Abrupt coverage-induced enhancement of the self-metalation of tetraphenylporphyrin with Cu(111) - Röckert, Michael; Ditze, Stefanie; Stark, Michael Werner; Xiao, Jie; Steinrück, Hans-Peter; Marbach, Hubertus; Lytken, Ole (Journal of Physical Chemistry C, 2014)
Using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), the coverage-dependent self-metalation of 2H- tetraphenylporphyrin (2HTPP) with Cu on Cu(111) at 400 K has been studied. At low coverages the porphyrin molecules are adsorbed as isolated molecules, and the rate of metalation is slow. As the coverage is increased beyond ∼0.36 molecules/nm, a supramolecular checkerboard structure is formed, with every second molecule slightly elevated above the surface. The appearance of this checkerboard structure coincides with a dramatic increase in the rate of metalation. This enhancement is attributed to a smaller activation barrier for the elevated molecules, which have an internal conformation similar to that of the free molecule, whereas the less reactive molecules in direct contact with the surface are strongly distorted. © 2013 American Chemical Society.

A combined parametric shape optimization and ersatz material approach - Stingl, Michael; Wein, Fabian (Structural and Multidisciplinary Optimization, 2018)
This article describes a parametric shape optimization approach using vertical or horizontal structures with a fine parametrization of their center lines and profiles. In this context horizontal means a lateral connection from left to right and vertical means a bottom-up connection. These structures are projected to a pseudo density field associated with a fixed mesh using a differentiable mapping. This enables the use of existing topology optimization tools with respect to the solution of the state problem based on the pseudo density field. The approach belongs to a class of geometry projection onto a fictitious domain methods. It therefore shares the property that sensitivity analysis is reduced to extend the well known gradient calculation from topology optimization by chain using the sensitivity of the mapping from shape variables to pseudo density. The contribution lies in the combination with our specific shape parametrization and the associated regularization. Optimization problems can be formulated concurrently in terms of shape variables and pseudo density. We discuss regularization, periodicity constraints, symmetry formulations and overhang constraints in terms of shape variables. Volume and perimeter constraints are easily formulated in terms of the pseudo density. We see our approach as being particularly beneficial for certain problem classes where it may be difficult to restrict the design space, e.g. restricting isolated structures or holes or where a strict control of solid to void transition is necessary. Consequently, we show examples for phononic band gap maximization, boundary driven heat optimization and perimeter maximization for a flow problem. We also present a formulation of overhang constraints for additive manufacturing in terms of shape variables.
Keywords: Parametric shape optimization; Topology optimization

Adaptive Behavior of Dynamic Orthoester Cryptands - Shyshov, Oleksandr; Brachvogel, Rene-Chris; Bachmann, Tobias; Srikantharajah, Rubitha; Segets, Doris; Hampel, Frank; Puchta, Ralph; Von Delius, Max (Angewandte Chemie International Edition, 2017)
The integration of dynamic covalent bonds into macrocycles has been a tremendously successful strategy for investigating noncovalent interactions and identifying effective host–guest pairs. While numerous studies have focused on the dynamic responses of macrocycles and larger cages to various guests, the corresponding constitutionally dynamic chemistry of cryptands remains unexplored. Reported here is that cryptands based on orthoester bridgeheads offer an elegant entry to experiments in which a metal ion selects its preferred host from a dynamic mixture of competing subcomponents. In such dynamic mixtures, the alkali metal ions Li+, Na+, K+, Rb+, and Cs+ exhibit pronounced preferences for the formation of cryptands of certain sizes and donor numbers, and the selection is rationalized by DFT calculations. Reported is also the first self-assembly of a chiral orthoester cryptate and a preliminary study on the use of stereoisomers as subcomponents.
Keywords: cryptands; dynamic combinatorial chemistry; supramolecular chemistry; host–guest chemistry; NMR spectroscopy

Aeromonas proteolytica aminopeptidase: An investigation of the mode of action using a quantum mechanical/molecular mechanical approach - Schürer, Gudrun; Lanig, Harald; Clark, Timothy (Biochemistry, 2004)
The aminopeptidase of Aeromonas proteolytica (AAP) belongs to the group of metallo-hydrolases that require two divalent cations for full activity. Such binuclear metal centers are found in several aminopeptidases, raising the question whether a common mechanism, at least partly, is likely. We have used a quantum mechanical/molecular mechanical (QM/MM) approach to investigate the reaction mechanism of AAP. Among several possibilities, one reaction path was found to be clearly the most favorable. Beside the chemical transformation steps, effects of the enzyme environment and the influence of the solvent on the catalytic reaction were included in the study. The results are in good agreement with experimental studies and correspond to a high degree to our previous QM/MM calculations on the reaction mechanism of the related binuclear bovine lens leucine aminopeptidase (blLAP), which, although related to the AAP, has different Zn2+-coordination spheres and a different catalytic residue. The mechanisms of the two enzymes as suggested in the literature differ on the mode of coordination of the nucleophile and the identity of the general base. However, the results of this and our previous work on blLAP allow us to identify a common mechanism for the two enzymes. This mechanism is probably quite general for binuclear zinc enzymes.

A topical collection on the occasion of Tim Clark's 65th birthday; Editorial - Lanig, Harald; Jaeger, Christof M.; Shubina, Tatyana (Journal of Molecular Modeling, 2015)
UnivIS-Import:2017-12-18:Pub.2015.zwiss.zisc.zentr.atopic

A Universal Ultracentrifuge Spectrometer Visualizes CNT-Intercalant-Surfactant Complexes - Karabudak, Engin; Backes, Claudia; Hauke, Frank; Schmidt, Cordula; Cölfen, Helmut; Hirsch, Andreas; Wohlleben, Wendel (ChemPhysChem, 2010)
Reel them in: Wavelength-resolved movies of the centrifugal fractionation of a single-walled carbon nanotube dispersion (see picture) are used to obtain the composition and absorption profiles of all fractions even in a complex dispersion, where nanotubes have been efficiently solubilized by an intercalant-surfactant mixture. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A widely applicable tool for modeling precipitation processes - Haderlein, Michael; Güldenpfennig, Andreas; Segets, Doris; Peukert, Wolfgang (Computers & Chemical Engineering, 2017)
This work presents a generalized tool for modeling precipitation processes for the parallel formation of multiple solid phases. A symmetric mixing model for T-mixers is presented which mimics the mixing process in a numerically highly efficient way. This model can easily be extended to other reactor types such as stirred tank reactors following the implementation given in this work. Modelling ion activities and ion complexation is strongly accelerated by the analytical formulation of the Jacobian of the corresponding system of equations. Solid formation processes are described via the numerically efficient Direct Quadrature Method of Moments (DQMOM) which is parallelized for treating multiple solid phases simultaneously. Expressions for agglomeration of multiple solid phases and for particle transfer between different mixer zones are given. Both the models of the individual processes and the entire precipitation tool are validated and tested in multiple scenarios proving the flexibility of the tool.
Keywords: Ion complexation; Mixing; Multi-phase; Population Balance Equation; Precipitation; T-Mixer

Comparative Molecular Field Analysis of Dopamine D4 Receptor Antagonists Including 3-[4-(4-Chlorophenyl)piperazin-1-ylmethyl]pyrazolo[1,5-a]pyridine (FAUC 113), 3-[4-(4-Chlorophenyl)piperazin-1-ylmethyl]-1H-pyrrolo[2,3-b]pyridine (L-745,870), and Clozapine - Lanig, Harald; Utz, Wolfgang; Gmeiner, Peter; Lanig, Harald (Journal of Medicinal Chemistry, 2001)
UnivIS-Import:2015-03-09:Pub.2001.nat.dchph.lphch.compar

Conformational Analysis of Tetracycline using Molecular Mechanical and Semiempirical MO-Calculations - Lanig, Harald; Clark, Timothy; Gottschalk, Maik; Schneider, Siegfried (Journal of Molecular Modeling, 1999)
UnivIS-Import:2015-03-05:Pub.1999.nat.dchph.lpc1.confor

Conformations and tautomers of tetracycline - Othersen, Olaf; Beierlein, Frank; Lanig, Harald; Clark, Timothy (Journal of Physical Chemistry B, 2003)
Density functional theory (DFT) has been used to investigate the conformations and tautomeric forms of neutral tetracycline in aqueous solution. The results suggest that the extended conformation is 3-3.5 kcal mol(-1) more stable than the twisted one for equivalent tautomers and that as many as six different tautomeric forms lie within 10 kcal mol(-1) of the most stable one. The energetic preference for the extended conformation is a solvent effect. Calculated infrared, NMR, and UV/vis spectra are used to suggest ways of differentiating between tautomers. and conformations experimentally. It is shown that the (13)C chemical shifts of C4a, C5, and C6 can be used to distinguish between the twisted and extended conformations.

Density gradient ultracentrifugation on carbon nanotubes according to structural integrity as a foundation for an absolute purity evaluation - Backes, Claudia; Bosch, Sebastian; Mundloch, Udo; Hauke, Frank; Hirsch, Andreas; Hauke, Frank (ChemPhysChem, 2011)
Ultrapure: The absolute purity of defect-free and structurally perfect single-walled carbon nanotubes in a bulk sample can be determined with density gradient ultracentrifugation (see picture). The experimental protocol offers a quick and reliable tool and is applicable to a broad variety of nanotube materials to evaluation production and purification procedures. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Determination of the quantum dot band gap dependence on particle size from optical absorbance and transmission electron microscopy measurements - Segets, Doris; Lukas, Matthew; Klupp Taylor, Robin; Scheele, Marcus; Zheng, Haimei; Alivisatos, Pa; Peukert, Wolfgang (Acs Nano, 2012)
This work addresses the determination of arbitrarily shaped particle size distributions (PSDs) from PbS and PbSe quantum dot (QD) optical absorbance spectra in order to arrive at a relationship between band gap energy and particle size over a large size range. Using a modified algorithm which was previously developed for ZnO, we take only bulk absorption data from the literature and match the PSDs derived from QD absorbance spectra with those from transmission electron microscopical (TEM) image analysis in order to arrive at the functional dependence of the band gap on particle size. Additional samples sized solely from their absorbance spectra with our algorithm show excellent agreement with TEM results. We investigate the influence of parameters of the TEM image analysis such as threshold value on the final result. The band gap versus size relationship developed from analysis of just two samples lies well within the bounds of a number of published data sets. We believe that our methodology provides an attractive shortcut for the study of various novel quantum-confined direct band gap semiconductor systems as it permits the band gap energies of a broad size range of QDs to be probed with relatively few synthetic experiments and without quantum mechanical simulations. © 2012 American Chemical Societ
Keywords: absorbance spectra; automated TEM image analysis; optical properties; particle size distribution; PbS(e); quantum dot

Determination of the surfactant density on SWCNTs by analytical ultracentrifugation - Backes, Claudia; Karabudak, Engin; Schmidt, Cordula; Hauke, Frank; Hirsch, Andreas; Wohlleben, Wendel (Chemistry - A European Journal, 2010)
We report on the extensive characterization of single-walled carbon nanotubes (SWCNTs) dispersed in a variety of surfactants, such as sodium dodecyl benzene sulfonate (SDBS), sodium cholate (SC), and three synthesized perylene-based surfactants, by using differential sedimentation in H O and D O. Multidimensional evaluation of the absorption profiles over radius, wavelength, and time allows the determination of the anhydrous specific volumes of the SWCNT-surfactant complexes as well as the concentration of the surfactant reservoir in free micelles with very slow sedimentation coefficients (<1 Svedberg). Among the perylene bisimide surfactants, the smallest derivative is densely adsorbed on the nanotube backbone with an anhydrous specific volume significantly above that of SC or SDBS. Bulky Newkome dendritic groups on one or both ends of the perylene moiety gradually reduce the adsorption density, in accord with the absolute adsorption between 0.66 and 1.7 mmol surfactant per gram SWCNTs. Furthermore, hydrodynamic analysis reveals that SDBS favors the "tails-on" configuration. The distribution of sedimentation coefficients of SWCNTs prepared by high-pressure carbon monoxide decomposition (HiPco) is broader and shifted to faster sedimentation than those prepared by using cobalt-molybdenum catalysis (CoMoCAT), which reflects the polydispersity in diameter and length. Nanotube detergents: Deep insights into the arrangement of various surfactants noncovalently bound to the sidewall of single-walled carbon nanotubes (SWCNTs, see figure) have been obtained by analysis of the sedimentation coefficients with analytical ultracentrifugation. The investigation included classical detergents, as well as synthesized perylene-based surfactants. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Diameter dependence of the defect-induced Raman modes in functionalized carbon nanotubes - Laudenbach, Jan; Schmid, Daniel; Herziger, Felix; Frank, Hennrich; Kappes, Manfred; Muoth, M; Haluska, Miroslav; Hof, Ferdinand; Backes, Claudia; Hauke, Frank; Hirsch, Andreas; Maultzsch, Janina (Carbon, 2017)
Covalent functionalization of single-walled carbon nanotubes typically leads to an intensity increase of the defect-induced Raman mode (D mode). A large intensity ratio of the D and G modes (D/G ratio) is therefore often used as evidence for a successful functionalization. Here, we discuss the effect of the D mode resonance on the D/G ratio and compare pristine and covalently functionalized nanotubes. By resonance Raman spectroscopy we study the evolution of the lineshape and frequencies of the D and 2D modes of samples enriched with semiconducting and metallic nanotubes in comparison with the radial breathing mode. First, we experimentally demonstrate the dependence of the D- and 2D-mode frequencies on the tube diameter and derive an analytical expression for both frequencies as a function of the diameter and the optical transition. Furthermore, we demonstrate that the contribution of the D and 2D modes for small SWCNTs disappears in covalently functionalized samples due to partial destruction. In fact, this can change the measured D/G ratio significantly and has a fundamental impact on the determination of the degree of SWCNT functionalization by Raman spectroscopy. (C) 2016 Elsevier Ltd. All rights reserve

Dispersion of HiPco® and CoMoCAT®single-walled nanotubes (SWNTs) by water soluble pyrene derivatives-depletion of small diameter SWNTs - Backes, Claudia; Mundloch, Udo; Ebel, Alexander; Hauke, Frank; Hirsch, Andreas (Chemistry - A European Journal, 2010)
Nanotube surfactant design: The dispersion of SWNTs by designed surfactants based on water-soluble pyrene derivatives is reported. Significantly, nanotubes with small diameters are depleted in the supernatant after centrifugation, presenting the foundation for future nanotube separation by selective dispersion Chemical Equation Presentation © 2010 Wiley-VCH Verlag GmbH&Co. KGaA.
Keywords: nanotubes; noncovalent functionalization; polycycles; selectivity; surfactants

Enhanced adsorption affinity of anionic perylene-based surfactants towards smaller-diameter SWCNTs - Backes, Claudia; Mundloch, Udo; Schmidt, Cordula; Coleman, Jonathan N.; Wohlleben, Wendel; Hauke, Frank; Hirsch, Andreas (Chemistry - A European Journal, 2010)
We present evidence from multiple characterization methods, such as emission spectroscopy, zeta potential, and analytical ultracentrifugation, to shed light on the adsorption behavior of synthesized perylene surfactants on single-walled carbon nanotubes (SWCNTs). On comparing dispersions of smaller-diameter SWCNTs prepared by using cobalt-molybdenum catalysis (CoMoCAT) with the larger-diameter SWCNTs prepared by high-pressure carbon monoxide decomposition (HiPco), we find that the CoMoCAT-perylene surfactant dispersions are characterized by more negative zeta potentials, and higher anhydrous specific volumes (the latter determined from the sedimentation coefficients by analytical ultracentrifugation), which indicates an increased packing density of the perylene surfactants on nanotubes of smaller diameter. This conclusion is further supported by the subsequent replacement of the perylene derivatives from the nanotube sidewall by sodium dodecyl benzene sulfonate (SDBS), which first occurs on the larger-diameter nanotubes. The enhanced adsorption affinity of the perylene surfactants towards smaller-diameter SWCNTs can be understood in terms of a change in the supramolecular arrangement of the perylene derivatives on the scaffold of the SWCNTs. These findings represent a significant step forward in understanding the noncovalent interaction of π-surfactants with carbon nanotubes, which will enable the design of novel surfactants with enhanced selectivity for certain nanotube species. Nanotube surfactant design: The interactions of synthesized perylene-based surfactants with single-walled carbon nanotubes (SWCNTs) of various diameters have been investigated. The surfactants exhibit an enhanced adsorption affinity towards smaller-diameter SWCNTs (see figure), which could be of great importance for future nanotube separation by selective dispersion. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced Nucleation of Lysozyme Using Inorganic Silica Seed Particles of Different Sizes - Weichsel, Ulrike; Segets, Doris; Janeke, Stefanie; Peukert, Wolfgang (Crystal Growth and Design, 2015)
In this work we investigate the impact of differently sized plain silica nanoparticles (NPs) between 10 and 200 nm on the crystallization of lysozyme (LSZ). In the first part of our work we investigate the electrostatic interactions between LSZ and NPs by zeta potential measurements and place special emphasis on the adsorption behavior of LSZ@SiO2. The determined adsorption isotherms - derived from UV-vis spectroscopy - indicate that with increasing particle size more LSZ is adsorbed per NP surface area probably due to a size-dependent surface chemistry and the variation of surface curvature. Second, seeded crystallization experiments both at the microliter and milliliter scale and thus close to a technically relevant scale were performed. A clearly extended crystallization window upon the addition of seed particles toward lower protein and salt concentrations was found. Moreover, induction times of crystal formation and crystallization times were considerably reduced. These effects were intensified with the addition of larger seed particles. In general, with the addition of silica seed particles, a shift of the final crystal size distribution to larger structures is observed.

Establishing conditions for simulating hydrophobic solutes in electric fields by molecular dynamics Effects of the long-range van der Waals treatment on the apparent particle mobility - Milicevic, Zoran; Marrink, Siewert J.; Smith, Ana-Suncana; Smith, David M. (Journal of Molecular Modeling, 2014)
Despite considerable effort over the last decade, the interactions between solutes and solvents in the presence of electric fields have not yet been fully understood. A very useful manner in which to study these systems is through the application of molecular dynamics (MD) simulations. However, a number of MD studies have shown a tremendous sensitivity of the migration rate of a hydrophobic solute to the treatment of the long range part of the van der Waals interactions. While the origin of this sensitivity was never explained, the mobility is currently regarded as an artifact of an improper simulation setup. We explain the spread in observed mobilites by performing extensive molecular dynamics simulations using the GROMACS software package on a system consisting of a model hydrophobic object (Lennard-Jones particle) immersed in water both in the presence and absence of a static electric field. We retrieve a unidirectional field-induced mobility of the hydrophobic object when the forces are simply truncated. Careful analysis of the data shows that, only in the specific case of truncated forces, a non-zero van der Waals force acts, on average, on the Lennard-Jones particle. Using the Stokes law we demonstrate that this force yields quantitative agreement with the field-induced mobility found within this setup. In contrast, when the treatment of forces is continuous, no net force is observed. In this manner, we provide a simple explanation for the previously controversial reports.
Keywords: Molecular dynamics; Electrophoretic mobility; Van der Waals interactions; GROMACS

Facile Synthesis of Gallium (III)-Chitosan Complexes as Antibacterial Biomaterial - Akhtar, Muhammad Asim; Hadzhieva, Zoya; Ilyas, Kanwal; Ali, Muhammad Saad; Peukert, Wolfgang; Boccaccini, Aldo R. (Pharmaceutics, 2021)
Even though antibiotic treatment remains one of the most common tools to handle bacterial infections, the excessive antibiotic concentration at the target site may lead to undesired effects. Aiming at the fabrication of antibiotic-free biomaterials for antibacterial applications, in this work, we propose the synthesis of gallium (III)-chitosan (Ga (III)-CS) complexes with six different gallium concentrations via an in situ precipitation method. Fourier Transform infrared spectroscopy indicated the chelation of chitosan with Ga (III) by peak shifts and changes in the relative absorbance of key spectral bands, while energy-dispersive X-ray spectroscopy indicated the homogenous distribution of the metal ions within the polymer matrix. Additionally, similar to CS, all Ga (III)-CS complexes showed hydrophobic behavior during static contact-angle measurements. The antibacterial property of the complexes against both Gram-negative and Gram-positive bacteria was positively correlated with the Ga (III) concentration. Moreover, cell studies confirmed the nontoxic behavior of the complexes against the human osteosarcoma cell line (MG-63 cells) and mouse embryonic fibroblasts cell line (MEFs). Based on the results of this study, new antibiotic-free antibacterial biomaterials based on Ga (III)-CS can be developed, expanding the scope of CS applications in the biomedical field.

Force statistics and correlations in dense granular packings - Müller, Micha-Klaus; Luding, Stefan; Pöschel, Thorsten (Chemical Physics, 2010)
In dense, static, polydisperse granular media under isotropic pressure, the probability density and the correlations of particle-wall contact forces are studied. Furthermore, the probability density functions of the populations of pressures measured with different sized circular pressure cells are examined. The questions answered are: (i) What is the number of contacts that has to be considered so that the measured pressure lies within a certain error margin from its expectation value? (ii) What is the statistics of the pressure probability density as function of the size of the pressure cell? Astonishing non-random correlations between contact forces are evidenced that lead to a rapid decay of the width of the distribution and range at least 10-15 particle diameters. Finally, an experiment is proposed to tackle and better understand this issue. © 2010 Elsevier B.V. All rights reserved.
Keywords: DEM simulations; Dense static granular packings; Force and stress correlations; Pressure cells

Fractioning HiPco and CoMoCAT SWCNTs via density gradient ultracentrifugation by the aid of a novel perylene bisimide derivative surfactant - Backes, Claudia; Hauke, Frank; Schmidt, Cordula; Hirsch, Andreas (Chemical Communications, 2009)
HiPco and CoMoCAT single-walled carbon nanotubes (SWCNT) were fractionated with the aid of a novel perylene bisimide surfactant by combined co-surfactant and replacement density gradient ultracentrifugation (DGU). © The Royal Society of Chemistry 2009.

Functional consequence of fibulin-4 missense mutations associated with vascular and skeletal abnormalities and cutis laxa - Sasaki, Takako; Hanisch, Franz-Georg; Deutzmann, Rainer; Sakai, Lynn Y.; Sakuma, Tetsushi; Miyamoto, Tatsuo; Yamamoto, Takashi; Hannappel, Ewald; Chu, Mon-Li; Lanig, Harald; Mark, Klaus (Matrix Biology, 2016)
Fibulin-4 is a 60kDa calcium binding glycoprotein that has an important role in development and integrity of extracellular matrices. It interacts with elastin, fibrillin-1 and collagen IV as well as with lysyl oxidases and is involved in elastogenesis and cross-link formation. To date, several mutations in the fibulin-4 gene (FBLN4/EFEMP2) are known in patients whose major symptoms are vascular deformities, aneurysm, cutis laxa, joint laxity, or arachnodactyly. The pathogenetic mechanisms how these mutations translate into the clinical phenotype are, however, poorly understood. In order to elucidate these mechanisms, we expressed fibulin-4 mutants recombinantly in HEK293 cells, purified the proteins in native forms and analyzed alterations in protein synthesis, secretion, matrix assembly, and interaction with other proteins in relation to wild type fibulin-4. Our studies show that different mutations affect these properties in multiple ways, resulting in fibulin-4 deficiency and/or impaired ability to form elastic fibers. The substitutions E126K and C267Y impaired secretion of the protein, but not mRNA synthesis. Furthermore, the E126K mutant showed less resistance to proteases, reduced binding to collagen IV and fibrillin-1, as well as to LTBP1s and LTBP4s. The A397T mutation introduced an extra O-glycosylation site and deleted binding to LTBP1s. We show that fibulin-4 binds stronger than fibulin-3 and -5 to LTBP1s, 3, and 4s, and to the lysyl oxidases LOX and LOXL1; the binding of fibulin-4 to the LOX propeptide was strongly reduced by the mutation E57K. These findings show that different mutations in the fibulin-4 gene result in different molecular defects affecting secretion rates, protein stability, LOX-induced cross-linking, or binding to other ECM components and molecules of the TGF-? pathway, and thus illustrate the complex role of fibulin-4 in connective tissue assembly.
EVALuna2:10217

High population of individualized SWCNTs through the adsorption of water-soluble perylenes - Backes, Claudia; Schmidt, Cordula; Hauke, Frank; Böttcher, Christoph; Hirsch, Andreas; Hauke, Frank (Journal of the American Chemical Society, 2009)
The aqueous dispersion of SWCNTs in the presence of the water-soluble perylene derivatives 1 -3 is reported. Significantly, even very low concentrations of the perylenes such as 0.01 wt% of the amphiphilic derivative 3, cause an efficient dissolution of the SWCNTs in water accompanied by a very pronounced individualization. The individualization of SWCNTs in water after ultrasonication in the presence of water-soluble aromatic perylenes was investigated in detail by absorption, emission, and Raman spectroscopy as well as by AFM and cryo-TEM. These studies also revealed that the individualization of the SWCNTs caused by the adsorption of 3 is much more effective than that induced by SDBS, which is the most frequently used surfactant for SWCNT dispersion in water. The π-π-stacking interaction and the electronic interaction between the perylene unit and the nanotube surface is reflected, for example, by the distinct absorption and emission features in the UV/vis/nIR, which differ significantly from those observed for SWNTs dispersed in the presence of SDBS and by the quenching of the perylene fluorescence of 3 when being in contact with the tubes. © 2009 American Chemical Society.

In Situ Study on the Evolution of Multimodal Particle Size Distributions of ZnO Quantum Dots: Some General Rules for the Occurrence of Multimodalities - Schindler, Torben; Walter, Johannes; Peukert, Wolfgang; Segets, Doris; Unruh, Tobias (Journal of Physical Chemistry B, 2015)
Properties of small semiconductor nanoparticles (NPs) are strongly governed by their size. Precise characterization is a key requirement for tailored dispersities and thus for high-quality devices. Results of a careful analysis of particle size distributions (PSDs) of ZnO are presented combining advantages of UV/vis absorption spectroscopy, analytical ultracentrifugation, and small-angle X-ray scattering (SAXS). Our study reveals that careful cross-validation of these different methods is mandatory to end up with reliable resolution. PSDs of ZnO NPs are multimodal on a size range of 2-8 nm, a finding that is not yet sufficiently addressed. In the second part of our work the evolution of PSDs was studied using in situ SAXS. General principles for the appearance of multimodalities covering a temperature range between 15 and 45 °C were found which are solely determined by the aging state indicated by the size of the medium-sized fraction. Whenever this fraction exceeds a critical diameter, a new multimodality is identified, independent of the particular time-temperature combination. A fraction of larger particles aggregates first before a fraction of smaller particles is detected. Fixed multimodalities have not yet been addressed adequately and could only be evidenced due to careful size analysis.

Janssen effect in dynamic particulate systems - Windows-Yule, C. R. K.; Mühlbauer, Sebastian; Torres Cisneros, Luis Armando; Nair, Prapanch; Marzulli, Valentina; Pöschel, Thorsten (Physical Review E, 2019)
The Janssen model of stress redistribution within laterally bounded particulate assemblies is a longstanding and valuable theoretical framework, widely used in the design of industrial systems. However, the model relies on the assumption of a static packing of particles and has never been tested in a truly dynamic regime nor for a constraining system whose geometry is dynamically altered. In this paper, we explore the pressure distributions of granular beds housed within a container possessing a laterally mobile sidewall, allowing the depth, height, and cross-sectional areas of the systems studied to be dynamically altered, thus, inducing particle rearrangements and flow in the particulate system constrained thereby. We demonstrate that the systems studied can be successfully described by the Janssen model across a wide range of system expansion rates, including those for which liquidlike flow is clearly observed and propose an extension to the model allowing for an improved characterization of constrained dynamic systems.
CRIS-Team WoS Importer:2019-09-06

Manipulating single-wall carbon nanotubes by chemical doping and charge transfer with perylene dyes - Ehli, Christian; Oelsner, Christian; Guldi, Dirk Michael; Mateo-Alonso, Aurelio; Prato, Maurizio; Schmidt, Cordula; Backes, Claudia; Hauke, Frank; Hirsch, Andreas; Hauke, Frank (Nature Chemistry, 2009)
Single-wall carbon nanotubes (SWNTs) are emerging as materials with much potential in several disciplines, in particular in electronics and photovoltaics. The combination of SWNTs with electron donors or acceptors generates active materials, which can produce electrical energy when irradiated. However, SWNTs are very elusive species when characterization of their metastable states is required. This problem mainly arises because of the polydispersive nature of SWNT samples and the inevitable presence of SWNTs in bundles of different sizes. Here, we report the complete and thorough characterization of an SWNT radical ion-pair state induced by complexation with a perylene dye, which combines excellent electron-accepting and-conducting features with a five-fused ring-system. At the same time, the perylene dye enables the dispersion of SWNTs by means of- interactions, which gives individual SWNTs in solution. This work clears a path towards electronic and optoelectronic devices in which regulated electrical transport properties are important. © 2009 Macmillan Publishers Limited. All rights reserved.

