Ultrafast relaxation of highly excited hot electrons in Si: Roles of the L-X intervalley scattering - Ichibayashi, Taku; Tanaka, Shinichiro; Kanasaki, Junichi; Tanimura, Katsumi; Fauster, Thomas (Physical Review B, 2011)
Two-photon photoemission (2PPE) spectroscopy is used to reveal dynamic relaxation of highly excited electrons generated by 3 eV photons in Si. Monochromatic 2PPE at probe-photon energies ranging from 3.2 to 3.5 eV reveals a coherent 2PPE peak from the valence band maximum, and a transiently populated photoemission peak near L(1) in the conduction band. Time-resolved 2PPE measurements show that electrons injected into the L valley undergo L-to-X intervalley scattering with a time constant of 180 fs at 293 K. A deformation potential constant of 1.2 eV angstrom(-1) is obtained for the scattering. The highly excited electrons are relaxed down around the conduction band minimum to form a quasi-equilibrated hot electron distribution; the highest density is accumulated at 660 fs after excitation. The hot electron distribution is equilibrated with the lattice within 2 ps after excitation. These results are compared to relaxation processes of electrons injected directly into the X valley by photons with energies below 2.2 eV.

Ultrafast scanning electron microscope applied for studying the interaction between free electrons and optical near-fields of periodic nanostructures - Kozak, Martin; McNeur, Joshua; Schönenberger, Norbert; Illmer, Johannes; Li, Ang; Tafel, Alexander; Yousefi, Peyman; Eckstein, Timo; Hommelhoff, Peter (Journal of Applied Physics, 2018)
In this paper, we describe an ultrafast scanning electron microscope setup developed for the research of inelastic scattering of electrons at optical near-fields of periodic dielectric nanostructures. Electron emission from the Schottky cathode is controlled by ultraviolet femtosecond laser pulses. The electron pulse duration at the interaction site is characterized via cross-correlation of the electrons with an infrared laser pulse that excites a synchronous periodic near-field on the surface of a silicon nanostructure. The lower limit of 410 fs is found in the regime of a single electron per pulse. The role of pulse broadening due to Coulomb interaction in multielectron pulses is investigated. The setup is used to demonstrate an increase in the interaction distance between the electrons and the optical near-fields by introducing a pulse-front-tilt to the infrared laser beam. Furthermore, we show the dependence of the final electron spectra on the resonance condition between the phase velocity of the optical near-field and the electron propagation velocity. The resonance is controlled by adjusting the initial electron energy/velocity and by introducing a linear chirp to the structure period allowing the increase of the final electron energy gain up to a demonstrated value of 3.8 ke

Ultrafast Strong-Field Electron Emission and Collective Effects at a One-Dimensional Nanostructure - Paschen, Timo; Roussel, Ryan; Seiffert, Lennart; Kruse, Björn; Heide, Christian; Dienstbier, Philip; Mann, Joshua; Rosenzweig, James; Fennel, Thomas; Hommelhoff, Peter (ACS Photonics, 2023)
Enhanced near-fields at metallic nanostructures enable the generation of ultrafast nanometric electron pulses and the investigation of fundamental ultrafast dynamics in electron emission. Here we show strong-field induced photoemission from a nanometer-sharp tungsten-covered silicon nanoblade and report the systematic measurement of intensity-dependent electron energy spectra and yields. The observed plateau and cutoff features in the electron spectra indicate the presence of elastic electron rescattering in the enhanced near-fields at the surface of the one-dimensional nanostructure. For the first time, we can hence observe strong-field features from a one-dimensional object, as opposed to zero-dimensional needle tips employed so far. A comparison with results from classical and quantum simulations reveals that the extended geometry of the nanoblades and a cascaded near-field enhancement due to surface roughness leads to a broad energy distribution and high electron energies. A systematic analysis of the electron yield demonstrates nonlinear photoemission at moderate laser intensities and a clear transition to a regime with linear intensity dependence. This distinct feature is interpreted as the onset of space-charge trapping. The presented one-dimensional nanostructure enables us to generate above keV electrons without noticeable target damage and more than 13000 electrons per laser pulse, which is of utmost interest for novel classes of ultrafast photocathodes.
CRIS-Team Scopus Importer:2023-03-03
Keywords: FDTD; one-dimensional; photoemission; space-charge; strong-field; TDSE; ultrafast

Ultra-fast transistor-based detectors for precise timing of near infrared and THz signals - Preu, Sascha; Mittendorff, M.; Winnerl, Stefan; Lu, H.; Gossard, Art; Weber, Heiko B. (Optics Express, 2013)
A whole class of two-color experiments involves intense, short Terahertz radiation pulses. A fast and moderately sensitive detector capable to resolve both near-infrared and Terahertz pulses at the same time is highly desirable. Here we present the first detector of this kind. The detector element is a GaAs-based field effect transistor operated at room temperature. THz detection is successfully demonstrated at frequencies up to 4.9 THz. The THz detection time constant is shorter than 30 ps, the optical time constant is 150 ps. This detector is ideally suited for precise, simultaneous resolution of optical and THz pulses and for pulse characterization of high-power THz pulses up to tens of kW peak power levels. The dynamic range of the detector is as large as 65 +/- 3 dB/root Hz, enabling applications in a large variety of experiments and setups, also including table-top systems. (C) 2013 Optical Society of America

Ultra-high vacuum cleaver for the preparation of ionic crystal surfaces - Sander, Tim; LIU, YI; Pham, Tuan; Ammon, Maximilian Michael; Devarajulu, Mirunalini; Maier, Sabine (Review of Scientific Instruments, 2022)
Cleaving single crystals in situ under ultra-high vacuum conditions provides a reliable and straightforward approach to prepare clean and atomically well-defined surfaces. Here, we present a versatile sample cleaver to efficiently prepare ionic crystal surfaces under ultra-high vacuum conditions, which is suitable for preparation of softer materials, such as alkali halides, and harder materials, such as metal oxides. One of the advantages of the presented cleaver design is that the cleaving blade and anvil to support the crystal are incorporated into the device. Therefore, no particularly strong mechanical manipulator is needed, and it is compatible with existing vacuum chambers equipped with an xyz-manipulator. We demonstrate atomically flat terraces and the atomic structure of NaCl(001), KBr(001), NiO(001), and MgO(001) cleavage planes prepared in situ under ultra-high vacuum conditions and imaged by low-temperature non-contact atomic force microscopy.& nbsp;Published under an exclusive license by AIP Publishing
CRIS-Team WoS Importer:2022-06-03

Ultra-narrow linewidth CW sub-THz generation using GS based OFCG and n-i-pn-i-p superlattice photomixers - Criado, Ruben; de Dios, Christina; Döhler, Gottfried; Preu, Sascha; Malzer, Stefan; Bauerschmidt, Sebastian; Lu, Hong; Gossard, Art; Acedo, Pablo (Electronics Letters, 2012)
A report is presented on the photonic synthesis of ultra-narrow linewidth continuous-wave (CW) sub-THz signals using a gain-switching (GS) based optical frequency comb generator (OFCG), selective optical filtering and a n-i-pn-i-p superlattice photomixer. This setup provides continuous tunability with a tuning resolution in the range of 0.1Hz at 120GHz and full width at half maximum of the generated signals below the limits of the measurement setup (<10Hz). The advantages of this system make it a very good candidate for applications requiring extremely low phase noise and continuous tunability, such as high resolution spectroscopy in the sub-THz and THz range. © 2012 The Institution of Engineering and Technology.

Ultrashort laser oscillator pulses meet nano-structures: from attosecond physics at metal tips to dielectric laser accelerators - Thomas, Sebastian; Krüger, Michael; Breuer, John; Förster, Michael; Hommelhoff, Peter (Journal of Physics : Conference Series, 2013)
We report on two experiments about the interaction of femtosecond laser pulses with nano-scale structures. In the first experiment, we have observed strong-field effects at nanometer sharp metal tips, such as rescattering, the high-energy cut-off and a strong carrier-envelope phase dependence. All these effects are hallmarks of attosecond physics. We have used the new understanding of these processes at a solid tip to build a near-field sensor with record sensitivity of 1 nm. In the second experiment, we have demonstrated the acceleration of non-relativistic electrons with the optical near-field at a photonic grating structure, with an acceleration gradient of 25MeV/m. The grating serves to generate a near-field mode co-propagating with and efficiently imparting momentum onto the electron, which is impossible in vacuum over a macroscopic distance. For relativistic electrons we expect an acceleration gradient of more than 1 GeV/m with two-sided grating structures. © Published under licence by IOP Publishing Ltd.
UnivIS-Import:2015-04-14:Pub.2013.nat.dphy.IAP.exphys.ltrash

Unbiased High-Precision Cell Mechanical Measurements with Microconstrictions - Lange, Janina; Metzner, Claus; Richter, Sebastian; Schneider, Werner; Spermann, Monika; Kolb, Thorsten; Whyte, Graeme; Fabry, Ben (Biophysical Journal, 2017)

Unconventional conductivity increase in multilayer black phosphorus - Kolesnik-Gray, Maria; Meingast, Laura; Siebert, Martin; Unbehaun, Tim; Huf, Tobias; Ellrott, Günter; Abellan Saez, Gonzalo; Wild, Stefan; Lloret Segura, Vicente Josep; Mundloch, Udo; Schwarz, Julian; Niebauer, Michael; et al. (npj 2D Materials and Applications, 2023)
Multilayers of so-called 2D van der Waals materials have gained considerable attention as active components of next-generation electronic and optoelectronic technologies, with semiconducting black phosphorus (BP) regarded as one of the most promising systems. The applicability and performance limits of BP in both stand-alone and heterostructure-based multilayer devices are determined by individual flake charge transport properties, which synergistically depend on the number of layers and the strength of interlayer coupling between those. In this work, we study the DC electrical transport characteristics of high-quality BP field-effect devices within a wide range of flake thicknesses at room temperature. The experimental data show a non-trivial increase in conductivity and hole density with a reduced number of layers while maintaining constant field-effect mobility due to the prevalence of electron–phonon scattering. Based on the solution of the 1D Schrödinger–Poisson equation, we find that the observed phenomena are a direct consequence of non-negligible interlayer coupling, which in turn causes a local redistribution of free charge carriers towards the central layers. Our data show that due to the electrostatic conditions at the flake surfaces, a naturally protected 2D hole gas can be encapsulated in flakes as high as 10 nm, which preserves the bulk-like bandgap and effective carrier masses due to the electrostatic environment.
CRIS-Team Scopus Importer:2023-04-14

