Open(G)PIAS: An open-source solution for the construction of a high-precision acoustic startle response setup for tinnitus screening and threshold estimation in rodents - Gerum, Richard; Rahlfs, Hinrich; Streb, Matthias; Krauß, Patrick; Grimm, Jannik; Metzner, Claus; Tziridis, Konstantin; Günther, Michael; Schulze, Holger; Kellermann, Walter; Schilling, Achim (Frontiers in Behavioral Neuroscience, 2019)
The modulation of the acoustic startle reflex (ASR) by a pre-stimulus called pre-pulse inhibition (PPI, for gap of silence pre-stimulus: GPIAS) is a versatile tool to, e.g., estimate hearing thresholds or identify subjective tinnitus percepts in rodents. A proper application of these paradigms depends on a reliable measurement of the ASR amplitudes and an exact stimulus presentation in terms of frequency and intensity. Here, we introduce a novel open-source solution for the construction of a low-cost ASR setup. The complete software for data acquisition and stimulus presentation is written in Python 3.6 and is provided as an Anaconda package. Furthermore, we provide a construction plan for the sensor system based on low-cost hardware components. Exemplary GPIAS data from two animal models (Mus musculus, Meriones unguiculatus) show that the ratio histograms (1-GPIAS) of the gap-pre-stimulus and no pre-stimulus ASR amplitudes can be well described by a log-normal distribution being in good accordance to previous studies with already established setups. Furthermore, it can be shown that the PPI as a function of pre-stimulus intensity (threshold paradigm) can be approximated with a hard-sigmoid function enabling a reproducible sensory threshold estimation. Thus, we show that the open-source solution could help to further establish the ASR method in many laboratories and, thus, facilitate and standardize research in animal models of tinnitus and/or hearing loss.
CRIS-Team Scopus Importer:2019-07-16
Keywords: 3D acceleration sensor; Anaconda package; Animal model; Low-cost setup; Startle; Tinnitus

Optical and Structural Properties of Nitride Based Nanostructures - Bertram, Frank; Berger, Christoph; Christen, Jürgen; Eisele, Holger; Greif, Ludwig A.Th; Hoffmann, Axel; Maultzsch, Janina; Müller, Marcus; Poliani, Emanuele; Schmidt, Gordon; Veit, Peter; Wagner, Markus R. (Springer Science and Business Media Deutschland GmbH, 2020)
Advanced characterization methods with nanoscale resolution are powerful tools in order to overcome the continuing challenges in the optimization of nitride semiconductor nanostructures for more efficient nanophotonic devices in the UV and green spectral range. This chapter is devoted to the study of optical, electronic, and structural properties of these nitride based nanostructures. In the first part, we discuss several state-of-the-art nanoscale characterization techniques including scanning transmission electron microscopy cathodoluminescence (STEM-CL), tip-enhanced Raman spectroscopy (TERS), micro-photoluminescence (µPL), X-ray diffraction (XRD), and scanning tunneling microscopy and spectroscopy (STM/STS). This selection of complementary microscopic and spectroscopic techniques provides unique insights into a multitude of nanostructure properties such as charge carrier excitation, relaxation, diffusion, and recombination dynamics, vibrational and structural properties including strain, segregation, as well as clustering, and surface and interface morphology. In the second part, we apply and combine these techniques to obtain detailed information on nanoscale properties of nitride based micro-columns, quantum wires, and heterostructures. The study of these nitride nanostructures provides not only insight into device limitations, but also contributes to the fundamental understanding of structural and optical properties of III-nitride nanostructures.
CRIS-Team Scopus Importer:2022-04-14

Optical current generation in graphene: CEP control vs. ω + 2ω control - Heide, Christian; Boolakee, Tobias; Eckstein, Timo; Hommelhoff, Peter (Nanophotonics, 2021)
The injection of directional currents in solids with strong optical fields has attracted tremendous attention as a route to realize ultrafast electronics based on the quantum-mechanical nature of electrons at femto- to attosecond timescales. Such currents are usually the result of an asymmetric population distribution imprinted by the temporal symmetry of the driving field. Here we compare two experimental schemes that allow control over the amplitude and direction of light-field-driven currents excited in graphene. Both schemes rely on shaping the incident laser field with one parameter only: either the carrier-envelope phase (CEP) of a single laser pulse or the relative phase between pulses oscillating at angular frequencies ω and 2ω, both for comparable laser parameters. We observe that the efficiency in generating a current via two-color-control exceeds that of CEP control by more than two orders of magnitude (7 nA vs. 18 pA), as the ω + 2ω field exhibits significantly more asymmetry in its temporal shape. We support this finding with numerical simulations that clearly show that two-color current control in graphene is superior, even down to single-cycle pulse durations. We expect our results to be relevant to experimentally access fundamental properties of any solid at ultrafast timescales, as well as for the emerging field of petahertz electronics.<br

Optical gating and streaking of free electrons with sub-optical cycle precision - Kozak, Martin; McNeur, Joshua; Leedle, Kenneth; Deng, Hudan; Schönenberger, Norbert; Ruehl, Axel; Hartl, Ingmar; Harris, James; Byer, Robert; Hommelhoff, Peter (Nature Communications, 2017)
The temporal resolution of ultrafast electron diffraction and microscopy experiments is currently limited by the available experimental techniques for the generation and characterization of electron bunches with single femtosecond or attosecond durations. Here, we present proof of principle experiments of an optical gating concept for free electrons via direct time-domain visualization of the sub-optical cycle energy and transverse momentum structure imprinted on the electron beam. We demonstrate a temporal resolution of 1.2 +/- 0.3 fs. The scheme is based on the synchronous interaction between electrons and the near-field mode of a dielectric nano-grating excited by a femtosecond laser pulse with an optical period duration of 6.5 fs. The sub-optical cycle resolution demonstrated here is promising for use in laser-driven streak cameras for attosecond temporal characterization of bunched particle beams as well as time-resolved experiments with free-electron beam

Optical Landau state mapping with in-plane electric fields - Karmakar, Biswajit; Schardt, Michael; Malzer, Stefan; Arora, Brij Mohan; Döhler, Gottfried (Physica Status Solidi (C) Current Topics in Solid State Physics, 2007)
We report on a theoretical and experimental investigation of magneto-absorption in quantum wells (QWs) in the presence of a uniform in-plane electric field. From a simple theoretical model a linear real-space shift of the electron Landau level wave functions relative to the hole counterparts is expected under increasing in-plane electric field. As a result, quadratic Stark shifts, fading of the zero-field allowed transitions, and increasing oscillator strength for the originally forbidden transitions are predicted. These predictions are confirmed by experiments on GaAs/AlGaAs-QWs and found to be in reasonably good agreement with simulations based on a simple model. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

Optically detected magnetic resonance of the intrinsic luminescence in As2Se3 - Ristein, Jürgen; et al. (Journal of Non-Crystalline Solids, 1989)
Magnetic resonance of the excited luminescence centre in crystalline As2Se3, which was optically detected in a 16 GHz experiment, finally confirms the triplet character of the state, but reveals quite unusual spin parameters. The ODMR spectrum of bulk a-As2Se3 shows a superposition of a sharp peak at g=2 and a broad background signal, which is found to be consistent with the powder spectrum of the crystal. This indicates that part of the recombination in the glass involves the formation of similar intermediates states. © 1989.
UnivIS-Import:2015-03-05:Pub.1989.nat.dphy.IAP.exphys.optica

Optically detected magnetic resonance (OMDR) in a-Si1-xGex:H-alloys - Ristein, Jürgen; et al. (Solid State Communications, 1988)
UnivIS-Import:2015-03-05:Pub.1988.nat.dphy.IAP.exphys.optica

Optically pure, monodisperse cis-oligodiacetylenes: Aggregation-induced chirality enhancement - Chernick, Erin; Börzsönyi, Gabor; Steiner, Christian; Ammon, Maximilian Michael; Geßner, David; Frühbeißer, Sabine; Gröhn, Franziska; Maier, Sabine; Tykwinski, Rik (Angewandte Chemie International Edition, 2014)
Conformational changes in the conjugated backbone of poly- and oligodiacetylenes (PDAs and ODAs) play an important role in determining the electronic properties of these compounds. At the same time, conformational changes can also result in a folded structure that shows helical chirality. Using D-camphor as a chiral building block, we have designed a high-yielding, iterative synthesis of monodisperse, optically pure cis-oligodiacetylenes (ODAs). cis-ODAs up to the tridecamer have been formed, which is the longest monodisperse cis-ODA reported to date. UV/Vis spectroscopy suggests a large effective conjugation length in THF, likely the result of a linear, planar conformation in this solvent. High-resolution STM/AFM measurements of the nonamer cast from THF onto HOPG show a linear structure. In iPrOH, circular dichroism (CD) spectra suggest the formation of chiral aggregates for ODAs with at least nine D-camphor units, based on a strong CD response. Conformation, conjugation: A series of optically pure, monodisperse cis-oligodiacetylenes (cis-ODAs) based on D-camphor building blocks has been synthesized up to the tridecamer length, which represents the longest cis-ODA reported to date. Optical spectroscopy and STM/AFM measurements indicate that the oligomers assume a linear, planar conformation in THF. Conversely, in iPrOH solution ODAs with n≥9 form chiral aggregates. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optical measurement of the work function and the field reduction factor of metallic needle tips - Meier, Stefan; Heimerl, Jonas; Dienstbier, Philip; Hommelhoff, Peter (Review of Scientific Instruments, 2023)
Quintessential parameters for needle tip-based electron sources are the work function, the tip apex radius, and the field reduction factor. They determine the static emission properties and strongly influence laser-triggered photoemission experiments at these needle tips. We present a simple method based on photoemission with two different commonly available continuous-wave laser diodes to determine both parameters in situ. We demonstrate our technique at tungsten needle tips. In a first application, use the method to in situ monitor changes of the emitter caused by illumination with strong femtosecond laser pulses. After illumination, we observe an increase in the work function caused by laser-induced changes to the apex of the tip. These changes are reversible upon field evaporation and are accompanied by a change in the spatial electron emission distribution. We believe that this simple in situ work function determination technique is applicable to any metal and in many experimental settings.<br
Keywords: Work functions; Ultra-high vacuu; Field ion microscopy; Scanning electron microscopy; Femtosecond lasers; Optical materials; Optical metrology; Femtosecond electron pulse; Electron sources; Adsorption

Optical polymers with tunable refractive index for nanoimprint technologies - Landwehr, J.; Fader, R.; Rumler, Maximilian; Rommel, Mathias; Bauer, Anton; Frey, Lothar; Simon, B.; Fodor, B.; Petrik, P.; Schiener, Andreas; Winter, Benjamin; Spiecker, Erdmann (Nanotechnology, 2014)
In order to realize a versatile high throughput production of micro-optical elements, UV-curable polymer composites containing titanium dioxide nanoparticles were prepared and characterized. The composites are based on an industrial prototype epoxy polymer. Titanium dioxide nanoparticles smaller than 10 nm were synthesized by the nonaqueous sol method and in situ sterically stabilized by three different organic surfactants. The composites exhibit high transparency. Distinct alteration of optical transmission properties for visible light and near IR wavelength range could be avoided by adaption of the stabilizing organic surfactant. Most importantly, the refractive index (RI) of the composites that depends on the fraction of incorporated inorganic nanoparticles could be directly tuned. E.g. the RI at a wavelength of 635 nm of a composite containing 23 wt% titanium dioxide nanoparticles is increased to 1.626, with respect to a value of 1.542 for the pure polymer. Furthermore, it could be demonstrated that the prepared inorganic-organic nanocomposites are well suited for the direct fabrication of low-cost micro-optical elements by nanoimprint lithography. A low response of the optical composite properties to temperature treatment up to 220°C with a shrinkage of only about 4% ensures its application for integrated micro-optical elements in industrial production.
UnivIS-Import:2015-04-14:Pub.2014.tech.IE.LEB.optica
Keywords: Composite materials; Refractive index matching; Substrate conformal imprint lithography; TiO; UV polymers

Optimal geometry for efficient loading of an optical dipole trap - Szczepkowicz, Andrzej; Krzemień, Leszek; Wojciechowski, Adam; Brzozowski, Krzysztof; Krüger, Michael; Zawada, Michał; Witkowski, Marcin; Zachorowski, Jerzy; Gawlik, Wojciech (Physical Review A, 2009)
One important factor which determines efficiency of loading cold atoms into an optical dipole trap from a magneto-optical trap is the distance between the trap centers. By studying this efficiency for various optical trap depths  <span class="mjx-chtml MathJax_CHTML" id="MathJax-Element-1-Frame" style="box-sizing: border-box; display: inline-block; line-height: 0; font-size: 15px; word-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px;" tabindex="0">(2–110mK)  we find that for optimum dipole trap loading, longitudinal displacements up to  <span class="mjx-chtml MathJax_CHTML" id="MathJax-Element-2-Frame" style="box-sizing: border-box; display: inline-block; line-height: 0; font-size: 15px; word-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px;" tabindex="0">15mm  are necessary. An explanation for this observation is presented and compared with other work and a simple analytical formula is derived for the optimum distance between the trap centers.

Optimising the parameters for the synthesis of CuIn-nanoparticles by chemical reduction method for chalcopyrite thin film precursors - Schuster, Matthias; Möckel, Stefan; Wibowo, Rachmat Adhi; Hock, Rainer; Wellmann, Peter (Materials Research Society Symposium - Proceedings, 2013)
Roll-to-roll deposition techniques for the fabrication of chalcopyrite solar cells are of major interest and are a promising alternative to state of the art vacuum processes. However, for roll-to-roll processes the preparation of precursor materials like nanoparticle inks is a crucial point. In this work a study on the preparation technique of copper-indium intermetallic nanoparticles was conducted. The preparation of the nanoparticles is based on the chemical reduction of copper and indium cations with sodium borohydride. Different parameters are discussed regarding their influence on (1) size and shape of the nanoparticles, (2) Cu/In ratio within the synthesised nanoparticles and (3) yield of the synthesis. Results show a strong dependency of the Cu/In ratio of the nanoparticles and the yield of the synthesis on the synthesis parameters. The influence of different parameters like (a) the ratio of metal cations to BH anions, (b) the Cu/In cation ratio within the precursor solution and (c) the dropping rate of the copper-indium precursor solution are discussed. The Cu/In ratio within the nanoparticles can mainly be controlled by the Cu/In cation ratio and the dropping rate of the copper-indium precursor solution. The yield of the synthesis shows saturation behaviour depending on the ratio of metal cations to BH anions. Shape and size of the nanoparticles are independent of the varied parameters. © 2013 Materials Research Societ
Keywords: nanoscale; alloy; chemical synthesis

Optimization of growth parameters for growth of high quality heteroepitaxial 3C-SiC films at 1200 degrees C - Wilhelm, Martin; Rieth, Marcel; Brandl, Marco; Wibowo, Rachmat Adhi; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2015)
In order to reduce the residual stress caused by the mismatch of thermal expansion coefficients of 3C-SiC layers grown on Si after cooling down to room temperature, the growth temperature was reduced from usually above 1300 degrees C to 1200 degrees C. Epitaxial layers with high crystalline quality were grown on 1 x 1 cm(2) (100) Si substrates. The layers were evaluated by means of x-ray diffraction (XRD), Raman measurements, scanning electron microscopy and atomic force microscopy. Full width at half maximum values of 0.19 degrees for XRD rocking curve measurements of the (200) 3C-SiC peak were achieved, indicating high crystalline quality of the layers and epitaxial growth. For optimized growth at 1200 degrees C a high C/Si-ratio, on-axis substrates and a layer thickness of over 1 mu m are necessary. (C) 2015 Elsevier B.V. All rights reserved.
Keywords: Cubic silicon carbide; Heteroepitaxy; X-ray diffraction; Raman spectroscopy

Optofluidic rotation of living cells for single-cell tomography - Kolb, Thorsten; Albert, Sahradha; Haug, Michael; Whyte, Graeme (Journal of Biophotonics, 2014)
Flow cytometry provides a high throughput, multi-dimensional analysis of cells flowing in suspension. In order to combine this feature with the ability to resolve detailed structures in 3D, we developed an optofluidic device that combines a microfluidic system with a dual beam trap. This allows for the rotation of single cells in a continuous flow, around an axis perpendicular to the imaging plane. The combination of both techniques enables the tomographic reconstruction of the 3D structure of the cell. In addition this method is capable to provide detailed 3D structural data for flow cytometry, as it improves the reconstructed z-resolution of a standard microscopy system to produce images with isotropic resolution in all three axes.
EAM Import::2019-03-08

Orbital-Driven Rashba Effect in a Binary Honeycomb Monolayer AgTe - Unzelmann, Maximilian; Bentmann, Hendrik; Eck, Philipp; Kißlinger, Tilman; Geldiyev, Begmuhammet; Rieger, Janek; Moser, Simon; Vidal, Raphael C.; Kissner, Katharina; Hammer, Lutz; Schneider, M. Alexander; Fauster, Thomas; et al. (Physical Review Letters, 2020)
The Rashba effect is fundamental to the physics of two-dimensional electron systems and underlies a variety of spintronic phenomena. It has been proposed that the formation of Rashba-type spin splittings originates microscopically from the existence of orbital angular momentum (OAM) in the Bloch wave functions. Here, we present detailed experimental evidence for this OAM-based origin of the Rashba effect by angle-resolved photoemission (ARPES) and two-photon photoemission experiments for a monolayer AgTe on Ag(111). Using quantitative low-energy electron diffraction analysis, we determine the structural parameters and the stacking of the honeycomb overlayer with picometer precision. Based on an orbitalsymmetry analysis in ARPES and supported by first-principles calculations, we unequivocally relate the presence and absence of Rashba-type spin splittings in different bands of AgTe to the existence of OAM.
CRIS-Team WoS Importer:2020-05-15

Ordered arrangement of 9-aminoanthracene on Au(1 1 1) surfaces: A scanning tunneling microscopy study - Lauffer, Peter; Graupner, Ralf; Jung, Adrian; Hirsch, Andreas; Ley, Lothar (Surface Science, 2007)
We present a scanning tunneling microscopy (STM) investigation of 9-aminoanthracene (AA) on the reconstructed Au(1 1 1) surface. The bare Au(1 1 1) surface shows the herringbone reconstruction which is conserved upon deposition of the organic molecules. Most of the AA molecules are found to decorate the regions of fcc-stacking of the gold surface where a periodic linear arrangement is observed. The orientation of the long molecule axis of individual molecules is along the 〈 0 1 over(1, ̄) 〉-directions of the Au substrate. In addition, for individual domains of the surface reconstruction, one of the three possible orientations is preferred. On substrate areas which exhibit a high step density, the steps are completely decorated by AA molecules. A detailed analysis of the STM images reveals that the molecules are located on top terrace levels. The fine structure of individual molecules on the terrace shows a clear dependence on the tunneling voltage and resembles the molecular orbitals of the free AA molecule. © 2007 Elsevier B.V. All rights reserved.

Ordering aspects and intramolecular conformation of tetraphenylporphyrins on Ag(111) - Buchner, Florian; Kellner, Ina; Hieringer, Wolfgang; Görling, Andreas; Steinrück, Hans-Peter; Marbach, Hubertus (Physical Chemistry Chemical Physics, 2010)
A systematic scanning tunnelling microscopy study of the self-assembly, intramolecular conformation and supramolecular ordering of different tetraphenylporphyrins (xTPP) with or without a central metal atom (x = 2H, Fe, Co) on Ag(111) at room temperature is presented. The investigation covers a wide range, i.e. the adsorption behaviour from the low sub-monolayer up to the multilayer regime is described in detail and conclusively discussed in regard to molecule-molecule and molecule-substrate interactions. At monolayer coverage the molecules self-assemble in domains with a square unit cell caused by "T-type" intermolecular interactions, while the orientation of the domains along the symmetry axes is determined by adsorbate-substrate interactions. Interestingly for ordered monolayers domain boundaries always separate domains of different organizational chirality but same orientation of the square unit cell. This demonstrates that in the particular system chirality obviously restricts the long range order of the supramolecular TPP assemblies. In combination with DFT calculations it is also demonstrated that the previously reported intramolecular saddle shape deformation of TPPs upon adsorption is more pronounced for metallo-TPP than for 2HTPP. © 2010 the Owner Societies.

Organometallic perovskites for optoelectronic applications (Conference Presentation) - Levchuk, Ievgen; Högl, Florian; Brandl, Marco; Osvet, Andres; Herre, Patrick; Hock, Rainer; Schweizer, Peter; Spiecker, Erdmann; Batentschuk, Miroslaw; Brabec, Christoph; Peukert, Wolfgang (SPIE Nanoscience + Engineering, 2016, 2016)
Organometallic halide perovskites CH3NH3BX3 (B= Pb, Sn, Ge; X = I, Br, Cl) have become one of the most promising semiconductors for solar cell applications, reaching power conversion efficiencies beyond 20%. Improving our ability to harness the full potential of organometal halide perovskites requires the development of more reliable synthesis routines of well defined, reproducible and defect free reference systems allowing to study the fundamental photo-physical processes. In this study we present size and band gap engineering for organo-lead perovskites crystallites with various shapes and sizes ranging from the 5 nm regime all the way to 1 cm. Colloidal nano-crystals, micro-crystlline particles as well as single crystals are demonstrated with excellent purity and control in shape and size are demonstrated. The structural, optical and photo-physical properties of these reference materials are investigated and analyzed as function of their size and shape.
Keywords: particle; crystal; organometal; optoelectronics

Orientation dependence of magneto-resistance behaviour in a carbon nanotube rope - McIntosh, Gregory C.; Kim, Gyutae; Park, Jin-gyu; Krstic, Vojislav; Burghard, Marko; Jhang, Sung Ho; Lee, Sangwook; Roth, Siegmar; Park, YungWoo (Thin Solid Films, 2002)
The orientation dependence of magneto-resistance behaviour for a single-walled carbon nanotube (SWCN) rope is reported. A clear delineation of behaviours is observed between applying a magnetic field perpendicular or parallel to the rope axis. For a perpendicular field, monotonic negative magneto-resistance is observed due to two-dimensional weak localisation within the rope. By contrast, for a parallel field, complicated oscillatory behaviour is observed due to the Altshuler–Aronov–Spivak effect around closed electron trajectories on discrete cylinders within the SWCN rope. A dominant oscillatory mode can be identified which corresponds to closed paths around the outer circumference of the SWCN rope. However, due to the composite filamentary nature of the rope, the overall oscillatory behaviour is rather complicated and can be classified as universal conductance fluctuations. With a backgate voltage applied to the sample, Coulomb blockade peaks are observed in the transport current with additional peak structure superimposed due to resonant tunnelling. We find an interesting effect whereby these peaks are suppressed in the presence of a magnetic field.
Keywords: Magneto-resistance; Carbon nanotubes

Origin of Doping in Quasi-Free-Standing Graphene on Silicon Carbide - Ristein, Jürgen; Mammadov, Samir; Seyller, Thomas (Physical Review Letters, 2012)
We explain the robust p-type doping observed for quasi-free-standing graphene on hexagonal silicon carbide by the spontaneous polarization of the substrate. This mechanism is based on a bulk property of SiC, unavoidable for any hexagonal polytype of the material and independent of any details of the interface formation. We show that sign and magnitude of the polarization are in perfect agreement with the doping level observed in the graphene layer. With this mechanism, models based on hypothetical acceptor-type defects as they are discussed so far are obsolete. The n-type doping of epitaxial graphene is explained conventionally by donorlike states associated with the buffer layer and its interface to the substrate that overcompensate the polarization doping. © 2012 American Physical Society.
UnivIS-Import:2015-03-09:Pub.2012.nat.dphy.IAP.exphys.origin_7

Origin of logarithmic resistance correction in graphene - Jobst, Johannes; Weber, Heiko B. (Nature Physics, 2012)
Chen et al.1 recently presented data of a logarithmic low-temperature anomaly in the resistance of graphene flakes and attributed this to Kondo physics. The samples were irradiated beforehand with ions, and the appearance of a logarithmic anomaly was linked to the presence of induced defect states with unpaired electrons. Here, we present evidence that this assignment to Kondo physics is wrong. The observed effect is due to electron–electron interaction (EEI)2, which in the diffusive regime also gives a logarithmic correction to the resistance (in two dimensions). It is an effect that is based on very general assumptions, and that has been observed in many two-dimensional materials in excellent agreement with theory. It has been pinpointed in graphene recently3.