Mapping charge transport by electroluminescence in chirality-selected carbon nanotube networks - Jakubka, Florian; Backes, Claudia; Gannott, Florentina; Mundloch, Udo; Hauke, Frank; Hirsch, Andreas; Zaumseil, Jana (Acs Nano, 2013)
We demonstrate random network single-walled carbon nanotube (SWNT) field-effect transistors (FETs) in bottom contact/top gate geometry with only five different semiconducting nanotube species that were selected by dispersion with poly(9,9-dioctylfluorene) in toluene. These FETs are highly ambipolar with balanced hole and electron mobilities and emit near-infrared light with narrow peak widths (<40 meV) and good efficiency. We spatially resolve the electroluminescence from the channel region during a gate voltage sweep and can thus trace charge transport paths through the SWNT thin film. A shift of emission intensity to large diameter nanotubes and gate-voltage-dependent photoluminescence quenching of the different nanotube species indicates excitation transfer within the network and preferential charge accumulation on small band gap nanotubes. Apart from applications as near-infrared emitters with selectable emission wavelengths and narrow line widths, these devices will help to understand and model charge transport in realistic carbon nanotube networks. © 2013 American Chemical Society.

Modeling the Similarity and Divergence of Dopamine D2-like Receptors and Identification of Validated Ligand-Receptor Complexes - Böckler, Frank; Lanig, Harald; Gmeiner, Peter (Journal of Medicinal Chemistry, 2005)
Focusing on the similarity and divergence of GPCR subtypes and their ligand interactions, we generated dopamine D2, D3, and D 4 receptor models based on the rhodopsin crystal structure and refined these with an extensive MM/MD protocol. After validation by diagnostic experimental data, subtype-specific relative positions of TM1, 2, 6, and 7 and bending angles of TM7 were found. To sample the conformational space of the complex, we performed simulated-annealing runs of the receptor protein with the sub-nanomolar antagonist spiperone. Docking a representative set of ligands, we were able to identify one superior model for each subtype when excellent correlations between predicted energies of binding and experimental affinities (r2 = 0.72 for D2, 0.91 for D3 and 0.77 for D4) could be observed. Further analysis revealed general ligand interactions with ASP3.32 and aromatic residues in TM6/7 and individual key interactions with TM1 and TM2 residues of the D3 and D4 receptor models, respectively.
UnivIS-Import:2015-03-09:Pub.2005.nat.dchph.lphch.modeli

Molecular Building Kit of Fused-Proline-Derived Peptide Mimetics Allowing Specific Adjustment of the Dihedral Psi Angle - Einsiedel, Jürgen; Lanig, Harald; Waibel, Reiner; Gmeiner, Peter (Journal of Organic Chemistry, 2007)
(Chemical Equation Presented) Proline-derived peptide mimetics have become an area of paramount importance in peptide and protein chemistry. Since protein crystal structures frequently display Ψ angles of 140-170° for prolyl moieties, our intention was to design a completely novel series of 2,3-fused-proline-derived lactams covering this particular conformational space. Extending our recently described toolset of spirocyclic reverse-turn mimetics, we synthesized pyrrolidinyl-fused seven-, eight-, and nine-membered unsaturated lactam model peptides taking advantage of Grubbs' ring-closing metathesis. Investigating the seven-membered lactam 3a by means of IR and NMR spectroscopy and semiempirical molecular dynamics simulations, we could not observe a U-turn conformation; however, increasing the ring size to give eight- and nine-membered congeners revealed moderate and high type II β-turn inducing properties. Interestingly, the conformational properties of our model systems depend on both the ring size of the fused dehydro-Freidinger lactam and the position of the endocyclic double bond. Superior reverse-turn inducing properties could be observed for the fused azacyclononenone 3e. According to diagnostic transanular NOEs, a discrete folding principle of the lactam ring strongly deviating from the regioisomeric lactams 3c,f explains the conformational behavior. Hence, we were able to establish a molecular building kit that allows adjustments of a wide range of naturally occurring proline Ψ angles and thus can be exploited to probe molecular recognition and functional properties of biological systems. © 2007 American Chemical Society.
UnivIS-Import:2015-03-09:Pub.2007.nat.dchph.lphch.molecu

Molecular dynamics simulations of the tetracycline-repressor protein: The mechanism of induction - Lanig, Harald; Othersen, Olaf; Beierlein, Frank; Seidel, Ute; Clark, Timothy (Journal of Molecular Biology, 2006)
Molecular dynamics simulations on the tetracycline-repressor (TetR) protein, both in the absence of an inducer and complexed with the inducers tetracycline and 5a,6-anhydrotetracycline, show significant differences in the structures and dynamics of the induced and non-induced forms of the protein. C-alpha-density-difference plots, low-frequency normal vibrations and inter-residue interaction energies all point to a common mechanism of induction. The inducer displaces Asp156 from the magnesium ion in the binding pocket, leading to a short cascade of rearrangements of salt bridges that results in the allosteric change. The increased flexibility of the induced form of the protein is suggested to contribute to the decrease in binding affinity to DNA on induction. (c) 2006 Elsevier Ltd. All rights reserved.
Keywords: tetracycline repressor; molecular dynamics; signal transduction; essential dynamics; low frequency modes

Monitoring biological membrane-potential changes: A CI QM/MM study - Rusu, Catalin Florin; Lanig, Harald; Othersen, Olaf; Kryschi, Carola; Clark, Timothy (Journal of Physical Chemistry B, 2008)
In recent decades, new less-invasive, nonlinear optical methods have been proposed and optimized for monitoring fast physiological processes in biological cells. One of these methods allows the action potential (AP) in cardiomyocytes or neurons to be monitored by means of second-harmonic generation (SHG). We now present the first, to our knowledge, simulations of the dependency of the intensity of the second harmonic (/SHG) on variations of the transmembrane potential (TMP) in a cardiomyocyte during an action potential (AP). For this, an amphiphilic potential-sensitive styryl dye molecule with nonlinear optical properties was embedded in a dipalmitoylphosphatidylcholine (DPPC) bilayer, replacing one of the phospholipid molecules. External electrical fields with different strengths were applied across the membrane to simulate the AP of a heart-muscle cell. We used a combined classical/quantum mechanical approach to model the structure and the spectroscopic properties of the embedded chromophore. Two 10 ns molecular dynamics (MD) simulations provided input geometries for semiempirical molecular orbital (QM/MM) single-point configuration interaction (CI) calculations, which were used to calculate the wavelengths and oscillator strengths of electronic transitions in the di-8-ANEPPS dye molecule. The results were then used in a sum-over-states treatment to calculate the second-order hyperpolarizability. The square of the hyperpolarizability scales with the intensity of the second harmonic, which is used to monitor the action potentials of cardiomyocytes experimentally. Thus, we computed changes in the intensity of the second harmonic (ΔI ) as function of TMP changes. Our results agree well with experimental measurements. © 2008 American Chemical Society.

Nanotube surfactant design: The versatility of water-soluble perylene bisimides - Backes, Claudia; Schmidt, Cordula; Rosenlehner, Karin; Hauke, Frank; Hirsch, Andreas; Coleman, Jonathan N. (Advanced Materials, 2010)
The synthesis of perylene-based single-walled carbon nanotube (SWCNT) surfactants and the dispersion and exfoliation of SWCNTs in water by a variety of designed surfactants is investigated. The quality of the nanotube dispersions is evaluated by optical absorption and emission spectroscopy, zeta-potential measurements and statistical atomic force microscopy (AFM). Significantly the dispersion efficiency can be increased at higher pH, as water solubility of the surfactants is ensured by peripheral derivatization with carboxyl-functionalized first and second-order Newkome dendrimers. Even at very low perylene concentrations of 0.1 g L and a nanotube-to-surfactant ratio of 1:1, the nanotube supernatant after centrifugation contains up to 73% of the pristine material with exfoliation degrees (the number of fractions of individualized nanotubes N/N) of up to 76%. The adsorption of the perylene core to the nanotube scaffold is indicated by red-shifted perylene-absorption and SWCNT-emission features except for the smallest perylene amphiphile, where solubilization is presumably based on a micellar arrangement The nanotube fluorescence is significantly altered and reduced in intensity compared to nanotubes dispersed in sodium dodecylbenzene sulfonate (SDBS) being strongly dependent on the structure of the perylene surfactant. We attribute this observation to the homogeneity of the surfactant coverage, e.g., the supramolecular arrangement onto the nanotube backbone. This study represents a step forward in understanding the structure-property relationship of nanotube surfactants. Furthermore high-quality nanotube dispersions with increased degrees of exfoliation are highly desirable, as the efficiency of nanotube separation techniques relies on highly individualized samples. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

Noncovalent Functionalization of Carbon Nanotubes - Backes, Claudia; Hirsch, Andreas (John Wiley & Sons, Ltd., 2010)

Optical visualization of carbon nanotubes-a unifying linkage between microscopic and spectroscopic characterization techniques - Backes, Claudia; Englert, Jan; Bernhard, Nicolas; Hauke, Frank; Hirsch, Andreas; Hauke, Frank (Small, 2010)
The optical bright- and dark-field visualization (see image) of single-walled carbon nanotubes spin-casted onto Si/SiO2 substrates with a 300-nm-thick oxide coating is reported. This novel procedure gives access to a low-cost correlation of Raman spectroscopy with microscopic techniques (atomic force microscopy, scanning electron microscopy) greatly facilitating nanotube characterization.

Perylene-based nanotweezers: Enrichment of larger-diameter single-walled carbon nanotubes - Backes, Claudia; Schmidt, Cordula; Hauke, Frank; Hirsch, Andreas (Chemistry-An Asian Journal, 2011)
The solubilization of single-walled carbon nanotubes (SWCNTs) by a novel tweezer-shaped molecule with perylene bisimide moieties that act as aromatic anchoring groups is presented. Encouraging results of the tweezer-dispersion concept is combined with the outstanding exfoliation and dispersion efficiencies of designed perylene bisimide derivatives, which have previously turned out as most-powerful SWCNT dispersants. Based on the preferred interaction between the nanotweezer and SWCNTs with diameters larger than 0.8 nm, the supernatant was depleted after mild centrifugation in SWCNT species of smaller diameters. Characterization was carried out by a combination of UV/Vis and nIR absorption spectroscopy as well as emission spectroscopy of the SWCNTs and perylene. This study presents the foundation for a further improvement of selective SWCNT dispersion and sorting by designed molecules. Tubethumping: Selective dispersion of single-walled carbon nanotubes (SWCNTs) in order to preferentially solubilize distinct diameters or even chiralities can be considered as the definitive sorting tool. The enrichment of SWCNTs with diameters larger than 0.8 nm by a novel tweezer-type dispersant with perylene bis(imide) moieties as SWCNT anchor groups is presented. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Quantum mechanical/molecular mechanical (QM/MM) docking: an evaluation for known test systems - Beierlein, Frank; Lanig, Harald; Schürer, Gudrun; Horn, Anselm; Clark, Timothy (Molecular Physics, 2003)
A combined quantum mechanical/molecular mechanical (QM/MM) docking approach for the investigation of protein-inhibitor complexes is presented. Starting points for QM/MM optimizations are generated with AutoDock. The subsequent semiempirical AM1 QM/MM optimization of the complex obtained by the docking procedure gives a more detailed description of the binding mode and the electronic properties of the ligand. As we use a flexible protein environment in the QM/MM optimizations, we are able to simulate limited structural changes of the enzyme upon binding a ligand, even within a simple geometry optimization. The method was validated using a set of structurally known protein-inhibitor complexes, whose crystallographic data were taken from the Protein Data Bank. In addition to protein structures taken directly from complexes with the inhibitors, structures of uncomplexed HIV-1-protease and thrombin were also used successfully for QM/MM docking experiments. By comparing the resulting structures with those obtained using protein structures from protein-inhibitor complexes, we find that the method is able to simulate the effect of the induced fit when a simple optimization is adequate to reproduce the protein movement. Describing the ligand quantum mechanically gives a detailed view of its electronic properties, for example its polarization within the active site of the enzyme. This study suggests strongly that a QM/MM molecular dynamics approach will be able to simulate the induced fit in general cases.

Region-Selective Self-Assembly of Functionalized Carbon Allotropes from Solution - Wang, Zhenxing; Mohammadzadeh, Saeideh; Schmaltz, Thomas; Kirschner, Johannes; Khassanov, Artöm; Eigler, Siegfried; Mundloch, Udo; Backes, Claudia; Steinrück, Hans-Peter; Magerl, Andreas; Hauke, Frank; Hirsch, Andreas; et al. (Acs Nano, 2013)
Approaches for the selective self-assembly of functionalized carbon allotropes from solution are developed and validated for 0D-fullerenes, 1D-carbon nanotubes and 2D-graphene. By choosing the right molecular interaction of self-assembled monolayers (serving the surface) with the functionalization features of carbon materials, which provide the solubility but also serve the driving force for assembly, we demonstrate a region-selective and self-terminating assembly of the materials. Active layers of the carbon allotropes can be selectively deposited in the channel region of thin-film transistor (TFT) devices by this approach. As an example for a 0D system, molecules of C functionalized octadecylphosphonic acids are used to realize self-assembled monolayer field-effect transistors (SAMFETs) based on a selective molecular exchange reaction of stearic acid in the channel region. For noncovalently functionalized single-walled carbon nanotubes (SWCNTs) and graphene oxide (GO) flakes, the electrostatic Coulomb interactions between the functional groups of the carbon allotropes and the charged head groups of a SAM dielectric layer are utilized to implement the selective deposition. © 2013 American Chemical Societ

Reversible thermally induced phase transition in ordered domains of Co(II)-5,10,15,20-tetrakis-(3,5-di-tert-butylphenyl)-porphyrin on Cu(111) - Steinrück, Hans-Peter; Stark, Michael Werner; Ditze, Stefanie; Thomann, Michael; Lungerich, Dominik; Jux, Norbert; Marbach, Hubertus (Surface Science, 2016)
We investigated the adsorption behavior of Co(II)-5,10,15,20-tetrakis-(3,5-di-tert-butylphenyl)-porphyrin (CoTTBPP) on Cu(111) by scanning tunneling microscopy (STM). At room temperature (RT), the coverage dependent adsorption behavior follows an expected scheme: at low coverage step decoration is found, which evolves into supramolecular domains with a hexagonal order at higher coverage. Interestingly, upon cooling the sample to 180 K the occurrence of a clearly distinguishable coexisting herringbone phase is observed. Upon heating to RT again, the herringbone phase vanishes. Thus a temperature dependent, fully reversible phase transition was observed. High resolution STM micrographs allow for the determination of the intramolecular conformations which are different for the two supramolecular arrangements. In addition, we studied the bias voltage dependent appearance of the molecule in STM and assigned a dominant contribution of the central Co at negative bias voltages close to the Fermi edge to the occupied d orbital. Interestingly, the herringbone phase, which dominates at 180 K, exhibits a significantly higher molecular density than the monomodal hexagonal arrangement at RT, which is in line with the "normal" behavior of freezing substances.
Keywords: Bias voltage dependence; Intramolecular conformation; Porphyrin; Reversible phase transition; Scanning tunneling microscopy; Self-assembly

SCRF-DFT and NMR Comparison of Tetracycline and 5a,6-Anhydrotetracycline in Solution - Othersen, Olaf; Waibel, Reiner; Lanig, Harald; Gmeiner, Peter; Clark, Timothy (Journal of Physical Chemistry B, 2006)
A combination of structures, energies, and spectral data calculated using density functional theory (DFT) with experimental NMR data has been used to assign conformational equilibria for tetracycline and 5a,6anhydrotetracycline in water at pH 1, 7, and 10 and in chloroform (5a,6-anhydrotetracycline) and methanol (tetracycline). The results suggest that tetracycline always prefers the extended conformation but that 5a,6anhydrotetracycline exists in water as a mixture of the two conformers and in chloroform exclusively in the twisted conformation. The conformational equilibria are also shown to be pH dependent. © 2006 American Chemical Society.
UnivIS-Import:2015-03-09:Pub.2006.nat.dchph.lphch.adirec

Selective and caspase-independent cytotoxicity of bioactive glasses towards giant cell tumor of bone derived neoplastic stromal cells but not to bone marrow derived stromal cells. - Westhauser, Fabian; Arango Ospina, Marcela; Losch, Sarina; Wilkesmann, Sebastian; Lehner, Burkhard; Ali, Muhammad Saad; Peukert, Wolfgang; Boccaccini, Aldo R.; Fellenberg, Jörg (Biomaterials, 2021)
Semi-malignant giant cell tumors of bone (GCTB) are associated with large osteolytic defects and significant bone destructions. Surgical resection remains the standard therapy that is, however, associated with very high recurrence rates. Bioactive glasses (BGs) that are osteogenic but under certain conditions also cytotoxic might be suitable to achieve biological reconstruction with simultaneous reduction of tumor recurrence in GCTB. In this study, a concentration and time dependent cytotoxic effect of five different BG compositions towards neoplastic GCTB cells was identified while bone marrow derived mesenchymal stromal cells were mostly unaffected. Time course and extent of the cytotoxic effect were dependent on the BG composition and were not associated with caspases activation, indicating that apoptotic mechanisms are not involved. Rather, detection of BG-induced disruption of the cell membranes and a rapid drop of intracellular HMG1 (High Mobility Group Box 1 protein) levels suggest a necrotic cell death. Notably, the cytotoxic effects were dependent on a direct contact of cells and BGs and could not be observed using indirect cultivation settings. Our data suggest that BGs might represent promising materials for the treatment of GCTB in order to reduce tumor recurrence with simultaneous enhancement of bone regeneration.
Keywords: Apoptosis; Bioactive glass; Caspases; Cytotoxicity; Giant cell tumor of bone; Mesenchymal stromal cells; Necrosis

Selective polycarboxylation of semiconducting single-walled carbon nanotubes by reductive sidewall functionalization - Gebhardt, Benjamin; Hof, Ferdinand; Backes, Claudia; Müller, Matthias; Plocke, Thomas; Maultzsch, Janina; Thomsen, Christian; Hauke, Frank; Hirsch, Andreas (Journal of the American Chemical Society, 2011)
The efficient and controllable synthesis, the detailed characterization, and the chemical postfunctionalization of polycarboxylated single-walled carbon nanotubes SWCNT(COOH) are reported. This innovative covalent sidewall functionalization method is characterized by (a) the preservation of the integrity of the entire σ-framework of SWCNTs; (b) the possibility of achieving very high degrees of addition; (c) control of the functionalization degrees by the variation of the reaction conditions (reaction time, ultrasonic treatment, pressure); (d) the identification of conditions for the selective functionalization of semiconducting carbon nanotubes, leaving unfunctionalized metallic tubes behind; (e) the proof that the introduced carboxylic acid functionalities can serve as versatile anchor points for the coupling to functional molecules; and (f) the application of a subsequent thermal degradation step of the functionalized semiconducting tubes leaving behind intact metallic SWCNTs. Functional derivatives have been characterized in detail by means of Raman, UV-vis/nIR, IR, and fluorescence spectroscopy as well as by thermogravimetric analysis combined with mass spectrometry, atomic force microscopy, and zeta-potential measurements. © 2011 American Chemical Society.

Simulating FRET from tryptophan: Is the rotamer model correct? - Beierlein, Frank; Othersen, Olaf; Lanig, Harald; Schneider, Siegfried; Clark, Timothy (Journal of the American Chemical Society, 2006)
We present a computational model study designed to simulate the results of time-resolved fluorescence spectra of tryptophan in proteins. In such measurements, the occurrence of more than one fluorescence lifetime is generally attributed to the existence of several tryptophan rotamers and/or structural conformations of the protein structure. The protein system we chose for this initial study is the tetracycline repressor (TetR), an interesting model system for the investigation of the mechanisms of transcriptional regulation. Fluorescence resonance energy transfer (FRET) from tryptophan to tetracycline is frequently observed in complexes of the TetR with the antibiotic tetracycline. We use a combined classical/quantum mechanical approach to model the structure and the spectroscopic properties of the TetR-tetracycline complex. A classical molecular dynamics simulation provides input geometries for semiempirical quantum mechanical/molecular mechanical (OM/MM) single-point configuration interaction (CI) calculations, which are used to calculate tryptophan vertical absorption and fluorescence energies and intensities as well as relative FRET rate constants. These rate constants together with the Einstein coefficients for spontaneous emission and an assumed rate for nonradiative deactivation allow us to simulate fluorescence decay curves with and without FRET and for the entire ensemble as well as for individual rotamers. Our results indicate that the classical "rotamer model", used to explain the multiexponential fluorescence-decay curves of time-resolved tryptophan emission spectra, can be extended to systems with FRET acceptors present in the protein matrix but that the interpretation of the fitted lifetimes is different to that usually used.

Structural changes and binding characteristics of the tetracycline-repressor binding site on induction - Lanig, Harald; Othersen, Olaf; Seidel, Ute; Beierlein, Frank; Exner, Thomas; Clark, Timothy (Journal of Medicinal Chemistry, 2006)
The binding motif ( pharmacophore) for induction and the changes in the structure of the binding site that accompany induction have been determined from molecular-dynamics simulations on the tetracycline-repressor signal-transduction protein. The changes and the induction mechanism are discussed and compared with conclusions drawn from earlier X-ray structures. The differences in inducer strength of tetracycline and 5a, 6-anhydrotetracycline are discussed with respect to their interaction in the MD simulations.

Substrate misorientation as additional parameter for low temperature growth of GaAs - Schür, Carsten; Marek, Tamas; Strunk, Horst Paul; Tautz, Sönke; Steen, Christian; Kiesel, Peter; Malzer, Stefan; Döhler, Gottfried; Niecke, M.; Schröder, F.; Mayer, R.; Knappe, R. (Physik mikrostrukturierter Halbleiter, 2001)
UnivIS-Import:2015-04-14:Pub.2001.tech.IW.LM.substr

Systematic surface scan of the most favorable interaction sites of magnesium ions with tetracycline - Othersen, Olaf; Lanig, Harald; Clark, Timothy (Journal of Medicinal Chemistry, 2003)
AM1 semiempirical molecular orbital calculations have been used to probe the complexation sites for naked and hydrated magnesium ions to the different conformations and protonation states of tetracycline. The calculations reveal a wealth of possible magnesium complexation sites within a small energy range, but also indicate that magnesium complexation does not change the conformational behavior of tetracycline significantly. A hitherto unknown solvated conformation is suggested for deprotonated tetracycline.

The mode of action of phospholipase A(2): Semiempirical MO calculations including the protein environment - Schürer, Gudrun; Lanig, Harald; Clark, Timothy; Lanig, Harald (Journal of Physical Chemistry B, 2000)
Phospholipase A(2) is a calcium-dependent enzyme involved in inflammatory processes by releasing arachidonic acid from the sn-2 position of phosphatidyl-cholines. The catalyzed reaction is an ester hydrolysis that takes place in two proton transfer steps via an intermediate. Two mechanisms, which differ mainly in the rate-limiting step, have been proposed in the literature. The reaction has been calculated semiempirically (PM3) for a protein fragment containing the active site (156 atoms). To take long-range electrostatic interactions of the protein bulk with the active site into account, a classical-mechanical protein environment has been provided by a rigid point-charge array with associated van der Waals potentials. In this way a model system has been built that simulates the natural situation in an enzyme more realistically than a pure model of the active site. A comparison between the relative energy paths obtained by calculating the reaction in the isolated active site and within the classical mechanical environment shows that the long-range interactions have a strong influence on the mechanism. While the calculations of the smaller system indicate that the first reaction step, the formation of the intermediate, is rate-limiting, the calculations including the protein environment show that the decomposition of the intermediate is probably rate-limiting. The results clearly show that the protein environment cannot be disregarded during quantum-mechanical calculations of enzyme mechanisms.