Understanding and Controlling the Evolution of Nanomorphology and Crystallinity of Organic Bulk-Heterojunction Blends with Solvent Vapor Annealing - Harreiß, Christina; Langner, Stefan; Wu, Mingjian; Berlinghof, Marvin; Rechberger, Stefanie; Will, Johannes; Conroy, Michele; Bangert, Ursel; Unruh, Tobias; Brabec, Christoph; Spiecker, Erdmann (Solar RRL, 2022)
Solvent vapor annealing (SVA) has been shown to significantly improve the device performance of organic bulk-heterojunction solar cells, yet the mechanisms linking nanomorphology, crystallinity of the active layer, and performance are still largely missing. Here, the mechanisms are tackled by correlating the evolution of nanomorphology, crystallinity, and performance with advanced transmission electron microscopy methods systematically. Model system of DRCN5T:PC71BM blends are SVA treated with four solvents differing in their donor and acceptor solubilities. The choice of solvent drastically influences the rate at which the maximum device efficiency establishes, though similar values can be achieved for all solvents. The donor solubility is identified as a key parameter that controls the kinetics of diffusion and crystallization of the blend molecules, resulting in an inverse relationship between optimal annealing time and donor solubility. For the highest efficiency, optimum domain size and single-crystalline nature of DRCN5T fibers are found to be crucial. Moreover, the π–π stacking orientation of the crystallites is directly revealed and related to the nanomorphology, providing insight into the charge carrier transport pathways. Finally, a qualitative model relating morphology, crystallinity, and device efficiency evolution during SVA is presented, which may be transferred to other light-harvesting blends.
Created from Fastlane, Scopus look-up
Keywords: crystallinity; EF-ED; EFTEM; nanomorphology; organic BHJ solar cells; small molecules; SVA

Understanding double-resonant Raman scattering in chiral carbon nanotubes: Diameter and energy dependence of the D mode - Herziger, Felix; Vierck, Asmus; Laudenbach, Jan; Maultzsch, Janina (Physical Review B, 2015)
We present a theoretical model to describe the double-resonant scattering process in arbitrary carbon nanotubes (CNTs). We use this approach to investigate the defect-induced D mode in CNTs and unravel the dependence of the D-mode frequency on the CNT diameter and on the energy of the resonant optical transition. Our approach is based on the symmetry of the hexagonal lattice and geometric considerations; hence the method is independent of the exact model that is chosen to describe the electronic band structure or the phonon dispersion. We finally clarify the diameter dependence of this Raman mode that has been under discussion in the past and demonstrate that, depending on the experimental conditions, in general two different dependencies can be measured. We also prove that CNTs with an arbitrary chiral index can exhibit a D mode in their Raman spectrum, in contrast to previous symmetry-based arguments. Furthermore, we give a direct quantification of the curvature-induced phonon frequency corrections of the D mode in CNTs with respect to graphite.

Understanding of ultra-cold-neutron production in solid deuterium - Frei, Andreas; Gutsmiedl, Erwin; Morkel, Christoph; Müller, A. R.; Paul, Stephan; Rols, Stephane; Schober, Helmut; Unruh, Tobias (EPL - Europhysics Letters, 2010)
Our recent neutron scattering measurements of phonons and other quasi-particle excitations in solid deuterium (sD(2)) and the extraction of the density of states for phonons and rotational transitions in sD(2) have led us to a new understanding of the production of ultra-cold neutrons (UCN) in sD(2)(.) The UCN production rate reaches a maximum at an equivalent neutron temperature of T(n) = 40K for a neutron flux with Maxwellian energy distribution. The cross-section for UCN production in sD(2) has been determined by using the density of states G(1)(E) in combination with the incoherent approximation as well as by a direct calibration of our measured neutron cross-sections with the known cross-section of the J = 1 -> 0 rotational transition in deuterium. Using this cross-section we deduced the production rate of UCN in sD(2) which agrees quite well with direct measurements of this energy averaged UCN production cross-section. Copyright (C) EPLA, 2010

Understanding the growth mechanism of graphene on Ge/Si(001) surfaces - Dabrowski, J; Lippert, Gunther; Avila, J; Baringhaus, Jens; Colambo, I; Dedkov, Y; Herziger, Felix; Lupina, G; Maultzsch, Janina; Schaffus, T; Schroeder, Thomas; Sowinska, M; et al. (Scientific Reports, 2016)
The practical difficulties to use graphene in microelectronics and optoelectronics is that the available methods to grow graphene are not easily integrated in the mainstream technologies. A growth method that could overcome at least some of these problems is chemical vapour deposition (CVD) of graphene directly on semiconducting (Si or Ge) substrates. Here we report on the comparison of the CVD and molecular beam epitaxy (MBE) growth of graphene on the technologically relevant Ge(001)/Si(001) substrate from ethene (C2H4) precursor and describe the physical properties of the films as well as we discuss the surface reaction and diffusion processes that may be responsible for the observed behavior. Using nano angle resolved photoemission (nanoARPES) complemented by transport studies and Raman spectroscopy as well as density functional theory (DFT) calculations, we report the direct observation of massless Dirac particles in monolayer graphene, providing a comprehensive mapping of their low-hole doped Dirac electron bands. The micrometric graphene flakes are oriented along two predominant directions rotated by 30 degrees with respect to each other. The growth mode is attributed to the mechanism when small graphene "molecules" nucleate on the Ge(001) surface and it is found that hydrogen plays a significant role in this process.

Understanding UCN production in solid D-2: The generalized density of states measured via inelastic neutron scattering - Gutsmiedl, Erwin; Frei, Andreas; Müller, A. R.; Paul, Stephan; Urban, M.; Schober, Helmut; Morkel, Christoph; Unruh, Tobias (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2009)
The dynamics of solid deuterium [H. Nielsen, et all., Phys. Rev. B 7 (1973) 1626] (sD(2)) is studied by means of inelastic thermal neutron scattering (coherent and incoherent scattering) at different temperatures and para-ortho ratios. In this paper, the results for the generalized density of states (GDOS) are presented and discussed. The measurements were performed at the thermal time-of-flight (TOF) instrument IN4 at the ILL Grenoble, and at the cold neutron TOF instrument TofTof at the FIRM II. The GDOS contains beside the hcp phonon excitations of the sD(2) the rotational transition J = 0 -> 1 and 1 -> 2. The measured and expected intensities of these rotational excitations are strongly depended on the ortho concentration in the sD(2). Above E = 10meV there are still strong excitations, which are very likely smeared out higher energy optic phonons and multiphonon contributions. An empirical method of separation of the one- and multiphonon contributions to the GDOS will be presented and discussed. The impact of these measurements on the UCN production in sD(2) will be shown in detail. (C) 2009 Elsevier B.V. All rights reserved.
Keywords: Neutron; Phonons; Ultra-cold neutrons (UCN); UCN production

Unification of geminate and distant pair recombination statistics: low temperature photoelectronic properties in a-Si:H - Ristein, Jürgen (Journal of Non-Crystalline Solids, 1991)
On the basis of seperately existing theories the combined influence of geminate, non geminate and defect recombination on the low temperature photoinduced properties of a-Si:H is discussed. © 1991 Elsevier Science Publishers B.V. All rights reserved.
UnivIS-Import:2015-03-05:Pub.1991.nat.dphy.IAP.exphys.unific

Unimodular lattice triangulations as small-world and scale-free random graphs - Mecke, Klaus; Krüger, Benedikt; Schmidt, Ella (New Journal of Physics, 2015)
Real-world networks, e.g., the social relations or world-wide-web graphs, exhibit both small-world and scale-free behaviour. We interpret lattice triangulations as planar graphs by identifying triangulation vertices with graph nodes and one-dimensional simplices with edges. Since these triangulations are ergodic with respect to a certain Pachner flip, applying different Monte Carlo simulations enables us to calculate average properties of random triangulations, as well as canonical ensemble averages, using an energy functional that is approximately the variance of the degree distribution. All considered triangulations have clustering coefficients comparable with real-world graphs; for the canonical ensemble there are inverse temperatures with small shortest path length independent of system size. Tuning the inverse temperature to a quasi-critical value leads to an indication of scale-free behaviour for degrees k >= 5. Using triangulations as a random graph model can improve the understanding of real-world networks, especially if the actual distance of the embedded nodes becomes important.
Keywords: unimodular lattice triangulations; networks; maximal planar graphs

Universal solvent restructuring induced by colloidal nanoparticles - Zobel, Mirijam; Neder, Reinhard; Kimber, Simon A. J. (Science, 2015)
Colloidal nanoparticles, used for applications from catalysis and energy applications to cosmetics, are typically embedded in matrixes or dispersed in solutions. The entire particle surface, which is where reactions are expected to occur, is thus exposed. Here, we show with x-ray pair distribution function analysis that polar and nonpolar solvents universally restructure around nanoparticles. Layers of enhanced order exist with a thickness influenced by the molecule size and up to 2 nanometers beyond the nanoparticle surface. These results show that the enhanced reactivity of solvated nanoparticles includes a contribution from a solvation shell of the size of the particle itself.

