for the gold film profile and modifies the electromagnetic vacuum in the vicinity to the gold layer. Reflectance spectroscopy was applied to deconvolute the plasmonic and photonic bandgap components in the optical response of hybrid crystals as opposite to their mixed appearance in the transmission spectra.
EAM Import::2019-03-13

Gold intercalation of boron-doped graphene on Ni(111): XPS and DFT study - Zhao, Wei; Gebhardt, Julian; Gotterbarm, Karin; Höfert, Oliver; Gleichweit, Christoph; Papp, Christian; Görling, Andreas; Steinrück, Hans-Peter (Journal of Physics: Condensed Matter, 2013)
The intercalation of a graphene layer adsorbed on a metal surface by gold or other metals is a standard procedure. While it was previously shown that pristine, i.e., undoped, and nitrogen-doped graphene sheets can be decoupled from a nickel substrate by intercalation with gold atoms in order to produce quasi-free-standing graphene, we find the gold intercalation behavior for boron-doped graphene on a Ni(111) surface to be more complex: for low boron contents (2-5%) in the graphene lattice only partial gold intercalation occurs and for higher boron contents (up to 20%) no intercalation is observed. In order to understand this different behavior, a density functional theory investigation is carried out, comparing undoped as well as substitutional nitrogen- and boron-doped graphene on Ni(111). We identify the stronger binding of the boron atoms to the nickel substrate as the factor responsible for the different intercalation behavior in the case of boron doping. However, the calculations predict that this energetic effect prevents the intercalation process only for large boron concentrations and that it can be overcome for smaller boron coverages, in line with our x-ray photoelectron spectroscopy experiments. © 2013 IOP Publishing Ltd.

Gold platelets for high-quality plasmonics - Hoffmann, Björn; Feichtner, Thorsten; Christiansen, Silke (Materials Today, 2016)
No abstract available for this article

Graded Cellular Ceramics from Continuous Foam Extrusion - Ceron Nicolat, Bruno; Wolff, Friedrich; Dakkouri, Andrea S.; Fey, Tobias; Münstedt, Helmut; Greil, Peter (Advanced Engineering Materials, 2012)
Cylindrical SiOC foam filaments with a radial gradient in pore cell size were processed by continuous extrusion foaming of a methyl polysilsesquioxane. Upon leaving the extrusion nozzle foaming was initiated by pressure release which caused precipitation of supersaturated carbon dioxide from the polymer filament. Rapid cooling of the thin filaments generates a radial gradient of melt viscosity which gives rise for formation of closed cell morphology of isotropic pore cells in the core (diameter?<!–?200?mu m) and non-isotropic pore cells near the sur-face (shell; <20?mu m). After pyrolysis at temperatures ranging from 800 to 1400?degrees C the stabilized polymer gradient foams were converted into closed cell SiOC ceramic gradient foams. XRD reveals the SiOC residue to be amorphous up to 1200?degrees C whereas crystallization of beta-SiC was observed at 1400?degrees C. A superior compressive strength of 9?MPa and a Young's modulus of 7?GPa at a relative density of 0.18 were measured at an optimum pyrolysis temperature of 1000?degrees C.–>
Keywords: carbon dioxide foaming; graded porosity; polymer derived cellular ceramics

Grafting perylenes to ZnO nanoparticles - Schönamsgruber, Jörg; Zeininger, Lukas; Hirsch, Andreas (Chemistry - A European Journal, 2014)
A new prototype of dendritic perylenes suitable for the chemical functionalization of inorganic nanoparticles was synthesized and characterized. The bay-functionalized perylene core of these molecular architectures was coupled to a catechol moiety, which serves as an anchor group for the functionalization of metal oxides, in particular ZnO. To increase the solubility of both the perylene and the targeted hybrid nanostructures, a Newkome-type dendron bearing nine positive charges was introduced. This charge was also employed to stabilize the nanoparticles and further protect them from Ostwald ripening through Coulombic repulsion. ZnO quantum dots with an average diameter of 5nm were synthesized and functionalized with the perylene derivative. Successful functionalization was clearly demonstrated by dynamic light scattering, zeta-potential measurements, thermogravimetric analysis/MS, and UV/Vis and fluorescence spectroscopy. The generated particle dispersions were stable against agglomeration for more than eight weeks. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Grafting porphyrins (face-to-edge/orthogonal versus face-to-face/parallel) to ZnO en route toward dye-sensitized solar cells - Werner, Fabian; Gnichwitz, Jan-Frederik; Marczak, Renata; Palomares, Emilio; Peukert, Wolfgang; Hirsch, Andreas; Guldi, Dirk Michael (Journal of Physical Chemistry B, 2010)
Novel types of binding motives have been investigated within the context of sensitizing ZnO-based dyesensitized solar cells with metalloporphyrins. In particular, a complementary class of metalloporphyrin has been synthesized to probe the impact of a face-to-edge/orthogonal versus face-to-face/parallel orientation of the metalloporphyrin with respect to ZnO and has been compared to TiO-based dye-sensitized solar cells. Our studies provide a deep and detailed understanding of the individual electron-transfer processes at the ZnO/metalloporphyrin interface, that is, electron injection, recombination, and dye regeneration, by means of steady-state and time-resolved techniques. Interestingly, we found that for our novel ZnO/metalloporphyrin systems, the injection efficiencies are close to unity, despite their long, nonconjugated anchoring group length. © 2010 American Chemical Society.

Grain refinement and deformation mechanisms in heterogeneous ultrafine-grained materials processed by accumulative roll bonding - Göken, Mathias; Höppel, Heinz Werner; Hausöl, Tina; Bach, Jochen; Maier, Verena; Schmidt, Christian; et al. (Nanometals - status and perspective, 2012)
Grain refinement by severe plastic deformation is nowadays intensively used to process pure metals and alloys. These ultrafine-grained and homogeneous materials show already a great potential concerning their mechanical properties. Recently, heterogeneous ultrafine-grained materials consisting of different metals or different alloys became also very attractive. A very promising production process for such multicomponent materials is accumulative roll bonding (ARB) which allows producing laminates with finely distributed micrometer-sized layers. Interesting heterogeneous materials can also be produced by particle incorporation in the ARB process. Hard ceramic particles lead to additional grain refinement of the surrounding metal matrix by flow around the spherical particles. Similar extra grain refinement processes occur also at the interfaces in heterogeneous laminates. Although the deformation mechanisms in such UFG materials have been investigated quite intensively, a generally accepted view is still missing. Especially the question if grain boundary sliding or thermally activated dislocation processes are the dominant deformation mechanism has to be clearly answered. It is generally accepted that the strain rate sensitivity of nanomaterials is significantly enhanced compared to coarse grained materials, which probably is the dominant contribution to the often reported enhanced ductility. In the literature some indications can be found that also grain boundary sliding occurs under specific conditions and is sometimes considered as the dominant deformation mechanism in nanomaterials. Here, different arguments based on macroscopic deformation experiments such as strain rate jump tests and fatigue tests are discussed. The results show that thermally activated dislocation processes at the grain boundaries are the dominant deformation mechanisms in UFG materials. In addition nanoindentation experiments and focused ion beam investigations indicate that grain boundary sliding occurs only at free surfaces but not in the bulk volume of ultrafine-grained materials. This leads to the suggestion that thermally activated deformation processes at grain boundaries are dominant in ultrafinegrained materials with grain size of some hundred nanometers.
EAM Import::2019-03-13

Granular dampers: does particle shape matter? - 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 fi nd 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 fi nd that spherical particles lead to more ef fi cient energy dissipation compared to complex shaped particles of the same mass. In this regime, a dependence on the damper ’ sef fi ciency on the particle shape is found.
Keywords: granular matter; numerical simulations; discrete element method; granular dampers

Granular dampers for the reduction of vibrations of an oscillatory saw - Heckel, Michael; Sack, Achim; Kollmer, Jonathan; Pöschel, Thorsten (Physica A-Statistical Mechanics and Its Applications, 2012)
Instruments for surgical and dental application based on oscillatory mechanics submit unwanted vibrations to the operator's hand. Frequently the weight of the instrument's body is increased to dampen its vibration. Based on recent research regarding the optimization of granular damping we developed a prototype granular damper that attenuates the vibrations of an oscillatory saw twice as efficiently as a comparable solid mass. © 2012 Elsevier B.V. All rights reserved.
Keywords: Dissipation mechanism; Granular damper; Granular system; Vibrations

Granular hydrodynamics and pattern formation in vertically oscillated granular disk layers - Carrillo, José A.; Pöschel, Thorsten; Salueña, Clara (Journal of Fluid Mechanics, 2008)
The goal of this study is to demonstrate numerically that certain hydrodynamic systems, derived from inelastic kinetic theory, give fairly good descriptions of rapid granular flows even if they are way beyond their supposed validity limits. A numerical hydrodynamic solver is presented for a vibrated granular bed in two dimensions. It is based on a highly accurate shock capturing state-of-the-art numerical scheme applied to a compressible Navier - Stokes system for granular flow. The hydrodynamic simulation of granular flows is challenging, particularly in systems where dilute and dense regions occur at the same time and interact with each other. As a benchmark experiment, we investigate the formation of Faraday waves in a two-dimensional thin layer exposed to vertical vibration in the presence of gravity. The results of the hydrodynamic simulations are compared with those of event-driven molecular dynamics and the overall quantitative agreement is good at the level of the formation and structure of periodic patterns. The accurate numerical scheme for the hydrodynamic description improves the reproduction of the primary onset of patterns compared to previous literature. To our knowledge, these are the first hydrodynamic results for Faraday waves in two-dimensional granular beds that accurately predict the wavelengths of the two-dimensional standing waves as a function of the perturbation's amplitude. Movies are available with the online version of the paper. © 2008 Cambridge University Press.

Granular jet impact: Probing the ideal fluid description - Müller, Patric; Formella, Arno; Pöschel, Thorsten (Journal of Fluid Mechanics, 2014)
We investigate the impact of a granular jet on a finite target by means of particle simulations. The resulting hydrodynamic fields are compared with theoretical predictions for the corresponding flow of an incompressible and rotation-free fluid. The degree of coincidence between the field obtained from the discrete granular system and the idealized continuous fluid flow depends on the characteristics of the granular system, such as granularity, packing fraction, inelasticity of collisions, friction and target size. In certain limits we observe a granular-continuum transition under which the geometric and dynamic properties of the particle jet and the fluid jet become almost identical. © 2014 Cambridge University Press.
Keywords: complex fluids; granular media; jets

Graphene on Ni(111): Coexistence of different surface structures - Zhao, Wei; Kozlov, Sergey M.; Höfert, Oliver; Gotterbarm, Karin; Lorenz, Michael Peter Andreas; Vines, Francesc; Papp, Christian; Görling, Andreas; Steinrück, Hans-Peter (Journal of Physical Chemistry Letters, 2011)
A combined high-resolution X-ray photoelectron spectroscopy (HR-XPS) and ab initio density functional theory study on graphene on Ni(111) shows the coexistence of two structures, a bridge-top and a top-fcc structure, that have almost identical energies according to DFT calculations. Consequently, both geometries are detected simultaneously on the Ni(111) surface by HR-XPS, while their relative fractions depend on minor surface defect concentrations (pinning sites). The two structures are identified due to their different core level shifts that are in line with DFT calculations. © 2011 American Chemical Society.

Graphene oxide: A stable carbon framework for functionalization - Eigler, Siegfried; Grimm, Stefan; Hof, Ferdinand; Hirsch, Andreas (Journal of Materials Chemistry A, 2013)
The effect of NaOH and HCl on the stability of the carbon framework in graphene oxide (GO) after substitution or etherification reaction in GO is demonstrated at 10 °C and 40 °C, respectively. Our results allow the preparation of functionalized GO based architectures with an intact σ-framework of carbon atoms. © 2013 The Royal Society of Chemistry.

Graphene-Templated Growth of Pd Nanoclusters - Gotterbarm, Karin; Steiner, Christian; Bronnbauer, Carina; Bauer, Udo; Steinrück, Hans-Peter; Maier, Sabine; Papp, Christian (Journal of Physical Chemistry C, 2014)
Graphene grown on Rh(111) was used as a template for the growth of Pd nanoclusters. Using high-resolution synchrotron radiation-based X-ray photoelectron spectroscopy, we studied the deposition of Pd on corrugated graphene in situ. From the XP spectra, we deduce a cluster-by-cluster growth mode. The formation of clusters with 3 nm diameter was confirmed by low-temperature scanning tunneling microscopy measurements. The investigation of the thermal stability of the Pd particles showed three characteristic temperature regimes: Up to 550 K restructuring of the particles takes place, between 550 and 750 K the clusters coalesce into larger agglomerates, and finally between 750 and 900 K Pd intercalates between the graphene layer and the Rh surface.

Green Processing of Metal Oxide Core–Shell Nanoparticles as Low-Temperature Dielectrics in Organic Thin-Film Transistors - Portilla Berlanga, Luis; Etschel, Sebastian; Tykwinski, Rik; Halik, Marcus (Advanced Materials, 2015)
TiO2, Fe3O4, AlOx , ITO (indium tin oxide), and CeO2 nanoparticles are tailored to exhibit excellent dispersability in deionized water and alcohols. The latter provides an ecofriendly solution for processing metal oxide nanoparticles at a neutral pH. Water processed dielectrics from the metal oxide nanoparticles are incorporated into organic thin-film transistors fabricated on rigid and flexible substrates.

Group theory of circular-polarization effects in chiral photonic crystals with four-fold rotation axes applied to the eight-fold intergrowth of gyroid nets - Saba, Matthias; Turner, Mark D.; Mecke, Klaus; Gu, Min; Schröder-Turk, Gerd (Physical Review B, 2013)
We use group or representation theory and scattering matrix calculations to derive analytical results for the band structure topology and the scattering parameters, applicable to any chiral photonic crystal with body-centered-cubic symmetry I432 for circularly polarized incident light. We demonstrate in particular that all bands along the cubic [100] direction can be identified with the irreducible representations E-+/-, A, and B of the C-4 point group. E+ and E- modes represent the only transmission channels for plane waves with wave vector along the Delta line, and E- and E+ are identified as noninteracting transmission channels for right-and left-circularly polarized light, respectively. Scattering matrix calculations provide explicit relationships for the transmission and reflectance amplitudes through a finite slab which guarantee equal transmission rates for both polarizations and vanishing ellipticity below a critical frequency, yet allowing for finite rotation of the polarization plane. All results are verified numerically for the so-called 8-srs geometry, consisting of eight interwoven equal-handed dielectric gyroid networks embedded in air. The combination of vanishing losses, vanishing ellipticity, near-perfect transmission, and optical activity comparable to that of metallic metamaterials makes this geometry an attractive design for nanofabricated photonic materials.

Growth and electronic structure of boron-doped graphene - Gebhardt, Julian; Koch, Roland; Zhao, Wei; Höfert, Oliver; Gotterbarm, Karin; Mammadov, Samir; Papp, Christian; Görling, Andreas; Steinrück, Hans-Peter; Seyller, Thomas (Physical Review B, 2013)
The doping of graphene to tune its electronic properties is essential for its further use in carbon-based electronics. Adapting strategies from classical silicon-based semiconductor technology, we use the incorporation of heteroatoms in the 2D graphene network as a straightforward way to achieve this goal. Here, we report on the synthesis of boron-doped graphene on Ni(111) in a chemical vapor deposition process of triethylborane on the one hand and by segregation of boron from the bulk of the substrate crystal on the other hand. The chemical environment of boron was determined by x-ray photoelectron spectroscopy, and angle-resolved photoelectron spectroscopy was used to analyze the impact on the band structure. Doping with boron leads to a shift of the graphene bands to lower binding energies. The shift depends on the doping concentration and for a doping level of 0.3 ML a shift of up to 1.2 eV is observed. The experimental results are in agreement with density-functional calculations. Furthermore, our calculations suggest that doping with boron leads to graphene preferentially adsorbed in the top-fcc geometry, since the boron atoms in the graphene lattice are then adsorbed at substrate fcc-hollow sites. The smaller distance of boron atoms incorporated into graphene compared to graphene carbon atoms leads to a bending of the doped graphene sheet in the vicinity of the boron atoms. By comparing calculations of doped and undoped graphene on Ni(111), as well as the respective freestanding cases, we are able to distinguish between the effects that doping and adsorption have on the band structure of graphene. Both doping and bonding to the surface result in opposing shifts on the graphene bands. © 2013 American Physical Society.

Growth and electronic structure of nitrogen-doped graphene on Ni(111) - Koch, Roland; Weser, M.; Zhao, Wei; Vines, Francesc; Gotterbarm, Karin; Kozlov, Sergey M.; Höfert, Oliver; Ostler, Markus; Papp, Christian; Gebhardt, Julian; Steinrück, Hans-Peter; Görling, Andreas; et al. (Physical Review B, 2012)
We report on experimental and theoretical investigations of nitrogen-doped graphene. The incorporation of nitrogen was achieved during chemical-vapor deposition on Ni(111) using pyridine as a precursor. The obtained graphene layers were investigated using photoelectron spectroscopy. By studying C 1s and N 1s core levels, we show that the nitrogen content is influenced by the growth temperature and determine the atomic arrangement of the nitrogen atoms. Valence-band photoelectron spectra show that the incorporation of nitrogen leads to a broadening of the photoemission lines and a shift of the π band. Density functional calculations for two possible geometric arrangements, the substitution of carbon atoms by nitrogen and vacancies in the graphene sheet with pyridinic nitrogen at the edges, reveal that the two arrangements have opposite effects on the band structure. For the present experimental approach, vacancies with pyridinic nitrogen are dominant. In the latter case the vacancies generated by the nitrogen doping, not the nitrogen itself, have the main effect on the band structure. By intercalating gold between the doped graphene layer and the Ni(111) substrate electronic decoupling is achieved. After intercalation the doping remains. © 2012 American Physical Society.

Growth and luminescent properties of TbAlO3 - Zorenko, Yu.; Gorbenko, V.; Vozniak, T.; Batentschuk, Miroslaw; Osvet, Andres; Winnacker, Albrecht; et al. (physica status solidi (a), 2010)
The paper is dedicated to the investigation of growth processes by liquid phase epitaxy (LPE) and the luminescent properties of single-crystalline films (SCFs) of TbAlO_3 terbium-aluminum perovskite (TbAP) perovskite doped with manganese ions. We found that the Mn2+ and Mn3+ or even Mn5+ states can occur in TbAP:Mn SCF depending on the concentration of manganese ions in the 0.01–1.1 at.% range. The Mn2+ ions in TbAP host possess orange luminescence in the band peaked at 572 nm with a lifetime of 1.24 ms at 300 K that is caused by the ^4T1 i̊ghtarrow6 A1 radiative transitions. The cascade energy-transfer processes can be realized in TbAP:Mn SCF: (i) from 5d–4f states of Tb3+ cations to Mn2+ ions; (ii) from Mn2+ ions to 4f states of Tb3+ cations. The latest process strongly decreases the efficiency of Mn2+ luminescence in TbAlO_3 perovskite with respect to the Tb_3Al5O12 garnet host.
EAM Import::2019-03-13

Growth and oxidation of graphene on Rh(111) - Gotterbarm, Karin; Zhao, Wei; Höfert, Oliver; Gleichweit, Christoph; Papp, Christian; Steinrück, Hans-Peter (Physical Chemistry Chemical Physics, 2013)
The growth and oxidation of graphene supported on Rh(111) was studied in situ by high-resolution X-ray photoelectron spectroscopy. By variation of propene pressure and surface temperature the optimum growth conditions were identified, yielding graphene with low defect density. Oxidation of graphene was studied at temperatures between 600 and 1000 K, at an oxygen pressure of ∼2 × 10 mbar. The oxidation follows sigmoidal reaction kinetics. In the beginning, the reaction rate is limited by the number of defects, which represent the active sites for oxygen dissociation. After an induction period, the reaction rate increases and graphene is rapidly removed from the surface by oxidation. For graphene with a high defect density we found that the oxidation is faster. In general, a reduction of the induction period and a faster oxidation occur at higher temperatures. © 2013 The Owner Societies.

