Lipid Dynamics in Membranes Slowed Down by Transmembrane Proteins - Ebersberger, Lisa; Schindler, Torben; Kirsch, Sonja; Pluhackova, Kristyna; Schambony, Alexandra; Seydel, Tilo; Böckmann, Rainer; Unruh, Tobias (Frontiers in Cell and Developmental Biology, 2020)
Lipids and proteins, as essential components of biological cell membranes, exhibit a significant degree of freedom for different kinds of motions including lateral long-range mobility. Due to their interactions, they not only preserve the cellular membrane but also contribute to many important cellular functions as e.g., signal transport or molecular exchange of the cell with its surrounding. Many of these processes take place on a short time (up to some nanoseconds) and length scale (up to some nanometers) which is perfectly accessible by quasielastic neutron scattering (QENS) experiments and molecular dynamics (MD) simulations. In order to probe the influence of a peptide, a transmembrane sequence of the transferrin receptor (TFRC) protein, on the dynamics of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) large unilamellar vesicles (LUVs) on a nanosecond time scale, high-resolution QENS experiments and complementary MD simulations have been utilized. By using different scattering contrasts in the experiment (chain-deuterated lipids and protonated lipids, respectively), a model could be developed which allows to examine the lipid and peptide dynamics separately. The experimental results revealed a restricted lipid lateral mobility in the presence of the TFRC transmembrane peptides. Also the apparent self-diffusion coefficient of the lateral movement of the peptide molecules could be determined quantitatively for the probed short-time regime. The findings could be confirmed very precisely by MD simulations. Furthermore, the article presents an estimation for the radius of influence of the peptides on the lipid long-range dynamics which could be determined by consistently combining results from experiment and simulation.
CRIS-Team WoS Importer:2020-11-27

Liquid Crystalline Phase Formation in Suspensions of Solid Trimyristin Nanoparticles - Gehrer, Simone; Schmiele, Martin; Westermann, Martin; Steiniger, Frank; Unruh, Tobias (Journal of Physical Chemistry B, 2014)
The presence of liquid crystalline phases in suspensions of solid lipid nanoparticles can increase the risk of their gelling upon administration through fine needles. Here we study the formation of liquid crystalline phases in aqueous suspensions of platelet-like shaped solid lipid nanoparticles. A native lecithin-stabilized trimyristin (20 wt %) suspension was investigated at different dilution levels by small-angle X-ray scattering (SAXS) and visual inspection of their birefringence between two crossed polarizers. For trimyristin concentrations phi(MMM) < 6 wt %, the dispersed platelets are well separated from each other whereas they start to self-assemble into stacked lamellae for 6 wt % <= phi(MMM) < 12 wt %. For phi(MMM) >= 12 wt %, the SAXS patterns become increasingly anisotropic, which is a signature of an evolving formation of a preferred orientation of the platelets on a microscopic scale. Simultaneously, the suspensions become birefringent, which proves the existence of an anisotropic liquid crystalline phase formed in the still low viscous liquid suspensions. Spatially resolved SAXS scans and polarization microscopy indicate rather small domains in the (sub)micrometer size range in the nematic liquid crystalline phase and the presence of birefringent droplets (tactoids). The observed critical concentrations for the formation of stacks and the liquid crystalline phase are significantly higher as for equivalent suspensions prepared from triglycerides with longer chains. This can be explained with the lower aspect ratio of trimyristin platelets. Special emphasis is put on the isotropic-liquid crystalline phase transition as a function of the ionic strength of the dispersion medium and phi(MMM). Higher salt concentrations allow shifting of the phase transition to higher trimyristin concentrations. This can be attributed to a partial screening of the repulsive forces between the platelets, which allows higher packing densities within the platelet stacks and of remaining isolated platelets.

Liquids under shear explored by neutron scattering: A problem in lubrication - Magerl, Andreas; Hock, Rainer; et al. (Materials Research Society Symposium - Proceedings, 2002)
Considering the atomic scatterng cross sections for neutrons they are an excellent tool to investigate lubrication problems. Two different shear cells have been built to investigate both the dynamics and structural properties of liquids under shear: one cell has been optimised for quasielastic and inelastic neutron scattering while another one has been designed for reflectivity and diffraction work. The dynamical aspects have been studied on the high-resolution backscattering instrument (INI16 at Institut Laue-Langevin (ILL)). Data with a commercial motor oil as a sample have been taken in contact with an aluminium boundary showing directly the developing anisotropy of diffusion under shear. Furthermore within the same set-up it has been possible to monitor the macroscopic velocity distribution including surface slip. In addition, a diffraction experiment has been carried out, demonstrating from a measurement of the position and the profile of the graphite 002 reflection that the ordering of macroscopic graphite particles in a flowing liquid can be studied with neutrons and an ordering with a tilt angle of the particles of 5° to the flow has been determined.
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.IAP.LK.liquid

Localized B-0 shimming based on Na-23 MRI at 7 T - Gast, Lena; Henning, Anke; Hensel, Bernhard; Uder, Michael; Nagel, Armin Michael (Magnetic Resonance in Medicine, 2019)
Purpose To validate the feasibility of localized B-0 shimming based on B-0 maps acquired with sodium (Na-23) MRI. Methods A localized B-0 shimming routine based on a constrained regularized algorithm in combination with Na-23 MRI data acquired with a 3D density-adapted radial readout scheme was implemented on a 7T MR system. Measurements were performed using a dual-tuned Na-23/H-1 head coil. The quality of B-0 maps reconstructed from Na-23 images and the resulting shim values was examined depending on the acquisition duration between 10 minutes and 15 seconds to examine clinical applicability. The B-0 shimming based on Na-23 B-0 maps was performed both for phantom and human head of 6 healthy volunteers, and the resulting B-0 homogeneity was compared with the vendor-provided H-1 MRI-based gradient-echo brain shimming routine. Results The proposed Na-23 MRI-based shimming routine showed a reduction in B-0 variation comparable to the vendor-provided shim both in phantom and in vivo measurements. Within the examined multicompartment phantom, the B-0 variations could be reduced by up to 77% using the Na-23 MRI-based shim. In human head, B-0 variations were reduced by approximately 50% using an acquisition time of 15 seconds for the Na-23 B-0 maps and only 1 iteration of B-0 shimming. Conclusion The Na-23 MRI-based localized B-0 shimming is possible at 7 T within clinically acceptable acquisition durations (< 1 minute). It was shown that using the proposed Na-23 MRI-based shimming approach, the Na-23 image quality at ultrahigh field strength can be strongly improved.
CRIS-Team WoS Importer:2019-10-22

Localized mechanical stress induces time-dependent actin cytoskeletal remodeling and stiffening in cultured airway smooth muscle cells - Deng, L.; Fairbank, Nigel Jack; Fabry, Ben; SMITH, PAUL M.; Maksym, Geoffrey N. (American Journal of Physiology-Cell Physiology, 2004)
Mechanical stress (MS) causes cytoskeletal (CSK) and phenotypic changes in cells. Such changes in airway smooth muscle (ASM) cells might contribute to the pathophysiology of asthma. We have shown that periodic mechanical strain applied to cultured ASM cells alters the structure and expression of CSK proteins and increases cell stiffness and contractility (Smith PG, Moreno R, and Ikebe M. Am J Physiol Lung Cell Mol Physiol 272: L20-L27, 1997; and Smith PG, Deng L, Fredberg JJ, and Maksym GN. Am J Physiol Lung Cell Mol Physiol 285: L456-L463, 2003). However, the mechanically induced CSK changes, altered cell function, and their time courses are not well understood. Here we applied MS to the CSK by magnetically oscillating ferrimagnetic beads bound to the CSK. We quantified CSK remodeling by measuring actin accumulation at the sites of applied MS using fluorescence microscopy. We also measured CSK stiffness using optical magnetic twisting cytometry. We found that, during MS of up to 120 min, the percentage of beads associated with actin structures increased with time. At 60 min, 68.1 ± 1.6% of the beads were associated with actin structures compared with only 6.7 ± 2.8% before MS and 38.4 ± 5.5% in time-matched controls (P < 0.05). Similarly, CSK stiffness increased more than twofold in response to the MS compared with time-matched controls. These changes were more pronounced than observed with contractile stimulation by 80 mM KCl or 10 -4 M acetylcholine. Together, these findings imply that MS is a potent stimulus to enhance stiffness and contractility of ASM cells through CSK remodeling, which may have important implications in airway narrowing and dilation in asthm
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.IAP.lpmt.locali
Keywords: Actin cytoskeleton; Airway constriction and dilation; Airway smooth muscle cell; Asthma; Mechanical stress; Optical magnetic twisting cytometry; Stiffness

Local measurement of hot-electron phase-coherence at metal surfaces - Schneider, M. Alexander; Wahl, P; Vitali, L; Diekhöner, L; Vogelgesang, Ralf; Kern, Klaus (Applied Physics A: Materials Science and Processing, 2007)
We use scanning tunneling microscopy and spectroscopy to study the energy dependence of hot-electron scattering processes on metal surfaces via the determination of the energy-dependent phase-coherence length. From this an electron lifetime can be determined, which in the case of electrons in the surface state of Ag(111) and in the case of the n=1 image-potential state on Cu(100) shows good agreement with theoretical modeling and other experimental data. The method is based on the quantitative analysis of electron interference patterns. A theoretical analysis shows that the phase-coherence length can be determined in confining nanostructures of a characteristic length scale smaller than the phase-coherence length.<br
Keywords: Scanning Tunneling Microscopy; Coherence Length; Noise Band; Scanning Tunneling Spectroscopy; Standing Wave Pattern

Local spectroscopy of the Kondo lattice YbAl3: Seeing beyond the surface with scanning tunneling microscopy and spectroscopy - Wahl, Peter; Diekhöner, Lars; Schneider, M. Alexander; Treubel, F.; Lin, C.T.; Kern, Klaus (Physical Review B, 2011)
We report on an atomic-scale study of the Kondo lattice compound YbAl3 using scanning tunneling microscopy (STM) and spectroscopy (STS). An analysis of the surface orientation and structure is performed based on STM images containing more than one crystal facet. We compare tunneling spectra acquired on different facets and discuss their relation with the temperature scales observed in measurements of bulk quantities and the states observed in photoemission spectra. On specific facets, we observe strong additional resonances close to the Fermi energy which are not consistent with the characteristic energy scales found in bulk measurements, and which we interpret in terms of a modified Kondo state of the near-surface Ytterbium atoms.

Local work function measurements of epitaxial graphene - Filleter, Tobin; Emtsev, Konstantin; Seyller, Thomas; Bennewitz, Roland (Applied Physics Letters, 2008)
The work function difference between single layer and bilayer graphene grown epitaxially on 6H-SiC(0001) has been determined to be 135±9 meV by means of the Kelvin probe force microscopy. Bilayer films are found to increase the work function as compared to single layer films. This method allows an unambiguous distinction between interface layer, single layer, and bilayer graphene. In combination with high-resolution topographic imaging, the complex step structure of epitaxial graphene on SiC can be resolved with respect to substrate and graphene layer steps.
EAM Import::2019-03-12

Longitudinal Optical Phonons in Metallic and Semiconducting Carbon Nanotubes - Fouquet, Martin; Telg, Hagen; Maultzsch, Janina; Wu, Yang; Chandra, Bhupesh; Hone, James; Heinz, Tony F.; Thomsen, Christian (Physical Review Letters, 2009)
We analyze the high-energy Raman modes, G(+) and G(-), in a pair of one metallic and one semiconducting nanotubes. By combining Rayleigh scattering with Raman resonance profiles of the radial breathing mode and the high-energy modes, we show that the observed G(-) and G(+) peaks can originate from longitudinal optical phonons of different tubes. The G(-) peak is the longitudinal mode of the metallic tube; it is broadened and downshifted due to strong electron-phonon coupling in the metallic nanotube. The G(+) peak is due to the longitudinal mode in the semiconducting tube. This result resolves an ongoing debate in the literature.

Long-term stability of aerophilic metallic surfaces underwater - Tesler, Alexander; Kolle, Stefan; Prado, Lucia; Thievessen, Ingo; Böhringer, David; Backholm, Matilda; Karunakaran, Bhuvaneshwari; Nurmi, Heikki A.; Latikka, Mika; Fischer, Lena; Stafslien, Shane; Cenev, Zoran M.; et al. (Nature Materials, 2023)
Aerophilic surfaces immersed underwater trap films of air known as plastrons. Plastrons have typically been considered impractical for underwater engineering applications due to their metastable performance. Here, we describe aerophilic titanium alloy (Ti) surfaces with extended plastron lifetimes that are conserved for months underwater. Long-term stability is achieved by the formation of highly rough hierarchically structured surfaces via electrochemical anodization combined with a low-surface-energy coating produced by a fluorinated surfactant. Aerophilic Ti surfaces drastically reduce blood adhesion and, when submerged in water, prevent adhesion of bacteria and marine organisms such as barnacles and mussels. Overall, we demonstrate a general strategy to achieve the long-term stability of plastrons on aerophilic surfaces for previously unattainable underwater applications.
CRIS-Team Scopus Importer:2023-09-29

Looking beyond the Surface: The Band Gap of Bulk Methylammonium Lead Iodide - Schuster, Oskar; Wientjes, Peter; Shrestha, Shreetu; Levchuk, Ievgen; Sytnyk, Mykhailo; Matt, Gebhard; Osvet, Andres; Batentschuk, Miroslaw; Heiß, Wolfgang; Brabec, Christoph; Fauster, Thomas; Niesner, Daniel (Nano Letters, 2020)
Despite the intense research on photovoltaic lead halide perovskites, reported optical properties as basic as the absorption onset and the optical band gap vary significantly. To unambiguously answer the question whether the discrepancies are a result of differences between bulk and "near-surface" material, we perform two nonlinear spectroscopies with drastically different information depths on single crystals of the prototypical (CH3NH3)PbI3 methylammonium lead iodide. Two-photon absorption, detected via the resulting generation of carriers and photocurrents (2PI-PC), probes the interband transitions with an information depth in the millimeter range relevant for bulk (single-crystal) material. In contrast, the transient magneto-optical Kerr effect (trMOKE) measured in a reflection geometry determines the excitonic transition energies in the region near (hundreds of nm) the surface which also determine the optical properties in typical thin films. To identify differences between structural phases, we sweep the sample temperature across the orthorhombic-tetragonal phase transition temperature. In the application-relevant room-temperature tetragonal phase (at 170 K), we find a bulk band gap of 1.55 ± 0.01 eV, whereas in the near-surface region excitonic transitions occur at 1.59 ± 0.01 eV. The latter value is consistent with previous reflectance measurements by other groups and considerably higher than the bulk band gap. The small band gap of the bulk material explains the extended infrared absorption of crystalline perovskite solar cells, the low-energy bands which carry optically driven spin-polarized currents, and the narrow bandwidth of crystalline perovskite photodetectors making use of the spectral filtering at the surface.
CRIS-Team Scopus Importer:2020-05-22
Keywords: band gap; CH3NH3PbI3; lead halide perovskite; magneto-optical Kerr effect; nonlinear absorption

Low-Energy Electron Potentiometry: Contactless Imaging of Charge Transport on the Nanoscale - Kautz, J.; Jobst, J.; Sorger, Christian; Tromp, R. M.; Weber, Heiko B.; Van Der Molen, S. J. (Scientific Reports, 2015)
Charge transport measurements form an essential tool in condensed matter physics. The usual approach is to contact a sample by two or four probes, measure the resistance and derive the resistivity, assuming homogeneity within the sample. A more thorough understanding, however, requires knowledge of local resistivity variations. Spatially resolved information is particularly important when studying novel materials like topological insulators, where the current is localized at the edges, or quasi-two-dimensional (2D) systems, where small-scale variations can determine global properties. Here, we demonstrate a new method to determine spatially-resolved voltage maps of current-carrying samples. This technique is based on low-energy electron microscopy (LEEM) and is therefore quick and non-invasive. It makes use of resonance-induced contrast, which strongly depends on the local potential. We demonstrate our method using single to triple layer graphene. However, it is straightforwardly extendable to other quasi-2D systems, most prominently to the upcoming class of layered van der Waals materials.

LOW-ENERGY ION-SCATTERING FROM A NI(001) SURFACE - Fauster, Thomas; et al. (Surface Science, 1986)

Low-frequency vibrational excitations in a niobium-phosphate glass for Raman gain applications - Schulte, Alfons; Guo, Y.; Schirmacher, Walter; Unruh, Tobias; Cardinal, Thierry (Vibrational Spectroscopy, 2008)
Raman gain for all-optical amplification depends significantly on the cross section for spontaneous Raman scattering. We present measurements of the Raman spectrum of binary niobium-phosphate glasses in the frequency range from 5 to 1300 cm(-1). The spectra of these glasses show a low-frequency enhancement of the vibrational density of states ('Boson peak') suggesting a significant gain profile for application in Raman amplifiers as well as providing an additional mechanism for Raman gain. To separate the effects of density of states from the light-vibration coupling we carried out an inelastic neutron scattering investigation of 40Nb(2)O(5)-60NaPO(3) using the time-of-flight spectrometer (TOFrOF) at the FRM II neutron source in Munich. The Boson peak appears between 40 and 70 cm(-1) as an increase of the reduced density of states over the flat Debye approximation. Possible mechanisms contributing to the low-frequency excitations such as disorder-induced irregular vibrational states are discussed. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: Raman spectroscopy; Boson peak; Raman gain; neutron scattering

Low-temperature ballistic transport in nanoscale epitaxial graphene cross junctions - Weingart, S.; Bock, C.; Kunze, Ulrich; Speck, Florian; Seyller, Thomas; Ley, Lothar (Applied Physics Letters, 2009)
We report on the observation of inertial-ballistic transport in nanoscale cross junctions fabricated from epitaxial graphene grown on SiC(0001). Ballistic transport is indicated by a negative bend resistance of R ≈-170 ω, which is measured in a nonlocal, four-terminal configuration at 4.2 and which vanishes as the temperature is increased above 80 K. © 2009 American Institute of Physics.

Low-temperature conductance measurements on single molecules - Reichert, Joachim; Weber, Heiko B.; Mayor, Marcel; von Löhneysen, Hilbert (Applied Physics Letters, 2003)
An experimental protocol which allows to perform conductance spectroscopy on organic molecules at low temperatures (T approximate to 30 K) has been developed. This extends the method of mechanically controlled break junctions which has recently demonstrated to be suitable to contact single molecules at room temperature. The conductance data obtained at low T with a conjugated sample molecule show a highly improved data quality with a higher stability, narrower linewidth, and substantially reduced noise. Thus, the comparability of experimental data with other measurements as well as with theoretical simulations is considerably improved. (C) 2003 American Institute of Physics.

Low temperature formation of CuIn1 - xGaxSe2solar cell absorbers by all printed multiple species nanoparticulate Se + Cu-In + Cu-Ga precursors - Möckel, Stefan; Wernicke, Tobias; Arzig, Matthias; Köder, Philipp; Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Peukert, Wolfgang; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2015)
In this work an all nanoparticulate precursor for application in Cu(InGa)Sesolar cell absorbers is presented. Binary Cu-In nanoparticles, Cu-Ga powder and elemental Se nanoparticles were mixed in dispersion and deposited on Mo-coated substrates. Research was focused on Cu(InGa)Selayer formation kinetics, phase composition characterised by differential scanning calorimetry and in-situ X-ray diffraction (XRD). Furthermore phase composition and morphology were studied by ex-situ XRD, Raman spectroscopy and scanning electron microscopy. The results revealed a fast consumption of the precursor and the formation of CuInSebelow 340 °C. Binary secondary phases were not observed at any temperature.
Keywords: Low-temperature; Copper indium gallium diselenide; Chalcopyrite; Nanoparticulate precursors; In-situ X-ray diffraction; Bimetallic nanoparticles

Low-Temperature Solution-Processed Kesterite Solar Cell Based on in Situ Deposition of Ultrathin Absorber Layer - Hou, Yi; Azimi, Seyed Hamed; Gasparini, Nicola; Savador, Michael; Chen, Wei; Khanzada, Laraib Sarfraz; Brandl, Marco; Hock, Rainer; Brabec, Christoph (ACS Applied Materials and Interfaces, 2015)
The production of high-performance, solution-processed kesterite Cu2ZnSn(Sx,Se1-x)4 (CZTSSe) solar cells typically relies on high-temperature crystallization processes in chalcogen-containing atmosphere and often on the use of environmentally harmful solvents, which could hinder the widespread adoption of this technology. We report a method for processing selenium free Cu2ZnSnS4 (CZTS) solar cells based on a short annealing step at temperatures as low as 350 °C using a molecular based precursor, fully avoiding highly toxic solvents and high-temperature sulfurization. We show that a simple device structure consisting of ITO/CZTS/CdS/Al and comprising an extremely thin absorber layer (∼110 nm) achieves a current density of 8.6 mA/cm2. Over the course of 400 days under ambient conditions encapsulated devices retain close to 100% of their original efficiency. Using impedance spectroscopy and photoinduced charge carrier extraction by linearly increasing voltage (photo-CELIV), we demonstrate that reduced charge carrier mobility is one limiting parameter of low-temperature CZTS photovoltaics. These results may inform less energy demanding strategies for the production of CZTS optoelectronic layers compatible with large-scale processing techniques.
Keywords: CZTS; device stability; kesterite solar cells; low-temperature processing; molecular based precursor

Low threshold electron emission from diamond - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review B, 1999)
We have studied the photoassisted electron emission of single-crystal diamond (111) for photon energies from just above the diamond band gap of 5.5 eV well into the sub-band-gap regime (hν≈2.8eV). As an independent parameter, the electron affinity was varied between -1.27 eV [negative electron affinity (NEA)] and +0.38 eV [positive electron affinity (PEA)] by changing the hydrogen coverage of the surface. A substantial sub-band-gap emission band with constant intensity is observed in all cases. Except for the NEA surfaces, it dominates the electron flux. We attribute this intense band to nanometer-size graphitic patches which cover less than 1% of the surface area. The low-energy threshold for this emission band is, however, not determined by intrinsic properties of graphite, but controlled by the work function of the surrounding diamond matrix. The details of this inhomogeneous emission model, which may have implications for the field emission from nanocrystalline diamond films, are discussed. ©1999 The American Physical Society.
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.IAP.exphys.lowthr

Low-Voltage Self-Assembled Monolayer Field-Effect Transistors on Flexible Substrates - Schmaltz, Thomas; Amin, Atefeh Y.; Khassanov, Artöm; Meyer-Friedrichsen, Timo; Steinrück, Hans-Georg; Magerl, Andreas; Segura, Juan Jose; Voitchovsky, Kislon; Stellacci, Francesco; Halik, Marcus (Advanced Materials, 2013)
Self-assembled monolayer field-effect transistors (SAMFETs) of BTBT functionalized phosphonic acids are fabricated. The molecular design enables device operation with charge carrier mobilities up to 10 cm V s and for the first time SAMFETs which operate on rough, flexible PEN substrates even under mechanical substrate bending. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetically Guided Titania Nanotubes for Site-Selective Photocatalysis and Drug Release - Shrestha, Nabeen Kumar; Macák, Jan; Schmidt-Stein, F.; Hahn, Robert; Mierke, Claudia; Fabry, Ben; Schmuki, Patrik (Angewandte Chemie, 2008)
Quick release: The spatial and temporal delivery of active molecules (dyes or drugs) can be precisely controlled by the photocatalytic activity of TiO_2 nanotubes (see picture). The cleavage of the link between the active molecule and the nanotubes, which are filled with magnetic Fe_3O_4 nanoparticles, occurs by photoinduced chain scission under UV light; the load can be released before photodegradation by action of photogenerated radicals can occur.

