Hybrid functional calculations of the Al impurity in α quartz: Hole localization and electron paramagnetic resonance parameters - Gillen, Roland; Robertson, John (Physical Review B - Condensed Matter and Materials Physics, 2012)

Hybridized intervalley moiré excitons and flat bands in twisted WSe2 bilayers - Brem, Samuel; Lin, Kai Qiang; Gillen, Roland; Bauer, Jonas M.; Maultzsch, Janina; Lupton, John M.; Malic, Ermin (Nanoscale, 2020)
The large surface-to-volume ratio in atomically thin 2D materials allows to efficiently tune their properties through modifications of their environment. Artificial stacking of two monolayers into a bilayer leads to an overlap of layer-localized wave functions giving rise to a twist angle-dependent hybridization of excitonic states. In this joint theory-experiment study, we demonstrate the impact of interlayer hybridization on bright and momentum-dark excitons in twisted WSe2 bilayers. In particular, we show that the strong hybridization of electrons at the Λ point leads to a drastic redshift of the momentum-dark K-Λ exciton, accompanied by the emergence of flat moiré exciton bands at small twist angles. We directly compare theoretically predicted and experimentally measured optical spectra allowing us to identify photoluminescence signals stemming from phonon-assisted recombination of layer-hybridized dark excitons. Moreover, we predict the emergence of additional spectral features resulting from the moiré potential of the twisted bilayer lattice.
CRIS-Team Scopus Importer:2020-06-05

Hybrid Moiré Excitons and Trions in Twisted MoTe2-MoSe2 Heterobilayers - Zhao, Shen; Huang, Xin; Gillen, Roland; Li, Zhijie; Liu, Song; Watanabe, Kenji; Taniguchi, Takashi; Maultzsch, Janina; Hone, James; Högele, Alexander; Baimuratov, Anvar S. (Nano Letters, 2024)
We report experimental and theoretical studies of MoTe2-MoSe2 heterobilayers with rigid moiré superlattices controlled by the twist angle. Using an effective continuum model that combines resonant interlayer electron tunneling with stacking-dependent moiré potentials, we identify the nature of moiré excitons and the dependence of their energies, oscillator strengths, and Landé g-factors on the twist angle. Within the same framework, we interpret distinct signatures of bound complexes among electrons and moiré excitons in nearly collinear heterostacks. Our work provides a fundamental understanding of hybrid moiré excitons and trions in MoTe2-MoSe2 heterobilayers and establishes the material system as a prime candidate for optical studies of correlated phenomena in moiré lattices.
CRIS-Team Scopus Importer:2024-04-19
Keywords: hybridization; moiré excitons; moiré potential; transition metal dichalcogenides; two-dimensional semiconductors; van der Waals heterostructures

Hydration dependent studies of highly aligned multilayer lipid membranes by neutron scattering - Trapp, Marcus; Gutberlet, Thomas; Juranyi, Fanni; Unruh, Tobias; Demé, Bruno; Tehei, Moeava; Peters, Judith (Journal of Chemical Physics, 2010)
We investigated molecular motions on a picosecond timescale of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) model membranes as a function of hydration by using elastic and quasielastic neutron scattering. Two different hydrations corresponding to approximately nine and twelve water molecules per lipid were studied, the latter being the fully hydrated state. In our study, we focused on head group motions by using chain deuterated lipids. Information on in-plane and out-of-plane motions could be extracted by using solid supported DMPC multilayers. Our studies confirm and complete former investigations by Konig et al. [J. Phys. II (France) 2, 1589 (1992)] and Rheinstadter et al. [Phys. Rev. Lett. 101, 248106 (2008)] who described the dynamics of lipid membranes, but did not explore the influence of hydration on the head group dynamics as presented here. From the elastic data, a clear shift of the main phase transition from the P-beta ripple phase to the L-alpha liquid phase was observed. Decreasing water content moves the transition temperature to higher temperatures. The quasielastic data permit a closer investigation of the different types of head group motion of the two samples. Two different models are needed to fit the elastic incoherent structure factor and corresponding radii were calculated. The presented data show the strong influence hydration has on the head group mobility of DMPC. (C) 2010 American Institute of Physics. [doi:10.1063/1.3495973]

Hydrodynamic thickening of lubricating fluid layer beneath sliding mesothelial tissues - Lin, Judy L.; Moghani, Taraneh; Fabry, Ben; Butler, James P.; Loring, Steven H. (Journal of Biomechanics, 2008)

Hydrogenated anatase TiO2 single crystals: defects formation and structural changes as microscopic origin of co-catalyst free photocatalytic H2 evolution activity - Will, Johannes; Wierzbicka, Ewa; Wu, Mingjian; Götz, Klaus; Yokosawa, Tadahiro; Liu, Ning; Tesler, Alexander; Stiller, Markus; Unruh, Tobias; Altomare, Marco; Schmuki, Patrik; Spiecker, Erdmann (Journal of Materials Chemistry A, 2021)
Herein we systematically investigate the influence of hydrogenation time and temperature on defects formation, structural changes, and co-catalyst free photocatalytic activity for epitaxially grown anatase thin films on strontium titanate single crystals. The photocatalytic activity trend of the anatase epi layers is similar to that of anatase powders and brookite single crystals in reported recent literature, that is, the H2 evolution rate exhibits a typical maximum upon hydrogenation under moderate annealing temperatures (500 °C). By combining surface sensitive X-ray diffraction methods and analytical high-resolution electron microscopy techniques we reveal quantitatively the oxygen loss from the epi-layer ascribed to the hydrogenation (H2 reduction) treatment. We observe specific physicochemical changes associated with the introduction of oxygen vacancies: (i) the formation of a nanoscale strained crystal surface, (ii) the agglomeration of point defects in the bulk of the anatase epi layer, and (iii) a transition towards a Ti2O3 like symmetry at the film surface, i.e. an evident oxygen deficiency at the epi layer surface in particular prominent for the most active sample as a function of the hydrogenation parameters. These extensive experimental findings allow us to propose an empirical model, which links detrimental and beneficial effects of Ti3+ centers and oxygen vacancies in the bulk and at the surface and their abundance to an optimum point defect configuration for water splitting via “grey” anatase.

Hydrogenation of 6H-SiC as a Surface Passivation Stable in Air - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 2001)
We have terminated the hexagonal (0001) and (0001̄) surfaces of 6H-SiC with a monolayer of hydrogen by exposing the SiC crystal to pure hydrogen at elevated temperatures. The surfaces exhibit sharp, background-free, and unreconstructed LEED patterns and the photoemission spectra show only bulk-related Si and C components and give no indication of additional unwanted absorbates. On the Si-terminated (0001) surface, a sharp doublet at 2130 cm -1 with a splitting of 6 cm -1 is observed in surface-sensitive infrared spectroscopy, which is due to monohydride Si-H stretching modes. The origin of the splitting is discussed. The hydrogenated surfaces are passivated chemically and electronically. The oxygen uptake is less than 2 at.% after 2 h air exposure without any sign of Si-O or C-O bond formation. The surface Fermi level is unpinned and exhibits its bulk position on n- and p-type samples. © 2001 Elsevier Science B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.hydrog
Keywords: Carbide (SiC); Chemical passivation; Electronic passivation; Hydrogen termination

Hydrogen bonding analysis in amorphous hydrogenated carbon by a combination of infrared absorption and thermal effusion experiments - Ristein, Jürgen; Ley, Lothar; et al. (Journal of Non-Crystalline Solids, 1996)
A detailed analysis of the bonding configurations of hydrogen in amorphous carbon has been performed by measuring infrared (IR) absorption spectra and mass separated thermal effusion transients on a series of a-C:H samples deposited under self bias potentials of the substrate electrode between 0 and -1000 V. The C-H stretching as well as the bending modes of the IR absorption spectra were analysed quantitatively using IR absorption cross-sections of organic molecules for the various vibrational modes. Thermal effusion from the same samples was monitored with a quadrupole mass analyser recording eighteen relevant masses between 1 and 44 amu simultaneously and comparing the observed fragmentation patterns quantitatively with those of H2, CH4, C2H4, C2H6, C3H6 and C3H8 as calibration gases.
UnivIS-Import:2015-04-14:Pub.1996.nat.dphy.IAP.exphys.hydrog

Hydrogen-terminated diamond electrodes: I. Charges, potentials, energies - Ristein, Jürgen; Zhang, Wenying; Ley, Lothar (Physical Review E, 2008)
Hydrogen-terminated intrinsic diamond is a most unusual insulator since in contact with air or electrolyte it develops a hole accumulation layer just below the surface. When immersed in electrolyte the hole concentration responds to ionic charges and potentials and this response can be monitored by measuring the conductance of the hole accumulation layer without interference form the bulk conductivity. This feature has been widely used for chemical sensors in the form of solution-gate field effect transistors (SGFET). Here we analyze the charge and the potential profiles in the diamond and the electrolyte, as well as the static differential capacitance of the diamond electrode under controlled potential conditions. From this analysis we derive expressions for the transfer characteristics of diamond-based SGFET's that faithfully describe experimental data presented here as well. This holds in particular for the threshold region of the transfer characteristics that can only be modeled if the unusual semiconducting properties of the diamond electrode are taken into account properly. From fits to our data we derive (among other things) a value of χ=-0.50±0.02 eV for the electron affinity of the hydrogen-terminated diamond surface in contact with aqueous electrolyte. © 2008 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2008.nat.dphy.IAP.exphys.hydrog

Hydrogen-terminated diamond electrodes: II. Redox activity - Zhang, Wenying; Ristein, Jürgen; Ley, Lothar (Physical Review E, 2008)
One of the most attractive features of diamond is its robust p -type surface conductivity that develops spontaneously under atmospheric conditions on hydrogen-terminated samples. An electrochemical charge transfer between diamond and an air-borne redox couple has been suggested to be responsible for the spontaneous appearance of surface-near holes. We present direct proof for the redox activity of the diamond surface by measuring pH -dependent open circuit potentials and quasistatic polarization curves for hydrogen-terminated and partially oxidized diamond electrodes. Under open circuit conditions we find in fact a mixed (or corrosion) potential that is consistent with the simultaneous equilibriation of the electrode versus both the hydrogen-hydronium and the oxygen-hydroxyl redox couple. Our data show extremely long-time constants for establishing the redox equilibrium and very low exchange current densities making the identification and characterization of the redox process a demanding experimental task. © 2008 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2008.nat.dphy.IAP.exphys.hydrog_1

Hydrogen termination and electron emission from CVD diamond surfaces: a combined SEM, PEEM, photoelectron yield, and field emission study - Ley, Lothar; Ristein, Jürgen; Stammler, Martin; et al. (Diamond and Related Materials, 2000)
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.IAP.exphys.hydrog

Identification of carbon interstitials in electron irradiated 6H-SiC by use of a 13C enriched specimen - Ley, Lothar; Hundhausen, Martin; et al. (Physical Review B, 2002)
Samples of 6H-SiC have been electron-irradiated with electron energies in the range 100-300 keV in a transmission electron microscope. After irradiation the samples were transferred to microscopic low-temperature photoluminescence spectrometers and excited by 325-nm, 488-nm, and 514.5-nm lasers. Optical centers were observed that had high-energy local modes and, when samples that had been enriched with 13C during growth were examined, these local modes were split into triplets. The observations are interpreted as C-C dumb bells created from C interstitials generated during the irradiation process. This is the reported identification of self-interstitial atoms by photoluminescence in SiC.
UnivIS-Import:2015-04-14:Pub.2002.nat.dphy.IAP.LAP.identi

Identification of DAPK as a scaffold protein for the LIMK/cofilin complex in TNF-induced apoptosis - Ivanovska, Jelena; Tregubova, Alexandra; Mahadevan, Vijayalakshmi; Chakilam, Saritha; Gandesiri, Muktheshwar; Benderska, Natalya; Ettle, Benjamin; Hartmann, Arndt; Söder, Stephan; Ziesche, Elisabeth; Fischer, Thomas; Lautscham, Lena; et al. (International Journal of Biochemistry and Cell Biology, 2013)
The role of cytoskeleton-associated proteins during TNF-induced apoptosis is not fully understood. A potential candidate kinase that might connect TNF signalling to actin reorganization is the death-associated protein kinase (DAPK). To identify new DAPK interaction partners in TNF-induced apoptosis, we performed a peptide array screen. We show that TNF-treatment enhanced the phosphorylation of LIMK at threonine508 and its downstream target cofilin at serine3 (p-cofilin(Ser3)). Modulation of DAPK activity and expression by DAPK inhibitor treatment, siRNA knockdown, and overexpression affected the phosphorylation of both proteins. We propose a 3D structural model where DAPK functions as a scaffold for the LIMK/cofilin complex and triggers a closer interaction of both proteins under TNF stimulation. Upon TNF a striking redistribution of LIMK, DAPK, and cofilin to the perinuclear compartment was observed. The pro-apoptotic DAPK/LIMK/cofilin multiprotein complex was abrogated in detached cells, indicating that its signaling was no longer needed if cells committed to apoptosis. P-cofilin(Ser3) was strongly accumulated in cells with condensed chromatin, pronounced membrane blebs and Annexin V up-regulation. From studying different cofilin(Ser3) mutants we suggest that p-cofilin(Ser3) is an indicator of TNF-induced apoptosis. Collectively, our findings identify a novel molecular cytoskeleton-associated mechanism in TNF-induced DAPK-dependent apoptosis.

Image-potential-induced surface state at Si(100) - Kutschera, Michael; Weinelt, Martin; Rohlfing, M; Fauster, Thomas (Applied Physics A-Materials Science & Processing, 2007)
We have identified a surface state on Si(100) (2x1) at a binding energy of 0.69 +/- 0.05 eV with respect to the vacuum level. Band-structure calculations within the GW method reveal that almost 80% of the probability density of the resonance is located in front of the surface. We therefore assign the surface resonance to an image-potential state. It has a lifetime of about 10 fs and contributes significantly to two-photon photoemission from Si(100

Image-potential states and work function of graphene - Niesner, Daniel; Fauster, Thomas (Journal of Physics: Condensed Matter, 2014)
Image-potential states of graphene on various substrates have been investigated by two-photon photoemission and scanning tunneling spectroscopy. They are used as a probe for the graphene-substrate interaction and resulting changes in the (local) work function. The latter is driven by the work function difference between graphene and the substrate. This results in a charge transfer which also contributes to core-level shifts in x-ray photoemission. In this review article, we give an overview over the theoretical models and the experimental data for image-potential states and work function of graphene on various substrates.
Keywords: work function; graphene; image-potential states

Image potential states as a quantum probe of graphene interfaces - Bose, Sangita; Silkin, V. M.; Ohmann, Robin; Brihuega, Ivan; Vitali, Lucia; Michaelis, Christian; Mallet, P.; Veuillen, J.Y.; Schneider, M. Alexander; Chulkov, E. V.; Echenique, P. M.; Kern, Klaus (New Journal of Physics, 2010)
Image potential states (IPSs) are electronic states localized in front of a surface in a potential well, formed by the surface projected bulk band gap on one side and the image potential barrier on the other. In the limit of a two-dimensional solid, a double Rydberg series of IPSs has been predicted, which is in contrast to a single series present in three-dimensional solids. Here, we confirm this prediction experimentally for mono- and bilayer graphene. The IPSs of epitaxial graphene on SiC are measured by scanning tunneling spectroscopy and the results are compared with ab-initio band structure calculations. Despite the presence of the substrate, both calculations and experimental measurements show that the first pair of the double series of IPSs survives and eventually evolves into a single series for graphite. Thus, IPSs provide an elegant quantum probe of the interfacial coupling in graphene systems.

Image-potential states of graphene on noble-metal surfaces - Nobis, David; Potenz, Marco Adolf; Niesner, Daniel; Fauster, Thomas (Physical Review B, 2013)
Time-, angle-, and energy-resolved two-photon photoelectron spectroscopy is used to study image-potential states of weakly bound monolayer graphene on the noble-metal surfaces Pt(111), Au/Ir(111), Au/Ni(111), and Ir(100). Binding energies are increased relative to the substrates, and lifetimes are similar for all systems under investigation. The properties of the image-potential states are mainly determined by the graphene layer with reduced influence of the substrate. Substrate-related occupied surface states close to the Fermi level are observed for graphene on fcc(111) substrates.

Image-potential states on bcc (110) surfaces of iron and tungsten - Thomann, Ulrich; Reuss, Christian; Fauster, Thomas; et al. (Physical Review B, 2000)
Image-potential states have been measured for W(110) and for bce Fe(110) films on W(110) and Cu(100) substrates. Energies and linewidths are reported and for the W(110) substrate an unusually small effective mass of 0.5m(e) is found. For Fe(110), the majority and minority spin contributions were separated using polarization-dependent two-photon photoemission without magnetizing the sample.

Image-potential states on stepped Cu (001) surfaces - Roth, Manfred; Pickel, Martin; Wang, Jinxiong; Weinelt, Martin; Fauster, Thomas (Applied Physics B-Lasers and Optics, 2002)
Image-potential states on Cu (117) and Cu (119) surfaces were studied by means of two-photon photoelectron spectroscopy. The regular array of steps generates a lateral potential on the vicinal surfaces, which modifies the surface-electronic structure. Compared to Cu(001), the band bottom of the n = 1 image-potential states shifts by 40 meV to lower binding energy. The periodicity of the step-induced superlattice manifests itself as back-folding of the n = 1 and 2 dispersion bands. At the surface Brillouin zone boundary a mini-gap opens with a width of 135 meV for the first image-potential state on Cu (117). On the vicinal surfaces the lifetime of the image-potential states is reduced by a factor of three as compared to Cu (001). This is attributed to a narrowing of the surface-projected bulk-band gap when projected along the [I In] direction. While the dephasing rate of the first image-potential state is close to the decay rate, higher members of the Rydberg-like series show negligible dephasing.

IMAGE STATES AND LOCAL WORK FUNCTION FOR AG/PD(111) - Fauster, Thomas; et al. (Physical Review Letters, 1993)
Two-photon photoemission spectroscopy was employed for an investigation of the image states on Pd(111) with various coverages of Ag. Image states from areas with different thicknesses of the Ag layer can be observed simultaneously. This proves the applicability of the concept of a local work function. The decay length of the wave function of the image state on Ag(111) into the metal was determined experimentally to be 7.6 +/- 1.2 angstrom, and the probability to find the electron in the metal is estimated as 10%.

IMAGE STATES AND THE PROPER WORK FUNCTION FOR A SINGLE LAYER OF NA AND K ON CU(111), CO(0001), AND FE(110) - Fauster, Thomas; et al. (Physical Review B, 1993)
High-resolution photoemission and two-photon photoemission spectroscopy have been used for a comparative study of the electronic structure of a single layer of Na and K on Cu(111), Co(0001), and Fe(110). All systems under investigation exhibit an occupied alkali-induced state near the Fermi energy as well as a series of unoccupied states converging toward the vacuum energy, which are identified as image-potential states. For Na (K) on any of the substrates we find the lowest image state to be located at an energy of 2.04+/-0.03 eV (1.62+/-0.03 eV) above the Fermi level. From this and from the convergence behavior of the image-state series we conclude that the work function for the perfect single alkali layer is independent of the substrates investigated, and is characteristic for the alkali metal. This is in contrast to results of conventional work-function measurements, but in accordance with the theoretical expectation.

Image states of Ag on Au(111) - Reuss, Christian; Wallauer, Wolfgang; Fauster, Thomas (Surface Review and Letters, 1996)
The image states for thin Ag layers on Au(111) have been studied with two-photon photoemission. The energies of the states show the behavior characteristic for a layer-by-layer growth of large terraces with their characteristic local work function. Image states with rather large linewidths are observed at energies outside the band gap of the projected bulk band structure. The identification of the states is complicated by the dominating signal from the occupied surface state.

IMAGE STATES ON CO(0001) AND FE(110) PROBED BY 2-PHOTON PHOTOEMISSION - Fauster, Thomas; et al. (Physical Review B, 1992)
Up to three members of the Rydberg series of image states are observed on Co(0001) and Fe(110) surfaces using high-resolution, two-photon photoemission. Their binding energies and widths are determined. The first image state becomes broader when going from Ni to Co to Fe. The lack of an observable splitting provides an upper limit for a possible magnetic splitting.

Imaging localized neuronal activity at fast time scales through biomechanics - Patz, Samuel; Fovargue, Daniel; Schregel, Katharina; Nazari, Navid; Palotai, Miklos; Barbone, Paul E.; Fabry, Ben; Hammers, Alexander; Holm, Sverre; Kozerke, Sebastian; Nordsletten, David; Sinkus, Ralph (Science Advances, 2019)
Mapping neuronal activity noninvasively is a key requirement for in vivo human neuroscience. Traditional functional magnetic resonance (MR) imaging, with a temporal response of seconds, cannot measure high-level cognitive processes evolving in tens of milliseconds. To advance neuroscience, imaging of fast neuronal processes is required. Here, we show in vivo imaging of fast neuronal processes at 100-ms time scales by quantifying brain biomechanics noninvasively with MR elastography. We show brain stiffness changes of ∼10% in response to repetitive electric stimulation of a mouse hind paw over two orders of frequency from 0.1 to 10 Hz. We demonstrate in mice that regional patterns of stiffness modulation are synchronous with stimulus switching and evolve with frequency. For very fast stimuli (100 ms), mechanical changes are mainly located in the thalamus, the relay location for afferent cortical input. Our results demonstrate a new methodology for noninvasively tracking brain functional activity at high speed.
CRIS-Team Scopus Importer:2019-05-02

Imaging the field inside nanophotonic accelerators - Fishman, Tal; Haeusler, Urs; Dahan, Raphael; Yannai, Michael; Adiv, Yuval; Abudi, Tom Lenkiewicz; Shiloh, Roy; Eyal, Ori; Yousefi, Peyman; Eisenstein, Gadi; Hommelhoff, Peter; Kaminer, Ido (Nature Communications, 2023)
Controlling optical fields on the subwavelength scale is at the core of nanophotonics. Laser-driven nanophotonic particle accelerators promise a compact alternative to conventional radiofrequency-based accelerators. Efficient electron acceleration in nanophotonic devices critically depends on achieving nanometer control of the internal optical nearfield. However, these nearfields have so far been inaccessible due to the complexity of the devices and their geometrical constraints, hampering the design of future nanophotonic accelerators. Here we image the field distribution inside a nanophotonic accelerator, for which we developed a technique for frequency-tunable deep-subwavelength resolution of nearfields based on photon-induced nearfield electron-microscopy. Our experiments, complemented by 3D simulations, unveil surprising deviations in two leading nanophotonic accelerator designs, showing complex field distributions related to intricate 3D features in the device and its fabrication tolerances. We envision an extension of our method for full 3D field tomography, which is key for the future design of highly efficient nanophotonic devices.
CRIS-Team Scopus Importer:2023-07-07

Imaging the field profile inside dielectric laser acceleration nanostructures - Fishman, Tal; Häusler, Urs; Dahan, Raphael; Yannai, Michael; Adiv, Yuval; Abudy, Tom Lenkiewicz; Eyal, Ori; Yousefi, Peyman; Shiloh, Roy; Eisenstein, Gadi; Hommelhoff, Peter; Kaminer, Ido (Optics InfoBase Conference Papers, 2022)
We present deep sub-wavelength measurement of the field distribution inside nanophotonic dielectric laser accelerator structures, using photon-induced nearfield electron microscopy. Comparing the measured field with theory provides new insight into accelerators' performance and structural sensitivity.
CRIS-Team Scopus Importer:2022-09-09

Imaging viscoelastic properties of living cells by AFM: Power-law rheology on the nanoscale - Hecht, Fabian M.; Rheinlaender, Johannes; Schierbaum, NIcolas; Goldmann, Wolfgang; Fabry, Ben; Schaeffer, Tilman E. (Soft Matter, 2015)

Imbalances in protein homeostasis caused by mutant desmin - Clemen, C.; Winter, L.; Unger, A.; Berwanger, C.; Spörrer, Marina; Linke, W.; Schröder, Rolf (NEUROMUSCULAR DISORDERS, 2019)
CRIS-Team WoS Importer:2019-10-11

