Breakthrough in neutron backscattering spectroscopy: Energy resolution improved by one order of magnitude using the GaAs 200 reflection - Kuhlmann, Kristijan; Appel, Markus; Frick, Bernhard; Magerl, Andreas (Review of Scientific Instruments, 2019)
We have developed and tested a demonstrator for a neutron backscattering spectrometer with a tenfold enhanced energy resolution. This is made possible by taking advantage of the narrow intrinsic linewidth of the GaAs 200 Bragg reflection, which is one order of magnitude smaller than the linewidth of the currently used Si 111. First measurements yielded an unprecedented energy resolution of 78 neV FWHM, a factor of 10 narrower than the standard Si 111 configuration and about a factor of 4 smaller than the highest energy resolution currently available with Si 111. These measurements provide proof of concept for the construction of a full-scale user instrument. Published under license by AIP Publishing.

Breast Cancer Cells Adapt Contractile Forces to Overcome Steric Hindrance - Condor, Mar; Mark, Christoph; Gerum, Richard; Grummel, Nadine; Bauer, Andreas; Garcia-Aznar, Jose M.; Fabry, Ben (Biophysical Journal, 2019)
Cell migration through the extracellular matrix is governed by the interplay between cell-generated propulsion forces, adhesion forces, and resisting forces arising from the steric hindrance of the matrix. Steric hindrance in turn depends on matrix porosity, matrix deformability, cell size, and cell deformability. In this study, we investigate how cells respond to changes in steric hindrance that arise from altered cell mechanical properties. Specifically, we measure traction forces, cell morphology, and invasiveness of MDA-MB 231 breast cancer cells in three-dimensional collagen gels. To modulate cell mechanical properties, we either decrease nuclear deformability by twofold overexpression of the nuclear protein lamin A or we introduce into the cells stiff polystyrene beads with a diameter larger than the average matrix pore size. Despite this increase of steric hindrance, we find that cell invasion is only marginally inhibited, as measured by the fraction of motile cells and the mean invasion depth. To compensate for increased steric hindrance, cells employ two alternative strategies. Cells with higher nuclear stiffness increase their force polarity, whereas cells with large beads increase their net contractility. Under both conditions, the collagen matrix surrounding the cells stiffens dramatically and carries increased strain energy, suggesting that increased force polarity and increased net contractility are functionally equivalent strategies for overcoming an increased steric hindrance.
CRIS-Team WoS Importer:2019-04-18

Breathing pattern and additional work of breathing in spontaneously breathing patients with different ventilatory demands during inspiratory pressure support and automatic tube compensation - Fabry, Ben; et al. (Intensive Care Medicine, 1997)

Brightly Luminescent and Color-Tunable Formamidinium Lead Halide Perovskite FAPbX3 (X = Cl, Br, I) Colloidal Nanocrystals - Levchuk, Ievgen; Osvet, Andres; Tang, Xiaofeng; Brandl, Marco; Perea, Jose Dario; Högl, Florian; Matt, Gebhard; Hock, Rainer; Batentschuk, Miroslaw; Brabec, Christoph (Nano Letters, 2017)
In the past few years, hybrid organic-inorganic and all-inorganic metal halide perovskite nanocrystals have become one of the most interesting materials for optoelectronic applications. Here, we report a facile and rapid room temperature synthesis of 15-25 nm formamidinium CH(NH2)2PbX3 (X = Cl, Br, I, or mixed Cl/Br and Br/I) colloidal nanocrystals by ligand-assisted reprecipitation (LARP). The cubic and platelet-like nanocrystals with their emission in the range of 415-740 nm, full width at half-maximum (fwhm) of 20-44 nm, and radiative lifetimes of 5-166 ns enable band gap tuning by halide composition as well as by their thickness tailoring; they have a high photoluminescence quantum yield (up to 85%), colloidal and thermodynamic stability. Combined with surface modification that prevents degradation by water, this nanocrystalline material is an ideal candidate for optoelectronic devices and applications. In addition, optoelectronic measurements verify that the photodetector based on FAPbI3 nanocrystals paves the way for perovskite quantum dot photovoltaics. © 2017 American Chemical Society.
Keywords: Chelation; Energy gap; Hybrid materials; Ligands; Metal halides; Nanocrystalline materials; Optoelectronic devices; Perovskite; Photoluminescence; Semiconductor quantum dots; Surface treatment; Colloidal nanocrystals; Formamidinium; Hybrid organic-inorganic; Optoelectronic applications; Optoelectronic measurements; Photoluminescence quantum yields; Re-precipitation; Room temperature synthesis; Nanocrystals

Broadband 7 mu m OPCPA pumped by a 2 mu m picosecond Ho: YLF CPA system - Sanchez, D.; Hemmer, M.; Baudisch, M.; Cousin, S. L.; Zawilski, K.; Schunemann, P.; Smirnov, Vadim; Hoogland, Heinar; Holzwarth, R.; Chalus, O.; Simon-Boisson, C.; Biegert, J. (SPIE Proceedings 9730, 2016)
We generate 260 mu J energy optical pulses at 7 mu m with an OPCPA pumped by an optically synchronized 2 mu m picosecond CPA system. The mid-IR pulses exhibit a bandwidth supporting sub-4 optical cycle duratio

Broadband mid-infrared pulses from potassium titanyl arsenate/zinc germanium phosphate optical parametric amplifier pumped by Tm, Ho-fiber-seeded Ho:YAG chirped-pulse amplifier - Malevich, Pavel; Kanai, Tsuneto; Hoogland, Heinar; Holzwarth, Ronald; Baltuska, Andrius; Pugzlys, Audrius (Optics Letters, 2016)
We present a concept of a white-light-seeded-cascaded mid-infrared (mid-IR) optical parametric amplifier (OPA) based on potassium titanyl arsenate and zinc germanium phosphate nonlinear optical crystals and producing 100-mu J level pulses centered at 5300 nm, with the spectrum supporting four-optical-cycle pulse duration. The OPA is pumped by 2090-nm master oscillator/power amplifier based on a Tm, Ho-fiber laser seeder and a Ho:YAG regenerative amplifier delivering 3.8-mJ sub-ps pulses at a repetition rate of 1 kHz. We validate that output parameters of the OPA are scalable by means of increasing the pulse energy, decreasing the pulse duration and redshifting the central wavelength. (C) 2016 Optical Society of America

Broadband mid-IR frequency comb with CdSiP2 and AgGaS2 from an Er,Tm:Ho fiber laser - Sanchez, Daniel; Hemmer, Michael; Baudisch, Matthias; Zawilski, Kevin; Schunemann, Peter G.; Hoogland, Heinar; Holzwarth, Ronald; Biegert, Jens (Optics Letters, 2014)
We report on the generation of a 2500 nm bandwidth frequency comb at 6.5 μm central wavelength based on critically phase-matched parametric down-conversion in the nonlinear crystalCdS(CSP), driven by a compact Er,Tm:Ho fiber laser. The generated ultra-broadband pulses show a transform-limited duration of 2.3 optical cycles and carry up to 150 pJ of energy at a 100 MHz pulse repetition rate. For comparison, the spectrum generated in AgGaS2 (AGS) spans from 6.2 to 7.4 μm at full-width at half-maximum (FWHM) with a pulse energy of 3 pJ. A full 3D nonlinear wave propagation code is used for optimization of the noncollinear angle, propagation direction, and crystal thickness.

Broadband THz detection and homodyne mixing using GaAs highelectron- Mobility transistor rectifiers - Preu, Sascha; Regensburger, Stefan; Kim, S.; Mittendorff, M.; Winnerl, Stephan; Malzer, Stefan; Lu, Hong; Burke, P.G.; Gossard, Art; Weber, Heiko B.; Sherwin, Mark S. (6th International Conference on Millimetre Wave and Terahertz Sensors and Technology, 2013)
We report on Terahertz (THz) detectors based on III-V high-electron- mobility field-effect transistors (FET). The detection results from a rectification process that is still highly efficient far above frequencies where the transistor provides gain. Several detector layouts have been optimized for specific applications at room temperature: we show a broadband detector layout, where the rectifying FET is coupled to a broadband logarithmic-periodic antenna. Another layout is optimized for mixing of two orthogonal THz beams at 370 GHz or, alternatively, 570 GHz. A third version uses a large array of FETs with very low access resistance allowing for detection of very short high-power THz pulses. We reached a time resolution of 20 ps. © 2013 SPIE.
Keywords: THz detection; field effect transistor; ultrafast detector; mixing

Building and refining complete nanoparticle structures with total scattering data - Page, Katharine; Hood, Taylor C.; Proffen, Thomas; Neder, Reinhard (Journal of Applied Crystallography, 2011)
High-energy X-ray and spallation neutron total scattering data provide information about each pair of atoms in a nanoparticle sample, allowing for quantitative whole-particle structural modeling based on pair distribution function analysis. The realization of this capability has been hindered by a lack of versatile tools for describing complex finite structures. Here, the implementation of whole-particle refinement for complete nanoparticle systems is described within two programs, DISCUS and DIFFEV, and the diverse capabilities they present are demonstrated. The build-up of internal atomic structure (including defects, chemical ordering and other types of disorder), and nanoparticle size, shape and architecture (including core-shell structures, surface relaxation and ligand capping), are demonstrated using the program DISCUS. The structure refinement of a complete nanoparticle system (4 nm Au particles with organic capping ligands at the surface), based on neutron pair distribution function data, is demonstrated using DIFFEV, a program using a differential evolutionary algorithm to generate parameter values. These methods are a valuable addition to other probes appropriate for nanomaterials, adaptable to a diverse and complex set of materials systems, and extendable to additional data-set types.
Keywords: nanoparticles; total scattering data; whole-particle modeling; pair distribution functions

Bulk and surface electron dynamics in a p-type topological insulator SnSb2Te4 - Niesner, Daniel; Otto, Sebastian; Hermann, Volker; Fauster, Thomas; Menshchikova, T. V.; Eremeev, S. V.; Aliev, Z. S.; Amiraslanov, I. R.; Babanly, M. B.; Echenique, P. M.; Chulkov, E. V. (Physical Review B, 2014)
Time-resolved two-photon photoemission was used to study the electronic structure and dynamics at the surface of SnSb2Te4, a p-type topological insulator. The Dirac point is found 0.32 +/- 0.03 eV above the Fermi level. Electrons from the conduction band minimum are scattered on a time scale of 43 +/- 4 fs to the Dirac cone. From there they decay to the partly depleted valence band with a time constant of 78 +/- 5 fs. The significant interaction of the Dirac states with bulk bands is attributed to their bulk penetration depth of similar to 3 nm as found from density functional theory calculations.

Bulk growth of SiC - Wellmann, Peter; Müller, Ralf; Sakwe, Aloysius; Künecke, Ulrike; Hens, Philip; Stockmeier, Matthias; Konias, Katja; Hock, Rainer; Magerl, Andreas; Pons, Michel (Materials Research Society Symposium - Proceedings, 2008)
The paper reviews the basics of SiC bulk growth by the physical vapor transport (PVT) method and discusses current and possible future concepts to improve crystalline quality. In-situ process visualization using x-rays, numerical modeling and advanced doping techniques will be briefly presented which support growth process optimization. The ,,pure" PVT technique will be compared with related developments like the so called Modified-PVT, Continuous-Feeding-PVT, High-Temperature-CVD and Halide-CVD. Special emphasis will be put on dislocation generation and annihilation and concepts to reduce dislocation density during SiC bulk crystal growth. The dislocation study is based on a statistical approach. Rather than following the evolution of a single defect, statistic data which reflect a more global dislocation density evolution are interpreted. In this context a new approach will be presented which relates thermally induced strain during growth and dislocation patterning into network
Keywords: Silicon carbide; bulk growth; physical vapor transport (PVT); in-situ visualization; numerical modeling; doping; dislocations; strain

Bulk growth of SiC - review on advances of SiC vapor growth for improved doping and systematic study on dislocation evolution - Sakwe, Aloysius; Stockmeier, Matthias; Hens, Philip; Müller, Ralf; Queren, Desiree; Künecke, Ulrike; Konias, Katja; Hock, Rainer; Magerl, Andreas; Pons, Michel; Winnacker, Albrecht; Wellmann, Peter (physica status solidi (b), 2008)
The paper reviews research on advanced crystal growth of SiC. A brief review highlights the benefits of the so called Modified Physical Vapor Transport Technique which uses an additional gas pipe for fine tuning of the growth cell of a conventional Physical Vapor Transport setup with additional gases. Main emphasis, however, will be laid on a systematic dislocation evolution study for various growth parameter sets. Besides doping, growth temperature was considered. Two main results were found: (i) In p-type SiC, irrespective of the incorporation of aluminum or boron acceptors, basal plane dislocations that are harmful for bipolar power devices appear less pronounced or are even absent compared to n-type SiC. (ii) Growth at elevated seed temperature (i.e. 2300 degrees C and higher) is beneficial for low dislocation densities. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Crystal growth; bulk; silicon carbide; SiC; Modified Physical Vapor Transport (MPVT); dislocations; basal plane dislocations; doping; growth temperature

BULK, SURFACE AND THERMAL EFFECTS IN INVERSE PHOTOEMISSION SPECTRA FROM CU(100), CU(110) AND CU(111) - Fauster, Thomas; et al. (Zeitschrift für Physik B Condensed Matter, 1986)

Calcium supplementation of bioinks reduces shear stress-induced cell damage during bioprinting - Fischer, Lena; Nosratlo, Mojtaba; Hast, Katharina; Karakaya, Emine; Ströhlein, Nadi; Esser, Tilman; Gerum, Richard; Richter, Sebastian; Engel, Felix; Detsch, Rainer; Fabry, Ben; Thievessen, Ingo (Biofabrication, 2022)
During bioprinting, cells are suspended in a viscous bioink and extruded under pressure through small diameter printing needles. The combination of high pressure and small needle diameter exposes cells to considerable shear stress, which can lead to cell damage and death. Approaches to monitor and control shear stress-induced cell damage are currently not well established. To visualize the effects of printing-induced shear stress on plasma membrane integrity, we add FM 1-43 to the bioink, a styryl dye that becomes fluorescent when bound to lipid membranes, such as the cellular plasma membrane. Upon plasma membrane disruption, the dye enters the cell and also stains intracellular membranes. Extrusion of alginate-suspended NIH/3T3 cells through a 200 mu m printing needle led to an increased FM 1-43 incorporation at high pressure, demonstrating that typical shear stresses during bioprinting can transiently damage the plasma membrane. Cell imaging in a microfluidic channel confirmed that FM 1-43 incorporation is caused by cell strain. Notably, high printing pressure also impaired cell survival in bioprinting experiments. Using cell types of different stiffnesses, we find that shear stress-induced cell strain, FM 1-43 incorporation and cell death were reduced in stiffer compared to softer cell types and demonstrate that cell damage and death correlate with shear stress-induced cell deformation. Importantly, supplementation of the suspension medium with physiological concentrations of CaCl2 greatly reduced shear stress-induced cell damage and death but not cell deformation. As the sudden influx of calcium ions is known to induce rapid cellular vesicle exocytosis and subsequent actin polymerization in the cell cortex, we hypothesize that calcium supplementation facilitates the rapid resealing of plasma membrane damage sites. We recommend that bioinks should be routinely supplemented with physiological concentrations of calcium ions to reduce shear stress-induced cell damage and death during extrusion bioprinting.
CRIS-Team WoS Importer:2022-08-26

Calculating the Universal Energy Level Alignment of Organic Molecules on Metal Oxides - Ley, Lothar; Smets, Yaou; Pakes, Christopher I.; Ristein, Jürgen (Advanced Functional Materials, 2013)
Recently, Greiner et al. [Nat. Mater. 2012, 11, 76] published a survey of the level alignment of about 40 metal oxide/organic molecule interfaces. They observed a striking regularity in the electronic level alignment of the highest occupied molecular orbital (HOMO) and the Fermi level that depends solely on the difference between the substrate work function and the ionization energy of the molecule independent of the details of the electronic structure of the oxide. The authors could reproduce their data under the assumption of thermodynamic equilibrium occupation of the HOMO using four adjustable parameters. A model that quantifies well-established concepts in heterojunction physics and achieves the same result without any adjustable parameters is presented here. This approach explains why the level alignment is rather independent of the experimental details, such as the electronic structure of the oxide, defects in the oxide, and the thickness of oxide and overlayer. The model can also be extended to organic molecules or polymers on metals without any intermediate oxide as long as certain conditions are met. It also sheds new light on the large polaronic binding energy required to interpret the electronic level alignment of metal-polymer interfaces. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.IAP.exphys.calcul
Keywords: energy-level alignment; full theory; organic electronics

CALCULATION OF SURFACE-STATES USING A ONE-DIMENSIONAL SCATTERING MODEL - Fauster, Thomas (Applied Physics A-Materials Science & Processing, 1994)
The complex electronic band structure of a one-dimensional solid is described using a one-dimensional scattering approach. The method yields the value of the wave function and its derivative between the atomic layers. These values can be matched at the surface to the corresponding values of the wave function on the vacuum side. The method is compared to the two-band approximation of the nearly free electron model. Advantages of the proposed scheme are the easy adaption for layered systems and alloys.

CALCULATION OF THE INVERSE PHOTOEMISSION FROM NI(111) - Fauster, Thomas; et al. (Physical Review B, 1984)

CameraTransform: A Python package for perspective corrections and image mapping - Gerum, Richard; Richter, Sebastian; Winterl, Alexander; Mark, Christoph; Fabry, Ben; Le Bohec, Céline; Paranhos Zitterbart, Daniel (SoftwareX, 2019)
Camera images and video recordings are simple and non-invasive tools to investigate animals in their natural habitat. Quantitative evaluations, however, often require an exact reconstruction of object positions, sizes, and distances in the image. Here, we provide an open source software package to perform such calculations. Our approach allows the user to correct for perspective distortion, transform images to “bird's-eye” view projections, or transform image-coordinates to real-world coordinates and vice versa. The extrinsic camera parameters that are necessary to perform such image corrections and transformations (elevation, tilt/roll angle, and heading of the camera) are obtained from the image using contextual information such as a visible horizon, GPS coordinates of landmarks, known object sizes, or images of the same object obtained from different viewing angles. All mathematical operations are implemented in the Python package CameraTransform. The performance of the implementation is evaluated using computer-generated synthetic images with known camera parameters. Moreover, we test our algorithm on images of emperor penguin colonies, and demonstrate that the camera tilt and roll angles can be estimated with an error of less than one degree, and the camera elevation with an error of less than 5%. The CameraTransform software package simplifies camera matrix-based image transformations and the extraction of quantitative image information. An extensive documentation and usage examples in an ecological context are provided at http://cameratransform.readthedocs.io.
CRIS-Team Scopus Importer:2019-10-08
Keywords: Camera lens distortions; Geo-referencing; Perspective projection; Quantitative image analysis

CameraTransform: a Scientific Python Package for Perspective Camera Corrections - Gerum, Richard; Richter, Sebastian; Winterl, Alexander; Fabry, Ben; Paranhos Zitterbart, Daniel (arXiv, 2017)

Can a Quantum Electron Microscope Achieve Low - Damage (Biological) Imaging? - Thomas, Sebastian; Hammer, Jakob; Weber, Philipp; Hommelhoff, Peter (Microscopy and Microanalysis, 2015)

Can infrasound from wind turbines affect myocardial contractility? A critical review - Swen, Mueller; Stefan, Holzheu; Hundhausen, Martin; Susanne, Koch (Noise & Health, 2022)
CRIS-Team Scopus Importer:2022-08-12

Carbon Nanotubes: Basic Concepts and Physical Properties - Reich, Stephanie; Thomsen, Christian; Maultzsch, Janina (Wiley-VCH, 2004)
Keywords: carbon nanotubes

Carbon SWNTs as wires and structural templates between nanoelectrodes - Burghard, Marko; Krstic, Vojislav; Duesberg, Georg S.; Philipp, Günther; Muster, Jörg; Roth, Siegmar; Journet, Catherine; Bernier, Patrick (Synthetic Metals, 1999)
The adsorption of carbon SWNTs from purified aqueous dispersions on electrode patterns is described. As an alternative approach to electrically contacted SWNTs, mixed Langmuir films consisting of surfactant molecules and SWNTs were transferred onto electrode arrays. Room temperature conductivity measurements on both types of samples revealed a (two point) resistance in the MΩ range. From these values, the presence of a closed surfactant layer between the tubes and electrode surface is excluded. As a step towards increasing the functionality of SWNTs, gold particles were attached to SWNT ropes after chemical tube modification by a two-step oxidation process. Using this technique, lateral electrode lines (100 nm distance) can be connected by a chain of closely arranged nanoparticles.
Keywords: Fullerenes and derivatives; Langmuir-Blodgett films; chemical surface modification

Carrier dynamics on surfaces studied by two-photon photoemission - Fauster, Thomas; Weinelt, Martin (Surface Science, 2005)
The lifetime of electronic excitations at surfaces, play an important role for desorption processes induced by electronic transitions. Two-photon photoemission with time, energy, and angular resolution allows to study the scattering processes of excited electrons in detail. For electronic surface states various scattering channels can be identified, such as elastic vs. inelastic or intraband vs. interband. As examples the scattering of electrons in image-potential states by copper adatoms on Cu(001) and the decay and exciton formation in the dangling-bond surface conduction band at the Si(100) c(4 x 2) surface are, presented. These studies of the carrier dynamics at surfaces imply that photochemical or electronic desorption processes are influenced by surface defects and are more efficient at semiconductor than on metal surfaces. (c) 2005 Elsevier B.V. All rights reserved.
Keywords: surface electronic phenomena; angle resolved photoemission; two-photon photoemission; surface states; image-potential states; femtosecond dynamics

Carrier-envelope frequency stabilization of a Ti:sapphire oscillator using different pump lasers - Vernaleken, Andreas; Schmidt, Bernhard; Wolferstetter, Martin; Haensch, Theodor W.; Holzwarth, Ronald; Hommelhoff, Peter (Optics Express, 2012)
We investigate the suitability of various commercially available pump lasers for operation with a carrier-envelope offset frequency stabilized Ti:sapphire oscillator. Although the tested pump lasers differ in their setup and properties (e.g., single vs. multi-mode), we find that they are all well-suited for the purpose. The residual rms phase noise (integrated between 20Hz and 5MHz) of the stabilized oscillator is found to be below 160mrad with each pump laser, corresponding to less than 1/40 of an optical cycle. Differences in performance vary slightly. In particular, our results indicate that the latest generation of multi-mode pump lasers can be used for applications where precise phase control of the oscillator is strictly required. © 2012 Optical Society of America.
UnivIS-Import:2015-03-09:Pub.2012.nat.dphy.IAP.exphys.carrie

Carrier-envelope frequency stabilization of a Ti:sapphire oscillator using different pump lasers: part II - Vernaleken, Andreas; Schmidt, Bernhard; Haensch, Theodor W.; Holzwarth, Ronald; Hommelhoff, Peter (Applied Physics B-Lasers and Optics, 2014)
Complementing an earlier report (Vernaleken et al. in Opt Exp 20:18387, 2012), we investigate the residual phase jitter of a carrier-envelope frequency stabilized Ti:sapphire oscillator when pumped by additional commercially available pump lasers that were not part of the first study. We find that all tested pump lasers allow stabilization of the oscillator with a residual rms phase noise (integrated between 2 Hz and 5 MHz) of less than 150 mrad despite their different design and properties. Possible sources of technical noise and their elimination for specific models are discussed.
UnivIS-Import:2015-03-09:Pub.2014.nat.dphy.IAP.exphys.carrie

Carrier-envelope-phase-stable soliton-based pulse compression to 4.4 fs and ultraviolet generation at the 800 kHz repetition rate - Ermolov, Alexey; Heide, Christian; Dienstbier, Philip; Köttig, Felix; Tani, Francesco; Hommelhoff, Peter; Russell, Philip St.J. (Optics Letters, 2019)
In this Letter, we report the generation of a femtosecond supercontinuum extending from the ultraviolet to the near-infrared spectrum and detection of its carrier-envelope-phase (CEP) variation by f-to-2f interferometry. The spectrum is generated in a gas-filled hollow-core photonic crystal fiber, where soliton dynamics allows the CEP-stable self-compression of the optical parametric chirped-pulse amplifier pump pulses at 800 nm to a duration of 1.7 optical cycles, followed by dispersive wave emission. The source provides up to 1 μJ of pulse energy at the 800 kHz repetition rate, resulting in 0.8 W of average power, and it can be extremely useful, for example in strong-field physics, pump–probe measurements, and ultraviolet frequency comb metrology.<br
Keywords: supercontinuum generation; carrier-envelope-phase; hollow-core photonic crystal fiber; ultraviolet ultraviolet frequency comb metrology