Growth of GaN micro- and nanorods on graphene-covered sapphire: Enabling conductivity to semiconductor nanostructures on insulating substrates - Heilmann, Martin; Sarau, George; Göbelt, Manuela; Latzel, Michael; Sadhujan, Sumesh; Tessarek, Christian; Christiansen, Silke (Crystal Growth and Design, 2015)
The self-catalyzed growth of vertically aligned and hexagonally shaped GaN micro- and nanorods on graphene transferred onto sapphire is achieved through metal-organic vapor phase epitaxy. However, a great influence of the underlying substrate is evident, since vertically aligned structures with a regular shape could not be grown on graphene transferred to SiO2. The optical properties of the regular GaN nanorods were investigated by spatially and spectrally resolved cathodoluminescence showing defect related emission only near the interface between the sapphire substrate and nanorods but not from their upper part. Micro-raman spectroscopy confirms that the single-layer graphene remains virtually unchanged in terms of the Raman signal, even after undergoing high temperatures (∼1200 °C) during nanorod growth. Furthermore, Raman mapping demonstrates that GaN structures predominantly grow on defective parts of graphene, giving new insight into the nucleation and growth mechanism of semiconductors on graphene. To validate the conductivity of graphene, when being attached to the sapphire substrate and after the nanorod growth, current-voltage investigations were carried out on single, as-grown, GaN nanorods with a nanoprober in a scanning electron microscope. These measurements demonstrate the viability of graphene as a conductive electrode, for example, as a back contact for GaN nanorods grown on insulating sapphire.

Growth of GaN Nanorods and Wires and Spectral Tuning of Whispering Gallery Modes in Tapered GaN Wires - Tessarek, Christian; Dieker, Christel; Spiecker, Erdmann; Christiansen, Silke (Japanese Journal of Applied Physics, 2013)
This paper reports on the growth of GaN nanorods and wires by metal-organic vapor phase epitaxy. Density, height and diameter are strongly influenced by the growth time. A deposition time of a few minutes leads to the formation of GaN nanorods. Increasing the deposition time up to 1 h yields wires with heights exceeding 47 mu m. Transmission electron microscopy and convergent beam electron diffraction measurements are showing the presence of N- and Ga-polar GaN in a single nanorod. Cathodoluminescence measurements are performed showing the appearance of whispering gallery modes. Due to slight tapering of the wires the whispering gallery modes can be spectrally tuned by changing the position of the exposing electron beam at the sidewall facet of the rod. (C) 2013 The Japan Society of Applied Physics

Growth of ordered anodic SnO2 nanochannel layers and their use for H2 gas sensing - Palacios-Padros, A.; Altomare, Marco; Tighineanu, Alexei; Kirchgeorg, Robin; Shrestha, Nabeen Kumar; Diez-Perez, Ismael; Caballero-Briones, Felipe; Sanz, F.; Schmuki, Patrik (Journal of Materials Chemistry A, 2014)
In the current work, we present a new self-organizing anodization approach of metallic Sn layers to obtain vertically aligned tin oxide nanochannel structures. For this, we use a sulphide-containing electrolyte and a set of optimized anodizing parameters. The resulting high aspect ratio nanochannel morphologies can be converted into crystalline SnO2 by high temperature annealing and show highly promising H2 sensing properties. We show that these anodic layers can operate at relatively low temperatures ( 80 °C), detecting concentrations as low as 9 ppm, and with extremely fast response and recovery times. This excellent gas-sensing performance is ascribed to the advanced structure, characterized by a crack-free, straight and top-open nanochannel geometry.
EAM Import::2019-03-13

Growth of Stable Surface Oxides on Pt(111) at Near-Ambient Pressures - Fantauzzi, Donato; Krick Calderon, Sandra; Mueller, Jonathan E.; Grabau, Mathias; Papp, Christian; Steinrück, Hans-Peter; Senftle, Thomas P.; van Duin, Adri C. T.; Jacob, Timo (Angewandte Chemie-International Edition, 2017)
Detailed knowledge of the structure and degree of oxidation of platinum surfaces under operando conditions is essential for understanding catalytic performance. However, experimental investigations of platinum surface oxides have been hampered by technical limitations, preventing in situ investigations at relevant pressures. As a result, the time-dependent evolution of oxide formation has only received superficial treatment. In addition, the amorphous structures of many surface oxides have hindered realistic theoretical studies. Using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) we show that a time scale of hours (t≥4 h) is required for the formation of platinum surface oxides. These experimental observations are consistent with ReaxFF grand canonical Monte Carlo (ReaxFF-GCMC) calculations, predicting the structures and coverages of stable, amorphous surface oxides at temperatures between 430–680 K and an O partial pressure of 1 mbar.
Keywords: interfaces; kinetics; oxidation; phase transitions; surface chemistry

Guideline for Efficiency Enhancement in Semi-Transparent Thin-Film Organic Photovoltaics with Dielectric Mirrors - Bronnbauer, Carina; Gasparini, Nicola; Brabec, Christoph; Forberich, Karen (Advanced Optical Materials, 2016)
Semi-transparent organic solar cells (ST-OSCs) show a unique potential to be integrated in windows due to their outstanding characteristics such as high transparency and color-adjustability. In order to achieve both, high transparency and high efficiency, the use of dielectric mirrors is an excellent concept. However, such a mirror will not only improve the photocurrent generated by a solar cell but also cause losses in transparency. In this work, a theoretical model is developed that predicts the effect of the dielectric mirror on the balance between photocurrent enhancement and transparency loss depending on the spectral shape of the ST-OSC absorption. Experimental investigations with three fully printed ST-OSCs showing different absorption characteristics underline the validity of these studies. It is concluded that ST-OSCs with broad absorption spectra ranging from the short wavelength region over the visible to at least 950 nm are most suitable for the implementation of a dielectric mirror. A narrower absorption spectrum or a shift of the spectrum toward longer wavelengths makes an increase in photoactive layer thickness more beneficial than the attachment of a dielectric mirror. Moreover, the dielectric mirror approach is an excellent strategy to obtain high photocurrents for materials which cannot be processed at high active layer thicknesses.
Keywords: bragg mirrors; dielectric mirrors; organic photovoltaics; printing; semi-transparent

Harmonic distortions enhance circular dichroism of dielectric single gyroids - Hielscher, Johannes; Pouya, Caroline; Vukusic, Peter; Schroeder-Turk, Gerd E. (Optics Express, 2017)
The departure from strict periodic order in two-phase dielectric materials can offer properties that are otherwise inaccessible to perfectly ordered photonic crystals. Herewith, we investigate the circular dichroism of the single gyroid photonic crystal in the presence of spatial distortions. FDTD simulations and microwave transmission measurements on 3D-printed replicas show that certain harmonic long-wavelength spatial distortions (chirp) nearly doubles the imbalance of the circular polarisation reflectances, as well as significantly strengthens polarisation-incoherent reflectance. The observed changes are partially rationalised by comparison with simpler distortion models (linear chirp and tetragonal deformation) of the Gyroid.
EAM Import::2019-03-13

Heaping and secondary flows in sheared granular materials - Börzsönyi, Tamás; Fischer, David; Schiochet Nasato, Daniel; Pöschel, Thorsten; Stannarius, Ralf (New Journal of Physics, 2016)
Cylindrical containers with a rotating bottom disk (so-called split-bottom geometry) are well established devices to shear granular materials in a continuous way, and to generate well-defined localized shear bands in the granular bed. When material composed of shape-anisotropic grains is sheared in such a container, a secondary flow is generated that leads to the formation of a considerable heap of material near the rotation center. We demonstrate that this effect can be found not only with prolate grains, as shown in a previous study, but also for oblate particle shapes. In addition, the quantitative influence of geometric and dynamic parameters is studied systematically. It is shown that the fill height of the container has considerable influence on the time scale for heap formation, but much less effect on the heap height. Results of numerical simulations agree with the experimental findings and provide insight in the particle dynamics.

Heat release process in three-dimensional macro-cellular SiC reactor under Diesel engine-like conditions - Cypris, J.; Schlier, Lorenz; Travitzky, Nahum; Greil, Peter; Weclas, M. (Fuel, 2012)
A specially developed macro-cellular SiC non-foam reactor has been used for investigations into Diesel-fuel injection, mixture formation and the heat release process inside a porous structure under piston-engine conditions. The heat release process has been compared to a free Diesel combustion indicating a significant influence of the reactor heat capacity on the thermodynamics of the process. Generally, the low- and high-temperature oxidation processes in a porous reactor are much faster, because of shorter delay time as compared to a free non-premixed combustion. High heat capacity of the porous reactor as compared to the gas heat capacity results in significantly reduced combustion temperature and corresponding combustion pressure peaks. Foam reactors with low and high pore density have also been compared in this investigation. The mixture formation, heat transfer and heat release processes performed in a porous reactor are very complex and depend on a number of different parameters of the combustion reactor in question: reactor structure, its heat capacity, pore size, specific surface area and wall junction geometry. Distribution of characteristic regions plotted in p-T areas indicates qualitative similarity of heat release process as performed under Diesel-like and in porous reactor conditions. © 2012 Elsevier Ltd. All rights reserved.
Keywords: Clean flameless combustion under pressure; Combustion in porous reactors; Diesel injection; Macro-cellular silicon carbide; Three dimensional printing

Heat transfer performance of structured catalytic reactors packed with metal foam supports: Influence of wall coupling - Razza, S.; Heidig, Tobias; Bianchi, Enrico; Groppi, G.; Schwieger, Wilhelm; Tronconi, E.; Freund, Hannsjörg (Catalysis Today, 2016)
Based on previous lab-scale heat transfer experiments performed in a test tube filled with metallic foams, extensive simulations of conjugated heat transfer were performed to systematically investigate the role of different coupling scenarios between the foam structure and the tube wall, using a 3D scanned foam geometry to enable the comparison of simulation results with experiments. The goal of this analysis is to gain insight into the prominent role of the wall coupling for radial heat transfer in a structured catalytic reactor packed with metal foams as catalyst supports. In the current numerical investigation the focus is on the characterization of the contact area between the foam and the reactor wall. Starting from perfect contact between the two, the contact area was decreased by selecting randomly some boundary spots of the foam and considering them as adiabatic. Moreover, the local distribution of the adiabatic struts was restricted to regions near the reactor inlet to additionally investigate the influence of the local distribution of the adiabatic struts at same overall contact areas. Eventually, all the contacts between the foam and the reactor wall were considered adiabatic as the other limiting case, wherein heat transfer at the foam/wall interface was governed solely by convection. The numerical analysis revealed that even if only a limited fraction of the struts have a direct contact with the tube wall, the heat transfer rate is significantly enhanced in comparison to the adiabatic case. In analogy with the previous experimental study, the numerical investigation was carried out for two different gases, nitrogen and helium, in order to address the influence of the thermal conductivity of the fluid phase. For further experimental verification, additional heat transfer measurements were performed for the case of a foam directly sintered to the tube in order to realize a perfect contact between foam and wall.

Heat transfer properties of metal foam supports for structured catalysts: Wall heat transfer coefficient - Bianchi, Enrico; Heidig, Tobias; Visconti, Carlo Giorgio; Groppi, Gianpiero; Freund, Hannsjörg; Tronconi, Enrico (Catalysis Today, 2013)
In this work we investigate the heat transfer within single phase tubular reactors packed with open-cell metal foams. Special focus is on the role of the coupling between the foam packing and the reactor tube wall. Steady-state heat transfer experiments were carried out in a tube of 28 mm inner diameter packed with different open-cell foams using N-2 or He at a flow rate ranging from 15 to 35 Nl/min. The foam samples were made of either FeCrAlY or aluminum with porosities in the range of 89-95% and pore densities ranging from 10 to 40 PPI (nominal pores per linear inch). For this purpose, axial and radial temperature profiles along the tested foam samples and along the tube wall were collected in heating and cooling runs within a temperature range from 400 to 800 K. The effective radial and axial conductivity and the wall heat transfer coefficient were then estimated for each run by nonlinear regression, using a 2D pseudo-homogeneous heat transfer model. The collected data allowed deriving a correlation for the wall heat transfer coefficient as a function of the process conditions and of the foam structural properties. Complementary to these experimental investigations, a numerical study in a 3D geometry of a foam sample reconstructed from X-ray micro-computed tomography data was carried out in order to analyze the heat transfer process close to the wall. For this, the conjugated heat transfer in both the solid and the fluid phase was investigated by finite volume analysis for selected experimental conditions. Both experiments and simulations confirm that the wall heat transfer resistance depends strongly on the gas conductivity and on the foam geometry, but more weakly on the flow velocity. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: Metal foams; Sponges; Heat transfer; Process intensification; Optimized supports; Structured reactors

Helical inner-wall texture prevents jamming in granular pipe flows - Verbücheln, Felix; Ribeiro Parteli, Eric Josef; Pöschel, Thorsten (Soft Matter, 2015)
Granular pipe flows are characterized by intermittent behavior and large, potentially destructive solid fraction variations in the transport direction. By means of particle-based numerical simulations of gravity-driven flows in vertical pipes, we show that it is possible to obtain steady material transport by adding a helical texture to the inner-wall of the pipe. The helical texture leads to a more homogeneous mass flux along the pipe, prevents the emergence of large density waves and substantially reduces the probability of plug formation thus avoiding jamming of the particulate flow. We show that the granular mass flux Q through a pipe of diameter D with a helical texture of wavelength λ follows the equation Q = Q0·1 - Bsin[arctan(2πD/λ)], where Q0 is the flow without helix, predicted from the well-known Beverloo equation. Our new expression yields, thus, a modification of the Beverloo equation with only one additional fit parameter, B, and describes the particle mass flux with the helical texture with excellent quantitative agreement with simulation results. Future application of the method proposed here has the potential to improve granular pipe flows in a broad range of processes without the need for energy input from any external source.

Herstellung hochfester Aluminiumblechwerkstoffe mittels Accumulative Roll Bonding - Böhm, Wolfgang; Merklein, Marion (Internationale Konferenz "Neuere Entwicklungen in der Blechumformung", 2014)
Ein entscheidender Aspekt bei der Produktentwicklung nachhaltiger Erzeugnisse ist die Berücksichtigung der Energieaufwendungen während des Herstellungsprozesses, der gesamten Nutzungsdauer und für das Recycling. Um den Treibstoffverbrauch und damit den Schadstoffausstoß während der Nutzung von PKWs zu minimieren, ist der Leichtbau im Karosseriebereich eine vielversprechende Strategie. Das Ziel dabei ist die Reduktion der Wanddicke der Komponenten bei gleichzeitiger Sicherstellung der Crashanforderungen. Dies erfordert den Einsatz hochfester Leichtbauwerkstoffe. Ein innovativer Fertigungsprozess zur Herstellung von Aluminiumblechen mit gesteigerter Festigkeit ist das Accumulative Roll Bonding (ARB). Hierbei werden mehrlagige Bleche hergestellt, die ein nanokristallines Gefüge aufweisen. Neben einer signifikant gesteigerten Festigkeit und einer erhöhten Dehnratensensitivität weisen diese Blechwerkstoffe in der Regel eine reduzierte Duktilität auf. Im Sinne einer wirtschaftlichen Weiterverarbeitung dieser Werkstoffe zu Karosseriekomponenten müssen jedoch effiziente Umformtechnologien zum Einsatz kommen. Um das Formgebungsvermögen zu erhöhen, wird die Technologie der Tailored Heat Treated Blanks (THTB) eingesetzt. Dabei wird vor der Umformung durch eine Kurzzeitwärmebehandlung in bestimmten Platinenbereichen die Festigkeit definiert reduziert. Über die geeignete Positionierung der Wärmebehandlungszonen kann die Umformbarkeit der gesamten Platine gesteigert und der Einsatz dieser hochfesten, mehrlagigen Aluminiumblechwerkstoffe im Bereich der Karosseriefertigung ermöglicht werden. Darüber hinaus bietet der ARB-Prozess ein großes Potential für die Verarbeitung großflächiger Recycling-Blechwerkstoffe, die beispielsweise aus Dachelementen oder Motorhauben entnommen wurden. Dies ermöglicht die Herstellung von Aluminiumhalbzeugen mit gesteigerter Festigkeit, die dann für tragende Komponenten außerhalb des Sichtbereichs im PKW eingesetzt werden können. Zudem sind im ARB-Prozess energetisch effiziente und kostengünstige Materialverbunde durch die angewandte Prozessstrategie realisierbar. Hierbei können beispielsweise zur Einsparung von Primärwerkstoff bzw. zur Realisierung bestimmter Materialeigenschaften an der Außenseite aufbereitete Recyclingwerkstoffe und die gewünschten Aluminiumgüten miteinander durch Walzplattieren gefügt werden. Vorab ist jeweils durch eine gewisse Anzahl an ARB-Zyklen eine Verbesserung der mechanischen Eigenschaften denkbar.
EAM Import::2019-03-13

Heterogeneous gold catalysts for efficient access to functionalized lactones - Neatu, Florentina; Li, Zhi; Richards, Ryan; Toullec, Patrick Y.; Genet, Jean-Pierre; Dumbuya, Karifala; Gottfried, Michael; Steinrück, Hans-Peter; Parvulescu, Vasile I.; Michelet, Veronique (Chemistry - A European Journal, 2008)
A novel class of heterogeneous gold catalysts supported on zeolite beta-NH was prepared by the deposition-precipitation method. This new class of catalyst showed interesting catalytic activities for the intramolecular cycloisomerization of γ-acetylenic carboxylic acids leading to functionalized γ-alkylidene γ-butyrolactones. Analysis of the supported gold species with in situ X-ray photoelectron spectroscopy (in situ XPS) suggests that cationic Au (possibly Au) can play an important role in such reactions. The high discrepancy in catalyst stability in favor of the Au supported on the zeolite system over bulk AuO is explained by 1) the size of the particles and 2) the reversibility of the redox deactivating process (Au→Au ) in the presence of oxygen for the supported system. The efficiency of this system allowed reaction under mild heterogeneous conditions. The potential for catalyst recycling was also highlighted. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

Heterogeneous nucleation and surface conformal growth of silver nanocoatings on colloidal silica in a continuous flow static T-mixer - Meincke, Thomas; Bao, Huixin; Pflug, Lukas; Stingl, Michael; Klupp Taylor, Robin (Chemical Engineering Journal, 2017)
Dielectric-metal core-shell particles with morphologically tunable optical properties are highly promising candidates for applications ranging from theranostics, energy harvesting and storage to pigments and sensors. Most structures of interest have, until now, been produced in small volume wet chemical batch approaches which are difficult to scale. In extension to the growing interest in continuous flow process for the scalable synthesis of single phase nanomaterials, here we describe the formation of two-phase core-shell particles. Specifically, the coating of silver onto colloidal silica particles using a static T-mixer approach is presented. The coating is achieved in a single reaction step in which careful control of educt concentration and process conditions leads to nucleation and surface conformal growth of silver. Through two generations of reactor, good coating yield and process reproducibility are demonstrated. In particular, the ability to control the characteristic time of mixing, as verified by the Villermaux-Dushmann reaction, was shown to be crucial in narrowing the range of morphologies obtained in the product particles. Moreover we could tune, through process parameters, the degree of coating of the core particles, leading to patchy particles, Janus particles and even complete nanoshells. Since silver nanostructures have a strong structure-dependent plasmon resonance, we could verify the coating morphologies via optical spectroscopy and electrodynamic simulations. Optical measurements were also used in order to optimize, via trial and error, the continuous flow process parameters to produce a high coating yield. This opens up future potential for feedback-driven optimization of particle coating. Finally, we demonstrate that the silver coatings can be morphologically stabilized, opening up the possibility of effective formulation for applications.
Keywords: Continuous flow nanoparticle synthesis; Diffusion limited growth; Metal nanoshell; Microreactor; Patchy particle; Plasmon resonance

Hierarchical decoration of anodic TiO2 nanorods for enhanced photocatalytic degradation properties - Tsui, Lok-Kun; Nguyen, Nhat Truong; Wang, Lei; Kirchgeorg, Robin; Zangari, Giovanni; Schmuki, Patrik (Electrochimica Acta, 2015)
In the present work vertically aligned TiO2 nanorods were fabricated by anodization of Al/Ti dual layer structures. Anodization of Al leads to the formation of a porous alumina layer which is used as a template for the growth of TiO2 nanorods. We have studied the characteristics of these nanorods after annealing by high resolution TEM, showing a core–shell structure along the length of the nanorods formed from the expansion of the TiO2 nanorod into the alumina template during growth. Modification of the nanorods by spin coating of a solution of titanium isopropoxide (TIPO) in isopropanol yields enhanced photocatalytic activity up to 12 times due to the increase in surface area, light absorption volume, and the creation of a crystalline coating with an anatase-phase.
EAM Import::2019-03-13

Hierarchical DSSC structures based on 'single walled' TiO2 nanotube arrays reach a back-side illumination solar light conversion efficiency of 8% - So, Seulgi; Hwang, Imgon; Schmuki, Patrik (Energy and Environmental Science, 2015)
In the present work we introduce a path to the controlled construction of DSSCs based on hierarchically structured single walled, self-organized TiO2 layers. In a first step we describe a simple approach to selectively remove the inner detrimental shell of anodic TiO2 nanotubes (NTs). This then allows controlled well-defined layer-by-layer decoration of these TiO2-NT walls with TiO2 nanoparticles (in contrast to conventional TiO2 nanotubes). We show that such defined multiple layered decoration can be optimized to build dye sensitized solar cells that (under back-side illumination conditions) can yield solar light conversion efficiencies to the extent of 8%. The beneficial effects observed can be ascribed to a combination of three factors: (1) improved electronic properties of the ``single walled'' tubes themselves, (2) a further improvement of the electronic properties by the defined TiCl4 treatment, and (3) a higher specific dye loading that becomes possible for the layer-by-layer decorated single walled tubes.
EAM Import::2019-03-13

Hierarchically-structured porous materials: from basic understanding to applications - Hartmann, Martin; Schwieger, Wilhelm (Chemical Society Reviews, 2016)
No abstract available for this article

Hierarchical on-surface synthesis and electronic structure of carbonyl-functionalized one- and two-dimensional covalent nanoarchitectures - Steiner, Christian; Gebhardt, Julian; Ammon, Maximilian Michael; Yang, Zechao; Heidenreich, Alexander; Hammer, Natalie; Görling, Andreas; Kivala, Milan; Maier, Sabine (Nature Communications, 2017)
The fabrication of nanostructures in a bottom-up approach from specific molecular precursors offers the opportunity to create tailored materials for applications in nanoelectronics. However, the formation of defect-free two-dimensional (2D) covalent networks remains a challenge, which makes it difficult to unveil their electronic structure. Here we report on the hierarchical on-surface synthesis of nearly defect-free 2D covalent architectures with carbonyl-functionalized pores on Au(111), which is investigated by low-temperature scanning tunnelling microscopy in combination with density functional theory calculations. The carbonyl-bridged triphenylamine precursors form six-membered macrocycles and one-dimensional (1D) chains as intermediates in an Ullmann-type coupling reaction that are subsequently interlinked to 2D networks. The electronic band gap is narrowed when going from the monomer to 1D and 2D surface-confined π-conjugated organic polymers comprising the same building block. The significant drop of the electronic gap from the monomer to the polymer confirms an efficient conjugation along the triphenylamine units within the nanostructures.