The potential of perylene bisimide derivatives for the solubilization of carbon nanotubes and graphene - Backes, Claudia; Hauke, Frank; Hirsch, Andreas (Advanced Materials, 2011)
Carbon nanotubes and graphene are outstanding materials of the 21 century with a broad spectrum of applications. However, major challenges are faced such as the intrinsically low solubility of both sp carbon allotropes. To overcome this hurdle the potential of noncovalent functionalization is summarized with a special focus on the establishment of the perylene bisimide unit as aromatic anchor to the graphitic surface. Rational surfactant design is unmasked as the key to solubilization of the carbon allotropes, while at the same time tailoring their surface properties, or even electronic properties in a fully reversible fashion. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The structure of 5a,6-anhydrotetracycline and its Mg2+ complexes in aqueous solution - Othersen, Olaf; Lanig, Harald; Clark, Timothy (Journal of Molecular Modeling, 2006)
Semiempirical molecular orbital theory has been used for a systematic scan of the binding positions for a Mg2+ ion with 5a,6-anhydrotetracycline taking both conformational flexibility and possible different tautomeric forms into account. The magnesium ion has been calculated alone and with four or five complexed water molecules in order to simulate the experimental situation more closely. The results are analyzed by comparing the behavior of the title compound with that of tetracycline itself and possible causes for the stronger induction of the Tetracycline Receptor (TetR) by 5a,6-anhydrotetracycline than by tetracycline are considered.
Keywords: AM1; 5a; 6-anhydrotetracycline; conformational analysis; magnesium interactions

Tuning the adsorption of perylene-based surfactants on the surface of single-walled carbon nanotubes - Backes, Claudia; Hauke, Frank; Hirsch, Andreas; Hauke, Frank (physica status solidi (b), 2013)
Despite tremendous progress in dispersion and sorting of carbon nanotubes using surfactant systems in water, the effect of the surrounding aqueous medium is only poorly understood. Herein we present a study on the effect of pH and ionic strength on the adsorption behavior of surfactants on the SWCNT scaffold and the related differences in dispersion and individualization. We have turned to an anionic perylene bisimide dye as model surfactant, as the rich spectroscopy allows us to trace the interaction with and the packing densities on the SWCNTs. We show that higher ionic strength and high packing density is beneficial for the dispersion yield, while high net charge density on the surface is the crucial factor for exfoliation. The accessible tuning of the packing densities furthermore enabled the investigation of preferential interaction of the dye with certain nanotube species. Environmental effects: crucial factors for nanomaterial dispersion and exfoliation as demonstrated with the aid of a nanotube-perylene bisimide model system. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Von den ›Ingenieuren im Wald‹ zur größten Fakultät der FAU - Strategien der Bebauungsgeschichte der Technischen Fakultät - Kreis, Oliver; Ryssel, Heiner; Tyrach, Annette (Festschrift 50 Jahre Technische Fakultät der FAU, 2016)
Seit der Grundsteinlegung 1964 wuchs die Technische Fakultät (TF) rasant. Von den ersten Gebäuden und Lehrstühlen der 60er Jahre entwickelte sie sich in den 80er und 90er Jahren zur Fakultät der »Ingenieure im Wald«, wie sie Studierende der anderen Fakultäten scherzhaft betitelten. Aufgrund des rasanten Anstiegs der Zahl an Lehrstühlen, Forschungsprojekten und Studierenden musste die Bebauungsstrategie mehrfach verändert werden.<br

[2,2]Paracyclophane-Based π-Conjugated Molecular Wires Reveal Molecular-Junction Behavior - Molina-Ontoria, Agustin; Wielopolski, Mateusz; Gebhardt, Julian; Gouloumis, Andreas; Clark, Timothy; Guldi, Dirk Michael; Martin, Nazario (Journal of the American Chemical Society, 2011)
The electronic coupling as well as the attenuation factor ( extgreekb), which depends primarily on the nature of the molecular bridge and is used as a benchmark to test the molecular wire behavior, have been determined in a systematic study carried out on a series of ZnP/C60 conjugates connected through a [2,2′]paracyclophane-oligophenylenevinylene (pCp-oPPV). The convergent synthesis involves a series of Horner-Emmons olefination reactions or double palladium-catalized Heck-type reactions. ZnP-pCp-C60 conjugates were finally obtained by the 1,3-dipolar cycloaddition reaction of the in situ-generated azomethyne ylide containing the ZnP-pCp moiety to the [60]fullerene using Prato conditions. Experimental (UV-vis, fluorescence, transient absorption spectroscopy, and solution electrochemistry) and theoretical studies revealed that the pCps act as molecular junctions. If hole transfer is assumed to be the dominant charge transfer (CT) mechanism, CT is facilitated in one direction (from C60 to ZnP via pCp) but disfavored in the other direction (from ZnP to C60 via pCp).
EAM Import::2019-03-13

2D analysis of polydisperse core-shell nanoparticles using analytical ultracentrifugation - Walter, Johannes; Gorbet, Gary; Akdas, Tugce; Segets, Doris; Demeler, Borries; Peukert, Wolfgang (Analyst, 2017)
Accurate knowledge of the size, density and composition of nanoparticles (NPs) is of major importance for their applications. In this work the hydrodynamic characterization of polydisperse core-shell NPs by means of analytical ultracentrifugation (AUC) is addressed. AUC is one of the most accurate techniques for the characterization of NPs in the liquid phase because it can resolve particle size distributions (PSDs) with unrivaled resolution and detail. Small NPs have to be considered as core-shell systems when dispersed in a liquid since a solvation layer and a stabilizer shell will significantly contribute to the particle's hydrodynamic diameter and effective density. AUC measures the sedimentation and diffusion transport of the analytes, which are affected by the core-shell compositional properties. This work demonstrates that polydisperse and thus widely distributed NPs pose significant challenges for current state-of-the-art data evaluation methods. The existing methods either have insufficient resolution or do not correctly reproduce the core-shell properties. First, we investigate the performance of different data evaluation models by means of simulated data. Then, we propose a new methodology to address the core-shell properties of NPs. This method is based on the parametrically constrained spectrum analysis and offers complete access to the size and effective density of polydisperse NPs. Our study is complemented using experimental data derived for ZnO and CuInS NPs, which do not have a monodisperse PSD. For the first time, the size and effective density of such structures could be resolved with high resolution by means of a two-dimensional AUC analysis approac
Keywords: nanoparticles; centrifugation; resolution; core-shell; ZnO; analysis

2H-Tetrakis(3,5-di-tert-butyl)phenylporphyrin on a Cu(110) Surface: Room-Temperature Self-Metalation and Surface-Reconstruction-Facilitated Self-Assembly - Zhang, Liang; Lepper, Michael; Stark, Michael Werner; Schuster, Ralf; Lungerich, Dominik; Jux, Norbert; Steinrück, Hans-Peter; Marbach, Hubertus (Chemistry - A European Journal, 2016)
The adsorption behavior of 2H-tetrakis(3,5-di-tert-butyl)phenylporphyrin (2HTTBPP) on Cu(110) and Cu(110)-(2x1)O surfaces have been investigated by using variable-temperature scanning tunneling microscopy (STM) under ultrahigh vacuum conditions. On the bare Cu(110) surface, individual 2HTTBPP molecules are observed. These molecules are immobilized on the surface with a particular orientation with respect to the crystallographic directions of the Cu(110) surface and do not form supramolecular aggregates up to full monolayer coverage. In contrast, a chiral supramolecular structure is formed on the Cu(110)-(2x1)O surface, which is stabilized by van der Waals interactions between the tert-butyl groups of neighboring molecules. These findings are explained by weakened molecule-substrate interactions on the Cu(110)-(2x1)O surface relative to the bare Cu(110) surface. By comparison with the corresponding results of Cu-tetrakis(3,5-di-tert-butyl)phenylporphyrin (CuTTBPP) on Cu(110) and Cu(110)-(2x1)O surfaces, we find that the 2HTTBPP molecules can self-metalate on both surfaces with copper atoms from the substrate at room temperature (RT). The possible origins of the self-metalation reaction at RT are discussed. Finally, peculiar irreversible temperature-dependent switching of the intramolecular conformations of the investigated molecules on the Cu(110) surface was observed and interpreted.
Keywords: adsorption; porphyrinoids; scanning tunneling microscopy; self-assembly; surfaces and interfaces

3D numerical simulations of passive mixing in a microchannel with nozzle-diffuser-like obstacles - Ritter, Paul; Osorio Nesme, Anuhar; Delgado, Antonio (International Journal of Heat and Mass Transfer, 2016)
A novel passive chaotic advection micromixer with periodic nozzle-diffuser-like (NDL) obstacles is proposed. Lattice Boltzmann simulations of two incoming flows were performed for Reynolds numbers in the range 1 łeq Re łeq 100 and two Schmidt numbers Sc = 1 and 50. The numerical study focuses on the evaluation of the mixing efficiency of the new design and the analysis of mass transfer as a function of the Péclet number. The flow was identified as spatially periodic. The results are compared with those for a plain rectangular channel. The asymmetric design and placement of the obstacles lead to splitting and recombination of the flows, promoting transverse flow. Two principal characteristics of chaotic advection were observed at high Pe: helical, intertwined streamlines and hyperbolic points in transverse planes. The mixing efficiency was found to increase with channel length, whereas for the proposed channel the mixing efficiency was observed higher than that for the rectangular channel for Pe > 100.
UnivIS-Import:2018-09-11:Pub.2016.tech.ITC.stmmec.3dnume
Keywords: Chaotic advection; Microchannel; Mixing

3D structural analysis: sensitivity of Minkowski functionals - Arns, C. H.; Knackstedt, M. A.; Mecke, Klaus (Journal of Microscopy, 2010)
The Minkowski functionals, a family of statistical measures based on the Euler-Poincare characteristic of n-dimensional space, are the complete set of additive morphological measures and can be simply calculated from local contributions. As such, they have found a wide range of applications. We consider the effects of distortions (drift, noise and blurring) on the morphological properties of complex random models, representative of a wide range of structure. Such distortions arise experimentally in imaging techniques due to diffraction, absorption and sample drift. The question is asked, how critically these distortions effect image quality as measured by the Minkowski functionals. Defining a length scale based on the two-point correlation function, we consider how distortion at different scales can lead to quantitative errors in morphological measures.
Keywords: Morphology; complex materials; porous media; Minkowski functional

3D thermo-fluid dynamic simulations of high-speed-extruded starch based products - Cubeddu, Alessandro; Rauh, Cornelia; Delgado, Antonio (Open Journal of Fluid Dynamics, 2014)
This paper aims to investigate a method to perform non-isothermal flow simulations in a complex geometry for generalised Newtonian fluids. For this purpose, 3D numerical simulations of starch based products are performed. The geometry of a co-rotating twin-screw extruder is considered. Process conditions concern high rotational speed (up to 1800 rpm), different flow rates (30, 40 and 60 kg/h) and water contents (22% and 36%), for a total of 54 simulations. To cope with the geometry complexity a Mesh Superposition Technique (MST) was adopted. The pseudoplastic behaviour of the fluid is taken into account by considering viscosity as function of shear rate (Ostwaldde Waele relationship) and temperature (Arrhenius law). Simulated temperature variations are compared with measurements at same process conditions for validation. Qualitative behaviour of temperature T and shear stress 𝛕 along the screw are analysed and comparisons of different process conditions are presented. By these simulations a database is formed to develop a process control strategy for novel extruder operating points in food technolog
UnivIS-Import:2015-03-09:Pub.2014.tech.ITC.stmmec.3dther
Keywords: High Speed Extrusion; Non-Isothermal Numerical Simulation; Ostwald-De Waele Model

Abandoned Functionality of Thin-Film Opal Photonic Crystals - Kuechenmeister, Jens; Wolff, Christian; Busch, Kurt; Peschel, Ulf; Romanov, Sergey (Advanced Optical Materials, 2013)
Angle-resolved polarized transmission spectra of thin-film opals are studied experimentally and theoretically as a function of the azimuthal rotation of the plane of incidence at different angles of light incidence. In such 3-dimensional lattices, the refraction acquires the form of diffraction orders, each with a distinct spectrum, that propagate simultaneously along different directions. The corresponding continuous and patchy stop-bands in the photonic energy band structure of the opal photonic crystal are determined numerically. For diffraction at high Miller index planes, the diffraction pattern is often distorted due to multiple-wave diffraction. The finite stacking of hexagonally close-packed layers leads to an intrinsic 3-fold rotation symmetry of these spectra, which is particularly pronounced in transmission for frequencies that correspond to wave vectors within the 1st Brillouin zone. Despite the cubic symmetry of the opal lattice, cross-polarization coupling effects occur in the volume of the opal crystal. These effects are associated with the fact that, the opal eigenmodes are Bloch waves whose electromagnetic field distributions and dispersion relations are markedly different from plane waves.
EAM Import::2019-03-13

Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing - Li, Ning; Perea, José Darío; Kassar, Thaer; Richter, Moses; Heumüller, Thomas; Matt, Gebhard; Hou, Yi; Güldal, Nusret Sena; Chen, Haiwei; Chen, Shi; Langner, Stefan; Berlinghof, Marvin; et al. (Nature Communications, 2017)
The performance of organic solar cells is determined by the delicate, meticulously optimized bulk-heterojunction microstructure, which consists of finely mixed and relatively separated donor/acceptor regions. Here we demonstrate an abnormal strong burn-in degradation in highly efficient polymer solar cells caused by spinodal demixing of the donor and acceptor phases, which dramatically reduces charge generation and can be attributed to the inherently low miscibility of both materials. Even though the microstructure can be kinetically tuned for achieving high-performance, the inherently low miscibility of donor and acceptor leads to spontaneous phase separation in the solid state, even at room temperature and in the dark. A theoretical calculation of the molecular parameters and construction of the spinodal phase diagrams highlight molecular incompatibilities between the donor and acceptor as a dominant mechanism for burn-in degradation, which is to date the major short-time loss reducing the performance and stability of organic solar cells.

Absence of circular polarisation in reflections of butterfly wing scales with chiral Gyroid structure - Saba, Matthias; Wilts, Bodo D.; Hielscher, Johannes; Schröder-Turk, Gerd (Materials Today, 2014)
The single Gyroid, a triply-periodic ordered chiral network of cubic symmetry, appears as a nanostructure in the green-colored wing scales of various butterflies. In lossless and perfectly ordered single Gyroid materials, the structural chirality leads to circularly polarized reflections from crystals oriented in the [100] direction. Here we report a circular polarisation study of the macroscopic reflections of the wing scales of Callophrys rubi and Teinopalpus imperialis that reveals no circular dichroism, that is, we find no significant difference in the reflectance values for left- and right-circularly polarized light. The reasons for the absence of circularly polarized reflections is likely to be a compound effect of various factors, including crystallite orientation, presence of both leftand right-handed single Gyroid enantiomers, and structural disorder. Each of these factors weakens, but does not fully extinguish, the circular polarisation signal. We further find a substantial amount of blue-absorbing pigment in those wing scales of C. rubi that are structured according to the single Gyroid. Numerical simulations demonstrate that absorption, while evidently reducing overall reflectance, does generally not reduce the circular dichroism strength. The experimental findings of this paper, however, clearly demonstrate that circular dichroism is absent from the reflections of the butterfly wing scale. Henceforth, the chiro-optical response of the idealised structure does not fulfil a biological photonic function.
EAM Import::2019-03-13

Absence of subharmonic response in vibrated granular systems under microgravity conditions - Kollmer, Jonathan; Tupy, Martin; Heckel, Michael; Sack, Achim; Pöschel, Thorsten (Physical Review Applied, 2015)
By means of experiments in microgravity conditions, we show that granular systems subjected to sinusoidal vibrations respond either by harmonic or gaslike dynamics, depending on the parameters of the vibration, amplitude and frequency, and the container size, while subharmonic response is unstable, except for extreme material properties and particular initial conditions. The absence of subharmonic response in vibrated granular systems implies that granular dampeners cannot reveal higher-order resonances, which makes them even more attractive for technical applications. Extensive molecular dynamics simulations support our findings.

A carbon-carbon hybrid - immobilizing carbon nanodots onto carbon nanotubes - Strauß, Volker; Margraf, Johannes; Clark, Timothy; Guldi, Dirk Michael (Chemical Science, 2015)
The thrust of this work is to integrate small and uniformly sized carbon nanodots (CNDs) with single-walled carbon nanotubes (SWCNT) of different diameters as electron donors and electron acceptors, respectively, and to test their synergetic interactions in terms of optoelectronic devices. CNDs (denoted pCNDs, where p indicates pressure) were prepared by pressure-controlled microwave decomposition of citric acid and urea. pCNDs were immobilized on single-walled carbon nanotubes by wrapping the latter with poly(4-vinylbenzyl trimethylamine) (PVBTA), which features positively charged ammonium groups in the backbone. Negatively charged surface groups on the CNDs lead to attractive electrostatic interactions. Ground state interactions between the CNDs and SWCNTs were confirmed by a full-fledged photophysical investigation based on steady-state and time-resolved techniques. As a complement, charge injection into the SWCNTs upon photoexcitation was investigated by ultra-short time-resolved spectroscopy.

Accelerated degradation of Al3+ doped ZnO thin films using damp heat test - Litzov, Ivan; Azimi, Seyed Hamed; Matt, Gebhard; Kubis, Peter; Stubhan, Tobias; Popov, Georgi; Brabec, Christoph (Organic Electronics, 2014)
Two different types of aluminum-doped zinc oxide (AZO) thin films were fabricated using low cost sol-gel technique. By applying damp heat testing, the optical and electrical properties of those films were investigated under the influence of accelerated degradation from moisture or moisture vapor. Complementary measurements of optical transmittance, work function, and conductivity allowed exploring the degradation of AZO thin films and the corresponding OPV devices. We found that optical properties like transmittance, absorption coefficient, and band gap are not influenced by temperature and moisture. However, an increase in the work function, and a decrease in the conductivity of AZO films were observed upon damp heat exposure indicating the formation of a barrier or depletion layer at the metal oxide semiconductor interface. © 2013 Elsevier B.V. All rights reserved.
Keywords: Aluminum-doped zinc oxide; Conductivity; Damp heat test; Work function

Accelerated grain refinement during accumulative roll bonding by nanoparticle reinforcement - Schmidt, Christian; Knieke, Catharina; Maier, Verena; Höppel, Heinz Werner; Peukert, Wolfgang; Göken, Mathias (Scripta Materialia, 2011)
Ceramic nanoparticles produced by comminution are introduced homogeneously during accumulative roll bonding (ARB) in aluminium AA1050A by airgun spraying from a stabilized aqueous suspension. In the so-produced nanoparticle-reinforced ultrafine-grained material, acceleration of microstructural evolution during the early ARB cycles as well as reduced grain sizes at higher cycles are observed, both caused by additional local straining around the embedded nanoparticles and accompanied by further strengthening. The presented method of nanoparticle application allows homogeneous as well as graded particle distributio

Accelerating Oxygen-Reduction Catalysts through Preventing Poisoning with Non-Reactive Species by Using Hydrophobic Ionic Liquids - Zhang, Guirong; Munoz, Macarena; Etzold, Bastian (Angewandte Chemie International Edition, 2016)
Developing cost-effective electrocatalysts for the oxygen reduction reaction (ORR) is a prerequisite for broad market penetration of low-temperature fuel cells. A major barrier stems from the poisoning of surface sites by nonreactive oxygenated species and the sluggish ORR kinetics on the Pt catalysts. Herein we report a facile approach to accelerating ORR kinetics by using a hydrophobic ionic liquid (IL), which protects Pt sites from surface oxidation, making the IL-modified Pt intrinsically more active than its unmodified counterpart. The mass activity of the catalyst is increased by three times to 1.01 A mg-1Pt@0.9 V, representing a new record for pure Pt catalysts. The enhanced performance of the IL-modified catalyst can be stabilized after 30 000 cycles. We anticipate these results will form the basis for an unprecedented perspective in the development of high-performing electrocatalysts for fuel-cell applications.
EAM Import::2019-03-13

Accumulative Roll Bonding: Forming Behavior, Tailored Properties and Upscaling Approach - Merklein, Marion; Böhm, Wolfgang (Advanced Materials Research, 2014)
The Accumulative Roll Bonding (ARB) process enables the manufacturing of high strength sheet metals with outstanding mechanical properties by repeated rolling. However, the significant increase in strength leads to loss in ductility, especially regarding aluminum alloys of the 6000 series. The low formability obviously limits the implementation of these sheet products for formed components in automotive applications. To enhance formability, a local short term heat treatment according to the Tailored Heat Treated Blanks technology is used. For the finite element based design of forming operations accurate information about the plastic behavior of these tailored materials is required. Therefore, different stress - strain paths are considered using the tensile test and the layer compression test. In this context, heat treated and non-heat treated specimens out of ARB processed AA6016 were tested at room temperature. With the experimental results true stress – strain curves and yield loci determined from different criteria and represented in a principal stress state were established. Regarding the experimental setup of the ARB process, an upscaling is essential for the production of sufficiently large strips to cut out blanks for the forming of components such as B-pillars. However, this requires the adaptation of the different process steps of the ARB process. In this context, the surface treatment before rolling of such large sheets is investigated, since it is particularly relevant for obtaining a strong bonding between the sheets. Another aspect is the investigation of the rolling process using the finite element analysis. In this regard, a thermalmechanical coupled simulation model of the roll bonding operation will be developed for the evaluation of different material combinations, different process temperatures and varying roller geometries. These investigations will enable the production of lightweight automotive components made of ARB processed high strength aluminum sheet metal with tailored properties.
EAM Import::2019-03-13

Accumulative Roll Bonding of precipitation-hardenable aluminum alloys of the 6000 series in a warm rolling process - Merklein, Marion; Herrmann, Jürgen (Proc. ROLLING Conference, 2016)
In several industrial fields there is a persistent trend to lightweight construction. An auspicious possibility to cope with this challenge is the application of high strength aluminum, produced by accumulative roll bonding (ARB). Key idea of the ARB approach, which was originally invented by Saito et al. (1998), is the subsequent stacking and rolling of sheet material in order to gain an ultrafine-grained microstructure. The grain refinement results from the high deformations and shear stresses during each cycle of ARB. At the moment aluminum alloys of the 6000 series are pre-heated and rolled at room temperature. Within this contribution sheets of an AA6014 alloy are manufactured in a warm rolling process for the first time. The aluminum sheets are characterized regarding their mechanical properties and in particular their flow behavior. Furthermore, the bond strength of the respectively last bonded layer is examined using T-peel tests. Both testing methods are carried out after two and four rolling cycles. Based on these investigations a process strategy for the production of multilayered sheets in a warm rolling process is derived.
EAM Import::2019-03-13

Accurate Intermolecular Interaction Energies from a Combination of MP2 and TDDFT Response Theory - Pitonak, Michal; Heßelmann, Andreas (Journal of Chemical Theory and Computation, 2010)
A new method is presented that improves the supermolecular second-order Møller-Plesset (MP2) method for dimer systems with strong dispersion interactions while preserving the generally good performance of MP2 for other types of intermolecular interactions, e.g., hydrogen-bonded systems. This is achieved by adding a correction term to the supermolecular MP2 energy that is determined using time-dependent density functional (TDDFT) response theory and that accounts for the error of the dispersion energy contained in the supermolecular MP2 method. It is shown for the S22 database set of noncovalent complexes and some potential energy curves of noncovalent bound aromatic dimers that the approach gives strong improvements over MP2 if compared to coupled-cluster singles, doubles, and perturbative triples (CCSD(T)) reference energies. An efficient computer implementation of the method is presented that is shown to scale only with the fourth power of the system size and thus leads only to a slightly higher computational cost than that of the supermolecular MP2 itself.
EAM Import::2019-03-13

Accurate tuning of ordered nanotubular platinum electrodes by galvanic plating - Roscher, Valentin; Licklederer, Markus; Schumacher, Johannes; Rios, Grisell Reyes; Hoffmann, Bjoern; Christiansen, Silke; Bachmann, Julien (Dalton Transactions, 2014)
Platinum nanotubes are created by galvanic deposition inside porous templates. The effects of the electrolyte's ion concentration and pH, of the applied potential and of the deposition duration on the morphology of the tubes are investigated systematically. The system provides a model electrode platform with accurately tunable geometry for the fundamental investigation of electrochemical transformations. For slow electrochemical reactions, we observe a linear increase of the galvanic current with the length of the nanotubes, and therefore with the specific surface area of the electrode. In contrast to this, inherently fast electrochemical transformations are diffusion-limited and give rise to the same current density independently of the geometry. These results delineate a strategy for optimizing the performance of electrochemical energy conversion devices systematically via nanostructuring the electrode surfaces.

A Chiral Beamsplitter Inspired by Butterfly Nanostructures - Turner, Mark D.; Saba, Matthias; Zhang, Qiming; Cumming, Benjamin P.; Schröder-Turk, Gerd; Gu, Min (Frontiers in Optics 2013, 2013)
Here we present a chiral analog of the linearly polarizing beamsplitter. This microscopic device was built from a biomimetic chiral photonic crystal and separates left and right-handed circularly polarized light at near-infrared wavelengths.
EAM Import::2019-03-13

A cohesive crack propagation model: Mathematical theory and numerical solution - Prechtel, Marina; Leugering, Günter; Steinmann, Paul; Stingl, Michael (Communications on Pure and Applied Analysis, 2013)
We investigate the propagation of cracks in 2-d elastic domains, which are subjected to quasi-static loading scenarios. As we take cohesive effects along the crack path into account and impose a non-penetration condition, inequalities appear in the constitutive equations describing the elastic behavior of a domain with crack. In contrast to existing approaches, we consider cohesive effects arising from crack opening in normal as well as in tangential direction. We establish a constrained energy minimization problem and show that the solution of this problem satisfies the set of constitutive equations. In order to solve the energy minimization problem numerically, we apply a finite element discretization using a combination of standard continuous finite elements with so-called cohesive elements. A particular strength of our method is that the crack path is a result of the minimization process. We conclude the article by numerical experiments and compare our results to results given in the literature.
Keywords: Energy minimization; cohesive elements; crack problems.

A colloidoscope of colloid-based porous materials and their uses - Phillips, Katherine R.; England, Grant T.; Sunny, Steffi; Shirman, Elijah; Shirman, Tanya; Vogel, Nicolas; Aizenberg, Joanna (Chemical Society Reviews, 2016)
Nature evolved a variety of hierarchical structures that produce sophisticated functions. Inspired by these natural materials, colloidal self-assembly provides a convenient way to produce structures from simple building blocks with a variety of complex functions beyond those found in nature. In particular, colloid-based porous materials (CBPM) can be made from a wide variety of materials. The internal structure of CBPM also has several key attributes, namely porosity on a sub-micrometer length scale, interconnectivity of these pores, and a controllable degree of order. The combination of structure and composition allow CBPM to attain properties important for modern applications such as photonic inks, colorimetric sensors, self-cleaning surfaces, water purification systems, or batteries. This review summarizes recent developments in the field of CBPM, including principles for their design, fabrication, and applications, with a particular focus on structural features and materials' properties that enable these applications. We begin with a short introduction to the wide variety of patterns that can be generated by colloidal self-assembly and templating processes. We then discuss different applications of such structures, focusing on optics, wetting, sensing, catalysis, and electrodes. Different fields of applications require different properties, yet the modularity of the assembly process of CBPM provides a high degree of tunability and tailorability in composition and structure. We examine the significance of properties such as structure, composition, and degree of order on the materials' functions and use, as well as trends in and future directions for the development of CBPM.

A combination of Al-doped ZnO and a conjugated polyelectrolyte interlayer for small molecule solution-processed solar cells with an inverted structure - Min, Jie; Zhang, Hong; Stubhan, Tobias; Luponosov, Yuriy N.; Kraft, Mario; Ponomarenko, Sergei A.; Ameri, Tayebeh; Scherf, Ullrich; Brabec, Christoph (Journal of Materials Chemistry A, 2013)
We successfully demonstrate a smart strategy to use aluminum doped ZnO (AZO) and the thiophene-based conjugated polyelectrolyte P3TMAHT as an interfacial layer in small molecule solution-processed inverted solar cells. Modification of AZO with a thin P3TMAHT layer increases the photovoltaic properties of the inverted cell as a result of reduction in the work function of the cathode with well aligned frontier orbital energy levels for efficient charge transport and reduced surface recombination. The inverted device achieved 16% performance improvement dominantly by recapturing part of the Voc losses when going from conventional to the inverted architecture. In addition, the inverted device using the AZO/P3TMAHT interlayer shows improved device stability in air compared to conventional devices.
Keywords: Aluminum-doped ZnO; Conjugated polyelectrolytes; Frontier orbital energies; Inverted architectures; Inverted solar cells; Photovoltaic property; Solution-processed; Surface recombinations Engineering controlled terms: Molecules; Polyelectrolytes; Zinc oxide Engineering main heading: Solar cells

A combined density-functional and IRAS study on the interaction of NO with Pd nanoparticles: Identifying new adsorption sites with novel properties - Vines Solana, Francesc; Desikusumastuti, Aine; Staudt, T.; Görling, Andreas; Libuda, Jörg; Neyman, Konstantin M. (Journal of Physical Chemistry C, 2008)
Nanocrystalline particles expose special adsorption sites close to edges and corners, giving rise to novel adsorption and reaction properties. The spectroscopic identification of these sites represents a great challenge, however. Here, we present results of a combined experimental and theoretical study on the adsorption of NO on Pd nanoparticles, using infrared reflection absorption spectroscopy (IRAS) and calculations based on density-functional theory (DFT). This approach facilitates identification of the adsorption sites available on the nanoparticles and reveals detailed information on their bonding properties, on the vibrational parameters of NO adsorbed on these sites, and on their sequence of occupation. With respect to all these aspects, the adsorption behavior of NO on the Pd nanoparticles notably differs from any single crystal reference data available. The IRAS studies are performed on well-defined Pd nanoparticles supported on an ordered AlO film on NiAl(110). The growth and structure of these particles has been characterized previously, predominately exposing (111) and a small fraction of (100) facets. Here, we systematically monitor the NO adsorption as a function of exposure in a temperature region between 100 and 300 K by means of time-resolved IRAS in combination with molecular beam (MB) dosing. We interpret these experimental data with the help of DFT calculations on the adsorption of NO on unsupported cuboctahedral Pd clusters cut from Pd bulk and containing up to 140 atoms; for comparison, calculations of the reference adsorption complexes of NO on single-crystal Pd(111) surface have also been performed. NO molecules are shown to most favorably adsorb on hollow μ-sites on (111) facets of Pd clusters, closely followed by bridge μ-sites at the edges between adjacent (111) facets. Both sites give rise to characteristic features in the vibrational spectrum and are populated sequentially. At higher coverage (and low temperature) on-top μ-sites on the (111) facets begin to be occupied. At variance with the adsorption on Pd(111) surface, however, additional on-top-sites are available at the particle edges and corners, which reveal stronger NO adsorption. In spite of the strong adsorption in bridge (μ) coordination geometry at edges, our calculations predict that intermolecular repulsion between adjacent μ-NO species gives rise to the formation of mixed bridge/on-top structures at high coverage. Similarly to the bridge NO at particle edges, the edge- and corner-related μ-NO species reveal characteristic vibrational frequencies, allowing for direct verification of this prediction by IRAS. The present results make possible the identification and monitoring of the occupation of specific sites on Pd nanoparticles by NO during adsorption and reaction processes. © 2008 American Chemical Society.