Carrier-envelope phase stable sub-two-cycle pulses tunable around 1.8um at 100 kHz - Homann, Christian; Bradler, Maximilian; Förster, Michael; Hommelhoff, Peter; Riedle, Eberhard (Optics Letters, 2012)
UnivIS-Import:2015-04-14:Pub.2012.nat.dphy.IAP.exphys.carrie_9

Carrier Mobility and Lifetime in a-Si:H determined by the Moving Grating Technique - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Non-Crystalline Solids, 1993)
We have applied the moving grating technique (MGT) to amorphous silicon (a-Si:H) in order to determine the electron and hole mobilities and their lifetime. In this technique a short circuit current is induced by an interference grating moving with an adjustable velocity across the sample. The continuity equations for electrons and holes and Poisson's equation are solved to derive a theoretical expression for the short circuit current. We fit this expression to experimental data of the short circuit current as a function of the velocity and spatial period of the grating and obtain good agreement between theory and experiment. The electron mobility and the lifetime obtained from this fit is 7.7·10-2cm2/Vs and 2.1·10-6s, respectively, whereas the hole mobility is 15 times smaller than that for the electrons. © 1993.
UnivIS-Import:2015-03-05:Pub.1993.nat.dphy.IAP.exphys.carrie

Carrier Recombination in Doping-Superlattices of a-Si:H - Hundhausen, Martin; Ley, Lothar; et al. (Proc. 17th Int. Conf. on the Physics of Semiconductors, 1984)
UnivIS-Import:2015-04-16:Pub.1984.nat.dphy.IAP.exphys.carrie

Carrier recombination kinetics in amorphous doping superlattices - Ley, Lothar; Hundhausen, Martin (Disordered semiconductors, 1987)
Research activities on nipi structures are reported, along with conductivity measurements as a function of layer thickness. The salient features of these measurements are discussed. The authors consider the kinetics of photocarrier recombination in nipi samples below 20 K, as well as persistent photoconductivity.
UnivIS-Import:2015-04-17:Pub.1987.nat.dphy.IAP.exphys.carrie

Carrier Recombination Times in Amorphous-Silicon Doping Superlattices - Hundhausen, Martin; Ley, Lothar; et al. (Physical Review Letters, 1984)
Doping superlattices, i.e., multilayer structures consisting of ultrathin (50 < d< 400 ) n-type, intrinsic, and p-type layers of a-Si: H (nipi structures), have been produced. Up to a tenfold increase in their infrared photoconductivity after band-gap illumination compared to unstructured a-Si: H is observed. The results are well described by a simple model for the carrier recombination kinetics that takes into account the spatial separation of electrons and holes due to the modulation of the band energies. © 1984 The American Physical Society.
UnivIS-Import:2015-03-05:Pub.1984.nat.dphy.IAP.exphys.carrie_2

CAS directly interacts with vinculin to control mechanosensing and focal adhesion dynamics - Janoštiak, Radoslav; Brabek, Jan; Auernheimer, Vera; Tatárová, Zuzana; Lautscham, Lena; Dey, Tuli; Gemperle, Jakub; Merkel, Rudolf; Goldmann, Wolfgang; Fabry, Ben; Rosel, Daniel (Cellular and Molecular Life Sciences, 2014)

Cavity-mediated thermal control of metal-to-insulator transition in 1T-TaS2 - Jarc, Giacomo; Mathengattil, Shahla Yasmin; Montanaro, Angela; Giusti, Francesca; Rigoni, Enrico Maria; Sergo, Rudi; Fassioli Olsen, Francesca; Winnerl, Stephan; Dal Zilio, Simone; Mihailovic, Dragan; Prelovšek, Peter; Eckstein, Martin; et al. (Nature, 2023)
Placing quantum materials into optical cavities provides a unique platform for controlling quantum cooperative properties of matter, by both weak and strong light–matter coupling1,2. Here we report experimental evidence of reversible cavity control of a metal-to-insulator phase transition in a correlated solid-state material. We embed the charge density wave material 1T-TaS2 into cryogenic tunable terahertz cavities3 and show that a switch between conductive and insulating behaviours, associated with a large change in the sample temperature, is obtained by mechanically tuning the distance between the cavity mirrors and their alignment. The large thermal modification observed is indicative of a Purcell-like scenario in which the spectral profile of the cavity modifies the energy exchange between the material and the external electromagnetic field. Our findings provide opportunities for controlling the thermodynamics and macroscopic transport properties of quantum materials by engineering their electromagnetic environment.
CRIS-Team Scopus Importer:2023-10-27

C-axis transport of pnictide superconductors - Müller, Paul; Koval, Yury; Lazareva, Irina; Steiner, Christian; Wurmehl, Sabine; Büchner, Bernd; Stürzer, Tobias; Johrendt, Dirk (physica status solidi (b), 2017)
The generic structure of most high T superconductors is a stacking sequence of superconducting planes separated by so-called charge reservoir layers. It is well known that carrier doping of these materials is achieved either by substitution of atoms or by nonstoichiometry in the charge reservoir layer. The alternating type of stacking causes yet another two important consequences. First, the transport anisotropy of these materials can be so high, that in the superconducting state the c-axis transport is governed by the intrinsic Josephson effect. Whereas the anisotropy of our investigated LaOFFeAs samples was not sufficient, optimum-doped Ca(FeAs)PtAs showed hysteretic c-axis current–voltage characteristics. Together with the Ambegaokar–Baratoff like temperature dependence of the critical current, this is a strong indication of intrinsic Josephson effects. Second, it is possible to deposit in the charge reservoir layers a substantial amount of charge only by injecting large c-axis currents. By charge compensation, this decreases the concentration of mobile electrons in the conducting layers of electron-doped materials. We were able to verify this in all details by c-axis transport measurements of LaOFFeAs single crystals and pure and Pt doped (CaFePtAs)PtAs single crystals. After current injection, we observed a decrease of T for doping levels at or below the T maximum, and a T increase for doping levels beyond the maximum. In all cases, the resistivity of the samples increased significantly. In both material classes, heavily overdoped samples showed a spectacular T increase by more than 10 K only accomplished by carrier injection. Generic stacking sequence of layered superconductors and crystal structure of the pnictide LaOFeAs.
Keywords: c-axis transport; carrier doping; carrier injection; intrinsic Josephson effect; pnictides; superconductivity

CD24 induces localization of beta1 integrin to lipid raft domains - Runz, Steffen; Mierke, Claudia; Joumaa, Safwan; Behrens, Jürgen; Fabry, Ben; Altevogt, Peter (Biochemical and Biophysical Research Communications, 2008)

Celebrating 100 years of the Debye scattering equation - Scardi, Paolo; Billinge, Simon J. L.; Neder, Reinhard; Cervellino, Antonio (ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 2016)
Keywords: Editorial; P. Debye; Debye scattering equation; nanomaterials

Cell Adhesion on Surface-Functionalized Magnesium - Wagener, Victoria; Schilling, Achim; Mainka, Astrid; Hennig, Diana; Gerum, Richard; Kelch, Marie-Luise; Keim, Simon; Fabry, Ben; Virtanen, Sannakaisa (ACS Applied Materials and Interfaces, 2016)
The biocompatibility of commercially pure magnesium-based (cp Mg) biodegradable implants is compromised of strong hydrogen evolution and surface alkalization due to high initial corrosion rates of cp Mg in the physiological environment. To mitigate this problem, the addition of corrosion-retarding alloying elements or coating of implant surfaces has been suggested. In the following work, we explored the effect of organic coatings on long-term cell growth. cp Mg was coated with aminopropyltriehtoxysilane + vitamin C (AV), carbonyldiimidazole (CDI), or stearic acid (SA). All three coatings have been previously suggested to reduce initial corrosion and to enhance protein adsorption and hence cell adhesion on magnesium surfaces. Endothelial cells (DH1+/+) and osteosarcoma cells (MG63) were cultured on coated samples for up to 20 days. To quantify Mg corrosion, electrochemical impedance spectroscopy (EIS) was measured after 1, 3, and 5 days of cell culture. We also investigated the speed of initial cell spreading after seeding using fluorescently labeled fibroblasts (NIH/3T3). Hydrogen evolution after contact with cell culture medium was markedly decreased on AV- and SA-coated Mg compared to uncoated Mg. These coatings also showed improved cell adhesion and spreading after 24 h of culture comparable to tissue-treated plastic surfaces. On AV-coated cp Mg, a confluent layer of endothelial cells formed after 5 days and remained intact for up to 20 days. Together, these data demonstrate that surface coating with AV is a viable strategy for improving long-term biocompatibility of cp Mg-based implants. EIS measurements confirmed that the presence of a confluent cell layer increased the corrosion resistance.
Keywords: cell adhesion; corrosion protection; impedance spectroscopy; magnesium; organic coating

Cell and tissue mechanics in cell migration - Lange, Janina; Fabry, Ben (Experimental Cell Research, 2013)

CEP-stable generation of close to single-cycle and ultrashort UV pulses at 800 kHz repetition rate using a gas-filled hollow-core PCF - Ermolov, Alexey; Heide, Christian; Dienstbier, Philip; Tani, Francesco; Köttig, Felix; Hommelhoff, Peter; Russell, Philip St. John (2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019, 2019)
Ultrashort laser pulses at high repetition rates are a fundamental tool in a wide range of applications in strong-field physics and attosecond science, where particular attention has to be given to the stability of the carrier to envelope phase (CEP) of the ultrashort optical waveform [1]. Here we report the generation of close to single-cycle pulses with stable CEP at 800 kHz repetition rate, obtained via soliton-effect self-compression in a gas-filled kagomé-type hollow-core photonic crystal fibre (kagomé-PCF) [2]. In addition, we have measured for the first time the CEP stability of soliton-emitted dispersive waves (DWs) lying in the ultraviolet spectral region.
CRIS-Team Scopus Importer:2019-11-15

Chain dynamics in a hexadecane melt as seen by neutron scattering and identified by molecular dynamics simulations - Morhenn, Humphrey; Busch, Sebastian; Unruh, Tobias (Journal of Physics: Condensed Matter, 2012)
Different local and global chain dynamics in a C16H34 melt could be revealed by resolution resolved time-of-flight quasielastic neutron scattering and complementary molecular dynamics simulations. Thereby it has been demonstrated that the measured intermediate scattering functions can validate the simulated data on the pico- to nanosecond timescale. Remarkably the shape of the experimentally measured intermediate scattering functions can be reproduced excellently by molecular dynamics simulations. It was found that although the extracted apparent activation energy corresponds to the long-range diffusion value, the molecular dynamics in this time range are mainly due to local bond rotations and the rotation of entire molecules.

Challenges in simulating beam dynamics of dielectric laser acceleration - Niedermayer, Uwe; Adelmann, Andreas; Bettoni, Simona; Calvi, Marco; Dehler, Micha; Ferrari, Eugenio; Frei, Franziska; Hauenstein, Dominique; Hermann, Benedikt; Hiller, Nicole; Ischebeck, Rasmus; Lombosi, Csaba; et al. (International Journal of Modern Physics A, 2019)
Dielectric Laser Acceleration (DLA) achieves the highest gradients among structure-based electron accelerators. The use of dielectrics increases the breakdown field limit, and thus the achievable gradient, by a factor of at least 10 in comparison to metals. Experimental demonstrations of DLA in 2013 led to the Accelerator on a Chip International Program (ACHIP), funded by the Gordon and Betty Moore Foundation. In ACHIP, our main goal is to build an accelerator on a silicon chip, which can accelerate electrons from below 100 keV to above 1 MeV with a gradient of at least 100 MeV/m. For stable acceleration on the chip, magnet-only focusing techniques are insufficient to compensate the strong acceleration defocusing. Thus, spatial harmonic and Alternating Phase Focusing (APF) laser-based focusing techniques have been developed. We have also developed the simplified symplectic tracking code DLAtrack6D, which makes use of the periodicity and applies only one kick per DLA cell, which is calculated by the Fourier coefficient of the synchronous spatial harmonic. Due to coupling, the Fourier coefficients of neighboring cells are not entirely independent and a field flatness optimization (similarly as in multi-cell cavities) needs to be performed. The simulation of the entire accelerator on a chip by a Particle In Cell (PIC) code is possible, but impractical for optimization purposes. Finally, we have also outlined the treatment of wake field effects in attosecond bunches in the grating within DLAtrack6D, where the wake function is computed by an external solver.
Keywords: Dielectric; laser; accelerator; chip; ACHIP

Change of the effective spin degeneracy in CeNi9-xCuxGe4 due to the interplay between Kondo and crystal field effects - Peyker, Ludwig; Gold, Christian; Scherer, Wolfgang; Michor, Herwig; Unruh, Tobias; Simeoni, Giovanna G.; Senyshyn, Anatoliy; Adroja, D. T.; Stockert, Oliver; Scheidt, Ernst-Wilhelm (EPL - Europhysics Letters, 2011)
Elastic and inelastic neutron scattering experiments were carried out on the heavy-fermion systems CeNi8.6Cu0.4Ge4 and CeNi8CuGe4 to study i) the influences of Ni/Cu substitution on the crystal field parameters and to identify ii) the driving forces of quantum criticality in CeNi9-xCuxGe4. The relevance of competing RKKY and Kondo interactions and changes of the crystal field parameters is discussed. The crystallographic site where the Ni replacement by copper atoms takes place is identified by neutron powder diffraction studies. Furthermore, quasi-elastic and inelastic neutron scattering studies provide detailed information regarding the Kondo properties and the changes of the crystal field parameters resulting from the Ni/Cu replacement. Hence, a reduction of the effective spin degeneracy of the crystal field ground state with increasing Cu concentration is identified as one important control parameter of quantum criticality in CeNi9-xCuxGe4. The results of these experiments are complemented by measurements of the thermopower. Copyright (C) EPLA, 2011

Changes of the occupied density of defect states of a-Si:H upon illumination - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review B, 1996)
We study the light-induced transient changes of the near surface density of occupied states g(E) of undoped and boron-doped a-Si:H with photomodulated total photoelectron yield spectroscopy. The data show an increase of g(E) upon illumination between 0.35 eV above E F and 0.7 eV below E F (towards the valence band) and a decrease in the region of deep valence-band-tail states. The difference signal depends sublinearly on the laser intensity and reaches a maximum of Δg ≈ 10 17 cm -3 eV -1 at a laser intensity of 30 mW cm -2 (λ=532 nm). Time-resolved measurements reveal rise and decay times of the order of milliseconds. The experimental results are explained quantitatively by a recombination model. In the framework of this model, a range of deep defects around mid-gap energy are singly occupied and neutral at probe-light intensities. Additional illumination with a laser leads to double occupation of these defects and a decrease of the valence-band-tail occupation.
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.IAP.exphys.change

Changes within the stabilizing layer of ZnO nanoparticles upon washing - Schindler, Torben; Schmutzler, Tilo; Schmiele, Martin; Lin, Wei; Segets, Doris; Peukert, Wolfgang; Appavou, Marie-Sousia; Kriele, Armin; Gilles, Ralph; Unruh, Tobias (Journal of Colloid and Interface Science, 2017)
In detail, it was observed that the diffuse acetate shell shrinks to the size of a monolayer upon washing but the acetate content of this monolayer is higher than within the diffuse shell of the particles of the native dispersion. A second washing cycle reduces the acetate concentration within the stabilizing shell and the stability of the dispersion drops accordingly. After another (third) washing cycle strong agglomeration was observed for all investigated samples. (C) 2017 Elsevier Inc. All rights reserved.
Keywords: Small angle scattering; Stabilization; Quantum dots; Purification; Stabilizing shell

Characteristics of solution gated field effect transistors on the basis of epitaxial graphene on silicon carbide - Ristein, Jürgen; Zhang, Wenying; Speck, Florian; Ostler, Markus; Ley, Lothar; Seyller, Thomas (Journal of Physics D-Applied Physics, 2010)
A solution gated field effect transistor has been fabricated on epitaxial single-layer graphene on 6H-SiC(0 0 0 1). Output and transfer characteristics were systematically studied as a function of electrolyte pH. The transfer characteristics of the device show a pH dependent shift of 19 ± 1 mV/pH. From the minimum sheet conductivity observed, an average charge carrier mobility of 1800 ± 100 cm 2 V -1 s -1 at room temperature has been inferred. It turns out that the Fermi level in the graphene layer is strongly pinned in the vicinity of the Dirac point. The analysis of the transfer characteristics is consistent with a concentration of 4 × 10 14 cm -2 interface states at 0.1 eV below the Dirac energy that is presumably associated with the (6√3 × 6√3)R30°-reconstruction at the interface between SiC(0 0 0 1) and graphene. © 2010 IOP Publishing Ltd.
UnivIS-Import:2015-03-09:Pub.2010.nat.dphy.IAP.exphys.charac

Characterization of cubic bulk SiC and temperature induced polytype conversion in cubic CVD SiC studied by Raman spectroscopy - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Applied Physics, 2004)
UnivIS-Import:2015-04-14:Pub.2004.nat.dphy.IAP.LAP.charac

Characterization of defects in silicon carbide by Raman spectroscopy - Hundhausen, Martin; Püsche, Roland; Röhrl, Jonas; Ley, Lothar (physica status solidi (b), 2008)
We demonstrate the application of Raman spectroscopy as an optical non-contact method for the characterization of silicon carbide (SiC). The Raman spectra provide information about the polytype and thus can give direct information about microscopic inclusions of hexagonal polytypes in 3C-SiC grown by chemical vapor deposition (CVD) after annealing at elevated temperatures. Polytype conversion sets in at a about 1700°C and at higher temperatures eventually results in larger domains of 6H-SiC where twin boundaries act as barriers against a complete polytype conversion. We study shallow donor states of phosphorus- and nitrogen-doped SiC using low temperature electronic Raman spectroscopy. The various low frequency transitions observed in nitrogen doped SiC are assigned to the valley-orbit transitions of electrons in the 1s-ground states of donors that occupy inequivalent lattice sites. During vacuum annealing at elevated temperature graphitization of the SiC surface occurs. Raman spectroscopy is used to verify that under well controlled conditions a monoatomic graphene layer exists. We observe a phonon hardening of that layer compared to free standing graphene that we ascribe mainly to strain induced by different thermal expansion coefficients of graphite and SiC. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
UnivIS-Import:2015-03-09:Pub.2008.nat.dphy.IAP.exphys.charac

Characterization of dye molecules and carbon nanostructures by tip-enhanced Raman spectroscopy - Peica, Niculina; Roehrig, Serge; Ruediger, Andreas; Brose, Katharina; Thomsen, Christian; Maultzsch, Janina (physica status solidi (b), 2009)
Tip-enhanced Raman spectroscopy (TERS) is a high sensitivity and high spatial resolution analytical technique based on the strong field enhancement provided by a sharp metallic tip. Using a commercial atomic force microscope (AFM) combined with a confocal optical setup in reflection geometry, we are targeting samples on non-transparent electrodes. The resulting design challenges with respect to quantum efficiency, optical accessibility of the tip and the optics themselves, were balanced and taken into consideration for the presented ultra-high vacuum-TERS setup. Second, we describe the development of a TERS setup at normal pressure in air, and we present the confocal Raman and TERS spectra of dye molecules and other nanostructures. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Characterization of Ge-doped homoepitaxial layers grown by chemical vapor deposition - Sledziewski, Tomasz; Beljakowa, Svetlana; Alassaad, Kassem; Kwasnicki, Pavel; Arvinte, Roxana; Juillaguet, Sandrine; Zielinski, Marcin; Souliere, Veronique; Ferro, Gabriel; Weber, Heiko B.; Krieger, Michael (Materials Science Forum, 2014)
We have investigated the electrical properties of n-type 4H-SiC in-situ germanium-doped homoepitaxial layers grown by chemical vapor deposition. Germanium is an isoelectronic impurity and, therefore, not expected to contribute to the conductivity. However, Hall effect measurements taken on samples with and without germanium revealed an enhanced mobility by a factor of ≈2 at T ≈ 55 K in the germanium-doped sample despite equal free electron concentration and equal compensation. Deep level transient spectroscopy (DLTS) measurements taken on germanium-doped samples reveal negative peaks indicating the presence of charged extended defects. © (2014) Trans Tech Publications, Switzerland.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.LAP.charac
Keywords: Admittance spectroscopy; DLTS; Ge-doping; Hall effect; Hall mobility

Characterization of Growth Behavior and the Resulting Forces Applied by Pollen Tubes in a 3D Matrix - Reimann, Ronny; Kah, Delf-Thorge Eric (Pollen and Pollen Tube Biology, 2020)
The question of how pollen tubes orient themselves on their way to the egg cell is a major focus of plant reproduction research. The role of physical guidance through the tissues of the pistil in relation to the mechanical perception and growth adaptation of the pollen tubes has not been sufficiently investigated. In order to advance research on the mechanical perception of pollen tubes and their force application during invasive growth, we present simple methods for the observation and mechanical characterization of pollen tubes in vitro, which can be established with little effort in any biological laboratory with standard equipment. Pollen grains are germinated in a hydrogel containing agarose and their growth is recorded in 3D using brightfield microscopy. Using suitable analysis software, parameters such as growth rate and pollen tube diameter can then be determined to estimate the exerted penetration force.
CRIS-Team Scopus Importer:2020-06-23
Keywords: 3D matrix; Agarose; ClickPoints; Force measurement; Hydrogel; Indentation; Mechanical guidance; Microindenter; Polar growth; Pollen tube; Single cell

Characterization of kesterite thin films fabricated by rapid thermal processing of stacked elemental layers using spatially resolved cathodoluminescence - Künecke, Ulrike; Hetzner, Christina; Möckel, Stefan; Yoo, Hye Sun; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2015)
We report on the microstructure analysis of kesterite (Cu2ZnSnSe4) layers from rapid thermal processing of sequential elemental layers by spatially resolved cathodoluminescence in a scanning electron microscope. Energy dispersive X-ray fluorescence, X-ray diffraction and Raman spectroscopy were carried out for the validation of the findings. Special emphasis is put on the discussion of the occurrence of the secondary phases Cu2SnSe3, Cu2Se, ZnSe and SnSe. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Cu2ZnSnSe4; Cathodoluminescence; Secondary phases; Microstructure

Characterization of lipid nanoparticles by differential scanning calorimetry, X-ray and neutron scattering - Bunjes, Heike; Unruh, Tobias (Advanced Drug Delivery Reviews, 2007)
Differential scanning calorimetry and X-ray diffraction play a prominent role in the characterization of lipid nanoparticle (LNP) dispersions. This review shortly outlines the measurement principles of these two techniques and summarizes their applications in the field of nanodispersions of solid lipids. These methods are particularly useful for the characterization of the matrix state, polymorphism and phase behavior of the nanoparticles which may be affected by, for example, the small particle size and the composition of the dispersions. The basics of small angle Xray and neutron scattering which are also very promising methods for the characterization of LNPs are explained in some more detail. Examples for their use in the area of solid LNPs regarding the evaluation of particle size effects and the formation of superstructures in the nanoparticle dispersions are given. Some technical questions concerning the use of the different characterization techniques in the field of LNP research are also addressed. (c) 2007 Elsevier BY. All rights reserved.
Keywords: colloidal drug carriers; glycerides; cholesterol esters; fatty acids; physicochemical characterization

Characterization of superlattices based on amorphous silicon - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Applied Physics, 1986)
UnivIS-Import:2015-04-14:Pub.1986.nat.dphy.IAP.exphys.charac

Charge carrier diffusion profiles in wide band gap semiconductors - Ristein, Jürgen (Diamond and Related Materials, 2004)
Although n-type doping by phosphorous meanwhile opens the route to ambipolar electronics on the basis of diamond, the majority of devices so far realized rely on hole transport only. Unipolar charge carrier diffusion is therefore a widely spread and important phenomenon for diamond electronics. Even without equilibrium between electrons and holes inside the semiconductor, the holes alone will establish a well-defined density and thus potential profile based on the detailed local balance between field and diffusion current. In this paper it will be shown, for holes in diamond as an example, how the basic physics of such diffusion tails can be discussed quantitatively by a simple analytical approach. Depending, as the only boundary condition, on the carrier density enforced at the surface or interface of the semiconductor layer, potential and charge carrier density profiles are established which will be discussed for a semi-infinite and a symmetric finite intrinsic diamond layer of arbitrary thickness. The concepts discussed are relevant for the surface conductivity of diamond, and for hetero-systems like metal contacts, growth sectors with differing doping concentrations, and hetero-junctions of wide band semiconductors in general. © 2003 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.IAP.exphys.charge
Keywords: Diamond crystal; Doping; Electronic properties characterization; Electronic surface properties

Charge-carrier transport in large-area epitaxial graphene - Kißlinger, Ferdinand; Popp, Matthias Albert; Jobst, Johannes; Shallcross, Sam; Weber, Heiko B. (Annalen Der Physik, 2017)

