Resonance behavior of defect-induced modes in metallic and semiconducting single-walled carbon nanotubes - Laudenbach, Jan; Hennrich, Frank; Kappes, Manfred; Maultzsch, Janina (physica status solidi (b), 2012)
We analyze the defect-induced Raman mode (D mode) and the second order 2D mode of samples enriched with metallic and semiconducting single-walled carbon nanotube (SWCNT). By resonance Raman spectroscopy, we study the evolution of the line shape of the D and 2D mode. We compared the radial-breathing mode (RBM) frequencies with different components of the D and 2D mode in the enriched samples and a non-enriched SWCNT reference material. We show that the components of the broad D mode can be assigned to different species of nanotubes and that this assignment is not necessarily correlated to the RBM for the same excitation energy. Raman intensity of the 2D mode for differently enriched samples and comparison with a reference sample. The gray spectrum is the sum of the spectra from the enriched samples.
Keywords: SWCNT; enriched; resonance Raman; D mode

Resonance behavior of the defect-induced Raman mode of single-chirality enriched carbon nanotubes - Laudenbach, Jan; Hennrich, Frank; Telg, Hagen; Kappes, Manfred; Maultzsch, Janina (Physical Review B, 2013)
We present a resonance Raman study of the disorder-induced D mode in a sample highly enriched with semiconducting (9,7) single-walled carbon nanotubes in the excitation energy range of 1.49-2.05 eV. The intensity of the D mode shows a resonance behavior near the optical transition of the (9,7) tube. The well-known dispersion of the D-mode frequency, on the other hand, is not observed at the resonance, but only above a certain excitation energy. We explain our results by numerical simulations of the D-mode spectra. DOI: 10.1103/PhysRevB.87.165423

Resonance Profiles of Valley Polarization in Single-Layer MoS2 and MoSe2 - Tornatzky, Hans; Kaulitz, Anne-Marie; Maultzsch, Janina (Physical Review Letters, 2018)

Resonant photoconductor structures for the generation of microwave currents: Importance of space charges - Hundhausen, Martin; Ley, Lothar; et al. (proc. 23rd Int. Conf. on the Physics of Semiconductors, 1996)
UnivIS-Import:2015-04-16:Pub.1996.nat.dphy.IAP.exphys.resona

Resonant-Raman intensities and transition energies of the E-11 transition in carbon nanotubes - Telg, Hagen; Maultzsch, Janina; Reich, Stephanie; Thomsen, Christian (Physical Review B, 2006)
We observed the lowest optical transitions (E-11(S)) in separated carbon nanotubes by resonant Raman spectroscopy. Radial breathing mode spectra were collected varying the excitation energy in the near-infrared from 1.15 to 1.48 eV. From resonance profiles we obtained the E-11(S) energies of 11 nanotubes, extending the experimental Kataura plot. Strong Raman signal from tubes with nu=(n-m)mod3=+1 and from tubes that were absent in photoluminescence support the theory of exciton resonance. The measured Raman intensities agree well with the calculated optical absorption and electron-phonon coupling obtained with first-principles and empirical methods. A remaining factor of similar to 3 can be due to a higher abundance of armchairlike tubes or differences of the absorption and vibrational coupling between correlated (excitons) and uncorrelated electron-hole pairs.

Resonant Raman profiles and micro-photoluminescence of atomically thin layers of molybdenum disulfide - Scheuschner, Nils; Ochedowski, Oliver; Schleberger, Marika; Maultzsch, Janina (physica status solidi (b), 2012)
Schematic crystal structure of molybdenum disulfide. (a) Top view (slightly tilted). (b) Side view. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Keywords: excitons; molybdenum disulfide; photoluminescence; Raman

Resonant Raman scattering in GaAs induced by an embedded InAs monolayer - Maultzsch, Janina; et al. (Physical Review B, 2001)
We studied the resonant Raman intensity of GaAs optical phonons when the laser energy is tuned to the optical transition of an InAs monolayer embedded in the bulklike GaAs. The GaAs longitudinal-optical modes interact with heavy and light holes of the InAs via elastic scattering followed by Frohlich interaction. The redshift of the Raman profile compared to photoluminescence excitation measurements and the vanishing of the GaAs resonance around 30 K are explained by the homogeneous exciton Linewidth in the InAs monolayer.

Resonant Raman scattering on carbon nanotubes covalently functionalized with lithium decyne - Müller, Matthias; Meinke, Reinhard; Maultzsch, Janina; Gebhardt, Benjamin; Hauke, Frank; Hirsch, Andreas; Thomsen, Christian (physica status solidi (b), 2010)
We present resonant Raman measurements on single-walled carbon nanotubes covalently functionalized with lithium decyne. We study the influence of the functional moieties on the optical transitions of the nanotubes. From the extracted resonance profiles of the radial breathing modes the chiral indices of the corresponding tubes are assigned. Slight red shifts of the optical transitions are observed, which implies only a little charge transfer due to the chemical reaction. The reaction shows a pronounced diameter dependence as previously observed for comparable reactions with different addends.Carbon nanotubes covalently functionalized with decyne moieties. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Resonant Raman spectroscopy of nanotubes - Maultzsch, Janina; et al. (Philosophical Transactions of the Royal Society A-Mathematical Physical and Engineering Sciences, 2004)
Single and double resonances in Raman scattering are introduced and six criteria for the observation and identification of double resonances stated. The experimental situation in carbon nanotubes is reviewed in view of these criteria. The evidence for the D mode and the high-energy mode is found to be overwhelming for a double-resonance process to take place, whereas the nature of the radial breathing-mode Raman process remains undecided at this point. Consequences for the application of Raman scattering to the characterization of nanotubes are discussed.
Keywords: carbon nanotubes; double resonance; Raman scattering; defects

Resonant Vibrations, Peak Broadening, and Noise in Single Molecule Contacts: The Nature of the First Conductance Peak - Secker, Daniel; Wagner, Stefan; Ballmann, Stefan Dieter; Härtle, Rainer; Thoss, Michael; Weber, Heiko B. (Physical Review Letters, 2011)
We carry out experiments on single-molecule junctions at low temperatures, using the mechanically controlled break junction technique. Analyzing the results obtained with various molecules, the nature of the first peak in the differential conductance spectra is elucidated. We observe an electronic transition with a vibronic fine structure, if the first peak occurs at small voltages. This regime can accurately be described by the resonant tunneling model. At higher voltages, additional smearing is observed and no fine structure can be resolved. A detailed analysis of the noise signal indicates that the onset of current is associated with strong fluctuations as a precursor of current flow. The data indicate that a complex fluctuation-driven transport mechanism takes over in this regime. © 2011 American Physical Society.
UnivIS-Import:2015-04-14:Pub.2011.nat.dphy.IAP.LAP.resona

Respiratory comfort of automatic tube compensation and inspiratory pressure support in conscious humans - Fabry, Ben; et al. (Intensive Care Medicine, 1997)

Restoring the surface layer of Bi2Sr2CaCu2O8+? single crystals by current injection - Simsek, Yilmaz; Müller, Paul (Surfaces and Interfaces, 2022)
In 2010, we reported a new method to electronically tailor the hole concentration of the high-Tc superconductor Bi2Sr2CaCu2O8+delta (Bi-2212). We discovered that current injection along the c-axis of Bi-2212 provides a convenient tool to reversibly increase the carrier concentration. In this study, we have investigated the current injection effect on the surface junction of Bi-2212 by a series of current injection experiments carried out in samples of slightly overdoped and of extremely underdoped Bi-2212 crystals. The c-axis transport characteristics of bulk and surface intrinsic Josephson junctions are examined in a wide range of doping by current injection. Before injection treatment, typically, our samples demonstrate non-superconducting characteristics across their surface junctions, because standard preparation procedures cause the topmost CuO2 layers to be heavily degraded by oxygen loss. The electronic doping enables to substantially restore the hole concentration of the topmost CuO2 layers. The contact resistance is significantly reduced, and the intrinsic junction at the surface gets back its superconducting tunneling characteristic. We examine systematically the doping results of surface and bulk junction stacks and discuss the enhancement of their superconducting properties.
CRIS-Team WoS Importer:2022-09-02

Revealing the origin of high-energy Raman local mode in nitrogen doped ZnO nanowires - Khachadorian, Sevak; Gillen, Roland; Thon-Tat, C; Zhu, L. C.; Maultzsch, Janina; Phillips, Matthew R.; Hoffmann, Axel (Physica Status Solidi-Rapid Research Letters, 2016)
Raman scattering experiments complemented by density functional theory (DFT) calculations of phonon frequencies have been performed to understand the origin of observed high-energy local Raman modes at 2269 cm(-1) and 2282 cm(-1) on N-plasma treated ZnO nanowires (NWs). We show that these modes increase in intensity with prolonged N-plasma treatment. Our results reveal that the origin of the high-energy Raman local mode is a loosely bound N-2 molecule in the vicinity of a zinc vacancy, which according to our latest work acts as a shallow acceptor and leads to the donor-acceptor-pair transition at 3.232 eV [Phys. Rev. B 92, 024103 (2015)]. Moreover the results provide a more thorough description of nitrogen related complexes in ZnO NWs. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhe
Keywords: zinc oxide; nanowires; nitrogen; doping; Raman spectroscopy; phonons; density function theory

Revealing the strain-associated physical mechanisms impacting the performance and stability of perovskite solar cells - Meng, Wei; Zhang, Kaicheng; Osvet, Andres; Zhang, Jiyun; Gruber, Wolfgang; Forberich, Karen; Meyer, Bernd; Heiß, Wolfgang; Unruh, Tobias; Li, Ning; Brabec, Christoph (Joule, 2022)
Identification and investigation of strain at buried interfaces in halide perovskite photovoltaics are crucial for directing research on the performance and stability of perovskite solar cells. In this work, we find a gradual shift in the band gap of up to 60 meV over a perovskite layer thickness of 300 nm caused by interfacial strain. This graded band gap is desired insofar as it relates to the aspect of device engineering. However, in parallel, the increased defect density causes charge recombination at the buried interface. These two effects compensate for each other, resulting in an overall performance improvement under standard 1 sun illumination. Nevertheless, the disadvantage of enhanced defect density is clearly observed at low-light intensities, where the device performance becomes dominated by charge recombination and ion migration. Moreover, the strained interfaces are proven to induce enhanced defect densities, causing significantly accelerated device degradation under illumination as well as in the dark.
CRIS-Team Scopus Importer:2022-03-18
Keywords: device stability; graded band gap; interface engineering; low-light PV applications; perovskite solar cells; strain engineering

Reversible Basal Plane Hydrogenation of Graphene - Ryu, Sunmin; Han, Melinda Y.; Maultzsch, Janina; Heinz, Tony F.; Kim, Philip; Steigerwald, Michael L.; Brus, Louis E. (Nano Letters, 2008)
We report the chemical reaction of single-layer graphene with hydrogen atoms, generated in situ by electron-induced dissociation of hydrogen silsesquioxane (HSQ). Hydrogenation, forming sp(3) C-H functionality on the basal plane of graphene, proceeds at a higher rate for single than for double layers, demonstrating the enhanced chemical reactivity of single sheet graphene. The net H atom sticking probability on single layers at 300 K is at least 0.03, which exceeds that of double layers by at least a factor of 15. Chemisorbed hydrogen atoms, which give rise to a prominent Raman D band, can be detached by thermal annealing at 100 similar to 200 degrees C. The resulting dehydrogenated graphene is "activated" when photothermally heated it reversibly binds ambient oxygen, leading to hole doping of the graphene. This functionalization of graphene can be exploited to manipulate electronic and charge transport properties of graphene devices.

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

Reviews and syntheses: A framework to observe, understand and projectecosystem response to environmental change in the East Antarctic SouthernOcean - Gutt, Julian; Arndt, Stefanie; Barnes, David Keith Alan; Bornemann, Horst; Brey, Thomas; Eisen, Olaf; Flores, Hauke; Griffiths, Huw; Haas, Christian; Hain, Stefan; Hattermann, Tore; Held, Christoph; et al. (Biogeosciences, 2022)
Systematic long-term studies on ecosystem dynamics are largelylacking from the East Antarctic Southern Ocean, although it is wellrecognized that they are indispensable to identify the ecological impactsand risks of environmental change. Here, we present a framework forestablishing a long-term cross-disciplinary study on decadal timescales. Weargue that the eastern Weddell Sea and the adjacent sea to the east, offDronning Maud Land, is a particularly well suited area for such a study,since it is based on findings from previous expeditions to this region.Moreover, since climate and environmental change have so far beencomparatively muted in this area, as in the eastern Antarctic in general, asystematic long-term study of its environmental and ecological state canprovide a baseline of the current situation, which will be important for anassessment of future changes from their very onset, with consistent andcomparable time series data underpinning and testing models and theirprojections. By establishing an Integrated East Antarctic MarineResearch (IEAMaR) observatory, long-term changes in ocean dynamics,geochemistry, biodiversity, and ecosystem functions and services will besystematically explored and mapped through regular autonomous and ship-basedsynoptic surveys. An associated long-term ecological research (LTER)programme, including experimental and modelling work, will allow forstudying climate-driven ecosystem changes and interactions with impactsarising from other anthropogenic activities. This integrative approach willprovide a level of long-term data availability and ecosystem understandingthat are imperative to determine, understand, and project the consequencesof climate change and support a sound science-informed management of futureconservation efforts in the Southern Ocean.
CRIS-Team WoS Importer:2022-12-16

RFIDeep: Unfolding the potential of deep learning for radio-frequency identification - Bardon, Gaël; Cristofari, Robin; Winterl, Alexander; Barracho, Téo; Benoiste, Marine; Ceresa, Claire; Chatelain, Nicolas; Courtecuisse, Julien; Fernandes, Flávia A.N.; Gauthier-Clerc, Michel; Gendner, Jean Paul; Handrich, Yves; et al. (Methods in Ecology and Evolution, 2023)
Automatic monitoring of wildlife is becoming a critical tool in the field of ecology. In particular, Radio-Frequency IDentification (RFID) is now a widespread technology to assess the phenology, breeding and survival of many species. While RFID produces massive datasets, no established fast and accurate methods are yet available for this type of data processing. Deep learning approaches have been used to overcome similar problems in other scientific fields and hence might hold the potential to overcome these analytical challenges and unlock the full potential of RFID studies. We present a deep learning workflow, coined “RFIDeep”, to derive ecological features, such as breeding status and outcome, from RFID mark-recapture data. To demonstrate the performance of RFIDeep with complex datasets, we used a long-term automatic monitoring of a long-lived seabird that breeds in densely packed colonies, hence with many daily entries and exits. To determine individual breeding status and phenology and for each breeding season, we first developed a one-dimensional convolution neural network (1D-CNN) architecture. Second, to account for variance in breeding phenology and technical limitations of field data acquisition, we built a new data augmentation step mimicking a shift in breeding dates and missing RFID detections, a common issue with RFIDs. Third, to identify the segments of the breeding activity used during classification, we also included a visualisation tool, which allows users to understand what is usually considered a “black box” step of deep learning. With these three steps, we achieved a high accuracy for all breeding parameters: breeding status accuracy = 96.3%; phenological accuracy = 86.9%; and breeding success accuracy = 97.3%. RFIDeep has unfolded the potential of artificial intelligence for tracking changes in animal populations, multiplying the benefit of automated mark-recapture monitoring of undisturbed wildlife populations. RFIDeep is an open source code to facilitate the use, adaptation, or enhancement of RFID data in a wide variety of species. In addition to a tremendous time saving for analysing these large datasets, our study shows the capacities of CNN models to autonomously detect ecologically meaningful patterns in data through visualisation techniques, which are seldom used in ecology.
CRIS-Team Scopus Importer:2023-11-10
Keywords: artificial intelligence; behaviour; machine learning; RFID; wildlife monitoring

Rheology of airway smooth muscle cells is associated with cytoskeletal contractile stress - Stamenovic, Dimitrije; Suki, Bela; Fabry, Ben; Wang, Ning; Fredberg, Jeffrey (Journal of Applied Physiology, 2004)
Recently reported data from mechanical measurements of cultured airway smooth muscle cells show that stiffness of the cytoskeletal matrix is determined by the extent of static contractile stress borne by the cytoskeleton (Wang N, Tolić-Nørrelykke IM, Chen J, Mijailovich SM, Butler JP, Fredberg JJ, and Stamenović D. Am J Physiol Cell Physiol 282, C606-C616, 2002). On the other hand, rheological measurements on these cells show that cytoskeletal stiffness changes with frequency of imposed mechanical loading according to a power law (Fabry B, Maksym GN, Butler JP, Glogauer M, Navajas DF, and Fredberg JJ. Phys Rev Lett 87: 148102, 2001). In this study, we examine the possibility that these two empirical observations might be interrelated. We combine previously reported data for contractile stress of human airway smooth muscle cells with new data describing rheological properties of these cells and derive quantitative, mathematically tractable, and experimentally verifiable empirical relationships between contractile stress and indexes of cell rheology. These findings reveal an intriguing role of the contractile stress: although it maintains structural stability of the cell under applied mechanical loads, it may also regulate rheological properties of the cytoskeleton, which are essential for other cell function
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.IAP.lpmt.rheolo
Keywords: Contractility; Cytometry; Mechanics; Power law; Stiffness

Roadmap on organic-inorganic hybrid perovskite semiconductors and devices - Schmidt-Mende, Lukas; Dyakonov, Vladimir; Olthof, Selina; Ünlü, Feray; Lê, Khan Moritz Trong; Mathur, Sanjay; Karabanov, Andrei D.; Lupascu, Doru C.; Herz, Laura M.; Hinderhofer, Alexander; Schreiber, Frank; Chernikov, Alexey; et al. (APL Materials, 2021)
Metal halide perovskites are the first solution processed semiconductors that can compete in their functionality with conventional semiconductors, such as silicon. Over the past several years, perovskite semiconductors have reported breakthroughs in various optoelectronic devices, such as solar cells, photodetectors, light emitting and memory devices, and so on. Until now, perovskite semiconductors face challenges regarding their stability, reproducibility, and toxicity. In this Roadmap, we combine the expertise of chemistry, physics, and device engineering from leading experts in the perovskite research community to focus on the fundamental material properties, the fabrication methods, characterization and photophysical properties, perovskite devices, and current challenges in this field. We develop a comprehensive overview of the current state-of-the-art and offer readers an informed perspective of where this field is heading and what challenges we have to overcome to get to successful commercialization.
CRIS-Team Scopus Importer:2021-11-19

Robot-Based High-Throughput Engineering of Alcoholic Polymer: Fullerene Nanoparticle Inks for an Eco-Friendly Processing of Organic Solar Cells - Xie, Chen; Tang, Xiaofeng; Berlinghof, Marvin; Langner, Stefan; Chen, Shi; Späth, Andreas; Li, Ning; Fink, Rainer; Unruh, Tobias; Brabec, Christoph (ACS Applied Materials and Interfaces, 2018)
Development of high-quality organic nanoparticle inks is a significant scientific challenge for the industrial production of solution processed organic photovoltaics (OPVs) with eco-friendly processing methods. In this work, we demonstrate a novel, robot-based, high throughput procedure performing automatic poly(3-hexylthio-phene-2,5-diyl) and indene-C-60 bisadduct nanoparticle ink synthesis in nontoxic alcohols. A novel methodology to prepare particle dispersions for fully functional OPVs by manipulating the particle size and solvent system was studied in detail. The ethanol dispersion with a particle diameter of around 80-100 nm exhibits reduced degradation, yielding a power conversion efficiency of 4.52%, which is the highest performance reported so far for water/alcohol-processed OPV devices. By successfully deploying the high-throughput robot-based approach for an organic nanoparticle ink preparation, we believe that the findings demonstrated in this work will trigger more research interest and effort on eco-friendly industrial production of OPVs.
Keywords: organic photovoltaics; eco-friendly industrial production; robot-based systems; high-throughput organic nanoparticle synthesis; stable organic nanoparticle inks; organic nanoparticle size control

Robust graphene membranes in a silicon carbide frame - Waldmann, Daniel; Butz, Benjamin; Bauer, Sebastian; Englert, Jan; Jobst, Johannes; Ullmann, Konrad; Fromm, Felix; Ammon, Maximilian Michael; Enzelberger-Heim, Michael; Hirsch, Andreas; Maier, Sabine; Schmuki, Patrik; et al. (ACS nano, 2013)
We present a fabrication process for freely suspended membranes consisting of bi- and trilayer graphene grown on silicon carbide. The procedure, involving photoelectrochemical etching, enables the simultaneous fabrication of hundreds of arbitrarily shaped membranes with an area up to 500 μm(2) and a yield of around 90%. Micro-Raman and atomic force microscopy measurements confirm that the graphene layer withstands the electrochemical etching and show that the membranes are virtually unstrained. The process delivers membranes with a cleanliness suited for high-resolution transmission electron microscopy (HRTEM) at atomic scale. The membrane, and its frame, is very robust with respect to thermal cycling above 1000 °C as well as harsh acidic or alkaline treatment.

Robustness of Momentum-Indirect Interlayer Excitons in MoS2/WSe2 Heterostructure against Charge Carrier Doping - Khestanova, Ekaterina; Ivanova, Tatyana; Gillen, Roland; D'Elia, Alessandro; Lacey, Oliver Nicholas Gallego; Wysocki, Lena; Grueneis, Alexander; Kravtsov, Vasily; Strupinski, Wlodek; Maultzsch, Janina; Kandyba, Viktor; Cattelan, Mattia; et al. (ACS Photonics, 2022)
Monolayer transition-metal dichalcogenide (TMD) semiconductors exhibit strong excitonic effects and hold promise for optical and optoelectronic applications. Yet, electron doping of TMDs leads to the conversion of neutral excitons into negative trions, which recombine predominantly nonradiatively at room temperature. As a result, the photoluminescence (PL) intensity is quenched. Here we study the optical and electronic properties of a MoS2/WSe2 heterostructure as a function of chemical doping by Cs atoms performed under ultrahigh vacuum conditions. By PL measurements, we identify two interlayer excitons and assign them to the momentum-indirect Q-Γ and K-Γ transitions. The energies of these excitons are in very good agreement with ab initio calculations. We find that the Q-Γ interlayer exciton is robust to the electron doping and is present at room temperature even at a high charge carrier concentration (∼1013 cm-2). Submicrometer angle-resolved photoemission spectroscopy (μ-ARPES) reveals a charge transfer from deposited Cs adatoms to both the upper MoS2 and the lower WSe2 monolayers without changing the band alignment. This leads to a small (∼10 meV) energy shift of interlayer excitons. Robustness of the momentum-indirect interlayer exciton to charge doping opens up an opportunity for using TMD heterostructures in light-emitting devices that can work at room temperature at high densities of charge carriers.
CRIS-Team Scopus Importer:2023-03-27
Keywords: alkali metal-doped TMDs; clean TMD heterobilayer; indirect excitons in WSe; photoluminescence in doped TMD heterobilayers; Γ-Q exciton in WSe

Robust Pore Size Analysis of Filamentous Networks from Three-Dimensional Confocal Microscopy - Mickel, Walter; Münster, Stefan; Jawerth, Louise M.; Vader, David A.; Weitz, David A.; Sheppard, Adrian P.; Mecke, Klaus; Fabry, Ben; Schröder-Turk, Gerd (Biophysical Journal, 2008)
We describe a robust method for determining morphological properties of. lamentous biopolymer networks, such as collagen or other connective tissue matrices, from confocal microscopy image stacks. Morphological properties including pore size distributions and percolation thresholds are important for transport processes, e. g., particle diffusion or cell migration through the extracellular matrix. The method is applied to fluorescently labeled fiber networks prepared from rat-tail tendon and calf-skin collagen, at concentrations of 1.2, 1.6, and 2.4 mg/ml. The collagen fibers form an entangled and branched network. The medial axes, or skeletons, representing the collagen fibers are extracted from the image stack by threshold intensity segmentation and distance-ordered homotopic thinning. The size of the fiuid pores as defined by the radii of largest spheres that fit into the cavities between the collagen fibers is derived from Euclidean distance maps and maximal covering radius transforms of the fluid phase. The size of the largest sphere that can traverse the fluid phase between the collagen fibers across the entire probe, called the percolation threshold, was computed for both horizontal and vertical directions. We demonstrate that by representing the fibers as the medial axis the derived morphological network properties are both robust against changes of the value of the segmentation threshold intensity and robust to problems associated with the point-spread function of the imaging system. We also provide empirical support for a recent claim that the percolation threshold of a fiber network is close to the fiber diameter for which the Euler index of the networks becomes zero.

