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

Surface conductivity of diamond: a novel transfer doping mechanism - Ristein, Jürgen; Ley, Lothar; et al. (Physica B-Condensed Matter, 2006)
A novel doping mechanism is presented for the case of diamond that does not rely on the incorporation of dopant atoms into the crystal lattice as in conventional doping. Instead, adsorbates provide the acceptor level into which electrons are transferred, leading to a two-dimensional subsurface hole accumulation layer with an areal concentration of up to 10 13 cm -2. Two acceptor systems are discussed. One is based on the charge exchange between diamond and solvated H + ions in a water layer that forms spontaneously on all surfaces in air. The other relies on the high electron affinity of fullerenes and fluorinated fullerenes that act as efficient acceptors when physisorbed at the surface. In either case, the extremely low ionization energy of hydrogen terminated diamond that is matched by no other semiconductor is a necessary requirement for transfer doping. © 2006 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.exphys.surfac_7
Keywords: Devices; Diamond; Doping; Surfaces

Surface Conductivity of Diamond as a Function of Nitrogen Doping - Ristein, Jürgen; Ley, Lothar; et al. (physica status solidi (a), 2001)
The surface conductivity of diamond has recently attracted a lot of interest since a number of electronic applications proposed for diamond are based on this effect. Nevertheless, its microscopic origin is still a matter of debate. We describe in the following experiments in which the impact of the balk defect concentration of diamond on the surface conductivity is investigated. The experiments show that surface conductivity is suppressed in the presence of donor-like nitrogen defects although the surfaces are clearly hydrogen (or deuterium) terminated. We suggest compensation of the surface or surface near acceptors to be the reason for this suppression. A quantitative discussion shows that the doping capability of the surface acceptors is exhausted at lateral concentrations of about 3 × 1013 cm-2.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.surfac

Surface conductivity of nitrogen-doped diamond - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 2002)
Synthetic type Ib diamond crystals with (001) surfaces that expose growth sectors of different nitrogen content have been used to study the phenomenon of p-type surface conductivity upon plasma hydrogenation and upon overgrowth with thin epitaxial CVD diamond layers. We found that an unbiased microwave-driven hydrogen plasma leads to surface conductivity only on well-defined regions on the substrates that correlate with growth sectors of low nitrogen content; whereas no conductive layer is found on top of growth sectors with higher nitrogen concentrations in the range of 200 ppm. After growing a homoepitaxial intrinsic diamond layer of only 20 nm on top of the nitrogen doped diamond, these differences are no longer observed and surface conductivity is established homogeneously over the whole sample. The same effect can be achieved by exposing the Ib substrates to a pure hydrogen plasma provided the sample is biased with an additional DC voltage of -250 V. Both results can be understood in the framework of the surface transfer doping model suggested earlier by Maier and colleagues when the compensation of nitrogen donors by surface acceptors and their passivation by hydrogen is taken into account. The quantitative discussion shows that the doping capability of the surface acceptors is exhausted at lateral concentrations of approximately 1×1013 cm-2, which also corresponds to the maximum hole concentration usually observed in hydrogen-induced p-type conductive layers. © 2002 Elsevier Science B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2002.nat.dphy.IAP.exphys.surfac
Keywords: Diamond defects; Electronic states; Impurities; Surface

Surface doping: a special feature of diamond - Ristein, Jürgen; Ley, Lothar; et al. (Journal of Physics: Condensed Matter, 2001)
A unique feature of diamond surfaces is a highly conductive p-type layer, which is usually observed when the surfaces are hydrogen terminated. This phenomenon has recently attracted a lot of interest since a number of electronic applications proposed for diamond are based on the effect. Nevertheless, its microscopic origin is still a matter of debate. In this paper we propose an electron transfer from the diamond valence band to adsorbates at the surface to be the effective doping mechanism. These adsorbates act not as isolated species but as components of a mildly acidic aqueous surface layer and thus charge exchange has to be described by electrochemical arguments. The model is supported by experiments, which show that the hydrogenation of the surface is necessary but not sufficient for inducing the hole accumulation layer at the surface.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.surfac_8

Surface electronic properties of diamond - Ristein, Jürgen; Maier, Florian; Ley, Lothar; et al. (physica status solidi (a), 2000)
The influence of surface states, defects and adsorbates on the electronic properties of diamond surfaces are discussed. As far as surface states and reconstructions are concerned the principal crystallographic surfaces, (100), (111) and (110), are essentially understood in their adsorbate free form and also when terminated by hydrogen. The role of surface defects is addressed and the correlation between the position of the surface Fermi level and the concentration of surface defects is discussed quantitatively for p-type diamond. Hydrogen passivation leads to a negative electron affinity of diamond surfaces due to a dipole layer which is induced by the heteropolar carbon-hydrogen bonds of the surface atoms. This aspect is discussed quantitatively. Finally, an experiment in which photoelectron spectroscopy and in situ conductivity measurements were combined to elucidate the surface conductivity of diamond is described and analyzed.
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.IAP.exphys.surfac

Surface electronic structure and dynamics of lead halide perovskites - Niesner, Daniel (APL Materials, 2020)
A number of studies investigating the electronic structure of well-defined lead halide perovskite surfaces have emerged in the last five years. Surfaces and their interfaces can not only have considerable effects on the performance of devices such as solar cells but also open a window into the intrinsic electronic properties of lead halide perovskites. This is particularly true for angle-resolved photoelectron spectroscopy, which is possibly the technique giving the most direct access to the electronic (band) structure of a material. The pump-probe version of the technique, two-photon photoelectron spectroscopy, gives information about the femtosecond and picosecond electron dynamics following optical excitation. This review summarizes the recent progress made using these surface-sensitive techniques. In addition, differences between the optical and electronic properties between the near-surface (hundreds of nm) and the deep bulk material of single crystals are discussed. We point out critical issues concerning the comparability between individual results arising from the different depths and timescales probed, or from differing environmental conditions such as the temperature or the surrounding atmosphere.
CRIS-Team Scopus Importer:2020-10-23

Surface Fermi level position of hydrogen passivated Si (111) surfaces - Ristein, Jürgen; Ley, Lothar; et al. (Applied Physics Letters, 1996)
Core and valence band photoemission data of hydrogen passivated Si(111):H surfaces yield surface Fermi level positions that are indicative of a near-surface depletion layer for n- as well as p-type samples. The bulk Fermi level positions are attained after annealing at ∼400°C. These observations are explained in terms of a hydrogen induced passivation of donors and acceptors in a surface layer of the order of a μm as a result of the wet-chemical etching procedure. © 1996 American Institute of Physics.
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.IAP.exphys.surfac

SURFACE GEOMETRY DETERMINATION BY LARGE-ANGLE ION-SCATTERING - Fauster, Thomas (Vacuum, 1988)

Surface morphology on a nanometer scale studied by two-photon photoelectron spectroscopy - Fauster, Thomas (1995)
Keywords: metal epitaxy; surface morphology; image-potential states; photoelectron spectroscopy

Surface Physics - Fauster, Thomas; Hammer, Lutz; Heinz, Klaus; Schneider, M. Alexander (De Gruyter Oldenbourg, 2020)
This work introduces concisely into modern and experimental Surface Physics. Based on many years of teaching experience, the authors present surface-specific properties and complex processes in a plain and descriptive way. Ideal for exam preparation through tasks and comprehension questions. Concepts of Surface Physics: From sample preparation to diverse analysis methods. Many chapters for advanced studies. Prepares for examinations.

Surface science of diamond: familiar and amazing - Ristein, Jürgen (Surface Science, 2006)
The crystal structure of diamond is identical with that of its more common semiconductor relatives silicon and germanium. Consequently, a number of surface properties in terms of reconstructions, surface states and surface band diagrams are similar as in the case of Si or Ge. But diamond also exhibits a number of unusual and potentially very useful surface properties. Particularly when the surface dangling bonds are saturated by monovalent hydrogen atoms (donor-like), surface states are removed from the gap, the electron affinity changes sign and becomes negative, and the material becomes susceptible to an unusual type of transfer doping where holes are injected by acceptors located at the surface instead of inside the host lattice. These surface acceptors can in the simplest case be adsorbed molecules conveniently chosen by their electron affinity, but they can also be solvated ions within atmospheric water layers or electrolytes in contact with the hydrogenated diamond surface. In this article the surface properties of diamond will be reviewed with special emphasis on this new kind of doping mechanism. © 2006 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.exphys.surfac_0
Keywords: Adsorption; Density functional calculations; Diamond; Electrical transport measurements; Electron emission measurements; Surface electrical transport; Surface electronic phenomena; Surface relaxation and reconstruction