Unoccupied dimer-bond state at Si(001) surfaces - Fauster, Thomas; Tanaka, Shinichiro; Tanimura, Katsumi (Physical Review B, 2011)
Two-photon photoemission is used to identify the unoccupied dimer-bond state on the Si(001) surface at an energy 2.83 eV above the valence-band maximum. A strong resonance enhancement is found for excitation from the occupied dangling-bond state. The azimuthal and polarization dependence proves the orientation of the observed state along the dimer axis. The dispersion is dominated by the occupied initial state described by -0.50 free-electron masses in one- and two-photon photoemission.

UNOCCUPIED ELECTRONIC STATES AND SURFACE BARRIERS AT CU SURFACES - Fauster, Thomas; et al. (Journal of Physics: Condensed Matter, 1993)
The surface potential barrier shape of the low-index faces of copper was determined by an analysis of inverse photoemission and two-photon photoemission measurements making use of the one-step model of photoemission. The barrier potentials obtained in this way allow for a consistent description of the energetic positions and effective masses of all known surface states for the various faces. It is found, in agreement with previous theoretical predictions, that the most open surface, Cu(110). exhibits the strongest saturation of the image potential with an image plane lying nearest to the topmost atomic layer and with the weakest image force outside the crystal. A comparison with theoretical slab calculations shows that in these calculations the position of the image plane is always significantly further outside the crystal than derived in the present study. Dynamical effects in the effective potential are found to be negligible for electronic states up to 6 eV above the Fermi level E(F), but are probably responsible for systematic discrepancies between theory and experiment for unoccupied bulk states in the energy range 10-15 eV above E(F).

Unoccupied electronic states in atomic chains on Si(557)-Au: Time-resolved two-photon photoemission investigation - Rügheimer, Tilman; Fauster, Thomas; Himpsel, F. J. (Physical Review B, 2007)
The prototypical one-dimensional Si(557)-Au surface is investigated with time-resolved two-photon photoemission. Three new states are found near (Gamma) over bar, two of them in the band gap of silicon. These states cannot be explained by existing band calculations. As a possible solution, we suggest a closer examination of the atomic and electronic structure near the step edge.

UNOCCUPIED ELECTRONIC STATES IN THE BAND-STRUCTURE OF NIAL(110) - Fauster, Thomas; et al. (Physical Review B, 1992)
The unoccupied electronic states of the clean NiAl(110) surface have been studied with angle-resolved inverse photoemission along the GAMMA-BAR XBAR and GAMMA-BAR YBAR directions of the surface Brillouin zone. The use of a rotatable electron gun allows an independent variation of the incidence angle of the electrons and the exit angle of the photons. Measurements of the photon-emission characteristic of the dipole transitions observed in inverse photoemission can be used to determine the symmetry of the electronic states. For normal incidence of the electron beam, transitions along the GAMMA-M line of the bulk Brillouin zone are detected and the results are compared to band-structure calculations available for the high-symmetry lines.

UNOCCUPIED ELECTRONIC STATES OF EPITAXIAL IRON LAYERS ON CU(100) - Fauster, Thomas; et al. (Zeitschrift für Physik B Condensed Matter, 1992)
Inverse photoemission spectra were taken for thin epitaxial iron films on Cu(100). For a film thickness of eight monolayers the observed electronic states are characteristic for a fcc(100) surface. The d-bands of iron show a ferromagnetic exchange splitting of 1.1 eV, considerably smaller than the bulk value of 1.8 eV, which we observe for film thicknesses above 18 monolayers.

Unoccupied topological states on bismuth chalcogenides - Niesner, Daniel; Fauster, Thomas; Eremeev, S. V.; Menshchikova, T. V.; Koroteev, Yu. M.; Protogenov, A. P.; Chulkov, E. V.; Tereshchenko, O. E.; Kokh, K. A.; Alekperov, O.; Nadjafov, A.; Mamedov, N. (Physical Review B, 2012)
The unoccupied part of the band structure of topological insulators Bi2TexSe3-x (x = 0,2,3) is studied by angle-resolved two-photon photoemission and density functional theory. For all surfaces linearly dispersing surface states are found at the center of the surface Brillouin zone at energies about 1.3 eV above the Fermi level. Theoretical analysis shows that this feature appears in a spin-orbit-interaction-induced and inverted local energy gap. This inversion is insensitive to variation of electronic and structural parameters in Bi2Se3 and Bi2Te2Se. In Bi2Te3 small structural variations can change the character of the local energy gap, depending on whether or not an unoccupied Dirac state exists. Circular dichroism measurements confirm the expected spin texture. From these findings we assign the observed state to an unoccupied topological surface state.

Unraveling Complexity: A Strategy for the Characterization of Anisotropic Core Multishell Nanoparticles - Lin, Wei; Greve, Christoph; Härtner, Sebastian; Götz, Klaus; Walter, Johannes; Wu, Mingjian; Rechberger, Stefanie; Spiecker, Erdmann; Busch, Sebastian; Schmutzler, Tilo; Avadhut, Yamini; Hartmann, Martin; et al. (Particle & Particle Systems Characterization, 2020)
In this work, a widely applicable routine to characterize the core, surface, stability, and optical properties of CdSe/CdS/ZnS core–shell–shell nanorods after multiple growth steps is established. First, size, shape, and shell thickness of the nanorods are characterized by transmission electron microscopy (TEM), analytical ultracentrifugation (AUC), and small angle X-ray/neutron scattering (SAXS/SANS). In the next step, Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and SANS measurements are applied to determine the surface species of nanorods. Then, the colloidal stability of the nanorods is investigated by UV–vis spectroscopy and dynamic light scattering (DLS) after different washing cycles. Finally, photoluminescence quantum yield (PLQY) of the nanorods during washing and sample storage is determined. With this highly complementary routine for particle characterization, the core, surface, stability, and optical properties of nanorods after multiple growth steps are resolved. The results demonstrate the importance of the developed toolbox to characterize such highly complex, anisotropic nanorods for a technical environment. This is of major importance for the handling of colloidal quantum materials and their quality control in industrial applications.
CRIS-Team Scopus Importer:2020-09-11
Keywords: anisotropic; characterization; core multishell; nanoparticles

Unraveling the Microstructure-Related Device Stability for Polymer Solar Cells Based on Nonfullerene Small-Molecular Acceptors - Du, Xiaoyan; Heumüller, Thomas; Gruber, Wolfgang; Almora, Osbel; Classen, Andrej; Qu, Jianfei; He, Feng; Unruh, Tobias; Li, Ning; Brabec, Christoph (Advanced Materials, 2020)
As the power conversion efficiency (PCE) of organic solar cells (OSCs) has surpassed the 17% baseline, the long-term stability of highly efficient OSCs is essential for the practical application of this photovoltaic technology. Here, the photostability and possible degradation mechanisms of three state-of-the-art polymer donors with a commonly used nonfullerene acceptor (NFA), IT-4F, are investigated. The active-layer materials show excellent intrinsic photostability. The initial morphology, in particular the mixed region, causes degradation predominantly in the fill factor (FF) under illumination. Electron traps are formed due to the reorganization of polymers and diffusion-limited aggregation of NFAs to assemble small isolated acceptor domains under illumination. These electron traps lead to losses mainly in FF, which is in contradistinction to the degradation mechanisms observed for fullerene-based OSCs. Control of the composition of NFAs close to the thermodynamic equilibrium limit while keeping adequate electron percolation and improving the initial polymer and NFA ordering are of the essence to stabilize the FF in NFA-based solar cells, which may be the key tactics to develop next-generation OSCs with high efficiency as well as excellent stability.
CRIS-Team Scopus Importer:2020-03-10
Keywords: bulk-heterojunction microstructure; morphology stability; nonfullerene acceptors; organic solar cells; photostability

Unravelling the Mechanisms of Gold−Silver Core−Shell Nanostructure Formation by in Situ TEM Using an Advanced Liquid Cell Design - Hutzler, Andreas; Schmutzler, Tilo; Jank, Michael P. M.; Branscheid, Robert; Unruh, Tobias; Spiecker, Erdmann; Frey, Lothar (Nano Letters, 2018)
The growth of silver shells on gold nanorods is investigated by in situ liquid cell transmission electron microscopy using an advanced liquid cell architecture. The design is based on microwells in which the liquid is confined between a thin Si3N4 membrane on one side and a few-layer graphene cap on the other side. A well-defined specimen thickness and an ultraflat cell top allow for the application of high-resolution TEM and the application of analytical TEM techniques on the same sample. The combination of high-resolution data with chemical information is validated by radically new insights into the growth of silver shells on cetrimonium bromide stabilized gold nanorods. It is shown that silver bromide particles already formed in the stock solution play an important role in the exchange of silver ions. The Ag shell growth can be directly correlated with the layer-by-layer dissolution of AgBr nanocrystals, which can be controlled by the electron flux density via distinctly generated chemical species in the solvent. The derived model framework is confirmed by in situ UV–vis absorption spectroscopy evaluating the blue shift in the longitudinal surface plasmon resonance of anisotropic NRs in a complementary batch experimen
Keywords: Liquid cell TEM; Ag@Au; core−shell; electron beam-induced growth; plasmonic structures; graphene

Unusually weak electron-phonon coupling in the Shockley surface state on Pd(111) - Sklyadneva, I. Yu.; Heid, R.; Silkin, V. M.; Melzer, Andrea Christine; Bohnen, K. P.; Echenique, P. M.; Fauster, Thomas; Chulkov, E. V. (Physical Review B, 2009)
Electron-phonon (e-ph) coupling in the (Gamma) over bar unoccupied surface state on Pd(111) is studied using density-functional perturbation-theory calculation and two-photon photoemission measurements. Also, an ab initio GW calculation is performed to combine it with the e-ph coupling evaluation in the study of the surface-state linewidth. We show that the e-ph coupling in the surface state is unusually weak. It is smaller by a factor of 5 than that at the Fermi surface of bulk Pd. Temperature-dependent two-photon photoemission measurements confirm this result indicating an important role of interband scattering from surface to bulk states.