Magnetic Conveyor Belt for Transporting and Merging Trapped Atom Clouds - Hänsel, Wolfgang; Reichel, Jakob; Hommelhoff, Peter; Haensch, Theodor W. (Physical Review Letters, 2001)
A magnetic conveyor belt that transports trapped atoms to very precisely controlled positions near a surface is experimentally demonstrated. An extension of this belt allows the merging of atom clouds trapped in two adjacent Ioffe-Pritchard (IP) traps. The transfer is complete and, under suitable conditions, occurs without loss of phase space density.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.magnet

Magnetic microchip traps and single-atom detection - Long, Romain; Steinmetz, Tilo; Hommelhoff, Peter; Hänsel, Wolfgang; Hänsch, Theodor; Reichel, Jakob (Philosophical Transactions of the Royal Society A-Mathematical Physical and Engineering Sciences, 2003)
Microchip traps provide a promising approach to quantum information processing and communication (QIPC) with neutral atoms: strong and complex potentials can be produced for acting on the qubit atoms, and the potentials can be scaled to higher qubit numbers by virtue of the microfabrication process. We describe experimental results that are relevant to use in QIPC, such as the transport of Bose-Einstein-condensed atomic ensembles along the chip surface with the help of a magnetic conveyor belt. The second part of the paper is devoted to single-atom detection on the chip.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.IAP.exphys.magnet
Keywords: BEC; Detector; Microchip; Neutral atom; Qubit; Single atom

Magnetic Properties of the Distorted Kagome Lattice Mn-3(1,2,4-O2C)(3)C6H3)(2) - Mole, Richard A.; Greene, Stephen; Henry, Paul F.; Humphrey, Simon M.; Rule, Kirrily C.; Unruh, Tobias; Weldon, Gerald F.; Yu, Dehong; Stride, John A.; Wood, Paul T. (Inorganic Chemistry, 2017)
Kagome lattice types have been of intense interest as idealized examples of extended frustrated spin systems. Here we demonstrate how the use of neutron diffraction and inelastic neutron scattering coupled with spin wave theory calculations can be used to elucidate the complex magnetic interactions of extended spin networks. We show that the magnetic properties of the coordination polymer Mn-3(1,2,4-(O2C)(3)C6H3)(2), a highly distorted kagome lattice, have been erroneously characterized as a canted antiferromagnet in previous works. Our results demonstrate that, although the magnetic structure is ferrimagnetic, with a net magnetic moment, frustration persists in the system. We conclude by, showing that the conventions Goodenough-Kanamori rules, which are often applied to similar magnetic exchange interactions, are not relevant in this case.

Magnetic resonance field fingerprinting - Koerzdoerfer, Gregor; Jiang, Yun; Speier, Peter; Pang, Jianing; Ma, Dan; Pfeuffer, Josef; Hensel, Bernhard; Gulani, Vikas; Griswold, Mark; Nittka, Mathias (Magnetic Resonance in Medicine, 2019)
Purpose: To develop and evaluate the magnetic resonance field fingerprinting method that simultaneously generates T-1, T-2, B-0, and B-1(+) maps from a single continuous measurement.
CRIS-Team WoS Importer:2019-04-09

Magneto-chiral anisostropy of the free electron on a helix - Krstic, Vojislav; Rikken, Geert L.J.A. (Chemical Physics Letters, 2002)
The free electron on a helix as a simple model of a molecular chiral conductor is considered. In the presence of a static magnetic field parallel to the helix axis, it is found that both ballistic and diffusive electrical transport along the helix show a conductivity that depends linearly on the current and the magnetic field and on the handedness of the helix. These results agree qualitatively with the recently experimentally observed electrical magneto-chiral anisotropy in carbon nanotubes

Magnetochiral anisotropy - Rikken, Geert L.J.A.; Raupach, E.; Krstic, Vojislav; Roth, Siegmar (Molecular Physics, 2002)
In biology, chemistry and physics one often deals with systems that can occur in two forms that are each other's mirror image. A new magneto-optical effect called magnetochiral anisotropy (MChA) is described that establishes a link between chirality and magnetic fields and that can discriminate between the two enantiomers (mirror images) of chiral systems. It is shown that through MChA a magnetic field can lead to an enantiomeric excess in a photochemical reaction with unpolarized light. The existence of MChA can be deduced from general symmetry arguments, and the question comes to mind whether this effect can manifest itself in other magnetotransport phenomena in chiral media. Theoretical evidence is presented that indeed MChA is a general phenomenon, and its existence is demonstrated experimentally in the electrical conductivity of carbon nanotubes.

Magneto-chiral anisotropy in charge transport through single-walled carbon nanotubes - Krstic, Vojislav; Roth, Siegmar; Burghard, Marko; Kern, Klaus; Rikken, Geert L.J.A. (Journal of Chemical Physics, 2002)
Carbon nanotubes are chiral molecular objects and therefore exist in two forms that are each other’s mirror image. Many aspects of these fascinating new materials have recently been explored but their chirality has hardly been addressed. We have investigated the charge transport through individual single-walled carbon nanotubes in the presence of a magnetic field parallel to the tube axis. For most of the investigated tubes, a dependence of the resistance that is odd in both the magnetic field and in the current through the tube is observed. This effect is ascribed to the chirality of the nanotube and is called electrical magneto-chiral anisotropy.

Magneto-dynamics of chiral carbon nanotubes - Krstic, Vojislav; Wagnière, Georges H.; Rikken, Geert L.J.A. (Chemical Physics Letters, 2004)
Carbon nanotubes exist in achiral and chiral forms. The chiral nanotubes exist as two enantiomers which are each others' mirror image. By means of symmetry arguments it can be shown that a magnetic field imparts a linear momentum to the chiral nanotube. Inversely, a moving chiral nanotube generates a magnetic field. In order to quantify the first effect, the chiral nanotube is approximated by the quantum mechanical model of a free electron on a helix.

Magneto-optical spectroscopy of excitons in carbon nanotubes - Shaver, J.; Kono, Junichiro; Portugall, Oliver; Krstic, Vojislav; Rikken, Geert L.J.A.; Miyauchi, Y.; Maruyama, Shigeo; Perebeinos, Vasili (Physica Status Solidi-Rapid Research Letters, 2006)
We describe recent results of optical experiments on single-walled carbon nanotubes in high magnetic fields, probing the influence of a tube-threading magnetic flux on their band structure and excitonic states. The magnetic flux breaks the time-reversal symmetry and thus lifts the K –K ′ valley degeneracy, and the amount of state splitting is determined by the Aharonov–Bohm phase. We show experimental evidence that this field-induced symmetry breaking overcomes the Coulomb-induced exciton splitting which is predicted to make the lowest singlet exciton state optically inactive (or “dark”). Thus, a magnetic field applied parallel to the tube axis “brightens” the dark exciton, resulting in a drastic increase in photoluminescence intensity with magnetic field. We also find that the amount of brightening increases with decreasing temperature.

Magnetoresistance of multiple electron gas wires at the AlGaAs/GaAs heterointerface - Hundhausen, Martin; et al. (Applied Physics Letters, 1988)
A parallel arrangement of thin wires has been fabricated in the Al xGa1-xAs/GaAs heterostructure with holographic lithography. The observed anisotropy of the conductivity parallel versus perpendicular to the wires proves the existence of isolated conduction paths. Transverse magnetoresistance is negative at 4 K and exhibits a shoulder at a magnetic field, where the diameter of the cyclotron orbit amounts to 90 nm, which is supposed to be the effective wire width.
UnivIS-Import:2015-03-05:Pub.1988.nat.dphy.IAP.exphys.magnet

Magneto spectroscopy of single-walled carbon nanotubes - Portugall, Oliver; Krstic, Vojislav; Rikken, Geert L.J.A.; Kono, Junichiro; Shaver, J.; Zaric‬, ‪Sasa; Moore, Valerie C.; Hauge, Robert H.; Smalley, Richard E.; Miyauchi, Y.; Maruyama, Shigeo (International Journal of Modern Physics B, 2007)
Carbon nano-tubes (CNTs) are attracting tremendous interest as the object of fundamental studies in condensed matter and molecular physics as well as possible functional units for future nano-devices. Some of the most striking features of CNTs are related to the symmetry breaking effect of high magnetic fields threading the tube axis. In the present paper we review the results of recent magneto-optical studies of single-walled CNTs in pulsed magnetic fields up to 71 T and at temperatures between 4.2 and 300 K. We present clear evidence for (a) the effect of the Aharonov-Bohm phase on the bandstructure of CNTs, (b) the existence of dark excitons in CNTs due to Coulomb mixing and (c) the effect of magnetic brightening, i.e. the increase of the quantum yield of CNTs under the influence of an external field. Experimental data was derived from large ensembles of individualized tubes in either aligned films or in liquid suspension. A brief discussion of the effect of dynamic magnetic alignment of suspended tubes will be included.
Keywords: Carbon nanotubes; Dark excitons; Aharonov-Bohm effect; Photoluminescence; Pulsed magnetic fields

Magnetotransport through Single-Walled Carbon Nanotubes - Krstic, Vojislav; Weis, Jürgen; Roth, Siegmar (Synthetic Metals, 2003)
Single-Walled Carbon Nanotubes were connected to noble metal leads with low contact resistance between tube and metal. Electrical transport measurements have been performed below 0.1 K in a magnetic field applied perpendicularly to the Single-Walled Carbon Nanotubes longitudinal axis. We have investigated in these measurements the dependence of the electrical transport through the nanotubes on magnetic field strength and direction, and on source-drain-voltage. Oscillatory behaviour as a function of the magnetic field and the source-drain-voltage is observed.
Keywords: Fullerenes and derivatives; Magnetotransport; Graphite and related compounds

Many-body interactions in photo-excited lead iodide perovskite - Trinh, M. Tuan; Wu, Xiaoxi; Niesner, Daniel; Zhu, X-Y (Journal of Materials Chemistry A, 2015)
Lead halide perovskite is emerging as a promising semiconductor material for thin film solar cells. Despite a large number of recent photophysical studies, the nature of photo-excitation in lead halide perovskite remains a subject of debate. Here we use transient absorption spectroscopy to re-examine lead halide perovskite thin films that have been reported to give very high solar cell efficiencies. We focus on many-body interactions that are manifested in (1) the transient Stark effect exerted by hot carriers on subsequent e-h pair generation; and (2) the Auger recombination due to three-body carrier-carrier interactions. These observations establish the dominance of free carriers from above band-gap excitation in lead halide perovskite. We also suggest the effective dynamic screening of charge carriers, likely due to orientational freedom of methylammonium cations in the perovskite lattice, and the presence of negligible charge carrier trapping in lead halide perovskite thin films grown in the presence of chloride precursors.

MAPPING OF UNOCCUPIED MINORITY SPIN BANDS OF CO AND NI USING INVERSE PHOTOEMISSION - Fauster, Thomas; et al. (Physical Review B, 1982)

Mapping the band structure of GeSbTe phase change alloys around the Fermi level - Kellner, Jens; Bihlmayer, Gustav; Liebmann, Marcus; Otto, Sebastian; Pauly, Christian; Boschker, Jos Emiel; Bragaglia, Valeria; Cecchi, Stefano; Wang, Rui Ning; Deringer, Volker L.; Küppers, Philipp; Bhaskar, Priyamvada; et al. (Communications Physics, 2018)

Maximization of the optical intra-cavity power of whispering-gallery mode resonators via coupling prism - Santamaría-Botello, G.A.; Garcia Munoz, Luis Enrique; Sedlmeir, Florian; Preu, Sascha; Preu, Sascha; Segovia-Vargas, Daniel; Atia Abdalmalak, K.; Llorente Romano, S.; García Lampérez, A.; Malzer, Stefan; Döhler, Gottfried; Schwefel, Harald; et al. (Optics Express, 2016)
In this paper, a detailed description of the optical coupling into a Whispering Gallery Mode (WGM) resonator through a prism via frustrated total internal reflection (FTIR) is presented. The problem is modeled as three media with planar interfaces and closed expressions for FTIR are given. Then, the curvature of the resonator is taken into account and the mode overlap is theoretically studied. A new analytical expression giving the optimal geometry of a disc-shaped or ring-shaped resonator for maximizing the intra-cavity circulating power is presented. Such expression takes into consideration the spatial distribution of the WGM at the surface of the resonator, thus being more accurate than the currently used expressions. It also takes into account the geometry of the prism. It is shown an improvement in the geometry values used with the current expressions of about 30%. The reason why the pump laser signal can be seen in experiments under critical coupling is explained on this basis. Then, the conditions required for exciting the highest possible optical power inside the resonator are obtained. The aim is to achieve a highly-efficient up-conversion of a THz signal into the optical domain via the second-order nonlinearity of the resonator material. (C) 2016 Optical Society of America

Measurement of Skeletal Muscle Fiber Contractility with High-Speed Traction Microscopy - Böhringer, David; Rausch, Martin; Steinmann, Martin; Schrüfer, Stefan; Schubert, Dirk W.; Haertl, Annamaria; Mark, Christoph; Fabry, Ben (BIOPHYSICAL JOURNAL, 2020)
CRIS-Team WoS Importer:2020-03-13

Measurement of Skeletal Muscle Fiber Contractility with High-Speed Traction Microscopy - Rausch, Martin; Böhringer, David; Steinmann, Martin; Schubert, Dirk W.; Schrüfer, Stefan; Mark, Christoph; Fabry, Ben (Biophysical Journal, 2020)
We describe a technique for simultaneous quantification of the contractile forces and cytosolic calcium dynamics of muscle fibers embedded in three-dimensional biopolymer gels under auxotonic loading conditions. We derive a scaling law for linear elastic matrices such as basement membrane extract hydrogels (Matrigel) that allows us to measure contractile force from the shape of the relaxed and contracted muscle cell and the Young's modulus of the matrix without further knowledge of the matrix deformations surrounding the cell and without performing computationally intensive inverse force reconstruction algorithms. We apply our method to isolated mouse flexor digitorum brevis (FDB) fibers that are embedded in 10 mg/mL Matrigel. Upon electrical stimulation, individual FDB fibers show twitch forces of 0.37 ± 0.15 μN and tetanic forces (100-Hz stimulation frequency) of 2.38 ± 0.71 μN, corresponding to a tension of 0.44 ± 0.25 kPa and 2.53 ± 1.17 kPa, respectively. Contractile forces of FDB fibers increase in response to caffeine and the troponin-calcium stabilizer tirasemtiv, similar to responses measured in whole muscle. From simultaneous high-speed measurements of cell length changes and cytosolic calcium concentration using confocal line scanning at a frequency of 2048 Hz, we show that twitch and tetanic force responses to electric pulses follow the low-pass filtered calcium signal. In summary, we present a technically simple high-speed method for measuring contractile forces and cytosolic calcium dynamics of single muscle fibers. We expect that our method will help to reduce preparation time, costs, and the number of sacrificed animals needed for experiments such as drug testing.
CRIS-Team Scopus Importer:2020-01-24

Measurement of the PtH defect depth profiles in fully processed silicon high-voltage diodes by improved current transient spectroscopy - Bergmann, Lena; Pobegen, Gregor; Schlogl, Daniel; Schulze, Holger; Weber, Heiko B.; Krieger, Michael (Proceedings of the International Symposium on Power Semiconductor Devices and ICs, 2022)
A new, simplified, and more versatile current transient spectroscopy (CTS) measurement setup is demonstrated. With this setup, the depth profile of the platinum-hydrogen (PtH) defect in fully processed silicon high-voltage (HV) test diodes is investigated. It is shown that a proton field stop (FS) at the backside of these test devices suppresses the in-diffusion of hydrogen (H) leading to a significant reduction of the PtH defect concentration throughout the entire volume of the diode. Furthermore, a strong correlation of the depth profile of the PtH defect and the leakage current is observed. Thus, we conclude that the PtH defect is the main generation center in the investigated devices.
CRIS-Team Scopus Importer:2023-03-17
Keywords: characterization; cryogenic; diode; high voltage current transient spectroscopy; minority carrier lifetime control; platinum; silicon point defects

Measurements of the Electric Field of Zero-Point Optical Phonons in GaAs Quantum Wells Support the Urbach Rule for Zero-Temperature Lifetime Broadening - Bhattacharya, Rupak; Mondal, Richarj; Khatua, Pradip; Rudra, Alok; Kapon, Eli; Malzer, Stefan; Döhler, Gottfried; Pal, Bipul; Bansal, Bhavtosh (Physical Review Letters, 2015)
We study a specific type of lifetime broadening resulting in the well-known exponential "Urbach tail" density of states within the energy gap of an insulator. After establishing the frequency and temperature dependence of the Urbach edge in GaAs quantum wells, we show that the broadening due to the zero-point optical phonons is the fundamental limit to the Urbach slope in high-quality samples. In rough analogy with Welton's heuristic interpretation of the Lamb shift, the zero-temperature contribution to the Urbach slope can be thought of as arising from the electric field of the zero-point longitudinal-optical phonons. The value of this electric field is experimentally measured to be 3 kV cm(-1), in excellent agreement with the theoretical estimate.

Measures of complexity derived from automata theory for characterising cardiological time series - Kirchner, Jens; Meyer, Wolfgang; Schwab, Jörg; Hensel, Bernhard (Biomedizinische Technik. Biomedical engineering, 2005)
In order to obtain information about the regulatory mechanisms of the human cardiovascular system, measures of complexity are used to characterise heart rate variability. A method introduced by Crutchfield and Young [1] for constructing an abstract automaton, which produces a given time series, is applied to cardiological data. We use measures of complexity derived from this model to detect differences between patients with congestive heart failure (CHF) and a reference group of healthy persons.<br

Mechanical control of cyclic AMP signalling and gene transcription through integrins - Meyer, Christian J.; Alenghat, Francis J.; Rim, Paul; Fong, Jenny Hwai-Jen; Fabry, Ben; Ingber, Donald E. (Nature Cell Biology, 2000)

Mechanically controlled tunneling of a single atomic defect - Weber, Heiko B.; et al. (EPL - Europhysics Letters, 2001)
This letter reports experiments on the conductance of mesoscopic Bi films which are polycrystalline and contain single atomic two-level tunneling systems. These defects act as electron scattering centers and give rise to random telegraph signals in the conductance. External strain, applied to the samples at low temperatures, changes the asymmetry energy of the double-well potential of the tunneling particle and thus controls its average dwell time in either well. The measurements allow to determine in a direct way the deformation potential of a particular tunneling defect.
UnivIS-Import:2017-11-07:Pub.2001.nat.dphy.IAP.LAP.mechan

Mechanical plasticity of cells - Bonakdar, Navid; Gerum, Richard; Kuhn, Michael; Spörrer, Marina; Lippert, Anna Helena; Schneider, Werner; Aifantis, Katerina E.; Fabry, Ben (Nature Materials, 2016)

Mechanical properties of cultured human airway smooth muscle cells from 0.05 to 0.4 Hz - Maksym, Geoffrey N.; Fabry, Ben; Butler, James P.; Navajas, Daniel; Tschumperlin, Daniel J.; Laporte, Johanne D.; Fredberg, Jeffrey (Journal of Applied Physiology, 2000)

Mechanical Regulation of Epithelial Tissue Homeostasis - Kaliman, Sara; Hubert, Maxime; Wollnik, Carina; Nuic, Lovro; Vurnek, Damir; Gehrer, Simone; Lovrić, Jakov; Dudziak, Diana; Rehfeldt, Florian; Smith, Ana-Suncana (Physical Review X, 2021)
Despite recent efforts to understand homeostasis in epithelial tissues, there are many unknowns surrounding this steady state. It is considered to be regulated by mechanoresponse, but unlike for single cells, this idea remains heavily debated for tissues. Here, we show that changes in matrix stiffness induce a nonequilibrium transition from tubular to squamous Madin-Darby Canine Kidney II tissues. Nonetheless, despite different cell morphologies and densities, all homeostatic tissues display equivalent topologies, which, hence, must be actively targeted and regulated. On the contrary, the mechanoresponse induces dramatic changes in the large-scale organization of the colonies. On stiff gels, this yields an unreported cooperative state of motile cells displaying higher densities than in the arrested homeostatic state, which suggests a more complex relation between cell density and motility than previously anticipated. Our results unequivocally relate the mechanosensitive properties of individual cells to the evolving macroscopic structures, an effect that could be important for understanding the emergent pathologies of living tissues.
CRIS-Team WoS Importer:2021-08-20

Mechanische Aspekte bei der Entwicklung künstlicher Herzklappen - Bolz, Armin; Schaldach, Max; Winter, Werner (Biomedizinische Technik, 1990)
UnivIS-Import:2015-03-05:Pub.1990.tech.FT.FT-TM.mechan

Mechanism of etching and surface relief development of PMMA under low-energy ion bombardment - Koval, Yury (Journal of Vacuum Science & Technology B, 2004)
The structure of the subsurface layer of polymethylmethacrylate (PMMA) formed by bombardment with low-energy ions of Ar was studied. The reduction in the energy of ions results in the modification of only a thin subsurface layer of a polymer. It was observed that the subsurface region contains a graphitized, cross-linked, and low-molecular weight layers. It was found that the ion etching causes various defects and typical features to appear on the surface of PMMA.

Mechanism of reaktive Ion etching of 6H-SiC in CHF3/O2 gas mixtures - Ristein, Jürgen; Ley, Lothar; et al. (Materials Science Forum, 1998)
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.IAP.exphys.mechan

Mechano-coupling and regulation of contractility by the vinculin tail domain - Goldmann, Wolfgang; Mierke, Claudia; Kollmannsberger, Philip; Zitterbart, Daniel Paranhos; Smith, James; Fabry, Ben; Goldmann, Wolfgang Heinrich (Biophysical Journal, 2007)
UnivIS-Import:2015-03-09:Pub.2007.nat.dphy.IAP.lpmt.mechan

Mechanosensing of Cells in Laminin-Fuctionalized Biomembrane-Mimicking Substrates - Lautscham, Lena; Lin, Corey Y.; Auernheimer, Vera; Minner, Daniel; Goldmann, Wolfgang; Naumann, Christoph A.; Fabry, Ben (Biophysical Journal, 2013)

Mechanotransduction, asthma, and airway smooth muscle - Fabry, Ben; Fredberg, Jeffrey (Drug Discovery Today: Disease Models, 2007)

Mechanotransduction: use the force(s) - Paluch, Ewa K.; Nelson, Celeste; Biais, Nicolas; Fabry, Ben; Möller, Jens; Pruit, Beth L.; Wollnik, Carina; Kudryasheva, Galina; Rehfeldt, Florian; federle, walter (BMC Biology, 2015)

Memory Effect of Self-Assembled PS-b-PEO Block Copolymer Films with Selectively Embedded Functionalized TiO2 Nanoparticles - Kirschner, Johannes; Will, Johannes; Rejek, Tobias; Portilla Berlanga, Luis; Berlinghof, Marvin; Schweizer, Peter; Spiecker, Erdmann; Steinrück, Hans-Georg; Unruh, Tobias; Halik, Marcus (Advanced Materials Interfaces, 2017)
The memory effect in organic thin film transistors is described with a dielectric hybrid material composed of selectively localized charge trapping titania nanoparticles in a polystyrene-b-polyethyleneoxide (PS-b-PEO) diblock copolymer film. Upon solvent annealing in toluene atmosphere, the films readily form nanophase-separated features of PEO cylinders in a matrix of PS. X-ray reflectivity (XRR) investigations reveal that the TiO2 particles are selectively distributed in the top half of the hybrid layers. Applied in organic thin film transistor devices with 2-tridecyl-[1]benzothieno[3,2-b][1]benzothiophen (mono-C13-BTBT) semiconductor, the hybrid layers induce clockwise drain current hysteresis with promising memory ratio, long-term stability, and endurance. The occurrence of nonvolatile charge trapping directly relates to the hierarchically assembled nanostructure of the nanoparticles in the block copolymer since reference devices with PS homopolymers blended with TiO2 are found to be hysteresis free. Morphological characterization of the hybrid dielectric layers by atomic force microscopy and XRR experiments is presented to shed light on the internal electron density distribution. The layers are subsequently tested in capacitor stacks and transistors.

Mesenchymal-Like Migration Strategies of Immune Cells in a 3D Environment - Czerwinski, Tina; Mark, Christoph; Roessner, Susanne; Bosch-Voskens, Caroline; Bhattacharjee, Tapomoy; Angelini, Thomas E.; Fabry, Ben (BIOPHYSICAL JOURNAL, 2020)
CRIS-Team WoS Importer:2020-03-13

Mesoscopic-scale structure and dynamics near the morphotropic phase boundary of (1-x)PbTiO3-xBiScO3 - Datta, Kaustuv; Richter, Andreas; Göbbels, Matthias; Neder, Reinhard; Mihailova, Boriana (Physical Review B - Condensed Matter and Materials Physics, 2015)
A range of compelling information on the local structure and dynamics of the ferroelectric perovskite-type (ABO3) system (1-x)PbTiO3-xBiScO3 has been revealed through analyzing room-temperature x-ray pair distribution functions and temperature-dependent Raman scattering data for compositions ranging across the morphotropic phase boundary (MPB). Raman scattering data have provided exclusive evidence for distinct dynamical responses from the A-site Pb/Bi and the B-site Ti/Sc cations as a function of composition and temperature. Both pair distribution function and Raman scattering analyses indicate improved coherence between the A-site and B-site off-center displacements for x above the MPB composition. The distinguishable dynamical features were spotted between two sets of compositional range from which x=0.34 could be assigned as a critical composition of "local" MPB: the composition at which the pathway of mesoscopic-scale temperature-driven coupling and transformation processes changes. This differs from the previous reports based on the analysis of the average structure, suggesting the response function of a system may not necessarily follow the evolution of the average structure from which however the MPB has so far been ascribed for a particular system. The individual features of the cations revealed here will further help in understanding the structure-property correlations for similar ferroelectric solid solutions.