Charged particle guiding and beam splitting with auto-ponderomotive potentials on a chip - Zimmermann, Robert; Seidling, Michael; Hommelhoff, Peter (Nature Communications, 2021)
Electron and ion beams are indispensable tools in numerous fields of science and technology, ranging from radiation therapy to microscopy and lithography. Advanced beam control facilitates new functionalities. Here, we report the guiding and splitting of charged particle beams using ponderomotive forces created by the motion of charged particles through electrostatic optics printed on planar substrates. Shape and strength of the potential can be locally tailored by the lithographically produced electrodes’ layout and the applied voltages, enabling the control of charged particle beams within precisely engineered effective potentials. We demonstrate guiding of electrons and ions for a large range of energies (from 20 to 5000 eV) and masses (from 5 · 10−4 to 131 atomic mass units) as well as electron beam splitting for energies up to the keV regime as a proof-of-concept for more complex beam manipulation.<br
Keywords: electron optics; electron beam splitter; ponderomotive forces

Charge pumping measurements on differently passivated lateral 4H-SiC MOSFETs - Salinaro, Alberto; Pobegen, Gregor; Aichinger, Thomas; Zippelius, Bernd; Peters, Dethard P.; Friedrichs, Peter; Frey, Lothar (IEEE Transactions on Electron Devices, 2015)
This paper shows a successful transfer of the charge pumping (CP) method, which is extensively applied on silicon (Si) transistors, to Si carbide (SiC) lateral MOSFETs to characterize the quality of the SiC/SiO interface near the conduction and valence band edges. In particular, the constant base technique provides more accuracy and flexibility with respect to the most commonly used constant amplitude technique. Anomalous phenomena previously reported in literature, such as the so-called geometric component, are absent if the measurements are performed on transistors with optimized geometry and if the parameters of the applied CP gate pulses are carefully chosen. Furthermore, interface properties of gate oxides subjected to different postoxidation treatments are compared using this technique and the influence of the measurement parameters and temperature on the resulting CP signal is discussed.
Keywords: Charge pumping (CP); interface state density; near-interface states; nitrogen passivation; silicon carbide (SiC) MOSFETs

Charge transfer doping of Silicon - Rietwyk, K. J.; Smets, Y.; Bashouti, M.; Christiansen, S. H.; Schenk, A.; Tadich, A.; Edmonds, M. T.; Ristein, Jürgen; Ley, Lothar; Pakes, C. I. (Physical Review Letters, 2013)
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.IAP.exphys.charge

Charge transport across single-molecule junctions: charge reconfiguration and structural dynamics - Secker, Daniel; Weber, Heiko B. (physica status solidi (b), 2007)
The charge transport across single-molecule junctions is often considered as a pure electronic phenomenon. Analysing experiments performed with the mechanically controlled break junction technique, we show that, additionally, both polarization and dynamic motion of the geometric structure of the molecule give important contributions to the charge transport across single-molecule junctions. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Charge Transport in C60-based Single-Molecule Junctions with Graphene Electrodes - Leitherer, Susanne; Brana Coto, Pedro; Ullmann, Konrad; Weber, Heiko B.; Thoss, Michael (Nanoscale, 2017)
We investigate charge transport in C60-based single-molecule junctions with graphene electrodes employing a combination of density functional theory (DFT) electronic structure calculations and Landauer transport theory. In particular, the dependence of the transport properties on the conformation of the molecular bridge and the type of termination of the graphene electrodes is investigated. Furthermore, electron pathways through the junctions are analyzed using the theory of local currents. The results reveal, in agreement with previous experiments, a pronounced dependence of the transport properties on the bias polarity, which is rationalized in terms of the electronic structure of the molecule. It is also shown that the edge states of zigzag-terminated graphene induce additional transport channels, which dominate transport at low voltages. The importance of the edge states for transport depends profoundly on the interface geometry of the junctions.

Charge Transport Through a Cardan-Joint Molecule - Ruben, Mario; Landa, Aitor; Lörtscher, Emanuel; Riel, Heike; Mayor, Marcel; Görls, Helmar; Weber, Heiko B.; Arnold, Andreas; Evers, Ferdinand (Small, 2008)
The charge transport through a single ruthenium. atom clamped by two terpyridine hinges is investigated, both experimentally and theoretically. The metal-bis(terpyridyl) core is equipped with rigid, conjugated linkers of para-acetyl-mercapto phenylacetylene to establish electrical contact in a two-terminal configuration using Au electrodes. The structure of the [Ru(II)(L)(2)](PF(6))(2) molecule is determined using single-crystal X-ray crystallography, which yields good agreement with calculations based on density functional theory (LIFT). By means of the mechanically controllable break-junction technique, current voltage (I-V), characteristics of [RU(II)(L)(2)](PF(6))(2) are acquired on a single-molecule level under ultra-high vacuum (UHV) conditions at various temperatures. These results are compared to ab initio transport calculations based on DFT. The simulations show that the cardan-joint structural element of the molecule controls the magnitude of the current. Moreover, the fluctuations in the cardan. angle leave the positions of steps in the I-V curve largely invariant. As a consequence, the experimental I-V characteristics exhibit lowest-unoccupied-molecular-orbit-based conductance peaks at particular voltages, which are also found to be temperature independent.
Keywords: break junctions; molecular electronics; ruthenium complexes; single-molecule studies

Charge Transport through Molecular Rods with Reduced pi-Conjugation - Lörtscher, M.; Elbing, Mark; Tschudy, Meinrad; von Hänisch, Carsten; Weber, Heiko B.; Mayor, Marcel; Riel, Heike (ChemPhysChem, 2008)
A series of oligophenylene rods of increasing lengths is synthesized to investigate the charge-transport mechanisms. Methyl groups are attached to the phenyl rings to weaken the electronic overlap of the pi-subsystems along the molecular backbones. Out-of-plane rotation of the phenyl rings is confirmed in the solid state by means of X-ray analysis and in solution by using UV/Vis spectroscopy. The influence of the reduced pi-conjugation on the resonant charge transport is studied at the single-molecule level by using the mechanically controllable break-junction technique. Experiments are performed under ultra-high-vacuum conditions at low temperature (50 K). A linear increase of the conductance gap with increasing number of phenyl rings (from 260 meV for one ring to 580 meV for four rings) is revealed. In addition, the absolute conductance of the first resonant peaks does not depend on the length of the molecular wire. Resonant transport through the first molecular orbital is found to be dominated by charge-carrier injection into the molecule, rather than by the intrinsic resistance of the molecular wire length.
Keywords: charge transport; molecular electronics; oligophenylenes; single-molecule studies; structure-functionality relationship

Chemical chaperone ameliorates pathological protein aggregation in plectin-deficient muscle - Winter, Lilli; Staszewska, Ilona; Mihailovska, Eva; Fischer, Irmgard; Goldmann, Wolfgang; Schröder, Rolf; Wiche, Gerhard (Journal of Clinical Investigation, 2014)
The ubiquitously expressed multifunctional cytolinker protein plectin is essential for muscle fiber integrity and myofiber cytoarchitecture. Patients suffering from plectinopathy-associated epidermolysis bullosa simplex with muscular dystrophy (EBS-MD) and mice lacking plectin in skeletal muscle display pathological desmin-positive protein aggregation and misalignment of Z-disks, which are hallmarks of myofibrillar myopathies (MFMs). Here, we developed immortalized murine myoblast cell lines to examine the pathogenesis of plectinopathies at the molecular and single cell level. Plectin-deficient myotubes, derived from myoblasts, were fully functional and mirrored the pathological features of EBS-MD myofibers, including the presence of desmin-positive protein aggregates and a concurrent disarrangement of the myofibrillar apparatus. Using this cell model, we demonstrated that plectin deficiency leads to increased intermediate filament network and sarcomere dynamics, marked upregulation of HSPs, and reduced myotube resilience following mechanical stretch. Currently, no specific therapy or treatment is available to improve plectin-related or other forms of MFMs; therefore, we assessed the therapeutic potential of chemical chaperones to relieve plectinopathies. Treatment with 4-phenylbutyrate resulted in remarkable amelioration of the pathological phenotypes in plectin-deficient myotubes as well as in plectin-deficient mice. Together, these data demonstrate the biological relevance of the MFM cell model and suggest that this model has potential use for the development of therapeutic approaches for EBS-MD.
EVALuna2:7203

Chemical fingerprints of large organic molecules in scanning tunneling microscopy: Imaging adsorbate-substrate coupling of metalloporphyrins - Buchner, Florian; Warnick, Karl-Georg; Wölfle, Thorsten; Görling, Andreas; Steinrück, Hans-Peter; Hieringer, Wolfgang; Marbach, Hubertus (Journal of Physical Chemistry C, 2009)
In this combined experimental and theoretical work we demonstrate at the example of tetraphenylporphyrins on Ag(111) how differences in individual adsorbate orbitals and their interaction with the substrate can be exploited to switch the appearance of the adsorbate in scanning tunneling microscopy (STM) experiments, such that electronically and chemically very similar large molecules become distinguishable in STM. In particular, an intermixed layer consisting of 2HTPP (TPP ) tetraphenylporphyrin), CoTPP, and FeTPP molecules on Ag(111) was investigated, and it is demonstrated that STM images acquired with different bias voltages constitute fingerprints of the different molecules within the intermixed layer. By means of density functional calculations the observed features could be explained in detail and traced back to a direct orbital interaction of the adsorbed molecule with the surface. The explicit consideration of the surface in the calculations therefore turned out to be decisive to achieve good agreement with experiment. © 2009 American Chemical Society.

Chemical trends of defects at HfO2:GaAs and Al2O 3:GaAs/InAs/InP/GaSb interfaces - Lin, Liang; Guo, Yuzheng; Gillen, Roland; Robertson, John (Journal of Applied Physics, 2013)

Chemical Vapor Deposition of 3C-SiC on [100] Oriented Silicon at low Temperature < 1200°C for Photonic Applications - Kollmuß, Manuel; Köhler, Johannes; Ou, H.; Fan, W.; Chaussende, D.; Hock, Rainer; Wellmann, Peter (Materials Science Forum, 2022)
3C-SiC films have been grown on [100] n-doped Si substrates in a horizontal cold wall CVD reactor. Without the use of plasma enhancement, the precursors silane and propane are used to deposit silicon carbide films at T < 1200°C. The structure of the grown films has been investigated via FESEM, XRD and Raman spectroscopy. It has been found that the growth rates are between 200 and 300 nm/h. Additionally, structural analysis give evidence of polycrystalline phases. Reasons for that could be insufficient cracking of the precursors and homogenous nucleation of Si species in the gas phase.
CRIS-Team Scopus Importer:2022-12-16
Keywords: 3C-SiC; cold wall reactor; CVD; heteroepitaxy; low temperature; void

Chip-based electrostatic beam splitting of guided kiloelectron volt electrons - Seidling, Michael; Zimmermann, Robert; Hommelhoff, Peter (Applied Physics Letters, 2021)
We present a beam splitter for guided electrons using an electrostatic guiding potential created above the surface of two opposing planar microstructured printed circuit boards. The electric fields acting on the electrons result in a ponderomotive potential. We show that we can smoothly transition the ponderomotive potential from a single-well into a double-well, which leads to the splitting of the electron beam. Efficient beam splitting is observed over a large range of kinetic energies starting at 200 eV up to 1700 eV. We discuss future work needed to reach adiabatic beam splitting for quantum state-selective electron optics. This will pave the way for an electron interferometer on a chip and, therefore, result in until now not possible elements for electron optics and microscopy.<br
Keywords: electron optics; electron beam splitter; ponderomotive potential; adiabatic beam splitting; Quantum Electron Microscope

Chiral Ag Nanostructure Arrays as Optical Antennas - Gough, John; McCloskey, David; Caridad, Jose M.; Krstic, Vojislav; Müller, M.; Gaponik, Nikolai; Bradley, Louise (Advanced Electromagnetic Materials in Microwaves and Optics, 2016)
Directional and circularly polarised emission from quantum dots coupled with chiral Ag nanostructures has been demonstrated. Semiconductor quantum dots were deposited onto the chiral structures using the Layer-by-Layer deposition technique. Time-resolved photoluminescence measurements demonstrated a lifetime quenching efficiency of 82%, confirming the strong interaction between the emitters and the antennas. Angle- and polarisation-resolved photoluminescence measurements revealed that the chiral nanostructures influence the far-field emission properties of the quantum emitters through dipole coupling. The far-field emission from the quantum dots coupled to the chiral nanostructures displays directionality in the emission pattern and more than 17% circular polarisation, following the handedness of the chiral structure.
Keywords: Chiral; quantumdots; nanohelices; optical antennas

Chiral Ag Nanostructure Arrays as Optical Antennas - Krstic, Vojislav; Gough, J. J.; McCloskey, D.; Caridad, J. M.; Krstic, V.; Muller, M.; Gaponik, N.; Bradley, A. L. (2015 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), 2015)
Directional and circularly polarised emission from quantum dots coupled with chiral Ag nanostructures has been demonstrated. Semiconductor quantum dots were deposited onto the chiral structures using the Layer-by-Layer deposition technique. Time-resolved photoluminescence measurements demonstrated a lifetime quenching efficiency of 82%, confirming the strong interaction between the emitters and the antennas. Angle- and polarisation-resolved photoluminescence measurements revealed that the chiral nanostructures influence the far-field emission properties of the quantum emitters through dipole coupling. The far-field emission from the quantum dots coupled to the chiral nanostructures displays directionality in the emission pattern and more than 17% circular polarisation, following the handedness of the chiral structure.<br
UnivIS-Import:2017-12-18:Pub.2015.nat.dphy.IAP.LAP.chiral
Keywords: Antenna arrays; Indium tin oxide; Optical device fabrication; Optical polarization; Quantum dots; Solids; Substrates

Chiral Index Dependence of the G(+) and G(-) Raman Modes in Semiconducting Carbon Nanotubes - Telg, Hagen; Duque, Juan G.; Staiger, Matthias; Tu, Xiaomin; Hennrich, Frank; Kappes, Manfred M.; Zheng, Ming; Maultzsch, Janina; Thomsen, Christian; Doorn, Stephen K. (Acs Nano, 2012)
Raman spectroscopy on the radial breathing mode Is a common tool to determine the diameter d or chiral indices (n,m) of single-wall carbon nanotubes. In this work we present an alternative technique to determine d and (n,m) based on the high-energy G(-) mode. From resonant Raman scattering experiments on 14 highly purified single chirality (n,m) samples we obtain the diameter, chiral angle, and family dependence of the G(-) and G(+) peak position. Considering theoretical predictions we discuss the origin of these dependences with respect to rehybridization of the carbon orbitals, confinement, and electron-electron interactions. The relative Raman intensities of the two peaks have a systematic chiral angle dependence in agreement with theories considering the symmetry of nanotubes and the associated phonons.
Keywords: single-wall carbon nanotubes; Raman spectroscopy; G mode; LO/TO phonons; diameter determination; (n; m) assignment

Chirality distribution and transition energies of carbon nanotubes - Maultzsch, Janina; et al. (Physical Review Letters, 2004)
From resonant Raman scattering on isolated nanotubes we obtained the optical transition energies, the radial breathing mode frequency, and the Raman intensity of both metallic and semiconducting tubes. We unambiguously assigned the chiral index (n(1),n(2)) of approximate to50 nanotubes based solely on a third-neighbor tight-binding Kataura plot and find omega(RBM)=(214.4+/-2) cm(-1) nm/d+(18.7+/-2) cm(-1). In contrast to luminescence experiments we observe all chiralities including zigzag tubes. The Raman intensities have a systematic chiral-angle dependence confirming recent ab initio calculations.

Chirality-selective Raman scattering of the D mode in carbon nanotubes - Maultzsch, Janina; et al. (Physical Review B, 2001)
We show that D-mode Raman scattering in single-walled carbon nanotubes is due to a double-resonant Raman process. The unusual shift of the D-mode frequency with excitation energy is even expected for a single nanotube. The magnitude of the shift and the D-mode frequency depend strongly on the tube's diameter and chirality. Only tubes with (n(1)-n(2))/3n integer contribute to the D-mode spectrum because of the particular electronic structure of carbon nanotubes.

Chromatic dispersion based wide-band, fiber-coupled, tunable light source for hyperspectral imaging - Sharma, Gargi; Naveed, Sheeza Kainat; Parmar, Asha; Singh, Kanwarpal (IEEE Access, 2021)
Hyperspectral imaging is a powerful label-free imaging technique that provides topological and spectral information at once. In this work, we have designed and characterized a hyperspectral source based on the chromatic dispersion property of off-the-shelf lenses and converted a supercontinuum laser light source into a hyperspectral imaging light source for 490 nm to 900 nm wavelength range with a spectral resolution of 3.5 nm to 18 nm respectively. The potential of the source was demonstrated by imaging two color dots with different absorption bands. Further, we generated the hypercube of the lily ovary and dense connective tissue and measured their spectral signature as a function of wavelength. We also imaged the lower tongue of a healthy volunteer at 540 nm, 630 nm, and white light. Our simple hyperspectral light source design can easily be incorporated in a standard endoscope or microscope to perform hyperspectral imaging.
CRIS-Team Scopus Importer:2021-04-19
Keywords: Biomedical optical imaging; Broadband communication; Chromatic dispersion; Hyperspectral imaging; Hyperspectral imaging; Imaging; Lenses; Light sources; Light sources; Liquid crystals; Microscopy; Spectroscopy

Chromatographic size separation of single-wall carbon nanotubes - Duesberg, Georg S.; Muster, Jörg; Krstic, Vojislav; Burghard, Marko; Roth, Siegmar (Applied Physics A: Materials Science and Processing, 1998)
The efficient purification of single-wall carbon nanotubes (SWNTs) is reported. Carbon nanospheres, metal particles, and amorphous carbon could be successfully removed by size exclusion chromatography (SEC) applied to surfactant stabilised dispersions of SWNT raw material. In addition, length separation of the tubes was achieved. The SWNTs obtained can be adsorbed in high densities onto chemically modified substrates. As determined by AFM investigations, the purified material consists of about equal fractions of both individual SWNTS and ropes of SWNTs.

Classification at the accuracy limit: facing the problem of data ambiguity - Metzner, Claus; Schilling, Achim; Traxdorf, Maximilian; Tziridis, Konstantin; Maier, Andreas; Schulze, Holger; Krauß, Patrick (Scientific Reports, 2022)
Data classification, the process of analyzing data and organizing it into categories or clusters, is a fundamental computing task of natural and artificial information processing systems. Both supervised classification and unsupervised clustering work best when the input vectors are distributed over the data space in a highly non-uniform way. These tasks become however challenging in weakly structured data sets, where a significant fraction of data points is located in between the regions of high point density. We derive the theoretical limit for classification accuracy that arises from this overlap of data categories. By using a surrogate data generation model with adjustable statistical properties, we show that sufficiently powerful classifiers based on completely different principles, such as perceptrons and Bayesian models, all perform at this universal accuracy limit under ideal training conditions. Remarkably, the accuracy limit is not affected by certain non-linear transformations of the data, even if these transformations are non-reversible and drastically reduce the information content of the input data. We further compare the data embeddings that emerge by supervised and unsupervised training, using the MNIST data set and human EEG recordings during sleep. We find for MNIST that categories are significantly separated not only after supervised training with back-propagation, but also after unsupervised dimensionality reduction. A qualitatively similar cluster enhancement by unsupervised compression is observed for the EEG sleep data, but with a very small overall degree of cluster separation. We conclude that the handwritten letters in MNIST can be considered as ’natural kinds’, whereas EEG sleep recordings are a relatively weakly structured data set, so that unsupervised clustering will not necessarily re-cover the human-defined sleep stages.
CRIS-Team Scopus Importer:2023-03-07

Click-Functionalization of Silanized Carbon Nanotubes: From Inorganic Heterostructures to Biosensing Nanohybrids - Manoharan, Gririraj; Bösel, Petra; Thien, Jannis; Holtmannspötter, Michael; Meingast, Laura; Schmidt, Mercedes; Eickmeier, Henning; Haase, Markus; Maultzsch, Janina; Steinhart, Martin; Wollschläger, Joachim; Palma, Matteo; et al. (Molecules, 2023)
Here we present an approach to functionalize silanized single-walled carbon nanotubes (SWNTs) through copper-free click chemistry for the assembly of inorganic and biological nanohybrids. The nanotube functionalization route involves silanization and strain-promoted azide–alkyne cycloaddition reactions (SPACC). This was characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and Fourier transform infra-red spectroscopy. Silane–azide-functionalized SWNTs were immobilized from solution onto patterned substrates through dielectrophoresis (DEP). We demonstrate the general applicability of our strategy for the functionalization of SWNTs with metal nanoparticles (gold nanoparticles), fluorescent dyes (Alexa Fluor 647) and biomolecules (aptamers). In this regard, dopamine-binding aptamers were conjugated to the functionalized SWNTs to perform real-time detection of dopamine at different concentrations. Additionally, the chemical route is shown to selectively functionalize individual nanotubes grown on the surface of silicon substrates, contributing towards future nano electronic device applications.
CRIS-Team Scopus Importer:2023-03-24
Keywords: carbon nanotubes; click chemistry; functionalization; nano biosensor; nanohybrids; silanization; SPAAC

ClickPoints: an expandable toolbox for scientific image annotation and analysis - Gerum, Richard; Richter, Sebastian; Fabry, Ben; Paranhos Zitterbart, Daniel (Methods in Ecology and Evolution, 2016)

Clinorotation inhibits myotube formation by fluid motion, not by simulated microgravity - Mansour, Janet; Berwanger, Carolin; Jung, Marcel; Eichinger, Ludwig; Fabry, Ben; Clemen, Christoph S. (European Journal of Cell Biology, 2023)
To study processes related to weightlessness in ground-based cell biological research, a theoretically assumed microgravity environment is typically simulated using a clinostat – a small laboratory device that rotates cell culture vessels with the aim of averaging out the vector of gravitational forces. Here, we report that the rotational movement during fast clinorotation induces complex fluid motions in the cell culture vessel, which can trigger unintended cellular responses. Specifically, we demonstrate that suppression of myotube formation by 2D-clinorotation at 60 rpm is not an effect of the assumed microgravity but instead is a consequence of fluid motion. Therefore, cell biological results from fast clinorotation cannot be attributed to microgravity unless alternative explanations have been rigorously tested and ruled out. We consider two control experiments mandatory, i) a static, non-rotating control, and ii) a control for fluid motion. These control experiments are also highly recommended for other rotation speed settings and experimental conditions. Finally, we discuss strategies to minimize fluid motion in clinorotation experiments.
CRIS-Team Scopus Importer:2023-07-21
Keywords: Clinostat; Fluid flow; Fluid motion; Gravity; Mammalian cell culture; Myoblasts; Myotubes; Shear stress; Simulated microgravity

Coherence in laser-driven electrons at the surface and in the volume of solid matter - Hommelhoff, Peter (Applied Physics B-Lasers and Optics, 2017)
The femtosecond frequency comb allows controlling the carrier field of ultrashort laser pulses. We show two examples on how this control over fields oscillating with a few hundred terahertz can be utilized to control electrons at the surface and in the volume of solids. After a brief discussion of strong-field physics at metal needle tips, we show how ultrafast two-color laser pulses allow quantum path interference to dramatically alter the emission current from sharp tips, with an interference visibility of 94%. With carrier-envelope phase-controlled laser pulses, we show furthermore how light-field sensitive currents can be excited in monolayer graphene via an interplay of interband and intraband electron dynamics including multiple Landau–Zener transitions.