Role of disorder on transport in boron-doped multiwalled carbon nanotubes - Krstic, Vojislav; Blumentritt, Siegmar; Muster, Jörg; Roth, Siegmar; Rubio, Angel (Physical Review B, 2003)
Electrical transport measurements on boron-doped multiwalled carbon nanotubes deposited on top of predefined electrode patterns have been performed. The temperature dependence of the conductance reveals through two-point configuration, the appearance of a zero-bias anomaly which was found to be not compatible with the existence of a Luttinger-liquid-like state in the doped multiwalled carbon nanotubes. The experimental findings indicate that, in order to properly interpret the charge transport properties of multiwalled carbon nanotubes, the doping as well as the energy window in which the experiments are performed are crucial points.

Role of ERK MAP kinases in responses of cultured human airway smooth muscle cells to IL-1beta - Laporte, Johanne D.; Moore, Paul E.; Abraham, Jonathan H.; Maksym, Geoffrey N.; Fabry, Ben; Panettieri, Reynold A.; Shore, Stephanie A. (American Journal of Physiology, 1999)

Role of Fiber Thickness and Surface Treatment of Electrospun Polycaprolactone Matrices on the Growth of Different Breast Cancer‐Associated Cells - Sivakumar, Sankaranarayanan; Schmid, Rafael; Wieland, Annalena; Strissel, Pamela; Strick, Reiner; Fischer, Lena; Thievessen, Ingo; Kataev, Elmar; Arkudas, Andreas; Horch, Raymund E.; Schubert, Dirk W.; Kengelbach-Weigand, Annika (Advanced Materials Interfaces, 2022)
Cancer models mimicking the tumor microenvironment are necessary to successfully develop and predict responses of oncological drugs. In this study, electrospun polycaprolactone (PCL) matrices are tested for the development of an in vitro breast cancer model. The effects of fiber thickness and plasma-treatment of the matrices on in vitro growth of breast cancer-associated cells, namely breast cancer cells MDA-MB-231, primary adipose-derived stem cells (ADSCs) and primary endothelial progenitor cells (EPCs) are evaluated. Surface treatment of the matrices by air-plasma leads to increased oxygen/carbon ratio and hydrophilicity. WST-8 analysis reveals that the proliferation of all three cell types increased exponentially over 12 d on all matrices. MDA-MB-231 and ADSC show a higher proliferation on nanofibers due to enhanced cellular adhesion compared to microfibers. In contrast, EPCs show a significantly higher proliferation on microfibers than on nanofibers at day 12 which can further be significantly improved by air-plasma treatment. Cross-sectioning analysis shows that cells grow on the surface of nanofibers, while microfibers have considerable cellular infiltration. These findings suggest that the electrospun PCL matrices are a suitable tool for the development of breast cancer models containing several cell types, which can ultimately lead to designing novel tumor therapies.<br

Role of Heat Shock Protein 27 in Cytoskeletal Remodeling of the Airway Smooth Muscle Cell - An, Steven S.; Fabry, Ben; Mellema, Mathew; Bursac, Predrag; Gerthoffer, William T.; Kayyali, Usamah S.; Gaestel, Matthias; Shore, Stephanie A.; Fredberg, Jeffrey (Journal of Applied Physiology, 2004)

ROOM-TEMPERATURE INSTABILITY OF CO/CU(111) - Fauster, Thomas; et al. (Physical Review Letters, 1994)

Room-temperature sol-gel synthesis of organic ligand-capped ZnO nanoparticles - Zobel, Mirijam; Chatterjee, Haimantee; Matveeva, Galina; Kolb, Ute; Neder, Reinhard (Journal of Nanoparticle Research, 2015)
Powders of zinc oxide nanoparticles with individual particle sizes below 10 nm in diameter are readily produced in base-induced sol-gel processes from ethanolic solutions of zinc acetate dihydrate. These particles are covered with acetate molecules and without further stabilization, they grow when stored as a powder. Here, we present three organic ligands, which reproducibly stabilize individual particle sizes <5 nm within the agglomerated powders for extended periods of time, up to months. Citric acid and 1,5-diphenyl-1,3,5-pentanetrione result in average diameters of 3 nm, whereas dimethyl-L-tartrate stabilizes 2.1 nm. X-ray diffraction and pair distribution function analysis were used to investigate the structural properties of the particles. TEM data confirm the individual particle size and crystallinity and show that the particles are agglomerated without structural coherence. Besides the introduction of these novel ligands for ZnO nanoparticles, we investigated, in particular, the influence of each synthesis step onto the final nanoparticle size in the powder. Previous studies often reported the employed synthesis parameters, but did not motivate the reasoning for their choice based on detailed experimental observations. Herein, we regard separately the steps of (i) the synthesis of the colloids, (ii) their precipitation, and (iii) the drying of the resulting gel to understand the role of the ligands therein. ZnO particles only covered with acetate grow to 5 nm during the drying process, whereas particles with any of the additional ligands retain their colloidal size of 2-3 nm. This clearly shows the efficient binding and effect of the presented ligands.
Keywords: ZnO; Nanoparticle; Sol-gel synthesis; Organic ligand; Room temperature synthesis

Room temperature terahertz detection by rectifying field effect transistors - Preu, Sascha; Regensburger, Stefan; Lu, Hong; Gossard, A. C. (8th German Microwave Conference, GeMiC 2014, 2019)
Rectifying field effect transistors have become versatile Terahertz detectors. We will discuss the detection mechanism. The state of the art in rectifying field effect transistors will be reviewed, showing that this novel detector concept is already comparable to well developed Schottky diode technology. The paper will discuss advantages and disadvantages of III-V materials vs. Si-based transistors. We report on ultrafast direct detection with large area GaAs-based field effect transistors at room temperature.
CRIS-Team Scopus Importer:2019-10-22
Keywords: Field effect transistor; Rectification; THz detection

Sample size estimation: Current practice and considerations for original investigations in MRI technical development studies - Hanspach, Jannis; Nagel, Armin Michael; Hensel, Bernhard; Uder, Michael; Koros, Leon; Laun, Frederik Bernd (Magnetic Resonance in Medicine, 2020)
Purpose: To investigate and to provide guidance for sample size selection based on the current practice in MR technical development studies in which healthy volunteers are examined. Methods: All original articles published in Magnetic Resonance in Medicine between 2017 and 2019 were investigated and categorized according to technique, anatomical region, and magnetic field strength. The number of examined healthy volunteers (ie, the sample size) was collected and evaluated, whereas the number of patients was not considered. Papers solely measuring patients, animals, phantoms, specimens, or studies using existing data, for example, from an open databank, or consisting only of theoretical work or simulations were excluded. Results: The median sample size of the 882 included studies was 6. There were some peaks in the sample size distribution (eg, 1, 5, and 10). In 49.9%, 82.1%, and 95.6% of the studies, the sample size was smaller or equal to 5, 10, and 20, respectively. Conclusion: We observed a large variance in sample sizes reflecting the variety of studies published in Magnetic Resonance in Medicine. Therefore, it can be concluded that it is current practice to balance the need for statistical power with the demand to minimize experiments involving healthy humans, often by choosing small sample sizes between 1 and 10. Naturally, this observation does not release an investigator from ensuring that sufficient data are acquired to reach statistical conclusions.
CRIS-Team Scopus Importer:2020-10-23
Keywords: current practice; methodological MRI developments; number of subjects; number of volunteers; proof-of-principle studies; sample size estimation

Sample thickness effect of thermal vibration correction within X-ray dynamical theory for germanium-doped silicon - Li, Zhen; Will, Johannes; Dong, Peng; Yang, Daren (Journal of Applied Physics, 2017)
As of today, highly germanium doped Czochralski silicon crystals are used in applications. However, it is not clear how a germanium content in the range of 10(18) atoms/cm(3) influences the oxygen precipitation behavior, which is highly relevant for the gettering potential of the wafer. In this context, high energy X-ray diffraction is a promising tool to monitor real-time the strain introduced by the oxygen agglomeration and growth. Nevertheless, in particular, in the dynamical limit of X-ray diffraction and at elevated temperatures, the strain originating from the precipitation process has to be clearly distinguished from the intensity contribution of thermal vibrations. In Laue geometry, dynamical effects can even lead to an increment of the integrated intensity with temperature completely unexpected in the kinematical limit, where temperature is tackled solely by a Debye-Waller factor. In the following, an approach is presented allowing us to completely correct the influence of thermal vibrations in the dynamical limit. This approach is applied to undoped and highly germanium doped silicon crystals, clearly revealing an enhanced inventory of grown-in precipitates with germanium doping and suggesting a morphological transformation towards a phase of higher strain of the grown-in precipitates in the range between room temperature and 800 degrees C. Published by AIP Publishing.

Saw Palmetto may fight prostate cancer - Goldmann, Wolfgang (Cell Biology International, 2023)
CRIS-Team Scopus Importer:2023-06-30

Scalable production of graphene sheets by mechanical delamination - Knieke, Catharina; Berger, Angela; Voigt, Michael; Klupp Taylor, Robin; Röhrl, Jonas; Peukert, Wolfgang (Carbon, 2010)
Mono- and multilayer graphene sheets have been successfully produced from commercial graphite powder in a wet grinding process under mild milling conditions. The shear forces in the milling chamber lead to a continuous delamination of ultrathin graphene flakes which are dispersed in a liquid medium. To avoid agglomeration of the exfoliated flakes the anionic surfactant sodium dodecyl sulfate was used. By adjusting the process parameters in a way to overcome the weak interlayer forces between the sheets without breaking them leads to the fabrication of thin flakes with high aspect ratios. The presented scalable process allows a high-yield and low-cost production of free-standing graphene sheets for various application
Keywords: monolayer; graphene; graphite; wet; grinding; interlayer; forces; flake; scaleable; sheet

Scaling the laws of thermal imaging–based whale detection - Zitterbart, Daniel P.; Smith, Heather R.; Flau, Michael; Richter, Sebastian; Burkhardt, Elke; Beland, Joe; Bennett, Louise; Cammareri, Alejandro; Davis, Andrew; Holst, Meike; Lanfredi, Caterina; Michel, Hanna; et al. (Journal of Atmospheric and Oceanic Technology, 2020)
Marine mammals are under growing pressure as anthropogenic use of the ocean increases. Ship strikes of large whales and loud underwater sound sources including air guns for marine geophysical prospecting and naval midfrequency sonar are criticized for their possible negative effects on marine mammals. Competent authorities regularly require the implementation of mitigation measures, including vessel speed reductions or shutdown of acoustic sources if marine mammals are sighted in sensitive areas or in predefined exclusion zones around a vessel. To ensure successful mitigation, reliable at-sea detection of animals is crucial. To date, ship-based marine mammal observers are the most commonly implemented detection method; however, thermal (IR) imaging–based automatic detection systems have been used in recent years. This study evaluates thermal imaging–based automatic whale detection technology for its use across different oceans. The performance of this technology is characterized with respect to environmental conditions, and an automatic detection algorithm for whale blows is presented. The technology can detect whales in polar, temperate, and subtropical ocean regimes over distances of up to several kilometers and outperforms marine mammal observers in the number of whales detected. These results show that thermal imaging technology can be used to assist in providing protection for marine mammals against ship strike and acoustic impact across the world’s oceans.
CRIS-Team Scopus Importer:2020-06-05

Scaling the microrheology of living cells - Fabry, Ben; Maksym, Geoffrey N.; Butler, James P.; Glogauer, Michael; Navajas, Daniel; Fredberg, Jeffrey (FOUND PHYS LETT, 2001)

Scanning electron microscopical examination of the impact of laser patterning on microscopic inhomogeneities of Cu(In,Ga)(Se,S)2 absorbers produced by rapid thermal processing - Künecke, Ulrike; Hölzing, Astrid; Jost, Stefan; Lechner, Robert; Vogt, Helmut; Heiss, Andreas; Palm, Jörg; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2013)
Laser scribing of the Mo back electrode is commonly applied to define the cell structure of Cu(In,Ga)(Se,S) (CIGSSe) thin film solar cells. The patterning process was performed on laboratory samples using ns and ps pulse length laser processes. After structuring, CIGSSe absorbers were processed by rapid thermal processing (RTP) of stacked elemental layer precursors. Microscopic inhomogeneities were investigated on different sample positions. For samples structured with ns pulse, the absorber morphology in the laser line vicinity is different as compared to the morphology in the unstructured cell area. Scanning electron microscopy and energy-dispersive X-ray spectroscopy show significant changes in the absorber grain size and chemical composition. Close to the laser line, the typically observed Ga accumulation on the back contact is less pronounced and more Ga is incorporated closer to the surface leading to a smaller grain size. The observed changes are attributed to partial damaging of a diffusion barrier between glass and Mo induced by the ns laser process, which allows diffusion of sodium from the glass substrate into the absorber during RTP. The enhanced Ga incorporation closer to the surface is an indication for the influence of sodium on the local phase development during RTP. The damages of the diffusion barrier can be effectively prevented by the application of a ps laser scribing process. CIGSSe absorbers processed on samples structured with ps pulse length do not show the described microscopic inhomogeneities around the laser line. © 2013 Elsevier B.V.
Keywords: Cu(In; Ga)(Se; S)2; Chalcopyrite; Solar cells; Laser patterning; Sodium; SEM; Mo back contact; SEL-RTP

Scattering by Cu adatoms between image-potential bands on Cu(001) - Boger, Klaus; Weinelt, Martin; Wang, Jinxiong; Fauster, Thomas (Applied Physics A-Materials Science & Processing, 2004)
With the increasing resolution and sensitivity of photoelectron spectroscopy, the influence of defects is becoming more and more obvious. Scattering processes induced by adsorbate atoms can be studied by time- and angle-resolved two-photon photoemission. We have examined the dynamics of electrons in image-potential states on the Cu(001) surface for statistically distributed Cu adatoms and have identified different scattering mechanisms. Scattering of electrons from the second (n=2) to the bottom of the first (n=1) image-potential band is observed, which we attribute to inelastic interband scattering with electrons in the bulk. At energies above the bottom of the n=2 band, resonant interband scattering from the n=2 to the n=1 image-potential band is found. The rate for these processes can be determined by modeling the time-resolved measurements via optical Bloch equations of a four-level system. Comparison of the transition and decay rates reveals that the decay rate of the n=2 electrons is almost exclusively changed by additional resonant interband-scattering processes upon adsorption.

Scattering of electrons in image-potential states by steps - Roth, Manfred; Fauster, Thomas; Weinelt, Martin (Applied Physics A-Materials Science & Processing, 2007)
Image-potential states on several stepped copper surfaces were studied by time, energy, and angle-resolved two-photon photoelectron spectroscopy. For different step densities binding energies and effective masses were determined in the energy-resolved and decay rates in the time-resolved mode of two-photon photoemission. The asymmetry with respect to the electron motion up or down the steps of the total decay rates is enhanced for less-ordered step arrangements. Elastic interband scattering strongly depends on details of the backfolding of the bands by the periodic step structure. Elastic intraband scattering is of similar importance as inelastic decay may contribute significantly to the asymmetry of the decay rates.

Scattering of electrons on the Cu(001) surface by Co adatoms - Hirschmann, Michaela; Fauster, Thomas (Applied Physics A-Materials Science & Processing, 2007)
Excited electrons at surfaces can be scattered by adsorbate atoms or defects, which changes the energy or momentum. Such scattering processes can be studied by energy, time and angle-resolved two-photon photoelectron spectroscopy. In this article the influence of statistically distributed Co adatoms on a Cu(001) surface on the dynamics of electrons in image-potential states is investigated. Different scattering mechanisms, such as interband, intraband, and bulk scattering are identified and analyzed quantitatively. Cobalt adatoms cause mainly quasielastic scattering of electrons in image-potential states. Inelastic processes are due to interactions with electrons in the substrate and are not significantly increased by Co adatoms. The results are compared to previous experimental and theoretical work on Cu adatoms.

Scattering of electrons with acoustic phonons in single-walled carbon nanotubes - Dyatlova, Olga A.; Koehler, Christopher; Malic, Ermin; Gomis-Bresco, Jordi; Maultzsch, Janina; Tsagan-Mandzhiev, Andrey; Watermann, Tobias; Knorr, Andreas; Woggon, Ulrike (Conference on Lasers and Electro-Optics (CLEO), 2012)
We perform two-color pump-probe experiments on (8,7), (10,2), (11,3) and (12,1) nanotubes. The density matrix formalism reveals that the measured few picosecond component of the relaxation dynamics is due to intraband carrier-acoustic phonon scattering.

Scattering of hot electrons by adatoms at metal surfaces - Boger, Klaus; Weinelt, Martin; Fauster, Thomas (Physical Review Letters, 2004)
The scattering of electrons in image-potential states by Cu adatoms on Cu(001) surfaces has been investigated by means of time- and angle-resolved two-photon photoemission. Several interband and intraband-scattering mechanisms have been identified and their contributions to the total decay of the states determined quantitatively. The adsorbates mainly cause quasielastic scattering processes. Inelastic processes in contrast are due to interactions with electrons in the substrate and are not significantly increased by Cu adatoms. Quasielastic scattering into bulk bands contributes significantly to the depopulation of surface states.

Scattering of image-potential-state electrons by steps on Cu(001) - Fauster, Thomas; Schneider, M. Alexander; et al. (Applied Physics A-Materials Science & Processing, 2004)
Scanning tunneling spectroscopy (STS) reveals a distinct asymmetry in the scattering properties of an isolated step for the n=1 image-potential state on Cu(001). The elastic scattering probability for an electron traveling downstairs is determined from the strength of density oscillations in front of a step edge and is found to be approximately two times higher than for the opposite upstairs direction. A one-dimensional scattering model is extended to the case of asymmetric transmission and reflection coefficients. The calculations using the asymmetry measured by STS explain the dispersion and the decay rate of the n=1 band on Cu(119) measured by two-photon photoemission. In particular, the asymmetry of the decay rate can be described quantitatively with a minimum of adjustable parameters. While the results can also be transferred successfully to the Cu(1115) surface, the limit of applicability is reached for Cu(117) with a step separation of 3.5 nearest-neighbor distances.

Screening in crystalline liquids protects energetic carriers in hybrid perovskites - Zhu, Haiming; Miyata, Kiyoshi; Fu, Yongping; Wang, Jue; Joshi, Prakriti P.; Niesner, Daniel; Williams, Kristopher W.; Jin, Song; Zhu, X. -Y. (Science, 2016)
Hybrid lead halide perovskites exhibit carrier properties that resemble those of pristine nonpolar semiconductors despite static and dynamic disorder, but how carriers are protected from efficient scattering with charged defects and optical phonons is unknown. Here, we reveal the carrier protection mechanism by comparing three single-crystal lead bromide perovskites: CH3NH3PbBr3, CH(NH2)(2)PbBr3, and CsPbBr3. We observed hot fluorescence emission from energetic carriers with similar to 10(2)-picosecond lifetimes in CH3NH3PbBr3 or CH(NH2)(2)PbBr3, but not in CsPbBr3. The hot fluorescence is correlated with liquid-like molecular reorientational motions, suggesting that dynamic screening protects energetic carriers via solvation or large polaron formation on time scales competitive with that of ultrafast cooling. Similar protections likely exist for band-edge carriers. The long-lived energetic carriers may enable hot-carrier solar cells with efficiencies exceeding the Shockley-Queisser limit.

Search for Dark Matter Annihilation Signals from Unidentified Fermi-LAT Objects with HESS - Abdalla, H.; Spencer, Samuel; Aharonian, Felix; Ait Benkhali, F.; Anguner, E. O.; Arcaro, C.; Armand, C.; Armstrong, T.; Ashkar, H.; Backes, M.; Baghmanyan, V.; Barbosa-Martins, V.; et al. (Astrophysical Journal, 2021)
Cosmological N-body simulations show that Milky Way-sized galaxies harbor a population of unmerged dark matter (DM) subhalos. These subhalos could shine in gamma-rays and eventually be detected in gamma-ray surveys as unidentified sources. We performed a thorough selection among unidentified Fermi-Large Area Telescope Objects (UFOs) to identify them as possible tera-electron-volt-scale DM subhalo candidates. We search for very-high-energy (E greater than or similar to 100 GeV) gamma-ray emissions using H.E.S.S. observations toward four selected UFOs. Since no significant very-high-energy gamma-ray emission is detected in any data set of the four observed UFOs or in the combined UFO data set, strong constraints are derived on the product of the velocity-weighted annihilation cross section sigma v by the J factor for the DM models. The 95% confidence level observed upper limits derived from combined H.E.S.S. observations reach sigma vJ values of 3.7 x 10(-5) and 8.1 x 10(-6) GeV(2 )cm(-2 )s(-1) in the W (+) W (-) and tau (+) tau (-) channels, respectively, for a 1 TeV DM mass. Focusing on thermal weakly interacting massive particles, the H.E.S.S. constraints restrict the J factors to lie in the range 6.1 x 10(19)-2.0 x 10(21) GeV(2 )cm(-5) and the masses to lie between 0.2 and 6 TeV in the W (+) W (-) channel. For the tau (+) tau (-) channel, the J factors lie in the range 7.0 x 10(19)-7.1 x 10(20) GeV(2 )cm(-5) and the masses lie between 0.2 and 0.5 TeV. Assuming model-dependent predictions from cosmological N-body simulations on the J-factor distribution for Milky Way-sized galaxies, the DM models with masses >0.3 TeV for the UFO emissions can be ruled out at high confidence level.
CRIS-Team WoS Importer:2021-09-10

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

Self- and interdiffusion in dilute liquid germanium-based alloys - Weis, H.; Kargl, F.; Kolbe, M.; Koza, M. M.; Unruh, Tobias; Meyer, A. (Journal of Physics: Condensed Matter, 2019)
Self- and inter-diffusion coefficients in liquid Ge and dilute Ge-based Ge-Si, Ge-Au, Ge-In, Ge-Ce and Ge-Gd alloys-containing 2 at% additions, respectively, are measured using a comprehensive approach of measuring techniques: quasi-elastic neutron scattering, in situ long-capillary experiments combined with x-ray radiography, and a long-capillary experiment under microgravity conditions. Resulting inter-and Ge self-diffusion coefficients are equal within error bars for each investigated alloy. The interdiffusion coefficients are smaller for the alloys containing Ce and Gd, However, no dependence of the atomic mass of the minor additions, that varies by about a factor of seven between Si and Au, on the diffusion coefficients could be observed. This demonstrates that in a loosely-packed metallic liquid with fast diffusive dynamics the diffusion mechanism is highly collective in nature.
CRIS-Team WoS Importer:2019-09-06

Self-Assembled Monolayer Field-Effect Transistors based on Oligo-9,9’-dioctylfluorene Phosphonic Acids - Gothe, Bastian; de Roo, Tjaard; Will, Johannes; Unruh, Tobias; Mecking, Stefan; Halik, Marcus (Nanoscale, 2017)
The use of functional oligomers of pi-conjugated oligofluorenes led to a region-selective assembly of amorphous monolayers which exhibit robust lateral charge transport pathways in self-assembled monolayer field-effect transistors over long distances and even in mixed monolayers of semiconducting and insulating molecules. This oligomer concept might stimulate a new molecular design of self-assembling semiconducting materials.

Self-Assembly and Stability of Hydrogen-Bonded Networks of Bridged Triphenylamines on Au(111) and Cu(111) - Steiner, Christian; Gliemann, Bettina; Meinhardt, Ute; Gurrath, Martin; Meyer, Bernd; Kivala, Milan; Maier, Sabine (Journal of Physical Chemistry C, 2015)
The adsorption, chemical nature, and self-assembly of diaminotriazinyl- and carboxyl-substituted triphenylamines with dimethylmethylene bridges were studied on Au(111) and Cu(111) at submonolayer coverage by low-temperature scanning tunneling microscopy and density functional theory. On Au(111), both molecules form extended porous honeycomb networks. The geometry of the networks agrees well with density functional theory optimized hydrogen-bonded gas phase structures. Therefore, the self-assemblies on Au(111) are strongly directed by intermolecular hydrogen bond interactions. In contrast, on Cu(111) both molecules aggregate in dense islands owing to the stronger moleculesurface interaction. While the carboxyl substituents partially deprotonate at room temperature on Cu(111), the diaminotriazinyl-substituted triphenylamines adsorb mainly intact. The diaminotriazinyl groups deprotonate gradually at increased adsorption temperatures.