Origin of nonsaturating linear magnetoresistivity - Kißlinger, Ferdinand; Ott, Christian; Weber, Heiko B. (Physical Review B, 2017)

Origin of spin-polarized photocurrents in the topological surface states of Bi2Se3 - Ketterl, A. S.; Otto, Sebastian; Bastian, M.; Andres, B.; Gahl, C.; Minar, J.; Ebert, H.; Braun, J.; Tereshchenko, O. E.; Kokh, K. A.; Fauster, Thomas; Weinelt, M. (Physical Review B, 2018)
For the generation of spin-polarized photocurrents in topological insulators, a coupling between photon angular momentum and electron spin is often assumed. Such a coupling seems to be supported by dichroism reported in E(k(y))-intensity maps in photoemission. We show in three dimensional two-photon photoemission and one-step photoemission calculations that the circular dichroism is in fact threefold in E(k(x), k(y)) maps although it may appear antisymmetric in E(k(y)). The threefold symmetry is inconsistent with the previously assumed coupling between photon momentum and electron's chiral spin via the orbital momentum. Instead it reflects the surface point group. The only antisymmetric patterns appear in the energy range in which surface and bulk states hybridize. In general, a threefold-symmetric dichroic signal does not support unidirectional photocurrents. Nevertheless, the residual asymmetry of up to 3.5% in our photoemission spectra is compatible with previously observed helicity-dependent photocurrents.

Origin of surface conductivity in diamond - Ristein, Jürgen; Maier, Florian; Ley, Lothar; et al. (Physical Review Letters, 2000)
Experimental evidence is presented which supports an electrochemical model for the pronounced surface conductivity of hydrogen-terminated diamond. In this model hydrogenation rises the valence band maximum (VBM) of diamond sufficiently with respect to the vacuum level to place it just above the chemical potential of electrons in the liquid phase (μe) of a mildly acidic water layer physisorbed at the surface. Electron transfer from diamond to the H3O+/(H2O + H2) redox couple accounts for the hole accumulation layer. In equilibrium, the diamond surface Fermi level position is pinned at μe which coincides essentially with the VBM. Small variations in that Fermi level position with respect to VBM and thus variations in conductivity with the pH value of the wetting layer and the H2 partial pressure are quantitatively accounted for via Nernst's equation.
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.IAP.exphys.theori

Oscillatory magnetic tweezers based on ferromagnetic beads and simple coaxial coils - Trepat, Xavier; Grabulosa, Mireia Herrando; Buscemi, Lara; Rico, Felix; Fabry, Ben; Fredberg, Jeffrey; Farrè, Ramon (Review of Scientific Instruments, 2003)

Outline of a dielectric laser acceleration experiment at SwissFEL - Eduard, Prat; Bettoni, Simona; Calvi, Marco; Dehler, Micha; Frei, Franziska; Hommelhoff, Peter; Kozak, Martin; McNeur, Joshua; C. Ozkan, Loch; Reiche, Sven; Romann, Albert; Ischebeck, Rasmus (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2017)
The Accelerator on a Chip International Program (ACHIP), funded by the Gordon and Betty Moore Foundation for a 5. year period, pursues basic research and development for a super-compact accelerator on a chip, where the accelerating structure is a dielectric microstructure excited by femtosecond laser pulses. The Paul Scherrer Institute (PSI) will contribute to this by providing the international collaboration access to the high-brightness electron beams in SwissFEL, where we plan to do a proof-of-principle demonstration of the acceleration of a highly relativistic beam. In this contribution we present the conceptual layout of the experiment, in which we will focus the beam down to sub-micrometer beam sizes. Start-to-end simulation results of the tracked electron beam, and first calculations of the accelerating field of the microstructure will be show
Keywords: Dielectric laser acceleration

Overcoming efficiency and stability limits in water-processing nanoparticular organic photovoltaics by minimizing microstructure defects - Xie, Chen; Heumüller, Thomas; Gruber, Wolfgang; Tang, Xiaofeng; Classen, Andrej; Schuldes, Isabel; Bidwell, Matthew; Späth, Andreas; Fink, Rainer; Unruh, Tobias; Mcculloch, Iain; Li, Ning; et al. (Nature Communications, 2018)
There is a strong market driven need for processing organic photovoltaics from eco-friendly solvents. Water-dispersed organic semiconducting nanoparticles (NPs) satisfy these premises convincingly. However, the necessity of surfactants, which are inevitable for stabilizing NPs, is a major obstacle towards realizing competitive power conversion efficiencies for water-processed devices. Here, we report on a concept for minimizing the adverse impact of surfactants on solar cell performance. A poloxamer facilitates the purification of organic semiconducting NPs through stripping excess surfactants from aqueous dispersion. The use of surfactant-stripped NPs based on poly(3-hexylthiophene) / non-fullerene acceptor leads to a device efficiency and stability comparable to the one from devices processed by halogenated solvents. A record efficiency of 7.5% is achieved for NP devices based on a low-band gap polymer system. This elegant approach opens an avenue that future organic photovoltaics processing may be indeed based on non-toxic water-based nanoparticle inks.
Keywords: microstructure-recombination correlation; organic photovoltaics; polymer-fullerene nanoparticles; water processed

Overcoming the Thermal Instability of Efficient Polymer Solar Cells by Employing Novel Fullerene-Based Acceptors - Zhang, Chaohong; Mumyatov, Alexander; Langner, Stefan; Perea Ospina, Jose Dario; Kassar, Thaer; Min, Jie; Ke, Lili; Chen, Haiwei; Gerasimov, Kirill L.; Anokhin, Denis V.; Ivanov, Dimitri A.; Ameri, Tayebeh; et al. (Advanced Energy Materials, 2017)
Solution-processed organic solar cells with promising photovoltaic performance and extraordinary high thermal stability are achieved by employing novel fullerene-based acceptors in combination with two state-of-the-art polymer donors. The findings demonstrated in this work underline the necessity and importance of novel acceptor design rules for highly efficient organic solar cells with excellent device stability.
Keywords: Miscibility; Morphological analysis; Novel fullerene-based acceptors; Organic photovoltaics; Thermal stability

Overpotentials and Faraday Efficiencies in CO2 Electrocatalysis-the Impact of 1-Ethyl-3-Methylimidazolium Trifluoromethanesulfonate - Neubauer, Sebastian; Krause, Ralf K.; Schmid, Bernhard; Guldi, Dirk Michael; Schmid, Guenter (Advanced Energy Materials, 2016)
The mixtures of room temperature ionic liquid 1-ethyl-3-methylimidazolium trifl uoromethanesulfonate ([EMIM]TFO) and water as electrolytes for reduction of CO2 to CO are reported. Linear sweep voltammetry shows overpotentials for CO2 reduction and the competing hydrogen evolution reaction (HER), both of which vary as a function of [EMIM]TFO concentration in the range from 4 × 10-3 M (0.006 mol%) to 4869 × 10-3 M (50 mol%). A steady lowering of overpotentials up to an optimum for 334 × 10-3 M is identifi ed. At 20 mol% and more of [EMIM]TFO, a signifi cant CO2 reduction plateau and inhibition of HER, which is limited by H2 O diffusion, is noted. Such a plateau in CO2 reduction correlates to high CO Faraday effi ciencies. In case of 50 mol% [EMIM]TFO, a broad plateau spanning over a potential range of 0.58 V evolves. At the same time, the overpotential for HER is increased by 1.20 V when compared to 334 × 10-3 M and, in turn, HER is largely inhibited. The Faraday effi ciencies for CO and H2 formation feature 95.6% ± 6.8% and 0.5% ± 0.3%, respectively, over a period of 3 h in a separator divided cell. Cathodic as well as anodic electrochemical stability of the electrolyte throughout this time period is corroborated in 1 H NMR spectroscopic measurements.
EAM Import::2019-03-08

Oxidation and phase transition in covalently functionalized MoS2 - Moses Badlyan, Narine; Pettinger, Nina; Enderlein, Niklas; Gillen, Roland; Chen, Xin; Zhang, Wanzheng; Knirsch, Kathrin; Hirsch, Andreas; Maultzsch, Janina (Physical Review B, 2022)
We present a Raman study of MoS2 powders and MoS2 individual layers covalently functionalized with organic molecules. In MoS2 powders, the defect-induced "LA"Raman mode shows evidence for successful functionalization. Increasing temperature induces oxidation of both functionalized and nonfunctionalized MoS2 into MoO3. In contrast, mechanically exfoliated individual MoS2 layers do not transfer into MoO3 under the same conditions. Instead, the Raman spectra show that the procedure of covalent functionalization leads to a partial transition from the 2H into the 1T' crystallographic phase in few-layer MoS2. We support the identification of the 1T' phase by DFT calculations of the corresponding vibrational modes in the mono- and bilayer 1T'-MoS2.
CRIS-Team Scopus Importer:2022-09-30

Oxidative stress-induced posttranslational modifications of alpha-synuclein: specific modification of alpha-synuclein by 4-hydroxy-2-nonenal increases dopaminergic toxicity - Xiang, Wei; Schlachetzki, Johannes; Helling, Stefan; Bussmann, Julia C.; Berlinghof, Marvin; Schäffer, Tilman; Marcus, Katrin; Winkler, Jürgen; Klucken, Jochen; Becker, Cord-Michael; Klucken, Jochen (Molecular and Cellular Neuroscience, 2013)
Aggregation and neurotoxicity of misfolded alpha-synuclein (?Syn) are crucial mechanisms for progressive dopaminergic neurodegeneration associated with Parkinson's disease (PD). Posttranslational modifications (PTMs) of ?Syn caused by oxidative stress, including modification by 4-hydroxy-2-nonenal (HNE-?Syn), nitration (n-?Syn), and oxidation (o-?Syn), have been implicated to promote oligomerization of ?Syn. However, it is yet unclear if these PTMs lead to different types of oligomeric intermediates. Moreover, little is known about which PTM-derived ?Syn species exerts toxicity to dopaminergic cells. In this study, we directly compared aggregation characteristics of HNE-?Syn, n-?Syn, and o-?Syn. Generally, all of them promoted ?Syn oligomerization. Particularly, HNE-?Syn and n-?Syn were more prone to forming oligomers than unmodified ?Syn. Moreover, these PTMs prevented the formation of amyloid-like fibrils, although HNE-?Syn and o-?Syn were able to generate protofibrillar structures. The cellular effects associated with distinct PTMs were studied by exposing modified ?Syn to dopaminergic Lund human mesencephalic (LUHMES) neurons. The cellular toxicity of HNE-?Syn was significantly higher than other PTM species. Furthermore, we tested the toxicity of HNE-?Syn in dopaminergic LUHMES cells and other cell types with low tyrosine hydroxylase (TH) expression, and additionally analyzed the loss of TH-immunoreactive cells in HNE-?Syn-treated LUHMES cells. We observed a selective toxicity of HNE-?Syn to neurons with higher TH expression. Further mechanistic studies showed that HNE-modification apparently increased the interaction of extracellular ?Syn with neurons. Moreover, exposure of differentiated LUHMES cells to HNE-?Syn triggered the production of intracellular reactive oxygen species, preceding neuronal cell death. Antioxidant treatment effectively protected cells from the damage triggered by HNE-?Syn. Our findings suggest a specific pathological effect of HNE-?Syn on dopaminergic neurons.
EVALuna2:4685

Oxide-free hybrid silicon nanowires: From fundamentals to applied nanotechnology - Bashouti, Muhammad Y.; Sardashti, Kasra; Schmitt, Sebastian W.; Pietsch, Matthias; Ristein, Jürgen; Haick, Hossam; Christiansen, Silke H. (Progress in Surface Science, 2013)
The ability to control physical properties of silicon nanowires (Si NWs) by designing their surface bonds is important for their applicability in devices in the areas of nano-electronics, nano-photonics, including photovoltaics and sensing. In principle a wealth of different molecules can be attached to the bare Si NW surface atoms to create e.g. Si-O, Si-C, Si-N, etc. to mention just the most prominent ones. Si-O bond formation, i.e. oxidation usually takes place automatically as soon as Si NWs are exposed to ambient conditions and this is undesired is since a defective oxide layer (i.e. native silicon dioxide-SiO 2) can cause uncontrolled trap states in the band gap of silicon. Surface functionalization of Si NW surfaces with the aim to avoid oxidation can be carried out by permitting e.g. Si-C bond formation when alkyl chains are covalently attached to the Si NW surfaces by employing a versatile two-step chlorination/alkylation process that does not affect the original length and diameter of the NWs. Termination of Si NWs with alkyl molecules through covalent Si-C bonds can provide long term stability against oxidation of the Si NW surfaces. The alkyl chain length determines the molecular coverage of Si NW surfaces and thus the surface energy and next to simple Si-C bonds even bond types such as CC and CC can be realized. When integrating differently functionalized Si NWs in functional devices such as field effect transistors (FETs) and solar cells, the physical properties of the resultant devices vary. © 2013 Elsevier Ltd. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.IAP.exphys.oxidef
Keywords: Field effect transistors; Heterojunction; Hybrid functionalization; Silicon nanowire; Solar cells

Oxygen diffusivity in silicon derived from dynamical X-ray diffraction - Will, Johannes; Gröschel, Alexander; Kot, Dawid; Bergmann, Christoph; Steinrück, Hans-Georg; Schubert, M. A.; Kissinger, Gurdrun; Magerl, Andreas (Journal of Applied Physics, 2013)
Thickness dependent Pendellösung oscillations are highly sensitive to strain fields from defects in a host crystal. Based on this, we present a novel technique to measure the precipitation kinetics of oxygen in silicon already at its early stage of clustering at high temperatures. At 900 °C, precipitates with a radius smaller than 4 nm and with a density of 1 ± 0.5 × 10 1/cm were observed. The technique was calibrated by complementary scanning transmission electron microscope and energy dispersive X-ray measurements in the range of normal diffusivity yielding a diffusion constant of 1.7 ± 0.1 × 10 - 12 cm / s, which is close to the literature value of 2.074 × 10 - 12 cm / s. The measurements have been made with the characteristic K-line of a high voltage tungsten X-ray tube at 59.31 keV, which provides the opportunity to illuminate through complex sample environments like high temperature scattering furnaces. © 2013 American Institute of Physics.

Oxygen mobility in the perovskite SrTi1-xFexO3-ð (x = 0.8) - Mashkina, Elena; Magerl, Andreas; Ollivier, Jacques; Göbbels, Matthias; Seifert, Friedrich (Physical Review B - Condensed Matter and Materials Physics, 2006)
The dynamics of long range translation and local motions of oxygen in SrTi0.2 Fe0.8 O3-δ have been studied by electrical conductivity and quasielastic neutron scattering. The activation energy of the translational ionic diffusion measured by electrical conductivity is 0.97 eV for T>900°C. Both quasielastic linewidths and quasielastic intensities in neutron scattering show the presence of two motions. The Q independences indicate a localized character for these oxygen diffusion modes with activation energies of 0.43 and 0.27 eV for the "fast" and the "slow" local jumps, respectively. A model for the local oxygen motion is proposed involving oxygen jumps in the (0 k 0) plane either directly to the next unit cell or performing detours combining two and two site jumps resulting in the same final momentum transfer. © 2006 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2006.nat.dgeo.IGM.LM.oxygen

Oxygen precipitation in Ge-doped Czochralski-silicon at 900 °c investigated by in situ high energy x-ray diffraction - Li, Zhen; Will, Johannes; Yang, Deren (AIP Advances, 2020)
In this study, we compare the real-time oxygen (O) precipitation kinetics of heavily germanium (Ge)-doped Czochralski-silicon (Cz-Si) at 900 °C - under different pre-annealing conditions - with those of undoped Cz-Si. We follow in situ the evolution of the Bragg intensity in Laue transmission geometry at elevated temperature and identify both diffusion-driven growth and Ostwald ripening of the O precipitates. We build on our past results, where we observed that although Ge-doping at 800 °C facilitates grown-in precipitates, it has no influence on the nucleation rate. Our present results indicate that within a diffusion-driven growth model, Ge-doping influences the nucleation rate at 650 °C and has no impact at 450 °C. These results shed further light on the origin of various thermal historical effects in Cz-Si samples with high levels of Ge doping.
CRIS-Team Scopus Importer:2020-11-06

Ozone-Mediated Polymerization of Fullerene and Fluorofullerene Thin Films - Strobel, Paul; Ristein, Jürgen; Ley, Lothar (Journal of Physical Chemistry C, 2010)
Films of an oxygen-linked fullerene polymer were synthesized by exposing about 15-nm-thick fullerite layers to ozone at room temperature. Moderate ozone exposure was found to lead to a polyoxifulleride that was stable in a vacuum up to at least 800 K. The oxidation and polymerization process was monitored by corelevel and valence-band photoelectron spectroscopy, which suggested that the bonding between fullerenes was by furan-like oxygen bridges and that the resulting polymer was three-dimensionally linked. The redox potential of the film was unaffected by this kind of polymerization, as witnessed by the unimpaired fullereneinduced surface conductivity of diamond. Hence, in addition to stabilization of the diamond surface conductivity, the polymerization is expected to be of considerable importance for C60-based bulk heterojunction organic solar cells, as well as for C60-based field-effect transistors. Similar albeit less effective thermal stabilization was also achieved for the fluorofullerene C60F48. © 2010 American Chemical Society.
UnivIS-Import:2015-03-09:Pub.2010.nat.dphy.IAP.exphys.ozonem

Parallel Crystallization of a "Static" and a Spin-Crossover Polymorph of an Iron(II) Complex from the Same Solution - Haryono, Marco; Heinemann, Frank Wilhelm; Petukhov, Konstantin; Gieb, Klaus; Müller, Paul; Grohmann, Andreas (European Journal of Inorganic Chemistry, 2009)
The ligand 2,6-bis(1H-pyrazol-1-yl)-4-(thiocyanatomethyl)pyridine (L) has been prepared from the hydroxymethyl precursor by OH/Br exchange and subsequent thiocyanate substitution. Two polymorphs of the unsolvated iron(II) complex [Fe(L)(2)](BF(4))(2) crystallize at room temperature from the same solution (MeOH), and side by side. One (yellow) is high spin between 4 and 350 K, whereas the other (red-brown) shows spin crossover, with a thermal spin-transition centred at 272 K (width ca. 50 K). Both forms have been fully characterized by variable-temperature structure determination and magnetic susceptibility measurements. At a given temperature, the solid-state structures differ strongly with respect to the coordination geometry at iron(II), the orientation of the thiocyanatomethyl substituents, and cation-anion contacts. The implications of these structural differences for the observed spin behaviour are discussed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Keywords: Iron; Spin crossover; Polymorphism; N ligands; Magnetic properties

Parameter-free binarization and skeletonization of fiber networks from confocal image stacks - Krauss, Patrick; Metzner, Claus; Lange, Janina; Lang, Nadine; Fabry, Ben (PLoS ONE, 2012)
We present a method to reconstruct a disordered network of thin biopolymers, such as collagen gels, from three-dimensional (3D) image stacks recorded with a confocal microscope. The method is based on a template matching algorithm that simultaneously performs a binarization and skeletonization of the network. The size and intensity pattern of the template is automatically adapted to the input data so that the method is scale invariant and generic. Furthermore, the template matching threshold is iteratively optimized to ensure that the final skeletonized network obeys a universal property of voxelized random line networks, namely, solid-phase voxels have most likely three solid-phase neighbors in a 3×3×3 neighborhood. This optimization criterion makes our method free of user-defined parameters and the output exceptionally robust against imaging noise. © 2012 Krauss et a

Parametric amplification of 100 fs mid-infrared pulses in ZnGeP2 driven by a Ho:YAG chirped-pulse amplifier - Kanai, Tsuneto; Malevich, Pavel; Kangaparambil, Sarayoo Sasidharan; Ishida, Kakuta; Mizui, Makoto; Yamanouchi, Kaoru; Hoogland, Heinar; Holzwarth, Ronald; Pugzlys, Audrius; Baltuska, Andrius (Optics Letters, 2017)
We report on the parametric generation of 100 fs sub-6-cycle 40 mu J pulses with the center wavelength at 5.2 mu m using a 1 ps 2.1 mu m pump laser and a dispersion management scheme based on bulk material. Our optically synchronized amplifier chain consists of a Ho: YAG chirped-pulse amplifier and white-light-seeded optical parametric amplifiers providing simultaneous passive carrier-envelope phase locking of three ultrashort longwave pulses at the pump, signal, and idler wavelengths corresponding, respectively, to 2.1, 3.5, and 5.2 mu m. We also demonstrate bandwidth enhancement and efficient control over nonlinear spectral phase in the regime of cascaded chi(2) nonlinearity in ZnGeP2. (C) 2017 Optical Society of America

Particle acceleration using top-illuminated nanophotonic dielectric structures - Shiloh, Roy; Chlouba, Tomas; Yousefi, Peyman; Hommelhoff, Peter (Optics Express, 2021)
In dielectric laser acceleration, nanostructures etched into silicon are used to convert free-space ultrashort laser pulses, incident from the side and parallel to the wafer substrate, to accelerate particles. This current approach is experimentally challenging and, as it turns out, not quite necessary for most experiments and practical applications. Here, we experimentally demonstrate and numerically verify the efficacy of top-illuminated structures, and measure a maximum acceleration gradient of 49.2 ± 3.1 MeV/m. We discuss how, in practice, this approach proves superior to the current standard in the field, and expect it to become the definitive choice for nanophotonic particle laser acceleratio
Keywords: Dielectric laser acceleration; top illumination

Partner, Neighbor, Housekeeper and Dimension: 3D versus 2D Glomerular Co-Cultures Reveal Drawbacks of Currently Used Cell Culture Models - Rederer, Anna; Rose, Victoria; Krüger, René; Schmittutz, Linda; Swierzy, Izabela; Fischer, Lena; Thievessen, Ingo; Bauer, Julian; Friedrich, Oliver; Schiffer, Mario; Müller-Deile, Janina (International Journal of Molecular Sciences, 2023)
Signaling-pathway analyses and the investigation of gene responses to different stimuli are usually performed in 2D monocultures. However, within the glomerulus, cells grow in 3D and are involved in direct and paracrine interactions with different glomerular cell types. Thus, the results from 2D monoculture experiments must be taken with caution. We cultured glomerular endothelial cells, podocytes and mesangial cells in 2D/3D monocultures and 2D/3D co-cultures and analyzed cell survival, self-assembly, gene expression, cell–cell interaction, and gene pathways using live/dead assay, time-lapse analysis, bulk-RNA sequencing, qPCR, and immunofluorescence staining. Without any need for scaffolds, 3D glomerular co-cultures self-organized into spheroids. Podocyte- and glomerular endothelial cell-specific markers and the extracellular matrix were increased in 3D co-cultures compared to 2D co-cultures. Housekeeping genes must be chosen wisely, as many genes used for the normalization of gene expression were themselves affected in 3D culture conditions. The transport of podocyte-derived VEGFA to glomerular endothelial cells confirmed intercellular crosstalk in the 3D co-culture models. The enhanced expression of genes important for glomerular function in 3D, compared to 2D, questions the reliability of currently used 2D monocultures. Hence, glomerular 3D co-cultures might be more suitable in the study of intercellular communication, disease modelling and drug screening ex vivo.
Created from Fastlane, Scopus look-up
Keywords: 3D co-culture; bulk-RNA sequencing; cell culture model; cell matrix; cell–cell communication; glomerular spheroids

Passivation and generation of states at P-implanted thermally grown and deposited n-type 4H-SiC / SiO2 interfaces - Sledziewski, Tomasz; Weber, Heiko B.; Krieger, Michael (Materials Science Forum, 2016)

Patient-specific modeling of the heart: Applications to cardiovascular disease management - Ionasec, Razvan; Voigt, Ingmar; Mihalef, Viorel; Grbic, Sasa; Vitanovski, Dime; Wang, Yabin; Zheng, Yefeng; Hornegger, Joachim; Navab, Nassir; Georgescu, Bogdan; Comaniciu, Dorin (Springer-verlag, 2010)
As decisions in cardiology increasingly rely on non-invasive methods, fast and precise image analysis tools have become a crucial component of the clinical workflow. Especially when dealing with complex cardiovascular disorders, such as valvular heart disease, advanced imaging techniques have the potential to significantly improve treatment outcome as well as to reduce procedure risks and related costs. We are developing patient-specific cardiac models, estimated from available multi-modal images, to enable advanced clinical applications for the management of cardiovascular disease. In particular, a novel physiological model of the complete heart, including the chambers and valvular apparatus is introduced, which captures a large spectrum of morphological, dynamic and pathological variations. To estimate the patient-specific model parameters from four-dimensional cardiac images, we have developed a robust learning-based framework. The model-driven approach enables a multitude of advanced clinical applications. Gold standard clinical methods, which manually process 2D images, can be replaced with fast, precise, and comprehensive model-based quantification to enhance cardiac analysis. For emerging percutaneous and minimal invasive valve interventions, cardiac surgeons and interventional cardiologists can substantially benefit from automated patient selection and virtual valve implantation techniques. Furthermore, the complete cardiac model enables for patient-specific hemodynamic simulations and blood flow analysis. Extensive experiments demonstrated the potential of these technologies to improve treatment of cardiovascular disease. © 2010 Springer-Verlag Berlin Heidelberg.
UnivIS-Import:2015-04-16:Pub.2010.tech.IMMD.IMMD5.patien

Patterning and visualizing self-assembled monolayers with low-energy electrons - Krupke, Ralph; Malik, S.; Weber, Heiko B.; Hampe, Oliver; Kappes, Manfred; von Löhneysen, Hilbert (Nano Letters, 2002)
We show that a trimethylsilyl (TMS) self-assembled monolayer on a silicon surface is a self-developing positive resist, which can be patterned with low energy electrons. Contact angle measurements have been used to quantify the efficiency of the exposure as a function of exposure dose and acceleration voltage. Ash formation was negligible, as a 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer could be formed on the patterned area without an intermediate development stage. APTES/TMS patterns have been visualized with scanning electron microscopy at low energy and atomic force microscopy. The functionality of the patterns has been tested by selective deposition of carbon nanotubes.