Coherence in laser-driven electrons at the surface and in the volume of solid matter - Hommelhoff, Peter (Springer International Publishing, 2018)
The femtosecond frequency comb allows controlling the carrier field of ultrashort laser pulses. We show two examples on how this control over fields oscillating with a few hundred terahertz can be utilized to control electrons at the surface and in the volume of solids. After a brief discussion of strong-field physics at metal needle tips, we show how ultrafast two-color laser pulses allow quantum path interference to dramatically alter the emission current from sharp tips, with an interference visibility of 94%. With carrier-envelope phase-controlled laser pulses, we show furthermore how light-field sensitive currents can be excited in monolayer graphene via an interplay of interband and intraband electron dynamics including multiple Landau-Zener transitions.
CRIS-Team Scopus Importer:2022-06-05

Coherence in microchip traps - Treutlein, Philipp; Hommelhoff, Peter; Steinmetz, Tilo; Hänsch, Theodor; Reichel, Jakob (Physical Review Letters, 2004)
The coherent manipulation of internal atomic states in a magnetic microchip trap, was investigated. At the distances of 5-130 μm from the microchip surface coherence lifetime exceeding 1 s were observed. An atomic clock in the chip trap was analyzed and the relative stability of its transition frequency was also measured. The results show that in combination with state-independent static magnetic traps, the potential geometries required for quantum information processing (QIP) can be estimated.
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.IAP.exphys.cohere

Coherent atomic states in microtraps - Treutlein, Philipp; Hommelhoff, Peter; Haensch, Theodor W.; Reichel, Jakob (Proceedings of the XVI International Conference on Laser Spectroscopy, 2003)
UnivIS-Import:2015-04-16:Pub.2003.nat.dphy.IAP.exphys.cohere

Coherent control at gold needle tips approaching the strong-field regime - Dienstbier, Philip; Paschen, Timo; Hommelhoff, Peter (Nanophotonics, 2021)
We demonstrate coherent control in photoemission from a gold needle tip using an ω − 2ω field composed of strong few-cycle laser pulses with a nearfield intensity of ∼4 TW/cm2. We obtain the nearfield intensity from electron energy spectra, showing the tell-tale plateau of field-driven electron rescattering at the metal surface induced by the fundamental field. Changing the relative phase between the fundamental field centered at 1560 nm and its second harmonic modulates the total emitted photocurrent with visibilities of up to 80% despite the strong and broadband excitation of the plasmonic material. Our work combines a two-color coherent control scheme and strong-field physics enabled by a nanoplasmonic emitte
Keywords: electron emission; gold needle tips; strong-field physics; two-color coherent control

Coherent control of two-color above-threshold photoemission from tungsten nanotips - Paschen, Timo; Förster, Michael; Krüger, Michael; Lemell, Christoph O; Wachter, G.; Libisch, Florian; Madlener, T.; Burgdorfer, J.; Hommelhoff, Peter (Journal of Physics: Conference Series, 2017)
Synopsis We demonstrate coherently controlled two-color above-threshold photoemission from a single crystal tungsten nanotip. With optimized fundamental and second harmonic intensities near perfect phase contrast can be obtained.
CRIS-Team Scopus Importer:2022-06-05

Coherent Electron Trajectory Control in Graphene - Heide, Christian; Higuchi, Takuya; Weber, Heiko B.; Hommelhoff, Peter (Physical Review Letters, 2018)
We investigate coherent electron dynamics in graphene, interacting with the electric field waveform of two orthogonally polarized, few-cycle laser pulses. Recently, we demonstrated that linearly polarized driving pulses lead to sub-optical-cycle Landau-Zener quantum path interference by virtue of the combination of intraband motion and interband transition [Higuchi et al., Nature 550, 224 (2017)]. Here we introduce a pulsed control laser beam, orthogonally polarized to the driving pulses, and observe the ensuing electron dynamics. The relative delay between the two pulses is a tuning parameter to control the electron trajectory, now in a complex fashion exploring the full two-dimensional reciprocal space in graphene. Depending on the relative phase, the electron trajectory in the reciprocal space can, e.g., be deformed to suppress the quantum path interference resulting from the driving laser pulse. Intriguingly, this strong-field-based complex matter wave manipulation in a two-dimensional conductor is driven by a high repetition rate laser oscillator, rendering unnecessary complex and expensive amplified laser system

Coherent nanophotonic electron accelerator - Chlouba, Tomas; Shiloh, Roy; Kraus, Stefanie; Brückner, Leon; Litzel, Julian; Hommelhoff, Peter (Nature, 2023)
Particle accelerators are essential tools in a variety of areas of industry, science and medicine1,2,3,4. Typically, the footprint of these machines starts at a few square metres for medical applications and reaches the size of large research centres. Acceleration of electrons with the help of laser light inside of a photonic nanostructure represents a microscopic alternative with potentially orders-of-magnitude decrease in cost and size5,6,7,8,9,10,11,12,13,14,15,16. Despite large efforts in research on dielectric laser acceleration17,18, including complex electron phase space control with optical forces19,20,21, noteworthy energy gains have not been shown so far. Here we demonstrate a scalable nanophotonic electron accelerator that coherently combines particle acceleration and transverse beam confinement, and accelerates and guides electrons over a considerable distance of 500 μm in a just 225-nm-wide channel. We observe a maximum coherent energy gain of 12.3 keV, equalling a substantial 43% energy increase of the initial 28.4 keV to 40.7 keV. We expect this work to lead directly to the advent of nanophotonic accelerators offering high acceleration gradients up to the GeV m−1 range utilizing high-damage-threshold dielectric materials22 at minimal size requirements14. These on-chip particle accelerators will enable transformative applications in medicine, industry, materials research and science14,23,24.<br
Keywords: Nanophotonics and plasmonics; Photonic devices; Ultrafast photonics

Coherent scattering of an optically modulated electron beam by atoms - Morimoto, Yuya; Hommelhoff, Peter; Madsen, Lars Bojer (Physical Review A, 2021)
Recent technological advances allowed the coherent optical manipulation of high-energy electron wavepackets with attosecond precision. Here we theoretically investigate the collision of optically modulated pulsedelectron beams with field-free atomic targets and reveal a quantum interference associated with different momentum components of the incident broadband electron pulse, which coherently modulates both the elastic and inelastic scattering cross sections. We show that the quantum interference has a high spatial sensitivity at the level of angstroms, offering potential applications in high-resolution ultrafast electron microscopy. Our findings are rationalized by a simple mode
Keywords: attosecond physics; modulated electron wavepackets; ultrafast electron microscopy; quantum interference; atomic physics

Collagen Hydrogel Containing Polyethylenimine-Gold Nanoparticles for Drug Release and Enhanced Beating Properties of Engineered Cardiac Tissues - Roshanbinfar, Kaveh; Kolesnik-Gray, Maria; Angeloni, Miriam; Schrüfer, Stefan; Fiedler, Maren; Schubert, Dirk W.; Ferrazzi, Fulvia; Krstic, Vojislav; Engel, Felix (Advanced Healthcare Materials, 2023)
Cardiac tissue engineering is a promising strategy to prevent heart failure. However, several issues remain unsolved, including efficient electrical coupling and incorporating factors to enhance tissue maturation and vascularization. Herein, a biohybrid hydrogel that enhances beating properties of engineered cardiac tissues and allows drug release concurrently is developed. Gold nanoparticles (AuNPs) with different sizes (18–241 nm) and surface charges (33.9–55.4 mV) are synthesized by reducing gold (III) chloride trihydrate using branched polyethyleneimine (bPEI). These nanoparticles increase gel stiffness from ≈91 to ≈146 kPa, enhance electrical conductivity of collagen hydrogels from ≈40 to 49–68 mS cm−1, and allow slow and steady release of loaded drugs. Engineered cardiac tissues based on bPEI-AuNP-collagen hydrogels and either primary or human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes show enhanced beating properties. hiPSC-derived cardiomyocytes exhibit more aligned and wider sarcomeres in bPEI-AuNP-collagen hydrogels compared to collagen hydrogels. Furthermore, the presence of bPEI-AuNPs result in advanced electrical coupling evidenced by synchronous and homogenous calcium flux throughout the tissue. RNA-seq analyses are in agreement with these observations. Collectively, this data demonstrate the potential of bPEI-AuNP-collagen hydrogels to improve tissue engineering approaches to prevent heart failure and possibly treat diseases of other electrically sensitive tissues.
CRIS-Team Scopus Importer:2023-04-21
Keywords: collagen; gold nanoparticles; heart; tissue engineering

Collective forces of tumor spheroids in three-dimensional biopolymer networks - Mark, Christoph; Grundy, Thomas J.; Strissel, Pamela; Böhringer, David; Grummel, Nadine; Gerum, Richard; Steinwachs, Julian; Hack, Carolin; Beckmann, Matthias; Eckstein, Markus; Strick, Reiner; O'Neill, Geraldine M.; et al. (eLife, 2020)
We describe a method for quantifying the contractile forces that tumor spheroids collectively exert on highly nonlinear three-dimensional collagen networks. While three-dimensional traction force microscopy for single cells in a nonlinear matrix is computationally complex due to the variable cell shape, here we exploit the spherical symmetry of tumor spheroids to derive a scale-invariant relationship between spheroid contractility and the surrounding matrix deformations. This relationship allows us to directly translate the magnitude of matrix deformations to the total contractility of arbitrarily sized spheroids. We show that our method is accurate up to strains of 50% and remains valid even for irregularly shaped tissue samples when considering only the deformations in the far field. Finally, we demonstrate that collective forces of tumor spheroids reflect the contractility of individual cells for up to 1 hr after seeding, while collective forces on longer timescales are guided by mechanical feedback from the extracellular matrix.
CRIS-Team WoS Importer:2020-05-22

Collective Intermolecular Motions Dominate the Picosecond Dynamics of Short Polymer Chains - Morhenn, Humphrey; Busch, Sebastian; Meyer, Hendrik; Richter, Dieter; Petry, Winfried; Unruh, Tobias (Physical Review Letters, 2013)
Neutron scattering and extensive molecular dynamics simulations of an all atom C100H202 system were performed to address the short-time dynamics leading to center-of-mass self-diffusion. The simulated dynamics are in excellent agreement with resolution resolved time-of-flight quasielastic neutron scattering. The anomalous subdiffusive center-of-mass motion could be modeled by explicitly accounting for viscoelastic hydrodynamic interactions. A model-free analysis of the local reorientations of the molecular backbone revealed three relaxation processes: While two relaxations characterize local bond rotation and global molecular reorientation, the third component on intermediate times could be attributed to transient flowlike motions of atoms on different molecules. The existence of these collective motions, which are clearly visualized in this Letter, strongly contribute to the chain relaxations in molecular liquids.

Collectively Enhanced Giant Circular Dichroism of Germanium Nanohelix Square Lattice Arrays - Ellrott, Günter; Beck, Paul; Sultanov, Vitaliy; Rothau, Sergej; Lindlein, Norbert; Chekhova, Maria; Krstic, Vojislav (Advanced Photonics Research, 2023)
Circular dichroism is a unique chiroptical signature of the chirality of a system and is a prevalent way to characterize and distinguish systems on a fundamental level and for their technological applicability. Thus, engineering and maximizing the chiroptical response of a single chiral object or a metasurface composed of chiral entities is a formidable task. Current efforts strongly focus on individual metallic nanostructures and their periodic ensembles to harvest on (resonant) plasmonic properties and interactions. This route, however, waives the advantages of high-refractive-index nanoscale materials embracing low dissipative losses at optical wavelengths and electromagnetic fields penetrating and propagating in such materials. Herein, a strong circular dichroism is demonstrated in square lattices of nanohelices made of the high-refractive-index semiconductor germanium, with dissymmetry factors outperforming metal-based ensembles. The observation of a much higher dissymmetry emerges for illumination with spatially coherent light, in comparison to spatially incoherent light. High dissymmetry is attributed to cooperative coupling between single helices, resulting from the combination of dielectric resonances of both the individual helical building blocks and the highly ordered lattice.<br

Collective Synchronization of Contractile Forces in Tumor Spheroids - Böhringer, David; Mark, Christoph; Grummel, Nadine; Strissel, Pamela; Strick, Reiner; Grundy, Thomas J.; O'Neill, Geraldine M.; Fabry, Ben (BIOPHYSICAL JOURNAL, 2020)
CRIS-Team WoS Importer:2020-03-13

Combination of BMP2 and MSCs Significantly Increases Bone Formation in the Rat Arterio-Venous Loop Model - Bührer, Gregor; Balzer, Amelie; Arnold, Isabel; Beier, Justus; Körner, Carolin; Bleiziffer, Oliver; Brandl, Andreas; Weis, Christian; Horch, Raymund E.; Kneser, Ulrich; Arkudas, Andreas (Tissue Engineering - Part A, 2015)

Combined imaging of potassium and sodium in human skeletal muscle tissue at 7 T - Gast, Lena; Volker, Stefanie; Utzschneider, Matthias; Linz, Peter; Wilferth, Tobias; Müller, Max; Kopp, Christoph; Hensel, Bernhard; Uder, Michael; Nagel, Armin Michael (Magnetic Resonance in Medicine, 2020)
Purpose: To validate the feasibility of quantitative combined potassium (39K) and sodium (23Na) MRI in human calf muscle tissue, as well as to evaluate the reproducibility of the apparent tissue potassium concentration (aTPC) and apparent tissue sodium concentration (aTSC) determination in healthy muscle tissue. Methods: Quantitative 23Na and 39K MRI acquisition protocols were implemented on a 7 T MR system. A double-resonant 23Na/39K birdcage RF coil was used. Measurements of human lower leg were performed in a total acquisition time of TANa = 10:54 min/TAK = 8:06 min and using a nominal spatial resolution of 2.5 × 2.5 × 15 mm3/7.5 × 7.5 × 30 mm3 for 23Na/39K MRI. Two aTSC and aTPC examinations in muscle tissue were performed during the same day on 10 healthy subjects. Results: The proposed acquisition and postprocessing workflow for 23Na and 39K MRI data sets provided reproducible aTSC and aTPC measurements. In human calf muscle tissue, the coefficient of variation between scan and re-scan was 5.7% for both aTSC and aTPC determination. Overall, mean values of aTSC = (17 ± 1) mM and aTPC = (85 ± 5) mM were measured. Moreover, for 39K in calf muscle tissue, (Formula presented.) components of (Formula presented.) = (1.2 ± 0.2) ms and (Formula presented.) = (7.9 ± 0.9) ms, as well as a residual quadrupolar interaction of (Formula presented.) = (143 ± 17) Hz, were determined. The fraction of the fast component was f = (58 ± 4)%. Conclusion: Using the presented measurement and postprocessing approach, a reproducible aTSC and aTPC determination using 23Na and 39K MRI at 7 T in human skeletal muscle tissue is feasible in clinically acceptable acquisition durations.
CRIS-Team Scopus Importer:2020-09-11
Keywords: 7 T; potassium MRI; sodium MRI; tissue potassium concentration; tissue sodium concentration; ultrahigh field strengths

Comment on "Effect of average grain size on the work function of diamond films" - Ristein, Jürgen; Ley, Lothar (Applied Physics Letters, 2002)
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.IAP.exphys.commen

Comment on quantum confinement effect in diamond nanocrystals studied by x-ray-absorption spectroscopy - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review Letters, 2000)
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.IAP.exphys.commen

Compact, low-cost, and high-resolution interrogation unit for optical sensors - Kiesel, Peter; Schmidt, Oliver; Mohta, S.; Johnson, Noble; Malzer, Stefan (Applied Physics Letters, 2006)
Compact wavelength detectors that resolve wavelength changes in the subpicometer range over a broad spectral range are presented. A photodiode array or position sensor device is coated with a linear variable filter that converts the wavelength of the incident light into a spatial intensity distribution. The centroid of the spatial distribution is determined by a differential readout of the two elements of the photodiode array or the position sensor device. The device can interrogate any optical sensor that produces a wavelength shift in response to a stimulus. The potential of this device was tested by interrogating fiber-Bragg-grating sensors. © 2006 American Institute of Physics.

Compact polarization-maintaining 2.05-mu m fiber laser at 1-MHz and 1-MW peak power - Hoogland, Heinar; Holzwarth, Ronald (Optics Letters, 2015)
We report on a compact all-polarization-maintaining 2.05-mu m chirped pulse fiber amplifier system emitting pulses at up to 1-MW peak power level at 371-fs pulse duration. The seed pulse repetition rate provided by an inhouse-built oscillator is reduced to around 1 MHz using a pulse picker. In combination with a two stage fiber amplifier, output pulse energies up to 570 nJ are obtained without the need of a high-power large-mode area amplifier. Both temporal stretching and compression of the chirped pulse amplifier design are achieved using a single chirped volume Bragg grating. (C) 2015 Optical Society of America

Compact Ultrashort Pulsed 2.05 mu m All-PM Fiber Laser For Dielectric Laser Acceleration of Non-relativistic Electrons - Hoogland, Heinar; McNeur, Joshua; Kozak, Martin; Hommelhoff, Peter; Holzwarth, Ronald (OSA Technical Digest, 2016)
A compact all-polarization maintaining 2.05 mu m fiber laser system emitting femtosecond pulses at 1-MW peak power is studied and applied to dielectric laser acceleration of non-relativistic electrons obtaining acceleration gradients up to similar to 50 MeV/m.

Comparative Raman studies of amorphous carbon films using infra red and visible excitation - Hundhausen, Martin; et al. (Microchimica Acta, 1997)
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.IAP.exphys.compar

Comparison of optimized intensity correction methods for 23Na MRI of the human brain using a 32-channel phased array coil at 7 Tesla - Lachner, Sebastian; Ruck, Laurent; Niesporek, Sebastian C.; Utzschneider, Matthias; Lott, Johanna; Hensel, Bernhard; Dörfler, Arnd; Uder, Michael; Nagel, Armin Michael (Zeitschrift für Medizinische Physik, 2019)
Purpose: To correct for the non-homogeneous receive profile of a phased array head coil in sodium magnetic resonance imaging (23Na MRI). Methods: 23Na MRI of the human brain (n = 8) was conducted on a 7T MR system using a dual-tuned quadrature 1H/23Na transmit/receive birdcage coil, equipped with a 32-channel receive-only array. To correct the inhomogeneous receive profile four different methods were applied: (1) the uncorrected phased array image and an additionally acquired birdcage image as reference image were low-pass filtered and divided by each other. (2) The second method substituted the reference image by a support region. (3) By averaging the individually calculated receive profiles, a universal sensitivity map was obtained and applied. (4) The receive profile was determined by a pre-scanned large uniform phantom. The calculation of the sensitivity maps was optimized in a simulation study using the normalized root-mean-square error (NRMSE). All methods were evaluated in phantom measurements and finally applied to in vivo 23Na MRI data sets. The in vivo measurements were partial volume corrected and for further evaluation the signal ratio between the outer and inner cerebrospinal fluid compartments (CSFout:CSFin) was calculated. Results: Phantom measurements show the correction of the intensity profile applying the given methods. Compared to the uncorrected phased array image (NRMSE = 0.46, CSFout:CSFin = 1.71), the quantitative evaluation of simulated and measured intensity corrected human brain data sets indicates the best performance utilizing the birdcage image (NRMSE = 0.39, CSFout:CSFin = 1.00). However, employing a support region (NRMSE = 0.40, CSFout:CSFin = 1.17), a universal sensitivity map (NRMSE = 0.41, CSFout:CSFin = 1.05) or a pre-scanned sensitivity map (NRMSE = 0.42, CSFout:CSFin = 1.07) shows only slightly worse results. Conclusion: Acquiring a birdcage image as reference image to correct for the receive profile demonstrates the best performance. However, when aiming to reduce acquisition time or for measurements without existing birdcage coil, methods that use a support region as reference image, a universal or a pre-scanned sensitivity map provide good alternatives for correction of the receive profile.
CRIS-Team Scopus Importer:2019-12-31
Keywords: 7 Tesla; Intensity correction; Multi-channel array coil; Phased array coil; Receive profile; Sodium MRI

Competition between Dehydrogenative Organometallic Bonding and Covalent Coupling of an Unfunctionalized Porphyrin on Cu(111) - Xiang, Feifei; Gemeinhardt, Anja; Schneider, M. Alexander (Acs Nano, 2018)
We studied the formation of linked porphyrin oligomers from 5,15-diphenylporphyrin (2H-DPP) by thermal, substrate-assisted organometallic and dehydrogenation coupling on Cu(111) by scanning tunneling microscopy. In the range of 300-620 K, we find three distinct stages, at 300 K, the intact 2H-DPP molecules self-assemble into linear structures held together by van der Waals forces. Increasing the substrate temperature, self-metalation and intramolecular ring-closing reactions result in planar and isolated DPP species on the surface. By C-H cleavage, porphyrin oligomers bonded by organometallic and covalent bonds between the modified DPP are formed. The amount of covalently bonded DPP oligomers increases strongly with annealing time and temperature, and they become the dominant species at 570 K. In contrast, the number of organometallically bonded DPP oligomers increases moderately even up to 620 K, indicating that in this case the organometallic bond is no precursor of the covalent bond.
Keywords: scanning tunneling microscopy; on-surface synthesis; polymerization; molecular wire; metalation

Complementary Molecular Dynamics and X-ray Reflectivity Study of an Imidazolium-Based Ionic Liquid at a Neutral Sapphire Interface - Brkljaca, Zlatko; Klimczak, Michael; Milicevic, Zoran; Weißer, Matthias; Taccardi, Nicola; Wasserscheid, Peter; Smith, David M.; Magerl, Andreas; Smith, Ana-Suncana (Journal of Physical Chemistry Letters, 2015)
Understanding the molecular-level behavior of ionic liquids (ILs) at IL–solid interfaces is of fundamental importance with respect to their application in, for example, electrochemical systems and electronic devices. Using a model system, consisting of an imidazolium-based IL ([C2Mim][NTf2]) in contact with a sapphire substrate, we have approached this problem using a complementary combination of high-resolution X-ray reflectivity measurements and atomistic molecular dynamics (MD) simulations. Our strategy enabled us to compare experimental and theoretically calculated reflectivities in a direct manner, thereby critically assessing the applicability of several force-field variants. On the other hand, using the best-matching MD description, we are able to describe the nature of the model IL–solid interface in appreciable detail. More specifically, we find that characteristic interactions between the surface hydroxyl groups and donor and acceptor sites on the IL constituents have a dominant role in inducing a multidimensional layering profile of the cations and anions.

Complex manifold of Rashba and image-potential states on Bi/Ag(111) - Rosenzweig, Philipp; Otto, Sebastian; Fauster, Thomas (Physical Review B, 2018)
Angle-resolved, mono- and bichromatic two-photon photoemission was used to study the electronic structure at the surface of the giant Rashba system Bi/Ag(111). The photoemission intensity maps are exceptionally rich in structure due to a large manifold of initial and intermediate states that allow for various resonant interband transitions. Using different photon energies, we succeeded in disentangling the complex experimental data. Close to the Fermi level the unoccupied, Rashba-split p(x)p(y) (m(j) = 1/2) surface state can be identified with a Rashba parameter of 3.0 +/- 0.2 eV A and a lifetime of 26 +/- 5 fs. At higher energies the spin-split p(x)p(y) (m(j) = 3/2) and p(z) bands as well as the first three members of a series of image-potential resonances were observed. Circular dichroism was used to gain information on the spin structure of both the initial and intermediate states and to corroborate the assignment to Rashba bands.