Hierarchical quantum master equation approach to electronic-vibrational coupling in nonequilibrium transport through nanosystems - Schinabeck, Christian; Erpenbeck, André; Haertle, R.; Thoss, Michael (Physical Review B, 2016)
Within the hierarchical quantum master equation (HQME) framework, an approach is presented, which allows a numerically exact description of nonequilibrium charge transport in nanosystems with strong electronic-vibrational coupling. The method is applied to a generic model of vibrationally coupled transport considering a broad spectrum of parameters ranging from the nonadiabatic to the adiabatic regime and including both resonant and off-resonant transport. We show that nonequilibrium effects are important in all these regimes. In particular, in the off-resonant transport regime, the inelastic cotunneling signal is analyzed for a vibrational mode in full nonequilibrium, revealing a complex interplay of different transport processes and deviations from the commonly used G0/2 rule of thumb. In addition, the HQME approach is used to benchmark approximate master equation and nonequilibrium Green's function methods.
EAM Import::2019-03-13

Hierarchy concepts: classification and preparation strategies for zeolite containing materials with hierarchical porosity - Schwieger, Wilhelm; Machoke, Albert; Weissenberger, Tobias; Inayat, Amer; Selvam, Thangaraj; Klumpp, Michael; Inayat, Alexandra (Chemical Society Reviews, 2016)
'Hierarchy' is a property which can be attributed to a manifold of different immaterial systems, such as ideas, items and organisations or material ones like biological systems within living organisms or artificial, man-made constructions. The property 'hierarchy' is mainly characterised by a certain ordering of individual elements relative to each other, often in combination with a certain degree of branching. Especially mass-flow related systems in the natural environment feature special hierarchically branched patterns. This review is a survey into the world of hierarchical systems with special focus on hierarchically porous zeolite materials. A classification of hierarchical porosity is proposed based on the flow distribution pattern within the respective pore systems. In addition, this review might serve as a toolbox providing several synthetic and post-synthetic strategies to prepare zeolitic or zeolite containing material with tailored hierarchical porosity. Very often, such strategies with their underlying principles were developed for improving the performance of the final materials in different technical applications like adsorptive or catalytic processes. In the present review, besides on the hierarchically porous allzeolite material, special focus is laid on the preparation of zeolitic composite materials with hierarchical porosity capable to face the demands of industrial application.

High-Aspect-Ratio Dye-Sensitized Solar Cells Based on Robust, Fast-Growing TiO2 Nanotubes - So, Seulgi; Lee, Kiyoung; Schmuki, Patrik (Chemistry - A European Journal, 2013)
The mechanical attachment of TiO2 nanotube layers to a substrate can be a determining factor for the performance of these layers in dye-sensitized solar cells (DSSCs). Self-organized TiO2 nanotube layers grown in an electrolyte that contained lactic acid are shown to have considerably improved anchoring on the Ti metal substrate, which allows the construction of stable and efficient solar cells with >50 extgreekmm nanotube length.
EAM Import::2019-03-13

High aspect ratio, self-ordered iron oxide nanopores formed by anodization of Fe in ethylene glycol/NH4F electrolytes - Albu, Sergiu; Ghicov, Andrei; Schmuki, Patrik (Physica Status Solidi-Rapid Research Letters, 2009)
In the present work we show that highly self-ordered iron oxide nanopores can be anodically grown to high aspect ratios, in optimized fluoride-containing ethylene glycol electrolytes. The as-formed layers are amorphous and contain a significant amount of fluorides. By annealing the layers can be crystallized and the fluorides can be removed. At elevated electrolyte temperatures the nanoporous system shows a transition to a nanotubular structure.
EAM Import::2019-03-13

High efficiency and stability small molecule solar cells developed by bulk microstructure fine-tuning - Min, Jie; Jiao, Xuechen; Sgobba, Vito; Kan, Bin; Heumüller, Thomas; Rechberger, Stefanie; Spiecker, Erdmann; Guldi, Dirk Michael; Wan, Xiangjian; Chen, Yongsheng; Ade, Harald; Brabec, Christoph (Nano Energy, 2016)
Morphological control over the bulk heterojunction (BHJ) microstructure of a high-efficiency small molecule photovoltaic system composed of a quinquethiophene based molecule (DRCN5T) as electron donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) as electron acceptor is demonstrated using three different post-processing strategies, including thermal annealing (TA), solvent vapor annealing (SVA), and two-step annealing (TA-SVA) treatments. We systematically analyze the processing condition-microstructure-device property relationships, explore the corresponding morphology evolution and their effects on carrier transport and recombination dynamics in BI-Js as well as understand the nature of phase-separation process resulting in light-induced degradation mechanisms. Within the investigated results, the causative relations between annealing sequence, photovoltaic parameters, morphology evolution and charge carrier dynamics are for the first time delineated. In addition, the observed trade-offs in device efficiency and stability with respect to the well-defined morphologies are highlighted. The in-depth picture of the bulk microstructure formation and its kinetic evolution as a function of the specific post-processing approaches is a valuable asset for the design of new photovoltaic materials and thin film nanoscale architectures that are more efficient and better aid future commercialization efforts. (C) 2016 Elsevier Ltd. All rights reserved.
Keywords: Blend microstructure; Morphological control; Annealing sequence; Phase-separation; Charge carrier dynamics; Degradation mechanisms

High fill factor polymer solar cells comprising a transparent, low temperature solution processed doped metal oxide/metal nanowire composite electrode - Stubhan, Tobias; Krantz, Johannes; Li, Ning; Guo, Fei; Litzov, Ivan; Steidl, Matthias; Richter, Moses; Matt, Gebhard; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2012)
In this paper we report on the replacement for the commonly used ITO electrode material by a low temperature solution processed silver nanowire/(doped) metal oxide composite. Devices employing silver nanowires (AgNWs)/buffer layer electrodes with a photoactive layer of poly(3- hexylthiophene) (P3HT) and [6,6]-phenyl-C butyric acid methyl ester (PCBM) are showing a comparable performance to the ITO reference cell with fill factors (FF) of over 62% and a power conversion efficiency of ∼2.7%. Zinc oxide (ZnO) and highly conductive Al doped ZnO (AZO) are used as buffer layer. AgNW devices without a buffer layer have a high open circuit voltage (V ) but the FF and the short circuit current density (j ) are substantially lower. Overall it is demonstrated that AgNWs and the low temperature solution process of the buffer layer are an attractive device concept towards an indium free organic solar cell. © 2012 Elsevier B.V. All rights reserved.
Keywords: Aluminum-doped zinc oxide; Metal nanowires; Organic solar cells; Solution processed; Transparent electrode; Zinc oxide

High fill factor polymer solar cells incorporating a low temperature solution processed WO3 hole extraction layer - Stubhan, Tobias; Li, Ning; Luechinger, Norman A.; Halim, Samuel C.; Matt, Gebhard; Brabec, Christoph (Advanced Energy Materials, 2012)
We demonstrate solution-processed tungsten trioxide (WO) incorporated as hole extraction layer (HEL) in polymer solar cells (PSCs) with active layers comprising either poly(3-hexylthiophene) (P3HT) or poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2, 6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,50-diyl] (Si-PCPDTBT) mixed with a fullerene derivative. The WO layers are deposited from an alcohol-based, surfactant-free nanoparticle solution. A short, low-temperature (80 °C) annealing is sufficient to result in fully functional films without the need for an oxygen-plasma treatment. This allows the application of the WO buffer layer in normal as well as inverted architecture solar cells. Normal architecture devices based on WO HELs show comparable performance to the PEDOTPSS reference devices with slightly better fill factors and open circuit voltages. Very high shunt resistances (over 1 MO cm) and excellent diode rectification underline the charge selectivity of the solution-processed WO layers. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA.
Keywords: 1; 3-benzothiadiazole; Active Layer; Fill factor; Fullerene derivative; Functional films; High fills; Low temperature solutions; Low temperatures; Nanoparticle solutions; Oxygen-plasma treatment; PEDOT-PSS; Poly-3-hexylthiophene; Polymer Solar Cells; Reference devices; Shunt resistances; Solution-processed; Surfactant-free; Tungsten trioxide Engineering controlled terms: Open circuit voltage; Plasma applications; Solar cells; Tungsten Engineering main heading: Temperature

High index-contrast all-solid photonic crystal fibers by pressure-assisted melt infiltration of silica matrices - Da, Ning; Wondraczek, Lothar; Schmidt, Markus A.; Granzow, Nicolai; Russell, Philip St. John (Journal of Non-Crystalline Solids, 2010)
All-solid photonic crystal fibers (PCFs) are created by pressure-assisted filling of low-melting-point chalcogenide and tellurite glasses into silica matrix fibers with channel diameters as small as 200 nm. Overcoming to a large extent the problem of viscosity and, thus, process incompatibility of silica and non-silicate optical glasses, the technique provides a unique way of producing waveguiding devices with high core-cladding index-contrast, high optical non-linearity and a transmission range that extends into the mid infrared. In this paper, as a prerequisite for waveguide production, the rheologic properties and controlled flow of highly-viscous liquids under geometrically confined conditions are considered, and deviations from Newtonian behavior are discussed. Because the filling process requires only very small quantities of filling material that do not come into contact with the environment, and because ultra-high cooling rates can be achieved, the technique enables the use of difficult-to-handle or reactive optical glasses.
EAM Import::2019-03-13

Highly-conductive energetic coherent interfaces subject to in-plane degradation - Esmaeili, Ali; Javili, Ali; Steinmann, Paul (Mathematics and Mechanics of Solids, 2016)
The presence of an interface can influence the thermo-mechanical response of a body. This influence is especially pronounced at small scales where the interface area to bulk volume ratio significantly increases. Since the thermo-mechanical properties of an interface can differ from those of the bulk, within interface continuum theory an interface is endowed with its own thermo-mechanical energetic structure. To date, the effects of interface in-plane damage on the thermo-mechanical response of a highly conductive interface have not been accounted for. Therefore in this contribution the computational aspects of thermo-mechanical solids containing highly conductive interfaces subject to in-plane degradation are studied. To this end, the equations governing a fully non-linear 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 highly conductive interface formulation.

Highly dispersed Pd nanoparticles within silica: Synthesis and characterization - Ofili, Ifeanyi Jimmy; Steinrück, Hans-Peter; Schwieger, Wilhelm; Ramakrishnan, Ayyappan; Dumbuya, K.; Gottfried, Michael (Applied Clay Science, 2011)
Well dispersed and homogeneously distributed Pd nanoparticles within a silica matrix were synthesized by a two stage process: (1) intercalation of palladium tetrammine ions into the layered aluminium-free silicate Na ilerite followed by (2) a self-reduction of the complex through decomposition of the tetrammine ligands by calcination at 550°C for 5h under N or air. Samples calcined in N predominantly contained nanoparticles of metallic Pd, while calcination in air led largely to the formation of PdO, as confirmed by XPS and supported by XRD and TGA. Thus, the Pd/PdO loading in the silica can be selectively tuned through this method. The intercalates were characterized by standard methods such as XRD, TGA, ICP and TEM. TGA of the intercalates indicated that the stabilization of the palladium tetrammine complex was enhanced by intercalation into Na ilerite. Based on ICP analysis, the Pd loadings in the intercalates were estimated to be about 18mass-%, which was also in agreement with the results from TGA. TEM revealed that the Pd/PdO nanoparticles were well dispersed in the silica matrix with an average particle size of approximately 8-10nm after calcination in air. © 2010 Elsevier B.V.

Highly Effective Pt-Based Water-Gas Shift Catalysts by Surface Modification with Alkali Hydroxide Salts - Kusche, Matthias Manfred; Bustillo, Karen; Agel, Friederike; Wasserscheid, Peter (ChemCatChem, 2015)
Herein, we describe an economical and convenient method to improve the performance of Pt/alumina catalysts for the water-gas shift reaction through surface modification of the catalysts with alkali hydroxides according to the solid catalyst with ionic liquid layer approach. The results are in agreement with our findings reported earlier for methanol steam reforming. This report indicates that alkali doping of the catalyst plays an important role in the observed catalyst activation. In addition, the basic and hygroscopic nature of the salt coating contributes to a significant improvement in the performance of the catalyst. During the reaction, a partly liquid film of alkali hydroxide forms on the alumina surface, which increases the availability of H2O at the catalytically active sites. Kinetic studies reveal a negligible effect of the KOH coating on the rate dependence of CO and H2O partial pressures. TEM studies indicate an agglomeration of the active Pt clusters during catalyst preparation; restructuring of Pt nanoparticles occurs under reaction conditions, which leads to a highly active and stable system over 240 h time on stream. Excessive pore fillings with KOH introduce a mass transfer barrier as indicated in a volcano-shaped curve of activity versus salt loading. The optimum KOH loading was found to be 7.5 wt%.
Keywords: electron microscopy; heterogeneous catalysis; ionic liquids; platinum; water-gas shift reaction

Highly enantioselective Ru-catalyzed asymmetric hydrogenation of β-keto ester in ionic liquid/methanol mixtures - Öchsner, Eva; Schneiders, Karola; Junge, Kathrin; Beller, Matthias; Wasserscheid, Peter (Applied Catalysis A-General, 2009)
The enantioselective hydrogenation of methyl acetoacetate (MAA) was studied in detail using a ruthenium-monodentate binaphthophosphepine complex in a homogeneous solution formed by different ionic liquids and methanol. Remarkably, ionic liquid additives did not only open an attractive way for catalyst recycling in repetitive batch-mode but also led to significantly increased catalytic activity compared to pure methanol. Enantioselectivities up to 95% have been achieved in mixed ionic liquid/methanol systems which are comparable to the values obtained in pure methano

Highly Intact and Pure Oxo-Functionalized Graphene:Synthesis and Electron-Beam-Induced Reduction - Butz, Benjamin; Dolle, Christian; Halbig, Christian Eberhard; Spiecker, Erdmann; Eigler, Siegfried (Angewandte Chemie International Edition, 2016)
Controlling the chemistry of graphene is necessary to enable applications in materials and life sciences. Research beyond graphene oxide is targeted to avoid the highly defective character of the carbon framework. Herein, we show how to optimize the synthesis of oxo-functionalized graphene (oxo-G) to prepare high-quality monolayer flakes that even allow for direct transmission electron microscopy investigation at atomic resolution (HRTEM). The role of undesired residuals is addressed and sources are eliminated. HRTEM provides clear evidence for the exceptional integrity of the carbon framework of such oxo-G sheets.The patchy distribution of oxo-functionality on the nm-scale,observed on our highly clean oxo-G sheets,corroborates theoretical predictions. Moreover, defined electron-beam irradiation facilitates gentle defunctionalization of oxo-G sheets, a new route towards clean graphene, which is a breakthrough for localized graphene chemistry.