Unveiling the Mechanism of Water Partial Dissociation on Ru(0001) - Maier, Sabine; Stass, Ingeborg; Cerda, Jorge I.; Salmeron, Miquel (Physical Review Letters, 2014)
We have studied the mechanism of the partial dissociation of water on Ru(0001) by high resolution scanning tunneling microscopy (STM). The thermal evolution of water at submonolayer coverage has been tracked in the 110-145 K temperature range to identify the precursor structures for the partial dissociation. These were found to consist of hexagons arranged in thin stripes aligned along the close packed Ru [2 (11) over bar0] directions. The partially dissociated phase, on the other hand, contains a mixture of H2O and OH hexagons arranged into wider stripes and rotated by 30 degrees with respect to the intact water stripes. The atomic structure of both types of stripes is determined with the aid of density functional theory and STM simulations, providing insights into the partial dissociation reaction path. The reaction is found to be exothermic by around 0.4 eV and initiating at the edges of the intact water stripes. Hydrogen atoms, from water dissociation or already present at the surface, are found to play an important role in the kinetics of the reactions.

Unveiling the oxidation behavior of liquid-phase exfoliated antimony nanosheets - Assebban, Mhamed; Gibaja, Carlos; Fickert, Michael; Torres, Inigo; Weinreich, Erik; Wolff, Stefan; Gillen, Roland; Maultzsch, Janina; Varela, Maria; Rong, Sherman Tan Jun; Loh, Kian Ping; Michel, Enrique G.; et al. (2D Materials, 2020)
Antimonene, a monolayer of beta-antimony, is increasingly attracting considerable attention, more than that of other monoelemental two-dimensional materials, due to its intriguing physical and chemical properties. Under ambient conditions, antimonene exhibits a high thermodynamic stability and good structural integrity. Some theoretical calculations predicted that antimonene would have a high oxidation tendency. However, it remains poorly investigated from the experimental point of view. In this work, we study the oxidation behavior of antimonene nanosheets (ANS) prepared by ultrasonication-assisted liquid-phase exfoliation. Using a set of forefront analytical techniques, a clear effect of sonication time on the surface chemistry of prepared ANS is found. A dynamic oxidation behavior has been observed, which upon annealing at moderate temperature (210 degrees C) resulted in a semiconducting behavior with a bandgap of approximately 1 eV measured by ultraviolet photoelectron spectroscopy. This study yields valuable information for future applications of antimonene and paves the way towards novel modification approaches in order to tailor its properties and complement its limitations.
CRIS-Team WoS Importer:2020-04-07

Up-regulation of Rho/ROCK Signaling in Sarcoma Cells Drives Invasion and Increased Generation of Protrusive Forces - Roesel, Daniel; Brabek, Jan; Tolde, Ondrej; Mierke, Claudia; Paranhos Zitterbart, Daniel; Raupach, Carina; Bicanova, K.; Kollmannsberger, Philip; Pankova, D. V.; Vesely, Pavel; Folk, Petr; Fabry, Ben (Molecular Cancer Research, 2008)

Using a quantum well heterostructure to study the longitudinal and transverse electric field components of a strongly focused laser beam - Malzer, Stefan; Leuchs, Gerd; et al. (Journal of Applied Physics, 2006)
We report a method to measure the electric energy density of longitudinal and transverse electric field components of strongly focused polarized laser beams. We used a quantum well photodetector and exploited the polarization dependent optical transitions of light holes and heavy holes to probe the electric field distribution in the focal region. A comparison of the measured photocurrent spectra for radially and azimuthally polarized beams at the light and heavy hole absorption peaks provides a measure of the amount of the longitudinal electric field component. © 2006 American Institute of Physics.

Using the focal phase to control attosecond processes - Hoff, Dominik; Krüger, Michael; Maisenbacher, Lothar; Paulus, Gerhard G.; Hommelhoff, Peter; Sayler A, M (Journal of Optics A-Pure and Applied Optics, 2017)
The spatial evolution of the electric field of focused broadband light is crucial for many emerging attosecond technologies. Here the effects of the input beam parameters on the evolution of few-cycle laser pulses in the focus are discussed. Specifically, we detail how the frequency-dependent input beam geometry, chirp and chromatic aberration can affect the spatial dependence of the carrier-envelope phase (CEP), central frequency and pulse duration in the focus. These effects are confirmed by a direct, three-dimensional measurement of the CEP-evolution in the focus of a typical few-cycle pulse laser using electron rescattering at metal nanotips in combination with a CEP-metre. Moreover, we demonstrate a simple measurement technique to estimate the focal CEP evolution by input-beam parameters. These parameters can be used in novel ways in order to control attosecond dynamics and tailor highly nonlinear light–matter interaction
Keywords: attosecond physics; carrier-envelope phase; few-cycle pulse; supercontinuum generation; high harmonic generation; femtochemistry; strong field laser physics

Valence band and gap state spectroscopy of amorphous carbon by photoelectron emission techniques - Ristein, Jürgen; Ley, Lothar; et al. (Amorphous Carbon:State of the Art, 1998)
UnivIS-Import:2015-04-16:Pub.1998.nat.dphy.IAP.exphys.valenc

Variable doping sensitivity of the TO phonon dispersion branch of metallic nanotubes: A double resonant Raman scattering study - Rafailov, Peter M.; Maultzsch, Janina; Thomsen, Christian; Dettlaff-Weglikowska, Urszula; Roth, Siegmar (physica status solidi (b), 2009)
We applied Raman spectroscopy to investigate the response to electrochemical doping of the second-order D*-band in single-walled carbon nanotube (SWNT) bundles. A dramatic increase of the D*-band sensitivity to doping is found upon moving the laser excitation to the red end of the visible spectrum and beyond. Basing on the double resonance (DR) Raman scattering model we interpret this phenomenon as an increasing doping sensitivity of the TO phonon dispersion branch of metallic SWNTs towards its minimum. From D*-band measurements we are thus able to draw conclusions on the wave-vector dependence of the doping sensitivity and the electron-phonon coupling (EPC) around the TO branch minimum. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Variable electron-phonon coupling in isolated metallic carbon nanotubes observed by Raman scattering - Maultzsch, Janina; et al. (Physical Review Letters, 2007)
We report the existence of broad and weakly asymmetric features in the high-energy (G) Raman modes of freely suspended metallic carbon nanotubes of defined chiral index. A significant variation in peak width (from 12 cm(-1) to 110 cm(-1)) is observed as a function of the nanotube's chiral structure. When the nanotubes are electrostatically gated, the peak widths decrease. The broadness of the Raman features is understood as the consequence of coupling of the phonon to electron-hole pairs, the strength of which varies with the nanotube chiral index and the position of the Fermi energy.

Variation of self-seeded germanium nanowire electronic device functionality due to synthesis condition determined surface states - Connaughton, Stephen; Hobbs, Richard; Lotty, Olan; Holmes, Justin D.; Krstic, Vojislav (Advanced Materials Interfaces, 2015)
An approach to direct the intrinsic electronic transport properties of self-seeded germanium nanowires at room temperature by in situ synthesis conditions is presented. The electrical response is varied between quasi-metallic and p-type semiconductors with memristive signatures. Electron transfer between nanowire core and core–shell surface states governs both conduction regimes and a simplified developed model reproduces the main memristive features.

Versatile bioactive and antibacterial coating system based on silica, gentamicin, and chitosan: Improving early stage performance of titanium implants - Ballarre, Josefina; Aydemir, T.; Liverani, Liliana; Roether, Judith; Goldmann, Wolfgang; Boccaccini, Aldo R. (Surface & Coatings Technology, 2019)
The aim of this work is to develop and characterize a multifunctional and dual surface coating system for titanium orthopedic implants by applying two different cost-effective, scalable, and non-complex coating technologies (spray and electrophoretic deposition). The first deposit is formed by a sprayed hybrid sol-gel layer combined with bioactive glass particles (45S5, BG), and the outer part of the dual coating consists of a chitosan-gelatin/silica (Si) - antibiotic (gentamicin, Ge) composite layer applied by electrophoretic deposition. The application of sol-gel enclosed BG drops onto the surface was done to enhance the bioactivity of the double-layered surface coating system. After the BG is dissolved, thus generating a calcium‑silicon rich medium, the re-deposition of hydroxyl‑carbonate apatite occurs. Regarding the antibacterial inhibition properties, antibacterial activity to both strains used (S. aureus and E. coli) was obtained for the chitosan/gelatin/Si[sbnd]Ge nanoparticle coatings on titanium substrates, showing a large inhibition area around the samples. Both the bare Ti samples and the coatings with chitosan/gelatin matrix did not successfully inhibit bacterial growth. As expected, the presence of silica-based glasses and coatings based on amorphous silica enhanced cell viability. The deposition of BG was done with the aim of extending the bioactive effect of the system, considering the presence of a porous degradable organic layer deposited on top, which was shown to be partially degraded after 7 days. The sol gel sprayed BG layer combined with chitosan/gelatin biopolymers filled with Si[sbnd]Ge nanoparticles presents a suitable technology to generate bioactive and antibacterial surfaces to enhance Ti implant performance.
CRIS-Team Scopus Importer:2019-12-13
Keywords: Antibacterial effect; Bioactive glass; Bioactivity; Electrophoretic deposition; Silica-gentamicin nanoparticles; Titanium

Vibrational and molecular dynamics of a nanoconfined liquid crystal - Schönhals, Andreas; Frunza, Stefan; Frunza, Ligia; Unruh, Tobias; Frick, Bernhard; Zorn, Rainer (European Physical Journal - Special Topics, 2010)
The effect of a nanometer confinement on the vibrational and molecular dynamics of a liquid crystals E7 was studied by dielectric spectroscopy (DS) and neutron scattering (NS). E7 undergoes a glass transition phenomenon besides the nematic to isotropic phase transition. As confining host a molecular sieve of the MCM-41 type is used having cylindrical pores with a radius of 1.25 nm. The results obtained by both methods are compared in detail.

