Dehydrogenation of Ammonia on Ru(0001) by Electronic Excitations - Maier, Sabine; Stass, Ingeborg; Feng, Xiaofeng; Sisto, Aaron; Zayak, Alexey; Neaton, Jeffrey B.; Salmeron, Miquel (Journal of Physical Chemistry C, 2015)
We study the mechanism leading to the breaking of the N-H bonds in ammonia on Ru(0001) by means of scanning tunneling microscopy (STM). Our results support a model where injection of electrons or holes into antibonding (LUMO) and bonding (HOMO) orbitals of the molecule is far more effective than thermal excitations for molecular dissociation. We also found that a critical electric field between tip and surface is necessary to shape the tunneling barrier to obtain efficient rates of electrons from the tip or surface. First principle DFT calculations allow us to explain the observations and show that the applied electric field cannot by itself account for the observed dissociation. Since electron injection is the process governing photo- and electrochemical reactions, our STM study provides a detailed view of the reaction mechanism at the single molecular level in these nonthermal reactions.

Delayed derecruitment after removal of PEEP in patients with acute lung injury - Fabry, Ben; et al. (Acta Anaesthesiologica Scandinavica, 1997)

Densification of Silica Spheres: A New Pathway to Nano-Dimensioned Zeolite-Based Catalysts - Machoke, Albert; Apeleo Zubiri, Benjamin; Leonhardt, Rainer; Marthala, Venkata; Schmiele, Martin; Unruh, Tobias; Hartmann, Martin; Spiecker, Erdmann; Schwieger, Wilhelm (Chemistry - A European Journal, 2017)
Nanosized materials are expected to play a unique role in the development of future catalytic processes. Herein, pre-prepared and geometrically well-defined amorphous silica spheres are densified into silica-rich zeolites with nanosized dimensions. After the densification, the obtained nanosized zeolites exhibit the same spherical morphology like the starting precursor but characterized by a drastically reduced size, higher density, and high crystallinity. The phase transformation into crystalline zeolite material and the densification effect are achieved through a well-controlled steam-assisted treatment of the larger precursor particles so that the transformation process proceeds always towards the center of the spheres, just like a shrinking process. Furthermore, this procedure is applicable also to commercially available silica particles, as well as aluminum-containing systems (precursors) leading to acidic nano-catalysts with improved catalytic performance.
Keywords: catalytic cracking; crystallization; heterogeneous catalysis; nanoparticles; silica-rich zeolites

Density functional theory screened-exchange approach for investigating electronical properties of graphene-related materials - Gillen, Roland; Robertson, John (physica status solidi (b), 2010)

Density of states in solid deuterium: Inelastic neutron scattering study - Frei, Andreas; Gutsmiedl, Erwin; Morkel, Christoph; Müller, A. R.; Paul, Stephan; Urban, M.; Schober, Helmut; Rols, Stephane; Unruh, Tobias; Hölzel, Markus (Physical Review B, 2009)
The dynamics of solid deuterium (sD(2)) is studied by means of inelastic scattering (coherent and incoherent) of thermal and cold neutrons 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 neutron time-of-flight (TOF) instrument IN4 at ILL Grenoble and at the cold neutron TOF instrument TOFTOF at FRM II Garching. The GDOS comprises besides the hcp phonon excitations of the sD(2) the rotational transitions J=0&1 and J=1&2. The intensities of these rotational excitations depend strongly on the ortho-D(2) molecule concentration c(o) in sD(2). Above E=10 meV there are still strong excitations, which very likely may originate from higher-energy damped optical phonons and multiphonon contributions. A method for separating the one-phonon and multiphonon contributions to the density of states will be presented and discussed.
Keywords: deuterium; neutron diffraction; phonons; quantum solids; rotational states; solid hydrogen

Dependence of the seed layer quality on different temperature ramp-up conditions for 3C-SiC hetero-epitaxy on Si (100) - Hens, Philip; Wagner, G.; Hölzing, Astrid; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2012)
Usually a waiting step at around 1000 degrees C to 1100 degrees C is implemented during the carbonization for 3C-SiC epitaxy on silicon in order to form a closed carbon layer which prevents the formation of voids by evaporation of Si. On the other hand, such a process step may lead to non-ideal nucleation conditions resulting in a low layer quality with high densities of defects and domain boundaries. Our investigations indicate that a continuous temperature ramp-up with the highest possible heating rate and no waiting step is preferable and results in an improved layer quality concerning domain sizes as confirmed by X-ray diffraction measurements of the full width at half maximum of the SiC(200) reflection. The result can be understood within the framework of the Tammann theory for the temperature dependence of nucleation and growth. The two thermal regimes, as proposed by Tammann, had been located at temperatures of around 1000-1100 degrees C for nucleation and > 1200 degrees C for growth. (C) 2011 Elsevier B. V. All rights reserved.
Keywords: Growth models; Chemical vapor deposition processes; Inorganic compounds; Semiconducting silicon compounds; Cubic silicon carbide; Heteroepitaxy

Dephasing of image-potential states on Cu(100) upon CO adsorption measured by femtosecond two-photon photoemission spectroscopy - Reuss, Christian; Kutschera, Michael; Shumay, Igor; Thomann, Ulrich; Weinelt, Martin; Fauster, Thomas; Höfer, Ulrich (Springer Verlag, 1998)
The relaxation dynamics of the image-potential states of Cu(100) under the influence of CO adsorption is investigated by time-resolved Two-Photon Photoemission Spectroscopy (2PPE). Pure dephasing due to elastic scattering leads to a fast decay of quantum-beat patterns of energetically close-lying image states at already very low CO coverages. For higher CO exposure an increase in structural order is correlated with a decrease in pure dephasing rates.

Deriving the kinetic parameters for Pt-silicide formation from temperature ramped in situ ellipsometric measurements - Hundhausen, Martin; Ley, Lothar; et al. (Thin Solid Films, 2000)
Single-wavelength ellipsometry is employed to monitor in situ the reaction of 23 nm platinum layers with Si(100) to form platinum silicides during heating at constant rates up to 100 K/min. A previous study showed that by the use of 'Kissinger' plots the activation energy of the intermediate silicide phase Pt2Si and that of the final PtSi can be determined with an accuracy of 50 meV. It is the purpose of the present paper to extend the study one step further and obtain also the pre-exponential growth factor by directly modeling the evolution of the ellipsometric data as they were obtained during the temperature ramp. To do so, the chemical composition of the reaction products and the thickness of the formed layers were identified at crucial stages of the reaction via RES. Additionally, the optical constants of the constituent phases Pt, Pt2Si and PtSi were calculated from spectroscopic ellipsometry measurements in the range from 1.5 to 4.5 eV. With this input information the evolution of the ellipsometric angles during the reaction of Pt and Si were modeled quantitatively. The analysis yields good fits to the data for different ramp rates with activation energies of 1.50 and 1.70 eV and reaction coefficients of 37 and 27 cm(2)/s for the Pt/Si to Pt2Si and Pt2Si to PtSi formation, respectively. A significant improvement of the fit is obtained when the activation energies are allowed to be distributed about their mean value with a width of 47 meV. This distribution takes inhomogeneities in the reaction process into account and leads to a broadening of the reaction fronts. (C) 2000 Elsevier Science S.A. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.IAP.exphys.derivi
Keywords: ellipsometry; optical properties; reaction kinetics; silicides

Designs for a quantum electron microscope - Kruit, Pieter; Hobbs, Richard G.; Kim, Chung-Soo; Yang, Yujia; Manfrinato, Vitor R.; Hammer, Jakob; Thomas, Sebastian; Weber, Philipp; Klopfer, Brannon; Kohstall, Christoph; Juffmann, Thomas; Kasevich, Mark A.; et al. (Ultramicroscopy, 2016)
One of the astounding consequences of quantum mechanics is that it allows the detection of a target using an incident probe, with only a low probability of interaction of the probe and the target. This 'quantum weirdness' could be applied in the field of electron microscopy to generate images of beam-sensitive specimens with substantially reduced damage to the specimen. A reduction of beam-induced damage to specimens is especially of great importance if it can enable imaging of biological specimens with atomic resolution. Following a recent suggestion that interaction-free measurements are possible with electrons, we now analyze the difficulties of actually building an atomic resolution interaction-free electron microscope, or "quantum electron microscope". A quantum electron microscope would require a number of unique components not found in conventional transmission electron microscopes. These components include a coherent electron beam-splitter or two-state-coupler, and a resonator structure to allow each electron to interrogate the specimen multiple times, thus supporting high success probabilities for interaction-free detection of the specimen. Different system designs are presented here, which are based on four different choices of two-state-couplers: a thin crystal, a grating mirror, a standing light wave and an electro-dynamical pseudopotential. Challenges for the detailed electron optical design are identified as future directions for development. While it is concluded that it should be possible to build an atomic resolution quantum electron microscope, we have also identified a number of hurdles to the development of such a microscope and further theoretical investigations that will be required to enable a complete interpretation of the images produced by such a microscope.
Keywords: Interaction free measurement; Quantum electron microscope; Quantum interrogation; Radiation damage; Transmission electron microscope

DesR349P Mutation Results in Ultrastructural Disruptions and Compromise of Skeletal Muscle Biomechanics Already at Preclinical Stages in Young Mice before the Onset of Protein Aggregation - Diermeier, Stefanie; Haug, Michael; Reischl, Barbara; Buttgereit, Andreas; Schürmann, Sebastian; Spörrer, Marina; Goldmann, Wolfgang; Fabry, Ben; Elhimine, F.; Stehle, Robert; Pfitzer, Gabriele; Winter, L.; et al. (Elsevier (Cell Press) / Biophysical Society, 2016)
Mutations in the extra-sarcomeric protein desmin give rise to protein aggregate myopathies that interfere with cellular function. The R350P mutation is the most common human desminopathy. A murine DesR349P model of human DesR350P desminopathy was previously engineered. In this study, we followed the hypothesis of whether muscle cytoarchitecture and biomechanical properties are already altered in preclinical stages of R349P desminopathy. We applied non-linear second harmonic generation (SHG) and 2-photon fluorescence morphometry analysis to single fibres of fast- and slow-twitch muscle to analyze sarcomeric architecture and nuclear morphology. We found a vast disruption of the lateral sarcomere lattice (indicated by large ‘vernier’ densities) and myofibrillar angular deviations (indicated by cosine angle sums) in single DesR349P fibres. Homozygous fibres were more severely affected than heterozygous. The former showed a marked nuclear pathology with spheric nuclei, increased nuclear number and density. For biomechanics, we assessed active and passive properties. Axial stiffness of DesR349P muscle was much increased, both in fibre and myofibrillar homozygous bundles. Lateral stiffness of the membrane complex in myoblasts was increased in cells heterozygous for DesR349P while homozygous were similar to wt. Caffeine-induced force was compromised in heterozygous fibre bundles but increased in homozygous bundles. This was explained by a marked shift of myofibrillar Ca2+ sensitivity: heterozygous bundles being less sensitive but homozygous more sensitive to Ca2+. This points towards a specific compensatory mechanism in homozygous mutation to cope with otherwise compromised force production already at preclinical stages of desminopathy. Our findings provide a very first complete picture to explain compromised force in heterozygous DesR350P patients: increased muscle stiffness, higher susceptibility towards stretch-induced injury, disrupted myofibrillar alignment and compromised active force productio

Detecting long-range interactions between migrating cells - Metzner, C.; Hörsch, F.; Mark, Christoph; Czerwinski, Tina; Winterl, Alexander; Voskens, Caroline; Fabry, Ben (Scientific Reports, 2021)
Chemotaxis enables cells to systematically approach distant targets that emit a diffusible guiding substance. However, the visual observation of an encounter between a cell and a target does not necessarily indicate the presence of a chemotactic approach mechanism, as even a blindly migrating cell can come across a target by chance. To distinguish between the chemotactic approach and blind migration, we present an objective method that is based on the analysis of time-lapse recorded cell migration trajectories: For each movement step of a cell relative to the position of a potential target, we compute a p value that quantifies the likelihood of the movement direction under the null-hypothesis of blind migration. The resulting distribution of p values, pooled over all recorded cell trajectories, is then compared to an ensemble of reference distributions in which the positions of targets are randomized. First, we validate our method with simulated data, demonstrating that it reliably detects the presence or absence of remote cell-cell interactions. In a second step, we apply the method to data from three-dimensional collagen gels, interspersed with highly migratory natural killer (NK) cells that were derived from two different human donors. We find for one of the donors an attractive interaction between the NK cells, pointing to a cooperative behavior of these immune cells. When adding nearly stationary K562 tumor cells to the system, we find a repulsive interaction between K562 and NK cells for one of the donors. By contrast, we find attractive interactions between NK cells and an IL-15-secreting variant of K562 tumor cells. We therefore speculate that NK cells find wild-type tumor cells only by chance, but are programmed to leave a target quickly after a close encounter. We provide a freely available Python implementation of our p value method that can serve as a general tool for detecting long-range interactions in collective systems of self-driven agents.
CRIS-Team Scopus Importer:2021-08-06

Detection and Cryogenic Characterization of Defects at the SiO2/4H-SiC Interface in Trench MOSFET - Berens, Judith; Rasinger, Fabian; Aichinger, Thomas; Heuken, Michael; Krieger, Michael; Pobegen, Gregor (IEEE Transactions on Electron Devices, 2019)
We employed the thermal dielectric relaxation current (TDRC) method for the detection and cryogenic characterization of traps at the 4H-SiC/SiO2 interface in n-channel trench MOSFETs and n-MOS trench capacitors. The interface of trench devices on the (11-20)-plane atomically differs from the interface of standard lateral devices [(0001)-plane]. In the MOSFET, two TDRC signal peaks originating from electron traps were found and characterized by parameter variation in TDRC measurements. One peak corresponds to interface states located 0.13 eV below the 4H-SiC conduction band edge EC. The otherone is attributed to the near-interface traps (NITs) with an electron emission barrier of 0.3 eV. The NIT peak shows an inverse dependence on the discharging voltage compared to regular interface states. In contrast to the MOSFET, only NITs were measured in n-type MOS capacitors. The results found in trench devices were also confirmed for lateral devices. Therefore, we show that the study of SiC MOS capacitors is not sufficient for the understanding of degradation mechanisms in SiC MOSFETs. The interface states at EC-0.13 eV detected in MOSFETs are assumed to contribute to the degradation of the apparent channel mobility and ON-resistance of SiC MOSFETs. These states are strongly reduced by annealing in NO compared to N2.<br
Keywords: 4H-SiC; interface traps; mobility; MOSFET; near-interface traps (NITs); nitric oxide (NO) postoxidation anneal (POA); thermal dielectric relaxation current (TDRC).

Detection of iv-gadolinium leakage from the cortical veins into the CSF using MR fingerprinting - Naganawa, Shinji; Nakane, Toshiki; Kawai, Hisashi; Taoka, Toshiaki; Kawaguchi, Hirokazu; Maruyama, Katsuya; Murata, Katsutoshi; Körzdörfer, Gregor; Pfeuffer, Josef; Nittka, Mathias; Sone, Michihiko (Magnetic Resonance in Medical Sciences, 2020)
Purpose: It has been reported that leakage of intravenously administered gadolinium-based contrast agents (IV-GBCAs) into the cerebrospinal fluid (CSF) from the cortical veins even in healthy subjects can be detected using a highly sensitive pulse sequence such as heavily T2-weighted 3D fluid-attenuated inversion recovery and 3D-real inversion recovery (IR). The purpose of this study was to evaluate the feasibility of MR fingerprinting to detect GBCA leakage from the cortical veins after IV-GBCA. Materials: Fourteen patients with suspected endolymphatic hydrops (EH) who received a single dose of IV-GBCA (39–79 years old) were included. The real IR images as well as MR fingerprinting images were obtained at 4 h after IV-GBCA. T1 and T2 values were obtained using MR fingerprinting and analyzed in ROIs covering intense GBCA leakage, and non-leakage areas of the CSF as determined on real IR images. The scan time for real IR imaging was 10 min and that for MR fingerprinting was 41 s. Results: The mean T1 value of the ROI in the area of GBCA leakage was 2422 ± 261 ms and that in the non-leakage area was 3851 ± 235 ms (P < 0.01). There was no overlap between the T1 values in the area of GBCA leakage and those in the non-leakage area. The mean T2 value in the area of GBCA leakage was 319 ± 90 ms and that in the non-leakage area was 670 ± 166 ms (P < 0.01). There was some overlap between the T2 values in the area of GBCA leakage and those in the non-leakage area. Conclusion: Leaked GBCA from the cortical veins into the surrounding CSF can be detected using MR fingerprinting obtained in <1 min.
CRIS-Team Scopus Importer:2020-05-12
Keywords: Cortical vein; Gadolinium; Magnetic resonance fingerprinting; Magnetic resonance imaging

Detection of the Faraday Chiral Anisotropy - Caridad, José M.; Tserkezis, Christos; Santos, Jaime E.; Plochocka, Paulina; Venkatesan, Munuswamy; Coey, J. M.D.; Mortensen, N. Asger; Rikken, Geert L.J.A.; Krstic, Vojislav (Physical Review Letters, 2021)
The connection between chirality and electromagnetism has attracted much attention through the recent history of science, allowing the discovery of crucial nonreciprocal optical phenomena within the context of fundamental interactions between matter and light. A major phenomenon within this family is the so-called Faraday chiral anisotropy, the long-predicted but yet unobserved effect which arises due to the correlated coaction of both natural and magnetically induced optical activities at concurring wavelengths in chiral systems. Here, we report on the detection of the elusive anisotropic Faraday chiral phenomenon and demonstrate its enantioselectivity. The existence of this fundamental effect reveals the accomplishment of envisioned nonreciprocal electromagnetic metamaterials referred to as Faraday chiral media, systems where novel electromagnetic phenomena such as negative refraction of light at tunable wavelengths or even negative reflection can be realized. From a more comprehensive perspective, our findings have profound implications for the general understanding of parity-violating photon-particle interactions in magnetized media.
CRIS-Team Scopus Importer:2021-05-21

Detection of the Kondo effect in the resistivity of graphene: Artifacts and strategies - Jobst, Johannes; Kißlinger, Ferdinand; Weber, Heiko B. (Physical Review B, 2013)
We discuss the difficulties in discovering the Kondo effect in the resistivity of graphene. Similarly to the Kondo effect, electron-electron interaction effects and weak localization appear as logarithmic corrections to the resistance. In order to disentangle these contributions, a refined analysis of the magnetoconductance and the magnetoresistance is introduced. We present numerical simulations which display the discrimination of both effects. Further, we present experimental data of magnetotransport. When magnetic molecules are added to graphene, a logarithmic correction to the conductance occurs, which apparently suggests Kondo physics. Our thorough evaluation scheme, however, reveals that this interpretation is not conclusive: The data can be equally explained by electron-electron interaction corrections in an inhomogeneous sample. Despite our refined analysis, we conclude that additional spectroscopic information will be necessary to unambiguously identify the Kondo effect. © 2013 American Physical Society.
UnivIS-Import:2015-04-14:Pub.2013.nat.dphy.IAP.LAP.detect

Determination of 3D electrostatic field at an electron nano-emitter - Wu, Mingjian; Tafel, Alexander; Hommelhoff, Peter; Spiecker, Erdmann (Applied Physics Letters, 2019)

Determination of optical cross sections for electron and hole emission from deep defects in low-temperature-grown GaAs - Malzer, Stefan; et al. (PHYSICS OF SEMICONDUCTORS: 27th International Conference on the Physics of Semiconductors, ICPS-27, 2005)
We report on optical cross sections of electrons and holes in thin layers of LT-GaAs embedded in hetero-pin-diodes. With an appropriate design, the time dependent change of the n-layer conductance directly reflects the change in the charge state of the deep levels. The original completely filled (or empty) defect states can be created by an electrical bias or illumination by laser light. For samples annealed at 700 °C we find a defect signature very similar to the EL2 defect in the literature. © 2005 American Institute of Physics.

Determination of Performance-Relevant Trapped Charge in 4H Silicon Carbide MOSFETs - Rasinger, Fabian; Pobegen, Gregor; Aichinger, Thomas; Weber, Heiko B.; Krieger, Michael (Materials Science Forum, 2018)

Determination of performance-relevant trapped charge in 4H silicon carbide MOSFETs - Rasinger, Fabian; Pobegen, Gregor; Aichinger, Thomas; Weber, Heiko B.; Krieger, Michael (Materials Science Forum, 2018)
Current-voltage characterization and thermal dielectric relaxation current (TDRC) measurements are carried out on 4H silicon carbide (SiC) n-channel MOSFETs processed with different post oxidation anneals (POAs) in O2, N2O, and NO atmospheres at high temperature. In all samples we observe a distinct peak at a temperature of 70 K in the TDRC spectra due to a defect close to the conduction band of 4H-SiC having a high density of states (>1013 cm-2eV-1). We show that this defect is related to the degradation of the device performance such as the MOSFET conductivity. Comparing the different POAs, NO strongly reduces the density of states close to the conduction band and thus increases the amount of free channel electrons. Based on TDRC measurements we want to suggest a method for more accurate estimation of the true channel mobility accounting for the reduced channel electron density due to trapping.
CRIS-Team Scopus Importer:2022-04-14
Keywords: 4H-SiC MOSFET; Electron trapping; Interface defects; Post oxidation anneal; TDRC

Determination of piezo-electric fields in spontaneously ordered InGaAsP - Malzer, Stefan; et al. (PHYSICS OF SEMICONDUCTORS: 27th International Conference on the Physics of Semiconductors, ICPS-27, 2005)
We report on observation of a piezo-electric field in InGaAsP-QWs embedded in InP induced by the spontaneous ordering of the MOCVD-grown InGaAsP-layer. The structure was embedded in the intrinsic layer of a p-i-n diode allowing for the internal field determination by the quantum confined Stark effect in photocurrent spectroscopy. The sign and magnitude of this piezo field was determined to 80±2 kV/cm for an In Ga As P /InP layer system. © 2005 American Institute of Physics.

Determination of self-diffusion coefficients by quasielastic neutron scattering measurements of levitated Ni droplets - Meyer, Andreas; Stüber, Sebastian; Holland-Moritz, Dirk; Heinen, Oliver; Unruh, Tobias (Physical Review B, 2008)
Conventional techniques to measure diffusion coefficients in liquid metals and alloys are hampered by buoyancy-driven convective fluid flow and chemical reactions of the liquids with container material. To overcome these obstacles we combined containerless processing via electromagnetic levitation with quasielastic neutron scattering. This combination allowed us to study the atomic self-motion in liquid nickel within a broad temperature range from 200 K above to more than 200 K below the melting point, in the metastable regime of an undercooled melt. Other than in liquid Sn the temperature dependence of the Ni self-diffusion coefficient is well described with an Arrhenius law.