A Combined SAXS/SANS Study for the in Situ Characterization of Ligand Shells on Small Nanoparticles: The Case of ZnO - Schindler, Torben; Schmiele, Martin; Schmutzler, Tilo; Kassar, Thaer; Segets, Doris; Peukert, Wolfgang; Radulescu, Aurel; Kriele, Armin; Gilles, Ralph; Unruh, Tobias (Langmuir, 2015)
ZnO nanoparticles (NPs) have great potential for their use in, e.g., thin film solar cells due to their electro-optical properties adjustable on the nanoscale. Therefore, the production of well-defined NPs is of major interest. For a targeted production process, the knowledge of the stabilization layer of the NPs during and after their formation is of particular importance. For the study of the stabilizer layer of ZnO NPs prepared in a wet chemical synthesis from zinc acetate, only ex situ studies have been performed so far. An acetate layer bound to the surface of the dried NPs was found; however, an in situ study which addresses the stabilizing layer surrounding the NPs in a native dispersion was missing. By the combination of small angle scattering with neutrons and X-rays (SANS and SAXS) for the same sample, we are now able to observe the acetate shell in situ for the first time. In addition, the changes of this shell could be followed during the ripening process for different temperatures. With increasing size of the ZnO core (dcore) the surrounding shell (dshell) becomes larger, and the acetate concentration within the shell is reduced. For all samples, the shell thickness was found to be larger than the maximum extension of an acetate molecule with acetate concentrations within the shell below 50 vol %. Thus, there is not a monolayer of acetate molecules that covers the NPs but rather a swollen shell of acetate ions. This shell is assumed to hinder the growth of the NPs to larger macrostructures. In addition, we found that the partition coefficient μ between acetate in the shell surrounding the NPs and the total amount of acetate in the solution is about 10% which is in good agreement with ex situ data determined by thermogravimetric analysis.
Keywords: nanoparticle; solar; cell; electroptical; property

A Comparison of Different Approaches in the Multi-Scale Computation of Configurational Forces - Mergheim, Julia; Steinmann, Paul; Ricker, Sarah; Müller, Ralf (International Journal of Fracture, 2010)
In the present work the FE2 scheme is extended towards the homogenization of material quantities like the Eshelby stress and material node point forces. Therefore, in contrast to standard computational homogenization schemes volume forces on the micro-and on the macro-level have to be taken into account which emerge in the material motion problem due to inhomogeneities in the material. Different approaches in the determination of the material stresses are compared and it is shown that the direct calculation of the material stresses in terms of averaged material quantities requires an internal extra term to fulfill the energy consistency represented by a Hill-Mandel type condition. Furthermore, two approaches based on the average of the material two-point stress and the Eshelby stress are compared which require a further scale-transition which is performed within a postprocessing step. The influence of different micro-structures onto the macroscopic material quantities is studied within numerical examples. © 2010 Springer Science+Business Media B.V.
UnivIS-Import:2015-03-09:Pub.2010.tech.FT.FT-TM.acompa
Keywords: Computational homogenization; Configurational forces; FE; Multi-scale mechanics

A Comprehensive Brownian Dynamics-Based Forward Model for Analytical (Ultra)Centrifugation - Thajudeen, Thaseem; Walter, Johannes; Uttinger, Maximilian; Peukert, Wolfgang (Particle & Particle Systems Characterization, 2017)
In this study, it is demonstrated how Brownian dynamics (BD) simulations can be used as a comprehensive forward model for analytical ultracentrifugation (AUC) and analytical centrifugation experiments. BD simulations are a versatile alternative to the numerical solution of Lamm's equation. Time dependent concentration profiles can be accurately predicted by means of the BD simulations even for colloidal systems with multiple species. It is shown that in combination with Mie's theory for light scattering, BD simulations can be extended to generate data mimicking a multiwavelength detector for AUC. The forward model can be utilized as a comprehensive tool for developing and testing sophisticated data analyzing tools that can enhance the capabilities of using centrifugation-based techniques for characterizing nanoparticles. The model is validated using common analysis tools developed for the evaluation of sedimentation velocity data generated by a single wavelength extinction detector. The accuracy of the code is also proved using the recently developed and highly versatile High Dynamic Range-MULTIwavelength FITting tool for accurately predicting particle size distributions via gravitational sweep experiments performed in AUCs equipped with multiwavelength detectors.
Keywords: Brownian dynamics; analytical ultracentrifugation; Mie scattering; extinction coefficient; multiwavelength detectors

A comprehensive study on the mechanism behind formation and depletion of Cu2ZnSnS4 (CZTS) phases - Ahmad, Rameez; Brandl, Marco; Distaso, Monica; Herre, Patrick; Spiecker, Erdmann; Hock, Rainer; Peukert, Wolfgang (Crystengcomm, 2015)
High efficiency kesterite based solar cells have vigorously raised the research interests in this material. The challenge lies in understanding the formation and co-existence of more than 10 possible by-products during and after the synthesis of Cu2ZnSnS4 (CZTS) and their various different structural and electronic defects. The present contribution shows an in-depth study on the stages of formation and depletion of nanoparticulate CZTS. Employing a hot injection synthesis method, we give direct experimental evidence of the co-existence of cubic, tetragonal and defected CZTS structures and different by-products as a function of time and temperature. SEM, (HR) TEM, XRD, EDX, ICP-OES, Raman spectroscopy and UV-Vis-NIR spectroscopy have been used in order to better evaluate and interpret data for crystal structures and compositions. The obtained understanding on the formation of different phases suggests 250 degrees C as the most favourable synthesis temperature. Based on our study, general strategies can be developed for controlling the amount of formed phases, the by-products and the defects in kesterite and other similar multicomponent nanoparticles as well as in bulk systems.

A computational study on possible active species in nickel(II)-catalyzed 1-butene dimerization in [BMIM](+)[AlCl4](-) ionic liquid solution - Görling, Andreas; Hieringer, Wolfgang; Nikiforidis, Ioannis (Journal of Coordination Chemistry, 2015)
The butene insertion step of nickel complex-catalyzed butene dimerization in the presence of a [BMIM](+)[AlCl4](-) ionic liquid has been studied using density functional theory. The possibility of anion coordination from the ionic liquid to the catalyst complex has explicitly been taken into account. The calculated relative energies of various possible active catalyst complexes suggest that anion coordination to the nickel center may be thermodynamically favorable. Phosphine-free complexes which are only coordinated by one or two AlCl4- anions are higher in energy and show higher activation barriers for butene insertion. The lowest activation barrier has been found for a mono-phosphine nickel complex. Explanations for the calculated barriers based on structural data are offered.
Keywords: Olefin dimerization; Olefin insertion; Homogeneous catalysis; Density functional theory; Computational chemistry

Activation energy for the self-metalation reaction of 2H- tetraphenylporphyrin on Cu(111) - Ditze, Stefanie; Stark, Michael Werner; Drost, Martin; Buchner, Florian; Steinrück, Hans-Peter; Marbach, Hubertus (Angewandte Chemie International Edition, 2012)
By simply counting individual molecules in STM images after defined heating steps, the kinetic parameters and the activation energy of a complex surface reaction can be determined quantitatively. This procedure was demonstrated for the metalation of 2H-tetraphenylporphyrin (2HTPP) with substrate atoms on a Cu(111) surface. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Activation parameters for deformation of ultrafine-grained aluminium as determined by indentation strain rate jumps at elevated temperature - Wheeler, J. M.; Maier, Verena; Durst, Karsten; Göken, Mathias; Michler, Johann (Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2013)
The hardness and strain rate sensitivity of ultrafine-grained (UFG) aluminium was examined as a function of temperature using in situ strain rate jump indentation in a SEM at temperatures up to 250 °C. Measured strain rate sensitivities were in good agreement with earlier bulk compression measurements. Activation energies and volumes for deformation were extracted and discussed. Transitions in the deformation mechanism are observed at lower temperatures for smaller grain sizes.
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Adaptive finite elements based on sensitivities for topological mesh changes - Leugering, Günter; Friederich, Jan; Steinmann, Paul (Control and Cybernetics, 2014)
We propose a novel approach to adaptive refinement in FEM based on local sensitivities for node insertion. To this end, we consider refinement as a continuous graph operation, for instance by splitting nodes along edges. Thereby, we introduce the concept of the topological mesh derivative for a given objective function. For its calculation, we rely on the first-order asymptotic expansion of the Galerkin solution of a symmetric linear second-order elliptic PDE. In this work, we apply this concept to the total potential energy, which is related to the approximation error in the energy norm. In fact, our approach yields local sensitivities for minimization of the energy error by refinement. Moreover, we prove that our indicator is equivalent to the classical explicit a posteriori error estimator in a certain sense. Numerical results suggest that our method leads to efficient and competitive adaptive refinement.
Keywords: Adaptive mesh refinement; Asymptotic expansion; Sensitivity-based refinement; Topological sensitivity

Adaptive optics enhanced direct laser writing of high refractive index gyroid photonic crystals in chalcogenide glass - Cumming, Benjamin P.; Turner, Mark D.; Schröder-Turk, Gerd; Debbarma, Sukanta; Luther-Davies, Barry; Gu, Min (Optics Express, 2014)
Chiral gyroid photonic crystals are fabricated in the high refractive index chalcogenide glass arsenic trisulfide with an adaptive optics enhanced direct laser writing system. The severe spherical aberration imparted when focusing into the arsenic trisulfide is mitigated with a defocus decoupled aberration compensation technique that reduces the level of aberration that must be compensated by over an order of magnitude. The fabricated gyroids are shown to have excellent uniformity after our adaptive optics method is employed, and the transmission spectra of the gyroids are shown to have good agreement with numerical simulations that are based on a uniform and diffraction limited fabrication resolution.
EAM Import::2019-03-13

Additive fabrication of nanostructures with focused soft X-rays - Späth, Andreas; TU, Fan; Vollnhals, Florian; Drost, Martin; Krick Calderon, Sandra; Watts, Benjamin; Fink, Rainer; Marbach, Hubertus (RSC Advances, 2016)
We report on a novel technique for the fabrication of metallic nanostructures via soft X-ray irradiation of precursor molecules supplied from the gas phase. With this technique we were able to produce localized Co nanostructures with a growth rate and purity competitive with electron beam induced deposition. We demonstrate that our approach exhibits significant selectivity with respect to incident photon energy leading to enhanced growth for resonant absorption energy of the precursor molecule. Based on this finding we propose a unique new pathway of selective deposition from precursor mixtures. Furthermore, we investigated the growth rate with respect to precursor pressure and growth time and discuss the potential resolution limits of this new technique.
EAM Import::2019-03-13

Additive Fertigung durch selektives Elektronenstrahlschmelzen - Markl, Matthias; Lodes, Matthias; Franke, Martin; Körner, Carolin (Schweissen und Schneiden, 2017)
Die additive Fertigung umfasst alle Verfahren, die ein Bauteil schichtweise anhand eines dreidimensionalen Computermodells aufbauen. Der additive Aufbau ermöglicht komplexe geometrische Formen, die nahezu keinen Restriktionen unterliegen und dadurch mit konventionellen Fertigungsverfahren nicht oder nur mit hohem Aufwand realisierbar wären. Das selektive Elektronenstrahlschmelzen (SEBM) ist ähnlich dem selektiven Laserstrahlschmelzen ein pulverbettbasierter additiver Fertigungsprozess, bei dem die Pulverpartikel durch den Strahl lokal aufgeschmolzen und konsolidiert werden. Der Elektronenstrahl ermöglicht die Verarbeitung hochschmelzender und reaktiver Metalle unter Vakuum sowie eine für additive Fertigungsprozesse hohe Baurate durch hohe Leistungsdichten und schnelle Ablenkgeschwindigkeiten. In diesem Artikel werden der Anlagenaufbau und der Prozessablauf beim SEBM beschrieben sowie die bisher untersuchten Werkstoffklassen, ausgewählten Anwendungen und die numerische Simulation dieses Verfahrens vorgestellt.

Additive Manufacturing of Ceramic-Based Materials - Travitzky, Nahum; Bonet, Alexander; Dermeik, Benjamin; Fey, Tobias; Filbert-Demut, Ina; Schlier, Lorenz; Schlordt, Tobias; Greil, Peter (Advanced Engineering Materials, 2014)
This paper offers a review of present achievements in the field of processing of ceramic-based materials with complex geometry using the main additive manufacturing (AM) technologies. In AM, the geometrical design of a desired ceramic-based component is combined with the materials design. In this way, the fabrication times and the product costs of ceramic-based parts with required properties can be substantially reduced. However, dimensional accuracy and surface finish still remain crucial features in today's AM due to the layer-by-layer formation of the parts. In spite of the fact that significant progress has been made in the development of feedstock materials, the most difficult limitations for AM technologies are the restrictions set by material selection for each AM method and aspects considering the inner architectural design of the manufactured parts. Hence, any future progress in the field of AM should be based on the improvement of the existing technologies or, alternatively, the development of new approaches with an emphasis on parts allowing the near-net formation of ceramic structures, while optimizing the design of new materials and of the part architecture.

Additive manufacturing of metallic components by selective electron beam melting - A review - Körner, Carolin (International Materials Reviews, 2016)
Selective electron beam melting (SEBM) belongs to the additive manufacturing technologies which are believed to revolutionise future industrial production. Starting from computer-aided designed data, components are built layer by layer within a powder bed by selectively melting the powder with a high power electron beam. In contrast to selective laser melting (SLM), which can be used for metals, polymers and ceramics, the application field of the electron beam is restricted to metallic components since electric conductivity is required. On the other hand, the electron beam works under vacuum conditions, can be moved at extremely high velocities and a high beam power is available. These features make SEBM especially interesting for the processing of high-performance alloys. The present review describes SEBM with special focus on the relationship between process characteristics, material consolidation and the resulting materials and component properties.
Keywords: Additive manufacturing; Alloys; Metals; Microstructure; Properties; Review; Selective electron beam melting

Adjusting Optimized Material Properties for Tailored Heat Treated Blanks - Merklein, Marion; Hung Nguyen, (Key Engineering Materials, 2011)
Aluminum alloys have great potential for lightweight construction. In order to achieve an optimized properties distribution for the forming operation and to enhance the formability of aluminum alloys, so called Tailored Heat Treated Blanks (THTB) are developed. In this context, this paper is about the local precipitation hardening of sheet metals for the application of THTB. By using a specific, short-term heat treatment via conductive heating plates the thermal induced hardening of the fast hardenable alloy AA6181PX is quantified and qualified. Considering the processibility of the local precipitation hardening for THTB, a process window for the heat treatment parameters is presented allowing a precise setting of the mechanical material properties.
EAM Import::2019-03-13

Adsorption and Activation of CO on Co3O4(111) Thin Films - Ferstl, Pascal; Mehl, Sascha; Arman, M. A.; Schuler, Marina; Toghan, A.; Laszlo, B.; Lykhach, Yaroslava; Brummel, Olaf; Lundgren, Edvin; Knudsen, J.; Hammer, Lutz; Schneider, M. Alexander; et al. (Journal of Physical Chemistry C, 2015)
To explore the catalytic properties of cobalt oxide at the atomic level, we have studied the interaction of CO and O2 with well-ordered Co3O4(111) thin films using scanning tunneling microscopy (STM), high-resolution X-ray photoelectron spectroscopy (HR-XPS), infrared reflection absorption spectroscopy (IRAS), and temperature-programmed desorption spectroscopy (TPD) under ultrahigh vacuum (UHV) conditions. At low coverage and temperature, CO binds to surface Co2+ ions on the (111) facets. At larger exposure, a compressed phase is formed in which additional CO is located at sites in between the Co2+ ions. In addition, a bridging carbonate species forms that is associated with defects such as step edges of Co3O4(111) terraces or the side facets of the (111) oriented grains. Preadsorbed oxygen neither affects CO adsorption at low coverage nor the formation of the surface carbonate, but it blocks formation of the high coverage CO phase. Desorption of the molecularly bound CO occurs up to 180 K, whereas the surface carbonate decomposes in a broad temperature range up to 400 K under the release of CO and, to a lesser extent, of CO2. Upon strong loss of crystalline oxygen, the Co3O4 grains eventually switch to the CoO rocksalt structure.

Adsorption and Decomposition of Formic Acid on Model Ceria and Pt/Ceria Catalysts - Lykhach, Yaroslava; Happel, Markus; Johanek, Viktor; Skala, Tomas; Kollhoff, Fabian; Tsud, Nataliya; Dvorak, Filip; Prince, Kevin C.; Matolin, Vladimir; Libuda, Jörg (Journal of Physical Chemistry C, 2013)
Adsorption and reaction of formic acid on stoichiometric CeO2(111), partially reduced CeO2-x, and Pt/CeO2(111) films prepared on Cu(111) were studied by means of synchrotron radiation photoelectron spectroscopy (SRPES), resonant photoemission spectroscopy (APES), infrared reflection absorption spectroscopy (IRAS), and temperature-programmed desorption (TPD). On all studied samples, the principal species formed during formic acid adsorption below 160 K were formate and molecular formic acid. In the presence of Pt particles, formate species were predominantly localized on Pt at 100 K, and on ceria at or above 300 K. Below 400 K, molecular formic acid decomposes to formate with partial release of CO2, CO, hydrogen, and water. Analysis of the TPD fragmentation suggests additional evolution of methane. Above 400 K, desorption of CO2, CO, hydrogen, and water is observed. This process is controlled by the stoichiometry of ceria and the presence of Pt particles. In particular, desorption of CO2 is suppressed on CeO2-x but is enhanced on Pt/CeO2. APES suggests that the reaction of formic acid does not alter the oxidation state of cerium cations on CeO2(111). By contrast, we observed significant reoxidation on partially reduced CeO2-x, between 250 and 400 K, followed by reduction between 400 and 500 K.

Adsorption and reaction of acetylene on clean and oxygen-precovered Pd(100) studied with high-resolution X-ray photoelectron spectroscopy - Höfert, Oliver; Lorenz, Michael Peter Andreas; Streber, Regine; Zhao, Wei; Bayer, Andreas; Steinrück, Hans-Peter; Papp, Christian (Journal of Chemical Physics, 2013)
We investigated the adsorption and thermal evolution of acetylene on clean Pd(100) and Pd(100) precovered with 0.25 ML oxygen. The measurements were performed in situ by fast XPS at the synchrotron radiation facility BESSY II. On Pd(100) acetylene molecularly adsorbs at 130 K. Upon heating transformation to a CCH species occurs around 390 K along with the formation of a completely dehydrogenated carbon species. On the oxygen-precovered surface partial CCH formation already occurs upon adsorption at 130 K, and the dehydrogenation temperature and the stability range of CCH are shifted to lower temperatures by ∼200 K. © 2013 AIP Publishing LLC.

Adsorption and reaction of NO2 on ordered alumina films and mixed baria-alumina nanoparticles: Cooperative versus non-cooperative reaction mechanisms - Desikusumastuti, Aine; Staudt, Thorsten; Happel, Markus; Laurin, Mathias; Libuda, Jörg (Journal of Catalysis, 2008)
In order to obtain insights into the mechanism and kinetics of adsorption and reaction of NO2 on aluminum and barium oxide surfaces, we have performed systematic adsorption experiments on single-crystal-based model materials. As a model surface, we use BaO containing nanoparticles grown by physical vapor deposition (PVD) of Ba under ultrahigh vacuum (UHV) conditions on an ordered Al2O3 film on NiAl(110) and subsequent oxidation and annealing. The growth behavior, the morphology and the chemical composition of the three-dimensional mixed barium aluminum oxide particles (BaAl2xO1+3x) formed via this procedure have previously been characterized by scanning tunneling microscopy (STM) and high-resolution photoelectron spectroscopy (HR-PES). In order to monitor adsorption and reaction processes on these systems, we perform time-resolved infrared reflection absorption spectroscopy (TR-IRAs) during exposure to a molecular beam (MB) of NO2. In a first step, the interaction of NO2 with the Al2O3/NiAl(110) model support is probed. At 100 K, only molecular adsorption occurs in form of the D-2h dimer (N2O4) in all coverage regions from the submonolayer up to multilayers. At 300 K, a slow surface reaction occurs, initially leading to the formation of surface nitrites and, subsequently, of surface nitrates in bridging adsorption geometry. On the BaAl2xO1+3x, particles on Al2O3/NiAl(110), NO2 shows a very different and strongly temperature-dependent behavior. At 100 K, molecular adsorption of the D-2h dimer (N2O4) is accompanied by a highly efficient reaction channel, leading to the formation of surface nitrites and nitrates. With the surface temperature increasing to 300 K, however, the reaction probability decreases by several orders of magnitude. In contrast to reaction at 100 K, surface nitrites in flat-lying adsorption geometry are the only primary product, indicating a temperature-dependent change in the reaction mechanism from a cooperative to a non-cooperative pathway. With increasing exposure, the nitrite coverage increases and, finally, the surface nitrites are converted into bridging and monodentate Surface nitrates. The latter reaction shows a complex kinetics, including an initial induction period. For temperatures of 400 K and above, nitrate formation becomes more efficient, eventually resulting in the formation of ionic nitrates. The vibrational properties of these ionic species sensitively depend on the reaction temperature, indicating the formation of well-defined structures in a narrow temperature interval around 500 K. The mechanism of the NOx storage process and the vibrational assignments of the related surface species are critically discussed on the basis of the present results. (C) 2008 Elsevier Inc. All rights reserved.
Keywords: Nitrogen dioxide; Barium oxide; Aluminum oxide; Supported model catalysts; NSR catalysts; Scanning tunneling microscopy; IR reflection absorption spectroscopy; Molecular beams

Adsorption and reaction of SO2 on clean and oxygen precovered Pd(100) - A combined HR-XPS and DF study - Luckas, Nicola; Gotterbarm, Karin; Streber, Regine; Lorenz, Michael Peter Andreas; Höfert, Oliver; Vines, Francesc; Papp, Christian; Görling, Andreas; Steinrück, Hans-Peter (Physical Chemistry Chemical Physics, 2011)
We studied the adsorption and reactivity of SO on clean and oxygen precovered Pd(100) with high resolution X-ray photoelectron spectroscopy and density functional calculations. Upon adsorption at 120 K two different SO species were detected, which were identified as upright-standing and flat-lying molecules by comparing the calculated core level shifts. In agreement with the relative stabilities determined by the calculations the intensities of the photoelectron spectra indicate that the majority species are upright-standing SO . Upon heating the quantitative analysis of the data indicates desorption of SO and formation of atomic sulfur. On the oxygen precovered surface small amounts of SO are formed already upon SO adsorption at low temperatures. Upon heating stepwise oxidation of SO to SO and, eventually, to SO is found. Two different SO species were detected, which are assigned to SO bound in the proximity of or remote from oxygen adatoms, according to core level shift estimates. © 2011 the Owner Societies.

Adsorption and Reaction of SO2 on Graphene-Supported Pt Nanoclusters - Gotterbarm, Karin; Späth, Florian; Bauer, Udo; Steinrück, Hans-Peter; Papp, Christian (Topics in Catalysis, 2015)
Atomic sulfur and its oxides are common catalyst poisons and intriguing research subjects. Recently, graphene-supported nanoclusters were introduced as suitable model catalysts. We investigated the adsorption and reaction of SO2 on graphene-supported Pt nanocluster arrays with high-resolution X-ray photoelectron spectroscopy. SO2 adsorbs in two geometries-perpendicular and parallel to the surface-on both cluster facets and steps. Further insight is gained from the comparison of our results to previous data of SO2 on Pt(111) and two stepped single crystal surfaces-Pt(322) and Pt(355)-with (100) and (111) steps, respectively. We find a remarkable similarity to the adsorption situation on Pt(322). However, thermal evolution experiments revealed several similarities to both Pt(322) and Pt(355), showing that the Pt nanoclusters exhibit a mixture of (100) and (111) steps.
Keywords: XPS; Platinum; Nanoclusters; SO2; Graphene

Adsorption and reaction of terephthaloyl chloride on Ag(111): X-ray photoelectron spectroscopy and density functional theory investigations - Schmid, Martin; Hieringer, Wolfgang; Schmitz, Christoph H.; Steinrück, Hans-Peter; Sokolowski, Moritz; Gottfried, Michael (Journal of Physical Chemistry C, 2011)
The adsorption and reaction of terephthaloyl chloride (TPC) on a Ag(111) surface was investigated with X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. Below 120 K, TPC forms multilayers without reacting with the Ag(111) substrate. Multilayer desorption starts above 120 K and is accompanied by a chemical reaction between the TPC molecules and the Ag surface. This reaction involves scission of the carbon-chlorine bond, resulting in the formation of adsorbed chlorine atoms and a p-phenylene dicarbonyl (pPDC) species. This molecular fragment is stable at room temperature and does not undergo further decomposition, presumably due to stabilization by adsorbate-substrate interactions and/or oligomerization. The DFT calculations confirm that pPDC is a possible intermediate or final reaction product and show that the two carbonyl C atoms form covalent bonds to the Ag substrate. © 2011 American Chemical Society.

Adsorption Behavior of a Cyano-Functionalized Porphyrin on Cu(111) and Ag(111): From Molecular Wires to Ordered Supramolecular Two-Dimensional Aggregates - Lepper, Michael; Schmitt, Tobias; Gurrath, Martin; Raschmann, Marco; Zhang, Liang; Stark, Michael Werner; Hölzel, Helen; Jux, Norbert; Meyer, Bernd; Schneider, M. Alexander; Steinrück, Hans-Peter; Marbach, Hubertus (Journal of Physical Chemistry C, 2017)
We investigate the impact of peripheral cyano functionalization of the previously well-studied 2H-tetraphenylporphyrin (2HTPP) by scanning tunneling microscopy (STM) and density functional theory (DFT). The adsorption behavior of 2H-tetralds(p-cyano)-phenylporphyrin (2HTCNPP) is studied at room temperature and at 80 K on Cu(111) and Ag(111). Interestingly, the cyano-functionalized porphyrins tend to form isolated ID chains on Cu(111), in particular after mild annealing at 350 K. The individual 2HTCNPPs as well as the formed chains are oriented along the main crystallographic directions of the Cu(111) substrate due to a strongly attractive and site-specific interaction between the iminic nitrogens of the 2HTCNPP and Cu substrate atoms. The linking within the 1D molecular chains is realized by Cu adatoms as evidenced by comparison of STM and DFT. In contrast, on Ag(111) the molecules assemble into 2D supramolecular layers with long-range order and a square unit cell, stabilized by molecule-molecule interactions. The orientation of the molecules with respect to the unit cell lattice vectors leads to organizational chirality. By codeposition of cobalt, the porphyrin molecules are metalated at room temperature. We did not observe any evidence for metal-organic network formation on Ag(111), even after varying the deposition parameters or the order of metal and porphyrin deposition. Our study shows that cyano functionalization of porphyrins can give rise to novel and unique self-assembled structures like 1D molecular chains without any cross-connections via adatom linking.

Adsorption, Ordering, and Metalation of Porphyrins on MgO Nanocube Surfaces: The Directional Role of Carboxylic Anchoring Groups - Schneider, Johannes; Kollhoff, Fabian; Schindler, Torben; Bichlmaier, Stephan; Bernardi, Johannes; Unruh, Tobias; Libuda, Jörg; Berger, Thomas; Diwald, Oliver (Journal of Physical Chemistry C, 2016)
The understanding of porphyrin adsorption on oxide nanoparticles including knowledge about coverages and adsorbate geometries is a prerequisite for the improvement and optimization of hybrid materials. The combination of molecular spectroscopies with small-angle X-ray scattering provides molecular insights into porphyrin adsorption on MgO nanocube dispersions in organic solvents. In particular, we address the influence of terminal carboxyl groups on the adsorption of free base porphyrins, on their chemical binding, on the metalation reaction as well as on the coverage and orientation of adsorbate molecules. We compare the free base form 5,10,15,20-tetraphenyl-21,23H-porphyrin (2HTPP) with the carboxyl-functionalized 5,10,15,20-tetrakis(4-carboxyphenyl)-21,23H-porphyrin (2HTCPP) and show that without carboxylic anchoring groups the free base form metalates on the nanocube surface and adopts a flat-lying adsorbate geometry. The saturation limit for flat-lying adsorption on nanocubes with an average edge length of 6 nm corresponds to 90 14 molecules per particle. This limit is surpassed when 2HTCPP molecules attach via their terminal carboxyl groups to the surface. The resulting upright adsorption geometry suppresses self-metalation, on the one hand, and allows for much higher porphyrin coverages, on the other (at porphyrin concentrations in the stock solution of 2 X 10(-2) mol.L-1). UV-vis diffuse reflectance results are perfectly consistent with conclusions from SAXS data analysis. The experiments reveal concentration dependent 2HTCPP coverages in the range between 0.4 to 1.9 molecules nm(-2) which correspond to the formation of a shell of upright standing porphyrin molecules around the MgO nanocubes. In contrast, after adsorption and metalation of nonfunctionalized 2HTPP the resulting porphyrin shells are in the range of a tenth of a nanometer and thus too thin to be captured by SAXS measurements. Related insights advance our opportunities to prepare well-defined nanohybrids containing highly organized porphyrin films.