Surface sensitive K-edge absorption spectroscopy of clean and hydrogen terminated diamond (111) and (100) surfaces - Ristein, Jürgen; Ley, Lothar; et al. (Physical Review B, 1999)
We present a detailed electron yield spectroscopy study of the pre-K-edge features of single-crystal diamond (100) and (111) surfaces which are induced by optical transitions from the C 1s core level into excited states. Both hydrogen-terminated and hydrogen-free surfaces were investigated. A sharp maximum at ℏω =287.2 eV in the spectra of the (111) and (100) surfaces is characteristic of the monohydrogenated surfaces, which is interpreted as a strongly localized intramolecular excitation within the C-H bond of a surface atom. The clean diamond surfaces show maxima in the absorption spectra at ℏω=284.6 eV for the (111) surface, and at 284.15 and 286.3 eV for the (100) surface which are interpreted as surface core excitons. From the polarization dependence of the intensities of these features and by using dipole selection rules, the point-group symmetry of the excited states involved in the optical transition is deduced. The transition energies of the absorption maxima of the clean surface are discussed in terms of pertinent band-structure calculations and excitonic effects. ©1999 The American Physical Society.
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.IAP.exphys.surfac

Surface state dispersions on diamond (100) and (111) surfaces - Ristein, Jürgen; Ley, Lothar; et al. (the Physics of Semiconductors, 1996)
UnivIS-Import:2015-04-20:Pub.1996.nat.dphy.IAP.exphys.surfac_7

Surface States and Adsorbate-Induced Electronic Structure - Fauster, Thomas; Petek, Hrvoje; Wolf, Martin (Dynamics at Solid State Surfaces and Interfaces, 2012)
Keywords: Electron affinity; Image potential states; Image-charge interaction; Intrinsic surface states; Probability density; Surface Brillouin zone

Surface structure and stacking of the commensurate (√13×√13)R13.9∘ charge density wave phase of 1T−TaS2(0001) - Von Witte, Gevin; Kißlinger, Tilman; Horstmann, Jan Gerrit; Rossnagel, Kai; Schneider, M. Alexander; Ropers, Claus; Hammer, Lutz (Physical Review B, 2019)

SURFACE-STRUCTURE DETERMINATION OF THE (2 X 1)O-CU(110) RECONSTRUCTION BY LOW-ENERGY ION-SCATTERING - Fauster, Thomas; et al. (Surface Science, 1991)
Using impact collision ion scattering we show, that the reconstruction of the (2 x 1)O-Cu(110) surface is of the missing-row type where every other [001] row of copper atoms is missing. The oxygen atoms are located 0.08 +/- 0.15 angstrom below the copper atoms of the remaining rows. The second layer copper atoms are shifted laterally 0.12 +/- 0.07 angstrom away from the oxygen atoms in a pairing-row type reconstruction. The first layer is relaxed outward over 0.23 +/- 0.04 angstrom compared to the ideal spacing, whereas the distance between the second and third layer remains unchanged. A critical comparison of our results with the data available in the literature shows that the position of copper and oxygen atoms can be determined with an accuracy of about 0.05 and 0.15 angstrom, respectively.

Surface telluride phases on Pt(111): Reconstructive formation of unusual adsorption sites and well-ordered domain walls - Kißlinger, Tilman; Schewski, Alexandra; Raabgrund, Andreas; Loh, Hannah; Hammer, Lutz; Schneider, M. Alexander (Physical Review B, 2023)
For the production of transition-metal dichalcogenides by molecular beam epitaxy, an understanding of the interaction between chalcogenide atoms and metal surfaces is of fundamental interest. Here, we describe the occurrence of stable surface telluride phases when reacting submonolayer amounts of tellurium with a Pt(111) surface. We find that when approaching a Te amount of 0.44 monolayers from below, a disordered Te adsorbate phase is converted into a long-range ordered Pt(111)-(3×3)-4Te surface telluride, which is stable against loss of Te up to 890 K. Adding further Te, heavy domain walls develop that condense into a well-ordered domain structure with (10×10) periodicity. It hosts 49 Te atoms per unit cell and is thermally stable up to 770 K. These two phases are the only existing Te-induced surface reconstructions in the submonolayer regime. The atomic structure of the two phases is determined using low-energy electron diffraction intensity analysis, scanning tunneling microscopy, and density functional theory. The resulting complex surface structures are revealed with picometer accuracy and a great agreement between the employed methods. In particular, the analysis of the (10×10) structure demonstrates the currently achievable state-of-the-art for low-energy electron diffraction structural analyses in terms of experimental surface preparation and data collection but also of computational methods, and it leads the way to building up a structural database for two-dimensional materials and their interfaces.
CRIS-Team Scopus Importer:2023-12-01

Surface transfer doping of diamond - Ristein, Jürgen; Ley, Lothar; et al. (Nature, 2004)
The electronic properties of many materials can be controlled by introducing appropriate impurities into the bulk crystal lattice in a process known as doping. In this way, diamond (a well-known insulator) can be transformed into a semiconductor, and recent progress in thin-film diamond synthesis has sparked interest in the potential applications of semiconducting diamond. However, the high dopant activation energies (in excess of 0.36 eV) and the limitation of donor incorporation to (111) growth facets only have hampered the development of diamond-based devices. Here we report a doping mechanism for diamond, using a method that does not require the introduction of foreign atoms into the diamond lattice. Instead, C60 molecules are evaporated onto the hydrogen-terminated diamond surface, where they induce a sub-surface hole accumulation and a significant rise in two-dimensional conductivity. Our observations bear a resemblance to the so-called surface conductivity of diamond seen when hydrogenated diamond surfaces are exposed to air, and support an electrochemical model in which the reduction of hydrated protons in an aqueous surface layer gives rise to a hole accumulation layer. We expect that transfer doping by C60 will open a broad vista of possible semiconductor applications for diamond.
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.IAP.exphys.surfac

Surface transfer doping of diamond by fullerene - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 2005)
Fifteen years after Landstrass and Ravi [1] [I.M. Landstrass, K.V. Ravi, App. Phys. Lett, 55 (1989) 975] reported a hydrogen induced surface conductivity of diamond, it has now been established that the phenomenon is based on a sub-surface hole accumulation layer. A quantitative model for the origin of this layer has been proposed by our group earlier and is based on the charge exchange between the diamond surface and solvated ions in a water layer that forms spontaneously on all surfaces in air. The process relies on the particularly low ionization energy of the hydrogenated diamond surface [2] [F. Maier, M. Riedel, B. Mantel, J. Ristein, and L. Ley, Phys. Rev. Lett. 85 (2000) 3472]. Here, we report on fullerenes (C60) and fluorinated fullerenes (C60F48) as alternative adsorbate systems. They induce surface conductivity on a level comparable (C60) or even higher (C60F48) than that observed under atmospheric conditions. Whereas in the case of C60 efficient doping requires the formation of the van-der Waals solid on top of the surface of diamond, C60F 48 acts as surface acceptor even as isolated molecule. In both cases, the doping efficiency can be modeled by considering the electrochemical equilibrium between the diamond and the adsorbate layer. © 2005 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.IAP.exphys.surfac
Keywords: Diamond film; p-type doping; Surface electronic properties

Surface transfer doping of semiconductors - Ristein, Jürgen (Science, 2006)
The local conductivity of semiconductors can be changed by incorporating various atoms into the semiconductor material. New work shows that manipulation of the surface can produce the same effect.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.exphys.surfac_2

Switching of a coupled spin pair in a single-molecule junction - Wagner, Stefan; Kißlinger, Ferdinand; Ballmann, Stefan; Schramm, Frank; Chandrasekar, Rajadurai; Bodenstein, Tilmann; Fuhr, Olaf; Secker, Daniel; Fink, Karin; Ruben, Mario; Weber, Heiko B. (Nature Nanotechnology, 2013)
Single-molecule spintronics investigates electron transport through magnetic molecules that have an internal spin degree of freedom. To understand and control these individual molecules it is important to read their spin state. For unpaired spins, the Kondo effect has been observed as a low-temperature anomaly at small voltages. Here, we show that a coupled spin pair in a single magnetic molecule can be detected and that a bias voltage can be used to switch between two states of the molecule. In particular, we use the mechanically controlled break-junction technique to measure electronic transport through a single-molecule junction containing two coupled spin centres that are confined on two Co 2+ ions. Spin-orbit configuration interaction methods are used to calculate the combined spin system, where the ground state is found to be a pseudo-singlet and the first excitations behave as a pseudo-triplet. Experimentally, these states can be assigned to the absence and occurrence of a Kondo-like zero-bias anomaly in the low-temperature conductance data, respectively. By applying finite bias, we can repeatedly switch between the pseudo-singlet state and the pseudo-triplet state. © 2013 Macmillan Publishers Limited. All rights reserved.
UnivIS-Import:2015-04-14:Pub.2013.nat.dphy.IAP.LAP.switch