Self-assembly of triglyceride nanocrystals in suspension - Unruh, Tobias; Westesen, Kirsten; Boesecke, Peter; Lindner, Peter; Koch, Michel (Langmuir, 2002)
The interparticle interactions in aqueous monoacid triglyceride nanosuspensions prepared by melt homogenization are strongly influenced by the thickness distribution of the platelet-shaped particles. Small-angle X-ray scattering and transmission electron microscopy investigations on the native, undiluted tripalmitin dispersions stabilized with phospholipids and sodium glycocholate indicate that the dispersed nanocrystals can form aggregates of particles which are oriented in the same direction (stacked lamellae) with interparticle distances around 20 nm. The relative concentration of the particles in the stacks increases with the total triglyceride concentration in a dispersion. The stacked lamellae almost disappear after dilution with the aqueous phase or by increasing the temperature just below the onset of melting of the tripalmitin nanocrystals. This observation indicates that the energy gained by the formation of a stack is of the order of k(B)T. The tendency to form stacked lamellae is reduced for trimyristin and even more for trilaurin suspensions, despite the fact that they also contain platelet-shaped nanocrystals.

Self-diffusion in molecular liquids: Medium-chain n-alkanes and coenzyme Q(10) studied by quasielastic neutron scattering - Smuda, Christoph; Busch, Sebastian; Gemmecker, Gerd; Unruh, Tobias (Journal of Chemical Physics, 2008)
A systematic time-of-flight quasielastic neutron scattering (TOF-QENS) study on diffusion of n-alkanes in a melt is presented for the first time. As another example of a medium-chain molecule, coenzyme Q(10) is investigated in the same way. The data were evaluated both in the frequency and in the time domain. TOF-QENS data can be satisfactorily described by different models, and it turned out that the determined diffusion coefficients are largely independent of the applied model. The derived diffusion coefficients are compared with values measured by pulsed-field gradient nuclear magnetic resonance (PFG-NMR). With increasing chain length, an increasing difference between the TOF-QENS diffusion coefficient and the PFG-NMR diffusion coefficient is observed. This discrepancy in the diffusion coefficients is most likely due to a change of the diffusion mechanism on a nanometer length scale for molecules of medium-chain length. (C) 2008 American Institute of Physics.

Self-diffusion of 3d transition metals in liquid silicon alloys - Pommrich, Ines; Unruh, Tobias; Meyer, Andreas (High Temperatures-High Pressures, 2013)
Self-diffusion coefficients of titanium and cobalt in a silicon melt with 10 at.% metal content were measured in a temperature range between 180K above and below the liquidus temperature, respectively, with quasielastic neutron scattering. The chemical reactive melts were processed container-less by electromagnetic levitation. Whereas, in crystalline silicon self diffusion coefficients of Ti and Co impurities differ by more than 3 orders of magnitude close to the melting point, in the liquid state values of self-diffusion coefficients of Ti and Co, are equal within error bars and are of the order of 10(-8) m(2)/s. This is in line with a liquid-like, collective transport mechanism that is dominated by the mobility of the surrounding Si atoms.
Keywords: Liquid silicon; liquid silicon based alloys; self-diffusion; quasielastic neutron scattering

Self-Healing Cs3Bi2Br3I6 Perovskite Wafers for X-Ray Detection - Daum, Manuel; Deumel, Sarah; Sytnyk, Mykhailo; Afify, Hany A.; Hock, Rainer; Eigen, Andreas; Zhao, Baolin; Halik, Marcus; These, Albert; Matt, Gebhard; Brabec, Christoph; Tedde, Sandro F.; et al. (Advanced Functional Materials, 2021)
Self-healing of defects imposed by external stimuli such as high energy radiation is a possibility to sustain the operational lifetime of electronic devices such as radiation detectors. Cs3Bi2Br3I6 polycrystalline wafers are introduced here as novel X-ray detector material, which not only guarantees a high X-ray stopping power due to its composition with elements with high atomic numbers, but also outperforms other Bi-based semiconductors in respect to detector parameters such as detection limit, transient behavior, or dark current. The polycrystalline wafers represent a size scalable technology suitable for future integration in imager devices for medical applications. Most astonishingly, aging of these wafer-based devices results in an overall improvement of the detector performance—dark currents are reduced, photocurrents are increased, and one of the most problematic properties of X-ray detectors, the base line drift is reduced by orders of magnitude. These aging induced improvements indicate self-healing effects which are shown to result from recrystallization. Optimized synthetic conditions also improve the as prepared X-ray detectors; however, the aged device outperforms all others. Thus, self-healing acts in Cs3Bi2Br3I6 as an optimization tool, which is certainly not restricted to this single compound, it is expected to be beneficial also for many further polycrystalline ionic semiconductors.
CRIS-Team Scopus Importer:2021-08-27
Keywords: bismuth halides; lead-free perovskites; photoconductors; self-healing; X-ray detection

Self-Metalation of Porphyrins by Cobalt Oxide: Photoemission Spectroscopic Investigation - Wang, Can; Wang, Ruimei; Hauns, Jakob; Fauster, Thomas (Journal of Physical Chemistry C, 2020)
Understanding the electronic structure between porphyrins and ultrathin metal-oxide film interfaces is vital for the rational design of functional molecular architectures. Here, we have studied the interfacial electronic properties of porphyrin molecular thin films on well-ordered thin layers of CoO(111) and metallic Co(100) surfaces by means of X-ray and ultraviolet photoemission spectroscopies. In this work, we observed the direct self-metalation of free-base porphyrin molecules at the interface to CoO(111) at room temperature by monitoring the N 1s core-level evolution. On metallic Co(100) films, no metalation occurs, but it can be induced by exposure to oxygen. The oxygen-induced metalation has, to the best of our knowledge, not been reported until now and might play an important role in processes where porphyrins are exposed to metals in a reactive environment.
CRIS-Team Scopus Importer:2020-07-24

Self-Organized Growth, Structure, and Magnetism of Monatomic Transition-Metal Oxide Chains - Ferstl, Pascal; Hammer, Lutz; Sobel, Christopher; Gubo, Matthias; Heinz, Klaus; Schneider, M. Alexander; Mittendorfer, Florian; Redinger, Josef (Physical Review Letters, 2016)
We report on the self-organized growth of monatomic transition-metal oxide chains of (3×1) periodicity and unusual MO2 stoichiometry (M=Ni, Co, Fe, Mn) on Ir(100). We analyze their structural and magnetic properties by means of quantitative LEED, STM, and density functional theory (DFT) calculations. LEED analyses reveal a fascinating common atomic structure in which the transition-metal atoms sit above a missing-row structure of the surface and are coupled to the substrate only via oxygen atoms. This structure is confirmed by DFT calculations with structural parameters deviating by less than 1.7 pm. The DFT calculations predict that the NiO2 chains are nonmagnetic, CoO2 chains are ferromagnetic, while FeO2 and MnO2 are antiferromagnetic. All structures show only weak magnetic interchain coupling. Further, we demonstrate the growth of oxide chains of binary alloys of Co and Ni or Fe on Ir(100), which allows us to produce well-controlled ensembles of ferromagnetic chains of different lengths separated by nonmagnetic or antiferromagnetic segments.

Self-organized tungsten nanospikes grown on subwavelength ripples induced by femtosecond laser pulses - Malzer, Stefan; Zhao, Quanzhong; Wang, Lijun (Optics Express, 2007)
We report on the formation of nanoscale tungsten spikes generated on subwavelength periodic ripples which built up by single beam 800 nm femtosecond laser pulses. The nanospikes have a diameter ranging from 10 to 100 nm and are up to 250 nm in length. The nanospikes orientate from the ridges toward the valleys of the ripple structures independent of the polarization of the light. The heterogeneous nucleation of the liquid phase at the irradiated surface and the inhomogeneous surface roughness are considered as the mechanism of this nanospike formation. © 2007 Optical Society of America.

Self-probing of metal nanotips by rescattered electrons reveals the nano-optical near-field - Krüger, Michael; Thomas, Sebastian; Förster, Michael; Hommelhoff, Peter (Journal of Physics B: Atomic, Molecular and Optical Physics, 2014)
Self-probing of atoms or molecules by their own electrons is a powerful tool for exploring structural dynamics with high spatial and temporal resolution. Spectra from high-harmonic generation or photoelectron rescattering reveal the quantities of interest, such as the electronic structure of the system under scrutiny. Recently, we have observed the rescattering effect at solids, in particular at metal nanotips. Here we use the self-probing approach in order to investigate an effect inherent to nano-scale systems: laser light incident on nanotips generates strongly enhanced optical near-fields that crucially depend on their geometry and material. In our experiment, we determine the strength of the near-field of tungsten and gold tips from the high-energy cut-off of rescattered electrons. Detailed experimental results are compared with a numerical solution of the time-dependent Maxwell equations. © 2014 IOP Publishing Ltd.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.exphys.selfpr
Keywords: nano-optics; nanostructures; nanotips; photoemission; rescattering

Semitransparency in interaction-free measurements - Thomas, Sebastian; Kohstall, Christoph; Kruit, Pieter; Hommelhoff, Peter (Physical Review A - Atomic, Molecular, and Optical Physics, 2014)
We discuss the effect of semitransparency in a quantum-Zeno-like interaction-free measurement setup, a quantum-physics based approach that might significantly reduce sample damage in imaging and microscopy. With an emphasis on applications in electron microscopy, we simulate the behavior of probe particles in an interaction-free measurement setup with semitransparent samples, and we show that the transparency of a sample can be measured in such a setup. However, such a measurement is not possible without losing (i.e., absorbing or scattering) probe particles in general, which causes sample damage. We show how the amount of lost particles can be minimized by adjusting the number of round trips through the setup, and we explicitly calculate the amount of lost particles in measurements which either aim at distinguishing two transparencies or at measuring an unknown transparency precisely. We also discuss the effect of the sample causing phase shifts in interaction-free measurements. Comparing the resulting loss of probe particles with a classical measurement of transparency, we find that interaction-free measurements only provide a benefit in two cases: first, if two semitransparent samples with a high contrast are to be distinguished, interaction-free measurements lose less particles than classical measurements by a factor that increases with the contrast. This implies that interaction-free measurements with zero loss are possible if one of the samples is perfectly transparent. A second case where interaction-free measurements outperform classical measurements is if three conditions are met: the particle source exhibits Poissonian number statistics, the number of lost particles cannot be measured, and the transparency is larger than approximately 12. In all other cases, interaction-free measurements lose as many probe particles as classical measurements or more. Aside from imaging of gray levels, another possible application for interaction-free measurements is the detection of arbitrarily small phase shifts in transparent samples.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.exphys.semitr

SEMPAI: a Self-Enhancing Multi-Photon Artificial Intelligence for Prior-Informed Assessment of Muscle Function and Pathology - Mühlberg, Alexander; Ritter, Paul; Langer, Sabine; Goossens, Chloë; Nübler, Stefanie; Schneidereit, Dominik; Taubmann, Oliver; Denzinger, Felix; Nörenberg, Dominik; Haug, Michael; Schürmann, Sebastian; Horstmeyer, Roarke; et al. (Advanced Science, 2023)
Deep learning (DL) shows notable success in biomedical studies. However, most DL algorithms work as black boxes, exclude biomedical experts, and need extensive data. This is especially problematic for fundamental research in the laboratory, where often only small and sparse data are available and the objective is knowledge discovery rather than automation. Furthermore, basic research is usually hypothesis-driven and extensive prior knowledge (priors) exists. To address this, the Self-Enhancing Multi-Photon Artificial Intelligence (SEMPAI) that is designed for multiphoton microscopy (MPM)-based laboratory research is presented. It utilizes meta-learning to optimize prior (and hypothesis) integration, data representation, and neural network architecture simultaneously. By this, the method allows hypothesis testing with DL and provides interpretable feedback about the origin of biological information in 3D images. SEMPAI performs multi-task learning of several related tasks to enable prediction for small datasets. SEMPAI is applied on an extensive MPM database of single muscle fibers from a decade of experiments, resulting in the largest joint analysis of pathologies and function for single muscle fibers to date. It outperforms state-of-the-art biomarkers in six of seven prediction tasks, including those with scarce data. SEMPAI's DL models with integrated priors are superior to those without priors and to prior-only approaches.
CRIS-Team Scopus Importer:2023-08-25
Keywords: deep learning; explainable artificial intelligence; meta-learning; multiphoton microscopy; muscle research; prior information integration; scientific machine learning

Sensing current and forces with SPM - Park, Jeong Y.; Maier, Sabine; Hendriksen, Bas; Salmeron, Miquel (Materials Today, 2010)
Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) are well established techniques to image surfaces and to probe material properties at the atomic and molecular scale. In this review, we show hybrid combinations of AFM and STM that bring together the best of two worlds: the simultaneous detection of atomic scale forces and conduction properties. We illustrate with several examples how the detection of forces in STM and the detection of currents in AFM can give valuable additional information of the nanoscale material properties.

Sensitive Direct Converting X-Ray Detectors Utilizing Crystalline CsPbBr3 Perovskite Films Fabricated via Scalable Melt Processing - Matt, Gebhard; Levchuk, Ievgen; Knüttel, Judith; Dallmann, Johannes; Osvet, Andres; Sytnyk, Mykhailo; Tang, Xiaofeng; Elia, Jack; Hock, Rainer; Heiß, Wolfgang; Brabec, Christoph (Advanced Materials Interfaces, 2020)
Here the fabrication of an inorganic metal-halide perovskite CsPbBr3 based X-ray detector is reported utilizing a simple, scalable, and cost-sensitive melt processing directly on substrate of any size. X-ray diffraction analysis on the several 100 mm thick melt processed films confirms crystalline domains in the cm(2) range. The CsPbBr3 film features a resistance of 8.5 G omega cm and a hole mobility of 18 cm(2) V-1 s(-1). An X-ray to current conversion rate of 1450 mC Gy(air)(-1) cm(-2) at an electric field of 1.2 x 10(4) V cm(-1) and a detection limit in the sub mu Gy(air) s(-1) regime is demonstrated. The high crystallinity and chemical purity of the melt processed CsPbBr3 films are suggested to be responsible for a performance which is on par to current state-of-the-art Cd(Zn)Te based X-ray detector technology.
Keywords: X-ray detection; metal-halide perovskites; photophysics

Sensitive measurement of laser induced photocarrier gratings in semiconductors by optical heterodyne detection - Hundhausen, Martin; Ley, Lothar; et al. (proc. 23rd Int. Conf. on the Physics of Semiconductors, 1996)
UnivIS-Import:2015-04-16:Pub.1996.nat.dphy.IAP.exphys.sensit

Separation of blood cells with differing deformability using deterministic lateral displacement - Holmes, David; Whyte, Graeme; Bailey, Joe; Vergara-Irigaray, Nuria; Ekpenyong, Andrew; Guck, Jochen; Duke, Tom (Interface Focus, 2014)
Determining cell mechanical properties is increasingly recognized as a marker-free way to characterize and separate biological cells. This emerging realization has led to the development of a plethora of appropriate measurement techniques. Here, we use a fairly novel approach, deterministic lateral displacement (DLD), to separate blood cells based on their mechanical phenotype with high throughput. Human red blood cells were treated chemically to alter their membrane deformability and the effect of this alteration on the hydrodynamic behaviour of the cells in a DLD device was investigated. Cells of defined stiffness (glutaraldehyde cross-linked erythro-cytes) were used to test the performance of the DLD device across a range of cell stiffness and applied shear rates. Optical stretching was used as an independent method for quantifying the variation in stiffness of the cells. Lateral displacement of cells flowing within the device, and their subsequent exit position from the device were shown to correlate with cell stiffness. Data showing how the isolation of leucocytes from whole blood varies with applied shear rate are also presented. The ability to sort leucocyte sub-populations (T-lymphocytes and neutrophils), based on a combination of cell size and deformability, demonstrates the potential for using DLD devices to perform continuous fractionation and/or enrichment of leucocyte sub-populations from whole blood.
CRIS-Team Scopus Importer:2022-08-05
Keywords: Blood separation; Cell deformability; Deterministic lateral displacement; Digital holography; microfluidics; Optical stretching

Sequence of Quantum Phase Transitions in Bi2Sr2CaCu2 O8+δ Cuprates Revealed by in Situ Electrical Doping of One and the Same Sample - Jacobs, T.; Simsek, Yilmaz; Koval, Yury; Müller, Paul; Krasnov, Vladimir (Physical Review Letters, 2016)
Our recently discovered electrical doping technique allows a broad-range variation of carrier concentration without changing the chemical composition. We show that it is possible to induce superconductivity in a nondoped insulating sample and to tune it reversibly all the way to an overdoped metallic state. This way, we can investigate the whole doping diagram of one and the same sample. Our study reveals two distinct critical points. The one at the overdoped side is associated with the onset of the pseudogap and with the metal-to-insulator transition in the c-axis transport. The other at optimal doping is associated with the appearance of a "dressed" electron energy. Our study confirms the existence of multiple phase transitions under the superconducting dome in cuprates.

Shaping of Electron Beams Using Sculpted Thin Films - Roitman, Dolev; Shiloh, Roy; Lu, Peng Han; Dunin-Borkowski, Rafal E.; Arie, Ady (ACS Photonics, 2021)
Electron beam shaping by sculpted thin films relies on electron-matter interactions and the wave nature of electrons. It can be used to study physical phenomena of special electron beams and to develop technological applications in electron microscopy that offer new and improved measurement techniques and increased resolution in different imaging modes. In this Perspective, we review recent applications of sculpted thin films for electron orbital angular momentum sorting, improvements in phase contrast transmission electron microscopy, and aberration correction. For the latter, we also present new results of our work toward correction of the spherical aberration of Lorentz scanning transmission electron microscopes and suggest a method to correct chromatic aberration using thin films. This review provides practical insight for researchers in the field and motivates future progress in electron microscopy.
CRIS-Team Scopus Importer:2021-12-31
Keywords: Aberration correction; Beam shaping; Electron microscope; Orbital angular momentum; Phase masks

Shubnikov-de Haas and Hall quantum oscillations in graphite - Stamenov, Plamen; Krstic, Vojislav; Coey, J. M.D. (Journal of Magnetism and Magnetic Materials, 2005)
Resistance and Hall effect are measured for graphite in fields of up to 23 T in the temperature range 0.3–300 K. Quantum oscillations appear below 50 K when the field is parallel to the c-axis. No oscillations are observed above 8 T, when all the electrons in the system occupy the lowest Landau level. Cyclotron masses for the lowest Landau levels range from 0.6me to 0.04me. The extremal cross section for the electron Fermi surface is 4.2×1016 m−2 and the hole cross section is similar. The Dingle temperature for the highly oriented pyrolytic graphite sample is 7 K.
Keywords: Landau quantization; Graphite; Shubnikov-de Haas effect

Signature of the two-dimensional phonon dispersion in graphene probed by double-resonant Raman scattering - May, Patrick; Lazzeri, Michele; Venezuela, Pedro; Herziger, Felix; Callsen, Gordon; Reparaz, Juan S.; Hoffmann, Axel; Mauri, Francesco; Maultzsch, Janina (Physical Review B, 2013)
The contributions of the two-dimensional phonon dispersion to the double-resonant Raman scattering process in graphene is determined from the line shape of the two-phonon combination mode around 2450 cm(-1). This mode is usually referred to as G* or D + D ''. By combining Raman experiments with excitation energies up to 2.8 eV and a full two-dimensional calculation of the double-resonant Raman process based on fourth-order perturbation, we can describe in detail the composition of this two-phonon mode and explain the asymmetry on the high-frequency side. The asymmetry directly reflects phonon contributions with wave vectors away from the high-symmetry lines in the Brillouin zone. The main peak of this mode originates from the K Gamma high-symmetry line highlighting and supporting two important findings: first, the existence of so-called inner processes and, second, the dominant contribution along the high-symmetry line. DOI: 10.1103/PhysRevB.87.075402

Signature of the weak bond-dangling bond conversion process in a-Si:H as seen by total photoelectron yield spectroscopy - Ristein, Jürgen; Ley, Lothar; et al. (MRS Proceedings, 1993)
Photoelectron Yield Spectroscopy is one of the most direct methods to study the density of gap states of amorphous semiconductors. We have made use of it to investigate the transient changes of the density of gap states of a-Si:H upon illumination with above-band-gap light. An excitation density of 50 mW/cm2 of 532 nm light from a frequency doubled Nd-YAG laser was modulated with frequencies between 0.1 Hz and 10 KHz and the transient response of the photoelectron yield signal was monitored by gated electron counting or a lock-in amplifier. From this we deduce a reversible increase of the occupied density of defect states under illumination with a maximum Δg to approximately 1017 cm-3 eV-1 at about 0.3 eV below the Fermi energy and a decrease below EF-0.75 eV, i.e. in the region of deep tail states. The effect exhibits a wide spectrum of time constants involved. Based on additional transient surface photo voltage measurements as well as numerical simulations we argue that the observed redistribution of states is not due to a light induced change in surface band bending or due to a mere excitation of electrons from occupied to empty states. Instead, we interpret the observed effect as a conversion of weak to dangling bonds, i.e. a precursor of the Staebler-Wronski Effect, lacking however the final step of hydrogen stabilization necessary for the creation of metastable defects.
UnivIS-Import:2015-04-16:Pub.1993.nat.dphy.IAP.exphys.signat

Silicon Carbide and Related Materials 2009 - Parts 1 and 2 - Bauer, Anton; Friedrichs, Peter; Krieger, Michael; Pensl, Gerhard; Rupp, Roland; Seyller, Thomas (Trans Tech Publications, 2010)
UnivIS-Import:2017-03-24:Pub.2010.nat.dphy.IAP.LAP.silico

Silicon Carbide and Related Materials (ECSCRM 2000) - Hundhausen, Martin; et al. (Trans Tech Publications LTD, 2001)
UnivIS-Import:2017-03-24:Pub.2001.nat.dphy.IAP.LAP.silico

Silicon dual pillar structure with a distributed Bragg reflector for dielectric laser accelerators: Design and fabrication - Yousefi, Peyman; McNeur, Joshua; Kozak, Martin; Niedermayer, Uwe; Gannott, Florentina; Lohse, Olga; Boine-Frankenheim, Oliver; Hommelhoff, Peter (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2018)
Dielectric laser accelerators (DLAs) have proven to be good candidates for miniaturized particle accelerators. They rely on micro-fabricated dielectrics which are able to modulate the kinetic energy of the incoming electron beam under a proper laser illumination. In this paper we demonstrate a dual pillar structure with a distributed Bragg reflector to mimic a double sided illumination to the electron path. The structure is fabricated by an electron beam lithography technique followed by a cryogenic reactive ion etching process. Such a structure can accelerate the injected 28 keV electrons by a gradient of approximately 150 MeV/m which can be further optimized towards the GeV/m regim
Keywords: Dielectric laser accelerators; Dual pillar structure; Distributed Bragg reflector; Electron beam lithography; Cryogenic reactive ion etching