PCL micro-dumbbells - A new class of polymeric particles reveals morphological biofunctionality - Sonnleitner, David; Schaefer, Natascha; Wieland, Annalena; Fischer, Lena; Pasberg, Patrick; Thievessen, Ingo; Lang, Gregor (Applied Materials Today, 2021)
Biopolymeric particles can be fibrous or spherical, highly determining their areas of medical applications such as biomimetic fibers for tissue engineering or injectable capsules. In this work, we present a completely novel morphology, combining structural features of fibers and spheres in dumbbell-shaped Poly-epsilon-Caprolactone (PCL) micro-particles. Strikingly, such complex structures could be achieved by simply balancing out the parameters of a standard electrospinning setup together with fine-tuned spinning dope compositions. In-situ entropy-elastic snapping of deposited fibers could be triggered by combining PCL with different molecular weights, allowing for control over the aspect ratio of generated dumbbells in an accurate manner. With a single electrospinning nozzle, high production rates in the range of 80.000 dumbbells per second were achieved. To assess morphologically induced biofunctionality, dumbbell suspending and surface modification with collagen was performed and in vitro-testing with U87 reporter cells demonstrated significantly enhanced integrin-based cell adhesion on PCL-dumbbells as compared to continuous PCL-fibers. The results clearly unravel the remarkable potential of such structures in the field of tissue engineering. Revealing this new class of polymeric particles will also open the door to various new approaches including injectables, biofabrication and cosmetics, moreover, defining a novel type of filler material. (C) 2021 The Authors. Published by Elsevier Ltd.
CRIS-Team WoS Importer:2021-09-24

Pd, Au and codeposited Pd-Au ultrathin films on Ru(001) - Fauster, Thomas; et al. (Surface Science, 1997)
The growth of ultrathin Pd, An and codeposited Pd/Au films on Ru(001) at 470 K is studied by low-energy ion scattering. Both Pd and Au grow as flat two-dimensional layers up to two monolayers. The first layer of the codeposited films also grows (nearly) as a two-dimensional monolayer, independent of the deposition sequence. The data are most easily explained assuming only little (or no) Pd-Au alloying. (C) 1997 Elsevier Science B.V.
Keywords: epitaxy; gold; low energy ion scattering; low index single crystal surfaces; palladium; ruthenium; surface structure; morphology; roughness; and topography

Pentanary chalcopyrite compounds without tetragonal deformation in the heptanary system Cu(Al,Ga,In)(S,Se,Te)(2) - Hock, Rainer; et al. (Solar Energy Materials and Solar Cells, 2007)
The c/a ratios of the nine ternary Cu-III VI2 compounds in the system Cu(Al,Ga,In)(S,Se,Te)(2) range from 1.939 for CuAlSe2 to 2.014 (CuInS2) at room temperature. The validity of. Vegard's law was presumed to determine the tetragonal deformation 1-c/(2a) for all pentanary mixed crystal compounds Cu-(III,III)-(VI-VI)(2). For six of these nine compounds it is possible to achieve zero tetragonal deformation by adjusting the correct cation and anion substitution. The calculations are performed for room temperature as well as for 500 degrees C, which is a typical temperature for the synthesis of thin films of these semiconductor compounds. (c) 2006 Elsevier B.V. All rights reserved.
Keywords: semiconductors; chalcopyrite compounds; alloys

Persistent Conductivity in n-type 3C-SiC Observed at Low Temperatures - Beljakowa, Svetlana; Hauck, Martin; Bockstedte, Michel Georg; Fromm, Felix; Hundhausen, Martin; Nagasawa, H.; Weber, Heiko B.; Pensl, Gerhard; Krieger, Michael (Materials Science Forum, 2014)
Persistent conductivity in n-type 3C-SiC is investigated in a wide temperature range down to 3 K by Hall effect, admittance spectroscopy, low temperature photoluminescence (LTPL) and Raman spectroscopy. We propose a model, which clearly explains the persistent behavior of the electron density η below 50 K. It is experimentally verified that the persistent conductivity results from doped SF bunches, which can be considered nano-polytype inclusions in 3C-SiC. © (2014) Trans Tech Publications, Switzerland.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.LAP.persis
Keywords: 3C-SiC; Hall effect; Persistent conductivity; Raman spectroscopy; Stacking faults (SFs)

Persistent Energetic Electrons in Methylammonium Lead Iodide Perovskite Thin Films - Niesner, Daniel; Zhu, Haiming; Miyata, Kiyoshi; Joshi, Prakriti P.; Evans, Tyler. J. S.; Kudisch, Bryan. J.; Trinh, M. Tuan; Marks, Manuel; Zhu, X. -Y. (Journal of the American Chemical Society, 2016)
In conventional semiconductor solar cells, carriers are extracted at the band edges and the excess electronic energy (E*) is lost as heat. If E* is harvested, power conversion efficiency can be as high as twice the Shockley-Queisser limit. To date, materials suitable for hot carrier solar cells have not been found due to efficient electron/optical-phonon scattering in most semiconductors, but our recent experiments revealed long-lived hot carriers in single-crystal hybrid lead bromide perovskites. Here we turn to polycrystalline methylammonium lead iodide perovskite, which has emerged as the material for highly efficient solar cells. We observe energetic electrons with excess energy < E*> approximate to 0.2S eV above the conduction band minimum and with lifetime as long as similar to 100 ps, which is 2-3 orders of magnitude longer than those in conventional semiconductors. The energetic carriers also give rise to hot fluorescence emission with pseudo-electronic temperatures as high as 1900 K. These findings point to a suppression of hot carrier scattering with optical phonons in methylammonium lead iodide perovskite. We address mechanistic origins of this suppression and, in particular, the correlation of this suppression with dynamic disorder. We discuss potential harvesting of energetic carriers for solar energy conversion.

Persistent Photoconductivity in Doping-modulated amorphous silicon superlattices - Hundhausen, Martin; Ley, Lothar (Journal of Non-Crystalline Solids, 1985)
Doping superlattices prepared by depositing successively 105 Å thick layers of n-type, intrinsic, and p-type amorphous hydrogenated silicon, respectively (nipi structures), exhibit persistent photoconductivity (PPC) at room temperature. We prove that PPC is a bulk effect and that its creation is thermally activated with an activation energy of ∼0.4 eV; a slightly higher activation energy (∼0.7 eV) is necessary for the quenching of PPC. The thermal activation of PPC is incompatible with an explanation of this effect simply in terms of metastable carriers which are spatially separated in the space charge fields of the nipi structure. We propose instead that holes are trapped in acceptor-like centers, AX, in the p-regions of the sample whereas the balancing concentration of electrons, confined to the n-layers by the nipi fields and thus prevented from recombining with the holes, are responsible for PPC. The AX centers possess, in analogy to the DX centers in Ga1-xAlxAs, a strong electron-lattice coupling which accounts for the thermal activation energies of hole capture and ionization. © 1985.
UnivIS-Import:2015-03-05:Pub.1985.nat.dphy.IAP.exphys.persis

Personalized Modeling and Assessment of the Aortic-Mitral Coupling from 4D TEE and CT - Ionasec, Razvan; Voigt, Ingmar; Georgescu, Bogdan; Wang, Yabin; Houle, Helene; Hornegger, Joachim; Navab, Nassir; Comaniciu, Dorin (Springer-verlag, 2009)
The anatomy, function and hemodynamics of the aortic and mitral valves are known to be strongly interconnected. An integrated quantitative and visual assessment of the aortic-mitral coupling may have an impact on patient evaluation, planning and guidance of minimal invasive procedures. In this paper, we propose a novel model-driven method for functional and morphological characterization of the entire aortic-mitral apparatus. A holistic physiological model is hierarchically defined to represent the anatomy and motion of the two left heart valves. Robust learning-based algorithms are applied to estimate the patient-specific spatial-temporal parameters from four-dimensional TEE and CT data. The piecewise affine location of the valves is initially determined over the whole cardiac cycle using an incremental search performed in marginal spaces. Consequently, efficient spectrum detection in the trajectory space is applied to estimate the cyclic motion of the articulated model. Finally, the full personalized surface model of the aortic-mitral coupling is constructed using statistical shape models and local spatial-temporal refinement. Experiments performed on 65 4D TEE and 69 4D CT sequences demonstrated an average accuracy of 1.45mm and speed of 60 seconds for the proposed approach. Initial clinical validation on model-based and expert measurement showed the precision to be in the range of the inter-user variability. To the best of our knowledge this is the first time a complete model of the aortic-mitral coupling estimated from TEE and CT data is proposed. © 2009 Springer-Verlag.
UnivIS-Import:2015-04-16:Pub.2009.tech.IMMD.IMMD5.person_6

Phase breaking in three-terminal contacted single-walled carbon nanotube bundles - Krstic, Vojislav; Roth, Siegmar; Burghard, Marko (Physical Review B, 2000)
The three-terminal electrical transport through single-walled carbon nanotube bundles with low resistive metal contacts is investigated at room temperature. After correcting for the lead resistance, two-probe resistances close to the value expected for a metallic single-walled carbon nanotube are found. Analysis of the experimental data in the frame of the Landauer-Büttiker formalism reveals the phase- and momentum-randomizing effect of the third electrode, which is at floating potential, on the quasiballistic transport. Within this model, the phase-coherence length of the charge carriers is estimated to be ≈300 nm at room temperature.

Phase relations in the ternary Cu-Ga-In system - Hock, Rainer; et al. (ELSEVIER SCIENCE SA, 2007)
The phase relations of the Cu-Ga-ln system were investigated in a composition range which is relevant for the production of Cu(In,Ga)Se, based thin film solar cells. The alloys CU16(In-1 -gamma Ga gamma)(9), Cu-9(Ga,In)(4) and elemental In could be identified as the equilibrium phases of a ternary subsystem in the Cu-Ga-In phase diagram. The coexisting phases are well developed until 220 degrees C. In the case of Cu9Ga4 it is remarkable that the solubility of In in Cu9Ga4 highly increases with increasing temperature. Consequences for the selenization of metallic Cu-In-Ga precursors are discussed. (C) 2006 Elsevier B.V. All rights reserved.
Keywords: CuInSe2; CuGaSe2; X-ray diffraction; DC-magnetron sputtering; phase equilibria

Phase-Resolved Electron Guiding in Optimized Chip-Based Microwave Potentials - Hammer, Jakob; Hoffrogge, Johannes; Heinrich, Stephan; Hommelhoff, Peter (Physical Review Applied, 2014)
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.exphys.phaser

Phase-stable single-pass cryogenic amplifier for high repetition rate few-cycle laser pulses - Ozawa, Akira; Schneider, Waldemar; Haensch, Theodor W.; Udem, Thomas; Hommelhoff, Peter (New Journal of Physics, 2009)
We demonstrate cryogenic Ti:sapphire single-pass amplification of sub-7 fs laser pulses with 80 MHz repetition rate. We amplify the output of a broadband Ti:sapphire oscillator by more than a factor of two, re-compress the pulses down to sub-7 fs, and show that the rms carrier-envelope phase jitter stays below 70 as after amplification. The amplified output exceeds 2 MW of peak power and 1W of average power. In addition, we demonstrate amplification of ∼200fs, 75MHz oscillator pulses up to 1.6 W with a gain of four. This work opens a new way to explore phase sensitive and highly nonlinear phenomena at the full oscillator repetition rate. As a first example, we demonstrate white light generation in a bulk crystal at the full oscillator repetition rate. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
UnivIS-Import:2015-03-09:Pub.2009.nat.dphy.IAP.exphys.phases

Phase transformation and photocatalytic characteristics of anodic TiO2 nanotubular film - Oh, Han-Jun; Hock, Rainer; Schurr, Roland; Hölzing, Astrid; Chi, Choong-Soo (Journal of Physics and Chemistry of Solids, 2013)
A self-organized film with titania nanotubular architecture was synthesized by anodization. The dynamic characteristics and kinetic parameters of the nanotubular film during annealing were investigated using real-time resolved, in situ X-ray diffraction (XRD). The XRD results revealed that the onset activation energy for the self-organized titania nanotubular film was 135.6 kJ/mol. The rate constant for aniline blue degradation was dependent on the nanotube length, and the best photocatalytic efficiency of the TiO2 nanotube was obtained at an optimum tube length of 430 nm. (C) 2013 Elsevier Ltd. All rights reserved.
Keywords: Nanostructures; Oxides; X-ray diffraction; Phase transitions

Phase Transition Behavior and Oriented Aggregation During Precipitation of In(OH)3 and InOOH Nanocrystals - Klaumünzer, Martin; Mackovic, Mirza; Ferstl, Pascal; Voigt, Michael; Spiecker, Erdmann; Meyer, Bernd; Peukert, Wolfgang (Journal of Physical Chemistry C, 2012)
The phase transition behavior and oriented aggregation (OA) during colloidal synthesis of In(OH)3 nanocrystals in water are investigated by TEM, SEM, X-ray diffraction, and density functional theory (DFT) calculations. Besides the cubic In(OH)3 phase, also orthorhombic InOOH is formed in a precipitation route using indium acetate as the In3+ source. Well-developed nano- and microcuboids are observed that consist solely of In(OH)3. In contrast, the InOOH phase remains semicrystalline even for long reaction (refluxing) times. The irregular growth of the InOOH phase is explained by proton transfers from hydroxyl groups to oxygen ions within the InOOH lattice that lead to OH disorder and lattice strain. DFT calculations of the surface energies of ideal and water-saturated low-index InOOH and In(OH)3 surfaces predict that the In(OH)3 phase becomes energetically more favorable than InOOH above a critical crystallite size. This explains why InOOH is formed before the In(OH)3 phase, which is an unusual pathway for a hydrothermal process. Once InOOH has transformed to In(OH)3 by incorporation of water, the crystallites can grow without restriction due to the disappearance of OH-disorder-induced strain. Finally, for the In(OH)3 cuboids a three-step formation process is suggested: In the first step, one-dimensional OA under formation of nanorods occurs. In the second step, parallel bundles are formed from the nanorods. In the third step these bundles merge into cuboids by three-dimensional O

Phase transitions in huddling emperor penguins - Richter, Sebastian; Gerum, Richard; Winterl, Alexander; Houstin, A.; Seifert, Maria; Peschel, J.; Fabry, Ben; Le Bohec, Celine; Paranhos Zitterbart, Daniel (Journal of Physics D: Applied Physics, 2018)
Emperor penguins (Aptenodytes forsteri) are highly adapted to the harsh conditions of the Antarctic winter: they are able to fast for up to 134 days during breeding. To conserve energy, emperor penguins form tight groups (huddles), which is key for their reproductive success. The effect of different meteorological factors on the huddling behaviour, however, is not well understood. Using time-lapse image recordings of an emperor penguin colony, we show that huddling can be described as a phase transition from a fluid to a solid state. We use the colony density as order parameter, and an apparent temperature that is perceived by the penguins as the thermodynamic variable. We approximate the apparent temperature as a linear combination of four meteorological parameters: ambient temperature, wind speed, global radiation and relative humidity. We find a wind chill factor of -2.9 °C (ms-1)-1, a humidity chill factor of -0.5 °C/%rel. humidity, and a solar radiation heating factor of 0.3 °C (Wm-2)-1. In the absence of wind, humidity and solar radiation, the phase transition temperature (50% huddling probability) is -48.2 °C for the investigated time period (May 2014). We propose that higher phase transition temperatures indicate a shrinking thermal insulation and thus can serve as a proxy for lower energy reserves of the colony, integrating pre-breeding foraging success at sea and energy expenditure at land due to environmental conditions. As current global change is predicted to have strong detrimental effects on emperor penguins within the next decades, our approach may thus contribute towards an urgently needed long-term monitoring system for assessing colony health.
CRIS-Team Scopus Importer:2022-08-05
Keywords: climate variability; collective behaviour; emperor penguin; environmental conditions; huddling; phase transition

Phonon dispersion of carbon nanotubes - Maultzsch, Janina; et al. (Solid State Communications, 2002)
We present the phonon dispersion relations of single-wall carbon nanotubes calculated within a force-constants approach. By using the full symmetry group of the tubes, we are able to calculate the dispersion relations for any chirality starting from one single carbon atom. We find an overbending in the highest optical branch between 6 and 12 cm(-1) independent of the tube diameter. The order of the high-energy modes at the Gamma-point differs from the results derived from simple zone folding. The splitting between the two Raman active optical modes with A, symmetry at the F-point of chiral tubes is approximate to 4 cm(-1) for typical diameters; it increases with decreasing tube diameter. (C) 2002 Elsevier Science Ltd. All rights reserved.
Keywords: carbon nanotubes; phonons

Phonon dispersion of graphite by inelastic x-ray scattering - Maultzsch, Janina; et al. (Physical Review B, 2007)
We present the full in-plane phonon dispersion of graphite obtained from inelastic x-ray scattering, including the optical and acoustic branches, as well as the midfrequency range between the K and M points in the Brillouin zone, where the experimental data have been unavailable so far. The existence of a Kohn anomaly at the K point is further supported. We fit a fifth-nearest neighbor force-constant model to the experimental data, making improved force-constant calculations of the phonon dispersion in both graphite and carbon nanotubes available.

Phonon dispersion of MoS2 - Tornatzky, Hans; Gillen, Roland; Uchiyama, Hiroshi; Maultzsch, Janina (Physical Review B, 2019)
We present the phonon dispersion of bulk MoS2 in the high-symmetry directions of the Brillouin zone, determined by inelastic x-ray scattering. Our results underline the two-dimensional nature of MoS2. In combination with state-of-the-art first-principles calculations, we determine the phonon displacement patterns, symmetry properties, and scattering intensities. The results will be the basis for future experimental and theoretical work regarding electron-phonon interactions, intervalley scattering, as well as phonons in related 2D materials.
CRIS-Team Scopus Importer:2019-05-14

Photoelectron spectroscopy of clean and hydrogen exposed diamond (111) surfaces - Ristein, Jürgen; Ley, Lothar; et al. (Surface Science, 1994)
The modifications of the (111) surfaces of a type-IIb natural diamond and a CVD diamond film upon annealing and exposure to atomic hydrogen have been examined by ultraviolet-excited (UPS) and X-ray excited (XPS) photoelectron spectroscopy. Besides the two surface configurations commonly described in the literature, i.e. the clean reconstructed surface and the one associated with a monohydride passivation, a third configuration which evolves upon extreme hydrogen exposure has been observed. © 1994.
UnivIS-Import:2015-03-05:Pub.1994.nat.dphy.IAP.exphys.photoe

Photoelectron spectroscopy of tetraphenylporphyrin layers on MgO films on Ag(100) - Helmreich, Rebecca; Fauster, Thomas (Surface Science, 2022)
The molecular orbitals of magnesium tetraphenyl porphyrin (MgTPP) deposited on epitaxial MgO films on Ag(100) are studied by ultraviolet photoelectron spectroscopy and two-photon photoemission. The energies of the electronic states are pinned to the vacuum level and the band gap is 3.88±0.07 eV largely independent of the MgO layer thickness.
CRIS-Team Scopus Importer:2022-01-28
Keywords: Magnesium oxide; Photoelectron spectroscopy; Porphyrin molecules

Photoelectron spectroscopy of tetraphenylporphyrin layers on MgO films on Ag(100) - Helmreich, Rebecca; Fauster, Thomas (Surface Science, 2022)
The molecular orbitals of magnesium tetraphenyl porphyrin (MgTPP) deposited on epitaxial MgO films on Ag(100) are studied by ultraviolet photoelectron spectroscopy and two-photon photoemission. The energies of the electronic states are pinned to the vacuum level and the band gap is 3.88 +- 0.07 eV largely independent of the MgO layer thickness.
Keywords: Magnesium oxide; Porphyrin molecules; Photoelectron spectroscopy

Photoelectron yield spectroscopy on negative electron affinity diamond surfaces: a contactless unipolar transport experiment - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 1998)
On the hydrogen-passivated negative electron affinity (100) and (111) surfaces of diamond no energy barrier prevents photoelectrons from exiting into the vacuum. Therefore, the photoelectron yield spectrum reflects volume rather than surface properties of the material, and the technique is in many aspects similar to photoconductivity experiments, albeit with the advantage of being selective to electrons exclusively (and not to holes). We have employed photoelectron yield spectroscopy to investigate deep defect states in natural and CVD diamond and to determine the electron diffusion length in type II b single crystals. For the latter aspect, the competition between electron and exciton transport plays an important role and the analysis of the yield spectra gives surprisingly large electron diffusion lengths of about 200 μm. © 1998 Elsevier Science S.A.
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.IAP.exphys.photoe
Keywords: Diamond surface; Negative electron affinity; Photoelectron spectroscopy; Unipolar transport

Photoemission from an ultrabright and ultrafast LaB6 nanowire electron emitter studied at atomic scale - Li, Ang; Zhang, Han; Meier, Stefan; Tafel, Alexander; Hommelhoff, Peter (2021 34TH INTERNATIONAL VACUUM NANOELECTRONICS CONFERENCE (IVNC), 2021)
CRIS-Team WoS Importer:2022-02-04

Photoemission from nanomaterials in strong few-cycle laser fields - Liu, Qingcao; Rupp, Philipp; Foerg, Benjamin; Schoetz, Johannes; Süßmann, Frederik; Okell, William A.; Passig, Johannes; Tiggesbäumker, Josef; Meiwes-Broer, Karl-Heinz; Seiffert, Lennart; Fennel, Thomas; Rühl, Eckart; et al. (Springer Verlag, 2017)
The application of ultra-short waveform-controlled laser fields to nanostructured materials enables the generation of localized near-fields with well-defined spatiotemporal field evolution. The optical fields that can be tailored on sub-wavelength spatial and attosecond temporal scales have a high potential for the control of ultrafast processes at the nanoscale, with important implications for laser-driven electron acceleration, extreme ultraviolet (XUV) light generation, and nanoscale electronics operating at optical frequencies.