Imbalances in protein homeostasis caused by mutant desmin - Winter, L.; Unger, A.; Berwanger, C.; Spörrer, Marina; Türk, Matthias; Chevessier, Frederic; Strucksberg, K. H.; Schlötzer-Schrehardt, Ursula; Wittig, I.; Goldmann, Wolfgang; Marcus, K.; Linke, W. A.; et al. (Neuropathology and Applied Neurobiology, 2019)
Aims: We investigated newly generated immortalized heterozygous and homozygous R349P desmin knock-in myoblasts in conjunction with the corresponding desminopathy mice as models for desminopathies to analyse major protein quality control processes in response to the presence of R349P mutant desmin. Methods: We used hetero- and homozygous R349P desmin knock-in mice for analyses and for crossbreeding with p53 knock-out mice to generate immortalized R349P desmin knock-in skeletal muscle myoblasts and myotubes. Skeletal muscle sections and cultured muscle cells were investigated by indirect immunofluorescence microscopy, proteasomal activity measurements and immunoblotting addressing autophagy rate, chaperone-assisted selective autophagy and heat shock protein levels. Muscle sections were further analysed by transmission and immunogold electron microscopy. Results: We demonstrate that mutant desmin (i) increases proteasomal activity, (ii) stimulates macroautophagy, (iii) dysregulates the chaperone assisted selective autophagy and (iv) elevates the protein levels of αB-crystallin and Hsp27. Both αB-crystallin and Hsp27 as well as Hsp90 displayed translocation patterns from Z-discs as well as Z-I junctions, respectively, to the level of sarcomeric I-bands in dominant and recessive desminopathies. Conclusions: Our findings demonstrate that the presence of R349P mutant desmin causes a general imbalance in skeletal muscle protein homeostasis via aberrant activity of all major protein quality control systems. The augmented activity of these systems and the subcellular shift of essential heat shock proteins may deleteriously contribute to the previously observed increased turnover of desmin itself and desmin-binding partners, which triggers progressive dysfunction of the extrasarcomeric cytoskeleton and the myofibrillar apparatus in the course of the development of desminopathies.
CRIS-Team Scopus Importer:2019-07-30
Keywords: desminopathy; immortalized myoblasts; protein homeostasis; protein quality control; R349P desmin knock-in mice

Impact of 2D Ligands on Lattice Strain and Energy Losses in Narrow-Bandgap Lead–Tin Perovskite Solar Cells - Zhang, Kaicheng; Vincze, Andrej; Metwalli, Ezzeldin; Zhang, Jiyun; Liu, Chao; Meng, Wei; Zhang, Boxue; Tian, Jingjing; Heumüller, Thomas; Xie, Zhiqiang; Luo, Junsheng; Osvet, Andres; et al. (Advanced Functional Materials, 2023)
Mixed lead and tin (Pb/Sn) hybrid perovskites exhibit a great potential in fabricating all-perovskite tandem devices due to their easily tunable bandgaps. However, the energy deficit and instability in Pb/Sn perovskite solar cells (PSCs) constrain their practical applications, which renders defect passivation engineering indispensable to develop highly efficient and long-term stable PSCs. Herein, the mechanisms of strain tailoring and defect passivation in Pb/Sn PSCs by 2D ligands are investigated. The 2D ligands include electroneutral cations with long alkyl chain (LAC), iodates with relatively short alkyl chain (SAC) and their mixtures. This study reveals that LAC ligands facilitate the relaxation of tensile strain in perovskite films while SAC ligands cause strain buildup. By mixing LAC/SAC ligands, tensile strain in perovskite films can be balanced which improves solar cell performance. PSCs with admixed β-guanidinopropionic acid (GUA)/phenethylammonium iodide (PEAI) exhibit enhanced open circuit voltage and fill factor, which is attributed to reduced nonradiative recombination losses in the bulk and at the interfaces. Furthermore, the operational stability of PSCs is slightly improved by the mixed 2D ligands. This work reveals the mechanisms of 2D ligands in strain tailoring and defect passivation toward efficient and stable narrow-bandgap PSCs.
CRIS-Team Scopus Importer:2023-07-07
Keywords: 2D ligand passivation; energy losses; lead/tin perovskite solar cells; stability; strain tailoring

Impact of crystalline defects in 4H-SiC epitaxial layers on the electrical characteristics and blocking capability of SiC power devices - Kodolitsch, Elisabeth; Sodan, Vice; Krieger, Michael; Weber, Heiko B.; Tsavdaris, Nikolaos (Materials Research Express, 2022)
In this study, we report the impact of structural 4H-SiC epitaxial defects on the electrical characteristics and blocking capabilities of SiC power devices. The detection and classification of the various crystal defects existing in 4H-SiC epitaxial layers and substrates was carried out with a commercial inspection tool using an optical microscope with a photoluminescence channel (PL). After the fabrication of dedicated test structures, devices that contain a single crystal defect were selected and electrically tested in reverse bias mode. Photon emission microscopy was performed to enable the localization of the leakage current spots within the devices. Thus, a direct correlation of the various crystal defects with the reduced blocking capability mechanism was made. This evaluation helps to set directions and build a strategy towards the reduction of critical defects in order to improve the performance of SiC devices for high power application

Impact of Epitaxial Defects on Device Behavior and their Correlation to the Reverse Characteristics of SiC Devices - Kodolitsch, Elisabeth; Sodan, Vice; Krieger, Michael; Tsavdaris, Nikolaos (Materials Science Forum, 2022)
In this work we report on the impact of various crystalline defects present in 4H-SiC epitaxial layers on the electrical blocking characteristics of SiC power devices. Dedicated test structures were fabricated and electrically characterized in reverse bias mode. SiC substrate and epitaxial crystal defects, as well defects due to front-end processing were detected and classified using commercial inspection tools. Devices with a single defect-type were studied which leads to a direct correlation of the leakage current spot position within the device and the obtained blocking characteristics. This gives a better understanding of each crystal defect impact on device ́s performance which leads to an improvement in the reliability and cost reduction of SiC power devices.<br

Impact of surface and twin-boundary scattering on the electrical transport properties of Ag nanowires - Kolesnik-Gray, Maria; Hansel, Stefan; Boese, Markus; Krstic, Vojislav (Solid State Communications, 2015)
Electrical transport properties of individual Ag nanowires are studied from room temperature down to low temperatures of a few Kelvin. The results show that surface scattering effects alone cannot account for the temperature-dependence of the nanowire resistivity and its unusually high residual resistivity compared to bulk Ag, whereas scattering at longitudinal twin planes and contributions due to phonon softening have to be considered. The impact of the twinning is observed in the marked reduction of the Debye temperature with respect to bulk silver. The findings also indicate that at low temperatures the scattering at the twin boundaries is more prominent than surface and electron–phonon scattering.

Implantation and Annealing of Aluminum in 4H Silicon Carbide - Rambach, Martin; Schmid, Frank; Krieger, Michael; Frey, Lothar; Bauer, Anton; Pensl, Gerhard; Ryssel, Heiner (Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2005)
Aluminum ions with a dose between 1.2 × 1014 cm -2 and 1.2 × 1015 cm-2 were implanted into 4H silicon carbide at room temperature, 650 °C, and 800 °C. High temperature furnace and lamp annealing of the implanted samples were investigated with respect to sheet resistance, hole mobility and free hole concentration. For an aluminum dose of 1.2 × 1015 cm -2 implanted at room temperature and subsequent furnace annealing at 1700 °C for 30 min, a sheet resistance of about 34 kΩ/□ and for lamp annealing at 1770 °C for 5 min, a slight increased sheet resistance of 38 kΩ/□ was obtained. Increasing implantation temperature to 800 °C and postimplantation furnace annealing resulted in a decreased sheet resistance of 18 kΩ/□. © 2005 Elsevier B.V. All rights reserved.
UnivIS-Import:2017-07-10:Pub.2005.nat.dphy.IAP.LAP.implan
Keywords: Annealing; Hall scattering factor; Implantation temperature; Mobility; Sheet resistance; Silicon carbide

Implanted bottom gate for epitaxial graphene on silicon carbide - Waldmann, Daniel; Jobst, Johannes; Fromm, Felix; Speck, Florian; Seyller, Thomas; Krieger, Michael; Weber, Heiko B. (Journal of Physics D-Applied Physics, 2012)
We present a technique to tune the charge density of epitaxial graphene via an electrostatic gate that is buried in the silicon carbide substrate. The result is a device in which graphene remains accessible for further manipulation or investigation. Via nitrogen or phosphor implantation into a silicon carbide wafer and subsequent graphene growth, devices can routinely be fabricated using standard semiconductor technology. We have optimized samples for room temperature as well as for cryogenic temperature operation. Depending on implantation dose and temperature we operate in two gating regimes. In the first, the gating mechanism is similar to a MOSFET, the second is based on a tuned space charge region of the silicon carbide semiconductor. We present a detailed model that describes the two gating regimes and the transition in between. © 2012 IOP Publishing Ltd.
UnivIS-Import:2015-04-14:Pub.2012.nat.dphy.IAP.LAP.implan

Implementing Functionality in Molecular Self-Assembled Monolayers - Kocic, Nemanja; Blank, Dominik; Abufager, Paula; Lorente, Nicolas; Decurtins, Silvio; Liu, Shi-Xia; Repp, Jascha (Nano Letters, 2019)
The planar heterocyclic molecules 1,6,7,12-tetraazaperylene on a Ag(111) metal substrate show different charging characteristics depending on their local environment: next to vacancies in self-assembled islands, molecules can be charged by local electric fields, whereas their charge state is fixed otherwise. This enables the activation of selected molecules inside islands by vacancy creation from scanning-probe-based manipulation. This concept allows for combining the precise mutual atomic-scale alignment of molecules by self-assembly, on one hand, and the implementation of specific functionality into otherwise homogeneous monolayers, on the other. Activated molecules in the direct neighborhood influence each other in their charging characteristics, suggesting their use as molecular quantum cellular automata. Surprisingly, only very few interacting molecules exhibit a rich spectroscopic signature, which offers the prospect of implementing complex functionality in such structures in the future.
CRIS-Team WoS Importer:2019-06-04

Implication of hydrogen-induced boron passivation in wet-chemically cleaned Si(111):H - Ristein, Jürgen; Ley, Lothar; et al. (Applied Surface Science, 1997)
Atomically-flat, hydrogen-terminated Si(111) surfaces with a boron concentration range of 4.5 ∼ 11 × 1018 cm-3 have been prepared by a standard RCA cleaning step and subsequent 40% NH4F immersion followed by pure water dipping. The surface Fermi level for as-prepared Si(111) lies near midgap as confirmed by X-ray or ultraviolet excited photoelectron spectroscopy (XPS/UPS) and Kelvin probe measurements although occupied gap states density as low as 1011 cm-2 at most is verified from an extremely low photoelectron yield for photons with energies below ∼ 5 eV. Annealing at 360°C for 5 min causes the Fermi level to shift towards the valence-band maximum top by ∼ 0.2 eV without an appreciable increase in the gap state density and a change in hydrogen surface termination. These observations imply a hydrogen-induced passivation of boron atoms in a surface layer during wet-chemical cleaning and the reactivation of such passivated boron atoms by 360°C annealing. For annealing temperatures above 460°C, hydrogen desorption from the surface results in a true pinning of the Fermi level close to midgap because of the generation of surface gap states.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.IAP.exphys.implic
Keywords: Hydrogen passivation; Kelvin probe; Photoelectron yield spectroscopy; Silicon; Valence band

Implications of heterogeneous bead behavior on cell mechanical properties measured with magnetic twisting cytometry - Fabry, Ben; Maksym, Geoffrey N.; Hubmayr, Rolf; Butler, James P.; Fredberg, Jeffrey (Journal of Magnetism and Magnetic Materials, 1999)

Imprinting the quantum statistics of photons on free electrons - Dahan, Raphael; Gorlach, Alexey; Haeusler, Urs; Karnieli, Aviv; Eyal, Ori; Yousefi, Peyman; Segev, Mordechai; Arie, Ady; Eisenstein, Gadi; Hommelhoff, Peter; Kaminer, Ido (Science, 2021)
The interaction between free electrons and light stands at the base of both classical and quantum physics, with applications in free-electron acceleration, radiation sources, and electron microscopy. Yet to this day, all experiments involving free-electron-light interactions are fully explained by describing the light as a classical wave. We observed quantum statistics effects of photons on free-electron-light interactions. We demonstrate interactions that pass continuously from Poissonian to super-Poissonian and up to thermal statistics, revealing a transition from quantum walk to classical random walk on the free-electron energy ladder. The electron walker serves as the probe in nondestructive quantum detection, measuring the second-order photon-correlation g(2)(0) and higher-orders g(n)(0). Unlike conventional quantum-optical detectors, the electron can perform both quantum weak measurements and projective measurements by evolving into an entangled joint state with the photons. These findings inspire hitherto inaccessible concepts in quantum optics, including free-electron-based ultrafast quantum tomography of light.
CRIS-Team Scopus Importer:2021-10-01

Imprinting the quantum statistics of photons on free electrons - Dahan, Raphael; Gorlach, Alexey; Häusler, Urs; Karnieli, Aviv; Eyal, Ori; Yousefi, Peyman; Segev, Mordechai; Arie, Ady; Eisenstein, Gadi; Hommelhoff, Peter; Kaminer, Ido (2021 Conference on Lasers and Electro-Optics, CLEO 2021 - Proceedings, 2021)
We observe for the first time the breakdown of the wave nature of light in free-electron-light interactions. Our experiment demonstrates a new way of measuring quantum states of light using high-precision electron energy spectroscopy.
CRIS-Team Scopus Importer:2021-12-24

IMPROVED RESOLUTION IN VUV ISOCHROMAT SPECTROSCOPY - Fauster, Thomas; et al. (Applied Physics A-Materials Science & Processing, 1986)

Improvement of computer simulation models for metallic melts via quasielastic neutron scattering: A case study of liquid titanium - Horbach, Jürgen; Rozas, Roberto; Unruh, Tobias; Meyer, Andreas (Physical Review B, 2009)
A combination of quasielastic neutron scattering (QNS) and molecular-dynamics (MD) simulation is used to modify an embedded atom method (EAM) potential for Ti with respect to the description of melt properties and crystallization from the melt. In the MD simulation, the EAM model is optimized such that agreement with accurate data of self-diffusion coefficients from QNS is achieved. As a result the density and the melting temperature are in good agreement with experiment.
Keywords: crystallisation; liquid metals; liquid theory; melting; molecular dynamics method; neutron diffraction; self-diffusion; titanium

Improving spray coated organic photodetectors performance by using 1,8-diiodooctane as processing additive - Montenegro Benavides, Cindy; Rechberger, Stefanie; Spiecker, Erdmann; Berlinghof, Marvin; Unruh, Tobias; Biele, Markus; Schmidt, Oliver; Brabec, Christoph; Tedde, Sandro F. (Organic Electronics, 2018)
In this work, we present and support the positive influence of 1,8-diiodooctane (DIO) as processing additive for the fabrication of solution processed near infrared (NIR) organic photodiodes (OPDs) based on the spray-coated blend of [6,6]phenyl-C70-butyric acid methyl ester (PC70BM) and poly[(2,5-bis(2-hexyldecyl)-2,3,5,6-tetrahydro-3,6-diox-opyrrolo[3,4-c]pyrrole-1,4-diyl)-alt-([2,2’:5′,2″-terthiophene]-5,5″-diyl)] (PDPP3T). Transmission electron microscopy (TEM) analysis show that the use of DIO improves donor–acceptor interfaces in the bulk heterojunction (BHJ) layer. Besides the enhancement of electron/hole transport pathways that leads to higher efficiencies, it reduces significantly the roughness of spray coated layers. The External Quantum Efficiency (EQE) is increased up to 35% at 900 nm and the dark current is decreased one order of magnitude in comparison to the reference down to 20 nA/cm2 at -5 V. The OPD's detectivity is increased from 1.66×1011 Jones to 3.34×1012 Jones and the linearity response is improved. A comprehensive morphological and electro-optical characterization of the generated layers and devices is the main focus of this work.
Keywords: DIO additive; organic photodetectors; spray coating; BHJ morphology

Impurity Conduction in Silicon Carbide - Krieger, Michael; Semmelroth, Kurt; Weber, Heiko B.; Pensl, Gerhard; Rambach, Martin; Frey, Lothar (Materials Science Forum, 2007)
We report on admittance spectroscopy (AS) investigations taken on aluminum (Al)doped 6H-SiC crystals at low temperatures. Admittance spectra taken on Schottky contacts of highly doped samples (NA≥ 7.2×10 17 cm-3) reveal two series of conductance peaks, which cause two different slopes of the Arrhenius plot. The steep slope is attributed to the Al acceptor, while the flatter one - obtained from the low temperature peaks - is attributed to the activation energy ε3 of nearest neighbor hopping. We propose a model, which explains the unexpected sharpness of the low temperature conductance peaks and the disappearance of these peaks for low acceptor concentrations. The model is verified by simulation, and the AS results are compared with corresponding results obtained from resistivity measurements taken on 4H- and the identical 6HSiC samples.
UnivIS-Import:2017-11-07:Pub.2007.nat.dphy.IAP.LAP.impuri
Keywords: Admittance spectroscopy; Hopping conduction; Impurity conduction

Incommensurate Moire overlayer with strong local binding: CoO(111) bilayer on Ir(100) - Tröppner, Carsten; Schmitt, Tobias; Reuschel, Martina; Hammer, Lutz; Schneider, M. Alexander; Mittendorfer, Florian; Redinger, Josef; Poudlucky, Raimund; Weinert, Michael (Physical Review B, 2012)
Incommensurate relaxed overlayer Moire structures are often interpreted as systems with weak lateral variations of the binding potential and thus no structural modulations in the overlayer material. We discuss here the example of a CoO(111) bilayer on Ir(100), which is a relaxed overlayer with strong structural response to the lateral modulation of interface properties but nevertheless is incommensurate. By means of density functional theory (DFT) calculations, we quantitatively reproduce all the structural parameters of the CoO(111) bilayer on Ir(100) as proposed by a recent low-energy electron diffraction analysis [Ebensperger et al., Phys. Rev. B 81, 235405 (2010)]. The calculations predict energetic degeneracies with respect to registry shifts of the CoO(111) film along [01 (1) over bar]. Large-scale, low-temperature scanning tunneling microscopy topographies reveal that the true structure of the film is incommensurate in this direction, exhibiting a one-dimensional Moire pattern with a period of about 9.4 a(Ir). From DFT calculations for limiting (periodic) models, we can sample the potential landscape of the cobalt and oxygen atoms in the Moire structure across the Ir(100) unit cell. We find that despite the non-commensurability of the film, the binding to the substrate is site specific with strong attraction and repulsion points for both cobalt and oxygen atoms, leading to severe local distortions in the film. The lateral modulation of the structural elements within the oxide film can be understood as a combination of the lateral variation in the Co-Ir binding potential and additional O-Ir binding. DOI: 10.1103/PhysRevB.86.235407

Increased Motility and Suppression of Ex Vivo–Expanded Regulatory T Cells Designed for Adoptive Transfer Therapy in Ulcerative Colitis - Müller, Tanja; Liu, Lijuan; Czerwinski, Tina; Wiesinger, Manuel; Dedden, Mark; Paap, Eva-Maria; Ullrich, Karen; Atreya, Imke; Siegmund, Britta; Atreya, Raja; Fabry, Ben; Berking, Carola; et al. (Cellular and Molecular Gastroenterology and Hepatology, 2023)
CRIS-Team Scopus Importer:2023-06-02

Indentification of Dumb-Bell Shaped Interstitials in Electron Irradiated 6H-SiC by Photoluminescence Spectroscopy - Ley, Lothar; Hundhausen, Martin; et al. (Materials Science Forum, 2003)
UnivIS-Import:2015-04-14:Pub.2003.nat.dphy.IAP.LAP.indent

Independent and coherent transitions between antiferromagnetic states of few-molecule systems - Besson, Claire; Stegmann, Philipp; Schnee, Michael; Zanolli, Zeila; Achilli, Simona; Wittemeier, Nils; Vierck, Asmus; Frielinghaus, Robert; Kögerler, Paul; Maultzsch, Janina; Ordejón, Pablo; Schneider, Claus M.; et al. (Physical Review B, 2023)
Spin-electronic devices are poised to become part of mainstream microelectronic technology. Downsizing them led to the field of molecular spintronics. Here, we provide proof-of-concept data that allow expanding this area from its traditional focus on single-molecule magnets to molecules in which spin centers are antiferromagnetically (AFM) coupled to result in a singlet ground state. In this context, and in contrast to all previous work on molecular spintronics, we develop a detection scheme of the spin state of the molecule that does not rely on a magnetic moment. Instead, we use quantum dot devices consisting of an isolated, contacted single-wall carbon nanotube covalently bound to a limited number of molecular AFMs, for which we chose representative coordination complexes incorporating four Mn(II) or Co(II) ions. Time-dependent quantum transport measurements along the functionalized nanotube show steplike transitions between several distinct current levels that we attribute to transitions between different AFM states of individual molecular complexes grafted on the nanotube. A statistical analysis of the switching events using factorial cumulants indicates that the cobalt complexes switch independently from each other, whereas a coherent superposition of the AFM spin states of the molecules along the nanotube is observed for the manganese complexes. The long coherence time of the superposition state (several seconds at 100 mK) is made possible by the absence of spin and orbital momentum in the relevant states of the manganese complex, while the cobalt complex includes a significant orbital momentum contribution due to the pseudo-octahedral coordination environment of the d7 metal centers.
CRIS-Team Scopus Importer:2023-08-04

Index assignment of a carbon nanotube rope using tip-enhanced Raman spectroscopy - Goss, Karin; Peica, Niculina; Thomsen, Christian; Maultzsch, Janina; Schneider, Claus M.; Meyer, Carola (physica status solidi (b), 2011)
We used tip-enhanced Raman spectroscopy to study the diameter-dependent Raman modes in a contacted carbon nanotube (CNT) rope. We show that with the near-field tip enhancement a large number of nanotubes within a rope can be identified, even if the nanotube modes cannot be distinguished in the far-field signal. Several metallic and semiconducting nanotubes can be identified and assigned to nanotube families. Additionally, we provide a tentative chiral index assignment. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Keywords: carbon nanotubes; Raman spectroscopy; TERS

Indirect doping effects from impurities in MoS2/h-BN heterostructures - Gillen, Roland; Robertson, John; Maultzsch, Janina (Physical Review B, 2014)
We performed density functional theory calculations on heterostructures of single layers of hexagonal BN and MoS2 to assess the effect of doping in the BN sheet and of interstitial Na atoms on the electronic properties of the adjacent MoS2 layer. Our calculations predict that n doping of the boron nitride subsystem by oxygen, carbon, and sulfur impurities causes noticeable charge transfer into the conduction band of the MoS2 sheet, while p doping by beryllium and carbon leaves the molybdenum disulphide layer largely unaffected. Intercalated sodium atoms lead to a significant increase of the interlayer distance in the heterostructure and to a metallic ground state of the MoS2 subsystem. The presence of such n dopants leads to a distinct change of valence-band and conduction-band offsets, suggesting that doped h-BN remains a suitable substrate and gate material for applications of n-type MoS

Indirect magnetic coupling in light-element-doped single-walled carbon nanotubes - Krstic, Vojislav; Krstic, Vojislav; Ewels, Christopher P.; Wagberg, Thomas; Ferreira, Mauro S.; Janssens, Anne M.; Stephan, Odile; Glerup, Marianne (ACS nano, 2010)
Single-walled carbon nanotubes substitutionally doped with the light-element phosphorus are synthesized and are investigated by electrical and nuclear magnetic resonance measurements. Decreased spin−lattice relaxation times compared to undoped tubes point toward enhanced spin-sensitive scattering. Temperature dependence of the zero-bias conductance shows step-like features, a signature of scattering from a very low density (few sites per nanotube) of localized spin moments at oxidized phosphorus sites, consistent with density functional calculations. This supports recent predictions that localized magnetic moments must be indirectly magnetically coupled through the nanotube conduction electrons.<br
Keywords: spintronics; transport; magnetism; NMR; doped nanocarbon; DFT

Individual electronic defect states in a-Si:H/a-SiNx double barrier structures - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Non-Crystalline Solids, 1991)
Random telegraphic noise (RTN) in large area a-Si:H/a-SiNx:H double barrier structures (DBS) is due to the charging and discharging of individual trap states in the barrier layer. The effective device area is confined to a path of less than 10 μm diameter. This is verified through the local effect a focused laser beam has on the noise characteristics. The capture (τ-c) and emission (τ-e) time constants of the current controlling trap can be determined separately. Temperature and bias dependence of the time constants are discussed within a model of acceptor-like traps with strong electron-lattice coupling that are situated in the nitride barrier and exchange charge with the conduction electrons in the adjacent n+a-Si:H layers. © 1991 Elsevier Science Publishers B.V. All rights reserved.
UnivIS-Import:2015-03-05:Pub.1991.nat.dphy.IAP.exphys.indivi

Inelastic neutron and low-frequency Raman scattering in a niobium-phosphate glass for Raman gain applications - Unruh, Tobias; Schulte, Alfons; Guo, Y.; Schirmacher, Walter; Schmid, B. (Journal of Non-Crystalline Solids, 2011)
We present measurements of the vibrational spectrum of a binary niobium-phosphate glass in the THz frequency range using inelastic neutron and Raman scattering. The spectra of these glasses show a low-frequency enhancement of the vibrational density of states ("boson peak"). Using a recently developed theory of vibrational excitations in disordered solids we are able to reconcile the measured neutron and Raman spectra using fluctuating elastic and Pockels constants as a model concept. As the spontaneous Raman susceptibility is a key parameter for Raman amplification our results suggest a significant gain profile for application of niobium-phosphate glasses in Raman amplifiers. (C) 2010 Elsevier B.V. All rights reserved.
Keywords: Raman scattering; Neutron scattering; Raman gain; Boson peak

Inelastic neutron and low-frequency Raman scattering in niobium-phosphate glasses: the role of spatially fluctuating elastic and elasto-optic constants - Schulte, Alfons; Schirmacher, Walter; Schmid, B.; Unruh, Tobias (Journal of Physics: Condensed Matter, 2011)
We investigate the low-frequency enhancement of vibrational excitations ('boson peak') in niobium-phosphate glasses through the combination of inelastic neutron and polarization-resolved Raman scattering. The spectra of these glasses reveal an enhancement of the vibrational density of states and of the cross section for spontaneous Raman scattering in the frequency range below 150 cm(-1). A recent theoretical model that is based on fluctuating elastic and elasto-optic (Pockels) constants provides a unified description of the measured neutron and Raman spectra, including the depolarization ratio.