Mesoscopic Structures of Triglyceride Nanosuspensions Studied by Small-Angle X-ray and Neutron Scattering and Computer Simulations - Schmiele, Martin; Schindler, Torben; Westermann, Martin; Steiniger, Frank; Radulescu, Aurel; Kriele, Armin; Gilles, Ralph; Unruh, Tobias (Journal of Physical Chemistry B, 2014)
Aqueous suspensions of platelet-like shaped tripalmitin nanocrystals are studied here at high tripalmitin concentrations (10 wt % tripalmitin) for the first time by a combination of small-angle X-ray and neutron scattering (SAXS and SANS). The suspensions are stabilized by different lecithins, namely, DLPC, DOPC, and the lecithin blend S100. At such high concentrations the platelets start to self-assemble in stacks, which causes interference maxima at low Q-values in the SAXS and SANS patterns, respectively. It is found that the stack-related interference maxima are more pronounced for the suspension stabilized with DOPC and in particular DLPC, compared to suspensions stabilized by S100. By use of the X-ray and neutron powder pattern simulation analysis (XNPPSA), the SAXS and SANS patterns of the native tripalmitin suspensions could only be reproduced simultaneously when assuming the presence of both isolated nanocrystals and stacks of nanocrystals of different size in the simulation model of the dispersions. By a fit of the simulated SAXS and SANS patterns to the experimental data, a distribution of the stack sizes and their volume fractions is determined. The volume fraction of stacklike platelet assemblies is found to rise from 70% for S100-stabilized suspensions to almost 100% for the DLPC-stabilized suspensions. The distribution of the platelet thicknesses could be determined with molecular resolution from a combined analysis of the SAXS and SANS patterns of the corresponding diluted tripalmitin (3 wt %) suspensions. In accordance with microcalorimetric data, it could be concluded that the platelets in the suspensions stabilized with DOPC, and in particular DLPC, are significantly thinner than those stabilized with S100. The DLPC-stabilized suspensions exhibit a significantly narrower platelet thickness distribution compared to DOPC- and S100-stabilized suspensions. The smaller thicknesses for the DLPC- and DOPC-stabilized platelets explain their higher tendency to self-assemble in stacks. The finding that the nanoparticles of the suspension stabilized by the saturated lecithin DLPC crystallize in the stable beta-tripalmitin modification with its characteristic platelet-like shape is surprising and can be explained by the fact that the main phase transformation temperature for DLPC is, as for unsaturated lecithins like DOPC and S100, well below the crystallization temperature of the supercooled tripalmitin emulsion droplets.

Metal- and Hydrogen-Bonding Competition during Water Adsorption on Pd(111) and Ru(0001) - Tatarkhanov, Mous; Ogletree, D. Frank; Rose, Franck; Mitsui, Toshiyuki; Fomin, Evgeny; Maier, Sabine; Rose, Mark; Cerda, Jorge I.; Salmeron, Miquel (Journal of the American Chemical Society, 2009)
The initial stages of water adsorption on the Pd(111) and Ru(0001) surfaces have been investigated experimentally by scanning tunneling microscopy in the temperature range between 40 and 130 K, and theoretically with density functional theory (DFT) total energy calculations and scanning tunneling microscopy (STM) image simulations. Below 125 K, water dissociation does not occur at any appreciable rate, and only molecular films are formed. Film growth starts by the formation of flat hexamer clusters where the molecules bind to the metal substrate through the O-lone pair while making H-bonds with neighboring molecules. As coverage increases, larger networks of linked hexagons are formed with a honeycomb structure, which requires a fraction of the water molecules to have their molecular plane perpendicular to the metal surface with reduced water-metal interaction. Energy minimization favors the growth of networks with limited width. As additional water molecules adsorb on the surface, they attach to the periphery of existing islands, where they interact only weakly with the metal substrate. These molecules hop along the periphery of the clusters at intermediate temperatures. At higher temperatures, they bind to the metal to continue the honeycomb growth. The water-Ru interaction is significantly stronger than the water-Pd interaction, which is consistent with the greater degree of hydrogen-bonded network formation and reduced water-metal bonding observed on Pd relative to Ru.

Metalated Graphyne-Based Networks as Two-Dimensional Materials: Crystallization, Topological Defects, Delocalized Electronic States, and Site-Specific Doping - Yang, Zechao; Sander, Tim; Gebhardt, Julian; Schaub, Tobias A.; Schonamsgruber, Jorg; Soni, Himadriben; Görling, Andreas; Kivala, Milan; Maier, Sabine (ACS nano, 2020)
Graphyne-based two-dimensional (2D) carbon allotropes feature extraordinary physical properties; however, their synthesis as crystalline single-layered materials has remained challenging. We report on the fabrication of large- area organometallic Ag-bis-acetylide networks and their structural and electronic properties on Ag(111) using low-temperature scanning tunneling microscopy combined with density functional theory (DFT) calculations. The metalated graphyne-based networks are robust at room temperature and assembled in a bottom-up approach via surface-assisted dehalogenative homocoupling of terminal alkynyl bromides. Large-area networks of several hundred nanometers with topological defects at domain boundaries are obtained due to the Ag-acetylide bonds' reversible nature. The thermodynamically controlled growth mechanism is explained through the direct observation of intermediates, which differ on Ag(111) and Au(111). Scanning tunneling spectroscopy resolved unoccupied states delocalized across the network. The energy of these states can be shifted locally by the attachment of a different number of Br atoms within the network. DFT revealed that free-standing metal-bis-acetylide networks are semimetals with a linear band dispersion around several high-symmetry points, which suggest the presence of Weyl points. These results demonstrate that the organometallic Ag-bis-acetylide networks feature the typical 2D material properties, which make them of great interest for fundamental studies and electronic materials in devices.
CRIS-Team WoS Importer:2021-01-22

Methyl group dynamics in glassy, polycrystalline, and liquid coenzyme Q(10) studied by quasielastic neutron scattering - Smuda, Christoph; Busch, Sebastian; Wagner, Bernd; Unruh, Tobias (Journal of Chemical Physics, 2008)
The methyl group rotation of coenzyme Q(10) confined in nanosized droplets was studied using quasielastic neutron scattering (QENS). Q(10) as an oligoisoprene derivative with ten isoprene units can easily be supercooled in nanodroplets. Fixed window scans and QENS spectra at several temperatures of glassy Q(10) were recorded to study the methyl group rotation which can be described by a logarithmic Gaussian distribution of hopping rates for temperatures below the glass transition temperature (T(g)approximate to 200 K). A mean activation energy of 4.8 kJ/mol with a distribution width of 2.1 kJ/mol was obtained from the evaluation of the QENS spectra. A corresponding analysis of a fixed window scan yielded an average activation energy of 5.1 kJ/mol with a distribution width of 1.8 kJ/mol. The results are compared and discussed with those of chain deuterated polyisoprene-d(5). For polycrystalline Q(10), the QENS spectra could be described by the same model yielding a similar average activation energy as found for glassy Q(10). However, no temperature dependence of the distribution width was observed. Based on the performed low-temperature measurements, the correlation times for the methyl group rotation were extrapolated to temperatures of liquid Q(10). The complex dynamics of liquid Q(10) could be described by a model yielding an apparent diffusion coefficient, the jump rate of the methyl groups, as well as an overall molecular rotational diffusion coefficient. The correlation times of the methyl group rotation in liquid Q(10) at a given temperature T(0) coincide with values determined in the glassy phase and extrapolated to T(0). (C) 2008 American Institute of Physics.

Methyl Group Dynamics in Polycrystalline and Liquid Ubiquinone Q(0) Studied by Neutron Scattering - Smuda, Christoph; Busch, Sebastian; Schellenberg, René; Unruh, Tobias (Journal of Physical Chemistry B, 2009)
We present a quasi-elastic neutron scattering (QENS) study on the methyl group dynamics of ubiquinone Q(0) in the solid and liquid state. For solid ubiquinone Q(0), the dynamics can be described with three Lorentzian functions in the framework of a jump model among three equidistant sites on a circle. According to the known molecular structure of Q(0) in the solid state, this is consistent with three nonequivalent methyl groups in the molecule. From the temperature-dependent analysis of the QENS spectra, the activation energies were determined. The barrier heights could be evaluated from librational bands in the inelastic part of the spectra. The results from neutron spectroscopy are compared to Gaussian 03 calculations leading to an assignment of the activation energies to the different methyl groups in Q(0). The dynamics of Q(0) in the liquid state is evaluated with a scattering function taking into account three different molecular motions. It is demonstrated that the temperature dependence of the long-range diffusion and isotropic rotational diffusion exhibit an Arrhenius-like behavior, whereas the process of methyl group rotation in the liquid phase is virtually free of a barrier.

micrObs – A customizable time-lapse camera for ecological studies - Winterl, Alexander; Richter, Sebastian; Houstin, Aymeric; Nesterova, Anna P.; Bonadonna, Francesco; Schneider, Werner; Fabry, Ben; Le Bohec, Céline; Paranhos Zitterbart, Daniel (HardwareX, 2020)
Camera traps for motion-triggered or continuous time-lapse recordings are readily available on the market. For demanding applications in ecology and environmental sciences, however, commercial systems often lack flexibility to freely adjust recording time intervals, suffer from mechanical component wear, and can be difficult to combine with auxiliary sensors such as GPS, weather stations, or light sensors. We present a robust time-lapse camera system that has been operating continuously since 2013 under the harsh climatic conditions of the Antarctic and Subantarctic regions. Thus far, we have recorded over one million images with individual cameras. The system consumes 122 mW of power in standby mode and captures up to 200,000 high-resolution (16 MPix) images without maintenance such as battery or image memory replacement. It offers time-lapse intervals between 2 s and 1 h, low-light or night-time power saving, and data logging capabilities for additional inputs such as GPS and weather data.
CRIS-Team Scopus Importer:2020-09-11
Keywords: Automated camera system; Collective behavior; Ecology; Image processing; Remote sensing; Wildlife monitoring

Microchip accelerators - England, R. Joel; Hommelhoff, Peter; Byer, Robert L. (Physics Today, 2021)
Particle accelerators are among the most important scientific tools of the modern age. Major accelerator facilities, such as the 27-km-circumference Large Hadron Collider in Switzerland, where the Higgs boson was recently discovered, allow scientists to uncover fundamental properties of matter and energy. But the particle energies needed to explore new regimes of physics have increased to the TeV scale and beyond, and accelerator facilities based on conventional technologies are becoming prohibitively large and costly. Even lower-energy, smaller-scale accelerators used in medicine and industry are often cumbersome devices; they can weigh several tons and cost millions of dollars.<br

Microconstriction Arrays for High-Throughput Quantitative Measurements of Cell Mechanical Properties - Lange, Janina; Steinwachs, Julian; Kolb, Thorsten; Lautscham, Lena; Harder, Irina; Whyte, Graeme; Fabry, Ben (Biophysical Journal, 2015)

Microrheology of human lung epithelial cells measured by atomic force microscopy - Alcaraz, Jordi; Buscemi, Lara; Grabulosa, Mireia Herrando; Trepat, Xavier; Fabry, Ben; Farrè, Ramon; Navajas, Daniel (Biophysical Journal, 2003)

Microscopic structure of the radiative centre in As2Se3 crystals - Ristein, Jürgen; et al. (Solid State Communications, 1988)
The dependence of the strongly Stokes shifted luminescence and of the photocurrent on the exciting light intensity points to the onset of bimolecular non radiative recombination of trapped geminate pairs at densities above 1018/cm3. Saturation of the luminescence is not observed which leads to the conclusion that excited pairs are self trapped by rapid lattice distortion. A microscopic model based on considerations of the chemical bonds and recent bandstructure calculations is proposed with the lattice distortion resulting from formation of an interlayer π bond involving Se lone pair states near an inversion centre. A precursor of the bond exists already in the ground state causing a small monoclinic distortion of the lattice and inequivalence of Se sites which in an isolated layer are related by mirror symmetry. © 1988.
UnivIS-Import:2015-03-05:Pub.1988.nat.dphy.IAP.exphys.micros

Microscopic structures and dynamics of high- and low-density liquid trans-1,2-dichloroethylene - Rovira-Esteva, Muriel; Murugan, A.; Pardo, Luis Carlos; Busch, Sebastian; Ruiz-Martin, M. D.; Appavou, Marie-Sousai; Tamarit, Josep Lluis; Smuda, Christoph; Unruh, Tobias; Bermejo, F. J.; Cuello, G. J.; Rzoska, S. J. (Physical Review B, 2010)
We present a study of the dynamics and structural changes for trans-1,2-dichloroethylene between high-and low-density liquids using neutron-scattering techniques (diffraction, small-angle neutron scattering, and time of flight spectroscopy) and molecular-dynamics simulations. We show that changes in the short-range ordering of molecules goes along with a change in the molecular dynamics: both structure and dynamics of the high-density liquid are more cooperative than those of the low-density liquid. The microscopic mechanism underlying the cooperative motions in the high-density liquid has been found to be related to the backscattering of molecules due to a strong correlation of molecular ordering.

Microwave chip-based beam splitter for low-energy guided electrons - Hammer, Jakob; Thomas, Sebastian; Weber, Philipp; Hommelhoff, Peter (Physical Review Letters, 2015)
We present a novel beam splitter for low-energy electrons using a micro-structured guiding potential created above the surface of a planar microwave chip. Beam splitting arises from smoothly transforming the transverse guiding potential for an electron beam from a single-well harmonic confinement into a double well, thereby generating two separated output beams with 5 mm lateral spacing. Efficient beam splitting is observed for electron kinetic energies up to 3 eV, in excellent agreement with particle tracking simulations. We discuss prospects of this novel beam splitter approach for electron-based quantum matter-wave optics experiments.

Microwave guiding of electrons on a chip - Hoffrogge, J.; Froehlich, R.; Kasevich, M. A.; Hommelhoff, Peter (Physical Review Letters, 2011)
We demonstrate the transverse confinement and guiding of a low energy electron beam of several electron volts in a miniaturized linear quadrupole guide. The guiding potential is generated by applying a microwave voltage to electrodes fabricated on a planar substrate, which allows the potential landscape to be precisely shaped on a microscopic scale. We realize transverse trapping frequencies of 100 MHz and guide electrons along a circular section of 37 mm length. A detailed characterization of the guiding properties in terms of potential depth and dynamic stability is given. This new technique of electron guiding promises various applications in guided matter-wave experiments such as electron interferometry. © 2011 American Physical Society.
UnivIS-Import:2015-03-09:Pub.2011.nat.dphy.IAP.exphys.microw

Migration in Confined 3D Environments Is Determined by a Combination of Adhesiveness, Nuclear Volume, Contractility, and Cell Stiffness - Lautscham, Lena; Kaemmerer, Christoph; Lange, Janina; Kolb, Thorsten; Mark, Christoph; Schilling, Achim; Strissel, Pamela; Strick, Reiner; Gluth, Caroline Laura Maria; Rowat, Amy C.; Metzner, Claus; Fabry, Ben (Biophysical Journal, 2015)
In cancer metastasis and other physiological processes, cells migrate through the three-dimensional (3D) extracellular matrix of connective tissue and must overcome the steric hindrance posed by pores that are smaller than the cells. It is currently assumed that low cell stiffness promotes cell migration through confined spaces, but other factors such as adhesion and traction forces may be equally important. To study 3D migration under confinement in a stiff (1.77 MPa) environment, we use soft lithography to fabricate polydimethylsiloxane (PDMS) devices consisting of linear channel segments with 20 ?m length, 3.7 ?m height, and a decreasing width from 11.2 to 1.7 ?m. To study 3D migration in a soft (550 Pa) environment, we use self-assembled collagen networks with an average pore size of 3 ?m. We then measure the ability of four different cancer cell lines to migrate through these 3D matrices, and correlate the results with cell physical properties including contractility, adhesiveness, cell stiffness, and nuclear volume. Furthermore, we alter cell adhesion by coating the channel walls with different amounts of adhesion proteins, and we increase cell stiffness by overexpression of the nuclear envelope protein lamin A. Although all cell lines are able to migrate through the smallest 1.7 ?m channels, we find significant differences in the migration velocity. Cell migration is impeded in cell lines with larger nuclei, lower adhesiveness, and to a lesser degree also in cells with lower contractility and higher stiffness. Our data show that the ability to overcome the steric hindrance of the matrix cannot be attributed to a single cell property but instead arises from a combination of adhesiveness, nuclear volume, contractility, and cell stiffness.
EVALuna2:17547

Miniature light-driven nanophotonic electron acceleration and control - Shiloh, Roy; Schönenberger, Norbert; Adiv, Yuval; Ruimy, Ron; Karnieli, Aviv; Hughes, Tyler; England, R. Joel; Leedle, Kenneth James; Black, Dylan S.; Zhao, Zhexin; Musumeci, Pietro; Byer, Robert L.; et al. (Advances in Optics and Photonics, 2022)
Dielectric laser accelerators (DLAs) are fundamentally based on the interaction of photons with free electrons, where energy and momentum conservation are satisfied by mediation of a nanostructure. In this scheme, the photonic nanostructure induces near-fields which transfer energy from the photon to the electron, similar to the inverse-Smith-Purcell effect described in metallic gratings. This, in turn, may provide ground-breaking applications, as it is a technology promising to miniaturize particle accelerators down to the chip scale. This fundamental interaction can also be used to study and demonstrate quantum photon-electron phenomena. The spontaneous and stimulated Smith-Purcell effect and the photon-induced near-field electron-microscopy (PINEM) effect have evolved to be a fruitful ground for observing quantum effects. In particular, the energy spectrum of the free electron has been shown to have discrete energy peaks, spaced with the interacting photon energy. This energy spectrum is corre-lated to the photon statistics and number of photon exchanges that took place during the interaction. We give an overview of DLA and PINEM physics with a focus on electron phase-space manipulation. (c) 2022 Optica Publishing Group
CRIS-Team WoS Importer:2023-02-24

Misfit strain of oxygen precipitates in Czochralski silicon studied with energy-dispersive X-ray diffraction - Gröschel, Alexander; Will, Johannes; Bergmann, Christoph; Magerl, Andreas (Journal of Applied Physics, 2014)
Annealed Czochralski Silicon wafers containing SiOx precipitates have been studied by high energy X-ray diffraction in a defocused Laue setup using a laboratory tungsten tube. The energy dispersive evaluation of the diffracted Bragg intensity of the 220 reflection within the framework of the statistical dynamical theory yields the static Debye-Waller factor E of the crystal, which gives access to the strain induced by the SiOx precipitates. The results are correlated with precipitate densities and sizes determined from transmission electron microscopy measurements of equivalent wafers. This allows for the determination of the constrained linear misfit epsilon between precipitate and crystal lattice. For samples with octahedral precipitates the values ranging from epsilon=0.39 (+0.28/-0.12) to epsilon=0.48 (+0.34/-0.16) indicate that self-interstitials emitted into the matrix during precipitate growth contribute to the lattice strain. In this case, the expected value calculated from literature values is epsilon=0.26 +/- 0.05. Further, the precise evaluation of Pendellosung oscillations in the diffracted Bragg intensity of as-grown wafers reveals a thermal Debye-Waller parameter for the 220 reflection B-220(293 K) of 0.5582 +/- 0.0039 angstrom(2) for a structure factor based on spherically symmetric scattering contributions. (C) 2014 AIP Publishing LLC.

Mixed Organic Ligand Shells: Controlling the Nanoparticle Surface Morphology toward Tuning the Optoelectronic Properties - Henkel, Christian; Wittmann, Judith; Träg, Johannes; Will, Johannes; Stiegler, Lisa; Strohriegl, Peter; Hirsch, Andreas; Unruh, Tobias; Zahn, Dirk; Halik, Marcus; Guldi, Dirk Michael (Small, 2020)
Precise control over the ratio of perylene bisimide (PBI) monomers and aggregates, immobilized on alumina nanoparticle (NP) surfaces, is demonstrated. Towards this goal, phosphonic acid functionalized PBI derivatives (PA-PBI) are shown to self-assemble into stoichiometrically mixed monolayers featuring aliphatic, glycolic, or fluorinated phosphonic acid ligands, serving as imbedding matrix (PA-M) to afford core-shell NPs. Different but, nevertheless, defined PBI monomer/aggregate composition is achieved by either the variation in the PA-PBI to PA-M ratios, or the utilization of different PA-Ms. Various steady-state as well as time-resolved spectroscopy techniques are applied to probe the core-shell NPs with respect to changes in their optical properties upon variations in the shell composition. To this end, the ratio between monomer and excimer-like emission assists in deriving information on the self-assembled monolayer composition, local ordering, and corresponding aggregate content. With the help of X-ray reflectivity measurements, accompanied by molecular dynamics simulations, the built-up of the particle shells, in general, and the PBI aggregation behavior, in particular, are explored in depth.
CRIS-Team WoS Importer:2019-12-10

Model for persistent photoconductivity in doping-modulated amorphous silicon superlattices - Hundhausen, Martin; Ley, Lothar (Physical Review B, 1985)
Doping superlattices prepared by depositing successively 105-AÌ-thick layers of n-type, intrinsic, and p-type amorphous hydrogenated silicon (n-i-p-i structures), exhibit persistent photoconductivity at room temperature. Persistent photoconductivity (PPC) is the excess dark conductivity that remains after the sample has been exposed to white, heat-filtered light and that decays on a time-scale of hours or days. We prove that PPC is a bulk effect and that the amount of light necessary to induce a certain level of PPC decreases exponentially with temperature. This temperature dependence corresponds to an activation energy of 1/40.4 eV for the creation of state PPC; a slightly higher activation energy (1/40.7 eV) for the quenching of PPC is deduced from the annealing behavior. Above around 400 K the sample can be transformed into a second metastable state C, which does not exhibit PPC. The fact that the generation of PPC is thermally activated 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 n-i-p-i structure. We propose instead that holes are trapped in acceptorlike centers, AX, in the p regions of the sample, whereas the balancing concentration of electrons, confined to the n layers by the n-i-p-i 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 The American Physical Society.
UnivIS-Import:2015-03-05:Pub.1985.nat.dphy.IAP.exphys.modelf

Modeling and optimization of single-pass laser amplifiers for high-repetition-rate laser pulses - Ozawa, Akira; Udem, Thomas; Zeitner, Uwe D.; Haensch, Theodor W.; Hommelhoff, Peter (Physical Review A, 2010)
We propose a model for a continuously pumped single-pass amplifier for continuous and pulsed laser beams. The model takes into account Gaussian shape and focusing geometry of pump and seed beam. As the full-wave simulation is complex we have developed a largely simplified numerical method that can be applied to rotationally symmetric geometries. With the tapered-shell model we treat (focused) propagation and amplification of an initially Gaussian beam in a gain crystal. The implementation can be done with a few lines of code that are given in this paper. With this code, a numerical parameter optimization is straightforward and example results are shown. We compare the results of our simple model with those of a full-wave simulation and show that they agree well. A comparison of model and experimental data also shows good agreement. We investigate in detail different regimes of amplification, namely the unsaturated, the fully saturated, and the intermediate regime. Because the amplification process is affected by spatially varying saturation and exhibits a nonlinear response against pump and seed power, no analytical expression for the expected output is available. For modeling of the amplification we employ a four-level system and show that if the fluorescence lifetime of the gain medium is larger than the inverse repetition rate of the seed beam, continuous-wave amplification can be employed to describe the amplification process of ultrashort pulse trains. We limit ourselves to this regime, which implies that if titanium:sapphire is chosen as gain medium the laser repetition rate has to be larger than a few megahertz. We show detailed simulation results for titanium:sapphire for a large parameter set. © 2010 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2010.nat.dphy.IAP.exphys.modeli

Modeling the evolution of ellipsometric data during the thermally induced Pt-silicide formation: activation energies and prefactors - Ley, Lothar; Hundhausen, Martin; et al. (Symposium. Materials Research Society, 1999)
The formation of Pt silicide (PtSi) by the thermally activated reaction of a 23 nm Pt layer on Si was monitored in situ by ellipsometry. Characteristic changes in the ellipsometric angles as a function of temperature signal the approach of two reaction fronts to the surface: one belonging to the Pt/Pt2Si and the other to the Pt2Si/PtSi interface. An analysis of the evolution of the ellipsometric angles as a function of temperature for different heating rates allows the accurate determination of the average activation energies of the two reactions. From a modeling of the optical data in terms of a specific reaction model further kinetic parameters such as the reaction rate constants and the actual distribution of activation energies have been deduced.
UnivIS-Import:2015-04-16:Pub.1999.nat.dphy.IAP.exphys.modeli

Modulational instability and solitons in excitonic semiconductor waveguides - Malzer, Stefan; Smyrnov, Oleksii; Biancalana, Fabio (Physical Review B, 2011)
Nonlinear light propagation in a single-mode micron-size waveguide made of semiconducting excitonic material has been theoretically studied in terms of exciton polaritons by using an analysis based on macroscopic fields. When a light pulse is spectrally centered in the vicinity of the ground-state Wannier exciton resonance, it interacts with the medium nonlinearly. This optical cubic nonlinearity is caused by the repulsive exciton-exciton interactions in the semiconductor, and at resonance it is orders of magnitude larger than the Kerr nonlinearity (e.g., in silica). We demonstrate that a very strong and unconventional modulational instability takes place, which has not been previously reported. After reducing the problem to a single nonlinear Schrödinger-like equation, we also explore the formation of solitary waves both inside and outside the polaritonic gap and find evidence of spectral broadening. A realistic physical model of the excitonic waveguide structure is proposed. © 2011 American Physical Society.