Photoemission study of amorphous carbon modifications and comparison with calculated densities of states - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review B, 1996)
In this study we present photoemission data for three different types of amorphous carbon modifications (a-C:H, ia-C:H, and ta-C) that owe their properties to their different preparations by radio frequency plasma, plasma beam, or arc discharge. Their properties are investigated by means of their characteristic plasmon loss following the C 1s core level, the core-level shape itself, and by their valence bands. For all three amorphous modifications as well as for the two crystalline ones, diamond and graphite, we present density of states calculations which in the amorphous case are based on molecular-dynamics simulations. The electronic density of states is fitted to the data using photoemission cross sections and a model for the lifetime broadening. The agreement achieved is very good and confirms the validity of the predicted structures that do not possess any significant larger π clusters.
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.IAP.exphys.photoe

Photoemission study of the silicate adlayer reconstruction on 6H-SiC(0001) - Ristein, Jürgen; Ley, Lothar; et al. (Materials Science Forum, 2000)
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.IAP.exphys.photoe

Photoinduced degradation of methylammonium lead triiodide perovskite semiconductors - Tang, Xiaofeng; Brandl, Marco; May, Benjamin; Levchuk, Ievgen; Hou, Yi; Richter, Moses; Chen, Haiwei; Chen, Shi; Kahmann, Simon; Osvet, Andres; Maier, Florian; Steinrück, Hans-Peter; et al. (Journal of Materials Chemistry A, 2016)
Photoinduced degradation is a critical obstacle for the real application of novel semiconductors for photovoltaic applications. In this paper, the photoinduced degradation of CHNHPbI in a vacuum and air (relative humidity 40%) is analyzed by ex situ and advanced in situ technologies. Without light illumination, CHNHPbI films slowly degrade under vacuum and air within 24 hours. However, we find that CHNHPbI converts to metallic lead (Pb) when exposed to vacuum and light illumination. Further, a series of lead salts (e.g. PbO, Pb(OH) and PbCO) are formed when CHNHPbI is degraded under environmental conditions, i.e. under the combination of light, oxygen and moisture. Photoinduced degradation is found to be determined by the environmental atmosphere as CHNHPbI films remain very stable under nitrogen conditions. The results from vacuum conditions underpin that the high volatility of the organic component (CHNHI) is in conflict with reaching excellent intrinsic stability due to its role in creating ion vacancies. The degradation in air suggests that both oxygen and water contribute to the fast photodecomposition of CHNHPbI into lead salts rather than water alone. Given these basic yet fundamental understandings, the design of hydrophobic capping layers becomes one prerequisite towards long-term stable perovskite-based devices.
Keywords: Engineering controlled terms: Lead; Perovskite; Salts; Slow light Environmental conditions; Intrinsic stability; Light illumination; Organic components; Photo-decomposition; Photoinduced degradation; Photovoltaic applications; Real applications Engineering main heading: Photodegradation

Photoluminescence of freestanding single- and few-layer MoS 2 - Scheuschner, Nils; Ochedowski, Oliver; Kaulitz, Anne-Marie; Gillen, Roland; Schleberger, Marika; Maultzsch, Janina (Physical Review B - Condensed Matter and Materials Physics, 2014)

Photonic-based laser driven electron beam deflection and focusing structures - Plettner, T.; Byer, R. L.; Mcguinness, C.; Hommelhoff, Peter (Physical Review Special Topics-Accelerators and Beams, 2009)
UnivIS-Import:2015-03-09:Pub.2009.nat.dphy.IAP.exphys.photon

pH-responsive anodic titanium dioxide nanotubes and nanocylinders for cancer drug delivery - Hasanzadeh Kafshgari, Morteza; Mazare, Anca Valentina; Distaso, Monica; Goldmann, Wolfgang; Peukert, Wolfgang; Fabry, Ben; Schmuki, Patrik (AMER SOC CELL BIOLOGY, 2018)

Physical and Antibacterial Properties of Peppermint Essential Oil Loaded Poly (epsilon-caprolactone) (PCL) Electrospun Fiber Mats for Wound Healing - Ünalan, Irem; Slavik, Benedikt; Büttner, Andrea; Goldmann, Wolfgang; Frank, Gerhard; Boccaccini, Aldo R. (Frontiers in Bioengineering and Biotechnology, 2019)
The aim of this study was to fabricate and characterize various concentrations of peppermint essential oil (PEP) loaded on poly(epsilon-caprolactone) (PCL) electrospun fiber mats for healing applications, where PEP was intended to impart antibacterial activity to the fibers. SEM images illustrated that the morphology of all electrospun fiber mats was smooth, uniform, and bead-free. The average fiber diameter was reduced by the addition of PEP from 1.6 +/- 0.1 to 1.0 +/- 0.2 mu m. Functional groups of the fibers were determined by Raman spectroscopy. Gas chromatography-mass spectroscopy (GC-MS) analysis demonstrated the actual PEP content in the samples. In vitro degradation was determined by measuring weight loss and their morphology change, showing that the electrospun fibers slightly degraded by the addition of PEP. The wettability of PCL and PEP loaded electrospun fiber mats was measured by determining contact angle and it was shown that wettability increased with the incorporation of PEP. The antimicrobial activity results revealed that PEP loaded PCL electrospun fiber mats exhibited inhibition against Staphylococcus aureus (gram-positive) and Escherichia coli (gram-negative) bacteria. In addition, an in-vitro cell viability assay using normal human dermal fibroblast (NHDF) cells revealed improved cell viability on PCL, PCLPEP1.5, PCLPEP3, and PCLGEL6 electrospun fiber mats compared to the control (CNT) after 48 h cell culture. Our findings showed for the first time PEP loaded PCL electrospun fiber mats with antibiotic-free antibacterial activity as promising candidates for wound healing applications.
CRIS-Team WoS Importer:2019-12-27
Keywords: wound healing; peppermint essential oil; poly (ε-caprolactone); electrospinning; antibacterial activity

Physicochemical characterization of silicon-containing glycolipids by DSC, FT-Raman spectroscopy and X-ray diffraction - Uhr, Michael; Wartewig, S.; Unruh, Tobias; Richter, H. (Chemistry and Physics of Lipids, 2003)
Derivatives of dimethylalkylchlorosilanes are novel substances which may be used in formulations for drug targeting. In order to design their properties it is essential to perform physicochemical characterization. For this purpose, a combination of differential scanning calorimetry (DSC), FT-Raman spectroscopy and X-ray diffraction is well suited. For the starting material dimethyloctadecylchlorosilane (DMOC), the assignment of Raman bands is discussed. The influence of sugar-containing head groups on the structures of the hydrocarbon chains of 1-O-(dimethyldodecylsilyl)-[2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside] and 1-O-(dimethyloctadecylsilyl)-[2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside] was investigated using the band position of the symmetric methylene mode. The temperature dependence of conformationally sensitive bands in the CH2-stretching region (2800-2900cm(-1)), C-C-stretching region (1000-1150cm(-1)) and CH3-rocking region (830-900cm(-1)) was studied to characterize the state of order of the alkyl chains. Using X-ray diffraction, the repeating distances of layered structures was determined. The phase transitions occurring were found to be completely reversible. The subcell of DMOC shows an orthorhombic perpendicular packing structure in the crystalline state. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.
Keywords: dimethyloctadecylchlorosilane; FT-Raman spectroscopy; X-ray diffraction; differential scanning calorimetry

Picosecond dynamics in haemoglobin from different species: A quasielastic neutron scattering study - Stadler, Andreas M.; Garvey, Christopher J.; Embs, Jan Peter; Koza, Michael Marek; Unruh, Tobias; Artmann, Gerhard; Zaccai, Giuseppe (Biochimica Et Biophysica Acta-General Subjects, 2014)
General significance: The measured dynamic quantities showed significant and systematic variations between the investigated species, suggesting that they are the signature of an evolutionary adaptation process stimulated by the different physiological environments of the respective protein. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Haemoglobin; Body temperature adaptation; Protein dynamics; Picosecond dynamics; Quasielastic neutron scattering

Planar microwave structures for electron guiding - Hoffrogge, J.; Hommelhoff, Peter (New Journal of Physics, 2011)
We present microwave electrode structures suited for guiding electrons propagating in a purely electric, alternating quadrupole field. In a first experiment using a standing wave on an electrically short structure, we previously demonstrated the general concept of electron confinement in microwave fields. Here, we discuss the extension to electrically long structures supporting travelling microwave excitations. This requires a modal decomposition of the voltage patterns on the multiconductor transmission line formed by the electrodes. We show that the use of a general five-wire structure leads to the distortion of the guiding potential upon propagation due to differing modal propagation constants. This can be avoided by implementing a coupled microstrip configuration with elevated signal electrodes. With structures like these, complex geometries connecting different beam manipulation elements can be realized, enabling new forms of electron experiments with guided matter waves.
UnivIS-Import:2015-03-09:Pub.2011.nat.dphy.IAP.exphys.aplana

Planar π-extended cycloparaphenylenes featuring an all-armchair edge topology - Xiang, Feifei; Maisel, Sven; Beniwal, Sumit; Akhmetov, Vladimir; Ruppenstein, Cordula; Devarajulu, Mirunalini; Dörr, Andreas; Papaianina, Olena; Görling, Andreas; Amsharov, Konstantin; Maier, Sabine (Nature Chemistry, 2022)
The [n]cycloparaphenylenes ([n]CPPs)—npara-linked phenylenes that form a closed-loop—have attracted substantial attention due to their unique cyclic structure and highly effective para-conjugation leading to a myriad of fascinating electronic and optoelectronic properties. However, their strained topology prevents the π-extension of CPPs to convert them either into armchair nanobelts or planarized CPP macrocycles. Here we successfully tackle this long-standing challenge and present the bottom-up synthesis and characterization of atomically precise in-plane π-extended [12]CPP on Au(111) by low-temperature scanning probe microscopy and spectroscopy combined with density functional theory. The planar π-extended CPP is a nanographene with an all-armchair edge topology. The exclusive para-conjugation at the periphery yields delocalized electronic states and the planarization maximizes the overlap of p orbitals, which both reduce the bandgap compared to conventional CPPs. Calculations predict ring currents and global aromaticity in the doubly charged system. The intriguing planar ring topology and unique electronic properties make planar π-extended CPPs promising quantum materials. [Figure not available: see fulltext.]
CRIS-Team Scopus Importer:2022-07-08

Plectin Deficiency in Fibroblasts Deranges Intermediate Filament and Organelle Morphology, Migration, and Adhesion - Zrelski, Michaela M.; Hösele, Sabrina; Kustermann, Monika; Fichtinger, Petra; Kah, Delf-Thorge Eric; Athanasiou, Ioannis; Esser, Philipp R.; Wagner, Anja; Herzog, Rebecca; Kratochwill, Klaus; Goldmann, Wolfgang H.; Kiritsi, Dimitra; et al. (Journal of Investigative Dermatology, 2024)
Plectin, a highly versatile and multifunctional cytolinker, has been implicated in several multisystemic disorders. Most sequence variations in the human plectin gene (PLEC) cause epidermolysis bullosa simplex with muscular dystrophy (EBS-MD), an autosomal recessive skin-blistering disorder associated with progressive muscle weakness. In this study, we performed a comprehensive cell biological analysis of dermal fibroblasts from three different patients with EBS-MD, where PLEC expression analyses revealed preserved mRNA levels in all cases, whereas full-length plectin protein content was significantly reduced or completely absent. Downstream effects of pathogenic PLEC sequence alterations included massive bundling of vimentin intermediate filament networks, including the occurrence of ring-like nuclei-encasing filament bundles, elongated mitochondrial networks, and abnormal nuclear morphologies. We found that essential fibroblast functions such as wound healing, migration, or orientation upon cyclic stretch were significantly impaired in the cells of patients with EBS-MD. Finally, EBS-MD fibroblasts displayed reduced adhesion capacities, which could be attributed to smaller focal adhesion contacts. Our study not only emphasizes plectin's functional role in human skin fibroblasts, it also provides further insights into the understanding of EBS-MD–associated disease mechanisms.
CRIS-Team Scopus Importer:2024-03-01

Plectin ensures intestinal epithelial integrity and protects colon against colitis - Krausova, Alzbeta; Buresova, Petra; Sarnova, Lenka; Oyman-Eyrilmez, Gizem; Skarda, Jozef; Wohl, Pavel; Bajer, Lukas; Sticova, Eva; Bartonova, Lenka; Pacha, Jiri; Koubkova, Gizela; Prochazka, Jan; et al. (Mucosal Immunology, 2021)
Plectin, a highly versatile cytolinker protein, provides tissues with mechanical stability through the integration of intermediate filaments (IFs) with cell junctions. Here, we hypothesize that plectin-controlled cytoarchitecture is a critical determinant of the intestinal barrier function and homeostasis. Mice lacking plectin in an intestinal epithelial cell (IEC; PleΔIEC) spontaneously developed colitis characterized by extensive detachment of IECs from the basement membrane (BM), increased intestinal permeability, and inflammatory lesions. Moreover, plectin expression was reduced in the colons of ulcerative colitis (UC) patients and negatively correlated with the severity of colitis. Mechanistically, plectin deficiency in IECs led to aberrant keratin filament (KF) network organization and the formation of dysfunctional hemidesmosomes (HDs) and intercellular junctions. In addition, the hemidesmosomal α6β4 integrin (Itg) receptor showed attenuated association with KFs, and protein profiling revealed prominent downregulation of junctional constituents. Consistent with the effects of plectin loss in the intestinal epithelium, plectin-deficient IECs exhibited remarkably reduced mechanical stability and limited adhesion capacity in vitro. Feeding mice with a low-residue liquid diet that reduced mechanical stress and antibiotic treatment successfully mitigated epithelial damage in the PleΔIEC colon.
CRIS-Team Scopus Importer:2021-03-19

Plectin-mediated cytoskeletal crosstalk controls cell tension and cohesion in epithelial sheets - Prechova, Magdalena; Adamova, Zuzana; Schweizer, Anna Lena; Maninova, Miloslava; Bauer, Andreas; Kah, Delf-Thorge Eric; Meier-Menches, Samuel M.; Wiche, Gerhard; Fabry, Ben; Gregor, Martin (The Journal of Cell Biology, 2022)
The coordinated interplay of cytoskeletal networks critically determines tissue biomechanics and structural integrity. Here, we show that plectin, a major intermediate filament-based cytolinker protein, orchestrates cortical cytoskeletal networks in epithelial sheets to support intercellular junctions. By combining CRISPR/Cas9-based gene editing and pharmacological inhibition, we demonstrate that in an F-actin-dependent context, plectin is essential for the formation of the circumferential keratin rim, organization of radial keratin spokes, and desmosomal patterning. In the absence of plectin-mediated cytoskeletal cross-linking, the aberrant keratin-desmosome (DSM)-network feeds back to the actin cytoskeleton, which results in elevated actomyosin contractility. Also, by complementing a predictive mechanical model with Förster resonance energy transfer-based tension sensors, we provide evidence that in the absence of cytoskeletal cross-linking, major intercellular junctions (adherens junctions and DSMs) are under intrinsically generated tensile stress. Defective cytoarchitecture and tensional disequilibrium result in reduced intercellular cohesion, associated with general destabilization of plectin-deficient sheets upon mechanical stress.
CRIS-Team Scopus Importer:2022-03-04

Polarisation-sensitive switch: An integrated intensity-independent solution for 1.3 μm based on the polarisation anisotropy of ordered InGaAsP - Malzer, Stefan; et al. (physica status solidi (a), 2005)
Ordered materials provide new possibilities for optical device applications. Through a strong polarisation anisotropy of absorption a high functional polarisation-sensitive switch can be fabricated which in addition is nearly independent on the optical power. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polarised Raman measurements of beta-carotene encapsulated in SWNTs - Brose, Katharina; Tschirner, Norman; Zouni, Athina; Mueh, Frank; Yanagi, Kazuhiro; Kataura, Hiromichi; Thomsen, Christian; Maultzsch, Janina (physica status solidi (b), 2010)
The knowledge of the vibrational properties is of key importance to understand their function of beta-carotene molecules in the reaction centre of the light harvesting complexes. We present polarisation-dependent Raman spectroscopy on beta-carotene molecules in two different environments: first single dimeric photosystem II crystal, and second encapsulated beta-carotene in single-wall carbon nanotube bundles. Both systems have nearly perpendicular or parallel onentated beta-carotene molecules. We compare the dependence of their Raman spectra on the polarisation of incident and scattered light. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Keywords: beta-carotene; photosystem II; crystal; photosynthesis; polarisation dependence

Polarised Raman measurements on the core complex of crystallised photosystem II - Brose, Katharina; Zouni, Athina; Broser, Matthias; Mueh, Frank; Maultzsch, Janina (physica status solidi (b), 2009)
In photosynthesis the sunlight is collected by antenna pigments and transmitted to special molecule structures called photosystem I (PS I) and photosystem II (PS II), where the energy of light is transformed into a separation of charge. In the PS II reaction centre (RC), there are two beta-carotene molecules Car(D1) and Car(D2), which are oriented perpendicular to each other. The role of these molecules in the photosynthesis process is still unknown. We use Raman spectroscopy to study the two beta-carotenes. We present polarised Raman measurements of the beta-carotene vibrational modes in single crystals of photosystem II (PS II) and discuss the possible origin of the observed polarisation dependence. These measurements are important for the basic understanding of the beta-carotene vibrational properties and guide future investigations of PS II. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Polarization sensitive lateral photoconductivity in GaAs/AlGaAs quantum well based structures on low-temperature grown GaAs(001) - Arora, Ashish; Gosh, Sandip; Arora, Brij Mohan; Malzer, Stefan; Döhler, Gottfried (Applied Physics Letters, 2010)
Polarization-resolved lateral-photoconductivity measurements are reported on device structures made of GaAs/ Al Ga As quantum wells sandwiched between low-temperature grown GaAs(001) layers. The mesa device structures have long length (3 mmy) and narrow width (10 and 20 μmx) in the (001) plane. For light incident along [001], the ground state light-hole exciton transition is much stronger for light polarization Ex, compared to Ey. The heavy-hole exciton transition shows a weaker polarization anisotropy of opposite sign, being stronger for Ey. Through calculations based on the Bir-Pikus Hamiltonian, the observed in-plane optical polarization anisotropy is shown to arise from valence band mixing induced by anisotropic strain in the plane of quantum wells. © 2010 American Institute of Physics.

Polymer dynamics under cylindrical confinement featuring a locally repulsive surface: A quasielastic neutron scattering study (vol 146, 203306, 2017) - Krutyeva, M.; Pasini, S.; Monkenbusch, M.; Allgaier, J.; Maiz, Jon; Mijangos, C.; Hartmann-Azanza, B.; Steinhart, Martin; Jalarvo, N.; Ivanova, O.; Holderer, O.; Radulescu, A.; et al. (Journal of Chemical Physics, 2017)

Polymer surfaces graphitization by low-energy He+ ions irradiation - Geworski, Andreas; Lazareva, Irina; Gieb, Klaus; Koval, Yury; Müller, Paul (Journal of Applied Physics, 2014)
The electrical and optical properties of surfaces of polyimide and AZ5214e graphitized by low-energy (1 keV) He irradiation at different polymer temperatures were investigated. The conductivity of the graphitized layers can be controlled with the irradiation temperature within a broad range and can reach values up to ∼1000 S/cm. We show that the electrical transport in low-conducting samples is governed by thermally activated hopping, while the samples with a high conductivity show a typical semimetallic behavior. The transition from thermally activated to semimetallic conductance governed by the irradiation temperature could also be observed in optical measurements. The semimetallic samples show an unusually high for graphitic materials carrier concentration, which results in a high extinction coefficient in the visible light range. By analyzing the temperature dependence of the conductance of the semimetallic samples, we conclude that the scattering of charge carriers is dominated by Coulomb interactions and can be described by a weak localization model. The transition from a three to two dimensional transport mechanism at low temperatures consistently explains the change in the temperature dependence of the conductance by cooling, observed in experiments. © 2014 AIP Publishing LLC.

Ponderomotive Generation and Detection of Attosecond Free-Electron Pulse Trains - Kozak, Martin; Schönenberger, Norbert; Hommelhoff, Peter (Physical Review Letters, 2018)
Atomic motion dynamics during structural changes or chemical reactions have been visualized by pico- and femtosecond pulsed electron beams via ultrafast electron diffraction and microscopy. Imaging the even faster dynamics of electrons in atoms, molecules, and solids requires electron pulses with subfemtosecond durations. We demonstrate here the all-optical generation of trains of attosecond free-electron pulses. The concept is based on the periodic energy modulation of a pulsed electron beam via an inelastic interaction, with the ponderomotive potential of an optical traveling wave generated by two femtosecond laser pulses at different frequencies in vacuum. The subsequent dispersive propagation leads to a compression of the electrons and the formation of ultrashort pulses. The longitudinal phase space evolution of the electrons after compression is mapped by a second phase-locked interaction. The comparison of measured and calculated spectrograms reveals the attosecond temporal structure of the compressed electron pulse trains with individual pulse durations of less than 300 as. This technique can be utilized for tailoring and initial characterization of suboptical-cycle free-electron pulses at high repetition rates for stroboscopic time-resolved experiments with subfemtosecond time resolutio

Poresizes in random line networks - Metzner, Claus; Krauß, Patrick; Fabry, Ben (arXiv, 2011)

Porphyrin adsorption and ligand exchange at the (110)-TiO2 / organic liquid interface - Götz, Klaus; Stollberg, Isabella; Prihoda, Annemarie; Bertram, Florian; Metwalli, Ezzeldin; Zech, Tobias; Unruh, Tobias (Surface Science, 2022)
Highly efficient dye-sensitized solar cells (DSSCs) have been prepared on the basis of porphyrin dyes with significant success. Recent studies have demonstrated a correlation between the solar cell efficiency and the configuration of the adsorbed porphyrin molecules at the surface of the semiconducting support material. The preparation of dense self assembled monolayers (SAMs) of upright standing porphyrin molecules on TiO2 surfaces was achieved from toluene solutions only when using a molecular exchange reaction. Here, an exchange study of an oleic acid (OLA) SAM on a <110> TiO2 surface by porphyrin molecules is presented. The exchange reaction has been studied by ex-situ as well as in-situ X-ray reflectometry (XRR) measurements. It was found that an almost complete exchange of OLA with porphyrins can be achieved. With increasing coating times the orientation of the porphyrin molecules relative to the substrate surface changed from flat lying to upright standing.
CRIS-Team Scopus Importer:2022-04-15
Keywords: DESY; functionalization; interface; porphyrin; rutile; X-ray reflectometry

Post-synthetic modification of divalent nickel acetate cubanes with carboxylates - Korzekwa, Jana; Scheurer, Andreas; Heinemann, Frank Wilhelm; Kroener, Wolfgang; Gieb, Klaus; Müller, Paul; Meyer, Karsten (Journal of Coordination Chemistry, 2017)
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Keywords: N; O ligands; carboxylate ligands; cubanes; nickel; post-synthetic modification

Präziser Einblick ins Innerste von Siliziumkarbid-MOSFETs - Hauck, Martin; Krieger, Michael (Elektronikpraxis - Profiline, 2019)
Keywords: Siliziumkarbid; SiC; MOSFET; Grenzflächendefekte; Near-Interface-Traps; NITs

Precipitation of In(OH)3 and InOOH nanocrystals for the use in nanoelectronics: Phase transition behavior and oriented aggregation - Klaumünzer, Martin; Mackovic, Mirza; Ferstl, Pascal; Voigt, Michael; Spiecker, Erdmann; Meyer, Bernd; Peukert, Wolfgang (Nanotechnology 2013: Advanced Materials, CNTs, Particles, Films and Composites - 2013 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2013, 2013)
With respect to diverse applications in the wide field of nanoelectronics we characterize a specific phase transition behaviour and oriented aggregation (OA) during wet chemical synthesis of In(OH) nanocrystals as a wide band gap- and precursor material for InO. Contiguous to the cubic In(OH) phase, also orthorhombic InOOH is formed in a precipitation route with indium acetate as the In3+ source. Nano- and microcuboids are observed that consist exclusively of In(OH). The InOOH phase stays semi-crystalline even for long reaction times. On the basis of DFT calculations we find that for small crystallites the InOOH phase is more stable than the In(OH) phase, leading to a size-dependent transition from the InOOH phase to In(OH) above a critical crystallite size.
Keywords: Indium oxohydroxide; Nanocrystals; Oriented aggregation indium hydroxide; Precipitation

Predicted formation reactions for the solid-state syntheses of the semiconductor materials Cu2SnX3 and Cu2ZnSnX4 (X = S, Se) starting from binary chalcogenides - Hock, Rainer; et al. (ELSEVIER SCIENCE SA, 2007)
The compounds CU2ZnSnX4 and Cu2SnX3 (X = S or Se) are promising semiconductor materials for thin film photovoltaic applications. Based on a crystallographic growth model we derive the solid-state reactions for these four compounds starting from the binary sulphides and selenides of copper, zinc and tin. Exploiting these predicted solid-state reactions which are promoted by epitaxial relations between the educts will result in fast formation reactions as preferred in technical processes. The direct formation of Cu2ZnSnX4 is concurring with a two-step process in which Cu2SnX3 occurs as an intermediate product. (C) 2006 Elsevier B.V. All fights reserved.
Keywords: semiconductors; crystal growth epitaxy