Inelastic Neutron Scattering on an Mn-10 Supertetrahedron: Assessment of Exchange Coupling Constants, Ferromagnetic Spin Waves and an Analogy to the Huckel Method - Stuiber, Stefan; Wu, Gang; Nehrkorn, Joscha; Dreiser, Jan; Lan, Yanhua; Novitchi, Ghenadie; Anson, Christopher E.; Unruh, Tobias; Powell, Anni K.; Waldmann, Oliver (Chemistry - A European Journal, 2011)
The synthesis, crystal structure and magnetic characterisation by magnetisation and inelastic neutron scattering (INS) of a mixed-valent Mn-10 supertetrahedral aggregate [(Mn6Mn4II)-Mn-III(mu(4)-O)(4)(mu(3)-N-3)(3)(mu(3)-Br)-(Hmpt)(6)(Br)]Br-0.7(N-3)(0.3)center dot 2MeOH center dot 3MeCN (1) (H(3)mpt = 3-methylpentan-1,3,5-triol) is reported. The magnetic core of the molecule can be described as an octahedron of six S=2 Mn-III ions with four faces, each capped by a S=5/2 Mn-II ion such as to form the supertetrahedron. Unlike most related complexes, the molecular symmetry is slightly reduced from approximately T-d to C-3. The magnetic data reveal a total spin of S=22 in the ground state due to ferromagnetic exchange couplings within the molecule. The combined INS and magnetic data permits the accurate determination of the exchange coupling constants. Two types are found. The couplings between the Mn-III ions in the inner octahedron are characterised by J(a)=18.4(3) K, whereas the couplings between the apical Mn-II ions to the neighbouring Mn-III ions are given by J(b)=7.3(2) K. The significantly larger coupling strength J(a) as compared to J(b), and the near-T-d symmetry have profound consequences on the energy spectrum, which are discussed and carefully analysed. In particular, the observed INS spectra can consistently be reproduced by a simplified model in which the inner octahedron is replaced by one large spin of length S-0=12. This model provides intuitive insight into the structure of the magnetic spectrum. Additionally, the magnetic excitations at low temperature are analysed within the frame of ferromagnetic linear spin-wave theory, which permits an analytical calculation of the energy levels. For ferromagnetic clusters, a close analogy to the Huckel method of electronic structure calculation can be drawn, which allows one to grasp the results of the spin-wave theory or the magnetic excitation spectrum, respectively, in a chemical language.
Keywords: coordination clusters; inelastic neutron scattering; magnetic properties; manganese; spin-wave theory

Inelastic ponderomotive scattering of electrons at a high-intensity optical travelling wave in vacuum - Kozak, Martin; Eckstein, Timo; Schönenberger, Norbert; Hommelhoff, Peter (Nature Physics, 2018)
In the early days of quantum mechanics Kapitza and Dirac predicted that matter waves would scatter off the optical intensity grating formed by two counter-propagating light waves1. This interaction, driven by the ponderomotive potential of the optical standing wave, was both studied theoretically and demonstrated experimentally for atoms<a href="https://www.nature.com/articles/nphys4282#ref2" title="Gould, P. L., Ruff, G. A. & Pritchard, D. E. Diffraction of atoms by light: the near-resonant Kapitza–Dirac effect. Phys. Rev. Lett. 56, 827–830 (1986).">2 and electrons3,4,5. In the original version of the experiment1,5, only the transverse momentum of particles was varied, but their energy and longitudinal momentum remained unchanged after the interaction. Here, we report on the generalization of the Kapitza–Dirac effect. We demonstrate that the energy of sub-relativistic electrons is strongly modulated on the few-femtosecond timescale via the interaction with a travelling wave created in vacuum by two colliding laser pulses at different frequencies. This effect extends the possibilities of temporal control of freely propagating particles with coherent light and can serve the attosecond ballistic bunching of electrons6, or for the acceleration of neutral atoms or molecules by ligh
Keywords: attosecond bunching; Kapitza-Dirac effect; few-femtosecond laser pulses; temporal control of freely propagating particles

Influence of adsorbates on the image states of Pd(111) - Fauster, Thomas; et al. (Surface Science, 1996)
High-resolution two-photon photoemission spectroscopy was used to investigate the energy shift and lifetime broadening of the first image state on Pd(111) under adsorption of CO, O-2 and H-2 at room temperature and at 90 K. For all adsorbates the binding energy increases with coverage, which clearly shows that the image state is sensitive not only to the shift of the vacuum level, but also to the variation of the potential in the vicinity of the surface caused by the adsorbate The intrinsic linewidth of the image state increases under adsorption and implies a reduced lifetime of the electron in the image state. It can be explained in terms of elastic scattering of the image state at confining adcenters and inelastic scattering by these adcenters into bulk states.
Keywords: angle resolved photoemission; carbon monoxide; hydrogen; low-index single crystal surfaces; oxygen; palladium; surface electronic phenomena

Influence of ambient humidity on the surface conductivity of hydrogenated diamond - Mares, J. J.; Hubik, Pavel; Kristofik, Jozef; Ristein, Jürgen; Strobel, Paul; Ley, Lothar (Diamond and Related Materials, 2008)
The enhancement of the electrical conductivity of hydrogen-terminated diamond surfaces due to the adsorption of various chemical species represents a challenging problem and has a high application potential as well. In the transfer doping model of Maier et al. the presence of a water layer that forms spontaneously in moist atmospheres on any surface plays a crucial role. Hence, in the present contribution we have focused our attention on the influence of the relative humidity (RH) on the surface conductivity. In order to perform conductivity measurements in a wet atmosphere an original technique eliminating leakage effects due to adsorbed water was developed. The conductivity was measured at room temperature for RH between 2% and 100%. Despite a rather weak dependence on RH, three well distinguished regions can be identified in the conductivity as a function of RH. Not pretending to offer a first-principles account for this behaviour, a phenomenological explanation of the data is given. © 2008 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2008.nat.dphy.IAP.exphys.influe
Keywords: Humidity; Hydrogenated diamond; Surface conductivity; Water monolayer

Influence of doping on the optical properties and on the covalent bonds in plasma deposited amorphous silicon - Ristein, Jürgen; et al. (Solar Energy Materials, 1985)
The optical properties of doped glow discharge silicon films have been studied in the range between 0.5 and 10 eV. Boron doping has a strong influence on the covalent network, which becomes obvious from an increase of the refractive index and of the strength of the εlunate2 peak. Comparison of the refractive index in the IR and the UV reflectance points for highly boron-doped samples (> 103 ppm) to differences between bulk and surface properties which arise probably from a thin hydrogen-rich surface layer. These differences diminish upon annealing at 400°C. Density measurements reveal an increase of the mass density with boron doping which, in highly doped films, is close to the density of crystalline silicon. The influence of phosphorus on the optical properties is smaller and noticeable only at high doping levels. © 1985.
UnivIS-Import:2015-03-05:Pub.1985.nat.dphy.IAP.exphys.influe

Influence of drying methods on the physical properties of bacterial nanocellulose - Andree, Verena; Niopek, Daniel; Müller, Christine; Eiselt, Jan-Philipp; Foh, Nina; Rzany, Alexander; Hensel, Bernhard (Materials Research Express, 2021)
Bacterial nanocellulose (BNC) is a promising material for the use in medical implants.BNCdoes not induce unwanted reactions in vivo, is long term stable and possesses unique mechanical properties. However, to make the most of these features,BNCmust be carefully processed. Details of the cultivation and post-synthetic methods offer various ways to control the properties of BNC. The focus of this work is put on drying of the BNC. Different unconstrained drying methods (climate chamber at 23°C, oven at 100°C, freeze-drying) and constrained drying under excertion of uniaxial pressure at various temperatures have been investigated. The reduction of the high water content of nativeBNC (≈98%) causes a thickness reduction of the samples. For oven or climate chamber drying a thickness reduction of 98% is observed, while freeze-drying widely preserves the nano- or micro-structure of the fibrous material and leads to a thickness reduction of only≈13%. During drying or pressing at high temperature (100°C), i.e. by evaporation of the water, intermolecular hydrogen bonds are formed and interconnect the individual fibres and strands. Consequently mechanical stiffening is observed in tensile tests at small strains. After drying, a densified cellulose nano-fibre network is observed by scanning electron microscopy. Due to the irreversibility of drying by evaporation, the water content and water retention capacity ofBNCare not recovered by rehydration. Applying uniaxial pressure before drying further enhances the irreversible reinforcement of the fibre network, while this is not the case when pressing the samples after drying. The presented results show that the properties ofBNC can be widely controlled by post-processing steps. Thus, taylor-madeBNCcan be produced for biomedical applications.
CRIS-Team Scopus Importer:2021-03-05
Keywords: Bacterial Nanocellulose; Biomaterial; Drying methods; Mechanical Properties; Post-synthetic methods

Influence of light on individual defect noise in a-Si:H/a-SiNx:H double barrier structures - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Applied Physics, 1994)
This paper investigates the effect of illumination on the trapping and detrapping properties of individual electronic defect states, by demonstrating this access to the microscopic mechanisms of capture and release of charge carriers at the site of a single trap. The stability of the environment of an individual defect is also probed using the noise behavior. It is concluded that individual defect noise in a-Si:H/a-SiNx:H double barrier structures is affected by low and medium intensity illumination, because of the changed occupation of the trap state responsible for random telegraph noise. High intensity illumination results in metastable modification of the individual defect configuration.
UnivIS-Import:2015-03-05:Pub.1994.nat.dphy.IAP.exphys.influe

Influence of space charges on the resonant photoconductor employing a moving laser inducde grating - Hundhausen, Martin; Ley, Lothar; et al. (Applied Physics Letters, 1996)
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.IAP.exphys.influe

Influence of structural changes on diffusion in liquid germanium - Chathoth, Suresh Mavila; Damaschke, Bernd; Unruh, Tobias; Samwer, Konrad (Applied Physics Letters, 2009)
Liquid germanium exhibits a change in the bonding character from being more covalent to more metallic while heating. We used quasielastic neutron scattering to measure the absolute value of self-diffusion coefficients in this liquid. Compared to other monoatomic liquids, such as liquid Ni or Ti, the self-diffusivity is an order faster near the melting temperature and shows a non-Arrhenius-like behavior. Above 1325 K, the activation energy for self-diffusion is low and obeys Stokes-Einstein relation. Even though the packing density of liquid germanium is less than that of simple metallic melts such as Pb or Sn, the temperature dependence of self-diffusivity does not exhibit D proportional to T(n)(n similar or equal to 2) form, which is observed for uncorrelated binary collisions of hard-spheres.
Keywords: germanium; liquid metals; melting; neutron diffraction; self-diffusion

Influence of substrate bias on the properties of a-C:H films prepared by plasma CVD - Hundhausen, Martin; Ristein, Jürgen; Ley, Lothar; et al. (Journal of Non-Crystalline Solids, 1993)
We have measured photoluminescence (PL) and Raman spectra for a series of amorphous carbon (a-C:H) films prepared in a RF-plasma CVD system. The negative bias voltage was varied between 0V and 950V. The samples seem to consist of two components. One polymeric component has a high band gap and gives strong luminesence above 2.1 eV with 0.6 eV band width. The second component shows the Raman spectrum that is typical for the sp2-clusters of hard carbon. We find that the hard carbon component seems to be absent for zero bias voltage. The PL for this sample, however, is strongest. We find a fatiguing of the luminescence during laser excitation. This fatiguing is weaker at 120 K, resulting in a higher PL-efficiency for this temperature. © 1993.
UnivIS-Import:2015-03-05:Pub.1993.nat.dphy.IAP.exphys.influe

Influence of surface morphology on surface states for Cu on Cu(111) - Fauster, Thomas; Reuss, Christian; Shumay, Igor; Weinelt, Martin; Theilmann, Florian; Goldmann, Albrecht (Physical Review B, 2000)
We have exploited angle-resolved one-photon photoemission, two-photon photoemission, and spot-profile analysis of low-energy electron diffraction to monitor the influence of surface morphology on the occupied and empty surface states observed at Gamma on Cu(111). Surface morphology changes were induced by homoepitaxial growth of Cu on Cu(111). A simple model of electron localization on terraces successfully explains energy shifts and linewidth broadening of both surface states. Obviously, surface states may be used as sensitive probes of terrace-width distributions and other structural properties.

Influence of Tail Groups during Functionalization of ZnO Nanoparticles on Binding Enthalpies and Photoluminescence - Segets, Doris; Lin, Wei; Schmidt, Jochen; Peukert, Wolfgang; Mahler, Michael; Schindler, Torben; Unruh, Tobias; Meyer, Bernd (Langmuir, 2017)
We report on the tailoring of ZnO nanoparticle (NP) surfaces by catechol derivatives (CAT) with different functionalities: tert-butyl group (tertCAT), hydrogen (pyroCAT), aromatic ring (naphCAT), ester group (esterCAT), and nitro group (nitroCAT). The influence of electron-donating/-withdrawing properties on enthalpy of ligand binding (ΔH) was resolved and subsequently linked with optical properties. First, as confirmed by ultraviolet/visible (UV/vis) and Fourier transform infrared (FT-IR) spectroscopy results, all CAT molecules chemisorbed to ZnO NPs, independent of the distinct functionality. Interestingly, the ζ-potentials of ZnO after functionalization shifted to more negative values. Then, isothermal titration calorimetry (ITC) and a mass-based method were applied to resolve the heat release during ligand binding and the adsorption isotherm, respectively. However, both heat- and mass-based approaches alone did not fully resolve the binding enthalpy of each molecule adsorbing to the ZnO surface. This is mainly due to the fact that the Langmuir model oversimplifies the underlying adsorption mechanism, at least for some of the tested CAT molecules. Therefore, a new, fitting-free approach was developed to directly access the adsorption enthalpy per molecule during functionalization by dividing the heat release measured via ITC by the amount of bound molecules determined from the adsorption isotherm. Finally, the efficiency of quenching the visible emission caused by ligand binding was investigated by photoluminescence (PL) spectroscopy, which turned out to follow the same trend as the binding enthalpy. Thus, the functionality of ligand molecules governs the binding enthalpy to the particle surface, which in turn, at least in the current case of ZnO, is an important parameter for the quenching of visible emission. We believe that establishing such correlations is an important step toward a more general way of selecting and designing ligand molecules for surface functionalization. This allows developing strategies for tailored colloidal surfaces beyond empirically driven formulation on a case by case basi
Keywords: functionalization; nanoparticle; photoluminesence

Influence of the growth conditions of epitaxial graphene on the film topography and the electron transport properties - Weingart, S.; Bock, C.; Kunze, Ulrich; Emtsev, Konstantin; Seyller, Thomas; Ley, Lothar (Physica E-Low-Dimensional Systems & Nanostructures, 2010)
In this work we report on temperature-dependent magnetotransport measurements on epitaxial graphene grown on SiC(0 0 0 1) under different preparation conditions. We demonstrate that the temperature dependence of the charge carrier density and mobility is correlated to the annealing conditions during the graphitization process. As recently shown, SiC substrates annealed in an Ar atmosphere near atmospheric pressure exhibit continuous monolayer graphene films over 2 - 3 μ m wide and more than 50 μ m long terraces. For these films we determine a constant charge carrier density in the range from 1.4 K up to room temperature and an electron mobility exceeding 3000 cm (V s) at low temperatures. © 2009 Elsevier B.V. All rights reserved.
Keywords: Charge carrier density; Charge carrier mobility; Epitaxial graphene; Magnetotransport

Influence of the layer number and stacking order on out-of-plane phonons in few-layer graphene - Herziger, Felix; Maultzsch, Janina (physica status solidi (b), 2013)
We investigate the stacking-order dependence of the double-resonant LO-ZO Raman combination mode, also called N mode, in ABA- and ABC-stacked trilayer graphene. By tuning the laser energy, we observe different N mode dispersions for both stackings and show that these shifts are indicative for the stacking type. We explain the different shifts with stacking-related changes in the electronic bands and the phonon dispersion. Additionally, we performed simulations of the double-resonant Raman spectra of the N mode in bilayer graphene. Our calculations predict a splitting of the N mode for laser excitation energies above 2.6eV due to different contributions from both bands. We also analyzed the subpeaks of the N mode in few-layer graphene and explain their appearance only at even numbers of graphene layers. Graphical illustration of the in-plane LO and out-of-plane ZO -point vibrations in Bernal-stacked (AB-stacked) bilayer graphene. The unit-cell atoms are highlighted in blue. The dashed vertical lines denote the unit cell atoms that are directly above each other. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Keywords: few-layer graphene; out-of-plane vibrations; Raman spectroscopy; stacking order

Influence of zinc ions on structure, bioactivity, biocompatibility and antibacterial potential of melt-derived and gel-derived glasses from CaO-SiO2 system - Wajda, Aleksandra; Goldmann, Wolfgang; Detsch, Rainer; Boccaccini, Aldo R.; Sitarz, Maciej (Journal of Non-Crystalline Solids, 2019)
Several different compositions of zinc-containing glasses in the CaO-SiO2 system were obtained by both traditional melting technique and the sol-gel method. The influence of zinc ions addition in the glass composition was evaluated using different spectroscopic methods (FTIR and Si-29 MAS-NMR). It was demonstrated that ZnO has a significant effect on glass structure and, as a consequence, on thermal properties, texture and bioactivity. EDX and ICP data showed that zinc ions reduce glass bioactivity and incorporate in the newly forming HCA layer. Evaluation of the in vitro biocompatibility of the obtained materials was performed by indirect tests using MG-63 osteoblast-like cells. All samples were found to be biocompatible and zinc ions enhanced the cell viability. Antibacterial tests against gram-negative (E. coli) and gram-positive bacteria (S. aureus) were carried out to evaluate the antibacterial potential of the zinc-doped glasses.
CRIS-Team WoS Importer:2019-04-18

Infrared Interlayer Exciton Emission in MoS2/WSe2 Heterostructures - Karni, Ouri; Barré, Elyse; Lau, Sze Cheung; Gillen, Roland; Ma, Eric Yue; Kim, Bumho; Watanabe, Kenji; Taniguchi, Takashi; Maultzsch, Janina; Barmak, Katayun; Page, Ralph H.; Heinz, Tony F. (Physical Review Letters, 2019)
We report light emission around 1 eV (1240 nm) from heterostructures of MoS2 and WSe2 transition metal dichalcogenide monolayers. We identify its origin in an interlayer exciton (ILX) by its wide spectral tunability under an out-of-plane electric field. From the static dipole moment of the state, its temperature and twist-angle dependence, and comparison with electronic structure calculations, we assign this ILX to the fundamental interlayer transition between the K valleys in this system. Our findings gain access to the interlayer physics of the intrinsically incommensurate MoS2/WSe2 heterostructure, including moiré and valley pseudospin effects, and its integration with silicon photonics and optical fiber communication systems operating at wavelengths longer than 1150 nm.
CRIS-Team Scopus Importer:2019-12-27

Infrared spectroscopy of C-D vibrational modes on diamond (100) surfaces - Ley, Lothar; Ristein, Jürgen; et al. (Surface Science, 1999)
A high resolution analysis of C-D vibrational modes on single crystal diamond using Fourier transform infrared spectroscopy is reported. This method has the advantage over high resolution electron energy loss spectroscopy of a far superior resolution (< 1 cm-1 versus approx. 10 cm-1). The inherently low surface sensitivity of the former method was overcome by measuring the IR absorption in the attenuated total reflection mode employing a Ge prism. The use of deuterium instead of hydrogen avoids the interference from airborne hydrocarbon contamination. We present data on the diamond (100) surface that was deuterated in a microwave plasma and subjected to a series of isothermal annealing treatments at 700°C. The C-D stretching mode at 2181 cm-1) and the bending mode at 1054 cm-1 could be followed down to a tenth of a monolayer coverage. From the intensity ratio of these bands measured in s- and p-polarization the essentially perpendicular disposition of the C-D bonds has been inferred.
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.IAP.exphys.infrar

Inhibition of Rho kinases increases directional motility of microvascular endothelial cells - Breyer, Johannes; Samarin, Jana; Rehm, Margot; Lautscham, Lena; Fabry, Ben; Goppelt-Strübe, Margarete (Biochemical Pharmacology, 2012)

Initial stages in the growth of polycrystalline diamond on silicon - Ristein, Jürgen; Hundhausen, Martin; Ley, Lothar; et al. (Diamond and Related Materials, 1993)
Polycrystalline diamond films prepared in a hot filament chemical vapour deposition reactor were investigated with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) in order to identify chemically and structurally distinguishable phases during nucleation and early stages of diamond growth. This was achieved by investigating a series of films grown under identical conditions for 5 min to 4 h. In addition, the interface between a solid diamond film and its silicon substrate was studied after the film had been removed from the substrate. Carbon deposition commences initially with the simultaneous growth of diamond crystallites along scratches and a layer of microcrystalline graphite covering the remainder of the substrate. Small amounts of SiC could also be identified during the first 100 min of deposition. Once the individual diamond crystallites have grown together to form a continuous layer, the graphitic phase in the spectra is replaced by an amorphous carbon phase which we attribute to the grain boundaries between the crystals. Inspection of the film backside revealed that the amorphous carbon had merely overgrown the microcrystalline graphite which was still present as the major component. Only after prolonged growth times (24 h) did the Raman and XPS spectra exhibit the characteristic diamond features free from any other contributions. On the basis of these observations a model for the initial stages of diamond growth on Si is developed. © 1993.
UnivIS-Import:2015-03-05:Pub.1993.nat.dphy.IAP.exphys.initia

INITIAL-STAGES OF EPITAXIAL COSI(2) FORMATION ON SI(100) SURFACES - Fauster, Thomas; et al. (Physical Review B, 1994)
The initial stages of the CoSi2 formation on Si(100) surfaces after room-temperature Co deposition and subsequent annealing were studied using Auger electron spectroscopy, low-energy electron diffraction, and valence-band and core-level photoemission spectroscopy with synchrotron radiation. CoSi2 formation does not take place at room temperature. A coverage dependence of the reaction temperature on Si(100) is observed which is attributed to a change of the Co adsorption sites at room temperature above a Co coverage of approximately 2.5 monolayer. This is related to the formation of CoSi2 grains and of pinholes. Co-rich and Si-rich CoSi2 surfaces were observed and characterized for different annealing temperatures. A Si termination of the Co-rich surface is inferred from our data. A c(4x4) reconstruction of the Si-rich surface is observed.