Highly Integrated Organic–Inorganic Hybrid Architectures by Noncovalent Exfoliation of Graphite and Assembly with Zinc Oxide Nanoparticles - Marcia, Mario; Vinh, Chau; Dolle, Christian; Abellan Saez, Gonzalo; Schönamsgruber, Jörg; Schunk, Torsten; Butz, Benjamin; Spiecker, Erdmann; Hauke, Frank; Hirsch, Andreas (Advanced Materials Interfaces, 2016)
Liquid-phase exfoliated few-layer graphene flakes are noncovalently functionalized with tailor-made cationic water-soluble perylene diimides. By using a straightforward dip-coating approach, homogeneous ultrathin films consisting of interpenetrated nanoarchitectures can be achieved by incorporation of anionic ZnO nanoparticles. These 0D/2D assemblies pave the way for the development of novel graphene-based composite materials.
Keywords: graphene; hybrid materials; layer-by-layer assembly; nanoparticles; supramolecular chemistry

Highly magnetizable superparamagnetic colloidal aggregates with narrowed size distribution from ferrofluid emulsion - Lobaz, Volodymyr; Klupp Taylor, Robin; Peukert, Wolfgang (Journal of Colloid and Interface Science, 2012)
The formation of spherical superparamagnetic colloidal aggregates of magnetite nanoparticles by emulsification of a ferrofluid and subsequent solvent evaporation has been systematically studied. The colloidal aggregates occur as a dense sphere with magnetite nanoparticles randomly packed and preserved particle-particle separation due to chemisorbed oleic acid. The voids between nanoparticles are filled with solvent and free oleic acid. The latter was found to influence the formation of colloidal aggregates and their surface properties. The choice of surfactant, whether low molecular weight or polymeric, was shown to lead to the colloidal aggregates having tailored interfacial behavior. Magnetization measurements at ambient temperature revealed that the magnetite colloidal aggregates preserve the superparamagnetic properties of the starting nanoparticle units and show high saturation magnetization values up to 57. emu/g. The size distribution of magnetite nanoparticle colloidal aggregates produced by such an approach was found to be a function of emulsion droplet breakup - coalescence and stabilization kinetics and therefore is influenced by the emulsification process conditions and concentrations of the emulsion compounds. © 2012 Elsevier In
Keywords: Colloidal aggregate; Emulsion; Magnetite nanoparticle; Superparamagnetic particle

Highly ordered nanoporous Ta2O5 formed by anodization of Ta at high temperatures in a glycerol/phosphate electrolyte - Lee, Kiyoung; Schmuki, Patrik (Electrochemistry Communications, 2011)
In the present work, we investigate the anodization of Ta in a K2HPO4 containing glycerol electrolyte at elevated temperatures (180 °C). Under optimized conditions, uniformly over the entire anodized surface, self-organized porous Ta2O5 structures can be formed, that consist of highly aligned pores of 25 nm diameter and several tens of micrometers in length.
EAM Import::2019-03-13

Highly ordered TiO2 nanotube-stumps with memristive response - Yoo, Jeong Eun; Lee, Kiyoung; Tighineanu, Alexei; Schmuki, Patrik (Electrochemistry Communications, 2013)
In the present work, we produce highly ordered and defined short aspect ratio self-organized TiO2 nanotubes – so called titania nanotube stumps [TNS] – by anodizing Ti in a HF/H3PO4 electrolyte. These TNS-layers are ideal for a conformal filling by metal sputter deposition. After decorating amorphous TNS with a Pt top contact, we investigate the solid-state current–voltage behavior and find a strongly pronounced memristic behavior. We ascribe the finding to the high vacancy density present in TNS bottoms prepared under high ion flux conditions.
EAM Import::2019-03-13

Highly p-doped regions in silicon solar cells quantitatively analyzed by small angle beveling and micro-Raman spectroscopy - Becker, M.; Goesele, U.; Hofmann, A.; Christiansen, Silke (Journal of Applied Physics, 2009)
Highly p-doped regions in multicrystalline silicon solar cells, such as the back surface field region, are analyzed by means of small angle beveling and micro-Raman spectroscopy. Small angle beveling and subsequent Secco etching are used to enhance the lateral resolution of the micro-Raman spectroscopic measurements and to investigate the microstructure of the back surface field region in detail. The position-dependent analysis of the free carrier concentrations within the back surface field region is based on the Raman specific Fano resonances. The Raman spectroscopic measurement results are compared to results obtained from electrochemical capacitance-voltage measurements, which allows a subsequent calibration of the Raman data for the quantitative analysis of the free carrier concentrations within the highly p-doped regions of silicon solar cells and other devices. Our investigations show that the free carrier as well as the dopant concentration profiles within the back surface field region exhibit a nearly step-functional shape instead of the extended gradient shape which the electrochemical capacitance-voltage measurements suggest. Moreover, we show that the shape of the back surface field is often influenced by grain boundaries and other defects that occur in multicrystalline silicon wafers.
EAM Import::2019-03-13

Highly resolved analysis of the chemistry and mechanical properties of an a-C:H coating system by nanoindentation and auger electron spectroscopy - Schmid, Christoph; Maier, Verena; Schaufler, Jens; Butz, Benjamin; Spiecker, Erdmann; Meier, S.; Göken, Mathias; Durst, Karsten (Thin Solid Films, 2013)
The small-angle cross-section method was applied to a multi-layered hydrogenated amorphous carbon coating (a-C:H) system deposited by plasma enhanced chemical vapour deposition. The investigated system consists of a silicon rich adhesion layer and an adjacent ramp layer with a graded chemical composition to the a-C:H coating. The mechanical properties and the corresponding chemical gradients of the coating system were analysed by a combination of the small-angle cross-section method together with auger electron spectroscopy and nanoindentation. Furthermore, energy filtered transmission electron microscopy on a thin lamella was used to check the reliability of the auger electron spectroscopy results. It was found that local gradients in the chemical composition within the coating relate well to gradients observed in the local mechanical properties. The used combination of the different methods enables to resolve the correlation between the microstructure, chemical composition and mechanical properties of thin film systems with high spatial resolution. (c) 2012 Elsevier B.V. All rights reserve
Keywords: a-C:H; Nanoindentation; Small-angle cross-section; Focused ion beam; Adhesion layer; Chemical composition; DLC

Highly Selective Aromatic Alkylation of Phenol and Anisole by Using Recyclable Brønsted Acidic Ionic Liquid Systems - Titze-Frech, Karin; Ignatiev, Nikolai; Uerdingen, Marc; Schulz, Peter; Wasserscheid, Peter (European Journal of Organic Chemistry, 2013)
A highly efficient ionic liq. catalyst system for selective alkylation of phenol and anisole with alkenes is described. By using Bronsted acidic triflate ionic liqs. contg. the SO3H group attached to the cation, it was possible to recycle the catalyst and reuse it after a simple workup procedure. Moreover, selectivity towards the monoalkylated products e. g., I, was improved to 93 % by using a biphasic system. [on SciFinder(R)]
Keywords: alkyl phenol alkyl anisole prepn; phenol anisole alkene alkylation ionic liq catalyst

Highly self-ordered nanochannel TiO2 structures by anodization in a hot glycerol electrolyte - Lee, Kiyoung; Kim, Dam-Hee; Schmuki, Patrik (Chemical Communications, 2011)
In the present work, we report on the self-organized growth of TiO2 layers consisting of a highly aligned nanochannel morphology. We show that an electrochemical anodization process of Ti in a hot glycerol/K2HPO4 electrolyte can be adjusted to yield these self-organized TiO2 structures. The channel diameter and length are controllable by the anodization parameters. This directional structure can, for example, find application in dye-sensitized solar cells.
EAM Import::2019-03-13

High-mobility metal-oxide thin-film transistors by spray deposition of environmentally friendly precursors - Oertel, Susanne; Jank, Michael; Teuber, Erik; Bauer, Anton; Frey, Lothar (Thin Solid Films, 2014)
The synthesis of versatile, and non-toxic precursors for ambient-air deposition of semiconducting metal-oxide thin films by spray pyrolysis is reported. The resulting thin films yield stable and reproducible performance in thin-film transistors. The precursors are based on reactions of metal salts and an organic ammonium source in water. The precursor preparation is highly versatile with respect to low-level handling requirements (i.e. in air) and miscibility for the synthesis of customized mixed metal oxides. The precursor solutions are deposited by spray pyrolysis and integrated into bottom-gate test structures with staggered source and drain contacts. Indium zinc oxide thin films deposited from a precursor with an [In]/[Zn] ratio of 3:1 exhibit an on-off current ratio of 10 with a calculated saturation mobility of 14.1 cm V s ± 1.1 cm V s at a drain voltage of 40 V. The demonstrated route to non-toxic molecular precursors for low-temperature thin-film processing in ambient atmosphere benefits from low cost of educts, environmentally friendly solvents, minimized health risk when compared to nanoparticle processing, and an excellent performance for electronic applications. © 2013 Elsevier B.V. All rights reserved.
Keywords: Indium zinc oxide; Metal oxide semiconductors; Precursor; Solution processing; Spray pyrolysis

High-Mobility ZnO Nanorod Field-Effect Transistors by Self-Alignment and Electrolyte-Gating - Thiemann, Stefan; Gruber, Mathias; Lokteva, Irina; Halik, Marcus; Zaumseil, Jana (ACS Applied Materials and Interfaces, 2013)
High mobility, solution-processed field-effect transistors are important building blocks for flexible electronics. Here we demonstrate the alignment of semiconducting, colloidal ZnO nanorods by a simple solvent evaporation technique and achieve high electron mobilities in field-effect transistors at low operating voltages by electrolyte‐gating with ionic liquids. The degree of alignment varies with nanorod length, concentration and solvent evaporation rate. We find a strong dependence of electron mobility on the degree of alignment but less on the length of the nanorods. Maximum field-effect mobilities reach up to 9 cm2 V−1 s−1 for optimal alignment. Because of the low process temperature (150 °C), ZnO nanorod thin films are suitable for application on flexible polymer substrates.

High performance all-small-molecule solar cells: Engineering the nanomorphology: Via processing additives - Min, Jie; Kwon, Oh Kyu; Cui, Chaohua; Park, Jung-Hwa; Wu, Yue; Park, Soo Young; Li, Yongfang; Brabec, Christoph (Journal of Materials Chemistry A, 2016)
The use of small volumes of solvent additives (SAs) or little amounts of non-volatile additives is a processing approach that has been implemented in many high/record performing bulk heterojunction (BHJ) organic solar cells (OSCs). Here, the effects of six SA systems and a molecular additive di-2-thienyl-2,1,3-benzothiadiazole (DTBT) were studied with respect to the photovoltaic parameters of solution-processed all small molecule solar cells (all-SMSCs) based on the BDTT-S-TR:NIDCS-MO system. An effective strategy with binary additives has been employed in this all-SM system, where a small amount, 0.75 vol% 1,8-diiodooctane (DIO) and 2 wt% DTBT were added to the casting solution. This efficient SA approach yielded the highest power conversion efficiency (PCE) of 5.33%. The relevant additives facilitate phase separation in the nm domains and improve bulk transport as evidenced by photoluminescence (PL), atomic force microscopy (AFM), X-ray diffraction (XRD) and space charge limited current (SCLC) measurements.
Keywords: Engineering controlled terms: Additives; Atomic force microscopy; Cell engineering; Heterojunctions; Molecules; Organic solar cells; Phase separation; Photovoltaic effects; Solar power generation; X ray diffraction 1; 3-benzothiadiazole; Bulk heterojunction (BHJ); Molecular additives; Photovoltaic parameters; Power conversion efficiencies; Processing approach; Solution-processed; Space-charge-limited current Engineering main heading: Solar cells

High-performance direct conversion X-ray detectors based on sintered hybrid lead triiodide perovskite wafers - Shrestha, Shreetu; Fischer, Rene; Matt, Gebhard; Feldner, Patrick; Michel, Thilo; Osvet, Andres; Levchuk, Ievgen; Merle, Benoit; Golkar, Saeedeh; Chen, Haiwei; Tedde, Sandro F.; Schmidt, Oliver; et al. (Nature Photonics, 2017)
Lead halide perovskite semiconductors are in general known to have an inherently high X-ray absorption cross-section and a significantly higher carrier mobility than any other low-temperature solution-processed semiconductor. So far, the processing of several-hundred-micrometres-thick high-quality crystalline perovskite films over a large area has been unresolved for efficient X-ray detection. In this Article, we present a mechanical sintering process to fabricate polycrystalline methyl ammonium lead triiodide perovskite (MAPbI(3)) wafers with millimetre thickness and well-defined crystallinity. Benchmarking of the MAPbI(3) wafers against state-of-the-art CdTe detectors reveals competitive conversion efficiencies of 2,527 mu C Gy(air)(-1) cm(-2) under 70 kV(p) X-ray exposure. The high ambipolar mobility-lifetime product of 2 x 10(-4) cm(2) V-1 is suggested to be responsible for this exceptionally high sensitivity. Our findings inform a new generation of highly efficient and low-cost X-ray detectors based on perovskite wafer

High-Performance Organic Solar Cells Based on a Small Molecule with Alkylthio-Thienyl-Conjugated Side Chains without Extra Treatments - Cui, Chaohua; Guo, Xia; Min, Jie; Guo, Bing; Cheng, Xiao; Zhang, Maojie; Brabec, Christoph; Li, Yongfang (Advanced Materials, 2015)
A new 2D-conjugated small molecule with alkylthio-thienyl-conjugated side chains (BDTT-S-TR) is synthesized for application as a donor material in organic solar cells (OSCs). The OSCs based on BDTT-S-TR/PCBM demonstrate a power conversion efficiency (PCE) of 9.20% without extra treatment. Moreover, an encouraging PCE of 6.68% is achieved from the device with active area of 144 mm.
Keywords: conjugated side chains; organic molecules; organic solar cells; solution processability

High-performance semitransparent perovskite solar cells with solution-processed silver nanowires as top electrodes - Guo, Fei; Azimi, Seyed Hamed; Hou, Yi; Przybilla, Thomas; Hu, Mengyao; Bronnbauer, Carina; Langner, Stefan; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (Nanoscale, 2015)
In this work, we report efficient semitransparent perovskite solar cells using solution-processed silver nanowires (AgNWs) as top electrodes. A thin layer of zinc oxide nanoparticles is introduced beneath the AgNWs, which fulfills two essential functionalities: it ensures ohmic contact between the PC60BM and the AgNWs and it serves as a physical foundation that enables the solution-deposition of AgNWs without causing damage to the underlying perovskite. The as-fabricated semitransparent perovskite cells show a high fill factor of 66.8%, V-oc = 0.964 V, J(sc) = 13.18 mA cm(-2), yielding an overall efficiency of 8.49% which corresponds to 80% of the reference devices with reflective opaque electrode

High performance ternary organic solar cells with thick active layer exceeding 11% efficiency - Gasparini, Nicola; Lucera, Luca; Salvador, Michael Filipe; Prosa, Mario; Spyropoulos, Georgios; Kubis, Peter; Egelhaaf, Hans Joachim; Brabec, Christoph; Ameri, Tayebeh (Energy and Environmental Science, 2017)
We present a novel ternary organic solar cell with uncommonly thick active layer (>300 nm), featuring thickness invariant charge carrier recomb ination and delivering 11% power conversion efficiency (PCE). The ternary blend was used to demonstrate photovoltaic modules of high technological relevance both on gla ss and flexible substrates, yielding 8.2% and 6.8% PCE, respectively.

High precision processing of flexible P3HT/PCBM modules with geometric fill factor over 95% - Kubis, Peter; Lucera, Luca; Machui, Florian; Spyropoulos, Georgios; Cordero, Johann; Frey, Alfred; Kaschta, Joachim; Voigt, Monika; Matt, Gebhard; Zeira, Eitan; Brabec, Christoph (Organic Electronics, 2014)
Flexible OPV modules, based on P3HT:PCBM as absorber layer, were manufactured with a power conversion efficiency over 3% and for a total area of 3500 mm(2) consisting of 14 in series interconnected cells. The modules utilize the excellent mechanical and the outstanding optical properties of sputtered transparent ITO-Metal-ITO (IMI) electrodes deposited on the PET foil on the one hand, and the combination of large area slot-die coating with high resolution ultrafast laser patterning on the other hand. The manufacturing of modules with outstanding performance was found to be reproducible. The right combination of innovative electrodes and smart roll-to-roll compatible processing technologies demonstrates a viable path towards high efficient industrial module technology. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Flexible transparent electrode; Flexible OPV module; Slot-die coating; Ultra-fast laser patterning; High geometric fill factor

High Resolution Scanning Tunneling Microscopy of a 1D Coordination Polymer with Imidazole-Based N,N,O Ligands on HOPG - Fischer, Nina V.; Mitra, Utpal; Warnick, Karl-Georg; Dremov, Viatcheslav; Stocker, Michael; Wölfle, Thorsten; Hieringer, Wolfgang; Heinemann, Frank Wilhelm; Burzlaff, Nicolai; Görling, Andreas; Müller, Paul (Chemistry - A European Journal, 2014)
Novel k(3)-N,N,O ligands tend to form 1D coordination polymer strands. Deposition of 1D structures on highly oriented pyrolytic graphite (HOPG) was achieved from diluted solutions and polymer strands have been studied on HOPG by AFM/STM. Single strands were mapped by STM and their electronic properties were subsequently characterized by current imaging tunneling spectroscopy (CITS). Periodic density functional calculations simulating a polymer strand deposited on a HOPG surface are in agreement with the zig-zag structure indicated by experimental findings. Both the observed periodicity and the Zn-Zn distances can be reproduced in the simulations. Van der Waals interactions were found to play a major role for the geometry of the isolated polymer strand, for the adsorption geometry on HOPG, as well as for the adsorption energy.
Keywords: atomic force microscopy; coordination polymers; ligand design; scanning tunneling microscopy; zinc

High-Resolution spectroScopic mapping of the chemical contrast from nanometer domains in P3HT:PCBM organic blend films for Solar-Cell applications by - Wang, Xiao; Zhang, Dai; Braun, Kai; Egelhaaf, Hans-Joachim; Brabec, Christoph; Meixner, Alfred J. (Advanced Functional Materials, 2010)
A high-resolution near-field spectroscopic mapping technique is successfully applied to investigate the influence of thermal annealing on the morphology of a poly(3-hexylthiophene) and [6,6]-penyl-C butyric acid methyl ester (P3HT:PCBM) blend film. Based on the simultaneously recorded morphological and spectroscopic information, the interplay among the blend film morphology, the local P3HT:PCBM molecular distribution, and the P3HT photoluminescence (PL) quenching efficiency are systematically discussed. The PL and Raman signals of the electron donor (P3HT) and acceptor (PCBM) are probed at an optical resolution of approximately 10 nm, which allows the chemical nature of the different domains to be identified directly. In addition, the local PL quenching efficiency, which is related to the electron transfer from P3HT to PCBM, is quantitatively revealed. From these experimental results, it is proposed that high-resolution near-field spectroscopic imaging is capable of mapping the local chemical composition and photophysics of the P3HT:PCB M blends on a scale of a few nanometers. © 2010 WlLEY-VCH Verlag GmbH & Co. KGaA,.

High selectivity of TiC-CDC for CO2/N2 separation - Silvestre-Albero, Ana; Rico-Frances, Soledad; Rodriguez-Reinoso, Francisco; Kern, Andreas; Klumpp, Michael; Etzold, Bastian; Silvestre-Albero, Joaquin (Carbon, 2013)
A series of carbide-derived carbons (CDC) have been prepared starting from TiC and using different chlorine treatment temperatures (500–1200 °C). Contrary to N2 adsorption measurements at -196 °C, CO2 adsorption measurements at room temperature and high pressure (up to 1 MPa) together with immersion calorimetry measurements into dichloromethane suggest that the synthesized CDC exhibit a similar porous structure, in terms of narrow pore volume, independently of the temperature of the reactive extraction treatment used (samples synthesized below 1000 °C). Apparently, these carbide-derived carbons exhibit narrow constrictions were CO2 adsorption under standard conditions (0 °C and atmospheric pressure) is kinetically restricted. The same accounts for a slightly larger molecule as N2 at a lower adsorption temperature (-196 °C), i.e. textural parameters obtained from N2 adsorption measurements on CDC must be underestimated. Furthermore, here we show experimentally that nitrogen exhibits an unusual behavior, poor affinity, on these carbide-derived carbons. CH4 with a slightly larger diameter (0.39 nm) is able to partially access the inner porous structure whereas N2, with a slightly smaller diameter (0.36 nm), does not. Consequently, these CDC can be envisaged as excellent sorbent for selective CO2 capture in flue-gas streams.
EAM Import::2019-03-13

High shunt resistance in polymer solar cells comprising a MoO3 hole extraction layer processed from nanoparticle suspension - Stubhan, Tobias; Ameri, Tayebeh; Salinas Batallas, Michael; Krantz, Johannes; Machui, Florian; Halik, Marcus; Brabec, Christoph (Applied Physics Letters, 2011)
In this report, we present solution processed molybdenum trioxide (MoO3) layers incorporated as hole extraction layer (HEL) in polymer solar cells (PSCs) and demonstrate the replacement of the commonly employed poly(3,4-ethylene dioxythiophene):(polystyrene sulfonic acid) (PEDOT:PSS). MoO3 is known to have excellent electronic properties and to yield more stable devices compared to PEDOT:PSS. We demonstrate fully functional solar cells with up to 65 nm thick MoO3 HEL deposited from a nanoparticle suspension at low temperatures. The PSCs with an active layer comprising a blend of poly(3-hexylthiophene) and [6,6]-phenyl-C61 butyric acid methyl ester and a MoO3 HEL show comparable performance to reference devices with a PEDOT:PSS HEL. The best cells with MoO3 reach a fill factor of 66.7% and power conversion efficiency of 2.92%. Moreover, MoO3 containing solar cells exhibit an excellent shunt behavior with a parallel resistance of above 100 kΩ cm2.

High-temperature thermographic phosphor mixture YAP/YAG:Dy3+ and its photoluminescence properties - Chepyga, Liudmyla M.; Osvet, Andres; Brabec, Christoph; Batentschuk, Miroslaw (Journal of Luminescence, 2017)
In this work we report on the investigation of high-temperature thermographic phosphors Dy3+-doped yttrium aluminum garnet and the mixture of yttrium aluminum perovskite / yttrium aluminum garnet (YAP/YAG). The phosphors were synthesized by conventional high temperature solid-state method using lithium fluoride (LiF) as a flux. The latter serves also as a source of co-doping Li+ and F- ions affecting the luminescent properties. The photoluminescence intensity of YAP/YAG:Dy (75/25%) mixture was doubled at room temperature compared to YAG:Dy and the intensity ratio of the lines in the regions 450–460 and 480–500 nm was increased from 0.45 to 0.63 at 1293 K, favoring temperature measurements. Therefore, the mixture of YAlO3/Y3Al5O12:Dy is promising material for high temperature phosphor thermometry. © 2017 Elsevier B.V.
Keywords: Aluminum; Dysprosium; Garnets; Light emission; Luminescence; Mixtures; Photoluminescence; Temperature measurement; Thermometers; Yttrium; High temperature solid state methods; Lithium fluoride; Luminescent property; Phosphor thermometry; Photoluminescence intensities; Photoluminescence properties; Thermographic phosphors; Yttrium aluminum garnet; Phosphors

Homogeneous cooling of mixtures of particle shapes - Hidalgo, Raúl Cruz; Serero, Dan; Pöschel, Thorsten (Physics of Fluids, 2016)
In this work, we examine theoretically the cooling dynamics of binary mixtures of spheres and rods. To this end, we introduce a generalized mean field analytical theory, which describes the free cooling behavior of the mixture. The relevant characteristic time scale for the cooling process is derived, depending on the mixture composition and the aspect ratio of the rods. We simulate mixtures of spherocylinders and spheres using a molecular dynamics algorithm implemented on graphics processing unit (GPU) architecture. We systematically study mixtures composed of spheres and rods with several aspect ratios and varying the mixture composition. A homogeneous cooling state, where the time dependence of the system’s intensive variables occurs only through a global granular temperature, is identified. We find cooling dynamics in excellent agreement with Haff’s law, when using an adequate time scale. Using the scaling properties of the homogeneous cooling dynamics, we estimated numerically the efficiency of the energy interchange between rotational and translational degrees of freedom for collisions between spheres and rods.