Silicone-Based Lubricant-Infused Slippery Coating Covalently Bound to Aluminum Substrates for Underwater Applications - Prado, Lucia; Böhringer, David; Mazare, Anca Valentina; Sotelo, Lamborghini; Sarau, George; Christiansen, Silke; Fabry, Ben; Schmuki, Patrik; Virtanen, Sannakaisa; Goldmann, Wolfgang; Tesler, Alexander (ACS Applied Materials and Interfaces, 2023)
Wetting of solid surfaces is crucial for biological and industrial processes but is also associated with several harmful phenomena such as biofouling and corrosion that limit the effectiveness of various technologies in aquatic environments. Despite extensive research, these challenges remain critical today. Recently, we have developed a facile UV-grafting technique to covalently attach silicone-based coatings to solid substrates. In this study, the grafting process was evaluated as a function of UV exposure time on aluminum substrates. While short-time exposure to UV light results in the formation of lubricant-infused slippery surfaces (LISS), a flat, nonporous variant of slippery liquid-infused porous surfaces, longer exposure leads to the formation of semi-rigid cross-linked polydimethylsiloxane (PDMS) coatings, both covalently bound to the substrate. These coatings were exposed to aquatic media to evaluate their resistance to corrosion and biofouling. While the UV-grafted cross-linked PDMS coating effectively inhibits aluminum corrosion in aquatic environments and allows organisms to grow on the surface, the LISS coating demonstrates improved corrosion resistance but inhibits biofilm adhesion. The synergy between facile and low-cost fabrication, rapid binding kinetics, eco-friendliness, and nontoxicity of the applied materials to aquatic life combined with excellent wetting-repellent characteristics make this technology applicable for implementation in aquatic environments.
CRIS-Team Scopus Importer:2023-07-21
Keywords: anti-biofouling; biofilms; corrosion resistance; cross-linking; lubricant-infused slippery surfaces; polydimethylsiloxane; UV-grafting

Silicon nitride as top gate dielectric for epitaxial graphene - Wehrfritz, Peter; Fromm, Felix; Malzer, Stefan; Seyller, Thomas (Silicon Carbide and Related Materials 2012, 2013)
Silicon nitride (SiN) was deposited by plasma enhanced chemical vapor deposition (PECVD) as a top gate dielectric on epitaxial graphene on 6H-SiC(0001). We compare x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transport measurements which were performed before and after the SiN deposition. We demonstrate that closed layers of SiN are formed without the need for surface activation and that the plasma process leads only to a minor degradation of the graphene. The SiN layer induces strong n-type doping. For a limited gate voltage range, a small hysteresis of 0.2 V is observed in top-gated field effect devices. © (2013) Trans Tech Publications, Switzerland.
Keywords: Doping; Epitaxial Graphene; Field Effect; Silicon Nitride

Simple model of cytoskeletal fluctuations - Metzner, Claus; Raupach, Carina; Paranhos Zitterbart, Daniel; Fabry, Ben (Physical Review E, 2007)
The spontaneous motion of microbeads bound to the cytoskeleton of living cells is not an ordinary random walk. Unlike Brownian motion, the mean-square displacement undergoes a transition from subdiffusive to superdiffusive behavior with time. This transition is associated with characteristic changes of the turning angle distribution. Recent experimental data demonstrated that force fluctuations measured in an elastic hydrogel matrix beneath the cell correlate with the bead motion. These data indicate that the bead trajectory is driven by motor forces originating from the actomyosin network and that cytoskeletal remodeling processes with short- and long-time dynamics are mainly responsible for the non-Brownian behavior. We show that the essential statistical properties of the spontaneous bead motion can be reproduced by a particle diffusing in a potential well with a slowly drifting minimum position. Based on this simple model, which can be solved analytically, we develop a biologically plausible numerical model of a tensed and continuously remodeling actomyosin network that accounts quantitatively for the measured data. © 2007 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2007.nat.dphy.IAP.lpmt.simple

Simulations of the polarisation-dependent Raman intensity of beta-carotene in photosystem II crystals - Brose, K.; Zouni, A.; Mueh, F.; Mroginski, M. A.; Maultzsch, Janina (Chemical Physics, 2013)
In order to clarify possibilities to identify the beta-carotene (beta-Car) radicals in secondary electron transfer (ET) reactions in the photosystem II core complex (PSIIcc), Raman intensities of all 96 beta-Car cofactors in the unit cell of PSIIcc-dimer crystals as a function of polarisation and crystal orientation were simulated based on the 2.9 angstrom resolution structure. The Raman-active symmetry A(g) in the C-2h group is assigned to the beta-Car modes nu(66) and nu(67). Simulations are in agreement with experiment for off-resonant excitation at 1064 nm. Resonant measurements at 476 and 532 nm excitation can not be explained, which is attributed to mode mixing in the excited state and the existence of different spectral pools. The identity of the beta-Car oxidised in secondary ET can not be resolved by Raman measurements on PSIIcc-dimer crystals. Additional simulations show that similar measurements on PSIIcc-monomer crystals could provide a possible route to solve this issue. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: Photosystem II; beta-Carotene; Raman spectroscopy; Polarisation dependence; Simulations

Simultaneous deposition of individual single-walled carbon nanotubes onto microelectrodes via AC-dielectrophoresis - Oron, Matti; Krupke, Ralph; Frank, Hennrich; Weber, Heiko B.; Beckmann, Detlef; von Löhneysen, Hilbert; Kappes, Manfred (Electric Properties of Synthetic Nanostructures : XVII International Winterschool/Euroconference on Electronic Properties of Novel Materials (IWEPNM 2004),, 2004)
Based on AC-dielectrophoresis, we succeeded to deposit simultaneously individual single-walled carbon nanotubes (SWNTs). Using only two bond-wires, the individual tubes are site-selectively deposited onto many pairs of sub-micron electrodes from a surfactant stabilized tube suspension. The presented method goes well beyond previous efforts, in which single bundles of SWNTs were deposited [1-2], and is therefore a step towards a fast deposition and characterization of individual SWNTs. Atomic force microscopy and scanning electron microscopy techniques were used to demonstrate the presence of single tubes trapped between electrode pairs.

Simultaneous deposition of metallic bundles of single-walled carbon nanotubes using ac-dielectrophoresis - Krupke, Ralph; Frank, Hennrich; Weber, Heiko B.; Kappes, Manfred; von Löhneysen, Hilbert (Nano Letters, 2003)
A simple and scalable scheme based on alternating current (ac-) dielectrophoresis is used for the simultaneous and site-selective deposition of single bundles of single-walled carbon nanotubes (SWNTs) onto a large number of contacts requiring only one bond wire. This allows for a large number of transport measurements that show that the deposited bundles contain at least one metallic SWNT dominating the transport. With high-voltage pulses, metallic bundles are transformed into Schottky-barrier-type field-effect transistors with p-type, ambipolar, or n-type behavior. From a simple electromechanical model, we derive the fact that ac-dielectrophoresis selectively deposits bundles containing metallic tubes.

Simultaneous SAXS/SANS Method at D22 of ILL: Instrument Upgrade - Metwalli, Ezzeldin; Götz, Klaus; Zech, Tobias; Bär, Christian; Schuldes, Isabel; Martel, Anne; Porcar, Lionel; Unruh, Tobias (Applied Sciences, 2021)
A customized portable SAXS instrument has recently been constructed, installed, and tested at the D22 SANS instrument at ILL. Technical characteristics of this newly established plug-and-play SAXS system have recently been reported (J. Appl. Cryst. 2020, 53, 722). An optimized lead shielding arrangement on the SAXS system and a double energy threshold X-ray detector have been further implemented to substantially suppress the unavoidable high-energy gamma radiation background on the X-ray detector. The performance of the upgraded SAXS instrument has been examined systematically by determining background suppression factors (SFs) at various experimental conditions, including different neutron beam collimation lengths and X-ray sample-to-detector distances (SDDX-ray). Improved signal-to-noise ratio SAXS data enables combined SAXS and SANS measurements for all possible experimental conditions at the D22 instrument. Both SAXS and SANS data from the same sample volume can be fitted simultaneously using a common structural model, allowing unambiguous interpretation of the scattering data. Importantly, advanced in situ/real time investigations are possible, where both the SAXS and the SANS data can reveal time-resolved complementary nanoscale structural information.<br
CRIS-Team Scopus Importer:2021-07-16
Keywords: Nanomaterials; SANS; SAS; SAXS; Small angle neutron scattering; Small angle X-ray scattering

Single-cell response to stiffness exhibits muscle-like behavior - Mitrossilis, Démosthène; Fouchard, Jonathan; Guiroy, Axel; Desprat, Nicolas; Nicolas Rodriguez,, Nicolas; Fabry, Ben; Asnacios, Atef (Proceedings of the National Academy of Sciences of the United States of America, 2009)

Single molecular precursor ink for AgBiS2 thin films: synthesis and characterization - Gu, Ening; Lin, Xianzhong; Tang, Xiaofeng; Matt, Gebhard; Osvet, Andres; Hou, Yi; Jäger, Sebastian; Xie, Chen; Karl, André; Hock, Rainer; Brabec, Christoph (Journal of Materials Chemistry C, 2018)
Recently, AgBiS2 has been demonstrated to be a promising non-toxic, earth-abundant absorber material for solar energy application. In this work, a novel route to deposit AgBiS2 thin films from single molecular precursor ink is presented. It is found that the amount of thiourea has a crucial impact on the formulation of a stable molecular ink. Understanding the coordination chemistry of the molecular precursor ink is important for getting better control over the thin film processing. With the assistance of Raman spectroscopy, possible complexation mechanisms and general coordination states within the molecular ink are studied. In addition, the influence of ink composition as well as the annealing temperature on the structure and morphology of resulting AgBiS2 films is systematically investigated. It is found that the crystallinity and particle size increase with higher annealing temperature. The obtained AgBiS2 thin films show a cubic structure with a preferred orientation in [111] direction. Optical and electrical measurements demonstrate that the obtained AgBiS2 is an indirect band gap material, which features two transition mechanisms with an indirect band gap of around 0.87 eV and a direct one of around 1.21 eV. The high absorption coefficient, low Urbach energy and fast transient photoconductivity confirm its potential as an absorber for photovoltaic applications.

Single-Molecule Junctions with Epitaxial Graphene Nanoelectrodes - Ullmann, Konrad; Brana Coto, Pedro; Leitherer, Susanne; Molina-Ontoria, Agustin; Martin, Nazario; Thoss, Michael; Weber, Heiko B. (Nano Letters, 2015)
On the way to ultraflat single-molecule junctions with transparent electrodes, we present a fabrication scheme based on epitaxial graphene nanoelectrodes. As a suitable molecule, we identified a molecular wire with fullerene anchor groups. With these two components, stable electrical characteristics could be recorded, Electrical measurements show that single-molecule junctions with graphene and with gold electrodes display a striking agreement. This motivated a hypothesis that the differential Conductance spectra are rather insensitive to the electrode material. It is further corroborated by the assignment of asymmetries and spectral features to internal molecular,degrees of freedom. The demonstrated open access graphene electrodes and the electrode-insensitive, molecules provide a model system that will allow for a thorough investigation of an individual single,molecule contact with additional probes.
Keywords: Epitaxial graphene nanoelectrodes; electroburning; single-molecule junctions; fullerene end groups; switching

Single pass high harmonic generation at 20.8 MHz repetition rate - Vernaleken, Andreas; Weitenberg, Johannes; Sartorius, Thomas; Russbueldt, Peter; Schneider, Waldemar; Stebbings, Sarah L.; Kling, Matthias Friedrich; Hommelhoff, Peter; Hoffmann, Hans Dieter; Poprawe, Reinhart; Krausz, Ferenc; Hänsch, Theodor W.; et al. (Optics Letters, 2011)
We report on single-pass high-harmonic generation (HHG) with amplified driving laser pulses at a repetition rate of 20.8 MHz. An Yb:YAG Innoslab amplifier system provides 35 fs pulses with 20W average power at 1030nm after external pulse compression. Following tight focusing into a xenon gas jet, we observe the generation of high-harmonic radiation of up to the seventeenth order. Our results show that state-of-the-art amplifier systems have become a promising alternative to cavity-assisted HHG for applications that require high repetition rates, such as frequency comb spectroscopy in the extreme UV. © 2011 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2011.nat.dphy.IAP.exphys.single

Single-Step Process for Titanium Surface Micro-and Nano-Structuring and In Situ Silver Nanoparticles Formation by Ultra-Short Laser Patterning - Aceti, Dante Maria; Filipov, Emil; Angelova, Liliya; Sotelo, Lamborghini; Fontanot, Tommaso; Yousefi, Peyman; Christiansen, Silke; Leuchs, Gerd; Stanimirov, Stanislav; Trifonov, Anton; Buchvarov, Ivan; Daskalova, Albena (Materials, 2022)
Ultra-short laser (USL)-induced surface structuring combined with nanoparticles synthesis by multiphoton photoreduction represents a novel single-step approach for commercially pure titanium (cp-Ti) surface enhancement. Such a combination leads to the formation of distinct topographical features covered by nanoparticles. The USL processing of cp-Ti in an aqueous solu-tion of silver nitrate (AgNO3) induces the formation of micron-sized spikes surmounted by silver nanoparticles (AgNPs). The proposed approach combines the structuring and oxidation of the Ti surface and the synthesis of AgNPs in a one-step process, without the use of additional chemicals or a complex apparatus. Such a process is easy to implement, versatile and sustainable compared to alternative methodologies capable of obtaining comparable results. Antimicrobial surfaces on medical devices (e.g., surgical tools or implants), for which titanium is widely used, can be realized due to the simultaneous presence of AgNPs and micro/nano-structured surface topography. The pro-cessed surfaces were examined by means of a scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and Raman spectroscopy. The surface morphology and the oxidation, quality and quantity of AgNPs were analyzed in relation to process parameters (laser scanning speed and AgNO3 concentration), as well as the effect of AgNPs on the Raman signal of Titanium oxide.
CRIS-Team Scopus Importer:2022-07-22
Keywords: laser ablation; multiphoton photo-reduction; silver nanoparticles; surface patterning; titanium; ultra-short laser processing

Size-selective separation of macromolecules by nanochannel titania membrane with self-cleaning (declogging) ability - Roy, Poulumi; Dey, Tuli; Lee, Kiyoung; Kim, Doo Hun; Fabry, Ben; Schmuki, Patrik (Journal of the American Chemical Society, 2010)

Solid-State Chemistry on the Nanoscale: Ion Transport through Interstitial Sites or Vacancies? - Bothe, Cornelia; Kornowski, Andreas; Tornatzky, Hans; Schmidtke, Christian; Lange, Holger; Maultzsch, Janina; Weller, Horst (Angewandte Chemie International Edition, 2015)
How can ion-exchange process occur in nanocrystals without the size and shape changing and why is the ion transport much faster than in classical interdiffusion processes in macrocrystalline solids? We have investigated these processes at the molecular level by means of high-resolution and analytical electron microscopy in temperature-dependent kinetic experiments for several model reactions. The results clearly show a diffusion process that proceeds exclusively through the interstitial lattice positions with a subsequent "kick out" to remove individual ions from lattice sites without the formation of vacancies. This mechanism has not been observed in nanocrystalline systems before.
Keywords: cation exchange; nanoparticles; PbSe; reaction kinetics; ZnSe

Soluble graphene: Generation of aqueous graphene solutions aided by a perylenebisimide-based bolaamphiphile - Englert, Jan; Röhrl, Jonas; Schmidt, Cordula; Graupner, Ralf; Hundhausen, Martin; Hauke, Frank; Hirsch, Andreas (Advanced Materials, 2009)
(Figure Presented) Single-layer graphene (SLG) is deposited onto Si/SiO substrates from aqueous dispersions using a scalable and quick detergent-based method (see figure). The deposits are analyzed using absorption and Raman spectroscopy and atomic force and optical microscopy. Evaluation of the two-phonon defect-induced Raman peak of individual particles on the substrate is used to confirm exfoliation into graphene monolayers. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

Solution-Growth Liquid-Phase Epitaxy of CsPbBr3 on NaCl by Optimizing the Substrate Dissolution - Elia, Jack; Levchuk, Ievgen; Hou, Yi; Matt, Gebhard; These, Albert; Zhao, Yicheng; Zhang, Jiyun; Forberich, Karen; Osvet, Andres; Götz, Klaus; Prihoda, Annemarie; Wu, Mingjian; et al. (Journal of Physical Chemistry C, 2023)
Since the earliest days of liquid-phase epitaxy (LPE) research, substrate stability has been a prerequisite for investigating nucleation and epitaxial growth. For flux- and melt-growth LPE, soluble substrates have always been viewed as problematic and difficult. However, solution-growth LPE transforms this disadvantage into a benefit by facilitating the creation of graded interfaces. In this study, we investigated the nucleation and growth of solution-grown LPE in the evaporation mode of soluble CsPbBr3 on freshly cleaved NaCl single-crystal substrates. Only two of the four main types of CsPbBr3 crystallization observed are epitaxial. The microscopic observation of composition gradients at the interface of CsPbBr3 grains and substrates reveals a promising opportunity to manipulate the lattice constant at the interface by simply controlling the temperature and concentration.
CRIS-Team Scopus Importer:2023-12-08

Solving the Hydrogen and Lithium Substructure of Poly(triazine imide)/LiCl Using NMR Crystallography - Mesch, Maria B.; Baerwinkel, Kilian; Krysiak, Yasar; Martineau, Charlotte; Taulelle, Francis; Neder, Reinhard; Kolb, Ute; Senker, Juergen (Chemistry - A European Journal, 2016)
Poly(triazine imide) with incorporated lithium chloride has recently attracted substantial attention due to its photocatalytic activity for water splitting. However, an apparent H/Li disorder prevents the delineation of structure-property relationships, for example, with respect to bandgap tuning. Herein, we show that through a combination of one-and two-dimensional, multinuclear solid-state NMR spectroscopy, chemical modelling, automated electron diffraction tomography, and an analysis based on X-ray pair distribution functions, it is finally possible to resolve the H/Li substructure. In each cavity, one hydrogen atom is bound to a bridging nitrogen atom, while a second one protonates a triazine ring. The two lithium ions within each cavity are positioned between two nitrogen atoms of neighbouring triazine rings. The thereby induced local dipole moments cause slight buckling of the framework and lateral displacements of the Cl- ions at a coherence length below 2 nm. Nevertheless, the average structure conforms to space group P2(1)2(1)2(1). In this way, we demonstrate that, in particular, the above-mentioned techniques allow for smart interplay in delineating the real structure of PTI/LiCl.
Keywords: electron diffraction; NMR crystallography; NMR spectroscopy; poly(triazine imide); structure elucidation

Sonication-assisted liquid phase exfoliation of two-dimensional CrTe3 under inert conditions - Synnatschke, Kevin; Moses Badlyan, Narine; Wrzesińska, Angelika; Lozano Onrubia, Guillermo; Hansen, Anna Lena; Wolff, Stefan; Tornatzky, Hans; Bensch, Wolfgang; Vaynzof, Yana; Maultzsch, Janina; Backes, Claudia (Ultrasonics Sonochemistry, 2023)
Liquid phase exfoliation (LPE) has been used for the successful fabrication of nanosheets from a large number of van der Waals materials. While this allows to study fundamental changes of material properties’ associated with reduced dimensions, it also changes the chemistry of many materials due to a significant increase of the effective surface area, often accompanied with enhanced reactivity and accelerated oxidation. To prevent material decomposition, LPE and processing in inert atmosphere have been developed, which enables the preparation of pristine nanomaterials, and to systematically study compositional changes over time for different storage conditions. Here, we demonstrate the inert exfoliation of the oxidation-sensitive van der Waals crystal, CrTe3. The pristine nanomaterial was purified and size-selected by centrifugation, nanosheet dimensions in the fractions quantified by atomic force microscopy and studied by Raman, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX) and photo spectroscopic measurements. We find a dependence of the relative intensities of the CrTe3 Raman modes on the propagation direction of the incident light, which prevents a correlation of the Raman spectral profile to the nanosheet dimensions. XPS and EDX reveal that the contribution of surface oxides to the spectra is reduced after exfoliation compared to the bulk material. Further, the decomposition mechanism of the nanosheets was studied by time-dependent extinction measurements after water titration experiments to initially dry solvents, which suggest that water plays a significant role in the material decomposition.
CRIS-Team Scopus Importer:2023-08-11
Keywords: 2D materials; Degradation; Liquid phase exfoliation; Sonication

Sparsity through evolutionary pruning prevents neuronal networks from overfitting - Gerum, Richard; Erpenbeck, André; Krauß, Patrick; Schilling, Achim (Neural Networks, 2020)
Modern Machine learning techniques take advantage of the exponentially rising calculation power in new generation processor units. Thus, the number of parameters which are trained to solve complex tasks was highly increased over the last decades. However, still the networks fail – in contrast to our brain – to develop general intelligence in the sense of being able to solve several complex tasks with only one network architecture. This could be the case because the brain is not a randomly initialized neural network, which has to be trained from scratch by simply investing a lot of calculation power, but has from birth some fixed hierarchical structure. To make progress in decoding the structural basis of biological neural networks we here chose a bottom-up approach, where we evolutionarily trained small neural networks in performing a maze task. This simple maze task requires dynamic decision making with delayed rewards. We were able to show that during the evolutionary optimization random severance of connections leads to better generalization performance of the networks compared to fully connected networks. We conclude that sparsity is a central property of neural networks and should be considered for modern Machine learning approaches.
CRIS-Team Scopus Importer:2020-06-02
Keywords: Artificial neural networks; Biological plausibility; Evolution; Evolutionary algorithm; Maze task; Overfitting

Spatial Control of Graphene Functionalization by Patterning a 2D Substrate: Implications for Graphene Based van-der-Waals Heterostructures - Dierke, Tobias; Dasler, Daniela; Nagel, Tamara; Hauke, Frank; Hirsch, Andreas; Maultzsch, Janina (ACS Applied Nano Materials, 2022)
We present an experimental study on the degree of covalent functionalization of graphene exfoliated on top of hBN stripes on Si/SiO2as well as on other two-dimensional (2D) materials. The underlying substrate has a strong effect on the degree of functionalization of graphene. Our results indicate that the functionalization of graphene is less effective on hBN than on SiO2, as shown by higher defect-induced modes in the graphene Raman spectra on SiO2. Other underlying 2D materials like MoS2, WS2, and MoO3show less contrast in functionalization density than hBN or lead to even higher degree of functionalization than the Si/SiO2substrate. Patterning the underlying material is therefore a versatile method for spatially defined functionalization of graphene because it preserves the intrinsic high-quality properties of graphene, a clear advantage over other patterning approaches based on masks or introduction of defects. Our work shows that the rich variety of 2D materials offers numerous possibilities to integrate graphene with different degrees of functionalization into van-der-Waals heterostructures and devices.
CRIS-Team Scopus Importer:2022-05-13
Keywords: 2D materials; functionalization pattern; graphene; hBN; Raman spectroscopy; van-der-Waals heterostructures

Spatial extent of a Landauer residual-resistivity dipole in graphene quantified by scanning tunnelling potentiometry - Willke, Philip; Druga, Thomas; Ulbrich, Rainer G.; Schneider, M. Alexander; Wenderoth, Martin (Nature Communications, 2015)
Electronic transport on a macroscopic scale is described by spatially averaged electric fields and scattering processes summarized in a reduced electron mobility. That this does not capture electronic transport on the atomic scale was realized by Landauer long ago. Local and non-local scattering processes need to be considered separately, the former leading to a voltage drop localized at a defect, the so-called Landauer residual-resistivity dipole. Lacking precise experimental data on the atomic scale, the spatial extent of the voltage drop remained an open question. Here, we provide an experimental study showing that the voltage drop at a monolayer-bilayer boundary in graphene clearly extends spatially up to a few nanometres into the bilayer and hence is not located strictly at the structural defect. Moreover, different scattering mechanisms can be disentangled. The matching of wave functions at either side of the junction is identified as the dominant process, a situation similar to that encountered when a molecule bridges two contacts.