INITIAL-STAGES OF THE THERMAL NITRIDATION OF THE SI(100) SURFACE WITH NH3 AND NO - A SURFACE SENSITIVE STUDY OF SI 2P CORE-LEVEL SHIFTS - Fauster, Thomas; et al. (Surface Science, 1994)
During thermal nitridation of the Si(100) surface, nitride regions grow laterally on the surface. Already at small coverages they have nearly the thickness which is found for the closed him. This thickness depends on the annealing temperature and is 10 Angstrom for 800 K and 15 Angstrom for 1200 K. The coordination of the silicon atoms with nitrogen atoms is determined by the heating temperature. At 800 K only a small fraction of the silicon atoms in the nitride is bound to four nitrogen atoms, whereas for 1200 K the majority of the silicon atoms is found in this environment, which is characteristic for stoichiometric silicon nitride. For 1200 K, growth mode, thickness, and chemical composition are independent of the nitrogen containing gases. For the stoichiometric closed nitride film we measured the edges of the band gap and the position of the Fermi level therein. Defect-induced unoccupied states could be detected within the band gap.

In operandi observation of dynamic annealing: A case study of boron in germanium nanowire devices - Kolesnik-Gray, Maria; Sorger, Christian; Biswas, Subhajit; Holmes, Justin D.; Weber, Heiko B.; Krstic, Vojislav (Applied Physics Letters, 2015)
We report on the implantation of boron in individual, electrically contacted germanium nanowires with varying diameter and present a technique that monitors the electrical properties of a single device during implantation of ions. This method gives improved access to study the dynamic annealing ability of the nanowire at room temperature promoted by its quasi-one-dimensional confinement. Based on electrical data, we find that the dopant activation efficiency is nontrivially diameter dependent. As the diameter decreases, a transition from a pronounced dynamic-annealing to a radiation-damage dominated regime is observed.

Insights into Theranostic Properties of Titanium Dioxide for Nanomedicine - Hasanzadeh Kafshgari, Morteza; Goldmann, Wolfgang (Nano-Micro Letters, 2020)
Titanium dioxide (TiO2) nanostructures exhibit a broad range of theranostic properties that make them attractive for biomedical applications. TiO2 nanostructures promise to improve current theranostic strategies by leveraging the enhanced quantum confinement, thermal conversion, specific surface area, and surface activity. This review highlights certain important aspects of fabrication strategies, which are employed to generate multifunctional TiO2 nanostructures, while outlining post-fabrication techniques with an emphasis on their suitability for nanomedicine. The biodistribution, toxicity, biocompatibility, cellular adhesion, and endocytosis of these nanostructures, when exposed to biological microenvironments, are examined in regard to their geometry, size, and surface chemistry. The final section focuses on recent biomedical applications of TiO2 nanostructures, specifically evaluating therapeutic delivery, photodynamic and sonodynamic therapy, bioimaging, biosensing, tissue regeneration, as well as chronic wound healing.[Figure not available: see fulltext.].
CRIS-Team Scopus Importer:2020-01-21
Keywords: Bioimaging; Biosensing; Drug delivery systems; TiO; Tissue regeneration

In Situ and Ex Situ Energy-Filtered Transmission Electron Microscopy Studies on the Nanomorpholgy Evolution of Organic Bulk Heterojunction Solar Cells - Harreiß, Christina; Langner, Stefan; Berlinghof, Marvin; Rechberger, Stefanie; Will, Johannes; Unruh, Tobias; Brabec, Christoph; Spiecker, Erdmann (Microscopy and Microanalysis, 2019)

In situ characterization methods for evaluating microstructure formation and drying kinetics of solution-processed organic bulk-heterojunction films - Güldal, Nusret Sena; Kassar, Thaer; Berlinghof, Marvin; Unruh, Tobias; Brabec, Christoph (Journal of Materials Research, 2017)
Recently, in situ characterization methods have attracted increasing attention, especially in organic photovoltaics (OPV) field, since they provide greater insight into the mechanism of film formation, thus help to identify optimized processing conditions used to process the most efficient organic bulk-heterojunction thin films. In combination with various powerful X-ray-based characterization methods, several studies observed the morphological changes under the influence of different processing conditions. In this review, we summarize the fundamentals and implementation of X-ray-based and optical characterization methods, utilized in in situ mode and introduce the reader a better overview of the information acquired from a given technique in terms of microstructure formation in OPV. While we give a chronological development of in situ characterization methods in the field of OPV, we discuss the interplay between thermodynamics of solutions and drying kinetics of different types of organic blends. © 2017 Materials Research Society.
Keywords: Characterization; Drying; Heterojunctions; Microstructure; Thermodynamics; Thin films; Characterization methods; In-situ characterization; Microstructure formation; Optical characterization; Organic bulk heterojunctions; Organic photovoltaics; Photovoltaic; Thermodynamics of solutions; In situ processing

In-situ characterization of chemical annealing of a-Si:H by photoelectron spectroscopy - Ristein, Jürgen; Ley, Lothar; et al. (Journal of Non-Crystalline Solids, 1993)
The effect of chemical annealing with atomic hydrogen on a-Si:H samples was investigated in situ using surface sensitive spectroscopies. Changes in the hydrogen concentration and configuration as well as in the near surface defect state density are observed and are compared to the corresponding changes with deposition temperature. © 1993.
UnivIS-Import:2015-03-05:Pub.1993.nat.dphy.IAP.exphys.insitu

In-situ Er-doping of SiC bulk single crystals - Müller, Ralf; Desperrier, Patrick; Seitz, Christoph; Weißer, Matthias; Magerl, Andreas; Maier, Manfred; Winnacker, Albrecht; Wellmann, Peter (Materials Science Forum, 2004)
In this work the first PVT grown in-situ erbium doped SiC bulk crystal, to our knowledge, is presented. The crystal was characterised by secondary ion mass spectrometry (SIMS) and photoluminescence measurements. SIMS investigations show erbium concentrations in the range of 1.1 (.) 10" cm(-3) to 2.9 (.) 10(14) cm(-3). photoluminescence measurements between 1450 run and 1650 nm were conducted at 19 K, 77 K and 300 K. A distinct luminescence at 1540 nm corresponding to the 4 I-4(13/2) –> I-4(15/2) transition was detected even at room temperature. In the investigated temperature range, luminescence intensity shows only, a slight decrease of 16 %. Measurements with different laser powers suggest a saturation of erbium related luminescence in our experimental condition
Keywords: Erbium; PVT Method; Rare Earth Doping; SiC Bulk Growth

In situ investigation of the formation of Cu(In,Ga)Se-2 from selemsed metallic precursors by X-ray diffraction - The impact of Gallium, Sodium and Selenium excess - Hock, Rainer; et al. (PERGAMON-ELSEVIER SCIENCE LTD, 2005)
The chemical reactions during rapid thermal processing of stacked elemental layers were investigated by angle-dispersive in situ X-ray diffraction. With a time resolution of 5 diffractograms per minute four different solid state reactions resulting in ternary chalcopyrites were identified: (A) CuSe + InSe -> CuInSe2, (B) Cu2Se + 2InSe + Se -> 2CuInSe(2), (C) Cu2Se + In2Se3 -> 2CuInSe(2), (D) Cu2Se + Ga2Se3 -> 2CuGaSe(2). All these reactions form pure tenary chalcopyrites. The reaction resulting in the mixed crystal Cu(In,Ga)Se-2 starts not before (B) has begun. The reaction speed of (A) and the fraction of CuInSe2 formed by (B) depend on Na-doping and Se-pressure, (C) takes place only, if the reaction paths (A) and (B) are suppressed. Reaction (D) is observed only, if 25% In is replaced by Ga in the precursor. The diffractograms were evaluated by Rietveld refinement to give the phase contents of the samples as a function of reaction time. (c) 2005 Elsevier Ltd. All rights reserved.
Keywords: chalcogenides; thin films; crystal growth; x-ray diffraction; phase transitions

In situ investigation of two-step nucleation and growth of CdS nanoparticles from solution - Schiener, Andreas; Magerl, Andreas; Krach, A.; Seifert, Soenke; Steinrück, Hans-Georg; Zagorac, Jelena; Zahn, D.; Weihrich, R. (Nanoscale, 2015)
We report on a combined ultra-fast in situ SAXS and WAXS study along a free-jet providing insight into the evolution of the morphology and crystalline structure of CdS quantum dots in the very early stage of nucleation between 100 μs and 2.5 ms with a time resolution down to 10 μs. Accessing this yet unexplored time regime provides direct evidence of a two-step mechanism via formation of prenucleation clusters followed by nanoparticle nucleation from coalescing precursors. Using ab initio calculations, the latter species is identified as Cd13S4(SH)18 clusters, the stability of which results from a compact surface and inner structure.

In-situ measurement of thickness-dependent Pendellosung oscillations from a precipitation process in silicon at 650 degrees C - Will, Johannes; Gröschel, Alexander; Bergmann, Christoph; Magerl, Andreas (2012)
The time dependent agglomeration of oxygen in silicon at an annealing temperature of 650 degrees C is followed in-situ via the variation of the thickness-dependent Pendellosung fringes. The measurement of the 400-reflection of a wedge shaped sample with the characteristic tungsten K-alpha 1-line at 59.31 keV allows to observe changes of the static Debye-Waller factor of about 0.001%. Within the model of spherical precipitates and the classical theory of diffusion-driven precipitation we determine from this a diffusion constant 4.7x10(-15) cm(2)/s for oxygen in silicon at 650 degrees C which appears enhanced by a factor of 2.4 as compared to normal oxygen diffusion. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Keywords: silicon; oxygen precipitation; dynamical X-ray diffraction

In situ neutron diffraction on DxNb2O5 - Unruh, Tobias; Schwitzgebel, Günter; Ritter, Clemens (Zeitschrift für Naturforschung Section B-A Journal of Chemical Sciences, 1998)
DxNb2O5 is thermodynamically unstable. Therefore, neutron diffraction measurements were performed in the electrochemical cell used for the intercalation of deuterium into sintered Nb2O5 powder samples. Diffraction patterns were recorded at equilibrium potentials of -443, -428 -332 and -197 mV vs. NHE (corresponding to x = 0.232, x = 0.23, x = 0.21 and x = 0.06). The structural changes in Nb2O5 caused by the deuterium insertion are small but could be determined reproducibly. The lattice parameters of the host lattice exhibit a characteristic dependence on the deuterium content of the bronze. A model has been developed for the partially inhomogeneous distribution of the deuterium in the Nb2O5 unit cell, which explains the changes of the peak intensities observed in the low angle region (6 degrees less than or equal to 2 theta less than or equal to 18 degrees).
Keywords: neutron diffraction; electrochemical cell; niobium-(V)-oxide; niobium hydrogen bronze; hydrogen distribution

In-situ Observation of Polytype Switches During SiC PVT Bulk Growth by High Energy X-ray Diffraction - Wellmann, Peter; Konias, Katja; Hens, Philip; Hock, Rainer; Magerl, Andreas (Materials Science Forum, 2009)
This work reports on the in-situ observation of a polytype switch during physical vapor transport (PVT) growth of bulk SiC crystals by x-ray diffraction. A standard PVT reactor for 2 '' and 3 '' bulk growth was set up in a high-energy x-ray diffraction lab. Due to the high penetration depth of the high-energy x-ray beam no modification of the PVT reactor was necessary in order to measure Laue diffraction patterns of the growing crystal with good signal to noise ratio. We report for the first time upon the in-situ observation of polytype switching during SiC bulk PVT growt
Keywords: bulk crystal growth; physical vapor transport; in-situ growth control; polytypes

In-Situ observation of the oxygen nucleation in silicon with X-Ray single crystal diffraction - Will, Johannes; Gröschel, Alexander; Bergmann, Christoph; Magerl, Andreas (2011)
The measurement of Pendellosungs oscillations was used to observe the time dependent nucleation of oxygen in a Czochralski grown single crystal at 750 degrees C. It is shown, that the theoretical approach of the statistical dynamical theory describes the data well. Within the framework of this theory it is possible to determine the static Debye-Waller-factor as a function of the annealing time by evaluating the mean value of the Bragg intensity and the period length. The temperature influence on the Pendellosungs distance was corrected for by measurement of a Float-zone sample at the same temperature.
Keywords: Silicon; static Debye-Waller factor; statistical dynamical theory; single crystal diffraction; oxygen nucleation; in-situ; X-Ray; wedge shaped geometry; annealing

In-situ phase formation study of copper indium diselenide absorber layers from CuIn nanoparticles and evaporated selenium - Möckel, Stefan; Hölzing, Astrid; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2013)
In this work CuInSe (CISe) thin films were fabricated by rapid thermal processing of printed CuIn nanoparticles and thermally evaporated selenium as precursor layer. Research is focused on real-time investigations such as in-situ X-ray diffraction and dynamic scanning calorimetry. These measurements show CISe formation starting at 300 C. Significant amount of intermediate phases as reported for state-of-the-art rapid thermal processing of stacked elemental layer was not observed. The morphology of the nanoparticulate layers was examined by field emission scanning electron microscopy. Grain size developed from nanosized binary CuIn nanoparticles to microsized CISe grains. Porosity decreases in the temperature range from 340 C to 540 C. © 2012 Elsevier B.V.
Keywords: Chalcopyrite; CuInSe2; Dynamic scanning calorimetry; Intermetallic nanoparticles; Real-time investigation; XRD

In-situ Raman study of laser-induced graphene oxidation - Herziger, Felix; Mirzayev, Rasim; Poliani, Emanuele; Maultzsch, Janina (physica status solidi (b), 2015)
We present in-situ Raman measurements of laser-induced oxidation in exfoliated single-layer graphene. By using high-power laser irradiation, we can selectively and in a controlled way initiate the oxidation process and investigate its evolution over time. Our results show that the laser-induced oxidation process is divided into two separate stages, namely tensile strain due to heating and subsequent pp-type doping due to oxygen binding. We discuss the temporal evolution of the D/G-mode ratio during oxidation and explain the unexpected steady decrease of the defect-induced D-mode at long irradiation times. Our results provide a deeper understanding of the oxidation process in single-layer graphene and demonstrate the possibility of sub-micrometer patterning of graphene by an optical method.
Keywords: defects; graphene; oxidation; Raman spectroscopy

In Situ Study on the Evolution of Multimodal Particle Size Distributions of ZnO Quantum Dots: Some General Rules for the Occurrence of Multimodalities - Schindler, Torben; Walter, Johannes; Peukert, Wolfgang; Segets, Doris; Unruh, Tobias (Journal of Physical Chemistry B, 2015)
Properties of small semiconductor nanoparticles (NPs) are strongly governed by their size. Precise characterization is a key requirement for tailored dispersities and thus for high-quality devices. Results of a careful analysis of particle size distributions (PSDs) of ZnO are presented combining advantages of UV/vis absorption spectroscopy, analytical ultracentrifugation, and small-angle X-ray scattering (SAXS). Our study reveals that careful cross-validation of these different methods is mandatory to end up with reliable resolution. PSDs of ZnO NPs are multimodal on a size range of 2-8 nm, a finding that is not yet sufficiently addressed. In the second part of our work the evolution of PSDs was studied using in situ SAXS. General principles for the appearance of multimodalities covering a temperature range between 15 and 45 °C were found which are solely determined by the aging state indicated by the size of the medium-sized fraction. Whenever this fraction exceeds a critical diameter, a new multimodality is identified, independent of the particular time-temperature combination. A fraction of larger particles aggregates first before a fraction of smaller particles is detected. Fixed multimodalities have not yet been addressed adequately and could only be evidenced due to careful size analysis.

In situ visualization of SiC physical vapor transport crystal growth - Wellmann, Peter; Herro, Ziad Georges; Winnacker, Albrecht; Püsche, Roland; Hundhausen, Martin; Masri, P.; Kulik, A.; Bogdanov, M.; Karpov, S.; Ramm, M.; Makarov, Y. (Journal of Crystal Growth, 2005)
We review a digital X-ray imaging technique which permits in situ 2D imaging of the crucible interior during physical vapor transport growth of SiC. In addition, we use 13C-labeling experiments to determine the mass transport paths in the growth cell interior. The combination of both experimental techniques enabled the analysis of the global SiC growth process like determination of growth rate, quantitative analysis of the evolution of the source material morphology, interaction of Si- and C-containing gas species with the graphite crucible wall, etc. The data will be used for comparison with numerical modeling of the SiC growth process including calculation of temperature field, mass transport and changes of the source material morphology, i.e. porosity and graphitization. In addition to the application of X-ray imaging for fundamental growth studies, monitoring of routine growth runs will also be pointed out. © 2004 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.IAP.exphys.insitu
Keywords: Characterization; Computer simulation; Growth from vapor; Semiconducting silicon compounds

In-situ X-ray diffraction analysis of the recrystallization process in Cu2ZnSnS4nanoparticles synthesised by hot-injection - Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Azimi, Seyed Hamed; Hou, Yi; Peukert, Wolfgang; Brabec, Christoph; Hock, Rainer (Thin Solid Films, 2015)
Kesterite CuZnSnS(CZTS) is a promising material for thin film solar cell applications. The biggest advantages of this compound lie in the abundance and non-toxicity of the contained elements. Low temperature hot injection synthesis can provide an economic way to produce CZTS nanoparticles for application in solution processed solar cells. Powder X-ray diffraction (PXRD) measurements on the as-synthesised particles suggest that the crystal structure is cubic and can be best described as sphalerite-like. This means that the cations in the CZTS are statistically distributed on the cation sites of the crystal lattice rather than well-ordered like in the tetragonal kesterite structure. An in-situ PXRD measurement while annealing the particles up to 550 °C revealed a recrystallization process that transforms the structure from cubic to tetragonal meaning an ordering of the cations.
Keywords: Copper zinc tin sulphide; Cubic phase; Hot-injection synthesis; In-situ; Phase transition; Tetragonal phase; X-ray diffraction

In-Situ X-ray Diffraction Analysis of the Recrystallization Process in Cu2ZnSnS4 Nano Particles Synthesized by Hot-Injection - Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Azimi, Hamed; Hou, Yi; Peukert, Wolfgang; Brabec, Christoph; Hock, Rainer (Thin Solid Films, 2015)
Kesterite Cu2ZnSnS4 (CZTS) is a promisingmaterial for thin film solar cell applications. The biggest advantages of this compound lie in the abundance and non-toxicity of the contained elements. Low temperature hot injection synthesis can provide an economic way to produce CZTS nanoparticles for application in solution processed solar cells. Powder X-ray diffraction (PXRD) measurements on the as-synthesised particles suggest that the crystal structure is cubic and can be best described as sphalerite-like. This means that the cations in the CZTS are statistically distributed on the cation sites of the crystal lattice rather than well-ordered like in the tetragonal kesterite structure. An in-situ PXRD measurement while annealing the particles up to 550 °C revealed a recrystallization process that transforms the structure from cubic to tetragonal meaning an ordering of the cations.
EAM Import::2019-03-13

In-situ X-ray measurements of defect generation during PVT growth of SiC - Konias, Katja; Hock, Rainer; Stockmeier, Matthias; Wellmann, Peter; Miller, Michael; Ossege, Stefan; Magerl, Andreas (Materials Science Forum, 2007)
A standard inductively heated PVT growth furnace modified for diffraction experiments with high energy x-rays in focussing Laue geometry was built. The growth furnace will be placed in front of a tungsten anode high energy x-ray source. The Laue diffraction pattern of the growing crystal can be detected on a CCD camera detector. Evolution of crystalline defects as a function of the growth process parameters will be infered from the diffraction experiments. The furnace design and results of first test measurements serving as proof of concept are reporte
Keywords: PVT; crystal growth; growth furnace; x-ray diffraction; high energy x-rays; focussing Laue geometry; defects

In-situ XRD investigation of re-crystallization and selenization of CZTS nanoparticles - Sayed, Mohamed H.; Brandl, Marco; Chory, Christine; Hammer-Riedel, Ingo; Parisi, Juergen; Guetay, Levent; Hock, Rainer (Journal of Alloys and Compounds, 2016)
Cu2ZnSnS4 nanoparticles have been produced by a facile and high-yield wet-chemical method at low synthesis temperature. In order to remove the organic residues the synthesis was followed by a pre-annealing procedure at 250 degrees C in nitrogen atmosphere. Data evaluation of ex-situ XRD measurements on the pre-annealed sample showed, that the diffraction pattern of the as-synthesized powder can be well modeled by diffraction of a hexagonal and a disordered cubic CZTS structure. The CZTS nanoparticles were annealed under nitrogen atmosphere up to 550 degrees C without and with the addition of selenium powder and diffraction patterns were recorded in-situ as a function of temperature in order to investigate the structural phase transitions during the re-crystallization and selenization of the powders. The in-situ XRD measurements showed a structural phase transition into the tetragonal CZTS structure for pure CZTS and with the addition of selenium. With the addition of selenium, an exchange reaction between sulfur and selenium during the heating process was observed by the shift in the diffraction peaks and subsequent refinement of the lattice parameters of the crystal structures. (C) 2016 Elsevier B.V. All rights reserved.
Keywords: CZTS nanoparticles; In-situ XRD; Structural phase transition; Selenization

In-situ XRD investigation of selenization of CZTS nanoparticles - Brandl, Marco; Sayed, Mohamed H.; Chory, Christine; Hammer-Riedel, Ingo; Parisi, Juergen; Hock, Rainer; Guetay, Levent (Journal of Alloys and Compounds, 2017)
CZTS nanoparticles produced by a wet-chemical method were mixed with different proportions of Selenium powder to observe the sulfur selenium exchange reaction during selenization and the effect of the varying Selenium supply on the tetragonal ordering and recrystallization of the originally disordered cubic structure. Evaluation of the diffraction angle shift of the reflections in in-situ XRD measurements during the selenization process yields the temperature dependent composition of the CZTSSe. The presence of selenium in small to medium amounts seems to benefit the ordering of the cations as well as the crystallite growth, whereas very high proportions seem to reverse the positive effects. (C) 2017 Elsevier B.V. All rights reserved.
Keywords: CZTS nanoparticles; In-situ XRD; Structural phase transition; Selenization

Integrin adhesion and force coupling are independently regulated by localized PtdIns(4,5)2 synthesis - Legate, Kyle R.; Takahashi, Seiichiro; Bonakdar, Navid; Boettiger, David; Zent, Roy; Fässler, Reinhard; et al. (EMBO Journal, 2011)

Intensity distribution of the eight-beam case of the Si-888 reflection in backscattering geometry - Hock, Rainer; et al. (Zeitschrift für Kristallographie, 2004)
The eight-beam case of the Si-888 reflection in backscattering has been studied by scanning the eight simultaneously excited reflections Si 888, Si 088, Si 880, Si 808, Si 800, Si 080, Si 008 and Si 000 in wavelength and two independent rocking angles. Largely different widths of the individual reflection profiles found are explained from the Ewald representation as suggested by kinematic diffraction theory. The intensity profiles demonstrate a coupling of the eight simultaneously excited wave fields as expected from dynamic diffraction theory.
Keywords: multi beam diffraction; backscattering; eight beam case; dynamical diffraction; X-ray diffraction

Interaction of carrier envelope phase-stable laser pulses with graphene:the transition from the weak-field to the strong-field regime - Heide, Christian; Boolakee, Tobias; Higuchi, Takuya; Weber, Heiko B.; Hommelhoff, Peter (New Journal of Physics, 2019)
Ultrafast control of electron dynamics in solid state systems has recently found particular attention. By increasing the electric field strength of laser pulses, the light-matter interaction in solids might turn from a perturbative into a novel non-perturbative regime, where interband transitionsfrom the valence to the conduction band become strongly affected by intraband motion. We have demonstrated experimentally and numerically that this combined dynamics can be controlled in graphene with the electric field waveform of phase-stabilized few-cycle laser pulses. Here we show new experimental data and matching simulation results at comparably low optical fields, which allows us to focus on the highly interesting transition regime where the light-matter interaction turns from perturbative to non-perturbative. We find a 5th order power-law scaling of the laser induced waveform-dependent current at low optical fields, which breaks down for higher optical fields, indicating the transitio
Keywords: Ultrafast control of electron dynamics; graphene; intraband motion; transition regime

Interaction of free-base tetraphenylporphyrin with magnesium oxide: Influence of MgO morphology on metalation - di Filippo, Gianluca; Classen, Andrej; Pöschel, Rebecca; Fauster, Thomas (Journal of Chemical Physics, 2017)
Using x-ray photoemission spectroscopy, we investigated the self-metalation of free-base tetraphenylporphyrin (2HTPP) on thin MgO(100) films on Ag(100). The deposition of one monolayer 2HTPP on MgO results in the formation of magnesium(ii) tetraphenylporphyrin (MgTPP) at room temperature. We demonstrate that the efficiency of the reaction drastically depends on the morphology of the oxide layers. The latter is changed by varying the substrate temperature during the oxide growth. We observe the complete metalation of the 2HTPP monolayer when the MgO films are grown at 393 K. The increase of the growth temperature to 573 K leads to the reduction of the percentage of metalated molecules to ∼50%. We ascribe these results to the fact that MgTPP formation takes place through the hydroxilation of steps and defects on the MgO surface, which leads to an increase of the OH component in the O 1s line.