Symmetry-based analysis of the electron-phonon interaction in graphene - Milosevic, Ivanka; Kepcija, N.; Dobardzic, E.; Mohr, Marcel; Maultzsch, Janina; Thomsen, Christian; Damnjanovic, Milan (physica status solidi (b), 2009)
Symmetry-based analysis of the electron-phonon interaction in graphene is performed. Some nontrivial physical properties of graphene are shown to be direct consequence of symmetry, independent on the applied dynamical model. Namely, it is found that there are vibronically uncoupled non symmetric modes which thus might be responsible for the stability of the honeycomb lattice. Symmetry also predicts vanishing of the electron-phonon interaction for quite a number of the normal displacements. Consequently, lattice dynamics along these degrees of freedom is governed by the ion repulsion which leads to the anharmonic terms, being linear in absolute elongation. In particular, this effect is attributed to the K and Gamma points of the Brillouin zone, giving insight into origin of the Kohn anomaly. The results are further numerically confirmed within full and tight-binding density functional calculations and force constants model. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA Weinheim

Symmetry based analysis of the Kohn anomaly and electron-phonon interaction in graphene and carbon nanotubes - Milosevic, Ivanka; Kepcija, N.; Dobardzic, E.; Mohr, Marcel; Maultzsch, Janina; Thomsen, Christian; Damnjanovic, Milan (Physical Review B, 2010)
Symmetry based analysis of the electron-phonon coupling in graphene and carbon nanotubes is performed and Kohn anomalies, their Brillouin-zone positions together with the complete set of good quantum numbers are predicted. Interestingly, graphene dynamical representation is found to contain only a small portion of quite a large set of inequivalent irreducible representations of the relevant full symmetry group. Besides, vanishing of the electron-phonon interaction for majority of the normal displacements is also shown to be a consequence of the symmetry. The results are further numerically confirmed within full and tight-binding density-functional calculations and force constants model and enhanced coupling to the Fermi level electrons of the Dirac point A(1g) mode with respect to the Gamma point E(2g) mode is confirmed. Finally, energy dispersion of the kink phonon spectrum is analytically evaluated and compared to the classical phonon spectrum.

Symmetry properties of vibrational modes in graphene nanoribbons - Gillen, Roland; Mohr, Marcel; Maultzsch, Janina (Physical Review B, 2010)
We present symmetry properties of the lattice vibrations of graphene nanoribbons with pure armchair (AGNRs) and zigzag edges (ZGNRs). In nonsymmorphic nanoribbons, the phonon modes at the edge of the Brillouin zone are twofold degenerate whereas the phonon modes in symmorphic nanoribbons are nondegenerate. We identified the Raman-active and infrared-active modes. We predict 3N and 3 (N+1) Raman-active modes for N-ZGNRs and N-AGNRs, respectively (N is the number of dimers per unit cell). These modes can be used for the experimental characterization of graphene nanoribbons. Calculations based on density-functional theory suggest that the frequency splitting of the LO and TO modes in AGNRs (corresponding to the E-2g mode in graphene) exhibits characteristic width and family dependence. Further, all graphene nanoribbons have a Raman-active breathing like mode, the frequency of which is inversely proportional to the nanoribbon width and thus might be used for experimental determination of the width of graphene nanoribbon

Syntheses, Characterization, and Magnetic Studies of Copper(II) Complexes with the Ligand N,N,N ',N '-Tetrakis(2-pyridylmethyl)-1,3-benzenediamine (1,3-tpbd) and its Phenol Derivative 2,6-Bis[bis(2-pyridylmethyl)amino]-p-cresol] (2,6-Htpcd) - Turba, Sabrina; Foxon, Simon P.; Beitat, Alexander; Heinemann, Frank Wilhelm; Petukhov, Konstantin; Müller, Paul; Walter, Olaf; Lloret, Francesc; Julve, Miguel; Schindler, Siegfried (Inorganic Chemistry, 2012)
The copper(II) complexes [Cu-4(1,3-tpbd)(2)(H2O)(4)(NO3)(4)](n)(NO3)(4n)center dot 13nH(2)O (1), [Cu-4(1,3-tpbd)(2)(AsO4)(ClO4)(3)(H2O)](ClO4)(2)center dot 2H(2)O center dot 0.5CH(3)OH (2), [Cu-4(1,3-tpbd)(2)(PO4)(ClO4)(3)(H2O)](ClO4)(2)center dot 2H(2)O.0.5CH(3)OH (3), [Cu-2(1,3-tpbd)-(PhO)(2)PO2(2)](2)(ClO4)(4) (4), and [Cu-2(1,3-tpbd)(PhO)PO3(2)(H2O)(0.69)-(CH3CN)(0.31)](2)(BPh4)(4)center dot Et2O center dot CH3CN (5) [1,3-tpbd=N,N,N',N'-tetrakis(2-pyridylmethyl)-1,3-benzenediarnine, BPh4- = tetraphenylborate] were prepared and structurally characterized. Analyses of the magnetic data of 2, 3, 4, and [Cu-2(2,6-tpcd)(H2O)Cl](ClO4)(2) (6) [2,6-tpcd = 2,6-bis[bis(2-pyridylmethyl)amino]-p-cresolate] show the occurrence of weak antiferromagnetic interactions between the copper(II) ions, the bis-terdentate 1,3-tpbd/2,6-tpcd, mu(4)-XO4 (X = As and P) mu(1,2)-OPO and mu-O-phenolate appearing as poor mediators of exchange interactions in this series of compounds. Simple orbital symmetry considerations based on the structural knowledge account for the small magnitude of the magnetic couplings found in these copper(II) compounds.

Synthesis and characterisation of new MO(OH)(2) (M = Zr, Hf) oxyhydroxides and related Li2MO3 salts - Baklanova, Yana V.; Denisova, Tatyana A.; Maksimova, Lidiya G.; Tyutyunnik, Alexander P.; Baklanova, Inna V.; Shein, Igor R.; Neder, Reinhard; Tarakina, Nadezda V. (Dalton Transactions, 2014)
Two new solid MO(OH)(2) (M = Zr, Hf) oxyhydroxides have been synthesised by an ion-exchange reaction from Li2MO3 (M = Zr, Hf) precursors obtained by a citrate combustion technique. The crystal structure of the oxyhydroxides has been solved by direct methods and refined using Rietveld full profile fitting based on X-ray powder diffraction data. Both oxyhydroxides crystallize in a P2(1)/c monoclinic unit cell and have a structure resembling that of the related salts. Detailed characterisation of the fine-structure features and chemical bonding in precursors and oxyhydroxide powders has been performed using vibrational spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, pair distribution function analysis and quantum-chemical modelling.

Synthesis and Characterization of Nanotubes from Misfit (LnS)(1+y)TaS2 (Ln=Pr, Sm, Gd, Yb) Compounds - Serra, Marco; Stolovas, Dalit; Houben, Lothar; Popovitz-Biro, Ronit; Pinkas, Iddo; Kampmann, Felix; Maultzsch, Janina; Joselevich, Ernesto; Tenne, Reshef (Chemistry - A European Journal, 2018)
The synthesis and characterization of nanotubes from misfit layered compounds (MLCs) of the type (LnS)(1+y)TaS2 (denoted here as LnS-TaS2; Ln=Pr, Sm, Gd, and Yb), not reported before, are described (the bulk compound YbS-LaS2 was not previously documented). Transmission electron microscopy and selected area electron diffraction showed that the interlayer spacing along the c axis decreased with an increase in the atomic number of the lanthanide atom, which suggested tighter interaction between the LnS layer and TaS2 for the late lanthanides. The Raman spectra of the tubules were studied and compared to those of the bulk MLC compounds. Similar to the bulk MLCs, the Raman spectra could be divided into the low-frequency modes (110-150cm(-1)) of the LnS lattice and the high-frequency modes (250-400cm(-1)) of the TaS2 lattice. The Raman spectra indicated that the vibrational lattice modes of the strained layers in the tubes were stiffer than those in the bulk compounds. Furthermore, the modes of the late lanthanides were higher in energy than those of the earlier lanthanides, which suggested larger charge transfer between the LnS and TaS2 layers for the late lanthanides. Polarized Raman measurements showed the expected binodal intensity profile (antenna effect). The intensity ratio of the Raman signal showed that the E-2g mode of TaS2 was more sensitive to the light-polarization effect than its A(1g) mode. These nanotubes are expected to reveal interesting low-temperature quasi-1D transport behavior.
Keywords: lanthanides; misfit compounds; nanomaterials; nanotubes; two-dimensional materials

Synthesis and characterization of silver-doped mesoporous bioactive glass and its applications in conjunction with electrospinning - Ciraldo, Francesca; Liverani, Liliana; Gritsch, Lukas; Goldmann, Wolfgang; Boccaccini, Aldo R. (Materials, 2018)
Keywords: Bioactive glass; Antimicrobial; Ordered mesoporous glass; Electrospinning; Silver; Scaffolds