Predicted reaction paths for the formation of multinary chalcopyrite compounds - Hock, Rainer; et al. (physica status solidi (a), 2006)
We apply the concept of epitaxy, which has been proven to be essential for the formation of CuInSe2 and CuGaSe2 out of binary selenide compounds to multinary compounds. We show that the formation of quaternary chalcopyrites is possible starting either with binary or with mixed crystal chalcogenide compounds. The complete sets of chemical solid-state reactions equations are given. The solid-state reactions are expected to proceed faster, if only one sublattice needs to be rearranged. It shows out, that ternary and quaternary chalcopyrite compounds can be synthesised by fast reaction mechanisms directly from chalcogenide compounds. The fastest way to obtain chalcopyrites containing more than four elements is a stepwise process. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Predicting Cell Stress and Strain during Extrusion Bioprinting - Müller, Sebastian J.; Fabry, Ben; Gekle, Stephan (Physical Review Applied, 2023)
Bioprinting of living cells can cause major shape deformations, which may severely affect cell survival and functionality. While the shear stresses occurring during cell flow through the printer nozzle have been quantified to some extent, the extensional stresses occurring as cells leave the nozzle into the free printing strand have been mostly ignored. Here we use lattice Boltzmann simulations together with a finite-element based cell model to study cell deformation inside the nozzle and at its exit. Our simulation results are in good qualitative agreement with experimental microscopy images. We show that, for cells flowing in the center of the nozzle, extensional stresses can be significant while, for cells flowing off-center, their deformation is dominated by the shear flow inside the nozzle. From the results of these simulations, we develop two simple methods that only require the printing parameters (nozzle diameter, flow rate, bioink rheology) to (i) accurately predict the maximum cell stress occurring during the three-dimensional bioprinting process and (ii) approximately predict the cell strains caused by the elongational flow at the nozzle exit.
CRIS-Team Scopus Importer:2023-07-21

Prediction of solid-state reactions for the formation of the chalcopyrites CuInS2, CuGaS2,CuAlS2 and CuAlSe2 starting from binary compounds - Hock, Rainer; et al. (physica status solidi (a), 2006)
In a recent work we have described the importance of epitaxy for the formation of CuInSe2 and CuGaSe2. In this article we identify epitaxial relations between binary selenide compounds serving as educts for the formation of the title compounds. From this we derive a set of possible chemical reaction equations for those solid-state reactions, which will preferably take place. By exploiting these reactions the chalcopyrite compounds can be synthesised smartly in short annealing processes at relatively low temperatures. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Preparation and characterization of hydrogen terminated 6H-SiC - Ristein, Jürgen; Ley, Lothar; et al. (Materials Science Forum, 2001)
A hydrogen termination of the (0001) and (0001̄) 6H-SiC surfaces is achieved by a thermal treatment in ultra pure hydrogen. This results in unreconstructed and quasi-bulk terminated surfaces as demonstrated by a (1×1) LEED patterns which are stable in air. Photoelectron spectra show only bulk related Si 2p and C 1s lines and give no indication of any contamination. Using Fourier transform infrared spectroscopy (FTIR) in the attenuated total reflection (ATR) configuration Si-H stretching modes around 2130 cm-1 have been observed in p-polarization but not in s-polarization. This indicates that the Si-H bonds are oriented perpendicular to the surface. Electronically, hydrogenation leads to a complete passivation of the surface with no pinning of the Fermi level. After annealing at 800°C in UHV the hydrogen completely desorbs and the surface periodicity changes from (1×1) to (√3×√3)R30°. The photoemission spectra of this (√3×√3)R30° structure are characteristic for a surface with Si adatoms in T4 configuration which is formed via a disproportionation of SiC at the surface.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.prepar

Pressure-driven collective growth mechanism of planar cell colonies. - Metzner, Claus; Lange, Janina; Krauß, Patrick; Wunderling, Nico; Übelacker, Julian; Martin, Florian; Fabry, Ben (Journal of Physics D-Applied Physics, 2018)

Pressure-driven collective growth mechanism of planar cell colonies. - Metzner, Claus; Lange, Janina; Krauß, Patrick; Wunderling, Nico; Übelacker, Julian; Martin, Florian; Fabry, Ben (Journal of Physics D: Applied Physics, 2018)
The growth of cell colonies is determined by the migration and proliferation of the individual cells. This is often modeled with the Fisher-Kolmogorov (FK) equation, which assumes that cells diffuse independently from each other, but stop to proliferate when their density reaches a critial limit. However, when using measured, cell-line specific parameters, we find that the FK equation drastically underestimates the experimentally observed increase of colony radius with time. Moreover, cells in real colonies migrate radially outward with superdiffusive trajectories, in contrast to the assumption of random diffusion. We demonstrate that both dicrepancies can be resolved by assuming that cells in dense colonies are driven apart by repulsive, pressure-like forces. Using this model of proliferating repelling particles (PRP), we find that colony growth exhibits different dynamical regimes, depending on the ratio between a pressure-related equilibrium cell density and the critial density of proliferation arrest.
EVALuna2:210450

Principle and mechanism of direct porphyrin metalation: Joint experimental and theoretical investigation - Shubina, Tatyana; Marbach, Hubertus; Flechtner, Ken; Kretschmann, Andreas; Jux, Norbert; Buchner, Florian; Steinrück, Hans-Peter; Clark, Timothy; Gottfried, Michael (Journal of the American Chemical Society, 2007)
The direct metalation of tetraphenylporphyrin with bare metal atoms (Co and Zn) was studied with X-ray photoelectron spectroscopy, scanning tunneling microscopy, and temperature-programmed reaction measurements on ordered monolayer films of the molecules adsorbed on a Ag(111) surface. The mechanism of this novel type of surface reaction was investigated using density functional theory (DFT) calculations for the related gas-phase reactions of the unsubstituted porphyrin with the metals Fe, Co, Ni, Cu, and Zn. The reaction starts with the formation of an initial complex, in which the metal atom is coordinated by the intact unreduced porphyrin. This complex resembles the sitting-atop complex proposed for porphyrin metalation with metal ions in solution. In two subsequent steps, the pyrrolic hydrogen atoms are transferred to the metal atom, forming H , which is eventually released. The activation barriers of the H-transfer steps vary for the different metal atoms. DFT calculations suggest that metalations with Fe, Co, and Ni show two-state reactivity, while those with Cu and Zn proceed on a single potential energy surface. For metalation with Zn, we calculated a barrier of the first hydrogen transfer step of 32.6 kcal mol , in good agreement with the overall experimental activation energy of 31 kcal mol . © 2007 American Chemical Society.

Probing local strain and composition in Ge nanowires by means of tip-enhanced Raman scattering - Reparaz, J. S.; Peica, N.; Kirste, R.; Goni, A. R.; Wagner, M. R.; Callsen, G.; Alonso, M. I.; Garriga, Miquel; Marcus, I. C.; Ronda, A.; Berbezier, Isabelle; Maultzsch, Janina; et al. (Nanotechnology, 2013)
Local strain and Ge content distribution in self-assembled, in-plane Ge/Si nanowires grown by combining molecular beam epitaxy and the metal-catalyst assisted-growth method were investigated by tip-enhanced Raman scattering. We show that this technique is essential to study variations of physical properties of single wires at the nanoscale, a task which cannot be achieved with conventional micro-Raman scattering. As two major findings, we report that (i) the Ge distribution in the (001) crystallographic direction is inhomogeneous, displaying a gradient with a higher Ge content close to the top surface, and (ii) in contrast, the (uncapped) wires exhibit essentially the same small residual compressive strain everywhere along the wire.

Probing of optical near-fields by electron rescattering on the 1nm scale - Thomas, Sebastian; Krüger, Michael; Förster, Michael; Schenk, Markus; Hommelhoff, Peter (Nano Letters, 2013)
UnivIS-Import:2015-04-14:Pub.2013.nat.dphy.IAP.exphys.probin

Probing semiconductor gap states with resonant tunneling - Malzer, Stefan; et al. (Physical Review Letters, 2006)
Tunneling transport through the depletion layer under a GaAs 110 surface is studied with a low temperature scanning tunneling microscope (STM). The observed negative differential conductivity is due to a resonant enhancement of the tunneling probability through the depletion layer mediated by individual shallow acceptors. The STM experiment probes, for appropriate bias voltages, evanescent states in the GaAs band gap. Energetically and spatially resolved spectra show that the pronounced anisotropic contrast pattern of shallow acceptors occurs exclusively for this specific transport channel. Our findings suggest that the complex band structure causes the observed anisotropies connected with the zinc blende symmetry. © 2006 The American Physical Society.

PROBING VALENCE STATES WITH PHOTOEMISSION AND INVERSE PHOTOEMISSION - Fauster, Thomas; et al. (Journal of Vacuum Science & Technology A, 1984)

Production of sharp gold tips with high surface quality - Eisele, Max; Krüger, Michael; Schenk, Markus; Ziegler, Alexander; Hommelhoff, Peter (Review of Scientific Instruments, 2011)
We present a simple method to produce sharp gold tips with excellent surface quality based on electrochemical etching with potassium chloride. Radii of curvature lie in the range of 20-40 nm and the surface roughness is measured to less than 0.8 nm. The tips are well suited for field emission, field ion microscopy, and likely for tip-enhanced Raman scattering as well as tip-enhanced near-field imaging. © 2011 American Institute of Physics.
UnivIS-Import:2015-04-14:Pub.2011.nat.dphy.IAP.exphys.produc

Proteinase 3 associated with Wegener's granulomatosis - Goldmann, Wolfgang (Cell Biology International, 2022)
Wegener's granulomatosis (WG) is a form of systemic vasculitis characterized by granulomatous inflammation of the upper and lower airways, vasculitis, and necrotizing glomerulonephritis. It is strongly associated with anti-neutrophil cytoplasmic antibodies against proteinase 3 (PR3-ANCAs). Various in vitro observations provided strong evidence that autoimmune PR3-ANCAs are directly involved in glomerular and vascular inflammation. However, little is known about the pathogenic significance of PR3-ANCAs in vivo. Therefore, the generation of animal models helped to validate the suggested autoimmune origin and pathophysiology in WG. To characterize and improve the models, numerous studies were carried out to elucidate the effect of mouse/rat PR3-ANCAs on neutrophil function as well as the role of CD4/CD8 in T and B cells and antibodies in the pathogenesis of the disease. Understanding the pathogenesis is therefore critical to relate these models to human studies hoping that they will be useful for better insight of WG and the development of specific therapies for the disease.
CRIS-Team WoS Importer:2022-01-14

PSMA SPECT/CT with 99mTc-MIP-1404 in biochemical recurrence of prostate cancer: predictive factors and efficacy for the detection of PSMA-positive lesions at low and very-low PSA levels - Schmidkonz, Christian; Götz, Theresa; Kuwert, Torsten; Ritt, Philipp; Prante, Olaf; Bäuerle, Tobias; Goebell, Peter; Cordes, Michael (Annals of Nuclear Medicine, 2019)
Background: The in vivo expression of the prostate-specific membrane antigen (PSMA) can be investigated using the SPECT-suitable tracer 99mTc-MIP-1404. We investigated the performance of 99mTc-MIP-1404 PSMA SPECT/CT in the detection of PSMA-positive tumor lesions in patients suffering from biochemical recurrence of prostate cancer presenting with serum levels of the prostate-specific antigen (PSA) below 1 ng/mL. Methods: We retrospectively analyzed 99mTc-MIP-1404-SPECT/CT scans of 50 patients (25 with low PSA levels between > 0.5 and 1 ng/mL and 25 with very low PSA levels between 0.2 and 0.5 ng/mL) that had undergone whole-body planar scintigraphy and SPECT/CT of the thorax, abdomen and pelvis 3–4 h p.i. of 691 ± 72 MBq 99mTc-MIP-1404. All datasets were evaluated for the presence and location of PSMA-positive tumor lesions, in which maximal standardized uptake values (SUVmax) were also measured. Based on the results of the quantitative evaluation as well as on biochemical and histological parameters, predictive factors for a positive 99mTc-MIP-1404 scan result were determined. The influence of 99mTc-MIP-1404 PSMA SPECT/CT on further therapy planning was assessed, based on the decision-making of the interdisciplinary tumor board. Results: Pathological 99mTc-MIP-1404 uptake was detected in a total of 25 patients (50%). In the very low PSA subgroup, detection rates of PSMA-positive lesions suggestive of tumor recurrence were 44%, in the low-PSA subgroup 56%. Gleason scores ≥ 8 and the presence of antiandrogen deprivation therapy were further significant predictors of pathological 99mTc-MIP-1404 uptake. This was paralleled by significantly higher lesional SUVmax patients with PSA levels > 0.5 ng/mL and Gleason scores ≥ 8 compared to those without these two features. Changes in therapeutic strategy following MIP-1404 imaging were recommended by the interdisciplinary tumor board in 25/50 of patients. Conclusion: 99mTc-MIP-1404 PSMA-SPECT/CT demonstrated a high performance in detecting PSMA-positive lesions suggestive of tumor recurrence in patients with biochemical recurrence of prostate cancer and low and very low serum PSA levels. Results from MIP-1404 PSMA SPECT/CT have therapeutic impact in one-half of the patients examined by this technology.
CRIS-Team Scopus Importer:2019-10-29
Keywords: Low PSA levels; MIP-1404; Prostate cancer; PSMA; Quantitative SPECT/CT; SPECT/CT

Publisher's Note: Aluminum acceptor activation and charge compensation in implanted p-type 4H-SiC (AIP Advances (2019) 9 (055308) DOI: 10.1063/1.5096440) - Weiße, Julietta; Hauck, Martin; Krieger, Michael; Bauer, A. J.; Erlbacher, T. (AIP Advances, 2019)
This article was originally published online on 9 May 2019. Due to a production error, the last sentence of the abstract and the second paragraph, second sentence of the conclusions appeared incorrectly. AIP Publishing apologizes for this error. All online versions of the article were corrected on 16 May 2019.
CRIS-Team Scopus Importer:2019-07-23

Pulling it together in three dimensions - Trepat, Xavier; Fabry, Ben; Fredberg, Jeffrey (Nature Methods, 2010)

Pulsed laser deposition of Co and growth of CoSi2 on Si(111) - Löffler, Matthias; Cordon, J.; Weinelt, Martin; Ortega, J. E.; Fauster, Thomas (Applied Physics A-Materials Science & Processing, 2005)
Monolayers of Co were prepared by pulsed laser deposition (PLD) and thermal deposition (TD) on Si(111) substrates. The surface structure and morphology were studied as a function of annealing temperature with scanning tunneling microscopy and low-energy electron diffraction (LEED). Comparing PLD to TD in the monolayer regime, we find surface phases with lower Co content in the top layer for annealing temperatures below 500 degrees C, indicating an implantation of Co into the Si substrate. The implanted Co leads to an increased intermixing of Co and Si and a higher density of nucleation centers for Co multilayers produced by PLD compared to TD. Multilayer PLD films therefore show an improved film quality, which is detected by an increased intensity of the LEED reflectivity.

pyTFM: A tool for traction force and monolayer stress microscopy - Bauer, Andreas; Prechová, Magdalena; Fischer, Lena; Thievessen, Ingo; Gregor, Martin; Fabry, Ben (PLoS Computational Biology, 2021)
Cellular force generation and force transmission are of fundamental importance for numerous biological processes and can be studied with the methods of Traction Force Microscopy (TFM) and Monolayer Stress Microscopy. Traction Force Microscopy and Monolayer Stress Microscopy solve the inverse problem of reconstructing cell-matrix tractions and inter- and intra-cellular stresses from the measured cell force-induced deformations of an adhesive substrate with known elasticity. Although several laboratories have developed software for Traction Force Microscopy and Monolayer Stress Microscopy computations, there is currently no software package available that allows non-expert users to perform a full evaluation of such experiments. Here we present pyTFM, a tool to perform Traction Force Microscopy and Monolayer Stress Microscopy on cell patches and cell layers grown in a 2-dimensional environment. pyTFM was optimized for ease-of-use; it is open-source and well documented (hosted at https://pytfm.readthedocs.io/) including usage examples and explanations of the theoretical background. pyTFM can be used as a standalone Python package or as an add-on to the image annotation tool ClickPoints. In combination with the ClickPoints environment, pyTFM allows the user to set all necessary analysis parameters, select regions of interest, examine the input data and intermediary results, and calculate a wide range of parameters describing forces, stresses, and their distribution. In this work, we also thoroughly analyze the accuracy and performance of the Traction Force Microscopy and Monolayer Stress Microscopy algorithms of pyTFM using synthetic and experimental data from epithelial cell patches.
CRIS-Team Scopus Importer:2021-07-09

Qualitative und quantitative Auswertung regelmäßig durchgeführter aIR-Inspektionen von PV-Anlagen mit typischem PID-Muster - Fecher, Frank W.; Buerhop-Lutz, Claudia; Pickel, Tobias; Hundhausen, Martin; Zetzmann, Cornelia; Camus, Christian; Hauch, Jens; Brabec, Christoph (32. Symposium Photovoltaische Solarenergie, 2017)
Potential induzierte Degradation (PID) von Photovoltaik (PV)-Anlagen wird immer öfter an PV-Anlagen diagnostiziert und kann den Ertrag innerhalb weniger Jahre nach der Installation drastisch reduzieren. Als Ursachen werden lange Modulstrings mit hoher Systemspannung von ca. 800 V oder mehr sowie Temperatur und Feuchte im Wechselspiel mit der Verkapselung genannt [1]. Neuste Untersuchungen gehen davon aus, dass grob geschätzt 19 % der PV-Anlagen in Deutschland PID-Probleme haben [2]. Da PID zu einer zeitlich fortscheitenden Verschlechterung der Anlagen führt, ist es wichtig, möglichst frühzeitig PID und dessen Schadensgrad festzustellen, um erfolgreich Gegenmaßnahmen zu ergreifen. Zur Verifikation von PID wird vielfach Elektrolumineszenz (EL) aber auch Infrarot (IR)-Thermographie herangezogen [3, 4]. Da IR-Inspektionen schnell, zuverlässig und kosteneffizient Hinweise auf PID in Solaranlagen ohne Betriebsunterbrechung geben, ist es unser Ziel, eine Methode zur schnellen Diagnose von PID vorzustellen, die gleichzeitig eine quantitative Bestimmung des Schädigungsgrads und regelmäßige Nachmessungen erlaubt. In diesem Artikel stellen wir typische PID-Muster anhand von Infrarotluftaufnahmen (aIR) vor. Die Auswertung dieser zeigte auch erste Zusammenhänge zum Leistungsverlust der PV-Anlage. Des Weiteren wurde das Fortschreiten der PID in den Anlagen regelmäßig sowie der Einsatz von PID-Regenerationsboxen untersucht.

Quantifying cell-to-cell variation in power-law rheology - Cai, PinGen; Mizutani, Yusuke; Tsuchiya, Masahiro; Maloney, John M.; Fabry, Ben; Van Vliet, Krystyn; Okajima, Takaharu (Journal of Biochemistry, Molecular Biology and Biophysics, 2013)

Quantifying the causes and consequences of variation in satellite-derived population indices: a case study of emperor penguins - Labrousse, Sara; Iles, David; Viollat, Lise; Fretwell, Peter; Trathan, Philip N.; Paranhos Zitterbart, Daniel; Jenouvrier, Stephanie; Larue, Michelle (Remote Sensing in Ecology and Conservation, 2021)
Very high-resolution satellite (VHR) imagery is a promising tool for estimating the abundance of wildlife populations, especially in remote regions where traditional surveys are limited by logistical challenges. Emperor penguins Aptenodytes forsteri were the first species to have a circumpolar population estimate derived via VHR imagery. Here we address an untested assumption from Fretwell et al. (2012) that a single image of an emperor penguin colony is a reasonable representation of the colony for the year the image was taken. We evaluated satellite-related and environmental variables that might influence the calculated area of penguin pixels to reduce uncertainties in satellite-based estimates of emperor penguin populations in the future. We focused our analysis on multiple VHR images from three representative colonies: Atka Bay, Stancomb-Wills (Weddell Sea sector) and Coulman Island (Ross Sea sector) between September and December during 2011. We replicated methods in Fretwell et al. (2012), which included using supervised classification tools in ArcGIS 10.7 software to calculate area occupied by penguins (hereafter referred to as ‘population indices’) in each image. We found that population indices varied from 2 to nearly 6-fold, suggesting that penguin pixel areas calculated from a single image may not provide a complete understanding of colony size for that year. Thus, we further highlight the important roles of: (i) sun azimuth and elevation through image resolution and (ii) penguin patchiness (aggregated vs. distributed) on the calculated areas. We found an effect of wind and temperature on penguin patchiness. Despite intra-seasonal variability in population indices, simulations indicate that reliable, robust population trends are possible by including satellite-related and environmental covariates and aggregating indices across time and space. Our work provides additional parameters that should be included in future models of population size for emperor penguins.
CRIS-Team Scopus Importer:2021-08-20
Keywords: Emperor penguin; intra-seasonal variability; population estimates; population trend; satellite imagery; VHR imagery

Quantitative analysis of deformability-based cell separation using deterministic lateral displacement and optical stretching - Holmes, David; Whyte, Graeme; Ekpenyong, Andrew; Guck, Jochen; Duke, Thomas (Proceedings of the 16th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2012, 2012)
In this work we present data showing deformability-based cell separation in a deterministic lateral displacement (DLD) device. We use cells of defined stiffness (glutaraldehyde cross-linked erythrocytes) to test the performance of the device across a range of cell stiffness and applied shear rates. Optical stretching is used as an independent method of quantifying the stiffness of the cells, thus allowing better understanding of the DLD system for deformability based cell separation. Displacement is shown to correlate with cell stiffness as measured across a range of flow rates. Data showing how the isolation of leukocytes from whole blood varies with shear rate is also presented.
CRIS-Team Scopus Importer:2022-08-05
Keywords: Blood; Cell deformability; Deterministic lateral displacement; Optical stretching; Shear rate

Quantitative analysis of diffuse electron scattering in the lithium-ion battery cathode material Li1.2Ni0.13Mn0.54Co0.13O2 - Poppe, Romy; Vandemeulebroucke, Daphne; Neder, Reinhard; Hadermann, Joke (ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 2021)
CRIS-Team WoS Importer:2022-04-01

Quantitative analysis of diffuse electron scattering in the lithium-ion battery cathode material Li1.2Ni0.13Mn0.54Co0.13O2 - Poppe, Romy; Vandemeulebroucke, Daphne; Neder, Reinhard; Hadermann, Joke (IUCrJ, 2022)
In contrast to perfectly periodic crystals, materials with short-range order produce diffraction patterns that contain both Bragg reflections and diffuse scattering. To understand the influence of short-range order on material properties, current research focuses increasingly on the analysis of diffuse scattering. This article verifies the possibility to refine the short-range order parameters in submicrometre-sized crystals from diffuse scattering in single-crystal electron diffraction data. The approach was demonstrated on Li1.2Ni0.13Mn0.54Co0.13O2, which is a state-of-the-art cathode material for lithium-ion batteries. The intensity distribution of the 1D diffuse scattering in the electron diffraction patterns of Li1.2Ni0.13Mn0.54Co0.13O2 depends on the number of stacking faults and twins in the crystal. A model of the disorder in Li1.2Ni0.13Mn0.54Co0.13O2 was developed and both the stacking fault probability and the percentage of the different twins in the crystal were refined using an evolutionary algorithm in DISCUS. The approach was applied on reciprocal space sections reconstructed from 3D electron diffraction data since they exhibit less dynamical effects compared with in-zone electron diffraction patterns. A good agreement was achieved between the calculated and the experimental intensity distribution of the diffuse scattering. The short-range order parameters in submicrometre-sized crystals can thus successfully be refined from the diffuse scattering in single-crystal electron diffraction data using an evolutionary algorithm in DISCUS.
CRIS-Team WoS Importer:2022-09-30

Quantitative analysis of the cardiorespiratory system during paced respiration - Leutheuser, Heike; Schaffer, Thorsten; Hensel, Bernhard; Weigand, Christian; Schüttler, Jürgen; Jeleazcov, Christian (7th Russian-Bavarian Conference on Biomedical Engineering (RBC), 2011)
The phase relationship between respiration and cardio- vascular system is investigated under the influence of paced respiration with respiratory rates from 4 to 25 breaths per minute. Particularly, the phase shift dependency on breathing rate as well as the correlation between respiratory sinus arrhythmia (RSA) and breathing frequency is examined. It can be shown that there is an increasing phase relationship between RSA and breathing frequency and that RSA diminishes with rising breathing frequenc
Keywords: respiratory sinus arrhythmia; paced respiration; cardiorespiratory system

Quantitative determination of Cu(117) multilayer surface relaxations by LEED - Walter, Sebastian; Baier, Holger; Weinelt, Martin; Heinz, Klaus; Fauster, Thomas (Physical Review B, 2001)
The relaxation of the first seven atomic layers of Cu(117) was determined by quantitative low-energy electron diffraction (LEED). Intensity versus energy spectra, I(E), were measured for the primary beam at near-normal incidence to the (001) terraces. The data collected cover a cumulative energy range of 3200 eV. Computation of I(E) spectra was performed in the angular momentum representation by considering the surface as a single atomic slab. For the variation of parameters, tensor LEED was applied. The experimental spectra are well reproduced over the entire energy range even for regions of low intensity. The first four layer spacings relax in a way to smooth the surface corrugation, whereby the relative changes Deltad/d(0) amount (from top) to -13%, -2.0%, -10%, and +7%. This leads to a reduction of the vertical distance between step and corner atoms by 0.13 Angstrom. Comparison with experimental results for Cu(115) shows that this modification of the step shape is rather independent of the terrace width. Comparison to theoretical results exhibits, however, some discrepancies with respect to both the expansion/contraction sequence and the amplitudes of the layer relaxations.