Interaction of hydrogen with accessible metal sites in the metal-organic frameworks M-2(dhtp) (CPO-27-M; M = Ni, Co, Mg) - Dietzel, Pascal D. C.; Georgiev, Peter A.; Eckert, Juergen; Blom, Richard; Strässle, Thierry; Unruh, Tobias (Chemical Communications, 2010)
Hydrogen molecules adsorbed in the nickel, cobalt, and magnesium analogs of the CPO-27 metal-organic framework at low loadings interact significantly more strongly than those adsorbed successively as a consequence of the strong interaction of hydrogen with the coordinatively unsaturated metal cations in the framework.

Interaction of ultrashort laser pulses with metal nanotips: a model system for strong-field phenomena - Krüger, Michael; Schenk, Markus; Hommelhoff, Peter; Wachter, Georg; Lemell, Christoph; Burgdoerfer, Joachim (New Journal of Physics, 2012)
We discuss the interaction of ultrashort near-infrared laser pulses with sharp metal tips at moderate nominal intensities (I 0 ∼ 10 11W cm -2). As external electric fields are strongly enhanced at such tips (enhancement factor ∼10) our system turns out to be an ideal miniature laboratory to investigate strong-field effects at solid surfaces. We analyse the electron-energy spectra as a function of the strength of the laser field and the static extraction field and present an intuitive model for their interpretation. The size of the effective field acting on the metal electrons can be determined from the electron spectra. The latter are also reproduced by time-dependent density functional theory (TDDFT) simulations. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
UnivIS-Import:2015-04-14:Pub.2012.nat.dphy.IAP.exphys.intera

Interface between Water-Solvent Mixtures and a Hydrophobic Surface - Prihoda, Annemarie; Will, Johannes; Duchstein, Patrick; Becit, Bahanur; Lossin, Felix; Schindler, Torben; Berlinghof, Marvin; Steinrück, Hans Georg; Bertram, Florian; Zahn, Dirk; Unruh, Tobias (Langmuir, 2020)
The mechanism behind the stability of organic nanoparticles prepared by liquid antisolvent (LAS) precipitation without a specific stabilizing agent is poorly understood. In this work, we propose that the organic solvent used in the LAS process rapidly forms a molecular stabilizing layer at the interface of the nanoparticles with the aqueous dispersion medium. To confirm this hypothesis, n-octadecyltrichlorosilane (OTS)-functionalized silicon wafers in contact with water-solvent mixtures were used as a flat model system mimicking the solid-liquid interface of the organic nanoparticles. We studied the equilibrium structure of the interface by X-ray reflectometry (XRR) for water-solvent mixtures (methanol, ethanol, 1-propanol, 2-propanol, acetone, and tetrahydrofuran). The formation of an organic solvent-rich layer at the solid-liquid interface was observed. The layer thickness increases with the organic solvent concentration and correlates with the polar and hydrogen bond fraction of Hansen solubility parameters. We developed a self-consistent adsorption model via complementing adsorption isotherms obtained from XRR data with molecular dynamics simulations.
CRIS-Team Scopus Importer:2020-10-30

Interface Engineering of Molecular Charge Storage Dielectric Layers for Organic Thin-Film Memory Transistors - Khassanov, Artöm; Schmaltz, Thomas; Steinrück, Hans-Peter; Magerl, Andreas; Hirsch, Andreas; Halik, Marcus (Advanced Materials Interfaces, 2014)
Mixed self-assembled monolayers of C60-functionalized and different long-chained insulating phosphonic acids provide molecular scale non-volatile memory dielectrics for low-voltage organic thin-film transistors. The memory retention depends on the insulation of the C60 moiety and can be improved by embedding into the insulating SAM matrix and covering by corresponding insulating molecules.

Interface formation between hydrogen terminated Si (111) and amorphous hydrogenated carbon (a-C:H) - Ristein, Jürgen; Ley, Lothar; et al. (Journal of Vacuum Science & Technology A, 1997)
In the last few years heterostructures consisting of a-C:H on top of crystalline silicon have revealed a number of interesting properties for electronic applications, for example, as a photodiode (see Ref. 1) or, very recently, as cold cathode electron emitter (see Ref. 2). For those applications the interface properties of the heterostructure play a key role. In this article the electronic and chemical nature of the interface between plasma deposited a-C:H in the form of diamondlike carbon (DLC) and hydrogen terminated silicon (111) was determined by in situ core level and valence band photoemission spectroscopy. The quantitative analysis of core level shifts and intensities indicate that both, an interface layer of mixed composition and a pure a-C:H layer, grow simultaneously with relative growth rates of 2:1 during the initial stages of the interface formation. The interface layer is first carbon rich and then approaches stoichiometric composition which is reached at an interface thickness of 18 Å. Then a reactive SiC interface is completed and acts as a diffusion barrier which prevents further extension of the interface region when the deposition of a-C:H proceeds. Aside from an acceptor passivation of the Si substrate, due to H atoms from the plasma, no overlayer induced band bending is measured. The valence band offset between Si and DLC is determined as 0.7±0.1 eV with the valence band edge of DLC below that of silicon. © 1997 American Vacuum Society.
UnivIS-Import:2015-03-05:Pub.1997.nat.dphy.IAP.exphys.interf

Interface formation during silica encapsulation of colloidal CdSe/CdS quantum dots observed by in situ Raman spectroscopy - Biermann, Amelie; Aubert, Tangi; Baumeister, Philipp; Drijvers, Emile; Hens, Zeger; Maultzsch, Janina (Journal of Chemical Physics, 2017)
We investigate the encapsulation of CdSe/CdS quantum dots (QDs) in a silica shell by in situ Raman spectroscopy and find a distinct shift of the CdS Raman signal during the first hours of the synthesis. This shift does not depend on the final silica shell thickness but on the properties of the initial core-shell QD. We find a correlation between the Raman shift rate and the speed of the silica formation and attribute this to the changing configuration of the outermost layers of the QD shell, where an interface to the newly formed silica is created. This dependence of Raman shift rate on the speed of silica formation process will give rise to many possible studies concerning the growth mechanism in the water-in-oil microemulsion, rendering in situ Raman a valuable instrument in monitoring this type of reaction. Published by AIP Publishing.

Interface Molecular Engineering for Laminated Monolithic Perovskite/Silicon Tandem Solar Cells with 80.4% Fill Factor - Ramírez Quiroz, César Omar; Spyropoulos, Georgios; Salvador, Michael; Roch, Loïc M.; Berlinghof, Marvin; Darío Perea, José; Forberich, Karen; Dion-Bertrand, Laura Isabelle; Schrenker, Nadine J.; Classen, Andrej; Gasparini, Nicola; Chistiakova, Ganna; et al. (Advanced Functional Materials, 2019)
A multipurpose interconnection layer based on poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS), and d-sorbitol for monolithic perovskite/silicon tandem solar cells is introduced. The interconnection of independently processed silicon and perovskite subcells is a simple add-on lamination step, alleviating common fabrication complexities of tandem devices. It is demonstrated experimentally and theoretically that PEDOT:PSS is an ideal building block for manipulating the mechanical and electrical functionality of the charge recombination layer by controlling the microstructure on the nano- and mesoscale. It is elucidated that the optimal functionality of the recombination layer relies on a gradient in the d-sorbitol dopant distribution that modulates the orientation of PEDOT across the PEDOT:PSS film. Using this modified PEDOT:PSS composite, a monolithic two-terminal perovskite/silicon tandem solar cell with a steady-state efficiency of 21.0%, a fill factor of 80.4%, and negligible open circuit voltage losses compared to single-junction devices is shown. The versatility of this approach is further validated by presenting a laminated two-terminal monolithic perovskite/organic tandem solar cell with 11.7% power conversion efficiency. It is envisioned that this lamination concept can be applied for the pairing of multiple photovoltaic and other thin film technologies, creating a universal platform that facilitates mass production of tandem devices with high efficiency.
Keywords: density functional theory; lamination; molecular dynamics; monolithic tandem; perovskite/silicon; transparent-conductive-adhesive

Interface screening and imprint in poly(vinylidene fluoride/ trifluoroethylene) ferroelectric field effect transistors - Koval, Yury; Lazareva, Irina; Müller, Paul; Müller, Klaus; Schmeisser, Dieter; et al. (Journal of Applied Physics, 2009)
We investigated the imprint effect in ferroelectric capacitors and field effect transistors (FETs) with a poly(vinylidene fluoride/trifluoroethylene) [P(VDF-TrFE)] ferroelectric insulator. The shift in switching voltages and the change in the ferroelectric FET (FeFET) channel conductance were measured as a function of time and the thickness of the ferroelectric layer. Analyzing our experimental data, we show that the imprint originates from interface-induced processes, which effectively screen polarization charges in P(VDF-TrFE). This phenomenon significantly influences the retention of FeFET channel conductance and the memory functionality of FeFET with P(VDF-TrFE). © 2009 American Institute of Physics.

Interface states in a-Si:H as probed by optically induced ESR - Ristein, Jürgen; et al. (AIP Conference Proceedings, 1991)
UnivIS-Import:2015-04-16:Pub.1991.nat.dphy.IAP.exphys.interf

Interface structure of ultrathin CoSi2 films epitaxially grown on Si(111) - Seubert, Armin; Schardt, Judith; Weiss, Wolfgang; Starke, Ulrich; Heinz, Klaus; Fauster, Thomas (Applied Physics Letters, 2000)
The interface structure of ultrathin CoSi2 films grown on Si(111) was investigated by quantitative low-energy electron diffraction. Codeposition of the elements leads to a film composed of domains with two and three Si-Co-Si trilayers in CaF2 structure. As within the film, Co atoms at the interface are eightfold coordinated. The lateral unit cells of the film and substrate are mutually rotated by 60 degrees (B-type orientation). The interfacial trilayer is substantially distorted, its distance to the substrate expanded, and its sublayer spacings considerably modified from the bulk. Also, the substrate's top spacing is expanded. The results compare almost quantitatively with recent density-functional calculations. (C) 2000 American Institute of Physics. [S0003-6951(00)04306-0].

Interference between two coherently driven monochromatic terahertz sources - Preu, Sascha; Malzer, Stefan; Döhler, Gottfried; Zhao, Quanzhong; Hanson, Micah; Zimmerman, Jeremy; Gossard, Art; Wang, Lijun (Applied Physics Letters, 2008)
We report the interference between two phase-locked, continuous-wave, and coherent terahertz (Thz) photomixers. Both spatial and temporal coherence are observed with a narrow linewidth of less than 10 MHz. Phase locking is achieved by using one pair of lasers for both sources. The concept of optical narrow linewidth (fiber) distribution of the mixing signal opens various applications. We outline the necessary steps to extend this scheme for very long base line interferometric THz detection in the tens of kilometer range and for the improvement of spatial resolution for active stand-off THz imaging. © 2008 American Institute of Physics.

Interferometer measurements of terahertz waves from Bi 2Sr 2CaCu 2O 8+d mesas - Turkoglu, F.; Koseoglu, H.; Demirhan, Y.; Ozyuzer, O.; Preu, Sascha; Malzer, Stefan; Simsek, Yilmaz; Müller, Paul; Yamamoto, T.; Kadowaki, K. (Superconductor Science & Technology, 2012)
We fabricated rectangular mesa structures of superconducting Bi Sr CaCu O (Bi2212) using e-beam lithography and Ar ion beam etching techniques for terahertz (THz) emission. c-axis resistance versus temperature (R-T), current-voltage (I-V) characteristics and bolometric THz power measurements were performed to characterize Bi2212 mesas. The emission frequency of mesas was determined using a Michelson interferometer setup which also demonstrates polarized emission. Interference patterns of THz radiation from Bi2212 mesas were detected by various detectors such as a liquid helium cooled silicon composite bolometer, a Golay cell and a pyroelectric detector. An emitted power as high as 0.06mW was detected from Bi2212 mesas. For the first time, most of the pumped power was extracted as THz emission from a Bi2212 mesa. The radiation at 0.54THz was detected using the Michelson interferometric setup. © 2012 IOP Publishing Ltd.

Intergrown niobian rutile phases with Sc- and W-rich ferrocolumbite: An electron-microprobe and Rietveld study - Hock, Rainer; et al. (American Mineralogist, 2003)
A pegmatite from Diethensdorf, Saxonian Granulite Massif, Germany, contains fine-grained aggregates of at least three different varieties of niobian rutile and a (W, Sc)-rich ferrocolumbite. In addition, rutile I occurs as larger grains. Electron microprobe analyses of niobian rutile gave compositions close to the general formula (Fe,Mn)(x)(Nb,Ta)(2x)Ti3-3xO6 with Nb and Fe contents decreasing in the order rutile I –> rutile 2 –> rutile 3 and Ti increasing accordingly. The substitution of (Ti,Sn) by Fe + (Nb,Ta) is 35-32 at% in rutile 1, 28-26 at% in rutile 2, and 24-19 at% in rutile 3. The intergrown ferrocolumbite has Ta/(Nb + Ta) ratios of <0.10 and Mn/(Fe + Mn) ratios <0.25, and shows unusually high contents Of Sc2O3 and WO3 (UP to 4.0 and 8.8 wt%, respectively). Powder Xray diffraction (XRD) analysis with Guinier and Bragg-Brentano methods identified at least three rutile phases (herein termed A, 13, and C) with cell volumes decreasing with the Nb (+ Ta, W) contents. Nb/Ti ratios of rutiles estimated from Rietveld refinements roughly conform to the results of electron microprobe analysis. The cation distribution in the ferrocolumbite was refined on the basis of a two-scatterer model at sites 8d and 4c in space group Pbcn, leading to ordering of the heavy atoms on site 8d. Textural evidence suggests that the fine-grained intergrowths of ferrocolumbite + rutile 2 + rutile 3 (+ rutile 1) were formed by exsolution from a precursor phase that most probably was not rutile 1.

Interlayer Excitonic Spectra of Vertically Stacked MoSe2/WSe2 Heterobilayers - Gillen, Roland (physica status solidi (b), 2021)
The optical spectra of vertically stacked MoSe2/WSe2 heterostructures contain additional "interlayer" excitonic peaks that are absent in the individual monolayer materials and exhibit a significant spatial charge separation in out-of-plane direction. A many-body perturbation theory approach is used to simulate the excitonic spectra of MoSe2/WSe2 heterobilayers with three stacking orders, considering both momentum-direct and momentum-indirect excitons. The small oscillator strengths and the optical responses of the interlayer excitons are significantly stacking-dependent and give rise to high radiative lifetimes in the range of 5-200 ns at low temperature for the "bright" interlayer excitons. Solving the finite-momentum Bethe-Salpeter Equation (BSE), the lowest energy excitation is predicted to be an exciton over the fundamental indirect band gap, with a binding energy of 220 meV. However, in agreement with recent magneto-optics experiments and previous theoretical studies, the simulations of the effective excitonic g-factors suggest that the low energy momentum-indirect excitons are not experimentally observed. The existence of "interlayer" C excitons with significant exciton binding energies and optical oscillator strengths is further revealed, which are analogous to the prominent band nesting excitons in mono- and few-layer transition-metal dichalcogenides.
CRIS-Team WoS Importer:2021-05-28

Interlayer excitons in MoSe2/WSe2 heterostructures from first principles - Gillen, Roland; Maultzsch, Janina (Physical Review B, 2018)
Based on ab initio theoretical calculations of the optical spectra of vertical heterostructures of MoSe2 (or MoS2) and WSe2 sheets, we reveal two spin-orbit-split Rydberg series of excitonic states below the A excitons of MoSe2 and WSe2 with a significant binding energy on the order of 250 meV for the first excitons in the series. At the same time, we predict from accurate many-body G(0)W(0) calculations that crystallographically aligned MoSe2/WSe2 heterostructures exhibit an indirect fundamental band gap. Due to the type-II nature of the MoSe2/WSe2 heterostructure, the indirect transition and the exciton Rydberg series corresponding to a direct transition exhibit a distinct interlayer nature with spatial charge separation of the coupled electrons and holes. Our calculations confirm the recent experimental observation of a doublet nature of the long-lived states in photoluminescence spectra of MoX2/WY2 heterostructures, and we attribute these two contributions to momentum-direct interlayer excitons at the K point of the hexagonal Brillouin zone and to momentum-indirect excitons at the indirect fundamental band gap. Our calculations further suggest a noticeable effect of stacking order on the electronic band gaps and on the peak energies of the interlayer excitons and their oscillation strengths.
Keywords: excitons; TMDC; first-principles calculations; heterostructure

Interlayer resonant Raman modes in few-layer MoS2 - Scheuschner, Nils; Gillen, Roland; Staiger, Matthias; Maultzsch, Janina (Physical Review B, 2015)
We report two first-order Raman modes in the spectra of few-layer MoS2 at 286 and 471 cm(-1) that are only observed at excitation energies above 2.4 eV. We show that these normally not observed modes are interlayer modes related to symmetry-forbidden modes of the single layer. Based on group theory, we provide a general treatment and systematic classification of all phonon modes in few-layer crystals with inversion symmetry and/ or horizontal reflection symmetry. The results can thus be applied to different materials like few-layer graphene, transition-metal dichalcogenides, or BN. Moreover, the few-layer specific Raman modes are strongly resonant with the C optical transition in MoS2. We conclude that the corresponding exciton wave function is extended over all layers of the few-layer MoS2, in contrast to the A and B exciton

Intermediate Filaments - Goldmann, Wolfgang (De Gruyter, 2023)
CRIS-Team Scopus Importer:2023-04-21

Intermediate frequency modes in Raman spectra of Ar+-irradiated single-wall carbon nanotubes - Skakalova, Viera; Maultzsch, Janina; Osvath, Zoltan; Biro, Laszlo P.; Roth, Siegmar (Physica Status Solidi-Rapid Research Letters, 2007)
We study the effect of Ar+ irradiation on the intermediate frequency modes (IFM) in Raman spectra of single-wall carbon nanotubes. We observe new features in the intermediate frequency region from 386 to 635 cm(-1) as the defect concentration increases, whereas at the same time there is a decrease of other IFM modes. After annealing in vacuum, the IFM modes recover and become similar to those of the nanotubes before irradiation. We interpret the new features in the Raman spectra as originating from the phonon density of states that becomes visible in the Raman process due to the presence of defects.

Intermetallic compounds dynamic formation during annealing of stacked elemental layers and its influences on the crystallization of Cu2ZnSnSe4 films - Wibowo, Rachmat Adhi; Möckel, Stefan; Yoo, Hye Sun; Hetzner, Christina; Hölzing, Astrid; Wellmann, Peter; Hock, Rainer (Materials Chemistry and Physics, 2013)
A combined in-situ investigation using X-ray diffraction and differential scanning calorimetry during annealing was carried out to investigate the formation of intermetallic compounds in the stacked elemental layers and to reveal its influences on the crystallization of kesterite Cu2ZnSnSe4. The Mo/Cu/Zn, Mo/Cu/Sn/Zn, Mo/Cu/Zn/Se and Mo/Cu/Sn/Zn/Se stacked films were prepared with a composition resembling a typical kesterite Cu-poor and Zn-rich metallic composition. In-situ experiments during annealing of pure metallic stacked films reveal a dynamic intermetallic compounds formation of Cu5Zn8 -> CuZn -> Cu2Zn -> Cu3Zn and Cu6Sn5 -> Cu41Sn11. The Cu-Zn and Cu5Zn8 layer formed at the interface of metals/Se may prevent the stacked metallic layers from selenization below 320 degrees C. On the other side, the dynamic formation of Cu-Zn phases in the stacked films is found to be an origin of a ZnSe gradual formation starting from 320 degrees C. Phase analysis suggests that the ternary Cu2SnSe3 phase forms almost immediately after the formation of Cu2Se and SnSe. The formation of Cu2SnSe3 is indicated by the consumption of SnSe by the Cu2Se which occurs at 530-540 degrees C. Crystallization of kesterite takes place above 540 degrees C. On a phenomenological basis of present results, consequences for the thin film kesterite fabrication for solar cell application are discussed. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: Intermetallic compounds; Thin films; Annealing; Sputtering; Differential scanning calorimetry (DSC)

Internal Structure of Nanometer-Sized Droplets Prepared by Antisolvent Precipitation - Schuldes, Isabel; Noll, Dennis; Schindler, Torben; Zech, Tobias; Götz, Klaus; Appavou, Marie Sousai; Boesecke, Peter; Steiniger, Frank; Schulz, Peter; Unruh, Tobias (Langmuir, 2019)
Antisolvent precipitation (AP) is a low-cost and less-invasive preparation alternative for organic nanoparticles compared to top-down methods such as high-pressure homogenization or milling. Here we report on particularly small organic nanoparticles (NPs) prepared by AP. It has been found for various materials that these NPs in their liquid state exhibit a significant degree of molecular order at their interface toward the dispersion medium including ubiquinones (coenzyme Q10), triglycerides (trimyristin, tripalmitin), and alkanes (tetracosane). This finding is independent of the use of a stabilizer in the formulation. While this is obviously a quite general interfacial structuring effect, the respective structural details of specific NPs systems might differ. Here, a detailed structural characterization of very small liquid coenzyme Q10 (Q10) NPs is presented as a particular example for this phenomenon. The Q10 NPs have been prepared by AP in the presence of two different stabilizers, sodium dodecyl sulfate (SDS) and pentaethylene glycol monododecyl ether (C12E5), respectively, and without any stabilizer. The NPs' size is initially analyzed by photon correlation spectroscopy (PCS). The SDS-stabilized Q10 NPs have been studied further by differential scanning calorimetry (DSC), small-angle X-ray and neutron scattering (SAXS, SANS), wide-angle X-ray scattering (WAXS), and cryogenic transmission electron microscopy (CryoTEM). A simultaneous analysis of SAXS and contrast variation SANS studies revealed the molecular arrangement within the interface between the NPs and the dispersion medium. The Q10 NPs stabilized by SDS and C12E5, respectively, are small (down to 19.9 nm) and stable (for at least 16 months) even when no stabilizer is used. The SDS-stabilized Q10 NPs reported here, are therewith, to the best of our knowledge, the smallest organic NPs which have been reported to be prepared by AP so far. In particular, these NPs exhibit a core-shell structure consisting of an amorphous Q10 core and a surrounding shell, which is mainly composed of oriented Q10 molecules and aligned SDS molecules. This structure suggests a significant amphiphilic behavior and a rather unexpected stabilizing role of Q10 molecules.
CRIS-Team Scopus Importer:2019-10-22

Interpretation of atomic friction experiments based on atomistic simulations - Maier, Sabine; et al. (Journal of Vacuum Science & Technology B, 2007)
Atomic stick-slip experiments on the KBr(100) surface are analyzed using classical zero temperature atomistic simulations. Three different tip models exhibiting atomic stick-slip movement are studied in comparison with the experimental data and the Tomlinson model. The implications of a compliant tip apex for the stick-slip process and the dissipation pathways are discussed. © 2007 American Vacuum Society.
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Interpretation of diffuse scattering using superspace crystallography - Schmidt, Ella; Neder, Reinhard (Physical Review B, 2019)
Single-crystal diffuse scattering is generally interpreted using correlation parameters that describe probabilities for certain configurations on a local scale. In this paper we present an interpretation of diffuse maxima using a disordered superspace approach. In (D + d)-dimensional superspace two modulation functions are disordered along the superspace axis a(s,i) for i = 1, . . . , D, while the periodicity along the internal dimensions is maintained. This simple approach allows the generation of substitutionally disordered model structures that show diffuse maxima of any width at any position in reciprocal space. The extinction rules that are introduced by superspace symmetry are also fulfilled by the diffuse maxima from structures generated using the disordered superspace approach. In this paper we demonstrate the disordered superspace approach using a simple two-dimensional binary substitutionally disordered system. The extension of the approach to (3 + d)-dimensional superspace is trivial. The treatment of displacement and magnetic disorder as well as size-effect-like distortions in a similar manner is possible.
CRIS-Team WoS Importer:2019-08-16

Interpretation of small-angle X-ray scattering patterns of crystalline triglyceride nanoparticles in dispersion - Unruh, Tobias (Journal of Applied Crystallography, 2007)
Triglyceride nanocrystals in aqueous dispersion produced by high-pressure melt homogenization exhibit platelet-like shapes and clear but broadened Bragg reflections in the small-angle scattering regime. Because the particle thickness, the thickness of the stabilizer layer, the length scale of the crystalline structure of the nanoparticles and often the interparticle distances are of the same order of magnitude, the scattering of these structures mutually interferes. This leads to complicated small-angle scattering patterns which exhibit a lot of features, but it is not straightforward to discover the contained information on the structure of the system. In this contribution, a scattering model for such systems will be described, which is based on the kinematic scattering theory of X-rays. Using this scattering model an X-ray powder pattern simulation analysis is introduced to gain information on tripalmitin nanosuspensions which have been investigated by synchrotron small-angle X-ray scattering. It will be demonstrated that the results of this method provide a consistent description of all structural details mentioned above. In particular, information on the extension and the molecular packing density of the stabilizer layers can be achieved because these layers exhibit a comparatively large scattering contrast.