DETERMINATION OF THE GEOMETRY OF SULFUR ON NICKEL SURFACES BY LOW-ENERGY ION-SCATTERING - Fauster, Thomas; et al. (Surface Science, 1986)

Determination of the Photocarrier Lifetime in Amorphous Silicon with the Moving Photocarrier Grating Technique - Hundhausen, Martin; et al. (Japanese Journal of Applied Physics, 1994)
In this paper we have determined the lifetime of photogenerated carriers in semiconductors using a technique that does not require time or frequency resolved measurements of the photoconductivity. The lifetime is deduced from the DC-short circuit current that is induced by a laser interference grating of period Λ moving along the semiconductor surface with the velocity vgr. We observe a maximum short circuit current density jsc at a velocity that corresponds to a frequency ω-max/ = 2πvmax/Λ of the moving interference grating. Based on a theoretical analysis of jsc we show that ω-max/ equals the inverse of the photocarrier lifetime τ, if the dielectric relaxation-time τdiel is short compared to τ and if the grating period is chosen large compared to the ambipolar diffusion length.
UnivIS-Import:2015-03-05:Pub.1994.nat.dphy.IAP.exphys.determ

Determining the mechanical properties of plectin in mouse myoblasts and keratinocytes - Bonakdar, Navid; Schilling, Achim; Spörrer, Marina; Lennert, Pablo; Mainka, Astrid; Winter, Lilli; Walko, Gernot; Wiche, Gerhard; Fabry, Ben; Goldmann, Wolfgang (Experimental Cell Research, 2015)
Plectin is the prototype of an intermediate filament (IF)-based cytolinker protein. It affects cells mechanically by interlinking and anchoring cytoskeletal filaments and acts as scaffolding and docking platform for signaling proteins to control cytoskeleton dynamics. The most common disease caused by mutations in the human plectin gene, epidermolysis bullosa simplex with muscular dystrophy (EBS-MD), is characterized by severe skin blistering and progressive muscular dystrophy. Therefore, we compared the biomechanical properties and the response to mechanical stress of murine plectin-deficient myoblasts and keratinocytes with wild-type cells. Using a cell stretching device, plectin-deficient myoblasts exhibited lower mechanical vulnerability upon external stress compared to wild-type cells, which we attributed to lower cellular pre-stress. Contrary to myoblasts, wild-type and plectin-deficient keratinocytes showed no significant differences. In magnetic tweezer measurements using fibronectin-coated paramagnetic beads, the stiffness of keratinocytes was higher than of myoblasts. Interestingly, cell stiffness, adhesion strength, and cytoskeletal dynamics were strikingly altered in plectin-deficient compared to wild-type myoblasts, whereas smaller differences were observed between plectin-deficient and wild-type keratinocytes, indicating that plectin might be more important for stabilizing cytoskeletal structures in myoblasts than in keratinocytes. Traction forces strongly correlated with the stiffness of plectin-deficient and wild-type myoblasts and keratinocytes. Contrary to that cell motility was comparable in plectin-deficient and wild-type myoblasts, but was significantly increased in plectin-deficient compared to wild-type keratinocytes. Thus, we postulate that the lack of plectin has divergent implications on biomechanical properties depending on the respective cell type.
EVALuna2:7284

Development and Characterization of Bioactive Glass Containing Composite Coatings with Ion Releasing Function for Antibiotic-Free Antibacterial Surgical Sutures - Ciraldo, Francesca; Schnepf, Kristin; Goldmann, Wolfgang; Boccaccini, Aldo R. (Materials, 2019)
Resorbable (Vicryl((R)) Plus) sutures were coated with zinc-doped glass (Zn-BG) and silver-doped ordered mesoporous bioactive glass (Ag-MBG) particles by a dip coating technique. A multilayer approach was used to achieve robust coatings. The first coating was a polymeric layer (e.g., PCL or chitosan) and the second one was a composite made of BG particles in a polymer matrix. The coatings were characterized in terms of morphology by scanning electron microscopy (SEM), in vitro bioactivity, and antibacterial properties. Chitosan/Ag-MBG coatings showed the ability to form hydroxyl-carbonate-apatite on their surfaces after immersion in SBF. An antibacterial effect against Gram (+) and Gram (-) bacteria was confirmed, highlighting the potential application of the coated sutures for antibiotic-free approaches.
CRIS-Team WoS Importer:2019-03-22

Development of the local and average structure of a V-Mo-Nb oxide catalyst with Mo5O14-like structure during synthesis from nanostructured precursors - Kardash, Tatyana Yu.; Plyasova, Ludmilla M.; Kochubey, Dmitry I.; Bondareva, Valentina M.; Neder, Reinhard (Zeitschrift für Kristallographie, 2012)
A combination of X-ray and neutron PDF measurements with powder diffraction and EXAFS data was used to determine the structures of a V-Mo-Nb-oxide catalyst and its poorly crystallized precursors that exhibit the strongest catalytic activities. The crystalline material belongs to space group P (4) over bar2(1)m, a = 22.8, c = 4.002, and is build up of pentagonal MeO7 bipyramids surrounded by edge sharing Me-octahedrons (Me = Mo, V, Nb). In the average structure all MeO7 units are at the same z-level, while the local structure analysis shows systematic shifts along [001]. Samples synthesized at 300 degrees C and 400 degrees C exhibit a nanostructure, whose local structure predates the final crystalline structure. Initial nanoparticles are spherical and grow predominantly along the c-axis. The successful analysis required a reverse analysis that took the crystalline material as starting model for the samples synthesized at lower temperatures.
Keywords: Catalysis; Pair distribution function; Neutron powder diffraction; Disorder

Diameter-controlled solid-phase seeding of germanium nanowires: Structural characterization and electrical transport properties - Krstic, Vojislav; Barth, Sven; Kolesnik, Maria M.; Donegan, Keith; Krstic, Vojislav; Holmes, Justin D. (Chemistry of Materials, 2011)
Despite the huge progress recently made in understanding the phenomena of metal-promoted growth of one-dimensional (1D) semiconductors, the controlled formation of small diameter semiconductor nanowires is still challenging. Liquid growth promoters, such as the low melting Au/Ge eutectic, allow control of the aspect ratio, diameter, and structure of 1D crystals via external parameters, such as precursor feedstock, temperature, and operating pressure. However, the incorporation of metal atoms during the growth process, size variations of the nanowires due to agglomeration of the nucleating metal seeds, and surface diffusion of Au via the vapor–liquid–solid route have been reported. Here, we detail the influence of solid growth seeds, such as NiGe2 formed from Ni nanoparticles, on the lateral dimensions of Ge nanowires grown using a supercritical fluid growth process. Beneficial control over the mean nanowire diameter, in the sub-20 nm regime, with a predominantly ⟨110⟩ growth direction and low structural defect concentration was obtained using Ni seeds. In addition, the effect of prealloying of Ni–Fe films for the growth of Ge nanowires was investigated, which leads to a bimodal nanowire distribution. Electrical characterization performed on single nanowire devices showed p-type behavior for Ge nanowires grown from Ni and Ni/Fe seeds. Determination of resistivities, majority carrier concentrations, and mobilities suggest significant doping of the Ge nanowires by Ni when grown via a supercritical fluid–solid–solid (SFSS) mechanism.<br
Keywords: SFSS; solid-phase-seeding; germaniumn; nickel; nanowire

Diameter dependence of addition reactions to carbon nanotubes - Müller, Matthias; Maultzsch, Janina; Wunderlich, David; Hirsch, Andreas; Thomsen, Christian (physica status solidi (b), 2008)
We present resonant Raman measurements on carbon nanotubes functionalized with primary alkyl groups of different chain length. From the resonance profiles of the radial breathing mode (RBM) we assign the chiral indices of the tubes in order to study the selective reactivity of different tubes. We focus on diameter dependence showing inversely proportional behaviour to diameter for both metallic and semiconducting nanotubes. (Figure Presented) © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

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

Diameter-driven crossover in resistive behaviour of heavily doped self-seeded germanium nanowires - Connaughton, Stephen; Kolesnik-Gray, Maria; Hobbs, Richard; Lotty, Olan; Holmes, Justin D.; Krstic, Vojislav (Beilstein Journal of Nanotechnology, 2016)
The dependence of the resistivity with changing diameter of heavily-doped self-seeded germanium nanowires was studied for the diameter range 40 to 11 nm. The experimental data reveal an initial strong reduction of the resistivity with diameter decrease. At about 20 nm a region of slowly varying resistivity emerges with a peak feature around 14 nm. For diameters above 20 nm, nanowires were found to be describable by classical means. For smaller diameters a quantum-based approach was required where we employed the 1D Kubo–Greenwood framework and also revealed the dominant charge carriers to be heavy holes. For both regimes the theoretical results and experimental data agree qualitatively well assuming a spatial spreading of the free holes towards the nanowire centre upon diameter reduction.
Keywords: diameter-dependence; germanium; nanowire; resistivity; self-seeded

Diamond-based dielectric laser acceleration - Chlouba, Tomas; Shiloh, Roy; Forsberg, Pontus; Hamberg, Mathias; Karlsson, Mikael; Kozak, Martin; Hommelhoff, Peter (Optics Express, 2022)
The field of dielectric laser accelerators (DLA) garnered a considerable interest in the past six years as it offers novel opportunities in accelerator science and potentially transformative applications. Currently, the most widespread approach considers silicon-based structures due to their low absorption and high refractive index in the infrared spectral region and the well- developed silicon processing technology. In this paper we investigate a diamond as an alternative to silicon, mainly due to its considerably higher damage threshold. In particular, we find that our diamond grating allows a three times higher acceleration gradient (60 MeV/m) compared to silicon gratings designed for a similar electron energy. Using more complex geometries, GeV/m acceleration gradients are within reach for subrelativistic electron
Keywords: diamond-based; dielectric laser acceleration

Diamond growth during the bias pretreatment in microwave CVD of diamond - Ristein, Jürgen; Hundhausen, Martin; Ley, Lothar; et al. (Diamond and Related Materials, 1995)
UnivIS-Import:2015-03-05:Pub.1995.nat.dphy.IAP.exphys.diamon

Diamond surface conductivity experiments and photoelectron spectroscopy - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 2001)
A unique feature of diamond surfaces is a highly conductive p-type layer which is usually observed when the surfaces are hydrogen terminated. We present a combination of conductivity and photoelectron yield measurements on a variety of different diamond samples in order to elucidate the role of hydrogen and adsorbates for this phenomenon. The experiments show that hydrogen termination is a necessary but not a sufficient condition for the appearance of the surface conductivity. Additionally, adsorbates from the atmosphere are needed. On the basis of the experiments an electrochemical model is developed which can explain the effect of the hydrogen termination and also shows why hydrogen terminated diamond is the only semiconductor with p-type surface conductivity. © 2001 Elsevier Science. B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.diamon
Keywords: Diamond; Surface; Surface conductivity

Diamond surface conductivity under atmospheric conditions; theoretical approach - Ristein, Jürgen; et al. (Journal of Physical Chemistry B, 2005)
The electron transfer from an H-terminated diamond (100)-2 × 1 surface to a neutral or acidic water adlayer has been theoretically investigated, using quantum mechanical DFT calculations under periodic boundary conditions. A surface conductivity of p-type was found to be induced by the acidic environment. An electron transfer of 1.8 electrons per surface unit cell was observed to take place from the upper part of the diamond valence band to the lowest unoccupied molecular level of the aqueous adlayer that contains one H3O+1 ion. The result is a hole delocalized over the whole diamond model slab. Also, a pronounced weakening of the H3O + bonds by the interaction with the diamond surface is observed. © 2005 American Chemical Society.
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.IAP.exphys.diamon

Diamond Surfaces - Ley, Lothar; Ristein, Jürgen (Surface and Interface Science, 2012)
UnivIS-Import:2015-04-20:Pub.2012.nat.dphy.IAP.exphys.diamon

Diamond surfaces: familiar and amazing - Ristein, Jürgen (Applied Physics A-Materials Science & Processing, 2006)
Diamond is the only wide band gap representative of the elemental semiconductors, with a crystal structure identical to its more common relatives silicon and germanium. On first glance one might also expect similar surface properties in terms of reconstructions, surface states, and surface band diagrams. In part, this expectation is indeed fulfilled, but diamond also exhibits a number of unusual and potentially very useful surface properties. Particularly when the surface dangling bonds are saturated by monovalent hydrogen atoms, (donor-like) surface states are removed from the gap, the electron affinity changes sign and becomes negative, and the material becomes susceptible to an unusual type of transfer doping where holes are injected by acceptors located at the surface instead of inside the host lattice. These surface acceptors can in the simplest case be adsorbed molecules conveniently chosen by their electron affinity, but they can also be solvated ions within atmospheric water layers or electrolytes in contact with the hydrogenated diamond surface. The understanding of those phenomena requires in fact concepts of surface science, semiconductor physics, and electrochemistry, which makes the diamond surface a true 'interdisciplinary' research topic.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.exphys.diamon

Diamond surfaces with air-stable negative electron affinity and giant electron yield enhancement - O'Donnell, Kane M.; Edmonds, Mark T.; Ristein, Jürgen; Tadich, Anton; Thomsen, Lars; Wu, Qi-Hui; Pakes, Chris I.; Ley, Lothar (Advanced Functional Materials, 2013)
The presence of an air-stable negative electron affinity (NEA) on lithium-covered oxygen-terminated diamond after a thermal activation process is demonstrated. The NEA is unequivocally established by the onset of photoelectron yield at the bandgap energy of 5.5 eV. This surface exhibits a secondary electron yield enhancement by a factor of 200, compared to a surface with positive electron affinity. The surface chemistry leading to the necessary surface dipole was elucidated by core-level photoemission spectroscopy in conjunction with previous theoretical calculations. The insensitivity to the details of the deposition process opens a route to practical and robust negative-electron affinity devices based on diamond. A robust, air-stable negative electron affinity diamond surface with giant secondary electron yield enhancement is introduced. Starting with oxidized diamond (100), lithium deposition and annealing induce a structural and electronic change to a negative electron affinity surface showing electron yield enhancement greater than 200. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.IAP.exphys.diamon
Keywords: diamond; electron emission; lithiation; negative electron affinity; surface modification

Dielectric laser acceleration of 28 keV electrons with the inverse Smith-Purcell effect - Breuer, John; Hommelhoff, Peter (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014)
Dielectric laser acceleration exploiting the large optical field strength of short laser pulses and the proximity of a dielectric structure can support high acceleration gradients may therefore lead to much smaller accelerators, with future potential application in table-top free electron lasers. We report a proof-of-concept experiment demonstrating dielectric laser acceleration of non-relativistic 28 keV electrons derived from a conventional scanning electron microscope column at a single fused-silica grating. The electrons pass the grating as closely as 50 nm and interact with the third spatial harmonic, which is excited by 110 fs long 800 nm laser pulses with a peak electric field of 2.85 GV/m. The observed maximum acceleration gradient of 25 MeV/m is already comparable to state-of-the-art radio-frequency structures. This work thus represents a demonstration of scalable laser acceleration and of the inverse Smith-Purcell effect in the optical regime. For relativistic electrons and otherwise identical conditions up to two orders of magnitude larger acceleration gradients are expected. © 2013 Elsevier B.V.
UnivIS-Import:2015-03-09:Pub.2014.nat.dphy.IAP.exphys.dielec_7
Keywords: Dielectric grating accelerator; Inverse Smith-Purcell effect; Laser-driven particle acceleration; Non-relativistic electrons

Dielectric laser acceleration of electrons in the vicinity of single and double grating structures - theory and simulations - Breuer, John; McNeur, Joshua; Hommelhoff, Peter (Journal of Physics B: Atomic, Molecular and Optical Physics, 2014)
Dielectric laser acceleration of electrons close to a fused-silica grating has recently been observed (Peralta et al 2013 Nature 503 91, Breuer and Hommelhoff 2013 Phys. Rev. Lett. 111 134803). Here we present the theoretical description of the near-fields close to such a grating that can be utilized to accelerate non-relativistic electrons. We also show simulation results of electrons interacting with such fields in a single and double grating structure geometry and discuss dephasing effects that have to be taken into account when designing a photonic-structure-based accelerator for non-relativistic electrons. We further model the space charge effect using the paraxial ray equation and discuss the resulting expected peak currents for various parameter sets.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.exphys.dielec_65
Keywords: dielectric grating accelerator; inverse Smith-Purcell effect; laser-driven particle acceleration; non-relativistic electron beam

Dielectric laser acceleration of nonrelativistic electrons at a single fused silica grating structure: Experimental part - Breuer, John; Graf, Roswitha; Apolonski, Alexander; Hommelhoff, Peter (Physical Review Special Topics-Accelerators and Beams, 2014)
Recently, our group has demonstrated dielectric laser acceleration of nonrelativistic electrons at a scalable fused silica grating [J. Breuer and P. Hommelhoff, Phys. Rev. Lett. 111, 134803 (2013)]. This represents a demonstration of the inverse Smith-Purcell effect in the optical regime. The third spatial harmonic of the grating, which is excited by Titanium:sapphire laser pulses, synchronously accelerates 28 keV electrons derived from an electron microscope column. We observe a maximum acceleration gradient of 25 MeV/m. Here we present the experimental setup in detail. We describe grating-related issues such as surface charging and alignment as well as damage threshold measurements. A detailed explanation of the detection scheme is given. Furthermore, extensive numerical simulations are discussed, which agree well with the experimental results. © Published by the American Physical Society.
UnivIS-Import:2015-03-09:Pub.2014.nat.dphy.IAP.exphys.dielec

Dielectric laser acceleration of sub-relativistic electrons by few-cycle laser pulses - Kozak, Martin; Förster, Michael; McNeur, Joshua; Schönenberger, Norbert; Leedle, Kenneth; Deng, Hudan; Harris, James; Byer, Robert; Hommelhoff, Peter (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2017)
In this paper we show the application of few-cycle infrared laser pulses for dielectric laser acceleration of electrons in the vicinity of a silicon nanostructure. An ultrashort pulse duration of 20 fs (3.3 optical cycles) allows achieving high peak fields of 2.8GV/m without structural damage, leading to a peak acceleration gradient of G =210MeV/m for sub-relativistic electrons (v=0.33c
Keywords: Dielectric grating accelerator; Inverse Smith-Purcell effect; Laser-driven particle acceleration; Non-relativistic electrons

Dielectric laser accelerators - England, R. Joel; Noble, Robert J.; Bane, Karl; Dowell, David H.; Ng, Cho-Kuen; Spencer, James E.; Tantawi, Sami; Wu, Ziran; Byer, Robert L.; Peralta, Edgar; Soong, Ken; Chang, Chia-Ming; et al. (Reviews of Modern Physics, 2014)
The use of infrared lasers to power optical-scale lithographically fabricated particle accelerators is a developing area of research that has garnered increasing interest in recent years. The physics and technology of this approach is reviewed, which is referred to as dielectric laser acceleration (DLA). In the DLA scheme operating at typical laser pulse lengths of 0.1 to 1 ps, the laser damage fluences for robust dielectric materials correspond to peak surface electric fields in the GV/m regime. The corresponding accelerating field enhancement represents a potential reduction in active length of the accelerator between 1 and 2 orders of magnitude. Power sources for DLA-based accelerators (lasers) are less costly than microwave sources (klystrons) for equivalent average power levels due to wider availability and private sector investment. Because of the high laser-to-particle coupling efficiency, required pulse energies are consistent with tabletop microJoule class lasers. Combined with the very high (MHz) repetition rates these lasers can provide, the DLA approach appears promising for a variety of applications, including future high-energy physics colliders, compact light sources, and portable medical scanners and radiative therapy machines.
UnivIS-Import:2015-03-09:Pub.2014.nat.dphy.IAP.exphys.dielec_8

Dielectric laser electron acceleration in a dual pillar grating with a distributed Bragg reflector - Yousefi, Peyman; Schönenberger, Norbert; McNeur, Joshua; Kozak, Martin; Niedermayer, Uwe; Hommelhoff, Peter (Optics Letters, 2019)
We report on the efficacy of a novel design for dielectric laser accelerators by adding a distributed Bragg reflector (DBR) to a dual pillar grating accelerating structure. This mimics a double-sided laser illumination, resulting in an enhanced longitudinal electric field while reducing the deflecting transverse effects when compared to single-sided illumination. We improve the coupling efficiency of the incident electric field into the accelerating mode by 57%. The 12 μm long structures accelerate sub-relativistic 28 keV electrons with gradients of up to 200 MeV/m in theory and 133 MeV/m in practice. This Letter shows how lithographically produced nano-structures help to make novel laser accelerators more efficien

Dielectric Rod Waveguide Antenna as THz Emitter for Photomixing Devices - Rivera-Lavado, Alejandro; Preu, Sascha; Enrique Garcia-Munoz, Luis; Generalov, Andrey; Montero-de-Paz, Javier; Doehler, Gottfried; Lioubtchenko, Dmitri; Mendez-Aller, Mario; Sedlmeir, Florian; Schneidereit, Martin; Schwefel, Harald G. L.; Malzer, Stefan; et al. (IEEE Transactions on Antennas and Propagation, 2015)
We propose a dielectric rod waveguide antenna (DRW) integrated with a photomixer as a THz emitter. This represents a different approach as opposed to the classical solution of a substrate lens. Main goals are an inexpensive alternative to substrate lenses, reduction of both reflections on the semiconductor-air interface and scattering of terahertz-generated power into the substrate. A radiation pattern measured at 137 GHz is shown as a proof-of-concept. In order to increase radiated power, the improvement of the rod antenna is discussed. Finally, as an application example, evanescent coupling of the DRW into a high index whispering gallery mode resonator is shown.
Keywords: Dielectric rod waveguide (DRW) antenna; integrated emitter; photomixer; THz antenna; whispering gallery mode resonators

Dielectric screening effects on transition energies in aligned carbon nanotubes - Dyatlova, Olga A.; Gomis-Bresco, Jordi; Malic, Ermin; Telg, Hagen; Maultzsch, Janina; Zhong, Guofang; Geng, Junfeng; Woggon, Ulrike (Physical Review B, 2012)
The optical transition energies E-ii of carbon nanotubes (CNTs) strongly depend on the dielectric function epsilon(q) of the nanotubes and the dielectric background constant epsilon(bg) of their surroundings. It becomes particularly evident when CNTs in solution and free-standing, vertically aligned CNTs are compared via their optical spectra. Using photoluminescence-excitation spectroscopy, we determine the first two transition energies for these two types of carbon-nanotube samples, i.e., for CNT-solution and CNT-forest samples. We observe considerable energy shifts and explain them by microscopic calculations based on the density-matrix formalism. Combining experiment and theory, we determine the dielectric background constant of the CNT-forest and CNT-solution samples to be 1.3 +/- 0.1 and 1.8 +/- 0.1, respectively.

Differential calorimetry study of the initial stage of the sulphurisation process of CuInSe2 solar cell materials - Tang, K.; Künecke, Ulrike; Oehlschläger, Felix; Hölzing, Astrid; Schurr, R.; Hock, Rainer; Wellmann, Peter (Solar Energy Materials and Solar Cells, 2010)
Sulphurisation of CuInSe2 solar cell absorber materials is of particular interest for band gap engineering by means of compositional grading. We studied the chalcopyrite formation process of Cu-In-S-Se stacks with varying Se to S ratio from 100% Se (0% S) down to 0% Se (100% 5). Differential calorimetry (DSC) was applied as a fundamental characterization tool to track the crystal phase formation process. To verify the evolution of various crystallographic phases, DSC measurements were supplemented by temperature dependent in-situ X-ray diffraction (XRD) experiments of equivalent thin film compositions. For a S content of 25% the system is governed by sulphurisation of Cu and In, with the ternary phase CuIn5(S,Se)(8) and the binary phase Cu-2(S,Se) playing major roles in the chalcopyrite formation process. It is found that the chalcopyrite formation moves to higher temperatures if the S content is increased. (C) 2010 Elsevier B.V. All rights reserved.
Keywords: CuIn(S; Se)2; Chalcopyrite; Thin films; Sequential processing; Thermal analys

Differential response of patient-derived primary glioblastoma cells to environmental stiffness - Grundy, Thomas James; De Leon, Ellen; Griffin, Kaitlyn Rose; Stringer, Brett William; Day, Bryan William; Fabry, Ben; Cooper-White, Justin; O'Neill, Geraldine Margarete (Scientific Reports, 2016)

Diffuse single-crystal scattering corrected for molecular form factor effects - Schmidt, Ella; Neder, Reinhard (ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 2017)
This paper shows that chemical short-range order in two-component molecular crystals can be solved directly by separating the influence of the molecular form factor from the diffraction pattern. This novel technique is demonstrated by analysing the diffuse scattering of tris-tert-butyl-1,3,5-benzene tricarboxamid
Keywords: diffuse scattering; molecular form factors

Diffusion-driven precipitate growth and ripening of oxygen precipitates in boron doped silicon by dynamical x-ray diffraction - Will, Johannes; Gröschel, Alexander; Bergmann, Christoph; Spiecker, Erdmann; Magerl, Andreas (Journal of Applied Physics, 2014)
X-ray Pendellosung fringes from three silicon single crystals measured at 900 degrees C are analyzed with respect to density and size of oxygen precipitates within a diffusion-driven growth model and compared with TEM investigations. It appears that boron doped (p+) material shows a higher precipitate density and a higher strain than moderately (p-) boron crystals. In-situ diffraction reveals a diffusion-driven precipitate growth followed by a second growth regime in both materials. An interpretation of the second growth regime in terms of Ostwald ripening yields surface energy values (around 70 erg/cm(2)) similar to published data. Further, an increased nucleation rate by a factor of similar to 13 is found in the p+ sample as compared to a p- sample at a nucleation temperature of 450 degrees C. (C) 2014 AIP Publishing LLC.