Spatiotemporal sampling of near-petahertz vortex fields - Blöchl, Johannes; Schoetz, Johannes; Maliakkal, Ancyline; Šreibere, Natālija; Wang, Zilong; Rosenberger, Philipp; Hommelhoff, Peter; Staudte, Andre; Corkum, Paul B.; Bergues, Boris; Kling, Matthias Friedrich (Optica, 2022)
Measuring the field of visible light with high spatial resolution has been challenging, as many established methods only detect a focus-averaged signal. Here, we introduce a near-field method for optical field sampling that overcomes that limitation by employing the localization of the enhanced near-field of a nanometric needle tip. A probe field perturbs the photoemission from the tip, which is induced by a pump pulse, generating a field-dependent current modulation that can easily be captured with our electronic detection scheme. The approach provides reliable characterization of near-petahertz fields. We show that not only the spiral wavefront of visible femtosecond light pulses carrying orbital angular momentum (OAM) can be resolved but also the field evolution with time in the focal plane. Additionally, our method is polarization sensitive, which makes it applicable to vectorial field reconstructio
Keywords: optical angular momentum beams; tiptoe; waveform measurement; nearfield

Spectral Properties of Unimodular Lattice Triangulations - Krüger, Benedikt; Schmidt, Ella; Mecke, Klaus (Journal of Statistical Physics, 2016)
Random unimodular lattice triangulations have been recently used as an embedded random graph model, which exhibit a crossover behavior between an ordered, large-world and a disordered, small-world behavior. Using the ergodic Pachner flips that transform such triangulations into another and an energy functional that corresponds to the degree distribution variance, Markov chain Monte Carlo simulations can be applied to study these graphs. Here, we consider the spectra of the adjacency and the Laplacian matrix as well as the algebraic connectivity and the spectral radius. Power law dependencies on the system size can clearly be identified and compared to analytical solutions for periodic ground states. For random triangulations we find a qualitative agreement of the spectral properties with well-known random graph models. In the microcanonical ensemble analytical approximations agree with numerical simulations. In the canonical ensemble a crossover behavior can be found for the algebraic connectivity and the spectral radius, thus combining large-world and small-world behavior in one model. The considered spectral properties can be applied to transport problems on triangulation graphs and the crossover behavior allows a tuning of important transport quantities.
Keywords: Triangulations; Random graphs; Networks; Spectral graph theory

SPECTROMETER FOR MOMENTUM-RESOLVED BREMSSTRAHLUNG SPECTROSCOPY - Fauster, Thomas; et al. (Review of Scientific Instruments, 1983)

Spectroscopic Investigations of Diamond/Hydrogen/Metal and Diamond/Metal Interfaces - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 2001)
The formation of metal contacts on diamond surfaces is of decisive importance for the material's application in semiconductor devices. We present an investigation of the barrier heights of metals on diamond (111) single crystal surfaces by a combination of spectroscopic and structural methods. Two metals with different work functions and chemical reactivities, aluminium and gold were chosen as model systems for Schottky and ohmic contacts, respectively. Particular attention was paid to the role hydrogen termination of diamond has for the metal film morphology and the barrier heights. To this end diamond/metal contacts on hydrogenated and dehydrogenated diamond were investigated. Core-level spectroscopy was used to monitor chemical reactions between diamond and metal, metal-induced band bending, and the barrier heights. The morphology of the evaporated metal films was investigated by low energy electron diffraction (LEED), atomic force microscopy (AFM), and secondary electron microscopy (SEM). © 2001 Elsevier Science B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.spectr
Keywords: Hydrogen; Metal-diamond interface; Schottky/ohmic contacts

Speedy BEC in a tiny trap: coherent matter waves on a microchip - Treutlein, Philipp; Hommelhoff, Peter; Long, Romain; Rom, Tim; Steinmetz, Tilo; Hänsch, Theodor (Proceedings of the XV International Conference on Laser Spectroscopy, 2002)
UnivIS-Import:2015-04-16:Pub.2002.nat.dphy.IAP.exphys.speedy

Spin lifetimes and strain-controlled spin precession of drifting electrons in GaAs - Malzer, Stefan; Metzner, Claus; et al. (EPL - Europhysics Letters, 2006)
We study the transport of spin-polarized electrons in n-GaAs using spatially resolved continuous-wave Faraday rotation. From the measured steady-state distribution, we determine spin relaxation times under drift conditions and, in the presence of strain, the induced spin splitting from the observed spin precession. Controlled variation of strain along [110] allows us to deduce the deformation potential causing this effect, while strain along [100] has no effect. The electric-field dependence of the spin lifetime is explained quantitatively in terms of an increase of the electron temperature. © EDP Sciences.

Spin-split silicon states at step edges of Si(553)-Au - Biedermann, Kerstin; Regensburger, Stefan; Fauster, Thomas; Himpsel, F. J.; Erwin, S. C. (Physical Review B, 2012)
The quasi-one-dimensional Si(553)-Au surface is investigated with time-resolved two-photon photoemission and laser-based photoemission. Several occupied and unoccupied states inside and outside the bulk band gap of silicon were found near the center of the surface Brillouin zone. A nondispersing unoccupied state 0.62 eV above the Fermi level with a lifetime of 125 fs matches the spin-split silicon step-edge state predicted by density functional theory calculations. Two occupied bands can be associated with the bands calculated for nonpolarized step-edge atoms.

Spin splitting of image-potential states on fcc Fe/Cu(100) - Thomann, Ulrich; Shumay, Igor; Weinelt, Martin; Fauster, Thomas (Applied Physics B-Lasers and Optics, 1999)
The ferromagnetic exchange splitting of the lowest image-potential states has been measured for Fe films on Cu(100). The majority and minority spin contributions were separated using polarization-dependent two-photon photoemission without magnetizing the sample. The results show an increased spin splitting for decreasing film thickness in agreement with the increasing magnetic moment found by band structure calculations. The lifetime of the states is between 3 fs and 15 fs with slightly shorter values for the minority state.

Splitting of monolayer out-of-plane A '(1) Raman mode in few-layer WS2 - Staiger, Matthias; Gillen, Roland; Scheuschner, Nils; Ochedowski, Oliver; Kampmann, Felix; Schleberger, Marika; Thomsen, Christian; Maultzsch, Janina (Physical Review B, 2015)
We present Raman measurements of mono-and few-layer WS2. We study the monolayer A'(1) mode around 420 cm(-1) and its evolution with the number of layers. We show that with increasing layer number there are an increasing number of possible vibrational patterns for the out-of-plane Raman mode: in N-layer WS2 there are N Gamma-point phonons evolving from the A'(1) monolayer mode. For an excitation energy close to resonance with the A excitonic transition energy, we were able to observe all of these N components, irrespective of their Raman activity. Density functional theory calculations support the experimental findings and make it possible to attribute the modes to their respective symmetries. The findings described here are of general importance for all other phonon modes in WS2 and other layered transition-metal dichalcogenide systems in the few-layer regim

Splitting of the Raman 2D band of graphene subjected to strain - Mohr, Marcel; Maultzsch, Janina; Thomsen, Christian (Physical Review B, 2010)
The Raman 2D band-important for the analysis of graphene-shows a splitting for uniaxial strain. The splitting depends on the strength and direction of the applied strain and on the polarization of the incident and outgoing light. We expand the double-resonance Raman model in order to explain the strain direction dependence and the polarization dependence of the splitting. The analysis of this splitting gives distinct insight into the origin of the 2D band. Our prediction of the strain direction and polarization dependence agrees well with recent experiments.

Splitting of the Raman 2D band of graphene subjected to strain (vol 82, 201409, 2010) - Maultzsch, Janina; et al. (Physical Review B, 2010)

Square-Planar Ruthenium(II) Complexes: Control of Spin State by Pincer Ligand Functionalization - Askevold, Bjorn; Khusniyarov, Marat; Kroener, Wolfgang; Gieb, Klaus; Müller, Paul; Herdtweck, Eberhardt; Heinemann, Frank Wilhelm; Diefenbach, Martin; Holthausen, Max C.; Vieru, Veacheslav; Chibotaru, Liviu F.; Schneider, Sven (Chemistry - A European Journal, 2015)
Functionalization of the PNP pincer ligand backbone allows for a comparison of the dialkyl amido, vinyl alkyl amido, and divinyl amido ruthenium(II) pincer complex series [RuClN(CH2CH2PtBu2)(2)], [RuClN(CHCHPtBu2)(CH2CH2PtBu2)], and [RuClN(CHCHPtBu2)(2)], in which the ruthenium( II) ions are in the extremely rare square-planar coordination geometry. Whereas the dialkylamido complex adopts an electronic singlet (S=0) ground state and energetically low-lying triplet (S=1) state, the vinyl alkyl amido and the divinyl amido complexes exhibit unusual triplet (S=1) ground states as confirmed by experimental and computational examination. However, essentially non-magnetic ground states arise for the two intermediate-spin complexes owing to unusually large zero-field splitting (D> +200 cm(-1)). The change in ground state electronic configuration is attributed to tailored pincer ligand-to-metal pi-donation within the PNP ligand serie
Keywords: computer chemistry; ligands; magnetic properties; NMR spectroscopy; ruthenium

STABILIZATION OF THE DYNAMIC BEHAVIOR OF THE CU(110) SURFACE UPON OXYGEN-ADSORPTION - Fauster, Thomas; et al. (EPL - Europhysics Letters, 1991)
We used inverse photoemission and impact collision ion scattering spectroscopy to study the dynamical behaviour of the Cu(110)-(2 x 1)O surface. In contrast to the clean Cu(110) surface, we find a linear increase of the mean square displacements of the copper surface atoms with temperature, which can be described by a Debye temperature of 240 K in agreement with surface phonon calculations. An explanation might be that the adsorption of oxygen removes the surface stress present on the clean Cu(110) surface and leads to a quite stable bond configuration.
Keywords: DYNAMICS OF SOLID SURFACES AND INTERFACE VIBRATIONS; FIELD-ION MICROSCOPY DETERMINATIONS; OTHER ELECTRON IMPACT PHENOMENA

STACKING OF AG LAYERS ON PT(111) - Fauster, Thomas; et al. (Surface Science, 1995)
Ultrathin Ag films grown epitaxially on Pt(111) were studied by photoelectron forward scattering using synchrotron radiation. The complete angular distributions of the Ag 3d electrons at similar to 500 eV kinetic energy were recorded in a cone with 88 degrees opening angle using a two-dimensional display-type analyzer. The images reveal that the second Ag layer grows at room temperature predominantly in a hcp stacking sequence with respect to the pseudomorphic first Ag layer, After annealing to 750 K most of the second layer Ag atoms assume fee sites, Further Ag layers continue to grow in a fee stacking sequence relative to the first two Ag layers. Annealing does not change the stacking of thicker films. Thick fee Ag films can be grown in a twin orientation with respect to the Pt(111) substrate at room temperature or in the substrate orientation if the second Ag layer is annealed.
Keywords: LOW INDEX SINGLE CRYSTAL SURFACES; PHOTOELECTRON DIFFRACTION; PLATINUM; SILVER; SINGLE CRYSTAL EPITAXY; SURFACE STRUCTURE; X-RAY PHOTOELECTRON SPECTROSCOPY

Stark Tuning of the Silicon Vacancy in Silicon Carbide - Rühl, Maximilian; Bergmann, Lena; Krieger, Michael; Weber, Heiko B. (Nano Letters, 2020)
We present a versatile scheme dedicated to exerting strong electric fields up to 0.5 MV/cm on color centers in hexagonal silicon carbide, employing transparent epitaxial graphene electrodes. In both the axial and basal direction equally strong electric fields can be selectively controlled. Investigating the silicon vacancy (V-Si) in ensemble photoluminescence experiments, we report Stark splitting of the V1' line of 3 meV by a basal electrical field and a Stark shift of the V1 line of 1 meV in an axial electric field. The spectral fine-tuning of the V-Si, being an important candidate for realizing quantum networks, paves the way for truly indistinguishable single-photon sources.
CRIS-Team WoS Importer:2020-01-31

Static structural analysis of condensed matter: from single-crystal to amorphous - Neder, Reinhard (Structures on Different Time Scales, 2018)
CRIS-Team WoS Importer:2019-06-28

Statistical analysis of single-molecule junctions - Mayor, Marcel; Weber, Heiko B. (Angewandte Chemie International Edition, 2004)
Keywords: electron transport; molecular electronics; scanning probe techniques; single-molecule studies; structure-property relationships

Statistical approach to investigating transport through single molecules - Lörtscher, M.; Weber, Heiko B.; Riel, Heike (Physical Review Letters, 2007)
We present a statistical approach that combines comprehensive current-voltage data acquisition during the controlled manipulation of a molecular junction with subsequent statistical analysis. Thereby the most probable transport characteristics can be determined. The excellent sensitivity of this impartial approach to even subnanometer-long molecules is illustrated by benzene-1,4-dithiol and 4,4 ''-bis(acetylthiol)-2,2',5',2 ''-tetramethyl-[1,1';4',1 ''] terphenyl results.

Statistics of multiphoton photoemission under coherent and non-classical illumination - Heimerl, Jonas; Mikhaylov, Alexander; Meier, Stefan; Höllerer, Henrick; Kaminer, Ido; Chekhova, Maria; Hommelhoff, Peter (Optics InfoBase Conference Papers, 2022)
We investigate experimentally how the photon statistics of light gets imprinted on multiphoton electron emission from needle tips. Coherent and bright squeezed vacuum light lead to entirely different electron statistics, matching with a quantum-optical analysis.
CRIS-Team Scopus Importer:2022-09-09

Steady-state hopping conduction in the conduction band tail of a-Si:H studied in thin - Hundhausen, Martin; Ley, Lothar; et al. (Physical Review B - Condensed Matter and Materials Physics, 1995)
UnivIS-Import:2015-03-05:Pub.1995.nat.dphy.IAP.exphys.steady

Stochastic Resonance Controlled Upregulation of Internal Noise after Hearing Loss as a Putative Cause of Tinnitus-Related Neuronal Hyperactivity - Krauß, Patrick; Tziridis, Konstantin; Metzner, Claus; Schilling, Achim; Hoppe, Ulrich; Schulze, Holger (Frontiers in Neuroscience, 2016)
Subjective tinnitus is generally assumed to be a consequence of hearing loss. In animal studies it has been demonstrated that acoustic trauma induced cochlear damage can lead to behavioral signs of tinnitus. In addition it was shown that noise trauma may lead to deafferentation of cochlear inner hair cells (IHC) even in the absence of elevated hearing thresholds, and it seems conceivable that such hidden hearing loss may be sufficient to cause tinnitus. Numerous studies have indicated that tinnitus is correlated with pathologically increased spontaneous firing rates and hyperactivity of neurons along the auditory pathway. It has been proposed that this hyperactivity is the consequence of a mechanism aiming to compensate for reduced input to the auditory system by increasing central neuronal gain, a mechanism referred to as homeostatic plasticity (HP), thereby maintaining mean firing rates over longer timescales for stabilization of neuronal processing. Here we propose an alternative, new interpretation of tinnitus-related development of neuronal hyperactivity in terms of information theory. In particular, we suggest that stochastic resonance (SR) plays a key role in both short- and long-term plasticity within the auditory system and that SR is the primary cause of neuronal hyperactivity and tinnitus. We argue that following hearing loss, SR serves to lift signals above the increased neuronal thresholds, thereby partly compensating for the hearing loss. In our model, the increased amount of internal noise-which is crucial for SR to work-corresponds to neuronal hyperactivity which subsequently causes neuronal plasticity along the auditory pathway and finally may lead to the development of a phantom percept, i.e., subjective tinnitus. We demonstrate the plausibility of our hypothesis using a computational model and provide exemplary findings in human patients that are consistent with that model. Finally we discuss the observed asymmetry in human tinnitus pitch distribution as a consequence of asymmetry of the distribution of auditory nerve type I fibers along the cochlea in the context of our model.
EVALuna2:33193

Storage of X-ray photons in a crystal resonator - Hock, Rainer; et al. (Nature, 2000)
The temporal structure and high brilliance of the X-ray beams produced by third-generation synchrotrons open up new possibilities in time-dependent diffraction and spectroscopy, where timescales down to the sub-nanosecond regime can now be accessed. These beam properties are such that one can envisage the development of the X-ray equivalent of optical components, such as photon delay lines and resonators, that have proved indispensable in a wide range of experiments-for example, pump-probe and multiple-interaction experiments-and (through shaping the temporal structure and repetition rate of the beams) time-dependent measurements in crystallography, physics, biology and chemistry(1-3). Optical resonators, such as those used in lasers, are available at wavelengths from the visible to soft X-rays(4,5). Equivalent components for hard X-rays have been discussed for more than thirty years(4,6,7), but have yet to be realized. Here we report the storage of hard X-ray photons (energy 15.817 keV) in a crystal resonator formed by two plates of crystalline silicon. The photons are stored for as many as 14 back-and-forth cycles within the resonator, each cycle separated by one nanosecond.

Strain and Charge in Epitaxial Graphene on Silicon Carbide Studied by Raman Spectroscopy - Röhrl, Jonas; Hundhausen, Martin; Speck, Florian; Seyller, Thomas (Materials Science Forum, 2010)
The phonon frequencies of epitaxial graphene on silicon carbide (SiC) depend on mechanical strain and charge transfer from the substrate to the epitaxial layer. Strain and doping depend on the preparation process and on the number of graphene layers. We measured the phonon frequencies by Raman spectroscopy and compare the results between epitaxial layers fabricated by high temperature annealing and by hydrogen intercalation of the covalently bound graphene layer of the 6√3 × 6√3 reconstructed SiC surface. Only the latter graphene layer shows tensile strain, which can partly be explained by lattice mismatch between substrate and epitaxial graphene. © (2010) Trans Tech Publications.
UnivIS-Import:2015-03-09:Pub.2010.nat.dphy.IAP.exphys.strain
Keywords: Epitaxial graphene; Raman spectroscopy; Strain

Strain-Dependent Photoluminescence Line Shifts of the TS Color Center in 4H-SiC - Lehmeyer, Johannes; Fuchs, Alexander; Bornträger, T.; Popp, Matthias Albert; Weber, Heiko B.; Krieger, Michael (Defect and Diffusion Forum, 2023)
We present a detailed study of the behavior of the photoluminescence (PL) of the TS color center in 4H-SiC under controlled mechanical strain. We have investigated the TS1 line under varying strain, including its reaction to compression and tension. We use emission polarization measurements to gain access to the orientation of the underlying defects. We put our results in context with previous findings and find good agreement, corroborating the proposed microscopic model.
CRIS-Team Scopus Importer:2023-11-03
Keywords: Color Center; Mechanical Strain; Photoluminescence; Photophysics

Strain Engineering in InP/(Zn,Cd)Se Core/Shell Quantum Dots - Rafipoor, Mona; Dupont, Dorian; Tornatzky, Hans; Tessier, Mickael D.; Maultzsch, Janina; Hens, Zeger; Lange, Holger (Chemistry of Materials, 2018)

Strain history dependence of the nonlinear stress response of fibrin and collagen networks - Münster, Stefan; Jawerth, Louise M.; Leslie, Beverly A.; Weitz, Jeffrey I.; Fabry, Ben; Weitz, David (Proceedings of the National Academy of Sciences of the United States of America, 2013)

Straining of atomically thin WSe2crystals: Suppressing slippage by thermal annealing - Hu, Wenshuai; Wang, Yabin; He, Kexin; He, Xiaolong; Bai, Yan; Liu, Chenyang; Zhou, Nan; Wang, Haolin; Li, Peixian; Ma, Xiaohua; Xie, Yong (Journal of Applied Physics, 2022)
The atomically thin two-dimensional (2D) transition-metal dichalcogenide (e.g., MoS2) material can withstand large strains up to 11% to change its energy band structure, thereby further tuning its optical, electrical, and other physical properties. However, the slippage of 2D materials on substrate hammers the further strain tuning of the properties of 2D materials. Hereby, a facile three points approach combined with a dry transfer method that can apply uniaxial strain to two-dimensional materials is provided. The slippage of WSe2 on polycarbonate (PC) substrate can be suppressed by thermally annealing WSe2/PC in low pressure Ar atmosphere above 100 °C for 3 h. Straining cycle evolution experiments revealed that the thermal annealing of (1L) WSe2 could suppress slippage from the surface of the PC. The spectral gauge factor of 1L WSe2 is found to be around -60 meV/%. After thermal treatment, WSe2/PC stacking can survive in DI water for at least 24 h without the degradation of the spectral gauge factor. Dome structures are formed after thermal treatments with the interplay of the viscoelasticity and surface tension of the PC and the 0.4% tensile strain on WSe2, and the RMS roughness of WSe2/PC increased from 820 to 1292 pm, indicating that there could be larger lateral friction force to suppress slippage following thermal annealing. Our findings enrich the strain engineering of 2D materials and their device applications.
CRIS-Team Scopus Importer:2022-09-16

Strain in InP/ZnSe, S core/shell quantum dots from lattice mismatch and shell thickness - Material stiffness influence - Rafipoor, Mona; Tornatzky, Hans; Dupont, Dorian; Maultzsch, Janina; Tessier, Mickael D.; Hens, Zeger; Lange, Holger (Journal of Chemical Physics, 2019)

Strain relief via silicon self-interstitial emission in highly boron-doped silicon: A diffuse X-ray scattering study of oxygen precipitation - Bergmann, Christoph; Gröschel, Alexander; Will, Johannes; Magerl, Andreas (Journal of Applied Physics, 2015)
Oxygen precipitation in highly boron-doped Czochralski silicon (5m Omega cm resistivity) was studied, and a strain-relieving mechanism involving the emission of silicon interstitial atoms (I-Si) was identified. Strain-sensitive X-ray diffraction was employed, and through a comparison with complementary electron microscopy measurements a linear misfit strain epsilon=0. 01 was determined. Different behavior concerning strain relaxation was measured for wafer-type samples (760 mu m thickness) and thick samples (2mm thickness), which was explained with out-diffusion of ISi in the thinner samples. Based on the experimental findings, a model was developed which invokes an increase in the solubility of interstitial silicon atoms upon boron doping. The model successfully accounts for different effects of boron doping on oxygen precipitation in silicon, which were reported on in literature such as preferential octahedral morphology of precipitates, enhanced nucleation, and relaxed accommodation of the precipitates with respect to the silicon lattice. (C) 2015 AIP Publishing LLC.

Strain-specific differences in pili formation and the interaction of Corynebacterium diphtheriae with host cells - Ott, Lisa; Höller, Martina; Rheinlaender, Johannes; Schäffer, Tilman; Hensel, Michael; Burkovski, Andreas (BMC Microbiology, 2010)
Background: Corynebacterium diphtheriae, the causative agent of diphtheria, is well-investigated in respect to toxin production, while little is known about C. diphtheriae factors crucial for colonization of the host. In this study, we investigated strain-specific differences in adhesion, invasion and intracellular survival and analyzed formation of pili in different isolates. Results: Adhesion of different C. diphtheriae strains to epithelial cells and invasion of these cells are not strictly coupled processes. Using ultrastructure analyses by atomic force microscopy, significant differences in macromolecular surface structures were found between the investigated C. diphtheriae strains in respect to number and length of pili. Interestingly, adhesion and pili formation are not coupled processes and also no correlation between invasion and pili formation was found. Using RNA hybridization and Western blotting experiments, strain-specific pili expression patterns were observed. None of the studied C. diphtheriae strains had a dramatic detrimental effect on host cell viability as indicated by measurements of transepithelial resistance of Detroit 562 cell monolayers and fluorescence microscopy, leading to the assumption that C. diphtheriae strains might use epithelial cells as an environmental niche supplying protection against antibodies and macrophages. Conclusions: The results obtained suggest that it is necessary to investigate various isolates on a molecular level to understand and to predict the colonization process of different C. diphtheriae strains. © 2010 Ott et al; licensee BioMed Central Ltd.
UnivIS-Import:2015-03-09:Pub.2010.nat.dphy.IAP.LAP.strain

Strain tunable interlayer and intralayer excitons in vertically stacked MoSe2/WSe2 heterobilayers - Li, L. L.; Gillen, Roland; Palummo, M.; Milošević, M. V.; Peeters, F. M. (Applied Physics Letters, 2023)
Recently, interlayer and intralayer excitons in transition metal dichalcogenide heterobilayers have been studied both experimentally and theoretically. In spite of a growing interest, these layer-resolved excitons in the presence of external stimuli, such as strain, remain not fully understood. Here, using density-functional theory calculations with many-body effects, we explore the excitonic properties of vertically stacked MoSe2/WSe2 heterobilayer in the presence of in-plane biaxial strain of up to 5%. We calculate the strain dependence of exciton absorption spectrum, oscillator strength, wave function, and binding energy by solving the Bethe-Salpeter equation on top of the standard GW approach. We identify the interlayer and intralayer excitons by analyzing their electron-hole weights and spatial wave functions. We show that with the increase in strain magnitude, the absorption spectrum of the interlayer and intralayer excitons is red-shifted and re-ordered, and the binding energies of these layer-resolved excitons decrease monotonically and almost linearly. We derive the sensitivity of exciton binding energy to the applied strain and find that the intralayer excitons are more sensitive to strain than the interlayer excitons. For instance, a sensitivity of −7.9 meV/% is derived for the intra-MoSe2-layer excitons, which is followed by −7.4 meV/% for the intra-WSe2-layer excitons, and by −4.2 meV/% for the interlayer excitons. Our results indicate that interlayer and intralayer excitons in vertically stacked MoSe2/WSe2 heterobilayer are efficiently tunable by in-plane biaxial strain.
CRIS-Team Scopus Importer:2023-08-11

Strength of radial breathing mode in single-walled carbon nanotubes - Machon, Maria; Reich, Stephanie; Telg, Hagen; Maultzsch, Janina; Ordejon, Pablo; Thomsen, Christian (Physical Review B, 2005)
We show by ab initio calculations that the electron-phonon coupling matrix element Me-ph of the radial breathing mode in single-walled carbon nanotubes depends strongly on tube chirality. For nanotubes of the same diameter the coupling strength -ph\(2) is up to one order of magnitude stronger for zigzag tubes than for armchair tubes. For (n(1),n(2)) tubes Me-ph depends on the value of (n(1)-n(2)) mod 3, which allows us to discriminate semiconducting nanotubes with similar diameter by their Raman scattering intensity. We show measured resonance Raman profiles of the radial breathing mode which support our theoretical predictions.