Vibrational dynamics of permanently densified GeO2 glasses: Densification-induced changes in the boson peak - Orsingher, Laura; Fontana, Aldo; Gilioli, Edmondo; Carini Jr., G.; Carini, G.; Tripodo, G.; Unruh, Tobias; Buchenau, Ulrich (Journal of Chemical Physics, 2010)
Vitreous GeO2, one of the main prototypes of strong glasses, was densified at several pressures up to 6 GPa, achieving more than 20% of densification. The density dependence of the vibrational density of states and of the low temperature properties of these glasses was investigated by means of inelastic neutron scattering and calorimetric measurements. With increasing density, both the boson peak and the bump in c(p)/T-3 versus T plot exhibit variations which are stronger than the elastic medium expectation. If one reduces the measured spectra to a common master curve, one finds that this is only possible for the densified samples; the first densification step has an additional effect, similar to other cases in the literature. Nevertheless, the existence of a master curve for the three densified samples proves that the total number of excess modes remains constant on further densification. The experimental data are discussed in the framework of different theoretical models.
Keywords: boson systems; densification; density; germanate glasses; high-pressure effects; neutron diffraction; specific heat; vibrational modes; vitreous state

Vibrational Properties and Charge Transfer in the Misfit-Layer Compound LaS-CrS2 - Kampmann, Felix; Panchakarla, Leela S.; Gillen, Roland; Tenne, Reshef; Maultzsch, Janina (Journal of Physical Chemistry C, 2021)
We present density functional theory calculations of the vibrational and electronic properties of the misfit-layer compound (MLC) LaS-CrS2 and its isolated sublayers to identify the vibrational modes of the compound. From the comparison of two model systems, (i) the fully relaxed misfit-layer compound supercell and (ii) its sublayers as isolated systems, we extract the charges, which are transferred between the two sublayers and the concomitant changes of the structural parameters upon formation of the supercell. The deformation within each sublayer indicates a strong influence of the charge transfer, confirming the important role of the interlayer interaction between the two sublayers. By comparing the vibrational properties of the two model systems, we assign several frequency regimes within the vibrations of the supercell to phonon branches of the sublayers. From polarized Raman spectra, we find that some of the Raman modes are directly inherited from the -point phonons of the hypothetical isolated 1T-CrS2 layer; other Raman modes are backfolded from the A1g-associated phonon branch of the 1T-CrS2 onto the misfit-layer compound MLC -point, which is a direct consequence of the supercell formation in LaS-CrS2.
CRIS-Team Scopus Importer:2021-05-14

Vibrational properties of graphene nanoribbons by first-principles calculations - Gillen, Roland; Mohr, Marcel; Thomsen, Christian; Maultzsch, Janina (Physical Review B, 2009)
We investigated the vibrational properties of graphene nanoribbons by means of first-principles calculations on the basis of density-functional theory. We confirm that the phonon modes of graphene nanoribbons with armchair- and zigzag-type edges can be interpreted as fundamental oscillations and their overtones. These show a characteristic dependence on the nanoribbon width. Furthermore, we demonstrate that a mapping of the calculated Gamma-point phonon frequencies of nanoribbons onto the phonon dispersion of graphene corresponds to an "unfolding" of nanoribbons' Brillouin zone onto that of graphene. We consider the influence of spin states with respect to the phonon spectra of zigzag nanoribbons and provide comparisons of our results with past studie

Vibrational signatures of diamondoid dimers with large intramolecular London dispersion interactions - Tyborski, Christoph; Hückstaedt, Tobias; Gillen, Roland; Otto, Tommy; Fokina, Nataliya A.; Fokin, Andrey A.; Schreiner, Peter R.; Maultzsch, Janina (Carbon, 2020)
We analyze the vibrational properties of diamondoid compounds via Raman spectroscopy. The compounds are interconnected with carbon-carbon single bonds that exhibit exceptionally large bond lengths up to 1.71A∘. Attractive dispersion interactions caused by well-aligned intramolecular H⋯H contact surfaces determine the overall structures of the diamondoid derivatives. The strong van-der-Waals interactions alter the vibrational properties of the compounds in comparison to pristine diamondoids. Supported by dispersion-corrected density functional theory (DFT) computations, we analyze and explain their experimental Raman spectra with respect to unfunctionalized diamondoids. We find a new set of dispersion-induced vibrational modes comprising characteristic CH/CH2 vibrations with exceptionally high energies. Further, we find structure-induced dimer modes that are indicative of the size of the dimers.
CRIS-Team Scopus Importer:2019-10-29

Vinculin, cell mechanics, and tumor cell invasion - Goldmann, Wolfgang; Auernheimer, Vera; Thievessen, Ingo; Fabry, Ben (Cell Biology International, 2013)

Vinculin facilitates cell invasion into three-dimensional collagen matrices - Mierke, Claudia; Kollmannsberger, Philip; Paranhos Zitterbart, Daniel; Diez, Gerold; Koch, Thorsten; Marg, Susanna; Ziegler, Wolfgang H.; Goldmann, Wolfgang; Fabry, Ben (Journal of Chemical Biology, 2010)

Vinculin is required for cell polarization, migration, and extracellular matrix remodeling in 3D collagen - Thievessen, Ingo; Fakhri, Nikta; Steinwachs, Julian; Kraus, Viola; McIsaac, R. Scott; Gao, Liang; Chen, Bi-Chang; Baird, Michelle A.; Davidson, Michael W.; Betzig, Eric; Oldenbourg, Rudolf; Waterman, Clare M.; et al. (The FASEB Journal, 2015)

Vinculin phosphorylation at residues Y100 and Y1065 is required for cellular force transmission. - Auernheimer, Vera; Lautscham, Lena; Leidenberger, Maria; Friedrich, Oliver; Kappes, Bärbel; Fabry, Ben; Goldmann, Wolfgang (Journal of cell science, 2015)
The focal adhesion protein vinculin connects the actin cytoskeleton via talin and integrin with the extracellular matrix. Vinculin consists of a globular head and tail domain, which undergo conformational changes from a closed auto-inhibited conformation in the cytoplasm to an open conformation in focal adhesions. Src-phosphorylation has been suggested to regulate this conformational switch. To explore the role of phosphorylation in vinculin activation, we used knock-out mouse embryonic fibroblasts re-expressing different vinculin mutants in traction microscopy, magnetic tweezer microrheology, FRAP, and actin-binding assays. Compared to cells expressing wildtype or constitutively active vinculin, we found reduced tractions, cytoskeletal stiffness, adhesion strength, and increased vinculin dynamics in cells expressing constitutively inactive vinculin or vinculin where Src-phosphorylation was blocked by replacing tyrosine at position 100 and/or 1065 with non-phosphorylatable phenylalanine. Replacing tyrosines with phospho-mimicking glutamic acid restored cellular tractions, stiffness, adhesion strength as well as vinculin dynamics, and facilitated vinculin-actin binding. These data demonstrate that Src-phosphorylation is necessary for vinculin activation, and that phosphorylation controls cytoskeletal mechanics by regulating force transmission between the actin cytoskeleton and focal adhesion proteins.

Viscoelastic properties of suspended cells measured with shear flow deformation cytometry - Gerum, Richard; Mirzahossein, Elham; Eroles, Mar; Elsterer, Jennifer; Mainka, Astrid; Bauer, Andreas; Sonntag, Selina; Winterl, Alexander; Bartl, Johannes; Fischer, Lena; Abuhattum, Shada; Goswami, Ruchi; et al. (eLife, 2022)
Numerous cell functions are accompanied by phenotypic changes in viscoelastic prop-erties, and measuring them can help elucidate higher level cellular functions in health and disease. We present a high-throughput, simple and low-cost microfluidic method for quantitatively measuring the elastic (storage) and viscous (loss) modulus of individual cells. Cells are suspended in a high-viscosity fluid and are pumped with high pressure through a 5.8 cm long and 200 µm wide microflu-idic channel. The fluid shear stress induces large, ear ellipsoidal cell deformations. In addition, the flow profile in the channel causes the cells to rotate in a tank-treading manner. From the cell deformation and tank treading frequency, we extract the frequency-dependent viscoelastic cell properties based on a theoretical framework developed by R. Roscoe [1] that describes the deformation of a viscoelastic sphere in a viscous fluid under steady laminar flow. We confirm the accuracy of the method using atomic force microscopy-calibrated polyacrylamide beads and cells. Our measurements demonstrate that suspended cells exhibit power-law, soft glassy rheological behavior that is cell-cycle-dependent and mediated by the physical interplay between the actin filament and intermediate filament networks.
CRIS-Team Scopus Importer:2022-10-28

Visualizing multiphase flow and trapped fluid configurations in a model three-dimensional porous medium - Krummel, Amber T.; Datta, Sujit S.; Münster, Stefan; Weitz, David A. (AIChE Journal, 2013)
We report an approach to fully visualize the flow of two immiscible fluids through a model three-dimensional (3-D) porous medium at pore-scale resolution. Using confocal microscopy, we directly image the drainage of the medium by the nonwetting oil and subsequent imbibition by the wetting fluid. During imbibition, the wetting fluid pinches off threads of oil in the narrow crevices of the medium, forming disconnected oil ganglia. Some of these ganglia remain trapped within the medium. By resolving the full 3-D structure of the trapped ganglia, we show that the typical ganglion size, as well as the total amount of residual oil, decreases as the capillary number Ca increases; this behavior reflects the competition between the viscous pressure in the wetting fluid and the capillary pressure required to force oil through the pores of the medium. This work thus shows how pore-scale fluid dynamics influence the trapped fluid configurations in multiphase flow through 3-D porous media. © 2012 American Institute of Chemical Engineers.
Created from Fastlane, Scopus look-up
Keywords: Capillarity; Fluid mechanics and transport phenomena; Multiphase flow; Permeability; Porous media; Wetting