Diffusion kurtosis imaging does not improve differentiation performance of breast lesions in a short clinical protocol - Palm, Theresa; Wenkel, Evelyn; Ohlmeyer, Sabine; Janka, Rolf Matthias; Uder, Michael; Weiland, Elisabeth; Bickelhaupt, Sebastian; Ladd, Mark E.; Zaitsev, Maxim; Hensel, Bernhard; Laun, Frederik Bernd (Magnetic Resonance Imaging, 2019)
Background: Diffusion weighted magnetic resonance imaging (DWI) is known to differentiate between malignant and benign lesions via the apparent diffusion coefficient (ADC). Here, the value of diffusion kurtosis imaging (DKI) for differentiation and further characterization of benign and malignant breast lesions and their subtypes in a clinically feasible protocol is investigated. Material and methods: This study included 85 patients (with 68 malignant and 73 benign lesions) who underwent 3 T breast DWI using three b values (50, 750, 1500 s/mm2), with a total measurement time < 5 min. ADC maps were calculated from b values 50, 750 s/mm2. The diffusion kurtosis model was fitted to the diffusion weighted images, yielding in each lesion the average kurtosis-corrected diffusion coefficient DK and mean kurtosis K. Histopathology was obtained of radiologically suspicious lesions; follow-up scans were used as a standard of reference for benign appearing lesions. Receiver operating characteristic curves were used to evaluate the parameters' diagnostic performance for differentiation of lesion types and grades. The difference in diffusion parameters between subgroups was analysed statistically using the Wilcoxon rank sum test and Kruskal-Wallis test, applying a Bonferroni correction for multiple testing where necessary. Results: ADC, DK and K showed significant differences between malignant and benign lesions (p < 10−5). All parameters had similar areas under the curve (AUC) (ADC: 0.92, DK: 0.91, K: 0.89) for differentiation of malignant and benign lesions. Sensitivity was highest for ADC (ADC: 0.96, DK: 0.94, K: 0.93), as well as specificity (ADC: 0.85, DK: 0.82, K: 0.82). ADC and DK showed significant differences between tumor histologic grades (p = 6.8⋅10−4, p = 6.6 · 10−5, respectively), whereas K did not (p = 0.99). All three parameters differed significantly between subtypes of benign lesions (ADC: p < 10−5, DK: p< 10−5, K: p = 4.1·10−4), but not between subtypes of malignant lesions (ADC: p = 0.21, DK: p = 0.25, K: p = 0.08). Conclusion: DKI parameters and conventional ADC can differentiate between malignant and benign lesions. Differentiation performance was best for ADC. Different tumor grades were significantly different in ADC and DK, which may have an impact on therapy planning and monitoring. In our study, K did not add value to the diagnostic performance of DWI in a clinical setting.
CRIS-Team Scopus Importer:2019-08-30
Keywords: Breast neoplasms; Diagnostic imaging; Diffusion kurtosis imaging; Diffusion magnetic resonance imaging; Neoplasms by histologic type

Diffusion, rotation, and surface chemical bond of individual 2 H-tetraphenylporphyrin molecules on Cu(111) - Buchner, Florian; Xiao, Jie; Zillner, Elisabeth; Chen, Min; Röckert, Michael; Ditze, Stefanie; Stark, Michael Werner; Steinrück, Hans-Peter; Gottfried, Michael; Marbach, Hubertus (Journal of Physical Chemistry C, 2011)
We address the dynamic behavior and the surface chemical bond of 2H-tetraphenylporphyrin (2HTPP) on Cu(111) around room temperature by variable-temperature scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) in ultrahigh vacuum. Between 280 and 345 K, the molecules predominantly display unidirectional diffusion along one of the three densely packed substrate 〈110〉 directions, which is attributed to a high site selectivity of the adsorbate-substrate bond. Above 305 K, the diffusion direction is found to change occasionally by ±120°. The activation barriers for the unidirectional diffusion and for rotation of the diffusion direction are determined to 0.71 ± 0.08 and 1.28 ± 0.12 eV, respectively. XPS shows that the iminic nitrogen atoms of 2HTPP interact strongly with the Cu surface. It is postulated that the local bonding situation is similar as in the initial complex (sitting-atop complex), which has previously been observed during the surface-confined in situ metalation of porphyrins. © 2011 American Chemical Society.

Diffusive motions in liquid medium-chain n-alkanes as seen by quasielastic time-of-flight neutron spectroscopy - Unruh, Tobias; Smuda, Christoph; Busch, Sebastian; et al. (Journal of Chemical Physics, 2008)
Different diffusive motions in liquid C(32)H(66) on a picosecond time scale could be disentangled by resolution resolved quasielastic time-of-flight neutron spectroscopy (QENS). It is demonstrated that at all observation times, the dominating motion causes a Q(2) proportionality of the QENS signal, which indicates a Fickian diffusion mechanism. The observed motions can be characterized by an observation time dependent apparent diffusion coefficient D(a)(t(o)), which is up to one order of magnitude larger than the molecular self-diffusion coefficient D(s). By comparison with molecular dynamics simulations, the identified motions are attributed to displacements of hydrogen atoms reflecting not only global but also local molecular trajectories. Despite the rodlike shape of the molecules, the center of mass diffusion was found to be essentially isotropic. A coherent picture of the diffusional processes ranging from the fast tumbling of CH(2) groups to the slow long range molecular diffusion is presented. (C) 2008 American Institute of Physics.

Dimensionality effects on nonequilibrium electronic transport in Cu nanobridges - Beckmann, Detlef; Weber, Heiko B.; von Löhneysen, Hilbert (Physical Review B, 2004)
We report on nonequilibrium electronic transport through normal-metal (Cu) nanobridges coupled to large reservoirs at low temperatures. We observe a logarithmic temperature dependence of the zero-bias conductance, as well as a universal scaling behavior of the differential conductance. Our results are explained by electron-electron interactions in diffusive metals in the zero-dimensional limit.

Direct 3D‐Bioprinting of hiPSC‐derived Cardiomyocytes to Generate Functional Cardiac Tissues - Esser, Tilman; Anspach, Annalise; Muenzebrock, Katrin; Kah, Delf-Thorge Eric; Schrüfer, Stefan; Schenk, Joachim; Heinze, Katrin G.; Schubert, Dirk W.; Fabry, Ben; Engel, Felix (Advanced Materials, 2023)
3D-bioprinting is a promising technology to produce human tissues as drug screening tool or for organ repair. However, direct printing of living cells has proven difficult. Here, we present a method to directly 3D-bioprint human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes embedded in a collagen-hyaluronic acid ink generating centimeter-sized functional ring- and ventricle-shaped cardiac tissues in an accurate and reproducible manner. The printed tissues contained hiPSC-derived cardiomyocytes with well-organized sarcomeres and exhibited spontaneous and regular contractions, which persisted for several months and were able to contract against passive resistance. Importantly, beating frequencies of the printed cardiac tissues could be modulated by pharmacological stimulation. This approach opens up new possibilities for generating complex functional cardiac tissues as models for advanced drug screening or as tissue grafts for organ repair or replacement.<br

Direct interpretation of the X-ray and neutron three-dimensional difference pair distribution functions (3D-ΔPDFs) of yttria-stabilized zirconia - Schmidt, Ella Mara; Neder, Reinhard; Martin, James D.; Minelli, Arianna; Lemée, Marie Hélène; Goodwin, Andrew L. (Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials, 2023)
Three-dimensional difference pair distribution functions (3D-ΔPDFs) from X-ray and neutron diffraction experiments are reported for yttria-stabilized zirconia (Zr0.82Y0.18O1.91). A quantitative analysis of the signatures in the three-dimensional difference pair distribution functions is used to establish that oxygen ions neighbouring a vacancy shift by 0.525 (5) Å along ⟨1, 0, 0⟩ towards the vacancy while metal ions neighbouring a vacancy shift by 0.465 (2) Å along ⟨1, 1, 1⟩ away from the vacancy. The neutron 3D-ΔPDF shows a tendency for vacancies to cluster along ⟨½, ½, ½⟩, which results in sixfold coordinated metal ions.
CRIS-Team Scopus Importer:2023-04-21
Keywords: cubic zirconia; diffuse scattering; three-dimensional difference pair distribution function (3D-ΔPDF)

Directionality of developing skeletal muscles is set by mechanical forces - Sunadome, Kazunori; Erickson, Alek G.; Kah, Delf-Thorge Eric; Fabry, Ben; Adori, Csaba; Kameneva, Polina; Faure, Louis; Kanatani, Shigeaki; Kaucka, Marketa; Dehnisch Ellström, Ivar; Tesarova, Marketa; Zikmund, Tomas; et al. (Nature Communications, 2023)
Formation of oriented myofibrils is a key event in musculoskeletal development. However, the mechanisms that drive myocyte orientation and fusion to control muscle directionality in adults remain enigmatic. Here, we demonstrate that the developing skeleton instructs the directional outgrowth of skeletal muscle and other soft tissues during limb and facial morphogenesis in zebrafish and mouse. Time-lapse live imaging reveals that during early craniofacial development, myoblasts condense into round clusters corresponding to future muscle groups. These clusters undergo oriented stretch and alignment during embryonic growth. Genetic perturbation of cartilage patterning or size disrupts the directionality and number of myofibrils in vivo. Laser ablation of musculoskeletal attachment points reveals tension imposed by cartilage expansion on the forming myofibers. Application of continuous tension using artificial attachment points, or stretchable membrane substrates, is sufficient to drive polarization of myocyte populations in vitro. Overall, this work outlines a biomechanical guidance mechanism that is potentially useful for engineering functional skeletal muscle.
CRIS-Team Scopus Importer:2023-07-07

Direct laser acceleration of 28 keV electrons at a single dielectric grating - Breuer, John; Hommelhoff, Peter (Workshop on Physics and Applications of High Brightness Beams: Towards a 5th Generation Light Source, 2014)
Direct laser acceleration exploiting the large optical field strength of short laser pulses and the proximity of a dielectric structure can support high acceleration gradients and may therefore lead to much smaller accelerators, with potential application in table-top free electron lasers. We report a proof-of-concept experiment demonstrating direct laser acceleration of non-relativistic 28 keV electrons derived from a conventional scanning electron microscope column at a single fused-silica grating. The electrons pass the grating as closely as 50 nm and interact with the third spatial harmonic, which is excited by 100 fs Titanium:sapphire laser pulses with a peak electric field of 2.85 GV/m. The observed maximum acceleration gradient of 25 MeV/m is already comparable to state-of-the-art RF structures. This work represents the first demonstration of scalable laser acceleration and of the inverse Smith-Purcell effect in the optical regime. © 2014 Elsevier B.V.
Keywords: Dielectric grating accelerator; Inverse Smith-Purcell effect; Laser-driven particle acceleration; Non-relativistic electrons

Direct mapping of microscopic polarization in ferroelectric x(BiScO3)-(1-x)(PbTiO3) throughout its morphotropic phase boundary - Datta, Kaustuv; Richter, Andreas; Göbbels, Matthias; Keen, David A.; Neder, Reinhard (Physical Review B - Condensed Matter and Materials Physics, 2016)
Pair distribution functions of ferroelectric xBiScO3-(1-x)PbTiO3, obtained from neutron total scattering data, were examined and modeled utilizing the reverse Monte Carlo technique to depict exclusively the local structure of this compound throughout its reported morphotropic phase boundary (MPB). Microscopic polarizations due to the cation shifts have been mapped out from the refined crystal structure as a function of composition in order to reveal individual cation behavior driven by the composition. Direct evidences are provided for large static displacements of the cations (∼0.2-0.5Å), local cation ordering between Ti and Sc, and a categorical change of favored polarization directions of the cations at the conjuncture of the MPB. Apart from Sc, all cations have demonstrated an apparent transition from a relatively defined directional distribution to a broad and random distribution at x=xMPB, suggesting a flattening of the local potential function for them. These features can further be correlated with the general concept of structural instability of a ferroelectric system at the MPB, which is often linked to the manifestation of enhanced physical properties.

Disappearance of the LO-Phonon line in the Raman spectrum of 6H-SiC - Hundhausen, Martin; Ley, Lothar; et al. (Materials Science Forum, 2000)
We undertook a study of the intensities of optical vibrational modes in the Raman spectrum of 6H-SiC as a function of excitation energy between 2.4 eV and 4.9 eV. A disappearance of the LO0 mode which is the longitudinal optical mode with the highest frequency is observed at 4.38 eV. The result is explained in the framework of a bond-Raman-polarizability model for the Raman scattering cross section as due to the cancellation of the energy dependent bond-Raman polarizabilities of intra- and inter-bilayer bonds that connect the Si and C planes in SiC.
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.IAP.exphys.disapp

Dislocations in bilayer graphene - Butz, Benjamin; Dolle, Christian; Niekiel, Florian; Weber, Konstantin; Waldmann, Daniel; Weber, Heiko B.; Meyer, Bernd; Spiecker, Erdmann; Spiecker, Erdmann (Nature, 2014)
Dislocations represent one of the most fascinating and fundamental concepts in materials science. Most importantly, dislocations are the main carriers of plastic deformation in crystalline materials. Furthermore, they can strongly affect the local electronic and optical properties of semiconductors and ionic crystals. In materials with small dimensions, they experience extensive image forces, which attract them to the surface to release strain energy. However, in layered crystals such as graphite, dislocation movement is mainly restricted to the basal plane. Thus, the dislocations cannot escape, enabling their confinement in crystals as thin as only two monolayers. To explore the nature of dislocations under such extreme boundary conditions, the material of choice is bilayer graphene, the thinnest possible quasi-two-dimensional crystal in which such linear defects can be confined. Homogeneous and robust graphene membranes derived from high-quality epitaxial graphene on silicon carbide provide an ideal platform for their investigation. Here we report the direct observation of basal-plane dislocations in freestanding bilayer graphene using transmission electron microscopy and their detailed investigation by diffraction contrast analysis and atomistic simulations. Our investigation reveals two striking size effects. First, the absence of stacking-fault energy, a unique property of bilayer graphene, leads to a characteristic dislocation pattern that corresponds to an alternating ABAC change of the stacking order. Second, our experiments in combination with atomistic simulations reveal a pronounced buckling of the bilayer graphene membrane that results directly from accommodation of strain. In fact, the buckling changes the strain state of the bilayer graphene and is of key importance for its electronic properties. Our findings will contribute to the understanding of dislocations and of their role in the structural, mechanical and electronic properties of bilayer and few-layer graphene. © 2014 Macmillan Publishers Limited. All rights reserved.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.LAP.disloc

Disordered structure of cadmium sulphide nanoparticles - Rempel', A. A.; Vorokh, A. S.; Neder, Reinhard; Magerl, Andreas (MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011)
Based on X-ray diffraction data obtained for thin polycrystalline CdS films and computer simulation using the Debye formula in the framework of the DISCUS program, it has been established that the location of close-packed Cd planes in CdS nanoparticles is disordered. The absence of strict periodicity of the atomic structure in the presence of close packing, with the mutual tetrahedral environment of Cd and S atoms, is a special feature of CdS in the nanostate. The average lattice of a disordered close-packed structure is described by space group P6 with parameters of the unit cell a = 0.236 and c =0.334 nm and a degree of occupation of crystal-lattice sites of 1/3.

Dispersion of surface states on diamond (100) and (111) - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review B, 1997)
We present angle-resolved photoelectron spectra and surface state dispersions for the clean, 2x1 reconstructed (111) and (100) surfaces of diamond. For the (100) surface a surface state is found in the gap of the projected bulk band structure around Ȳ, which has a binding energy of 2.7 eV at Ȳ (relative to the Fermi level) and a dispersion in the Γ̄-Ȳ direction of 0.5 eV, consistent with theory. At Γ̄ a surface resonance is observed at 1.4 eV binding energy. No surface states were observed above the valence-band maximum. Our results on the (111) surface show a strongly dispersing surface state that reaches its maximum 0.5 eV below the Fermi level at K̄. This result implies a gap of at least 0.5 eV in the surface electronic structure, which has consequences for the surface reconstruction in terms of a π-bonded chain model.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.IAP.exphys.disper

Do biophysical properties of the airway smooth muscle in culture predict airway hyperresponsiveness? - An, Steven S.; Fabry, Ben; Trepat, Xavier; Wang, Ning; Fredberg, Jeffrey (American Journal of Respiratory Cell and Molecular Biology, 2006)

Do bioresorbable polyesters have antimicrobial properties? - Gritsch, Lukas; Lovell, Christopher; Goldmann, Wolfgang; Boccaccini, Aldo R. (Journal of Materials Science: Materials in Medicine, 2018)

Doped single-walled carbon nanotubes and low-mobility graphene: Impact of disorder and dopants on electronic magnetotransport - Krstic, Vojislav; Krstic, Vojislav; Glerup, Marianne; Hansel, Stefan; Lafkioti, Myrsini (Physica Status Solidi-Rapid Research Letters, 2009)
The impact of disorder introduced by intentional and unintentional (environmental) dopants on the charge transport has been investigated in boron- and nitrogen-doped single-walled carbon nanotubes, and in low-mobility monolayer graphene. For doped single-walled nanotubes a theoretically not predicted plateau-like region and onsets of oscillatory behaviour in the conductance for boron- and nitrogen-doped nanotubes were observed, respectively. The oscillatory behaviour suggests interplay between the dopants and the helical movement of charges along the tube due to the magnetic field. For low-mobility graphene the simultaneous appearance of the filling-factor 2 and 3 plateau was observed in the Quantum-Hall regime. This is attributed to an electron-spin–isospin interaction mediated through the high disorder. <br

Doping of 4H-SiC with group IV elements - Krieger, Michael; Rühl, Maximilian; Sledziewski, Tomasz; Ellrott, Günter; Palm, Theresa; Weber, Heiko B.; Bockstedte, Michel Georg (Materials Science Forum, 2016)

Doping of single-walled carbon nanotube bundles by Brønsted acids - Graupner, Ralf; Abraham, Jürgen; Vencelová, Andrea; Seyller, Thomas; Hennrich, Frank; Kappes, Manfred; Hirsch, Andreas; Ley, Lothar (Physical Chemistry Chemical Physics, 2003)
Using X-ray induced photoelectron spectroscopy, the influence of Brønsted acids, namely sulfuric, nitric, and hydrochloric acid on the electronic properties of single-walled carbon nanotubes (SWCNTs) was investigated. Doping effects were monitored by changes in binding energy of the C 1s core level of the nanotubes. For all three acids, an acceptor type doping of the SWCNTs was observed by a shift of the C 1s core level towards lower binding energies. The inferred change of the Fermi-level position was 0.5 eV in the case of HSO, 0.2 eV in the case of HNO, and 0.1 eV in the case of HCl. For HNO and HCl the doping was found to be unstable. The S 2p, N 1s, and Cl 2p core level spectra of the corresponding acid showed spectral features which can be attributed to the respective oxidation state of these anions in the acid, indicating that doping was induced by intercalation.

Dose-dependent milling efficiencies of helium and nitrogen beams in PMMA - Ellrott, Günter; Ogawa, Shinichi; Uno, Munenori; Morita, Yukinori; Manoharan, Muruganathan; Kolesnik-Gray, Maria; Krstic, Vojislav; Mizuta, Hiroshi (Microelectronic Engineering, 2021)
Focused ion beams with varied exposure dose were used to mill rectangular trenches into PMMA on SiO2. The dose response was investigated by atomic force microscopy measurements. TRIM calculations were used to simulate the ion distributions and damages expected inside the target. The depth of the trenches measured by AFM showed an unexpected decrease for intermediate dosages of high energetic helium ions in contrast to low energetic helium and nitrogen ions. This has been attributed to the formation of metastable blisters in the PMMA layer.
CRIS-Team Scopus Importer:2021-09-17
Keywords: 3D lithography; FIB; Gas source ion beam; Helium ion beam milling; Nitrogen ion beam milling; PMMA blisters

Double quantum filtered 23 Na MRI with magic angle excitation of human skeletal muscle in the presence of B0 and B1 inhomogeneities - Gast, Lena; Gerhalter, Teresa; Hensel, Bernhard; Uder, Michael; Nagel, Armin Michael (NMR in Biomedicine, 2018)
Double quantum filtered 23 Na MRI with magic angle excitation (DQF-MA) can be used to selectively detect sodium ions located within anisotropic structures such as muscle fibers. It might therefore be a promising tool to analyze the microscopic environment of sodium ions, for example in the context of osmotically neutral sodium retention. However, DQF-MA imaging is challenging due to various signal dependences, on both measurement parameters and external influences. The aim of this work was to examine how B0 in combination with B1 inhomogeneities alter the DQF-MA signal intensity. We showed that, in the presence of B0 inhomogeneities, flip angle schemes with only one 54.7° pulse can be favorable compared with the classical 90°-54.7°-54.7° scheme. DQF-MA images of the human lower leg were acquired at B0 = 3 T with a nominal spatial resolution of 12 × 12 × 36 mm3 within an acquisition time of TAcq < 10 min, and compared with spin density weighted (DW), as well as triple quantum filtration (TQF) 23 Na images. We found mean normalized signal-to-noise ratios of TQF/DW = 13.7 ± 2.3% (tibialis anterior), 11.9 ± 2.3% (soleus) and 11.4 ± 2.2% (gastrocnemius medialis), as well as DQF-MA/DW = 4.7 ± 1.1% (tibialis anterior), 3.3 ± 0.73% (soleus) and 3.4 ± 0.6% (gastrocnemius medialis). These ratios might serve as additional measures in future clinical studies of sodium retention within human skeletal muscle. However, the influence of B0 and B1 inhomogeneities should be considered when interpreting DQF-MA images.
EVALuna2:36106

Double-resonant LA phonon scattering in defective graphene and carbon nanotubes - Herziger, Felix; Tyborski, Christoph; Ochedowski, Oliver; Schleberger, Marika; Maultzsch, Janina (Physical Review B, 2014)
We present measurements of the D '' Raman mode in graphene and carbon nanotubes at different laser excitation energies. The Raman mode around 1050-1150 cm(-1) originates from a double-resonant scattering process of longitudinal acoustic (LA) phonons with defects. We investigate its dependence on laser excitation energy, on the number of graphene layers, and on the carbon nanotube diameter. We assign this Raman mode to so-called inner processes with resonant phonons mainly from the Gamma-K high-symmetry direction. The asymmetry of the D '' mode is explained by additional contributions from phonons next to the Gamma-K line. Our results demonstrate the importance of inner contributions in the double-resonance scattering process and add a fast method to investigate acoustic phonons in graphene and carbon nanotubes by optical spectroscopy.

Double-resonant Raman processes in germanium: Group theory and ab initio calculations - Mohr, Marcel; Machon, Maria; Maultzsch, Janina; Thomsen, Christian (Physical Review B, 2006)
We study the excitation-energy-dependent Raman peaks of germanium in terms of double-resonant scattering. In our analysis we combine group theory and ab initio calculations to select scattering processes and contrast them with the experimental data. A surface-driven k-selective mechanism explains not only the dependence of the peak shifts on surface orientation, but also their polarization dependence in a cubic system.

Double-resonant Raman scattering in graphite: Interference effects, selection rules, and phonon dispersion - Maultzsch, Janina; et al. (Physical Review B, 2004)
We present a comprehensive analysis of double-resonant Raman scattering in graphite and derive an analytical expression for the Raman cross section of the D mode in one dimension. The extension to two dimensions does not change the double-resonant phonon wave vectors. In the full integration of the Raman cross section, the contributions by phonons from exactly the K point cancel due to destructive interference. We calculate the D mode explicitly based on recent experimental data of the graphite phonon dispersion. Applying the selection rules, a mapping of additional disorder-induced and second-order Raman modes onto the Brillouin zone of graphite is obtained.

Double-resonant Raman scattering with optical and acoustic phonons in carbon nanotubes - Tyborski, Christoph; Vierck, Asmus; Narula, Rohit; Popov, Valentin N.; Maultzsch, Janina (Physical Review B, 2018)
We analyze and assign two low-intensity, double-resonant Raman bands at around 1950 cm(-1) and 2450 cm(-1) in carbon nanotube ensembles. We present Raman spectra of a high-pressure carbon monoxide sample for laser energies in the visible range. By using density functional theory plus zone folding, we simulate both combination modes for various excitation energies with respect to the chiral-index distribution of carbon nanotubes in the sample. For a comparison, double-resonant Raman spectra of single carbon nanotubes are also modeled within a symmetry-based nonorthogonal tight-binding approach, resulting in a different assignment of the 1950-cm(-1) band. Apparent discrepancies in the assignments are discussed in the article.