Intracellular Drug Delivery with Anodic Titanium Dioxide Nanotubes and Nanocylinders - Hasanzadeh Kafshgari, Morteza; Mazare, Anca Valentina; Distaso, Monica; Goldmann, Wolfgang; Peukert, Wolfgang; Fabry, Ben; Schmuki, Patrik (ACS Applied Materials and Interfaces, 2019)
Titanium dioxide (TiO 2 ) holds remarkable promises for developing current theranostic strategies. Anodic TiO 2 nanostructures as a porous scaffold have offered a broad range of useful theranostic properties; however, previous attempts to generate single and uniform TiO 2 one-dimensional nanocarriers from anodic nanotube arrays have resulted in a broad cluster size distribution of arbitrarily broken tubes that are unsuitable for therapeutic delivery systems due to poor biodistribution and the risk of introducing tissue inflammation. Here, we achieve well-separated, uniformly shaped anodic TiO 2 nanotubes and nanocylinders through a time-varying electrochemical anodization protocol that leads to the generation of planar sheets of weakly connected nanotubes with a defined fracture point near the base. Subsequent sonication cleanly detaches the nanotubes from the base. Depending on the position of the fracture point, we can fabricate single-anodic nanocylinders that are open on both ends and nanotubes that are closed on one end. We proceed to show that anodic nanotubes and nanocylinders are nontoxic at therapeutic concentrations. When conjugated with the anticancer drug doxorubicin using a pH-responsive linker, they are readily internalized by cells and subsequently release their drug cargo into acidic intracellular compartments. Our results demonstrate that uniformly sized anodic TiO 2 nanotubes and nanocylinders are suitable for subcellular delivery of therapeutic agents in cancer therapy.
CRIS-Team Scopus Importer:2019-05-09
Keywords: electrochemical anodization; intracellular drug delivery; nanocylinders; nanotubes; titanium dioxide

Intracellular stress tomography reveals stress focusing and structural anisotropy in cytoskeleton of living cells - Hu, Shaohua; chen, jianxin; Fabry, Ben; Numaguchi, Yashushi; Gouldstone, Andrew; Ingber, Donald E.; Fredberg, Jeffrey; Butler, James P.; Wang, Ning (American journal of physiology. Cell physiology, 2003)

Intracellular stress tomography reveals stress focusing and structural anisotropy in cytoskeleton of living cells - Hu, Shaohua; chen, jianxin; Fabry, Ben; Numaguchi, Yashushi; Gouldstone, Andrew; Ingber, Donald E.; Fredberg, Jeffrey; Butler, James P.; Wang, Ning (American Journal of Physiology-Cell Physiology, 2003)

Intracellular stress tomography reveals stress focusing - Hu, Shaohua; chen, jianxin; Fabry, Ben; Numaguchi, Yashushi; Gouldstone, Andrew; Ingber, Donald E.; Fredberg, Jeffrey; Butler, James P.; Wang, Ning (American Journal of Physiology-Cell Physiology, 2003)
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.IAP.lpmt.intrac

Intracycle interference in the interaction of laser and electron beams - Morimoto, Yuya; Hommelhoff, Peter (Physical Review Research, 2020)
A high-energy electron beam coupled to an optical field experiences a quantized energy modulation by multiples of the photon energy, originating from the temporal periodicity of the optical field by virtue of intercycle interference. Here we investigate the quantum interference occurring at shorter timescales, namely, within half an optical cycle, which is called intracycle interference. We show that the sub-half-cycle energy and phase modulation are imprinted into and largely modulate electron energy spectra regardless of the laser pulse duration. The intracycle effect is universal, meaning that it shows up for almost any electron velocity and optical wavelength. It thus facilitates coherent control of free-electron beams in microscopes or accelerators with a resolution of below an optical cycle, i.e., on attosecond timescales. The results obtained also apply to multiphoton and attosecond physics in atoms, molecules, and solids.<br
Keywords: attosecond physics; energy modulation of electron beams; quantum interference

Intrinsic color centers in 4H-silicon carbide formed by heavy ion implantation and annealing - Kobayashi, Takuma; Rühl, Maximilian; Lehmeyer, Johannes; Zimmermann, Leonard; Krieger, Michael; Weber, Heiko B. (Journal of Physics D-Applied Physics, 2021)
We study the generation and transformation of intrinsic luminescent centers in 4H-polytype of silicon carbide via heavy ion implantation and subsequent annealing. Defects induced by the implantation of germanium (Ge) or tin (Sn) have been characterized by photoluminescence (PL) spectra recorded at cryogenic temperatures. We find three predominant but as-yet-unidentified PL signatures (labeled as DI1–3) at the wavelength of 1002.8 nm (DI1), 1004.7 nm (DI2), and 1006.1 nm (DI3) after high dose implantation (> 4 × 1013 cm-2) and high temperature annealing (> 1700°C). The fact that the DI lines co-occur and are energetically close together suggest that they originate from the same defect. Regardless of the implanted ion (Ge or Sn), a sharp increase in their PL intensity is observed when the implantation damage becomes high (vacancy concentration > 1022 cm-3), indicating that the lines stem from an intrinsic defect caused by the damage. By tracking the PL signals after stepwise annealing, we examine how the overall intrinsic defects behave in the temperature range of 500 – 1800○C; the silicon vacancies formed by the implantation transform into either divacancies or antisite-vacancy pairs with annealing at about 1000°C. These spectra signatures are strongly reduced at 1200°C where the so-called TS defects are maximized in luminescence. As a final stage, the DI defects, which are most likely formed of antisites and vacancies, emerge at 1700°C. Our results provide a knowledge on how to incorporate and manipulate the intrinsic luminescent centers in SiC with ion implantation and annealing, paving the way for fully integrated quantum technology employing SiC.<br

INTRINSIC LINEWIDTHS OF IMAGE-POTENTIAL STATES ON NI(111) - Fauster, Thomas; et al. (Physical Review B, 1990)

Intrinsic proton dynamics in hydrous silicate melts as seen by quasielastic neutron scattering at elevated temperature and pressure - Yang, F.; Hess, K. -U.; Unruh, Tobias; Mamontov, Eugene; Dingwell, D. B.; Meyer, Andreas (Chemical Geology, 2017)
We present quasielastic neutron scattering results on hydrous silica, sodium aluminosilicate, and sodium trisilicate melts with 10 mol% total water content, studied at high temperature under high pressure. Combining neutron time-of-flight spectrometry with neutron backscattering, intrinsic, microscopic proton dynamics is investigated on a time scale from 0.2 ps up to 1 ns between 850 K and 1250 K. All three hydrous silicate melts exhibit a relatively slow proton dynamics, although the melt viscosity is drastically reduced upon water dissolution. The self-diffusion coefficient of proton in the hydrous sodium trisilicate melt is on the order of 10(-11) m(2) s(-1), two orders of magnitude slower than the sodium dynamics in the corresponding anhydrous melt. The proton dynamics in hydrous silica and albite is not faster than that time scale. We show that the transport mechanism involves not only-OH but also molecular water species. All protons are mobile during the transport of the water instead of diffusion of a specific water speciation. These characteristics of the proton structural relaxation in the melt can be attributed to a transport in a complex H-bonding environment. (C) 2017 Elsevier B.V. All rights reserved.
Keywords: Hydrous silicate melts; Intrinsic proton dynamics; High temperature high pressure; Quasielastic neutron scattering

Inverse-Designed Narrowband THz Radiator for Ultrarelativistic Electrons - Hermann, Benedikt; Häusler, Urs; Yadav, Gyanendra; Kirchner, Adrian; Feurer, Thomas; Welsch, Carsten; Hommelhoff, Peter; Ischebeck, Rasmus (ACS Photonics, 2022)
THz radiation finds various applications in science and technology. Pump–probe experiments at free-electron lasers typically rely on THz radiation generated by optical rectification of ultrafast laser pulses in electro-optic crystals. A compact and cost-efficient alternative is offered by the Smith–Purcell effect: a charged particle beam passes a periodic structure and generates synchronous radiation. Here, we employ the technique of photonic inverse design to optimize a structure for Smith–Purcell radiation at a single wavelength from ultrarelativistic electrons. The resulting design is highly resonant and emits narrowbandly. Experiments with a 3D-printed model for a wavelength of 900 μm show coherent enhancement. The versatility of inverse design offers a simple adaption of the structure to other electron energies or radiation wavelengths. This approach could advance beam-based THz generation for a wide range of applications. <
Keywords: THz generation Smith−Purcell radiation inverse design light−matter interaction free-electron light sources

INVERSE PHOTOEMISSION FROM POLYCRYSTALLINE SAMPLES - Fauster, Thomas; et al. (Solid State Communications, 1984)

INVERSE PHOTOEMISSION IN THE UV - Fauster, Thomas; et al. (Journal of Luminescence, 1984)

"Inverted'' porphyrins: a distorted adsorption geometry of free-base porphyrins on Cu(111) - Lepper, Michael; Köbl, Julia; Schmitt, Tobias; Gurrath, Martin; De Siervo, Abner; Schneider, M. Alexander; Steinrück, Hans-Peter; Meyer, Bernd; Marbach, Hubertus; Hieringer, Wolfgang (Chemical Communications, 2017)
Based on density functional theory calculations combined with experimental results, we report and discuss an extremely distorted, "inverted'' adsorption geometry of free-base tetraphenylporphyrin on Cu(111). The current findings yield new insights into a wellstudied system, shedding light on the peculiar molecule-substrate interaction and the resulting intramolecular conformation.

Investigating and Improving Performance Ratio of Cu(In,Ga)(S,Se)2 Photovoltaic Devices - Weber, Alfons; Lechner, Robert; Grünsteidl, Stefan; Borowski, Peter; Schubbert, Christian; Dalibor, Thomas; Heise, Stephan J.; Ohland, Joerg; Savchenko, Iievgeniia; Ahmed, Hamsa; Hirwa, Hippolyte; Parisi, Juergen; et al. (EU PVSEC, 2020)
For a commercial photovoltaic product not only the efficiency under standard test conditions (1000 W/m², AM1.5, Tcell=25°C) but also the performance under different operating conditions in the field is of importance. In this contribution, first results and the current status of a new project for Yield maximized Cu(In,Ga)(S,Se)2 thin film solar modules by deliberately controlled parameters of performance ratio (MyCIGS)2 are presented. In a comprehensive approach MyCIGS covers the combination of material and process variations in the different device layers, material characterisation of these layers, opto-electrical characterisation of the resulting devices, device and performance simulation and finally outdoor module testing to identify and optimize the key contributors for the performance ratio. With Avancis and the Helmholtz-Zentrum Berlin, the MyCIGS project comprises two partners that can supply completely processed cell or module samples or the single layers starting from the back electrode and thus allowing for a large field of possible process and material variations. Material characterisation is done by all project partners with a focus at the University of Erlangen on absorber characterisation via X-ray diffraction, scanning electron microscopy and photoluminescence. With the various characterisation techniques the absorber composition and its grading with absorber thickness, quality of module patterning, optical properties and electrical properties of the complete device are investigated. Material and device characterisation are the basis for a TCAD3 device model by the University of Oldenburg to also allow for a simulation-based approach to optimise the different contributors to performance ratio. The impact of the tested process variations on the parameters of performance ratio is tested indoor and also outdoor on two newly installed field test setups in Munich and Berlin. In a first experimental series, various process parameters have been investigated: composition of the back electrode, composition of the absorber (Ga-poor and S-poor versus Ga-rich and S-rich), buffer material and ilayer. In this contribution we will show the results of the absorber variation in more detai
Keywords: solar cells; CIGSe; characterization; outdoor test; performance

Investigating Growth of Gold Nanorods by Simultaneous Small-Angle X-Ray and Neutron Scattering - Zech, Tobias; Metwalli, Ezzeldin; Götz, Klaus; Schuldes, Isabel; Porcar, Lionel; Unruh, Tobias (Particle & Particle Systems Characterization, 2022)
Increased usage of gold nanorods (AuNRs) in various biosensing and medical applications requires tight size and morphology control. This is often achieved by tuning the aggregation behavior of the stabilizing ligand cetrimonium bromide (CTAB). Because the role of CTAB during AuNR growth is still a matter of debate, simultaneous small-angle X-ray and neutron scattering experiments (SAXS/SANS) and measurements are performed. The SAXS/SANS measurements have enabled an instantaneous correlation between the size of evolving AuNR and the nanostructure of guiding CTAB moieties. Upon modifying the aggregation behavior of CTAB micelles by adding hexanol or pentanol as inert additives in the precursor solution, a marked change in reaction kinetics is observed. Alcohol-modified CTAB nanostructures have improved AuNR size uniformity compared to those prepared in alcohol-free CTAB solutions, which are attributed to different growth modes. The change in reaction kinetics is linked to a changed stabilization mechanism of reactants and nascent AuNR facilitated by CTAB micelles.
CRIS-Team WoS Importer:2022-02-18

Investigating H-2 Sorption in a Fluorinated Metal-Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering - Forrest, Katherine A.; Pham, Tony; Georgiev, Peter A.; Pinzan, Florian; Cioce, Christian R.; Unruh, Tobias; Eckert, Juergen; Space, Brian (Langmuir, 2015)
Simulations of H-2 sorption were performed in a metal organic framework (MOF) consisting of Zn2+ ions coordinated to 1,2,4-triazole and tetrafluoroterephthalate ligands (denoted [Zn(trz)(tftph)] in this work). The simulated H-2 Sorption isotherms reported in this work are consistent with the experimental data for the state points considered. The experimental H-2 isosteric heat of adsorption (Q(st)) values for this MOP are approximately 8.0 KJ mol(-1) for the considered loading range, which is in the proximity of those determined from simulation. The experimental inelastic neutron scattering (INS) spectra for H-2 in [Zn(trz)(tftph)] reveal at least two peaks that occur at low energies, which corresponds to high barriers to rotation for the respective sites. The most favorable sorption site in the MOF was identified from the simulations as sorption in the vicinity of a metal coordinated H2O molecule, an exposed fluorine atom, and a carboxylate oxygen atom in a confined region in the framework. Secondary sorption was observed between the fluorine atoms of adjacent tetrafluoroterephthalate ligands. The H-2 molecule at the primary sorption site in [Zn(trz)(tftph)] exhibits a rotational barrier that exceeds that for most neutral MOFs with open-metal sites according to an empirical phenomenological model, and this was further validated by calculating the rotational potential energy surface for H-2 at this site.

Investigation of mass transport during PVT growth of SiC by 13C labeling of source material - Herro, Ziad Georges; Wellmann, Peter; Püsche, Roland; Hundhausen, Martin; Ley, Lothar; Maier, Matthias; Masri, P.; Winnacker, Albrecht (Journal of Crystal Growth, 2003)
We have investigated experimentally mass transport during physical vapor transport growth of silicon carbide (SiC). 13C was used as trace in order to determine mass transport paths inside the SiC source material as well as inside the gas room. The 13C concentration inside the SiC crystal, SiC source material and parts of the graphite growth cell was measured using micro-Raman spectroscopy and secondary ion mass spectroscopy. The SiC growth process was monitored using digital X-ray imaging. The presented method for the first time provides experimental access to mass transport which is of particular interest (i) for fundamental investigations, and (ii) for the verification of numerical modeling tools which are currently widely in use for the improvement of the SiC growth proces
Keywords: Growth from vapor; Mass transfer; Si13C

Investigation of mass transport during PVT growth of SiC by 13C labelling of source material - Hundhausen, Martin; Winnacker, Albrecht; Ley, Lothar; et al. (Journal of Crystal Growth, 2003)
We have investigated experimentally mass transport during physical vapor transport growth of silicon carbide (SiC). 13C was used as trace in order to determine mass transport paths inside the SiC source material as well as inside the gas room. The 13 C concentration inside the SiC crystal, SiC source material and parts of the graphite growth cell was measured using micro-Raman spectroscopy and secondary ion mass spectroscopy. The SiC growth process was monitored using digital X-ray imaging. The presented method for the first time provides experimental access to mass transport which is of particular interest (i) for fundamental investigations, and (ii) for the verification of numerical modeling tools which are currently widely in use for the improvement of the SiC growth process. © 2003 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.IAP.exphys.invest_6
Keywords: A1. Mass transfer; A2. Growth from vapor; B1. Si

Investigation of mass transport during SiC PVT growth using digital X-Ray Imaging, 13C labeling of source material and numerical modeling - Durst, Franz; Hundhausen, Martin; Winnacker, Albrecht; Ley, Lothar; et al. (Materials Science Forum, 2003)
We have analyzed the mass transport during physical vapor transport growth of SiC using 13C for labeling of the SiC gas species (i.e. Si 2C and SiC2) paths and digital x-ray imaging in order to monitor the evolution of the SiC crystal and SiC source material. The distribution of Si13C was investigated after growth by Micro-Raman spectroscopy. The slow onset of the 13C incorporation into the SiC crystal as well as the enrichment of 13C in the residual source material indicate that the major mass transport is conducted through the center of the source material and not along the hot crucible walls where SiC consumption is observed first. Numerical modeling of sublimation and recrystallization inside the SiC source material has been carried out. Effects like the formation of a condensed disk on top of the source material, consumption of SiC close to the hot crucible walls, etc. are described well. The experimental as well as numerical methods are believed to be useful tools for scaling up current growth setups towards large single crystal diameters.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.IAP.exphys.invest
Keywords: Physical Vapor Transport Growth; Raman Spectroscopy; Si; Source Material; X-Ray Imaging

Investigation of mass transport during SiCPVT growth using digital X-ray imaging, C-13 labeling of source material and numerical modeling - Wellmann, Peter; Herro, Ziad Georges; Selder, Markus; Durst, F.; Püsche, Roland; Hundhausen, Martin; Ley, Lothar; Winnacker, Albrecht (Materials Science Forum, 2003)
We have analyzed the mass transport during physical vapor transport growth of SiC using C-13 for labeling of the SiC gas species (i.e. Si2C and SiC2) paths and digital x-ray imaging in order to monitor the evolution of the SiC crystal and SiC source material. The distribution of (SiC)-C-13 was investigated after growth by Micro-Raman spectroscopy. The slow onset of the C-13 incorporation into the SiC crystal as well as the enrichment of C-13 in the residual source material indicate that the major mass transport is conducted through the center of the source material and not along the hot crucible walls where SiC consumption is observed first. Numerical modeling of sublimation and recrystallization inside the SiC source material has been carried out. Effects like the formation of a condensed disk on top of the source material, consumption of SiC close to the hot crucible walls, etc. are described well. The experimental as well as numerical methods are believed to be useful tools for scaling up current growth setups towards large single crystal diameter
Keywords: Physical Vapor Transport Growth; Raman Spectroscopy; Si13C; Source Material; X-Ray Imaging

Investigation of sheared liquids by neutron backscattering and reflectivity - Magerl, Andreas; Hock, Rainer; et al. (The ILL Millenium Symposium 2001, 2001)
UnivIS-Import:2015-04-16:Pub.2001.nat.dphy.IAP.LK.wirdna

Investigation of sheared liquids by neutron backscattering and reflectivity - Magerl, Andreas; Hock, Rainer; et al. (Applied Physics A-Materials Science & Processing, 2002)
We have investigated by neutron scattering structural and dynamical properties of water solutions of the triblock copolymer P85 under shear. To this end a shear cell that suits the requirements for neutron backscattering and another for reflectivity experiments have been built. In reflectivity measurements we find the polymer concentration (nominal concentration of 33% by weight) to vary right at the surface between 12% and 52% for hydrophilic or hydrophobic coated silicon wavers, for temperatures between 18°C and 73°C and for shear rates up to 2500 s-1. Additional structural changes deeper in the bulk are also observed. On the backscattering instrument (IN 10 at ILL) we find that the liquid appears to stick to the plates of the shear cell, implying an unusual macroscopic velocity distribution that differs from that found earlier for lubrication oils. We report further on changes of the quasielastic line width in the direction of the shear gradient for different temperatures and shear rates.
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.IAP.LK.invest

Investigation of the solid state reactions by time-resolved X-ray diffraction while crystallizing kesterite Cu2ZnSnSe4 thin films - Yoo, Hye Sun; Wibowo, Rachmat Adhi; Hölzing, Astrid; Lechner, R.; Palm, J.; Jost, S.; Gowtham, M.; Sorin, F.; Louis, B.; Hock, Rainer (ELSEVIER SCIENCE SA, 2013)
The pentanary chalcogenide Cu2ZnSn(S,Se)(4) (CZTSSe) compound is attracting considerable attention as a low-cost and high-efficient solar cell. The band gap can be tuned by adding Se to pure kesterite Cu2ZnSnS4, which influences the crystallization kinetics. The investigation of the crystallization of the pure selenium (Se) compound Cu2ZnSnSe4 can be helpful in understanding the reaction path between the elements of CZTSSe. Sputtered Cu-poor intermetallic Cu-Zn-Sn precursors were deposited on Mo-coated polyimide foil and sequentially capped by a thermally evaporated Se layer. Two different amounts of Se were deposited: amount that exactly matches the composition of Cu2ZnSnSe4; and that corresponding to twofold excess of the compound's element ratio. These two compositions were chosen to investigate influences of the amount of Se on the reaction path and kinetics. Also, the reaction of pure metallic Sn with Se was studied by stacking Sn layers on Mo-coated foils for observing a Sn-loss phenomenon. It was also deposited with two different amounts of Se matching approximately the compositions of SnSe and SnSe2. Time-resolved X-ray diffraction was employed to measure the solid state reactions while increasing the sample temperature up to 550 degrees C at a rate of 0.5 K/s in an evacuated reaction chamber. After the experiment, sample is analyzed by Raman spectroscopy to distinguish the CZTSe from secondary phases. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: Cu2ZnSnSe(4); CZTSe; SnSe; Sputtering; Formation reaction; In-situ XRD; Raman