Molecular and electronic structure of PTCDA on bilayer graphene on SiC(0001) studied with scanning tunneling microscopy - Lauffer, Peter; Emtsev, Konstantin; Graupner, Ralf; Seyller, Thomas; Ley, Lothar (physica status solidi (b), 2008)
Epitaxial growth of graphene on SiC surfaces by solid state graphitization is a promising route for future development of graphene based electronics. In the present work we study the morphology and molecular scale structure of monolayer films of 3,4,9,10-perylene tetracarboxylic dianhydrid (PTCDA) on bilayer graphene on SiC(0001) by scanning tunneling microscopy (STM). First we discuss how the PTCDA molecules adsorb on bilayer graphene. We specially regard the density of PTCDA molecules at monolayer coverage. From the comparison with experiments on HOPG (Au(111) and Ag(110) from literature) we infer a non-planar adsorption geometry of PTCDA molecules on bilayer graphene. The electronic structure of the surrounding bilayer graphene substrate is investigated via scanning tunneling spectroscopy (STS) and reveals n-type doping of bilayer graphene during adsorption of PTCDA. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

Molecular assemblies on surfaces: towards physical and electronic decoupling of organic molecules - Maier, Sabine; Stohr, Meike (Beilstein Journal of Nanotechnology, 2021)
CRIS-Team WoS Importer:2021-09-03

Molecular beam epitaxy of graphene on mica - Lippert, G.; Dabrowski, J.; Yamamoto, Y.; Herziger, F.; Maultzsch, Janina; Baringhaus, J.; Tegenkamp, C.; Lemme, M. C.; Mehr, W.; Lupina, G. (physica status solidi (b), 2012)
Realization of graphene devices is often hindered by the fact that the known layer growth methods do not meet the requirements of the device fabrication in silicon mainstream technology. For example, the relatively straightforward method of decomposition of hexagonal SiC is not CMOS-compatible due to the high-thermal budget it requires [Moon et al., IEEE Electron Device Lett. 31, 260 (2010)]. Techniques based on layer transfer are restricted because of the uncertainty of residual metal contaminants, particles, and structural defects. Of interest is thus a method that would allow one to grow a graphene film directly in the device area where graphene is needed. Production of large area graphene is not necessarily required in this case, but high quality of the film and metal-free growth on an insulating substrate at temperatures below 1000 degrees C are important requirements. We demonstrate direct growth of defect-free graphene on insulators at moderate temperatures by molecular beam epitaxy. The quality of the graphene was probed by high-resolution Raman spectroscopy, indicating a negligible density of defects. The spectra are compared with those from graphene flakes mechanically exfoliated from native graphite onto mica. These results are combined with insights from density functional theory calculations. A model of graphene growth on mica and similar substrates is proposed.
Keywords: graphene; growth; insulator; MBE

Molecular beam growth of micrometer-size graphene on mica - Lippert, Gunther; Dabrowski, Jarek; Yamamoto, Yuji; Herziger, Felix; Maultzsch, Janina; Lemme, Max C.; Mehr, Wolfgang; Lupina, Grzegorz (Carbon, 2013)
We demonstrate molecular beam growth of graphene on biotite mica substrates at temperatures below 1000 degrees C. As indicated by optical and atomic force microscopy, evaporation of carbon from a high purity solid-state source onto biotite surface results in the formation of single-, bi-, and multilayer graphene with size in the micrometer regime. It is shown that the graphene grown directly on mica surface is of very high crystalline quality with the defect density below the threshold detectable by Raman spectroscopy. The interaction between graphene and the mica substrate is studied by comparison of the Raman spectroscopy and atomic force microscopy data with the corresponding results obtained for graphene flakes mechanically exfoliated onto biotite substrates. Experimental insights are combined with density functional theory calculations to propose a model for the initial stage of the van der Waals growth of graphene on mica surfaces. This work provides hints on how the direct growth of high quality graphene on insulators can be realized in general without exceeding the thermal budget limitations of Si technologies. (C) 2012 Elsevier Ltd. All rights reserved.

Molecular changes induced in melanoma by cell culturing in 3D alginate hydrogels - Kappelmann-Fenzl, M.; Schmidt, Sonja; Fischer, Stefan; Schmid, Rafael; Lämmerhirt, Lisa; Fischer, Lena; Schrüfer, Stefan; Thievessen, Ingo; Schubert, Dirk W.; Matthies, Alexander Oliver; Detsch, Rainer; Boccaccini, Aldo R.; et al. (Cancers, 2021)
Alginate hydrogels have been used as a biomaterial for 3D culturing for several years. Here, gene expression patterns in melanoma cells cultivated in 3D alginate are compared to 2D cultures. It is well-known that 2D cell culture is not resembling the complex in vivo situation well. However, the use of very intricate 3D models does not allow performing high-throughput screening and analysis is highly complex. 3D cell culture strategies in hydrogels will better mimic the in vivo situation while they maintain feasibility for large-scale analysis. As alginate is an easy-to-use material and due to its favorable properties, it is commonly applied as a bioink component in the growing field of cell encapsulation and biofabrication. Yet, only a little information about the transcriptome in 3D cultures in hydrogels like alginate is available. In this study, changes in the transcriptome based on RNA-Seq data by cultivating melanoma cells in 3D alginate are analyzed and reveal marked changes compared to cells cultured on usual 2D tissue culture plastic. Deregulated genes represent valuable cues to signaling pathways and molecules affected by the culture method. Using this as a model system for tumor cell plasticity and heterogeneity, EGR1 is determined to play an important role in melanoma progression.
CRIS-Team Scopus Importer:2021-08-20
Keywords: 3D cultivation; Biomaterials; EGR1; Melanoma; Whole transcriptome

Molecular electronics - Integration of single molecules in electronic circuits - Mayor, Marcel; Weber, Heiko B. (Chimia, 2002)
Electronic devices made with organic molecules may one day play an important role in integrated circuits. However, the research is still in its infancy. The mechanically controlled break-junction technique allows the measurement of the current through a single molecule junction. The current-voltage relations indicate a nonlinear conductance. Information about the junction can be provided by comparative studies of different molecules. It turns out that the conduction properties depend strongly on the molecular structure. This, in turn, encourages the idea of tailoring the electronic properties by an appropriate design of the molecule.
Keywords: break-junction; electron transport; molecular electronics; molecular wires; single-molecule studies

Molecular embroidering of graphene - Wei, Tao; Kohring, Malte; Weber, Heiko B.; Hauke, Frank; Hirsch, Andreas (Nature Communications, 2021)

Molecular Mechanism of Long-Range Diffusion in Phospholipid Membranes Studied by Quasielastic Neutron Scattering - Busch, Sebastian; Smuda, Christoph; Pardo, Luis Carlos; Unruh, Tobias (Journal of the American Chemical Society, 2010)

Molecular Stacking on Graphene - Wei, Tao; Liu, Xin; Kohring, Malte; Al-Fogra, Sabrin; Moritz, Michael; Hemmeter, Daniel; Paap, Ulrike; Papp, Christian; Steinrück, Hans-Peter; Bachmann, Julien; Weber, Heiko B.; Hauke, Frank; et al. (Angewandte Chemie International Edition, 2022)
The sequentialverticalpolyfunctionalizationof 2D addend-patternedgrapheneis still elusive.Here,we reporta practicalrealizationof this goalvia a “molecularbuildingblocks”approach,whichis basedon a combinationof alithography-assistedreductivefunctionalizationapproachanda post-functionalizationstepto sequentiallyandcontrollablylink the molecularbuildingblocksethylpyridine,cis-dichlorobis(2,2’-bipyridyl)ruthenium,and triphenyl-phosphine(4-methylbenzenethiol,respectively)on selectedlatticeregionsof a graphenematrix.The assembled2Dhetero-architecturesare unambiguouslycharacterizedby variousspectroscopicand microscopicmeasurements,revealingthe stepwisestackingof the molecularbuildingblockson the graphenesurface.Our methodovercomesthe currentlimitationof a one-layer-onlybindingto the graphenesurfaceand opensthe doorfor a verticalgrowthin the z-directio

Molecular wires in single-molecule junctions: Charge transport and vibrational excitations - Ballmann, Stefan; Hieringer, Wolfgang; Secker, Daniel; Zheng, Q.; Gladysz, John A.; Görling, Andreas; Weber, Heiko B. (ChemPhysChem, 2010)
We investigate the effect of vibrations on the electronic transport through single-molecule junctions, using the mechanically controlled break junction technique. The molecules under investigation are oligoyne chains with appropriate end groups, which represent both an ideally linear electrical wire and an ideal molecular vibrating string. Vibronic features can be detected as satellites to the electronic transitions, which are assigned to longitudinal modes of the string by comparison with density functional theory data. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

MOMENTUM-RESOLVED BREMSSTRAHLUNG SPECTROSCOPY WITH A TUNABLE PHOTON DETECTOR - Fauster, Thomas; et al. (Journal of Vacuum Science & Technology A, 1983)

Momentum transfer from quantum vacuum to magnetoelectric matter - van Tiggelen, ‪Bart; Rikken, Geert L.J.A.; Krstic, Vojislav (Physical Review Letters, 2006)
A recent publication [Phys. Rev. Lett. 92, 020404 (2004)] raises the possibility of momentum transfer from zero-point quantum fluctuations to matter, controlled by applied electric and magnetic fields. We present a Lorentz-invariant description using field-theoretical regularization techniques. We find no momentum transfer for homogeneous media, but predict a very small transfer for a Casimir-type geometry.

Monatomic Co, CoO2, and CoO3 nanowires on Ir(100) and Pt(100) surfaces: Formation, structure, and energetics - Ferstl, Pascal; Mittendorfer, Florian; Redinger, Josef; Schneider, M. Alexander; Hammer, Lutz (Physical Review B, 2017)
In this study, we investigate the structural and chemical changes of monatomic CoO2 chains grown self-organized on the Ir(100) surface [P. Ferstl et al., Phys. Rev. Lett. 117, 046101 (2016)] and on Pt(100) under reducing and oxidizing conditions. By a combination of quantitative low-energy electron diffraction, scanning tunneling microscopy, and density functional theory we show that the cobalt oxide wires are completely reduced by H-2 at temperatures above 320 K and a 3 x 1 ordered Ir2Co or Pt2Co surface alloy is formed. Depending on temperature, the surface alloy on Ir(100) is either hydrogen covered (T < 400 K) or clean and eventually undergoes an irreversible order-disorder transition at about 570 K. The Pt2Co surface alloy disorders with the desorption of hydrogen, whereby Co submerges into subsurface sites. Vice versa, applying stronger oxidants than O-2 such as NO2 leads to the formation of CoO3 chains on Ir(100) in a 3 x 1 superstructure. On Pt(100), such a CoO3 phase could not be prepared so far, which, however, is due to the ultrahigh vacuum conditions of our experiments. As revealed by theory, this phase will become stable in a regime of higher pressure. In general, the structures can be reversibly switched on both surfaces using the respective agents O-2, NO2, and H-2.

Monitoring of the nano-structure response of natural clay under mechanical perturbation using small angle X-ray scattering and digital image correlation - Birmpilis, Georgios; Hall, Stephen A.; Lages, Sebastian; Dijkstra, Jelke (Acta Geotechnica, 2019)
This paper introduces a new experimental method to monitor the evolving intra-particle, nanometre-scale response during hydro-mechanical tests on undisturbed wet clay samples using small angle X-ray scattering (SAXS). The method uses a newly developed miniature plane-strain one-dimensional compression cell that facilitates simultaneous full-field surface displacement measurements using digital image correlation and SAXS measurements. The 60–120 s acquisition times offered by SAXS at synchrotron facilities are beneficial to study time-dependent mechanisms in clays. The experimental results presented indicate that, for the natural sensitive clay tested in this work, no significant structural changes occur at the intra-particle scale during loading, even when large strains are measured at the macro-scale. In addition, changes that are observed at this scale occur after the end of perturbation, i.e. the creation of new intra-particle structures. Further information is obtained on the orientation evolution of the fabric by the comparative analysis of the individual mineral component response.
CRIS-Team Scopus Importer:2019-07-09
Keywords: Clay; DIC; Directional anisotropy; Nanoscale; Real-time; SAXS

Monolayer black phosphorus by sequential wet-chemical surface oxidation - Wild, Stefan; Lloret, Vicent; Vega-Mayoral, Victor; Vella, Daniele; Nuin, Edurne; Siebert, Martin; Kolesnik-Gray, Maria; Loeffler, Mario; Mayrhofer, Karl J. J.; Gadermaier, Christoph; Krstic, Vojislav; Hauke, Frank; et al. (RSC Advances, 2019)
We report a straightforward chemical methodology for controlling the thickness of black phosphorus flakes down to the monolayer limit by layer-by-layer oxidation and thinning, using water as solubilizing agent. Moreover, the oxidation process can be stopped at will by two different passivation procedures, namely the non-covalent functionalization with perylene diimide chromophores, which prevents the photooxidation, or by using a protective ionic liquid layer. The obtained flakes preserve their electronic properties as demonstrated by fabricating a BP field-effect transistor (FET). This work paves the way for the preparation of BP devices with controlled thickness.
CRIS-Team WoS Importer:2019-02-21

Monolithic circuits with epitaxial graphene/silicon carbide transistors - Hertel, Stefan; Krieger, Michael; Weber, Heiko B. (Physica Status Solidi, 2014)
A concept is presented that uses epitaxial graphene on silicon carbide (SiC) for digital circuits. It uses graphene as a metal and the underlying substrate SiC as semiconductor. On the base of transistors with excellent switching behavior, Inverter and NAND operation is demonstrated. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) A concept is presented that uses epitaxial graphene on silicon carbide (SiC) for digital circuits. It uses graphene as a metal and the underlying substrate SiC as semiconductor. On the base of transistors with excellent switching behavior, Inverter and NAND operation is demonstrated. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.LAP.monoli
Keywords: Digital logic; Electronic circuits; Epitaxial graphene; Silicon carbides

Morphology-Controlled Organic Solar Cells Improved by a Nanohybrid System of Single Wall Carbon Nanotubes Sensitized by PbS Core/Perovskite Epitaxial Ligand Shell Quantum Dots - Soltani, Rezvan; Katbab, Ali Asghar; Sytnyk, Mykhailo; Amin, Atefeh Y.; Killilea, Niall Andrew; Berlinghof, Marvin; Ahmadloo, Farzaneh; Osvet, Andres; Unruh, Tobias; Heiß, Wolfgang; Ameri, Tayebeh (Solar RRL, 2017)
In the present work, a new solution processed nanohybrid system comprising of single-wall carbon nanotubes (SWCNTs) loaded by PbS quantum dots (QD) capped with an epitaxial ligand shell of methylammonium lead iodide perovskite clusters (MA4PbI6) is designed and fabricated. Attachment of PbS/PbI6 QDs on the surface of SWCNT is followed and evidenced by performing Fourier Transform Infrared Spectroscopy, X-ray photoelectron spectroscopy, and Field Emission Scanning Electron Microscopy. The steady state and dynamic photoluminescence results reveal efficient charge transfer from photo-excited PbS/PbI6 to SWCNTs. Very low amount (0.3 wt.%) of the as-synthesized PbS/PbI6-SWCNT is further incorporated into a polymeric solar cell containing P3HT and PC61BM and exhibits a power conversion efficiency improvement of around 15% compared to the P3HT:PC61BM bulk heterojunction reference solar cell. Significantly, loading perovskite capped PbS QDs on the surface of SWCNT works more efficient rather than incorporating PbS/PbI6 or SWCNT separately onto the composition of the photoactive layer. While PbS/PbI6 broaden the absorption window of photoactive layer and enhance the photon harvesting, their loading on the SWCNT has a significant influence on the faster exciton splitting by efficient electron transfer as well as keeping the desired crystallinity and nanoscale morphology of host matrix upon addition of QDs.

Moving Grating Technique: A New Method for the Determination of Electron and Hole Mobilities and their Lifetime - Hundhausen, Martin; Ley, Lothar; et al. (Applied Physics Letters, 1993)
A new technique to determine the mobilities and lifetime of photogenerated electrons and holes in semiconductors relies on the short circuit current that is induced perpendicularly to a moving interference grating. Theoretical expressions for the short circuit current are derived that relate the carrier mobilities and their lifetime to the velocity and spatial period of the grating. The technique has been implemented and was successfully applied to a-Si:H.
UnivIS-Import:2015-03-05:Pub.1993.nat.dphy.IAP.exphys.moving

Moving Photocarrier Grating Technique for Mobility and Lifetime Measurements in Amorphous Semiconductors - Hundhausen, Martin; Ley, Lothar; et al. (Materials Research Society Symposium - Proceedings, 1994)
In this paper we describe a new method for the determination of the carrier lifetime (τ) and the carrier mobilities (μn, μp) in semiconductors. This technique utilizes a moving intensity grating that is generated by superposition of frequency shifted laser beams for the illumination of the sample. The material parameters are extracted from the short circuit current in the sample induced by the moving grating as a function of it's velocity (υgr). We solve the continuity equations and Poisson's equation in the small signal approach for the modulated electron and hole densities and show how these densities result in an electric field that in turn acts on the electrons and holes in order to yield a short circuit current density jsc. Erom a fit of this expression for jsc to experimental data we determine μn, μp and T. © 1994 Materials Research Society.
UnivIS-Import:2015-03-05:Pub.1994.nat.dphy.IAP.exphys.moving

Multifunctional and Tunable Surfaces Based on Pyrene Functionalized Nanoparticles - Wittmann, Judith; Stiegler, Lisa; Henkel, Christian; Träg, Johannes; Götz, Klaus; Unruh, Tobias; Zahn, Dirk; Hirsch, Andreas; Guldi, Dirk Michael; Halik, Marcus (Advanced Materials Interfaces, 2019)
The tuning of the optical properties of pyrene, immobilized on alumina nanoparticle surfaces, is demonstrated. To this end, phosphonic acid functionalized pyrene derivatives are shown to self‐assemble into stoichiometrically mixed monolayers featuring hydrophilic, hydrophobic, or fluorophilic phosphonic acid ligands and to form defined core–shell hybrids depending on the molecular mixing ratio and the nature of the ligand monomer, excimer, or mutual emission of both evolved. The spectroscopic observations are explained by the respective mobility of the dye molecules with respect to their fixed, specific anchor points and the resulting probability to form excimers and are supported by molecular dynamic simulations, X‐ray reflectivity measurements, and temperature‐dependent steady‐state fluorescence assays. In terms of an additional tuning of the emission color change and/or the on‐off switching of the fluorescence, the formation of core–shell–shell system is carried out by applying amphiphiles. The general concept is fully transferable to demobilized films of nanoparticles, thereby enabling a switchable solid‐state surfac

Multimodeling Approach to Ferromagnetic Spin-Wave Excitations in the High-Spin Cluster Mn18Sr Observed by Inelastic Neutron Scattering - Nekuruh, Siyavash; Nehrkorn, Joscha; Prsa, Krunoslav; Dreiser, Jan; Ako, Ayuk M.; Anson, Christopher E.; Unruh, Tobias; Powell, Annie K.; Waldmann, Oliver (Inorganic Chemistry, 2019)
The magnetism of the mixed-valence high-spin cluster [Mn18SrO8(N3)7Cl(MedhmpH)12(MeCN)6]Cl2 (1) exhibiting intramolecular ferromagnetic interactions was studied using inelastic neutron scattering (INS), and reliable values for the exchange coupling constants were determined based on the quality of simultaneous fits to the INS and magnetic data. The challenge of the huge size of the Hilbert space (3 375 000) and many exchange coupling constants (7 assuming a C3 symmetry) generally encountered in large spin clusters was resolved as follows: (a) The results of the restricted Hilbert space ferromagnetic cluster spin wave theory were compared to the experimental spectroscopic data. The observed INS transitions were thus assigned to spin wave excitations in a bounded ferromagnetic spin cluster and moreover could be visualized in a straightforward way based on this theory. (b) Simultaneously, Quantum Monte Carlo (QMC) calculations of the temperature-dependent magnetic susceptibility with the same parameter set were compared to the experimental data. Application of state-of-the-art QMC algorithms, as available in the open source ALPS package, in ferromagnetic clusters avoids the full Hamiltonian diagonalization without sacrificing calculation accuracy of the magnetic susceptibility down to the lowest temperatures, which was crucial for the successful analysis. The combined fits revealed two exchange-coupling models with equally good overall agreement to the data. Our preferred model was inspired by magnetostructural correlations and is consistent with them. The model involves three different exchange interactions, one describing the interaction between the core MnIII spins Ja = 14.3(1.0) K and two interactions linking the core and the peripheral MnII spins: Jb = 8.3(4) K and J6 = 3.6(4) K. The use of open-source QMC software and our systematic approach to fitting multiple sets of data obtained by different experimental techniques are described in detail and are generally applicable for understanding large ferromagnetically coupled clusters.
CRIS-Team Scopus Importer:2019-09-03

Multiphoton electron emission with non-classical light - Heimerl, Jonas; Mikhaylov, Alexander; Meier, Stefan; Höllerer, Henrick; Kaminer, Ido; Chekhova, Maria; Hommelhoff, Peter (Nature Physics, 2024)
Photon number distributions of classical and non-classical light sources have been studied extensively, yet their impact on photoemission processes is largely unexplored. In this article, we present measurements of electron number distributions from metal needle tips illuminated with ultrashort light pulses with various photon quantum statistics. By varying the photon statistics of the exciting light field between classical (Poissonian) and quantum (super-Poissonian), we demonstrate that the measured electron distributions are changed substantially. Using single-mode bright squeezed vacuum light, we measure extreme statistics events with up to 65 electrons from one light pulse at a mean of 0.27 electrons per pulse—the likelihood for such an event equals 10−128 with Poissonian statistics. By changing the number of modes of the exciting bright squeezed vacuum, we can tailor the electron number distribution on demand. Most importantly, our results demonstrate that the photon statistics is imprinted from the driving light to the emitted electrons, opening the door to new sensor devices and to strong-field optics with quantum light and electrons.<br
Keywords: Nanophotonics and plasmonics; Nonlinear optics; Quantum optics