Driving Current through Single Organic Molecules - Reichert, Joachim; Ochs, Rolf; Beckmann, Detlef; Weber, Heiko B.; Mayor, Marcel; von Löhneysen, Hilbert (Physical Review Letters, 2002)
UnivIS-Import:2017-11-07:Pub.2002.nat.dphy.IAP.LAP.drivin

Dual-wavelength stopped-flow analysis of the lateral and longitudinal assembly kinetics of vimentin - Schween, Lovis; Mücke, Norbert; Portet, Stéphanie; Goldmann, Wolfgang; Herrmann, Harald; Fabry, Ben (Biophysical Journal, 2022)
Vimentin is a highly charged intermediate filament protein that inherently forms extended dimeric coiled coils, which serve as the basic building blocks of intermediate filaments. Under low ionic strength conditions, vimentin filaments dissociate into uniform tetrameric complexes of two anti-parallel-oriented, half-staggered coiled-coil dimers. By addition of salt, vimentin tetramers spontaneously reassemble into filaments in a time-dependent process: 1) lateral assembly of tetramers into unit-length filaments, 2) longitudinal annealing of unit-length filaments, and 3) longitudinal assembly of filaments coupled with subsequent radial compaction. To independently determine the lateral and longitudinal assembly kinetics, we measure with a stopped-flow instrument the static light scattering signal at two different wavelengths (405 and 594 nm) with a temporal resolution of 3 ms and analyze the signals based on Rayleigh-Gans theory. This theory considers that the intensity of the scattered light depends not only on the molecular weight of the scattering object but also on its shape. This shape dependence is more pronounced at shorter wavelengths, allowing us to decompose the scattered light signal into its components arising from lateral and longitudinal filament assembly. We demonstrate that both the lateral and longitudinal filament assembly kinetics increase with salt concentration.
CRIS-Team Scopus Importer:2022-10-21

Durotropic Growth of Pollen Tubes(1)([OPEN]) - Reimann, Ronny; Kah, Delf-Thorge Eric; Mark, Christoph; Dettmer, Jan; Reimann, Theresa; Gerum, Richard; Geitmann, Anja; Fabry, Ben; Dietrich, Petra; Kost, Benedikt (Plant Physiology, 2020)
To reach the female gametophyte, growing pollen tubes must penetrate different tissues within the pistil, the female reproductive organ of a flower. Past research has identified various chemotropic cues that guide pollen tubes through the transmitting tract of the pistil, which represents the longest segment of its growth path. In addition, physical mechanisms also play a role in pollen tube guidance; however, these processes remain poorly understood. Here we show that pollen tubes from plants with solid transmitting tracts actively respond to the stiffness of the environment. We found that pollen tubes fromNicotiana tabacumand other plant species with a solid or semisolid transmitting tract increase their growth rate in response to an increasing matrix stiffness. By contrast, pollen tubes fromLilium longiflorumand other plant species with a hollow transmitting tract decrease their growth rate with increasing matrix stiffness, even though the forces needed to maintain a constant growth rate remain far below the maximum penetration force these pollen tubes are able to generate. Moreover, when confronted with a transition from a softer to a stiffer matrix, pollen tubes fromN. tabacumdisplay a greater ability to penetrate into a stiffer matrix compared with pollen tubes fromL. longiflorum,even though the maximum force generated by pollen tubes fromN. tabacum(11 mu N) is smaller than the maximum force generated by pollen tubes fromL. longiflorum(36 mu N). These findings demonstrate a mechano-sensitive growth behavior, termed here durotropic growth, that is only expressed in pollen tubes from plants with a solid or semisolid transmitting tract and thus may contribute to an effective pollen tube guidance within the pistil.
CRIS-Team WoS Importer:2020-07-10

Durotropic Growth of Pollen Tubes - Reimann, Ronny; Kah, Delf-Thorge Eric; Mark, Christoph; Dettmer, Jan; Reimann, Theresa; Gerum, Richard; Geitmann, Anja; Fabry, Ben; Dietrich, Petra; Kost, Benedikt (Plant Physiology, 2020)
To reach the female gametophyte, growing pollen tubes must penetrate different tissues within the pistil, the female reproductive organ of a flower. Past research has identified various chemotropic cues that guide pollen tubes through the transmitting tract of the pistil, which represents the longest segment of its growth path. In addition, physical mechanisms also play a role in pollen tube guidance; however, these processes remain poorly understood. Here we show that pollen tubes from plants with solid transmitting tracts actively respond to the stiffness of the environment. We found that pollen tubes from Nicotiana tabacum and other plant species with a solid or semisolid transmitting tract increase their growth rate in response to an increasing matrix stiffness. By contrast, pollen tubes from Lilium longiflorum and other plant species with a hollow transmitting tract decrease their growth rate with increasing matrix stiffness, even though the forces needed to maintain a constant growth rate remain far below the maximum penetration force these pollen tubes are able to generate. Moreover, when confronted with a transition from a softer to a stiffer matrix, pollen tubes from N. tabacum display a greater ability to penetrate into a stiffer matrix compared with pollen tubes from L. longiflorum, even though the maximum force generated by pollen tubes from N. tabacum (11 µN) is smaller than the maximum force generated by pollen tubes from L. longiflorum (36 µN). These findings demonstrate a mechano-sensitive growth behavior, termed here durotropic growth, that is only expressed in pollen tubes from plants with a solid or semisolid transmitting tract and thus may contribute to an effective pollen tube guidance within the pistil. Animal sperm cells have the ability to freely swim by rhythmic movements of their flagella (Malo et al., 2006). By contrast, sperm cells of angiosperm plants have lost this ability (Dresselhaus et al., 2016) and are contained within the cytoplasm of the vegetative cell of a pollen grain. Upon germination, the vegetative pollen cell forms a long tubular protrusion, the pollen tube, which rapidly elongates through the pistil and transports the enclosed immobile sperm cells toward the egg cell and the central cell for double fertilization (Zhang et al., 2017). As opposed to cell division, pollen tubes elongate by tip growth. This process depends on a fine-tuned interplay between turgor pressure and vesicle trafficking, which delivers material required for cell wall and plasma membrane extension exclusively to the pollen tube tip (Lord, 2000; Chebli et al., 2013; Hafidh et al., 2016a; Grebnev et al., 2017; Luo et al., 2017). Therefore, only the surface at the pollen tube tip changes its relative position with respect to the environment during cell elongation, giving rise to a low-friction and thus energetically favorable growth process that has also been observed in other invasively growing cell types, such as root hairs, fungal hyphae, and neurons (Palanivelu and Preuss, 2000; Sanati Nezhad and Geitmann, 2013). This mechanism enables pollen tubes of some plant species to grow at rates of more than 300 µm·min−1 (Williams et al., 2016), faster than any other plant cell (Shamsudhin et al., 2016). To reach the female gametophyte, growing pollen tubes must penetrate different tissues within the pistil. After initial growth on the surface of the stigma, pollen tubes subsequently elongate through the transmitting tract within the style and the ovary, penetrate the septum epidermis to leave the transmitting tract, continue to elongate on the surface of the funiculus and through the micropyle of the ovule, and finally enter a synergid cell, where they burst and discharge their cytoplasm together with the enclosed sperm cells (Hulskamp et al., 1995; Crawford et al., 2007). Over the past two decades, many factors have been identified that are involved in the guidance of pollen tubes along their path toward the female gametophyte, including sugars, calcium ions, nitric oxide, lipids, and secreted peptides (Hulskamp et al., 1995; Ray et al., 1997; Wolters-Arts et al., 1998; Mollet et al., 2000; Higashiyama et al., 2003; Prado et al., 2004; Chae and Lord, 2011; Sanati Nezhad et al., 2014; Qu et al., 2015; Hafidh et al., 2016b; Higashiyama and Yang, 2017; Jiao et al., 2017). Most of these chemical signals guide the pollen tubes toward and inside the ovule following their emergence from the transmitting tract. However, the transmitting tract of the pistil typically represents the longest section of the pollen tube growth path in situ (de Graaf et al., 2003; Crawford and Yanofsky, 2008). Because chemical gradients are more difficult to maintain over longer distances, physical guidance mechanisms are thought to play an important role in directing pollen tube growth within the transmitting tract (Lennon et al., 1998; Lush et al., 2000), but this has so far not been characterized in detail. Flowers of different plant species display a highly diverse pistil and transmitting tract anatomy, which complicates the investigation of physical pollen tube guidance. Within the transmitting tract of hollow (sometimes called “open”) styles, as observed for example in Lilium longiflorum flowers, pollen tubes grow on the epidermal surface of a cell-free canal filled with a viscous extracellular matrix (Sanders and Lord, 1992; de Graaf et al., 2001; Erbar, 2003). By contrast, the transmitting tract in solid (sometimes called “closed”) styles, as found in Arabidopsis (Arabidopsis thaliana) and Nicotiana tabacum flowers, is filled with tissue composed of cells embedded in an extracellular matrix, which pollen tubes need to penetrate (Lennon et al., 1998; Cheung et al., 2000; Erbar, 2003). The tissue within the transmitting tract imposes a substantial physical resistance on pollen tube growth (Agudelo et al., 2012), in particular as intercellular spaces in this tissue are typically smaller than the pollen tube diameter (Lennon et al., 1998; Roy et al., 1999; Cheung et al., 2000). The maximum (or stalling) force that a growing pollen tube can generate to overcome the mechanical resistance restricting its expansion within pistil tissues is determined by the product of the hydrostatic turgor pressure and the cross-sectional area of the tube at its tip. Maximum forces generated by L. longiflorum tubes measured with capacitive force sensors (Burri et al., 2018) were found to be in the range of 9.6 ± 1.6 µN, whereas forces generated by Camellia japonica pollen tubes measured with soft microcantilevers (Ghanbari et al., 2018) were found to be around 1.5 µN. However, direct force measurements using capacitive force sensors or microcantilevers are technically highly demanding (Agudelo et al., 2013; Ghanbari et al., 2014; Sanati Nezhad et al., 2014). Moreover, measurements of the maximum stalling force cannot provide information on the penetration force of a pollen tube growing inside a pistil under physiological conditions, as this force depends on the growth rate and the mechanical impedance of the surrounding matrix (Sanati Nezhad et al., 2013). In this study, we present a method to estimate the penetration force generated by a pollen tube tip during its growth through matrices of different stiffness. With this method, we investigated pollen tubes from plant species, both with hollow and with solid styles, and measured the relationship between penetration force and growth rate for matrices with different mechanical properties. We found that pollen tubes from plants with solid styles, but not those from plants with hollow styles, increase their growth rate in matrices with higher physical resistance, indicating that an active mechanosensory mechanism controls the tropic growth of these pollen tubes, which may help them to navigate through the complex architecture of the pistil to reach the female gametophyte. We propose the term durotropism for this mechanosensory mechanism that guides pollen tubes from plants with solid styles toward stiffer environments, analogous to the term durotaxis that describes the preferential migration of mammalian mesenchymal cells toward regions with higher substrate rigidity (Lo et al., 2000

Dynamically reconfigurable fibre optical spanner - Kolb, Thorsten; Albert, Sahradha; Haug, Michael; Whyte, Graeme (Lab on A Chip, 2014)
In this paper we describe a pneumatically actuated fibre-optic spanner integrated into a microfluidic Lab-on-a-Chip device for the controlled trapping and rotation of living cells. The dynamic nature of the system allows interactive control over the rotation speed with the same optical power. The use of a multi-layer device makes it possible to rotate a cell both in the imaging plane and also in a perpendicular plane allowing tomographic imaging of the trapped living cell. The integrated device allows easy operation and by combining it with high-resolution confocal microscopy we show for the first time that the pattern of rotation can give information regarding the sub-cellular composition of a rotated cell.
EAM Import::2019-03-13

Dynamical properties of the hydration shell of fully deuterated myoglobin - Achterhold, Klaus; Ostermann, Andreas; Moulin, Martine; Haertlein, Michael; Unruh, Tobias; Parak, Fritz G. (Physical Review E, 2011)
Freeze-dried perdeuterated sperm whale myoglobin was kept in a water-saturated atmosphere in order to obtain a hydration degree of 335 (1)H(2)O molecules per one myoglobin molecule. Incoherent neutron scattering was performed at the neutron spectrometer TOFTOF at the FRM II in an angular range of q from 0.6 to 1.8 angstrom(-1) and a temperature range from 4 to 297 K. We used neutrons with a wavelength of lambda = 6 angstrom and an energy resolution of about 65 mu eV corresponding to motions faster than 10 ps. At temperatures above 225 K, broad lines appear in the spectra caused by quasielastic scattering. For an explanation of these lines, we assumed that there are only two types of protons, those that are part of the hydration water (72%) and those that belong to the protein (28%). The protons of the hydration water were analyzed with the diffusion model of Singwi and Sjolander [Phys. Rev. 119, 863 (1960)]. In this model, a water molecule stays for a time tau(0) in a bound state performing oscillatory motions. Thereafter, the molecule performs free diffusion for the time tau(1) in a nonbound state followed again by the oscillatory motions for tau(0) and so forth. We used the general formulation with no simplifications as tau(0) >> tau(1) or tau(1) >> tau(0). At room temperature, we obtained tau(0) = 104 ps and tau(1) = 37 ps. For the protein bound hydrogen, the dynamics is described by a Brownian oscillator where the protons perform overdamped motions in limited space.

Dynamical synchronization transition in interacting electron systems - Nag, Tanay; Slager, Robert-Jan; Higuchi, Takuya; Oka, Takashi (Physical Review B, 2019)
Synchronization is a ubiquitous phenomenon in nature and we propose its new perspective in ultrafast dynamics in interacting electron systems. In particular, using graphene irradiated by an intense bicircular pulse laser as a prototypical and experimental viable example, we theoretically investigate how to selectively generate a coherent oscillation of electronic order such as charge density orders (CDOs). The key is to use tailored fields that match the crystalline symmetry broken by the target order. After the pump, a macroscopic number of electrons start oscillating and coherence is built up through a transition. The resulting physics is detectable as a coherent light emission at the synchronizion frequency and may be used as a purely electronic way of realizing Floquet states respecting exotic space-time crystalline symmetries. In the process, we also explore possible flipping of existing static CDOs and generation of higher harmonics. The general framework for the coherent electronic order is found to be analogous with the celebrated Kuramoto model, describing the classical synchronization of coupled pendulums.
CRIS-Team WoS Importer:2019-10-18

Dynamic delay time compensation for sampling capillaries used in respiratory mass spectrometry - Eberhard, Luc; Haberthür, Christoph; Fabry, Ben; Guttmann, Josef (Technology and Health Care, 1999)

Dynamic equilibration of airway smooth muscle contraction during physiological loading - Latourelle, Jeanne; Fabry, Ben; Fredberg, Jeffrey (Journal of Applied Physiology, 2002)

Dynamic processes in biological membrane mimics revealed by quasielastic neutron scattering. - Lautner, Lisa; Pluhackova, Kristyna; Barth, Nicolai; Seydel, Tilo; Lohstroh, Wiebke; Böckmann, Rainer; Unruh, Tobias (Chemistry and physics of lipids, 2017)
Neutron scattering is a powerful tool to study relaxation processes in biological membrane mimics in space and time. Combining different inelastic and quasielastic neutron scattering techniques, a large dynamic range can be covered: from atomic to mesoscopic lengths and from femto- to some hundreds of nanoseconds in time. This allows studies on e.g. the diffusion of lipids, the membrane undulation motions, the dispersion of sound waves in membranes as well as the mutual interactions of membrane constituents such as lipids, proteins, and additives. In particular, neutron scattering provides a quite direct experimental approach to the inter-atomic and inter-molecular potentials on length and time scales which are perfectly accessible by molecular dynamics (MD) simulations. Neutron scattering experiments may thus substantially support the further refinement of biomolecular force fields for MD simulations by supplying structural and dynamical information with high spatial and temporal resolution. In turn, MD simulations support the interpretation of neutron scattering data. The combination of both, neutron scattering experiments and MD simulations, yields an unprecedented insight into the molecular interactions governing the structure and dynamics of biological membranes. This review provides an overview of the molecular dynamics in biological membrane mimics as revealed by neutron scattering. It focuses on the latest findings such as the fundamental molecular mechanism of lateral lipid diffusion as well as the influence of additives and proteins on the short-time dynamics of lipids. Special emphasis is placed on the comparison of recent neutron scattering and MD simulation data with respect to molecular membrane dynamics on the pico- to nanosecond time scale.

Dynamics and adsorption sites for guest molecules in methyl chloride hydrate - Prager, Michael; Desmedt, Arnaud; Unruh, Tobias; Allgaier, Jürgen (Journal of Physics: Condensed Matter, 2008)
Methyl rotational tunneling, quasielastic spectra and phonon densities of states measured with neutrons at energy transfers from 35 mu eV to 40 meV are used to characterize the adsorption sites and potentials of CH(3)Cl guest molecules in the two kinds of cages of cubic I methyl chloride hydrate. The model of adsorption to hydrogen bonds of the ice cage explains the broad tunnel spectrum as a superposition of four bands. Up to a temperature T similar to 80 K the quasielastic scattering is influenced by quantum motion. Only above T similar to 80 K does the effective linewidth follow an Arrhenius behavior with an average activation energy. Rotational potentials contain a significant sixfold component supporting the proposed adsorption to hydrogen bonds with their mirror symmetry. Positional disorder of protons in the hydrogen bonds of the host ice lattice leads to potential distributions of large relative widths delta V/(V) over bar <= 0.35.

Dynamics of bound states of dihydrogen at Cu(I) and Cu(II) species coordinated near one and two zeolite framework aluminium atoms: A combined sorption, INS, IR and DFT study - Georgiev, P. A.; Drenchev, N.; Hadjiivanov, K. I.; Ollivier, J.; Unruh, Tobias; Albinati, A. (International Journal of Hydrogen Energy, 2021)
Ambient conditions sorption isotherms of dihydrogen in a series of various levels of Cu-exchanged ZSM-5 zeolites, with two different Si/Al ratios, namely 11.5 and 25, show the presence of different amount of Cu centres able to strongly bind H2. Although the isosteric heats of adsorption derived from these isotherms are rather similar, of the order of 30 kJ/mol H2, Inelastic Neutron Scattering (INS) of adsorbed dihydrogen and Fourier-Transformed Infra-Red (FTIR) spectroscopy measurements of adsorbed CO and NO reveal that copper is encountered in two oxidation states. At least two types of Cu(I) ions are clearly detected as well as some heterogeneity of the Cu(II) species. The number of these Cu species is different in the two investigated ZSM-5 materials and depends on the Cu exchange level. With the aid of DFT model cluster calculations we find that under different coordination environments, determined by the Al distribution, both mono- and divalent Cu ions could bind H2 with a different strength. Unprecedentedly, we found that Cu-ions compensating two Al atoms, i.e. formally Cu(II) species, relatively far apart from each other, may behave very similarly to the monovalent Cu-species or alternatively viewed – as Cu(I) species that compensate for two framework Al-atoms. Such Cu-species also form stable η2 dihydrogen complexes.
CRIS-Team Scopus Importer:2021-07-16
Keywords: Catalysis; DFT modelling; Hydrogen adsorption; MFI zeolite; Spectroscopic characterisation

Dynamics of exciton formation at the Si(100) c(4x2) surface - Weinelt, Martin; Kutschera, Michael; Fauster, Thomas; Rohlfing, Michael (Physical Review Letters, 2004)
Carrier recombination at the Si(100) c(4x2) surface and the underlying surface electronic structure is unraveled by a combination of two-photon photoemission and many-body perturbation theory: An electron excited to the silicon conduction band by a femtosecond infrared laser pulse scatters within 220 ps to the unoccupied surface band, needs 1.5 ps to jump to the band bottom via emission of optical phonons, and finally relaxes within 5 ps with an excited hole in the occupied surface band to form an exciton living for nanoseconds.

Dynamics of image-potential states on stepped Cu(001) surfaces - Roth, Manfred; Pickel, Martin; Weinelt, Martin; Fauster, Thomas (Applied Physics A-Materials Science & Processing, 2004)
The dynamical properties of image-potential states on stepped Cu(117) and Cu(118) surfaces were studied by time- and angle-resolved two-photon photoelectron spectroscopy. The interaction with the step-induced potential leads to quasielastic anisotropic scattering between image-potential-state bands. In particular, resonant interband scattering from image-potential states with quantum numbers ngreater than or equal to2 to the n=1 band and quasielastic intraband scattering within the n=1 band show high efficiency. In spite of the higher step density of Cu(117), resonant scattering is about four times larger on Cu(118). This distinction is attributed to the different step distributions of the two surfaces and to the concomitant correlation of the step arrangement on short- and long-range scales, which has been studied by scanning tunneling microscopy. Details of the surface band structure lead to different boundary conditions and may weakly affect scattering probabilities.

Dynamics of strain relaxation studied by in situ x-ray diffraction immediately after layer heteroepitaxy - Horbaschk, M.; Benkert, A.; Schumacher, C.; Brunner, K.; Neder, Reinhard (Applied Physics Letters, 2009)
The temporal development of strain relaxation is monitored during and immediately after heteroepitaxy by x-ray diffraction with high resolution in strain and time. ZnSe layers on (001)GaAs with thicknesses just a little above the onset of plastic relaxation reveal inhomogeneous, partial relaxation which continues with a time constant of 50 s immediately after the stop of layer growth. A model of generation, glide, and blocking of dislocations well explains the observation that the degree of relaxation finally reached after growth stop is determined by the density of dislocations rapidly generated prior to it.
Keywords: dislocation density; gallium arsenide; plasticity; semiconductor epitaxial layers; stress relaxation; X-ray diffraction; zinc compounds

Dynamics of supercooled water in highly compacted clays studied by neutron scattering - González Sánchez, Fátima; Juranyi, Fanni; Gimmi, Thomas; Van Loon, Luc R.; Seydel, Tilo; Unruh, Tobias (Journal of Physics: Condensed Matter, 2008)
The freezing behavior of water confined in compacted charged and uncharged clays (montmorillonite in Na-and Ca-forms, illite in Na-and Ca-forms, kaolinite and pyrophyllite) was investigated by neutron scattering. Firstly, the amount of frozen (immobile) water was measured as a function of temperature at the IN16 backscattering spectrometer, Institute Laue-Langevin (ILL). Water in uncharged, partly hydrophobic (kaolinite) and fully hydrophobic (pyrophyllite) clays exhibited a similar freezing and melting behavior to that of bulk water. In contrast, water in charged clays which are hydrophilic could be significantly supercooled. To observe the water dynamics in these clays, further experiments were performed using quasielastic neutron scattering. At temperatures of 250, 260 and 270 K the diffusive motion of water could still be observed, but with a strong reduction in the water mobility as compared with the values obtained above 273 K. The diffusion coefficients followed a non-Arrhenius temperature dependence well described by the Vogel-Fulcher-Tammann and the fractional power relations. The fits revealed that Na-and Ca-montmorillonite and Ca-illite have similar Vogel-Fulcher-Tammann temperatures (T-VFT, often referred to as the glass transition temperature) of similar to 120 K and similar temperatures at which the water undergoes the 'strong-fragile' transition, T-s similar to 210 K. On the other hand, Na-illite had significantly larger values of T-VFT similar to 180 K and T-s similar to 240 K. Surprisingly, Ca-illite has a similar freezing behavior of water to that of montmorillonites, even though it has a rather different structure. We attribute this to the stronger hydration of Ca ions as compared with the Na ions occurring in the illite clays.

Dynamics of Water Absorbed in Polyamides - Laurati, M.; Sotta, P.; Long, D. R.; Fillot, L. A.; Arbe, Arantxa; Alegria, A.; Embs, Jan Peter; Unruh, Tobias; Schneider, Gerald J.; Colmenero, Juan (Macromolecules, 2012)
We investigate the dynamics of water absorbed in amorphous and semicrystalline aromatic polyamide copolymers. The combination of dielectric spectroscopy and quasi-elastic neutron scattering experiments allows us to characterize the water dynamics over a wide range of temperatures (dielectric spectroscopy) and at microscopic length scales (neutron scattering). The dielectric investigation evidences two relaxations associated with water motions: a fast process corresponding to motions of loosely bonded water molecules and a slower process corresponding to motions of amide-water complexes. While the slower process presents the characteristic Arrhenius temperature dependence of a secondary local relaxation over the whole temperature range, the fast process shows a crossover from Arrhenius to Vogel-Fulcher-Tamman (VFT) behavior at T approximate to 225 K, characteristic of confined water dynamics. The microscopic investigation by neutron scattering shows than in the VFT regime of the fast process the dynamics present a diffusive nature similar to bulk water. A large distribution of diffusion coefficients indicates possible differences in the connectivity of the hydrogen bond network. Diffusive heterogeneous dynamics can arise from a nonuniform distribution of water. The confinement effect of the polymer matrix is detected as a considerable reduction of the diffusion coefficient of water with respect to bulk. The presence of a crystalline phase results in a slowing down of both the fast and slow processes involving water motions. This could give a hint to the presence of a rigid amorphous phase in the semicrystalline material.

Dynamics of well-folded and natively disordered proteins in solution: a time-of-flight neutron scattering study - Gaspar, A. M.; Appavou, Marie-Sousai; Busch, Sebastian; Unruh, Tobias; Doster, Wolfgang (European Biophysics Journal, 2008)
Casein proteins belong to the class of natively disordered proteins. The existence of disordered biologically active proteins questions the assumption that a well-folded structure is required for function. A hypothesis generally put forward is that the unstructured nature of these proteins results from the functional need of a higher flexibility. This interplay between structure and dynamics was investigated in a series of time-of-flight neutron scattering experiments, performed on casein proteins, as well as on three well-folded proteins with distinct secondary structures, namely, myoglobin (alpha), lysozyme (alpha/beta) and concanavalin A (beta). To illustrate the subtraction of the solvent contribution from the scattering spectra, we used the dynamic susceptibility spectra emphasizing the high frequency part of the spectrum, where the solvent dominates. The quality of the procedure is checked by comparing the corrected spectra to those of the dry and hydrated protein with negligible solvent contamination. Results of spectra analysis reveal differences in motional amplitudes of well-folded proteins, where beta-sheet structures appear to be more rigid than a cluster of alpha-helices. The disordered caseins display the largest conformational displacements. Moreover their global diffusion rates deviate from the expected dependence, suggesting further large-scale conformational motions.

Dynamic superlubricity on insulating and conductive surfaces in ultra-high vacuum and ambient environment - Gnecco, Enrico; Socoliuc, Anisoara; Maier, Sabine; Gessler, Jonas; Glatzel, Thilo; Baratoff, Alexis; Meyer, Ernst (Nanotechnology, 2009)
Atomic-scale friction between a sharp tip at the end of a micro-fabricated silicon cantilever and atomically flat surfaces (NaCl, KBr, HOPG and mica) can be significantly reduced by piezo-induced perpendicular mechanical oscillations at specific resonance frequencies of the cantilever in gentle contact with the sample. The reported measurements confirm and extend the applicability of the effect recently demonstrated using electro-capacitive actuation on alkali halide surfaces in ultra-high vacuum (Socoliuc et al 2006 Science 313 208). A controlled reduction of friction is now observed even on a conductive surface and under ambient conditions, which is quite promising for applications to micro-electromechanical devices. The theory previously used to interpret 'dynamic superlubricity' is supported by new measurements showing that the contact can be maintained in that regime and that the initial reduction of friction is linear versus oscillation amplitude. The calibration of the oscillating component of the normal force is also discussed.