Homogeneous ruthenium-based water–gas shift catalysts via supported ionic liquid phase (SILP) technology at low temperature and ambient pressure - Werner, Sebastian; Szesni, Normen; Fischer, Richard; Haumann, Marco; Wasserscheid, Peter (Physical Chemistry Chemical Physics, 2009)
Novel ruthenium-based supported ionic liquid phase (SILP) catalysts for the water–gas shift (WGS) reaction are reported which, compared to classical low temperature shift systems, operate at much lower temperatures and even at ambient pressure.

Hourglass of constant weight - Becker, Volker; Pöschel, Thorsten (Granular Matter, 2008)
In contrast to a still common belief, a steadily flowing hourglass changes its weight over the course of time (Shen and Scott in Am J Phys 53(8):787-788, 1985). We will show that, nevertheless, it is possible to construct hourglasses that do not change their weight. © 2007 Springer-Verlag.
Keywords: Granular flow; Hour glass flow

How Does Water Wet a Surface? - Maier, Sabine; Salmeron, Miquel (Accounts of Chemical Research, 2015)
In this Account, a selection of recent STM results on the water adsorption and dissociation on close-packed metal surfaces is reviewed, with a particular focus on Ru(0001). The Ru(0001) surface is one where water adsorbs intact in a metastable state at low temperatures and where partially dissociated layers are formed at temperatures above similar to 150 K. First, we will describe the structure of intact water clusters starting with the monomer up to the monolayer. We show that icelike wetting layers do not occur on close-packed metal surfaces but instead hydrogen bonded layers in the form of a mixture of pentagonal, hexagonal, and heptagonal molecular rings are observed. Second, we will discuss the dissociation mechanism of water on Ru(0001). We demonstrate that water adsorption changes from dissociative to molecular as a function of the oxygen preadsorbed on Ru. Finally, we briefly review recent STM experiments on bulk ice (I-h and I-c) and water adsorption on insulating thin films. We conclude with an outlook illustrating the manipulation capabilities of STM in respect to probe the proton and hydrogen dynamics in water clusters.

Hungry Porphyrins: Protonation and Self-Metalation of Tetraphenylporphyrin on TiO2(110)-1 x 1 - Köbl, Julia; Wang, Tao; Wang, Cici; Drost, Martin; TU, Fan; Xu, Qian; Ju, Huanxin; Wechsler, Daniel; Franke, Matthias; Pan, Haibin; Marbach, Hubertus; Steinrück, Hans-Peter; et al. (ChemistrySelect, 2016)
We have studied the adsorption and self-metalation of tetraphenylporphyrin (2HTPP) on TiO2(110) -1 x 1 with X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM). Upon adsorption at room temperature the first monolayer of 2HTPP is protonated by protons from the surface, forming porphyrin diacid (4HTPP(2+)). In STM, single molecules with low mobility and no long-range order were observed. As the surface is heated to 400 K, any unprotonated 2HTPP molecules in the second layer metalate, forming titanyl tetraphenylporphyrin (TiOTPP), but the protonated molecules in the first layer remain. As the surface is heated further to 550 K even the protonated 4HTPP(2+) molecules metalate and only TiOTPP remain on the surface.
Keywords: Adsorption; Porphyrinoids; Oxide Surfaces; Surface Chemistry; Titania

Hybrid artificial neural network for prediction and control of process variables in food extrusion - Cubeddu, Alessandro; Rauh, Cornelia; Delgado, Antonio (Innovative Food Science & Emerging Technologies, 2014)
Two hybrid Artificial Neural Network (ANN) chains have been implemented and tested for configuration and control of a food extrusion process. The first architecture (Configuration Chain) predicts the process variables screw speed N and water content w starting from product characteristics. It calculates also energy and flow variables as Specific Mechanical Energy, shaft torque, shear stress, pressure and temperature variations. The second architecture (Control Chain) is a closed loop ANN-chain in which a differential neurocontroller regulates the extrusion process by calculating adjustments of N and w. Both chains are feedforward multilayer ANNs trained using the Back Propagation Algorithm. The ANNs in each chain are built using the programme MemBrain and are triggered and automated by an AngelScript code. A total of 42 patterns have been used (24 for training and 18 for verification). For both ANN-chains the quality of each ANN is presented as well as proof of concept of the whole chain. Industrial relevance The present study is intended to offer a method to efficiently optimise in an innovative way the process of extrusion in the food industy. In particular, the research aims to develop two Artificial Neural Network chains for (1) prediction of optimal process variables (screw speed and water content are considered) starting from desired product characteristics and (2) prevent process instabilities on the predicted variables by using a neurocontroller. The advantages for the industry are the opportunity to select the best machine variables for each reasonable desired product and the possibility to stabilise and regulate in a connectionistic way a multivariable system like the extrusion process which is difficult to be regulated in a deterministic manner. © 2013 Elsevier Ltd.
UnivIS-Import:2015-03-09:Pub.2014.tech.ITC.stmmec.hybrid
Keywords: Artificial neural networks; Differential neurocontroller; Extrusion process control; Process variable prediction

Hybrid Colloidal Plasmonic-Photonic Crystals - Romanov, Sergei G.; Korovin, Alexander V.; Regensburger, Alois; Peschel, Ulf (Advanced Materials, 2011)
We review the recently emerged class of hybrid metal-dielectric colloidal photonic crystals. The hybrid approach is understood as the combination of a dielectric photonic crystal with a continuous metal film. It allows to achieve a strong modification of the optical properties of photonic crystals by involving the light scattering at electronic excitations in the metal component into moulding of the light flow in series to the diffraction resonances occurring in the body of the photonic crystal. We consider different realizations of hybrid plasmonic-photonic crystals based on two- and three-dimensional colloidal photonic crystals in association with flat and corrugated metal films. In agreement with model calculations, different resonance phenomena determine the optical response of hybrid crystals leading to a broadly tuneable functionality of these crystals.
EAM Import::2019-03-13

Hybrid lattice-Boltzmann and finite-difference simulation of electroosmotic flow in microchannel - Masilamani, Kannan; Ganguly, Suvankar; Feichtinger, Christian; Rüde, Ulrich (Fluid Dynamics Research, 2011)
A three-dimensional (3D) transient mathematical model is developed to simulate electroosmotic flows (EOFs) in a homogeneous, square cross-section microchannel, with and without considering the effects of axial pressure gradients. The general governing equations for electroosmotic transport are incompressible Navier-Stokes equations for fluid flow and the nonlinear Poisson-Boltzmann (PB) equation for electric potential distribution within the channel. In the present numerical approach, the hydrodynamic equations are solved using a lattice-Boltzmann (LB) algorithm and the PB equation is solved using a finite-difference (FD) method. The hybrid LB-FD numerical scheme is implemented on an iterative framework solving the system of coupled time-dependent partial differential equations subjected to the pertinent boundary conditions. Transient behavior of the EOF and effects due to the variations of different physicochemical parameters on the electroosmotic velocity profile are investigated. Transport characteristics for the case of combined electroosmotic- and pressure-driven microflows are also examined with the present model. For the sake of comparison, the cases of both favorable and adverse pressure gradients are considered. EOF behaviors of the non-Newtonian fluid are studied through implementation of the power-law model in the 3D LB algorithm devised for the fluid flow analysis. Numerical simulations reveal that the rheological characteristic of the fluid changes the EOF pattern to a considerable extent and can have significant consequences in the design of electroosmotically actuated bio-microfluidic systems. To improve the performance of the numerical solver, the proposed algorithm is implemented for parallel computing architectures and the overall parallel performance is found to improve with the number of processors. © 2011 The Japan Society of Fluid Mechanics and IOP Publishing Ltd.
UnivIS-Import:2015-03-09:Pub.2011.tech.IMMD.lsinfs.hybrid

Hybrid Simulation of Heterogeneous Cell Populations - Waldherr, Steffen; Trennt, Philip; Hussain, Mubashir (Life Sciences Letters, 2016)
The modeling of heterogeneous dynamic cell populations based on population balance equations is an important tool to describe the interaction between intracellular dynamics and population dynamics. However, the numerical simulation of such models remains challenging for models with high-dimensional intracellular dynamics, when these dynamics influence the growth rate of the cells. To cope with this challenge, we propose a hybrid simulation scheme based on the method of partial characteristics. We show that important features of the population density function, such as its moments or marginals, can be approximated by this scheme in a statistically converging way. In a case study with a population of differentiating cells, we illustrate how to obtain the growth dynamics of the individual subpopulations and deduce the extent of cell differentiation under a time-varying stimulus.
EAM Import::2019-03-13

Hydrodynamics at the Navier-Stokes level applied to fast, transient, supersonic granular flows - Almazan Torres, Lidia; Salueña, Clara; Garzó, Vicente; Carrillo, José A.; Pöschel, Thorsten (28th International Symposium on Rarefied Gas Dynamics 2012, RGD 2012, 2012)
We perform two-dimensional hydrodynamic simulations on a paradigmatic problem of granular dynamics, the Faraday instability, using two different approximations to the Navier-Stokes granular equations: the constitutive equations and kinetic coefficients derived from the assumption of vanishing inelasticity (Jenkins-Richman approach) obtained by solving the Enskog equation disks by means of Grad's method, and the ones obtained by solving the Enskog equation with the Chapman-Enskog method (Garzó-Dufty-Lutsko approach). The comparison reveals important qualitative and quantitative differences with respect to the hydrodynamic fields obtained by averaging results from particle simulations of the same system. © 2012 American Institute of Physic
Keywords: Faraday instability; hydrodynamic simulations; molecular dynamics; Rapid granular flows

Hydrodynamics of binary mixtures of granular gases with stochastic coefficient of restitution - Pöschel, Thorsten; Serero, Dan; Gunkelmann, Nina (Journal of Fluid Mechanics, 2015)
A hydrodynamic description of dilute binary gas mixtures comprising smooth inelastic spheres interacting by binary collisions with a random coefficient of restitution is presented. Constitutive relations are derived using the Chapman-Enskog perturbative method, associated with a computer-aided method to allow high-order Sonine polynomial expansions. The transport coefficients obtained are checked against DSMC simulations. The resulting equations are applied to the analysis of a vertically vibrated system. It is shown that differences in the shape of the distributions of the coefficient of restitution are sufficient to produce partial segregation.
Keywords: granular media; granular mixing; kinetic theory

Hydrogen activation on Pt-Sn nanoalloys supported on mixed Sn-Ce oxide films - Neitzel, Armin; Lykhach, Yaroslava; Skala, Tomas; Tsud, Nataliya; Johanek, Viktor; Vorokhta, Mykhailo; Prince, Kevin C.; Matolin, Vladimir; Libuda, Jörg (Physical Chemistry Chemical Physics, 2014)
We have studied the interaction of H-2 with Pt-Sn nanoalloys supported on Sn-Ce mixed oxide films of different composition by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy. The model catalysts are prepared in a three step procedure that involves (i) the preparation of well-ordered CeO2(111) films on Cu(111) followed by subsequent physical vapor deposition of (ii) metallic Sn and (iii) metallic Pt. The formation of mixed Sn-Ce oxide is accompanied by partial reduction of Ce4+ cations to Ce3+. Pt deposition leads to the formation of Pt-Sn nanoalloys accompanied by the partial re-oxidation of Ce3+ to Ce4+. Subsequent annealing promotes further Pt-Sn alloy formation at expense of the Sn content in the Sn-Ce mixed oxide. Adsorption of H-2 on Pt-Sn/Sn-Ce-O at 150 K followed by stepwise annealing results in reversible reduction of Ce cations caused by spillover of dissociated hydrogen between 150 and 300 K. Above 500 K, annealing of Pt-Sn/Sn-Ce-O in a hydrogen atmosphere results in irreversible reduction of Ce cations. This reduction is caused by the reaction of hydrogen with oxygen provided by the mixed oxide substrate via the reverse spillover to Pt-Sn nanoalloy. The extent of the hydrogen and oxygen spillover strongly depends on the amount of Sn in the Sn-Ce mixed-oxide. We observe an enhancement of hydrogen spillover on Pt-Sn/Sn-Ce-O at low Sn concentration as compared to Sn-free Pt/CeO2. Although the extent of hydrogen spillover on Pt-Sn/Sn-Ce-O with high Sn concentration is comparable to Pt/CeO2, the reverse oxygen spillover is substantially suppressed on these samples.

Hydrogenated Anatase: Strong Photocatalytic Dihydrogen Evolution without the Use of a Co-Catalyst - Liu, Ning; Schneider, Christopher; Freitag, Detlef; Venkatesan, Uma Maheswari; Marthala, Venkata; Hartmann, Martin; Winter, Benjamin; Spiecker, Erdmann; Osvet, Andres; Zolnhofer, Eva; Meyer, Karsten; Nakajima, Tomohiko; et al. (Angewandte Chemie International Edition, 2014)
The high-pressure hydrogenation of commercially available anatase or anatase/rutile TiO2 powder can create a photocatalyst for H-2 evolution that is highly effective and stable without the need for any additional co-catalyst. This activation effect cannot be observed for rutile; however, for anatase/rutile mixtures, a strong synergistic effect can be found (similar to results commonly observed for noble-metal-decorated TiO2). EPR and PL measurements indicated the intrinsic co-catalytic activation of anatase TiO2 to be due to specific defect centers formed during hydrogenation. These active centers can be observed specifically for high-pressure hydrogenation; other common reduction treatments do not result in this effect.
Keywords: co-catalyst; hydrogenation; titanium(III); TiO2; water splitting

Hydrogenation and dehydrogenation of nitrogen-doped graphene investigated by X-ray photoelectron spectroscopy - Späth, Florian; Zhao, Wei; Gleichweit, Christoph; Gotterbarm, K.; Bauer, Udo; Höfert, Oliver; Steinrück, Hans-Peter; Papp, Christian (Surface Science, 2015)
We studied the hydrogenation and dehydrogenation of nitrogen-doped graphene (NDG) by in situ high-resolution X-ray photoelectron spectroscopy (XPS) and temperature-programmed XPS (TPXPS). Nitrogen-doped graphene was prepared by low energy nitrogen implantation in pristine graphene on Ni(111). Hydrogenation of NDG was performed by exposure to atomic hydrogen. Upon hydrogenation the XP spectra in the C 1s region reveal one new peak, shifted to lower binding energies as compared to graphene, which is associated with newly formed CH groups. In the N 1s region two ne wpeaks, shifted to higher binding energies are observed; these are associated with hydrogenated pyridinic and graphitic nitrogen. TPXPS spectra reveal a different thermal stability of the two hydrogenated nitrogen species,while the C–H groups of graphene show no significant changes compared to undoped hydrogenated graphene.

Hydrogenation of the liquid organic hydrogen carrier compound dibenzyltoluene – reaction pathway determination by 1H NMR spectroscopy - Do, Truong Giang; Preuster, Patrick; Aslam, Rabya; Bösmann, Andreas; Müller, Karsten; Arlt, Wolfgang; Wasserscheid, Peter (Reaction Chemistry & Engineering, 2016)
The catalytic hydrogenation of the LOHC compound dibenzyltoluene (H0-DBT) was investigated by 1H NMR spectroscopy in order to elucidate the reaction pathway of its charging process with hydrogen in the context of future hydrogen storage applications. Five different reaction pathways during H0-DBT hydrogenation were considered including middle-ring preference (middle-side-side, MSS), side-middle-side order of hydrogenation (SMS), side-ring preference (SSM), simultaneous hydrogenation of all three rings without intermediate formation and statistical hydrogenation without any ring preference. Detailed analysis of the 1H NMR spectra of the H0-DBT hydrogenation over time revealed that the reaction proceeds with a very high preference for the SSM order at temperatures between 120 °C and 200 °C and 50 bar in the presence of a Ru/Al2O3-catalyst. HPLC analysis supported this interpretation by confirming an accumulation of H12-DBT species prior to full hydrogenation to H18-DBT with middle ring hydrogenation as the final step.

Hydrogen bonding mediated orthogonal and reversible self-assembly of porphyrin sensitizers onto TiO2 nanoparticles - Zeininger, Lukas; Lodermeyer, Fabian; Costa Riquelme, Rubén Dario; Guldi, Dirk Michael; Hirsch, Andreas (Chemical Communications, 2016)
We report on the orthogonal, highly directional and reversible self-assembly of porphyrins onto TiO2 nanoparticles by means of hydrogen bonding interactions. Unifying the stable covalent surface attachment of tailored, synthesized Hamilton receptors with the advantages of a non-covalent supramolecular immobilization of porphyrin cyanurates resulted in a redox- and photo-active nanohybrid. The latter was successfully implemented into a new type of supramolecular dye-sensitized solar cells.

Hydrogen spillover monitored by resonant photoemission spectroscopy - Lykhach, Yaroslava; Staudt, Thorsten; Vorokhta, Mykhailo; Skala, Tomas; Johanek, Viktor; Prince, Kevin C.; Matolin, Vladimir; Libuda, Jörg (Journal of Catalysis, 2012)
We have employed resonant photoemission spectroscopy to investigate the phenomenon of hydrogen spillover on well-defined model Pt/ceria catalysts. On Pt/CeO2(111)/Cu(111), hydrogen spillover and reverse spillover give rise to reversible changes of the oxidation state of the surface cerium ions. These changes are monitored with highest sensitivity via resonant enhancement of Ce3+- and Ce4+-related features in the valence band photoemission spectra. The temperature regions are precisely determined in which specific processes such hydrogen spillover, Ce3+ transport, and reverse spillover are activated. (C) 2011 Elsevier Inc. All rights reserved.
Keywords: Ceria; Platinum; Hydrogen; Hydrogen spillover; Model catalyst; Heterogeneous catalysis; Resonant photoemission spectroscopy

Hydrogen storage on metal oxide model clusters using density-functional methods and reliable van der Waals corrections - Görling, Andreas; Bleiziffer, Patrick; Vines Solana, Francesc; Hieringer, Wolfgang; Gebhardt, Julian (Physical Chemistry Chemical Physics, 2014)
We investigate the capability of low-coordinated sites on small model clusters to act as active centers for hydrogen storage. A set of small magic clusters with the formula (XY)(6) (X = Mg, Ba, Be, Zn, Cd, Na, Li, B and Y = O, Se, S, F, I, N) and a "drumlike'' hexagonal shape showing a low coordination number of three was screened. Oxide clusters turned out to be the most promising candidates for hydrogen storage. For these ionic compounds we explored the suitability of different van der Waals (vdW) corrections to density-functional calculations by comparing the respective H-2 physisorption profile to highly accurate CCSD(T) (Coupled Cluster Singles Doubles with perturbative Triples) calculations. The Grimme D3 vdW correction in combination with the Perdew-Burke-Ernzerhof exchange-correlation functional was found to be the best approach compared to CCSD(T) hydrogen physisorption profiles and is, therefore, suited to study these and other light metal oxide systems. H-2 adsorption on sites of oxide model clusters is found to meet the adsorption energy criteria for H-2 storage, with bond strengths ranging from 0.15 to 0.21 eV. Energy profiles and estimates of kinetic constants for the H-2 splitting reaction reveal that H-2 is likely to be adsorbed molecularly on sites of (MgO)(6), (BaO)(6), and (BeO)(6) clusters, suggesting a rapid H-2 uptake/release at operating temperatures and moderate pressures. The small mass of beryllium and magnesium makes such systems appealing for meeting the gravimetric criterion for H-2 storage.