Multiple cyclic nucleotide-gated channels coordinate calcium oscillations and polar growth of root hairs - Brost, Christa; Studtrucker, Tanja; Reimann, Ronny; Denninger, Philipp; Czekalla, Jennifer; Krebs, Melanie; Fabry, Ben; Schumacher, Karin; Grossmann, Guido; Dietrich, Petra (Plant Journal, 2019)
Calcium gradients underlie polarization in eukaryotic cells. In plants, a tip-focused Ca2+-gradient is fundamental for rapid and unidirectional cell expansion during epidermal root hair development. Here we report that three members of the cyclic nucleotide-gated channel family are required to maintain cytosolic Ca2+ oscillations and the normal growth of root hairs. CNGC6, CNGC9 and CNGC14 were expressed in root hairs, with CNGC9 displaying the highest root hair specificity. In individual channel mutants, morphological defects including root hair swelling and branching, as well as bursting, were observed. The developmental phenotypes were amplified in the three cngc double mutant combinations. Finally, cngc6/9/14 triple mutants only developed bulging trichoblasts and could not form normal root hair protrusions because they burst after the transition to the rapid growth phase. Prior to developmental defects, single and double mutants showed increasingly disturbed patterns of Ca2+ oscillations. We conclude that CNGC6, CNGC9 and CNGC14 fulfill partially but not fully redundant functions in generating and maintaining tip-focused Ca2+ oscillations, which are fundamental for proper root hair growth and polarity. Furthermore, the results suggest that these calmodulin-binding and Ca2+-permeable channels organize a robust tip-focused oscillatory calcium gradient, which is not essential for root hair initiation but is required to control the integrity of the root hair after the transition to the rapid growth phase. Our findings also show that root hairs possess a large ability to compensate calcium-signaling defects, and add new players to the regulatory network, which coordinates cell wall properties and cell expansion during polar root hair growth.
CRIS-Team Scopus Importer:2019-09-03
Keywords: Arabidopsis thaliana; calcium channel; polar growth; R-GECO1; RootChip; trichoblast

Multiple quantum wires in GaAs/GaAlAs - Hundhausen, Martin; et al. (Extended abstracts of the 48th Autum meeting of the Jap. Soc. of Appl. Phys., 1987)
UnivIS-Import:2015-03-05:Pub.1987.nat.dphy.IAP.exphys.multip

Mutated lamin A modulates stiffness in muscle cells - Chatzifrangkeskou, Maria; Kah, Delf-Thorge Eric; Lange, Janina; Goldmann, Wolfgang; Muchir, Antoine (Biochemical and Biophysical Research Communications, 2020)
The cytoskeleton is a complex network interlinking filaments that extend throughout the cytoplasm from the nucleus to the plasma membrane. Three major types of filaments are found in the cytoskeleton: actin filaments, microtubules, and intermediate filaments. They play a key role in the ability of cells to both resist mechanical stress and generate force. However, the precise involvement of intermediate filament proteins in these processes remains unclear. Here, we focused on nuclear A-type lamins, which are connected to the cytoskeleton via the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex. Using micro-constriction rheology, we investigated the impact of A-type lamins (p.H222P) mutation on the mechanical properties of muscle cells. We demonstrate that the expression of point mutation of lamin A in muscle cells increases cellular stiffness compared with cells expressing wild type lamin A and that the chemical agent selumetinib, an inhibitor of the ERK1/2 signaling, reversed the mechanical alterations in mutated cells. These results highlight the interplay between A-type lamins and mechano-signaling, which are supported by cell biology measurements.
CRIS-Team Scopus Importer:2020-06-19
Keywords: A-type lamin (LMNA); Cell mechanical properties; Cell nucleus; Chemical substance selumetinib; ERK1/2 signaling; Micro-constriction rheology

NaGdSi2O6 – A novel antiferromagnetically coupled silicate with Vierer chain structure - Kamutzki, Franz; Bekheet, Maged F.; Selve, Sören; Kampmann, Felix; Siemensmeyer, Konrad; Kober, Delf; Gillen, Roland; Wagner, Markus; Maultzsch, Janina; Gurlo, Aleksander; Hanaor, Dorian A.H. (Journal of Solid State Chemistry, 2023)
Ceramics based on pyroxenes and pyroxenoids present new pathways towards diverse functional materials. In this study, a novel sodium gadolinium pyroxene of the composition NaGdSi2O6 was successfully synthesised via a chelation-polymerization based sol-gel method and its crystal structure was determined by Rietveld refined synchrotron X-ray powder diffraction. NaGdSi2O6 crystallises in monoclinic symmetry with space group P21/c and unit cell parameters of a ​= ​5.44069(8) Å, b ​= ​13.83410(17) Å, c ​= ​7.66897(9) Å and β ​= ​109.9929(6)° (Z ​= ​4). The structure has been identified to be an inosilicate with a strongly undulated single tetrahedral chain along c with a chain periodicity of 4 (Vierer chain). Vierer chain-type NaGdSi2O6 shows a weak antiferromagnetic coupling, however there is no evidence for long-range magnetic order above 2 ​K.
CRIS-Team Scopus Importer:2022-11-04
Keywords: Density functional theory; Pyroxenes; Pyroxenoids; Silicate ceramics; Vierer chain

NANOMAGNETISM A matter of orientation - Schneider, M. Alexander (2008)
Detailed investigation of a single atomic spin on a surface reveals that its Kondo interaction with the substrate electrons depends strongly on the spin's relative orientation.

Nanometerâscale modification of the tribological properties of Si(100) by scanning force microscope - Hundhausen, Martin; Ley, Lothar; et al. (Applied Physics Letters, 1995)
Hydrogenâterminated Si(100) surfaces were patterned on the nanometer scale using a conductingâprobe scanning force microscope (SFM) operating in air ambient. To generate the nanostructures, negative voltages were applied to the conductive SFM tip with respect to the sample while scanning in contact mode. After structuring, the same SFM tip was used to measure simultaneously the sample topography and the friction force between tip and sample. An increase in height by about three nanometers resulting from fieldâenhanced oxidation is observed in areas where the tip had been negatively biased with constant voltages above 7 V. The topographical change is accompanied by a relative increase of the friction force of about 20% over the structured areas. © 1995, American Institute of Physics. All rights reserved.
UnivIS-Import:2015-04-14:Pub.1995.nat.dphy.IAP.exphys.nanome
Keywords: ATOMIC FORCE MICROSCOPY; FRICTION; HYDROGENATION; NANOSTRUCTURES; OXIDATION; SILICON; STM; TOPOLOGY; TRIBOLOGY

Nanometer-scale field-induced oxidation if Si(111): H by a conducting-probe scanning force microscope: Doping dependence and kinetics - Hundhausen, Martin; Ley, Lothar; et al. (Applied Physics Letters, 1995)
Hydrogen-terminated Si(111) was patterned on the nanometer scale by field-induced oxidation using a biased conducting-probe scanning force microscope. The kinetics of oxide growth as well as its dependence on doping are investigated. Field-induced oxidation is observed for voltages exceeding a doping dependent threshold above which oxidation kinetics follows a power law.© 1995 American Institute of Physics.
UnivIS-Import:2015-04-14:Pub.1995.nat.dphy.IAP.exphys.nanome_5

Nanometer-scale modification of the tribological properties of Si(111):H surfaces performed and investigated by a conducting-probe scanning force microscope - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Vacuum Science & Technology B: Microelectronics Processing and Phenomena, 1996)
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.IAP.exphys.nanome

Nano-optical imaging of van der Waals crystals: from ultrafast exciton dynamics to anisotropic waveguide modes - Mooshammer, Fabian; Xu, X.; Trovatello, C.; Shao, Y.; Zhang, S.; Schuck, P. J.; Basov, D. N. (Proceedings of SPIE - The International Society for Optical Engineering, 2023)
Near-field microscopy has emerged as a powerful tool for investigating the optoelectronic properties of van der Waals crystals on deeply subwavelength length scales. Complementary information may be obtained by interrogating the layered materials with electromagnetic radiation oscillating at vastly different frequencies: In the terahertz spectral range, for example, the polarizability of excitons in transition metal dichalcogenide (TMDC) heterostructures can be recorded on subcycle timescales - granting access to ultrafast formation dynamics or the exciton Mott transition with nanometer precision. In contrast, visible or near-infrared light propagates through thin van der Waals slabs in the form of waveguide modes (WMs). By resolving interference patterns in maps of the scattered electric field, the anisotropic dielectric tensor of layered materials is retrieved and signatures of strong light-matter coupling in the dispersion of the WMs are revealed. This approach also allows for boosting the potential of 3R-stacked TMDCs for applications in nonlinear optics by quantifying their birefringence, thus providing essential parameters for future phase-matched waveguide second harmonic generation and compact on-chip optical devices in general.
CRIS-Team Scopus Importer:2023-11-24
Keywords: anisotropy; exciton; near-field microscopy; near-infrared; terahertz; van der Waals; waveguide modes

Nanoscale analyses of Corynebacterium diphtheriae pili by atomic force microscopy - Rheinlaender, Johannes; Gräbner, Anna; Ott, Lisa; Burkovski, Andreas; Schäffer, Tilman (European Biophysics Journal, 2012)

Nanoscale Imaging of InN Segregation and Polymorphism in Single Vertically Aligned InGaN/GaN Multi Quantum Well Nanorods by Tip-Enhanced Raman Scattering - Poliani, E.; Wagner, M. R.; Reparaz, J. S.; Mand, M.; Strassburg, M.; Kong, X.; Trampert, A.; Sotomayor Torres, C. M.; Hoffmann, A.; Maultzsch, Janina (Nano Letters, 2013)
Vertically aligned GaN nanorod arrays with nonpolar InGaN/GaN multi quantum wells (MQW) were grown by MOVPE on c-plane GaN-on-sapphire templates. The chemical and structural properties of single nanorods are optically investigated with a spatial resolution beyond the diffraction limit using tip-enhanced Raman spectroscopy (TERS). This enables the local mapping of variations in the chemical composition, charge distribution, and strain in the MQW region of the nanorods. Nanoscale fluctuations of the In content in the InGaN layer of a few percent can be identified and visualized with a lateral resolution below 35 nm. We obtain evidence for the presence of indium clustering and the formation of cubic inclusions in the wurtzite matrix near the QW layers. These results are directly confirmed by high-resolution TEM images, revealing the presence of stacking faults and different polymorphs close to the surface near the MQW region. The combination of TERS and HRTEM demonstrates the potential of this nanoscale near-field imaging technique, establishing TERS as a very potent, comprehensive, and nondestructive tool for the characterization and optimization of technologically relevant semiconductor nanostructures.
Keywords: Tip-enhanced Raman scattering; optical near-field spectroscopy; subwayelength chemical imaging; InGaN quantum wells; indium segregation

Nanoscale Morphology of PTB7 Based Organic Photovoltaics as a Function of Fullerene Size - Roehling, John D.; Baran, Derya; Sit, Joseph; Kassar, Thaer; Ameri, Tayebeh; Unruh, Tobias; Brabec, Christoph; Moule, Adam J. (Scientific Reports, 2016)
High efficiency polymer:fullerene photovoltaic device layers self-assemble with hierarchical features from ångströms to 100's of nanometers. The feature size, shape, composition, orientation, and order all contribute to device efficiency and are simultaneously difficult to study due to poor contrast between carbon based materials. This study seeks to increase device efficiency and simplify morphology measurements by replacing the typical fullerene acceptor with endohedral fullerene LuN@PC BEH. The metal atoms give excellent scattering contrast for electron beam and X-ray experiments. Additionally, LuN@PC BEH has a lower electron affinity than standard fullerenes, which can raise the open circuit voltage of photovoltaic devices. Electron microscopy techniques are used to produce a detailed account of morphology evolution in mixtures of Lu 3 N@PC 80 BEH with the record breaking donor polymer, PTB7 and coated using solvent mixtures. We demonstrate that common solvent additives like 1,8-diiodooctane or chloronapthalene do not improve the morphology of endohedral fullerene devices as expected. The poor device performance is attributed to the lack of mutual miscibility between this particular polymer:fullerene combination and to co-crystallization of Lu 3 N@PC 80 BEH with 1,8-diiodooctane. This negative result explains why solvent additives mixtures are not necessarily a morphology cure-all.

Nanoscale structure of Si/SiO2/organics interfaces - Steinrück, Hans-Georg; Schiener, Andreas; Schindler, Torben; Will, Johannes; Magerl, Andreas; Konovalov, Oleg; Li Destri, Giovanni; Seeck, Oliver; Mezger, Markus; Haddad, Julia; Deutsch, Moshe; Checco, Antonio; et al. (ACS nano, 2014)
X-ray reflectivity measurements of increasingly more complex interfaces involving silicon (001) substrates reveal the existence of a thin low-density layer intruding between the single-crystalline silicon and the amorphous native SiO terminating it. The importance of accounting for this layer in modeling silicon/liquid interfaces and silicon-supported monolayers is demonstrated by comparing fits of the measured reflectivity curves by models including and excluding this layer. The inclusion of this layer, with 6-8 missing electrons per silicon unit cell area, consistent with one missing oxygen atom whose bonds remain hydrogen passivated, is found to be particularly important for an accurate and high-resolution determination of the surface normal density profile from reflectivities spanning extended momentum transfer ranges, now measurable at modern third-generation synchrotron source
Keywords: native silicon oxide; self-Assembled monolayers; thin films; X-ray reflectivity

Nanotransport in polyacetylene single fiber: Toward the intrinsic properties - Park, Jin-gyu; Kim, Gyutae; Krstic, Vojislav; Kim, Byung-hoon; Lee, Sang-hun; Roth, Siegmar; Burghard, Marko; Park, YungWoo (Synthetic Metals, 2001)
The electrical transport properties of iodine doped polyacetylene (PA) nanofibers were measured as function of temperature in micron and sub-micron scale. Polyacetylene fiber network measured in micron scale shows weaker temperature dependence of resistivity and smaller negative magnetoresistance (MR) at T=1.5K compared to those of bulk PA film. The reaction of Au electrodes with dopant became serious in submicron experiment, so that stripes of Pt electrodes with 100nm separation were patterned on top of the SiO2 substrate to prevent the reaction, Non-ohmic I-V charactersitics are observed in PA nanofiber, The gate dependence shows the charge carrier to be hole with mobility mu (FET) similar to 4.4x10(-5)cm(2)/Vs at 233K. The non-ohmic I-V dependence at high electric fields could be originated from the soliton tunneling conduction in PA nanofiber.
Keywords: Polymetylene; FET; Nanofiber; Electrical transport

Narrow inhomogeneous distribution of spin-active emitters in silicon carbide - Nagy, Roland; Dasari, Durga B. R.; Babin, Charles; Liu, Di; Vorobyov, Vadim; Niethammer, Matthias; Widmann, Matthias; Linkewitz, Tobias; Gediz, Izel; Stoehr, Rainer; Weber, Heiko B.; Ohshima, Takeshi; et al. (Applied Physics Letters, 2021)
Optically active solid-state spin registers have demonstrated their unique potential in quantum computing, communication, and sensing. Realizing scalability and increasing application complexity require entangling multiple individual systems, e.g., via photon interference in an optical network. However, most solid-state emitters show relatively broad spectral distributions, which hinders optical interference experiments. Here, we demonstrate that silicon vacancy centers in semiconductor silicon carbide (SiC) provide a remarkably small natural distribution of their optical absorption/emission lines despite an elevated defect concentration of ≈0.43 μm−3. In particular, without any external tuning mechanism, we show that only 13 defects have to be investigated until at least two optical lines overlap within the lifetime-limited linewidth. Moreover, we identify emitters with overlapping emission profiles within diffraction-limited excitation spots, for which we introduce simplified schemes for the generation of computationally relevant Greenberger–Horne–Zeilinger and cluster states. Our results underline the potential of the CMOS-compatible SiC platform toward realizing networked quantum technology applications.<br

Narrow long Josephson junctions - Koval, Yury; Wallraff, Andreas; Fistul, Mikhail; Thyssen, N.; Kohlstedt, H.; Ustinov, Alexey (IEEE Transactions on Applied Superconductivity, 1999)
Long Josephson junctions of width down to less than 0.3 pm are fabricated using electron beam lithography. The junctions are made in niobiumaluminum-oxide trilayer technology using cross-linked PMMA for insulation. We measured the fluxon penetration field, the magnetic field period of the critical current modulation, and the Fiske step voltages of the junctions. A strong dependence of these quantities on the junction width is observed. Assuming a general-type relation between the spatial derivative of the phase and the spatial variation of the magnetic field along the plane of the junction, we derive a scaling relation between the measured quantities depending on the junction width. The derived relation is consistent with the experimental data. © 1999 IEEE.
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.IAP.pephys.narrow

Native point defects of semiconducting layered Bi2O2Se - Li, Huanglong; Xu, X.; Zhang, Y.; Gillen, Roland; Shi, L.; Robertson, John (Scientific Reports, 2018)

Natural dimethyl sulfide gradients would lead marine predators to higher prey biomass - Owen, Kylie; Saeki, Kentaro; Warren, Joseph D.; Bocconcelli, Alessandro; Wiley, David N.; Ohira, Shin Ichi; Bombosch, Annette; Toda, Kei; Paranhos Zitterbart, Daniel (Communications Biology, 2021)
Finding prey is essential to survival, with marine predators hypothesised to track chemicals such as dimethyl sulfide (DMS) while foraging. Many predators are attracted to artificially released DMS, and laboratory experiments have shown that zooplankton grazing on phytoplankton accelerates DMS release. However, whether natural DMS concentrations are useful for predators and correlated to areas of high prey biomass remains a fundamental knowledge gap. Here, we used concurrent hydroacoustic surveys and in situ DMS measurements to present evidence that zooplankton biomass is spatially correlated to natural DMS concentration in air and seawater. Using agent simulations, we also show that following gradients of DMS would lead zooplankton predators to areas of higher prey biomass than swimming randomly. Further understanding of the conditions and scales over which these gradients occur, and how they are used by predators, is essential to predicting the impact of future changes in the ocean on predator foraging success.
CRIS-Team Scopus Importer:2021-02-12

Nature of the electronic band gap in lanthanide oxides - Gillen, Roland; Clark, Steward; Robertson, John (Physical Review B - Condensed Matter and Materials Physics, 2013)

N-cadherin-functionalized polymer-tethered multi-bilayer: a cell surface-mimicking substrate to probe cellular mechanosensitivity - Ge, Y.; Lin, N. H.; Lautscham, Lena; Goldmann, Wolfgang; Fabry, Ben; Naumann, Christoph A. (Soft Matter, 2016)

Near-thermal equilibrium growth of SiC by physical vapor transport - Hundhausen, Martin; et al. (Materials Science and Engineering B-Advanced Functional Solid-State Materials, 1999)
Silicon carbide single crystals of the 4H-, 6H- and 15R- polytype are grown by using physical vapor transport (PVT). The crystal growth is performed at conditions where the growth chamber is close to thermal equilibrium. Micropipe-free growth of 6H-SiC on both the C- and Si-face of a 6H-SiC seed is demonstrated. 4H/15R bulk material has been grown on 4H-/15R-seeds, respectively. The growth of 4H-/15R-SiC can not yet be stabilized for the entire boule. Micropipe generation is observed in the neighborhood of polytype transitions, where Raman spectroscopy reveals internal stress. Nitrogen donor concentrations and concentrations of the compensation range from 5.9 × 1017 to 1.5 × 1018 cm-3 and from 3 × 1017 to 6 × 1017 cm-3, respectively. The maximum of the electron Hall mobility is about 200 cm2 (Vs)-1 (6H-SiC) and 300 cm2 (Vs)-1 (4H- and 15R-SiC). © 1999 Elsevier Science S.A. All rights reserved.
UnivIS-Import:2015-04-14:Pub.1999.nat.dphy.IAP.LAP.nearth
Keywords: Defects; Electronic properties; Raman; Silicon carbide; Sublimation growth

NEDD9 stabilizes focal adhesions, increases binding to the extra-cellular matrix and differentially effects 2D versus 3D cell migration - Zhong, Jessie; Baquiran, Jamie B.; Bonakdar, Navid; Lees, Justin; Ching, Yu Wooi; Pugacheva, Elena; Fabry, Ben; O'Neill, Geraldine Margarete (PLoS ONE, 2012)

Negative electron affinity of adamantane on Cu(111). - Li, Jieru; Niesner, Daniel; Fauster, Thomas (Journal of Physics: Condensed Matter, 2021)
Photoelectron spectroscopy is used to show that thick adamantane films on Cu(111) have a negative electron affinity of -0.3 ± 0.1 eV. The ionization potential is obtained as 8.55 ± 0.15 eV resulting in a band gap of 8.9 ± 0.1 eV. For films of about 1.4 monolayer thickness the electron affinity is close to zero and the valence bands are shifted toward the Fermi energy due to charge transfer from Cu 3d bands.

Negative electron affinity opens quantum well in MgO layers on Ag(100) - Helmreich, Rebecca; Classen, Andrej; Fauster, Thomas (Journal of Physics: Condensed Matter, 2022)
Epitaxial MgO films on Ag(100) were studied by photoelectron spectroscopy. From the low-energy part of the spectra we obtain a negative electron affinity of about -0.9 eV. Even though electrons in the lowest conduction band are not confined by a potential barrier at the surface, quantum-well resonances are observed. The dispersion of the conduction band is determined in good agreement with theoretical calculations. Aspects of observing image-potential states predicted by theory on MgO films are discussed.
Created from Fastlane, WoS look-up

Neutron scattering experiments on liquid droplets using electrostatic levitation - Kordel, Tobias; Holland-Moritz, Dirk; Yang, Fan; Peters, Judith; Unruh, Tobias; Hansen, Thomas; Meyer, Andreas (Physical Review B, 2011)
We present a compact electrostatic levitator as a sample environment for high quality neutron scattering experiments on melts. By this containerless approach we are able to investigate chemically highly reactive melts in a broad temperature range from high temperatures down to very low temperatures in the metastable liquid. The sample volume typical for former electrostatic levitation facilities was increased by one order of magnitude to a sample diameter of 6 mm. A minimized amount of scattering material in the vicinity of the neutron beam results in a low background of the device and thus in a significantly improved signal-to-noise ratio. Even in these large samples the temperature gradient induced by laser heating is less than 20 K. As a first result the Ni self-diffusion coefficient in Zr64Ni36 was measured by quasielastic neutron scattering at the time-of-flight spectrometer TOFTOF at the FRM II as a function of temperature. At an undercooling of 167 K below the melting point deviations from an Arrhenius-type temperature dependence as observed in bulk metallic glass forming alloys become evident. Neutron diffraction experiments were performed at the high flux diffractometer D20 at the ILL. With a neutron wavelength of 0.94 angstrom a high quality total structure factor of Zr64Ni36 wasmeasured in a broad temperature range at wave numbers between 0.6 and 12 angstrom(-1).

Neutron scattering study of the dynamics of a polymer melt under nanoscopic confinement - Krutyeva, Margarita; Martin, Jaime; Arbe, Arantxa; Colmenero, Juan; Mijangos, Carmen; Schneider, Gerald J.; Unruh, Tobias; Su, Yixi; Richter, Dieter (Journal of Chemical Physics, 2009)
Poly(ethylene oxide) confined in an anodic aluminum oxide solid matrix has been studied by different neutron scattering techniques in the momentum transfer (Q) range 0.2 < Q=vertical bar Q vertical bar < 1.9 A degrees(-1). The cylindrical pores of the matrix present a diameter (40 nm) much smaller than their length (150 mu m) and are parallel and hexagonally ordered. In particular, we investigated the neutron intensity scattered for two orientations of the sample with respect to the incident beam, for which the Q direction was either parallel or perpendicular to the pores for a scattering angle of 90 degrees. Diffuse neutron scattering at room temperature has shown that the aluminum oxide has amorphous structure and the polymer in the nanoporous matrix is partially crystallized. Concerning the dynamical behavior, for Q < 1 A degrees(-1), the spectra show Rouse-like motions indistinguishable from those in the bulk within the uncertainties. In the high-Q limit we observe a slowing down of the dynamics with respect to the bulk behavior that evidences an effect of confinement. This effect is more pronounced for molecular displacements perpendicular to the pore axis than for parallel displacements. Our results clearly rule out the strong corset effect proposed for this polymer from nuclear magnetic resonance (NMR) studies and can be rationalized by assuming that the interactions with the pore walls affect one to two adjacent monomer monolayers.
Keywords: aluminium compounds; anodes; monolayers; neutron diffraction; nuclear magnetic resonance; polymer melts; polymers

Neutron spectroscopic study of crystal-field excitations and the effect of the crystal field on dipolar magnetism in LiRF4 (R = Gd, Ho, Er, Tm, and Yb) - Babkevich, P.; Finco, A.; Jeong, M.; Piazza, B. Dalla; Kovacevic, I.; Klughertz, G.; Kraemer, K. W.; Kraemer, C.; Adroja, D. T.; Goremychkin, E.; Unruh, Tobias; Straessle, T.; et al. (Physical Review B, 2015)
We present a systematic study of the crystal-field interactions in the LiRF4 (R = Gd, Ho, Er, Tm, and Yb) family of rare-earth magnets. Using detailed inelastic neutron scattering measurements, we have been able to quantify the transition energies and wave functions for each system. This allows us to quantitatively describe the high-temperature susceptibility measurements for the series of materials and make predictions based on a mean-field approach for the low-temperature thermal and quantum phase transitions. We show that coupling between crystal field and phonon states leads to line-shape broadening in LiTmF4 and level splitting in LiYbF4. Furthermore, using high-resolution neutron scattering from LiHoF4, we find anomalous broadening of crystal-field excitations which we attribute to magnetoelastic coupling.