Dynamic traction force measurements of migrating immune cells in 3D matrices - Böhringer, David; Cóndor, Mar; Bischof, Lars; Czerwinski, Tina; Gampl, Niklas; Ngo, Phuong; Bauer, Andreas; Bosch-Voskens, Caroline; Lopez Posadas, Rocío; Franze, Kristian; Budday, Silvia; Mark, Christoph; et al. (2025)
Immune cells such as natural killer (NK) cells migrate with high speeds of several µm/min through dense tissue, but the traction forces are unknown. We present a method to measure dynamic traction forces of fast migrating cells in non-linear biopolymer matrices. The method accounts for the mechanical non-linearity of the 3D tissue matrix and can be applied to time series of confocal or bright-field image stacks. The method is highly sensitive over a large range of forces and object sizes, from ∼1 nN for axon growth cones up to ∼10 µN for mouse intestinal organoids. We find that NK cells display bursts of large traction forces that increase with matrix stiffness and facilitate migration through tight constrictions.<br
https://cris.fau.de/converis/publicweb/Publication/321683487

Early signs of architectural and biomechanical failure in isolated myofibers and immortalized myoblasts from desmin-mutant knock-in mice - Diermeier, Stefanie; Iberl, Julian; Vetter, Karoline; Haug, Michael; Pollmann, Charlotte; Reischl, Barbara; Buttgereit, Andreas; Schürmann, Sebastian; Spörrer, Marina; Goldmann, Wolfgang; Fabry, Ben; Elhamine, Fatiha; et al. (Scientific Reports, 2017)
In striated muscle, desmin intermediate filaments interlink the contractile myofibrillar apparatus with mitochondria, nuclei, and the sarcolemma. The desmin network's pivotal role in myocytes is evident since mutations in the human desmin gene cause severe myopathies and cardiomyopathies. Here, we investigated skeletal muscle pathology in myofibers and myofibrils isolated from young hetero- and homozygous R349P desmin knock-in mice, which carry the orthologue of the most frequent human desmin missense mutation R350P. We demonstrate that mutant desmin alters myofibrillar cytoarchitecture, markedly disrupts the lateral sarcomere lattice and distorts myofibrillar angular axial orientation. Biomechanical assessment revealed a high predisposition to stretch-induced damage in fiber bundles of R349P mice. Notably, Ca(2)(+)-sensitivity and passive myofibrillar tension were decreased in heterozygous fiber bundles, but increased in homozygous fiber bundles compared to wildtype mice. In a parallel approach, we generated and subsequently subjected immortalized heterozygous R349P desmin knock-in myoblasts to magnetic tweezer experiments that revealed a significantly increased sarcolemmal lateral stiffness. Our data suggest that mutated desmin already markedly impedes myocyte structure and function at pre-symptomatic stages of myofibrillar myopathies.
EVALuna2:7360

Early stages of oxide growth in H-terminated silicon nanowires: determination of kinetic behavior and activation energy - Bashouti, Muhammad Y.; Sardashti, Kasra; Ristein, Jürgen; Christiansen, Silke H. (Physical Chemistry Chemical Physics, 2012)
Silicon nanowires (Si NWs) terminated with hydrogen atoms exhibit higher activation energy under ambient conditions than equivalent planar Si(100). The kinetics of sub-oxide formation in hydrogen-terminated Si NWs derived from the complementary XPS surface analysis attribute this difference to the Si-Si backbond and Si-H bond propagation which controls the process at lower temperatures (T < 200°C). At high temperatures (T ≥ 200°C), the activation energy was similar due to self-retarded oxidation. This finding offers the understanding of early-stage oxide growth that affects the conductance of the near-gap channels leading towards more efficient Si NW electronic devices. This journal is © 2012 the Owner Societies.
UnivIS-Import:2015-03-09:Pub.2012.nat.dphy.IAP.exphys.earlys

Echo time dependence of biexponential and triexponential intravoxel incoherent motion parameters in the liver - Führes, Tobit; Riexinger, Andreas; Loh, Martin; Martin, Jan; Wetscherek, Andreas; Kuder, Tristan Anselm; Uder, Michael; Hensel, Bernhard; Laun, Frederik Bernd (Magnetic Resonance in Medicine, 2021)
Purpose Intravoxel incoherent motion (IVIM) studies are performed with different acquisition protocols. Comparing them requires knowledge of echo time (TE) dependencies. The TE-dependence of the biexponential perfusion fraction f is well-documented, unlike that of its triexponential counterparts f(1) and f(2) and the biexponential and triexponential pseudodiffusion coefficients D*, D1*, and D2*. The purpose was to investigate the TE-dependence of these parameters and to check whether the triexponential pseudodiffusion compartments are associated with arterial and venous blood. Methods Fifteen healthy volunteers (19-58 y; mean: 24.7 y) underwent diffusion-weighted imaging of the abdomen with 24 b-values (0.2-800 s/mm(2)) at TEs of 45, 60, 75, and 90 ms. Regions of interest (ROIs) were manually drawn in the liver. One set of bi- and triexponential IVIM parameters per volunteer and TE was determined. The TE-dependence was assessed with the Kruskal-Wallis test. Results TE-dependence was observed for f (P < .001), f(1) (P = .001), and f(2) (P < .001). Their median values at the four measured TEs were: f: 0.198/0.240/0.274/0.359, f(1): 0.113/0.139/0.146/0.205, f(2): 0.115/0.155/0.182/0.194. D, D*, D1*, and D2* showed no significant TE-dependence. Their values were: diffusion coefficient D (10(-4) mm(2)/s): 9.45/9.63/9.75/9.41, biexponential D* (10(-2) mm(2)/s): 5.26/5.52/6.13/5.82, triexponential D1* (10(-2) mm(2)/s): 1.73/2.91/2.25/2.51, triexponential D2* (mm(2)/s): 0.478/1.385/0.616/0.846. Conclusion f(1) and f(2) show similar TE-dependence as f, ie, increase with rising TE; an effect that must be accounted for when comparing different studies. The diffusion and pseudodiffusion coefficients might be compared without TE correction. Because of the similar TE-dependence of f(1) and f(2), the triexponential pseudodiffusion compartments are most probably not associated to venous and arterial blood.
CRIS-Team WoS Importer:2021-09-10

Edge and confinement effects allow in situ measurement of size and thickness of liquid-exfoliated nanosheets - Backes, Claudia; Smith, Ronan J.; McEvoy, Niall; Berner, Nina; McCloskey, David; Nerl, Hannah C.; O'Neill, Arlene; King, Paul J.; Higgins, Tom; Hanlon, Damien; Scheuschner, Nils; Maultzsch, Janina; et al. (Nature Communications, 2014)
Two-dimensional nanomaterials such as MoS2 are of great interest both because of their novel physical properties and their applications potential. Liquid exfoliation, an important production method, is limited by our inability to quickly and easily measure nanosheet size, thickness or concentration. Here we demonstrate a method to simultaneously determine mean values of these properties from an optical extinction spectrum measured on a liquid dispersion of MoS2 nanosheets. The concentration measurement is based on the size-independence of the low-wavelength extinction coefficient, while the size and thickness measurements rely on the effect of edges and quantum confinement on the optical spectra. The resultant controllability of concentration, size and thickness facilitates the preparation of dispersions with pre-determined properties such as high monolayer-content, leading to first measurement of A-exciton MoS2 luminescence in liquid suspensions. These techniques are general and can be applied to a range of two-dimensional materials including WS2, MoSe2 and WSe2.

Effective Ligand Engineering of the Cu2ZnSnS4 Nanocrystal Surface for Increasing Hole Transport Efficiency in Perovskite Solar Cells - Khanzada, Laraib Sarfraz; Levchuk, Ievgen; Hou, Yi; Azimi, Seyed Hamed; Osvet, Andres; Ahmad, Rameez; Brandl, Marco; Herre, Patrick; Distaso, Monica; Hock, Rainer; Peukert, Wolfgang; Batentschuk, Miroslaw; et al. (Advanced Functional Materials, 2016)
Effective engineering of surface ligands in semiconductor nanocrystals can facilitate the electronic interaction between the individual nanocrystals, making them promising for low-cost optoelectronic applications. Here, the use of high purity CuZnSnS (CZTS) nanocrystals as the photoactive layer and hole-transporting material is reported in low-temperature solution-processed solar cells. The high purity CZTS nanocrystals are prepared by engineering the surface ligands of CZTS nanocrystals, capped originally with the long-chain organic ligand oleylamine. After ligand removal, CZTS nanocrystals show substantial improvement in photoconductivity and mobility, displaying also an appreciable photoresponse in a simple heterojunction solar cell architecture. More notably, CZTS nanocrystals exhibit excellent hole-transporting properties as interface layer in perovskite solar cells, yielding power conversion efficiency (PCE) of 15.4% with excellent fill factor (FF) of 81%. These findings underscore the importance of removing undesired surface ligands in nanocrystalline optoelectronic devices, and demonstrate the great potential of CZTS nanocrystals as both active and passive material for the realization of low-cost efficient solar cells.
Keywords: CZTS solar cells; HTM; Inorganic nanocrystals; Ligand exchange; Perovskite

Effective Wavelength Scaling of and Damping in Plasmonic Helical Antennae - Caridad, Jose M.; McCloskey, David; Rossella, Francesco; Bellani, Vittorio; Donegan, John F.; Krstic, Vojislav (ACS Photonics, 2015)
We report on the optical performance of metallic nanohelices as the extension of the helical antenna concept into the optical wavelength range. These helical nanoparticles exhibit a structure and material dependent optical response due to the existence of a longitudinal localized-plasmon resonance which scales linearly with the total length of the helix; thus, comprising the number of turns and the single-turn length of the nanohelix. This is in contrast with macroscopic metallic helices, where the scaling of their operational mode is only determined by the length of a single turn. We show how the plasmon damping is radiated or absorbed depending on the interband activity of the metal forming the nanohelix. This study demonstrates the ability of helical structures to control and manipulate optical fields at the nanometer scale according to their specific shape and material composition.

Effect of Bromide on the Surfactant Stabilization Layer Density of Gold Nanorods - Zech, Tobias; Schmutzler, Tilo; Noll, Dennis; Appavou, Marie-Sousai; Unruh, Tobias (Langmuir, 2022)
Some studies have speculated that the concentration of bromide ions plays a crucial role in the surfactant density surrounding gold nanorods (AuNR). Small-angle X-ray and neutron scattering (SAXS and SANS) experiments were conducted to analyze any influence the bromide ions might have on the stabilization layer and the aggregation behavior of the ligand CTAB molecules in general. The AuNR were immersed in solutions containing a fixed CTA+ concentration of 2 mM and varying bromide ion concentrations from 0 to 22 mM. A patchy AuNR stabilization shell at low bromide ion concentrations was found, contrary to previously published SANS studies on the AuNR stabilization shell. However, with increasing bromide ion concentration, the density of the stabilization shell increases asymptotically toward a closed/collapsed bilayer configuration. AuNR grown under similar conditions show higher anisotropy with larger bromide ion concentrations. Both results indicate that anisotropic growth strongly depends on a sufficiently dense stabilization layer established by high bromide ion concentrations.
CRIS-Team WoS Importer:2022-03-18

Effect of compression garments on muscle perfusion in delayed-onset muscle soreness: A quantitative analysis using intravoxel incoherent motion MR perfusion imaging - Riexinger, Andreas; Laun, Frederik Bernd; Hoeger, Svenja Alina; Wiesmüller, Marco; Uder, Michael; Hensel, Bernhard; Forst, Raimund; Hotfiel, Thilo; Heiß, Rafael (NMR in Biomedicine, 2021)
The aim of this prospective cohort study was to evaluate the effect of compression garments under resting conditions and after the induction of delayed-onset muscle soreness (DOMS) by MR perfusion imaging using intravoxel incoherent motion (IVIM). Magnetic resonance imaging of both lower legs of 16 volunteers was performed before and after standardized eccentric exercises that induced DOMS. A compression garment (21–22 mmHg) was worn during and for 6 h after exercise on one randomly selected leg. IVIM MR imaging, represented as total muscle perfusion D*f, perfusion fraction f and tissue diffusivity D, were compared between baseline and directly, 30 min, 6 h and 48 h after exhausting exercise with and without compression. Creatine kinase levels and T2-weighted images were acquired at baseline and after 48 h. DOMS was induced in the medial head of the gastrocnemius muscle (MGM) in all volunteers. Compression garments did not show any significant effect on IVIM perfusion parameters at any time point in the MGM or the tibialis anterior muscle (p > 0.05). Microvascular perfusion in the MGM increased significantly in both the compressed and noncompressed leg between baseline measurements and those taken directly after and 30 min after the exercise: the relative median f increased by 31.5% and 24.7% in the compressed and noncompressed leg, respectively, directly after the exercise compared with the baseline value. No significant change in tissue perfusion occurred 48 h after the induction of DOMS compared with baseline. It was concluded that compression garments (21–22 mmHg) do not alter microvascular muscle perfusion at rest, nor do they have any significant effect during the regeneration phase of DOMS. In DOMS, only a short-term effect of increased muscle perfusion (30 min after exercise) was observed, with normalization occurring during regeneration after 6–48 h. The normalization of perfusion independently of compression after 6 h may have implications for diagnostic and therapeutic strategies and for the better understanding of pathophysiological pathways in DOMS.
CRIS-Team Scopus Importer:2021-03-05
Keywords: calf; exercise; intravoxel incoherent motion; magnetic resonance imaging; muscle injury

Effect of gap modes on graphene and multilayer graphene in tip-enhanced Raman spectroscopy - Poliani, Emanuele; Nippert, Felix; Maultzsch, Janina (physica status solidi (b), 2012)
The experimental system formed by an electrochemically etched Au tip and an Au substrate is studied in a tip-enhanced Raman spectroscopy (TERS) setup with side illumination. A resonant optical cavity is created allowing the interaction between localized surface plasmons (LSPs) from the tip and surface plasmon polaritons (SPPs) from the substrate, the so called gap modes. We investigate the interaction between multilayer graphene and gap modes as well as localized emission of defects and inner unknown molecules enhanced by this coupling. The effect of this intense localized electromagnetic field is also studied on monolayer graphene deposited on SiO2. Graphical representation of TERS on graphene.
Keywords: amorphization; gap modes; graphene; TERS

Effect of germanium doping on electrical properties of n-type 4H-SiC homoepitaxial layers grown by chemical vapor deposition - Sledziewski, Tomasz; Vivona, M.; Alassaad, K.; Kwasnicki, P.; Arvinte, R.; Beljakowa, Svetlana; Weber, Heiko B.; Giannazzo, F.; Peyre, H.; Souliere, V.; Chassagne, T.; Zielinski, M.; et al. (Journal of Applied Physics, 2016)
The effect of germanium (Ge) on n-type 4H-SiC is experimentally studied by electrical characterization of homoepitaxial layers grown by chemical vapor deposition (CVD). Measurements show that electrical properties of epitaxial layers can be changed by intentional incorporation of germane (GeH4) gas during the deposition process. On the nanoscale, two-dimensional mappings acquired with conductive atomic force microscopy show preferential conductive paths on the surface of Ge-doped samples, which are related to the presence of this isoelectronic impurity. Hall effect measurements confirm that also macroscopic electrical properties of n-type 4H-SiC are improved due to incorporation of Ge into SiC during CVD growth. In particular, despite equal free electron concentration, enhanced mobility in a wide temperature range is measured in Ge-doped samples as compared to a pure 4H-SiC layer. Based on our results from Hall effect measurements as well as admittance spectroscopy and deep level transient spectroscopy, it is speculated that Ge influences the generation and annealing of other point defects and thus helps to reduce the total concentration of defects. Published by AIP Publishing.

Effect of mechanical activation on ignition and combustion of Ti-BN and Ti-SiC-C blends - Shkodich, N. F.; Rogachev, A. S.; Vadchenko, S. G.; Sachkova, N. V.; Neder, Reinhard; Magerl, Andreas (International Journal of Self-Propagating High-Temperature Synthesis, 2011)
Explored was the effect of mechanical activation on ignition and combustion of Ti-BN and Ti-SiC-C blends. Activated blends and combustion products were characterized by high-precision XRD and SEM. SHS in the systems under study was found to proceed in a mode of solid flame (no melted intermedi-ates/products). © 2011 Allerton Press, Inc.
Keywords: Combustion; Ignition; Mechanical activation; SHS; Ti-BN; Ti-SiC-C

Effect of shallow n-doping on field effect mobility in p-doped channels of 4H-SiC MOS field effect transistors - Noll, Stefan; Rambach, Martin; Grieb, Michael; Scholten, Dick; Bauer, Anton; Frey, Lothar (Trans Tech Publications Ltd, 2014)
A high inversion channel mobility is a key parameter of normally off Silicon-Carbide MOS field effect power transistors. The mobility is limited by scattering centers at the interface between the semiconductor and the gate-oxide. In this work we investigate the mobility of lateral normally-off MOSFETs with different p-doping concentrations in the channel. Additionally the effect of a shallow counter n-doping at the interface on the mobility was determined and, finally, the properties of interface traps with the charge pumping method were examined. A lower p-doping in the cannel reduces the threshold voltage and increases the mobility simultaneously. A shallow counter n-doping shows a similar effect, but differences in the behavior of the charge pumping current can be observed, indicating that the nitrogen has a significant effect on the electrical properties of the interface, too. © (2014) Trans Tech Publications, Switzerland.
Keywords: 4H-SiC MOSFET; Doping; Threshold voltage

Effect of spiral undersampling patterns on FISP MRF parameter maps - Körzdörfer, Gregor; Pfeuffer, J.; Kluge, Thomas; Gebhardt, Matthias; Hensel, Bernhard; Meyer, Craig H.; Nittka, Mathias (Magnetic Resonance Imaging, 2019)
Purpose: Artifacts arising from undersampling are not always treatable as incoherent noise for the pattern matching process in Magnetic Resonance Fingerprinting (MRF). To estimate the effect of undersampling artifacts on MRF quantitative results, spiral sampling trajectories and their temporal variation is examined. Methods: The effect of sampling trajectories and their variation during the MRF experiment was assessed by characterizing aliasing artifacts. Temporal rearrangements of sampling trajectories were tested and evaluated in simulations and scans of phantoms and in a volunteer brain. Results: Results show that some temporal variations of sampling patterns can lead to spatial biases in MRF parameter maps. Observed effects are consistent with derived performance indicators for different interleaving schemes, leading to substantially improved MRF sampling patterns. Conclusion: With the help of the presented simulation framework, MRF implementations can be investigated and improved. This was demonstrated for a spiral FISP (Fast imaging with steady-state free precession) MRF implementation, where a significantly improved interleaving scheme was identified, and confirmed by experiment.
CRIS-Team Scopus Importer:2019-07-19
Keywords: Magnetic Resonance Fingerprinting; Quantitative MRI; Spiral imaging

Effect of Structure and Disorder on the Charge Transport in Defined Self-Assembled Monolayers of Organic Semiconductors - Schmaltz, Thomas; Gothe, Bastian; Krause, Andreas; Leitherer, Susanne; Steinrück, Hans-Georg; Thoss, Michael; Clark, Timothy; Halik, Marcus (Acs Nano, 2017)
Self-assembled monolayer field-effect transistors (SAMFETs) are not only a promising type of organic electronic device but also allow detailed analyses of structure-property correlations. The influence of the morphology on the charge transport is particularly pronounced, due to the confined monolayer of 2D- extgreekp-stacked organic semiconductor molecules. The morphology, in turn, is governed by relatively weak van-der-Waals interactions and is thus prone to dynamic structural fluctuations. Accordingly, combining electronic and physical characterization and time-averaged X-ray analyses with the dynamic information available at atomic resolution from simulations allows us to characterize self-assembled monolayer (SAM) based devices in great detail. For this purpose, we have constructed transistors based on SAMs of two molecules that consist of the organic p-type semiconductor benzothieno[3,2-b][1]benzothiophene (BTBT), linked to a C11 or C12 alkylphosphonic acid. Both molecules form ordered SAMs; however, our experiments show that the size of the crystalline domains and the charge-transport properties vary considerably in the two systems. These findings were confirmed by molecular dynamics (MD) simulations and semiempirical molecular-orbital electronic-structure calculations, performed on snapshots from the MD simulations at different times, revealing, in atomistic detail, how the charge transport in organic semiconductors is influenced and limited by dynamic disorder.

Effect of TCNQ Layer Cover on Oxidation Dynamics of Black Phosphorus - Meingast, Laura; Kolesnik-Gray, Maria; Siebert, Martin; Abellán, Gonzalo; Wild, Stefan; Lloret, Vicent; Mundloch, Udo; Hauke, Frank; Hirsch, Andreas; Krstic, Vojislav (Physica Status Solidi-Rapid Research Letters, 2018)
Keywords: Dynamics; Oxidation; Black phosphorus; TCNQ

Effect of TCNQ Layer Cover on Oxidation Dynamics of Black Phosphorus - Meingast, Laura; Kolesnik-Gray, Maria; Siebert, Martin; Abellan Saez, Gonzalo; Wild, Stefan; Lloret Segura, Vicente Josep; Mundloch, Udo; Hauke, Frank; Hirsch, Andreas; Krstic, Vojislav (Physica Status Solidi-Rapid Research Letters, 2018)
The puckered surface of black phosphorus represents an ideal substrate for an unconventional arrangement of physisorbed species and the resulting specific two-dimensional chemistry of this system. This opens the way to investigate the chemical and physical properties of locally confined areas of black phosphorus without the necessity for further physical downscaling of the material. We have evaporated tetracyanoquinodimethane (TCNQ) on top of black phosphorus under over-saturation non-equilibrium conditions in vacuum. The evolution of linear density and height of droplets formed through oxidation during exposure to air is studied time dependently by scanning-force microscopy. Our study suggests that the TCNQ molecules spontaneously arrange in a thin layer of the order of a few nm height, which, however, is fragmented with a periodicity of about 100nm. It is shown that within the confined space separating the layer fragments the chemical dynamics of the oxidation process is remarkably different than on a bare black phosphorus surface.
Keywords: black phosphorus; dynamics; oxidation; TCNQ

Effects of annealing on optical and structural properties of zinc oxide nanocrystals - Khachadorian, Sevak; Gillen, Roland; Choi, S.; Thon-Tat, C; Kliem, Andre; Maultzsch, Janina; Phillips, Matthew R.; Hoffmann, Axel (physica status solidi (b), 2015)
The optical and vibrational properties of zinc oxide nanocrystals (ZnO NCs), grown by chemical precipitation method, were investigated following thermal annealing treatments in oxygen, argon, and zinc vapors at temperatures up to 900 degrees C. Raman scattering and photoluminescence techniques were utilized to show the effect of temperature annealing in various environments on optical and structural properties of ZnO NCs, referring them to the reduction and increase of certain intrinsic defect concentrations. The experimental results are complemented by density functional theory calculations for understanding the correlation between Raman modes induced with different annealing procedures and certain intrinsic point defects. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhe
Keywords: annealing; density functional theory; nanocrystals; photoluminescence; Raman spectroscopy; ZnO

Effects of geometry of nano-structured materials on their thermal expansion: tellurium nanocylinders as model system - Krstic, Vojislav; Rikken, Geert L.J.A.; Kaempgen, Martti; Roth, Siegmar; Beukes, Jon A. (International Journal of Materials and Structural Integrity, 2007)
The temperature-dependence of the atomic bond-lengths and -angles of the unit cell of crystalline tellurium nanocylinders (a few µm in length and some 100 nm in diameter) have been investigated by X-ray diffraction in the range from 370 K to 100 K. With decrease in temperature, significant deviations from the established temperature-dependence of the bulk tellurium lattice parameters are observed. The observations in the temperature expansion are attributed to the nano-size and symmetry of the tellurium nanocylinders. The study demonstrates that a qualitative change in the material's properties is achieved when approaching the nano-scale. This opens the road for the possibility of deliberate tailoring of materials properties by proper choice of size and symmetry for thermo-mechanical applications.
Keywords: nano-cylinder; tellurium; nano-material; X-ray diffraction; thermal properties

Effects of mechanical unloading/loading on respiratory loop gain and periodic breathing in man - Haberthür, Christoph; Fabry, Ben; Zappe, Detlef; Guttmann, Josef (RESP PHYSIOL, 1998)

Effektive correlation energies for defects in a-C:H from a comparison of photoelectron yield and electron spin resonance experiments - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 1995)
UnivIS-Import:2015-03-05:Pub.1995.nat.dphy.IAP.exphys.effekt

Efficient III-V tunneling diodes with ErAs recombination centers - Preu, Sascha; Malzer, Stefan; Döhler, Gottfried; Lu, Hong; Gossard, Art; Wang, Lijun (Semiconductor Science and Technology, 2010)
We report on recombination diodes containing monolayer depositions of ErAs between highly doped n- and p-layers in the (Al)GaAs and In(Al)GaAs material system. The ErAs material provides metallic states across the band gap of the host semiconductor that act as efficient recombination centers. Both electrons and holes can tunnel into the ErAs, resulting in extremely high tunneling current densities in the tens of kA cm range. A device resistance area product of 1-2 × 10 Ω cm at low bias (±0.2 V) has been measured. Measurements on In(Al)GaAs and (Al)GaAs diodes will be compared to a simple theoretical model. Low band gap and high (p-) doping levels are identified as key parameters for achieving highest recombination currents. Compared to ErAs-free diodes, ErAs-enhanced recombination diodes provide orders of magnitude higher current densities at both moderate and low forward and reverse bias. This is attributed to the smaller and narrower tunnel barriers from the n- and p-layers into the ErAs compared to tunneling from the n- to the p-side through the whole depletion region. © 2010 IOP Publishing Ltd.