WATCHING NANODEFECTS GROW IN SI CRYSTALS - Magerl, Andreas (ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 2019)
CRIS-Team WoS Importer:2020-08-07

Watching the life of electrons at surfaces with two-photon photoemission - Fauster, Thomas (Surface Science, 2002)
An electron put on a metal surface is attracted by the image force. A Rydberg-like series of image-potential states is formed which describes loosely bound electrons which can move freely parallel to the surface. With time-resolved two-photon photoemission spectroscopy the electronic band Structure and the femtosecond dynamics of these states are studied in the energy- and time-domain. The decay of the image-potential-state Population is attributed to electron-electron interaction with metal electrons, Which Constitutes an inelastic scattering process. Defects (or phonons) may lead to elastic scattering which changes the phase of the electronic wave function without changing the population. With time-resolved two-photon photoemission inelastic and elastic scattering processes can be separated. From these experiments we can extract information on the lifetime of excited electrons at surfaces in excellent agreement with theoretical calculations by Echenique and co-workers. The interaction of image-potential states with adsorbates or steps gives insight into the inelastic and clastic scattering by the various surface defects which are not accessible by any other technique. (C) 2002 Published by Elsevier Science B.V.
Keywords: surface electronic phenomena (work function; surface potential; surface states. etc.) photoelectron emission; eletron emission

Water adsorption on metals and nanostructured interfaces - Maier, Sabine (Elsevier, 2018)
The adsorption and reaction of water on surfaces is of great importance in many fundamental and technological processes at interfaces, since ultra-thin water films cover most hydrophilic surfaces under ambient conditions. Examples of processes that take part at the solid/liquid interface are photocatalytic water splitting, heterogeneous catalysis, and electrochemistry. On metal surfaces, the adsorption energy of water is comparable to the hydrogen bond strength among water molecules. Therefore, the delicate balance between competing water-water and the water-metal interactions leads to a rich variety of structures that form at the interface between water and seemingly simple, flat metal surfaces. In this article, we review recent experimental and theoretical advances in the molecular-level understanding of water adsorption, dissociation, and clustering on metals and nanostructured surfaces. This includes mainly surface science experiments and at low temperatures in ultra-high vacuum.
CRIS-Team Scopus Importer:2022-04-14
Keywords: Cubic ice; Dehydrogenation; Dissociation; Hexagonal ice; Hydrogen bonding; Hydroxyl; Ice; Metal surfaces; Scanning probe techniques; Water; Water splitting; Wetting

Water at surfaces and interfaces: From molecules to ice and bulk liquid - Shimizu, Tomoko; Maier, Sabine; Verdaguer, Albert; Velasco-Velez, Juan-Jesus; Salmeron, Miquel (Progress in Surface Science, 2018)
The structure and growth of water films on surfaces is reviewed, starting from single molecules to two-dimensional wetting layers, and liquid interfaces. This progression follows the increase in temperature and vapor pressure from a few degrees Kelvin in ultra-high vacuum, where Scanning Tunneling and Atomic Force Microscopies (STM and AFM) provide crystallographic information at the molecular level, to ambient conditions where surface sensitive spectroscopic techniques provide electronic structure information. We show how single molecules bind to metal and non-metal surfaces, their diffusion and aggregation. We examine how water molecules can be manipulated by the STM tip via excitation of vibrational and electronic modes, which trigger molecular diffusion and dissociation. We review also the adsorption and structure of water on non-metal substrates including mica, alkali halides, and others under ambient humid conditions. We finally discuss recent progress in the exploration of the molecular level structure of solid-liquid interfaces, which impact our fundamental understanding of corrosion and electrochemical processes.

Water-induced surface reconstruction of oxygen (2x1) covered Ru(0001) - Maier, Sabine; Cabrera-Sanfelix, Pepa; Stass, Ingeborg; Sánchez-Portal, Daniel; Arnau, Andrés; Salmeron, Miquel (Physical Review B, 2010)
Low-temperature scanning tunneling microscopy and density-functional theory (DFT) were used to study the adsorption of water on a Ru(0001) surface covered with half monolayer of oxygen. The oxygen atoms occupy hcp sites in an ordered structure with (2x1) periodicity. DFT predicts that water is weakly bound to the unmodified surface, 86 meV compared to the similar to 200 meV water-water H bond. Instead, we found that water adsorption causes a shift of half of the oxygen atoms from hcp sites to fcc sites, creating a honeycomb structure where water molecules bind strongly to the exposed Ru atoms. The energy cost of reconstructing the oxygen overlayer, around 230 meV per displaced oxygen atom, is more than compensated by the larger adsorption energy of water on the newly exposed Ru atoms. Water forms hydrogen bonds with the fcc O atoms in a (4x2) superstructure due to alternating orientations of the molecules. Heating to 185 K results in the complete desorption of the water layer, leaving behind the oxygen-honeycomb structure, which is metastable relative to the original (2x1). This stable structure is not recovered until after heating to temperatures close to 260 K.

Water Splits Epitaxial Graphene and Intercalates - Feng, Xiaofeng; Maier, Sabine; Salmeron, Miquel (Journal of the American Chemical Society, 2012)
The adsorption and reactions of small molecules, such as water and oxygen, with graphene films is an area of active research, as graphene may hold the key to unique applications in electronics, batteries, and other technologies. Since the graphene films produced so far are typically polycrystalline, with point and line defects that can strongly affect gas adsorption, there is a need to understand their reactivity with environmentally abundant molecules that can adsorb and alter their properties. Here we report a study of the adsorption and reactions of water, oxygen, hydrogen, and ammonia on epitaxial graphene grown on Ru and Cu substrates using scanning tunneling microscopy (STM). We found that on Ru(0001) graphene line defects are extremely fragile toward chemical attack by water, which splits the graphene film into numerous fragments at temperatures as low as 90 K, followed by water intercalation under the graphene. On Cu(111) water can also split graphene but far less effectively, indicating that the chemical nature of the substrate strongly affects the reactivity of the C-C bonds in epitaxial graphene. Interestingly, no such effects were observed with other molecules, including oxygen, hydrogen, and ammonia also studied here.

Wavelet based noise reduction in CT-images using correlation analysis - Borsdorf, Anja; Raupach, Rainer; Flohr, Thomas; Hornegger, Joachim (IEEE Transactions on Medical Imaging, 2008)
The projection data measured in computed tomography (CT) and, consequently, the slices reconstructed from these data are noisy. We present a new wavelet based structure-preserving method for noise reduction in CT-images that can be used in combination with different reconstruction methods. The approach is based on the assumption that data can be decomposed into information and temporally uncorrected noise. In CT two spatially identical images can be generated by reconstructions from disjoint subsets of projections: using the latest generation dual source CT-scanners one image can be reconstructed from the projections acquired at the first, the other image from the projections acquired at the second detector. For standard CT-scanners the two images can be generated by splitting up the set of projections into even and odd numbered projections. The resulting images show the same information but differ with respect to image noise. The analysis of correlations between the wavelet representations of the input images allows separating information from noise down to a certain signal-to-noise level. Wavelet coefficients with small correlation are suppressed, while those with high correlations are assumed to represent structures and are preserved. The final noise-suppressed image is reconstructed from the averaged and weighted wavelet coefficients of the input images. The proposed method is robust, of low complexity and adapts itself to the noise in the images. The quantitative and qualitative evaluation based on phantom as well as real clinical data showed, that high noise reduction rates of around 40% can be achieved without noticable loss of image resolution. © 2008 IEEE.

Wave-packet excitation and quantum-beat spectroscopy of image-potential states - Höfer, Ulrich; Shumay, Igor; Reuss, Christian; Thomann, Ulrich; Fauster, Thomas (Proceedings of SPIE, 1998)
The ultrafast dynamics of electrons in image-potential states on a Cu(100) surface is studied by means of femtosecond time-resolved two-photon photoemission (2PPE). By coherently exciting several eigenstates of the Rydberg series we observe periodic oscillations of the 2PPE signal as a function of the delay time between pump and probe pulses. These quantum beats allow us to determine the spacing of high-order states (quantum number n greater than or equal to 4) that are difficult to resolve by conventional electron spectroscopy. The superposition of several states around n = 7 creates an electron wave packet that describes the quasi-classical periodic motion of weakly bound electrons. Its distance from the surface is reflected in the strength of the photoemission signal. The electron is observed to move about 100 atomic distances away from the surface and oscillates back and forth with a period of 800 femtoseconds. The results demonstrate the power of coherent laser spectroscopy for surface studies.
Keywords: ultrafast surface dynamics; time-resolved two-photon photoemission; coherent spectroscopy; electron wave packets; quantum beats

Weak measurements and quantum-to-classical transitions in free electron–photon interactions - Pan, Yiming; Cohen, Eliahu; Karimi, Ebrahim; Gover, Avraham; Schönenberger, Norbert; Chlouba, Tomas; Wang, Kangpeng; Nehemia, Saar; Hommelhoff, Peter; Kaminer, Ido; Aharonov, Yakir (Light: Science & Applications, 2023)
How does the quantum-to-classical transition of measurement occur? This question is vital for both foundations and applications of quantum mechanics. Here, we develop a new measurement-based framework for characterizing the classical and quantum free electron–photon interactions and then experimentally test it. We first analyze the transition from projective to weak measurement in generic light–matter interactions and show that any classical electron-laser-beam interaction can be represented as an outcome of weak measurement. In particular, the appearance of classical point-particle acceleration is an example of an amplified weak value resulting from weak measurement. A universal factor, exp(− Γ 2/ 2) , quantifies the measurement regimes and their transition from quantum to classical, where Γ corresponds to the ratio between the electron wavepacket size and the optical wavelength. This measurement-based formulation is experimentally verified in both limits of photon-induced near-field electron microscopy and the classical acceleration regime using a DLA. Our results shed new light on the transition from quantum to classical electrodynamics, enabling us to employ the essence of the wave-particle duality of both light and electrons in quantum measurement for exploring and applying many quantum and classical light–matter interactions.
CRIS-Team Scopus Importer:2023-11-17

Wet Chemical Synthesis of Graphene - Eigler, Siegfried; Enzelberger-Heim, Michael; Grimm, Stefan; Hofmann, Philipp; Kroener, Wolfgang; Geworski, Andreas; Dotzer, Christoph; Röckert, Michael; Xiao, Jie; Papp, Christian; Lytken, Ole; Steinrück, Hans-Peter; et al. (Advanced Materials, 2013)
A suitable technology for the preparation of graphene based on versatile wet chemistry is presented for the first time. The protocol allows the wet chemical synthesis of graphene from a new form of graphene oxide that consists of an intact hexagonal extgreeks-framework of C-atoms. Thus, it can be easily reduced to graphene that is no longer dominated by defects.