Adsorption sites, metal-support interactions, and oxygen spillover identified by vibrational spectroscopy of adsorbed CO: A model study on Pt/ceria catalysts - Happel, Markus; Myslivecek, Josef; Johanek, Viktor; Dvorak, Filip; Stetsovych, Oleksandr; Lykhach, Yaroslava; Matolin, Vladimir; Libuda, Jörg (Journal of Catalysis, 2012)
Vibrational spectroscopy of adsorbed CO is commonly used for the characterization of oxide-supported metal catalysts, in spite of persisting ambiguities concerning the band assignment. Here, we present reference data on well-defined Pt/CeO2(1 1 1)/Cu(1 1 1) model catalysts aiming at clear identification of the related features. Growth and morphology of the Pt particles are investigated by scanning tunneling microscopy (STM), the adsorption properties are probed by temperature programmed desorption (TPD), and the electronic structure has previously been studied by photoelectron spectroscopy (PES) and resonant photoelectron spectroscopy (RPES). Combining molecular beam (MB) methods and infrared reflection absorption spectroscopy (IRAS), we correlate this information to the interaction with CO.Two types of defect adsorption sites are identified on the ceria support (2097 cm(-1), 2120 cm(-1)), which are assigned to structural defects and reduced Ce3+ centers. The relative abundance of these sites changes upon thermal treatment. On the Pt nanoparticles, CO first adsorbs on-top at step and edge sites (2066 cm(-1)), before adsorption on the (1 1 1) facets occurs in bridging (1875 cm(-1)) and on-top (2080-2097 cm(-1)) geometry. For the first time, we identify vibrational CO features, which arise from electronic metal-support interactions and from oxygen reverse spillover. On reduced CeO2-x(1 1 1), a red-shifted band at 2053 cm(-1) appears, which is attributed to increased pi-backbonding from Pt to CO, as a result of a change in electronic metal-oxide interaction. Thermal treatment also activates oxygen reverse spillover from the support to the Pt nanoparticle, which gives rise to a blue-shifted feature in the CO spectrum (2090-2105 cm(-1)) due to coadsorbed oxygen next to CO sites. (C) 2012 Elsevier Inc. All rights reserved.
Keywords: Model catalysis; Cerium oxide; Platinum; Metal-oxide interaction; Carbon monoxide; Infrared spectroscopy; Scanning tunneling microscopy

Advanced Geometries of PEDOT Formed in Titania Nanotubes - Kowalski, Damian; Schmuki, Patrik (ChemPhysChem, 2012)
In and out of tube: Robust poly-3,4-ethylene-dioxythiophene nanostructures in the form of nanopore arrays and inverse nanotube arrays are obtained by site-selective deposition into TiO2 nanotubes. The deposition process critically depends on the applied potential (see picture) and is in line with three-dimensional (3D) progressive and 3D instantaneous nucleation-growth mechanism, leading to the construction of polymer blocks or polymer/semiconductor hybrids.
EAM Import::2019-03-13

Advancements in Polymer-Filler Derived Ceramics - Greil, Peter (Journal of the Korean Ceramic Society, 2012)
Microstructure tailoring of filler loaded preceramic polymer systems offers a high potential for property improvement of Si-based ceramics and composites. Advancements in manufacturing of bulk materials by controlling microstructure evolution during thermal induced polymer-ceramic transforma-tion and polymer-filler reactions will be presented. Rate controlled pyrolysis, multilayer gradient laminate design and surface modification by gas solid reaction are demonstrated to yield ceramic components of high fractional density and superior mechanical properties. Emerging fields of applications are presented.
EAM Import::2019-03-13

Advances in Colloidal Assembly: The Design of Structure and Hierarchy in Two and Three Dimensions - Vogel, Nicolas; Retsch, Markus; Fustin, Charles-Andre; Del Campo, Aranzazu; Jonas, Ulrich (Chemical Reviews, 2015)
No abstract available for this article

Aerosol synthesis of silicon nanoparticles with narrow size distribution-Part 1: Experimental investigations - Körmer, Richard; Jank, Michael; Ryssel, Heiner; Schmid, Hans-Joachim; Peukert, Wolfgang (Journal of Aerosol Science, 2010)
A study on the feasibility of aerosol processing of nearly monodisperse silicon nanoparticles via pyrolysis of monosilane in a hot wall reactor is presented. For optimal conditions silicon nanoparticles with a geometric standard deviation of 1.06 were synthesized at a production rate of 0.7 g/h. The size of the particles could be precisely controlled in the range of 20–40 nm, whilst maintaining a geometric standard deviation in the range of 1.06–1.08, by proper choice of the governing parameters temperature, residence time and precursor concentration. The results show that narrow particle size distributions can only be obtained in the temperature range between 900 and 1100 °C, as long as both the initial silane concentration (1 mbar silane partial pressure) and the reactor total pressure are low (25 mbar). This regime for the production of narrow particle size distributions has not been identified in prior work on the thermal decomposition of silane. Narrowly distributed particles can be obtained under conditions where nucleation and particle growth are separated and the agglomeration rates are negligible.

Aerosol synthesis of silicon nanoparticles with narrow size distribution-Part 2: Theoretical analysis of the formation mechanism - Körmer, Richard; Schmid, Hans-Joachim; Peukert, Wolfgang (Journal of Aerosol Science, 2010)
This work investigates the mechanisms which lead to the formation of silicon nanoparticles with narrow size distributions by means of population balance modeling. The model accounts for the full aerosol process, including chemical reaction, nucleation from supersaturated vapor, growth and agglomeration. The results are in good agreement with experimental data. The effects of the process parameters temperature, silane concentration and reactor total pressure are systematically investigated. The simulation allows an in-depth insight into the particle formation mechanism and reveals the key requirements which are necessary for the generation of narrow particle size distributions. In this mechanism, only a short nucleation burst occurs, while surface growth plays the dominant role in silane precursor consumption. A key role is attributed to condensation, because the numerical calculations can only reflect the experimental observations, if the condensation mechanism is included in the model.

A facile approach to synthesize an oxo-functionalized graphene/polymer composite for low-voltage operating memory devices - Wang, Zhenxing; Eigler, Siegfried; Ishii, Yoshitaka; Hu, Yichen; Papp, Christian; Lytken, Ole; Steinrück, Hans-Peter; Halik, Marcus (Journal of Materials Chemistry C, 2015)
Memory devices are a key technology of our era and one of the constant challenges is the reduction of their power consumption. Herein, we demonstrate that graphene oxide with very few defects, that is, about 1 nm thin oxo-functionalized graphene derivative, can be used in memory devices operating at 3 V. A memory device stores charges in the material of the active channel. Thereby, writing and erasing information can be performed at low voltage, facilitating low power consumption. To enable operation at low voltage, a novel synthetic approach is necessary. We find that the selective non-covalent electrostatic functionalization of mainly organosulfate ions is possible with dodecylammonium. This functionalization allows the non-covalent coating of flakes with a polystyrene-derivative as nm-thin dielectric medium. The resulting polymer-wrapped composite has a height of about 5 nm. We find that the thin coating of a few nm is mandatory to make the memory device work at low voltage. Furthermore, a self-assembled monolayer of an imidazolium derivative further enhances the function of the memory device. The prepared composite materials are characterized by state-of-the-art analysis including solid state nuclear magnetic resonance spectroscopy and thermogravimetric analysis coupled with gas chromatography, mass spectroscopy or infrared spectroscopy. Reference experiments prove the importance of the controlled synthesis to enable the function of the memory device.

A facile one-step method to reduce surface impurities in solution-processed CuInS2 nanocrystal solar cells - Stahl, Melissa S.; Azimi, Seyed Hamed; Brabec, Christoph (Journal of Materials Chemistry A, 2015)
The presence of impurities and disorders presents a potential barrier for the success of solution processed inorganic nanocrystalline devices. The removal of impurities typically requires harsh conditions and complex procedures that limit utility. This paper demonstrates the successful use of a set of solvents, which can efficaciously remove the surface impurities formed during in situ deposition of CuInS2 nanocrystals. These impurities include a hard-to-remove byproduct melamine that is formed by the decomposition of thiourea at elevated temperatures, and other organic residues like amines, conjugated organic systems, as well as ketones, aldehydes or esters. This work provides some design rules for the selection of solvents for removal purposes that could potentially be used for other absorber materials as well.

A facile route to water-soluble coronenes and benzo[ghi]perylenes - Schmidt, Cordula; Lang, Nina; Jux, Norbert; Hirsch, Andreas (Chemistry - A European Journal, 2011)
Click reactions at the bay-position of perylenes and a new route to benzo[ghi]perylenes and coronenes are presented. Irradiation with light leads to an electrocyclic reaction of the newly formed triazole ring(s) with the neighbouring bay-positions of the perylene core and after oxidation by air, the benzo[ghi]perylenes and coronenes are obtained. By using Newkome dendrimers as substituents for perylene diimides (PDIs), water solubility can be achieved after removal of the tert-butyl protecting groups. The aggregation and optical properties of the bay-functionalised PDIs, benzo[ghi]perylenes and coronenes are investigated by absorption and fluorescence spectroscopy. Given the green light: Click reactions at the bay-positions of perylene diimides were carried out for the first time. The newly formed triazole units undergo electrocyclisation reactions with the neighbouring perylene bay-position to form benzoperylenes or coronenes (see scheme). The reactions occur in solution in 55-87%yield by irradiation with light, providing a simple, new and environmentally friendly route to coronenes and benzoperylenes. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A fast-adaptive composite grid algorithm for solving the free-space Poisson problem on the cell broadband engine - Ritter, Daniel; Stürmer, Markus; Rüde, Ulrich (Numerical Linear Algebra With Applications, 2010)
Fast solvers for Poisson's equation with boundary conditions at infinity are an important building block for molecular dynamics. One issue that arises when this equation is solved numerically is the infinite size of the domain. This prevents a direct solution so that other concepts have to be considered. Within this paper a method is discussed that employs hierarchically coarsened grids to overcome this problem. Special attention has to be paid to the discretization at the grid interfaces. A finite volume approach is used for the same. The resulting set of linear equations is solved using a fast-adaptive composite grid algorithm. Emphasis is put on the implementation of the method on the STI cell broadband engine, a modern multi core processor, that is powerful in floating point operations and memory bandwidth. Code optimization techniques are applied as well as parallelization of the code to get maximum performance on this processor. For validation of the performance test runs are executed and the runtime is analyzed in detail. © 2010 John Wiley & Sons, Ltd.
UnivIS-Import:2015-03-09:Pub.2010.tech.IMMD.lsinfs.afasta
Keywords: Adaptive grids; Cell broadband engine; Potential equation

A fiber optic temperature sensor based on the combination of epoxy and glass particles with different thermo-optic coefficients - Wildner, Wolfgang; Drummer, Dietmar (Photonic Sensors, 2016)
This paper describes the development and function of an optical fiber temperature sensor made out of a compound of epoxy and optical glass particles. Because of the different thermo-optic coefficients of these materials, this compound exhibits a strong wavelength and temperature dependent optical transmission, and it therefore can be employed for fiber optic temperature measurements. The temperature at the sensor, which is integrated into a polymer optical fiber (POF), is evaluated by the ratio of the transmitted intensity of two different light-emitting diodes (LED) with a wavelength of 460 nm and 650 nm. The material characterization and influences of different sensor lengths and two particle sizes on the measurement result are discussed. The temperature dependency of the transmission increases with smaller particles and with increasing sensor length. With glass particles with a diameter of 43 extgreekmm and a sensor length of 9.8 mm, the intensity ratio of the two LEDs decreases by 60% within a temperature change from 10℃ to 40℃.
UnivIS-Import:2017-01-09:Pub.2016.tech.FT.FT-KT.afiber
Keywords: epoxy; fiber optic sensors; glass particles; Temperature sensors; thermo-optic coefficient

A Fiber Optic Temperature Sensor Based on the Combination of Two Materials with Different Thermo-Optic Coefficients - Wildner, Wolfgang; Drummer, Dietmar (IEEE Sensors Journal, 2016)
The design and development of a plastic optical fiber (POF) temperature sensor is presented: By combining two materials with different thermo-optic coefficients (in this case: a transparent oil or polymer and glass-particles) in a compound, a temperature dependent transmission can be achieved. With the use of more than one light source with different wavelengths, a spectrometer for the analysis of the measurement is no longer necessary.
UnivIS-Import:2016-02-10:Pub.2015.tech.FT.FT-KT.afiber

A Finite Element Framework for Continua with Boundary Energies. Part I: The Two-Dimensional Case - Javili, Ali; Steinmann, Paul (Computer Methods in Applied Mechanics and Engineering, 2009)
This contribution deals with the implications of boundary potential energies on the two-dimensional deformations of solids in the framework of the finite element method. Common modelling in continuum mechanics takes exclusively the bulk into account, nevertheless, neglecting possible contributions from the boundary. However, boundary effects sometimes play a dominant role in the material behavior, the most prominent example being surface tension. Within this contribution the boundary potentials are allowed, in general, to depend not only on the boundary deformation but also on the boundary deformation gradient and the spatial boundary tangent. For the finite element implementation, a suitable curvilinear convected coordinate system attached to the boundary is defined and corresponding geometrical and kinematical derivations completely based on a tensorial representation are carried out. Afterwards, the discretization of the generalized weak formulation, including boundary potentials, is performed and eventually numerical examples are presented to demonstrate the boundary effects due to different proposed material models. © 2009 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2009.tech.FT.FT-TM.afinit
Keywords: Boundary potentials; Surface tension

A first-principles based force-field for Li+ and OH- in ethanolic solution - Milek, Theodor; Meyer, Bernd; Zahn, Dirk (Journal of Chemical Physics, 2013)
We report on the development of force-field parameters for accurately modeling lithium and hydroxide ions in ethanol in solution. Based on quantum calculations of small molecular clusters mimicking the solvent structure of individual ions as well as the solvated LiOH dimer, significant improvements of off-the-shelf force-fields are obtained. The quality of our model is demonstrated by comparison to ab initio molecular dynamics of the bulk solution and to experimental data available for ethanol/water mixtures.
EAM Import::2019-03-13

A flexible method for the preparation of thin film samples for in situ TEM characterization combining shadow-FIB milling and electron beam-assisted etching - Liebig, Jan Philipp; Göken, Mathias; Richter, Gunther; Mackovic, Mirza; Przybilla, Thomas; Spiecker, Erdmann; Pierron, O. N.; Merle, Benoit (Ultramicroscopy, 2016)
A new method for the preparation of freestanding thin film samples for mechanical testing in transmission electron microscopes is presented. It is based on a combination of focused ion beam.(FIB) milling and electron-beam-assisted etching with xenon difluoride (XeF2) precursor gas. The use of the FIB allows for the target preparation of microstructural defects and enables well-defined sample geometries which can be easily adapted in order to meet the requirements of various testing setups. In contrast to existing FIB-based preparation approaches, the area of interest is never exposed to ion beam irradiation which preserves a pristine microstructure. The method can be applied to a wide range of thin film material systems compatible with XeF2 etching. Its feasibility is demonstrated for gold and alloyed copper thin films and its practical application is discussed. (C) 2016 Elsevier B.V. All rights reserved.
Keywords: Thin films; FIB; Electron-beam-assisted etching; XeF2; Micromechanical testing

A flexible Patch-based lattice Boltzmann parallelization approach for heterogeneous GPU-CPU clusters - Feichtinger, Christian; Köstler, Harald; Hager, Georg; Rüde, Ulrich; Wellein, Gerhard; Habich, Johannes (Parallel Computing, 2011)
Sustaining a large fraction of single GPU performance in parallel computations is considered to be the major problem of GPU-based clusters. We address this issue in the context of a lattice Boltzmann flow solver that is integrated in the WaLBerla software framework. Our multi-GPU implementation uses a block-structured MPI parallelization and is suitable for load balancing and heterogeneous computations on CPUs and GPUs. The overhead required for multi-GPU simulations is discussed in detail. It is demonstrated that a large fraction of the kernel performance can be sustained for weak scaling on InfiniBand clusters, leading to excellent parallel efficiency. However, in strong scaling scenarios using multiple GPUs is much less efficient than running CPU-only simulations on IBM BG/P and x86-based clusters. Hence, a cost analysis must determine the best course of action for a particular simulation task and hardware configuration. Finally we present weak scaling results of heterogeneous simulations conducted on CPUs and GPUs simultaneously, using clusters equipped with varying node configurations. © 2011 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2011.tech.IMMD.lsinfs.aflexi
Keywords: CUDA; Heterogeneous computations; Lattice Boltzmann method; MPI

A Fully Conjugated TTF-π-TCAQ System: Synthesis, Structure, and Electronic Properties - Santos, Jose; Illescas, Beatriz M.; Martin, Nazario; Adrio, Javier; Carretero, Juan C.; Viruela, Rafael; Orti, Enrique; Spänig, Fabian; Guldi, Dirk Michael (Chemistry - A European Journal, 2011)
The synthesis of the first fully conjugated tetrathiafulvalene–tetracyano-p-quinodimethane ((TTF)–TCNQ)-type system has been carried out by means of a Julia–Kocienski olefination reaction. In particular, a tetracyanoanthraquinodimethane (TCAQ) formyl derivative and two new sulfonylmethyl-exTTFs (exTTF=2-[9-(1,3-dithiol-2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole)—prepared as new building blocks—were linked. A variety of experimental conditions reveal that the use of sodium hexamethyldisilazane (NaHMDS) as base in THF afforded the E olefins with excellent stereoselectivity. Theoretical calculations at the B3LYP/6-31G** level point to highly distorted exTTF and TCAQ that form an almost planar stilbene unit between them. Although calculations predicted appreciable electronic communication between the donor and the acceptor, cyclic voltammetric studies did not substantiate this effect. It was only in photophysical assays that the electronic communication emerged in the form of a charge-transfer (CT) absorption and emission. Once photoexcited (i.e., the locally excited state or excited charge-transfer state), an ultrafast, subpicosecond charge separation leads to a radical ion pair state in which the spectroscopic features of the radical cation of exTTF as well as the radical anion of TCAQ are discernable. The radical ion pair is metastable and undergoes a fast ((1.0±0.2)ps) charge recombination to reconstitute the electronic ground state. Such ultrafast charge separation and recombination processes come as a consequence of the very short vinyl linkage between the two electroactive units.
EAM Import::2019-03-13

A future energy supply based on Liquid Organic Hydrogen Carriers (LOHC) - Teichmann, Daniel; Arlt, Wolfgang; Wasserscheid, Peter; Freymann, Raymond (Energy and Environmental Science, 2011)
This contribution describes a concept for the establishment of a competitive energy distribution network based on Liquid Organic Hydrogen Carrier (LOHC) compounds. These compounds are characterized by the fact that they can be loaded and un-loaded with considerable amounts of hydrogen in a cyclic process. This concept links the technical challenge of storing temporary and local energy over-production from regenerative sources with the vision of a sustainable, hydrogen-based mobility. The proposed LOHC compounds have many physico-chemical similarities to diesel. Thus, LOHCs could make use of the existing energy infrastructure (e.g. tank ships, storage tanks or fueling stations) and enable a slow and step-wise replacement of the existing hydrocarbon fuels by alternative LOHC fuels. We consider LOHCs as an attractive way to provide wind and solar energy for mobility applications in the form of liquid energy carrying molecules of similar energy storage densities and manageability as today's fossil fuels.

A General Approach To Study the Thermodynamics of Ligand Adsorption to Colloidal Surfaces Demonstrated by Means of Catechols Binding to Zinc Oxide Quantum Dots - Lin, Wei; Walter, Johannes; Burger, Alexandra; Maid, Harald; Hirsch, Andreas; Peukert, Wolfgang; Segets, Doris (Chemistry of Materials, 2015)
A general strategy to study the thermodynamics of ligand adsorption to colloidal surfaces was established. The versatility of our approach is demonstrated by means of catechols binding to ZnO quantum dots (QDs). First, isothermal titration calorimetry (ITC) was used to extract all relevant thermodynamic parameters, namely association constant, enthalpy, entropy, and free energy of ligand binding. Noteworthy, the determined ΔG of −20.3 ± 0.4 kJ mol–1 indicates a strong, reproducible, and exothermic interaction between the catechol anchor group and the oxide particle surface. To confirm the characterization of ligand binding by measuring the heat of adsorption, the free energy was cross-validated by mass-based adsorption isotherms. A combination of inductively coupled plasma optical emission spectroscopy (ICP-OES) and UV/vis spectroscopy was developed to quantitatively determine the mass of bound catechols with respect to the available particle surface. The association constant K was determined by a Langmuir fit to be 2618 M–1 which leads to ΔG = −19.50 kJ mol–1 according to ΔG = −RTln K. To close the mass balance, analytical ultracentrifugation (AUC) was applied to detect the amount of the free, unbound catechol in solution. Finally, Raman spectroscopy and nuclear magnetic resonance spectroscopy (NMR) were performed to quantify the amount of remaining acetate from particle synthesis and to distinguish bound (chemisorbed) and unbound (physisorbed) catechol. Our results reveal that approximately 65 wt % of acetate is replaced, and physisorbed catechol will not affect the amount of remaining acetate on the ZnO surface. Moreover, no pronounced chemical shift peak as it would be expected for free catechol is observed by NMR at all. This indicates a highly dynamic adsorption–desorption equilibrium between the free and the physisorbed state of catechol on the particle surface. Our concept of combined analytics is seen to be a generally applicable strategy for particle-ligand interfacial studies. It gives detailed insight into thermodynamics, binding states, and ligand composition and is thus considered as an important step toward tailored colloidal surface properties.

A generic concept to overcome bandgap limitations for designing highly efficient multi-junction photovoltaic cells - Guo, Fei; Li, Ning; Fecher, Frank W.; Gasparini, Nicola; Ramírez Quiroz, César Omar; Bronnbauer, Carina; Hou, Yi; Radmilovic, Vuk V.; Radmilovic, Velimir R.; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (Nature Communications, 2015)
The multi-junction concept is the most relevant approach to overcome the Shockley-Queisser limit for single-junction photovoltaic cells. The record efficiencies of several types of solar technologies are held by series-connected tandem configurations. However, the stringent current-matching criterion presents primarily a material challenge and permanently requires developing and processing novel semiconductors with desired bandgaps and thicknesses. Here we report a generic concept to alleviate this limitation. By integrating series- and parallel-interconnections into a triple-junction configuration, we find significantly relaxed material selection and current-matching constraints. To illustrate the versatile applicability of the proposed triple-junction concept, organic and organic-inorganic hybrid triple-junction solar cells are constructed by printing methods. High fill factors up to 68% without resistive losses are achieved for both organic and hybrid triple-junction devices. Series/parallel triple-junction cells with organic, as well as perovskite-based subcells may become a key technology to further advance the efficiency roadmap of the existing photovoltaic technologies.
Keywords: GEOBASE Subject Index: fuel cell; photovoltaic system; solar power EMTREE medical terms: Article; electric current; electric potential; electrical equipment; multi junction photovoltaic cell

A generic interface to reduce the efficiency-stability-cost gap of perovskite solar cells - Hou, Yi; Du, Xiaoyan; Scheiner, Simon; McMeekin, David P.; Wang, Zhiping; Li, Ning; Killian, Manuela; Chen, Haiwei; Richter, Moses; Levchuk, Ievgen; Schrenker, Nadine; Spiecker, Erdmann; et al. (Science, 2017)
A major bottleneck delaying the further commercialization of thin-film solar cells based on hybrid organohalide lead perovskites is the interface losses in state-of-the-art devices. We present a generic interface architecture that combines solution-processed, reliable, and cost-efficient hole-transporting materials, without compromising efficiency, stability or scalability of perovskite solar cells. Tantalum doped tungsten oxide (Ta-WOx)/conjugated polymer multilayers offer a surprisingly small interface barrier and form quasi-ohmic contacts universally with various scalable conjugated polymers. Using a simple regular planar architecture device, Ta-WOx doped interface-based perovskite solar cells achieve maximum efficiencies of 21.2% and combined with over 1000 hours of light stability based on a self-assembled monolayer. By eliminating additional ionic dopants, these findings open up the whole class of organics as scalable hole-transporting materials for perovskite solar cell

Aggregation behaviour of chiral ionic liquids - Schulz, Peter; Schneiders, Karola; Wasserscheid, Peter (Tetrahedron-Asymmetry, 2009)
The diastereomeric ionic liquid (IL) (1R,2S)-ephedrinium (RS)-methoxytrifluorophenylacetate 1 was synthesized and its aggregation behavior and diastereomeric interaction were investigated using two independent methods. The aggregation number of the IL in methylene chloride was determined by diffusion ordered NMR spectroscopy. Furthermore the concentration dependence of the signal split of the two diastereomeric ILs (1R,2S)-ephedrinium (R)-methoxytrifluorophenylacetate and (1R,2S)-ephedrinium (S)-methoxytrifluorophenylacetate was measured and could be linked to the aggregation number. © 2009 Elsevier Ltd. All rights reserved.

Aggregation Models of Potential Cyclical Trimethylsulfonium Dicyanamide Ionic Liquid Clusters - Carper, W. Robert; Langenwalter, Kevin; Nooruddin, Naveed S.; Kullman, Michael J.; Gerhard, Dirk; Wasserscheid, Peter (Journal of Physical Chemistry B, 2009)
Raman and infrared spectra of trimethylsulfonium dicyanamide [(CH3)3SN(CN)2] are reported and accurately reproduced by DFT methods (B3LYP and B3PW91), MP2, and MP3, and to a lesser extent by the RHF method. The (CH3)3SN(CN)2 ionic liquid forms two isomeric dimers that are of cyclic structure, one of which is 13 kcal/mol lower in energy than the other. Both isomeric cyclic pairs (versions 1 and 2), [(CH3)3SN(CN)2]2, have the potential to further combine and form a common structure containing four pairs of (CH3)3SN(CN)2. This structure can then conceivably undergo a stacking procedure to form extended ionic liquid nanotubes of eight ionic liquids, [(CH3)3SN(CN)2]8. The possible formation of gas phase ionic liquid clusters of two, four, and eight trimethylsulfonium dicyanamide ionic liquids is supported by highly exergonic free energy changes obtained from B3LYP/(6-311+G(d,p)) density functional calculations.