Synthesis, characterization, antibacterial properties, and in vitro studies of selenium and strontium co-substituted hydroxyapatite - Maqbool, Muhammad; Nawaz, Qaisar; Ur Rehman, Muhammad Atiq; Cresswell, Mark; Jackson, Phil; Hurle, Katrin; Detsch, Rainer; Goldmann, Wolfgang; Shah, Asma Tufail; Boccaccini, Aldo R. (International Journal of Molecular Sciences, 2021)
In this study, as a measure to enhance the antimicrobial activity of biomaterials, the selenium ions have been substituted into hydroxyapatite (HA) at different concentration levels. To balance the potential cytotoxic effects of selenite ions (SeO32−) in HA, strontium (Sr2+) was co-substituted at the same concentration. Selenium and strontium-substituted hydroxyapatites (Se-Sr-HA) at equal molar ratios of x Se/(Se + P) and x Sr/(Sr + Ca) at (x = 0, 0.01, 0.03, 0.05, 0.1, and 0.2) were synthesized via the wet precipitation route and sintered at 900 °C. The effect of the two-ion concentration on morphology, surface charge, composition, antibacterial ability, and cell viability were studied. Xray diffraction verified the phase purity and confirmed the substitution of selenium and strontium ions. Acellular in vitro bioactivity tests revealed that Se-Sr-HA was highly bioactive compared to pure HA. Se-Sr-HA samples showed excellent antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus carnosus) bacterial strains. In vitro cell–material interaction, using human osteosarcoma cells MG-63 studied by WST-8 assay, showed that Se-HA has a cytotoxic effect; however, the co-substitution of strontium in Se-HA offsets the negative impact of selenium and enhanced the biological properties of HA. Hence, the prepared samples are a suitable choice for antibacterial coatings and bone filler applications.
CRIS-Team Scopus Importer:2021-04-30
Keywords: Antibacterial; Co-substituted hydroxyapatite; Cytocompatibility; Selenium; Strontium

Synthesis, magnetic properties, and STM spectroscopy of an unprecedented octanuclear chloro-bridged nickel(II) double cubane. - Scheurer, Andreas; Gieb, Klaus; Alam, Mohammad S.; Heinemann, Frank Wilhelm; Saalfrank, Rolf; Kroener, Wolfgang; Petukhov, Konstantin; Stocker, Michael; Müller, Paul (Dalton Transactions, 2012)
Reaction of nickel(II) chloride hexahydrate with N-n-butyldiethanolamine H(2)L (3) in the presence of LiH in anhydrous THF leads to the formation of the unique octanuclear chloro-bridged nickel(II) double cubane [(Ni(II)(4)(μ(3)-OH)Cl(3)(HL)(3)μ(2)-Cl)(2)] (4) in 57% yield. According to single crystal X-ray structure analysis, complex 4·4CH(2)Cl(2) possesses a [(Ni(4)(μ(3)-OH)(μ(3)-O)(3)(OH)(3)(N)(3)(Cl)(3)μ(2)-Cl)(2)] core and crystallizes in the monoclinic space group P2(1)/c with a = 18.292(2), b = 19.8972(5), c = 23.295(2) Å, β = 98.408(6)°, V = 8387.3(8) Å(3), and four molecules in the unit cell. The analysis of the SQUID magnetic susceptibility data identified 4 as a weakly coupled dimer (J(1) = 14.5 K, J(2) = -0.6 K) with a ground state of S = 0, resulting from two S = 4 states of each Ni(4) subunits. Although complex 4 does not show an ac out-of-phase signal in a zero dc field at temperatures of 1.8 K and higher, low-temperature magnetization measurements revealed that complex 4 is a single-molecule magnet and shows hysteretic magnetization characteristics with typical temperature and sweep-rate dependencies. The eye-catching feature of complex 4 is the presence of two different blocking temperatures (0.9 K around zero field and 1.3 K at higher fields). The origin of this highly unusual behavior can be assigned to the dimer-nature of the interaction between the two S = 4 units. Furthermore STM and current imaging tunnelling spectroscopy (CITS) were performed on aggregates of 4 drop-coated on highly oriented pyrolytic graphite (HOPG) surfaces. CITS measurements show a strong contrast in the area of the nickel centers and a HOMO-LUMO gap of approximately 0.8 V.

Synthesis, magnetic properties, and STM spectroscopy of cobalt(II) Cubanes [Co(II) (4)(Cl)(4)(HL)(4)]. - Scheurer, Andreas; Ako, Ayuk Manase; Saalfrank, Rolf; Heinemann, Frank Wilhelm; Hampel, Frank; Petukhov, Konstantin; Gieb, Klaus; Stocker, Michael; Müller, Paul (Chemistry - A European Journal, 2010)
Reaction of cobalt(II) chloride hexahydrate with N-substituted diethanolamines H(2)L(2-4) (3) in the presence of LiH in anhydrous THF leads under anaerobic conditions to the formation of three isostructural tetranuclear cobalt(II) complexes [Co(II) (4)(Cl)(4)(HL(2-4))(4)] (4) with a [Co(4)(mu(3)-O)(4)](4+) cubane core. According to X-ray structural analyses, the complexes 4 a,c crystallize in the tetragonal space group I4(1)/a, whereas for complex 4 b the tetragonal space group Par 4 was found. In the solid state the orientation of the cubane cores and the formation of a 3D framework were controlled by the ligand substituents of the cobalt(II) cubanes 4. This also allowed detailed magnetic investigations on single crystals. The analysis of the SQUID magnetic susceptibility data for 4 a gave intramolecular ferromagnetic couplings of the cobalt(II) ions (J(1) approximately 20.4 K, J(2) approximately 7.6 K), resulting in an S=6 ground-state multiplet. The anisotropy was found to be of the easy-axis type (D=-1.55 K) with a resulting anisotropy barrier of Delta approximately 55.8 K. Two-dimensional electron-gas (2DEG) Hall magnetization measurements revealed that complex 4 a is a single-molecule magnet and shows hysteretic magnetization characteristics with typical temperature and sweep-rate dependencies below a blocking temperature of about 4.4 K. The hysteresis loops collapse at zero field owing to fast quantum tunneling of the magnetization (QTM). The structural and electronic properties of cobalt(II) cubane 4 a, deposited on a highly oriented pyrolytic graphite (HOPG) surface, were investigated by means of STM and current imaging tunneling spectroscopy (CITS) at RT and standard atmospheric pressure. In CITS measurements the rather large contrast found at the expected locations of the metal centers of the molecules indicated the presence of a strongly localized LUMO.

Synthesis, Magnetic Properties, and X-ray Spectroscopy of Divalent Cobalt(II) and Nickel(II) Cubanes [M4II(HL2)4(OAc)4] - Scheurer, Andreas; Korzekwa, Jana; Nakajima, Takayuki; Hampel, Frank; Buling, Anna; Derks, Christine; Neumann, Manfred; Joly, Loic; Petukhov, Konstantin; Gieb, Klaus; Müller, Paul; Kuepper, Karsten; et al. (European Journal of Inorganic Chemistry, 2015)
Under anaerobic conditions, the reactions of cobalt(II) and nickel(II) acetate tetrahydrate with 2,6-pyridinedimethanol (H2L2, 3) in anhydrous acetonitrile afforded two tetranuclear metal(II) complexes [MII4(HL2)4(OAc)4] (4; MII = Co2+, Ni2+) with a [M4(μ3-O)4]4+ cubane core. X-ray structural analyses revealed that both MII cubanes 4a·2CH3OH and 4b·2CH3OH are isostructural and crystallize in the tetragonal space group I41/acd with eight molecules in the unit cell. In the solid state, the orientation of the cubane cores of 4 and the formation of a 3D framework were controlled by π–π interactions as well as intra- and intermolecular O–H···O hydrogen bonds. Variable-temperature magnetic susceptibility measurements revealed that the cubanes 4 show a ferrimagnetic coupling scheme that leads to a diamagnetic ground state for both complexes. Core-level X-ray photoelectron spectroscopy confirmed that the Co and Ni ions in 4a and 4b are in a divalent state. X-ray magnetic circular dichroism was performed to extract the spin and orbital contributions to the Co and Ni magnetic moments. We compared the experimental results of the local electronic structures around the Co2+ ions in 4a and the Ni2+ ions in 4b with charge-transfer multiplet simulations.
Keywords: N; O ligands; Cubanes; Magnetic properties; X-ray absorption spectroscopy; X-ray photoelectron spectroscopy