Efficient optical up-conversion by coherent sum-frequency generation for highly sensitive terahertz detection - Sedlmeir, Florian; Schwefel, Harald; Strekalov, Dmitry V.; Bauerschmidt, Sebastian; Preu, Sascha; Malzer, Stefan; Döhler, Gottfried; Leuchs, Gerd (2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011, 2011)
Detection of weak THz signals is very challenging due to the extremely low energy of one THz photon (temperature equivalent of 48K). Frequency up-conversion to the near infra-red (NIR) and subsequent detection of the up-converted photon with sensitive, low-noise detectors is one way to achieve this task, albeit suffering form extremely poor conversion rates. Whispering gallery mode resonators (WGMRs), however, support well confined modes with high quality factors (Q) and extremely high field intensities inside the resonator, thus allowing efficient non-linear conversion rates. © 2011 IEEE.

Efficient Polymer Solar Cells Based on Non-fullerene Acceptors with Potential Device Lifetime Approaching 10 Years - Du, Xiaoyan; Heumüller, Thomas; Gruber, Wolfgang; Classen, Andrej; Unruh, Tobias; Li, Ning; Brabec, Christoph (Joule, 2019)
Organic solar cells (OSCs) based on non-fullerene acceptors (NFAs) have developed very fast in recent years. A proper balance among power conversion efficiency (PCE), stability, and production cost needs further elaboration. Here we investigate the industrial viability of highly efficient OSCs based on several representative NFAs. The most stable OSCs exhibit PCE of ∼8% along with extrapolated T 80 lifetime (80% of the initial PCE) of over 11,000 hr under equivalent 1 sun illumination, which would lead to a very impressive operational lifetime approaching 10 years. Photo-stability is strongly dependent on the end-group and side-chain engineering of the NFAs. Breaking of conjugation during photo-aging leads to increased energetic traps. Fluorination of the end-group stabilizes molecules against light soaking, while adding methyl groups shows an opposite trend. Side-chain modification can significantly influence the morphological stability. Reducing synthetic complexity of this class of NFAs will ultimately push the organic photovoltaics technology into real-life applications. © 2018 Elsevier Inc. We investigate the industrial viability of highly efficient organic solar cells (OSCs) based on several representative non-fullerene acceptors (NFAs) by taking into consideration the three essential parameters: power conversion efficiency, photo-stability, and materials cost. End-group and side-chain modifications of NFAs strongly influence long-term photo-stability. Promising extrapolated operational lifetime approaching 10 years has been demonstrated with the most stable system. Industrial figure of merit (i-FoM) analysis highlights the importance of lowering the synthetic complexity of the NFAs for commercialization of this technology. © 2018 Elsevier Inc. Organic solar cells with non-fullerene acceptors (NFAs) have developed rapidly in recent years. Breakthroughs in power conversion efficiency (PCE) have significantly raised the confidence in the community for commercialization of this technology. In the phase of developing new materials via molecular engineering, more attention should be paid on industrial figure of merit (i-FoM), which considers the balance of PCE, stability, and production cost. Here we investigate industrial viability of highly efficient organic solar cells based on several representative NFAs. Molecular engineering on both end-groups and side chains significantly influences the long-term stability of organic solar cells by altering the intrinsic chemical stability of the molecules under light soaking as well as morphological stability. Promising lifetime approaching 10 years is demonstrated in stable candidates. Reducing synthetic complexity is highlighted in order to push this technology into real-life appli
Keywords: non-fullerene acceptors; organic photovoltaics; device operational stability; industrial figure of merit; bulk-heterojunction morphology

Efficient solution of particle shape functions for the analysis of powder total scattering data - Leonardi, Alberto; Neder, Reinhard; Engel, Michael (Journal of Applied Crystallography, 2022)
Structural characterization of powder samples via total scattering methods, in either real or reciprocal space, must take into account the effect of particle shape. Here, the shape contribution of a set of ideally isolated particles to the small-angle scattering (SAS) component of the intensity profile is modelled using the shape function [Svergun & Koch (2003). Rep. Prog. Phys. 66, 17351782]. The shape function is obtained by orientational averaging of common volume functions (CVFs) for a discrete set of directions. The effects of particle size and size dispersity are accounted for via scaling of the CVFs and their convolution with the underlying probability distribution. The method is applied to shapes with CVFs expressed analytically or by using discrete tables. The accurate calculation of SAS particle shape contributions up to large momentum transfer demonstrates the reliability and flexibility of modelling shape functions from sets of CVFs. The algorithm presented here is computationally efficient and can be directly incorporated into existing routines for analysis of powder total scattering data.
CRIS-Team WoS Importer:2022-04-22

Efficient terahertz emission from ballistic transport enhanced n-i-p-n-i-p superlattice photomixers - Preu, Sascha; Renner, Frank; Malzer, Stefan; Döhler, Gottfried; Wang, Lijun; Hanson, Micah; Gossard, Art; Wilkinson, T.L.J.; Brown, Elliott R. (Applied Physics Letters, 2007)
The authors report on photomixing terahertz sources that overcome the transit time versus RC -time trade-off and allow for independent optimization of both of them, using a n-i-p-n-i-p superlattice. Furthermore, they take advantage of ballistic transport for reduced transit times. Apart from more favorable material parameters, In(Al)GaAs photomixers benefit from the advanced telecommunication laser technology around 1.55 μm as compared to GaAs. In such devices, a terahertz-power output of 1 μW has been achieved at 0.4 THz at a photocurrent of 3.8 mA. A comparison between corresponding GaAs- and InGaAs-based n-i-p-n-i-p photomixers reveals an improvement of performance by at least an order of magnitude for the latter one. © 2007 American Institute of Physics.

Elasticity of single-crystalline graphite: Inelastic x-ray scattering study - Maultzsch, Janina; et al. (Physical Review B, 2007)
The five independent elastic moduli of single-crystalline graphite are determined using inelastic x-ray scattering. At room temperature the elastic moduli are, in units of GPa, C-11=1109, C-12=139, C-13=0, C-33=38.7, and C-44=4.95. Our experimental results are compared with predictions of ab initio calculations and previously reported incomplete and contradictory data sets. We obtain an upper limit of 1.1 TPa for the on-axis Young's modulus of homogeneous carbon nanotube, thus providing important constraints for further theoretical advances and quantitative input to model elasticity in graphite nanotubes.

Elastic scattering in image-potential bands observed by two-photon photoemission - Boger, Klaus; Fauster, Thomas; Weinelt, Martin (New Journal of Physics, 2005)
Adsorbate atoms on surfaces cause considerable scattering of electrons. In image-potential bands, elastic scattering rates can be determined by measuring the linewidth in angle-, time- and energy-resolved two-photon photoelectron spectroscopy. From these data, the total cross section for elastic scattering of electrons in the first image-potential band on the Cu(0 0 1) surface by statistically distributed Cu adatoms has been determined. For large parallel momenta of the electron, the scattering by an adatom can be described by a dipole potential.

Electrical conduction of carbon nanotube forests through sub-nanometric films of alumina - Robertson, John; Esconjauregui, Santiago; Xie, Rongxi; Guo, Yuzheng; Pfaendler, Sieglinde; Fouquet, Martin; Gillen, Roland; Cepek, C; Castellarin-Cudia, C.; Eslava, S. (Applied Physics Letters, 2013)

Electrical Conductivity in BaTi1-xFexO3-d system - Göbbels, Matthias; Hock, Rainer; Magerl, Andreas; Mashkina, Elena; Demin, A.G.; et al. (Proceeding of Fifth European Solid Oxide Fuel Cell Forum, 2002)
UnivIS-Import:2015-04-16:Pub.2002.nat.dphy.IAP.LK.electr_32

Electrical investigations on metal/ferroelectric/insulator/semiconductor structures using poly[vinylidene fluoride trifluoroethylene] as ferroelectric layer for organic nonvolatile memory applications - Henkel, Karsten; Lazareva, Irina; Mandal, Dipankar; Paloumpa, Johanna; Koval, Yury; Müller, Paul; et al. (Journal of Vacuum Science & Technology B, 2009)
Poly[vinylidene fluoride trifluoroethylene] (P[VDF/TrFE]) is a ferroelectric polymer and a candidate for the application in a ferroelectric field effect transistor, which is considered as a nonvolatile and nondestructive readout memory cell. In this contribution the authors focus on metal/ferroelectric/insulator/semiconductor capacitor structures with P[VDF/TrFE] as ferroelectric layer. Measuring the capacitance of Al/P [VDF/TrFE] / SiO2 /Si stacks in dependence of the applied bias and analyzing the oxide capacitance in dependence of the thickness of the ferroelectric layer, they observe a formation of an interfacial nonferroelectric layer. This layer is responsible for reduced values of polarization profound for thinner P[VDF/TrFE] layers in this system. Capacitance-time measurements at such stacks show the possibility to distinguish between a higher and a lower capacitance state for more than 5 days. Long-time measurements revealed imprint and fatigue-like behavior. © 2009 American Vacuum Society.

Electrical nanocharacterization of epitaxial graphene/silicon carbide Schottky contacts - Giannazzo, Filippo; Hertel, Stefan; Albert, Andreas; La Magna, Antonino; Roccaforte, Fabrizio; Krieger, Michael; Weber, Heiko B. (Materials Science Forum, 2014)
Epitaxial graphene fabricated by thermal decomposition of the Si-face of silicon carbide (SiC) forms a defined interface to the SiC substrate. As-grown monolayer graphene with buffer layer establishes an ohmic interface even to low-doped (e. g. [N] ≈ 1015 cm-3) SiC, and a specific contact resistance as low as ρC = 5.9×10-6 Ωcm2 can be achieved on highly n-doped SiC layers. After hydrogen intercalation of monolayer graphene, the so-called quasi-freestanding graphene forms a Schottky contact to n-type SiC with a Schottky barrier height of 1.5 eV as determined from C-V analysis and core level photoelectron spectroscopy (XPS). This value, however, strongly deviates from the respective value of less than 1 eV determined from I-V measurements. It was found from conductive atomic force microscopy (C-AFM) that the Schottky barrier is locally lowered on other crystal facets located at substrate step edges. For very small Schottky contacts, the barrier height extracted from I-V curves approaches the value of 1.5 eV from C-V and XPS. © (2014) Trans Tech Publications, Switzerland.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.LAP.electr
Keywords: Conductive AFM; Epitaxial graphene; H intercalation; Ohmic contact; Schottky barrier

Electrical properties of the hydrogen intercalated epitaxial graphene/SiC interface investigated by nanoscale current mapping - Giannazzo, F.; Hertel, Stefan; Albert, Andreas; Fisichella, G.; La Magna, A.; Roccaforte, F.; Krieger, Michael; Weber, Heiko B. (Materials Science Forum, 2015)
The electrical properties of the interface between quasi free standing bilayer graphene (QFBLG) and SiC(0001) have been investigated by nanoscale resolution current measurements using conductive atomic force microscopy (C-AFM). I-V analyses were carried out on Au-capped QFBLG contacts with different sizes (from 200 μm down to 0.5 m) fabricated on SiC samples with different miscut angles (from on-axis to 3.5° off-axis). The extracted QFBLG/SiC Schottky barrier height (SBH) was found to depend on the contact size. SBH values (0.9-1) eV were obtained for large contacts, whereas a gradual increase was observed below a critical (micrometer scale) contact size (depending on the SiC miscut angle) up to values approaching 1.5 eV. Nanoscale resolution current mapping on bare QFLBG contacts revealed that SiC step edges and facets represent preferential current paths causing the effective SBH lowering for larger contacts. The reduced barrier height in these regions can be explained in terms of a reduced doping of QFBLG from SiC substrate at (11-20) step edges with respect to the p-type doping on the (0001) terraces.
UnivIS-Import:2017-11-07:Pub.2015.nat.dphy.IAP.LAP.electr
Keywords: Conductive AFM; Epitaxial graphene; H intercalation; Schottky barrier

Electrical Transport in Devices Based on Edge-Fluorinated Graphene - Kolesnik-Gray, Maria; Sysoev, Vitalii I.; Gollwitzer, Stefan; Pinakov, Dmitry V.; Chekhova, Galina N.; Bulusheva, Lyubov G.; Okotrub, Alexander V.; Krstic, Vojislav (Advanced Electronic Materials, 2018)
The conductivity of few- and monolayer graphene with covalently bound moieties is a key-point in the potential application of these materials in any electrical and optoelectronic device. In particular, fluorination of such graphene-based systems is of interest, as fluorine is expected to have a strong influence on the charge-carrier density due to its high electronegativity, and therefore modify the electrical transport properties significantly. Here it is shown that, depending on the device architecture, the electrical properties of fluorinated graphene-based devices are significantly different. It is found that the conductivity of thin films of few-layer graphene decreases by several orders of magnitude with fluorine content increasing from 2.4 to 16.6 at%, whereas individual flakes show a significant increase in both conductivity and charge carrier mobility. This observation, combined with Raman microscopy study, points toward the fact that the edges of the flakes are primary sites for fluorine within the experimental range of fluorine content. The strong decrease in conductivity in the film devices is therefore associated with the high contact resistance between the fluorine saturated edges of the individual flakes.
Keywords: Fluorographene; Electrical properties; Fluorine content; Edge functionalization; Covalent functionalization

Electrical transport in single-walled carbon nanotube bundles embedded in Langmuir-Blodgett monolayers - Krstic, Vojislav; Muster, Jörg; Duesberg, Georg S.; Philipp, Günther; Burghard, Marko; Roth, Siegmar (Synthetic Metals, 2000)
Langmuir films consisting of single-walled carbon nanotubes and surfactant molecules were deposited on substrates with lithographically defined electrode arrays. Atomic force microscopy revealed a different matrix structure of the Langmuir–Blodgett monolayers compared to monolayers on bare substrates. Electrical transport measurements were performed on individual thin bundles at room temperature and 4.2 K. At low temperatures, the current/voltage characteristics show a non-linear dependence with step-like features, which are critically discussed in the frame of Coulomb charging theory and electron tunneling through discrete energy levels.
Keywords: Langmuir–Blodgett techniques; Atomic force microscopy; Transport measurements; Fullerene-like materials

Electrical transport through individual vanadium pentoxide nanowires - Muster, Jörg; Kim, Gyutae; Krstic, Vojislav; Park, Jin-gyu; Park, YungWoo; Roth, Siegmar; Burghard, Marko (Advanced Materials, 2000)
The controlled deposition of individual V2O5 nanowires on chemically modified SiO2 substrates is reported here. Electrical transport measurements were performed on individual fibers (see Figure) and on thin fiber networks, and the conductivity of an individual V2O5 nanowire was estimated to be ∼0.5 S/cm at room temperature. The structure of the fibers was investigated using scanning force microscopy.

Electric current through a molecular rod - Relevance of the position of the anchor groups - Mayor, Marcel; Weber, Heiko B.; Reichert, Joachim; Elbing, Mark; von Hänisch, Carsten; Beckmann, Detlef; Fischer, Matthias (Angewandte Chemie International Edition, 2003)
Keywords: anchor-group position; electron transport; molecular electronics; single-molecule studies; structure-activity relationships

Electrifying model catalysts for understanding electrocatalytic reactions in liquid electrolytes - Faisal, Firas; Stumm, Corinna; Bertram, Manon; Waidhas, Fabian; Lykhach, Yaroslava; Cherevko, Serhiy; Xiang, Feifei; Ammon, Maximilian Michael; Vorokhta, Mykhailo; Smid, Bretislav; Skala, Tomas; Tsud, Nataliya; et al. (Nature Materials, 2018)
Electrocatalysis is at the heart of our future transition to a renewable energy system. Most energy storage and conversion technologies for renewables rely on electrocatalytic processes and, with increasing availability of cheap electrical energy from renewables, chemical production will witness electrification in the near future(1-3). However, our fundamental understanding of electrocatalysis lags behind the field of classical heterogeneous catalysis that has been the dominating chemical technology for a long time. Here, we describe a new strategy to advance fundamental studies on electrocatalytic materials. We propose to 'electrify' complex oxide-based model catalysts made by surface science methods to explore electrocatalytic reactions in liquid electrolytes. We demonstrate the feasibility of this concept by transferring an atomically defined platinum/cobalt oxide model catalyst into the electrochemical environment while preserving its atomic surface structure. Using this approach, we explore particle size effects and identify hitherto unknown metal-support interactions that stabilize oxidized platinum at the nanoparticle interface. The metal-support interactions open a new synergistic reaction pathway that involves both metallic and oxidized platinum. Our results illustrate the potential of the concept, which makes available a systematic approach to build atomically defined model electrodes for fundamental electrocatalytic studies.

Electrochemical etching strategy for shaping monolithic 3D structures from 4H-SiC wafers - Hochreiter, André; Möller, Morris -Niklas; Groß, Fabian; Krieger, Michael; Weber, Heiko B. (Scientific Reports, 2023)
Silicon Carbide (SiC) is an outstanding material, not only for electronic applications, but also for projected functionalities in the realm of spin‑based quantum technologies, nano‑mechanical resonators and photonics on‑a‑chip. For shaping 3D structures out of SiC wafers, predominantly dry‑etching techniques are used. SiC is nearly inert with respect to wet‑etching, occasionally photoelectrochemical etching strategies have been applied. Here, we propose an electrochemical etching strategy that solely relies on defining etchable volumina by implantation of p‑dopants. Together with the inertness of the n‑doped regions, very sharp etching contrasts can be achieved. We present devices as different as monolithic cantilevers, disk‑shaped optical resonators and membranes etched out of a single crystal wafer. The high quality of the resulting surfaces can even be enhanced by thermal treatment, with shape‑stable devices up to and even beyond 1550 °C. The versatility of our approach paves the way for new functionalities on SiC as high‑performance multi‑functional wafer platform.<br

ELECTROCHEMICAL INVESTIGATIONS OF POLYCRYSTALLINE HXNB2O5 - Schwitzgebel, Günter; Unruh, Tobias (Journal of Solid State Chemistry, 1995)
Polycrystalline samples of HxNb2O5 were prepared by electrochemical reduction of pressed and sintered powder samples of the H-Nb2O5 modification. The hydrogen content of the bronze was determined by redox titration. The electrode potential showed that the bronze is thermodynamically unstable with respect to decomposition into Nb2O5 and gaseous hydrogen. The hydrogen loss obeys a second order rate law. The electrode potential fulfills Nernst's law with a square dependence on the hydrogen content. The specific resistance of H0.18Nb2O5 determined by four-point de measurements amounts to rho(30 degrees C) = (0.0110 +/- 0.0015) Omega cm. The protonic conductivity of the bronze was substantiated by polarization experiments and the diffusion coefficient of H-. (D approximate to 5 x 10(-9) cm(2)/sec) was estimated from the rate law of the depolarization voltage. (C) 1995 Academic Press, Inc.

Electrochemical surface transfer doping: the mechanism behind the surface conductivity of hydrogen terminated diamond - Ristein, Jürgen; Ley, Lothar; et al. (Journal of The Electrochemical Society, 2004)
Intrinsic diamond with a bandgap of 5.4 eV exhibits a surface conductivity (SC) of the order of 10-5 Ω-1 when terminated by hydrogen. This conductivity is carried by a hole-accumulation layer close to the surface with an areal carrier concentration of about 1013 cm -2, and it has already been utilized for a unique kind of field effect transistor [H. Kawarada, Surf. Sci. Rep., 26, 205 (1996)]. Although the microscopic doping mechanism is still under debate. Based on the results of a variety of surface-sensitive experiments we propose a new surface-transfer doping mechanism by which electron transfer from the valence band to adsorbed, hydrated ionic species at the surface creates the holes for the surface conductivity. In order to draw a complete picture of the surface conductivity concepts from surface and semiconductor physics as well as electrochemistry have to be adopted. © 2004 The Electrochemical Society. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.IAP.exphys.electr

Electrochemical switching of the Peierls-like transition in metallic single-walled carbon nanotubes - Rafailov, Peter M.; Maultzsch, Janina; Thomsen, Christian; Kataura, Hiromichi (Physical Review B, 2005)
The high-energy vibrational modes of metallic carbon nanotubes are believed to be softened compared to the semiconducting ones by a Peierls-like transition. The Raman modes, when excited with a red laser to enhance the metallic tubes, were found to exhibit an exceptionally high sensitivity to electrochemical doping. Our data may be interpreted as controlling the Peierls-like instability in metallic tubes with the applied potential. We also discuss the limits of applicability of the double-layer charging model and show Raman evidence for a hysteretic transition to a chemical doping regime.

Electroluminescence of self-assembled InAs quantum dots in p-i-n diodes - Malzer, Stefan; et al. (physica status solidi (b), 2001)
Carrier injection and subsequent radiative recombination in InAs/GaAs self-assembled quantum dots (SADs) is investigated by means of a double-hetero (DH) p-i-n structure, where a SAD laver is embedded at the center of the narrow intrinsic GaAs region. Low temperature electroluminescence shows clearly the filling of electronic states of the dots with increasing voltage. Relating the experimental data to the calculated band structure, the onset of excited SAD-level luminescence is closely related to the occupation of the excited hole levels, whereas the electron levels seem to be filled to a higher degree throughout the investigated voltage regime.

Electron acceleration in moving laser-induced gratings produced by chirped femtosecond pulses - Kozak, Martin (Journal of Physics B: Atomic, Molecular and Optical Physics, 2015)
We propose nonrelativistic electron acceleration in a vacuum using interaction with two crossed chirped femtosecond laser pulses at different frequencies. Electron energy gain is optimized by the phase-matching of accelerated electron velocity to a maximum of ponderomotive force in the moving intensity grating by linear chirping of both pulses. Particle tracking simulations show acceleration gradients as high as 40 GeV m-1 (energy gain of hundreds of keV) using 25 fs pulses with peak power ≤500 GW. The dependence of electron energy gain and the deflection angle on experimental parameters (the amplitude of the electric field of laser pulses, and the initial phase shift between the electron and intensity grating) was studied in detail.
Keywords: chirped pulse; energy gain; laser acceleration; laser-induced grating

Electron affinities of diamond surfaces - Ristein, Jürgen (Growth, Properties and Application of Diamond, 2001)
UnivIS-Import:2015-04-20:Pub.2001.nat.dphy.IAP.exphys.electr_4

Electron affinity and band bending of the single crystal diamond (111) surface - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 1999)
The electron affinity and band bending of a single crystal diamond (111) surface have been investigated as a function of hydrogen coverage via work function measurements, photoelectron yield spectroscopy, X-ray-excited photoelectron spectroscopy (XPS), and low-energy electron diffraction (LEED). The hydrogen desorption and the 1×1-2×1 surface phase transition were achieved by electron-beam irradiation at room temperature as well as annealing at high temperature. The electron affinity ranges from -1.27 eV for the fully hydrogen-covered 1×1 surface to 0.38 eV for the hydrogen-free 2×1 reconstructed surface. Electron beam irradiation is demonstrated to be an effective method to induce hydrogen desorption and surface reconstruction. However, this irradiation process does not change the surface band bending on type IIb diamond, which is generally increased by annealing. It is concluded that the electron-affinity change is caused by the C-H dipole layer, whereas the band bending is not directly related to hydrogen coverage or reconstruction but rather due to charged surface defects that are created simultaneously with the thermal treatment.
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.IAP.exphys.electr_2
Keywords: Diamond; Electron affinity; Photoelectron emission spectroscopy; Surface band bending

Electron affinity of plasma-hydrogenated and chemically oxidized diamond (100) surfaces - Ristein, Jürgen; Maier, Florian; Ley, Lothar (Physical Review B, 2001)
The electron affinity (EA) χ of single crystal diamond (100) is determined as a function of hydrogen and oxygen coverage by a combination of work function and photoemission experiments. For the fully hydrogenated (100)-(2×1):H surface an EA of -1.3 eV and for the oxidized surface C(100)-(1×1):O χ = +1.7 eV are obtained. These are the lowest and the highest electron affinities, respectively, ever reported for any diamond surface. The variation in χ with O and H coverage is well described by a simple dipole model provided that the depolarization is properly taken into account for high adsorbate densities. This analysis favors the bridge position (etherlike) for oxygen on C(100). By mixing H and O adsorbates on a microscopic scale the EA of C(100) can be adjusted at will over 3 eV between the extreme values without jeopardizing the chemical passivation of the diamond surface afforded by H or O termination.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.electr

Electron affinity of the bare and hydrogen covered single crystal diamond (111) surface - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review Letters, 1998)
The electron affinity chi and the band diagram of single crystal diamond (111) surfaces was determined as a function of hydrogen coverage by combining work function measurements with photoelectron yield and core level photoemission spectroscopy. chi ranges from -1.27 eV for the fully hydrogen covered (1 X 1) surface to +0.38 eV for the hydrogen free (2 X 1) reconstructed surface. This change is quantitatively explained by a surface dipole model provided a coverage dependent depolarization is included. The dipole moment of the C-H bond on diamond (111) is found to be 0.09 e Angstrom.
UnivIS-Import:2015-03-05:Pub.1998.nat.dphy.IAP.exphys.theele

Electron-beam-induced deposition and post-treatment processes to locally generate clean titanium oxide nanostructures on Si(100) - Schirmer, Michael; Walz, Marie-Madeleine; Vollnhals, Florian; Lukasczyk, Thomas; Sandmann, Achim; Chen, C.; Steinrück, Hans-Peter; Marbach, Hubertus (Nanotechnology, 2011)
We have investigated the lithographic generation of TiO nanostructures on Si(100) via electron-beam-induced deposition (EBID) of titanium tetraisopropoxide (TTIP) in ultra-high vacuum (UHV) by scanning electron microscopy (SEM) and local Auger electron spectroscopy (AES). In addition, the fabricated nanostructures were also characterized ex situ via atomic force microscopy (AFM) under ambient conditions. In EBID, a highly focused electron beam is used to locally decompose precursor molecules and thereby to generate a deposit. A drawback of this nanofabrication technique is the unintended deposition of material in the vicinity of the impact position of the primary electron beam due to so-called proximity effects. Herein, we present a post-treatment procedure to deplete the unintended deposits by moderate sputtering after the deposition process. Moreover, we were able to observe the formation of pure titanium oxide nanocrystals (>100 nm) in situ upon heating the sample in a well-defined oxygen atmosphere. While the nanocrystal growth for the as-deposited structures also occurs in the surroundings of the irradiated area due to proximity effects, it is limited to the pre-defined regions, if the sample was sputtered before heating the sample under oxygen atmosphere. The described two-step post-treatment procedure after EBID presents a new pathway for the fabrication of clean localized nanostructures. © 2011 IOP Publishing Ltd.