Neutron spectroscopy on protein solutions employing backscattering with an increased energy range - Beck, Christian; Appel, Markus; Grimaldo, Marco; Roosen-Runge, Felix; Zhang, Fajun; Frick, Bernhard; Schreiber, Frank; Seydel, Tilo (Physica B-Condensed Matter, 2019)
Novel cold neutron backscattering spectrometers contribute substantially to the understanding of the diffusive dynamics of proteins in dense aqueous suspensions. Such suspensions are fundamentally interesting for instance in terms of the so-called macromolecular crowding, protein cluster formation, gelation, and self-assembly. Notably, backscattering spectrometers with the highest flux can simultaneously access the center-of-mass diffusion of the proteins and the superimposed internal molecular diffusive motions. The nearly complete absence of protein-protein collisions on the accessible nanosecond observation time scale even in dense protein suspensions implies that neutron backscattering accesses the so-called short-time limit for the center-of-mass diffusion. This limit is particularly interesting in terms of a theoretical understanding by concepts from colloid physics. Here we briefly review recent progress in studying protein dynamics achieved with the latest generation of backscattering spectrometers. We illustrate this progress by the first data from a protein solution using the backscattering-and-time-of-flight option BATS on IN16B at the ILL and we outline future perspectives.
CRIS-Team WoS Importer:2019-04-30

Neutrophil morphology and migration are affected by substrate elasticity - Oakes, Patrick W.; Patle, Dipan C.; Morin, Nicole A.; Paranhos Zitterbart, Daniel; Fabry, Ben; Reichner, Jonathan S.; Tang, Jay X. (Blood, 2009)

New insight into recombination and thermalization in As2Se3 - Ristein, Jürgen; et al. (Journal of Non-Crystalline Solids, 1987)
Simultaneous studies of photoluminescence and photoconductance in high electric fields reveal that emission of light occurs in single crystals of As2Se3 by geminate pair recombination only. After rapid thermalization excited carriers form free excitons which within a few picoseconds become self-trapped. The detailed picture which evolves for recombination in crystals, however, apparently does not apply to the glass. © 1987.
UnivIS-Import:2015-03-05:Pub.1987.nat.dphy.IAP.exphys.newins

New SiC epitaxial growth process with up to 100% BPD to TED defect conversion on 150mm hot-wall CVD reactor - Höchbauer, Tobias; Heidorn, Christian; Tsavdaris, Nikolaos (Materials Science Forum, 2019)
The future challenges for SiC device technology are cost reduction and increased reliability. A key point to achieve that is the increase of yield during epitaxial layer growth through the reduction of structural defects (such as basal plane dislocations and triangle defects), an increased thickness and doping uniformity, and a high growth rate. Despite significant advancements in SiC epitaxial growth technology, it still constitutes a big challenge to find the optimum working point at which all those requirements are fulfilled. By implementing a new epitaxial layer growth process, we are able to grow basal plane dislocation free epitaxial layers, while the density of other structural defects remains low. Additionally, intra-wafer thickness and doping uniformities of the epitaxial layers are further improved.
CRIS-Team Scopus Importer:2019-09-17
Keywords: Basal plane dislocation; Chemical vapor deposition; Epitaxy

New sources and instrumentation for neutrons in biology - Teixeira, S. C. M.; Zaccai, G.; Ankner, J.; Bellissent-Funel, M. C.; Bewley, R.; Blakeley, M. P.; Callow, P.; Coates, L.; Dahint, R.; Dalgliesh, R.; Dencher, N. A.; Forsyth, V. T.; et al. (Chemical Physics, 2008)

New-surface dopant passivation after wet-chemical preparation of Si (111):H surfaces - Ley, Lothar; Ristein, Jürgen; et al. (Journal of Vacuum Science & Technology B, 1996)
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.IAP.exphys.newsur

New zeolite-like RUB-5 and its related hydrous layer silicate RUB-6 structurally characterized by electron microscopy - Krysiak, Yasar; Marler, Bernd; Barton, Bastian; Plana-Ruiz, Sergi; Gies, Hermann; Neder, Reinhard; Kolba, Ute (IUCrJ, 2020)
This study made use of a recently developed combination of advanced methods to reveal the atomic structure of a disordered nanocrystalline zeolite using exit wave reconstruction, automated diffraction tomography, disorder modelling and diffraction pattern simulation. By applying these methods, it was possible to determine the so far unknown structures of the hydrous layer silicate RUB-6 and the related zeolite-like material RUB-5. The structures of RUB-5 and RUB-6 contain the same dense layer-like building units (LLBUs). In the case of RUB-5, these building units are interconnected via additional SiO4/2 tetrahedra, giving rise to a framework structure with a 2D pore system consisting of intersecting 8-ring channels. In contrast, RUB-6 contains these LLBUs as separate silicate layers terminated by silanol/siloxy groups. Both RUB-6 and RUB-5 show stacking disorder with intergrowths of different polymorphs. The unique structure of RUB-6, together with the possibility for an interlayer expansion reaction to form RUB-5, make it a promising candidate for interlayer expansion with various metal sources to include catalytically active reaction centres.
CRIS-Team Scopus Importer:2020-05-22
Keywords: 3D electron diffraction; computational modelling; diffuse scattering; electron crystallography; exit wave reconstruction; framework-structured solids; inorganic materials.; microporous materials; polymorph prediction; stacking faults

NH3 AND NO INTERACTION WITH SI(100)-(2X1) SURFACES - Fauster, Thomas; et al. (Physical Review B, 1991)
The adsorption of NH3 and NO on Si(100)-(2 x 1) surfaces at room temperature and the stepwise nitridation have been studied by high-resolution Si 2p core-level photoemission spectroscopy. Both molecules adsorb dissociatively, but only for NO does a reaction occur beyond the first monolayer. For the growth of stoichiometric silicon nitride, annealing to 1200 K is necessary.

n-Hexanol Enhances the Cetyltrimethylammonium Bromide Stabilization of Small Gold Nanoparticles and Promotes the Growth of Gold Nanorods - Schmutzler, Tilo; Schindler, Torben; Zech, Tobias; Lages, Sebastian; Thoma, Martin; Appavou, Marie-Sousai; Peukert, Wolfgang; Spiecker, Erdmann; Unruh, Tobias (ACS Applied Nano Materials, 2019)
Gold nanorods (AuNRs) are of interest for many applications, since their absorption in the regime of visible light can easily be tuned by their exact shape. To produce these AuNRs, a two-step synthesis that starts from small seed particles is used. These seed particles are stabilized by cetyltrimethyl-ammonium bromide (CTAB), which forms micelles at the used concentration (0.1 mol/L). In this work, the influence of the micelle morphology on the stabilization of these seed particles and the consequences on the formation of AuNRs is reported. The elongation of CTAB micelles by the addition of n-hexanol leads to much more stable seed particle dispersions and thus less polydisperse AuNRs. In contrast, a higher number of micelles compared to pure CTAB dispersions result from the addition of n-pentanol. This promotes the formation of larger seed particles and leads to lower yields of AuNRs. The gold nanoparticles are characterized by UV-vis-NIR absorption spectroscopy, transmission electron microscopy, and small-angle X-ray scattering (SAXS). The morphology of the micelles has been determined by a combination of SAXS and small-angle neutron scattering (SANS). The experimental results were used to calculate the collision kinetics of seed particles by using an improved approach of classical coagulation theory to consider the anisotropy of the micelles. The combination of these experiments with the calculations strongly supports the mechanistic model-that these gold seed particles are not stabilized by a CTAB bilayer but by the micelles itself. For the first time, the influence of the micellar size and shape on the stabilization mechanism of noble metal nanoparticles could be clarified. Theses findings contribute to the development of targeted design routes for distinct nanoparticle morphologies by the use of suitable dispersions.
CRIS-Team WoS Importer:2019-06-18

Nickel self-diffusion in silicon-rich Si-Ni melts - Pommrich, Ines; Meyer, Andreas; Holland-Moritz, Dirk; Unruh, Tobias (Applied Physics Letters, 2008)
The nickel self-diffusion coefficient in Si-Ni melts was measured for compositions up to 20 at. % Ni in a temperature range from 270 K below to 200 K above the liquidus temperature by using quasielastic neutron scattering in combination with electromagnetic levitation. Ni self-diffusion coefficients are in the order of 10(-8) m(2)/s, fairly independent of the Ni concentration. Diffusion coefficients calculated from viscosity data of pure liquid silicon via the Stokes-Einstein relation compare well with the Ni self-diffusion obtained here, indicating a strong correlation between the mobility of the silicon and nickel atoms. (C) 2008 American Institute of Physics.

Ni self-diffusion in refractory Al-Ni melts - Stüber, Sebastian; Holland-Moritz, Dirk; Unruh, Tobias; Meyer, Andreas (Physical Review B, 2010)
This work presents investigations on the Ni self-diffusion coefficient in Al-Ni melts forming the technological relevant intermetallic phases Al50Ni50 and Al25Ni75 by quasielastic neutron scattering. We found that the Ni self-diffusivity at constant temperature is nearly independent of the composition within the composition range between 0 and 50 at. % Al. This may be a result of the small composition dependence of the atomic volume observed in the same range of composition.

Nitrogen doping of metallic single-walled carbon nanotubes:n-type conduction and dipole scattering - Krstic, Vojislav; Rikken, Geert L.J.A.; Bernier, Patrick; Roth, Siegmar; Glerup, Marianne (EPL - Europhysics Letters, 2007)
The charge transport properties of individual, metallic nitrogen doped, single-walled carbon nanotubes are investigated. It is demonstrated that n-type conduction can be achieved by nitrogen doping. Evidence was obtained by appealing to electric-field effect measurements at ambient condition. n-type conduction is attributed to the presence of graphite-type nitrogen. The observed temperature dependencies of the zero-bias conductance indicate a disordered electron system with electric-dipole scattering, caused mainly by pyridine-type nitrogen atoms in the honeycomb lattice.

N,N,O ligands based on triazoles and transition metal complexes thereof - Hübner, Eike; Fischer, Nina; Heinemann, Frank Wilhelm; Mitra, Utpal; Dremov, Viatcheslav; Müller, Paul; Burzlaff, Nicolai (European Journal of Inorganic Chemistry, 2010)
The reaction of 2H-benzotriazole (1) with dichloroacetic acid leads to the symmetric bis(2H-benzotriazol-2-yl)methane (2c) in 40 % yield. Deprotonation of 2c at the bridging methylene group and subsequent carboxylation with CO yielded the new tripodal N,N,O ligand bis(2H-benzotriazol-2-yl) acetic acid Hbbta (3). The sterically less demanding sodium bis(1H- ,4-triazol-1-yl)propionate Na[btp] (5) was obtained by saponification of methyl -bis(1H- ,4-triazol-1-yl)propionate (4). The heteroscorpionate hgand 3 viras treated with [MnBr(CO) ] and [RuCl (PPh J ] to form the manganese tricarbonyl complex [Mn(bbta)(CO) ] (6) and the air stable ruthenium complex [Ru(bbta)Cl(PPh ) ] (7). DFT calculations and the IR spectra of the carbonyl complex 6 reveal ligand 3 to be a less electron-donating ligand compared to the Ms(1Hpyrazol-1-yl)acetic acid Hbpza. In case of the 1H- ,4-triazole-based ligand 5 formation of coordination polymers were observed as proven by the synthesis of [Zn(btp)2∞ (8) and [Mn(btp) ]∞ (9). Polymer 8 crystallises in linear chains of zinc atoms bridged by two molecules of ligand 5 each. These polymer chains show an interesting π-stacking interaction between uncoordinated triazole residues of the ligands. Deposition of the coordination polymer on highly ordered pyrolytic graphite (HOPG) was successful and was analysed by scanning tunnelling microscopy (STM). Reaction of Na[btp] (5) with MnSO -H O resulted in a metal organic framework (MOF) [Mn(Mp) ]∞ (9). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

NOBF4-Functionalized Au-Fe3O4 Nanoheterodimers for Radiation Therapy: Synergy Effect Due to Simultaneous Reactive Oxygen and Nitrogen Species Formation - Klein, Stefanie; Harreiß, Christina; Menter, Christina; Hümmer, Julian; Distel, Luitpold; Meyer, Karsten; Hock, Rainer; Kryschi, Carola (ACS Applied Materials and Interfaces, 2018)
Snowman-shaped Au-Fe3O4 nanoheterodimers were synthesized by thermal decomposition of iron oleate on presynthesized Au nanoparticles. Subsequently performed ligand exchange with nitrosyl tetrafluoroborate provided water solubility and enabled X-ray-induced NO release. These Au-Fe3O4 nanoheterodimers combine high-Z material with catalytically active Fe3O4 surfaces and, moreover, plasmonic properties with superparamagnetic performance. We could establish synergetic interactions between X-radiation and both the Au and Fe3O4 surfaces, which resulted in the simultaneous production of the nitric oxide radical at the Fe3O4 surface and the superoxide radical at the Au surface. The surface-confined reaction between these radicals generated peroxynitrite. This highly reactive species may cause nitration of mitochondrial proteins and lipid peroxidation and induce DNA strand breaks. Therefore, high concentrations of peroxynitrite are expected to give rise to severe cellular energetic derangements and thereupon entail rapid cell death. As providing a common platform for X-ray-induced formation of the highly superoxide, and peroxynitrite, nitrosyl tetrafluoroborate functionalized Au-Fe3O4 nanosnowmen were shown to exhibit excellent performance as X-ray-enhancing agents in radiation therapy.
Keywords: Au-Fe3O4 nanoheterodimers; nitrosyl tetrafluoroborate coating; radiation therapy; reactive oxygen species; reactive nitrogen species

No evidence of microplastic ingestion in emperor penguin chicks (Aptenodytes forsteri) from the Atka Bay colony (Dronning Maud Land, Antarctica) - Leistenschneider, Clara; Le Bohec, Céline; Eisen, Olaf; Houstin, Aymeric; Neff, Simon; Primpke, Sebastian; Paranhos Zitterbart, Daniel; Burkhardt-Holm, Patricia; Gerdts, Gunnar (Science of the Total Environment, 2022)
Microplastic (<5 mm; MP) pollution has been an emerging threat for marine ecosystems around the globe with increasing evidence that even the world's most remote areas, including Antarctica, are no longer unaffected. Few studies however, have examined MP in Antarctic biota, and especially those from Antarctic regions with low human activity, meaning little is known about the extent to which biota are affected. The aim of this study was to investigate, for the first time, the occurrence of MP in the emperor penguin (Aptenodytes forsteri), the only penguin species breeding around Antarctica during the austral winter, and an endemic apex predator in the Southern Ocean. To assess MP ingestion, the gizzards of 41 emperor penguin chicks from Atka Bay colony (Dronning Maud Land, Antarctica), were dissected and analyzed for MP >500 μm using Attenuated Total Reflection Fourier-transform Infrared (ATR-FTIR) spectroscopy. A total of 85 putative particles, mostly in the shape of fibers (65.9 %), were sorted. However, none of the particles were identified as MP applying state-of-the-art methodology. Sorted fibers were further evidenced to originate from contamination during sample processing and analyses. We find that MP concentrations in the local food web of the Weddell Sea and Dronning Maud Land coastal and marginal sea-ice regions; the feeding grounds to chick-rearing emperor penguin adults, are currently at such low levels that no detectable biomagnification is occurring via trophic transfer. Being in contrast to MP studies on other Antarctic and sub-Antarctic penguin species, our comparative discussion including these studies, highlights the importance for standardized procedures for sampling, sample processing and analyses to obtain comparable results. We further discuss other stomach contents and their potential role for MP detection, as well as providing a baseline for the long-term monitoring of MP in apex predator species from this region.
CRIS-Team Scopus Importer:2022-09-16
Keywords: Antarctica; Aptenodytes forsteri; ATR-FTIR; Microplastics; Stomach content; Weddell Sea & Dronning Maud Land

Noise and critical phenomena in biochemical signaling cycles at small molecule numbers - Fabry, Ben; Metzner, Claus; Sajitz-Hermstein, M.; Schmidberger, M. (Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2009)

Noise reduction for single-shot grating-based phase-contrast imaging at an x-ray backlighter - Schreiner, Stephan; Akstaller, Bernhard; Dietrich, Lisa; Meyer, Pascal; Neumayer, Paul; Schuster, Max; Wolf, Andreas; Zielbauer, Bernhard; Ludwig, Veronika; Michel, Thilo; Anton, Gisela; Funk, Stefan (Journal of Imaging, 2021)
X-ray backlighters allow the capture of sharp images of fast dynamic processes due to extremely short exposure times. Moiré imaging enables simultaneously measuring the absorption and differential phase-contrast (DPC) of these processes. Acquiring images with one single shot limits the X-ray photon flux, which can result in noisy images. Increasing the photon statistics by repeating the experiment to gain the same image is not possible if the investigated processes are dynamic and chaotic. Furthermore, to reconstruct the DPC and transmission image, an additional measurement captured in absence of the object is required. For these reference measurements, shot-to-shot fluctuations in X-ray spectra and a source position complicate the averaging of several reference images for noise reduction. Here, two approaches of processing multiple reference images in combination with one single object image are evaluated regarding the image quality. We found that with only five reference images, the contrast-to-noise ratio can be improved by approximately 13% in the DPC image. This promises improvements for short-exposure single-shot acquisitions of rapid processes, such as laser-produced plasma shock-waves in high-energy density experiments at backlighter X-ray sources such as the PHELIX high-power laser facility.
CRIS-Team Scopus Importer:2021-09-17
Keywords: Grating-based phase-contrast; Image processing; Image quality improvement; Single-shot X-ray phase-contrast imaging; X-ray back-lighter; X-ray generators and sources

NOMAD CAMELS: Configurable Application for Measurements, Experiments and Laboratory Systems - Fuchs, Alexander; Lehmeyer, Johannes; Junkes, Heinz; Weber, Heiko B.; Krieger, Michael (Journal of Open Source Software, 2024)

NOMAD CAMELS - Configurable Application for Measurements, Experiments and Laboratory Systems - Lehmeyer, Johannes; Fuchs, Alexander; Krieger, Michael; Weber, Heiko B. (2021)

Nonadiabatic dynamics of electron scattering from adsorbates in surface bands - Gumhalter, Branko; Siber, Antonio; Buljan, Hrvoje; Fauster, Thomas (Physical Review B, 2008)
We present a comparative study of nonadiabatic dynamics of electron scattering in quasi-two-dimensional surface band which is induced by the long-range component of the interactions with a random array of adsorbates. Using three complementary model descriptions of intraband spatiotemporal propagation of quasiparticles that go beyond the single-adsorbate scattering approach we are able to identify distinct subsequent regimes of evolution of an electron following its promotion into an unoccupied band state: (i) early quadratic or ballistic decay of the initial-state survival probability within the Heisenberg uncertainty window, (ii) preasymptotic exponential decay governed by the self-consistent Fermi golden rule scattering rate, and (iii) asymptotic decay described by a combined inverse power-law and logarithmic behavior. The developed models are applied to discuss the dynamics of intraband adsorbate-induced scattering of hot electrons excited into the n=1 image-potential band on Cu(100) surface during the first stage of a two-photon photoemission process. Estimates of crossovers between the distinct evolution regimes enable assessments of the lifespan of a standard quasiparticle behavior and thereby of the range of applicability of the widely used Fermi golden rule and optical Bloch equations approach for description of adsorbate-induced quasiparticle decay and dephasing in ultrafast experiments.

Nonadiabatic ponderomotive effects in photoemission from nanotips in intense midinfrared laser fields - Schoetz, Johannes; Mitra, Sambit; Fuest, Harald; Neuhaus, Marcel; Okell, William A.; Förster, Michael; Paschen, Timo; Ciappina, Marcelo F.; Yanagisawa, Hirofumi; Wnuk, Pawel; Hommelhoff, Peter; Kling, Matthias Friedrich (Physical Review A, 2018)
Transient near fields around metallic nanotips drive many applications, including the generation of ultrafast electron pulses and their use in electron microscopy. We have investigated the electron emission from a gold nanotip driven by midinfrared few-cycle laser pulses. We identify a low-energy peak in the kinetic energy spectrum and study its shift to higher energies with increasing laser intensities from 1.7 to 8.9×1011 W/cm2. The experimental observation of the upshift of the low-energy peak is compared to a simple model and numerical simulations, which show that the decay of the near field on a nanometer scale results in nonadiabatic transfer of the ponderomotive potential to the kinetic energy of emitted electrons and in turn to a shift of the peak. We derive an analytic expression for the nonadiabatic ponderomotive shift, which, after the previously found quenching of the quiver motion, com- pletes the understanding of the role of inhomogeneous fields in strong-field photoemission from nanostructures.

Non-classical behaviour in an S=5/2 chain with next nearest neighbour interactions observed from the inelastic neutron scattering of Mn-2(OD)(2)(C4O4) - Mole, Richard A.; Stride, John A.; Unruh, Tobias; Wood, Paul T. (Journal of Physics: Condensed Matter, 2009)
Low-dimensional and frustrated magnetic systems often show interesting quantum phenomena. The use of large moments such as S = 5/2 within such materials is uncommon, partly due to the evidence that the large manifold of states associated with these centres results in pseudo-classical behaviour. Here we report on the inelastic neutron scattering of Mn-2(OD)(2)(C4O4), a well-isolated chain with next nearest neighbour interactions. We observe a magnetic excitation spectrum below 30 K whose characteristics resemble those of quantum spin singlets. Inelastic neutron scattering from a powdered sample is shown to yield a great deal of information about the nature of these effects.