Stress controls the mechanics of collagen networks - Licup, Albert James; Münster, Stefan; Sharma, Abhinav; Sheinman, Michael; Jawerth, Louise M.; Fabry, Ben; Weitz, David A.; MacKintosh, Fred C. (Proceedings of the National Academy of Sciences of the United States of America, 2015)

Stress fluctuations and motion of cytoskeletal-bound markers - Raupach, Carina; Paranhos Zitterbart, Daniel; Mierke, Claudia; Metzner, Claus; Müller, Frank A.; Fabry, Ben (Physical Review E, 2007)
Cytoskeletal (CSK) dynamics such as remodeling and reorganization can be studied by tracking the spontaneous motion of CSK-bound particles. Particle motion is thought to be driven by local, ATP-dependent intracellular force fluctuations due to polymerization processes and motor proteins, and to be impeded by a viscoelastic, metastable cytoskeletal network. The mechanisms that link particle motion to force fluctuations and the CSK dynamics remain unclear. We report simultaneous measurements of the spontaneous motion of CSK-bound particles and of cellular force fluctuations. Cellular force fluctuations were measured by tracking fluorescent markers embedded in an elastic polyacrylamide hydrogel substrate that served as an extracellular matrix (ECM). The motion of CSK-bound particles and markers embedded in the ECM showed both persistence and superdiffusive behavior. Moreover, the movements of CSK-bound beads were temporally and spatially correlated with force fluctuations in the ECM. The findings suggest that the spontaneous motion of CSK-bound beads is driven not by random, local stress fluctuations within a viscoelastic continuum or cage, but rather by stress fluctuations within a tensed and constantly remodeling CSK network that transmits stresses over considerable distances to the ECM. © 2007 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2007.nat.dphy.IAP.lpmt.stress

Stress relaxation amplitude of hydrogels determines migration, proliferation, and morphology of cells in 3-D culture - Hazur, Jonas; Endrizzi, Nadine; Schubert, Dirk W.; Boccaccini, Aldo R.; Fabry, Ben (Biomaterials Science, 2021)
The viscoelastic behavior of hydrogel matrices sensitively influences the cell behavior in 3-D culture and biofabricated tissue model systems. Previous reports have demonstrated that cells tend to adhere, spread, migrate and proliferate better in hydrogels with pronounced stress relaxation. However, it is currently unknown if cells respond more sensitively to the amplitude of stress relaxation, or to the relaxation time constant. To test this, we compare the behavior of fibroblasts cultured for up to 10 days in alginate and oxidized alginate hydrogels with similar Young's moduli but diverging stress relaxation behavior. We find that fibroblasts elongate, migrate and proliferate better in hydrogels that display a higher stress relaxation amplitude. By contrast, the cells' response to the relaxation time constant was less pronounced and less consistent. Together, these data suggest that it is foremost the stress relaxation amplitude of the matrix that determines the ability of cells to locally penetrate and structurally remodel the matrix on a molecular level, which subsequently leads to better spreading, faster migration, and higher cell proliferation. We conclude that the stress relaxation amplitude is a central design parameter for optimizing cell behavior in 3-D hydrogels.
CRIS-Team WoS Importer:2021-12-10

Strong and Weak 3D Topological Insulators Probed by Surface Science Methods - Morgenstern, Markus; Pauly, Christian; Kellner, Jens; Liebmann, Marcus; Pratzer, Marco; Bihlmayer, Gustav; Eschbach, Markus; Plucinski, Lukacz; Otto, Sebastian; Rasche, Bertold; Ruck, Michael; Richter, Manuel; et al. (physica status solidi (b), 2020)
The contributions of surface science methods to discover and improve 3D topological insulator materials are reviewed herein, illustrated with examples from the authors’ own work. In particular, it is demonstrated that spin-polarized angular-resolved photoelectron spectroscopy is instrumental to evidence the spin-helical surface Dirac cone, to tune its Dirac point energy toward the Fermi level, and to discover novel types of topological insulators such as dual ones or switchable ones in phase change materials. Moreover, procedures are introduced to spatially map potential fluctuations by scanning tunneling spectroscopy and to identify topological edge states in weak topological insulators.
CRIS-Team Scopus Importer:2020-05-22
Keywords: angular-resolved photoelectron spectroscopy; scanning tunneling spectroscopy; spin-polarized topological insulators

Strong-Field Above-Threshold Photoemission from Sharp Metal Tips - Schenk, Markus; Krüger, Michael; Hommelhoff, Peter (Physical Review Letters, 2010)
We present energy-resolved measurements of electron emission from sharp metal tips driven with low energy pulses from a few-cycle laser oscillator. We observe above-threshold photoemission with a photon order of up to 9. At a laser intensity of ∼2×1011 W/cm2 the suppression of the lowest order peak occurs, indicating the onset of strong-field effects. We also observe peak shifting linearly with intensity, with a slope of around −1.0 eV/(1012 W/cm2). We attribute the magnitude of the laser field effects to field enhancement taking place at the tip’s surfac
Keywords: nanotips; electron emission; strong field physics; above-threshold photoemission

Strong-Field-Assisted Measurement of Near-Fields and Coherent Control of Photoemission at Nanometric Metal Tips - Förster, Michael; Paschen, Timo; Thomas, Sebastian; Krüger, Michael; Hommelhoff, Peter (Progress in Ultrafast Intense Laser Science, 2017)
Metal nanotips are an ideal testbed for ultrafast and strong-field physics at solids due to the superb control they allow over their very apex and the near-field at this apex that enhances an incident laser field. Particular attention has recently been devoted to the study of laser-induced electron emission from nanotips, where an enhanced fundamental understanding contributes to the implementation of nanotips as a source of femtosecond electron pulses. In this chapter we present photoemission studies at nanotips illuminated with femtosecond lasers. We demonstrate a new technique to measure the strength of near-fields at nanostructures by using our knowledge of the occurring strong-field physics. Electrons rescattering with the surface of the nanotip after emission give access to the prevalent near-field intensity on the nanometer scale. Our measurements fit well with independent simulations of Maxwell’s equations. In the second part we show that by employing a synthesized light field of a fundamental and a second harmonic laser pulse we achieve almost perfect coherent control of the photoemission process. We demonstrate that we can interpret our findings in terms of interfering quantum pathways.

Strong-field effects and attosecond control of electrons in photoemission from a nanoscale metal tip - Krüger, Michael; Schenk, M.; Hommelhoff, Peter (12th International Conference on Multiphoton Processes, ICOMP 2011 and the 3rd International Conference on Attosecond Physics, ATTO 2011, 2012)
We focus few-cycle Titanium:sapphire oscillator pulses on a sharp tungsten tip and measure spectra of the emitted electrons. We observe abovethreshold photoemission with a photon order of up to nine, peak shifting and peak suppression, and carrier-envelope phase sensitive photoemission. In a first attempt to understand the underlying physics we model the behavior with theory models borrowed from atomic physics, namely the Three-Step Model and an integration of the one-dimensional time-dependent Schr̈odinger equation. The models match the high-energy part of the spectra surprisingly well, and we infer that re-scattering and much of the well-known underlying physics of the Three-Step Model takes also place here, even though the parameters are such that this is almost surprising; for instance, the classical excursion of the electrons is only slightly larger than one atomic diameter. © Springer-Verlag Berlin Heidelberg 2012.

Strong-field electron emission from gold needle tips - Heimerl, Jonas; Meier, Stefan; Kirchner, Adrian; Weitz, Tobias; Hommelhoff, Peter (Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics, 2023)
We show strong-field electron energy spectra from nanometric gold needle tips triggered by femtosecond laser pulses. For this, we use two different wavelengths, 800 nm with 12 fs pulse duration and 1550 nm with 170 fs pulse duration. With an extended plateau and cutoff of rescattered electrons, the recorded electron spectra show the tell-tale features of strong-field physics. Furthermore, the spectra clearly show above-threshold photoemission peaks. Such energy spectra are an ideal tool to benchmark current theory models.
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Strong-Field Perspective on High-Harmonic Radiation from Bulk Solids - Higuchi, Takuya; Stockman, Mark I.; Hommelhoff, Peter (Physical Review Letters, 2014)
Mechanisms of high-harmonic generation from crystals are described by treating the electric field of a laser as a quasistatic strong field. Under the quasistatic electric field, electrons in periodic potentials form dressed states, known as Wannier-Stark states. The energy differences between the dressed states determine the frequencies of the radiation. The radiation yield is determined by the magnitudes of the interband and intraband current matrix elements between the dressed states. The generation of attosecond pulses from solids is predicted. Ramifications for strong-field physics are discusse
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.exphys.strong

Strong-field physics: Harmonic radiation from crystals - Hommelhoff, Peter; Higuchi, Takuya (Nature, 2015)

Strong-field spectra and optical near-field enhancement at aluminium needle tips - Paschen, Timo; Nauk, Constantin; Dienstbier, Philip; Hommelhoff, Peter (Journal of Physics B: Atomic, Molecular and Optical Physics, 2021)
We study the rescattering of photoemitted electrons at aluminium needle tips. For various laser intensities we measure electron energy spectra to identify telltale features of strong-field rescattering, in particular a plateau with near-constant count rate and a high-energy cutoff. This rescattering process is used to investigate the geometry-dependent enhanced optical near-field at the apex of the aluminium tip. A large near-field enhancement, extracted from the spectral data, is supported by 3D finite-difference time-domain simulations. A systematic theoretical investigation of the near-field enhancement at aluminium tips shows a strong dependence on tip opening angle and radius of curvatur
Keywords: electron sources; aluminium needle tips; strong-field physics; rescattering; optical near-fields

Strong-field spectral interferometry using the carrier-envelope phase - Ott, C.; Schoenwald, M.; Raith, P.; Kaldun, A.; Sansone, G.; Krüger, Michael; Hommelhoff, Peter; Patil, Yogesh; Zhang, Yizhu; Meyer, Karsten; Laux, M.; Pfeifer, T. (New Journal of Physics, 2013)
The carrier-envelope phase (CEP) of ultrashort laser pulses is an important parameter in strong-field physics that controls temporally localized events on a sub-cycle timescale. The relative timing of these events is directly encoded into the measured spectral intensity distribution, and can be accessed by the use of spectral interferometry. Here, we combine this analysis with CEP control in a two-dimensional way, creating a novel spectroscopic method to explore the temporal dynamics of strong-field processes. We apply this general method to CEP-dependent high-harmonic generation and find that contributions of three different sub-cycle electron quantum paths can be separated, allowing one to quantify the dipole-phase dependence on the CEP in the non-adiabatic regime. The CEP-dependent time delay between two full-cycle spaced attosecond pulses was determined to modulate by 54 ± 16 as. We confirm the generality of the method by further applying it to CEP-dependent photoemission from a nanoscale metal tip. © IOP Publishing and Deutsche Physikalische Gesellschaft.

Strongly anisotropic spin and orbital Rashba effect at a tellurium - noble metal interface - Geldiyev, B.; Ünzelmann, M.; Eck, P.; Kißlinger, Tilman; Schusser, J.; Figgemeier, T.; Kagerer, P.; Tezak, N.; Krivenkov, M.; Varykhalov, A.; Fedorov, A.; Nicolaï, L.; et al. (Physical Review B, 2023)
We study the interplay of lattice, spin, and orbital degrees of freedom in a two-dimensional model system: a flat square lattice of Formula Presented atoms on a Formula Presented surface. The atomic structure of the Te monolayer is determined by scanning tunneling microscopy and quantitative low-energy electron diffraction. Using spin- and angle-resolved photoelectron spectroscopy and density functional theory, we observe a Te-Au interface state with highly anisotropic Rashba-type spin-orbit splitting at the Formula Presented point of the Brillouin zone. Based on a profound symmetry and tight-binding analysis, we show how in-plane square lattice symmetry and broken inversion symmetry at the Te-Au interface together enforce a remarkably anisotropic orbital Rashba effect which strongly modulates the spin splitting.
CRIS-Team Scopus Importer:2023-10-06

Strong magneto-chiral dichroism in enantiopure chiral ferromagnets - Train, Cyrille; Gheorghe, Ruxandra; Krstic, Vojislav; Chamoreau, Lise-Marie; Ovanesyan, Nikolai S.; Rikken, Geert L.J.A.; Gruselle, Michel; Verdaguer, Michel (Nature Materials, 2008)
As materials science is moving towards the synthesis, the study and the processing of new materials exhibiting well-defined and complex functions, the synthesis of new multifunctional materials is one of the important challenges. One of these complex physical properties is magneto-chiral dichroism which arises, at second order, from the coexistence of spatial asymmetry and magnetization in a material. Herein we report the first measurement of strong magneto-chiral dichroism in an enantiopure chiral ferromagnet. The ab initio synthesis of the enantiopure chiral ferromagnet is based on an enantioselective self-assembly, where a resolved chiral quaternary ammonium cation imposes the absolute configurations of the metal centres within chromium–manganese two-dimensional oxalate layers. The ferromagnetic interaction between Cr(III) and Mn(II) ions leads to a Curie temperature of 7 K. The magneto-chiral dichroic effect is enhanced by a factor of 17 when entering into the ferromagnetic phase.

Strong phonon-plasmon coupled modes in the graphene/silicon carbide heterosystem - Koch, R. J.; Seyller, Thomas; Schaefer, J. A. (Physical Review B, 2010)
We report on strong coupling of the charge-carrier plasmon extgreekwPL in graphene with the surface-optical phonon extgreekwSO of the underlying SiC(0001) substrate with low-electron concentration (n=1.2×1015 cm-3) in the long-wavelength limit (qII->0). Energy-dependent energy-loss spectra give clear evidence of two coupled phonon-plasmon modes extgreekw± separated by a gap between extgreekwSO(qII->0) and extgreekwTO(qII->0), the transverse-optical-phonon mode, in particular, for higher primary electron energies (E0≥20 eV). A simplified model based on dielectric theory is able to simulate our energy-loss spectra as well as the dispersion of the two coupled phonon-plasmon modes extgreekw±. In contrast, Liu and Willis Phys. Rev. B 81 081406 (2010) postulate in their recent publication no gap and a discontinuous dispersion curve with a one-peak structure from their energy-loss data.
EAM Import::2019-03-13

Structural and electronic properties of diamond surfaces - Ristein, Jürgen (Thin Film Diamond (part II), 2004)
UnivIS-Import:2015-04-20:Pub.2004.nat.dphy.IAP.exphys.struct

Structural characterization and evaluation of antibacterial and angiogenic potential of gallium-containing melt-derived and gel-derived glasses from CaO-SiO2 system - Wajda, Aleksandra; Goldmann, Wolfgang; Detsch, Rainer; Grünewald, Alina; Boccaccini, Aldo R.; Sitarz, Maciej (Ceramics International, 2018)
Keywords: Angiogenesis; Antibacterial properties; Gallium oxide; Bioactive silicate glasses; Biocompatibility

Structural Characterization of Lecithin-Stabilized Tetracosane Lipid Nanoparticles. Part I: Emulsions - Schmiele, Martin; Busch, Sebastian; Morhenn, H.; Schindler, Torben; Schmutzler, Tilo; Schweins, R.; Lindner, P.; Boesecke, P.; Westermann, M.; Steiniger, F.; Funari, Sergio S.; Unruh, Tobias (Journal of Physical Chemistry B, 2016)
The structure of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)-stabilized colloidal tetracosane emulsions was investigated by photon correlation spectroscopy and small-angle X-ray and neutron scattering, using emulsions with different neutron scattering contrasts. Special emphasis was placed on the structure of the DMPC stabilizer layer covering the emulsion droplets. A monolayer, structurally similar to a half DMPC bilayer, with a thickness of 16 å is found. Thereby, the phosphocholine headgroups arrange flat at the oil-water interface. A deep penetration of the tetracosane oil into the stabilizer layer can be ruled ou

Structural Characterization of Lecithin-Stabilized Tetracosane Lipid Nanoparticles. Part II: Suspensions - Schmiele, Martin; Busch, Sebastian; Morhenn, H.; Schindler, Torben; Schmutzler, Tilo; Schweins, R.; Lindner, P.; Boesecke, P.; Westermann, M.; Steiniger, F.; Funari, Sergio S.; Unruh, Tobias (Journal of Physical Chemistry B, 2016)
Using photon correlation spectroscopy, transmission electron microscopy, microcalorimetry, wide-angle X-ray scattering (WAXS), and small-angle X-ray and neutron scattering (SAXS, SANS), the structure of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)-stabilized colloidal tetracosane suspensions was studied from the molecular level to the microscopic scale as a function of the temperature. The platelike nanocrystals exhibit for tetracosane an unusual orthorhombic low-temperature crystal structure. The corresponding WAXS pattern can be reproduced with a predicted orthorhombic unit cell (space group Pca2), which usually occurs only for much longer even-numbered n-alkanes. Special emphasis was placed on the structure of the DMPC stabilizer layer covering the nanocrystals. Their structure was investigated by SAXS and SANS, using suspensions with different neutron scattering contrasts. As for the emulsions in Part I, the crystallized nanoparticles are covered by a DMPC monolayer. Their significant smaller thickness of 10.5 å (for the emulsions in Part I: 16 å) could be related to a more tilted orientation of the DMPC molecules to cover the expanded surface of the crystallized nanoparticle

Structural characterization of the phospholipid stabilizer layer at the solid-liquid interface of dispersed triglyceride nanocrystals with small-angle x-ray and neutron scattering - Schmiele, Martin; Schindler, Torben; Unruh, Tobias; Busch, Sebastian; Morhenn, Humphrey; Westermann, Martin; Steiniger, Frank; Radulescu, Aurel; Lindner, Peter; Schweins, Ralf; Boesecke, Peter (Physical Review E, 2013)
Dispersions of crystalline nanoparticles with at least one sufficiently large unit cell dimension can give rise to Bragg reflections in the small-angle scattering range. If the nanocrystals possess only a small number of unit cells along these particular crystallographic directions, the corresponding Bragg reflections will be broadened. In a previous study of phospholipid stabilized dispersions of β-tripalmitin platelets, the x-ray powder pattern simulation analysis (XPPSA) was developed. The XPPSA method facilitates the interpretation of the rather complicated small-angle x-ray scattering (SAXS) curves of such dispersions of nanocrystals. The XPPSA method yields the distribution function of the platelet thicknesses and facilitates a structural characterization of the phospholipid stabilizer layer at the solid-liquid interface between the nanocrystals and the dispersion medium from the shape of the broadened 001 Bragg reflection. In this contribution an improved and extended version of the XPPSA method is presented. The SAXS and small-angle neutron scattering patterns of dilute phospholipid stabilized tripalmitin dispersions can be reproduced on the basis of a consistent simulation model for the particles and their phospholipid stabilizer layer on an absolute scale. The results indicate a surprisingly flat arrangement of the phospholipid molecules in the stabilizer layer with a total thickness of only 12 Å. The stabilizer layer can be modeled by an inner shell for the fatty acid chains and an outer shell including the head groups and additional water. The experiments support a dense packing of the phospholipid molecules on the nanocrystal surfaces rather than isolated phospholipid domains. © 2013 American Physical Society.

Structural defects in SiC crystals investigated by high energy x-ray diffraction - Weißer, Matthias; Seitz, Christoph; Wellmann, Peter; Hock, Rainer; Magerl, Andreas (Materials Science Forum, 2004)
High energy x-ray diffraction (up to 300 keV) has been used to analyse structural defects in an as grown SiC boule with a diameter of 55 nun, a thickness of 20 mm and in a 2 inch wafer. The crystals are 6H SiC grown by PVT method. In the wafer numerous grains can be identified and localised with a mosaicity in the order of 0.05degrees, whereas the whole wafer shows a mosaic spread of around 0.1degrees. The bulk crystal shows a pronounced domain structure and a bending in the lattice plane orientation. The local reflection broadening is between 0.2degrees and 2degrees, while the tilts of the lattice planes over the entire wafer are between 2 and 6degrees (2theta-values
Keywords: Domain Structure; High Energy Diffraction; Structural Defects; X-Ray Diffraction (XRD)

Structural Defect Studies of Semiconductor Crystals with Laue Topography - Gröschel, Alexander; Will, Johannes; Bergmann, Christoph; Grillenberger, Hannes; Eichler, Stefan; Scheffer-Czygan, M.; Magerl, Andreas (2011)
A defocused Laue diffractometer setup operating with the white beam of a high energy X-ray tube has been used for a topographic visualization of structural defects in semiconductor wafers. The laboratory white beam X-ray topograph of a Czochralski Si wafer with oxygen precipitates grown in an annealing process is compared to a mu PCD image. Further, the dislocation network in a VGF GaAs wafer is studied under thermal annealing up to 1140 degrees C and the in-situ capability of the setup is demonstrated.
Keywords: X-ray diffraction; topography; silicon; oxygen precipitates; GaAs; dislocations; annealing; in-situ

Structural, electronic, and vibrational properties of (4,4) picotube crystals - Machon, Maria; Reich, Stephanie; Maultzsch, Janina; Okudera, H; Simon, A; Herges, Rainer; Thomsen, Christian (Physical Review B, 2005)
The picotube molecule is a highly symmetric hydrocarbon, closely related to a very short (4,4) carbon nanotube. We present a thorough experimental and theoretical study of the physical properties of picotube crystals. In x-ray diffraction experiments we find the picotube molecules to display D-2d symmetry. We identify the most intense Raman peaks as A(1) modes with polarization-dependent Raman measurements. Ab initio calculations of the structural, electronic, and vibrational properties of picotubes are in excellent agreement with our experiments. We assign the measured vibrations to displacement eigenvectors including those analogous to the nanotube high-energy mode, the D mode, and the radial-breathing mode.