Quantitative evaluation of biaxial strain in epitaxial 3 C- SiC layers on Si(100) substrates by Raman spectroscopy - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Applied Physics, 2002)
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.IAP.exphys.quanti

Quantitative Investigation of Near Interface Traps in 4H-SiC MOSFETs via Drain Current Deep Level Transient Spectroscopy - Hauck, Martin; Weiße, Julietta; Lehmeyer, Johannes; Pobegen, Gregor; Weber, Heiko B.; Krieger, Michael (Materials Science Forum, 2016)
Keywords: MOSFET; drain current DLTS; Hall effect in MOS channel; interface traps; NITs; POA

QUANTIZATION OF ELECTRONIC STATES ON METAL-SURFACES - Fauster, Thomas (Applied Physics A: Solids and Surfaces, 1994)
An electron in front of a metal surface experiences an attractive force due to the induced image charge. Band gaps in the band structure can prevent a penetration into the metal along certain directions. The Coulomb-like potential supports bound states in front of the surface which correspond to a hydrogen atom in one dimension. These image states can be measured with high resolution by two-photon photoemission. The adsorption of metals modifies the states. If the electrons can penetrate into the metal, quantum-well states can develop corresponding to standing waves in the overlayer. Image states on small islands show the quantization effects due to the lateral localization. The spectroscopy of image states by two-photon photoemission permits the investigation of growth and morphology of deposited metal layers, a well as the illustration of fundamental quantum-mechanical effects.

Quantum-Coherent Light-Electron Interaction in an SEM - Chlouba, Tomas; Shiloh, Roy; Hommelhoff, Peter (Optics InfoBase Conference Papers, 2022)
Quantum-coherent light-free-electron interaction was shown more than a decade ago in a transmission electron microscope leading to a variety of applications. We now show the quantum-coherent interaction in a scanning electron microscope, offering substantial advantages over TEMs.
CRIS-Team Scopus Importer:2022-09-09

Quantum-Coherent Light-Electron Interaction in a Scanning Electron Microscope - Shiloh, Roy; Chlouba, Tomas; Hommelhoff, Peter (Physical Review Letters, 2022)
The last two decades experimentally affirmed the quantum nature of free electron wave packets by the rapid development of transmission electron microscopes into ultrafast, quantum-coherent systems. So far, all experiments were restricted to the bounds of transmission electron microscopes enabling one or two photon-electron interaction sites. We show the quantum coherent coupling between electrons and light in a scanning electron microscope, at unprecedentedly low, subrelativistic energies down to 10.4 keV. These microscopes not only afford the yet-unexplored energies from ∼0.5 to 30 keV providing the optimum electron-light coupling efficiency, but also offer spacious and easily configurable experimental chambers for extended, cascaded optical set ups, potentially boasting thousands of photon-electron interaction sites. Our results make possible experiments in electron wave packet shaping, quantum computing, and spectral imaging with low-energy electrons.
CRIS-Team Scopus Importer:2022-07-01

Quantum dissociation of a vortex-antivortex pair in a long Josephson junction - Fistul, Mikhail; Wallraff, Andreas; Koval, Yury; Lukashenko, Oleksandr; Malomed, B.; Ustinov, Alexey (Physical Review Letters, 2003)
The experimental and theoretical study of the thermal and quantum dissociation of a single vortex-antivortex (VAV pair) in a long josephson junction was presented. A pinning potential controlled by external magnetic field and bias current was used in the confinement of VAV pair. The dissociation of the pinned VAV pair resulted in the junction's switching from the superconducting to the resistive state. The obtained thermal and field dependence of the switching current distribution was in agreement with the analysis. At a temperature of about 100 mK, the crossover from the thermal to the macroscopic quantum tunneling dissociation mechanism was observed.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.IAP.pephys.quantu_3

Quantum dynamics of a single vortex - Wallraff, Andreas; Lukashenko, Oleksandr; Lisenfeld, J.; Kemp, A.; Fistul, Mikhail; Koval, Yury; Ustinov, Alexey (Nature, 2003)
Vortices occur naturally in a wide range of gases and fluids, from macroscopic to microscopic scales. In Bose-Einstein condensates of dilute atomic gases, superfluid helium and superconductors, the existence of vortices is a consequence of the quantum nature of the system. Quantized vortices of supercurrent are generated by magnetic flux penetrating the material, and play a key role in determining the material properties and the performance of superconductor-based devices. At high temperatures the dynamics of such vortices are essentially classical, while at low temperatures previous experiments have suggested collective quantum dynamics. However, the question of whether vortex tunnelling occurs at low temperatures has been addressed only for large collections of vortices. Here we study the quantum dynamics of an individual vortex in a superconducting Josephson junction. By measuring the statistics of the vortex escape from a controllable pinning potential, we demonstrate the existence of quantized levels of the vortex energy within the trapping well and quantum tunnelling of the vortex through the pinning barrier.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.IAP.pephys.quantu_5

Quantum information processing in optical lattices and magnetic microtraps - Treutlein, Philipp; Steinmetz, Tilo; Colombe, Yves; Lev, Benjamin; Hommelhoff, Peter; Reichel, Jakob; Greiner, Markus; Mandel, Olaf; Widera, Artur; Rom, Tim; Bloch, Immanuel; Haensch, Theodor W. (Fortschritte Der Physik-Progress of Physics, 2006)
We review our experiments on quantum information processing with neutral atoms in optical lattices and magnetic microtraps. Atoms in an optical lattice in the Mott insulator regime serve as a large qubit register. A spin-dependent lattice is used to split and delocalize the atomic wave functions in a controlled and coherent way over a defined number of lattice sites. This is used to experimentally demonstrate a massively parallel quantum gate array, which allows the creation of a highly entangled many-body cluster state through coherent collisions between atoms on neighbouring lattice sites. In magnetic microtraps on an atom chip, we demonstrate coherent manipulation of atomic qubit states and measure coherence lifetimes exceeding one second at micron-distance from the chip surface. We show that microwave near-fields on the chip can be used to create state-dependent potentials for the implementation of a quantum controlled phase gate with these robust qubit states. For single atom detection and preparation, we have developed high finesse fiber Fabry-Perot cavities and integrated them on the atom chip. We present an experiment in which we detected a very small number of cold atoms magnetically trapped in the cavity using the atom chip. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.exphys.quantu
Keywords: Atom chip; Fiber cavity; Microtrap; Microwave potential; Mott insulator; Optical lattice; Quantum information; Single atom detection

Quantum Information Processing in Optical Lattices and Magnetic Microtraps - Treutlein, Philipp; Steinmetz, Tilo; Colombe, Yves; Lev, Benjamin; Hommelhoff, Peter; Reichel, Jakob; Greiner, Markus; Mandel, Olaf; Widera, Arthur; Rom, Tim; Bloch, Immanuel; Haensch, Theodor W. (Elements of Quantum Information, 2007)
UnivIS-Import:2015-04-16:Pub.2007.nat.dphy.IAP.exphys.quantu
Keywords: Atom chip; Magnetic microtraps; Optical lattices; Quantum information processing; Qubit states

Quantum Interference Visibility Spectroscopy in Two-Color Photoemission from Tungsten Needle Tips - Li, Ang; Pan, Yiming; Dienstbier, Philip; Hommelhoff, Peter (Physical Review Letters, 2021)
When two-color femtosecond laser pulses interact with matter, electrons can be emitted through various multiphoton excitation pathways. Quantum interference between these pathways gives rise to a strong oscillation of the photoemitted electron current, experimentally characterized by its visibility. In this Letter, we demonstrate the two-color visibility spectroscopy of multiphoton photoemissions from a solid-state nanoemitter. We investigate the quantum pathway interference visibility over an almost octave-spanning wavelength range of the fundamental (ω) femtosecond laser pulses and their second harmonic (2ω). The photoemissions show a high visibility of 90% ± 5%, with a remarkably constant distribution. Furthermore, by varying the relative intensity ratio of the two colors, we find that we can vary the visibility between 0% and close to 100%. A simple but highly insightful theoretical model allows us to explain all observations, with excellent quantitative agreements. We expect this work to be universal to all kinds of photo-driven quantum interference, including quantum control in physics, chemistry, and quantum engineering.
Keywords: quantum pathway interference; visibility spectroscopy; electron emission

Quantum numbers and band topology of nanotubes - Maultzsch, Janina; et al. (Journal of Physics A: Mathematical and General, 2003)
Nanotubes as well as polymers and quasi-ID subsystems of 3D crystals have line group symmetry. This allows two types of quantum numbers: roto-translational and helical. The roto-translational quantum numbers are linear and total angular (not conserved) momenta, while the helical quantum numbers are helical and complementary angular momenta. Their mutual relations determine some topological properties of energy bands, such as systematic band sticking or van Hove singularities related to parities. The importance of these conclusions is illustrated by the optical absorption in carbon nanotubes: parity may prevent absorption peaks at van Hove singularities.

Quantum oscillations and quantum Hall effect in epitaxial graphene - Jobst, Johannes; Waldmann, Daniel; Speck, Florian; Hirner, R.; Maude, Duncan; Seyller, Thomas; Weber, Heiko B. (Physical Review B, 2010)
We investigate the transport properties of high-quality single-layer graphene, epitaxially grown on a 6H-SiC(0001) substrate. We have measured transport properties, in particular charge-carrier density, mobility, conductivity, and magnetoconductance of large samples as well as submicrometer-sized Hall bars which are entirely lying on atomically flat substrate terraces. The results display high mobilities, independent of sample size. The temperature dependence of the conductance indicates a rather strong coupling to the SiC substrate. An analysis of the Shubnikov-de Haas effect yields the Landau-level spectrum of single-layer graphene. When gated close to the Dirac point, the mobility increases substantially and the graphenelike quantum Hall effect occurs.

Quantum transport in carbon nanotubes - Roth, Siegmar; Krstic, Vojislav; Rikken, Geert L.J.A. (Current Applied Physics, 2002)
A survey will be given on selected experiments showing evidence of quantum transport in carbon nanotubes. The phenomena involve electron confinement, single electron effects and Coulomb–Blockade, Kondo-physics, conductance quantisation, Aharonov–Bohm effect, phase breaking in ballistic transport, and magnetochiral anisotropy.
Keywords: Electrical transport measurements; Carbon nanotubes

Quantum transport in low-dimensional organic nanostructures - Park, Jin-gyu; Kim, Gyutae; Park, June-hyoung; Yu, Han-young; McIntosh, Gregory C.; Krstic, Vojislav; Jhang, Sung Ho; Kim, Byung-hoon; Lee, Sang-hun; Lee, Sangwook; Burghard, Marko; Roth, Siegmar; et al. (Thin Solid Films, 2001)
We have studied three low-dimensional systems with sub-micron dimensions: a single polyacetylene (PA) nanofiber; a single-walled carbon nanotube (SWNT)-rope; and a lithographically prepared stripe of poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV). In each case, the sample was contacted to four-probe electrodes, with 100-nm spacing and various electronic transport properties such as the I–V characteristics, the temperature dependence of resistivity and the gate voltage dependence of the transport current were measured. The PA nanofiber was found to be non-ohmic with a room temperature conductivity of ∼0.1 S/cm. Its carriers were found to be hole-like with charge carrier mobility of μ=7.76×10−2 cm2/Vs. For the SWNT-rope, the temperature-dependence of resistivity exhibited signatures of a Luttinger liquid for temperatures below 30 K. With varying gate voltage, periodic peaks were seen in the nanotube current which would normally be attributed to the effects of Coulomb blockade. Interestingly, these peaks show three-way splitting, similar to observations in triple quantum dot experiments. The MEH-PPV stripe, which was produced using electron beam lithography, had I–V characteristics similar to that of a large band-gap semiconductor. In the high field region, these characteristics could be explained in terms of a single carrier device model which considers the field-dependent mobility along with space charge limited conduction (SCLC). All three samples can be considered as field-effect transistors (FETs), with potential use in future high density integrated electronic devices.
Keywords: Electrical transport; FET; Polyacetylene; MEH-PPV; Nanotube

Quantum transport in molecular nanowires transistors - Roth, Siegmar; Burghard, Marko; Krstic, Vojislav; Liu, Kun; Muster, Jörg; Philipp, Günther; Kim, Gyu-Tae; Park, Jin-gyu; Park, YungWoo (Current Applied Physics, 2001)
Nanotube-based field effect transistors can be prepared by laying carbon nanotubes over electrolithographically deposited gold electrodes on silicon chips. These devices can be used to study the physical properties of the nanotubes and to investigate the electrical behaviour of the contacts between the electrodes and the tubes. From the experience with these devices technologies of chemical self-assembly can be developed which will allow for integration densities higher than achievable by purely lithographic means.
Keywords: Molecular electronics; Quantum transport; Carbon nanotube; Field-effect transistor; Self-assembly

Quasielastic and inelastic neutron scattering study of methyl group rotation in solid and liquid pentafluoroanisole and pentafluorotoluene - Smuda, Christoph; Gemmecker, Gerd; Unruh, Tobias (Journal of Chemical Physics, 2008)
The rotational motion of the methyl group in pentafluoroanisole (PFA) and in pentafluorotoluene (PFT), respectively, was investigated by quasielastic neutron scattering (QENS). For solid PFA, the rotation can be described by a model for uniaxial rotational jumps between three equidistant sites on a circle. Similar to the molecular structure of alpha-toluene, two nonequivalent methyl groups in the unit cell with two different rotational barriers were found for solid PFT. From the analysis of the quasielastic scattering, the activation energies were determined. The barrier heights could be evaluated from bands in the inelastic part of the spectra. The methyl group dynamics in the liquid state is evaluated for both substances using different scattering functions, which are discussed. An empirical model for the description of the contribution of methyl groups in liquids of small organic molecules to the QENS spectra is presented. It is demonstrated that the process of methyl group rotation in the liquid phase is nearly free of a barrier. (c) 2008 American Institute of Physics.

Quasi-elastic scattering of electrons in image-potential states - Fauster, Thomas; Weinelt, Martin; Höfer, Ulrich (Progress in Surface Science, 2007)
Image-potential states provide a model system to study electron scattering at surfaces. With time-, energy- and angle-resolved two-photon photoemission quasi-elastic intraband and resonant interband scattering processes can be identified and resolved. The scattering sources are related to phonons and to imperfections of the surface such as defects and steps. (C) 2007 Elsevier Ltd. All rights reserved.
Keywords: surface electronic phenomena; angle-resolved photoemission; two-photon photoemission; surface states; image-potential states; femtosecond dynamics

Quasi-freestanding epitaxial graphene transistor with silicon nitride top gate - Wehrfritz, Peter; Fromm, Felix; Malzer, Stefan; Seyller, Thomas (Journal of Physics D-Applied Physics, 2014)
We report on top-gated field effect devices built from quasi-freestanding monolayer graphene (QFMLG) on 6H-SiC(0001) in combination with a silicon nitride (SiN) gate dielectric. SiN was grown by plasma enhanced chemical vapour deposition. The composition of the dielectric was investigated by x-ray photoelectron spectroscopy (XPS). Spectroscopic and electrical characterization of the graphene layers were done by XPS, Raman spectroscopy and Hall effect measurements before and after SiN deposition. In contrast to previous reports on SiN/graphene, we observe that our dielectric layer induces strong n-type doping. With such a gate insulator, the neutrality level of the QFMLG could be accessed by an appropriate gate voltage. © 2014 IOP Publishing Ltd.
UnivIS-Import:2015-03-09:Pub.2014.nat.dphy.IAP.LAP.quasif
Keywords: doping; epitaxial graphene; field effect; silicon nitride

Quasi-freestanding Graphene on SiC(0001) - Speck, Florian; Ostler, Markus; Röhrl, Jonas; Jobst, Johannes; Waldmann, Daniel; Hundhausen, Martin; Ley, Lothar; Weber, Heiko B.; Seyller, Thomas (Materials Science Forum, 2010)
We report on a comprehensive study of the properties of quasi-freestanding monolayer and bilayer graphene produced by conversion of the (6√3×6√3)R30° reconstruction into graphene via intercalation of hydrogen. The conversion is confirmed by photoelectron spectroscopy and Raman spectroscopy. By using infrared absorption spectroscopy we show that the underlying SiC(0001) surface is terminated by hydrogen in the form of Si-H bonds. Using Hall effect measurements we have determined the carrier concentration and type as well as the mobility which lies well above 1000 cm2/Vs despite a significant amount of short range scatterers detected by Raman spectroscopy. © (2010) Trans Tech Publications.
UnivIS-Import:2015-04-14:Pub.2010.nat.dphy.IAP.LAP.quasif
Keywords: ARPES; Graphene; Hydrogen; Infrared absorption spectroscopy; Intercalation; Raman spectroscopy; XPS

Quenching by electric fields of the luminescence of As2Se3 single crystals - Ristein, Jürgen; et al. (Solid State Communications, 1986)
High electric fields reduce the luminescence of As2Se3 at 77 K and increase simultaneously the photoconductivity. Comparison of both effects points to excitons as the source for emission of light whereas free carriers contributing to photoconductance recombine non radiatively. The field affects free excitons and their thermalization but does not ionize excitons trapped in radiative centres. At low excitation energy, in the range of indirect transitions, the field quenching of luminescence obeys a Poole-Frenkel behaviour. Such interpretation yields an exciton binding energy of 50 meV. The quantum efficiency of luminescence decreases to higher photon energy. Part of this decrease is related to an increase of the photoconductivity. © 1986.
UnivIS-Import:2015-03-05:Pub.1986.nat.dphy.IAP.exphys.quench

Radial breathing mode of single-walled carbon nanotubes: Optical transition energies and chiral-index assignment - Maultzsch, Janina; Telg, Hagen; Reich, Stephanie; Thomsen, Christian (Physical Review B, 2005)
We present a comprehensive study of the chiral-index assignment of carbon nanotubes in aqueous suspensions by resonant Raman scattering of the radial breathing mode. We determine the energies of the first optical transition in metallic tubes and of the second optical transition in semiconducting tubes for more than 50 chiral indices. The assignment is unique and does not depend on empirical parameters. The systematics of the so-called branches in the Kataura plot are discussed; many properties of the tubes are similar for members of the same branch. We show how the radial breathing modes observed in a single Raman spectrum can be easily assigned based on these systematics. In addition, empirical fits provide the energies and radial breathing modes for all metallic and semiconducting nanotubes with diameters between 0.6 and 1.5 nm. We discuss the relation between the frequency of the radial breathing mode and tube diameter. Finally, from the Raman intensities we obtain information on the electron-phonon coupling.

Radial oxygen precipitation of a 12 '' CZ silicon crystal studied in-situ with high energy X-ray diffraction - Bergmann, Christoph; Will, Johannes; Gröschel, Alexander; Weißer, Matthias; Magerl, Andreas (physica status solidi (a), 2014)
The radial oxygen nucleation and precipitation in Czochralski-grown silicon crystals is observed in real time via the local evolution of the X-ray Bragg intensity. Using a high X-ray energy and a divergent beam setup, it becomes possible to examine the impact of the local as-grown point defect configuration on the formation of bulk micro defects in a crystal of macroscopic dimensions. As a salient feature the transition from vacancy- to interstitial-dominated regions in a 12 crystal can be identified, and its influence on the precipitation kinetics is quantified through effective oxygen diffusion constant. It appears enhanced by up to a factor of six in vacancy-rich regions as compared to crystal volumes which are identified as point-defect free where it agrees well with the literature value.
Keywords: oxygen precipitation; point defects; silicon; X-ray diffraction

Radiation hardness of graphene and MoS2 field effect devices against swift heavy ion irradiation - Ochedowski, O.; Marinov, K.; Wilbs, G.; Keller, G.; Scheuschner, N.; Severin, D.; Bender, M.; Maultzsch, Janina; Tegude, F. J.; Schleberger, M. (Journal of Applied Physics, 2013)
We have investigated the deterioration of field effect transistors based on two-dimensional materials due to irradiation with swift heavy ions. Devices were prepared with exfoliated single layers of MoS2 and graphene, respectively. They were characterized before and after irradiation with 1.14 GeV U28+ ions using three different fluences. By electrical characterization, atomic force microscopy, and Raman spectroscopy, we show that the irradiation leads to significant changes of structural and electrical properties. At the highest fluence of 4 x 10(11) ions/cm(2), the MoS2 transistor is destroyed, while the graphene based device remains operational, albeit with an inferior performance. (C) 2013 AIP Publishing LLC.

Radiative recombination center in As2Se3 as studied by optically detected magnetic resonance - Ristein, Jürgen; et al. (Physical Review B, 1990)
The intrinsic luminescence of As2Se3 single crystals and glass has been studied by optically detected magnetic resonance (ODMR) using 16-GHz microwaves and magnetic fields up to 3 T. From these measurements we extract detailed structural information about a photoexcited center in a chalcogenide semiconductor. In the crystals a strong ODMR response is observed with the same spectral dependence as the luminescence spectrum. Resonant magnetic fields depend strongly on the orientation of the magnetic field. The measurements confirm that a self-trapped triplet exciton is the radiative state for midgap luminescence. Hyperfine splittings of the microwave transition and large zero-field splittings reveal a triplet state that is highly localized and anisotropic (almost uniaxial) with its symmetry axis oriented along a particular As-Se bond. Self-trapping of the exciton occurs at a center where lone-pair electronic states of Se interact strongly. The self-trapping leads to a redistribution of electronic charge that strengthens locally a weak intermolecular (intralayer) bond at the expense of covalent intralayer bonds. Magnetic fields enhance the luminescence efficiency, a fact that suggests the presence of a competing nonradiative recombination process, even at low temperatures, which is assumed to be related to diffusion of the self-trapped exciton. Comparison of the ODMR powder spectrum of the crystal with the ODMR spectrum of glassy As2Se3 indicates that similar relaxation processes also occur in amorphous As2Se3, where they precede at least a fraction of the recombination processes. © 1990 The American Physical Society.
UnivIS-Import:2015-03-05:Pub.1990.nat.dphy.IAP.exphys.radiat

Radiolysis‐Driven Evolution of Gold Nanostructures – Model Verification by Scale Bridging In Situ Liquid‐Phase Transmission Electron Microscopy and X‐Ray Diffraction - Fritsch, Birk; Zech, Tobias; Bruns, Mark; Körner, Andreas; Khadivianazar, Saba; Wu, Mingjian; Zargar Talebi, Neda; Virtanen, Sannakaisa; Unruh, Tobias; Jank, Michael; Spiecker, Erdmann; Hutzler, Andreas (Advanced Science, 2022)
Utilizing ionizing radiation for in situ studies in liquid media enables unique insights into nanostructure formation dynamics. As radiolysis interferes with observations, kinetic simulations are employed to understand and exploit beam-liquid interactions. By introducing an intuitive tool to simulate arbitrary kinetic models for radiation chemistry, it is demonstrated that these models provide a holistic understanding of reaction mechanisms. This is shown for irradiated HAuCl4 solutions allowing for quantitative prediction and tailoring of redox processes in liquid-phase transmission electron microscopy (LP-TEM). Moreover, it is demonstrated that kinetic modeling of radiation chemistry is applicable to investigations utilizing X-rays such as X-ray diffraction (XRD). This emphasizes that beam-sample interactions must be considered during XRD in liquid media and shows that reaction kinetics do not provide a threshold dose rate for gold nucleation relevant to LP-TEM and XRD. Furthermore, it is unveiled that oxidative etching of gold nanoparticles depends on both, precursor concentration, and dose rate. This dependency is exploited to probe the electron beam-induced shift in Gibbs free energy landscape by analyzing critical radii of gold nanoparticles.<br
Keywords: critical radius; gold nanoparticles; kinetic modelling; liquid-phase transmission electron microscopy; oxidative etching; particle growth; radiolysis

Raman 2D-Band Splitting in Graphene: Theory and Experiment - Frank, Otakar; Mohr, Marcel; Maultzsch, Janina; Thomsen, Christian; Riaz, Ibtsam; Jalil, Rashid; Novoselov, Kostya S.; Tsoukleri, Georgia; Parthenios, John; Papagelis, Konstantinos; Kavan, Ladislav; Galiotis, Costas (Acs Nano, 2011)
We present a systematic experimental and theoretical study of the two phonon (2D) Raman scattering in graphene undar uniaxial tension, The external perturbation unveils that the 2D mode excited with 785 nm has a complex,line-shape mainly due to the contribution of two distinct double resonance scattering processes (inner and outer) in the Raman signal. The splitting depends on the direction of the applied strain and the polarization of the incident light The results give new insight into the nature of the 2D band and have. significant implications for the use of graphene as reinforcement In composites since the 2D mode is crucial to assess how effectively graphene uptakes an applied stress or strain
Keywords: graphene; Raman spectroscopy; tensile strain; 2D mode

Raman-active modes in graphene nanoribbons - Gillen, Roland; Mohr, Marcel; Maultzsch, Janina (WILEY-V C H VERLAG GMBH, 2010)
We present the symmetry representations of the Raman-active modes in graphene nanoribbons (GNRs) with pure armchair (AGNR) or zigzag edges (ZGNR) and explain the representations in terms of fundamental modes and overtones in the Gamma-point phonon spectrum of GNRs. This provides possible means to assign Raman peaks in measured polarization-dependent spectra. We show simulated Raman spectra in zz-polarization for a 7-AGNR and a 4-ZGNR. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Keywords: graphene; phonons; symmetry; Raman

Raman‐active modes in graphene nanoribbons - Gillen, Roland; Mohr, Marcel; Maultzsch, Janina (physica status solidi (b), 2010)

Raman bands of nano-graphene flakes on carbon nanotubes after oxidation - Laudenbach, Jan; Gebhardt, Benjamin; Syrgiannis, Zois; Hauke, Frank; Hirsch, Andreas; Maultzsch, Janina (physica status solidi (b), 2013)
We present the Raman bands of nano-graphene flakes (NG flakes) produced by oxidation of single-walled carbon nanotubes. These bands overlap with the defect-induced Raman modes of carbon nanotubes. This can lead to an overestimation of the defect density in the nanotubes. Here we analyze the line shape and the dispersion of this superimposing Raman band of NG flakes. Furthermore, we investigate the predicted Raman band of NG flakes next to the high-energy Raman modes (G- and G+) of the nanotubes. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Raman characterization of boron-doped multiwalled carbon nanotubes - Maultzsch, Janina; et al. (Applied Physics Letters, 2002)
We present first- and second-order Raman spectra of boron-doped multiwalled carbon nanotubes. The Raman intensities are analyzed as a function of the nominal boron concentration. The intensities of both the D mode and the high-energy mode in the first-order spectra increase with increasing boron concentration, if normalized with respect to a second-order mode. We interpret this result as an indication that the high-energy mode in carbon nanotubes is defect-induced in a similar way as the D mode. Based on this result, we provide a preliminary quantitative relation between the boron concentration and the Raman intensity ratios. (C) 2002 American Institute of Physics.