Whole-brain quantitative CEST MRI at 7T using parallel transmission methods and B1+ correction - Liebert, Andrzej; Tkotz, Katharina; Herrler, Jürgen; Linz, Peter; Mennecke, Angelika; German, Alex; Liebig, Patrick; Gumbrecht, Rene; Schmidt, Manuel; Dörfler, Arnd; Uder, Michael; Zaiß, Moritz; et al. (Magnetic Resonance in Medicine, 2021)
Purpose: To enable whole-brain quantitative CEST MRI at ultra-high magnetic field strengths (B0 ≥ 7T) within short acquisition times. Methods: Multiple interleaved mode saturation (MIMOSA) was combined with fast online-customized (FOCUS) parallel transmission (pTx) excitation pulses and (Formula presented.) correction to achieve homogenous whole-brain coverage. Examinations of 13 volunteers were performed on a 7T MRI system with 3 different types of pulse sequences: (1) saturation in circular polarized (CP) mode and CP mode readout, (2) MIMOSA and CP readout, and (3) MIMOSA and FOCUS readout. For comparison, the inverse magnetic transfer ratio metric for relayed nuclear Overhauser effect and amide proton transfer were calculated. To investigate the number of required acquisitions for a good (Formula presented.) correction, 4 volunteers were measured with 6 different B1 amplitudes. Finally, time point repeatability was investigated for 6 volunteers. Results: MIMOSA FOCUS sequence using (Formula presented.) correction, with both single and multiple points, reduced inhomogeneity of the CEST contrasts around the occipital lobe and cerebellum. Results indicate that the most stable inter-subject coefficient of variation was achieved using the MIMOSA FOCUS sequence. Time point repeatability of MIMOSA FOCUS with single-point (Formula presented.) correction showed a maximum coefficient of variation below 8% for 3 measurements in a single volunteer. Conclusion: A combination of MIMOSA FOCUS with a single-point (Formula presented.) correction can be used to achieve quantitative CEST measurements at ultra-high magnetic field strengths. Compared to previous (Formula presented.) correction methods, acquisition time can be reduced as additional scans required for (Formula presented.) correction can be omitted.
CRIS-Team Scopus Importer:2021-03-12
Keywords: 7T; chemical exchange saturation transfer; fast-online customized pulses; multiple interleaved mode saturation; parallel transmission; spiral non-selective trajectory

Wie Molekülschwingungen Wärme leiten - Weber, Heiko B.; Popp, Matthias Albert (Physik Journal, 2019)

Windenergieanlagen und Infraschall: Keine Evidenz für gesundheitliche Beeinträchtigungen – eine physikalische, medizinische und gesellschaftliche Einordnung - Koch, Susanne; Holzheu, Stefan; Hundhausen, Martin (Deutsche Medizinische Wochenschrift, 2022)
Based on the recent discussion about health impacts of wind turbine noise and infrasound emissions, we present the physical facts and summarize related studies in a narrative review. We are exposed to infrasound emissions from different sources, where wind turbine farms do not cause particularly high infrasound emissions. Epidemiological studies found no association between wind turbine farms and the incidence of diabetes mellitus, heart attacks, strokes and medication with antihypertensive drugs, but a more frequent prescription of sleep medication. In contrast, key indicators of objective sleep outcomes are not impacted by wind turbine noise. Health complaints are more frequently proven, if anti-wind-turbine-groups were active, which is consistent with the psychogenic hypotheses with nocebo effects likely play an important role. Without evidence of health impacts from wind turbine farms, an ongoing slowdown in the urgently needed expansion of renewable energies is not justifiable.
CRIS-Team Scopus Importer:2022-02-11

Wind Energy Turbines and Sound Exposure in the audible and IFLN Range: High Evidence for severe Health Disturbances according to current Studies Reply - Koch, Susanne; Holzheu, S.; Hundhausen, Martin (Deutsche Medizinische Wochenschrift, 2022)
CRIS-Team WoS Importer:2022-09-23

Writing and reading of an arbitrary optical polarization state in an antiferromagnet - Satoh, Takuya; Iida, Ryugo; Higuchi, Takuya; Fiebig, Manfred; Shimura, Tsutomu (Nature Photonics, 2014)
The interaction between light and magnetism is considered a promising route to the development of energy-efficient data storage technologies. To date, however, ultrafast optical magnetization control has been limited to a binary process, whereby light in either of two polarization states generates (writes) or adopts (reads) a magnetic bit carrying either a positive or negative magnetization. Here, we report how the fundamental limitation of just two states can be overcome, allowing an arbitrary optical polarization state to be written magnetically. The effect is demonstrated using a three-sublattice antiferromagnet—hexagonal YMnO3. Its three magnetic oscillation eigenmodes are selectively excited by the three polarization eigenstates of the light. The magnetic oscillation state is then transferred back into the polarization state of an optical probe pulse, thus completing an arbitrary optomagnonic write–read cycl
Keywords: Electronic and spintronic devices; Magneto-optics; Ultrafast photonics

X-ray characterization of physical-vapor-transport-grown bulk AlN single crystals - Wicht, Thomas; Mueller, Stephan; Weingaertner, Roland; Epelbaum, Boris; Besendoerfer, Sven; Blaess, Ulrich; Weißer, Matthias; Unruh, Tobias; Meißner, Elke (Journal of Applied Crystallography, 2020)
AlN slices from bulk crystals grown under low thermomechanical stress conditions via the physical vapor transport (PVT) method were analyzed by X-ray methods to study the influence of the growth mode on the crystal quality. Defect types and densities were analyzed along axial [000 (1) over bar] as well as lateral growth directions. X-ray diffraction (0 (1) over bar 10) rocking-curve mappings of representative wafer cuts reveal a low mean FWHM of 13.4 arcsec, indicating the generally high crystal quality. The total dislocation density of 2 x 10(3) cm(-2) as determined by X-ray topography is low and dislocations are largely threading edge dislocations of b = 1/3 < 11 (2) over bar0 > type. The absence of basal plane dislocations in homogeneous crystal regions void of macroscopic defects can be linked to the low-stress growth conditions. Under the investigated growth conditions this high crystal quality can be maintained both along the axial [000 (1) over bar] direction and within lateral growth directions. Exceptions to this are some locally confined, misoriented grains and defect clusters, most of which are directly inherited from the seed or are formed due to the employed seed fixation technique on the outer periphery of the crystals. Seed-shaping experiments indicate no apparent kinetic limitations for an enhanced lateral expansion rate and the resulting crystal quality, specifically with regard to the growth mode on a-face facets.
CRIS-Team WoS Importer:2020-08-28

X-ray Dark-Field Imaging for Improved Contrast in Historical Handwritten Literature - Akstaller, Bernhard; Schreiner, Stephan; Dietrich, Lisa; Rauch, Constantin; Schuster, Max; Ludwig, Veronika; Hofmann-Randall, Christina; Michel, Thilo; Anton, Gisela; Funk, Stefan (Journal of Imaging, 2022)
If ancient documents are too fragile to be opened, X-ray imaging can be used to recover the content non-destructively. As an extension to conventional attenuation imaging, dark-field imaging provides access to microscopic structural object information, which can be especially advantageous for materials with weak attenuation contrast, such as certain metal-free inks in paper. With cotton paper and different self-made inks based on authentic recipes, we produced test samples for attenuation and dark-field imaging at a metal-jet X-ray source. The resulting images show letters written in metal-free ink that were recovered via grating-based dark-field imaging. Without the need for synchrotron-like beam quality, these results set the ground for a mobile dark-field imaging setup that could be brought to a library for document scanning, avoiding long transport routes for valuable historic documents.
CRIS-Team Scopus Importer:2022-10-07
Keywords: cultural heritage; grating-based phase-contrast imaging; X-ray dark-field imaging

XUV frequency combs - Ozawa, Akira; Vernaleken, Andreas; Gotlibovych, Igor; Hommelhoff, Peter; Udem, Thomas; Haensch, Theodor W. (Proceedings of SPIE, 2010)
While being the most precise measurement tool in physics, high precision laser spectroscopy is still limited to wavelengths in the range between the infrared and the near ultraviolet. The generation of XUV frequency combs might be a route to extend optical frequency metrology into extreme ultraviolet (XUV) spectral region where many elements have fundamental transitions. The method of choice for XUV frequency comb generation has been cavity-assisted high harmonic generation, where an infrared frequency comb is converted into the XUV inside a femtosecond enhancement cavity at the full repetition rate of the oscillator. Our recent efforts have been directed towards a significant improvement of the average power of XUV combs. To this end, we experimentally investigated the process of non-collinear high harmonic generation (NCHHG) and proved it to be useful as a combined method for efficient generation and outcoupling of XUV radiation. Also, we developed a high repetition rate single-pass amplifier which has the potential to boost the available power for intracavity HHG. © 2010 Copyright SPIE - The International Society for Optical Engineering.
UnivIS-Import:2015-04-16:Pub.2010.nat.dphy.IAP.exphys.xuvfre
Keywords: frequency comb; high harmonic generation; high precision spectroscopy