Structural fluctuations cause spin-split states in tetragonal (CH₃NH₃)PbI₃ as evidenced by the circular photogalvanic effect - Niesner, Daniel; Hauck, Martin; Shrestha, Shreetu; Levchuk, Ievgen; Matt, Gebhard; Osvet, Andres; Batentschuk, Miroslaw; Brabec, Christoph; Weber, Heiko B.; Fauster, Thomas (Proceedings of the National Academy of Sciences of the United States of America, 2018)
Lead halide perovskites are used in thin-film solar cells, which owe their high efficiency to the long lifetimes of photocarriers. Various calculations find that a dynamical Rashba effect could significantly contribute to these long lifetimes. This effect is predicted to cause a spin splitting of the electronic bands of inversion-symmetric crystalline materials at finite temperatures, resulting in a slightly indirect band gap. Direct experimental evidence of the existence or the strength of the spin splitting is lacking. Here, we resonantly excite photocurrents in single crystalline (CH3NH3)PbI3 with circularly polarized light to clarify the existence of spin splittings in the band structure. We observe a circular photogalvanic effect, i.e., the photocurrent depends on the light helicity, in both orthorhombic and tetragonal (CH3NH3)PbI3. At room temperature, the effect peaks for excitation photon energies ΔE=110 meV below the direct optical band gap. Temperature-dependent measurements reveal a sign change of the effect at the orthorhombic extendashtetragonal phase transition, indicating different microscopic origins in the two phases. Within the tetragonal phase, both ΔE and the amplitude of the circular photogalvanic effect increase with temperature. Our findings support a dynamical Rashba effect in this phase, i.e., a spin splitting caused by thermally induced structural fluctuations which break inversion symmetr
Keywords: organic–inorganic perovskite; lead halide perovskite; circular photogalvanic effect; dynamical Rashba; Rashba effect

Structural investigation of triangular defects in 4H-SiC epitaxial layers as nucleation source for bar shaped stacking faults (BSSFs) - Kodolitsch, Elisabeth; Kabakow, A.; Sodan,; Krieger, Michael; Weber, Heiko B.; Tsavdaris, N. (Journal of Physics D: Applied Physics, 2023)
The formation of recombination-induced bar shaped stacking faults (BSSFs) during forward voltage operation of SiC devices, can lead to increased voltage drop and enhanced device degradation. In this study, a triangular epitaxial defect is identified as a nucleation source for the growth of BSSF in forward-biased 4H-SiC p-n diode test structures. We performed low and high voltage current emission microscopy measurements in order to detect the position of BSSFs in the active area of the device and in-depth structural analysis to locate their nucleation source. It was found that basal plane dislocations that converted into threading screw dislocations, close to the surface of the epitaxial layer and included in the triangular defect, act as nucleation source for the BSSFs. Those BSSFs expand from the top towards the bottom of the epitaxial layer, which is a newly reported expansion mechanism compared to the already reported BSSFs growing from the substrate/epitaxial layer interface towards the epitaxial layer surface.
CRIS-Team Scopus Importer:2023-05-26
Keywords: 4H-SiC; bipolar degradation; single Shockley stacking faults; triangular defects

Structural investigation of triangular defects in 4H-SiC epitaxial layers as nucleation source for bar shaped stacking faults (BSSFs) - Kodolitsch, Elisabeth; Kabakow, A.; Sodan, Vice; Krieger, Michael; Weber, Heiko B.; Tsavdaris, Nikolaos (Journal of Physics D-Applied Physics, 2023)
The formation of recombination-induced bar shaped stacking faults (BSSFs) during forward voltage operation of SiC devices, can lead to increased voltage drop and enhanced device degradation. In this study, a triangular epitaxial defect is identified as a nucleation source for the growth of BSSF in forward-biased 4H-SiC p-n diode test structures. We performed low and high voltage current emission microscopy measurements in order to detect the position of BSSFs in the active area of the device and in-depth structural analysis to locate their nucleation source. It was found that basal plane dislocations that converted into threading screw dislocations, close to the surface of the epitaxial layer and included in the triangular defect, act as nucleation source for the BSSFs. Those BSSFs expand from the top towards the bottom of the epitaxial layer, which is a newly reported expansion mechanism compared to the already reported BSSFs growing from the substrate/epitaxial layer interface towards the epitaxial layer surface.<br

Structural Investigations of Self-Assembled Monolayers for Organic Electronics: Results from X-ray Reflectivity - Khassanov, Artöm; Steinrück, Hans-Georg; Schmaltz, Thomas; Magerl, Andreas; Halik, Marcus (Accounts of Chemical Research, 2015)
Self-assembled monolayers (SAMs) have been established as crucial interlayers and electronically active layers in organic electronic devices, such as organic light emitting diodes (OLEDs), organic photovoltaics (OPVs), organic thin film transistors (OTFTs), and nonvolatile memories (NVMs). The use of self-assembling functionalized organic molecules is beneficial due to mainly three advantages compared with common thin film deposition approaches. (1) Molecular self-assembly occurs with surface selectivity, determined by the interaction between the functional anchor group of the organic molecules and the target surface. (2) The film thickness of the resulting layers is perfectly controllable on the angstrom scale, due to the self-terminating film formation to only a single molecular layer. And finally, (3) the wide variability in the chemical structure of such molecules enables different SAM functionalities for devices, ranging from electrical insulation to charge storage to charge transport. The SAM approach can be further expanded by employing several functionalized molecules to create mixed SAMs with consequently mixed properties. The function of SAMs in devices depends not only on the chemical structure of the molecules but also on their final arrangement and orientation on the surface. A reliable and nondestructive in-depth characterization of SAMs on nonconductive oxide surfaces is still challenging because of the very small thickness and the impracticality of methods such as scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In this Account, we illustrate how X-ray reflectivity (XRR) provides analytical access to major questions of SAM composition, morphology, and even formation by means of investigations of pure and mixed SAMs based on phosphonic acids (PAs) of various chain structures on flat alumina (AlOx) surfaces. XRR is an analytical method that provides access to spatially averaged structural depth profiles over a relatively large area of several square micrometers. The key outcome of XRR, the surface-normal electron density profile of the SAMs, leads to precise information on the SAM thickness with subangstrom resolution and allows for the determination of molecular tilt angles and packing densities. We have systematically increased the chemical complexity of PA molecules and the resulting SAMs, utilizing XRR to provide insight into the SAM structures. In SAMs composed of functionalized molecules or complex chain structures, the distribution of electron rich and electron poor signatures is detected and thus the molecular order within the SAM is determined. In mixed SAMs of two different molecular species, electron density profiles reveal the morphology and how the surface-normal structure changes if one component of the mixed SAM is altered. Furthermore, XRR was applied to investigate in situ the self-assembly of functionalized PA molecules from solution by tracking the monolayer growth over time. Even though the results provided by XRR on in-plane molecular arrangement are limited, it presents excellent information on the molecular scale along the surface normal and in addition allows for drawing conclusions on the intermolecular interactions within the SAM.

Structural modification of ultra-thin Fe films on Cu(100) prepared by pulsed laser deposition - Weinelt, Martin; Baier, Holger; Schwarz, Sergej; Fauster, Thomas (Surface Science, 2000)
The structure and quality of ultra-thin iron films on Cu(100) prepared by pulsed laser deposition (PLD) were studied by means of low energy electron diffraction (LEED). As in the case of thermal deposition (TD), the film undergoes a structural transition from a tetragonally expanded phase to the undistorted fee structure at an iron coverage of 5 monolayers (ML). The changed structure of the Fe/Cu interface and the improved film quality are discussed in terms of the laser-fluence dependency of the deposited particle energies for PLD. (C) 2000 Elsevier Science B.V. All rights reserved.
Keywords: laser methods; low energy electron diffraction (LEED); metal-metal magnetic thin film structures

Structural organisation and dynamics in king penguin colonies - Gerum, Richard; Richter, Sebastian; Fabry, Ben; Le Bohec, Céline; Bonadonna, Francesco; Nesterova, Anna; Paranhos Zitterbart, Daniel (Journal of Physics D-Applied Physics, 2018)

Structural phase transition to disorder low-temperature phase in [Fe(ptz)(6)](BF4)(2) spin-crossover compounds - Kusz, Joachim; Zubko, Maciej; Neder, Reinhard; Guetlich, Phillipp (Acta Crystallographica Section B: Structural Science, 2012)
In the spin-crossover compound [Fe(ptz)(6)](BF4)(2) (where ptz=1-n-propyltetrazole) six different phases are observed. When a single crystal is slowly cooled from high temperatures to those below 125 K, the reflections broaden into diffuse maxima and split into two maxima along the c* direction [Kusz, Gutlich & Spiering (2004). Top. Curr. Chem. 234, 129-153]. As both maxima are broad along the c* direction, the short-range order exists only along the c direction and in the ab plane the structure remains long-range ordered. In this disordered phase additional satellite reflections appear. Upon heating above 135 K, the diffuse maxima return to their previous shape and this process is completely reversible. Rapidly cooled samples, on the other hand, do not show such splitting and the symmetry remains R (3) over bar, despite a jump in lattice parameters. We use a special technique to analyse the disorder model of the slowly cooled samples, which consists of layered domains shifted in the hexagonal ab plane. The low-spin disordered phase was solved in a novel approach to accommodate the very unusual twinning and refined in the non-standard space group C (1) over bar. In contrast to the ordered low-spin phase, the Fe ion is in a non-centrosymmetric coordination polyhedron and two of the six propyl groups change their conformation.

Structural properties and electronic states of carbon delta-layers in GaAs - Malzer, Stefan; et al. (PHYSICS OF SEMICONDUCTORS: 27th International Conference on the Physics of Semiconductors, ICPS-27, 2005)
We present a cross-sectional STM study of delta-doped GaAs on the nanoscale. GaAs (001) layers grown by MBE with a series of embedded carbon delta-layers having nominal sheet densities in the range 3×10 /cm to 1×10/cm were investigated. The dopant concentrations were checked with SIMS. The carbon concentration profiles in growth direction were determined, and found to be atomically sharp and symmetric up to the highest concentrations, with a FWHM of 0.85nm. This shows that even at the elevated growth temperature of 860K and up to 1×10/cm density neither segregation nor diffusion plays a significant role in carbon delta-doping of GaAs. The observed residual spreading of the profile is attributed to the generic surface roughness during epitaxial growth. In a second step we analyzed in detail the spectra in the delta-layer regions. In the vicinity of near surface acceptors we found a nonvanishing conductivity throughout the band gap energy range. This is markedly different from the discrete LDOS peak found in the band gap for isolated acceptors in bulk samples, and it indicates metallic conductivity. Inhomogeneities of the metallic conductance are found to be strongly correlated with the arrangement of dopant atoms in the delta-layer. © 2005 American Institute of Physics.

Structural relaxation as seen by quasielastic neutron scattering on viscous Zr-Ti-Cu-Ni-Be droplets - Yang, Fan; Kordel, Tobias; Holland-Moritz, Dirk; Unruh, Tobias; Meyer, Andreas (Journal of Physics: Condensed Matter, 2011)
In bulk glass forming Zr46.8Ti8.2Cu7.5Ni10Be27.5 (Vit4) the mean Ni, Ti, and Cu self-diffusion coefficient at the liquidus is about 10(-10) m(2) s(-1). Compared with these values, diffusion coefficients derived from various reported viscosity data by rescaling them via the Stokes-Einstein relation exhibit different temperature dependence and absolute values are a factor of 5-10 smaller. This raises the question of whether a slow Zr subsystem exists in the melt at temperatures well above the liquidus temperature. Here, we address this question by studying microscopic dynamics employing quasielastic neutron scattering. We utilized containerless sample processing in a novel electrostatic levitation apparatus. This excludes reactions between samples and crucible materials and gives access to a wide momentum transfer range of about 0.2-2.6 angstrom(-1). We studied the dynamics governed by the Ni, Ti, and Cu diffusive motion as well as by collective Zr motion. At 1255 K, both correlation functions decay to zero on a timescale of about 20 ps. This shows that there is neither a decoupling between the atomic dynamics of the various components nor a slow Zr subsystem in the equilibrium melt.

Structure and dynamics of liquid Ni36Zr64 studied by neutron scattering - Holland-Moritz, Dirk; Stüber, Sebastian; Hartmann, Helena; Unruh, Tobias; Hansen, Thomas; Meyer, Andreas (Physical Review B, 2009)
We report on investigations on the atomic dynamics and the static structure factors of binary Ni36Zr64 alloy melts. In order to undercool the melts deeply below the melting temperature and to avoid reactions with crucible materials, the liquids are containerlessly processed by the application of the electromagnetic levitation technique. This technique is combined with quasielastic neutron scattering at the time-of-flight spectrometer TOFTOF of the Munich research reactor (FRM II) and neutron diffraction at the diffractometer D20 of the Institut Laue-Langevin. Partial static structure factors of liquid Ni36Zr64 have been derived via isotopic substitution. The quasielastic neutron-scattering experiments indicate a large activation energy for Ni self-diffusion in liquid Ni36Zr64 of 0.64 eV. This may result from a peculiar short-range order of the Ni-Zr melts that differs from the icosahedral short-range order that was previously found to prevail in most melts of pure metals and of metallic alloys with a small difference of the atomic radii of the components and that is characterized by a high nearest-neighbor coordination number of < Z >approximate to 13.9, as found by elastic neutron scattering.
Keywords: liquid alloys; liquid structure; melting point; neutron diffraction; nickel alloys; self-diffusion; short-range order; time of flight spectra; zirconium alloys

Structure and electronic states of ultrathin SiO2 thermally grown on Si(100) and Si(111) surfaces - Ley, Lothar; Ristein, Jürgen; et al. (Applied Surface Science, 1997)
The chemical and electronic structures of ultrathin SiO2 thermally grown on Si(100) and Si(111) have been investigated by using Fourier-transform infrared attenuated total reflection (FT-IR-ATR) and X-ray or ultraviolet excited photoelectron spectroscopy (XPS/UPS), respectively. A red-shift of the p-polarized LO phonon peak observed for oxides thinner than 2 nm indicates that compressively strained Si-O-Si bonds exist near the SiO2/Si interface. The extent of the structural strain induced in the interface region is found to be smaller for SiO2 grown at 1000°C on Si(100) than 1000°C SiO2 on Si(111) or 800°C SiO2 on Si(100). It is also found that, from the onset of the energy loss signal for Ols photoelectrons, the bandgap of the oxides thicker than ∼ 2.3 nm is 8.95 ± 0.05 eV irrespective of the oxide thickness. For oxides thinner than ∼ 2.3 nm, a remarkable increase in the 5-9 eV energy loss signal for O1s photoelectrons is observed. This could be attributed to not only the contribution of suboxides at the interface but also the built-in stress in the interface region which causes the band edge tailing.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.IAP.exphys.struct

Structure and mechanics of fibrin clots formed under mechanical perturbation - Münster, Stefan; Jawerth, Louise M.; Fabry, Ben; Weitz, David A. (Journal of Thrombosis and Haemostasis, 2013)

Structure and ordering of oxygen on unreconstructed Ir(100) - Ferstl, Pascal; Schmitt, T.; Schneider, M. Alexander; Hammer, Lutz; Michl, A.; Mueller, S. (Physical Review B, 2016)
The adsorption of oxygen on the unreconstructed Ir(100) surface is investigated by a combination of experimental and theoretical methods comprising low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density-functional theory (DFT). Apart from the well-known (2 x 1)-O phase, we find a new (3 x 1)-O phase for temperatures below 180 K. Our DFT calculations predict these two phases to be the only fundamental ground states of the system in the coverage range up to 0.5 monolayers. An analysis of the phase transitions as a function of coverage reveals extended coexistence ranges between the clean surface and the 3 x 1 phase, or between the 3 x 1 and 2 x 1 phases, respectively. As a function of temperature, both phases undergo order-disorder transitions at about 650 K for the 2 x 1 phase and 180 K for the 3 x 1 phase, the latter being only partially reversible. The complete ordering behavior can be consistently explained by the energetics of model defect structures calculated by DFT. The crystallographic structure of the phases is determined by full-dynamical LEED intensity analyses, yielding excellent agreement between experimental and calculated data sets (Pendry R-factors: R-P approximate to 0.1). Oxygen was found to assume bridge sites always inducing significant relaxations within the substrate. The derived structural parameters coincide with the respective predictions from DFT on the picometer scale. It is also shown that remnants and precursor stages of the clean surface's reconstruction can only be detected through the application of real-space methods such as STM. The overarching objective of the present study is to demonstrate how precisely and accurately such an adsorption system can be investigated nowadays by using a concerted experimental and theoretical approach.

Structure determination of molecular nanocomposites by combining pair distribution function analysis and solid-state NMR - Bendeif, E. -E.; Gansmuller, A.; Hsieh, K. -Y.; Pillet, S.; Woike, Th.; Zobel, Mirijam; Neder, Reinhard; Bouazaoui, M.; El Hamzaoui, H.; Schaniel, Dominik (RSC Advances, 2015)
Transparent mesoporous silica monoliths of well-controlled porosity and a narrow pore size distribution around 6 nm have been used to prepare sodium nitroprusside (SNP) nanocomposites. The obtained nanomaterials could be characterised using X-ray total scattering coupled to atomic pair distribution function analysis (PDF) and solid-state NMR spectroscopy. The PDF analysis allows for a structural description of the confined species, as well as for the identification of the various coexisting phases: SNP isolated molecules and SNP crystalline nanoparticles. The model obtained suggests that the nanocrystals have the same molecular structure as the bulk crystalline material and measure about 6 nm in diameter. This result is quite exceptional because the space available inside the pores is only about ten times the size of the molecules. The multi-nuclei solid state NMR investigation confirms the structural model proposed by the PDF analysis and assigns the isolated molecules to the dynamic disorder of a solvated phase. The latter approach additionally provides quantitative information on the relative ratio between the dynamic molecules and the rigid nanocrystals. This result is exploited to study the evolution of the two confined SNP phases with respect to solvating water molecules. We show that the confined SNP nanocrystals can be easily dissolved when storing the nanocomposites at increasing atmospheric relative humidity.

Structure of epitaxial CoSi2 films on Si(111) studied with low-energy electron diffraction (LEED) - Starke, Ulrich; Schardt, Judith; Weiss, Wolfgang; Rangelov, Georgi; Fauster, Thomas; Heinz, Klaus (Surface Review and Letters, 1998)
Expitaxial films of CoSi2 on Si(111) were investigated by low-energy electron diffraction. Films of approximately 12 Angstrom thickness were prepared by simultaneous deposition of Co and Si and subsequent annealing. The films were found to crystallize in CaF2 structure in (111) orientation. Two (1 x 1) phases of different stoichiometry exist. The surface phase that contains more Co is found to be a CoSi2(111) bulklike structure terminated by a Si-Co-Si trilayer. The Si-rich phase is terminated by an additional nonrotated silicon bilayer with the lower silicon atoms bound to cobalt in the first CoSi2 layer. Consequently, these cobalt atoms have an eightfold coordination. Due to the lattice mismatch the silicide films are expanded by 0.5% in the lateral direction and contracted by 1.4% in the vertical direction.

Structure of interfaces in a-Si:H/a-SiNx:H superlattices - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Applied Physics, 1991)
UnivIS-Import:2015-03-05:Pub.1991.nat.dphy.IAP.exphys.struct

Structure of n-Alkyltrichlorosilane Mono layers on Si(100)/SiO2 - Steinrück, Hans-Georg; Will, Johannes; Magerl, Andreas; Ocko, B. (Langmuir, 2015)
The structure of n-alkyltrichlorosilane self-assembled monolayers (SAMs) of alkyl chain lengths n = 12, 14, 18, and 22 formed on the amorphous native oxide of silicon (100) has been investigated via angstrom-resolution surface X-ray scattering techniques, with particular focus on the proliferation of lateral order along the molecules' long axis. Grazing incidence diffraction shows that the monolayer is composed of hexagonally packed crystalline-like domains for n = 14, 18, and 22 with a lateral size of about 60 A. However, Bragg rod analysis shows that similar to 12 of the CH, units are not included in the crystalline-like domains. We assign this, and the limited lateral crystallites' size, to strain induced by the size mismatch between the optimal chain-chain and headgroup-headgroup spacings. Analysis of X-ray reflectivity profiles for n = 12, 14, and 22 shows that the density profile used to successfully model n = 18 provides an excellent fit where the analysis-derived parameters provide complementary structural information to the grazing incidence results.

Structure of ultrathin Fe films on Cu(100) prepared by pulsed laser deposition - Weinelt, Martin; Schwarz, Sergej; Baier, Holger; Müller, Stefan; Hammer, Lutz; Heinz, Klaus; Fauster, Thomas (Physical Review B, 2001)
The structures of ultrathin Fe films on Cu(100) prepared by pulsed laser deposition (PLD) and conventional thermal deposition (TD) are compared by means of low-energy electron diffraction (LEED). Below 5 ML coverage, PLD films exhibit up to four times higher integer-order LEED spot intensities, i.e., improved film quality, and show small but significant structural changes as compared to TD films. A quantitative tensor LEED analysis of the 4-ML PLD film reveals a similar 5 X 1 superstructure to that found previously for TD films, but with an enhanced surface buckling and a flat Cu bulklike iron interface layer. The latter is attributed to the incorporation of Cu atoms in the Fe interface caused by sputter effects in PLD. Above 6-ML coverage, both deposition methods yield comparable LEED I(E) spectra, revealing similar sum-face structures. The proposed structural models allow a consistent interpretation of the strongly altered magnetic properties observed for PLD-grown iron films.

Structure-property relationship of reversible magnetic chirality tuning - Qi, Jing; Weber, Paula M.; Kißlinger, Tilman; Hammer, Lutz; Schneider, M. Alexander; Bode, Matthias (Physical Review B, 2023)
The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction mediates collinear magnetic interactions via the conduction electrons of a nonmagnetic spacer, resulting in a ferro- or antiferromagnetic magnetization in magnetic multilayers. Recently it has been discovered that heavy nonmagnetic spacers are able to mediate an indirect magnetic coupling that is noncollinear and chiral. This Dzyaloshinskii-Moriya-enhanced RKKY interaction causes the emergence of a variety of interesting magnetic structures, such as skyrmions and spin spirals. Here, we show by spin-polarized scanning tunneling microscopy that the interchain coupling between manganese oxide chains on Ir(001) can reproducibly be switched from chiral to collinear antiferromagnetic by increasing the oxidation state of MnO2, while the reverse process can be induced by thermal reduction. The underlying structure-property relationship is revealed by low-energy electron diffraction intensity analysis. Density functional theory calculations suggest that the magnetic transition may be caused by a significant increase of the Heisenberg exchange which overrides the Dzyaloshinskii-Moriya interaction upon oxidation.
CRIS-Team Scopus Importer:2023-03-24

Studies on Cell Compatibility, Antibacterial Behavior, and Zeta Potential of Ag-Containing Polydopamine-Coated Bioactive Glass-Ceramic - Tejido Rastrilla, Rocío; Ferraris, Sara; Goldmann, Wolfgang; Grünewald, Alina; Detsch, Rainer; Baldi, Giovanni; Spriano, Silvia; Boccaccini, Aldo R. (Materials, 2019)
Dopamine is a small molecule that mimics the adhesive component (L-DOPA) of marine mussels with a catecholamine structure. Dopamine can spontaneously polymerize to form polydopamine (PDA) in a mild basic environment. PDA binds, in principle, to all types of surfaces and offers a platform for post-modification of surfaces. In this work, a novel Ag-containing polydopamine coating has been developed for the functionalization of bioactive glass-ceramics. In order to study the interactions between the surface of uncoated and coated samples and the environment, we have measured the surface zeta potential. Results confirmed that PDA can interact with the substrate through different chemical groups. A strongly negative surface zeta potential was measured, which is desirable for biocompatibility. The dual function of the material, namely the capability to exhibit bioactive behavior while being antibacterial and not harmful to mammalian cells, was assessed. The biocompatibility of the samples with MG-63 (osteoblast-like) cells was determined, as well as the antibacterial behavior against Gram-positive Staphylococcus carnosus and Gram-negative Escherichia coli bacteria. During cell biology tests, uncoated and PDA-coated samples showed biocompatibility, while cell viability on Ag-containing PDA-coated samples was reduced. On the other hand, antibacterial tests confirmed the strong antimicrobial properties of Ag-containing PDA-coated samples, although tailoring of the silver release will be necessary to modulate the dual effect of PDA and silver.
CRIS-Team WoS Importer:2019-03-22

Study of CeO2 and its native defects by density functional theory with repulsive potential - Gillen, Roland; Huang, Bolong; Robertson, John (Journal of Physical Chemistry C, 2014)

Study of the dynamics of poly(ethylene oxide) by combining molecular dynamic simulations and neutron scattering experiments - Brodeck, Martin; Alvarez, F.; Arbe, Arantxa; Juranyi, Fanni; Unruh, Tobias; Holderer, Olav; Colmenero, Juan; Richter, Dieter (Journal of Chemical Physics, 2009)
We performed quasielastic neutron scattering experiments and atomistic molecular dynamics simulations on a poly(ethylene oxide) (PEO) homopolymer system above the melting point. The excellent agreement found between both sets of data, together with a successful comparison with literature diffraction results, validates the condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field used to produce our dynamic runs and gives support to their further analysis. This provided direct information on magnitudes which are not accessible from experiments such as the radial probability distribution functions of specific atoms at different times and their moments. The results of our simulations on the H-motions and different experiments indicate that in the high-temperature range investigated the dynamics is Rouse-like for Q-values below approximate to 0.6 A(-1). We then addressed the single chain dynamic structure factor with the simulations. A mode analysis, not possible directly experimentally, reveals the limits of applicability of the Rouse model to PEO. We discuss the possible origins for the observed deviations.
Keywords: molecular dynamics method; neutron diffraction; polymer melts

Study of the temperature induced polytype conversion in cubic SiC by Raman spectroscopy - Hundhausen, Martin; Ley, Lothar; et al. (Materials Science Forum, 2004)
Using 3C-SiC crystals grown on undulant Si(100) substrates as seed crystals, bulk growth of 3C-SiC by the modified Lely method has been demonstrated. However, particularly at elevated growth temperatures, macroscopic 6H-SiC inclusions can be observed in the grown crystals. Here we investigate the temperature dependence of the 3C- to 6H-SiC transformation of the CVD substrate by Micro Raman Spectroscopy after annealing at temperatures between 1700°C and 2100°C. At temperatures above 1800°C 3C- to 6H-SiC polytype transformation is observed that proceeds from the top side of the crystals. However, the conversion appears to be stopped at domain boundaries that are oriented along 111 planes.
UnivIS-Import:2015-04-14:Pub.2004.nat.dphy.IAP.LAP.studyo
Keywords: Annealing CVD; Cubic SiC; Raman spectroscopy

Sub 100-fs, 5.2-µm ZGP Parametric Amplifier Driven by a ps Ho:YAG Chirped Pulse Amplifier and its application to high harmonic generation - Kanai, Tsuneto; Malevich, Pavel; Kangaparambil, Sarayoo Sasidharan; Hoogland, Heinar; Holzwarth, Ronald; Pugzlys, Audrius; Baltuska, Andrius (arXiv, 2016)
We report a 1 kHz repetition-rate mid-IR (MIR) optical parametric amplifier (OPA) system operating at a central wavelength of 5.2 μm with the tail-to-tail spectrum extending over 1.5 μm and delivering 40 μJ pulses that are compressed to 99 fs (5.6 optical cycles). Also we develop a novel pulse compression scheme for further pulse compression and wavelength tunability. As the first application of this laser system, we generated high harmonics in bulk ZnSe above the bandgap, dense exciton generation after 10-photon absorption, high order sum- and difference-frequency generation, ultrafast transition in the conduction band, which reflects the structure of conduction bands.