Non contact temperature measurements of diamond by Raman spectroscopy - Ristein, Jürgen; Ley, Lothar; et al. (Journal of Applied Physics, 1998)
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.IAP.exphys.noncon

Noncovalent Functionalization and Passivation of Black Phosphorus with Optimized Perylene Diimides for Hybrid Field Effect Transistors - Lloret, Vicent; Nuin, Edurne; Kohring, Malte; Wild, Stefan; Löffler, Mario; Neiß, Christian; Krieger, Michael; Hauke, Frank; Görling, Andreas; Weber, Heiko B.; Abellán, Gonzalo; Hirsch, Andreas (Advanced Materials Interfaces, 2020)
Amongst the different existing methods to passivate black phosphorus (BP) from environmental degradation, the noncovalent functionalization with perylene diimides (PDI) has been postulated as one of the most promising routes because it allows preserving its electronic properties. This work describes the noncovalent functionalization and outstanding environmental protection of BP with tailor made PDI having peri-amide aromatic side chains, which include phenyl and naphthyl groups, exhibiting a significantly increased molecule-BP interaction. These results are rationalized by density functional theory (DFT) calculations showing that the adsorption energies are mainly governed by van der Waals (vdW) interactions and increase concomitantly with the aromatic character of the side chains. The resulting hybrids are thoroughly characterized showing enhanced ambient and thermal stabilities. Last but not least, hybrid organic–inorganic BP-PDI field effect transistors (FETs) are studied for the first time showing the usefulness of PDI derivatives as efficient passivation layers while obtaining improved values of electron mobilities. These results pave the way for the use of optimized PDIs by molecular engineering to preserve the electronic properties of BP FETs, using straightforward wet chemical approaches.
CRIS-Team Scopus Importer:2020-10-16
Keywords: black phosphorus; noncovalent functionalization; organic field effect transistors; perylene diimides

Nonlinear viscoelasticity of adherent cells is controlled by cytoskeletal tension - Kollmannsberger, Philip; Mierke, Claudia; Fabry, Ben (Soft Matter, 2011)

Nonlocal electrodynamics of long ultranarrow Josephson junctions: Experiment and theory - Abdumalikov, Abdufarrukh; Kurin, V.; Helm, C.; De Col, A.; Koval, Yury; Ustinov, Alexey (Physical Review B, 2006)
We experimentally and theoretically investigate electromagnetic cavity modes in ultranarrow Al- AlOx -Al and Nb- AlOx -Nb long Josephson junctions. Experiments show that the voltage spacing between the Fiske steps on the current-voltage characteristics of sub- μm -wide and several hundred μm -long Al- AlOx -Al and Nb- AlOx -Nb Josephson junctions increases when decreasing the junction width. This effect is explained by stray magnetic fields, which become important for narrow junctions. Theoretical estimates of the Fiske step voltage based on a nonlocal wave propagation equation are in agreement with our experimental data. Using the nonlocal model, we determine the size and mass of a Josephson vortex by means of a variational approach, and relate the vortex size to the experimentally measured critical magnetic field of the junction. © 2006 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.pephys.nonloc

Non-stationary Langevin Equation in Cardiology - Kirchner, Jens; Meyer, Wolfgang; Hensel, Bernhard (IFMBE Proceedings 25/4, 2009)
As a model for RR-interval time series, a nonstationary linear Langevin equation is used. Approximating the time-dependent point of equilibrium by a piecewise constant function, an algorithm is presented to reconstruct the amplitudes of this trend. From these quantities a measure of activity is defined, which is shown to be an indicator of a deterioration of cardiac performance such as involved by congestive heart failur
Keywords: Congestive Heart Failure; Langevin Equation; NYHA Class; Cardiac Performance; Circadian Variation

Nonstationary Langevin equation: Statistical properties and application to explain effects observed in cardiological time series - Kirchner, Jens; Meyer, Wolfgang; Elsholz, Markus; Hensel, Bernhard (Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2007)
Using the Langevin equation we develop the model of a stochastic process subject to a given time-dependent regulatory mechanism. The effects of this nonstationarity on the statistical properties of the time series, i.e., on global and conditional probability densities and on the moments of the distribution, are derived. Application of these results on simple model trends allows one to approximate cardiological data and thus to explain effects recently observed in the reconstruction of the deterministic part of the Langevin equation for time series of heart rat

Nontoxic Liquid-Infused Slippery Coating Prepared on Steel Substrates Inhibits Corrosion and Biofouling Adhesion - Tesler, Alexander; Prado, Lucia; Thievessen, Ingo; Mazare, Anca Valentina; Schmuki, Patrik; Virtanen, Sannakaisa; Goldmann, Wolfgang (ACS Applied Materials and Interfaces, 2022)
Wetting of surfaces plays a vital role in many biological and industrial processes. There are several phenomena closely related to wetting such as biofouling and corrosion that cause the deterioration of materials, while the efforts to prevent the degradation of surface functionality have spread over several millennia. Antifouling coatings have been developed to prevent/delay both corrosion and biofouling, but the problems remain unsolved, influencing the everyday life of the modern society in terms of safety and expenses. In this study, liquid-infused slippery surfaces (LISSs), a recently developed nontoxic repellent technology, that is, a flat variation of omniphobic slippery liquid-infused porous surfaces (SLIPSs), were studied for their anti-corrosion and marine anti-biofouling characteristics on metallic substrates under damaged and plain undamaged conditions. Austenitic stainless steel was chosen as a model due to its wide application in aquatic environments. Our LISS coating effectively prevents biofouling adhesion and decays corrosion of metallic surfaces even if they are severely damaged. The mechanically robust LISS reported in this study significantly extends the SLIPS technology, prompting their application in the marine environment due to the synergy between the facile fabrication process, rapid binding kinetics, nontoxic, ecofriendly, and low-cost applied materials together with excellent repellent characteristics.
CRIS-Team Scopus Importer:2022-07-08
Keywords: algae; anti-biofouling coating; biofilms; corrosion resistance; diatoms; liquid-infused slippery surfaces; polydimethylsiloxane

NORMAL-INCIDENCE GRATING SPECTROGRAPH WITH LARGE ACCEPTANCE FOR INVERSE PHOTOEMISSION - Fauster, Thomas; et al. (Review of Scientific Instruments, 1985)

Novel Human Computer Interaction Principles for Cardiac Feedback using Google Glass and Android Wear - Richer, Robert; Maiwald, Tim; Pasluosta, Cristian Federico; Hensel, Bernhard; Eskofier, Björn (2015 IEEE 12th International Conference on Wearable and Implantable Body Sensor Networks (BSN), 2015)
<div class="pure-g" style="letter-spacing: -0.31em; text-rendering: optimizeSpeed; font-family: Helvetica, Arial, FreeSans, Arimo, "Droid Sans", sans-serif; flex-flow: row wrap; color: rgb(51, 51, 51); font-size: 15px; outline: 0px !important;"> <div class="ng-scope pure-u-1-1" ng-class="vm.details.graphicalAbstract ? 'pure-u-14-24 u-pr-1' : 'pure-u-1-1'" ng-if="::vm.details.impactStatement || vm.details.abstract || vm.details.scope || vm.details.purpose || vm.details.previewImage" style="letter-spacing: normal; word-spacing: normal; vertical-align: top; display: inline-block; text-rendering: auto; zoom: 1; width: 980px; outline: 0px !important; box-sizing: border-box; font-family: sans-serif;"> This work presents a system for unobtrusive cardiac feedback in daily life. It addresses the whole pipeline from data acquisition over data processing to data visualization including wearable integration. ECG signals are recorded with a novel ECG sensor supporting Bluetooth Low Energy, which is able to transmit raw ECG data as well as estimated heart rate. ECG signals are processed in real-time on a mobile device to automatically classify the user's heart beats. A novel application for Android-based mobile devices was developed for data visualization. It offers several modes for cardiac feedback, from measuring the current heart rate to continuously monitoring the user's heart status. It also allows to store acquired data in an internal database as well as in the Google Fit platform. Further, the application provides extensions for wearables like Google Glass and smartwatches running on Android Wear. Hardware performance evaluation was performed by comparing the course of heart rate between the novel ECG sensor and a commercial ECG sensor. The mean absolute error between the two sensors was 4.83 bpm with a standard deviation of 4.46 bpm, and a Pearson correlation of 0.922. A qualitative evaluation was performed for the Android application with special emphasis on the daily usability and the wearable integration. When the Google Glass was integrated, the subjects rated the application as 2.8/5 (0 = Bad, 5 = Excellent), whereas when the application was integrated with a smartwatch the rating increased to 4.2/5.

Novel Materials-based Laser Acceleration - Deng, Huiyang; Leedle, Kenneth J.; Miao, Yu; Black, Dylan S.; Urbanek, Karel; McNeur, Joshua; Kozak, Martin; Ceballos, Andrew; Hommelhoff, Peter; Solgaard, Olav; Byer, Robert L.; Harris, James S. (2021 Conference on Lasers and Electro-Optics, CLEO 2021 - Proceedings, 2021)
We demonstrate the first laser acceleration based on novel dielectric materials (Al2O3 and Ga2O3) with high laser damage thresholds, opening a new venue for performance optimization of dielectric laser accelerators.
CRIS-Team Scopus Importer:2021-12-24

NR4A1 Regulates Motility of Osteoclast Precursors and Serves as Target for the Modulation of Systemic Bone Turnover - Scholtysek, Carina; Ipseiz, Natacha; Böhm, Christina; Krishnacoumar, Brenda; Stenzel, Martin; Czerwinski, Tina; Palumbo-Zerr, Katrin; Rothe, Tobias; Weidner, Daniela; Klej, Alexandra; Stoll, Cornelia; Distler, Jörg; et al. (Journal of Bone and Mineral Research, 2018)
NR4A1 (Nur77 or NGFI-B), an orphan member of the nuclear receptor superfamily, has been identified as a key regulator of the differentiation and function of myeloid, lymphoid, and mesenchymal cells. The detailed role of NR4A1 in bone biology is incompletely understood. Here, we report a role for NR4A1 as novel factor controlling the migration and recruitment of osteoclast precursors during bone remodeling. Myeloid-specific but not osteoblast-specific deletion of NR4A1 resulted in osteopenia due to an increase in the number of bone-lining osteoclasts. Although NR4A1-deficient osteoclast precursors displayed a regular differentiation into mature osteoclasts, they showed a hyper-motile phenotype that was largely dependent on increased osteopontin expression, suggesting that expression of NR4A1 negatively controlled osteopontin-mediated recruitment of osteoclast precursors to the trabecular bone. Pharmacological activation of NR4A1, in turn, inhibited osteopontin expression and osteopontin-dependent migration of osteoclast precursors resulted in reduced abundance of bone-resorbing osteoclasts in vivo as well as in an ameliorated bone loss after ovariectomy in mice. This study identifies NR4A1 as a crucial player in the regulation of osteoclast biology and bone remodeling and highlights this nuclear receptor as a promising target for therapeutic intervention during the treatment of osteoporosis. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.
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Nucleophilic-alkylation-reoxidation: A functionalization sequence for single-wall carbon nanotubes - Graupner, Ralf; Abraham, Jürgen; Wunderlich, David; Vencelová, Andrea; Lauffer, Peter; Röhrl, Jonas; Hundhausen, Martin; Ley, Lothar; Hirsch, Andreas (Journal of the American Chemical Society, 2006)
A new reaction sequence for the chemical functionalization of single-wall carbon nanotubes (SWNTs) consisting of the nucleophilic addition of t-BuLi to the sidewalls of the tubes and the subsequent reoxidation of the intermediates t-BuSWNT leading to t-BuSWNT was developed. During the formation of the t-BuSWNT, a homogeneous dispersion in benzene was formed due to the electrostatic repulsion of the negatively charged intermediates causing debundling. The entire reaction sequence can be repeated, and the degree of functionalization of the products (t-Bu)SWNT (m = 1-3) increases with increasing m. Degrees of functionalization expressed as the carbon-to-addend ratio of up to 31 were reached. The reaction was studied in detail by photoelectron spectroscopy, Raman spectroscopy, and scanning tunneling microscopy (STM). The C 1s core level spectra reveal that the nucleophilic attack of the t-BuLi leads to negatively charged SWNTs. Upon oxidation, this negative charge is removed. The valence band spectra of the functionalized samples exhibit a significant reduction in the π-derived density of states. In STM, the covalently bonded t-butyl groups attached to the sidewalls have been visualized. Raman spectroscopy reveals that addition of the nucleophile to metallic tubes is preferred over the addition to semiconducting tubes. © 2006 American Chemical Society.

Nutrient-Poor Breeding Substrates of Ambrosia Beetles Are Enriched With Biologically Important Elements - Lehenberger, Maximilian; Foh, Nina; Göttlein, Axel; Six, Diana; Biedermann, Peter H.W. (Frontiers in Microbiology, 2021)
Fungus-farming within galleries in the xylem of trees has evolved independently in at least twelve lineages of weevils (Curculionidae: Scolytinae, Platypodinae) and one lineage of ship-timber beetles (Lymexylidae). Jointly these are termed ambrosia beetles because they actively cultivate nutritional “ambrosia fungi” as their main source of food. The beetles are obligately dependent on their ambrosia fungi as they provide them a broad range of essential nutrients ensuring their survival in an extremely nutrient-poor environment. While xylem is rich in carbon (C) and hydrogen (H), various elements essential for fungal and beetle growth, such as nitrogen (N), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), magnesium (Mg), and manganese (Mn) are extremely low in concentration. Currently it remains untested how both ambrosia beetles and their fungi meet their nutritional requirements in this habitat. Here, we aimed to determine for the first time if galleries of ambrosia beetles are generally enriched with elements that are rare in uncolonized xylem tissue and whether these nutrients are translocated to the galleries from the xylem by the fungal associates. To do so, we examined natural galleries of three ambrosia beetle species from three independently evolved farming lineages, Xyleborinus saxesenii (Scolytinae: Xyleborini), Trypodendron lineatum (Scolytinae: Xyloterini) and Elateroides dermestoides (Lymexylidae), that cultivate unrelated ambrosia fungi in the ascomycete orders Ophiostomatales, Microascales, and Saccharomycetales, respectively. Several elements, in particular Ca, N, P, K, Mg, Mn, and S, were present in high concentrations within the beetles’ galleries but available in only very low concentrations in the surrounding xylem. The concentration of elements was generally highest with X. saxesenii, followed by T. lineatum and E. dermestoides, which positively correlates with the degree of sociality and productivity of brood per gallery. We propose that the ambrosia fungal mutualists are translocating essential elements through their hyphae from the xylem to fruiting structures they form on gallery walls. Moreover, the extremely strong enrichment observed suggests recycling of these elements from the feces of the insects, where bacteria and yeasts might play a role.<br

Oberflächenphysik: Grundlagen und Methoden - Fauster, Thomas; Hammer, Lutz; Heinz, Klaus; Schneider, M. Alexander (Oldenbourg Wissenschaftsverlag, 2013)

Oberflächenphysik, Grundlagen und Methoden - Fauster, Thomas; Hammer, Lutz; Heinz, Klaus; Schneider, M. Alexander (De Gruyter, 2019)

Objective estimation of sensory thresholds based on neurophysiological parameters. - Schilling, Achim; Gerum, Richard; Krauß, Patrick; Metzner, Claus; Tziridis, Konstantin; Schulze, Holger (Frontiers in Neuroscience, 2019)

Objective estimation of sensory thresholds based on neurophysiological parameters - Schilling, Achim; Gerum, Richard; Krauß, Patrick; Metzner, Claus; Tziridis, Konstantin; Schulze, Holger (Frontiers in Neuroscience, 2019)
Reliable determination of sensory thresholds is the holy grail of signal detection theory. However, there exists no assumption-independent gold standard for the estimation of thresholds based on neurophysiological parameters, although a reliable estimation method is crucial for both scientific investigations and clinical diagnosis. Whenever it is impossible to communicate with the subjects, as in studies with animals or neonates, thresholds have to be derived from neural recordings or by indirect behavioral tests. Whenever the threshold is estimated based on such measures, the standard approach until now is the subjective setting-either by eye or by statistical means-of the threshold to the value where at least a “clear” signal is detectable. These measures are highly subjective, strongly depend on the noise, and fluctuate due to the low signal-to-noise ratio near the threshold. Here we show a novel method to reliably estimate physiological thresholds based on neurophysiological parameters. Using surrogate data we demonstrate that fitting the responses to different stimulus intensities with a hard sigmoid function, in combination with subsampling, provides a robust threshold value as well as an accurate uncertainty estimate. This method has no systematic dependence on the noise and does not even require samples in the full dynamic range of the sensory system. We prove that this method is universally applicable to all types of sensory systems, ranging from somatosensory stimulus processing in the cortex to auditory processing in the brain stem.
CRIS-Team Scopus Importer:2019-07-16
Keywords: Auditory cortex; Auditory neuroscience; Automated threshold estimation; Electrophysiology; Hearing; Psychometric function; Somatosensation; Somatosensory cortex

Observation of Breathing-like Modes in an Individual Multiwalled Carbon Nanotube - Spudat, Christian; Mueller, Matthias; Houben, Lothar; Maultzsch, Janina; Goss, Karin; Thomsen, Christian; Schneider, Claus M.; Meyer, Carola (Nano Letters, 2010)
We study collective vibrational breathing modes in the Raman spectrum of a multiwalled carbon nanotube. In correlation with high-resolution transmission electron microscopy, we find that these modes have energies differing by more than 23% from the radial breathing modes of the corresponding single-walled nanotubes. This shift in energy is explained with intershell interactions using a model of coupled harmonic oscillators. The strength of this interaction is related to the coupling strength expected for few-layer graphene.
Keywords: Carbon nanotubes; Raman spectroscopy; TEM; radial breathing mode; breathing-like modes

Observation of excitonic effects in metallic single-walled carbon nanotubes - May, Patrick; Telg, Hagen; Zhong, Guofang; Robertson, John; Thomsen, Christian; Maultzsch, Janina (Physical Review B, 2010)
Excitonic effects of metallic single-walled carbon nanotubes are measured with temperature-dependent resonant Raman spectroscopy. By changing the temperature in the range of 300-870 K, we observe variations in the optical transition energy E(ii) as well as in the maximum Raman intensity. We find both dependences to be different for semiconducting and metallic single-walled carbon nanotubes. We suggest an interpretation in terms of excitons dissociated into free electron-hole pairs at temperatures related to the exciton binding energy. We furthermore discuss how the oscillator strength is influenced by temperature.

Observation of folded-zone acoustical phonons by Raman scattering - Hundhausen, Martin; Ley, Lothar; et al. (Physical Review B - Condensed Matter and Materials Physics, 1985)
UnivIS-Import:2015-03-05:Pub.1985.nat.dphy.IAP.exphys.observ

Observation of individual molecules trapped on a nanostructured insulator - Nony, Laurent; Gnecco, Enrico; Baratoff, Alexis; Alkauskas, Audrius; Bennewitz, Roland; Pfeiffer, Oliver; Maier, Sabine; Wetzel, Adrian; Meyer, Ernst; Gerber, Christoph (Nano Letters, 2004)
For the first time, ordered polar molecules confined in monolayer-deep rectangular pits produced on an alkali halide surface by electron irradiation have been resolved at room temperature by noncontact atomic force microscopy. Molecules self-assemble in a specific fashion inside pits of width smaller than 15 nm. By contrast no ordered aggregates of molecules are observed on flat terraces. Conclusions regarding nucleation and ordering mechanisms are drawn. Trapping in pits as small as 2 nm opens a route to address single molecules.

Observation of lattice plane bending during SiC PVT bulk growth using in-situ high energy x-ray diffraction - Hock, Rainer; Konias, Katja; Perdicaro, Laura Maria Stella; Magerl, Andreas; Hens, Philip; Wellmann, Peter (Materials Science Forum, 2010)
We have investigated thermally induced strain in the SiC crystal lattice during physical vapor transport bulk growth. Using high energy x-ray diffraction lattice plane bending was observed in-situ during growth. With increasing growth rate increasing lattice plane bending and, hence, strain was observed. A comparison with numerical modeling of the growth process shows that the latter is related to the heat of crystallization which needs to be dissipated from the crystal growth front. The related temperature gradient as driving force for the dissipation of the heat of crystallization causes lattice plane bending. Optimization of the growth process needs to consider such effect
Keywords: Bulk Crystal Growth; PVT Growth

Observation of peak splitting in the Coulomb blockade regime of a carbon nanotube rope - McIntosh, Gregory C.; Kim, Gyutae; Park, Jin-gyu; Krstic, Vojislav; Roth, Siegmar; Park, YungWoo (Current Applied Physics, 2001)
Electronic transport measurements have been carried out on a single-walled carbon nanotube (SWCN) rope contacted to a 4-probe Au/Pd electrode in the Coulomb blockade regime. With varying substrate backgate voltage, the observed Coulomb blockade peaks exhibit interesting three-way splitting. We find that this peak splitting can be attributed to a contribution from resonant tunnelling through discrete energy levels of a finite length metallic SWCN within the rope. We also consider the role that interactions between `quantum dot' (Q-dot) regions within the rope can play in causing the peak splitting.
Keywords: Resonant tunneling; Fractional charge; Quantum dot; 71.20.Tx; 73.63.Fg; 73.23.Hk; Coulomb blockade; Carbon nanotube

Observation of Plasmarons in Quasi-Freestanding Doped Graphene - Bostwick, Aaron; Speck, Florian; Seyller, Thomas; Horn, Karsten; Polini, Marco; Asgari, Reza; Macdonald, Allan H.; Rotenberg, Eli (Science, 2010)
A hallmark of graphene is its unusual conical band structure that leads to a zero-energy band gap at a single Dirac crossing point. By measuring the spectral function of charge carriers in quasi-freestanding graphene with angle-resolved photoemission spectroscopy, we showed that at finite doping, this well-known linear Dirac spectrum does not provide a full description of the charge-carrying excitations. We observed composite ``plasmaron'' particles, which are bound states of charge carriers with plasmons, the density oscillations of the graphene electron gas. The Dirac crossing point is resolved into three crossings: the first between pure charge bands, the second between pure plasmaron bands, and the third a ring-shaped crossing between charge and plasmaron bands.
EAM Import::2019-03-08

Observation of size-dependent melting in lipid nanoparticles - Unruh, Tobias; Bunjes, Heike; Westesen, Kirsten; Koch, Michel (Journal of Physical Chemistry B, 1999)
The differential scanning calorimetry thermograms of suspensions of trimyristin nanoparticles in the stable P-polymorph display several melting events. Particle thickness distributions obtained by analysis of difference X-ray diffraction patterns recorded during melting reveal that these discrete events correspond to the melting of classes of particles differing in thickness by only one unit cell. A large increase in lattice constants with decreasing particle thickness was observed, indicating that classical surface thermodynamics is not applicable to particles consisting of only a few molecular layers.

Observing Oriented Attachment during Mesocrystal Growth with in Situ Dynamic Light Scattering (DLS) - Embrechts, Heidemarie; Zhang, Siqi; Hock, Rainer; Peukert, Wolfgang; Distaso, Monica (Crystal Growth & Design, 2020)
Despite rapidly growing interest in the application of mesocrystals in catalysis, energy storage, and sensing, the understanding of mesocrystal formation mechanisms remains a relatively unexplored field, due to the time and space overlapping of different reaction steps, namely, the nucleation and growth of solid phase and, possibly, their self-assembly in 3D superstructures. In particular, the role of polymers used as templating matrices requires more in-depth investigation. Here, ZnO–PVP mesocrystals are used as a model system and their formation from molecular precursors is followed with simultaneous in situ dynamic light scattering (DLS) and turbidity measurements. The formation of 10 nm primary building blocks during the early stages of the synthesis and their subsequent oriented attachment into 200–1200 nm mesocrystalline superstructures are both directly observed with in situ DLS. The primary particle concentration at which oriented attachment (OA) begins to occur at an observable rate is proportional to the colloidal primary particle stability and is compared for different synthesis conditions with inline turbidity measurements. Synthesis with higher PVP concentrations and molecular weights results in increasingly sterically stabilized primary particles and the formation of larger ZnO–PVP mesospheres. The larger diameter of mesocrystals synthesized at higher PVP educt concentrations is attributed to partial screening of (electrostatic repulsive) interparticle interactions between mesocrystals and primary particles by attached surface PV
Keywords: Oxides; Nanoparticles; Dynamic light scattering; Chemical synthesis; Metal oxide nanoparticles

Occupy tissue: The movement in cancer metastasis - Bradbury, Peta; Fabry, Ben; O'Neill, Geraldine Margarete (Cell Adhesion and Migration, 2012)

Oligothiophene Phosphonic Acids for Self-Assembled Monolayer Field-Effect Transistors - Zhao, Baolin; Gothe, Bastian; Groh, Arthur; Schmaltz, Thomas; Will, Johannes; Steinrueck, Hans-Georg; Unruh, Tobias; Mecking, Stefan; Halik, Marcus (ACS Applied Materials and Interfaces, 2021)
Semiconducting self-assembled monolayers (SAMs) represent highly relevant components for the fabrication of organic thin-film electronics because they enable the precise formation of active it-conjugates in terms of orientation and layer thickness. In this work, we demonstrate self-assembled monolayer field-effect transistors (SAMFETs) composed of phosphonic acid oligomers of 3-hexylthiophene (oligothiophenes-OT) with systematic variations of thiophene repeating units (5, 10, and 20). The devices exhibit stable lateral charge transport with increased mobility as a function of thiophene unit counts. Importantly, our work reveals the packing and intermolecular order of varied-chain-length SAMs at the molecular scale via X-ray reflectivity (XRR) and quantitative X-ray photoelectron spectroscopy (XPS). Short oligomers (OT5-PA and OT10-PA) arrange almost perpendicular to the substrate, forming highly ordered SAMs, whereas the long-chain OT20-PA exhibits a folded structure. By tuning the molecular order in the monolayers via the SAM substitution reaction, the OT20-PA devices show a tripling in mobility.
CRIS-Team WoS Importer:2021-07-30

On deep level transient spectroscopy of extended defects in n-type 4H-SiC - Weber, Jonas; Weber, Heiko B.; Krieger, Michael (Materials Science Forum, 2017)
We have performed capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements on Schottky contacts fabricated on triangular defects in 4H-SiC epitaxial layers. These measurements are a case study on the effect of a specific extended defect on the DLTS spectrum in order to contribute to the physical understanding of curious features occasionally observed in DLTS spectra. Our measurements reveal an inversion of the DLTS signal depending on applied voltages and filling pulse lengths, and a step in the C-V characteristic of the Schottky diode. We present a model that qualitatively describes the experimentally obtained data. In this model, we assume that stacking faults within a triangular defect form quantum wells, which can capture electrons from other defects during the DLTS measurement leading to the inversion of the DLTS spectrum. Moreover, by calculating the differential capacitance using a self-consistent Schrödinger- Poisson-Solver, the step in the C-V measurements is reproduced by our model.
CRIS-Team Scopus Importer:2022-04-14
Keywords: DLTS; Extended defects; Quantum well; Stacking faults; Triangular defect

One-dimensional potential for image-potential states on graphene - De Andres, P. L.; Echenique, P. M.; Niesner, Daniel; Fauster, Thomas; Rivacoba, A. (New Journal of Physics, 2014)
In the framework of dielectric theory, the static non-local self-energy of an electron near an ultra-thin polarizable layer has been calculated and applied to study binding energies of image-potential states near free-standing graphene. The corresponding series of eigenvalues and eigenfunctions have been obtained by numerically solving the one-dimensional Schrodinger equation. The imagepotential state wave functions accumulate most of their probability outside the slab. We find that the random phase approximation (RPA) for the nonlocal dielectric function yields a superior description for the potential inside the slab, but a simple Fermi-Thomas theory can be used to get a reasonable quasi-analytical approximation to the full RPA result that can be computed very economically. Binding energies of the image-potential states follow a pattern close to the Rydberg series for a perfect metal with the addition of intermediate states due to the added symmetry of the potential. The formalism only requires a minimal set of free parameters: the slab width and the electronic density. The theoretical calculations are compared with experimental results for the work function and image-potential states obtained by two-photon photoemission.