Composite Nanostructures of TiO2 and ZnO for Water Splitting Application: Atomic Layer Deposition Growth and Density Functional Theory Investigation - Kulmas, Marina; Paerson, Leanne; Höflich, Katja; Bashouti, Muhammad Y.; Wu, Yanlin; Göbelt, Manuela; Ristein, Jürgen; Bachmann, Julien; Meyer, Bernd; Christiansen, Silke (Advanced Functional Materials, 2016)
The commercialization of solar fuel devices requires the development of novel engineered photoelectrodes for water splitting applications which are based on redundant, cheap, and environmentally friendly materials. In the current study, a combination of titanium dioxide (TiO) and zinc oxide (ZnO) onto nanotextured silicon is utilized for a composite electrode with the aim to overcome the individual shortcomings of the respective materials. The properties of conformal coverage of TiO and ZnO layers are designed on the atomic scale by the atomic layer deposition technique. The resulting photoanode shows not only promising stability but also nine times higher photocurrents than an equivalent photoanode with a pure TiO encapsulation onto the nanostructured silicon. Density functional theory calculations indicate that segregation of TiO at the ZnO surfaces is favorable and leads to the stabilization of the ZnO layers in water environments. In conclusion, the novel designed composite material constitutes a promising base for a stable and effective photoanode for the water oxidation reaction.
Keywords: density functional theory; photoanodes; titanium dioxide; water oxidation; zinc oxide

Comprehensive Investigation and Analysis of Bulk-Heterojunction Microstructure of High-Performance PCE11:PCBM Solar Cells - Zhang, Chaohong; Heumüller, Thomas; Gruber, Wolfgang; Almora, Osbel; Du, Xiaoyan; Ying, Lei; Chen, Junwu; Unruh, Tobias; Cao, Yong; Li, Ning; Brabec, Christoph (ACS Applied Materials and Interfaces, 2019)
Worldwide research efforts have been devoted to organic photovoltaics in the hope of a large-scale commercial application in the near future. To meet the industrial production requirements, organic photovoltaics that can reach power conversion efficiency (PCE) of over 10% along with promising operational device stability are of utmost interest. In the study, we take PCE11:PCBM as a model system, which can achieve over 11% PCE when processed from nonhalogen solvents, to deeply investigate the morphology− performance−stability correlation. We demonstrate that four batches of PCE11 with varying crystalline properties can achieve similar high performance in combination with PCBM. Careful device optimization is necessary in each case to properly address the requirements for the quite distinct microstructures. The bulk-heterojunction (BHJ) microstructure is comprehensively investigated as a function of the macromolecular weight and crystallinity. It is demonstrated that small differences in morphology significantly affect the kinetics and thermodynamic equilibrium of the BHJ microstructure as well as the photostability and thermal stability of the PCE11:PCBM solar cells<br
Keywords: in situ capacitance spectroscopy; organic photovoltaics; bulk-heterojunction microstructures; film morphology; PCE11:PCBM solar cells

Comprehensive Raman study of orthorhombic kappa/epsilon-Ga2O3 and the impact of rotational domains - Janzen, Benjamin M.; Mazzolini, Piero; Gillen, Roland; Peltason, Vivien F. S.; Grote, Linus P.; Maultzsch, Janina; Fornari, Roberto; Bierwagen, Oliver; Wagner, Markus R. (Journal of Materials Chemistry C, 2021)
Gallium oxide (Ga2O3) is an ultra-wide bandgap material, which has recently attracted widespread attention for holding promising applications in power electronics and solar blind UV photodetectors, outclassing GaN or SiC in terms of a larger bandgap and higher breakdown voltages. The orthorhombic kappa phase (also referred to as epsilon) has sparked particular interest for offering higher symmetry than beta, while featuring ferroelectric behavior paired with a large predicted spontaneous polarization, paving the way to fabricating high-quality two-dimensional electron gases for application in heterostructure field effect transistors. The presently available kappa phase samples are characterized by a domain structure, in which orthorhombic domains are rotated 120 degrees against each other within the c-plane forming a pseudo-hexagonal structure, which has previously often been ascribed to epsilon-Ga2O3 and incorrectly been viewed as this polymorph's true crystal structure. A detailed investigation into the phonon modes of orthorhombic kappa-Ga2O3 provides insights into fundamental material properties such as crystal structure and orientation as well as the vibrational symmetries of Raman active modes. We investigate the Raman active phonon modes of an MBE-grown orthorhombic kappa-Ga2O3 thin film featuring the domain structure deposited on (0001)-Al2O3 by experiment and theory: Polarized micro-Raman spectroscopy measurements in conjunction with density functional perturbation theory (DFPT) calculations enable the identification of both the frequencies and vibrational symmetries of the Raman active phonons. Presenting comprehensive Raman spectra of the orthorhombic kappa phase, the experimental frequencies of more than 90 Raman modes are determined and correlated with the 117 modes predicted by the calculations. Angular-resolved Raman measurements are utilized to provide an experimental verification of phonon mode symmetries. We present an analytical tool to deal with the domain structure and its effect on the obtained Raman spectra.
CRIS-Team WoS Importer:2021-10-08

Compressed sensing and the use of phased array coils in 23Na MRI: a comparison of a SENSE-based and an individually combined multi-channel reconstruction - Lachner, Sebastian; Utzschneider, Matthias; Zaric, Olgica; Minarikova, Lenka; Ruck, Laurent; Zbýň, Štefan; Hensel, Bernhard; Trattnig, Siegfried; Uder, Michael; Nagel, Armin Michael (Zeitschrift für Medizinische Physik, 2020)
Purpose: To implement and to evaluate a compressed sensing (CS) reconstruction algorithm based on the sensitivity encoding (SENSE) combination scheme (CS-SENSE), used to reconstruct sodium magnetic resonance imaging (23Na MRI) multi-channel breast data sets. Methods: In a simulation study, the CS-SENSE algorithm was tested and optimized by evaluating the structural similarity (SSIM) and the normalized root-mean-square error (NRMSE) for different regularizations and different undersampling factors (USF = 1.8/3.6/7.2/14.4). Subsequently, the algorithm was applied to data from in vivo measurements of the healthy female breast (n = 3) acquired at 7 T. Moreover, the proposed CS-SENSE algorithm was compared to a previously published CS algorithm (CS-IND). Results: The CS-SENSE reconstruction leads to an increased image quality for all undersampling factors and employed regularizations. Especially if a simple 2nd order total variation is chosen as sparsity transformation, the CS-SENSE reconstruction increases the image quality of highly undersampled data sets (CS-SENSE: SSIMUSF=7.2 = 0.234, NRMSEUSF=7.2 = 0.491 vs. CS-IND: SSIMUSF=7.2 = 0.201, NRMSEUSF=7.2 = 0.506). Conclusion: The CS-SENSE reconstruction supersedes the need of CS weighting factors for each channel as well as a method to combine single channel data. The CS-SENSE algorithm can be used to reconstruct undersampled data sets with increased image quality. This can be exploited to reduce total acquisition times in 23Na MRI.
CRIS-Team Scopus Importer:2020-11-20
Keywords: Compressed sensing; Iterative reconstruction; Multi-channel; Prior knowledge; Sensitivity encoding; Sodium MRI

Compressed sensing reconstruction of 7 Tesla23Na multi-channel breast data using 1H MRI constraint - Lachner, Sebastian; Zaric, Olgica; Utzschneider, Matthias; Minarikova, Lenka; Zbýň, Štefan; Hensel, Bernhard; Trattnig, Siegfried; Uder, Michael; Nagel, Armin Michael (Magnetic Resonance Imaging, 2019)
Purpose: To reduce acquisition time and to improve image quality in sodium magnetic resonance imaging ( 23 Na MRI)using an iterative reconstruction algorithm for multi-channel data sets based on compressed sensing (CS)with anatomical 1 H prior knowledge. Methods: An iterative reconstruction for 23 Na MRI with multi-channel receiver coils is presented. Based on CS it utilizes a second order total variation (TV (2) ), adopted by anatomical weighting factors (AnaWeTV (2) )obtained from a high-resolution 1 H image. A support region is included as additional regularization. Simulated and measured 23 Na multi-channel data sets (n = 3)of the female breast acquired at 7 T with different undersampling factors (USF = 1.8/3.6/7.2/14.4)were reconstructed and compared to a conventional gridding reconstruction. The structural similarity was used to assess image quality of the reconstructed simulated data sets and to optimize the weighting factors for the CS reconstruction. Results: Compared with a conventional TV (2) , the AnaWeTV (2) reconstruction leads to an improved image quality due to preserving of known structure and reduced partial volume effects. An additional incorporated support region shows further improvements for high USFs. Since the decrease in image quality with higher USFs is less pronounced compared to a conventional gridding reconstruction, proposed algorithm is beneficial especially for higher USFs. Acquisition time can be reduced by a factor of 4 (USF = 7.2), while image quality is still similar to a nearly fully sampled (USF = 1.8)gridding reconstructed data set. Conclusion: Especially for high USFs, the proposed algorithm allows improved image quality for multi-channel 23 Na MRI data sets.
CRIS-Team Scopus Importer:2019-05-14
Keywords: 7 Tesla; Compressed sensing (CS); Iterative reconstruction; Multi-channel; Prior knowledge; Sodium (

Concentration dependent morphology and composition of n-alcohol modified cetyltrimethylammonium bromide micelles - Schmutzler, Tilo; Schindler, Torben; Götz, Klaus; Appavou, Marie-Sousai; Lindner, Peter; Prevost, Sylvain; Unruh, Tobias (Journal of Physics: Condensed Matter, 2018)
Cetyltrimethylammonitun bromide (CTAB) is one of the most commonly used surfactants in nanoparticle synthesis and stabilization. Usually, CTAB is used in high concentrations besides co-surfactants leading to well defined products but the complex mesoscopic CTAB structures stay mostly unknown. N-alcohols for instance are widely used co-surfactants which modify the properties of native CTAB dispersions. In this paper we report about a detailed structure analysis of n-alcohol modified CTAB micelles. In particular, n-pentanol and n-hexanol exhibit a significantly different influence on the size, shape and composition of CTAB micelles. Using a combination of small-angle x-ray spectroscopy (SAXS) and neutron scattering spectroscopy (SANS), we applied a method for a complete structural characterization of such micelles. The incorporation of n-pentanol into CTAB micelles generally does not influence the morphology but enhances the number of micelles due to the volume of the added alcohol. N-hexanol, however, leads to an elongation of the micelles as a function of its concentration. It was found by extended contrast variation measurements that this difference is caused by a different distribution of the alcohols between the micellar core and shell. N-pentanol molecules are generally located at the core-shell interface of the CTAB micelles with not only the head group but also two additional methylene bridging groups located in the micellar shell. This leads to an increase of its effective head group volume. In comparison, in n-hexanol modified micelles the whole alkyl chain is located within the micellar core. The detailed structure for n-alcohol modified CTAB micelles is described herein for the first time. The knowledge of the structural details found is indispensable for an in-depth understanding of CTAB-n-alcohol-water interfaces in general which is relevant for the synthesis of many functional nanostructures like mesoporous silica and gold or silver nanoparticles.
Keywords: CTAB; micelles; surfactants; co-surfactants; n-alcohols; SANS; SAXS

Conductance enhancement of polymethylmethacrylate bombarded by low-energy ions - Koval, Yury; Fistul, Mikhail; Müller, Paul (Journal of Vacuum Science & Technology A, 2005)
It has been found that films of polymethylmethacrylate (PMMA) show a substantial conductance after bombardment by Ar ions with energy of 250-1250 eV. The appearance of the conductance is attributed to graphitization processes in the subsurface layer. As the energy of ions increases, the conductivity of PMMA is greatly enhanced. We have found that, at low electric fields, the conductance is provided by variable range hopping with a strong influence of Coulomb interactions. At high electric fields, the transformed PMMA reveals non-Ohmic behavior: the conductance is an exponential function of ET. © 2005 American Vacuum Society.

Connection of anisotropic conductivity to tip-induced space-charge layers in scanning tunneling spectroscopy of p-doped GaAs - Loth, Sebastian; Wenderoth, Martin; Ulbrich, Rainer G.; Malzer, Stefan; Döhler, Gottfried (Physical Review B, 2007)
The electronic properties of shallow acceptors in p -doped GaAs110 are investigated with scanning tunneling microscopy (STM) at low temperature. Shallow acceptors are known to exhibit distinct triangular contrasts in STM images for certain bias voltages. Spatially resolved I (V) spectroscopy is performed to identify their energetic origin and behavior. A crucial parameter-the scanning tunneling microscope tip's work function-is determined experimentally. The voltage dependent potential configuration and band bending situation are derived. Ways to validate the calculations with the experiment are discussed. Differential conductivity maps reveal that the triangular contrasts are only observed with a depletion layer present under the STM tip. The tunnel process leading to the anisotropic contrasts calls for electrons to tunnel through vacuum gap and a finite region in the semiconductor. © 2007 The American Physical Society.

Contacting single bundles of carbon nanotubes with alternating electric fields - Krupke, Ralph; Frank, Hennrich; Weber, Heiko B.; Beckmann, Detlef; Hampe, Oliver; Malik, S.; Kappes, Manfred; von Löhneysen, Hilbert (Applied Physics A-Materials Science & Processing, 2003)
Single bundles of carbon nanotubes have been selectively deposited from suspensions onto sub-micron electrodes with alternating electric fields. We show that it is possible to control the trapping of a single bundle by the use of Ag as electrode material which, unlike Au, strongly interacts with the carboxyl functionalized carbon nanotubes. Excellent alignment of the bundles between Au or Ag electrodes occurs at frequencies above 1 kHz, with superior contacts being formed with Ag electrodes.

Contact resistivity and suppression of Fermi level pinning in side-contacted germanium nanowires - Kolesnik-Gray, Maria; Lutz, Tarek; Collins, Gillian; Biswas, Subhajit; Holmes, Justin D.; Krstic, Vojislav (Applied Physics Letters, 2013)
Electrical properties of contact-interfaces in germanium nanowire field effect transistor devices are studied. In contrast to planar bulk devices, it is shown that the active conduction channel and gate length extend between and underneath the contact electrodes. Furthermore, direct scaling of contact resistivity and Schottky barrier height with electrode metal function is observed. The associated pinning parameter was found to be gamma = 0.65 ± 0.03, which demonstrates a significant suppression of Fermi level pinning in quasi-one-dimensional structures.

Continuos Wave Terahertz Emitter Arrays for Spectroscopy and Imaging Applications - Bauerschmidt, Sebastian; Malzer, Stefan; Preu, Sascha; Döhler, Gottfried; Lu, Hong; Gossard, Art; Wang, Lijun (Proceedings of SPIE, 2010)
UnivIS-Import:2015-03-09:Pub.2010.nat.dphy.IAP.LAP.contin

Continuous calculation of intratracheal pressure in tracheally intubated patients - Fabry, Ben; et al. (Anesthesiology, 1993)

Continuous, crystalline Sb2S3 ultrathin light absorber coatings in solar cells based on photonic concentric p-i-n heterojunctions - Büttner, Pascal; Scheler, Florian; Döhler, Dirk; Barr, Maissa; Bosch, Michael; Rey, Marcel; Yokosawa, Tadahiro; Hinz, Sandra; Maultzsch, Janina; Spiecker, Erdmann; Vogel, Nicolas; Minguez Bacho, Ignacio; et al. (Nano Energy, 2022)
Many modern types of solar cells that rely exclusively on earth-abundant non-toxic materials include interfaces between a heavier metal chalcogenide and another type of semiconductor. Often, the chemical (adhesion) and physical (charge transfer) characteristics of those interfaces are the defining factors for the final device performance. Here, we describe that a ZnS adhesion layer is not sufficient to prevent the dewetting of Sb2S3 upon annealing a thin layer of it on an oxidic surface if the substrate is not planar and features highly curved surfaces. An ALD-coated sacrificial capping layer of ZnO prevents the morphological rearrangements of Sb2S3 during thermal crystallization and can be removed subsequently. When implemented towards a photovoltaic p-i-n heterojunction, this strategy furnishes perfect conformality of the layer stack but unsatisfactory performance. The correlation of interface chemistry with the electrical properties and the device performance identifies a reducing effect of ZnO atomic layer deposition chemistry on the Sb2S3 surface as the cause of Zn diffusion into the light absorbing semiconductor. This deleterious doping can be prevented by a preliminary oxidative treatment of the Sb2S3 surface with ozone. When applied to a structured substrate consisting of ordered arrays of nanospheres, this approach yields the first ever concentric p-i-n heterojunction solar cells with photonic light trapping effect—a geometry which in comparison with standard scattering layers'on top’ inherently generates a very large refractive index contrast. In the red part of the visible spectrum, light absorption amounts to the value expected with four passes through a planar layer of the thickness used here (35 nm Sb2S3). This effect allows us to demonstrate >5% overall solar energy conversion efficiency with only 35 nm of a simple light absorber phase that uses no toxic, rare materials
CRIS-Team Scopus Importer:2022-10-14
Keywords: Atomic layer deposition; Concentric semiconductor junctions; Antimony chalcogenides; Interfacial layers; Photonic structures; Gradient doping; Interface chemistry

Continuous-Wave Sub-THz Photonic Generation With Ultra-Narrow Linewidth, Ultra-High Resolution, Full Frequency Range Coverage and High Long-Term Frequency Stability - Malzer, Stefan; Criado, Ruben; de Dios, Christina; Preu, Sascha; Prior, E.; Acedo, Pablo; Döhler, Gottfried; Lu, Hong; Gossard, Art (IEEE Transactions on Terahertz Science and Technology, 2013)
We report on a photonic system for generation of high quality continuous-wave (CW) sub-THz signals. The system consists on a gain-switching-based optical frequency comb generator (GS-OFCG), a two-optical-modes selection mechanism and a n-i-pn-i-p superlattice photomixer. As mode selection mechanism, both selective tunable optical filtering using Fabry-Pérot tunable filters (FPTFs) and Optical Injection Locking (OIL) are evaluated. The performance of the reported system surpasses in orders of magnitude the performance of any commercially available optical mm-wave and sub-THz generation system in a great number of parameters. It matches and even overcomes those of the best commercially available electronic THz generation systems. The performance parameters featured by our system are: linewidth 10 Hz at 120 GHz, complete frequency range coverage (60-140 GHz) with a resolution in the order of 0.1 Hz at 120 GHz ( 10 of generated frequency), high long term frequency stability (5 Hz deviation over one hour). Most of these values are limited by the measurement instrumentation accuracy and resolution, thus the actual values of the system could be better than the reported ones. The frequency can be extended straightforwardly up to 1 THz extending the OFCG frequency span. This system is compact, robust, reliable, offers a very high performance, especially suited for sub-THz photonic local oscillators and high resolution spectroscopy.

Continuous wave terahertz emitter arrays for spectroscopy and imaging applications - Bauerschmidt, Sebastian; Preu, Sascha; Malzer, Stefan; Döhler, Gottfried; Wang, Lijun; Lu, Hong; Gossard, Art (Terahertz Physics, Devices, and Systems IV: Advanced Applications in Industry and Defense, 2010)
We report on arrays of THz-emitters based on n-i-pn-i-p-superlattice photomixers for imaging and spectroscopic applications. The output power of a n-i-pn-i-p superlattice photomixers recently has reached nearly 1 μW at 1 THz with a broadband antenna. There are no fundamental physical limitations at this stage for further improvement. Tunable continuous wave (CW) THz-sources for imaging and spectroscopy are highly desired tools for security and environmental applications. In particular, most stand-off imaging applications require a rather high THz power to allow for a sufficient dynamic range, and a narrow illumination spot size for high spatial resolution. Both goals can be reached by using an array of mutually coherent photomixers. We have simulated beam patterns for an arbitrary number of mutually coherent single sources with respect to a small beam size and high peak intensity. Here, we confirm the simulations experimentally by an array of 4 sources with a 4 inch THz optics. The beam profile is measured in the target plane at a stand-off distance of 4.2 m. As a result, the beam diameter is reduced by a factor of 6 and the peak intensity is enhanced by a factor of close to (4) = 16, in excellent agreement with our simulations. Such an arrangement allows not only for high resolution stand-off imaging but also for spectroscopic investigations at stand-off distances. The THz frequency can be tuned over more than a decade (i.e. 0.1 to 2.5 THz) by tuning the wavelength of the mixing lasers. The spectral linewidth of the THz sources is only limited by the linewidths of the mixing lasers and can be made extremely narrow. A straightforward demonstration is achieved by water vapor spectroscopy in laboratory air with a single source. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Contractile forces in tumor cell migration - Mierke, Claudia; Rosel, Daniel; Fabry, Ben; Brabek, Jan (European Journal of Cell Biology, 2008)

Contrast-to-noise ratio analysis of microscopic diffusion anisotropy indices in q-space trajectory imaging - Martin, Jan; Endt, Sebastian; Wetscherek, Andreas; Kuder, Tristan Anselm; Dörfler, Arnd; Uder, Michael; Hensel, Bernhard; Laun, Frederik Bernd (Zeitschrift für Medizinische Physik, 2019)
Diffusion anisotropy in diffusion tensor imaging (DTI) is commonly quantified with normalized diffusion anisotropy indices (DAIs). Most often, the fractional anisotropy (FA) is used, but several alternative DAIs have been introduced in attempts to maximize the contrast-to-noise ratio (CNR) in diffusion anisotropy maps. Examples include the scaled relative anisotropy (sRA), the gamma variate anisotropy index (GV), the surface anisotropy (UA surf ), and the lattice index (LI). With the advent of multidimensional diffusion encoding it became possible to determine the presence of microscopic diffusion anisotropy in a voxel, which is theoretically independent of orientation coherence. In accordance with DTI, the microscopic anisotropy is typically quantified by the microscopic fractional anisotropy (μFA). In this work, in addition to the μFA, the four microscopic diffusion anisotropy indices (μDAIs) μsRA, μGV, μUA surf , and μLI are defined in analogy to the respective DAIs by means of the average diffusion tensor and the covariance tensor. Simulations with three representative distributions of microscopic diffusion tensors revealed distinct CNR differences when differentiating between isotropic and microscopically anisotropic diffusion. q-Space trajectory imaging (QTI) was employed to acquire brain in-vivo maps of all indices. For this purpose, a 15 min protocol featuring linear, planar, and spherical tensor encoding was used. The resulting maps were of good quality and exhibited different contrasts, e.g. between gray and white matter. This indicates that it may be beneficial to use more than one μDAI in future investigational studies.
CRIS-Team Scopus Importer:2020-02-21
Keywords: Contrast-to-noise ratio; Diffusion; Microstructure; Multidimensional; q-Space trajectory

Contribution of the buffer layer to Raman spectrum of epitaxial graphene on SiC(0001) - Fromm, Felix; Oliveira, M. H.; Molina-Sanchez, A.; Hundhausen, Martin; Lopes, J. M. J.; Riechert, Henning; Wirtz, L.; Seyller, Thomas (New Journal of Physics, 2013)
We report a Raman study of the so-called buffer layer with (6√3 6√3)R30° periodicity which forms the intrinsic interface structure between epitaxial graphene and SiC(0001). We show that this interface structure leads to a non-vanishing signal in the Raman spectrum at frequencies in the range of the D- and G-band of graphene and discuss its shape and intensity. Ab initio phonon calculations reveal that these features can be attributed to the vibrational density of states of the buffer layer.
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.IAP.exphys.contri

Controllable growth of metallic nano-helices at room temperature conditions - Caridad, Jose M.; McCloskey, David; Donegan, John F.; Krstic, Vojislav (Applied Physics Letters, 2014)
We report on a method to produce multiple-pitch, regularly shaped, aligned, and freestanding metallic nano-helices at room temperature. This method overcomes the limitations of the standard glancing angle deposition approach through a heat-management technique devoid of active substrate cooling and is even applicable for metals with low melting point, that is, high surface adatom diffusion. The structural quality and optical activity response of these metal nano-helices are comparable to state of the art helices produced by employing substrates cooled down to cryogenic temperatures.