Air-processed polymer tandem solar cells with power conversion efficiency exceeding 10% - Li, Ning; Brabec, Christoph (Energy and Environmental Science, 2015)
The power conversion efficiencies (PCEs) of the state-of-the-art organic tandem solar cells are steadily improved in the range of 10-12%, which can be mainly attributed to the design and development of highly efficient absorbers with complementary absorption spectra. However, the impressive recorded efficiencies are only achieved for devices spin-coated in an inert atmosphere, which does not directly contribute to the commercialization of the organic photovoltaic technology. Herein, we perform a systematic study of PTB7-Th-based single-junction solar cells fabricated under various conditions. The relatively low photovoltaic performance and poor environmental stability of the air-processed devices are successfully improved by a post-treatment with alcohol-based solvents. The effect of solvent treatment is valid for both regular and inverted device architecture. Tandem devices fabricated by doctor-blading in air achieve a high PCE of 10.03% along with an unprecedentedly high FF of 76.6%.
Keywords: Engineering controlled terms: Conversion efficiency; Efficiency; Photovoltaic cells; Solar absorbers Design and Development; Efficient absorbers; Environmental stability; Organic photovoltaics; Photovoltaic performance; Polymer tandem solar cells; Power conversion efficiencies; Single junction solar cells Engineering main heading: Solar cells

A laboratory X-ray microscopy setup using a field emission electron source and micro-structured reflection targets - Stahlhut, P.; Ebensperger, T.; Zabler, S.; Hanke, R. (Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014)
We present a computed tomography (CT) setup for materials characterization with significantly improved resolution as compared to state of the art mirco- or sub extgreekm-CT systems. The system presented here is composed of a customized JEOL JSM7100-F scanning electron microscope with a thermal field-emission electron source allowing to focus an intense electron beam onto specially designed micro-structured reflection target thereby further reducing the size of the X-ray source spot by reducing the electron interaction zone and thus reducing image blur at high magnifications. With the proposed setup geometric magnifications up to M = 1000 and spatial resolutions down to 100 nm can be achieved. We also demonstrate the phase contrast capabilities of the setup.
EAM Import::2019-03-13

A large electrochemical setup for the anodization of aluminum towards highly ordered arrays of cylindrical nanopores - Assaud, Loic; Bochmann, Sebastian; Christiansen, Silke; Bachmann, Julien (Review of Scientific Instruments, 2015)
A new electrochemical setup and the associated procedures for growing ordered anodic aluminum oxide pore arrays on large surfaces are presented. The typical size of the samples is 14 x 14 cm(2). The most crucial experimental parameters that allow for the stabilization of the high-field procedures are a very efficient cooling of sample and electrolyte, as well as the initial ramping up of the voltage at an accurately defined rate. The morphology of the cylindrical, parallel alumina pores is similar to those obtained on smaller scales with standard setups. Our setup facilitates the availability of porous anodic alumina as a template system for a number of applications. (C) 2015 AIP Publishing LLC.

Aligning Single-Walled Carbon Nanotubes By Means Of Langmuir-Blodgett Film Deposition: Optical, Morphological, and Photo-electrochemical Studies - Giancane, Gabriele; Ruland, Andres; Sgobba, Vito; Manno, Daniela; Serra, Antonio; Farinola, Gianluca M.; Omar, Omar Hassan; Guldi, Dirk Michael; Valli, Ludovico (Advanced Functional Materials, 2010)
An alkoxy-substituted poly(phenylene thiophene) is used in order to suspend single-walled carbon nanotubes in an organic solvent. The suspension is spread on the air–water interface of a Langmuir trough and the floating film is characterized by means of Brewster angle microscopy and UV-visible reflection spectroscopy and the compression isotherm is recorded. The polymer/carbon-nanotube blend is transferred onto different substrates using the Langmuir–Blodgett technique. AFM measurements indicate the formation of globular structures for the samples transferred at low surface-pressure values and a tubular morphology for high-pressure-deposited samples. AFM analysis is repeated on a sample exposed to soft X-rays for about 5h and a highly organized structure of bundles of carbon nanotubes rises up. Samples with different numbers of layers are transferred onto ITO substrates by means of the Langmuir–Blodgett method and are tested as photocathodes in a photo-electrochemical cell. A Voc of 0.18 V, an Isc of 85.8 mA, FF of 40.0%, and η of (6.23×10−3)% are obtained.

Alignment of Lyapunov Vectors: A Quantitative Criterion to Predict Catastrophes? - Beims, Marcus W.; Gallas, Jason (Scientific Reports, 2016)
We argue that the alignment of Lyapunov vectors provides a quantitative criterion to predict catastrophes, i.e. the imminence of large-amplitude events in chaotic time-series of observables generated by sets of ordinary differential equations. Explicit predictions are reported for a Rössler oscillator and for a semiconductor laser with optoelectronic feedback.
EAM Import::2019-03-13

Alkali hydroxide-modified Ru/γ-Al2O3 catalysts for ammonia decomposition - Bajus, Stephanie; Agel, Friederike; Kusche, Matthias Manfred; Ní Bhriain, Nollaig; Wasserscheid, Peter (Applied Catalysis A-General, 2016)
We herein present an easy approach to increase drastically the catalytic activity of Ru/ extgreekg-Al2O3 catalysts in ammonia decomposition by surface modification with alkali hydroxides. The best activities have been achieved by a catalyst modification with lithium hydroxide in a Li/Al ratio of 1.7. In contrast, coatings with potassium and caesium hydroxide caused mass transfer limitations in the catalytic material already at low amounts (ratios alkali/Al <0.2–0.3). MAS ssNMR and XRD studies indicate the in-situ formation of alkali aluminates resulting in a basic modification of the support.
EAM Import::2019-03-13
Keywords: Ammonia decomposition; Ruthenium; Alkali doping; Support modification; Lithium aluminate

Alkalinity Initiated Decomposition of Mediating Imidazolium Ions in High Current Density CO 2 Electrolysis - Neubauer, Sebastian S.; Schmid, Bernhard; Reller, Christian; Guldi, Dirk Michael; Schmid, Guenter (ChemElectroChem, 2017)
Aqueous ionic liquid electrolytes featuring the promising 1,3-dialkyl- and 1,2,3-trialkyl-imidazolium cations are reported in CO2 electrolysis up to 200 mAcm-2. A close-to-application flow cell setup equipped with silver gas diffusion electrode to overcome CO2 mass transport limitations was used. Faraday efficiencies for CO as high as 68% were achieved, while inhibiting the hydrogen evolution reaction. Particular attention is paid to the stability of the ionic liquids, which is determined by 1H NMR spectroscopic measurements. The root cause of decomposition is the formation of hydroxide ions through reduction reactions. A high local pH arises that depends on the current density. The water content is also found to play a key role. An overall mechanism is proposed from analysis of the decomposition products including methylamine, ethylamine, formate, acetate and N1-ethyl-N2-methylethane-1,2-diamine. Methylation of the susceptible C2 position of the imidazolium ring fails to stabilize the system under high conversion rate electrolysis conditions.
EAM Import::2019-03-13

Alkyl Chain Engineering of Solution-Processable Star-Shaped Molecules for High-Performance Organic Solar Cells - Min, Jie; Luponosov, Yuriy N.; Gerl, Andreas; Polinskaya, Marina S.; Peregudova, Svetlana M.; Dmitryakov, Petr V.; Bakirov, Artem V.; Shcherbina, Maxim A.; Chvalun, Sergei N.; Grigorian, Souren; Kaush-Busies, Nina; Ponomarenko, Sergei A.; et al. (Advanced Energy Materials, 2014)
The impact of alkyl side-chain substituents on conjugated polymers on the photovoltaic properties of bulk heterojunction (BHJ) solar cells has been studied extensively, but their impact on small molecules has not received adequate attention. To reveal the effect of side chains, a series of star-shaped molecules based on a triphenylamine (TPA) core, bithiophene, and dicyanovinyl units derivatized with various alkyl end-capping groups of methyl, ethyl, hexyl and dodecyl is synthesiyed and studied to comprehensively investigate structure-properties relationships. UV-vis absorption and cyclic voltammetry data show that variations of alkyl chain length have little infl uence on the absorption and highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) levels. However, these seemingly negligible changes have a pronounced impact on the morphology of BHJ thin films as well as their charge carrier separation and transportation, which in turn influences the photovoltaic properties of these small-molecule-based BHJ devices. Solution-processed organic solar cells (OSCs) based on the small molecule with the shortest methyl end groups exhibit high short circuit current (Jsc) and fill factor (FF), with an efficiency as high as 4.76% without any post-treatments; these are among the highest reported for solution-processed OSCs based on star-shaped molecules.
Keywords: Engineering controlled terms: Charge carriers; Heterojunctions; Molecules; Solar cells; Stars Carrier separation; Highest occupied molecular orbital; Lowest unoccupied molecular orbital; Power conversion efficiencies; Side-chains; Star-shaped molecules; Structure property relationships; Structure-properties relationships Engineering main heading: Synthesis (chemical)

Alkyl chain length-dependent surface reaction of dodecahydro-N-alkylcarbazoles on Pt model catalysts - Gleichweit, Christoph; Amende, Maximilian; Bauer, Udo; Schernich, Stefan; Höfert, Oliver; Lorenz, Michael Peter Andreas; Zhao, Wei; Müller, Michael; Koch, Marcus; Bachmann, Philipp; Wasserscheid, Peter; Libuda, Jörg; et al. (Journal of Chemical Physics, 2014)
The concept of liquid organic hydrogen carriers (LOHC) holds the potential for large scale chemical storage of hydrogen at ambient conditions. Herein, we compare the dehydrogenation and decomposition of three alkylated carbazole-based LOHCs, dodecahydro-N-ethylcarbazole (H-NEC), dodecahydro-N- propylcarbazole (H-NPC), and dodecahydro-N-butylcarbazole (H -NBC), on Pt(111) and on AlO-supported Pt nanoparticles. We follow the thermal evolution of these systems quantitatively by in situ high-resolution X-ray photoelectron spectroscopy. We show that on Pt(111) the relevant reaction steps are not affected by the different alkyl substituents: for all LOHCs, stepwise dehydrogenation to NEC, NPC, and NBC is followed by cleavage of the C-N bond of the alkyl chain starting at 380-390 K. On Pt/AlO, we discern dealkylation on defect sites already at 350 K, and on ordered, (111)-like facets at 390 K. The dealkylation process at the defects is most pronounced for NEC and least pronounced for NBC. © 2014 AIP Publishing LLC.

All good things come in threes - Three beads learn to swim with lattice Boltzmann and a rigid body solver - Pickl, Kristina; Götz, Jan; Iglberger, Klaus; Pande, Jayant; Mecke, Klaus; Smith, Ana-Suncana; Rüde, Ulrich (Journal of Computational Science, 2012)
We simulate the self-propulsion of devices in a fluid in the regime of low Reynolds numbers. Each device consists of three bodies (spheres or capsules) connected with two damped harmonic springs. Sinusoidal driving forces compress the springs which are resolved within a rigid body physics engine. The latter is consistently coupled to a 3D lattice Boltzmann framework for the fluid dynamics. In simulations of three-sphere devices, we find that the propulsion velocity agrees well with theoretical predictions. In simulations where some or all spheres are replaced by capsules, we find that the asymmetry of the design strongly affects the propelling efficiency.
UnivIS-Import:2015-03-09:Pub.2011.tech.IMMD.lsinfs.allgoo

All-solid bandgap guiding in tellurite-filled silica photonic crystal fibers - Schmidt, Markus A.; Granzow, Nicolai; Da, Ning; Peng, Mingying; Wondraczek, Lothar; Russell, Philip St. J. (Optics Letters, 2009)
We report all-solid bandgap-guiding fibers formed by pumping molten tellurite glass into silica-air photonic crystal fiber at high pressure. The spectral positions of the guidance bands agree well with multipole simulations and bandgap calculations. The micrometer-diameter tellurite strands are found to contain microheterogeneities (most probably originating from devitrification), which increase the fiber attenuation, although no evidence of crystallization is seen in the bulk tellurite glass. The technique offers a potential route to employing difficult-to-handle glasses, or glasses unsuitable for fiber drawing, in fiber-based amplifiers, modulators, filters, and nonlinear devices.
EAM Import::2019-03-13

A Local Parallel Communication Algorithm for Polydisperse Rigid Body Dynamics - Eibl, Sebastian; Rüde, Ulrich (Parallel Computing, 2018)
The simulation of large ensembles of particles is usually parallelized by partitioning the domain spatially and using message passing to communicate between the processes handling neighboring subdomains. The particles are represented as individual geometric objects and are assigned to the subdomains. Handling collisions and migrating particles between subdomains, as required for proper parallel execution, requires a complex communication protocol. Typically, the parallelization is restricted to handling only particles that are smaller than a subdomain. In many applications, however, particle sizes may vary drastically with some of them being larger than a subdomain. In this article we propose a new communication and synchronization algorithm that can handle the parallelization without size restrictions on the particles. Despite the additional complexity and extended functionality, the new algorithm introduces only minimal overhead. We demonstrate the scalability of the previous and the new communication algorithms up to almost two million parallel processes and for handling ten billion (1010) geometrically resolved particles on a state-of-the-art petascale supercomputer. Different scenarios are presented to analyze the performance of the new algorithm and to demonstrate its capability to simulate polydisperse scenarios, where large individual particles can extend across several subdomains.
EAM Import::2019-03-13

Aluminum tailored heat treated blanks - Geiger, Manfred; Merklein, Marion; Vogt, Uwe (Production Engineering, 2009)
Tailored Heat Treated Blanks (THTB) are blanks, which exhibit locally different material properties optimized for the succeeding sheet metal forming process. The distribution of the material properties is obtained by a local, short-term heat treatment. As a result of the optimized property gradients in the sheet metal's plain, THTB allow enhancing the forming limits significantly. The research work covered in this paper focuses on THTB made out of aluminum alloys. The article presents the microstructural mechanisms due to a short-term heat treatment as well as design principles for the heat treatment layout for THTB made out of AlMgSi alloys and ultra-fine grained (UFG) aluminum alloys produced by the Accumulative Roll Bonding process.
EAM Import::2019-03-13

AM1* parameters for bromine and iodine - Kayi, Hakan; Clark, Timothy (Journal of Molecular Modeling, 2009)
Our extension of the AM1 semiempirical molecular orbital technique, AM1*, has been parameterized for the elements Br and I. The basis sets for both halogens contain a set of d-orbitals as polarization functions. AM1* performs as well as other MNDO-like methods that use dorbitals in the basis, and better than those that rely on an sp-basis. Thus, AM1* parameters are now available for H, C, N, O and F (which use the original AM1 parameters), Al, Si, P, S, Cl, Ti, Cu, Zn, Br, Zr, Mo and I.

AM1* parameters for cobalt and nickel - Kayi, Hakan; Clark, Timothy (Journal of Molecular Modeling, 2010)
We report the parameterization of AM1* for the elements Co and Ni. The basis sets for both metals contain one set each of s-, p- and d-orbitals. AM1* parameters are now available for H, C, N, O and F (which use the original AM1 parameters), Al, Si, P, S, Cl, Ti, V, Cr, Co, Ni, Cu, Zn, Br, Zr, Mo and I. The performance and typical errors of AM1* are discussed for Co and Ni and compared with available NDDO Hamiltonians.

AM1* parameters for gold - Kayi, Hakan (Journal of Molecular Modeling, 2010)
We report the parameterisation of AM1* for gold. The basis set for gold contains one set each of s-, p- and d-orbitals. AM1* parameters are now available for H, C, N, O and F (which use the original AM1 parameters), Al, Si, P, S, Cl, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Zr, Mo, I and Au. The performance and typical errors of AM1* for gold are discussed.
EAM Import::2019-03-13

AM1* parameters for manganese and iron - Kayi, Hakan; Clark, Timothy (Journal of Molecular Modeling, 2010)
We report the parameterization of AM1* for the elements manganese and iron. The basis sets for both metals contain one set each of s-, p- and d-orbitals. AM1* parameters are now available for H, C, N, O and F (which use the original AM1 parameters), Al, Si, P, S, Cl, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Zr, Mo, I and Au. The performance and typical errors of AM1* are discussed for Mn and Fe, and are compared with available NDDO Hamiltonians.

AM1* parameters for palladium and silver - Kayi, Hakan; Clark, Timothy (Journal of Molecular Modeling, 2011)
0.1,0.1,0.1We report the parameterization of AM1* for the elements palladium and silver. The basis sets for both metals contain one set each of 0.1,0.1,0.1s0.1,0.1,0.1-, 0.1,0.1,0.1p0.1,0.1,0.1- and 0.1,0.1,0.1d0.1,0.1,0.1-orbitals. AM1* parameters are now available for H, C, N, O and F (which use the original AM1 parameters), Al, Si, P, S, Cl, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Zr, Mo, Pd, Ag, I and Au. The performance and typical errors of AM1* are discussed for Pd and Ag and compared with the PM6 Hamiltonian.

AM1* parameters for vanadium and chromium - Kayi, Hakan; Clark, Timothy (Journal of Molecular Modeling, 2009)
Our extension of the AM1 semiempirical molecular orbital technique, AM1*, has been parameterized for the elements V and Cr. The basis sets for both metals contain one set each of s-, p- and d-orbitals. AM1* parameters are now available for H, C, N, O and F (which use the original AM1 parameters), Al, Si, P, S, Cl, Ti, V, Cr, Cu, Zn, Br, Zr, Mo and I. The performance and typical errors of AM1* are discussed for V and Cr and compared with available NDDO Hamiltonians.

Ambipolar, low-voltage and low-hysteresis PbSe nanowire field-effect transistors by electrolyte gating - Lokteva, Irina; Thiemann, Stefan; Gannott, Florentina; Zaumseil, Jana (Nanoscale, 2013)
Semiconductor nanowire field-effect transistors (FETs) are interesting for fundamental studies of charge transport as well as possible applications in electronics. Here, we report low-voltage, low-hysteresis and ambipolar PbSe nanowire FETs using electrolyte-gating with ionic liquids and ion gels. We obtain balanced hole and electron mobilities at gate voltages below 1 V. Due to the large effective capacitance of the ionic liquids and thus high charge carrier densities electrolyte-gated nanowire FETs are much less affected by external doping and traps than nanowire FETs with traditional dielectrics such as SiO2. The observed current–voltage characteristics and on/off ratios indicate almost completely transparent Schottky barriers and efficient ambipolar charge injection into a low band gap one-dimensional semiconductor. Finally, we explore the possibility of applying these ambipolar nanowire FETs in complementary inverters for printed electronics.
EAM Import::2019-03-13

A microspectroscopic insight into the resistivity switching of individual Ag-TCNQ nanocrystals - Rösner, Benedikt; Ran, Ke; Butz, Benjamin; Schmidt, Ute; Spiecker, Erdmann; Fink, Rainer (Physical Chemistry Chemical Physics, 2015)
We investigate the resistivity switching in individual Ag-TCNQ wires with on/off-ratios of up to 103. Raman and soft X-ray absorption microspectroscopy studies disclose reverse charge transfer. Quantifying of the fraction of neutral TCNQ within the switched material yields values up to 22.3%. These findings expedite the understanding of the switching process in Ag-TCNQ nanowires.

A mobile system for a comprehensive online-characterization of nanoparticle aggregates based on wide-angle light scattering and laser-induced incandescence - Huber, Franz; Altenhoff, Michael; Will, Stefan (Review of Scientific Instruments, 2016)
A mobile demonstrator for the comprehensive online-characterization of gas-borne nanoparticle aggregates is presented. Two optical measurement techniques are combined, both utilizing a pulsed Nd:YAG laser as light source. Aggregate size and fractal dimension are measured by Wide-Angle Light Scattering (WALS). An ellipsoidal mirror images elastically scattered light from scattering angles between 10. and 165. onto a CCD-camera chip resulting in an almost complete scattering diagram with high angular resolution. Primary particle size and volume fraction are measured by time-resolved Laser-Induced Incandescence (TiRe-LII). Here, particles are heated up to about 3000 K by the short laser pulse, the enhanced thermal radiation signal is detected with gated photomultiplier tubes. Analysis of the signal decay time and maximum LII-signal allows for the determination of primary particle diameter and volume fraction. The performance of the system is demonstrated by combined measurements on soot nanoparticle aggregates from a soot aerosol generator. Particle and aggregate sizes are varied by using different equivalence ratios of the combustion in the generator. Soot volume fraction can be adjusted by different levels of dilution with air. Online-measurements were carried out demonstrating the favorable performance of the system and the potential for industrial applications such as process control and product development. The particle properties obtained are confirmed through transmission electron microscopy analysis on representative samples. Published by AIP Publishing.

A model-based precipitation study of copper-based catalysts - Peukert, Wolfgang; Hartig, Martin Andreas Johannes; Jacobsen, Nikolas; Leuthold, Alexander (AIChE Journal, 2015)
Numerical methods of particle technology are used to model the formation of catalyst precursors with the purpose to control disperse properties. A multicomponent and multiphase population balance model is applied to the precipitation of catalyst precursors in a T-mixer. Copper precursors are chosen to be investigated in detail as a basis for catalysts with a broad range of applications such as in methanol synthesis, water-gas shift and hydrogenation reactions. The simulations results could be validated by ex situ measurements such as the pH of the suspension, the solid dry weight of the precipitate, and the yield. Simulations show that dissociation reactions of copper and carbonate species in water control significantly the formation of Georgeite. Consumption of the copper component by solid formation can be controlled in a range of 20-100% by the adjustment of the pH of the copper nitrate reactant solution.
Keywords: Catalyst preparation; Methanol synthesis; Mixing; Population balance; Precursor chemistry

A molecular Ce2@ih-C80 switch-unprecedented oxidative pathway in photoinduced charge transfer reactivity - Guldi, Dirk Michael; Feng, Lai; Radhakrishnan, Shankara Gayathri; Nikawa, Hidefumi; Yamada, Michio; Mizorogi, Naomi; Tsuchiya, Takahiro; Akasaka, Takeshi; Nagase, Shigeru; Angeles Herranz, M.; Martin, Nazario (Journal of the American Chemical Society, 2010)
We report for the first time the versatile Ce@I -C building block toward synthesizing a novel electron donor-acceptor conjugate, Ce@I-C-ZnP (1). A systematic investigation of the charge transfer chemistry documents a reductive charge transfer (i.e., formation of (Ce@I-C )-(ZnP)) in nonpolar media (i.e., toluene/THF), while an oxidative charge transfer (i.e., formation of (Ce@I-C)-(ZnP) ) dominates in polar media (i.e., benzonitrile/DMF). Reduction of the [Ce] cluster, which is highly localized and collinearly arranged with respect to the quaternary bridge carbon, is sufficiently exothermic in all solvents. Notably weak is the electronic coupling between the [Ce] cluster and the electron-donating ZnP. The oxidation of C and the simultaneous reduction of ZnP, on the other hand, necessitate solvent stabilization. In such a case, the strongly exothermic (Ce@I-C) -(ZnP) radical ion pair state formation is compensated within the framework of a nonadiabatic charge transfer by a C /ZnP electronic matrix element, as the sum of good overlap and short distance, that exceeds that for [Ce] /ZnP. © 2010 American Chemical Society.

A Molecular Placeholder Strategy To Access a Family of Transition-Metal-Functionalized Vanadium Oxide Clusters - Kastner, Katharina; Margraf, Johannes; Clark, Timothy; Streb, Carsten (Chemistry - A European Journal, 2014)
Systematic access to metal-functionalized polyoxometalates has thus far been limited to lacunary tungsten oxide and molybdenum oxide clusters. The first controlled, stepwise bottom-up assembly route to metal-functionalized molecular vanadium oxides is now presented. A di-vacant vanadate cluster with two metal binding sites, (DMA)(2)[V12O32Cl](3-) (DMA= dimethylammonium) is formed spontaneously in solution and characterized by single-crystal X-ray diffraction, ESI mass spectrometry, V-51 NMR spectroscopy, and elemental analyses. In the cluster, the metal binding sites are selectively blocked by hydrogen-bonded DMA placeholder cations. Reaction of the cluster with transition metals TM (Fe3+, Co2+, Cu2+, Zn2+) gives access to mono-functionalized vanadate clusters (DMA)[TM(L)V12O32Cl](n-) (L= ligand). Metal binding is accomplished by significant distortions of the vanadium oxide framework reminiscent of a pincer movement. Cluster stability under technologically relevant conditions in the solid-state and solution is demonstrated.
Keywords: functionalization; metal oxide clusters; polyoxometalates; polyoxovanadates; self-assembly

A Molecular Rationale of Shock Absorption and Self-Healing in a Biomimetic Apatite-Collagen Composite under Mechanical Load - Zahn, Dirk (Angewandte Chemie International Edition, 2010)
Once bitten: Compression along the c axis of apatite–collagen composites (see picture), such as that on tooth enamel during biting, reveals a molecular mechanism that accounts for the steel-like characteristics of these composites. Simulations reveal that before eventual failure, inelastic deformation is initiated near the collagen molecules followed by pseudo-elastic deformation. The composite may undergo self-healing after release of the mechanical load.
EAM Import::2019-03-13

Amphiphilic Perylene-Calix[4]arene Hybrids: Synthesis and Tunable Self-Assembly - Rodler, Fabian; Schade, Boris; Jaeger, Christof M.; Backes, Susanne; Hampel, Frank; Boettcher, Christoph; Clark, Timothy; Hirsch, Andreas (Journal of the American Chemical Society, 2015)
The first highly water-soluble perylene-calix[4]arene hybrid with the calixarene scaffold acting as a structure-determining central platform is presented. In this tetrahedrally shaped amphiphilic architecture the hydrophilic and hydrophobic subunits are oriented at the opposite side of the calixarene platform. The hydrophobic part contains the two perylene diimide moieties, which enable strong pi-pi interactions in self-assembly processes. Two hydrophilic Newkome-type dendrons provide sufficient water solubility at slightly basic conditions. The tetrahedrally shaped amphiphile displays an unprecedented aggregation behavior down to concentrations as low as 10(-7) mol L-1. The intriguing self-assembly process of the compound in water as well as under changed polarity conditions, achieved by addition of THF, could be monitored by the complemented use of cryogenic transmission electron microscopy (cryo-TEM), UV-vis spectroscopy, and fluorescence spectroscopy. Molecular-dynamics and molecular modeling simulations helped in understanding the interplay of supramolecular and optical behavior.

Amphiphilic TiO2 Nanotube Arrays: An Actively Controllable Drug Delivery System - Song, Yanyan; Schmidt-Stein, Felix; Bauer, Sebastian; Schmuki, Patrik (Journal of the American Chemical Society, 2009)
Amphiphilic TiO_2 nanotube arrays are faribricated by a two-step anodization procedure combined with hydrophobic monolayer modification after the first step. These tubes can be used as biomolecular carriers, where the outer hydrophobic barrier provides an efficient cap against drug leaching to the environment. By utilizing the photocatalytic ability of TiO_2, a precisely controlled removal of the cap and a highly controlled release of the hydrophilic payload (drug) can be achieved.
EAM Import::2019-03-13

A multi-agent quantum Monte Carlo model for charge transport: Application to organic field-effect transistors - Bauer, Thilo; Jäger, Christof; Jordan, Meredith J. T.; Clark, Timothy (Journal of Chemical Physics, 2015)
We have developed a multi-agent quantum Monte Carlo model to describe the spatial dynamics of multiple majority charge carriers during conduction of electric current in the channel of organic fieldeffect transistors. The charge carriers are treated by a neglect of diatomic differential overlap Hamiltonian using a lattice of hydrogen-like basis functions. The local ionization energy and local electron affinity defined previously map the bulk structure of the transistor channel to external potentials for the simulations of electron- and hole-conduction, respectively. The model is designed without a specific charge-transport mechanism like hopping- or band-transport in mind and does not arbitrarily localize charge. An electrode model allows dynamic injection and depletion of charge carriers according to source-drain voltage. The field-effect is modeled by using the source-gate voltage in a Metropolis-like acceptance criterion. Although the current cannot be calculated because the simulations have no time axis, using the number of Monte Carlo moves as pseudo-time gives results that resemble experimental I/V curves. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

A multiscale simulation framework of the accumulative roll bonding process accounting for texture evolution - Prakash, Aruna; Nöhring, Wolfram Georg; Lebensohn, R. A.; Höppel, Heinz Werner; Bitzek, Erik (Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2015)
The accumulative roll bonding process is one of the most prominent severe plastic deformation processes for obtaining sheet materials with ultra-fine-grained microstructures and high strength. The properties of such sheets differ significantly from those of conventionally rolled sheets. It is hence desirable to have a simulation framework that can accurately predict the material properties, including the evolving texture and anisotropy during processing. Here, we propose such a framework for multiple pass rolling using explicit finite elements and embedding the visco-plastic self-consistent (VPSC) polycrystal texture model for the material response. To facilitate multiple pass rolling, we propose a novel solution mapping scheme that transfers the material state from the deformed finite element mesh to a new one. Additionally, we implement a two-level parallelization scheme – with decomposition of the FE domain using message passing interface (MPI) and thread based parallelization of the material response using OPENMP – to ensure reduced simulation times. The predictive capabilities of the proposed framework are demonstrated by simulating the accumulative roll bonding of aluminum alloy AA5754 sheets. The simulations validate the working of the solution mapping scheme, and clearly show the development of a through thickness gradient of texture and anisotropy in the roll-bonded sheet after two passes.
WW1::1018

An advanced method to manufacture hierarchically structured carbide-derived carbon monoliths - Fey, Tobias; Zierath, Bodo; Kern, Andreas; Greil, Peter; Etzold, Bastian (Carbon, 2014)
The preparation of carbide-derived carbon (CDC) monoliths with a hierarchically structure in the mu m and pm range is presented. Basis is the manufacturing of porous cellular SiC ceramics based on a biomorphous approach with pm porosity and subsequent conformal conversion to CDC by reactive extraction with chlorine. The SiC ceramics can be sintered at low temperatures and short times (1500 degrees C, 2 h) compared to classical preparation methods. The SiC ceramics show a macro pore volume (1-10 mu m channel size) of 0.56 ml g(-1), which corresponds to 1.5 ml g(-1) in the resulting CDC. The final carbon material exhibits an additional nano pore volume of 0.525 ml g(-1) with a mean slit pore size of 0.86 nm. Mechanical stabilities of the highly porous CDC are excellent (bending strength 2.1 +/- 0.2 MPa, corrected Weibull modulus 8.7, characteristic strength 2.2 MPa and Youngs modulus 10.0 +/- 0.5 GPa). The reactive extraction of the carbide monoliths shows very high reaction rates, approx. two dimensions faster (95x) compared to non-porous samples. Thus the manufacturing of the structured carbide and CDC can be performed at lower costs. (C) 2013 Elsevier Ltd. All rights reserved.