Onset of charge interaction in strong-field photoemission from nanometric needle tips - Schoetz, Johannes; Seiffert, Lennart; Maliakkal, Ancyline; Blöchl, Johannes; Zimin, Dmitry; Rosenberger, Philipp; Bergues, Boris; Hommelhoff, Peter; Krausz, Ferenc; Fennel, Thomas; Kling, Matthias Friedrich (Nanophotonics, 2021)
Strong-field photoemission from nanostructures and the associated temporally modulated currents play a key role in the development of ultrafast vacuum optoelectronics. Optical light fields could push their operation bandwidth into the petahertz domain. A critical aspect of their functionality in the context of applications is the impact of charge interaction effects. Here, we investigated the photoemission and photocurrents from nanometric tungsten needle tips exposed to carrier-envelope phase (CEP)-controlled few-cycle laser fields. We report a characteristic rapid increase in the intensity-rescaled cutoff energies of emitted electrons beyond a certain intensity value. By comparison with simulations, we identify this feature as the onset of charge-interaction dominated photoemission dynamics. Our results are anticipated to be relevant also for the strong-field photoemission from other nanostructures, including photoemission from plasmonic nanobowtie antennas used in CEP-detection and for PHz-scale devices.<br

On-Surface Assembly of Hydrogen- and Halogen-Bonded Supramolecular Graphyne-Like Networks - Yang, Zechao; Fromm, Lukas; Sander, Tim; Gebhardt, Julian; Schaub, Tobias A.; Görling, Andreas; Kivala, Milan; Maier, Sabine (Angewandte Chemie International Edition, 2020)
Demonstrated here is a supramolecular approach to fabricate highly ordered monolayered hydrogen- and halogen-bonded graphyne-like two-dimensional (2D) materials from triethynyltriazine derivatives on Au(111) and Ag(111). The 2D networks are stabilized by N⋅⋅⋅H−C(sp) bonds and N⋅⋅⋅Br−C(sp) bonds to the triazine core. The structural properties and the binding energies of the supramolecular graphynes have been investigated by scanning tunneling microscopy in combination with density-functional theory calculations. It is revealed that the N⋅⋅⋅Br−C(sp) bonds lead to significantly stronger bonded networks compared to the hydrogen-bonded networks. A systematic analysis of the binding energies of triethynyltriazine and triethynylbenzene derivatives further demonstrates that the X3-synthon, which is commonly observed for bromobenzene derivatives, is weaker than the X6-synthon for our bromotriethynyl derivatives.
CRIS-Team Scopus Importer:2020-04-10
Keywords: graphyne; halogen bonds; hydrogen bonds; nanostructures; self-assembly; surface chemistry

On-Surface Synthesis of Chiral π-Conjugate Porphyrin Tapes by Substrate-Regulated Dehydrogenative Coupling - Xiang, Feifei; Lu, Yan; Wang, Zhongping; Ju, Huanxin; di Filippo, Gianluca; Li, Chao; Liu, Xiaoqing; Leng, Xinli; Zhu, Junfa; Wang, Li; Schneider, M. Alexander (Journal of Physical Chemistry C, 2019)
On-surface enantioselective covalent coupling of nonfunctionalized porphyrins is demonstrated without utilizing chirality transfer from a self-assembled enantiopure precursor structure. We achieved to synthesize chiral porphyrin tapes on the Ag(110) surface by thermally induced dehydrogenative coupling using 5,15-diphenylporphyrin (2H-DPP) as a precursor. We employ scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) to study the properties of the precursor molecules and resulting covalently bonded structures. Our analysis shows that the enantioselectivity is due to the specific molecule substrate interaction confining the orientation of the diffusing molecules and steric hindrance making non-enantiopure bonds energetically unfavorable.

On-Surface Synthesis of Porous Carbon Nanoribbons from Polymer Chains - Ammon, Maximilian Michael; Sander, Tim; Maier, Sabine (Journal of the American Chemical Society, 2017)
We demonstrate the on-surface synthesis of porous carbon nanoribbons on Ag(111) via a preprogrammed isomerization of conformationally flexible polymer chains followed by dehydrogenation reactions using thermal annealing. The carbon chains are fabricated by polymerization of prochiral 1,3,5-tris(3-bromophenyl)benzene (mTBPB) directly on the surface using an Ullmann-type reaction. At room temperature, mTBPB partially self-assembles in halogen-bonded 2D networks, which transform into organometallic chains and rings after debromination. The chain and ring formation is facilitated by conformational switching from a C3h to Cs symmetry of mTBPB via rotation of m-phenylene units. The high conformational selectivity toward Cs-conformers is templated by the twofold coordination to Ag adatoms. After thermally induced covalent-linking through aryl–aryl coupling, well-ordered nanoporous chains are created. Finally, the rotation of single phenylene units in combination with dehydrogenation cross-linking reactions within the polymer chains leads to the unexpected formation of porous carbon nanoribbons. We unveil the reaction mechanism in a low-temperature scanning tunneling microscopy study and demonstrate that the rotation of m-phenylene units is a powerful design tool to promote structural control in the synthesis of cyclic covalent organic nanostructures on metal surface

On-Surface Synthesis of Porous Carbon Nanoribbons on Silver: Reaction Kinetics and the Influence of the Surface Structure - Ammon, Maximilian Michael; Haller, Martin; Sorayya, Shadi; Maier, Sabine (ChemPhysChem, 2019)
We report on the influence of the surface structure and the reaction kinetics in the bottom-up fabrication of porous nanoribbons on silver surfaces using low-temperature scanning tunneling microscopy. The porous carbon nanoribbons are fabricated by the polymerization of 1,3,5-tris(3-bromophenyl)benzene directly on the Ag surface using an Ullmann-type reaction in combination with dehydrogenative coupling reactions. We demonstrate the successful on-surface synthesis of porous nanoribbons on Ag(111) and Ag(100) even though the self-assemblies of the intermediate organometallic structures and covalently-linked polymer chains are different on both surfaces. Furthermore, we present the formation of isolated porous nanoribbons by kinetic control. Our results give valuable insights into the role of substrate-induced templating effects and the reaction kinetics in the on-surface synthesis of conformationally flexible molecules.
CRIS-Team Scopus Importer:2019-09-24
Keywords: molecular self-assembly; on-surface reactions; scanning probe microscopy; surface chemistry; Ullmann-type reaction

On the dependence of the cardiac motion artifact on the breathing cycle in liver diffusion-weighted imaging - Riexinger, Andreas; Laun, Frederik Bernd; Bickelhaupt, Sebastian; Seuß, Hannes; Uder, Michael; Hensel, Bernhard; Saake, Marc (PLoS ONE, 2020)
Purpose The purpose of this study was to investigate whether the cardiac motion artifact that regularly appears in diffusion-weighted imaging of the left liver lobe might be reduced by acquiring images in inspiration, when the coupling between heart and liver might be minimal. Materials and methods 43 patients with known or suspected focal liver lesions were examined at 1.5 T with breath hold acquisition, once in inspiration and once in expiration. Data were acquired with a diffusion-weighted echo planar imaging sequence and two b-values (b50 = 50 s/mm2 and b800 = 800 s/mm2). The severity of the cardiac motion artifact in the left liver lobe was rated by two experienced radiologists for both b-values with a 5 point Likert scale. Additionally, the normalized signal S(b800)/S(b50) in the left liver lobe was computed. The Wilcoxon signed-rank test was used comparing the scores of the two readers obtained in inspiration and expiration, and to compare the normalized signal in inspiration and expiration. Results The normalized signal in inspiration was slightly higher than in expiration (0.349±0.077 vs 0.336±0.058), which would indicate a slight reduction of the cardiac motion artifact, but this difference was not significant (p = 0.24). In the qualitative evaluation, the readers did not observe a significant difference for b50 (reader 1: p = 0.61; reader 2: p = 0.18). For b800, reader 1 observed a significant difference of small effect size favouring expiration (p = 0.03 with a difference of mean Likert scores of 0.27), while reader 2 observed no significant difference (p = 0.62). Conclusion Acquiring the data in inspiration does not lead to a markedly reduced cardiac motion artifact in diffusion-weighted imaging of the left liver lobe and is in this regard not to be preferred over acquiring the data in expiration.
CRIS-Team Scopus Importer:2020-10-16

On the efficiency of chemotactic pursuit - Comparing blind search with temporal and spatial gradient sensing - Metzner, Claus (Scientific Reports, 2019)
In chemotaxis, cells are modulating their migration patterns in response to concentration gradients of a guiding substance. Immune cells are believed to use such chemotactic sensing for remotely detecting and homing in on pathogens. Considering that immune cells may encounter a multitude of targets with vastly different migration properties, ranging from immobile to highly mobile, it is not clear which strategies of chemotactic pursuit are simultaneously efficient and versatile. We tackle this problem theoretically and define a tunable response function that maps temporal or spatial concentration gradients to migration behavior. The seven free parameters of this response function are optimized numerically with the objective of maximizing search efficiency against a wide spectrum of target cell properties. Finally, we reverse-engineer the best-performing parameter sets to uncover strategies of chemotactic pursuit that are efficient under different biologically realistic boundary conditions. Although strategies based on the temporal or spatial sensing of chemotactic gradients are significantly more efficient than unguided migration, such 'blind search' turns out to work surprisingly well, in particular if the immune cells are fast and directionally persistent. The resulting simulated data can be used for the design of chemotaxis experiments and for the development of algorithms that automatically detect and quantify goal oriented behavior in measured immune cell trajectories.
CRIS-Team Scopus Importer:2019-10-11

On the energetics of conformational switching of molecules at and close to room temperature - Ditze, Stefanie; Stark, Michael Werner; Buchner, Florian; Aichert, André; Jux, Norbert; Luckas, Nicola; Görling, Andreas; Hieringer, Wolfgang; Hornegger, Joachim; Steinrück, Hans-Peter; Marbach, Hubertus (Journal of the American Chemical Society, 2014)
We observe and induce conformational switching of individual molecules via scanning tunneling microscopy (STM) at and close to room temperature. 2H-5,10,15,20-Tetrakis-(3,5-di-tert-butyl)-phenylporphyrin adsorbed on Cu(111) forms a peculiar supramolecular ordered phase in which the molecules arrange in alternating rows, with two distinct appearances in STM which are assigned to concave and convex intramolecular conformations. Around room temperature, frequent bidirectional conformational switching of individual molecules from concave to convex and vice versa is observed. From the temperature dependence, detailed insights into the energy barriers and entropic contributions of the switching processes are deduced. At 200 K, controlled STM tip-induced unidirectional switching is possible, yielding an information storage density of 4.9 × 10 bit/inch. With this contribution we demonstrate that controlled switching of individual molecules at comparably high temperatures is possible and that entropic effects can be a decisive factor in potential molecular devices at these temperatures. © 2014 American Chemical Society.

On the excitation mechanism of erbium and ytterbium in the quaternary compounds InGaAsP - Wellmann, Peter; Winnacker, Albrecht; Pensl, Gerhard (Materials Research Society Symposium - Proceedings, 1996)
An efficient transfer of excitonic energy to rare earth (RE) ions is crucial for possible optoelectronic applications of RE doped semiconductors. In order to investigate the energy transfer mechanism to RE ions after optical above bandgap excitation we studied the intensity of the 4I13/2 →4 4I15/2-transition of Er3+ (1.54μm) and the one of the 2F5/2 →2 F7/2 -transition of Yb3+ (lμm) (loped into InGaAsP-layers lattice matched to InP. By varying the composition of the quaternary compoun ds, the bandgap energy together with the RE bound exciton energy were tuned relative to the RE excitation energy, and the effect on the RE luminescence intensity was observed. The results can be interpreted by stating a) that the energy transfer to the RE proceeds via the RE bound exciton, and b) that the intensity of the RE luminescence is essentially determined by the rate of back transfer of the RE excitation energy ERE to the bound exciton (with excitation energy Ebe). In this back transfer the energy of the excited RE ion plus the energy of 0, 1, 2 ... L0-phonons (energy Elo) is used to reexcite the bound exciton, instead of being emitted as an RE luminescence photon. For compositions where Ebe = ERE + n. Elo (n = 0, 1, 2...) we have a maximum of back transfer and correspondingly a, minimum in RE luminescence. In between the intensity has a, maximu

On the Field Strength Dependence of Bi- and Triexponential Intravoxel Incoherent Motion (IVIM) Parameters in the Liver - Riexinger, Andreas; Martin, Jan; Rauh, Susanne; Wetscherek, Andreas; Pistel, Mona; Kuder, Tristan Anselm; Nagel, Armin Michael; Uder, Michael; Hensel, Bernhard; Müller, Lars; Laun, Frederik Bernd (Journal of Magnetic Resonance Imaging, 2019)
Background: Studies on intravoxel incoherent motion (IVIM) imaging are carried out with different acquisition protocols. Purpose: To investigate the dependence of IVIM parameters on the B0 field strength when using a bi- or triexponential model. Study Type: Prospective. Study Population: 20 healthy volunteers (age: 19–28 years). Field Strength/Sequence: Volunteers were examined at two field strengths (1.5 and 3T). Diffusion-weighted images of the abdomen were acquired at 24 b-values ranging from 0.2 to 500 s/mm2. Assessment: ROIs were manually drawn in the liver. Data were fitted with a bi- and a triexponential IVIM model. The resulting parameters were compared between both field strengths. Statistical Tests: One-way analysis of variance (ANOVA) and Kruskal–Wallis test were used to test the obtained IVIM parameters for a significant field strength dependency. Results: At b-values below 6 s/mm2, the triexponential model provided better agreement with the data than the biexponential model. The average tissue diffusivity was D = 1.22/1.00 μm2/msec at 1.5/3T. The average pseudodiffusion coefficients for the biexponential model were D* = 308/260 μm2/msec at 1.5/3T; and for the triexponential model D* = 81.3/65.9 μm2/msec, D* 2 = 2453/2333 μm2/msec at 1.5/3T. The average perfusion fractions for the biexponential model were f = 0.286/0.303 at 1.5/3T; and for the triexponential model f1 = 0.161/0.174 and f2 = 0.152/0.159 at 1.5/3T. A significant B0 dependence was only found for the biexponential pseudodiffusion coefficient (ANOVA/KW P = 0.037/0.0453) and tissue diffusivity (ANOVA/KW: P < 0.001). Data Conclusion: Our experimental results suggest that triexponential pseudodiffusion coefficients and perfusion fractions obtained at different field strengths could be compared across different studies using different B0. However, it is recommended to take the field strength into account when comparing tissue diffusivities or using the biexponential IVIM model. Considering published values for oxygenation-dependent transversal relaxation times of blood, it is unlikely that the two blood compartments of the triexponential model represent venous and arterial blood. Level of Evidence: 1. Technical Efficacy Stage: 2. J. Magn. Reson. Imaging 2019;50:1883–1892.
CRIS-Team Scopus Importer:2019-11-22
Keywords: intravoxel incoherent motion; IVIM; liver

On the lattice parameters of silicon carbide - Stockmeier, Matthias; Müller, Robin; Sakwe, Aloysius; Wellmann, Peter; Magerl, Andreas (Journal of Applied Physics, 2009)
The thermal expansion coefficients of the hexagonal SiC polytypes 4H and 6H and with Al and N dopants have been determined for temperatures between 300 and 1770 K. Further, a set of the room temperature lattice parameters in dependence on doping with N, Al, and B has been obtained. Data for the thermal expansion were taken on a triple axis diffractometer for high energy x rays with a photon energy of 60 keV, which allows the use of large single crystals with a volume of at least 6x6x6 mm(3) without the need to consider absorption. The room temperature measurements for samples with different dopants have been performed on a four-circle diffractometer. The thermal expansion coefficients along the a- and c-directions, alpha(11) and alpha(33), increase from 3x10(-6) K(-1) at 300 K to 6x10(-6) K(-1) at 1750 K. It is found that alpha(11) and alpha(33) are isotropic within 10(7) K(-1). At high temperatures both coefficients for doped samples are similar to 0.2x10(-6) and 0.3x10(-6) K(-1) lower than for the undoped material.
Keywords: Silicon Carbide; 4H SiC; 6H SiC; thermal expansion coefficients; x-ray diffraction

On the origin of charge compensation in aluminum-implanted n-type 4H-SiC by analysis of hall effect measurements - Weiße, Julietta; Hauck, Martin; Sledziewski, Tomasz; Krieger, Michael; Bauer, Anton; Mitlehner, Heinz; Frey, Lothar; Erlbacher, Tobias (Materials Science Forum, 2019)
Aluminum implanted 4H-SiC often shows an unexpected increase of the free hole density at elevated temperatures in Hall Effect measurements. Here, we exhibit that this phenomenon cannot solely be traced down to the Hall scattering factor and the presence of excited acceptor states. It is necessary to assume an additional defect center in the lower half of the band gap with ionization energies higher than that of aluminum to explain this behavior. Therefore, we investigated ionimplanted square van-der-Pauw samples with Hall Effect and complementary SIMS measurements. An analysis of the data using the neutrality equation reveals compensation ratios of 20 % to 90 %, depending on the aluminum concentration and the concentration of the deep defect center of up to 50 % of the doping.
CRIS-Team Scopus Importer:2019-09-17
Keywords: Activation; Aluminum implantation; Compensation; Hall Effect; High temperature implantation; Ionization energy

On the origin of drain current transients and subthreshold sweep hysteresis in 4H-SiC MOSFETs - Rasinger, Fabian; Hauck, Martin; Rescher, Gerald; Aichinger, Thomas; Weber, Heiko B.; Krieger, Michael; Pobegen, Gregor (Applied Physics Letters, 2019)

On the origin of threshold voltage instability under operating conditions of 4H-SiC n-channel MOSFETs - Pobegen, Gregor; Weiße, Julietta; Hauck, Martin; Weber, Heiko B.; Krieger, Michael (Materials Science Forum, 2016)

On the Spin Behaviour of Iron(II)-Dipyridyltriazine Complexes and Their Performance as Thermal and Photonic Spin Switches - Hain, Sophie K.; Heinemann, Frank Wilhelm; Gieb, Klaus; Müller, Paul; Hoerner, Gerald; Grohmann, Andreas (European Journal of Inorganic Chemistry, 2010)
The temperature-dependent and photodynamic spin behaviour of three iron(II) complexes with different 2,6-dipyridyl-4-phenyltriazine ligands L1-L3 was investigated in the solid state and in solution (DMSO). The ligands differ in the substituent R in the 4-position of the phenyl ring (L1: R = H; L2: R = OCH(3); L3: R = SAc), which allows the electronic properties of the ligands to be finetuned. The magnetic data for the complex [Fe(L3)(2)](BF(4))(2) in the solid state indicate an incomplete spin transition to the high-spin form upon warming from liquid helium temperature, reaching about 30% at 400 K, There is circumstantial evidence for paramagnetic contributions compatible with spin transitions, namely, temperature -dependent NMR spectroscopic line shifts and line broadening in solution (DMSO). However, an efficient thermally induced spin crossover in solution is hindered by the substitution lability of the complexes, as has been detected and analyzed in an extended temperature-dependent UV/Vis spectroscopic study. Essentially unaffected by thermally induced Substitution lability, the transient dynamics of the iron(II) complexes after nanosecond laser flash excitation of their metal-to-ligand charge-transfer bands provide good evidence for efficient photoinduced spin transitions in solution in all cases. The range of measured lifetimes of the high-spin quintet states is in accord with previously published data. Importantly, in our series of iron(II) complexes, the lifetimes of the high-spin state reflect the electron-donating character of the ligands.
Keywords: Iron; Spin crossover; Thermodynamic stability; N ligands; Magnetic properties

On the terminology for describing the length-force relationship and its changes in airway smooth muscle - Bai, T. R.; Bates, JHT; Brusasco, Vito; Camoretti-Mercado, Blanca; Chitano, Pasquale; Deng, L.; Dowell, M.; Fabry, Ben; Ford, L.E.; Fredberg, Jeffrey; Gerthoffer, William T.; Gilbert, Susan H.; et al. (Journal of Applied Physiology, 2004)

On the use of multi-dimensional scaling and electromagnetic tracking in high dose rate brachytherapy - Goetz, Th I.; Ermer, M.; Salas-Gonzalez, Diego; Kellermeier, Markus; Strnad, Vratislav; Bert, Christoph; Hensel, Bernhard; Tome, A. M.; Lang, E. W. (Physics in Medicine and Biology, 2017)
High dose rate brachytherapy affords a frequent reassurance of the precise dwell positions of the radiation source. The current investigation proposes a multi-dimensional scaling transformation of both data sets to estimate dwell positions without any external reference. Furthermore, the related distributions of dwell positions are characterized by uni-or bi-modal heavy-tailed distributions. The latter are well represented by α-stable distributions. The newly proposed data analysis provides dwell position deviations with high accuracy, and, furthermore, offers a convenient visualization of the actual shapes of the catheters which guide the radiation source during the treatment.
EVALuna2:33032

On the use of particle filters for electromagnetic tracking in high dose rate brachytherapy - Goetz, Th I.; Lahmer, Godehard; Brandt, Tobias; Kallis, Karoline; Strnad, Vratislav; Bert, Christoph; Hensel, Bernhard; Tome, A. M.; Lang, E. W. (Physics in Medicine and Biology, 2017)
Modern radiotherapy of female breast cancers often employs high dose rate brachytherapy, where a radioactive source is moved inside catheters, implanted in the female breast, according to a prescribed treatment plan. Source localization relative to the patient's anatomy is determined with solenoid sensors whose spatial positions are measured with an electromagnetic tracking system. Precise sensor dwell position determination is of utmost importance to assure irradiation of the cancerous tissue according to the treatment plan. We present a hybrid data analysis system which combines multi-dimensional scaling with particle filters to precisely determine sensor dwell positions in the catheters during subsequent radiation treatment sessions. Both techniques are complemented with empirical mode decomposition for the removal of superimposed breathing artifacts. We show that the hybrid model robustly and reliably determines the spatial positions of all catheters used during the treatment and precisely determines any deviations of actual sensor dwell positions from the treatment plan. The hybrid system only relies on sensor positions measured with an EMT system and relates them to the spatial positions of the implanted catheters as initially determined with a computed x-ray tomography.
EVALuna2:33033

On the way to graphane - Pronounced fluorescence of polyhydrogenated graphene - Schäfer, Ricarda; Englert, Jan; Wehrfritz, Peter; Bauer, Walter; Hauke, Frank; Seyller, Thomas; Hirsch, Andreas (Angewandte Chemie International Edition, 2013)
Chemistry meets graphane: A Birch-type reaction using frozen water as a gentle proton source causes the exfoliation of graphite and formation of hydrogenated graphene with electronically decoupled π-nanodomains. This highly functionalized graphene displays pronounced fluorescence. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Keywords: carbon allotropes; fluorescence; graphane; graphene; hydrogenation