Synthesis of multilamellar MFI-type zeolites under static conditions: The role of gel composition on their properties - Machoke, Albert; Knoke, I. Y.; Lopez-Orozco, S.; Schmiele, Martin; Selvam, Thangaraj; Marthala, V. R. R.; Spiecker, E.; Unruh, Tobias; Hartmann, Martin; Schwieger, Wilhelm; Hartmann, Martin; Spiecker, Erdmann (Microporous and Mesoporous Materials, 2014)
The formation of multilamellar MFI-type zeolite has been studied systematically by investigating the crystallization kinetics and the influence of different synthesis parameters under static conditions. Depending on the template amount and alkalinity, multilamellar MFI-type zeolites with different degrees of purity were obtained. In accordance with X-ray diffraction, SAXS and SEM results, highly crystalline multilamellar MFI-type zeolites were obtained within 4 days of crystallization time. Depending on the Si/Al ratio of the synthesis gel, different crystallization rates, textural properties and product morphologies were observed. (C) 2014 Elsevier Inc. All rights reserved.
Keywords: Nanosheets of MFI; Multilamellar MFI; Hierarchical zeolites; ZSM-5; Static conditions

Synthesis of multilamellar MFI-type zeolites under static conditions: The role of gel composition on their properties - Machoke, Albert; Knoke, I. Y.; Lopez-Orozco, S.; Schmiele, Martin; Selvam, Thangaraj; Marthala, Venkata; Spiecker, Erdmann; Unruh, Tobias; Hartmann, Martin; Schwieger, Wilhelm (Microporous and Mesoporous Materials, 2014)
The formation of multilamellar MFI-type zeolite has been studied systematically by investigating the crystallization kinetics and the influence of different synthesis parameters under static conditions. Depending on the template amount and alkalinity, multilamellar MFI-type zeolites with different degrees of purity were obtained. In accordance with X-ray diffraction, SAXS and SEM results, highly crystalline multilamellar MFI-type zeolites were obtained within 4 days of crystallization time. Depending on the Si/Al ratio of the synthesis gel, different crystallization rates, textural properties and product morphologies were observed. <br
Keywords: Hierarchical zeolites; Static conditions; ZSM-5; Multilamellar MFI; Nanosheets of MFI

Synthetic mucus for an ex vivo phonation setup: Creation, application, and effect on excised porcine larynges - Peters, Gregor; Jakubaß, Bernhard; Weidenfeller, Katrin; Kniesburges, Stefan; Böhringer, David; Wendler, Olaf; Mueller, Sarina K.; Gostian, Antoniu-Oreste; Berry, David A.; Döllinger, Michael; Semmler, Marion (Journal of the Acoustical Society of America, 2022)
Laryngeal mucus hydrates and lubricates the deformable tissue of the vocal folds and acts as a boundary layer with the airflow from the lungs. However, the effects of the mucus' viscoelasticity on phonation remain widely unknown and mucus has not yet been established in experimental procedures of voice research. In this study, four synthetic mucus samples were created on the basis of xanthan with focus on physiological frequency-dependent viscoelastic properties, which cover viscosities and elasticities over 2 orders of magnitude. An established ex vivo experimental setup was expanded by a reproducible and controllable application method of synthetic mucus. The application method and the suitability of the synthetic mucus samples were successfully verified by fluorescence evidence on the vocal folds even after oscillation experiments. Subsequently, the impact of mucus viscoelasticity on the oscillatory dynamics of the vocal folds, the subglottal pressure, and acoustic signal was investigated with 24 porcine larynges (2304 datasets). Despite the large differences of viscoelasticity, the phonatory characteristics remained stable with only minor statistically significant differences. Overall, this study increased the level of realism in the experimental setup for replication of the phonatory process enabling further research on pathological mucus and exploration of therapeutic options. (c) 2022 Acoustical Society of America.
CRIS-Team WoS Importer:2023-01-06

Systematic Surface Phase Transition of Ag Thin Films by Iodine Functionalization at Room Temperature: Evolution of Optoelectronic and Texture Properties - Bashouti, Muhammad Y.; Talebi, Razieh; Kassar, Thaer; Nahal, Arashmid; Ristein, Jürgen; Unruh, Tobias; Christiansen, Silke H. (Scientific Reports, 2016)
We show a simple room temperature surface functionalization approach using iodine vapour to control a surface phase transition from cubic silver (Ag) of thin films into wurtzite silver-iodid (beta-AgI) films. A combination of surface characterization techniques (optical, electronical and structural characterization) reveal distinct physical properties of the new surface phase. We discuss the AgI thin film formation dynamics and related transformation of physical properties by determining the work-function, dielectric constant and pyroelectric behavior together with morphological and structural thin film properties such as layer thickness, grain structure and texture formation. Notable results are: (i) a remarkable increase of the work-function (by 0.9 eV) of the Ag thin layer after short a iodine exposure time (<= 60 s), with simultaneous increase of the thin film transparency (by two orders of magnitude), (ii) pinning of the Fermi level at the valance band maximum upon iodine functionalization, (iii) 84% of all crystallites grain were aligned as a result of the evolution of an internal electric field. Realizing a nanoscale layer stack composed of a dielectric AgI layer on top of a metallic thin Ag layer with such a simple method has some technological implications e.g. to realize optical elements such as planar optical waveguides.

Tailoring Coulomb correlations in twisted WSe2bilayers - Merkl, Philipp; Mooshammer, Fabian; Brem, Samuel; Girnghuber, Anna; Lin, Kai Qiang; Weigl, Leonard; Yong, Chaw Keong; Gillen, Roland; Maultzsch, Janina; Lupton, John M.; Malic, Ermin; Huber, Rupert (2021 Conference on Lasers and Electro-Optics, CLEO 2021 - Proceedings, 2021)
Phase-locked few-cycle mid-infrared pulses trace how the twist angle alone renormalizes the binding energy of excitons in twisted WSe2 homobilayers by a factor of two and tunes their lifetime by a factor of twenty.
CRIS-Team Scopus Importer:2021-12-24

Tailoring the Dimensionality of 2D/3D Heterojunctions for Inverted Perovskite Solar Cells - Li, Chaohui; Zhang, Kaicheng; Maiti, Santanu; Peng, Zijian; Tian, Jingjing; Park, Hyoungwon; Byun, Jiwon; Xie, Zhiqiang; Dong, Lirong; Qiu, Shudi; Bornschlegl, Andreas; Liu, Chao; et al. (ACS Energy Letters, 2024)
Interface engineering is crucial to achieving stable perovskite photovoltaic devices. A versatile approach is developed to tailor interface properties via integrating co-assembled monolayers (co-SAMs) at the p-type buried interface and by capping a two-dimensional (2D) perovskite layer at the n-type upper interface with vacuum quenching. Optimized co-SAMs promote the coverage of the hole transport layer, significantly reducing the incidence of leakage currents. Based on this foundation, we develop damp-heat-stable perovskite solar cells by precisely tailoring the fragments of 2D perovskite layers through vacuum annealing with phenethylammonium iodide. An impressive open-circuit voltage of 1.216 V is achieved, corresponding to 92% of the value determined by the detailed-balance limit, along with a power conversion efficiency of 23.68%. Ultimately, integrating co-SAMs and the vacuum-assisted annealing fabricated devices maintain 96% and 80% of initial efficiencies after 1200 and 500 h of tracking at a maximum power point under 55 and 85 °C, respectively.
CRIS-Team Scopus Importer:2024-02-23

Tailoring the graphene/silicon carbide interface for monolithic wafer-scale electronics - Hertel, Stefan; Waldmann, Daniel; Jobst, Johannes; Albert, Andreas; Albrecht, Matthäus; Krieger, Michael; Reshanov, Sergey; Schöner, Adolf; Weber, Heiko B. (Nature Communications, 2012)
Graphene is an outstanding electronic material, predicted to have a role in post-silicon electronics. However, owing to the absence of an electronic bandgap, graphene switching devices with high on/off ratio are still lacking. Here in the search for a comprehensive concept for wafer-scale graphene electronics, we present a monolithic transistor that uses the entire material system epitaxial graphene on silicon carbide (0001). This system consists of the graphene layer with its vanishing energy gap, the underlying semiconductor and their common interface. The graphene/semiconductor interfaces are tailor-made for ohmic as well as for Schottky contacts side-by-side on the same chip. We demonstrate normally on and normally off operation of a single transistor with on/off ratios exceeding 10(4) and no damping at megahertz frequencies. In its simplest realization, the fabrication process requires only one lithography step to build transistors, diodes, resistors and eventually integrated circuits without the need of metallic interconnects.