An Alternative Strategy to Adjust the Recombination Mechanism of Organic Photovoltaics by Implementing Ternary Compounds - Gasparini, Nicola; Salvador, Michael Filipe; Fladischer, Stefanie; Katsouras, Athanasios; Avgeropoulos, Apostolos; Spiecker, Erdmann; Chochos, Christos L.; Brabec, Christoph; Ameri, Tayebeh (Advanced Energy Materials, 2015)
Trap-assisted recombination is one of the main loss mechanisms in bulk-heterojunction (BHJ) solar cells. Results suggest that introducing a near infrared (NIR) polymer into the 2,3-bis(3-(octyloxy)phenyl)quinoxaline (PIDTTQ):[6,6]-phenyl C butyric acid methyl ester (PCBM) host system suppresses trap-assisted recombination in the binary blend, leading to a significant improvement of ≈60% in power conversion efficiency for ternary organic solar cells at low light intensity.
Keywords: IR sensitization; low light intensity; organic solar cells; recombination; ternary blends

Analysis of influencing parameters in deformable roll coating of counter-rotating rolls - Grashof, Bettina; Delgado, Antonio (Journal of Coatings Technology and Research, 2015)
Roll coating is a comparatively simple and common technology for coating of continuous substrates like paper, coils, or foils, where the fluid is metered through the gap between two rolls. Rolls wrapped with a deformable rubber layer enable a precise metering for low fluid amounts and lead additionally to higher process stability. Many efforts have been made to investigate the influencing factors of deformable roll coating by experimental and numerical methods. Beside configurations with positive gaps, which are comparable to rigid roll setups, negative gaps, where only the elasticity of the rubber layer prevents overlapping of the rolls, are of interest as such configurations enable thin liquid layers. The main influencing factors on the volume flow rate through the gap are viscosity, average velocity, effective radius, Young’s modulus, load or pre-set gap height, and partly rubber thickness, when an influence of the layer height is assumed. The dependency is often given in empirically or numerically based power law relationships. In contrast to this, in the present study, an analytically based solution is used to investigate the influencing factors in deformable roll coating with negative gaps. This continues the authors' previous work, in which the analytical solution was derived. As a result, a general agreement with numerical and experimental results from literature is found. Additionally, the analytical approach allows for the first time the ability to quantify further trends. The proposed power law exponent for the dimensionless load and elasticity numbers from literature cannot be considered as constant in the whole common application range of roll coating but remarkable trends appear. Additionally, a new criterion for the critical rubber cover thickness is developed analytically which describes the limit value of the negligible influence of the rubber cover thickness on the volume flow rate. The present investigation enables the explanation of different literature results and offers a more general view in the understanding of roll coating processes.
UnivIS-Import:2015-03-09:Pub.2015.tech.ITC.stmmec.analys
Keywords: Analytical prediction; Deformable roll coating; Forward roll coating; Negative gap

Analysis of optical absorbance spectra for the determination of ZnO nanoparticle size distribution, solubility, and surface energy - Segets, Doris; Gradl, Johannes; Klupp Taylor, Robin; Vassilev, Vassil; Peukert, Wolfgang (Acs Nano, 2009)
We present a model to calculate particle size distributions (PSDs) of colloidal ZnO nanoparticles from their absorbance spectra. Using literature values for the optical properties of bulk ZnO and correlating the measurement wavelengths in the UV−visible regime with distinct particle sizes by a tight binding model (TBM), an algorithm deconvolutes the absorbance spectra into contributions from size fractions. We find an excellent agreement between size distributions determined from TEM images and the calculated PSDs. For further validation, bimodal PSDs have been investigated and an approach to determine not only particle size but also solid concentration is introduced. We will show the applicability of our model by the determination of temperature-dependent ripening rates, which enables the calculation of solubilities, surface tensions, and the activation enthalpy of ripening. In principle, our methodology is applicable to different semiconductor nanoparticles in various solvents as long as their bulk properties are known and scattering is negligible.

Analysis of particle size distributions of quantum dots: From theory to application - Segets, Doris (KONA Powder and Particle Journal, 2016)
Small, quantum-confined semiconductor nanoparticles, known as quantum dots (QDs) are highly important material systems due to their unique optoelectronic properties and their pronounced structure-property relationships. QD applications are seen in the emerging fields of thin films and solar cells. In this review, different characterization techniques for particle size distributions (PSDs) will be summarized with special emphasis on strategies developed and suggested in the past to derive data on the dispersity of a sample from optical absorbance spectra. The latter use the assumption of superimposed individual optical contributions according to the relative abundance of different sizes of a colloidal dispersion. In the second part, the high potential of detailed PSD analysis to get deeper insights of typical QD processes such as classification by size selective precipitation (SSP) will be demonstrated. This is expected to lead to an improved understanding of colloidal surface properties which is of major importance for the development of assumption-free interaction models.
Keywords: Classification by size selective precipitation; Quantum dot; Particle size distribution; Structure-property relationship; Solubility parameters

Analysis of the effect of germanium preamorphization on interface defects and leakage current for high-k metal-oxide-semiconductor field-effect transistor - Roll, G.; Jakschik, S.; Goldbach, M.; Wachowiak, A.; Mikolajick, Thomas; Frey, Lothar (Journal of Vacuum Science & Technology B: Microelectronics Processing and Phenomena, 2011)
In this article, the authors analyze the impact of germanium amorphization on the interface defect concentration of state of the art high-k metal gate metal-oxide-semiconductor field-effect transistors. The gate etch is a crucial process step for the high-k gate first integration approach. Germanium implantation is used to amorphize the annealed and, therefore, nanocrystalline hafnium silicon oxide. This ensures a well controlled wet etch removal. The quality of the gate oxide to the channel interface of the transistor samples is monitored by charge pumping. The influence of the damage caused by the germanium implant at the unprotected gate edge is analyzed for different gate stacks by measuring the gate induced drain leakage. The defect concentration at the gate edge can be reduced by adjusting the germanium amorphization energy.

Analysis of the molecular interactions governing the polymorphism of benzamide – a guide to syntheses? - Ectors, Philipp; Zahn, Dirk (Physical Chemistry Chemical Physics, 2013)
Dispersion-corrected density functional calculations are used to rationalize the subtle differences in the molecular interactions in benzamide crystals. The potential energy of the different polymorph structures is dominated by the interplay between intermolecular attraction and molecular torsion/deformation to accommodate favourable molecular packing. Using suitable proxies arranged in pseudo-crystalline setups we discriminate the contribution of hydrogen bonding, extgreekp– extgreekp interactions and intra-molecular interactions to the lattice energies of the most relevant (P1 and P3) benzamide polymorphs. Strikingly, these commonly anticipated binding/packing concepts cannot account for the observed ranking of benzamide structures, thus hinting at the importance of the interactions between the benzene rings and the polar amide groups. Moreover, individual structural motifs that account for the competition between the two crystal structure types are elaborated. On the basis of such in-depth understanding of molecular interactions – in terms of both structure and chemistry – we suggest nucleation scenarios as guides to a more controlled synthesis of the stable P1 form or to direct nucleation in favour of the P3 polymorph.
EAM Import::2019-03-13

Analysis of the structure of nanocomposites of triglyceride platelets and DNA - Schmiele, Martin; Knittel, Charlotte; Unruh, Tobias; Busch, Sebastian; Morhenn, Humphrey; Boesecke, Peter; Funari, Sergio S.; Schweins, Ralf; Lindner, Peter; Westermann, Martin; Steiniger, Frank (Physical Chemistry Chemical Physics, 2015)
DNA-complexes with platelet-like, cationically modified lipid nanoparticles (cLNPs) are studied with regard to the formation of nanocomposite structures with a sandwich-like arrangement of the DNA and platelets. For this purpose suspensions of platelet-like triglyceride nanocrystals, stabilized by a mixture of two nonionic (lecithin plus polysorbate 80 or poloxamer 188) and one cationic stabilizer dimethyldioctadecylammonium (DODAB), are used. The structure of the platelets in the native suspensions and their DNA-complexes, ranging from the sub-nano to the micron scale, is investigated with small- and wide-angle scattering (SAXS, SANS, WAXS), calorimetry, photon correlation spectroscopy, transmission electron microscopy and computer simulations. The appearance of strong, lamellarly ordered peaks in the SAXS patterns of the DNA-complexes suggests a stacked arrangement of the nanocrystals, with the DNA being partially condensed between the platelets. This finding is supported with computer simulated small-angle scattering patterns of nanocrystal stacks, which can reproduce the measured small-angle scattering patterns on an absolute scale. The influence of the choice of the nonionic stabilizers and the amount of the cationic stabilizer DODAB on the structure of the native suspensions and the inner structure of their DNA-complexes is studied, too. Using high amounts of DODAB, lecithins with saturated acyl chains and polysorbate 80 instead of poloxamer 188 produces thinner nanocrystals, and thus decreases their repeat distances in the nanocomposites. Such nanocomposites could be of interest as DNA carriers, where the triglyceride platelets protect the sandwiched DNA from degradation.

Analytical circuit model for split ring resonators in the far infrared and optical frequency range - Delgado, V.; Sydoruk, Oleksiy; Tatartschuk, Eugen; Marqués, R.; Freire, M. J.; Jelinek, L. (Metamaterials, 2009)
The article proposes an LC-circuit model for single split ring resonators (SRRs) operating at far infrared and optical frequencies. Taking the effects of magnetic and kinetic inductances as well as gap and surface capacitances into account, we obtain analytical expressions for the resonant frequency of the singly, doubly, and quadruply split SRRs. Comparing the analytical results with numerical simulations, we show that the numerical simulations agree better with the present model than with the models reported previously. We also discuss a size dependent correction to the electron collision frequency which takes into account electron collisions with SRR walls.
EAM Import::2019-03-13

Analytical considerations and dimensionless analysis for a description of particle interactions in high pressure processes - Rauh, Cornelia; Delgado, Antonio (High Pressure Research, 2010)
High pressures of up to several hundreds of MPa are utilized in a wide range of applications in chemical, bio-, and food engineering, aiming at selective control of (bio-)chemical reactions. Non-uniformity of process conditions may threaten the safety and quality of the resulting products because processing conditions such as pressure, temperature, and treatment history are crucial for the course of (bio-)chemical reactions. Therefore, thermofluid-dynamical phenomena during the high pressure process have to be examined, and numerical tools to predict process uniformity and to optimize the processes have to be developed. Recently applied mathematical models and numerical simulations of laboratory and industrial scale high pressure processes investigating the mentioned crucial phenomena are based on continuum balancing models of thermofluid dynamics. Nevertheless, biological systems are complex fluids containing the relevant (bio-)chemical compounds (enzymes and microorganisms). These compounds are particles that interact with the surrounding medium and between each other. This contribution deals with thermofluid-dynamical interactions of the relevant particulate (bio-)chemical compounds (enzymes and microorganisms) with the surrounding fluid. By consideration of characteristic time and length scales and particle forces, the motion of the (bio-)chemical compounds is characterized. © 2010 Taylor & Francis.
UnivIS-Import:2015-03-09:Pub.2010.tech.ITC.stmmec.analyt
Keywords: analytical considerations; dimensionless analysis; mathematical modelling; particle interactions

Analytical formulation for the resonant frequency of split rings - Sydoruk, Oleksiy; Tatartschuk, Eugen; Shamonina, E.; Solymar, L. (Journal of Applied Physics, 2009)
A simple approximate expression is derived for the resonant frequency of a singly split single ring that is among the first microwave resonators designed to be small relative to the wavelength. In addition to the usual gap capacitance the concept of surface capacitance is introduced. The surface capacitance is determined analytically by two different methods, first using analytical expressions for the electric field of a split cylinder, and second by using conformal mapping. Taking two practical examples the resonant frequency, found analytically, is shown to agree with that obtained by numerical simulations. The model could be used for studies of the resonant properties of split rings in the terahertz region.
EAM Import::2019-03-13

Analytical model for flux saturation in sediment transport - Ribeiro Parteli, Eric Josef; Herrmann, Hans J.; Kok, Jasper F.; Päthz, Thomas (Physical Review E, 2014)
The transport of sediment by a fluid along the surface is responsible for dune formation, dust entrainment, and a rich diversity of patterns on the bottom of oceans, rivers, and planetary surfaces. Most previous models of sediment transport have focused on the equilibrium (or saturated) particle flux. However, the morphodynamics of sediment landscapes emerging due to surface transport of sediment is controlled by situations out of equilibrium. In particular, it is controlled by the saturation length characterizing the distance it takes for the particle flux to reach a new equilibrium after a change in flow conditions. The saturation of mass density of particles entrained into transport and the relaxation of particle and fluid velocities constitute the main relevant relaxation mechanisms leading to saturation of the sediment flux. Here we present a theoretical model for sediment transport which, for the first time, accounts for both these relaxation mechanisms and for the different types of sediment entrainment prevailing under different environmental conditions. Our analytical treatment allows us to derive a closed expression for the saturation length of sediment flux, which is general and thus can be applied under different physical conditions.

Analytical prediction of roll coating with counter-rotating deformable rolls - Grashof, Bettina; Delgado, Antonio (Journal of Coatings Technology and Research, 2014)
Roll coating is a common technique for applying thin coating films on continuous substrates, e.g., papers and foils. Key advantages are the comparatively simple technology and the possibility of coating thin films using highly viscous fluids. Since roll coating is a self-metered process, the prediction of film thicknesses is of fundamental interest for industrial process control. In the present work, a new analytical approach for the prediction of the film thickness in roll coating with deformable rolls and negative gaps is developed. This method is based on the fluid dynamic theory of lubrication approximation. The film thickness is calculated depending on the geometry of the rolls (including the elasticity of the rubber), the fluid properties of the applied film and the roll velocities. This is gained by using boundary conditions for pressure and - in contrast to former literature - for force. The quality of the predicted results is validated with experimental data from literature. The comparison shows good agreement and thus the derived analytical model offers new possibilities for predicting film thickness and understanding of the associated influence parameters. © 2013 American Coatings Association & Oil and Colour Chemists' Association.
UnivIS-Import:2015-03-09:Pub.2014.tech.ITC.stmmec.predic
Keywords: Analytical prediction; Deformable roll; Negative gap; Roll coating

Analyzing X-ray tomographies of granular packings - Weis, Simon; Schröter, Matthias (Review of Scientific Instruments, 2017)
Starting from three-dimensional volume data of a granular packing, as, e.g., obtained by X-ray Computed Tomography, we discuss methods to first detect the individual particles in the sample and then analyze their properties. This analysis includes the pair correlation function, the volume and shape of the Voronoi cells, and the number and type of contacts formed between individual particles. We mainly focus on packings of monodisperse spheres, but we will also comment on other monoschematic particles such as ellipsoids and tetrahedra. This paper is accompanied by a package of free software containing all programs (including source code) and an example three-dimensional dataset which allows the reader to reproduce and modify all examples given.
EAM Import::2019-03-13

An augmented BV setting for feedback switching control - Hante, Falk; Leugering, Günter; Seidman, Thomas I. (Journal of Systems Science & Complexity, 2010)
This paper considers dynamical systems under feedback with control actions limited to switching. The authors wish to understand the closed-loop systems as approximating multi-scale problems in which the implementation of switching merely acts on a fast scale. Such hybrid dynamical systems are extensively studied in the literature, but not much so far for feedback with partial state observation. This becomes in particular relevant when the dynamical systems are governed by partial differential equations. The authors introduce an augmented BV setting which permits recognition of certain fast scale effects and give a corresponding well-posedness result for observations with such minimal regularity. As an application for this setting, the authors show existence of solutions for systems of semilinear hyperbolic equations under such feedback with pointwise observations.

Anchoring of a Carboxyl-Functionlized Norbornadiene Derivative to an Atomically-Defined Cobalt Oxide Surface - Schwarz, Matthias; Mohr, Susanne; Xu, Tao; Döpper, Tibor; Weiß, Cornelius; Civale, Katharina; Hirsch, Andreas; Görling, Andreas; Libuda, Jörg (Journal of Chemical Physics, 2017)
We have investigated the anchoring of the molecular energy carrier norbornadiene (NBD) to an atomically defined oxide surface. To this end, we synthesized a carboxyl-functionalized NBD derivative, namely 1-(2′-norbornadienyl)pentanoic acid (NBDA), and deposited it by physical vapor deposition (PVD) under ultrahigh vacuum (UHV) conditions onto a well-ordered Co3O4(111) film grown on Ir(100). In addition, we performed a comparative growth study with benzoic acid (BA) under identical conditions which was used as a reference. The interaction and orientation of NBDA and BA with the oxide surface were monitored in situ during film growth by isothermal time-resolved infrared reflection–absorption spectroscopy (TR-IRAS), both below and above the multilayer desorption temperature. The thermal behavior and stability of the films were investigated by temperature-programmed IRAS (TP-IRAS), with help of density functional (DF) calculations. BA binds to Co3O4(111) under formation of a symmetric chelating carboxylate with the molecular plane oriented nearly perpendicular to the surface. At low temperature (130 K), intact BA physisorbs in form of dimers on top of the saturated monolayer. Upon annealing to 155 K, a reordering transition is observed, in which BA in the multilayer adopts a more flat-lying orientation. The BA multilayer desorbs at 220 K, whereas the surface-anchored BA monolayer is stable up to 400 K. At higher temperature (400–550 K), desorption and decomposition are observed. Very similar to BA, NBDA binds to Co3O4(111) by formation of a symmetric chelating carboxylate. In the multilayer, which desorbs at 240 K, hydrogen-bonded NBDA dimers are formed. Upon PVD of NBDA at 300 K, only a surface anchored carboxylate is stable. The anchored NBDA film shows a characteristic restructuring behavior as a function of coverage. At low coverage the NBDA, adopts a flat-lying structure in which the norbornadiene unit interacts with the Co3O4 surface. With increasing coverage, the norbornadiene units detach from the oxide and the NBDA adopts an upright-standing orientation. Similar to BA, the anchored film is stable up to 400 K and decomposes in the temperature region between 400 and 550 K, leaving behind hydrocarbon residues on the oxide surface.

Anchoring of carboxyl-functionalized porphyrins on MgO, TiO2, and Co3O4 nanoparticles - Kollhoff, Fabian; Schneider, Johannes; Li, Gao; Barkaoui, Sami; Shen, Wenjie; Berger, Thomas; Diwald, Oliver; Libuda, Jörg (Physical Chemistry Chemical Physics, 2018)
Hybrid materials consisting of functional organic molecules on metal oxide nanomaterials are key components in emerging technologies, for example in energy conversion and molecular electronics. In this work, we present the results of a comparative study of carboxyl-functionalized porphyrins on different oxide nanomaterials. Specifically, we investigated the interaction of 5(3-carboxyphenyl)-10,15,20-triphenyl-21,23H-porphyrin (2H-3-MCTPP) and 5(4-carboxyphenyl)-10,15,20-triphenyl-21,23H-porphyrin (2H-4-MCTPP), on MgO, TiO2, and Co3O4 nanoparticles (NPs) using isothermal and temperature-programmed diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). We show that both porphyrins bind to the NPs, yielding stable monolayer films consisting of tilted surface carboxylates. In all cases, anchoring through the carboxylic acid group suppresses self-metalation of the porphyrin unit. Upon annealing, all anchored porphyrin films undergo metalation. The position of the acid group has no major influence on the reactivity. The same is true for the nature of the metal oxide, suggesting that the observed behaviour is general for most anchored porphyrin films on oxide nanomaterials.

An effective dialysis method for surface funtionalization of nanoparticles in liquid phase - Sample: Porphyrine derivatives @ ZnO-Nanorods - Klaumünzer, Martin; Münzel, C.; Burger, Alexandra; Mackovic, Mirza; Voigt, Michael; Spiecker, Erdmann; Hirsch, Andreas; Peukert, Wolfgang (Nanotechnology 2013: Advanced Materials, CNTs, Particles, Films and Composites - 2013 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2013, 2013)
In order to optimize electron transfer and optoelectronic properties in nanoparticulate thin films for electronics we show the surface functionalization of ZnO nanorods by exchanging the stabilizing 2-[2-(2-Mefhoxyefhoxy)-ethoxy] acetic acid at the ZnO surface with redoxactive organic molecules. Surface functionalization is undertaken by an efficient dialysis method. Emission- and absorption-spectroscopy indicate an effective electronic interaction between the ZnO nanorods and the pophyrine derivatives. In addition, we discuss on the binding mechanism and the ligand exchange kinetics of the porphyrine molecules. Our experiments suggest a better and faster binding to the ZnO nanorod surface for porphyrine A than for porphyrine B. This can be explained by steric effects. Moreover we claim a fourfold anchored binding for porphyrine A and we shed light on entropic effects during ligand exchange.

An electrochemically functional layer of hydrogenase extract on an electrode of large and tunable specific surface area - Schlicht, Stefanie; Assaud, Loic; Hansen, Moritz; Licklederer, Markus; Bechelany, Mikhael; Perner, Mirjam; Bachmann, Julien (Journal of Materials Chemistry A, 2016)
Electrode supports are generated by electrospinning of polyacrylonitrile fibers and subsequent coating of a thin electrically conductive TiO2 layer by atomic layer deposition. The supports are then functionalized with a [NiFe]-hydrogenase-containing membrane fraction from Escherichia coli and are characterized structurally and electrochemically. The hydrogenase suspension generates a micron-thick organic film around the fiber mat, which exhibits electrocatalytic activity for hydrogen evolution. Furthermore, the electrode geometric surface area is varied systematically via the electrospinning procedure, which reduces the charge transfer resistance and increases the hydrogen evolution current density to > 500 mu A cm(-2) at 0.3 V overpotential.

A new asymmetric Pseudo-Voigt function for more efficient fitting of XPS lines - Schmid, Martin; Steinrück, Hans-Peter; Gottfried, J. Michael (Surface and Interface Analysis, 2014)
Asymmetric peak profiles for the application in spectroscopy can be obtained in a simple way by substituting the usually constant full width at half maximum parameter in Pseudo-Voigt functions with an energy-dependent expression, for instance of sigmoidal shape. While this approach has been successfully applied to vibrational spectra, we find that the resulting curves are less suitable for least-squares fits of X-ray photoelectron spectroscopy (XPS) data. However, if one additionally allows a variable displacement of the sigmoidal step relative to the peak, excellent fitting results can be obtained. We demonstrate the applicability of our extended approach on several inherently asymmetric XPS lines, i.e. the C 1s signal of graphite and CH/Pd(100), the 3d-3d doublet of palladium, and the 4f-4f doublet of platinum. Comparison of the corresponding fit results with the results obtained by the application of more elaborate, theory-based line profiles (Doniach-Šunjić and Mahan functions) shows that the modified Pseudo-Voigt function gives practically identical results in terms of peak shape and area, while requiring much less computational effort since no convolution procedures are required for its calculation. Thus, this function is most suitable for application in one of the following situations: (i) the peak shape of a given signal is known but cannot be calculated with ease, and (ii) the theoretical peak shape is not (yet) known, however, one wants to perform a first quantitative screening of the data at issue. © 2014 John Wiley & Sons, Ltd.

A new class of double alkyl-substituted, liquid crystalline imidazolium ionic liquids - A unique combination of structural features, viscosity effects, and thermal properties - Wang, Xinjiao; Heinemann, Frank Wilhelm; Yang, Mei; Melcher, Berthold Ulrich; Fekete, Melinda; Mudring, Anja-Verena; Wasserscheid, Peter; Meyer, Karsten (Chemical Communications, 2009)
1,3-Didodecylimidazolium salts have been prepared as first representatives of a new class of ionic liquid crystals (ILCs), showing thermotropic liquid crystalline behaviour in an extended temperature range below 70 °C. Remarkably strong non-Newtonian viscosity behaviour was found for the liquid-crystalline state of these ILCs. © 2009 The Royal Society of Chemistry.

A New Crystal Phase Molybdate Yb2Mo4O15: The Synthesis and Upconversion Properties - Wang, Hai-Qiao; Mackovic, Mirza; Osvet, Andres; Litzov, Ivan; Epelbaum, Elena; Stiegelschmitt, Alfons; Batentschuk, Miroslaw; Spiecker, Erdmann; Brabec, Christoph (Particle & Particle Systems Characterization, 2015)
A new upconversion nanocrystal phase Yb2Mo4O15:Er is developed by using a facile aqueous-precipitation procedure combined with thermal annealing. Nanocrystals of Yb2Mo4O15 are exclusively synthesized, with particle sizes ranging from 1 to 20 nm. The optical properties are characterized and a high upconversion quantum yield is determined to be approximate to 1.3% at room temperature, under excitation of approximate to 500 mW cm(-2) IR (975 nm). To the best of our knowledge, this is the first work concerning the synthesis of nanocrystalline Yb2Mo4O15 and the characterization of its upconversion properties, which possesses the potential to be utilized in bio-probing and thin-film optoelectronic device applications.
Keywords: upconversion; Yb2Mo4O15:Er; nanocrystals; characterization

A New Non-linear Semidefinite Programming Algorithm with an Application to Multidisciplinary Free Material Optimization - Stingl, Michael; Kocvara, Michal; Leugering, Günter (Optimal control of coupled systems of partial differential equations, 2009)
A new method and algorithm for the efficient solution of a class of nonlinear semidefinite programming problems is introduced. The new method extends a concept proposed recently for the solution of convex semidefinite programs based on the sequential convex programming (SCP) idea. In the core of the method, a generally non-convex semidefinite program is replaced by a sequence of subproblems, in which nonlinear constraint and objective functions defined in matrix variables are approximated by block separable convex models. Global convergence is proved under reasonable assumptions. The article is concluded by numerical experiments with challenging Free Material Optimization problems subject to displacement constraints.