Electron beam induced surface activation: a method for the lithographic fabrication of nanostructures via catalytic processes - Marbach, Hubertus (Applied Physics A-Materials Science & Processing, 2014)
In focused electron beam induced processing (FEBIP), the very narrow electron beam of a scanning electron microscope or transmission electron microscope is used to locally modify matter on the nanometer scale. Recently, the family of FEBIP could be considerably expanded by the technique of focused electron beam induced surface activation (EBISA). In EBISA, the surface itself gets chemically activated by the impact of the electron beam without the presence of precursor molecules. In the second EBISA processing step, the surface is exposed to a precursor molecule which is then catalytically decomposed at the pre-irradiated/activated areas and eventually continues to grow autocatalytically upon prolonged precursor dosage. In this way, electron irradiation and precursor dosage are effectively separated. One of the advantages is that, due to the autocatalytic growth, the size of the corresponding nanostructures can be controlled by the precursor dosage and corresponding electron proximity effects can be omitted. Another advantage is the parallel processing of the pre-irradiated regions during precursor dosage. This bears the potential to significantly reduce the fabrication times for larger deposits compared to the classical electron beam induced deposition approach, in which precursor molecules are sequentially dissociated by the impact of the electron. The fundamentals and apparent further developments as well as the potential and challenges of the comparably new EBISA technique, and more general of catalytic effects in FEBIP are presented and discussed.
EAM Import::2019-03-14

Electron beam transverse phase space tomography using nanofabricated wire scanners with submicrometer resolution - Hermann, Benedikt; Guzenko, Vitaliy A.; Hürzeler, Orell R.; Kirchner, Adrian; Orlandi, Gian Luca; Prat, Eduard; Ischebeck, Rasmus (Physical Review Accelerators and Beams, 2021)
Characterization and control of the transverse phase space of high-brightness electron beams is required at free-electron lasers or electron diffraction experiments for emittance measurement and beam optimization as well as at advanced acceleration experiments. Dielectric laser accelerators or plasma accelerators with external injection indeed require beam sizes at the micron level and below. We present a method using nano-fabricated metallic wires oriented at different angles to obtain projections of the transverse phase space by scanning the wires through the beam and detecting the amount of scattered particles. Performing this measurement at several locations along the waist allows assessing the transverse distribution at different phase advances. By applying a novel tomographic algorithm the transverse phase space density can be reconstructed. Measurements at the ACHIP chamber at SwissFEL confirm that the transverse phase space of micrometer-sized electron beams can be reliably characterized using this method.
CRIS-Team Scopus Importer:2021-03-19

Electron Diagnostics for Extreme High Brightness Nano-Blade Field Emission Cathodes - Lawler, Gerard; Sanwalka, Kunal; Zhuang, Yumeng; Yu, Victor; Paschen, Timo; Robles, River; Williams, Oliver; Sakai, Yusuke; Naranjo, Brian; Rosenzweig, James (Instruments, 2019)
Electron beams are essential tools in modern science. They are ubiquitous in fields ranging from microscopy to the creation of coherent ultra-fast X-rays to lithography. To keep pace with demand, electron beam brightness must be continually increased. One of the main strategic aims of the Center for Bright Beams (CBB), a National Science Foundation Science and Technology Center, is to increase brightness from photocathodes by two orders of magnitude. Improving the state-of-the-art for photoemission-based cathodes is one possibility. Several factors have led to an alternative design becoming an increasing necessity; the nanoscale structure. Field emission sources from nano-tips would be an ideal candidate were it not for their low current and damage threshold. A 1-dimensional extended nano-fabricated blade, i.e., a projected tip, can solve the problems inherent in both designs. The novel geometry has been demonstrated to produce extremely high brightness electron beam bunches and is significantly more robust and easier to manufacture than traditional photocathodes. Theory indicates electron emission up to keV energies. We thus present a system of diagnostics capable of analyzing the cathodes and assessing their viability. The diagnostics are designed to measure the electron spectrum up to keV energies, with sub meV resolution at <100 eV, mean transverse energy (MTE), emission uniformity, and cathode lifetime. We also report preliminary data on total extracted charge and maximum detectable electron energy with a simplified retarding field spectromete
Keywords: diagnostics; electron spectrometer; nano-fabricated blade; electron source; high brightness

Electron dynamics at surfaces - Fauster, Thomas; Echenique, P. M.; Chulkov, E. V. (Surface and Interface Science, 2012)

Electron dynamics in graphene reaching the light-field-driven regime - Higuchi, Takuya; Heide, Christian; Ullmann, Konrad; Weber, Heiko B.; Hommelhoff, Peter (Optics InfoBase Conference Papers, 2017)
CRIS-Team Scopus Importer:2022-04-14

Electron Dynamics in Image Potential States at Metal Surfaces - Fauster, Thomas (Dynamics at Solid State Surfaces and Interfaces, 2010)
Keywords: Image potential states; Interband scattering; Intraband scattering; Pump-probe delay; Quasielastic scattering; Two-photon photoemission

Electron dynamics of unoccupied states in topological insulators - Niesner, Daniel; Otto, Sebastian; Fauster, Thomas; Chulkov, E. V.; Eremeev, S. V.; Tereshchenko, O. E.; Kokh, K. A. (Journal of Electron Spectroscopy and Related Phenomena, 2014)
The topological insulators Bi2Se3 and Bi2Te2Se have been shown to possess unoccupied topological surface states at the center of the surface Brillouin zone at energies around 1.3 eV above the Fermi level. Using time-resolved two-photon photoemission we study the electron dynamics of the unoccupied topological surface states, image-potential states and conduction bands on these surfaces. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Topological insulators; Surface states; Image-potential states; Two-photon photoemission; Electron dynamics

Electron-Electron Interaction in the Magnetoresistance of Graphene - Jobst, Johannes; Waldmann, Daniel; Gornyi, Igor; Mirlin, Alexander; Weber, Heiko B. (Physical Review Letters, 2012)
We investigate the magnetotransport in large area graphene Hall bars epitaxially grown on silicon carbide. In the intermediate field regime between weak localization and Landau quantization, the observed temperature-dependent parabolic magnetoresistivity is a manifestation of the electron-electron interaction. We can consistently describe the data with a model for diffusive ( magneto) transport that also includes magnetic-field-dependent effects originating from ballistic time scales. We find an excellent agreement between the experimentally observed temperature dependence of magnetoresistivity and the theory of electron-electron interaction in the diffusive regime. We can further assign a temperature-driven crossover to the reduction of the multiplet modes contributing to electron-electron interaction from 7 to 3 due to intervalley scattering. In addition, we find a temperature-independent ballistic contribution to the magnetoresistivity in classically strong magnetic fields.

Electronic and chemical passivation of hexagonal 6H-SiC surfaces by hydrogen termination - Ristein, Jürgen; Ley, Lothar; et al. (Applied Physics Letters, 2001)
Hydrogenation of 6H-SiC (0001) and (0001̄) is achieved by high-temperature hydrogen treatment. Both surfaces show a low-energy electron diffraction pattern representative of unreconstructed surfaces of extremely high crystallographic order. On SiC(0001), hydrogenation is confirmed by the observation of sharp Si-H stretching modes. The absence of surface band bending for n-and p-type samples is indicative of electronically passivated surfaces with densities of charged surface states in the gap of below 7 × 1010 cm-2 for p-type and 1.7 × 1012 cm-2 for n-type samples, respectively. Even after two days in air, the surfaces show no sign of surface oxide in x-ray photoelectron spectroscopy. © 2001 American Institute of Physics.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.electr_2

Electronic and structural properties of the a-Si:H/a-SiNx:H interface - Ristein, Jürgen; Ley, Lothar; et al. (Journal of Non-Crystalline Solids, 1993)
Valence band offsets and band bending were systematically investigated by photoelectron spectroscopy for the a-Si:H/a-SiNX:H heterojunction covering nitrogen concentrations between 0≤×≤1.63. The chemical structure and the defect density of the interfaces are determined. © 1993.
UnivIS-Import:2015-03-05:Pub.1993.nat.dphy.IAP.exphys.electr

Electronic and structural properties of the interface between c-Si (111) and diamond like carbon - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 1997)
The chemical and electronic structure of the interface between crystalline silicon- and diamond-like amorphous hydrogenated carbon (a-C:H) are investigated. Employing in situ photoelectron spectroscopy the formation of the interface between both materials is observed step by step in terms of chemical composition as well as in terms of band bending and band offset evolution. When the heterostructure is completed a stoichiometric SiC interface layer with a thickness of 18 Å has formed whose valence band maximum lies 0.28 eV below that of the silicon substrate and 0.4 eV above that of the a-C:H overlayer. © 1997 Elsevier Science S.A.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.IAP.exphys.electr_6
Keywords: Band bending; Band offset; c-Si:a-C:H interface; Photoelectron spectroscopy

Electronic and Vibrational Properties of Diamondoid Oligomers - Tyborski, Christoph; Gillen, Roland; Fokin, Andrey A.; Koso, Tetyana V.; Fokina, Natalie A.; Hausmann, Heike; Rodionov, Vladimir N.; Schreiner, Peter R.; Thomsen, Christian; Maultzsch, Janina (Journal of Physical Chemistry C, 2017)

Electronic Coherence and Coherent Dephasing in the Optical Control of Electrons in Graphene - Heide, Christian; Eckstein, Timo; Boolakee, Tobias; Gerner, Constanze; Weber, Heiko B.; Franco, Ignacio; Hommelhoff, Peter (Nano Letters, 2021)
Electronic coherence is of utmost importance for the access and control of quantum-mechanical solid-state properties. Using a purely electronic observable, the photocurrent, we measure a lower bound of the electronic coherence time of 22 ± 4 fs in graphene. The photocurrent is ideally suited to measure electronic coherence, as it is a direct result of coherent quantum-path interference, controlled by the delay between two ultrashort two-color laser pulses. The maximum delay for which interference between the population amplitude injected by the first pulse interferes with that generated by the second pulse determines the electronic coherence time. In particular, numerical simulations reveal that the experimental data yields a lower bound on the electronic coherence time, masked by coherent dephasing due to the broadband absorption in graphene. We expect that our results will significantly advance the understanding of coherent quantum control in solid-state systems ranging from excitation with weak fields to strongly driven system
Keywords: graphene; quantum-path interference; electronic coherence time; quantum control

Electronic Properties and Interlayer Interactions in Antimony Oxide Homo- and Heterobilayers - Wolff, Stefan; Gillen, Roland; Maultzsch, Janina (physica status solidi (b), 2023)
Antimony shows promise as a 2D mono-elemental crystal, referred to as antimonene. When exposed to ambient conditions, antimonene layers react with oxygen, forming new crystal structures, leading to significant changes in electronic properties. These changes are influenced by the degree of oxidation. Utilizing density-functional theory calculations, stable configurations of bilayer antimony oxide and their corresponding electronic properties are studied. Additionally, different stacking arrangements and their effects on the physical properties of the materials are investigated. Furthermore, the analysis encompasses strain-free heterobilayers containing both pristine and oxidized antimonene layers, aiming to understand the interplay between these materials and their collective impact on the bilayer properties. In the results, insight is provided into how the properties of antimony-based bilayer structures can be modified by adjusting stoichiometry and stacking configurations.
CRIS-Team Scopus Importer:2023-12-29
Keywords: 2D materials; antimonene; density-functional theory (DFT); tunable bandgaps

Electronic properties of diamond surfaces - blessing or curse for devices? - Ristein, Jürgen (Diamond and Related Materials, 2000)
For the potential electronic applications of diamond as a wide band gap semiconductor, the properties of its surfaces are of fundamental importance. These properties in general depend on the kind of passivation of the surface dangling bonds, either by chemisorbed adsorbates or by the formation of mutual chemical bonds as a consequence of surface reconstruction. The principal crystallographic surfaces, (100), (111) and (110), are essentially understood in their adsorbate free form in terms of surface states and reconstructions. The corresponding results are briefly summarized in Section 2. The consequences of adsorbate passivation are then discussed for the case of hydrogen as the most important radical for surface termination with emphasis on different aspects. Hydrogen passivation leads to a negative electron affinity due to a dipole layer which is induced by the heteropolar carbon-hydrogen bonds of the surface atoms. This aspect is discussed quantitatively in Section 3. Hydrogenation also reduces the amount of sp2 bonded carbon at the surface, which turns out to be the crucial parameter determining the position of the surface Fermi level and thus the surface band bending in diamond. This aspect is covered in Section 4. Finally, the combination of the electron affinity reduction by hydrogen and the supply of electrons at the Fermi level by sp2 bonded carbon phases has important consequences for the low threshold electron emission into vacuum. This is dealt with in the framework of an inhomogeneous emission model in Section 5. The model can be expected to be applicable for all system containing sp2 bonded or graphitic phases together with an sp3 bonded diamond matrix, especially for CVD diamond, and it should have important implications also for field emission from diamond films.
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.IAP.exphys.electr

Electronic properties of diamond surfaces - Ristein, Jürgen; et al. (Festkörperprobleme/Advances in Solid State Physics, 1997)
UnivIS-Import:2015-04-20:Pub.1997.nat.dphy.IAP.exphys.electr

Electronic properties of MoS2/h-BN heterostructures: Impact of dopants and impurities - Gillen, Roland; Robertson, John; Maultzsch, Janina (physica status solidi (b), 2014)
We report density functional theory calculations of the electronic properties of doped heterostructures of monolayer molybdenum disulphide and hexagonal boron nitride (h-BN). Extending on a recent study, we investigate the effect of doping the h-BN layer on the electronic structure of the MoS2 subsystem by a number of impurites. We consider the intrinsic n-type dopants S and Mo, the p-type dopant Mg, and interstitial K and Mn atoms. Magnesium and molybdenum substitutional impurities induce tails of occupied defect states into the band gap of the compound that reach up to the conduction band minimum of MoS2. This suggests easy charge transfer between the layers in these cases. Additionally, the d-electrons in the studied transition metal impurities induce localized magnetic momenta into the MoS2 subsystem, which might be exploited in spintronics applications. Our results contribute to the understanding of the interaction of MoS2 in vertical heterostructures with nearby impurities and offer insights into possible origins of intrinsic doping of experimental samples of MoS2. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhe
Keywords: DFT; dichalcogenides; doping; MoS2

Electronic properties of propylamine-functionalized single-walled carbon nanotubes. - Müller, Matthias; Meinke, Reinhard; Maultzsch, Janina; Syrgiannis, Zois; Hauke, Frank; Pekker, Áron; Kamarás, Katalin; Hirsch, Andreas; Thomsen, Christian (ChemPhysChem, 2010)
We present resonant Raman measurements on single-walled carbon nanotubes (SWCNT) functionalized with propylamine groups at different degrees. Direct nucleophilic addition based on in situ generated primary amides is used for attaching n-propylamine to the sidewalls of SWCNTs. The influence of the amino functionalities on the electronic structure of the nanotubes is investigated. From the Raman resonance profiles of the radial breathing modes (RBMs), the chiral indices of the corresponding tubes are assigned. We observe significant redshifts of the transition energies and a broadening of the resonance windows due to chemical modification of SWCNTs. Similar redshifts are derived from the analysis of the NIR/Vis transmission spectrum. The relative Raman intensities of the functionalized samples and the evaluation of their transmission spectra indicate a diameter dependence of the reactivity as it has been observed for other moieties. By analyzing the defect induced D mode we observe a considerable degree of functionalization accompanied by an almost unharmed tube structure, which ensures that the observed effects are mainly driven by changes of the electronic structure.

Electronic Properties of Semiconducting Polymer-Functionalized Single Wall Carbon Nanotubes - Kourkouli, Souzana N.; Siokou, Angeliki; Stefopoulos, Andreas A.; Ravani, Fotini; Plocke, Thomas; Mueller, Matthias; Maultzsch, Janina; Thomsen, Christian; Papagelis, Kostas; Kallitsis, Joannis K. (Macromolecules, 2013)
New hybrid materials were synthesized by functionalizing single wall carbon nanotubes (SWCNTs) with different semiconducting species. Vinyl quinoline monomers bearing electron accepting groups or even its ruthenium complex were used as organic semiconductors. UV-vis-NIR absorption spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis were used in order to qualify the resulted materials. Optical characteristics were studied by photoluminescence spectroscopy in neutral and acidic media. The electronic structure of the valence band and the surface electronic properties of the materials in the form of thin films developed on Si substrates were studied by ultraviolet photoelectron spectroscopy. Raman spectroscopy revealed the charge transfer mechanism between the polymer and the carbon nanotube while the recorded Raman resonance profiles showed significant changes in the transition energies and the widths of the resonance windows due to chemical modification of SWCNTs.

Electronic Properties of Si-Hx Vibrational Modes at Si Waveguide Interface. - Bashouti, Muhammad Y.; Yousefi, Peyman; Ristein, Jürgen; Christiansen, Silke H. (Journal of Physical Chemistry Letters, 2015)
Attenuated total reflectance (ATR) and X-ray photoelectron spectroscopy in suite with Kelvin probe were conjugated to explore the electronic properties of Si-Hx vibrational modes by developing Si waveguide with large dynamic detection range compared with conventional IR. The Si 2p emission and work-function related to the formation and elimination of Si-Hx bonds at Si surfaces are monitored based on the detection of vibrational mode frequencies. A transition between various Si-Hx bonds and thus related vibrational modes is monitored for which effective momentum transfer could be demonstrated. The combination of the aforementioned methods provides for results that permit a model for the kinetics of hydrogen termination of Si surfaces with time and advanced surface characterizing of hybrid-terminated semiconducting solids.

Electronic properties of single crystalline diamond surfaces - Ley, Lothar; Ristein, Jürgen; et al. (Carbon, 1999)
Key parameters of the surface electronic structure of diamond (111), such as surface core level shifts, surface state dispersion, band bending, and electron affinity, are presented and discussed. The first actual value for the negative electron affinity of diamond (111):H 1×1 is measured as χ = -1.27 eV. A model is given that describes the variation in χ with hydrogen coverage quantitatively in terms of C-H bond dipoles.
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.IAP.exphys.electr_8

ELECTRONIC QUASI-PARTICLE STRUCTURE OF FERROMAGNETIC BCC IRON - Fauster, Thomas; et al. (Zeitschrift für Physik B Condensed Matter, 1995)
We investigate the influence of electron correlations on the temperature-dependence of the electronic structure of ferromagnetic bcc iron by use of a many-body evaluation of a generalized model of magnetism. The single-particle part of the model-Hamiltonian is taken from an LDA band structure calculation. The many-body interactions are described by only two parameters, an intraband Coulomb interaction U and an interband exchange J. With U = 1.8 eV and J = 0.2 eV the self-consistent model solution yields a T = 0 moment of about 2.04 mu(B) and a Curie-temperature of 1044 K. Details of the magnetic behaviour of Fe can be traced back to a striking temperature variation of the quasiparticle density of states. A novel explanation for the experimentally-observed non-collapsing exchange splitting is demonstrated in terms of the temperature-dependent spectral density for wave-vectors near the GAMMA-point. Typical differences in the magnetic behaviour of Fe and Ni are worked out.

Electronic Raman Studies of Shallow Donors in Silicon Carbide - Püsche, Roland; Hundhausen, Martin; Ley, Lothar; Semmelroth, Kurt; Pensl, Gerhard; Desperrier, Patrick; Wellmann, Peter; Haller, Eugene E.; Ager, J.W.; Starke, Ulrich (Materials Science Forum, 2006)
We study electronic Raman scattering of phosphorus and nitrogen doped silicon carbide (SiC) as a function of temperature in the range 7 K < T < 300K. We observe a series of peaks in the Raman spectra which we assign to electronic transitions at nitrogen and phosphorus donors on different lattice sites. These transitions are identified as valley orbit transitions of the Is donor ground state. From the polarization dependence of the observed peaks, we find that all electronic Raman signals have E2-symmetry of C 6v for the hexagonal polytypes (6H-SiC and 4H-SiC) and E-syinmetry of C3., for 15R-SiC. Wc find a reduction of the intensities of all valley-orbit Raman signals with increasing temperature and ascribe this reduction to the decreasing occupation of donor state
UnivIS-Import:2015-04-14:Pub.2006.nat.dphy.IAP.LAP.electr
Keywords: Doping; Nitrogen-donor; Phosphorus-donor; Raman spectroscopy

Electronic states of an ordered oxide on C-terminated 6H-SiC - Maier, Florian; Ristein, Jürgen; Ley, Lothar; et al. (Surface Science, 1999)
An ordered oxide monolayer with (√3×3√3)R30° periodicity was obtained on carbon-terminated 6H-SiC(000̄3) after preparation with a hydrogen microwave plasma. The stoichiometry of this surface was investigated by X-ray-induced photoelectron spectroscopy. Most components of the Si 2p, C 1s, and O 1s core lines are in agreement with the recently published atomic structure of this ordered monolayer. Beyond this we found hydrocarbon contamination that could be removed by annealing, and small graphitized areas remaining on the surface. We used angle-resolved ultra-violet photoelectron spectroscopy to examine the electronic structure of the valence band. Besides the O 2s and the O 2p lone pair state at 24 eV and 6 eV respectively below the valence band maximum (VBM), we detected a dangling bond state slightly above the VBM and a Si hybrid-O 2p-derived bonding state dispersing between 9.1 and 11.0 eV below the VBM. For the dangling bond state the possibility of a Mott-Hubbard ground state is discussed. In order to clarify the origin of the oxygen-derived states our results are compared with previous investigations of silicon oxides.
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.IAP.exphys.electr

Electronic structure and defect density of states of hydrogenated amorphous carbon (a-C:H) as determined by photoelectron and photoelectron yield spectroscopy - Ristein, Jürgen; Ley, Lothar; et al. (Journal of Non-Crystalline Solids, 1993)
Amorphous hydrogenated carbon films were prepared by RF-PECVD of CH4 with the self bias varying from 0 to 200V. The films were analysed with x-ray and ultraviolet photoelectron spectroscopy as well as photoelectron yield spectroscopy. The densities as derived from the plasmon energies increase from 1.2 to 1.7 g/cm3 with bias voltage and the sp2/(sp3+sp2) ratio extracted from an analysis of the valence band spectra increases from 15 to 35% over the same range. Two defect bands were identified in the pseudogap, 1.4 eV and 2.4 eV above the π-bonding states with integrated densities that increase from 1·1020 to 7·1020 cm-3 with bias. © 1993.
UnivIS-Import:2015-03-05:Pub.1993.nat.dphy.IAP.exphys.electr_5

Electronic structure and electron dynamics at Si(100) - Weinelt, Martin; Kutschera, Michael; Schmidt, Roland; Orth, Christian; Fauster, Thomas; Rohlfing, Michael (Applied Physics A-Materials Science & Processing, 2005)
The electronic structure and electron dynamics at a Si( 100) surface is studied by two-photon photoemission (2PPE). At 90 K the occupied D-up dangling-bond state is located 150 +/- 50 meV below the valence-band maximum (VBM) at the center of the surface Brillouin zone (Gamma) over bar and exhibits an effective hole mass of (0.5 +/- 0.15) m(e). The unoccupied D-down band has a local minimum at (Gamma) over bar at 650 +/- 50 meV above the VBM and shows strong dispersion along the dimer rows of the c( 4 x 2) reconstructed surface. At 300 K the D-down position shifts comparable to the Si conduction-band minimum by 40 meV to lower energies but the dispersion of the dangling-bond states is independent of temperature. The surface band bending for p-doped silicon is less than 30 meV, while acceptor-type defects cause significant and preparation-dependent band bending on n-doped samples. 2PPE spectra of Si( 100) are dominated by interband transitions between the occupied and unoccupied surface states and emission out of transiently and permanently charged surface defects. Including electron - hole interaction in many-body calculations of the quasi-particle band structure leads us to assign a dangling-bond split-off state to a quasi-one-dimensional surface exciton with a binding energy of 130 meV. Electrons resonantly excited to the unoccupied D-down dangling-bond band with an excess energy of about 350 meV need 1.5 +/- 0.2 ps to scatter via phonon emission to the band bottom at (Gamma) over bar and relax within 5 ps with an excited hole in the occupied surface band to form an exciton living for nanoseconds.