Controlled Folding of Graphene: GraFold Printing - Hallam, Toby; Shakouri, Amir; Poliani, Emanuele; Rooney, Aidan P.; Ivanov, Ivan; Potie, Alexis; Taylor, Hayden; Bonn, Mischa; Turchinovich, Dmitry; Maultzsch, Janina; Haigh, Sarah; Duesberg, Georg S. (Nano Letters, 2015)
We have used elastomeric stamps with periodically varying adhesive properties to introduce structure and print folded graphene films. The structure of the induced folds is investigated with scanning probe techniques, high-resolution electron-microscopy, and tip-enhanced Raman spectroscopy. Furthermore, a finite element model is developed to show the fold formation process. Terahertz spectroscopy reveals induced anisotropy of carrier mobility along, and perpendicular to, the graphene folds. Graphene fold printing is a new technique which allows for significant modification of the properties of 2D materials without damaging or chemically modifying them.
Keywords: Graphene patterning; folding; contact printing; nanotechnology; spectroscopy

Controlled generation of intrinsic near-infrared color centers in 4H-SiC via proton irradiation and annealing - Rühl, Maximilian; Ott, Christian; Götzinger, Stephan; Krieger, Michael; Weber, Heiko B. (Applied Physics Letters, 2018)
We report on the generation and annihilation of color centers in 4H silicon carbide (SiC) by proton irradiation and subsequent annealing. Using low-temperature photoluminescence (PL), we study the transformation of PL spectra for different proton doses and annealing temperatures. Among well reported defect signatures, we observe omnipresent but not yet identified PL signatures consisting of three sharp and temperature stable lines (denoted TS1,2,3) at 768.8 nm, 812.0 nm, and 813.3 nm. These lines show a strong correlation throughout all measurement parameters, suggesting that they belong to the same microscopic defect. Further, a clear dependence of the TS1,2,3 line intensities on the initial implantation dose is observed after annealing, indicating that the underlying defect is related to implantation induced intrinsic defects. The overall data suggest a sequential defect transformation: proton irradiation initially generates isolated silicon vacancies which are transformed into antisite vacancy complexes which are, in turn, transformed into presumably intrinsic-related defects, showing up as TS1,2,3 PL lines. We present recipes for the controlled generation of these color center
Keywords: Farbzentren

Controlled silver-shell growth on gold nanorods studied by in situ liquid cell TEM techniques - Hutzler, Andreas; Branscheid, Robert; Schmutzler, Tilo; Jank, Michael; Frey, Lothar; Spiecker, Erdmann (Microscopy Conference 2017 (MC 2017) - Proceedings, 2017)
Liquid cell transmission electron microscopy (LCTEM) enables the observation of dynamic processes at the place of the event in real time that is in situ. An early concept of this method has already been suggested in 1944 by Abrams and McBain [1] and could be realized nearly 60 years later in 2003 by Williamson et al. [2]. Since that, much effort has been put into characterizing various reactions in material, biological, and electrochemical systems. Anisotropic core-shell nanostructures are highly attractive for plasmonic applications like e.g. sensors, light guiding or labeling, because their plasmon resonance frequency can be variably adjusted over a wide spectral range via a simple variation of the shell thickness as already shown by Becker et al. [3]. Here we apply LCTEM to induce and to investigate the growth of silver-shell from aqueous silver nitrate (AgNO3) solution on cetrimonium bromide (CTAB) stabilized gold nanorods. For this purpose, a new, simplified liquid cell design is utilized, which is not only capable being used for conventional, but also for analytic TEM techniques like energy dispersive x-ray spectroscopy (EDXS) and electron tomography. To achieve that, the fluid is enclosed between a structured silicon nitride membrane and a second few layer graphene membrane, leaving one side of the cell plane, as shown elsewhere [4]. For the experiments, a conventional TEM specimen holder is used together with a Philips CM 30 and a FEI Titan³ Themis, both operated at 300 kV. It could be shown that silver bromide (AgBr) is forming, which components are originating from CTAB and AgNO3. AgBr is subsequently being reduced by solvated electrons acting as reducing agent. These free electrons are generated intrinsically by electron beam irradiation of the aqueous solution. The silver atoms can then nucleate and crystallize at different nucleation centers. One possible nucleation center is the surface of the present gold nanorods, where an epitaxial, defect free growth of a silver shell can be observed (cf. Fig. 1 and Fig. 2). The whole process is slowed down compared to bulk reactions because of the confinement of the solution to a narrow channel and thus because of a higher liquid viscosity hindering diffusion. Nevertheless, the growth rate of silver perpendicular to the longitudinal direction of the nanorods is considerably higher compared to the growth rate in the parallel direction. Furthermore, a dose dependent and reversible layer-by-layer dissolution of AgBr particles, acting as silver sources, is observable (cf. Fig. 3). Here, the reduction, and thus the annihilation of solvated silver ions at higher electron dose rate conditions shifting the solubility product to nonequilibrium state, so that AgBr dissolves to restore this equilibrium. In contrast to this process, counter reactions prevail at lower dose conditions. Here, the formation of silver ions is favored until the solubility is being exceeded and crystallization of AgBr takes place. The experiments done within this study show that this new liquid cell design is appropriate for solving material scientific issues. In particular, the planar surface of the liquid cell as well as the large viewing areas allow for improved performance of analytical TEM techniques like EDXS and electron tomography making the cell architecture capable of more comprehensive investigations into complex material systems.<br
Keywords: LCTEM; Liquid Cell; in situ TEM; Core-Shell; Gold Nanorods

Controlling additive behavior to reveal an alternative morphology formation mechanism in polymer: Fullerene bulk-heterojunctions - Güldal, Nusret Sena; Berlinghof, Marvin; Kassar, Thaer; Du, Xiaoyan; Jiao, Xuechen; Meyer, Markus; Ameri, Tayebeh; Osvet, Andres; Li, Ning; Destri, Giovanni Li; Fink, Rainer; Ade, Harald; et al. (Journal of Materials Chemistry A, 2016)
One of the most employed morphology optimization methods to design better performing organic photovoltaic devices is ink formulation engineering with additives. In this work, by employing a suboptimal host solvent mixture and 1,8-diiodooctane (DIO) as a very optimal solvent for both components in poly-thieno[3,2b]thiophene-diketopyrrolopyrrole-co-thiophene (DPP-TT-T)-based bulk-heterojunctions (BHJ), an alternative, previously unknown mechanism of additive behavior on BHJ microstructure formation is presented. In situ characterization methods involving grazing incidence X-ray diffraction, white-light reflectometry, laser light scattering and photoluminescence during film drying reveal that the microstructure formation under the influence of DIO is led towards thermodynamic equilibrium during host solvent drying, and the kinetics of morphology formation (i.e. polymer crystallization, fullerene aggregation...) are controlled dominantly by the additive during its evaporation. Ex situ X-ray-based characterization methods, such as scanning transmission X-ray microspectroscopy (STXM) and resonant soft X-ray scattering (R-SoXS), additionally reveal that the microstructure of dried films favors smaller domain sizes with purer domains, smaller fullerene aggregates, bimodal polymer crystallization relative to the substrate and more face-on molecular orientation relative to the donor/acceptor interface, which at the end lead to better performing devices with power conversion efficiencies ranging from 1.25% to 4.68%.
Keywords: Engineering controlled terms: Additives; Fullerenes; Heterojunctions; Interfaces (materials); Light scattering; Microstructure; Molecular orientation; Morphology; Polymers; Solvents; Thiophene; X ray diffraction; X ray scattering Bulk heterojunction (BHJ); Characterization methods; Donor/acceptor interface; Grazing incidence X-ray diffraction; In-situ characterization; Microstructure formation; Organic photovoltaic devices; Power conversion efficiencies Engineering main heading: Polymer films

Control of antiferromagnetic domain distribution via polarization-dependent optical annealing - Higuchi, Takuya; Kuwata-Gonokami, Makoto (Nature Communications, 2016)
The absence of net magnetization inside antiferromagnetic domains has made the control of their spatial distribution quite challenging. Here we experimentally demonstrate an optical method for controlling antiferromagnetic domain distributions in MnF2. Reduced crystalline symmetry can couple an order parameter with non-conjugate external stimuli. In the case of MnF2, time-reversal symmetry is macroscopically broken reflecting the different orientations of the two magnetic sublattices. Thus, it exhibits different absorption coefficients between two orthogonal linear polarizations below its antiferromagnetic transition temperature under an external magnetic field. Illumination with linearly polarized laser light under this condition selectively destructs the formation of a particular antiferromagnetic order via heating. As a result, the other antiferromagnetic order is favoured inside the laser spot, achieving spatially localized selection of an antiferromagnetic order. Applications to control of interface states at antiferromagnetic domain boundaries, exchange bias and control of spin currents are expected.
Keywords: Magnetic properties and materials

Control of noise-induced coherent oscillations in three-neuron motifs - Boensel, Florian; Krauß, Patrick; Metzner, Claus; Yamakou, Marius (Cognitive Neurodynamics, 2021)
The phenomenon of self-induced stochastic resonance (SISR) requires a nontrivial scaling limit between the deterministic and the stochastic timescales of an excitable system, leading to the emergence of coherent oscillations which are absent without noise. In this paper, we numerically investigate SISR and its control in single neurons and three-neuron motifs made up of the Morris-Lecar model. In single neurons, we compare the effects of electrical and chemical autapses on the degree of coherence of the oscillations due to SISR. In the motifs, we compare the effects of altering the synaptic time-delayed couplings and the topologies on the degree of SISR. Finally, we provide two enhancement strategies for a particularly poor degree of SISR in motifs with chemical synapses: (1) we show that a poor SISR can be significantly enhanced by attaching an electrical or an excitatory chemical autapse on one of the neurons, and (2) we show that by multiplexing the motif with a poor SISR to another motif (with a high SISR in isolation), the degree of SISR in the former motif can be significantly enhanced. We show that the efficiency of these enhancement strategies depends on the topology of the motifs and the nature of synaptic time-delayed couplings mediating the multiplexing connections.
CRIS-Team WoS Importer:2021-12-31

Control of the dephasing of image-potential states by CO adsorption on Cu(100) - Reuss, Christian; Shumay, Igor; Thomann, Ulrich; Kutschera, Michael; Weinelt, Martin; Fauster, Thomas; Höfer, Ulrich (Physical Review Letters, 1999)
The dynamical behavior of image-potential states has been studied with two-photon photoemission for CO on Cu(100), Pure dephasing is observed as the loss of coherence in quantum beats, or derived from linewidth and lifetime measurements. energy electron diffraction is also established. A correlation to the surface order as observed by low-energy electron diffraction is also established. [S0031-9007(98)08070-3].

Control of the plasmonic near-field in metallic nanohelices - Caridad, Jose M.; Winters, Sinead; Mccloskey, David; Duesberg, Georg S.; Donegan, John F.; Krstic, Vojislav (Nanotechnology, 2018)
The optical response of metallic nanohelices is mainly governed by a longitudinal localised surface plasmon resonance (LSPR) which arises due to the helical anisotropy of the system. Up to now, experimental studies have predominantly addressed the far-field response, despite the fact that the LSPR being of broad interest for converting incoming light into strongly enhanced (chiral) optical near-fields. Here, we demonstrate the control and spatial reproducibility of the plasmon-induced electromagnetic near-field around metallic nanohelices via surface-enhanced Raman scattering. We discuss how the near-field intensity of these nanostructures can be custom-tailored through both the nanoscaled helical structure and the electronic properties of the constituting metals. Our experiments, which employ graphene as an accurate probing material, are in quantitative agreement with corresponding numerical simulations. The findings demonstrate metallic nanohelices as reference nanostructured surfaces able to provide and fine-tune optical fields for fundamental studies as well as sensing or (chiro-optical) imaging applications.<br
Keywords: chiro-optical plasmon; nanostructured thin films; near-field; graphene SERS; helical nanostructure; optical helical antennae

Control of Yu-Shiba-Rusinov States through a Bosonic Mode - Müller, Hartmut; Eckstein, Martin; Viola Kusminskiy, Silvia (Physical Review Letters, 2023)
We investigate the impact of a bosonic degree of freedom on Yu-Shiba-Rusinov states emerging from a magnetic impurity in a conventional superconductor. Starting from the Anderson impurity model, we predict that an additional p-wave conduction band channel opens up if a bosonic mode is coupled to the tunneling between impurity and host, which implies an additional pair of odd-parity Yu-Shiba-Rusinov states. The bosonic mode can be a vibrational mode or the electromagnetic field in a cavity. The exchange couplings in the two channels depend sensitively on the state of the bosonic mode (ground state, few quanta, or classically driven Floquet state), which opens possibilities for phononics or photonics control of such systems, with a rich variety of ground and excited states.
CRIS-Team Scopus Importer:2023-04-07

Coordination-Controlled C-C Coupling Products via ortho-Site C-H Activation - Zhang, Xue; Xue, Na; Li, Chao; Li, Na; Wang, Hao; Kocic, Nemanja; Beniwal, Sumit; Palotas, Krisztian; Li, Ruoning; Xue, Qiang; Maier, Sabine; Hou, Shimin; et al. (ACS nano, 2019)
The coordination-restricted ortho-site C-H bond activation and dehydrogenative homocoupling of 4,4'-(1,3-phenylene)dipyridine (1,3-BPyB) and 4,4'-(1,4-phenylene)dipyridine (1,4-BPyB) on different metal surfaces were studied by a combination of scanning tunneling microscopy, noncontact atomic force microscopy, and density functional theory calculations. The coupling products on Cu(111) exhibited certain configurations subject to the spatial restriction of robust two-fold Cu-N coordination bonds. Compared to the V-shaped 1,3-BPyB, the straight backbone of 1,4-BPyB helped to further reduce the variety of reactive products. By utilizing the three-fold coordination of Fe atoms with 1,4-BPyB molecules on Au(111), a large-scale network containing single products was constructed. Our results offer a promising protocol for controllable on-surface synthesis with the aid of robust coordination interactions.
CRIS-Team WoS Importer:2019-03-20

Correction: Collective forces of tumor spheroids in three-dimensional biopolymer networks. - Mark, Christoph; Grundy, Thomas J.; Strissel, Pamela; Böhringer, David; Grummel, Nadine; Gerum, Richard; Steinwachs, Julian; Hack, Carolin; Beckmann, Matthias; Eckstein, Markus; Strick, Reiner; O'Neill, Geraldine M.; et al. (eLife, 2020)
EVALuna2:417751

Correction: Ga and Ce ion-doped phosphate glass fibres with antibacterial properties and their composite for wound healing applications (Journal of Materials Chemistry B (2019) DOI: 10.1039/c9tb00820a) - Lapa, Agata; Cresswell, Mark; Campbell, Ian; Jackson, Phil; Goldmann, Wolfgang; Detsch, Rainer; Parsons, Andrew; Ahmed, Ifty; Boccaccini, Aldo R. (Journal of Materials Chemistry B, 2019)
The authors regret that in the original article the affiliation list is presented incorrectly. The corrected list is shown above. This change does not affect the affiliation tags used in the author list, which therefore remain the same. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.
CRIS-Team Scopus Importer:2019-12-03

Correlated disorder-to-order crossover in the local structure of KxFe2-ySe2-zSz - Mangelis, P.; Koch, R. J.; Lei, H.; Neder, Reinhard; Mcdonnell, M. T.; Feygenson, M.; Petrovic, C.; Lappas, A.; Bozin, E. S. (Physical Review B, 2019)
A detailed account of the local atomic structure and disorder at 5 K across the phase diagram of the high-temperature superconductor KxFe2-ySe2-zSz (0 <= z <= 2) is obtained from neutron total scattering and associated atomic pair distribution function (PDF) approaches. Various model-independent and model-dependent aspects of the analysis reveal a high level of structural complexity on the nanometer length scale. Evidence is found for considerable disorder in the c-axis stacking of the FeSe1-xSx slabs without observable signs of turbostratic character of the disorder. In contrast to the related FeCh (Ch = S, Se)-type superconductors, substantial Fe-vacancies are present in KxFe2-ySe2-zSz, deemed detrimental for superconductivity when ordered. Our study suggests that the distribution of vacancies significantly modifies the iron-chalcogen bond-length distribution, in agreement with observed evolution of the PDF signal. A crossoverlike transition is observed at a composition of z approximate to 1, from a correlated disorder state at the selenium end to a more vacancy-ordered (VO) state closer to the sulfur end of the phase diagram. The S-content-dependent measures of the local structure are found to exhibit distinct behavior on either side of this crossover, correlating well with the evolution of the superconducting state to that of a magnetic semiconductor toward the z approximate to 2 end. The behavior reinforces the idea of the intimate relationship of correlated Fe-vacancy order in the local structure and the emergent electronic properties.
CRIS-Team WoS Importer:2019-10-04

Correlated disorder-to-order crossover in the local structure of KxFe2-ySe2-zSz superconductor - Bozin, E. S.; Koch, R. J.; Mangelis, P.; Lei, H. C.; Neder, Reinhard; Mcdonnell, M.; Feygenson, M.; Petrovic, C.; Lappas, A. (ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 2021)
CRIS-Team WoS Importer:2022-04-01

Correlating Optical Microspectroscopy with 4×4 Transfer Matrix Modeling for Characterizing Birefringent Van der Waals Materials - Schwarz, Julian; Niebauer, Michael; Kolesnik-Gray, Maria; Szabo, Maximilian; Baier, Leander; Chava, Phanish; Erbe, Artur; Krstic, Vojislav; Rommel, Mathias; Hutzler, Andreas (Small Methods, 2023)
Van der Waals materials exhibit intriguing properties for future electronic and optoelectronic devices. As those unique features strongly depend on the materials' thickness, it has to be accessed precisely for tailoring the performance of a specific device. In this study, a nondestructive and technologically easily implementable approach for accurate thickness determination of birefringent layered materials is introduced by combining optical reflectance measurements with a modular model comprising a 4×4 transfer matrix method and the optical components relevant to light microspectroscopy. This approach is demonstrated being reliable and precise for thickness determination of anisotropic materials like highly oriented pyrolytic graphite and black phosphorus in a range from atomic layers up to more than 100 nm. As a key feature, the method is well-suited even for encapsulated layers outperforming state of-the-art techniques like atomic force microscopy.
Created from Fastlane, Scopus look-up
Keywords: anisotropy; birefringence; microspectroscopy; thickness determination; transfer matrix method; van der Waals materials

Correlation between Supercoiling and Conformational Motions of the Bacterial Flagellar Filament - Stadler, Andreas M.; Unruh, Tobias; Namba, Keiichi; Samatey, Fadel; Zaccai, Giuseppe (Biophysical Journal, 2013)
The bacterial flagellar filament is a very large macromolecular assembly of a single protein, flagellin. Various supercoiled states of the filament exist, which are formed by two structurally different conformations of flagellin in different ratios. We investigated the correlation between supercoiling of the protofilaments and molecular dynamics in the flagellar filament using quasielastic and elastic incoherent neutron scattering on the picosecond and nanosecond timescales. Thermal fluctuations in the straight L- and R-type filaments were measured and compared to the resting state of the wild-type filament. Amplitudes of motion on the picosecond timescale were found to be similar in the different conformational states. Mean-square displacements and protein resilience on the 0.1 ns timescale demonstrate that the L-type state is more flexible and less resilient than the R-type, whereas the wild-type state lies in between. Our results provide strong support that supercoiling of the protofilannents in the flagellar filament is determined by the strength of molecular forces in and between the flagellin subunits.

Correlations in strong-field-emitted ultrashort electron pulses from metal needle tips - Meier, Stefan; Heimerl, Jonas; Hommelhoff, Peter (Laser Physics Letters, 2024)
When two electrons are emitted from a metal needle tip with the help of femtosecond laser pulses, they show a strong anticorrelation signal in the energy domain. Depending on the wavelength and intensity of the driving laser pulses, the electron emission process can be either in a perturbative regime, like single- or multi-photon photoemission, or in the strong-field regime, where emission is dominated by the instantaneous electric field of the laser pulse, or in the intermediate regime. Here, we report on the two-electron anticorrelation signal and how it evolves from the multiphoton toward the strong-field emission regime. We show that in both cases, the resulting anticorrelation signal can be well explained by semi-classical simulations using a point-particle model, thus the dynamics is dominated by the center-of-mass dynamics of the individual electrons. However, the actual emission process of multiple interacting electrons requires improved quantum mechanical models and therefore remains the subject of future work. This paper is part of the Special Topic Collection: papers from the 31th Annual International Laser Physics Workshop 2023 (LPHYS 2023

Corrigendum: Atomic real-space perspective of light-field-driven currents in graphene (2022 New J. Phys. 24 033051) - Morimoto, Yuya; Shinohara, Yasushi; Ishikawa, Kenichi L.; Hommelhoff, Peter (New Journal of Physics, 2023)

Corrigendum to “alphavbeta3 integrin expression increases elasticity in human melanoma cells” [Biochem. Biophys. Res. Commun. 525 (2020)](S0006291X20304472)(10.1016/j.bbrc.2020.02.156) - Lacaria, L.; Lange, Joachim; Goldmann, Wolfgang; Rico, F.; Alonso, J. L. (Biochemical and Biophysical Research Communications, 2020)
The authors also thank Dr. M. Amin Arnaout, Massachusetts General Hospital for his support (Grant No. R01 DK48549). The authors would like to apologize for any inconvenience caused.
CRIS-Team Scopus Importer:2020-08-21

Corrosion of Mg alloy AZ91D in the presence of living cells - Virtanen, Sannakaisa; Seuß, Sigrid; Fabry, Ben; Turhan, Can Metehan; Seuß, Florian (Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2011)

Corynebacterium diphteriae invasion-associated protein (DIP1281) is involved in cell surface organization, adhesion and internalization in epithelial cells - Ott, Lisa; Höller, Martina; Gerlach, Roman G.; Hensel, Michael; Rheinlaender, Johannes; Schäffer, Tilman; Burkovski, Andreas (BMC Microbiology, 2010)
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 the function of surface-associated protein DIP1281, previously annotated as hypothetical invasion-associated protein. Microscopic inspection of DIP1281 mutant strains revealed an increased size of the single cells in combination with an altered less club-like shape and formation of chains of cells rather than the typical V-like division forms or palisades of growing C. diphtheriae cells. Cell viability was not impaired. Immuno-fluorescence microscopy, SDS-PAGE and 2-D PAGE of surface proteins revealed clear differences of wild-type and mutant protein patterns, which were verified by atomic force microscopy. DIP1281 mutant cells were not only altered in shape and surface structure but completely lack the ability to adhere to host cells and consequently invade these. Our data indicate that DIP1281 is predominantly involved in the organization of the outer surface protein layer rather than in the separation of the peptidoglycan cell wall of dividing bacteria. The adhesion- and invasion-negative phenotype of corresponding mutant strains is an effect of rearrangements of the outer surface. BACKGROUND RESULTS CONCLUSIONS
UnivIS-Import:2015-03-09:Pub.2010.nat.dphy.IAP.LAP.coryne

CoSi2 on Si(100): LEED investigations of the c(2x2) and (2 root 2x root 2) phases and comparison to a bulk crystal CoSi2(100) surface - Starke, Ulrich; Weiss, Wolfgang; Rangelov, Georgi; Fauster, Thomas; Heinz, Klaus; et al. (Surface Science, 1996)
A CoSi2(100) film of 12 Angstrom thickness was grown on Si(100) and investigated by low-energy electron diffraction (LEED). Two surface phases of the film can be prepared depending on the annealing temperature. The c(2 X 2) phase appearing first (350 degrees C) was compared to the c(2 X 2) structure of a bulk CoSi2(100) sample. Diffraction spot intensities are very similar for bulk and film samples. By a quantitative LEED analysis both surfaces are found to be arranged in a CaF2 structure terminated by its silicon layer. Additional Si adatoms in fourfold hollow sites form the c(2 X 2) periodicity. The second phase (600 degrees C) has a (2 root 2 X root 2)-R45 degrees periodicity. Here, the film is cracked and mixed with patches of clean (2 X 1)-Si(100), thus making the LEED pattern similar to a c(4 X 4) structure.
Keywords: low-energy electron diffraction (LEED); surface structure; surface relaxation and reconstruction; low index single crystal surfaces; epitaxy; solid phase epitaxy; silicon; cobalt; silicides

Coulomb effects in single-walled carbon nanotubes - Malic, Ermin; Hirtschulz, Matthias; Milde, Frank; Richter, Marten; Maultzsch, Janina; Reich, Stephanie; Knorr, Andreas (physica status solidi (b), 2008)
We present microscopic calculations of the excitonic absorption coefficient for single-wall carbon nanotubes. Our approach combines the density matrix formalism including the Coulomb and electron-light interaction with the tight-binding approximation. It allows the investigation of excitons in carbon nanotubes of arbitrary chiral index over a wide range of energy. We take all intra- and intersubband contributions into account and study the behavior of the Coulomb matrix elements for all relevant processes. The Coulomb interaction is found to decrease strongly with increasing momentum transfer perpendicular to the nanotube axis. Furthermore, we show that the band gap renormalization arising from the electron-electron interaction leads to a partial lifting of degeneracy in the spectra of zig-zag tubes. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Coulomb gap variable range hopping in graphitized polymer surfaces - Koval, Yury; Lazareva, Irina; Müller, Paul (Synthetic Metals, 2011)
The conductivity of several polymers was investigated after low-energy ion irradiation. The enhancement of conductance induced by the ions is discussed in terms of graphitization. We have found that the transport in the graphitized surfaces can be consistently described in terms of the 2D Coulomb gap variable range hopping theory. However, analyzing the properties of the pre-exponential factor in the temperature dependence of conductance and current-voltage characteristics we found several contradictions with existing theories. © 2011 Elsevier B.V.
Keywords: Graphitization; Ion irradiation; Polymers; Pre-exponential factor; Variable range hopping

Coulomb Interactions and the Spatial Coherence of Femtosecond Nanometric Electron Pulses - Meier, Stefan; Hommelhoff, Peter (ACS Photonics, 2022)
The transverse coherence of electrons is of utmost importance in high resolution electron microscopes, point-projection microscopes, low-energy electron microscopy, and various other applications. Pulsed versions of many of these have recently been realized, mostly relying on femtosecond laser-triggering electron emission from a sharp needle source. We here observe electron interference fringes and measure how the interference visibility becomes reduced as we increase the emitted electron bunch charge. Due to the extremely strong spatiotemporal confinement of the electrons generated here, we observe the visibility reduction already at average electron bunch charges of less than 1 electron per pulse, owing to the stochastic nature of the emission process. We can fully and quantitatively explain the loss of coherence based on model simulations. Via the van Cittert-Zernike theorem, we connect the visibility reduction to an increase in the effective source size. We conclude by discussing emittance, brightness, and quantum degeneracy, which have direct ramifications to many setups and devices relying on pulsed coherent electrons.
CRIS-Team Scopus Importer:2022-09-09
Keywords: Coherence; Electron correlations; Electron interference; Electron optics; Femtosecond lasers; Ultrafast electron emission

Coupled relaxation processes in a glass forming ZrTiNiCuBe liquid - Yang, Fan; Unruh, Tobias; Meyer, Andreas (EPL - Europhysics Letters, 2014)
We studied liquid Zr46.5Ti18.2Cu7.5Ni10Be27.5 in the temperature range from 1060 K to 1255 K using a combination of quasielastic neutron scattering and newly developed electrostatic levitation. We show that not only the microscopic incoherent and coherent relaxation times, and the derived mean self-diffusion coefficient of Ni/Cu/Ti, but also the macroscopic melt viscosity exhibit very similar temperature dependences. Thus, independent of the experimental time/length scales and the different natures of the relaxation times, the Maxwell relation of linear viscoelasticity holds, as a result of highly coupled structural relaxation processes in the melt. Copyright (C) EPLA, 2014