Investigation on particle self-assembly in solid lipid-based colloidal drug carrier systems - Illing, Andreas; Unruh, Tobias; Koch, Michel (Pharmaceutical Research, 2004)
Conclusions. Parallel alignment of tripalmitin nanoplatelets is a completely reversible and concentration-dependent effect that can be attributed to the overlap of the exclusion volumes of the anisometric particles. The usefulness of this effect might be explored for the formulation of drug delivery systems.
Keywords: nanoparticles; particle self-assembly; small-angle X-ray scattering; stacked lamellae; tripalmitin

Investigation on the flow behavior of dispersions of solid triglyceride nanoparticles - Unruh, Tobias; Illing, Andreas (International Journal of Pharmaceutics, 2004)
The flow behavior of low concentrated dispersions of solid lipid nanoparticles consisting of either trimyristin, tripalmitin or tristearin and different ionic and nonionic stabilizer blends were investigated using a rheometer with cone and plate apparatus and an Ubbelohde type capillary viscometer. The data demonstrate a remarkable influence of the matrix material, the stabilizer composition and the presence of small amounts of sodium chloride on the formulations' rheological properties. A significant increase in dispersion viscosity was found in the triglyceride sequence trimyristin < tripalmitin < tristearin. This effect can be clearly attributed to an increase in particle shape anisometry with increasing length of the lipid's fatty acid chains. Surfactants, which are present during the crystallization of the dispersed lipid seem to have an additional effect on the nanoparticle shape. Beyond this, ionic surfactants and other salts affect the dispersion viscosity by altering the dimension of the electrical double layer ("second electroviscous effect"). (C) 2004 Elsevier B.V. All rights reserved.
Keywords: solid lipid nanoparticles; rheology; particle shape; second electroviscous effect

Investigations on the melting behaviour of triglyceride nanoparticles - Unruh, Tobias; Bunjes, Heike; Westesen, Kirsten; Koch, Michel (Colloid and Polymer Science, 2001)
Suspensions of triglyceride nanoparticles have been proposed as carrier systems for intravenous administration of poorly water soluble drugs. Such nanosuspensions can easily be produced by homogenization of the melted triglyceride in an aqueous phase. Using special emulsifier blends it is possible to obtain suspensions with an average size of the recrystallized particles below 100 nm (photon correlation spectroscopy z-average). As can be observed by transmission electron microscopy the particles are very thin platelets with thicknesses in the range of only a few molecular layers. Nanoparticles of saturated monoacid triglycerides (smaller than 200 nm) exhibit uncommon melting behaviour, which is expressed in their differential scanning calorimetry curve by multiple endothermal peaks over a temperature range of about 10 degreesC. This effect was attributed earlier to the particle thickness distribution in the suspension rather than to polymorphic transitions since all the material exists in the stable P modification. Here we present experimental investigations on the correlation between the melting behaviour of trilaurin nanosuspensions and the particle thickness distribution determined by analysis of difference X-ray diffraction patterns recorded at progressively higher temperatures in the melting range of the particles. Because of the weak X-ray scattering of the systems investigated synchrotron radiation was used besides conventional sources. The Fourier analysis of the difference diffraction patterns is described in detail and the advantages and difficulties in using this method are discussed. It was observed that the molting temperatures of the nanoparticles increase with increasing particle thicknesses. Simultaneously a decrease in the interplanar (001) spacing with increasing particle thickness was found.
Keywords: trilaurin; nanoparticles; single-line Fourier analysis; broadening of X-ray reflections; difference diffraction patterns

In-Vivo Imaging of Cell Migration Using Contrast Enhanced MRI and SVM Based Post-Processing - Weis, Christian; Heß, Andreas; Budinsky, Lubos; Fabry, Ben (PLoS ONE, 2015)

Iron self diffusion in liquid pure iron and iron-carbon alloys - Meyer, A.; Hennig, L.; Kargl, F.; Unruh, Tobias (Journal of Physics: Condensed Matter, 2019)
With incoherent quasielastic neutron scattering self-diffusion coefficients D-s in pure iron, and iron-carbon alloys containing 8.7 at% and 16.9 at% carbon have been measured. At the melting point D-s in liquid iron is 2.8(1) x 10(-9) m(2) s(-1). For the close-to-eutectic Fe83.1C16.9 composition D-s = 1.33(12) x 10(-9) m(2) s(-1) at T-liq = 1432 K. Contradicting conclusions drawn from literature values of tracer diffusion experiments the addition of carbon has only a minor effect on the iron mobility: at a given temperature the self-diffusion coefficient in Fe83.1C16.9 is only 10% larger than in liquid iron, although mixing has a drastic effect on liquidus temperature and phase behavior.
CRIS-Team WoS Importer:2019-07-26

Island-size distributions of Ag on Pd(111) - Fauster, Thomas; et al. (Surface Review and Letters, 1996)
Island-size distributions of submonolayer Ag films on Pd(111) adsorbed at 90 K and after annealing of the film are recovered from two-photon photoemission spectra of the first image state. The inversion of the ill-conditioned problem with the maximum-entropy method reveals magic numbers in the island-size distributions. Hypothesis testing within the framework of Bayesian probability theory indicates a critical nucleus size i = 1. After annealing of the film large islands coexist with small clusters in a two-phase state.

ISOCHROMAT AND SXAPS STUDIES OF EMPTY ELECTRONIC STATES IN CHROMIUM, IRON AND NICKEL - Fauster, Thomas; et al. (Journal of Physics F. Metal Physics, 1981)

ISOCHROMAT SPECTROSCOPY USING SXAPS EQUIPMENT - Fauster, Thomas; et al. (Applied physics, 1979)

Isolated Rh atoms in dehydrogenation catalysis - Wittkämper, Haiko; Hock, Rainer; Weißer, Matthias; Dallmann, Johannes; Vogel, Carola; Raman, Narayanan; Tacardi, Nicola; Haumann, Marco; Wasserscheid, Peter; Hsieh, Tzung En; Maisel, Sven; Moritz, Michael; et al. (Scientific Reports, 2023)
Isolated active sites have great potential to be highly efficient and stable in heterogeneous catalysis, while enabling low costs due to the low transition metal content. Herein, we present results on the synthesis, first catalytic trials, and characterization of the Ga9Rh2 phase and the hitherto not-studied Ga3Rh phase. We used XRD and TEM for structural characterization, and with XPS, EDX we accessed the chemical composition and electronic structure of the intermetallic compounds. In combination with catalytic tests of these phases in the challenging propane dehydrogenation and by DFT calculations, we obtain a comprehensive picture of these novel catalyst materials. Their specific crystallographic structure leads to isolated Rhodium sites, which is proposed to be the decisive factor for the catalytic properties of the systems.
CRIS-Team Scopus Importer:2023-03-31

Isotope-Disorder-Induced Line Broadening of Phonons in the Raman Spectra of SiC - Hundhausen, Martin; Ley, Lothar; et al. (Physical Review Letters, 2001)
The linewidth of a phonon in isotopically disordered SiC was shown to be not depending on the degree of mass disorder but on the frequency of the phonons. The elastic scattering by mass fluctuations contributed to the linewidth and the scattering rate was proportional to the density of final phonon states.
UnivIS-Import:2015-04-14:Pub.2001.nat.dphy.IAP.LAP.isotop_54

Isotope Effects on the Raman Spectrum of SiC - Hundhausen, Martin; Ley, Lothar; et al. (Materials Science Forum, 2000)
Substituting 12C by the 13C isotope in SiC changes the Raman frequencies. We have used isotopic substitution in several polytypes of SiC (4H, 6H, 15R) to study the change in the phonon dispersion relation of SiC and compare the results with calculations based on a linear-chain model. In a second set of experiments we use isotopic substitution to study the incorporation of carbon from the crucible during the growth of SiC by the modified Lely technique. To this end, a stoichiometric mixture of silicon and pure 13C was used as the charge. The incorporation of 13C in the grown crystal as monitored by spatially resolved Raman spectroscopy yields a gradient of 13C that increases beginning at the seed crystal and reaches a maximum of approximately 40% within 300 μm; the equilibrium concentration of 13C is a mere 27% after 1.5 mm growth.
UnivIS-Import:2015-04-14:Pub.2000.nat.dphy.IAP.LAP.isotop

Isotopic study of Raman active phonon modes in β-Ga2O3 - Janzen, Benjamin M.; Mazzolini, Piero; Gillen, Roland; Falkenstein, Andreas; Martin, Manfred; Tornatzky, Hans; Maultzsch, Janina; Bierwagen, Oliver; Wagner, Markus R. (Journal of Materials Chemistry C, 2021)
Holding promising applications in power electronics, the ultra-wide band gap material gallium oxide has emerged as a vital alternative to materials like GaN and SiC. The detailed study of phonon modes in β-Ga2O3provides insights into fundamental material properties such as crystal structure and orientation and can contribute to the identification of dopants and point defects. We investigate the Raman active phonon modes of β-Ga2O3in two different oxygen isotope compositions (16O,18O) by experiment and theory: By carrying out polarized micro-Raman spectroscopy measurements on the (010) and (2̄01) planes, we determine the frequencies of all 15 Raman active phonons for both isotopologues. The measured frequencies are compared with the results of density functional perturbation theory (DFPT) calculations. In both cases, we observe a shift of Raman frequencies towards lower energies upon substitution of16O with18O. By quantifying the relative frequency shifts of the individual Raman modes, we identify the atomistic origin of all modes (Ga-Ga, Ga-O or O-O) and present the first experimental confirmation of the theoretically calculated energy contributions of O lattice sites to Raman modes. The DFPT results enable the identification of Raman modes that are dominated by the different, inequivalent O- or Ga-atoms of the unit cell. We find that oxygen substitution on the OIIIsite leads to an elevated relative mode frequency shift compared to OIand OIIsites. This study presents a blueprint for the future identification of different point defects in Ga2O3by Raman spectroscopy.
CRIS-Team Scopus Importer:2021-03-19

Is persistent photoconductivity in nipi-structures of amorphous silicon due to the Staebler Wronski e - Hundhausen, Martin; Ley, Lothar; et al. (Solid State Phenomena, 1995)
UnivIS-Import:2015-03-05:Pub.1995.nat.dphy.IAP.exphys.ispers

Josephson behavior of phase-slip lines in wide superconducting strips - Sivakov, A.; Glukhov, A.; Omelyanchouk, A.; Koval, Yury; Müller, Paul; Ustinov, Alexey (Physical Review Letters, 2003)
The phase slip lines in two different materials was discussed. The Shapiro steps under microwave radiation which showed that the frequency of the order parameter oscillation was equal to Josephson frequency was studied. It was observed that a periodic oscillation of a critical current versus the applied magnetic field was found in the strips with a hole in the middle. The evidences of macroscopic quantum interference across a phase-slip line were also elaborated.
UnivIS-Import:2015-03-09:Pub.2003.nat.dphy.IAP.pephys.joseph

Juvenile emperor penguin range calls for extended conservation measures in the Southern Ocean - Houstin, Aymeric; Paranhos Zitterbart, Daniel; Heerah, Karine; Eisen, Olaf; Planas-Bielsa, Victor; Fabry, Ben; Le Bohec, Celine (Royal Society Open Science, 2022)
To protect the unique and rich biodiversity of the Southern Ocean, conservation measures such as marine protected areas (MPAs) have been implemented. Currently, the establishment of several additional protection zones is being considered based on the known habitat distributions of key species of the ecosystems including emperor penguins and other marine top predators. However, the distribution of such species at sea is often insufficiently sampled. Specifically, current distribution models focus on the habitat range of adult animals and neglect that immatures and juveniles can inhabit different areas. By tracking eight juvenile emperor penguins in the Weddell Sea over 1 year and performing a meta-analysis including previously known data from other colonies, we show that conservation efforts in the Southern Ocean are insufficient for protecting this highly mobile species, and particularly its juveniles. We find that juveniles spend approximately 90% of their time outside the boundaries of proposed and existing MPAs, and that their distribution extends beyond (greater than 1500 km) the species' extent of occurrence as defined by the International Union for Conservation of Nature. Our data exemplify that strategic conservation plans for the emperor penguin and other long-lived ecologically important species should consider the dynamic habitat range of all age classes.
CRIS-Team WoS Importer:2022-09-16

Kinetics of field induced oxidation of hydrogen terminated Si(111) by means of a scanning force micoscope - Ley, Lothar; Hundhausen, Martin; et al. (Journal of Vacuum Science & Technology B: Microelectronics Processing and Phenomena, 1996)
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.IAP.exphys.kineti

Kinetics of platinum silicide formation followed in situ by spectroscopic ellipsometry - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Vacuum Science & Technology A, 1999)
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.IAP.exphys.kineti

Kinetics of the field induced commensurate to ferro-electric phase transition in thiourea - Hock, Rainer; et al. (IOP PUBLISHING LTD, 2003)
The paper examines the kinetics of the electric field induced, first-order transition from the commensurate to the ferro-electric phase in thiourea (SC(NH2)(2)) at 170 K. The satellite reflection from the modulated phase, locked in with a wave vector q = 1/9b* disappears when the phase transition is induced by a static electric field E-c along the a-axis. In order to study the kinetics of the phase transition, an oscillating electric voltage of rectangular shape was applied to the sample and photon events were acquired separately for ON- and OFF-field half-periods. Results received in a series of measurements at different amplitudes between 0 and 500 V and frequencies between 0.125 and 512 Hz lead to the conclusion that a slow and a fast relaxation time play a role for the OFF –> ON and the ON –> OFF transitions, respectively. Further, the highest frequency at which the phase transformation still follows the switching of the electric field depends linearly on the applied field amplitude. A qualitative explanation of the experimental results is given in terms of nucleation and growth of specific ferro-electric domains.

Kinetics of the reactive crystallization of CuInSe2 and CuGaSe2 chalcopyrite films for solar cell applications - Hock, Rainer; et al. (ELSEVIER SCIENCE BV, 2006)
The reaction kinetics of stacked layers of binary In-, Ga- and Cu-selenides is investigated by differential thermal analysis using different constant heating rates. We found that the kinetics of the formation of CuInSe2 depends on the binary selenides being present. The kinetic parameters of the reactive crystallization of CuInSe2 and CuGaSe2 were derived. (c) 2005 Elsevier B.V. All rights reserved.
Keywords: kinetics; in-situ monitoring; thermal analysis; CuGaSe2; CuInSe2

Kinetic study of H-terminated silicon nanowires oxidation in very first stages - Bashouti, Muhammad Y.; Sardashti, Kasra; Ristein, Jürgen; Christiansen, Silke (Nanoscale Research Letters, 2013)
Oxidation of silicon nanowires (Si NWs) is an undesirable phenomenon that has a detrimental effect on their electronic properties. To prevent oxidation of Si NWs, a deeper understanding of the oxidation reaction kinetics is necessary. In the current work, we study the oxidation kinetics of hydrogen-terminated Si NWs (H-Si NWs) as the starting surfaces for molecular functionalization of Si surfaces. H-Si NWs of 85-nm average diameter were annealed at various temperatures from 50°C to 400°C, in short-time spans ranging from 5 to 60 min. At high temperatures (T ≥ 200°C), oxidation was found to be dominated by the oxide growth site formation (made up of silicon suboxides) and subsequent silicon oxide self-limitation. Si-Si backbond oxidation and Si-H surface bond propagation dominated the process at lower temperatures (T < 200°C). © 2013 Bashouti; licensee Springer.
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.IAP.exphys.kineti
Keywords: Activation energy; Kinetics; Oxidation; Silicon nanowires

Known operator learning and hybrid machine learning in medical imaging - A review of the past, the present, and the future - Maier, Andreas; Köstler, Harald; Heisig, Marco; Krauss, Patrick; Yang, Seung Hee (Progress in Biomedical Engineering, 2022)
In this article, we perform a review of the state-of-the-art of hybrid machine learning in medical imaging. We start with a short summary of the general developments of the past in machine learning and how general and specialized approaches have been in competition in the past decades. A particular focus will be the theoretical and experimental evidence pro and contra hybrid modelling. Next, we inspect several new developments regarding hybrid machine learning with a particular focus on so-called known operator learning and how hybrid approaches gain more and more momentum across essentially all applications in medical imaging and medical image analysis. As we will point out by numerous examples, hybrid models are taking over in image reconstruction and analysis. Even domains such as physical simulation and scanner and acquisition design are being addressed using machine learning grey box modelling approaches. Towards the end of the article, we will investigate a few future directions and point out relevant areas in which hybrid modelling, meta learning, and other domains will likely be able to drive the state-of-the-art ahead.
CRIS-Team Scopus Importer:2022-04-15
Keywords: grey-box models; hybrid machine learning; known operator learning; machine learning; medical image processing; review

Kohn Anomaly and Electron-Phonon Interaction at the K-Derived Point of the Brillouin Zone of Metallic Nanotubes - Rafailov, Peter M.; Maultzsch, Janina; Thomsen, Christian; Dettlaff-Weglikowska, Urszula; Roth, Siegmar (Nano Letters, 2009)
We applied Raman spectroscopy to investigate the response to electrochemical doping of the second-order D* band in single-walled carbon nanotube (SWNT) bundles. Our study reveals a dramatic increase of the D* band sensitivity to doping upon moving the laser excitation to the red end of the visible spectrum and beyond. Using the double-resonance scattering model, we show that this phenomenon evidences a second Kohn anomaly in metallic SWNTs, located in the K-point-derived region of the Brillouin zone (BZ), which stems from the Kohn anomaly at the K-point of graphene. Our results will be compared to recent doping experiments on graphene with field-effect gating and can be used to investigate the wave-vector dependent electron-phonon coupling in the bulk of the BZ of metallic SWNTs.

Kohn anomaly in graphene - Milosevic, Ivanka; Kepcija, N.; Dobardzic, E.; Damnjanovic, Milan; Mohr, Marcel; Maultzsch, Janina; Thomsen, Christian (Materials Science and Engineering B-Advanced Functional Solid-State Materials, 2011)
Symmetry based analysis of the Kohn anomaly is performed. Kohn phonon frequencies and displacements are calculated by force constant method. It is shown that Kohn phonon vibrations cause electronic band gap opening. (C) 2010 Elsevier B.V. All rights reserved.
Keywords: Graphene; Kohn anomaly; Electron-phonon interaction; Symmetry

Labeling of cancer cells with magnetic nanoparticles for magnetic resonance imaging - Weis, Christian; West, Adrian; Blank, Fabian; Black, Gregory; Woodward, Robert C.; Carroll, Matthew R. J.; Mainka, Astrid; Kartmann, René; Brandl, Anna; Bruns, Heiko; Hallam, Elizabeth; Shaw, Jeremy; et al. (Magnetic Resonance in Medicine, 2014)
The process of invasion and metastasis formation of tumor cells can be studied by following the migration of labeled cells over prolonged time periods. This report investigates the applicability of iron oxide nanoparticles as a magnetic resonance imaging (MRI) contrast agent for cell labeling.?Fe2 O3 nanoparticles prepared with direct flame spray pyrolysis are biofunctionalized with poly-l-lysine (PLL). The nanoparticles within the cells were observed with transmission electron microscopy, bright-field microscopy, and magnetorelaxometry. MRI of labeled cells suspended in agarose was used to estimate the detection limit.PLL-coated particles are readily taken up, stored in intracellular clusters, and gradually degraded by the cells. During cell division, the nanoparticle clusters are divided and split between daughter cells. The MRI detection limit was found to be 25 cells/mm(3) for R2*, and 70 cells/mm(3) for R2. The iron specificity, however, was higher for R2 images. Due to the degradation of intracellular ?Fe2 O3 to paramagnetic iron ions within 13 days, the R1, R2, and R2* contrast gradually decreased over this time period to approximately 50% of its initial value.These results suggest that PLL-coated ?Fe2 O3 nanoparticles can be used as an MRI contrast agent for long-term studies of cell migration. Magn Reson Med 71:1896-1905, 2014. © 2013 Wiley Periodicals, In
EVALuna2:25706

Lamellar carbon-aluminosilicate nanocomposites with macroscopic orientation - Paripovic, Dragana; Hartmann, Lucia; Steinrück, Hans-Georg; Magerl, Andreas; Li-Destri, Giovanni; Fontana, Yannik; Fontcuberta I Morral, Anna; Oveisi, Emad; Bomal, Enzo; Frauenrath, Holger (Nanoscale, 2021)
Novel preparative approaches towards lamellar nanocomposites of carbon and inorganic materials are relevant for a broad range of technological applications. Here, we describe how to utilize the co-assembly of a liquid-crystalline hexaphenylene amphiphile and an aluminosilicate precursor to prepare carbon-aluminosilicate nanocomposites with controlled lamellar orientation and macroscopic order. To this end, the shear-induced alignment of a precursor phase of the two components resulted in thin films comprising lamellae with periodicities on the order of the molecular length scale, an "edge-on" orientation relative to the substrate and parallel to the shearing direction with order on the centimeter length scale. The lamellar structure, orientation, and macroscopic alignment were preserved in the subsequent pyrolysis that yielded the corresponding carbon-aluminosilicate nanocomposites.
CRIS-Team WoS Importer:2021-08-13

Landau-Zener-Stückelberg interferometer on attosecond timescales in graphene - Higuchi, Takuya; Heide, Christian; Ullmann, Konrad; Weber, Heiko B.; Hommelhoff, Peter (Proceedings of SPIE - The International Society for Optical Engineering, 2018)
When solids are exposed to intense optical fields, the intraband electron motion may influence interband transitions, potentially causing a transition of light-matter interaction from a quantum (photon-driven) regime to a semi-classical (field-driven) regime. We demonstrate this transition in monolayer graphene. We observe a carrier-envelope-phasedependent current in graphene irradiated with phase-stable two-cycle laser pulses, showing a striking reversal of the current direction as a function of the driving field amplitude at ∼2 V/nm. This reversal indicates the transition into the field-driven (or strong-field) regime. We show furthermore that in this regime electron dynamics are governed by suboptical-cycle Landau-Zener-Stückelberg interference, comprised of coherent repeated Landau-Zener transitions. We expect these results to have direct ramifications for light-wave driven electronics in graphene.
CRIS-Team Scopus Importer:2022-04-14
Keywords: attosecond physics; grapheme; light-field electronics; strong-field physics

Langmuir-Blodgett Films of Matrix-Diluted Single-Walled Carbon Nanotubes - Krstic, Vojislav; Duesberg, Georg S.; Muster, Jörg; Burghard, Marko; Roth, Siegmar (Chemistry of Materials, 1998)
Keywords: Thin films; Molecules; Monolayers; Colloids; Carbon nanotubes

Large optical field enhancement for nanotips with large opening angles - Thomas, Sebastian; Wachter, Georg; Lemell, Christoph; Burgdörfer, Joachim; Hommelhoff, Peter (New Journal of Physics, 2015)
We theoretically investigate the dependence of the enhancement of optical near-fields at nanometric tips on the shape, size, and material of the tip. We confirm the strong dependence of the field enhancement factor on the radius of curvature. In addition, we find a surprisingly strong increase of field enhancement with increasing opening angle of the nanotips. For gold and tungsten nanotips in the experimentally relevant parameter range (radius of curvature ≥5 nmat 800 nmlaserwavelength), we obtain field enhancement factors of up to ∼35 for Au and ∼12 for W for large opening angles. We confirm this strong dependence on the opening angle for many other materials featuring a wide variety in their dielectric response. For dielectrics, the opening angle dependence is traced back to the electrostatic force of the induced surface charge at the tip shank. For metals, the plasmonic response strongly increases the field enhancement and shifts the maximum field enhancement to smaller opening angle
Keywords: lightning rod effect; nano-optics; nanotips; optical field enhancement; plasmon resonance

Large-scale parallel arrays of silicon nanowires via block copolymer directed self-assembly - Krstic, Vojislav; Farrell, Richard A.; Kinahan, Niall T.; Hansel, Stefan; Stuen, Karl O.; Petkov, Nikolay; Shaw, Matthew T.; West, Laetitia E.; Djara, Vladimir; Dunne, Robert J.; Varona, Olga G.; Gleeson, Peter G.; et al. (Nanoscale, 2012)

Laser-based acceleration of nonrelativistic electrons at a dielectric structure - Breuer, John; Hommelhoff, Peter (Physical Review Letters, 2013)
A proof-of-principle experiment demonstrating dielectric laser acceleration of nonrelativistic electrons in the vicinity of a fused-silica grating is reported. The grating structure is utilized to generate an electromagnetic surface wave that travels synchronously with and efficiently imparts momentum on 28 keV electrons. We observe a maximum acceleration gradient of 25 MeV/m. We investigate in detail the parameter dependencies and find excellent agreement with numerical simulations. With the availability of compact and efficient fiber laser technology, these findings may pave the way towards an all-optical compact particle accelerator. This work also represents the demonstration of the inverse Smith-Purcell effect in the optical regime. © 2013 American Physical Society.
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.IAP.exphys.laserb

Laser-driven acceleration of subrelativistic electrons near a nanostructured dielectric grating: From acceleration via higher spatial harmonics to necessary elements of a dielectric accelerator - McNeur, Joshua; Kozak, Martin; Schönenberger, Norbert; Li, Ang; Tafel, Alexander; Hommelhoff, Peter (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016)
The experimental setup that allows for the observation of energy gain of electrons interacting with Dielectric Laser Accelerators (DLAs) is reviewed. Moreover, recent results, including acceleration due to electron interaction with third, fourth and fifth spatial harmonics of a nanostructured grating are discussed and an extended outlook is given. (C) 2016 Elsevier B.V. All rights reserved.
Keywords: Acceleration; High-gradient; Laser accelerators; Novel accelerators

Laser-Driven Structure-Based Accelerators - England, R. Joel; Filippetto, Daniele; Torrisi, Giuseppe; Bacci, Alberto; Della Valle, Giuseppe; Mascali, David; Mauro, Giorgio Sebastiano; Sorbello, G.; Musumeci, P.; Scheuer, Jakob; Cowan, B.; Schachter, L.; et al. (arXiv, 2022)
Particle acceleration in microstructures driven by ultrafast solid state lasers is a rapidly evolving area of advanced accelerator research, leading to a variety of concepts based on planar-symmetric dielectric gratings, hollow core fibers, photonic crystals, and plasmonic meta-surfaces. This approach leverages well-established industrial fabrication capabilities and the commercial availability of tabletop lasers to reduce cost, with demonstrated axial accelerating fields in the GV/m range. Wide-ranging international efforts have significantly improved understanding of gradient limits, structure design, particle focusing and transport, staging, and development of compatible low-emittance electron sources. With a near-term focus on low-current MeV-scale applications for compact scientific and medical instruments, as well as novel diagnostics capabilities, structure-based laser-driven accelerators have several key benefits that warrant consideration for future high-energy physics machines, including low beamstrahlung energy loss, modest power requirements, stability, and readiness of supporting technologies.