Z(1/2)- and EH6-Center in 4H-SiC: Not Identical Defects? - Zippelius, Bernd; Glas, Alexander; Weber, Heiko B.; Pensl, Gerhard; Kimoto, Tsunenobu; Krieger, Michael (Materials Science Forum, 2012)
Deep Level Transient Spectroscopy (DLTS) and Double-correlated DLTS (DDLTS) measurements have been conducted on Schottky contacts fabricated on n-type 4H-SiC epilayers using different contact metals in order to separate the EH6- and EH7-centers, which usually appear as a broad double peak in DLTS spectra. The activation energy of EH6 (E-C - E-T(EH6) = 1.203 eV) turns out to be independent of the electric field. As a consequence, EH6 is likely to be acceptor-like according to the missing Poole-Frenkel effect. In this case, it can be excluded that the EH6-center and the prominent acceptor-like Z(1/2)-center belong to different charge states of the same microscopic defect as theoretically suggested. It is proposed that EH6 is a complex containing a carbon vacancy and another component available at high concentrations. The activation energy of EH7 (E-C - E-r(EH7) = 1.58 eV) has been evaluated indirectly by fitting the DLTS spectra of the EH6/7 double peak taking the previously determined parameters of EH6 into account.
UnivIS-Import:2015-04-14:Pub.2012.nat.dphy.IAP.LAP.z12and
Keywords: Deep level transient spectroscopy; Z(1/2); EH6/7; charge state; intrinsic point defects; Poole-Frenkel effect

ZA-derived phonons in the Raman spectra of single-walled carbon nanotubes - Vierck, Asmus; Gannott, Florentina; Schweiger, Manuel; Zaumseil, Jana; Maultzsch, Janina (Carbon, 2017)
We report the observation of four Raman modes in individual, aligned single-walled carbon nanotubes, with frequencies between the RBM and D modes, and above the G(+/-) modes. By studying the diameter and excitation-energy dependence, we find that these strongly dispersive and comparatively intense modes share the lowest-frequency helical phonon branch as the origin, which can be derived from the out-of plane acoustic (ZA) phonon branch of graphene. This ZA phonon is observed due to a defect-assisted, double-resonant process, similar to the D mode; its two-phonon overtones and combinations with transverse optical (TO) phonons do not require defects. Our assignment is supported by a theoretical model based on sixth-nearest neighbour tight-binding and a force-constant approach. We present a complete theoretical evaluation of the diameter and excitation-energy dependence of the ZA, 2ZA, and TO +/- ZA modes, which fits very well to our experimental results and previous studies of the so-called region of intermediate frequency modes. (C) 2017 Elsevier Ltd. All rights reserved.

Z-Disk-Associated Plectin (Isoform 1d): Spatial Arrangement, Interaction Partners, and Role in Filamin C Homeostasis - Winter, Lilli; Staszewska-Daca, Ilona; Zittrich, Stefan; Elhamine, Fatiha; Zrelski, Michaela M.; Schmidt, Katy; Fischer, Irmgard; Jüngst, Christian; Schauss, Astrid; Goldmann, Wolfgang; Stehle, Robert; Wiche, Gerhard (Cells, 2023)
Plectin, a highly versatile cytolinker protein, is crucial for myofiber integrity and function. Accordingly, mutations in the human gene (PLEC) cause several rare diseases, denoted as plectinopathies, with most of them associated with progressive muscle weakness. Of several plectin isoforms expressed in skeletal muscle and the heart, P1d is the only isoform expressed exclusively in these tissues. Using high-resolution stimulated emission depletion (STED) microscopy, here we show that plectin is located within the gaps between individual α-actinin-positive Z-disks, recruiting and bridging them to desmin intermediate filaments (Ifs). Loss of plectin in myofibril bundles led to a complete loss of desmin Ifs. Loss of Z-disk-associated plectin isoform P1d led to disorganization of muscle fibers and slower relaxation of myofibrils upon mechanical strain, in line with an observed inhomogeneity of muscle ultrastructure. In addition to binding to α-actinin and thereby providing structural support, P1d forms a scaffolding platform for the chaperone-assisted selective autophagy machinery (CASA) by directly interacting with HSC70 and synpo2. In isoform-specific knockout (P1d-KO) mouse muscle and mechanically stretched plectin-deficient myoblasts, we found high levels of undigested filamin C, a bona fide substrate of CASA. Similarly, subjecting P1d-KO mice to forced swim tests led to accumulation of filamin C aggregates in myofibers, highlighting a specific role of P1d in tension-induced proteolysis activated upon high loads of physical exercise and muscle contraction.
CRIS-Team Scopus Importer:2023-05-26
Keywords: chaperone-assisted selective autophagy; cytolinker; desmin intermediate filaments; myofibril; plectin; skeletal muscle

Zinc (hydr)oxide/graphite based-phase composites: Effect of the carbonaceous phase on surface properties and enhancement in electrical conductivity - Krstic, Vojislav; Seredych, Mykola; Mabayoje, Oluwaniyi; Kolesnik, Maria M.; Krstic, Vojislav; Bandosz, Teresa J. (Journal of Materials Chemistry, 2012)

αvβ3 integrin expression increases elasticity in human melanoma cells - Lacaria, Leda; Lange, Janina; Goldmann, Wolfgang; Rico, Felix; Alonso, José Luis (Biochemical and Biophysical Research Communications, 2020)
Living cells interact with the extracellular matrix (ECM) transducing biochemical signals into mechanical cues and vice versa. Thanks to this mechano-transduction process, cells modify their internal organization and upregulate their physiological functions differently. In this complex mechanism integrins play a fundamental role, connecting the extracellular matrix with the cytoskeleton. Cytoskeletal rearrangements, such as the increase of the overall contractility, impact cell mechanical properties, the entire cell stiffness, and cell deformability. How cell mechanics is influenced via different integrins and their interaction with ECM in health and disease is still unclear. Here, we investigated the influence of αvβ3 integrin expression on the mechanics of human melanoma M21 cells using atomic force microscopy and micro-constriction. Evidence is provided that (i) αvβ3 integrin expression in human melanoma cells increases cell stiffness in both adherent and non-adherent conditions; (ii) replacing αvβ3 with αIIbβ3 integrin in melanoma cells, cell stiffness is increased under adherent, while decreased under non-adherent conditions; (iii) αvβ3 integrin cell stiffening is also maintained when cells adhere to fibronectin, but this phenomenon does not strongly depend on the fibronectin concentration. In all, this study sheds light on the role of αvβ3 in regulating cellular mechanics.
CRIS-Team Scopus Importer:2020-03-20
Keywords: and αIIbβ3; Atomic force microscopy; Cell elasticity; Integrin αvβ3; M21 human melanoma cell; Micro-constrictions; α5β1

G -factor and well-width fluctuations as a function of carrier density in the two-dimensional hole accumulation layer of transfer-doped diamond - Akhgar, Golrokh; Ley, Lothar; Creedon, Daniel L.; Stacey, Alastair; Mccallum, Jeffrey C.; Hamilton, Alex R.; Pakes, Christopher (Physical Review B, 2019)
The two-dimensional (2D) hole gas at the surface of transfer-doped diamond shows quantum-mechanical interference effects in magnetoresistance in the form of weak localization and weak antilocalization (WAL) at temperatures below about 5 K. Here we use the quenching of the WAL by an additional magnetic field applied parallel to the 2D plane to extract the magnitude of the in-plane g-factor of the holes and fluctuations in the well width as a function of carrier density. Carrier densities are varied between 1.71 and 4.35×1013cm-2 by gating a Hall bar device with an ionic liquid. Over this range, calculated values of |g| vary between 1.6 and 2.3 and the extracted well-width variation drops from 3 to 1.3 nm rms over the phase coherence length of 33 nm for a fixed geometrical surface roughness of about 1 nm as measured by atomic force microscopy. Possible mechanisms for the extracted variations in the presence of the ionic liquid are discussed.
CRIS-Team Scopus Importer:2019-08-02

MoO3 induces p-type surface conductivity by surface transfer doping in diamond - Xing, Kaijian; Xiang, Yang; Jiang, Ming; Creedon, Daniel L.; Akhgar, Golrokh; Yianni, Steve A.; Xiao, Haiyan; Ley, Lothar; Stacey, Alastair; McCallum, Jeffrey C.; Zhuiykov, Serge; Pakes, Christopher I.; et al. (Applied Surface Science, 2020)
Surface transfer doping of diamond using high electron affinity transition metal oxides (TMOs), such as MoO3, has emerged as a key enabling technology for the development of diamond-based surface two-dimensional (2D) electronics. However, the omission of a critical pre-annealing step in the device fabrication process to remove atmospheric adsorbates prior to TMO deposition, as seen in numerous studies, makes the role of TMOs ambiguous in light of air-induced surface conductivity, preventing a full understanding of the intrinsic surface transfer doping behavior of TMO-based surface acceptors. Here, using in-situ four-probe electrical measurements we explicitly show the insulating-to-conducting transition in diamond surface driven by MoO3 induced surface transfer doping. Variable-temperature Hall-effect measurements reveal weak temperature-dependence down to 250 mK, evidencing the 2D Fermi liquid nature of the resulting surface conducting channel on diamond. Using first-principles calculations, we confirm the interfacial charge exchange upon MoO3 adsorption leading to a degenerate hole conducting layer on diamond. This work provides significant insights into understanding the surface transfer doping of diamond induced by TMOs, and paves the way for the investigations of many interesting quantum transport properties in the resulting 2D hole conducting layer, such as phase-coherent magnetotransport, on diamond surface.
CRIS-Team Scopus Importer:2020-03-13
Keywords: 2DHG; Diamond; Molybdenum trioxide; Surface conductivity; Surface transfer doping