Raman excitation profiles of 3C-, 4H-, 6H-, 15R- and 21R-SiC - Hundhausen, Martin; Ley, Lothar; et al. (Materials Science Forum, 2003)
The excitation energy dependence of the Raman scattering intensities of longitudinal modes of various SiC-polytypes was measured in the UV-spectral range for excitation energies tuned between 3.8eV and 5eV. The Raman scattering intensity of the unfolded longitudinal optical mode shows a pronounced decrease for all polytypes in the UV-spectral range, except for 3C-SiC. It is shown, that the position of the decrease in the intensity is related with the bandgap of the polytype under consideration. We explain this decreasing scattering intensity by a destructive interference of a resonant and an non-resonant contribution to the Raman scattering cross-section.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.IAP.exphys.ramane
Keywords: Excitation Profiles; Hexagonality; Polytypes; Raman Spectroscopy

Raman intensities of the first optical transitions in carbon nanotubes - Telg, Hagen; Maultzsch, Janina; Reich, Stephanie; Hennrich, Frank; Thomsen, Christian (physica status solidi (b), 2006)
We performed resonant Raman spectroscopy on the lowest optical transition E11S of separated single-walled carbon nanotubes by studying the radial-breathing mode (RBM) spectra for excitation energies between 1.15 and 1.48 eV. We were able to extend the experimental Kataura plot to these energies by adding the E11S transition energies of 11 nanotube chiralities. We discuss also the relative Raman intensities; they are more similar for different family index v than those of the corresponding transitions of the E-22(S) [1] (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Raman scattering in carbon nanotubes revisited - Maultzsch, Janina; et al. (Physical Review B, 2002)
We explain the origin of the high-energy mode in the first-order Raman spectra of single-walled carbon nanotubes by double-resonant scattering. Following this interpretation, we calculate the multiple-peak structure as found in Raman experiments. The highest peak is above the graphite Gamma-point frequency; its amplitude is larger than that of the second peak. We derive positive and negative frequency shifts as a function of excitation energy, which we observe experimentally as well. We predict a difference in frequency and shape of the high-energy mode in Stokes and anti-Stokes scattering.

Raman scttering in polycrystalline 3C-SiC: influence of stacking faults - Hundhausen, Martin; Ley, Lothar; et al. (Physical Review B, 1998)
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.IAP.exphys.ramans

Raman spectra of epitaxial graphene on SiC(0001) - Röhrl, Jonas; Hundhausen, Martin; Emtsev, Konstantin; Seyller, Thomas; Graupner, Ralf; Ley, Lothar (Applied Physics Letters, 2008)
We present Raman spectra of epitaxial graphene layers grown on 63×63 reconstructed silicon carbide surfaces during annealing at elevated temperature. In contrast to exfoliated graphene a significant phonon hardening is observed. We ascribe that phonon hardening to a minor part to the known electron transfer from the substrate to the epitaxial layer, and mainly to mechanical strain that builds up when the sample is cooled down after annealing. Due to the larger thermal expansion coefficient of silicon carbide compared to the in-plane expansion coefficient of graphite this strain is compressive at room temperature. © 2008 American Institute of Physics.
UnivIS-Import:2015-03-09:Pub.2008.nat.dphy.IAP.exphys.ramans

Raman spectroscopy and electrical transport studies of free-standing epitaxial graphene: Evidence of an AB-stacked bilayer - Shivaraman, Shriram; Jobst, Johannes; Waldmann, Daniel; Weber, Heiko B.; Spencer, Michael (Physical Review B, 2013)
We fabricate free-standing graphene structures from epitaxial graphene on silicon carbide using a photoelectrochemical (PEC) etching process. A combination of Raman spectroscopy and magnetotransport measurements was used to investigate multiterminal devices in various geometries. From the analysis of Raman data and Shubnikov-de Haas oscillations, we conclude that the buffer layer is converted into a graphene layer and, thus, monolayer graphene on SiC gets converted to a free-standing AB-stacked bilayer. The bilayer exhibits inversion-symmetry breaking because of differential doping between the layers. Additionally, lateral inhomogeneities exist in the form of domains with nonuniform mobility. The same PEC process on a pure buffer layer, however, does not yield monolayer graphene.

Raman spectroscopy for quality control and process optimization of chalcopyrite thin films and devices - Hock, Rainer; et al. (ELSEVIER SCIENCE SA, 2007)
We will demonstrate in this paper that Raman scattering of visible light is a versatile tool both for research and industrial process monitoring of thin chalcopyrite films for solar cells. Thin films of Cu(In, Ga)(S,Se)(2) (CIGSSe) are produced by rapid thermal processing of stacked elemental Cu-In-Ga-Se layers. The Raman investigations are accompanied by grazing incidence X-ray diffraction (GI-XRD) and X-ray florescence (XRF) measurements. GI-XRD measurements confirm that the films show a two-fold elemental gradient: a sulfur gradient from the top and a Ga gradient from the CIGSSe/Mo interface. By Rietveld refinement of the GI-XRD spectra of the surface-near (similar to 100nm) ratio of sulfur to selenium can be obtained which corresponds well to the intensity ratio of the two Raman Al modes of CuInS2 and CuInSe2. The asymmetric line shape of both XRD diffractograms and Raman spectra is attributed to the sulfur gradient. In addition we show that the intensity ratio of the satellite Raman B and E modes shows a correlation with the Cu to In+ Ga ratio obtained by XRF. (C) 2006 Elsevier B.V. All rights reserved.
Keywords: CIS; chalcopyrites; thin films; Raman; X-ray diffraction

Raman spectroscopy of intercalated and misfit layer nanotubes - Staiger, Matthias; Bacic, Vladimir; Gillen, Roland; Radovsky, Gal; Gartsmann, Konstantin; Tenne, Reshef; Heine, Thomas; Maultzsch, Janina; Thomsen, Christian (Physical Review B, 2016)
We present Raman spectra of misfit layer (PbS)(1.14)NbS2 nanotubes and lead intercalated NbS2 nanotubes. They represent interesting model systems to investigate the nature of interlayer interaction in layered materials. A direct correlation to the Raman modes of the parent 2H-NbS2 compound exists, but some modes are seen drastically upshifted in frequency in the misfit layer and intercalated compound while others remain almost unchanged. On the basis of the Raman spectroscopic investigations and with the help of supporting calculations we examine different interlayer bonding mechanisms and contribute to the discussion as to why these frequency shifts occu

Raman Spectroscopy of Lithographically Defined Graphene Nanoribbons - Influence of Size and Defects - Kampmann, Felix; Scheuschner, Nils; Terres, Bernat; Joerger, Danny; Stampfer, Christoph; Maultzsch, Janina (Annalen Der Physik, 2017)

Raman Spectroscopy of Lithographically Patterned Graphene Nanoribbons - Ryu, Sunmin; Maultzsch, Janina; Han, Melinda Y.; Kim, Philip; Brus, Louis E. (Acs Nano, 2011)
Nanometer-scale graphene objects are attracting much research interest because of newly emerging properties originating from quantum confinement effects. We present Raman spectroscopy studies of graphene nanoribbons (GNRs), which are known to have nonzero electronic bandgap. GNRs of width ranging from 15 to 100 nm have been prepared by e-beam lithographic patterning of mechanically exfoliated graphene followed by oxygen plasma etching. Raman spectra of narrow GNRs can be characterized by an upshifted G band and a prominent disorder-related D band originating from scattering at the ribbon edges. The D-to-G band intensity ratio generally Increases with decreasing ribbon width. However, its decrease in width of <25 nm, partly attributed to amorphization at the edges, provides a valuable experimental estimate on D mode relaxation length of <5 nm. The upshift in the G band of the narrowest GNRs can be attributed to confinement effect or chemical doping by functional groups on the GNR edges. Notably, GNRs are much more susceptible to photothermal effects resulting in reversible hole doping caused by atmospheric oxygen than bulk graphene sheets. Finally we show that the 2D band is still a reliable marker in determining the number of layers of GNRs despite its significant broadening for very narrow GNRs.
Keywords: graphene nanoribbons; Raman spectroscopy; chemical doping; defects; phonon confinement effects

Raman spectroscopy of nondispersive intermediate frequency modes and their overtones in carbon nanotubes - Tyborski, Christoph; Herziger, Felix; Maultzsch, Janina (physica status solidi (b), 2015)
Keywords: carbon nanotubes; IFM; overtones; Raman spectroscopy

Raman spectroscopy of pentyl-functionalized carbon nanotubes - Müller, Matthias; Maultzsch, Janina; Wunderlich, David; Hirsch, Andreas; Thomsen, Christian (Physica Status Solidi-Rapid Research Letters, 2007)
We present Raman scattering on carbon nanotubes functionalized with pentyl groups. Studies of the intermediate frequency region and the C-H bond stretching signal along with the D mode show evidence of the addition reaction by Raman spectroscopy. From the resonance profiles of the radial breathing mode (RBM) we assign the chiral indices of the tubes and study the influence of the functionalization on the transition energies, shift and intensity of the RBM signal. The largest effect we observe is on the Raman intensity of the radial breathing mode. A figure is presented. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Raman spectroscopy of single wall carbon nanotubes functionalized with terpyridine-ruthenium complexes - Mueller, M.; Papagelis, K.; Maultzsch, Janina; Stefopoulos, A. A.; Pefkianakis, E. K.; Andreopoulou, A. K.; Kallitsis, J. K.; Thomsen, Christian (physica status solidi (b), 2009)

Raman Spectroscopy of Suspended MoS2 - O'Brien, Maria; Scheuschner, Nils; Maultzsch, Janina; Duesberg, Georg S.; Mcevoy, Niall (physica status solidi (b), 2017)
Keywords: MoS; Raman spectroscopy; suspended devices; transition metal dichalcogenides

Raman spectroscopy on chemically functionalized carbon nanotubes - Mueller, Matthias; Maultzsch, Janina; Wunderlich, David; Hirsch, Andreas; Thomsen, Christian (physica status solidi (b), 2007)
We present Raman spectroscopy on carbon nanotubes, functionalized with alkyl groups to different degrees and with different addition reactions. We observe effects in particular on the intensities of the radial breathing mode (RBM). From the RBM we can assign the diameter and chiral indices of the tubes and study the influence of functionalization on different tubes, their transition energies, Raman shifts and RBM intensities. We observe a diameter dependence of the chemical reaction under certain reaction conditions. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

Random telegraphic noise in large area a-Si:H/a:Si1􀀀xNx double barrier structures - Ley, Lothar; Hundhausen, Martin; et al. (Journal of Non-Crystalline Solids, 1989)
Random telegraphic noise (RTN) with an amplitude of about 1% has been observed in the current through a-Si:H/a-Si1-xNx:H double barrier structures. The area of the devices, 0.25 mm2, is five orders of magnitude larger than the area of the devices where RTN has previously been observed. The power spectra of the noise can be fitted by a superposition of Lorentzians from which average switching times are deduced. The switching times are thermally activated with activation energies between 0.2 and 0.6 eV and they depend on bias voltage. Assuming that the current through these structures is confined to microchannels of cross section area < 1μm2 the RTN and its characteristics are explained by the random charging and discharging of individual traps placed in the vicinity of the current channel.
UnivIS-Import:2015-03-05:Pub.1989.nat.dphy.IAP.exphys.random

Rapid fabrication and interface structure of highly faceted epitaxial Ni-Au solid solution nanoparticles on sapphire - Herre, Patrick; Will, Johannes; Dierner, Martin; Wang, Dong; Yokosawa, Tadahiro; Zech, Tobias; Wu, Mingjian; Przybilla, Thomas; Romeis, Stefan; Unruh, Tobias; Peukert, Wolfgang; Spiecker, Erdmann (Acta Materialia, 2021)
Supersaturated Ni-Au solid solution particles were synthesized by rapid solid-state dewetting of bilayer thin films deposited onto c-plane sapphire single-crystals. Rapid thermal annealing above the miscibility gap of the Ni-Au system followed by quenching to room temperature resulted in textured and faceted submicron-sized particles as a function of alloying content in the range of 0–28 at% Au. Morphologically, the observed kinetic crystal shapes are confined by close-packed planes; in addition, high-index facets are identified as a function of alloying content by TEM cross-sectioning and equilibrium crystal shape simulations. All samples exhibit a distinct 〈111〉 out-of-plane as well as in-plane texture along densely packed directions. Lattice parameters extracted from independent orthogonal X-ray and electron diffraction techniques prove the formation of a solid solution without tetragonal distortion imposed by the sapphire substrate. At the particle-substrate interface of highly alloyed particles segregation of Au atoms as well as dislocations in stand-off position are found. These observations are in-line with a semi-coherent interface, where Au segregation is triggered by the reduction of the overall strain energy due to: (i) a lower shear modulus on the particle side of the interface, (ii) the shifting of misfit dislocations in stand-off position further away from the stiffer substrate and (iii) a reduction of intrinsic misfit dislocation strain energy on the tensile side. In addition, the mechanical properties of pure and alloyed particles were characterized by in situ compression experiments in the SEM. Typical force-displacement data of defect-free single-crystals were obtained, reaching the theoretical strength of Ni for particles smaller than 400 nm. Alloying changes the mechanical response from an intermittent and discrete plastic flow behavior into a homogeneous deformation regime at large compressive strain.
CRIS-Team Scopus Importer:2021-10-22
Keywords: Solid-state dewetting; Orientation relationship; Interface segregation; Scanning electron microscopy; Compression test

Rat airway smooth muscle cell during actin modulation: rheology and glassy dynamics - Laudadio, Rachel E.; Millet, Emil J.; Fabry, Ben; An, Steven S.; Butler, James P.; Fredberg, Jeffrey (American Journal of Physiology-Cell Physiology, 2005)

Reaching the resolved tunnel regime for a femtosecond oscillator driven field emission electron source - Hommelhoff, Peter; Kealhofer, C.; Kasevich, M. A. (Laser Physics, 2009)
We report on electron emission from tungsten tips with the help of 800 nm-8 fs laser pulses from a Ti:sapphire laser oscillator. We have measured autocorrelation traces of the exciting laser pulse in the photoelectron current, which allows a measurement of the non-linearity as a function of DC voltage applied to the tip. These data are well described by a numerical integration of the one-dimensional Schrödinger equation. The simulation shows us that electron emission resolves the electric field structure of the driving laser pulse, a regime which is currently an extremely fruitful area of research with atoms in the gas phase. For an 8 fs laser pulse with the correct carrier-envelope phase setting the emission duration is as short as 800 nm. © 2009 Pleiades Publishing, Ltd.
UnivIS-Import:2015-03-09:Pub.2009.nat.dphy.IAP.exphys.reachi

REACTION OF ULTRATHIN CO LAYERS WITH SI(111) AND SI(100) SURFACES - Fauster, Thomas; et al. (Surface Science, 1994)
The initial stages of ultrathin epitaxial COSi2 formation on Si(111) and Si(100) surfaces were studied by core-level photoelectron spectroscopy with synchrotron radiation. A high surface sensitivity was obtained for electrons with kinetic energy of approximately 30 eV, where the mean free path is estimated to be less than 2.5 angstrom. Our Si2p data show that on Si(111) a part of the Co atoms are in a CoSi2-like environment at room temperature, the rest forms a Co-Si solid solution. For a complete reaction, annealing to approximately 350-degrees-C is needed. In this way we obtain the Co-rich CoSi2(111)-C surface termination free of pinholes which is stable up to at least 460-degrees-C. After annealing to approximately 550-degrees-C the Si-rich CoSi2(111)-S surface termination containing some pinholes appears. Contrary to the Si(111), Co deposition on Si(100) surface at room temperature does not lead to CoSi2 but only to a Co-Si solid solution. For coverages below 2.6 ML heating to approximately 460-degrees-C is necessary to obtain CoSi2, whereas for higher coverages heating to approximately 300-degrees-C is sufficient. This effect is attributed to a change of the Co diffusion mechanism at room temperature. The CoSi2 films on the Si(100) surface produced in this way always contain pinholes.

Real-time evaluation of thin film drying kinetics using an advanced, multi-probe optical setup - Güldal, Nusret Sena; Kassar, Thaer; Berlinghof, Marvin; Ameri, Tayebeh; Osvet, Andres; Pacios, Roberto; Li Destri, Giovanni; Unruh, Tobias; Brabec, Christoph (Journal of Materials Chemistry C, 2016)
Solution-processed organic photovoltaic devices are advantageous due to their low-cost large area manufacturing techniques, such as slot-die coating, gravure printing and roll-to-roll coating. The final microstructure of a polymer:fullerene bulk-heterojunction (BHJ) film is a fine interplay between solution thermodynamics (e.g. solubility, miscibility...) and kinetics (e.g. solvent evaporation, polymer ordering, phase separation...) during the drying process. In order to design better performing organic photovoltaic devices, gaining knowledge over the drying properties of polymer:fullerene thin films is essential. A novel in situ thin film drying characterization chamber, equipped with white-light reflectometry, laser light scattering and photoluminescence, is presented in combination with grazing-incidence X-ray diffraction on two different polymer:fullerene bulk heterojunctions based on poly-(3-hexylthiophene-2,5-diyl) (P3HT) and polythieno[3,2b]thiophene-diketopyrrolopyrrole-co-thiophene (DPP-TT-T) polymers. With photoluminescence applied for the first time as an in situ method for such drying studies, these single-chamber measurements track the fine interplay between thermodynamics and kinetics of thin film drying and provide invaluable information on solution behavior and microstructure formation.
Keywords: Engineering controlled terms: Coatings; Drying; Fullerenes; Heterojunctions; Kinetics; Light scattering; Microstructure; Phase separation; Photoluminescence; Plastic coatings; Polymer films; Polymers; Rolls (machine components); Solubility; Thermodynamics; Thiophene; X ray diffraction Bulk heterojunction (BHJ); Grazing incidence X-ray diffraction; Manufacturing techniques; Microstructure formation; Organic photovoltaic devices; Poly(3-hexylthiophene-2; 5-diyl); Solution thermodynamics; Thermodynamics and kinetics Engineering main heading: Thin films

Real-Time Investigation of Intercalation and Structure Evolution in Printed Polymer:Fullerene Bulk Heterojunction Thin Films - Kassar, Thaer; Güldal, Nusret Sena; Berlinghof, Marvin; Ameri, Tayebeh; Kratzer, Andreas; Schroeder, Bob C.; Li Destri, Giovanni; Hirsch, Andreas; Heeney, Martin; Mcculloch, Iain; Brabec, Christoph; Unruh, Tobias (Advanced Energy Materials, 2016)
The complex intermixing morphology is critical for the performance of the nanostructured polymer:fullerene bulk heterojunction (BHJ) solar cells. Here, time resolved in situ grazing incidence X-ray diffraction and grazing incidence small angle X-ray scattering are used to track the structure formation of BHJ thin films formed from the donor polymer poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) with different fullerene derivative acceptors. The formation of stable bimolecular crystals through the intercalation of fullerene molecules between the side chains of polymer crystallites is investigated. Such systems exhibit more efficient exciton dissociation but lower photo-conductance and faster decay of charges. On the basis of the experimental observations, intercalation obviously takes place before or with the formation of the crystalline polymer domains. It results in more stable structures whose volume remains constant upon further drying. Three distinct periods of drying are observed and the formation of unidimensional fullerene channels along the π-stacking direction of polymer crystallites is confirmed.
Keywords: fullerenes; grazing incidence diffraction; intercalation dynamics; organic solar cells; thin films

Real-time investigations of selenization reactions in the system Cu-In-Al-Se - Hock, Rainer; et al. (physica status solidi (a), 2006)
In this article we present results of a detailed study of selenization reactions in the quaternary system Cu-In-Al-Se and of the binary subsystem aluminum-selenium. The investigation of solid-state reactions involved in the formation of the compound semiconductor Cu(In,Al)Se-2 was performed using real-time X-ray diffraction (XRD) with a time resolution of 22.5 s while annealing an elemental layer stack of the metals covered with selenium. A temperature-resolved phase analysis shows that the formation of the semiconductor takes place via metal-selenides. Ex-situ XRD measurements of the processed thin films show a phase segregation concerning the aluminum content of the formed chalcopyrite. Subsequent Rietveld-refinement of real-time measurements reveals a formation reaction of the quaternary semiconductor Cu(In,AI)Se-2 from the gamma-In2Se3 related crystal structure of (Al,In)(2)Se-3 and Cu2Se as educts. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Real-time investigations on the formation of Cu(In,Ga)(S,Se)(2) while annealing Cu-In-Ga precursors with different sulphur-selenium mixtures - Hölzing, Astrid; Schurr, R.; Yoo, Hye Sun; Wibowo, Rachmat Adhi; Lechner, R.; Palm, J.; Jost, S.; Hock, Rainer (ELSEVIER SCIENCE SA, 2013)
The variation of anions yields a combined crystallisation path due to metal sulphoselenides with chalcogen exchange reactions upon heating, i.e. copper sulphoselenides act as a chalcogen buffer and afford substitution of S with Se during annealing. The extended chalcogen substitutions occur due to the complete solid solution of S and Se in Cu(S,Se) and Cu2-x(S,Se). On the contrary, different reaction paths are found for the cations. Although the metals show a good intermixture within the intermetallic alloys featuring In-Ga substitutions, no formation of a mixed or ternary (In,Ga)-chalcogenide is observed. This can be attributed to a narrow solid solution range of the (In,Ga)-chalcogenides. As a consequence the preceding formation of an In-rich and the delayed crystallisation of a Ga-rich chalcopyrite cause a vertical elemental gradient with Ga-accumulation near the back electrode. An interdiffusion of the In-and Ga-rich chalcopyrites is observed for increasing annealing time and temperature. The presented study is focused on quantification of the phase evolution, variation of lattice parameter and diffusion of elements as obtained by Rietveld refinements. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: Cu(In; Ga)(S; Se)(2); Chalcopyrite; Chalcogenisation; Sulphoselenisation; Formation reaction; Growth model