Laser-Triggered Bottom-Up Transcription of Chemical Information: Toward Patterned Graphene/MoS2 Heterostructures - Chen, Xin; Assebban, M'hamed; Kohring, Malte; Bao, Lipiao; Weber, Heiko B.; Knirsch, Kathrin; Hirsch, Andreas (Journal of the American Chemical Society, 2022)

Lattice-plane curvature and small-angle grain boundaries in SiC bulk crystals - Hock, Rainer; et al. (Journal of Applied Crystallography, 2006)
SiC crystals grown by the physical vapour transport process along the [001] direction show a curvature of the crystal growth front in correspondence with the shape of the isotherms. A large radius for the curvature of the isotherms enhances the formation of an extended facet. Under the facet, the lattice planes are flat with a high crystal quality as expressed by rocking-curve half widths of 0.022 degrees. In the non-faceted region, the lattice planes become bent, following the shape of the isotherms with a radius of typically 0.5 to 0.8 m and an increased rocking-curve half width of 0.3 degrees. A reduction of the growth rate from 300 mu m h(-1) to 70 mu m h(-1) does not affect this behaviour significantly. The lattice-plane curvature and the development of the facet are predominantly affected by the shape of the isotherms. For crystals grown in the [015] direction, the lattice planes adjust only in a one-dimensional manner to the isotherms. In all cases, the lattice-plane curvature results from the formation of a high density of small-angle grain boundaries. They are generated by the condensation of dislocations with Burgers vectors in the ab plane.

Lattice vibrations in graphene nanoribbons from density functional theory - Gillen, Roland; Mohr, Marcel; Maultzsch, Janina; Thomsen, Christian (physica status solidi (b), 2009)
This work shows results of our investigation of the lattice vibrations in graphene nanoribbons with zigzag and armchair type edges, which we performed by the use of density functional theory. The boundary conditions induced by the nanoribbon edges allow for an interpretation of the phonons as fundamental modes and their respective overtones. The calculated phonons show a characteristic dependence on the nanoribbon width. In this context, we considered a possible influence of the antiferromagnetic ground state of zigzag nanoribbons with respect to the phonons. Furthermore, we demonstrate that a mapping of the calculated Gamma-point phonon frequencies of nanoribbons onto the phonon dispersion of graphene corresponds to an "unfolding" of the nanoribbons' Brillouin zone onto that of graphene and yields good agreement. We further show symmetry properties of armchair and zigzag nanoribbons and full phonon dispersions for small-width nanoribbons. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhe

Layer-number determination in graphene by out-of-plane phonons - Herziger, Felix; May, Patrick; Maultzsch, Janina (Physical Review B, 2012)
We present and discuss a double-resonant Raman mode in few-layer graphene that is able to probe the number of graphene layers. This so-called N mode on the low-frequency side of the G mode results from a double-resonant Stokes-anti-Stokes process combining an longitudinal optical (LO) and an out-of-plane (ZO') phonon. Simulations of the double-resonant Raman spectra in bilayer graphene show very good agreement with the experiments.

LEED structure determination of the (100)-surface of a CoSi2 crystal and a CoSi2 film grown epitaxially on Si(100) - Weiss, Wolfgang; Starke, Ulrich; Heinz, Klaus; Rangelov, Georgi; Fauster, Thomas; et al. (Surface Science, 1996)
The surface structures of CoSi2(100) for a bulk crystal and a 12 Angstrom thin film grown epitaxially on Si(100) are compared by means of quantitative low energy electron diffraction (LEED). Similar LEED patterns are observed for both systems corresponding to a c(2 x 2) periodicity with respect to the Si(100) surface. Also, intensity versus energy curves are very similar for the film and bulk samples. Consequently, we derive practically the same best-fit model when fitting the experimental data with spectra obtained from full dynamical LEED calculations: the CoSi2 surface is arranged in CaF2 structure, terminated by one full Si layer with an additional c(2 x 2) Si overlayer of half monolayer coverage. The top silicon adatoms reside in four-fold symmetric hollow sites. The unfavourable energetics of this rather peculiar bonding geometry are obviously overcompensated by the energy gain from the saturation of dangling bonds on the surface. The geometry found is consistent with the chemical passivity of the surface.
Keywords: cobalt; epitaxy; low-energy electron diffraction (LEED); low index single crystal surfaces; silicides; silicon; surface relaxation and reconstruction; surface structure

Length-dependence of light-induced currents in graphene - Boolakee, Tobias; Heide, Christian; Wagner, Fabian; Ott, Christian; Schlecht, Maria-Theresa; Ristein, Jürgen; Weber, Heiko B.; Hommelhoff, Peter (Journal of Physics B-Atomic Molecular and Optical Physics, 2020)
We investigate the transport of optically injected currents in graphene, a (semi-) metal with exceptional optical and electronic properties. We have recently shown that ultrashort laser pulses with low temporal symmetry drive coupled intraband motion and interband (Landau-Zener) transitions resulting in residual ballistic currents in graphene. Here we show experimentally how this current scales as a function of the distance between the light-induced current injection region and the adjacent metal contact electrodes and propose an approach to model the results based on diffusive and field driven charge transport. We expect this study to contribute to ongoing discussions on the propagation of light-field-controlled currents, a requirement for future lightwave electronics, operating at petahertz clock rate

LIFETIME OF IMAGE-POTENTIAL STATES ON METAL-SURFACES - Fauster, Thomas; et al. (Physical Review B, 1992)
High-resolution bichromatic two-photon photoemission spectroscopy was used for an investigation of intrinsic linewidths and, thus, lifetimes of image-potential states on clean and adsorbate-covered metal surfaces. The linewidths of the first image state are 16+/-4 and 70+/-8 meV for Cu(111) and Ni(100), respectively. Together with the results for Ag(100) and Ni(111) published previously, a systematic comparison with theoretical predictions is presented. The discrepancies between experiment and theory can be understood qualitatively if the actual band structure is taken into account. A high density of unoccupied bulk or surface states offers many channels for the decay of the image state via electron-hole pair production and results in the large linewidth observed on the nickel surfaces. The opposite is found for Cu(111) where the band gap extends below E(F). For oxygen adsorption on Ni(100), an increase of the linewidth is observed, which can be explained by the lateral confinement of the image state and inelastic scattering by the adsorbate atoms.

LIFETIME OF IMAGE-POTENTIAL STATES ON METAL-SURFACES (VOL 46, PG 13539, 1992) - Fauster, Thomas; et al. (Physical Review B, 1993)

Lifetimes of image-potential states on Cu(100) and Ag(100) measured by femtosecond time-resolved two-photon photoemission - Shumay, Igor; Höfer, Ulrich; Reuss, Christian; Thomann, Ulrich; Wallauer, Wolfgang; Fauster, Thomas (Physical Review B, 1998)
We report time-resolved studies of image-potential stales on Cu(100) and Ag(100). Femtosecond ultraviolet-pump and infrared-probe techniques combined with two-photon photoemission have been used to measure relaxation dynamics of n = 1, 2, and 3 image-potential states. We found the lifetimes of these states on Cu(100) at room temperature to be 40+/-6, 120+/-15, and 300+/-20 fs, respectively. The corresponding values for Ag(100) are 55+/-5, 160+/-10, and 360+/-15 fs. [S0163-1829(98)06643-0].

Lifetimes of unoccupied surface states on Pd(111) - Shumay, Igor; Fauster, Thomas; Chulkov, E. V.; Echenique, P. M.; et al. (Physical Review B, 2000)
Using time-resolved two-photon photoemission we have measured the linewidths and lifetimes of the unoccupied Shockley surface state and first image-potential state on Pd(lll). Calculated values are in good agreement with the experimental results.

Ligand-assisted thickness tailoring of highly luminescent colloidal CH3NH3PbX3 (X = Br and I) perovskite nanoplatelets - Levchuk, Ievgen; Herre, Patrick; Brandl, Marco; Osvet, Andres; Hock, Rainer; Peukert, Wolfgang; Schweizer, Peter; Spiecker, Erdmann; Batentschuk, Miroslaw; Brabec, Christoph (Chemical Communications, 2017)
Quantum size-confined CHNHPbX (X = Br and I) perovskite nanoplatelets with remarkably high photoluminescence quantum yield (up to 90%) were synthesized by ligand-assisted re-precipitation. Thickness-tunability was realized by varying the oleylamine and oleic acid ligand ratio. This method allows tailoring the nanoplatelet thickness by adjusting the number of unit cell monolayers. Broadly tunable emission wavelengths (450-730 nm) are achieved via the pronounced quantum size effect without anion-halide mixing.

Light-field control of real and virtual charge carriers - Boolakee, Tobias; Heide, Christian; Garzón-Ramírez, Antonio; Weber, Heiko B.; Franco, Ignacio; Hommelhoff, Peter (Nature, 2022)
Light-driven electronic excitation is a cornerstone for energy and information transfer. In the interaction of intense and ultrafast light fields with solids, electrons may be excited irreversibly, or transiently during illumination only. As the transient electron population cannot be observed after the light pulse is gone, it is referred to as virtual, whereas the population that remains excited is called real1,<a title="Yamanishi, M. Field-induced optical nonlinearity due to virtual transitions in semiconductor quantum well structures. Phys. Rev. Lett. 59, 1014–1017 (1987)." href="https://www.nature.com/articles/s41586-022-04565-9#ref-CR2">2,3,4. Virtual charge carriers have recently been associated with high-harmonic generation and transient absorption5,<a title="Schlaepfer, F. et al. Attosecond optical-field-enhanced carrier injection into the GaAs conduction band. Nat. Phys. 14, 560–564 (2018)." href="https://www.nature.com/articles/s41586-022-04565-9#ref-CR6">6,<a title="Jürgens, P. et al. Origin of strong-field-induced low-order harmonic generation in amorphous quartz. Nat. Phys. 16, 1035–1039 (2020)." href="https://www.nature.com/articles/s41586-022-04565-9#ref-CR7">7,8, but photocurrent generation may stem from real as well as virtual charge carriers9,<a title="Higuchi, T., Heide, C., Ullmann, K., Weber, H. B. & Hommelhoff, P. Light-field-driven currents in graphene. Nature 550, 224–228 (2017)." href="https://www.nature.com/articles/s41586-022-04565-9#ref-CR10">10,11,12,<a title="Garzón-Ramírez, A. J. & Franco, I. Symmetry breaking in the Stark control of electrons at interfaces (SCELI). J. Chem. Phys. 153, 044704 (2020)." href="https://www.nature.com/articles/s41586-022-04565-9#ref-CR13">13,<a title="Hanus, V. et al. Light-field-driven current control in solids with pJ-level laser pulses at 80 MHz repetition rate. Optica 8, 570 (2021)." href="https://www.nature.com/articles/s41586-022-04565-9#ref-CR14">14. However, a link between the generation of the carrier types and their importance for observables of technological relevance is missing. Here we show that real and virtual charge carriers can be excited and disentangled in the optical generation of currents in a gold–graphene–gold heterostructure using few-cycle laser pulses. Depending on the waveform used for photoexcitation, real carriers receive net momentum and propagate to the gold electrodes, whereas virtual carriers generate a polarization response read out at the gold–graphene interfaces. On the basis of these insights, we further demonstrate a proof of concept of a logic gate for future lightwave electronics. Our results offer a direct means to monitor and excite real and virtual charge carriers. Individual control over each type of carrier will markedly increase the integrated-circuit design space and bring petahertz signal processing closer to reality<a title="Krausz, F. & Stockman, M. I. Attosecond metrology: from electron capture to future signal processing. Nat. Photon. 8, 205–213 (2014)." href="https://www.nature.com/articles/s41586-022-04565-9#ref-CR15">15,16</sup
Keywords: light-driven electronics; graphene; heterostructures; virtual and real charge carriers; ultrafast

Light-field driven currents in graphene - Higuchi, Takuya; Heide, Christian; Ullmann, Konrad; Weber, Heiko B.; Hommelhoff, Peter (arXiv, 2016)
Ultrafast electron dynamics in solids under strong optical fields has recently found particular attention. In dielectrics and semiconductors, various light-field-driven effects have been explored, such as high-harmonic generation, sub-optical-cycle interband population transfer and nonperturbative increase of transient polarizability. In contrast, much less is known about field-driven electron dynamics in metals because charge carriers screen an external electric field in ordinary metals. Here we show that atomically thin monolayer Graphene offers unique opportunities to study light-field-driven processes in a metal. With a comparably modest field strength of up to 0.3 V/Å, we drive combined interband and intraband electron dynamics, leading to a light-field-waveform controlled residual conduction current after the laser pulse is gone. We identify the underlying pivotal physical mechanism as electron quantum-path interference taking place on the 1-femtosecond (10-15s)timescale. The process can be categorized as Landau-Zener-St"uckelberg interferometry. These fully coherent electron dynamics in graphene take place on a hitherto unexplored timescale faster than electron-electron scattering (tens of femtoseconds) and electron-phonon scattering (hundreds of femtoseconds). These results broaden the scope of light-field control of electrons in solids to an entirely new and eminently important material class – metals – promising wide ramifications for band structure tomography and light-field-driven electronics.

Light-field-driven currents in graphene - Higuchi, Takuya; Heide, Christian; Ullmann, Konrad; Weber, Heiko B.; Hommelhoff, Peter (Nature, 2017)
The ability to steer electrons using the strong electromagnetic field of light has opened up the possibility of controlling electron dynamics on the sub-femtosecond (less than 10−15 seconds) timescale. In dielectrics and semiconductors, various light-field-driven effects have been explored, including high-harmonic generation1, 2, 3, 4, sub-optical-cycle interband population transfer5 and the non-perturbative change of the transient polarizability6, 7. In contrast, much less is known about light-field-driven electron dynamics in narrow-bandgap systems or in conductors, in which screening due to free carriers or light absorption hinders the application of strong optical fields6, 8. Graphene is a promising platform with which to achieve light-field-driven control of electrons in a conducting material, because of its broadband and ultrafast optical response, weak screening and high damage threshold9, 10. Here we show that a current induced in monolayer graphene by two-cycle laser pulses is sensitive to the electric-field waveform, that is, to the exact shape of the optical carrier field of the pulse, which is controlled by the carrier-envelope phase, with a precision on the attosecond (10−18 seconds) timescale. Such a current, dependent on the carrier-envelope phase, shows a striking reversal of the direction of the current as a function of the driving field amplitude at about two volts per nanometre. This reversal indicates a transition of light–matter interaction from the weak-field (photon-driven) regime to the strong-field (light-field-driven) regime, where the intraband dynamics influence interband transitions. We show that in this strong-field regime the electron dynamics are governed by sub-optical-cycle Landau–Zener–Stückelberg interference11, composed of coherent repeated Landau–Zener transitions on the femtosecond timescale. Furthermore, the influence of this sub-optical-cycle interference can be controlled with the laser polarization state. These coherent electron dynamics in graphene take place on a hitherto unexplored timescale, faster than electron–electron scattering (tens of femtoseconds) and electron–phonon scattering (hundreds of femtoseconds)12, 13, 14. We expect these results to have direct ramifications for band-structure tomography2 and light-field-driven petahertz electronics8</sup

Light field-driven electron dynamics in 2D-materials - Boolakee, Tobias; Heide, Christian; Weber, Heiko B.; Hommelhoff, Peter (2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021, 2021)
Two dimensional materials such as graphene offer exceptional optical and electronic properties and are therefore predestined for light-field controlled electron dynamics inside of matter. In particular, graphene with its Dirac-cone dispersion relation represents an ideal two-level system where intricately coupled intra-band motion and inter-band (Landau-Zener) electron transitions can be driven under the influence of a strong electric field, i.e., above 2 V/nm [1] , [2]. Using carrier-envelope phase-controlled few-cycle laser pulses, we have demonstrated such repeated Landau-Zener transitions to be driven fully coherently between valence and conduction band, separated only by half an optical period of 1.3 femtoseconds.
CRIS-Team Scopus Importer:2021-10-29

Light-field–driven electronics in the mid-infrared regime: Schottky rectification - Schlecht, Maria-Theresa; Knorr, Matthias; Schmid, Christoph; Malzer, Stefan; Huber, Rupert; Weber, Heiko B. (Science Advances, 2022)

Light induced dynamic magnetochiral anisotropy - Rikken, Geert L.J.A.; van Tiggelen, ‪Bart; Krstic, Vojislav; Wagnière, Georges H. (Chemical Physics Letters, 2005)
In this Letter, we show that chiral molecules subject to a magnetic field in isotropic radiation fields acquire a linear momentum along the field. We also show the existence of the inverse effect, where a chiral molecule moving in an isotropic radiation field acquires a magnetic moment along its velocity.

Light-induced transient changes of the occupied density of defect states of a-Si:H - Ristein, Jürgen; Ley, Lothar; et al. (Journal of Non-Crystalline Solids, 1993)
We have investigated transient changes of the defect density of states upon laser illumination using Photoelectron Yield Spectroscopy. The spectra show an increase of the occupied defect density of states (ODOS) upon illumination between EF and EF-0.75 eV and a decrease in the region of deep tail states. The signal depends sub-linearly on the laser intensity and reaches ΔODOS ≈ 1017 cm-3 eV-1 at an intensity of 50 mW cm-2, the highest intensity used. Time resolved measurements reveal fast rise and slow decay times. We interpret the observed effect either as a signature of weak bond-dangling bond conversion or as an energy relaxation of defects. © 1993.
UnivIS-Import:2015-03-05:Pub.1993.nat.dphy.IAP.exphys.lighti

Light-Matter Interactions in Two-Dimensional Transition Metal Dichalcogenides: Dominant Excitonic Transitions in Mono- and Few-Layer MoX2 and Band Nesting - Gillen, Roland; Maultzsch, Janina (IEEE Journal of Selected Topics in Quantum Electronics, 2017)
We report ab initio calculations of the dielectric function of six mono and bilayer molybdenum dichalcogenides based in a Bethe Salpeter equation+G(0)W(0) (BSE@G(0)W(0)) ansatz, focussing on the excitonic transitions dominating the absorption spectrum up to an excitation energy of 3.2 eV. Our calculations suggest that switching chalcogen atoms and the strength of interlayer interactions should affect the detailed composition of the high "C" peaks in an experimental optical spectra of molybdenum dichalcogenides and cause a significant spin-orbit-splitting of the contributing excitonic transitions in monolayerMoSe(2) and MoTe2. This can be explained through changes in the electronic dispersion around the Fermi energy along the chalcogen series S -> Se -> Te that move the van-Hove singularities in the density of states of the two-dimensional materials along the G-K line in the Brillouin zone. Further, we confirm the distinct interlayer character of the "C" peak transition in few-layer MoS2 that was predicted before from experimental data and show that a similar behavior can be expected for MoSe2 and MoTe2 as wel
Keywords: Nanocrystals; optical films; optical materials; transition metal dichalcogenides

Lightwave-controlled electron dynamics in graphene - Heide, Christian; Higuchi, Takuya; Ullmann, Konrad; Weber, Heiko B.; Hommelhoff, Peter (205, 2019)
We demonstrate that currents induced in graphene by ultrashort laser pulses are sensitive to the exact shape of the electric-field waveform. By increasing the field strength, we found a transition of the light–matter interaction from the weak-field to the strong-field regime at around 2 V/nm, where intraband dynamics influence interband transitions. In this strong-field regime, the light-matter interaction can be described by the wavenumber trajectories of electrons in the reciprocal space. For linearly polarized light the electron dynamics are governed by repeated sub-optical-cycle Landau-Zener transitions between the valence- and conduction band, resulting in Landau-Zener-Stuckelberg interference, whereas for circular polarized light this interference is supresse

Linear and Nonlinear Rheology of Living Cells - Kollmannsberger, Philip; Fabry, Ben (Annual Review of Materials Research, 2011)

Linearity and time-scale invariance of the creep function in living cells. - Lenormand, Guillaume; Millet, Emil J.; Fabry, Ben; Butler, James P.; Fredberg, Jeffrey (Journal of the Royal Society Interface, 2004)

Linear magnetoresistance in mosaic-like bilayer graphene - Kißlinger, Ferdinand; Ott, Christian; Heide, Christian; Kampert, Erik; Butz, Benjamin; Spiecker, Erdmann; Shallcross, Sam; Weber, Heiko B. (Nature Physics, 2015)
The magnetoresistance of conductors usually has a quadratic dependence on magnetic field(1), however, examples exist of non-saturating linear behaviour in diverse materials(2-6). Assigning a specific microscopic mechanism to this unusual phenomenon is obscured by the co-occurrence and interplay of doping, mobility fluctuations and a polycrystalline structure(7,8). Bilayer graphene has virtually no doping fluctuations, yet provides a built-in mosaic tiling due to the dense network of partial dislocations(9,10). We present magnetotransport measurements of epitaxial bilayer graphene that exhibits a strong and reproducible linear magnetoresistance that persists to B = 62 T at and above room temperature, decorated by quantum interference effects at low temperatures. Partial dislocations thus have a profound impact on the transport properties in bilayer graphene, a system that is frequently assumed to be dislocation-free. It further provides a clear and tractable model system for studying the unusual properties of mosaic conductors.