Hydrolysis of a Basic Bismuth Nitrate-Formation and Stability of Novel Bismuth Oxido Clusters - Miersch, Linda; Schlesinger, Maik; Troff, Ralf W.; Schalley, Christoph A.; Rueffer, Tobias; Lang, Heinrich; Zahn, Dirk; Mehring, Michael (Chemistry - A European Journal, 2011)
The synthesis of the nanoscaled bismuth oxido clusters [Bi38O45-(NO3)20(DMSO)28] (NO3)44 DMSO (1 a) and [Bi38O45(OH)2(pTsO)8- (NO3)12(DMSO)24](NO3)24 DMSO 2 H2O (2) starting from the basic bismuth nitrate [Bi6O4(OH)4](NO3)6H2O is reported herein. Single-crystal X-ray diffraction analysis, ESI mass spectrometry, thermogravimetric analysis, and molecular dynamics simulation were used to study the formation, structure, and stability of these large metal oxido clusters. Compounds 1 a and 2 are based on a [Bi38O45]24+ core, which is structurally related to extgreekd-Bi2O3. Examination of the fragmentation pathways of 1 a and 2 by infrared multi-photon dissociation (IRMPD) tandem MS experiments allows the identification of novel bismuth oxido cluster species in the gas phase.
EAM Import::2019-03-13

Hydrothermal growth of highly oriented single crystalline Ta2O5 nanorod arrays and their conversion to Ta3N5 for efficient solar driven water splitting - Su, Zixue; Wang, Lei; Grigorescu, Sabina Georgiana; Lee, Kiyoung; Schmuki, Patrik (Chemical Communications, 2014)
We grow vertically aligned single crystalline Ta2O5 nanorod arrays that can be converted to Ta3N5 nanorod arrays by nitridation. Combined with cobalt phosphate (Co-Pi) as a co-catalyst, such Ta3N5 nanorod photoanodes can yield photocurrent densities of ∼3.6 mA cm-2 at 1.23 VRHE and ∼8.2 mA cm-2 at 1.59 VRHE under AM 1.5G (100 mW cm-2) irradiation.
EAM Import::2019-03-13

Hyperfine coupling constants of the nitrogen and phosphorus atoms: A challenge for exact-exchange density-functional and post-Hartree-Fock methods - Kaupp, Martin; Arbuznikov, Alexei V.; Heßelmann, Andreas; Görling, Andreas (Journal of Chemical Physics, 2010)
The isotropic hyperfine coupling constants of the free N (S4) and P (S4) atoms have been evaluated with high-level post-Hartree-Fock and density-functional methods. The phosphorus hyperfine coupling presents a significant challenge to both types of methods. With large basis sets, MP2 and coupled-cluster singles and doubles calculations give much too small values for the phosphorus atom. Triple excitations are needed in coupled-cluster calculations to achieve reasonable agreement with experiment. None of the standard density functionals reproduce even the correct sign of this hyperfine coupling. Similarly, the computed hyperfine couplings depend crucially on the self-consistent treatment in exact-exchange density-functional theory within the optimized effective potential (OEP) method. Well-balanced auxiliary and orbital basis sets are needed for basis-expansion exact-exchange-only OEP approaches to come close to Hartree-Fock or numerical OEP data. Results from the localized Hartree-Fock and Krieger-Li-Iafrate approximations deviate notably from exact OEP data in spite of very similar total energies. Of the functionals tested, only full exact-exchange methods augmented by a correlation functional gave at least the correct sign of the P (S4) hyperfine coupling but with too low absolute values. The subtle interplay between the spin-polarization contributions of the different core shells has been analyzed, and the influence of even very small changes in the exchange-correlation potential could be identified. © 2010 American Institute of Physics.

Hypericin-bearing magnetic iron oxide nanoparticles for selective drug delivery in photodynamic therapy - Unterweger, Harald; Subatzus, Daniel; Tietze, Rainer; Janko, Christina; Poettler, Marina; Stiegelschmitt, Alfons; Schuster, Matthias; Maake, Caroline; Boccaccini, Aldo R.; Alexiou, Christoph (International Journal of Nanomedicine, 2015)
Combining the concept of magnetic drug targeting and photodynamic therapy is a promising approach for the treatment of cancer. A high selectivity as well as significant fewer side effects can be achieved by this method, since the therapeutic treatment only takes place in the area where accumulation of the particles by an external electromagnet and radiation by a laser system overlap. In this article, a novel hypericin-bearing drug delivery system has been developed by synthesis of superparamagnetic iron oxide nanoparticles (SPIONs) with a hypericin-linked functionalized dextran coating. For that, sterically stabilized dextran-coated SPIONs were produced by coprecipitation and crosslinking with epichlorohydrin to enhance stability. Carboxymethylation of the dextran shell provided a functionalized platform for linking hypericin via glutaraldehyde. Particle sizes obtained by dynamic light scattering were in a range of 55-85 nm, whereas investigation of single magnetite or maghemite particle diameter was performed by transmission electron microscopy and X-ray diffraction and resulted in approximately 4.5-5.0 nm. Surface chemistry of those particles was evaluated by Fourier transform infrared spectroscopy and ζ potential measurements, indicating successful functionalization and dispersal stabilization due to a mixture of steric and electrostatic repulsion. Flow cytometry revealed no toxicity of pure nanoparticles as well as hypericin without exposure to light on Jurkat T-cells, whereas the combination of hypericin, alone or loaded on particles, with light-induced cell death in a concentration and exposure time-dependent manner due to the generation of reactive oxygen species. In conclusion, the combination of SPIONs’ targeting abilities with hypericin’s phototoxic properties represents a promising approach for merging magnetic drug targeting with photodynamic therapy for the treatment of cancer.
Keywords: Hypericin; Magnetic drug targeting; Photodynamic therapy; SPION

Identification of elastoplastic microscopic material parameters within a homogenization scheme - Schmidt, Ulrike; Mergheim, Julia; Steinmann, Paul (International Journal for Numerical Methods in Engineering, 2015)
A two-scale parameter identification approach is investigated. The microscopic material parameters of a two-scale model are identified by comparing macroscopic simulation data with macroscopic full-field measurements of the micro-structured specimen. Gradient-based solution strategies are employed for the optimization problem of the two-scale parameter identification. In particular, two approaches for the gradient calculation are investigated: the finite difference method is compared with a newly introduced semi-analytical scheme. The focus lies on the identification of microscopic elastoplastic material parameters. The presented identification example with artificial data confirms a reduced computational effort and advantageous convergence for the semi-analytical approach within the two-scale parameter identification. A drawback is the increase in memory requirement.

Identifying the apparent and true grinding limit - Knieke, Catharina; Sommer, Marc; Peukert, Wolfgang (Powder Technology, 2009)
Comminution in stirred media mills enables the production of ultrafine particles down to the nanometer range. The grinding results are mainly determined by two contrary mechanisms: particle breakage and agglomeration of the so-created fragments. These competing phenomena often lead to a plateau in particle size above a certain energy input. The degree of agglomeration and therefore the final aggregate size can be controlled by the addition of stabilizers and by the applied shear forces. In this paper the agglomeration behavior of silica particles under different milling and stability conditions is presented. Furthermore the particle breakage behavior in the nanometer range as the other size-determining mechanism will be discussed. In long term grinding experiments with different materials the kinetics of particle breakage as well as the grinding limit as the minimal achievable particle size could be obtained. Graphical abstract In wet grinding processes most materials show after certain milling time no further grinding progress and a plateau in particle size is reached. One can distinguish between the apparent grinding limit, which is an agglomerate size strongly depending on the stability of the suspension, and the true grinding limit. This true grinding limit is determined by microstructural changes inside the particles and can be influenced by material and process parameters.

Immobilization of lipase in cage-type mesoporous organosilicas via covalent bonding and crosslinking - Zhou, Zhou; Piepenbreier, Frank; Marthala, Venkata; Hartmann, Martin; Karbacher, Karl (Catalysis Today, 2015)
Lipase from Thermomyces lanuginosus (TLL) was immobilized in cage-type mesoporous materials via two different protocols, viz, covalent bonding and cross-linking. The comparison between the biocatalysts generated by the two methods on both pure silica mesocellular siliceous foam (MCF) and cage-type large pore mesoporous organosilicas (PMOs) disclosed that cross-linking results in the immobilization of a larger amount of TLL and reduced diffusion problems compared to covalent bonding. Benzene-bridged PMOs positively influence the activity of immobilized lipase due to the hydrophobic properties of the surface. Furthermore, a transesterification reaction in organic solvent was carried out to verify the biocatalytic performance of differently immobilized lipase in both batch and fixed-bed reactors. The results further confirm the superiority of the PMO support compared to MCF and also reveal that the different immobilization protocols strongly influence the activity, stability and specificity of immobilized TLL. Moreover, two commercial available immobilize formed TLL were also used in a fixed-bed reactor under the same condition for comparison. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Lipase; PMO; Enzyme immobilization; CLEA; MCF; Mesoporous

Impact of delayed feedback of arbitrary duration in self-pulsations of a CO2 laser - Junges, Leandro; Gallas, Jason (Journal of the Optical Society of America, 2016)
feedback. Such a laser roughly displays three operational intervals of stability, which we characterize using highresolution stability charts and a video. Contrary to current belief, we find delays smaller than ∼1 μs to strongly “clean complexity,” namely, to prevent chaos and periodic pulsations with many spikes. In contrast, complex pulsations and chaos are significantly enhanced for τ > 1 μs. In this range, one finds a complex alternation of periodic and chaotic phases, which are sensitive to the delay duration. © 2016 Optical Society of America
Keywords: Lasers; carbn dioxide; nonlinear optics; Instabilities and chaos

Impact of oxygen plasma treatment on the device performance of zinc oxide nanoparticle based thin-film transistors - Halik, Marcus; Peukert, Wolfgang; Braunschweig, Björn; Klaumünzer, Martin; Hirschmann, Johannes; Faber, Hendrik (ACS Applied Materials and Interfaces, 2012)
Thin-films of zinc oxide nanoparticles were investigated by photoluminescence spectroscopy and a broad defect-related yellow-green emission was observed. Oxygen plasma treatment was applied in order to reduce the number of defects, and the emission intensity was quenched to 4% of the initial value. Thin-film transistors that incorporate the nanoparticles as active semiconducting layers show an improved device performance after oxygen plasma treatment. The maximum drain current and the charge carrier mobility increased more than 1 order of magnitude up to a nominal value of 23 cm2 V−1 s−1 and the threshold voltage was lowered.
Keywords: nanoparticles; Plasma treatment; thin-film transistors; zinc oxide

Impact of solvents and surfactants on the self-assembly of nanostructured amine functionalized silica spheres for CO2 capture - Berger, Edith; Hahn, Maximilian W.; Przybilla, Thomas; Winter, Benjamin; Spiecker, Erdmann; Jentys, Andreas; Lercher, Johannes A. (Journal of Energy Chemistry, 2016)
Macroscopic SiO2 spheres with a homogeneous amine distribution were synthesized by a one-step emulsion based synthesis approach in a flow column reactor. The CO2 adsorption capacity of the nano structured amine-functionalized silica spheres was studied in absence and presence of H2O. The structural properties were adjusted by varying solvents and surfactants during the synthesis and, at constant amine loadings, were found to be the main factor for influencing the CO2 sorption capacities. Under water-free conditions CO2 is bound to the amino groups via the formation of carbamates, which require two neighboring amino groups to adsorb one CO2 molecule. At constant amine concentrations sorbents with lower surface area allow to establish a higher amine density on the surface, which enhances the CO2 uptake capacities under dry conditions. In presence of H2O the CO2 adsorption changes to 1:1 stoichiometry due to stabilization of carbamates by protonation of H2O and formation of further species such as bicarbonates, which should in principle double the adsorption capacities. Low concentrations of physisorbed H2O (0.3 mmol/g) did not impair the adsorption capacity of the adsorbents for CO2, while at higher water uptakes (0.6 and 1.1 mmol/g) the CO2 uptake is reduced, which could be attributed to capillary condensation of H2O or formation of bulky reaction products blocking inner pores and access to active sites. (C) 2016 Science Press and Dalian Institute of Chemical Physics. All rights reserved.
Keywords: Amines; Bicarbonate; Carbamate; Carbon dioxide; Green solvent; Surfactant; Water (H2O)

Impact of stressing conditions and polymer-surfactant interactions on product characteristics of organic nanoparticles produced by media milling - Konnerth, Christoph-Günther; Flach, Frederik; Breitung-Faes, Sandra; Damm, Cornelia; Schmidt, Jochen; Kwade, Arno; Peukert, Wolfgang (Powder Technology, 2016)
Stirred media milling as a feasible method to produce organic nanoparticles was studied for the polycyclic aromatic hydrocarbon pyrene in aqueous environment using vinylpyrrolidone-vinyl acetate copolymer (KVA 64) and sodium dodecyl sulphate (SDS) as well as hydroxypropylcellulose (HPC-SSL) as stabilising agents during batch and continuous processing. The influence of stressing conditions described by means of stress energy, stress number as well as mass-specific energy input on product particle sizes is presented. Grinding kinetics observed for batch and continuous operation are comparable under similar stressing and formulation conditions. Furthermore, it was found that the use of small grinding media, i.e. stress conditions where low stress energies and high stress numbers apply, are advantageous with respect to fast kinetics and minimum energy consumption. Moreover, the relationship between product characteristics and formulation parameters, i.e. type and concentration of stabilising agents are thoroughly investigated. Complex formation of KVA 64 and SDS has been proven by means of tensiometry and fluorescence spectroscopy. It is demonstrated that solubilisation of pyrene occurs in the system and that product characteristics are not only determined by pure breakage events or colloidal stability issues but also by dissolution and ripening phenomena: Minimum product particle sizes at similar stressing conditions are observed under conditions where solubilisation and ripening are less pronounced, whereas larger product particles are observed in systems with high solubilisation capacities.
EAM Import::2019-03-13

Impact of Sulfur Poisoning on the NOx Uptake of a NOx Storage and Reduction (NSR) Model Catalyst - Happel, Markus; Desikusumastuti, Aine; Sobota, Marek; Laurin, Mathias; Libuda, Jörg (Journal of Physical Chemistry C, 2010)
Toward obtaining it more detailed understanding of the influence of SOx poisoning oil the mechanism of NOx uptake on a NOx storage and reduction (NSR) catalyst, we have performed a model Study under ultrahigh vacuum (UHV) conditions. A Supported model catalyst based oil a thin well-ordered alumina film grown oil a NiAl(110) single crystal is used Onto which BaO and Pd particles are deposited. Time-resolved (TR) infrared reflection absorption spectroscopy (IRAS) is applied to identify the species formed during NO2 uptake on the catalyst surface, which has been pretreated with SO2. These results are compared to the NO2 uptake on the corresponding fresh samples.It is shown that SO2 readily decomposes upon adsorption oil both the pristine Al2O3 surface and the BaO and Pd loaded model systems. NO2 reoxidizes the decomposition products 10 surface sulfites and sulfates. A pronounced influence of the SO2 species oil the interaction with NO2 is observed leading to reduced NO2 uptake and to a change of the preferential adsorption geometry from bridging to monodentate. A comparison of the integral intensity of the nitrate bands oil the Ba-free and the Ba-containing samples Furthermore Suggests that SO2 adsorbs preferentially on Ba2+ centers rather than oil the Al3+ centers.

Impact of twin boundaries on bulk elastic constants: Density-functional theory data for Young's modulus of Ag - Klöffel, Tobias; Bitzek, Erik; Meyer, Bernd (Data in Brief, 2015)
Experimental and theoretical studies on nanowires have reported a size-dependence of the Young's modulus in the axial direction, which has been attributed to the increasing influence of surface stresses with decreasing wire diameter. Internal interfaces and their associated interface stresses could lead to similar changes in the elastic properties. In Kobler et al., however, we reported results from atomistic calculations which showed for Ag that twin boundaries have a negligible effect on the Young's modulus. Here, we present data of density-functional theory calculations of elastic constants and Young's modulus for defect-free bulk Ag as well as for bulk Ag containing dense arrays of twin boundaries. It is shown that rigorous convergence tests are required in order to be able to deduce changes in the elastic properties due to bulk defects in a reliable way.
WW1::1026

Implanted bottom gate for epitaxial graphene on silicon carbide - Waldmann, Daniel; Jobst, Johannes; Fromm, Felix; Speck, Florian; Seyller, Thomas; Krieger, Michael; Weber, Heiko B. (Journal of Physics D-Applied Physics, 2012)
We present a technique to tune the charge density of epitaxial graphene via an electrostatic gate that is buried in the silicon carbide substrate. The result is a device in which graphene remains accessible for further manipulation or investigation. Via nitrogen or phosphor implantation into a silicon carbide wafer and subsequent graphene growth, devices can routinely be fabricated using standard semiconductor technology. We have optimized samples for room temperature as well as for cryogenic temperature operation. Depending on implantation dose and temperature we operate in two gating regimes. In the first, the gating mechanism is similar to a MOSFET, the second is based on a tuned space charge region of the silicon carbide semiconductor. We present a detailed model that describes the two gating regimes and the transition in between. © 2012 IOP Publishing Ltd.
UnivIS-Import:2015-04-14:Pub.2012.nat.dphy.IAP.LAP.implan

Implementation of redox gradients in hydrogen bonded complexes containing N,N-dimethylaniline, flavin and fullerene derivatives - Murakami, Motonobu; Ohkubo, Kei; Hasobe, Taku; Sgobba, Vito; Guldi, Dirk Michael; Wessendorf, Florian; Hirsch, Andreas; Fukuzumi, Shunichi (Journal of Materials Chemistry, 2010)
A variety of supramolecular complexes were formed by associating an electron donor-substituted flavin dyad (10-[4′-(N,N-dimethylamino)phenyl] isoalloxazine: DMA-Fl) and a family of fullerene derivatives that contain single and double hydrogen bond receptors (SRC and DRC). The stoichiometry of the corresponding complexes, that is, DMA-Fl and SRC or DRC, were examined by Job's plot analysis of the absorption changes linked to DMA-Fl at 470 nm. To this end, 1:1 and 1:2 complex stoichiometries were determined for DMA-Fl-SRC and (DMA-Fl) -DRC, respectively. Molecular aggregates in the form of remarkably stable clusters were formed by the fast injection method. Insights into these clusters came from transmission electron microscopy (TEM) measurements, which revealed network configurations for (DMA-Fl-SRC ) with diameters in the range between 200 and 500 nm, while uniform nanoparticles of about 40 nm diameter were discernible for [(DMA-Fl)-DRC]. The highly colored composite clusters were assembled onto an optically transparent electrode covered with nanostructured SnO films by the electrophoretic deposition technique. Important are the photocurrent action spectra providing maximum IPCE values that are twice as high for [(DMA-Fl)-DRC ] than for (DMA-Fl-SRC). To complement these studies the dynamics of electron transfer were investigated by femtosecond laser flash photolysis in the supramolecular clusters (i.e., (DMA-Fl-SRC) and [(DMA-Fl)-DRC ]). As a matter of fact, for the first time we were able to demonstrate the unidirectional electron transfer from the terminal electron donor (N,N-dimethylaniline) moiety to the terminal electron acceptor (fullerene) moiety. © The Royal Society of Chemistry 2010.

Implementation of Single-Walled Carbon Nanohorns into Solar Cell Schemes - Lodermeyer, Fabian; Costa, Ruben Dario; Guldi, Dirk Michael (Advanced Energy Materials, 2017)
Recent advances in dye-sensitized solar cells (DSSC), including the use of nanocarbons, resulted in breakthroughs relevant to both the academic and industrial sectors. Their relevance encompasses, on one hand, the development and integration of novel nanocarbon/dye hybrids for superior light-harvesting and improved charge injection properties and, on the other hand, the integration of nanocarbons into each part of DSSCs for enhancing the charge collection efficiency as well as the dye and electrolyte regeneration processes. In the context of the earlier, control over the electron injection and recombination rates is realized on the molecular level. In the context of the latter, i) the charge transport and charge collection efficiencies in the photoelectrode are increased, ii) the charge recombination processes are reduced, when used as a nanocarbon-based buffer layer, iii) the ion diffusion and catalytic effects into (quasi) solid-state electrolytes are improved, and iv) devices using Pt-free counter electrodes with similar device efficiencies are realized. Leading examples of nanocarbons are graphene, carbon black, multi-walled carbon nanotubes, and single-walled carbon nanotubes. In this review, the focus is on a novel carbon allotrope, namely single-walled carbon nanohorns (SWCNH), which is discussed in depth and in comparison with other nanocarbons.
EAM Import::2019-03-13

Implication of oxygen vacancies on current conduction mechanisms in TiN/Zr1-xAlxO2/TiN metal-insulator-metal structures - Paskaleva, A.; Lemberger, M.; Bauer, A. J.; Frey, Lothar (Journal of Applied Physics, 2011)
The dominating conduction mechanisms through TiN/Zr1-xAlxO2/TiN capacitors have been investigated over a wide temperature range (25 K to 430 K) in order to obtain information about the traps which cause the current transport. Single positive charged oxygen vacancies are the principal transport sites which participate in all mechanisms observed. However, the conduction mostly defined by intrinsic traps could also be strongly influenced by defects originating from undesirable high-k/metal gate interface reactions which could act as real traps or as transport sites.