Coupled whispering gallery mode resonators in the Terahertz frequency range - Malzer, Stefan; Schwefel, Harald; Preu, Sascha; Döhler, Gottfried; Wang, Lijun; Hanson, Micah; Zimmerman, Jeremy; Gossard, Art (Optics Express, 2008)
We report on coupling of two whispering gallery mode resonators in the Terahertz frequency range. Due to the long wavelength in the millimeter to submillimeter range, the resonators can be macroscopic allowing for accurate size and shape control. This is necessary to couple specific modes of two or more resonators. Sets of polyethylene (PE) and quartz disk resonators are demonstrated, with medium (loaded) quality (Q)-factors of 40-800. Both exhibit coinciding resonance frequency spectra over more than ten times the free spectral range. Loading effects of single resonators are investigated which provide strong Q-factor degradation and red-shifts of the resonances in the 0.2% range. By coupling two resonators of the same size, we observe mode splitting, in very good agreement with our numerical calculations. © 2008 Optical Society of America.
Keywords: Terahertz; whispering gallery mode resonator

COUPLING OF IMAGE STATES TO QUANTUM-WELL STATES FOR AU ON PD(111) - Fauster, Thomas; et al. (Physical Review B, 1995)

Covalent Bisfunctionalization of Two-Dimensional Molybdenum Disulfide - Chen, Xin; Bartlam, Cian; Lloret Segura, Vicente Josep; Moses Badlyan, Narine; Wolff, Stefan; Gillen, Roland; Stimpel-Lindner, Tanja; Maultzsch, Janina; Duesberg, Georg S.; Knirsch, Kathrin; Hirsch, Andreas (Angewandte Chemie International Edition, 2021)
Covalent functionalization of two-dimensional molybdenum disulfide (2D MoS2) holds great promise in developing robust organic-MoS2 hybrid structures. Herein, for the first time, we demonstrate an approach to building up a bisfunctionalized MoS2 hybrid structure through successively reacting activated MoS2 with alkyl iodide and aryl diazonium salts. This approach can be utilized to modify both colloidal and substrate supported MoS2 nanosheets. We have discovered that compared to the adducts formed through the reactions of MoS2 with diazonium salts, those formed through the reactions of MoS2 with alkyl iodides display higher reactivity towards further reactions with electrophiles. We are convinced that our systematic study on the formation and reactivity of covalently functionalized MoS2 hybrids will provide some practical guidance on multi-angle tailoring of the properties of 2D MoS2 for various potential applications.
CRIS-Team WoS Importer:2021-05-14

Covalently Doped Graphene Superlattices: Spatially Resolved Supratopic- and Janus-Binding - Bao, Lipiao; Kohring, Malte; Weber, Heiko B.; Hauke, Frank; Hirsch, Andreas (Journal of the American Chemical Society, 2020)
Rational design and fabrication of graphene nanoarchitectures with multifunctionality and multidimensionality remains quite a challenge. Here, we present a synthetic sequence, based on the combination of two advanced patterned-functionalization principles, namely, laser-writing and poly(methyl methacrylate) (PMMA)-assisted lithographic processes, leading to unprecedented covalently doped graphene superlattices. Spatially resolved supratopic- and Janus-binding were periodically weaved on the graphene sheet, leading to four different types of zones with distinct chemical doping and structural properties. Notably, this is also the first realization of patterned Janus graphene. The elaborate chemical doping with micrometer resolution is unequivocally evidenced by scanning Raman spectroscopy (SRS) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). The design of the pattern as well as the degree of chemical doping on both opposite sides of graphene can be easily manipulated, rendering exciting potential for graphene nanosystems.
CRIS-Team Scopus Importer:2020-09-25

Covalent Patterning of 2D MoS2 - Chen, Xin; Kohring, Malte; Assebban, M'hamed; Tywoniuk, Bartlomiej; Bartlam, Cian; Moses Badlyan, Narine; Maultzsch, Janina; Duesberg, Georg S.; Weber, Heiko B.; Knirsch, Kathrin; Hirsch, Andreas (Chemistry - A European Journal, 2021)
The development of an efficient method to patterning 2D MoS2 into a desired topographic structure is of particular importance to bridge the way towards the ultimate device. Herein, we demonstrate a patterning strategy by combining the electron beam lithography with the surface covalent functionalization. This strategy allows us to generate delicate MoS2 ribbon patterns with a minimum feature size of 2 μm in a high throughput rate. The patterned monolayer MoS2 domain consists of a spatially well-defined heterophase homojunction and alternately distributed surface characteristics, which holds great interest for further exploration of MoS2 based devices.
CRIS-Team Scopus Importer:2021-08-13
Keywords: functionalization; MoS; patterning; PL; Raman spectroscopy

Covalent sidewall functionalization of SWNTs by nucleophilic addition of lithium amides - Syrgiannis, Zois; Hauke, Frank; Röhrl, Jonas; Hundhausen, Martin; Graupner, Ralf; Elemes, Yiannis; Hirsch, Andreas (European Journal of Organic Chemistry, 2008)
The synthesis and characterization of sidewall-functionalized SWNT derivatives (nPrNH)-SWNTs containing n-propylamine addends is reported. The nucleophilic addition of in situ generated lithium n-propylamide to the sidewall of SWNTs and the subsequent reoxidation of charged intermediates of the type (nPrNH)-SWNT- leads to carbon nanotube derivatives with covalently attached amino groups. Based on the reaction sequence, a homogeneous dispersion of the carbon nanotube material is achieved as a result of the electrostatic repulsion of negatively charged intermediates. The solubility of the resulting propylamine-functionalized (nPrNH) -SWNT material in organic solvents is drastically increased. The functionalized tubes were characterized in detail by Raman spectroscopy, thermogravimetric analysis (TGA/MS), X-ray photoelectron spectroscopy (XPS) and UV/Vis/NIR spectroscopy. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Cove-Edged Chiral Graphene Nanoribbons with Chirality-Dependent Bandgap and Carrier Mobility - Liu, Kun; Zheng, Wenhao; Osella, Silvio; Qiu, Zhen Lin; Böckmann, Steffen; Niu, Wenhui; Meingast, Laura; Komber, Hartmut; Obermann, Sebastian; Gillen, Roland; Bonn, Mischa; Hansen, Michael Ryan; et al. (Journal of the American Chemical Society, 2024)
Graphene nanoribbons (GNRs) have garnered significant interest due to their highly customizable physicochemical properties and potential utility in nanoelectronics. Besides controlling widths and edge structures, the inclusion of chirality in GNRs brings another dimension for fine-tuning their optoelectronic properties, but related studies remain elusive owing to the absence of feasible synthetic strategies. Here, we demonstrate a novel class of cove-edged chiral GNRs (CcGNRs) with a tunable chiral vector (n,m). Notably, the bandgap and effective mass of (n,2)-CcGNR show a distinct positive correlation with the increasing value of n, as indicated by theory. Within this GNR family, two representative members, namely, (4,2)-CcGNR and (6,2)-CcGNR, are successfully synthesized. Both CcGNRs exhibit prominently curved geometries arising from the incorporated [4]helicene motifs along their peripheries, as also evidenced by the single-crystal structures of the two respective model compounds (1 and 2). The chemical identities and optoelectronic properties of (4,2)- and (6,2)-CcGNRs are comprehensively investigated via a combination of IR, Raman, solid-state NMR, UV-vis, and THz spectroscopies as well as theoretical calculations. In line with theoretical expectation, the obtained (6,2)-CcGNR possesses a low optical bandgap of 1.37 eV along with charge carrier mobility of ∼8 cm2 V-1 s-1, whereas (4,2)-CcGNR exhibits a narrower bandgap of 1.26 eV with increased mobility of ∼14 cm2 V-1 s-1. This work opens up a new avenue to precisely engineer the bandgap and carrier mobility of GNRs by manipulating their chiral vector.
CRIS-Team Scopus Importer:2024-01-26

Coverage-Dependent Anchoring of 4,4 '-Biphenyl Dicarboxylic Acid to CoO(111) Thin Films - Mohr, Susanne; Schmitt, Tobias; Döpper, Tibor; Xiang, Feifei; Schwarz, Matthias; Görling, Andreas; Schneider, M. Alexander; Libuda, Jörg (Langmuir, 2017)
We investigated the adsorption behavior of 4,4'-biphenhyl dicarboxylic acid (BDA) on well-ordered CoO(111) films grown on Ir(100) as a function of coverage and temperature using time-resolved and temperature programmed infrared reflection absorption spectroscopy (TR-IRAS, TP-IRAS) in combination with density functional theory (DFT) and scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. To compare the binding behavior of BDA as a function of the oxide film thickness, three different CoO(111) film thicknesses were explored: films of about 20 bilayers (BLs) (approximately 5 nm), 2 BLs, and 1 BL. The two carboxylic acid groups of BDA offer two potential anchoring points to the oxide surface. At 150 K, intact BDA adsorbs on 20 BL thick oxide films in planar geometry with the phenyl rings aligned parallel to the surface. With decreasing oxide film thickness, we observe an increasing tendency for deprotonation and the formation of flat-lying BDA molecules anchored as dicarboxylates. After saturation of the first monolayer, intact BDA multilayers grow with molecules aligned parallel to the surface. The BDA multilayer desorbs at around 360 K. Completely different growth behavior is observed if BDA is deposited above the multilayer desorption temperature. Initially, doubly deprotonated dicarboxylates are formed by adopting a flat-lying,orientation. With increasing exposure, however, the adsorbate layer transforms into upright standing monocarboxylates. A sharp OH stretching band (3584 cm(-1)) and a blue-shifted CO stretching band (1759 cm(-1)) indicate weakly interacting apical carboxylic acid groups at the vacuum interface. The anchored monocarboxylate phase slowly desorbs in a temperature range of up to 470 K. At higher temperature, a flat-lying doubly deprotonated BDA is formed, which desorbs and decomposes in a temperature range of up to 600 K.

COVERAGE-DEPENDENT ELECTRONIC-STRUCTURE OF NA ON CU(111) - Fauster, Thomas; et al. (Surface Science, 1994)
The electronic states of Na on Cu(111) have been studied by high-resolution two-photon photoemission. Image states which are well separated from alkali states are observed at all coverages. An abrupt change of the occupancy of the alkali state is observed at coverages between 0.40 and 0.45 ML. We interpret this as the transition from a more ionic bonding of alkali atoms on the surface to the metallic bond in alkali islands. Other alkali metals on close-packed surfaces show a very similar electronic structure as a function of alkali coverage.

Coverage-Induced Chiral Transition of Co(II)-5,15-Diphenylporphyrin Self-Assemblies on Cu(111) - Xiang, Feifei; Schneider, M. Alexander (Journal of Physical Chemistry C, 2022)
Wallach's rule elucidates the phenomenon that racemic crystals are denser than their enantiopure form. The rule applies to most chiral molecular systems with the exception of some amino acids. However, it remains unclear whether Wallach's rule applies to the special but important class of chiral systems where chirality is induced by the adsorption of prochiral molecules on substrates. In this work, we show that the exemplary system, Cobalt(II)-diphenylporphyrin (Co-DPP) on Cu (111), follows Wallach's rule. Co-DPP assumes chiral isomers upon adsorption and shows a phase transition from an enantiopure linear chain structure to a racemic close-packed structure with increasing molecular density. Density functional theory (DFT) reveals that the chiral recognition, separation, and phase mixture of Co-DPP are due to the synergistic mechanism of substrate-molecule and molecule-molecule interactions.
CRIS-Team Scopus Importer:2022-05-13

Cross-Sectional Scanning Tunneling and Scanning Force Microscopy of Amorphous Hydrogenated Silicon pn-Doping-Superlattices in Nitrogen and Air - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Vacuum Science & Technology B: Microelectronics Processing and Phenomena, 1994)
UnivIS-Import:2015-03-05:Pub.1994.nat.dphy.IAP.exphys.crosss

Cross-sectional scanning-tunneling-spectroscopy of a-Si:H pn-doping superlattices - Hundhausen, Martin; Ley, Lothar; et al. (Superlattices and Microstructures, 1994)
The electronic properties of amorphous hydrogenated silicon (a-Si:H) pn-doping-superlattices are investigated by cross-sectional current imaging tunneling spectroscopy (CITS) using a scanning tunneling microscope in dry nitrogen ambient. In the constant current mode a contrast between n- and p-type layers is found. In addition, the spatially resolved normalized differential conductivity is measured for different bias voltages applied to the sample with respect to the STM tip. For small bias voltage at which tunneling occurs between the tip and gap-states of the amorphous superlattice a contrast between p-type and n-type doped layers is observed in the normalized differential conductivity. This is in agreement with the different densities of states available for tunneling between the STM and the differently doped layers. However, the contrast is almost missing if a larger voltage is applied, so that tunneling mainly occurs between tip and sample band-states.
UnivIS-Import:2015-03-05:Pub.1994.nat.dphy.IAP.exphys.crosss_7

Cryopreservation impairs 3-D migration and cytotoxicity of natural killer cells - Mark, Christoph; Czerwinski, Tina; Roessner, Susanne; Mainka, Astrid; Hörsch, Franziska; Heublein, Lucas; Winterl, Alexander; Sanokowski, Sebastian; Richter, Sebastian; Bauer, Nina; Angelini, Thomas E.; Schuler, Gerold; et al. (Nature Communications, 2020)
Natural killer (NK) cells are important effector cells in the immune response to cancer. Clinical trials on adoptively transferred NK cells in patients with solid tumors, however, have thus far been unsuccessful. As NK cells need to pass stringent safety evaluation tests before clinical use, the cells are cryopreserved to bridge the necessary evaluation time. Standard degranulation and chromium release cytotoxicity assays confirm the ability of cryopreserved NK cells to kill target cells. Here, we report that tumor cells embedded in a 3-dimensional collagen gel, however, are killed by cryopreserved NK cells at a 5.6-fold lower rate compared to fresh NK cells. This difference is mainly caused by a 6-fold decrease in the fraction of motile NK cells after cryopreservation. These findings may explain the persistent failure of NK cell therapy in patients with solid tumors and highlight the crucial role of a 3-D environment for testing NK cell function.
CRIS-Team Scopus Importer:2020-10-23

Cryopreservation reduces the Ability to migrate and the Cytotoxicity of natural Killer Cells in 3D: Possible Effects on cellular Immunotherapy - Mark, Christoph; Czerwinksi, T.; Roessner, S.; Mainka, Astrid; Hoersch, F.; Heublein, L.; Winterl, Alexander; Sanokowski, Sebastian; Richter, S.; Bauer, N.; Angelini, T.; Schuler, Gerold; et al. (JOURNAL DER DEUTSCHEN DERMATOLOGISCHEN GESELLSCHAFT, 2020)
CRIS-Team WoS Importer:2020-09-11

Crystallization and Organic Field-Effect Transistor Performance of a Hydrogen-Bonded Quaterthiophene - Gebers, Jan; Oezen, Bilal; Hartmann, Lucia; Schaer, Michel; Suarez, Stephane; Bugnon, Philippe; Scopelliti, Rosario; Steinrück, Hans-Georg; Konovalov, Oleg; Magerl, Andreas; Brinkmann, Martin; Petraglia, Riccardo; et al. (Chemistry - A European Journal, 2020)
Crystalline thin films of pi-conjugated molecules are relevant as the active layers in organic electronic devices. Therefore, materials with enhanced control over the supramolecular arrangement, crystallinity, and thin-film morphology are desirable. Herein, it is reported that hydrogen-bonded substituents serve as additional structure-directing elements that positively affect crystallization, thin-film morphology, and device performance of p-type organic semiconductors. It is observed that a quaterthiophene diacetamide exhibits a denser packing than that of other quaterthiophenes in the single-crystal structure and, as a result, displays enhanced intermolecular electronic interactions. This feature was preserved in crystalline thin films that exhibited a layer-by-layer morphology, with large domain sizes and high internal order. As a result, organic field-effect transistors of these polycrystalline thin films showed mobilities in the range of the best mobility values reported for single-crystalline quaterthiophenes. The use of hydrogen-bonded groups may, thus, provide an avenue for organic semiconducting materials with improved morphology and performance.
CRIS-Team WoS Importer:2020-07-31

Crystallization of micelles at chemically terminated interfaces - Hock, Rainer; et al. (Physical Review Letters, 2004)
In aqueous solutions and for high concentrations triblock copolymers are known to aggregate. As a critical volume fraction of micelles is reached they crystallize. We report on grazing incident small angle neutron scattering as an experimental tool to investigate the crystallization of spherical polymer micelles in the immediate vicinity of a flat solid interface. We find for an attractive surface potential a face centered close packed structure with a random orientation perpendicular to the normal of the interface. For a repulsive potential crystallization is suppressed.

Crystallographic structure and energetics of the Rh(100)-(3 x 1)-2O phase - Kißlinger, Tilman; Ferstl, Pascal; Schneider, M. Alexander; Hammer, Lutz (Journal of Physics: Condensed Matter, 2017)
In this study we investigate the crystallographic structure of the Rh(100)-(3 x 1)-2O phase by quantitative low energy electron diffraction (LEED) and scanning tunnelling microscopy as well as the energetics of the system applying density functional theory calculations (DFT). The (3 x 1) structure forms upon exposing the clean Rh(100) surface to 1200 L of oxygen at 520 K. A full-dynamical LEED intensity analysis (Pendry R-factor R = 0.095) reveals an oxygen-induced shifted row-reconstruction of the rhodium top layer where every third Rh-row is displaced by half a surface lattice parameter along the [011]-direction. There are two oxygen atoms within the unit cell which assume threefold coordinated sites on both sides of the shifted Rh-row with one bond to the shifted and two bonds to the unshifted rows. DFT calculations yield a total energy gain of 0.27 eV per oxygen atom compared to adsorption on the unreconstructed surface. This by far overcompensates the energetic penalty of 0.10 eV per oxygen atom for shifting the Rh-row and thus drives the substrate reconstruction. A coadsorption of oxygen at remaining regular sites of the substrate is not observed in experiment and is found to be energetically unfavorable.
Keywords: quantitative low energy electron diffraction; scanning tunneling microscopy; density functional theory; Rh(100); oxygen adsorption; surface oxide

Crystal-structure of active layers of small molecule organic photovoltaics before and after solvent vapor annealing - Berlinghof, Marvin; Langner, Stefan; Harreiß, Christina; Schmidt, Ella; Siris, Rita; Bertram, Florian; Shen, Chen; Will, Johannes; Schindler, Torben; Prihoda, Annemarie; Rechberger, Stefanie; Duesberg, Georg; et al. (Zeitschrift fur Kristallographie - Crystalline Materials, 2020)
It is demonstrated by a detailed structural analysis that the crystallinity and the efficiency of small molecule based organic photovoltaics can be tuned by solvent vapor annealing (SVA). Blends made of the small molecule donor 2,2′-[(3,3′″,3″″,4′-tetraoctyl[2,2′:5′,2″:5″,2′″:5′″,2″″-quinquethiophene]-5,5″″-diyl)bis[(Z)-methylidyne(3-ethyl-4-oxo-5,2-thiazolidinediylidene)]]bis-propanedinitrile (DRCN5T) and the acceptor [6,6]-phenyl C71 butyric acid methyl ester (PC 71 BM) were annealed using solvent vapors with either a high solubility for the donor (tetrahydrofuran), the acceptor (carbon disulfide) or both (chloroform). The samples were analyzed by grazing-incidence wide-angle X-ray scattering (GIWAXS), electron diffraction, X-ray pole figures, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). A phase separation of DRCN5T and PC 71 BM is induced by SVA leading to a crystallization of DRCN5T and the formation of a DRCN5T enriched layer. The DRCN5T crystallites possess the two dimensional oblique crystal system with the lattice parameters a = 19.2 Å, c = 27.1 Å, and β = 111.1° for the chloroform case. No major differences in the crystal structure for the other solvent vapors were observed. However, the solvent choice strongly influences the size of the DRCN5T enriched layer. Missing periodicity in the [010]-direction leads to the extinction of all Bragg reflections with k ≠ 0. The annealed samples are randomly orientated with respect to the normal of the substrate (fiber texture

Crystal structure of a new HfO(OH)(2) oxyhydroxide - Tarakina, N. V.; Tyutyunnik, A. P.; Baklanova, Ya. V.; Maksimova, L. G.; Denisova, T. A.; Neder, Reinhard (J C P D S-INT CENTRE DIFFRACTION DATA, 2013)
The crystal structure of a new hafnium oxyhydroxide obtained by an ion-exchange reaction from a Li2HfO3 precursor has been solved by a direct method and refined using Rietveld full profile fitting based on X-ray powder diffraction data. HfO(OH)(2) crystallizes in a P2(1)/c monoclinic unit cell (a = 5.5578(5) angstrom, b = 9.0701(10) angstrom, c = 5.7174(5) angstrom, beta = 119.746(5)degrees); its structure can be described as a framework formed by edge-sharing HfO6 octahedra connected to each other via vertices. In addition, an analysis of the atomic pair distribution function obtained using synchrotron radiation was used to confirm the model and to describe fine-structure features.
Keywords: hafnium oxyhydroxide; crystal structure; powder diffraction; pair distribution function

Cu2ZnSnS4 thin film solar cells from electroplated precursors: Novel low-cost perspective - Ennaoui, Ahmed, Prof. Dr.; Lux-Steiner, M.; Weber, A.; Abou-Ras, D.; Koetschau, I.; Schock, H. -W.; Schurr, R.; Hölzing, Astrid; Jost, Stefan Georg; Hock, Rainer; Voss, T.; Schulze, J.; et al. (ELSEVIER SCIENCE SA, 2009)
Thin-film solar cells based on Cu2ZnSnS4 (CZTS) absorbers were fabricated successfully by solid-state reaction in H2S atmosphere of electrodeposited Cu-Zn-Sn precursors. These ternary alloys were deposited in one step from a cyanide-free alkaline electrolyte containing Cu(II), Zn(II) and Sn(IV) metal salts on Mo-coated glass substrates. The solar cell was completed by a chemical bath-deposited US buffer layer and a sputtered i-ZnO/ZnO:Al bilayer. The best solar cell performance was obtained with Cu-poor samples. A total area (0.5 cm(2)) efficiency of 3.4% is achieved (V-oc=563 mV, j(sc)=14.8 mA/cm(2), FF=41%) with a maximum external quantum efficiency (EQE) of 80%. The estimated band-gap energy from the external quantum efficiency (EQE) measurements is about 1.54 eV. Electron backscatter-diffraction maps of cross-section samples revealed CZTS grain sizes of up to 10 mu m. Elemental distribution maps of the CZTS absorber show Zn-rich precipitates, probably ZnS, and a Zn-poor region, presumably Cu2SnS3, close to the interface Mo/CZTS. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: Electroplating; Precursor sulfurisation; Cu-poor; Cu2ZnSnS4; Solar-cell

Cu2ZnSn(S,Se)(4) solar cells processed by rapid thermal processing of stacked elemental layer precursors - Lechner, R.; Jost, S.; Palm, J.; Gowtham, M.; Sorin, F.; Louis, B.; Yoo, Hye Sun; Wibowo, Rachmat Adhi; Hock, Rainer (ELSEVIER SCIENCE SA, 2013)
In this contribution we report on the development of a two-step process for the formation of Cu2ZnSn(S, Se)(4) thin films for solar cells. The two-step formation process of the pentanary kesterite consists of (i) sputter deposition of the metals Cu, Zn and Sn followed by thermal evaporation of chalcogen and (ii) rapid thermal processing of the metal/ chalcogen precursors in chalcogen containing ambient. After the absorber formation process, solar cells were processed by deposition of CdS buffer, window layer and metal grid. We evaluated different metal precursor compositions in the ternary Cu-Zn-Sn metal systems regarding their behavior as appropriate precursors for the crystallization of Cu2ZnSn(S, Se)(4) absorbers. X-ray diffraction analyses show the presence of secondary chalcogenide phases in absorbers with Cu-poor composition. In combination with Raman spectroscopy, the efficient sulfoselenization could be demonstrated. A broad compositional region is found giving cell efficiencies above 6% via this process route and the potentials for further improvements are discussed. The best solar cell measured so far reached 6.6% efficiency on 1.34 cm(2) cell size. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: Cu2ZnSn(S; Se)(4); Kesterite; Sulfo-selenization; Solar cells