Tailoring the Nature of Interface States in Efficient and Stable Bilayer Organic Solar Cells by a Transfer-Printing Technique - Wang, Rong; Jiang, Youyu; Gruber, Wolfgang; He, Yakun; Wu, Mingjian; Weitz, Paul; Zhang, Kaicheng; Lüer, Larry; Forberich, Karen; Unruh, Tobias; Spiecker, Erdmann; Deibel, Carsten; et al. (Advanced Materials Interfaces, 2022)
Bulk heterojunction organic solar cells (BHJ-OSCs) are designed to overcome inefficient charge generation and limited exciton diffusion of organic semiconductors. However, there are some disadvantages involving inherent voltage losses, microstructure control, and operational instability. Bilayer solar cells (BL-OSCs) without mixed regions are free from these problems and offer a platform to explore the photophysical processes at the donor-acceptor interface. Here, a breakthrough for n-i-p BL-OSCs in charge generation efficiency is reported. A gradual adjustment of the molecular interface orientation of the polymer donor (PM6) is accompanied by the evolution of charge-transfer states and Forster energy transfer. Besides, less recombination losses and superior morphological stability of BL-OSCs are achieved at a PCE comparable to that of BHJ-OSCs with similar layer thickness. This investigation confirms the feasibility of manufacturing BL-OSCs by a transfer printing method and provides a versatile architecture to study fundamental interface phenomena in OSCs independent from microstructure disorder.
CRIS-Team WoS Importer:2022-04-29

TE- and TM-polarization-resolved spectroscopy on quantum wells under normal incidence - Malzer, Stefan; Leuchs, Gerd; Schardt, Michael; et al. (Physica E-Low-Dimensional Systems & Nanostructures, 2006)
We present TE- and TM-polarization-resolved photocurrent measurements on quantum well pin diodes under normal incidence. Usually, optical experiments performed in such a geometry yield information only about transitions involving in-plane (p and p ) components of the hole wave functions because of the in-plane (TE) polarization of the light. Information on transitions sensitive to the p components can be obtained by focussing a radially polarized laser beam through a microscope objective with high numerical aperture ( NA = 0.9). With our setup, the electrical field vector at the focal tail has a significant component along the optical axis (TM-polarization!) which enables excitation of transitions sensitive to p components also. Additionally, the existence of a degenerate (azimuthally polarized) optical mode enables switching these p components on and off easily. Experimental evidence of these features has been achieved by exploiting the selection rules for e-hh and e-lh transitions in a quantum well structure. We present a comparison of our recorded spectra with theoretical predictions obtained from simple geometric optics assumptions. For our quantum wells the polarization effects are small because our measurement averages the intensity distribution of the whole focal plane. We plan to extend our measurements to polarization resolved single quantum dot spectroscopy. By restricting the detection region to the spatial extent of a single dot, one can exploit the almost pure TM-polarization on the optical axis for obtaining high contrast between heavy- and light-hole exciton absorption. © 2006.

Technical Note: A comparison of point set registration methods for electromagnetic tracking - Götz, T. I.; Wankerl, H.; Tomé, A. M.; Meyer-Baese, A.; Bert, Christoph; Hensel, Bernhard; Lang, E. W. (Medical Physics, 2019)
Purpose: High dose rate brachytherapy applies intense and destructive radiation. A treatment plan defines radiation source dwell positions to avoid irradiating healthy tissue. The study discusses methods to quantify any positional changes of source locations along the various treatment sessions. Methods: Electromagnetic tracking (EMT) localizes the radiation source during the treatment sessions. But in each session the relative position of the patient relative to the filed generator is changed. Hence, the measured dwell point sets need to be registered onto each other to render them comparable. Two point set registration techniques are compared: a probabilistic method called coherent point drift (CPD) and a multidimensional scaling (MDS) technique. Results: Both enable using EMT without external registration and achieve very similar results with respect to dwell position determination of the radiation source. Still MDS achieves smaller grand average deviations (CPD-rPSR: MD = 2.55 mm, MDS-PSR: MD = 2.15 mm) between subsequent dwell position determinations, which also show less variance (CPD-rPSR: IQR = 4 mm, MDS-PSR: IQR = 3 mm). Furthermore, MDS is not based on approximations and does not need an iterative procedure to track sensor positions inside the implanted catheters. Conclusion: Although both methods achieve similar results, MDS is to be preferred over rigid CPD while nonrigid CPD is unsuitable as it does not preserve topology.
CRIS-Team Scopus Importer:2019-05-17
Keywords: brachytherapy; electromagnetic tracking; multi-dimensional scaling; point set registration

TEMPERATURE-DEPENDENCE OF THE INVERSE PHOTOEMISSION FROM COPPER SURFACES - Fauster, Thomas; et al. (Physical Review B, 1990)

Temperature Dependence of the Primary Relaxation in 1-Hexyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide - Russina, Olga; Beiner, Mario; Papas, Catherine; Russina, Margarita; Arrighi, Valeria; Unruh, Tobias; Mullan, Claire L.; Hardacre, Christopher; Triolo, Alessandro (Journal of Physical Chemistry B, 2009)
We present results from complementary characterizations of the primary relaxation rate of a room temperature ionic liquid (RTIL), 1-hexyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide, [C(6)mim][Tf(2)N], over a wide temperature range. This extensive data set is successfully merged with existing literature data for conductivity, viscosity, and NMR diffusion coefficients thus providing, for the case of RTILs, a unique description of the primary process relaxation map over more than 12 decades in relaxation rate and between 185 and 430 K. This unique data set allows a detailed characterization of the VTF parameters for the primary process, that are: B = 890 K, T(0) = 155.2 K, leading to a fragility index m = 71, corresponding to an intermediate fragility. For the first time neutron spin echo data from a fully deuteriated sample of RTIL at the two main interference peaks, Q = 0.76 and 1.4 angstrom(-1) are presented. At high temperature (T > 250 K), the collective structural relaxation rate follows the viscosity behavior; however at lower temperatures it deviates from the viscosity behavior, indicating the existence of a faster process.

Temperature dependent band gap behavior and excitons in metallic carbon nanotubes - May, Patrick; Telg, Hagen; Thomsen, Christian; Maultzsch, Janina (WILEY-V C H VERLAG GMBH, 2010)
First optical transition E-11(M) of metallic nanotubes and sketch of a metallic (13,1) tube.
Keywords: metallic carbon nanotubes; excitons

TEMPERATURE-DEPENDENT ELECTRONIC-STRUCTURE OF NI, FE AND GD - Fauster, Thomas; et al. (Journal of Magnetism and Magnetic Materials, 1995)
We investigated the influence of electron correlations on the temperature dependence of the electronic structure of the prototypical ferromagnets Ni, Fe(bcc), and Gd using a many-body evaluation of a generalized model. of magnetism. The single-particle energies are taken from an LSDA band structure calculation. The many-particle interactions are described by just two parameters, an intraband Coulomb interaction U and an interband exchange J. The self-consistent model solution yields very realistic values for the T = 0 moments and the Curie temperatures. Typical differences as well as common features of the magnetism in Ni, Fe and Gd are worked out.

Temperature-dependent optical spectra of single-crystal (CH3NH3)PbBr3 cleaved in ultrahigh vacuum - Niesner, Daniel; Schuster, Oskar; Wilhelm, Max; Levchuk, Ievgen; Osvet, Andres; Shrestha, Shreetu; Batentschuk, Miroslaw; Brabec, Christoph; Fauster, Thomas (Physical Review B - Condensed Matter and Materials Physics, 2017)
We measure temperature-dependent one-photon and two-photon induced photoluminescence from (CH3NH3)PbBr3 single crystals cleaved in ultrahigh vacuum. An approach is presented to extract absorption spectra from a comparison of both measurements. Cleaved crystals exhibit broad photoluminescence spectra. We identify the direct optical band gap of 2.31 eV. Below 200 K, the band gap increases with temperature, and it decreases at elevated temperature, as described by the Bose-Einstein model. An excitonic transition is found 22 meV below the band gap at temperatures <200 K. Defect emission occurs at photon energies <2.16 eV. In addition, we observe a transition at 2.25 eV (2.22 eV) in the orthorhombic (tetragonal and cubic) phase. Below 200 K, the associated exciton binding energy is also 22 meV, and the transition redshifts at higher temperature. The binding energy of the exciton related to the direct band gap, in contrast, decreases in the cubic phase. High-energy emission from free carriers is observed with higher intensity than reported in earlier studies. It disappears after exposing the crystals to ai

Temperature induced polytype conversion in cubic silicon carbide studied by Raman spectroscopy - Hundhausen, Martin; Ley, Lothar; et al. (Journal of Applied Physics, 2004)
In this paper, we study the polytype transformation of cubic silicon carbide (3C-SiC) by micro Raman spectroscopy. Two sets of samples are investigated. First, physical vapor transport (PVT) grown samples, grown on chemical vapor deposition (CVD) substrates at growth temperatures between 1800 and 1950°C. The microscopic images of the cross sections and the Raman spectra taken on these grown crystals show a growing fraction of 6H-SiC inclusions with increasing growth temperature. To decide whether these polytype inclusions are induced by the PVT growth process or by the temperature treatment of the CVD substrates, we studied the temperature induced polytype coversion of cubic CVD substrates grown on undulant Si(100) surfaces which were used as seed crystals for the PVT growth. The CVD substrates were annealed in the temperature range between 1700 and 2100°C. The results of this annealing series are similar to the results we find in the PVT grown samples. Therefore we argue that the polytype conversion is not induced by the PVT growth process but a result of the heat treatment of the CVD seed crystals. © 2004 American Institute of Physics.
UnivIS-Import:2015-04-14:Pub.2004.nat.dphy.IAP.LAP.temper