Sub-cycle temporal evolution of light-induced electron dynamics in hexagonal 2D materials - Heide, Christian; Boolakee, Tobias; Higuchi, Takuya; Hommelhoff, Peter (JPhys Photonics, 2020)
Two-dimensional materials with hexagonal symmetry such as graphene and transition metal dichalcogenides are unique materials to study light-field-controlled electron dynamics inside of a solid. Around the K-point, the dispersion relation represents an ideal system to study intricately coupled intraband motion and interband (Landau-Zener) transitions driven by the optical field of phase-controlled few-cycle laser pulses. Based on the coupled nature of the intraband and interband processes, we have recently observed in graphene repeated coherent Landau-Zener transitions between valence and conduction band separated by around half an optical period of 1.3 fs [Higuchi et al., Nature 550, 224 (2017)]. Due to the low temporal symmetry of the applied laser pulse, a residual current density and a net electron polarization are formed. Here we show extended numerical data on the temporal evolution of the conduction band population of 2D materials with hexagonal symmetry during the light-matter interaction, yielding deep insights to attosecond-fast electron dynamics. In addition, we show that a residual ballistic current density is formed, which strongly increases when a band gap is introduced. Both, the sub-cycle electron dynamics and the resulting residual current are relevant for the fundamental understanding and future applications of strongly driven electrons in two-dimensional materials, including graphene or transition metal dichalcogenide monolayer

Submonolayer copper telluride phase on Cu(111): Ad-chain and trough formation - Kißlinger, Tilman; Schneider, M. Alexander; Hammer, Lutz (Physical Review B, 2021)
We present a so-far undetected submonolayer phase of copper telluride on Cu(111) with (5×3)rect periodicity and coverage of 0.40 ML tellurium (Te), which can be grown with perfect long-range order. It is structurally characterized by a combination of quantitative low-energy electron diffraction (LEED-IV), scanning tunneling microscopy (STM), and density functional theory (DFT). We find that Te induces the formation of two-Atom-wide zig-zag troughs within the Cu(111) top layer via replacing 4 Cu atoms per unit cell by two Te atoms. Additionally, the interspace between the troughs is decorated by Cu2Te2 ad-chains sitting at hcp sites. All Te atoms exhibit the same local sixfold coordination: They occupy threefold hollow sites of the substrate and are one-sided attached to another three Cu atoms. The presented structural model is verified by a LEED-IV analysis with Pendry R factor of R = 0.174 and quantitative agreement of structural parameters with DFT predictions. It also has by far the lowest energy of all models tested by DFT and simulated STM images agree perfectly with experiment. It turns out that the new (5×3)rect phase is the most dense surface telluride phase possible on Cu(111) before bulk-like copper telluride starts to grow.
CRIS-Team Scopus Importer:2021-11-19

Sub-Monolayer Growth of Titanium, Cobalt, and Palladium on Epitaxial Graphene - Sokolova, Anastasia; Kilchert, Franziska; Link, Stefan; Stoehr, Alexander; Starke, Ulrich; Schneider, M. Alexander (Annalen Der Physik, 2017)
We deposited metals (Ti, Co, Pd) typically used as seed layers for contacts on epitaxial graphene on SiC(0001) and studied the early stages of growth in the sub-monolayer regime by Scanning Tunneling Microscopy (STM). All three metals do not wet the substrate and Ostwalt ripening occurs at temperatures below 400K. The analysis of the epitaxial orientation of the metal adislands revealed their specific alignment to the graphene lattice. It is found that the apparent height of the islands as measured by STM strongly deviates from their true topographic height. This is interpreted as an indication of the presence of scattering processes within the metal particles that increase the transparency of the metal-graphene interface for electrons. Even large islands are easily picked up by the tip of the STM allowing insight into the bonding between metal island and graphene surface and into mechanisms leading to metal intercalation.
Keywords: Epitaxial graphene; metal contacts; metal growth; STM

Sub-optical-cycle control of free electrons by optical near-fields - Kozak, Martin; McNeur, Joshua; Leedle, Kenneth J.; Deng, Huiyang; Schönenberger, Norbert; Ruehl, Axel; Hartl, Ingmar; Harris, James S.; Byer, Robert L.; Hommelhoff, Peter (Optics InfoBase Conference Papers, 2017)
CRIS-Team Scopus Importer:2022-06-05

Substituting fossil-based with bio-based chemicals: the case of limonene as a greener pore expander for micellar templated silica - Sultan, Umair; Städtke, Katrin; Göpfert, Andreas; Lemmen, Daniel; Metwali, Ezzeldin; Maiti, Santanu; Schlumberger, Carola; Yokosawa, Tadahiro; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Vogel, Nicolas; Unruh, Tobias; et al. (RSC Sustainability, 2023)
Porous materials are widely used in applications such as adsorption, catalysis and separation. The use of expander molecules is a versatile route to enlarge the mesopore size in micellar templated mesoporous silica materials. Typical expanders used for this purpose are fossil-based organic molecules such as trimethylbenzene (TMB). In the course of making such syntheses greener and more sustainable, it is highly desirable to substitute such fossil-based chemicals with renewable ones. Here, we show that bio-based limonene can be used as an alternative expander molecule for the synthesis of large-pore templated silica. On the basis of electron microscopy, nitrogen physisorption and small angle X-ray scattering we show that the substitution of TMB by limonene leads to very similar material characteristics, reaching mean mesopore diameters of 17-19 nm. A comparative life-cycle assessment demonstrates the reduced environmental impact of limonene production from citrus peel waste compared to TMB production, supporting the call for more applications of renewable chemicals, ideally from waste-streams, also for the production of porous materials.
CRIS-Team Scopus Importer:2023-10-06

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

Substrate-Modulated Reductive Graphene Functionalization - Schäfer, Ricarda; Weber, Konstantin; Kolesnik-Gray, Maria; Hauke, Frank; Krstic, Vojislav; Meyer, Bernd; Hirsch, Andreas (Angewandte Chemie International Edition, 2016)
Covalently functionalizing mechanical exfoliated mono- and bilayer graphenides with λ-iodanes led to the discovery that the monolayers supported on a SiO2 substrate are considerably more reactive than bilayers as demonstrated by statistical Raman spectroscopy/microscopy. Supported by DFT calculations we show that ditopic addend binding leads to much more stable products than the corresponding monotopic reactions as a result of the much lower lattice strain of the reactions products. The chemical nature of the substrate (graphene versus SiO2) plays a crucial rol
Keywords: functionalised grapnene; substrate interactions; chemical reactivity

Subsurface cation vacancy stabilization of the magnetite (001) surface - Bliem, R.; Mcdermott, E.; Ferstl, Pascal; Setvin, Martin; Gamba, O.; Pavelec, J.; Schneider, M. Alexander; Schmid, Michael; Diebold, Ulrike; Blaha, Peter; Hammer, Lutz; Parkinson, G. S. (Science, 2014)
Iron oxides play an increasingly prominent role in heterogeneous catalysis, hydrogen production, spintronics, and drug delivery. The surface or material interface can be performance-limiting in these applications, so it is vital to determine accurate atomic-scale structures for iron oxides and understand why they form. Using a combination of quantitative low-energy electron diffraction, scanning tunneling microscopy, and density functional theory calculations, we show that an ordered array of subsurface iron vacancies and interstitials underlies the well-known (root 2 x root 2)R45 degrees reconstruction of Fe3O4(001). This hitherto unobserved stabilization mechanism occurs because the iron oxides prefer to redistribute cations in the lattice in response to oxidizing or reducing environments. Many other metal oxides also achieve stoichiometry variation in this way, so such surface structures are likely commonplace.

Sub-THz and THz Photonic generation with continuous tunability using gain switching based optical frequency comb generators and n-i-p-n-i-p superlattice photomixers - de Dios, Christina; Criado, Ruben; Döhler, Gottfried; Preu, Sascha; Malzer, Stefan; Bauerschmidt, Sebastian; Garcia-Munoz, Enrique; Segovia-Vargas, Daniel; Acedo, Pablo (2012 IEEE International Topical Meeting on Microwave Photonics, MWP 2012, 2012)
In this work we present a compact and versatile way to generate sub-THz and THz signals using an OFCG based on a Photonic Local Oscillator responsible to generate the two wavelengths to be mixed in the photomixer based on a Gain Switching (GS) Scheme and the use of Phase Modulation; and n-i-p-n-i-p superlattice photomixers. The proposed scheme is able to cover a wide span with continuous tunability. The description of the different components of the system (Photonic Local Oscillator and Photomixer) is covered as well as some preliminary data. © 2012 IEEE.

Sulfo-selenization of metallic thin films of Cu, In and Cu-In - Hölzing, Astrid; Schurr, R.; Schäfer, Horst; Jaeger, A.; Jost, S.; Palm, J.; Deseler, Klaus; Wellmann, Peter; Hock, Rainer (Thin Solid Films, 2009)
The affinity of the metals Cu and In is higher to sulfur. A crystallisation of mixed sulfo-selenides of Cu, In and Cu-In due to exchange reactions between S and Se is observed. Within the Cu-Se-S subsystem a wider solid solution range of S and Se is apparent as compared to the In-Se-S system. The reactions during the chalcopyrite crystallisation for chalcogen ratio [S]:[Se]=1:1 are similar to those of the pure sulfur system at least within the In-Se-S subsystem. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: CuIn(S; Se)2; Chalcopyrite; Thin films; Real-time X-ray diffraction

Sum rule for quadrature response frequency resolved photoluminescence spectra - Ristein, Jürgen (Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties, 1994)
UnivIS-Import:2015-03-05:Pub.1994.nat.dphy.IAP.exphys.sumrul

Superconductivity induced by carrier injection into non-superconducting Bi2Sr2CaCu2O8+δ - Simsek, Yilmaz; Koval, Yury; Gieb, Klaus; Müller, Paul (Superconductor Science and Technology, 2014)
Doping by carrier injection was investigated in strongly oxygen-depleted Bi2CaCu8 + δ. In order to perform four point c-axis measurements in non-superconducting samples, a new fabrication technique was developed. We were able to show that non-superconducting Bi 2CaCu8 + δ can be converted into a superconducting, even overdoped state only by applying a large bias current along the c-axis. A critical temperature of 91 K and a c-axis critical current density of 2000 A cm were achieved. Moreover, the doping effect is persistent and reversible resembling the resistive-memory switching effect observed earlier in various oxides. The mutual influence of oxygen doping and change of the charge carrier concentration by carrier injection is discussed. © 2014 IOP Publishing Ltd.
Keywords: Bi2212; charge carrier injection; doping; intrinsic Josephson junctions; superconductivity

Superlubricity of dry nanocontacts - Gnecco, Enrico; Maier, Sabine; Meyer, Ernst (Journal of Physics: Condensed Matter, 2008)
We discuss how various forms of dry superlubricity, recently observed on the nanoscale, have been interpreted by simple phenomenological models. In particular, we review the cases of static and dynamic single-contact lubricity, thermolubricity, and structural lubricity. All these phenomena have been studied by friction force microscopy and explained using the classical Prandtl-Tomlinson model and its extensions, including thermal activation, temporal and spatial variations of the surface energy corrugation, and multiple-contact effects. © 2008 IOP Publishing Ltd.
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Superparamagnetic iron oxide nanoparticles as novel x-ray enhancer for low-dose radiation therapy - Klein, Stefanie; Sommer, Anja; Distel, Luitpold; Hazemann, Jean-Louis; Kroener, Wolfgang; Neuhuber, Winfried; Müller, Paul; Proux, Olivier; Kryschi, Carola (Journal of Physical Chemistry B, 2014)
Superparamagnetic iron oxide nanoparticles (SPIONs) with a mixed phase composition (γ-FeO)(Fe O)and sizes between 9 and 20 nm were synthesized via coprecipitation and were either left uncoated or subsequently surface-stabilized with citrate or malate anions. The sizes, morphology, surface chemistry, and magnetic properties of the nanoparticles were characterized using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, and superconducting quantum interference device measurements, respectively. Cellular uptake and intracellular distribution in normal tissue and tumor cells were verified by TEM images. X-ray-induced changes of the oxidation state and site geometries of surface iron ions of uncoated and citrate-coated SPIONs were explored by collecting Fe K-edge X-ray absorption spectroscopy data. The potential applicability of citrate- and malate-coated SPIONs as an X-ray enhancer for radiation cancer therapy was substantiated by their drastic enhancement of the concentration of reactive oxygen species (ROS) in X-ray irradiated tumor cells. © 2014 American Chemical Society.

Super-Resolution for CEST MRI - Folle, Lukas; Tkotz, Katharina; Liebert, Andrzej; Gadjimuradov, Fasil; Kapsner, Lorenz; Fabian, Moritz; Bickelhaupt, Sebastian; Simon, David; Kleyer, Arnd; Krönke, Gerhard; Roemer, Frank; Zaiß, Moritz; et al. (Joint annual meeting ISMRM-ESMRMB ISMRT, 2022)
The resolution of chemical exchange saturation transfer (CEST) magnetic resonance imaging is limited by physical constraints. To visualize metabolic processes of small structures using CEST in patients knees, an increased resolution is necessary. In this work, we compared trilinear interpolation and zero-filling to neural network-based approaches to estimate a high-resolution image given the corresponding low-resolution data. We could show that a substantial quantitative improvement using neural networks could be achieved for unsaturated images while maintaining a comparable CEST contrast. Generalization of the method to brain CEST MRI was achieved without retraining of the networ
Keywords: MRI; Super-resolution

Superresolving Multiphoton Interferences with Independent Light Sources - Oppel, Steffen; Büttner, Teresa; Kok, P.; von Zanthier, Joachim (Physical Review Letters, 2012)
We propose to use multiphoton interferences from statistically independent light sources in combination with linear optical detection techniques to enhance the resolution in imaging. Experimental results with up to five independent thermal light sources confirm this approach to improve the spatial resolution. Since no involved quantum state preparation or detection is required, the experiment can be considered an extension of the Hanbury Brown-Twiss experiment for spatial intensity correlations of order N > 2. DOI: 10.1103/PhysRevLett.109.2336

Superstatistical analysis and modelling of heterogeneous random walks - Metzner, Claus; Mark, Christoph; Steinwachs, Julian; Lautscham, Lena; Stadler, Franz; Fabry, Ben (Nature Communications, 2015)

Supported liquid metals - A new class of robust dehydrogenation catalysts - Taccardi, Nicola; Grabau, Mathias; Debuschewltz, Jonas; Distaso, Monica; Brandl, Marco; Hock, Rainer; Maier, Florian; Papp, Christian; Erhard, Jannis; Neiß, Christian; Peukert, Wolfgang; Görling, Andreas; et al. (12th Natural Gas Conversion Symposium 2019, 2019)
CRIS-Team Scopus Importer:2019-12-10

Support of spontaneous breathing in the intubated patient: automatic tube compensation (ATC) and proportional assist ventilation (PAV) - Fabry, Ben; et al. (Acta Anaesthesiologica Scandinavica, 1997)

Suppression of pre- and post-pulses in a multipass Ti : sapphire amplifier - Wang, Jinxiong; Weinelt, Martin; Fauster, Thomas (Applied Physics B-Lasers and Optics, 2006)
A Ti:sapphire multipass amplifier producing 2.4 mJ, 26 fs pulses at a repetition rate of 1 kHz and 17 W pump power is described. An aperture mask is essential for a good performance of the multipass amplifier. Diffraction by the apertures is identified as one intrinsic source for pre- and post-pulses. A two-row beam path reduces these parasitic pulses effectively and improves the pulse contrast ratio by about one order of magnitude without reduction in power. The depolarization due to the oblique beam path through the Ti:sapphire crystal is proven to be negligible by measurements and calculations.

Suppression of short-range scattering via hydrophobic substrates and the fractional quantum Hall effect in graphene - Krstic, Vojislav; Hansel, Stefan; Lafkioti, Myrsini; Krstic, Vojislav (Physica Status Solidi-Rapid Research Letters, 2012)
We demonstrate that a hydrophobic layer between substrate and graphene largely eliminates Coulomb interaction between the graphene monolayer and charged impurities on the substrate, significantly reducing short-range scattering. At high carrier concentrations the mobilities thus obtained, deliver a ratio of Coulomb scattering mean free path to average charge carrier separation comparable to that of the highest mobility samples that exhibit the fractional quantum Hall effect (FQHE). We observe the FQHE in the lowest mobility samples reported up to now and conclude that increasing the ratio of Coulomb scattering mean free path to charge carrier separation overcomes the limitations for the observation of the FQHE imposed by overall mobility. <br
Keywords: Quantum Hall effect; Graphene; Surface functionalisation; Short-range scattering

Suppression of superconductor quasiparticle tunneling into single-walled carbon nanotubes - Krstic, Vojislav; Roth, Siegmar; Burghard, Marko; Weis, Jürgen; Kern, Klaus (Physical Review B, 2003)
Electrical transport through single-walled carbon nanotubes with weak electrical coupling to superconducting leads has been studied theoretically and experimentally. A simple model is considered to describe single-particle tunneling into a Luttinger-liquid-like state from electrically weak connected superconducting electrodes. This involves the superconductor’s quasiparticle and the Luttinger liquid’s excitation density of states. Experimentally, the suppression of quasiparticle tunneling induced current peaks was observed at temperatures below 0.1 K, which we attributed to the Luttinger-liquid-like excitation spectrum of the single-walled carbon nanotube.

Surface band bending and electron affinity as a function of hole accumulation density in surface conducting diamond - Edmonds, M. T.; Pakes, C. I.; Mammadov, Samir; Zhang, Wenying; Tadich, A.; Ristein, Jürgen; Ley, Lothar (Applied Physics Letters, 2011)
Simultaneous measurements of work function (φ) and C 1s core level shift were employed to determine the change in electron affinity (X) and band bending as a function of hole sheet density on H-terminated diamond for atmospheric and fullerene (C60 F48) induced surface conductivity. Contrary to earlier investigations, it is shown that changes in work function do not reflect variations in the position of the surface Fermi level in response to surface transfer doping. Instead, with a transition from -0.96 to -0.33 eV, X accounts for a significant amount of the change in φ for hole densities between 5× 108 and 4× 1013 cm-2. © 2011 American Institute of Physics.
UnivIS-Import:2015-03-09:Pub.2011.nat.dphy.IAP.exphys.surfac

Surface band bending and surface conductivity of hydrogenated diamond - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review B, 2003)
We establish a strict correlation between the total photoelectron yield spectra and the surface conductivity of hydrogenated diamond. The decomposition of the yield spectra into electron and exciton derived contributions requires an upward surface band bending to accompany surface conductivity, while an essentially flat band or downward band bending is observed after removing the surface conductivity by annealing in vacuum. Between the two competing models proposed for surface conductivity with a sheet hole density of 10 13 cm -2, these results favor the surface transfer-doping model strongly over the subsurface acceptor model.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.IAP.exphys.surfac

Surface carrier dynamics and diffusion in inorganic metal-halide perovskite films - Rieger, Janek; Hauner, Jonas; Niesner, Daniel; Fauster, Thomas (Physical Review B, 2023)
Carrier dynamics in metal-halide perovskites, in particular diffusion, has typically been investigated on micrometre-length scales and above. However, surfaces and interfaces modify the carrier dynamics, e.g., by interface band bending and recombination. To investigate the carrier dynamics and diffusion at the surface, we use time-resolved photoelectron spectroscopy which is sensitive to the photoexcited carriers in the topmost few nm of the material. We extract electron mobilities in well-ordered CsPbBr 3 (001) and CsSnBr3(001) films at room temperature of 31±6 and 13±1cm2V−1s−1, respectively. The mobility in CsPbBr3(001) increases to 200±8cm2V−1s−1 at 90 K, indicating strong electron-phonon coupling for electrons at the conduction band minimum. Temperature-dependent photoemission experiments find different phonon coupling mechanisms for high-energetic electrons and holes at the valence band maximum and in the main valence band

Surface conductivity induced by fullerenes on diamond: passivation and thermal stability - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 2006)
The surface conductivity of hydrogen terminated diamond under atmospheric conditions is a well known phenomenon. Inspired by the surface transfer doping model [F. Maier, M. Riedel, B. Mantel, J. Ristein, L. Ley, Phys. Rev. Lett. 85, (2000) 3472] we have recently investigated thin C60 layers as an alternative to atmospheric adsorbates. We could indeed show that C60 induces a sub-surface accumulation layer that results in a surface conductivity comparable to the air induced one [P. Strobel, M. Riedel, J. Ristein, L. Ley, Nature 430, (2004) 439]. In the present work we investigate fluorinated fullerenes, namely C60F18, C60F36, and C60F48, as transfer dopants. The surface conductivity induced by fluorinated fullerenes increases with higher fluorination and achieves for C60F48 a level that exceeds that observed under atmospheric conditions by up to a factor of three. Furthermore, we study the thermal stability of the fullerene layers on diamond and their stabilisation by passivation with different dielectric films (SiO, CaF2, and Si3N4). In the case of fluorinated fullerenes we observe a significant improvement in thermal stability after passivation with dielectrics but the pristine conductivity level cannot be kept. A different kind of stabilisation is achieved for C60. After the simultaneous exposure to oxygen, light, and temperature of about 150 °C the surface conductivity induced by C60 is stable up to 350 °C in vacuum with an undiminished doping efficiency. We ascribe this effect to an oxygen mediated polymerisation of the C60 layer. © 2005 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.exphys.surfac_6
Keywords: Fullerenes; p-type doping; Passivation; Thermal stability

Surface conductivity of diamond: a novel doping mechanism - Ristein, Jürgen; Strobel, Paul; Ley, Lothar (Advances in Science and Technology, 2006)
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.exphys.surfac_8