Improved activity and stability of lipase immobilized in cage-like large pore mesoporous organosilicas - Zhou, Zhou; Inayat, Alexandra; Schwieger, Wilhelm; Hartmann, Martin; Hartmann, Martin (Microporous and Mesoporous Materials, 2012)
Lipase from Thermomyces lanuginosus has been immobilized in different mesoporous organosilicas (PMOs) containing ethane and benzene groups with large cage-like pores. The immobilization of lipase as well as the application of these catalysts in hydrolysis and transesterification reactions is studied in detail. The results show that the structural properties of the support employed have a significant influence on the adsorption capacity. In general, materials with high specific surface areas and pore volumes show high adsorption capacity. However, in the case of monolayer adsorption, the hydrophobicity of the surface has a significant impact on the adsorption efficiency due to strong hydrophobic interactions. Furthermore, the transesterification of vinyl propionate with 1-butanol catalyzed by immobilized lipase was studied. The influence of lipase loading, the effect of water content in the reaction mixture and the influence of different solvents were investigated. The results show that lipase immobilized in the most hydrophobic material (LPbenzene) exhibits excellent catalytic performance, which is attributed to the enhanced interfacial activity of lipase due to the interaction between lipase and the hydrophobic surface of the material. In order to further disclose the influence of the hydrophobic surface on the lipase activity, ATR-FTIR spectroscopy was used to study the secondary structure of lipase immobilized on different supports. The results confirm that a structural transition of entrapped lipase to the open-lid conformation takes place on LPbenzene, which shows that the observed increase in enzymatic activity is triggered by interfacial activation of lipase. (C) 2012 Elsevier Inc. All rights reserved.
Keywords: Cage-like PMOs; Lipase; Transesterification; IR spectroscopy

Improved efficiency of TiO2 nanotubes in dye sensitized solar cells by decoration with TiO2 nanoparticles - Roy, Poulomi; Kim, Dam-Hee; Paramasivam, Indhumati; Schmuki, Patrik (Electrochemistry Communications, 2009)
In the present work we investigate the effect of TiCl_4 treatments on the photoconversion efficiency of TiO_2 arrays used in dye sensitized solar cell. The results clearly show that by an appropriate treatment the decoration of the TiO_2 nanotube arrays with TiO_2 nanocrystallites of a typical size of 3 nm can be achieved. These particles can be converted to mixture of anatase and rutile phase by annealing in air. This decoration of the TiO_2 nanotubes leads to a significantly higher specific dye loading and, for certain annealing treatments, to a doubling of the solar cell efficiency (in our case from 1.9% to 3.8% of AM 1.5 conditions) can be achieved.
EAM Import::2019-03-13

Improved High-Efficiency Perovskite Planar Heterojunction Solar Cells via Incorporation of a Polyelectrolyte Interlayer - Zhang, Hong; Azimi, Seyed Hamed; Hou, Yi; Ameri, Tayebeh; Przybilla, Thomas; Spiecker, Erdmann; Kraft, Mario; Scherf, Ullrich; Brabec, Christoph (Chemistry of Materials, 2014)
No abstract available for this article

Improved manufacturability of ZrO2 MIM capacitors by process stabilizing HfO2 addition - Mueller, J.; Boescke, T. S.; Schroeder, U.; Reinicke, M.; Oberbeck, L.; Zhou, Dayu; Weinreich, W.; Kuecher, P.; Lemberger, M.; Frey, Lothar (Microelectronic Engineering, 2009)
A broad compositional range of the dielectric material Zr1-xHfxO2 was evaluated with respect to its applicability in DRAM storage capacitors. The paper reports on phase composition, crystallization behavior, and electrical properties of the mixed system in planar metal-insulator-metal (MIM) capacitors. Admixture of HfO2 into ZrO2 proved to stabilize the deposition process at high temperatures without degrading the dielectric properties of the film. Compared to pure ZrO2 the 30–40% HfO2 containing films showed improved scalability (capacitance equivalent thickness 0.73 nm at 8 * 10-9 A/cm2) as well as improved reliability.
Keywords: ALD; Capacitor; Dielectric; DRAM; Hafnium; Hafnium zirconate; High-k; Metal-insulator-metal; MIM; Reliability; Zirconium

Improved photoelectrochemical water splitting of hematite nanorods thermally grown on Fe–Ti alloys - Wang, Lei; Lee, Chong-Yong; Schmuki, Patrik (Electrochemistry Communications, 2014)
Here we show that hematite ( extgreeka-Fe2O3) nanostructures with a high water splitting performance can be formed on Fe–Ti alloys using the most simple thermal treatment in air and Ar. The use of the Fe–Ti alloy suppresses the formation of thick suboxide underlayers that are strongly detrimental for the photoconversion efficiency. The formed nanorod structures show an onset potential of up to 0.6–0.7 VRHE. This beneficial effect is attributed to the combination of suppression of a thick suboxide and the nature of the extgreeka-Fe2O3 nanorods after Ar annealing.
EAM Import::2019-03-13

Improved supermolecular second order Mo̸ller-Plesset intermolecular interaction energies using time-dependent density functional response theory - Heßelmann, Andreas (Journal of Chemical Physics, 2008)
The supermolecular second order Møller-Plesset (MP2) intermolecular interaction energy is corrected by employing time-dependent density functional (TDDFT) response theory. This is done by replacing the uncoupled second order dispersion contribution contained in the supermolecular MP2 energy with the coupled dispersion energy obtained from the TDDFT approach. Preliminary results for the rare gas dimers He2, Ne2, and Ar2 and a few structures of the (HF)2 and (H2O)2 dimers show that the conventional MP2 interaction energies are considerably improved by this procedure if compared to coupled cluster singles doubles with perturbative triples [CCSD(T)] interaction energies. However, the quality of the interaction energies obtained in this way strongly depends on the exchange-correlation potential employed in the monomer calculations: It is shown that an exact exchange-only potential surprisingly often performs better than an asymptotically corrected hybrid exchange-correlation potential. Therefore the method proposed in this work is similar to the method by Cybulski and Lytle [J. Chem. Phys., 127, 141102 (2007)] which corrects the supermolecular MP2 energies with a scaled dispersion energy from time-dependent Hartree–Fock. The results in this work are also compared to the combination of density functional theory and intermolecular perturbation theory.
EAM Import::2019-03-13

Improvement of three-phase flow numerical simulations by means of novel hybrid methods - Diez Robles, Lucia; Rauh, Cornelia; Delgado, Antonio (Advanced Powder Technology, 2011)
Numerical simulations of three-phase flows are facing the challenge that their mathematical models include a lot of assumptions and the equation systems often deliver controversial solutions. The object of this study is the improvement of numerical simulations of a three-phase (solid, gas, liquid) flow according to the four-way coupling Eulerian-Eulerian frame. Following the strategy of incorporating a priori knowledge in a system, initial velocity information achieved by several experimental and numerical techniques is implemented in the numerical simulations. Particle image velocimetry (PIV) data are employed in a numeroexperimental hybrid and artificial neural network (ANN) data in numeroneuronal and neuroexperimental hybrids, where the ANNs are trained with numerical or PIV data, respectively. The employment of the three presented hybrid methods affords better convergence of the numerical simulations, delivers more accurate numerical results and enables saving of computational time, thus, more precise information about the behaviour of the fluid mechanical system is faster achieved. © 2011 The Society of Powder Technology Japan.
UnivIS-Import:2015-03-09:Pub.2011.tech.ITC.stmmec.improv_4
Keywords: Hybrid method; Mathematical modelling; Numerical simulation; Three-phase flow

Improving photocurrent generation: Supramolecularly and covalently functionalized single-wall carbon nanotubes-polymer/porphyrin donor-acceptor nanohybrids - Rahman, Aminur; Troeger, Anna; Sgobba, Vito; Guldi, Dirk Michael; Jux, Norbert; Tchoul, Maxim N.; Ford, Warren T.; Mateo-Alonso, Aurelio; Prato, Maurizio (Chemistry - A European Journal, 2008)
Novel nanohybrids based on covalently and noncovalently functionalized single-wall carbon nanotubes (SWNTs) have been prepared and assembled for the construction of photoactive electrodes. Polymer-grafted SWNTs were synthesized by free-radical polymerization of (vinylbenzyl)trimethylammonium chloride. Poly[(vinylbenzyl)trimethylammonium chloride] (PVBTA) was also noncovalently wrapped around SWNTs to form stable, positively charged SWNT/PVBTA suspensions in water. Versatile donor-acceptor nanohybrids were prepared by using the electrostatic/van der Waals interactions between covalent SWNT-PVBTA and/or noncovalent SWNT/PVBTA and porphyrins (HP and/or ZnP ). Several spectroscopic, microscopic, transient, and photoelectrochemical measurements were taken to characterize the resulting supramolecular complexes. Photoexcitation of the nanohybrids afforded long-lived radical ion pairs with lifetimes as long as 2.2 us. In the final part, photoactive electrodes were constructed by using a layer-by-layer technique on an indium tin oxide covered glass support. Photocurrent measurements gave remarkable internal photon-to-current efficiencies of 3.81 and 9.90% for the covalent ZnP-/SWNT-PVBTA and noncovalent ZnP /SWNT/PVBTA complex, respectively, when a potential of 0.5 V was applied. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

Improving the Charge Transport in Self-Assembled Monolayer Field-Effect Transistors: From Theory to Devices - Jäger, Christof; Schmaltz, Thomas; Novak, Michael; Khassanov, Artöm; Vorobiev, Alexei; Hennemann, Matthias; Krause, Andreas; Dietrich, Hanno; Zahn, Dirk; Hirsch, Andreas; Halik, Marcus; Clark, Timothy (Journal of the American Chemical Society, 2013)
A three-pronged approach has been used to design rational improvements in self-assembled monolayer field-effect transistors: classical molecular dynamics (MD) simulations to investigate atomistic structure, large-scale quantum mechanical (QM) calculations for electronic properties, and device fabrication and characterization as the ultimate goal. The MD simulations reveal the effect of using two-component monolayers to achieve intact dielectric insulating layers and a well-defined semiconductor channel. The QM calculations identify improved conduction paths in the monolayers that consist of an optimum mixing ratio of the components. These results have been used both to confirm the predictions of the calculations and to optimize real devices. Monolayers were characterized with X-ray reflectivity measurements and by electronic characterization of complete devices. © 2013 American Chemical Society.

Improving the Performance of Organic Thin-Film Transistors by Ion Doping of Ethylene-Glycol-Based Self-Assembled Monolayer Hybrid Dielectrics - Dietrich, Hanno; Scheiner, Simon; Portilla Berlanga, Luis; Zahn, Dirk; Halik, Marcus (Advanced Materials, 2015)
Tuning the electrostatics of ethylene-glycol-based self-assembled monolayers (SAMs) by doping with ions is shown. Molecular dynamics simulations unravel binding mechanisms and predict dipole strengths of the doped layers. Additionally, by applying such layers as dielectrics in organic thin-film transistors, the incorporated ions are proven to enhance device performance by lowering the threshold voltage and increasing conductivity.

Increased photocurrent response in Nb-doped TiO2 nanotubes - Yang, Mingjun; Jha, Himendra; Liu, Ning; Schmuki, Patrik (Journal of Materials Chemistry, 2011)
Nb-doped TiO2 nanotube (NT) layers were grown by electrochemical anodization of Ti–Nb alloys. To successfully activate Nb doping the oxide tubes need to be annealed at sufficiently high temperatures (650 °C). For tubes doped with 0.1 wt% Nb not only a considerable increase in the electrical conductivity but also a significantly enhanced photocurrent (superior to any pure TiO2 nanotube layer (anatase or rutile)) was obtained.
EAM Import::2019-03-13

Increased thermal stabilization of polymer photovoltaic cells with oligomeric PCBM - Ramanitra, Hasina H.; Dowland, Simon A.; Bregadiolli, Bruna A.; Salvador, Michael; Silva, Hugo Santos; Begue, Didier; Graeff, Carlos F. O.; Peisert, Heiko; Chasse, Thomas; Rajoelson, Sambatra; Osvet, Andres; Brabec, Christoph; et al. (Journal of Materials Chemistry C, 2016)
The first oligomerisation of phenyl-C-butyric acid methyl ester (PCBM) using a facile atom transfer radical addition polymerization (ATRAP) and its exploitation for organic photovoltaic devices is described. Oligo(phenyl-C-butyric acid methyl ester)-alt-[1,4-bis(bromomethyl)-2,5-bis(octyloxy)benzene] (OPCBMMB) shows opto-electronic properties equivalent to those of PCBM but has a higher glass transition temperature. When mixed with various band gap semiconducting polymers, OPCBMMB delivers performances similar to PCBM but with an enhanced stabilization of the bulk heterojunction in photovoltaic devices on plastic substrates under thermal stress, regardless of the degree of crystallinity of the polymer and without changing opto-electronic propertie
Keywords: Engineering controlled terms: Atom transfer radical polymerization; Electronic properties; Energy gap; Esters; Free radical reactions; Glass transition; Heterojunctions; Oligomers; Photoelectrochemical cells; Photovoltaic cells; Semiconducting polymers; Stabilization; Substrates Atom transfer radical addition; Bulk heterojunction; Degree of crystallinity; Optoelectronic properties; Organic photovoltaic devices; Photovoltaic devices; Polymer photovoltaic cells; Thermal stabilization Engineering main heading: Butyric acid

Increasing temperature of cooling granular gases - Brilliantov, Nikolai; Formella, Arno; Pöschel, Thorsten (Nature Communications, 2018)
The kinetic energy of a force-free granular gas decays monotonously due to inelastic collisions of the particles. For a homogeneous granular gas of identical particles, the corresponding decay of granular temperature is quantified by Haff’s law. Here, we report that for a granular gas of aggregating particles, the granular temperature does not necessarily decay but may even increase. Surprisingly, the increase of temperature is accompanied by the continuous loss of total gas energy. This stunning effect arises from a subtle interplay between decaying kinetic energy and gradual reduction of the number of degrees of freedom associated with the particles’ dynamics. We derive a set of kinetic equations of Smoluchowski type for the concentrations of aggregates of different sizes and their energies. We find scaling solutions to these equations and a condition for the aggregation mechanism predicting growth of temperature. Numerical direct simulation Monte Carlo results confirm the theoretical predictions.

Increasing the Fill Factor of Inverted P3HT:PCBM Solar Cells Through Surface Modification of Al-Doped ZnO via Phosphonic Acid-Anchored C60 SAMs - Stubhan, Tobias; Salinas Batallas, Michael; Ebel, Alexander; Krebs, Frederick C.; Hirsch, Andreas; Halik, Marcus; Brabec, Christoph (Advanced Energy Materials, 2012)
The influence of aluminum-doped zinc oxide (AZO) electron extraction layers modified with self-assembled monolayers (SAMs) on inverted polymer solar cells is investigated. It is found that AZO modification with phosphonic acid anchored Fullerene–SAMs leads to a reduction of the series resistance, while increasing the parallel resistance. This results in an increased efficiency from 2.9 to 3.3%.
Keywords: Al-doped ZnO; Aluminum-doped zinc oxide; Electron extraction; Fill factor; Inverted polymer solar cells; Parallel resistance; Phosphonic; Series resistances Engineering controlled terms: Electric resistance; Self assembled monolayers; Solar cells; Zinc oxide Engineering main heading: Organic acids

Indacenodithienothiophene-Based Ternary Organic Solar Cells - Gasparini, Nicola; García-Rodríguez, Amaranda; Prosa, Mario; Bayseç, Sebnem; Cando, Alex Palma; Katsouras, Athanasios; Avgeropoulos, Apostolos; Pagona, Georgia; Gregoriou, Vasilis G.; Chochos, Christos L.; Allard, Sybille; Scherf, Ullrich; et al. (Frontiers in Energy Research, 2017)
One of the key aspects to achieve high efficiency in ternary bulk-hetorojunction solar cells is the physical and chemical compatibility between the donor materials. Here, we report the synthesis of a novel conjugated polymer (P1) containing alternating pyridyl[2,1,3]thiadiazole between two different donor fragments, dithienosilole and indacenodithienothiophene (IDTT), used as a sensitizer in a host system of indacenodithieno[3,2-b]thiophene,2,3-bis(3-(octyloxy)phenyl)quinoxaline (PIDTTQ) and [6,6]-phenyl C70 butyric acid methyl ester (PC71BM). We found that the use of the same IDTT unit in the host and guest materials does not lead to significant changes in the morphology of the ternary blend compared to the host binary. With the complementary use of optoelectronic characterizations, we found that the ternary cells suffer from a lower mobility-lifetime (μτ) product, adversely impacting the fill factor. However, the significant light harvesting in the near infrared region improvement, compensating the transport losses, results in an overall power conversion efficiency enhancement of 7% for ternary blends as compared to the PIDTTQ:PC71BM devices.
Keywords: organic solar cells; ternary devices; OPV; IDTT; organic electronics

Indentation and Self-Healing Mechanisms of a Self-Assembled Monolayer-A Combined Experimental and Modeling Study - Meltzer, Christian; Paul, Jonas; Dietrich, Hanno; Jäger, Christof; Clark, Timothy; Zahn, Dirk; Braunschweig, Björn; Peukert, Wolfgang (Journal of the American Chemical Society, 2014)
A combination of in situ vibrational sum-frequency generation (SFG) spectroscopy and molecular-dynamics (MD) simulations has allowed us to study the effects of indentation of self-assembled octadecylphosphonic acid (ODPA) monolayers on α-Al2O3(0001). Stress-induced changes in the vibrational signatures of C-H stretching vibrations in SFG spectra and the results of MD simulations provide clear evidence for an increase in gauche-defect density in the monolayer as a response to indentation. A stress-dependent analysis indicates that the defect density reaches saturation at approximately 155 MPa. After stress is released, the MD simulations show an almost instantaneous healing of pressure-induced defects in good agreement with experimental results. The lateral extent of the contact areas was studied with colocalized SFG spectroscopy and compared to theoretical predictions for pressure gradients from Hertzian contact theory. SFG experiments reveal a gradual increase in gauche-defect density with pressure before saturation close to the contact center. Furthermore, our MD simulations show a spatial anisotropy of pressure-induced effects within ODPA domains: molecules tilted in the direction of the pressure gradient increase in tilt angle while those on the opposite side form gauche-defects.
Keywords: spectroscopy; monolayer; self-assembly

Individualization and Stabilization of Zinc Oxide Nanorods by Covalent Functionalization with Positively Charged Catechol Derivatives - Burger, Alexandra; Srikantharajah, Rubitha; Peukert, Wolfgang; Hirsch, Andreas (Chemistry - A European Journal, 2017)
We present the formation of individualized and stabilized zinc oxide (ZnO) nanorods by functionalization with positively charged catechol derivatives by means of ligand exchange reactions. The electrosteric stabilization of ZnO nanorods was studied using two catechol derivatives, introducing either three(1) or six(2) pH independent positive charges per molecule and sterically demanding groups onto the surface. ZnO nanorods providing initially acetate (Ac) or 2-[2-(2-methoxyethoxy)-ethoxy]acetic acid (TODA) ligands on their surface were used. The ligand exchange was performed by using mono and mixed functionalization approaches, utilizing either exclusively the positively charged catechols or mixtures of the latter with small commercially available catechol derivatives, namely 4-methylcatechol (Me-cat), 4-tert-butylcatechol (tBu-cat), and dopamine hydrochloride (Dop). Using a combination of various analytical methods such as zeta potential, dynamic light scattering (DLS), UV/Vis, and scanning electron microscopy (SEM) measurements we found that the initial surfactants on the nanorods surface, the number of positive charges per molecule, the steric demand, and the added amount of the catechol derivative strongly influence the colloidal behavior of the nanorods. Stable suspensions containing individualized ZnO nanorods were successfully formed upon functionalization of ZnO-TODA nanorods with 30monolayers (MLs) of the higher charged catechol (2), as well as using mixtures of 20/10 and 18/10MLs of 2/Dop.
Keywords: catechol; colloidal sabilization; ligand exchange; surface functionalization; ZnO nanorods