Curcumin-Containing Orthopedic Implant Coatings Deposited on Poly-Ether-Ether-Ketone/Bioactive Glass/Hexagonal Boron Nitride Layers by Electrophoretic Deposition - Virk, Ranjot; Ur Rehman, Muhammad Atiq; Munawar, Muhammad; Schubert, Dirk W.; Goldmann, Wolfgang; Dusza, Ján; Boccaccini, Aldo R. (Coatings, 2019)
Electrophoretic deposition (EPD) was used to produce a multilayer coatings system based on chitosan/curcumin coatings on poly-ether-ether-ketone (PEEK)/bioactive glass (BG)/hexagonal boron nitride (h-BN) layers (previously deposited by EPD on 316L stainless steel) to yield bioactive and antibacterial coatings intended for orthopedic implants. Initially, PEEK/BG/h-BN coatings developed on 316L stainless steel (SS) substrates were analyzed for wear studies. Then, the EPD of chitosan/curcumin was optimized on 316L SS for suspension stability, thickness, and homogeneity of the coatings. Subsequently, the optimized EPD parameters were applied to produce chitosan/curcumin coatings on the PEEK/BG/h-BN layers. The multilayered coatings produced by EPD were characterized in terms of composition, microstructure, drug release kinetics, antibacterial activity, and in vitro bioactivity. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) confirmed the deposition of chitosan/curcumin on the multilayer coating system. The release of curcumin upon immersion of multilayer coatings in phosphate-buffered saline (PBS) was confirmed by ultraviolet/visible (UV/VIS) spectroscopic analysis. The antibacterial effect of chitosan/curcumin as the top coating was determined by turbidity tests (optical density measurements). Moreover, the multilayer coating system formed an apatite-like layer upon immersion in simulated body fluid (SBF), which is similar in composition to the hydroxyapatite component of bone, confirming the possibility of achieving close bonding between bone and the coating surface.
Keywords: curcumin; chitosan; bioactive coatings; electrophoretic deposition; antibacterial coatings

Cu-releasing bioactive glass/polycaprolactone coating on Mg with antibacterial and anticorrosive properties for bone tissue engineering - Yang, Yuyun; Zheng, Kai; Liang, Ruifang; Mainka, Astrid; Taccardi, Nicola; Roether, Judith; Detsch, Rainer; Goldmann, Wolfgang; Virtanen, Sannakaisa; Boccaccini, Aldo R. (Biomedical Materials, 2017)
Copper (Cu)-containing bioactive glass nanoparticles (Cu-BGNs) were introduced in polycaprolactone (PCL) coating systems to improve the bioactivity, antibacterial property, and corrosion resistance of vulnerable magnesium matrices under physiological conditions. The influence of different amounts of Cu-BGNs in PCL coatings was thoroughly investigated determining the wettability, electrochemical properties, and antibacterial effects against Staphylococcus carnosus and Escherichia coli, as well as their cyto-compatibility. Cu-BGNs were observed randomly scattered in PCL coatings. Increasing concentration of Cu-BGNs resulted in slightly decreasing water contact angle, and reducing anti-corrosion properties of the Cu-BGNs composite coatings. Yet higher Cu-BGNs content in coatings led to more calcium phosphate formation on the surface after 7 days of immersion in DMEM, which was confirmed by FTIR and XPS. The growth of S. carnosus and E. coli was inhibited by Cu2+ ion released from Cu-BGN coatings. In addition, both direct and indirect cyto-compatibility experiments showed that the viability and proliferation of MG-63 cells on Cu-BGN coatings were highly increased compared to pure magnesium; however, an additional increase of Cu-BGNs concentration showed a slight decrease of cell proliferation and cell activity. In summary, Cu-BGN/PCL composite coatings impart magnesium-based biomaterials antibacterial and anticorrosive properties for clinical applications.
EVALuna2:13499

Current annealing and electrical breakdown of epitaxial graphene - Hertel, Stefan; Kißlinger, Ferdinand; Jobst, Johannes; Waldmann, Daniel; Krieger, Michael; Weber, Heiko B. (Applied Physics Letters, 2011)
We report on epitaxial graphene on silicon carbide at high current densities. We observe two distinguished regimes, and a final breakdown. First for low current densities the conductance is enhanced due to desorption of adsorbates. Second with increasing bias the sample locally starts to glow and is strongly heated. The silicon carbide material decomposes, graphitic material is formed and thus additional current paths are created. The graphene layer breaks down, which is, however, not visible in high bias data. The final breakdown is a self-amplifying process resulting in a locally destroyed sample but surprisingly with better conductance than the original sample. © 2011 American Institute of Physics.
UnivIS-Import:2015-04-14:Pub.2011.nat.dphy.IAP.LAP.curren

Current noise in single-molecule junctions induced by electronic-vibrational coupling - Schinabeck, Christian; Härtle, Rainer; Weber, Heiko B.; Thoss, Michael (Physical Review B, 2014)
The influence of multiple vibrational modes on current fluctuations in electron transport through single molecule junctions is investigated. Our analysis is based on a generic model of a molecular junction, which comprises a single electronic state on the molecular bridge coupled to multiple vibrational modes and fermionic leads, and employs a master equation approach. The results reveal that in molecular junctions with multiple vibrational modes, already weak to moderate electronic-vibrational coupling may result in high noise levels, especially at the onset of resonant transport, in accordance with the experimental findings of Secker et al. [Phys. Rev. Lett. 106, 136807 (2011)]. The underlying mechanisms are analyzed in some detail.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.LAP.curren

CuTe chains on Cu(111) by deposition of one-third of a monolayer of Te: Atomic and electronic structure - Kißlinger, Tilman; Raabgrund, Andreas; Geldiyev, Begmuhammet; Ammon, Maximilian Michael; Rieger, Janek; Hauner, Jonas; Hammer, Lutz; Fauster, Thomas; Schneider, M. Alexander (Physical Review B, 2020)
The surface atomic and electronic structure after deposition of one-third of a monolayer Te on Cu(111) was determined using a combination of low-energy electron diffraction (LEED), scanning tunneling microscopy and spectroscopy (STM/STS), angle-resolved single and two-photon photoelectron spectroscopy (ARPES /AR-2PPE), and density functional theory (DFT) calculations. Contrary to the current state in literature, Te does not create a two-dimensional surface alloy but forms Cu2Te2 adsorbate chains in a (2√3×√3)R30∘ superstructure. We establish this by a high-precision LEED-IV structural analysis with Pendry R factor of R=0.099 and corroborating DFT and STM results. The electronic structure of the surface phase is dominated by an anisotropic downward dispersing state at the Fermi energy EF and a more isotropic upward dispersing unoccupied state at E−EF=+1.43eV . Both states coexist with bulk states of the projected band structure, and are therefore surface resonance

Cutting and self-healing molecular wires studied by dynamic force microscopy - Kawai, Shigeki; Maier, Sabine; Glatzel, Thilo; Koch, Sascha; Such, Bartosz; Zimmerli, Lars; Fendt, Leslie A.; Diederich, François; Meyer, Ernst (Applied Physics Letters, 2009)
Tip-induced deformations of meso-(4-cyanophenyl)-substituted Zn(II) porphyrin molecular wires self-assembled on KBr(001) were studied by frequency modulation dynamic force microscopy. Since the wires are weakly bonded to the KBr substrate and to the neighboring molecules, they can easily be cut by the scanning tip. We found that the damaged molecular wires self-healed at room temperature.
Keywords: molecular electronics; organic compounds; self-assembly; wires (electric); zinc compounds

Cytoplasmic Water and Hydration Layer Dynamics in Human Red Blood Cells - Stadler, Andreas M.; Embs, Jan Peter; Digel, Ilya; Artmann, Gerhard; Unruh, Tobias; Büldt, Georg; Zaccai, Giuseppe (Journal of the American Chemical Society, 2008)
The dynamics of water in human red blood cells was measured with quasielastic incoherent neutron scattering in the temperature range between 290 and 320 K. Neutron spectrometers with time resolutions of 40, 13, and 7 ps were combined to cover time scales of bulk water dynamics to reduced mobility interfacial water motions. A major fraction of similar to 90% of cell water is characterized by a translational diffusion coefficient similar to bulk water. A minor fraction of similar to 10% of cellular water exhibits reduced dynamics. This slow water fraction was attributed to dynamically bound water on the surface of hemoglobin which accounts for approximately half of the hydration laye

Cytoskeletal mechanics in adherent human airway smooth muscle cells: probe specificity and scaling of protein-protein dynamics - Puig-de-Morales, Marina; Millet, Emil J.; Fabry, Ben; Navajas, Daniel; Wang, Ning; Butler, James P.; Fredberg, Jeffrey (American Journal of Physiology-Cell Physiology, 2004)

Cytoskeletal remodeling and slow dynamics in the living cell - Bursac, Predrag; Lenormand, Guillaume; Fabry, Ben; Oliver, Madavi; Weitz, David A.; Viasnoff, Virgile; Butler, James P.; Fredberg, Jeffrey (Nature Materials, 2005)
Forced and spontaneous motions of microbeads tightly bound to the cytoskeleton (CSK) of human muscle cells were analyzed. HASM cells in passages 6-7 were serum-deprived for 24 h; serum deprivation arrests the cell cylce in the G1/G00 phases. It was observed that these spontaneous bead motions reflecting nanoscale CSK arrangements depended on both the approach to glass transition and energy release due to ATP hydrolysis. The results show that the trapping, intermittency, and approach to kinetic arrest are mesoscale features of CSK protein-protein interaction that link integrative phenotypic functions to the molecular event
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.IAP.lpmt.cytosk

Cytoskeletal remodelling and slow dynamics in the living cell - Bursac, Predrag; Lenormand, Guillaume; Fabry, Ben; Oliver, Madavi; Weitz, David A.; Viasnoff, Virgile; Butler, James P.; Fredberg, Jeffrey (Nature Materials, 2005)

Cytoskeleton dynamics: Fluctuations within the network - Bursac, Predrag; Fabry, Ben; Trepat, Xavier; Lenormand, Guillaume; Butler, James P.; Wang, Ning; Fredberg, Jeffrey; An, Steven S. (Biochemical and Biophysical Research Communications, 2007)

Cytoskletal mechanics in adherent human airway smooth muscle cells: probe specificity and scaling of protein-protein dynamics - Puig-de-Morales, Marina; Millet, Emil J.; Fabry, Ben; Navajas, Daniel; Wang, Ning; Butler, James P.; Fredberg, Jeffrey (American Journal of Physiology-Cell Physiology, 2004)
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.IAP.lpmt.cytosk

Dark-Bright Soliton Bound States in a Microresonator - Zhang, Shuangyou; Bi, Toby; Ghalanos, George N.; Moroney, Niall P.; Del Bino, Leonardo; Del'Haye, Pascal (Physical Review Letters, 2022)
Dissipative Kerr solitons in microresonators have facilitated the development of fully coherent, chipscale frequency combs. In addition, dark soliton pulses have been observed in microresonators in the normal dispersion regime. Here, we report bound states of mutually trapped dark-bright soliton pairs in a microresonator. The soliton pairs are generated seeding two modes with opposite dispersion but with similar group velocities. One laser operating in the anomalous dispersion regime generates a bright soliton microcomb, while the other laser in the normal dispersion regime creates a dark soliton via Kerr-induced cross-phase modulation with the bright soliton. Numerical simulations agree well with experimental results and reveal a novel mechanism to generate dark soliton pulses. The trapping of dark and bright solitons can lead to light states with the intriguing property of constant output power while spectrally resembling a frequency comb. These results can be of interest for telecommunication systems, frequency comb applications, and ultrafast optics.
CRIS-Team WoS Importer:2022-02-11

Dark exciton-exciton annihilation in monolayer WSe2 - Erkensten, Daniel; Brem, Samuel; Wagner, Koloman; Gillen, Roland; Perea-Causin, Rauel; Ziegler, Jonas D.; Taniguchi, Takashi; Watanabe, Kenji; Maultzsch, Janina; Chernikov, Alexey; Malic, Ermin (Physical Review B, 2021)
The exceptionally strong Coulomb interaction in semiconducting transition-metal dichalcogenides (TMDs) gives rise to a rich exciton landscape consisting of bright and dark exciton states. At elevated densities, excitons can interact through exciton-exciton annihilation (EEA), an Auger-like recombination process limiting the efficiency of optoelectronic applications. Although EEA is a well-known and particularly important process in atomically thin semiconductors determining exciton lifetimes and affecting transport at elevated densities, its microscopic origin has remained elusive. In this joint theory-experiment study combining microscopic and material-specific theory with time- and temperature-resolved photoluminescence measurements, we demonstrate the key role of dark intervalley states that are found to dominate the EEA rate in monolayer WSe2. We reveal an intriguing, characteristic temperature dependence of Auger scattering in this class of materials with an excellent agreement between theory and experiment. Our study provides microscopic insights into the efficiency of technologically relevant Auger scattering channels within the remarkable exciton landscape of atomically thin semiconductors.
CRIS-Team WoS Importer:2022-01-07

Deactivation of nitrogen donors in silicon carbide - Schmid, Frank; Pensl, Gerhard; Bockstedte, Michel Georg; Mattausch, Alexander; Pankratov, Oleg; Ohshima, T.; Itoh, H.; Weber, Heiko B.; Reshanov, Sergey (Physical Review B, 2006)
Hexagonal SiC is either co-implanted with silicon (Si+), carbon (C+), or neon (Ne+) ions along with nitrogen (N+) ions or irradiated with electrons (e-) of 200 keV energy. During the subsequent annealing step at temperatures above 1450°C a deactivation of N donors and a reduction of the compensation are observed in the case of the Si+/N+ co-implantation and e- irradiation. The N donor deactivation is investigated as a function of the concentration of the co-implanted species and the annealing temperature. The formation of energetically deep defects is analyzed with deep level transient spectroscopy. A detailed theoretical analysis based on the density functional theory is conducted; it takes into account the kinetic mechanisms for the formation of N interstitial clusters and (N-vacancy) complexes. In accordance with all the experimental results, this analysis distinctly indicates that the (NC) 4 - VSi complex, which is thermally stable at high temperatures and which has no level in the band gap of 4H-SiC, is responsible for the N donor deactivation. © 2006 The American Physical Society.
UnivIS-Import:2015-04-14:Pub.2006.nat.dphy.IAP.LAP.deacti

Decay and dephasing of image-potential states due to surface defects and disorder - Weinelt, Martin; Reuss, Christian; Kutschera, Michael; Thomann, Ulrich; Shumay, Igor; Fauster, Thomas; Höfer, Ulrich; Theilmann, Florian; Goldmann, Albrecht (Applied Physics B-Lasers and Optics, 1999)
The dynamics of electrons in image-potential states has been studied by means of time- and energy-resolved two-photon photoemission. The loss of coherence in quantum-beat spectroscopy shows directly the influence of pure dephasing which can be determined also from the difference between the results of linewidth and decay rate measurements. We present several examples for the correlation of decay and dephasing with surface defects and disorder.

Deciphering the Role of Impurities in Methylammonium Iodide and Their Impact on the Performance of Perovskite Solar Cells - Levchuk, Ievgen; Hou, Yi; Gruber, Marco; Brandl, Marco; Herre, Patrick; Tang, Xiaofeng; Högl, Florian; Batentschuk, Miroslaw; Osvet, Andres; Hock, Rainer; Peukert, Wolfgang; Tykwinski, Rik; et al. (Advanced Materials Interfaces, 2016)
Solution-based perovskite solar cell fabrication typically involves rather complex processing sequences to yield highest performance. While most studies concentrate on the exploration of processing conditions, the purity levels of common perovskite precursor solutions have been investigated and a number of impurities that are critically important toward controlling the crystallization of perovskites are found. In this study, an in-depth chemical study of the possible impurities formed during CHNHI preparation is presented and their relevance on solar cell processing is revealed. A primary consideration is the chemical transformation of hypophosphorous acid, which plays the role of the stabilizer for HI. The detrimental role of the impurities is best demonstrated by comparing perovskite solar cell devices fabricated from impurity-free precursors versus precursors containing different concentrations of impurities. Most interestingly, it is revealed that a certain concentration of impurities is detrimental to the growth of large-grained crystals. PbHPO nanoparticles, which are formed after hypophosphorous acid transformation, actually cause crystal domain growth through serving as a nucleation center. This study gives valuable insight into the rate determining steps of perovskite crystal growth and further provides the basis for developing reliable and reproducible high-performance recipes for perovskite solar cell processing.
Keywords: Grain size; Impurities; Perovskites; Seed growth; Solar cells

DECONVOLUTION OF APPEARANCE POTENTIAL SPECTRA-II - Fauster, Thomas; et al. (Applied physics, 1979)

Decoupling the Graphene Buffer Layer SiC(0001) via Interface Oxidation - Ostler, Markus; Koch, Roland; Speck, Florian; Fromm, Felix; Vita, Hendrik; Hundhausen, Martin; Horn, Karsten; Seyller, Thomas (Materials Science Forum, 2012)
Epitaxial graphene (EG) grown on SiC(0001) resides on the so-called buffer layer. This carbon rich (6√3×6√3)R30® reconstruction is covalently bound to the topmost silicon atoms of the SiC. Decoupling the graphene buffer layer from the SiC interface is a well studied topic since successful intercalation has been shown for hydrogen [1-3]. Recently, intercalation was also shown for oxygen [4, 5]. We present angle-resolved photoemission spectroscopy (ARPES), x-ray induced photoelectron spectroscopy (XPS) and Raman spectroscopy studies to determine the quality of oxygen intercalated buffer layer samples in terms of decoupling and integrity of the transformed graphene layer. The decoupling effect is demonstrated by ARPES measurements showing a graphene-like π band. XPS shows whether the oxidation takes place in the buffer layer or at the interface. Raman spectroscopy is well suited to investigate oxygen induced defects in graphene-like material. © (2012) Trans Tech Publications.
UnivIS-Import:2015-03-09:Pub.2012.nat.dphy.IAP.exphys.decoup
Keywords: ARPES; Graphene; Intercalation; Oxidation; Raman spectroscopy; Si-face; XPS

Defect crystal structure of new TiO(OH)(2) hydroxide and related lithium salt Li2TiO3 - Tarakina, Nadezda V.; Neder, Reinhard; Denisova, Tatyana A.; Maksimova, Lidiya G.; Baklanova, Yana V.; Tyutyunnik, Alexander P.; Zubkov, Vladimir G. (Dalton Transactions, 2010)
Crystal structures of TiO(OH)(2) and Li2TiO3 have been studied in detail and refined using X-ray powder diffraction data. Both compounds possess a high concentration of defects in the structure. The crystal structure of the Li2TiO3 salt obtained at 700 degrees C reveals stacking faults of LiTi2 metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3(1)12. The possibility to stabilise this imperfect state increases the mobility of the Li+ ions in the structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)(2). The crystal structure of TiO(OH)(2) belongs to the layered double hydroxide structure type with the 3R(1) sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)(2)OTi2O(OH)(2)]. TiO(OH)(2) is the first layered double hydroxide structure formed by a cation with oxidation state +4 only.

Defect densities inside the conductive filament of RRAMs - Robertson, John; Gillen, Roland (Microelectronic Engineering, 2013)
Keywords: Oxygen vacancies; Conductive filament; Theory; RRAM

Defect Spectroscopy and Determination of the Electron Diffusion Length in Single Crystal Diamond by Total Photoelectron Yield Spectroscopy - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review Letters, 1997)
Novel photoelectron yield experiments performed with a dynamical range of 8 orders of magnitude reveal a new excitation channel for electron emission on diamond (100) and (111) surfaces with negative electron affinity which is due to defect states 2.0 and 4.1 eV below the conduction hand minimum. Analyzing the competition of free conduction band electrons excited out of defects and excitons with respect to final photoelectron production we determine that the electron diffusion length in p-type IIb diamond is between 150 and 250 μm.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.IAP.exphys.defect

Defect spectroscopy in a-Si:H using infrared excited luminescence and electron spin resonance - Ristein, Jürgen; et al. (Journal of Non-Crystalline Solids, 1989)
Defect spectroscopy with IR light of 1.17 eV photon energy surprisingly contradicts the commonly accepted assumption that singly occupied dangling bond states, D0, comprise the dominant deep defects in undoped a-Si:H films. Instead, evidence for a large concentration of diamagnetic states in dark equilibrium is found. They are at least three times more than the D0 states seen by dark ESR. D- states, possibly associated with the quartz interface of the films, are likely candidates for these defect states. © 1989.
UnivIS-Import:2015-03-05:Pub.1989.nat.dphy.IAP.exphys.defect

Defect States in a-Si:Nx:H - Hundhausen, Martin (Journal of Non-Crystalline Solids, 1983)
UnivIS-Import:2015-03-05:Pub.1983.nat.dphy.IAP.exphys.defect

Defect Structures in Neutron Irradiated 6H-SiC Studied by X-Ray Diffraction Line Profile Analysis - Magerl, Andreas; Hock, Rainer; et al. (Materials Research Society Symposium - Proceedings, 2001)
We have investigated by x-ray diffraction defect structures in 6H-SiC after neutron irradiation with different fluences and followed by different annealing procedures. An interpretation along a model of Klimanek [1,4-6] shows, that higher fluences lead to a stronger than linear reduction of the correlation length, whereas higher annealing temperatures correlate with a better recovery of the correlation length. In addition defects of 1st kind created by irradiation are reduced by annealing. We find that annealing changes the character of the defects and it accentuates a defect structure already present in the original samples.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.LK.defect

Degree of functionalisation dependence of individual Raman intensities in covalent graphene derivatives - Vecera, Philipp; Eigler, Siegfried; Kolesnik-Gray, Maria; Krstic, Vojislav; Vierck, Asmus; Maultzsch, Janina; Schafer, R; Hauke, Frank; Hirsch, Andreas (Scientific Reports, 2017)
Covalent functionalisation of graphene is a continuously progressing field of research. The optical properties of such derivatives attract particular attention. In virtually all optical responses, however, an enhancement in peak intensity with increase of sp3 carbon content, and a vanishing of the peak position shift in monolayer compared to few-layer systems, is observed. The understanding of these seemingly connected phenomena is lacking. Here we demonstrate, using Raman spectroscopy and in situ electrostatic doping techniques, that the intensity is directly modulated by an additional contribution from photoluminescent p-conjugated domains surrounded by sp3 carbon regions in graphene monolayers. The findings are further underpinned by a model which correlates the individual Raman mode intensities to the degree of functionalisation. We also show that the position shift in the spectra of solvent-based and powdered functionalised graphene derivatives originates predominantly from the presence of edge-to-edge and edge-to-basal plane interactions and is by large functionalisation independent.

Dehydrative pi-extension to nanographenes with zig-zag edges - Lungerich, Dominik; Papaianina, Olena; Feofanov, Mikhail; Liu, Jia; Devarajulu, Mirunalini; Troyanov, Sergey; Maier, Sabine; Amsharov, Konstantin (Nature Communications, 2018)
Zig-zag nanographenes are promising candidates for the applications in organic electronics due to the electronic properties induced by their periphery. However, the synthetic access to these compounds remains virtually unexplored. There is a lack in efficient and mild strategies origins in the reduced stability, increased reactivity, and low solubility of these compounds. Herein we report a facile access to pristine zig-zag nanographenes, utilizing an acid-promoted intramolecular reductive cyclization of arylaldehydes, and demonstrate a three-step route to nanographenes constituted of angularly fused tetracenes or pentacenes. The mild conditions are scalable to gram quantities and give insoluble nanostructures in close to quantitative yields. The strategy allows the synthesis of elusive low bandgap nanographenes, with values as low as 1.62 eV. Compared to their linear homologues, the structures have an increased stability in the solid-state, even though computational analyses show distinct diradical character. The structures were confirmed by X-ray diffraction or scanning tunneling microscopy.

Dehydrogenation and the surface phase transition on diamond (111): kinetics and electronic structure - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review B, 1999)
The (1×1) to (2×1) surface phase transition of the hydrogen-covered diamond (111) surface is investigated by core level spectroscopy, low-energy electron diffraction, and measurements of the electron affinity. The latter method is shown to be a reliable measure of the hydrogen coverage. Prolonged annealing of the surface at 1000 K converts the hydrogen-terminated (1×1) structure with an electron affinity of -1.27 eV to a hydrogen-free (2×1) reconstruction, increases the separation of valence-band maximum from the Fermi level EF from 0.68 to 0.88 eV, and results in a positive electron affinity of +0.38 eV. Annealing the surface at high temperature (up to 1400 K) yields the same (2×1) surface structure albeit with an increase in the separation of the valence-band maximum from EF to 1.42 eV and a positive electron affinity of 0.8 eV which is associated with a partial surface graphitization. An analysis of the kinetics of the thermally induced hydrogen desorption yields an activation energy of 1.25±0.2eV. It was found that hydrogen desorption and reconstruction are surface phase transitions which are not directly linked. Instead, an intermediate phase with a high concentration of dangling bonds (up to 70%) is observed. The (1×1) to (2×1) phase transition is phenomenologically well described by a first-order transition provided a critical density of dangling bonds of about 70% is included in the analysis in such a way that the rate constant for reconstruction vanishes below that value. © 1999 The American Physical Society.
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.IAP.exphys.dehydr