Terahertz generation with ballistic photodiodes under pulsed operation - Preu, Sascha; Müller-Landau, Christian; Malzer, Stefan; Weber, Heiko B.; Döhler, Gottfried; Winnerl, Stephan; Burke, P.G.; Gossard, Art (Semiconductor Science and Technology, 2018)
Keywords: terahertz generation; velocity overshoot; ballistic transport; photomixer

Terahertz response of patterned epitaxial graphene - Sorger, Christian; Preu, Sascha; Schmidt, J.; Winnerl, Stefan; Bludov, Y.V.; Peres, N.M.R.; Vasilevskiy, M.; Weber, Heiko B. (New Journal of Physics, 2015)
We study the interaction between polarized terahertz (THz) radiation and micro-structured large-area graphene in transmission geometry. In order to efficiently couple the radiation into the two-dimensional material, a lateral periodic patterning of a closed graphene sheet by intercalation doping into stripes is chosen. We observe unequal transmittance of the radiation polarized parallel and perpendicular to the stripes. The relative contrast, partly enhanced by Fabry-Perot oscillations reaches 20%. The effect even increases up to 50% when removing graphene stripes in analogy to a wire grid polarizer. The polarization dependence is analyzed in a large frequency range from <80 GHz to 3 THz, including the plasmon-polariton resonance. The results are in excellent agreement with theoretical calculations based on the electronic energy spectrum of graphene and the electrodynamics of the patterned structure.
Keywords: plasmon; graphene; THz

Terahertz wave emission from intrinsic Josephson junctions in high- T c superconductors - Ozyuzer, L.; Simsek, Yilmaz; Koseoglu, H.; Turkoglu, F.; Kurter, C.; Welp, U.; Koshelev, A.; Gray, K.; Kwok, W.; Yamamoto, T.; Kadowaki, K.; Koval, Yury; et al. (Superconductor Science & Technology, 2009)
Recently, we experimentally demonstrated that rectangular mesa structures of intrinsic Josephson junctions (IJJ) in BiSrCaCu O (Bi2212) can be used as a compact solid-state generator of continuous, coherent and polarized terahertz (THz) radiation. In the present work, we will exhibit tall mesas (over 600 junctions) which were fabricated using UV lithography, e-beam lithography with photoresist and e-beam lithography with a Ti selective etching technique. We will present measurements of the c-axis resistance as a function of temperature and of current-voltage characteristics of THz emitting mesas with lateral sizes ranging from 30 × 300 to 100 × 300νm. Furthermore, we will discuss the dependence of the characteristics of the mesa structures on the oxygen doping level of the Bi2212 crystals. We will also experimentally show that the voltage-frequency relation of the ac Josephson effect has to match the cavity resonance for successful emission. © 2009 IOP Publishing Ltd.

Tetracycline-encapsulated P(3HB) microsphere-coated 45S5 Bioglass®-based scaffolds for bone tissue engineering - Meng, D.; Francis, L.; Thompson, I. D.; Mierke, Claudia; Hübner, Holger; Amtmann, A.; Roy, I.; Boccaccini, Aldo R. (Journal of Materials Science: Materials in Medicine, 2013)
Bioglass®-based scaffolds for bone tissue engineering have been developed, which can also serve as carriers for drug delivery. For this, P(3HB) microspheres (PMSs) loaded with tetracycline were fabricated and immobilised on the scaffold surfaces by a modified slurry dipping technique. The sustained drug delivery ability in simulated body fluid was confirmed by using UV-Vis absorption spectroscopy measurements. The MTT assay using mouse fibroblast cells provided evidence that the tetracycline loaded microspheres produced in this study show limited cytotoxicity. The scaffolds developed in this work provide mechanical support, adequate 3D surface roughness, bioactivity and controlled drug delivery function, and are thus interesting candidates for bone tissue engineering applications. © 2013 Springer Science+Business Media New York.
UnivIS-Import:2015-03-09:Pub.2013.tech.IW.LM.tetrac

The ACHIP experimental chambers at PSI - Ferrari, Eugenio; Ischebeck, Rasmus; Hiller, Nicole; Borrelli, Simona; Frei, Franziska; Ozkan-Loch, Cigdem; Dehler, Micha; Prat, Eduard; Bettoni, Simona; Reiche, Sven; Romann, Albert; Raabe, Jörg; et al. (Proceedings of the 38th International Free-Electron Laser Conference, FEL 2017, 2017)
The Accelerator on a Chip International Program (ACHIP) is an international collaboration, funded by the Gordon and Betty Moore Foundation, whose goal is to demonstrate that laser-driven accelerator on a chip can be integrated to fully build an accelerator based on dielectric structures. PSI will provide access to the high brightness electron beam of Swiss-FEL to test structures, approaches and methods towards achieving the final goal of the project. In this contribution, we will describe the two interaction chambers installed on SwissFEL to perform the proof-of-principle experiments. In particular, we will present the positioning system for the samples, the magnets needed to focus the beam to submicrometer dimensions and the diagnostics to measure beam properties at the interaction point.
CRIS-Team Scopus Importer:2022-06-05
Keywords: ion; electron; experiment; FEL; laser

The ACHIP experimental chambers at the Paul Scherrer Institut - Ferrari, Eugenio; Ischebeck, Rasmus; Bednarzik, Martin; Bettoni, Simona; Borrelli, Simona; Braun, Hans-Heinrich; Calvi, Marco; David, Christian; Dehler, Micha; Frei, Franziska; Garvey, Terence; Guzenko, Vitaliy A.; et al. (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2018)
The Accelerator on a Chip International Program (ACHIP) is an international collaboration, funded by the Gordon and Betty Moore Foundation, with the goal of demonstrating that laser-driven accelerator can be integrated on a chip to fully build an accelerator based on dielectric structures. PSI will provide access to the high brightness electron beam of SwissFEL to test structures, approaches and methods towards achieving the final goal of the project. In this contribution, we will describe the two interaction chambers installed on SwissFEL to perform the proof-of-principle experiments. In particular, we will present the positioning system for the samples, the magnets needed to focus the beam to sub-micrometer dimensions and the diagnostics to measure beam properties at the interaction point.
CRIS-Team Scopus Importer:2022-06-05
Keywords: Dielectric laser acceleration; Experimental chamber; Free electron laser

The alteration of illite by Bad Nauheim and Gerolstein brine; Implications on fluid permeability in geothermal systems - Götz, Emilia; Neder, Reinhard; Kolb, Ute; Kleebe, Hans Joachim (Applied Clay Science, 2023)
Illite is one of the most abundant clay minerals on earth, yet its structure remains not fully solved. In hydrothermal reservoir sandstones, illites can display a fibrous growth within the pores and pore throats. The network created by them and the particles trapped therein during fluid flow lead to a dramatic decrease in permeability, which should be prevented if the reservoirs were to be used for geothermal energy extraction. In order to determine possible changes in structure, stacking or shape of the illite fibers, the interaction of a sandstone with two different brines was compared to an unaltered sandstone via environmental scanning electron microscopy and transmission electron microscopy. Moreover, three-dimensional electron diffraction experiments were performed using automated diffraction tomography. The 1Mtv structure of illite could be solved based on a single dataset of a 50 nm illite fiber. Illites that were altered with synthetic Gerolstein brine showed one-dimensional diffuse scattering, indicating a disorder in the stacking of the illite layers. The degree of disorder is dependent on the potassium content of the fluid, since the K+ ions of the interlayer can be released via the (010) facet. This causes a stability reduction of the structure, resulting in a high fragmentation and detachment of individual illite layers. Fluids interacting with the sandstone can then transport such mobile layer fragments, leading to entangling and interweaving of illite fibers. These new insights into the structure of illite fibers show a significant dependence of the arrangement of the fibers in the pores on the potassium content of the fluid. The increased migration and interweaving of illite fibers associated with a low potassium content can lead to severe clogging of the pores and thus to a reduction in fluid permeability. Altered sandstones with illitic pore filling are therefore less suitable for long-term geothermal projects.
CRIS-Team Scopus Importer:2023-08-11
Keywords: Fibrous illite; Hydrothermal alteration; Order-disorder; Reservoir sandstone; Structure solution; Three-dimensional electron diffraction