An experimental study of ultrafiltration for sub-10nm quantum dots and sub-150 nm nanoparticles through PTFE membrane and Nuclepore filters - Peukert, Wolfgang; Segets, Doris; Chen, Sheng-Chieh; Ling, Tsz-Yan; Pui, David (Journal of Membrane Science, 2016)
Ultrafiltration techniques (pore size of membrane below 100nm) are widely used in chemical engineering, semiconductor, pharmaceutical, food and beverage industries. However, for small particles, which are more and more attracting interests, the pore size often does not correlate well with sieving characteristics of the ultra-membranes. This may cause serious issues during modeling and prediction of retention efficiencies. Herein, a series of liquid filtration experiments with unfavorable conditions were performed. PTFE membranes (50, 100nm) and Nuclepore filters (50, 400nm) were challenged with 1.7nm manganese doped ZnS and 6.6 nm ZnO quantum dots (QDs), 12.4, 34.4 and 50 nm Au and 150 nm SiO nanoparticles. For larger and medium sized particles, sieving and eventually pore blockage phenomena were observed. In comparison, for small QDs, a high initial retention efficiency (>0.4) in both filters was monitored, followed by a reduced efficiency with ongoing particle loading. This high initial retention of small nanoparticles was attributed to diffusion deposition rather than to sieving since the ratio of pore size to particle size was significantly high (up to 58). Our experimental results allow a basic understanding of the deposition mechanism of small nanoparticles (diffusion vs. sieving) in different filter structures.
Keywords: Diffusion deposition; Loading effect; Quantum dot; Surface interactions; Ultrafiltration

An improved generalized AMBER force field (GAFF) for urea - Özpinar, Gül; Peukert, Wolfgang; Clark, Timothy (Journal of Molecular Modeling, 2010)
We describe an improved force field parameter set for the generalized AMBER force field (GAFF) for urea. Quantum chemical computations were used to obtain geometrical and energetic parameters of urea dimers and larger oligomers using AM1 semiempirical MO theory, density functional theory at the B3LYP/6-31G(d,p) level, MP2 and CCSD ab initio calculations with the 6-311++G (d,p), aug-cc-pVDZ, aug-cc-pVTZ, and aug-cc-pVQZ basis sets, and with the CBS-QB3 and CBS-APNO complete basis set methods. Seven different urea dimer structures were optimized at the MP2/aug-cc-pVDZ level to obtain accurate interaction energies. Atomic partial charges were calculated at the MP2/aug-cc-pVDZ level with the restrained electrostatic potential (RESP) fitting approach. The interaction energies computed with these new RESP charges in the force field are consistent with those obtained from CCSD and MP2 calculations. The linear dimer structure calculated using the force field with modified geometrical parameters and the new RESP charge set agrees well with available experimental data.

An improved long-term nanoindentation creep testing approach for studying the local deformation processes in nanocrystalline metals at room and elevated temperatures - Maier, Verena; Merle, Benoit; Göken, Mathias; Durst, Karsten (Journal of Materials Research, 2013)
The strain-rate sensitivity of ultrafine-grained aluminum (Al) and nanocrystalline nickel (Ni) is studied with an improved nanoindentation creep method. Using the dynamic contact stiffness thermal drift influences can be minimized and reliable creep data can be obtained from nanoindentation creep experiments even at enhanced temperatures and up to 10 h. For face-centered cubic (fcc) metals it was found that the creep behavior is strongly influenced by the microstructure, as nanocrystalline (nc) as well as ultrafine-grained (ufg) samples show lower stress exponents when compared with their coarse-grained (cg) counterparts. The indentation creep behavior resembles a power-law behavior with stress exponents n being ; 20 at room temperature. For higher temperatures the stress exponents of ufg-Al and nc-Ni decrease down to n ; 5. These locally determined stress exponents are similar to the macroscopic exponents, indicating that similar deformation mechanisms are acting during indentation and macroscopic deformation. Grain boundary sliding found around the residual indentations is related to the motion of unconstrained surface grains.
WW1::953

An improved method for point deflection measurements on rectangular membranes - Merle, Benoit; Nicholson, Kyle S.; Herbert, Erik G.; Göken, Mathias (Materials & Design, 2016)
In this work, the recent theoretical advances for evaluating point deflection experiments are reviewed and further refined. An improved experimental approach based on measuring the contact stiffness during nanoindentation is implemented and applied to the evaluation of the residual stress in SiNx and gold membranes. The accuracy of the point deflection experiments is assessed by evaluating the same set of samples with the bulge test reference technique and comparing the residual stress results. It is shown that the new experimental method greatly improves the reproducibility of the measurement and that the updated evaluation scheme leads to a more reliable residual stress value. (C) 2016 Elsevier Ltd. All rights reserved.
Keywords: Point deflection; Nanoindentation; Continuous stiffness measurement; Bulge test; Thin film; Residual stress

An inter-laboratory stability study of roll-to-roll coated flexible polymer solar modules - Gevorgyan, Suren A.; Medford, Andrew J.; Bundgaard, Eva; Sapkota, Subarna B.; Schleiermacher, Hans-Frieder; Zimmermann, Birger; Wuerfel, Uli; Chafiq, Amine; Lira-Cantu, Monica; Swonke, Thomas; Wagner, Michael; Haillant, Olivier O.; et al. (Solar Energy Materials and Solar Cells, 2011)
A large number of flexible polymer solar modules comprising 16 serially connected individual cells was prepared at the experimental workshop at Risø DTU. The photoactive layer was prepared from several varieties of P3HT (Merck, Plextronics, BASF and Risø DTU) and two varieties of ZnO (nanoparticulate, thin film) were employed as electron transport layers. The devices were all tested at Risø DTU and the functional devices were subjected to an inter-laboratory study involving the performance and the stability of modules over time in the dark, under light soaking and outdoor conditions. 24 laboratories from 10 countries and across four different continents were involved in the studies. The reported results allowed for analysis of the variability between different groups in performing lifetime studies as well as performing a comparison of different testing procedures. These studies constitute the first steps toward establishing standard procedures for an OPV lifetime characterization. © 2011 Elsevier B.V. All rights reserve
Keywords: Flexible modules; Inter-laboratory study; Outdoor testing; Polymer solar cells; R2R manufactured OPV; Round robin

Anodic Formation of Self-Organized Cobalt Oxide Nanoporous Layers - Lee, Chong-Yong; Lee, Kiyoung; Schmuki, Patrik (Angewandte Chemie International Edition, 2013)
High-aspect-ratio, ordered porous Co3O4 layers were formed by self-organizing anodization of a cobalt substrate and subsequent annealing. The key for successful formation of such layers is to sufficiently suppress competing oxygen evolution during anodization. The aligned Co3O4 channel layers behave as a highly efficient water oxidation catalyst.
EAM Import::2019-03-13

Anodic Formation of Thick Anatase TiO2 Mesosponge Layers for High-Efficiency Photocatalysis - Lee, Kiyoung; Kim, Dam-Hee; Roy, Poulomi; Paramasivam, Indhumati; Birajdar, Balaji; Spiecker, Erdmann; Schmuki, Patrik (Journal of the American Chemical Society, 2010)
We report a process for the flabrication of an anatase TiO2 mesosponge (TMS) layer by an optimized Ti anodization process in a hot glycerol electrolyte followed by a suitable etching process. Such layers can easily be grown to > 10 mu m thickness and have regular channels and structural features in the 5-20 nm range. The layers show high photocatalytic activity and are mechanically very robust. The layers therefore open new pathways to the wide field of TiO2(anatase) applications.

Anodic mesoporous TiO(2) layer on Ti for enhanced formation of biomimetic hydroxyapatite - Dey, Tuli; Roy, Poulumi; Fabry, Ben; Schmuki, Patrik (Acta Biomaterialia, 2010)
Ti surfaces can be very efficiently coated by a robust ( extgreekmm thick) mesoporous titania layer (MTL). These coatings are produced by anodization of Ti at elevated temperature in a glycerol/K2HPO4 electrolyte, followed by an appropriate etching process. In the present work we examine these layers with regard to their ability to form hydroxyapatite. Immersion tests in two types of simulated body fluids (Kokubo SBF and Bohner and Lemaitre SBF) combined with scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy investigations show that these MTL layers lead to a significant enhancement of HAp formation and anchoring in the structure compared with non-coated or even nanotubular Ti surface coatings (these were recently reported to be the most efficient in terms of HAp formation).

Anodic Nanotubular/porous Hematite Photoanode for Solar Water Splitting: Substantial Effect of Iron Substrate Purity - Lee, Chong-Yong; Wang, Lei; Kado, Yuya; Killian, Manuela; Schmuki, Patrik (ChemSusChem, 2014)
Anodization of iron substrates is one of the most simple and effective ways to fabricate nanotubular (and porous) structures that could be directly used as a photoanode for solar water splitting. Up to now, all studies in this field focused on achieving a better geometry of the hematite nanostructures for a higher efficiency. The present study, however, highlights that the purity of the iron substrate used for any anodic-hematite-formation approach is extremely important in view of the water-splitting performance. Herein, anodic self-organized oxide morphologies (nanotubular and nanoporous) are grown on different iron substrates under a range of anodization conditions, including elevated temperatures and anodization supported by ultrasonication. Substrate purity has not only a significant effect on oxide-layer growth rate and tube morphology, but also gives rise to a ninefold increase in the photoelectrochemical water-splitting performance (0.250 vs. 0.028mA cm-2 at 1.40V vs. reversible hydrogen electrode under AM1.5 100mW cm-2 illumination) for 99.99 % versus 99.5 % purity iron substrates of similar oxide geometry. Elemental analysis and model alloys show that particularly manganese impurities have a strong detrimental effect on the water-splitting performance.
EAM Import::2019-03-13

Anodic TiO2 nanotube layers: Why does self-organized growth occur-A mini review - Zhou, Xuemei; Nguyen, Nhat Truong; Özkan, Selda; Schmuki, Patrik (Electrochemistry Communications, 2014)
The present review gives an overview of the highlights of more than 10 years of research on synthesis and applications of ordered oxide structures (nanotube layers, hexagonal pore arrangements) that are formed by self-organizing anodization of metals. In particular we address the questions after the critical factors that lead to the spectacular self-ordering during the growth of anodic oxides that finally yield morphologies such as highly ordered TiO2 nanotube arrays and similar structures. Why are tubes and pores formed-what are the key parameters controlling these processes?
EAM Import::2019-03-13

Anodic TiO2 nanotubes: double walled vs. single walled - Liu, Ning; Mirabolghasemi, Hamed; Lee, Kiyoung; Albu, Sergiu; Tighineanu, Alexei; Altomare, Marco; Schmuki, Patrik (Faraday Discussions, 2013)
Electrochemical formation of self-organized TiO2 nanotube layers has been a highly active research field for more than 10 years. In the present manuscript we investigate the formation of two distinctly different anodic TiO2 nanotube morphologies, `single walled' and `double walled' tubes, which are formed mainly depending on the nature of the anodization electrolyte. While the widest used electrolytes are ethylene glycol (EG) based, forming double walled structures, tubes formed in dimethyl sulfoxide (DMSO) based electrolytes show a single tube walled morphology. Here we provide reasons for the formation of double walled tubes, characterize tubes for their composition, structure and certain properties, and give measures to suppress or minimize double wall formation. Except for the fact that in DMSO single walled tubes are formed, we also show that they grow sufficiently slowly to allow partial crystallization of the tubes during growth – this, in turn drastically influences their electronic properties. Finally we discuss the effects and potential consequences of double or single wall growth for TiO2 nanotube applications.
EAM Import::2019-03-13

Anodic TiO2 nanotubes: Influence of top morphology on their photocatalytic performance - Mazzarolo, Alice; Lee, Kiyoung; Vicenzo, Antonello; Schmuki, Patrik (Electrochemistry Communications, 2012)
The present work investigates the photocatalytic performance of TiO2 nanotubes with different tube top morphologies. Suchmorphological variations are obtained when growing self-organized nanotube arrays under different (but widely used) anodization conditions. We compare the most typical appearances of tube tops that are: i) ``grassy'' tubes, ii) tubes with initiation layers, iii) doubled anodized and iv) ``open'' tubes. The results show that tubes with an open, defined mouth have a significantly enhanced photocatalytic performance in open circuit, dye degradation experiments as well as when used as a photoanodes for photoelectrochemical water splitting.
EAM Import::2019-03-13

Anomalous transport of a tracer on percolating clusters - Spanner, Markus; Hoefling, Felix; Schröder-Turk, Gerd; Mecke, Klaus; Franosch, Thomas (Journal of Physics: Condensed Matter, 2011)
We investigate the dynamics of a single tracer exploring a course of fixed obstacles in the vicinity of the percolation transition for particles confined to the infinite cluster. The mean-square displacement displays anomalous transport, which extends to infinite times precisely at the critical obstacle density. The slowing down of the diffusion coefficient exhibits power-law behavior for densities close to the critical point and we show that the mean-square displacement fulfills a scaling hypothesis. Furthermore, we calculate the dynamic conductivity as a response to an alternating electric field. Last, we discuss the non-Gaussian parameter as an indicator for heterogeneous dynamics.

Anomalous yielding in the complex metallic alloy Al13Co4 - Walter, C.; Wheeler, J. M.; Barnard, J. S.; Raghavan, Rejin; Korte, Sandra; Gille, P.; Michler, Johann; Clegg, W. J. (Acta Materialia, 2013)
The single crystal deformation behaviour of orthorhombic Al13Co4 has been studied below the brittle-ductile transition temperature observed in bulk material from room temperature to 600° C, using indentation, microcompression and transmission electron microscopy. At room temperature, slip occurred most easily by dislocation motion on the (001)[010] slip system, as observed in the ductile regime at high temperatures. However, as the temperature was increased towards 600° C, the slip pattern changed to one consisting of linear defects running perpendicular to the loading axis. Serrated flow was observed at all temperatures, although at 600° C the magnitude of the serrations decreased. Anomalous yielding behaviour was also observed above 226° C, where both the yield and the 2% flow stress increased with temperature, almost doubling between 226 and 600° C. It has been suggested that this might arise due to the increasing stability of orthorhombic Al13Co4 with respect to the monoclinic form with increasing temperature. This is shown to be consistent with the theoretical predictions that exist.
EAM Import::2019-03-13

An operando DRIFTS-MS study of NH3 removal by supported ionic liquid phase (SILP) materials - Kaftan, Andre; Klefer, Heiko; Haumann, Marco; Laurin, Mathias; Wasserscheid, Peter; Libuda, Jörg (Separation and Purification Technology, 2017)
A novel gas purification material using a supported ionic liquid phase (SILP) has been investigated for removal of NH3 from ambient gas streams (1500 ppm NH3 in Ar). The SILP material is made of a thin film of an imidazolium based ionic liquid and a dissolved copper metal complex ([C(2)C(1)Im]Cl/CuC1(2)), which were dispersed in the pores of a silica 100 support. Diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) was used to investigate the irreversible absorption from a 1500 ppm NH3 gas stream and to identify species formed upon physisorption and chemisorption of ammonia. Additionally, temperature-programmed DRIFTS combined with in situ mass spectrometry were used to evaluate the reversibility and regenerability of the system. (C) 2016 Elsevier B.V. All rights reserved.
Keywords: Infrared spectroscopy; Online mass spectrometry; Ammonia absorption; Ionic liquid

A novel apparatus for in situ compression of submicron structures and particles in a high resolution SEM - Romeis, Stefan; Paul, Jonas; Ziener, Marc; Peukert, Wolfgang (Review of Scientific Instruments, 2012)
We report on the development and characterization of a novel in situ manipulation device to perform stressing experiments on the submicron scale inside a high resolution field emission scanning electron microscope. The instrument comprises two main assembly groups: an upper part for positioning and moving a mounted probe and a force sensor as well as a specimen support as lower part. The upper part consists of a closed loop tripod piezoelectric scanner mounted on a self-locking coarse positioning stage. Two interlocked steel springs and a linear variable differential transformer measuring the springs’ deflections compose the lower part of the instrument. This arrangement acts as force-sensor and sample support. In comparison to already well-established concepts a wide measuring range is covered by adjusting the spring constant between 30 N/m and 50000 N/m. Moreover, the new device offers striking advantages with respect to force calibration and sample deformation measurements. Force calibration is performed using the eigenfrequency of the force detection system directly inside the SEM. Deformation data are obtained with high accuracy by simultaneously recording displacements above and below the specimen. The detrimental apparatus compliance is determined, and the influence on measured data subsequently minimized: an easy to validate two-springs-in-series model is used for data correction. A force resolution in normal direction of 100 nN accompanied by a sample deformation resolution of 5 nm can be achieved with the instrument using an appropriate load cell stiffness. The capabilities and versatility of this instrument are exemplified by compression experiments performed on submicron amorphous silica particles.

A novel approach for preparation and in situ tensile testing of silica glass membranes in the TEM - Mackovic, Mirza; Przybilla, Thomas; Dieker, Christel; Herre, Patrick; Romeis, Stefan; Stara, Hana; Schrenker, Nadine; Peukert, Wolfgang; Spiecker, Erdmann (Frontiers in Materials, 2017)
The mechanical behavior of glasses in the micro- and/or nanometer regime increasingly gains importance in nowadays modern technology. However, suitable small scale preparation and mechanical testing approaches for a reliable assessment of the mechanical properties of glasses still remain a big challenge. In the present work, a novel approach for site-specific preparation and quantitative in situ tensile testing of thin silica glass membranes in the transmission electron microscope is presented. Thereby, advanced focused ion beam techniques are used for the preparation of nanoscale dog bone shaped silica glass specimens suitable for in situ tensile testing. Small amounts of gallium are detected on the surface of the membranes resulting from redeposition effects during the focused ion beam preparation procedure. Possible structural changes of silica glass upon irradiation with electrons and gallium ions are investigated by controlled irradiation experiments, followed by a structural analysis using Raman spectroscopy. While moderate electron beam irradiation does not alter the structure of silica glass, ion beam irradiation results in minor densification of the silica glass membranes. In situ tensile testing of membranes under electron beam irradiation results in distinctive elongations without fracture confirming the phenomenon of superplasticity. In contrast, in situ tensile testing in the absence of the electron beam reveals an elastic/plastic deformation behavior, and finally leads to fracture of the membranes. The Young’s moduli of the glass membranes pulled at beam off conditions in the TEM are comparable with values known for bulk fused silica, while the tensile strength is in the range of values reported for silica glass fibers with comparable dimensions. The impact of electron beam irradiation on the mechanical properties of silica glass membranes is further discussed. The results of the present work open new avenues for dedicated preparation and nanomechanical characterization of silica glasses, and further contribute to a fundamental understanding of the mechanical behavior of such glasses when being scaled down to the nanometer regim
Keywords: Silica glass; in situ TEM; in situ nanomechanical testing; Mechanical Properties; Electron beam irradiation; superplasticity; FIB; Raman spectroscopy

A novel Diameter-Selective functionalization of SWCNTs with lithium alkynylides - Gebhardt, Benjamin; Graupner, Ralf; Hauke, Frank; Hirsch, Andreas (European Journal of Organic Chemistry, 2010)
Covalent functionalization by addition to the sidewalls of single-walled carbon, nanotubes (SWCNTs) is one of the most important methods for the derivatization of carbon nanotubes. The nucleophilic addition of organometallic reagents (carbon- and nitrogen-based carbanions) has recently become a widely used tool for the introduction of functional moieties onto the surface of this new carbon allotrope. The extension, of this concept by the successful, nucleophilic addition of in situ generated lithium acetylides to the SWCNT scaffold is presented herein. The chemically derivatized SWCNTs have been characterized, in detail by TGA/MS, Raman, UV/Vis/NIR and fluorescence spectroscopy. On the basis of a detailed examination of the signals in the radial breathing-mode region of the Raman spectra, the preferred functionalization of smaller-diameter tubes has been clearly demonstrated. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Antimony sulfide as a light absorber in highly ordered, coaxial nanocylindrical arrays: preparation and integration into a photovoltaic device - Wu, Yanlin; Assaud, Loic; Kryschi, Carola; Capon, Boris; Detavernier, Christophe; Santinacci, Lionel; Bachmann, Julien (Journal of Materials Chemistry A, 2015)
We demonstrate the preparation of functional 'extremely thin absorber' solar cells consisting of massively parallel arrays of nanocylindrical, coaxial n-TiO2/i-Sb2S3/p-CuSCN junctions. Anodic alumina is used as an inert template that provides ordered pores of 80 nm diameter and 1-50 mu m length. Atomic layer deposition (ALD) then coats pores of up to 20 mm with thin layers of the electron conductor and the intrinsic light absorber. The crystallization of the initially amorphous Sb2S3 upon annealing is strongly promoted by an underlying crystalline TiO2 layer. After the remaining pore volume is filled with the hole conductor by solution evaporation, the resulting coaxial p-i-n junctions display stable diode and photodiode electrical characteristics. A recombination timescale of 40 ms is extracted from impedance spectroscopy in open circuit conditions, whereas transient absorption spectroscopy indicates that holes are extracted from Sb2S3 with a lifetime of 1 ns.

Antiperiodic oscillations - Freire, J. G.; Cabeza, C.; Marti, A. C.; Pöschel, Thorsten; Gallas, Jason (Scientific Reports, 2013)
The investigation of regular and irregular patterns in nonlinear oscillators is an outstanding problem in physics and in all natural sciences. In general, regularity is understood as tantamount to periodicity. However, there is now a flurry of works proving the existence of "antiperiodicity", an unfamiliar type of regularity. Here we report the experimental observation and numerical corroboration of antiperiodic oscillations. In contrast to the isolated solutions presently known, we report infinite hierarchies of antiperiodic waveforms that can be tuned continuously and that form wide spiral-shaped stability phases in the control parameter plane. The waveform complexity increases towards the focal point common to all spirals, a key hub interconnecting them all.

A numerical study of the Navier-Stokes transport coefficients for two-dimensional granular hydrodynamics - Garzó, Vicente; Almazan Torres, Lidia; Carrillo, José A.; Salueña, Clara; Pöschel, Thorsten (New Journal of Physics, 2013)
A numerical study that aims to analyze the thermal mechanisms of unsteady, supersonic granular flow by means of hydrodynamic simulations of the Navier-Stokes granular equation is reported in this paper. For this purpose, a paradigmatic problem in granular dynamics such as the Faraday instability is selected. Two different approaches for the Navier-Stokes transport coefficients for granular materials are considered, namely the traditional Jenkins-Richman theory for moderately dense quasi-elastic grains and the improved Garzó-Dufty-Lutsko theory for arbitrary inelasticity, which we also present here. Both the solutions are compared with event-driven simulations of the same system under the same conditions, by analyzing the density, temperature and velocity field. Important differences are found between the two approaches, leading to interesting implications. In particular, the heat transfer mechanism coupled to the density gradient, which is a distinctive feature of inelastic granular gases, is responsible for a major discrepancy in the temperature field and hence in the diffusion mechanisms. © IOP Publishing and Deutsche Physikalische Gesellschaft.

An unsymmetrical pentacene derivative with ambipolar behavior in organic thin-film transistors - Tykwinski, Rik; Etschel, Sebastian; Halik, Marcus; Jäger, Christof; Clark, Timothy; Margraf, Johannes; Waterloo, Andreas; Hampel, Frank; Yousefi Amin, Atefeh (Chemical Communications, 2013)
Three new unsymmetrical anthracenyl-pentacene derivatives have been synthesized, characterized using X-ray crystallography, and used as semiconductors in OTFTs. For one derivative, ambipolar charge carrier transport was observed with a hole mobility of 0.2 cm V s and an electron mobility of 0.03 cm V s. © 2013 The Royal Society of Chemistry.

A population balance model of quantum dot formation: Oriented growth and ripening of ZnO - Segets, Doris; Hartig, Martin Andreas Johannes; Gradl, Johannes; Peukert, Wolfgang (Chemical Engineering Science, 2012)
The precipitation of zinc oxide (ZnO) semiconductor quantum dots was investigated throughout the whole particle formation process, namely reaction, nucleation, growth and ripening and described by means of population balance equations (PBE). Regarding nucleation, the simulation revealed that the mechanism for the solid formation is by orders of magnitude lower than predicted by classical homogeneous nucleation theory. Thus, the earliest stages of particle formation were described by a combination of reaction kinetics determined by experiments for the formation of preformed clusters and subsequent oriented cluster aggregation. Finally, slow Ostwald ripening, i.e. the growth of larger structures at the expense of smaller particles, was modeled in good agreement with the already experimentally determined particle sizes for ripening temperatures between 10 and 50 °C.

Application of the Method of Generating Functions to the Derivation of Grad’s N-Moment Equations for a Granular Gas - Serero, Dan; Noskowicz, S. H. (Mathematical Modelling of Natural Phenomena, 2011)
A computer aided method using symbolic computations that enables the calculation of the source terms (Boltzmann) in Grad’s method of moments is presented. The method is extremely powerful, easy to program and allows the derivation of balance equations to very high moments (limited only by computer resources). For sake of demonstration the method is applied to a simple case: the one-dimensional stationary granular gas under gravity. The method should find applications in the field of rarefied gases, as well. Questions of convergence, closure are beyond the scope of this article.

Approximation of optimal control problems in the coefficient for the p-Laplace equation. I. Convergence result - Casas, Eduardo; Kogut, Peter I.; Leugering, Günter (SIAM Journal on Control and Optimization, 2016)
We study a Dirichlet optimal control problem for a quasi-linear monotone elliptic equation, the so-called weighted p-Laplacian problem. The coefficient of the -Laplacian, the weight u, we take as a control in BV (Ω) ∩ L∞(Ω). In this article, we use box-type constraints for the control such that there is a strictly positive lower and some upper bound. In order to handle the inherent degeneracy of the -Laplacian, we use a regularization, sometimes referred to as the -Laplacian. We derive existence and uniqueness of solutions to the underlying boundary value problem and the optimal control problem. In fact, we introduce a two-parameter model for the weighted -Laplacian, where we approximate the nonlinearity by a bounded monotone function, parametrized by κ. Further, we discuss the asymptotic behavior of the solutions to the regularized problem on each (ϵ, κ)-level as the parameters tend to zero and infinity, respectively.
Keywords: Control in coefficients; Nonlinear Dirichlet problem; Optimal control

A profound analysis of Rb2[PH] and Cs2[PH] and the role of [PH]2- ions during temperature-induced solid–solid phase transitions - Somer, M.; Schnering, H. G. V.; Hochrein, O.; Zahn, Dirk (Solid State Communications, 2014)
The temperature-induced solid–solid transformation of Rb2[PH] and Cs2[PH] is characterized from both experiment and theory. Neutron diffraction, IR-spectroscopy and ab-initio molecular dynamics simulations reveal an asymmetric shift of the lattice constants at 80 K. The molecular mechanism of the structural transformation as identified from IR-spectroscopy and ab-initio molecular dynamics simulations is closely connected to the orientation of the [PH]2- moieties which undergo a partial order– disorder phase transition.
EAM Import::2019-03-13

A push-pull unsymmetrical subphthalocyanine dimer - Zango, German; Zirzlmeier, Johannes; Claessens, Christian G.; Clark, Timothy; Victoria Martinez-Diaz, M.; Guldi, Dirk Michael; Torres, Tomas (Chemical Science, 2015)
Unsymmetrical subphthalocyanine fused dimers have been prepared from appropriate ortho-dinitrile SubPc precursors. In particular, either electron-donating or electron-accepting substituents have been introduced on each SubPc constituent unit, resulting in unprecedented push-pull pi-extended curved aromatic macrocycles. From fluorescence experiments in solvents of different polarity we conclude a dual fluorescence, namely a delocalized singlet excited state (1.73 eV) and a polarized charge transfer state (<1.7 eV). Pump probe experiments corroborate the dual nature of the fluorescence. On one hand, the delocalized singlet excited state gives rise to a several nanosecond lasting intersystem crossing yielding the corresponding triplet excited state. On the other hand, the polarized charge transfer state deactivates within a few picosesonds. Visualization of the charge transfer state was accomplished by means of molecular modeling with a slight polarization of the HOMO towards the electron donor and of the LUMO towards the electron acceptor.

Aqueous-phase reforming of xylitol over Pt/C and Pt/TiC-CDC catalysts: catalyst characterization and catalytic performance - Kirilin, Alexey V.; Hasse, Benjamin; Tokarev, Anton V.; Kustov, Leonid M.; Baeva, Galina N.; Bragina, Galina O.; Stakheev, Aleksandr Yu.; Rautio, Anne-Riikka; Salmi, Tapio; Etzold, Bastian; Mikkola, Jyri-Pekka; Murzin, Dmitry Yu. (Catalysis: Science and Technology, 2014)
The aqueous phase reforming (APR) of xylitol was studied over five Pt/C catalysts. The correlation between physico-chemical properties of the catalysts and catalytic performance was established. The Pt/C catalysts have different textural properties as well as different mean Pt cluster sizes and surface acidity. The average Pt cluster size was investigated by means of CO chemisorption as well as by TEM. The reaction was found to be structure sensitive and TOF linearly increases with increasing average Pt cluster size in the studied domain. The catalysts which possess higher surface acidity favoured higher rates of hydrocarbon production. On the contrary the Pt/C materials with lower acidities generated hydrogen with high selectivity and TOF.
EAM Import::2019-03-13