Industrially scalable and cost-effective Mn2+ doped ZnxCd1-xS/ZnS nanocrystals with 70% photoluminescence quantum yield, as efficient down-shifting materials in photovoltaics - Levchuk, Ievgen; Wuerth, C.; Krause, F.; Osvet, Andres; Batentschuk, Miroslaw; Resch-Genger, Ute; Kolbeck, Claudia; Herre, Patrick; Steinrück, Hans-Peter; Peukert, Wolfgang; Brabec, Christoph (Energy and Environmental Science, 2016)
We present colloidally stable and highly luminescent ZnxCd1-xS:Mn/ZnS core–shell nanocrystals (NCs) synthesized via a simple non-injection one-pot, two-step synthetic route, which can be easily upscaled. A systematic variation of the reaction component, parameters and thickness of the ZnS shell yielded doped nanocrystals with a very high photoluminescence quantum yield ( extgreekFpl) of 70%, which is the highest value yet reported for these Mn-doped sulfide-semiconductor NCs. These materials can be synthesized with high reproducibility in large quantities of the same high quality, i.e., the same extgreekFpl using accordingly optimized reaction conditions. The application of these zero-reabsorption high quality NCs in the light conversion layers, deposited on top of a commercial monocrystalline silicon (mono-Si) solar cell, led to a significant enhancement of the external quantum efficiency (EQE) of this device in the ultraviolet spectral region between 300 and 400 nm up to ca. 12%. EQE enhancement is reflected by an increase in the power conversion efficiency (PCE) by nearly 0.5 percentage points and approached the theoretical limit (0.6%) expected from down-shifting for this Si solar cell. The resulting PCE may result in a BoM (bill of materials) cost reduction of app. 3% for mono-Si photovoltaic modules. Such small but distinct improvements are expected to pave the road for an industrial application of doped semiconductor NCs as cost-effective light converters for silicon photovoltaic (PV) and other optoelectronic applications.
EAM Import::2019-03-14

Inexpensive Mie scattering experiment for the classroom manufactured by 3D printing - Scholz, Christian; Sack, Achim; Heckel, Michael; Pöschel, Thorsten (European Journal of Physics, 2016)
Scattering experiments are fundamental for structure analysis of matter on molecular, atomic and sub-atomic length scales. In contrast, it is not standard to demonstrate optical scattering experiments on the undergraduate level beyond simple diffraction gratings. We present an inexpensive Mie scattering setup manufactured with 3D printing and open hardware. The experiment can be used to determine the particle size in dilute monodisperse colloidal suspensions with surprisingly high accuracy and is, thus, suitable to demonstrate relations between scattering measurements and microscopic properties of particles within undergraduate lab course projects.
Keywords: Mie scattering; physics education experiments; 3D printing; open hardware

Inferring spatial organization of bonds within adhesion clusters by exploiting fluctuations of soft interfaces - Smith, Ana-Suncana; Fenz, S. F.; Sengupta, Kheya (EPL - Europhysics Letters, 2010)
Detecting the organization of bonds within adhesion domains connecting two interacting membranes is, at present, extremely challenging. Herein we present a technique, based on Reflection Interference Contrast Microscopy, which uses spontaneous thermal fluctuations of a soft interface as a tool to identify the organization of specific ligand-receptor bonds. The key is a time-resolved analysis of micro-interferometric data that systematically quantifies fluctuations and enables the detection of their suppression due to the formation of bonds, which, in turn, allows the identification of the bond organization without the use of fluorescent labelling. The identification of a new type of bond organization characterized by sparsely distributed bonds, as well as detection of pinning centres of nanometric size is presented. Copyright (C) EPLA, 2010
Keywords: INTERFERENCE CONTRAST MICROSCOPY; CELL-ADHESION; MULTICOMPONENT MEMBRANES; PHASE-SEPARATION; DIFFUSION

Infinite networks of hubs, spirals, and zig-zag patterns in self-sustained oscillations of a tunnel diode and of an erbium-doped fiber-ring laser - Francke, Ricardo; Pöschel, Thorsten; Gallas, Jason (2013)
A remarkably regular organization of spirals converging to a focal point in control parameter space was recently predicted and then observed in a nonlinear circuit containing two diodes. Such spiral organizations are relatively hard to observe experimentally because they usually emerge very compressed. Here we show that a circuit with a tunnel diode displays not one but two large spiral cascades. We show such cascades to exist over wide parameter ranges and, therefore, we expect them to be easier to observe experimentally. © Springer-Verlag Berlin Heidelberg 2013.

In-flight and collisional dissipation as a mechanism to suppress Fermi acceleration in a breathing Lorentz gas - Fregolente Mendes de Oliveira, Diego; Leonel, Edson D. (Chaos, 2012)
Some dynamical properties for a time dependent Lorentz gas considering both the dissipative and non dissipative dynamics are studied. The model is described by using a four-dimensional nonlinear mapping. For the conservative dynamics, scaling laws are obtained for the behavior of the average velocity for an ensemble of non interacting particles and the unlimited energy growth is confirmed. For the dissipative case, four different kinds of damping forces are considered namely: (i) restitution coefficient which makes the particle experiences a loss of energy upon collisions; and in-flight dissipation given by (ii) F = -eta V-2; (iii) F = -eta V-mu with mu not equal 1 and mu not equal 2 and; (iv) F = -eta V, where eta is the dissipation parameter. Extensive numerical simulations were made and our results confirm that the unlimited energy growth, observed for the conservative dynamics, is suppressed for the dissipative case. The behaviour of the average velocity is described using scaling arguments and classes of universalities are defined. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3697392]

Influence of anisotropic elasticity on the mechanical properties of fivefold twinned nanowires - Niekiel, Florian; Spiecker, Erdmann; Bitzek, Erik (Journal of the Mechanics and Physics of Solids, 2015)
Previous atomistic simulations and experiments have shown an increased Young's modulus and yield strength of fivefold twinned (FT) face-centered cubic metal nanowires (NWs) when compared to single crystalline (SC) NWs of the same orientation. Here we report the results of atomistic simulations of SC and FT Ag, Al, Au, Cu and Ni NWs with diameters between 2 and 50 nm under tension and compression. The simulations show that the differences in Young's modulus between SC and FT NWs are correlated with the elastic anisotropy of the metal, with Al showing a decreased Young's modulus. We develop a simple analytical model based on disclination theory and constraint anisotropic elasticity to explain the trend in the difference of Young's modulus between SC and FT NWs. Taking into account the role of surface stresses and the elastic properties of twin boundaries allows to account for the observed size effect in Young's modulus. The model furthermore explains the different relative yield strengths in tension and compression as well as the material and loading dependent failure mechanisms in FTNWs. (C) 2015 Elsevier Ltd. All rights reserve
Keywords: Fivefold twinning; Numerical algorithms; Anisotropic material; Microstructures; Strengthening and mechanisms

Influence of annealing temperature and measurement ambient on TFTs based on gas phase synthesized ZnO nanoparticles - Walther, Sabine; Schäfer, Stefan; Jank, M. P. M.; Thiem, H.; Peukert, Wolfgang; Frey, Lothar; Ryssel, Heiner (Microelectronic Engineering, 2010)
In this paper, we report on the applicability of gas phase synthesized ZnO nanoparticles for printed electronics. Electrical characteristics of thin film transistors with an active layer based on ZnO nanoparticle dispersions are presented. A low charge carrier mobility and a low Ion/Ioff ratio are found for the devices when measured in nitrogen atmosphere. The mobility is limited by the rough interface between semiconductor and dielectric. Additional electrical measurements in dry air reveal a dependency of the Ion/Ioff ratio on surface states of the ZnO particles. It is shown that adsorption of oxygen on ZnO nanoparticles leads to improved transistor characteristics.
Keywords: Nanoparticle; Printable electronics; Thin film transistor; Zinc oxide

Influence of anodization parameters on the expansion factor of TiO2 nanotubes - Albu, Sergiu; Schmuki, Patrik (Electrochimica Acta, 2013)
Growth of titania nanotubes was carried out in fluoride containing electrolytes using photolithographically defined thin film patterns to determine the amount of expansion when the metal is converted to oxide. This expansion of TiO2 nanotubes is studied for a large set of electrochemical conditions. We show that this parameter strongly depends on the applied anodization potential and the water content in the electrolyte whereas the fluoride content is only of minor influence. Expansion factors were found to vary between 1.3 and 2.8 depending on the anodizing parameters. This variation is explained in terms of efficiency of oxide growth, as well as of chemical composition, density, and porosity of the TiO2 nanotubular array.
EAM Import::2019-03-14

Influence of blend microstructure on bulk heterojunction organic photovoltaic performance - Brabec, Christoph; Heeney, Martin; Mcculloch, Iain; Nelson, Jenny (Chemical Society Reviews, 2011)
The performance of organic photovoltaic devices based upon bulk heterojunction blends of donor and acceptor materials has been shown to be highly dependent on the thin film microstructure. In this tutorial review, we discuss the factors responsible for influencing blend microstructure and how these affect device performance. In particular we discuss how various molecular design approaches can affect the thin film morphology of both the donor and acceptor components, as well as their blend microstructure. We further examine the influence of polymer molecular weight and blend composition upon device performance, and discuss how a variety of processing techniques can be used to control the blend microstructure, leading to improvements in solar cell efficiencies. © 2011 The Royal Society of Chemistry.

Influence of boundary conditions on quantum escape - Fregolente Mendes de Oliveira, Diego; Georgiou, Orestis; Gligoric, Goran; Lazarides, Achilleas; Bodyfelt, Joshua D.; Goussev, Arseni (EPL - Europhysics Letters, 2012)
It has recently been established that quantum statistics can play a crucial role in quantum escape. Here we demonstrate that boundary conditions can be equally important-moreover, in certain cases, may lead to a complete suppression of the escape. Our results are exact and hold for arbitrarily many particles. Copyright (c) EPLA, 2012

Influence of cross-rolling on the mechanical properties of an accumulative roll bonded aluminum alloy AA6014 - Ruppert, Mathis; Höppel, Heinz Werner; Göken, Mathias (Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2014)
Sheets of aluminum AA6014 (AlMgSi) were successfully accumulative roll bonded from T4 condition up to eight cycles. Using the conventional ARB route, processing was on the one hand performed at room temperature. On the other hand, sheets were pre-heated in a furnace for 2.5 min at 210 °C prior to each rolling step. Besides the conventional ARB route an ARB cross-rolling route, where the rolling direction is rotated around 90° after each cycle, was used at room temperature. For all three processing conditions an ultrafine-grained microstructure was obtained. Due to a change in strain path, the ultimate tensile strength and the yield strength of the cross-rolled AA6014 exceed those of the samples processed by conventional ARB. However, a strong decrease in terms of elongation to failure is visible after 6–8 cycles of ARB compared to the pre-heated ARB sheets. Fracture analysis reveals necking of individual layers for the samples processed at room temperature. Therefore, after 7 cycles of cross-rolling at RT, one last cross-rolling step at elevated temperature was performed in order to improve bonding quality. This leads to a high strength of about 475 MPa and a satisfactory elongation to failure of about 10%.
WW1::999

Influence of different anions on the surface composition of ionic liquids studied using ARXPS - Kolbeck, Claudia; Cremer, Till; Lovelock, Kevin; Paape, Natalia; Schulz, Peter; Wasserscheid, Peter; Maier, Florian; Steinrück, Hans-Peter (Journal of Physical Chemistry B, 2009)
Angle-resolved X-ray photoelectron spectroscopy has been used to study the influence of different types of anions on the surface composition of ionic liquids (ILs). We have investigated nine ILs with the same cation, 1-octyl-3-methylimidazolium [CCIm], but very different anions. In all cases, an enrichment of the cation alkyl chains is found at the expense of the polar cation head groups and the anions in the first molecular layer. This enhancement effect decreases with increasing size of the anion, which means it is most pronounced for the smallest anions and least pronounced for the largest anions. A simple model is proposed to explain the experimental observations. © 2009 American Chemical Society.

Influence of different substituents on the surface composition of ionic liquids studied using ARXPS - Lovelock, Kevin; Kolbeck, Claudia; Cremer, Till; Paape, Natalia; Schulz, Peter; Wasserscheid, Peter; Maier, Florian; Steinrück, Hans-Peter (Journal of Physical Chemistry B, 2009)
Angle resolved X-ray photoelectron spectroscopy has been used to study the surface composition of various nonfunctionalized and functionalized 1,3-dialkylimidazolium ionic liquids. For [C C Im][Tf N] (where n ) 2-16), an enrichment of the aliphatic carbon was observed for longer chains (n ≥ 4). Enrichment of the aliphatic carbon also occurs for alkyl chains attached to the anion, as observed for [C C Im][OcOSO ]. Oligo(ethyleneglycol)ether (PEG) functionalities in the cation lead to a surface composition close to bulk stoichiometry and thus a loss in enrichment of the chains. This effect is attributed to attractive interactions between the oxygen atoms on the cation to the hydrogen atoms on the imidazolium ring for [Et(EG) MIm][Tf N] and [Me(EG) MIm][Tf N]. © 2009 American Chemical Society.

Influence of Electron Doping on the Hydrogenation of Fullerene C60: A Theoretical Investigation - Dral, Pavlo; Shubina, Tatyana; Hirsch, Andreas; Clark, Timothy (ChemPhysChem, 2011)
The influence of electron attachment on the stability of the mono-and dihydrogenated buckminsterfullerene C was studied using density functional theory and semiempirical molecular orbital techniques. We have also assessed the reliability of computationally accessible methods that are important for investigating the reactivity of graphenic species and surfaces in general. The B3LYP and M06L functionals with the 6-311+G(d,p) basis set and MNDO/c are found to be the best methods for describing the electron affinities of C and C H . It is shown that simple frontier molecular orbital analyses at both the AM1 and B3LYP/6-31G(d) levels are useful for predicting the most favourable position of protonation of C H , that is, formation of the kinetically controlled product 1,9-dihydro[60]fullerene, which is also the thermodynamically controlled product, in agreement with experimental and previous theoretical studies. We have shown that reduction of exo-and endo-C H makes them more stable in contrast to the reduction of the exo,exo-1,9-C H , reduced forms of which decompose more readily, in agreement with experimental electrochemical studies. However, most other dihydro[60]fullerenes are stabilized by reduction and the regioselectivity of addition is predicted to decrease as the less stable isomers are stabilized more by the addition of electrons than the two most stable ones (1,9 and 1,7). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of FIB patterning strategies on the shape of 3D structures: Comparison of experiments with simulations - Rommel, Mathias; Jambreck, J. D.; Ebm, C.; Platzgummer, E.; Bauer, A. J.; Frey, Lothar (Microelectronic Engineering, 2010)
Today's focused ion beam (FIB) systems enable the fast and flexible fabrication of 3D structures with dimensions well below 100 nm. Due to secondary effects like redeposition of sputtered material, however, the fabrication of a targeted shape of the structure is not simple at all. In this work, the influence of the patterning strategy during the sputtering on the shape of a 3D structure with rotational symmetry is studied. Highly different shapes of 3D structures are achieved only due to different rastering strategies or duration times of the ion beam at each raster pixel. The final structure shape can be properly modeled with IonShaper∘ledR simulations. These results clearly prove that the selection of the patterning strategy is the key for appropriate FIB processing of 3D structures. Besides, it is shown that unconventional patterning strategies might enable new types of 3D shapes.
Keywords: FIB; FIB patterning; Focused ion beam; Patterning simulation; Patterning strategy

Influence of hydrodynamic conditions on growth and geometry of anodic TiO2 nanotubes and their use towards optimized DSSCs - Sanchez-Tovar, R.; Paramasivam, Indhumati; Lee, Kiyoung; Schmuki, Patrik (Journal of Materials Chemistry, 2012)
In the present work we grow anodic TiO2 nanotube layers under defined hydrodynamic conditions using a rotating Ti anode. We show that hydrodynamic control can be beneficially used to achieve two main effects. First, under conditions where tube growth is controlled by diffusion (for low concentration of fluoride ions in the electrolyte), growth can significantly be accelerated (or even be enabled) by increasing flow rates in the electrolyte. Second, ill-defined nanotube top morphologies can be avoided – this is particularly important in view of designing optimum tube geometries for the use of TiO2 nanotube layers in photoelectrochemical applications such as DSSCs.
EAM Import::2019-03-14

Influence of MWCNT dispersion on corrosion behaviour of their Mg composites - Li, Qianqian; Turhan, Can Metehan; Rottmair, Christian A.; Singer, Robert; Virtanen, Sannakaisa (Materials and Corrosion - Werkstoffe und Korrosion, 2012)
Carbon nanotubes (CNTs) have been demonstrated as good reinforcements to improve mechanical properties of magnesium alloys. This study reports on the influence of CNT dispersion on corrosion behaviour of their Mg composites. Experiments revealed that the corrosion rate is drastically increased by adding CNTs to the magnesium alloy due to galvanic coupling. Moreover, a homogeneous CNT dispersion leads to reduced corrosion resistivity. Surface pre-treatment is also found to be critical for the corrosion performance for both 1 and 5 wt% CNT composites.

Influence of Nanoparticle Reinforcement on the Mechanical Properties of Ultrafine-Grained Aluminium Produced by ARB - Schmidt, Christian; Knieke, Catharina; Maier, Verena; Höppel, Heinz Werner; Peukert, Wolfgang; Göken, Mathias (Materials Science Forum, 2011)
Dispersed nanoparticles are introduced from stabilized suspensions during the accumulative roll bonding process in aluminium AA1050A by air gun spraying up to a final volume fraction of 0.1 % after eight cycles. Additional strengthening caused by particle insertion is observed and strongly depends on the suspension medium and stabilizing agent as both influence interfacial bonding of the particles to the matrix. The particle insertion furthermore results in reduced peel strength of the sheets irrespective of particle material and size caused by a reduction of effective metal to metal bonding area during rolling through the presence of the particle

Influence of process parameters on breakage kinetics and grinding limit at the nanoscale - Knieke, Catharina; Romeis, Stefan; Peukert, Wolfgang (Aiche Journal, 2011)
In long-term milling experiments, in a stirred media mill, a grinding limit where no further particle breakage occurs was identified. During mechanical stressing of the particles, defects are generated in the crystalline lattice, which allows real fracture of nanoparticles. Below a critical size, defects cannot be stored or generated in the crystallites and the overall limit of grinding is reached. This limit is strongly influenced by material properties and hardly affected by most of the process conditions. However, the breakage kinetics strongly depend on the process parameters and suspension conditions as long as the grinding limit is not reached. Based on these findings, two mechanisms of nanoparticle breakage are proposed. Proper choice of process parameters saves not only up to 90% of the energy input to reach the grinding limit but also leads to a higher product quality in terms of crystallinity and less milling bead wear.

Influence of Resolution of Rasterized Geometries on Porosity and Specific Surface Area Exemplified for Model Geometries of Porous Media - Heidig, Tobias; Zeiser, Thomas; Freund, Hannsjörg (Transport in Porous Media, 2017)
Rasterized representations of geometrical structures are commonplace in science and engineering. They are used in analysis and design of complex geometrical structures; however, the introduced errors for volume and surface estimation are often not considered in detail. To provide insight and information on these effects, in this study model geometries of porous media (simple cubic, body-centered cubic, face-centered cubic) are used to investigate the influence of resolution (voxels per length) on volume and surface approximation. The numerically obtained results are compared with analytical solutions for porosity and specific surface area. Small deviations from the real volume are found for the rasterized geometry at reasonable resolution. For the estimated surface area, in contrast, when using marching cubes considerable deviations from the analytically calculated surface area are found even at relatively fine resolutions. These findings are especially important for the use of rasterized voxel data as input for engineering correlations to estimate characteristic physical transport properties such as pressure drop or effective heat transport.