Real-time investigations on the formation of CuInSe2 thin film solar cell absorbers from electrodeposited precursors - Hock, Rainer; et al. (Solar Energy Materials and Solar Cells, 2007)
In this article, we present results of a detailed real-time X-ray diffraction (XRD) study on the formation of CuInSe2 from electroplated precursors. The solid-state reactions observed during the selenisation of three different types of precursors are presented. The first type of precursors (I) consists of the nanocrystalline phases Cu2-xSe and InSe at room temperature, which react to CuInSe2 starting at 470 K. The second type of precursor (II) shows an inhibited CuInSe2 formation out of the initial phases Cu2-xSe and gamma-In2Se3 starting at 400 K. The third precursor type (III) shows completely different selenisation behaviour. Starting from the intermetallic compound Cul(11)In(9) and amorphous selenium, the formation of the binary selenides In4Se3 and CuSe is observed after the melting point of selenium at 494 K. After selenium transfer reactions, the compound semiconductor CuInSe2 is formed out of Cu2-xSe and InSe. This type (III) reaction path is well known for the selenisation of SEL precursors (stacked elemental layers of sputtered copper and indium and thermally evaporated selenium). (c) 2007 Elsevier B.V. All rights reserved.
Keywords: CuInSe2; chalcopyrites; thin films; real-time X-ray diffraction; electrodeposition

Real-Time Investigations on the Formation of CuIn(S,Se)(2) While Annealing Precursors With Varying Sulfur Content - Hölzing, Astrid; Schurr, Roland; Jost, Stefan; Palm, Jörg; Deseler, Klaus; Hock, Rainer; Wellmann, Peter (Materials Research Society Symposium - Proceedings, 2010)
CIS based chalcopyrite absorber materials are usually substituted in the cation and anion lattice to yield mixed pentanary crystals with the general composition Cu(In,Ga)(Se,S)(2) to achieve an optimised adaptation of the semiconductor bandgap to the terrestrial solar spectrum. Real-time investigations during the annealing of stacked elemental layers (SEL) of sputtered metals Cu and In and evaporated chalcogens S and Se with varying ratios were performed by angle-dispersive time-resolved XRD (X-ray diffraction) measurements. After qualitative phase analysis the measured powder diagrams were quantitatively analysed by the Rietveld method, the phases formed determined and their reaction kinetics obtained. Ternary indium and copper sulfoselenides form by the sulfoselenisation of the intermetallic alloy yielding different educts for the chalcopyrite formation with varying sulfur content. For S/(S+Se) >= 0.5 the formation of the chalcopyrite CuIn(S,Se)(2) is similar to the crystallisation path of CuInS(2). With increasing amount of selenium (S/(S+Se) = 0.25) different ternary sulfoselenides contribute to the semiconductor formation. For small amounts of sulfur, i.e. S/(S+Se) <= 0.1, the chalcopyrite crystallisation proceeds comparable to the one observed for sulfur-free Cu-In-Se precursors. The formation of CuIn(S,Se)(2) is accelerated and proceeds mainly after the peritectic decomposition of Cu(S,Se) to Cu(2)(S,Se). The sulfur content determines the crystallisation temperature of the semiconductor because Cu(S,Se) decomposes at higher temperatures with increasing sulfur. Upon heating S Se exchange reactions take place in the Cu-S-Se and Cu-In-S-Se syste
Keywords: phase transformation; mixture; thin film

Real-time investigations on the formation reactions during annealing of sulfurized Cu-Sn precursors - Schurr, R.; Hölzing, Astrid; Hock, Rainer (ELSEVIER SCIENCE SA, 2011)
We report on results of time-resolved and angle-dispersive XRD experiments during annealing comparing the formation reactions in sulfurized Cu-Sn precursors prepared by different deposition techniques. (C) 2010 Elsevier B.V. All rights reserved.
Keywords: Cu2ZnSnS4; CZTS; Cu2SnS3; Cu-Sn-S; Thin films; Real-time XRD; Formation reaction

Real-Time Study on Structure Formation and the Intercalation Process of Polymer: Fullerene Bulk Heterojunction Thin Films - Kassar, Thaer; Berlinghof, Marvin; Güldal, Nusret Sena; Schmutzler, Tilo; Zontone, Federico; Brandl, Marco; Metwalli, Ezzeldin; Will, Johannes; Li, Ning; Ameri, Tayebeh; Brabec, Christoph; Unruh, Tobias (Solar RRL, 2020)
Fullerene intercalation between the side chains of conjugated polymers has a detrimental impact on both charge separation and charge transport processes in bulk heterojunction (BHJ) organic photovoltaic cells (OPVs). In situ grazing incidence X-ray scattering experiments allow to characterize the structure formation, drying kinetics, and intercalation in blends of phenyl-c61-butyric acid methyl ester (PC60BM) and poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) named (pBTTT-C14) from their 1,2-orthodichlorobenzene (oDCB) solutions with different volume fractions of dodecanoic acid methyl ester (Me12) as a solvent additive. The structure formation process during evaporation of the solvent:additive mixture can be described by five periods, which are correlated to a multistep contraction of the lamellar stacking of the bimolecular crystals. The onset of crystallization is delayed by increasing the additive volume fraction in the coating solution leading to a promoted crystallinity. A conclusive picture of fullerene intercalation and additive-tuned structural evolution during the drying of thin films of the polymer:fullerene BHJ blends will be presented.
CRIS-Team WoS Importer:2020-02-04

Real-time XRD investigations during the formation of Cu(IngGa)Se-2 Thin films - Hock, Rainer; et al. (WILEY-V C H VERLAG GMBH, 2006)
Knowledge of the solid-state reactions providing the synthesis of the absorber material Cu(IngGa)Se-2 well below its melting point is an essential prerequisite for the further optimization of the technologically relevant production processes. Therefore, powder XRD has been applied as nondestructive tool to follow chemical solide-state reactions in-situ. Subsequent Rietveld refinement provides the quantitative phase evolution time.
Keywords: phase transitions; solid-state reactions; thin-film solar cell; X-ray diffraction

Recent experimental results and future directions of the DLA single grating project - McNeur, Joshua; Hammer, Jonas; Li, Ang; Tafel, Alexander; Hommelhoff, Peter; Tafel, Alexander; Hammer, Jakob (16th Advanced Accelerator Concepts Workshop, AAC 2014, 2016)
The recent demonstration of Dielectric Laser Acceleration of subrelativistic electrons is reviewed. In this experiment, a Ti:Sapphire laser is incident upon a fused silica grating, exciting fields that accelerated 28 keV electrons with a 25 MeV/m acceleration gradient. Upgrades and future directions of this DLA project are discussed.

Recombination of geminate pairs in As2Se3 single crystals - Ristein, Jürgen; et al. (Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties, 1986)
UnivIS-Import:2015-03-05:Pub.1986.nat.dphy.IAP.exphys.recomb

Reconstruction of Nanoscale Near Fields by Attosecond Streaking - Schoetz, Johannes; Foerg, Benjamin; Förster, Michael; Okell, William A.; Stockman, Mark I.; Krausz, Ferenc; Hommelhoff, Peter; Kling, Matthias Friedrich (IEEE Journal of Selected Topics in Quantum Electronics, 2017)
Recent advances in attosecond science in combination with the well-established techniques of nanofabrication have led to the new research field of attosecond nanophysics. One central goal is the characterization and manipulation of electromagnetic fields on the attosecond and nanometer scale. This has so far remained challenging both theoretically and experimentally. One major obstacle is the inhomogeneity of the electric fields. We present a general model below, which allows the description of attosecond streaking in near fields. It allows the classification into different regimes as well as the reconstruction of the electric fields at the surface. In addition, we discuss the case of parallel polarization of the streaking fields to the surface, which has so far not been considered for attosecond streaking from metallic surfaces. Finally, we review recent measurements of the electric field and response function of a gold nanotaper. Our results are highly relevant for future attosecond streaking experiments in inhomogeneous fields.
Keywords: nanotechnology; near fields; Ultrafast optics

Recovery of surface conductivity of H-terminated diamond after thermal annealing in vacuum - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review B, 2004)
A unique feature of diamond among other semiconductors is the formation of a high conductive p-type layer which is usually obtained after hydrogen-termination of the surface. It is generally accepted that the appearance of surface conductivity (SC) requires the presence of atmospheric adsorbates. We present a combination of conductivity and spectroscopic measurements dealing with the loss and the formation of SC as a function of annealing in vacuum (temperatures 60-900°C) and exposure to different atmospheres. For temperatures below 190°C in vacuum the SC decreases by more than five orders of magnitude and comes back to its initial value when the sample is exposed to air. After annealing between 250 and 700°C exposure to normal atmospheric conditions is no longer sufficient to recover SC, although the H termination is preserved. In this state the SC is fully restored upon air exposure after the surface has been exposed to ozone or oxygen radicals. We propose a model where oxygen-related sites are catalytically involved in the transfer-doping mechanism such that the rate of electron transfer from the diamond into solvated adsorbates is enhanced.
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.IAP.exphys.recove

"Recurrence Resonance" in Three-Neuron Motifs - Krauß, Patrick; Prebeck, Karin; Schilling, Achim; Metzner, Claus (Frontiers in Computational Neuroscience, 2019)
Stochastic Resonance (SR) and Coherence Resonance (CR) are non-linear phenomena, in which an optimal amount of noise maximizes an objective function, such as the sensitivity for weak signals in SR, or the coherence of stochastic oscillations in CR. Here, we demonstrate a related phenomenon, which we call "Recurrence Resonance" (RR): noise can also improve the information flux in recurrent neural networks. In particular, we show for the case of three-neuron motifs with ternary connection strengths that the mutual information between successive network states can be maximized by adding a suitable amount of noise to the neuron inputs. This striking result suggests that noise in the brain may not be a problem that needs to be suppressed, but indeed a resource that is dynamically regulated in order to optimize information processing.
CRIS-Team WoS Importer:2019-10-01

Reduced Grey Brookite for Noble Metal Free Photocatalytic H2 Evolution - Wierzbicka, Ewa; Altomare, Marco; Wu, Mingjian; Liu, Ning; Yokosawa, Tadahiro; Fehn, Dominik; Qin, Shanshan; Meyer, Karsten; Unruh, Tobias; Spiecker, Erdmann; Palmisano, Leonardo; Bellardita, Marianna; et al. (Journal of Materials Chemistry A, 2020)
Herein we introduce for the first time a reduced “grey” brookite TiO2 photocatalyst, produced by thermal hydrogenation of brookite nanoparticles, that shows a remarkable noble metal free photocatalytic H2 evolution. Its activity is substantially higher than that of other TiO2 polymorphs, i.e. anatase or rutile, comparably sized and activated by hydrogenation under optimized conditions. Along with brookite powders, an oriented brookite single crystal was investigated as a defined surface to confirm the effects of the hydrogenation treatment. By a combination of Electron paramagnetic resonance (EPR), electron and X-ray characterization techniques applied to the powders and single crystal, we find that hydrogenation forms in brookite a defective crystalline surface layer rich in Ti3+ states. Amorphization effects, i.e. forming the so called “amorphous shell” as reported in previous work for black anatase TiO2, were not detected. Overall, we provide experimental evidence that hydrogenation forms in brookite a surface strained zone with point defects that are mediators for electron transfer to H2O, leading to a significantly enhanced noble metal free photocatalytic H2 evolution in comparison to anatase.<br

Reduction of implantation-induced point defects by germanium ions in n-type 4H-SiC - Sledziewski, Tomasz; Ellrott, Günter; Rösch, Willi; Weber, Heiko B.; Krieger, Michael (Materials Science Forum, 2015)
We have investigated the electrical properties of germanium-implanted n-type 4H-SiC epitaxial layers. Deep level transient spectroscopy (DLTS) was employed in order to study the influence of germanium ions on implantation-induced point defects. In particular, we observe a decrease of the concentration of Z1/2 defect with increasing dose of implanted germanium.
UnivIS-Import:2017-12-18:Pub.2015.nat.dphy.IAP.LAP.reduct
Keywords: 4H-SiC; DLTS; Ion implantation; Point defects

Reductive diazotation of carbon nanotubes: an experimental and theoretical selectivity study - Schirowski, Milan; Tyborski, Christoph; Maultzsch, Janina; Hauke, Frank; Hirsch, Andreas; Goclon, Jakub (Chemical Science, 2019)
The reaction of neutral single-walled carbon nanotubes (SWCNTs) with diazonium salts proceeds with a high selectivity towards metallic carbon nanotube species; this reaction is well-understood and the mechanism has been elucidated. In the present joint theoretical and experimental study, we investigate the reaction of negatively charged SWCNTs -carbon nanotubides -with diazonium salts. Our density functional theory calculations predict a stronger binding of the aryl diazonium cations to charged metallic SWCNTs species and therefore lead to a preferential addend binding in the course of the reaction. The Raman resonance profile analysis on the reductive arylation of carbon nanotubides obtained by the solid state intercalation approach with potassium in varying concentrations confirms the predicted preferred functionalization of metallic carbon nanotubes. Furthermore, we were also able to show that the selectivity for metallic SWCNT species could be further increased when low potassium concentrations (K : C < 1 : 200) are used for an initial selective charging of the metallic species. Further insights into the nature of the bound addends were obtained by coupled thermogravimetric analysis of the functionalized samples.
CRIS-Team WoS Importer:2019-02-21

Refining short-range order parameters from the three-dimensional diffuse scattering in single-crystal electron diffraction data - Poppe, Romy; Roth, Nikolaj; Neder, Reinhard; Palatinus, Lukas; Iversen, Bo Brummerstedt; Hadermann, Joke (IUCrJ, 2024)
Our study compares short-range order parameters refined from the diffuse scattering in single-crystal X-ray and single-crystal electron diffraction data. Nb0.84CoSb was chosen as a reference material. The correlations between neighbouring vacancies and the displacements of Sb and Co atoms were refined from the diffuse scattering using a Monte Carlo refinement in DISCUS. The difference between the Sb and Co displacements refined from the diffuse scattering and the Sb and Co displacements refined from the Bragg reflections in single-crystal X-ray diffraction data is 0.012 (7) Å for the refinement on diffuse scattering in single-crystal X-ray diffraction data and 0.03 (2) Å for the refinement on the diffuse scattering in single-crystal electron diffraction data. As electron diffraction requires much smaller crystals than X-ray diffraction, this opens up the possibility of refining short-range order parameters in many technologically relevant materials for which no crystals large enough for single-crystal X-ray diffraction are available.
CRIS-Team Scopus Importer:2024-01-26
Keywords: 3D difference pair distribution functions; 3D electron diffraction; 3D-ΔPDF; 3DED; single-crystal diffuse scattering

Regimes of quantum transport in superlattices in a weak magnetic field - Malzer, Stefan; et al. (Journal of Physics: Condensed Matter, 2004)
Weak field magnetoresistance was explored in GaAs/AlGaAs superlattices with different strengths of disorder produced either by the random variation of the well thicknesses or by the interface roughness. Depending on the disorder strength, three different regimes of the quantum transport were distinguished: the regimes of weak localization identified as the regimes of propagative and diffusive Fermi surfaces and the strongly localized insulating regime. Our results imply different dephasing mechanisms in the weak and strong localization limits. The vertical coupling energies in the superlattices determined with the random variation of the well thicknesses revealed a significant decrease with increasing disorder strength.

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

Regular high-nuclearity species from square building blocks: A triangular 3 × [2 × 2] Ni 12 complex generated by the self-assembly of three [2 × 2] Ni 4 molecular grids - Moroz, Yurii S.; Demeshko, Serhiy; Haukka, Matti; Mokhir, Andriy; Mitra, Utpal; Stocker, Michael; Müller, Paul; Meyer, Franc; Fritsky, Igor O. (Inorganic Chemistry, 2012)
A dodecanuclear 3 × [2 × 2] nickel(II) complex has been obtained via the self-association of three tetranuclear [2 × 2] molecular grids. X-ray diffraction shows a "propeller-like" structure of the [Ni ] scaffold with a central μ -hydroxide. The dodecanuclear species remains stable in solution and can be deposited without decomposition on highly ordered pyrolytic graphite surfaces. © 2012 American Chemical Society.

Regulation of murine placentogenesis by the retroviral genes Syncytin-A, Syncytin-B and Peg10 - Henke, Christine; Ruebner, Matthias; Faschingbauer, Florian; Stolt, Claus; Schäfer, Natascha; Lang, Nadine; Beckmann, Matthias; Strissel, Pamela; Strick, Reiner (Differentiation, 2013)
The murine placenta has a trichorial structure with two multinucleated syncytiotrophoblast (SCT) layers representing a barrier between the maternal and fetal blood system. Genes of endogenous retroviruses and retrotransposon-derived paternally expressed genes (Peg), remnants of past infections and integrations in the genome, have essential functions in placentogenesis. Previous studies showed that the envelope genes Syncytin-A and Syncytin-B were essential for cell-cell fusion of the SCT. The goal of this study was to analyze the temporal localization and expression of nine genes throughout placental development from embryonic day (E)8.5 to E18.5 using in situ-hybridization and absolute RNA-quantification. These included a comparison of previously characterized genes from the labyrinth Syncytin-A, Syncytin-B, Gcm1, the junctional zone PL-1, PL-2, Plf, Tpbpa with two further characterized genes Peg10 and Tpbpb. Syncytin-A and Syncytin-B RNA localized to SCT-I and SCT-II, respectively. Peg10 RNA localized to all extraembryonic tissues, specifically to the parietal and sinusoidal TGC of the labyrinth layer, which is in contact with SCT-I and the maternal blood. All three retroviral/retrotransposon-derived genes showed the highest expression at E16.5, but Peg10 with 188,917.1 molecules/ng cDNA was 208-fold and 106.8-fold higher expressed than Syncytin-A and Syncytin-B, respectively. Tpbpb localized to the junctional zone and showed the highest expression at E16.5 along with PL-2, Plf, Tpbpa, but not PL-1, which decreased in expression at E10.5. To investigate a role of Syncytin-A, Syncytin-B and Peg10 in cell-cell fusion, we established a cell culture system with fractionated primary trophoblasts from murine placentae. Culturing trophoblasts for up to 72h partly resembled trophoblast development in vivo according to the nine marker genes. Knockdown of Syncytin-A demonstrated a functional regulation of cell-cell fusion, where knockdown of Peg10 showed no involvement in cell fusion. Due to the expression of Peg10 in TGCs, we propose an essential functional role in the fetal-maternal blood system.
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Remodeling of the airway smooth muscle cell: are we built of glass? - Fabry, Ben; et al. (Respiratory Physiology & Neurobiology, 2003)

Removing the orientational degeneracy of the TS defect in 4H-SiC by electric fields and strain - Rühl, Maximilian; Lehmeyer, Johannes; Nagy, Roland; Weißer, Matthias; Bockstedte, Michel; Krieger, Michael; Weber, Heiko B. (New Journal of Physics, 2021)

Reproducibility and Repeatability of MR Fingerprinting Relaxometry in the Human Brain - Koerzdoerfer, Gregor; Kirsch, Rainer; Liu, Kecheng; Pfeuffer, Josef; Hensel, Bernhard; Jiang, Yun; Ma, Dan; Gratz, Marcel; Baer, Peter; Bogner, Wolfgang; Springer, Elisabeth; Cardoso, Pedro Lima; et al. (Radiology, 2019)
Background: Only sparse literature investigates the reproducibility and repeatability of relaxometry methods in MRI. However, statistical data on reproducibility and repeatability of any quantitative method is essential for clinical application.
CRIS-Team WoS Importer:2019-08-02

Research Data Management for Experiments in Solid-State Physics: Concepts - Weber, Heiko B.; Brockhauser, Sandor; Koch, Christoph T.; Rettig, Laurenz; Aeschlimann, Martin; Hetaba, Walid; Grundmann, Marius; Kühbach, Markus; Krieger, Michael (1st Conference on Research Data Infrastructure, 2023)
FAIRmat develops concepts for paving the way to enable FAIR research data in solid-state physics. For selected theoretical data in this field, the NOMAD portal has developed mature concepts and technological solutions for storing data according to the FAIR principles. Extending this approach to experimental data is challenging due to their diversity and missing standards. In this paper we present our comprehensive approach to establish FAIR data in the field of experimental solid-state physics despite its heterogeneity. The concept includes elaboration of standards, community building and methods that facilitate the community’s transition to FAIR standards.<br

Resistive memory switching in layered oxides: A nB nO 3n+2 perovskite derivatives and Bi 2Sr 2CaCu 2O 8+δ high-T c superconductor - Koval, Yury; Chowdhury, Farzana; Jin, Xiaoyue; Simsek, Yilmaz; Lichtenberg, Frank; Pentcheva, Rossitza; Müller, Paul (physica status solidi (a), 2011)
Resistive memory switching was investigated in titanates and niobates of the type A B O and in the high-T superconductor Bi Sr CaCu O . We studied the switching by current injection perpendicular to the layers. Both dc and pulsed measurements were performed. Out-of-plane transport properties were investigated by measurements of the resistance and current-voltage characteristics (IVs) vs. temperature for different resistive states. The critical temperature of superconducting transition and the critical current of intrinsic Josephson junctions were also analyzed for different resistive states in Bi Sr CaCu O . The resistive memory switching was explained in terms of doping of the conducting layers, which is induced by trapped charges in the insulating layers. The charged insulating layers act as a floating gate and reduce or increase the carrier concentration in the conducting layers, respectively. We found that all studied materials demonstrate a different type of non-persistent resistive switching at low temperatures. This type of switching shows up in a specific form of current-voltage characteristics with a pronounced back-bending often called s-shaped IV. Both types of resistive switching with and without memory effect were analyzed in terms of electron overheating. We examine the role of hot electrons and discuss additional factors, which might lead to persistent resistive states. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: carrier injection; cuprate superconductors; current-voltage characteristics; perovskites; resistive memory switching; tunneling

Resistivity relaxation, a new approach to study ionic mobility in perovskite mixed conductors like CaTi0.7Fe0.3O3-ð - Mashkina, Elena; Baier, Markus; Magerl, Andreas; Göbbels, Matthias; Seifert, Friedrich (Ionics, 2005)
Oxygen transport of mixed ionic-electronic conductors can be measured by a 'relaxation' technique that permits to investigate the material dynamic properties with oxygen partial pressure change. However, for materials exhibiting higher electronic conductivity than ionic, the time for conductivity change is controlled by bulk ionic transport and any surface reaction can be neglected. By fitting the experimental relaxation data of CaTi 0.7Fe0.3O3-δ composition, the oxidation and reduction kinetics was found to be independent on oxygen partial pressure (PO2) and the rate constants were derived therefrom. From a relaxation experiment at a single PO2 we therefore obtain both the electronic and ionic contributions to the total conductivity as well as the chemical diffusion coefficient.
UnivIS-Import:2015-03-09:Pub.2005.nat.dgeo.IGM.LM.resist

Resolving diffusion in clay minerals at different time scales: Combination of experimental and modeling approaches - Churakov, Sergey V.; Gimmi, Thomas; Unruh, Tobias; Van Loon, Luc R.; Juranyi, Fanni (Applied Clay Science, 2014)
The size of the interlayer and the size of Mt particles are two characteristic dimensions which determine the time dependent behavior of water diffusion in Mt. MD simulations show that at very short time scales water dynamics has the characteristic features of an oscillatory motion in the cage formed by neighbors in the first coordination shell. At longer time scales, the interaction of water with the surface determines the water dynamics, and the effect of confinement on the overall water mobility within the interlayer becomes evident. At time scales corresponding to an average water displacement equivalent to the average size of Mt particles, the effects of tortuosity are observed in the meso- to macroscopic pore scale simulations. Consistent with the picture obtained in the simulations, the QENS data can be described using a (local) 3D diffusion at short observation times, whereas at sufficiently long observation times a 2D diffusive motion is clearly observed. The effects of tortuosity measured in macroscopic tracer diffusion experiments are in qualitative agreement with RW simulations. By using experimental data to calibrate molecular and mesoscopic theoretical models, a consistent description of water mobility in clay minerals from the molecular to the macroscopic scale can be achieved. In turn, simulations help in choosing optimal conditions for the experimental measurements and the data interpretation. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Restricted water diffusion; QENS; Molecular dynamics; 2D confinement; Montmorillonite

Resolving in situ specific-contact, current-crowding, and channel resistivity in nanowire devices: A case study with silver nanowires - Krstic, Vojislav; Kolesnik, Maria M.; Hansel, Stefan; Lutz, Tarek; Kinahan, Niall; Boese, Markus; Krstic, Vojislav (Small, 2011)
Keywords: nanodevices; nanowires; current crowding; electronics; contact resistance