ELECTRONIC-STRUCTURE OF A SINGLE LAYER OF NA ON CU(111) - Fauster, Thomas; et al. (Physical Review B, 1991)
High-resolution photoemission and two-photon photoemission have been used to investigate the electronic structure of a single layer of Na on Cu(111). In addition to an occupied Na-induced state 0.11 +/- 0.03 eV below the Fermi energy, we resolved three unoccupied states with binding energies relative to the vacuum energy of 0.72 +/- 0.03, 0.27 +/- 0.03, and 0.13 +/- 0.04 eV. These values are at variance to the predictions of a simple phase-analysis model. The effective mass of the lowest unoccupied state and the occupied Na-induced state were measured to be m*/m(e) = 1.3 +/- 0.1. This is considerably larger than the expected free-electron value. More refined theoretical models accounting for the atomic structure of the adsorbate are necessary for a realistic description of the electronic structure of single alkali-metal layers on metal surfaces.

Electronic structure of CoSi2 films on Si(111) studied using time-resolved two-photon photoemission - Kutschera, Michael; Groth, Tilman; Kentsch, Carsten; Shumay, Igor; Weinelt, Martin; Fauster, Thomas (Journal of Physics: Condensed Matter, 2009)
The occupied and unoccupied electronic structure of thin epitaxial CoSi2 films grown on Si(111) substrates was studied using time-resolved two-photon photoemission and valence-band photoemission spectroscopy. The work function of the sample surfaces and the Schottky barrier height at the metal-semiconductor interface were measured as a function of annealing temperature. The photoemission data reveal several occupied and unoccupied electronic states which exhibit a high sensitivity to the annealing temperature. Time-resolved measurements show a behavior typical for a short-lived hot-electron gas and indications for an image-potential resonance.

Electronic structure of lanthanide oxide high K gate oxides - Gillen, Roland; Robertson, John (Microelectronic Engineering, 2013)
Keywords: Electronic structure; Band gap; Lanthanide; High K oxide; Rare earth

Electronic structure of Si(100) surfaces studied by two-photon photoemission - Kentsch, Carsten; Kutschera, Michael; Weinelt, Martin; Fauster, Thomas; Rohlfing, Michael (Physical Review B, 2002)
The electronic structure of the valence and conduction bands at the Si(100) surface has been studied by two-photon photoemission over a wide photon-energy range. The ionization energy was determined to 5.40+/-0.03 eV. The occupied surface state at Gamma is placed 0.15+/-0.06 below the valence-band maximum. Several other spectral features are assigned to transitions involving surface states and between bulk bands including backfolded bands due to the surface reconstruction. The moderate agreement between experimental data and band-structure calculations calls for an improved theoretical description of the two-photon photoemission process at semiconductor surfaces incorporating, e.g., a one-step model and excitonic effects.

ELECTRONIC-STRUCTURE OF SI(111) SURFACES - Fauster, Thomas; et al. (Surface Science, 1983)

Electronic structure of SiC(0001) surfaces studied by two-photon photoemission - Wiets, Michael; Weinelt, Martin; Fauster, Thomas (Physical Review B, 2003)
Two-photon photoemission has been used to study the electronic structure of the valence and conduction bands at SiC(0001) surfaces. The various surface reconstructions show distinctly different spectra and work functions. The ionization energy is found independent of polytype and surface reconstruction to be 6.9+/-0.2 eV. For the (root3xroot3)R30degrees surface the occupied and unoccupied Mott-Hubbard bands are found with a splitting U=2.4+/-0.1 eV. A long-lived exciton between the Mott-Hubbard bands is identified with a binding energy of similar to0.7 eV.

Electronic structure of tetraphenylporphyrin layers on Ag(100) - Classen, Andrej; Pöschel, Rebecca; di Filippo, Gianluca; Fauster, Thomas; Malcioglu, Osman; Bockstedte, Michel Georg (Physical Review B, 2017)

Electronic structure of the Ru(0001) surface - Fauster, Thomas; et al. (Journal of Physics: Condensed Matter, 2000)
This paper deals with the electronic structure of ruthenium. Synchrotron radiation in the range from 15 to 45 eV and angle-resolved ultraviolet photoemission are used to map the energies of the electronic states. The Fermi surface of Ru is determined using angle-resolved ultraviolet photoemission spectroscopy. The experimental results an compared with calculated photoemission spectra obtained within the framework of the one-step model of photoemission.

Electronic Transport Properties of 1D-Defects in Graphene and Other 2D-Systems - Willke, P.; Schneider, M. Alexander; Wenderoth, M. (Annalen Der Physik, 2017)
The continuous progress in device miniaturization demands a thorough understanding of the electron transport processes involved. The influence of defects - discontinuities in the perfect and translational invariant crystal lattice - plays a crucial role here. For graphene in particular, they limit the carrier mobility often demanded for applications by contributing additional sources of scattering to the sample. Due to its two-dimensional nature graphene serves as an ideal system to study electron transport in the presence of defects, because one-dimensional defects like steps, grain boundaries and interfaces are easy to characterize and have profound effects on the transport properties. While their contribution to the resistance of a sample can be extracted by carefully conducted transport experiments, scanning probe methods are excellent tools to study the influence of defects locally. In this letter, the authors review the results of scattering at local defects in graphene and other 2D systems by scanning tunneling potentiometry, 4-point-probe microscopy, Kelvin probe force microscopy and conventional transport measurements. Besides the comparison of the different defect resistances important for device fabrication, the underlying scattering mechanisms are discussed giving insight into the general physics of electron scattering at defects.
Keywords: Graphene; scanning tunneling microscopy; scanning tunneling potentiometry; defects; Kelvin probe force microscopy; grain boundaries; wrinkles; monolayer-bilayer-interface; monoatomic step; defect resistance; sheet resistance; electron transport

Electronic transport through single conjugated molecules - Weber, Heiko B.; Reichert, Joachim; Weigend, Florian; Ochs, Rolf; Beckmann, Detlef; Mayor, Marcel; Ahlrichs, Reinhart; von Löhneysen, Hilbert (Chemical Physics, 2002)
We investigate electronic transport through single conjugated molecules, and compare our data to results of quantum chemical calculations. Conductance spectra of two types of molecules are studied in a metal-molecule-metal junction established using the mechanically controlled break-junction technique. We observe a suppressed conductance at low bias, characteristic step-like features at higher voltages, and strong sample-to-sample fluctuations. We develop a quantum-chemical model for our system using DFT calculations, with the electrodes modelled by small clusters. We consider the effects of different geometries of molecule-metal configurations and bonding as well as finite electric field, and are thereby able to account for the phenomenology of the experimental data. (C) 2002 Elsevier Science B.V. All rights reserve
UnivIS-Import:2017-11-07:Pub.2002.nat.dphy.IAP.LAP.electr_4

Electron phase-space control in photonic chip-based particle acceleration - Kraus, Stefanie; Shiloh, Roy; Illmer, Johannes; Chlouba, Tomas; Yousefi, Peyman; Schönenberger, Norbert; Niedermayer, U.; Mittelbach, Anna; Hommelhoff, Peter (Optics InfoBase Conference Papers, 2022)
We demonstrate complex electron phase-space control in a 77.7 micrometer long silicon-based nanostructure. This low-loss electron transport scheme is a prerequisite to the future mega-electron-volt electron accelerator on a photonic chip.
CRIS-Team Scopus Importer:2022-09-09

Electron phase-space control in photonic chip-based particle acceleration - Shiloh, Roy; Illmer, Johannes; Chlouba, Tomas; Yousefi, Peyman; Schonenberger, N.; Niedermayer, U.; Mittelbach, Anna; Hommelhoff, Peter (Nature, 2021)
Particle accelerators are essential tools in science, hospitals and industry1–6. Yet their costs and large footprint, ranging in length from metres to several kilometres, limit their use. The recently demonstrated nanophotonics-based acceleration of charged particles can reduce the cost and size of these accelerators by orders of magnitude7–9. In this approach, a carefully designed nanostructure transfers energy from laser light to the particles in a phase-synchronous manner, accelerating them. To accelerate particles to the megaelectronvolt range and beyond, with minimal particle loss10,11, the particle beam needs to be confined over extended distances, but the necessary control of the electron beam’s phase space has been elusive. Here we demonstrate complex electron phase-space control at optical frequencies in the 225-nanometre narrow channel of a silicon-based photonic nanostructure that is 77.7 micrometres long. In particular, we experimentally show alternating phase focusing10–13, a particle propagation scheme for minimal-loss transport that could, in principle, be arbitrarily long. We expect this work to enable megaelectronvolt electron-beam generation on a photonic chip, with potential for applications in radiotherapy and compact light sources9, and other forms of electron phase-space control resulting in narrow energy or zeptosecond-bunched beams14–16.
CRIS-Team Scopus Importer:2021-10-01

ELECTRON-PHONON COUPLING IN GRAPHENE - Milosevic, Ivanka; Kepcija, Nenad; Dobardzic, Edib; Damnjanovic, Milan; Mohr, Marcel; Maultzsch, Janina; Thomsen, Christian (International Journal of Modern Physics B, 2010)
Numerical and symmetry based analysis of the electron-phonon coupling in graphene have been performed. Symmetry alone predicts the Kohn anomalies, their positions in the Brillouin zone and all quantum numbers of the Kohn modes and the vectors of the Kohn displacements. Dispersion of kink phonons is calculated and found to be similar to the classical phonon spectrum. Interestingly, most of the Gamma (including all the acoustic phonons as well) and K modes are shown to be uncoupled to electrons.
Keywords: Graphene; electron-phonon interaction; Kohn anomaly; symmetry

Electron rescattering at metal nanotips induced by ultrashort laser pulses - Wachter, Georg; Lemell, Christoph; Burgdoerfer, Joachim; Schenk, Markus; Krüger, Michael; Hommelhoff, Peter (Physical Review B, 2012)
We investigate plateau and cutoff structures in photoelectron spectra from nanoscale metal tips interacting with few-cycle near-infrared laser pulses. These hallmarks of electron rescattering, well-known from atom-laser interaction in the strong-field regime, appear at remarkably low laser intensities with nominal Keldysh parameters of the order of ≳10. Quantum and quasiclassical simulations reveal that a large field enhancement near the tip and the increased backscattering probability at a solid-state target play a key role. Plateau electrons are by an order of magnitude more abundant than in comparable atomic spectra, reflecting the high density of target atoms at the surface. The position of the cutoff serves as an in situ probe for the locally enhanced electric field at the tip apex. © 2012 American Physical Society.
UnivIS-Import:2015-04-14:Pub.2012.nat.dphy.IAP.exphys.electr

Electron rescattering in photoemission from metal tips as a nanoscale probe of near-field enhancement - Thomas, Sebastian; Krüger, Michael; Förster, Michael; Hommelhoff, Peter (The European Conference on Lasers and Electro-Optics, CLEO_Europe 2013, 2013)

Electron scattering at steps: Image-potential states on Cu(119) - Roth, Manfred; Pickel, Martin; Wang, Jinxiong; Weinelt, Martin; Fauster, Thomas (Physical Review Letters, 2002)
The dynamics of image-potential states on Cu(119) have been studied with two-photon photoemission. Direction-dependent quasielastic scattering processes with large momentum transfer are attributed to the finite terrace-width distribution on the stepped surface. This effectively couples image-potential states via interband scattering and leads to an asymmetry of the decay rate. Electrons in the first image-potential state live apparently longer when running upstairs.

Electron spin resonance signature of the oxygen vacancy in HfO 2 - Gillen, Roland; Robertson, John; Clark, Steward (Applied Physics Letters, 2012)

Electrophoretic deposition of lawsone loaded bioactive glass (BG)/chitosan composite on polyetheretherketone (PEEK)/BG layers as antibacterial and bioactive coating. - Ur Rehman, Muhammad Atiq; Bastan, Fatih Erdem; Nawaz, Qaisar; Goldmann, Wolfgang; Maqbool, Muhammad; Virtanen, Sannakaisa; Boccaccini, Aldo R. (Journal of Biomedical Materials Research Part A, 2018)
In this study, chitosan/bioactive glass (BG)/lawsone coatings were deposited by electrophoretic deposition (EPD) on polyetheretherketone (PEEK)/BG layers (previously deposited by EPD on 316-L stainless steel) to produce bioactive and antibacterial coatings. First, the EPD of chitosan/BG/lawsone was optimized on stainless steel in terms of suspension stability, homogeneity and thickness of coatings. Subsequently, the optimized EPD parameters were used to produce bioresorbable chitosan/bioactive glass (BG)/lawsone coatings on PEEK/BG layers. The produced layered coatings were characterized in terms of composition, microstructure, corrosion resistance, in vitro bioactivity, drug release kinetics and antibacterial activity. Ultraviolet/Visible (UV/VIS) spectroscopic analyses confirmed the release of lawsone from the coatings. Moreover, the deposition of chitosan/BG coatings was confirmed by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared spectroscopy (FTIR). The coated specimens presented higher corrosion resistance (10 times) in comparison to that of bare 316-L stainless steel and showed convenient wettability for initial protein attachment. The presence of lawsone in the top layer provided antibacterial effects against Staphylococcus carnosus. Moreover, the developed coatings formed apatite-like crystals upon immersion in simulated body fluid, indicating the possibility of achieving close interaction between the coating surface and bone. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3111-3122, 2018.

Electrophoretic deposition of tetracycline hydrochloride loaded halloysite nanotubes chitosan/bioactive glass composite coatings for orthopedic implants - Radda'A, Namir S.; Goldmann, Wolfgang H.; Detsch, Rainer; Roether, Judith; Cordero-Arias, Luis; Virtanen, Sannakaisa; Moskalewicz, Tomasz; Boccaccini, Aldo R. (Surface & Coatings Technology, 2017)
Keywords: Antibacterial; Bioactive glass; Chitosan; Electrophoretic deposition; Halloysite nanotubes; Stainless steel; Tetracycline hydrochloride

Elektronen nahe Metalloberflächen: Bildpotentialzustände - Fauster, Thomas (Physik in unserer Zeit, 2002)
Elektronen werden von Metalloberflächen durch eine „Bildkraft” angezogen. So entstehen Bindungszustände, die Bildpotentialzustände heißen. Sie haben viele vom Wasserstoffatom bekannte Eigenschaften. So werden sie zu einem einfachen Modellsystem für grundlegende Phänomene der Quantenmechanik wie Quantisierung und Interferenz. Die Zweiphotonen-Photoemission eröffnet einen experimentellen Zugang zu den Bildpotentialzuständen mit hoher Energieauflösung im Millielektronenvoltbereich und hoher Zeitauflösung im Femtosekundenbereich. Sie macht die Bildpotentialzustände zu empfindlichen Sonden für die Messung unterschiedlicher Eigenschaften von Oberflächen und Adsorbaten.

Elements of a dielectric laser accelerator - McNeur, Joshua; Kozak, Martin; Schönenberger, Norbert; Leedle, Kenneth; Deng, Hudan; Ceballos, Andrew; Hoogland, Heinar; Ruehl, Axel; Hartl, Ingmar; Holzwarth, Ronald; Solgaard, Olav; Harris, James; et al. (arXiv, 2016)
The widespread use of high energy particle beams in basic research, medicine and coherent X-ray generation coupled with the large size of modern radio frequency (RF) accelerator devices and facilities has motivated a strong need for alternative accelerators operating in regimes outside of RF. Working at optical frequencies, dielectric laser accelerators (DLAs) - transparent laser-driven nanoscale dielectric structures whose near fields can synchronously accelerate charged particles - have demonstrated high-gradient acceleration with a variety of laser wavelengths, materials, and electron beam parameters, potentially enabling miniaturized accelerators and table-top coherent x-ray sources. To realize a useful (i.e. scalable) DLA, crucial developments have remained: concatenation of components including sustained phase synchronicity to reach arbitrary final energies as well as deflection and focusing elements to keep the beam well collimated along the design axis. Here, all of these elements are demonstrated with a subrelativistic electron beam. In particular, by creating two interaction regions via illumination of a nanograting with two spatio-temporally separated pulsed laser beams, we demonstrate a phase-controlled doubling of electron energy gain from 0.7 to 1.4 keV (2.5 percent to 5 percent of the initial beam energy) and through use of a chirped grating geometry, we overcome the dephasing limit of 25 keV electrons, increasing their energy gains to a laser power limited 10 percent of their initial energy. Further, optically-driven transverse focusing of the electron beam with focal lengths below 200 microns is achieved via a parabolic grating geometry. These results lay the cornerstone for future miniaturized phase synchronous vacuum-structure-based accelerators.

Elements of a dielectric laser accelerator - McNeur, Joshua; Kozak, Martin; Schönenberger, Norbert; Leedle, Kenneth J.; Deng, Huiyang; Ceballos, Andrew; Hoogland, Heinar; Ruehl, Axel; Hartl, Ingmar; Holzwarth, Ronald; Solgaard, Olav; Harris, J. S.; et al. (Optica, 2018)
We experimentally demonstrate several physical concepts necessary for the future development of dielectric laser accelerators—photonic elements that utilize the inelastic interaction between electrons and the optical near fields of laser-illuminated periodic nanostructures. To build a fully photonic accelerator, concatenation of elements, large energy gains, and beam steering elements are required. Staged acceleration is shown using two spatio-temporally separated interaction regions. Further, a chirped silicon grating is used to overcome the velocity dephasing of subrelativistic electrons with respect to its optical near fields, and last, a parabolic grating geometry serves for focusing of the electron bea
Keywords: dielectric laser acceleration

Elucidating structural order and disorder phenomena in mullite-type Al4B2O9 by automated electron diffraction tomography - Zhao, Haishuang; Krysiak, Yasar; Hoffmann, Kristin; Barton, Bastian; Molina-Luna, Leopoldo; Neder, Reinhard; Kleebe, Hans-Joachim; Gesing, Thorsten M.; Schneider, Hartmut; Fischer, Reinhard X.; Kolb, Ute (Journal of Solid State Chemistry, 2017)
The crystal structure and disorder phenomena of AlBO, an aluminum borate from the mullite-type family, were studied using automated diffraction tomography (ADT), a recently established method for collection and analysis of electron diffraction data. AlBO, prepared by sol-gel approach, crystallizes in the monoclinic space group C2/m. The ab initio structure determination based on three-dimensional electron diffraction data from single ordered crystals reveals that edge-connected AlO octahedra expanding along the b axis constitute the backbone. The ordered structure (A) was confirmed by TEM and HAADF-STEM images. Furthermore, disordered crystals with diffuse scattering along the b axis are observed. Analysis of the modulation pattern implies a mean superstructure (AAB) with a threefold b axis, where B corresponds to an A layer shifted by ½a and ½c. Diffraction patterns simulated for the AAB sequence including additional stacking disorder are in good agreement with experimental electron diffraction pattern
Keywords: Aluminum borate; Crystal structure determination; Disorder; Electron diffraction; Superstructure

Emergence of Asynchronous Local Clocks in Excitable Media - Gerum, Richard; Fabry, Ben; Metzner, Claus (PLoS ONE, 2015)

Emission of the THz waves from large area mesas of superconducting Bi 2Sr2CaCu2O8+δ by the injection of spin polarized current - Turkoglu, F.; Ozyuzer, O.; Koseoglu, H.; Demirhan, Y.; Preu, Sascha; Malzer, Stefan; Simsek, Yilmaz; Wang, H.B.; Müller, Paul (Physica C-Superconductivity and Its Applications, 2013)
Rectangular Au/Co/Au/BiSrCaCuO (Bi2212) mesa structures with large areas and high thicknesses were fabricated on as-grown Bi2212 single crystals in order to obtain small critical current from as-grown mesas by the injection of spin polarized current and so eliminate the adjustment of doping level for successful THz emission. We have performed c-axis resistance versus temperature (R-T), current-voltage (I-V) characteristics and bolometer measurements. It is the first time that THz emission has been observed from as-grown mesas due to injection of spin polarized current. © 2013 Elsevier Ltd. All rights reserved.
Keywords: THz waves; Intrinsic Josephson junction; Bi2212; Spin polarized current

EMPTY ORBITALS OF ADSORBATES DETERMINED BY INVERSE ULTRAVIOLET PHOTOEMISSION - Fauster, Thomas; et al. (Physical Review Letters, 1982)

ENERGY-DEPENDENCE OF CROSS-SECTIONS IN INVERSE PHOTOEMISSION - Fauster, Thomas; et al. (Physical Review B, 1984)

Enhanced In Vitro Biocompatibility and Water Dispersibility of Magnetite and Cobalt Ferrite Nanoparticles Employed as ROS Formation Enhancer in Radiation Cancer Therapy - Klein, Stefanie; Kizaloglu, Melek; Portilla Berlanga, Luis; Park, Hyoungwon; Rejek, Tobias; Hümmer, Julian; Meyer, Karsten; Hock, Rainer; Distel, Luitpold; Halik, Marcus; Kryschi, Carola (Small, 2018)

Enhanced Macroscopic Quantum Tunneling in Bi2Sr2CaCu2O8 Intrinsic Josephson Junction Stacks - Jin, X.Y.; Lisenfeld, J.; Koval, Yury; Lukashenko, Oleksandr; Ustinov, Alexey; Müller, Paul (Physical Review Letters, 2006)
We have investigated macroscopic quantum tunneling in Bi2Sr2CaCu2O8+δ intrinsic Josephson junctions at millikelvin temperatures using microwave irradiation. Measurements show that the escape rate for uniformly switching stacks of N junctions is about N2 times higher than that of a single junction having the same plasma frequency. We argue that this gigantic enhancement of the macroscopic quantum tunneling rate in stacks is boosted by current fluctuations which occur in the series array of junctions loaded by the impedance of the environment. © 2006 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.pephys.enhanc

Enhancement of Josephson phase diffusion by microwaves - Koval, Yury; Fistul, Mikhail; Ustinov, Alexey (Physical Review Letters, 2004)
The effect of microwave irradiation on the phase diffusion mesoscopic Josephson junctions was analyzed. Investigations show a smooth and incoherent enhancement of Josephson phase diffusion in small junctions by the microwaves. It was found that the voltage position Vtop of the peak increased with the power P of microwave irradiation and its current amplitude decreased with P. The results show the enhancement of incoherent superconducting current by the multiphoton absorption.
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.IAP.pephys.enhanc

Enhancement of optical absorption and photocurrent of 6H-SiC by laser surface nanostructuring - Zhao, Quanzhong; Ciobanu, Florin; Malzer, Stefan; Wang, Lijun (Applied Physics Letters, 2007)
Nanoscale ripple structures with spatial periods of up to 155 nm are generated by a single beam ultrashort pulsed laser structuring of 6H-SiC surface. The period of nanoripples does not depend on the laser fluence and the number of pulses. Optical absorption and photocurrent measurements on SiC samples are investigated before and after laser nanostructuring. Nearly 40% enhancement of optical absorption and a factor of 3 increase of photocurrent are achieved after laser nanostructuring. © 2007 American Institute of Physics.

Enhancement of the critical current of intrinsic Josephson junctions by carrier injection - Kizilaslan, O.; Simsek, Yilmaz; Aksam, M.; Koval, Yury; Müller, Paul (Superconductor Science and Technology, 2015)
We present a study of the doping effect by carrier injection of high-Tc superconducting Bi-based whiskers. The current was injected in the c-axis direction, i.e., perpendicular to the superconducting planes. Superconducting properties were investigated systematically as a function of the doping level. The doping level of one and the same sample was changed by current injection in very small steps from an underdoped state up to a slightly overdoped state. We have observed that Tc versus log (jc) exhibits a dome-shaped characteristic, which can be fitted by a parabola. As Tc versus carrier concentration has a parabolic form, too, it can be concluded that the critical current density jc increases exponentially with the doping level. The electron-trapping mechanism is interpreted in the framework of Phillips' microscopic theory. In addition, the Joule heating effect in the intrinsic Josephson junction (IJJ) was controlled by carrier injection, and the effect of the non-equilibrium quasiparticle on the I-V curves of the IJJs was also discussed.
Keywords: carrier injection; intrinsic Josephson junction; superconductivity

Ensemble modeling of very small ZnO nanoparticles - Niederdraenk, Franziska; Seufert, Knud; Stahl, Andreas; Bhalerao-Panajkar, Rohini S.; Marathe, Sonali; Kulkarni, Sulabha K.; Neder, Reinhard; Kumpf, Christian (Physical Chemistry Chemical Physics, 2011)
The detailed structural characterization of nanoparticles is a very important issue since it enables a precise understanding of their electronic, optical and magnetic properties. Here we introduce a new method for modeling the structure of very small particles by means of powder X-ray diffraction. Using thioglycerol-capped ZnO nanoparticles with a diameter of less than 3 nm as an example we demonstrate that our ensemble modeling method is superior to standard XRD methods like, e. g., Rietveld refinement. Besides fundamental properties (size, anisotropic shape and atomic structure) more sophisticated properties like imperfections in the lattice, a size distribution as well as strain and relaxation effects in the particles and-in particular-at their surface (surface relaxation effects) can be obtained. Ensemble properties, i.e., distributions of the particle size and other properties, can also be investigated which makes this method superior to imaging techniques like (high resolution) transmission electron microscopy or atomic force microscopy, in particular for very small nanoparticles. For the particles under study an excellent agreement of calculated and experimental X-ray diffraction patterns could be obtained with an ensemble of anisotropic polyhedral particles of three dominant sizes, wurtzite structure and a significant relaxation of Zn atoms close to the surface.