The build-up of strain fields in Czochralski-Si observed in real time by high energy x-ray diffraction - Hock, Rainer; et al. (2005)
The build-up of strain fields caused by the precipitation of oxygen in Czochralski-silicon during annealing up to 1200 degrees C and for process times up to 70 hours has been observed in real time by high energy x-ray diffraction. Five different processes are distinguished in the temperature evolution of the intensity and of the rocking width of the silicon 220-reflection. These features are attributed to different precipitation mechanisms. A fit to part of the data with a diffusion limited precipitation model leads to an activation energy for oxygen diffusion in silicon of 2.2 eV in the temperature range from 700 degrees C to 950 degrees C.
Keywords: Czochralski Si; internal gettering; high energy x-ray diffraction

The correlation between surface conductivity and adsorbate coverage on diamond as studied by infrared spectroscopy - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 2001)
A high-resolution analysis of C-H vibrational modes on a single crystal diamond(100) surface using Fourier-transform infrared (FTIR) spectroscopy in combination with conductivity measurements is reported. On a plasma-hydrogenated diamond(100) surface, the IR spectra measured in the multiple internal reflection mode reveal three absorption lines. Two of them at 2921 and 2854 cm-1 vanish in air at an annealing temperature of 190°C and are assigned to the antisymmetric and symmetric CH2 stretching modes of a physisorbed hydrocarbon species, respectively. The third band at 2897 cm-1 has a width of 16 cm-1, is stable up to 230°C and is associated with the stretching frequency of C2H2 monohydride units on the C(100) 2 × 1:2H surface. Upon annealing in air at temperatures lower than 200°C, the surface conductivity is reversibly reduced by up to five orders of magnitude. After cooling down to room temperature, it recovers the value of 1 × 10-5 Ω-1 measured immediately after the plasma hydrogenation with a time constant of several days. Annealing at 230°C destroys the surface conductivity irreversibly and yields conductance values below the measurement limit of 5 × 10-12 Ω-1. We show that the chemisorbed hydrogen in the C2H2 configuration, together with at least one physisorbed species, is responsible for the surface conductivity of hydrogen-terminated diamond(100). © 2001 Elsevier Science B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.thecor
Keywords: Diamond surfaces; Hydrogen bonding; IR spectroscopy; Surface conductivity

The crystallisation of Cu2ZnSnS4 thin film solar cell absorbers from co-electroplated Cu-Zn-Sn precursors - Schurr, R.; Hölzing, Astrid; Jost, Stefan Georg; Hock, Rainer; Voss, T.; Schulze, J.; Kirbs, A.; Ennaoui, Ahmed, Prof. Dr.; Lux-Steiner, M.; Weber, A.; Koetschau, I.; Schock, H. -W. (ELSEVIER SCIENCE SA, 2009)
The best CZTS solar cell so far was produced by co-sputtering continued with vapour phase sulfurization method. Efficiencies of up to 5.74% were reached by Katagiri et al. The one step electrochemical deposition of copper, zinc, tin and subsequent sulfurization is an alternative fabrication technique for the production of Cu2ZnSnS4 based thin film solar cells. A kesterite based solar cell (size 0.5 cm(2)) with a conversion efficiency of 3.4% (AM1.5) was produced by vapour phase sulfurization of co-electroplated Cu-Zn-Sn films. We report on results of in-situ X-ray diffraction (XRD) experiments during crystallisation of kesterite thin films from electrochemically co-deposited metal films. The kesterite crystallisation is completed by the solid state reaction of Cu2SnS3 and ZnS. The measurements show two different reaction paths depending on the metal ratios in the as deposited films. In copper-rich metal films Cu3Sn and CuZn were found after electrodeposition. In copper-poor or near stoichiometric precursors additional Cu6Sn5 and Sn phases were detected. The formation mechanism of Cu2SnS3 involves the binary sulphicles Cu2 -xS and SnS2 in the absence of the binary precursor phase Cu6Sn5. The presence of Cu6Sn5 leads to a preferred formation of Cu2SnS3 Via the reaction educts Cu2-xS and SnS2 in the presence of a SnS2(Cu4SnS6) melt. The melt phase may be advantageous in crystallising the kesterite, leading to enhanced grain growth in the presence of a liquid phase. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: Cu2ZnSnS4; CZTS; Kesterite; Thin films; Real-time XRD

The cytoskeleton as a soft glassy material. In: Cytoskeletal Mechanics: Models and Measurements. - Fredberg, Jeffrey; Fabry, Ben (Cambridge University Press, 2006)

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

The density of states of ta-C, ta-C:H and a-C:H as determined by x-ray excited photoelectron spectroscopy and molecular dynamics calculation - Ristein, Jürgen; Ley, Lothar; et al. (Journal of Non-Crystalline Solids, 1996)
The valence band spectra of amorphous carbon modifications with and without hydrogen covering the range from so-called diamond-like carbon to mainly tetrahedrally coordinated (ta-C, ta-C:H) carbon were determined by photoelectron spectroscopy. The results are compared with densities of states calculated for finite clusters with structures that were obtained from molecular dynamics calculations. From this comparison correlations between spectroscopic features and structural elements in the amorphous carbon modifications are derived.
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.IAP.exphys.theden

The desmin mutation R349P increases contractility and fragility of stem cell-generated muscle micro-tissues - Spörrer, Marina; Kah, Delf-Thorge Eric; Gerum, Richard; Reischl, Barbara; Huraskin, Danyil; Dessalles, Claire A.; Schneider, Werner; Goldmann, Wolfgang; Herrmann, Harald; Thievessen, Ingo; Clemen, Christoph S.; Friedrich, Oliver; et al. (Neuropathology and Applied Neurobiology, 2021)
Aims: Desminopathies comprise hereditary myopathies and cardiomyopathies caused by mutations in the intermediate filament protein desmin that lead to severe and often lethal degeneration of striated muscle tissue. Animal and single cell studies hinted that this degeneration process is associated with massive ultrastructural defects correlating with increased susceptibility of the muscle to acute mechanical stress. The underlying mechanism of mechanical susceptibility, and how muscle degeneration develops over time, however, has remained elusive. Methods: Here, we investigated the effect of a desmin mutation on the formation, differentiation, and contractile function of in vitro-engineered three-dimensional micro-tissues grown from muscle stem cells (satellite cells) isolated from heterozygous R349P desmin knock-in mice. Results: Micro-tissues grown from desmin-mutated cells exhibited spontaneous unsynchronised contractions, higher contractile forces in response to electrical stimulation, and faster force recovery compared with tissues grown from wild-type cells. Within 1 week of culture, the majority of R349P desmin-mutated tissues disintegrated, whereas wild-type tissues remained intact over at least three weeks. Moreover, under tetanic stimulation lasting less than 5 s, desmin-mutated tissues partially or completely ruptured, whereas wild-type tissues did not display signs of damage. Conclusions: Our results demonstrate that the progressive degeneration of desmin-mutated micro-tissues is closely linked to extracellular matrix fibre breakage associated with increased contractile forces and unevenly distributed tensile stress. This suggests that the age-related degeneration of skeletal and cardiac muscle in patients suffering from desminopathies may be similarly exacerbated by mechanical damage from high-intensity muscle contractions. We conclude that micro-tissues may provide a valuable tool for studying the organization of myocytes and the pathogenic mechanisms of myopathies.
CRIS-Team Scopus Importer:2021-12-17
Keywords: desmin; desminopathy; micro-tissue; skeletal muscle physiology; tissue engineering

THE DETERMINATION OF SHADOWING CRITICAL ANGLES IN IMPACT COLLISION ION-SCATTERING SPECTROSCOPY - Fauster, Thomas; et al. (Applied Physics A-Materials Science & Processing, 1988)

The dimensionality of ammonium reorientation in (NH4)(2)S2O8: the view from neutron spectroscopy - Prager, Michael; Grimm, H.; Natkaniec, I.; Nowak, D.; Unruh, Tobias (Journal of Physics: Condensed Matter, 2008)
The dynamics of the ammonium ion in ammonium persulfate is studied by inelastic neutron scattering at energy transfers between 0.7 mu eV and about 100 meV. NH4+ librational modes are clearly split into four energetically different bands, in agreement with the absence of symmetry at the ammonium site. One strong, one medium and two weak hydrogen bonds from the NH4 ion to neighboring oxygens lead to this unusual potential shape with one dominating overlap matrix elements hi. Therefore the ammonium dynamics seen by neutron tunneling spectroscopy looks like a rotation about a single axis, that of the strongest hydrogen bond. Quasi-elastic scattering up to T = 100 K is dominated by jumps about this specific axis, too. Jumps about the second weak axis modify the quasi-elastic scattering at higher temperature. Results of a previous nuclear magnetic resonance (NMR) quadrupole resonance experiment are consistently interpreted to show the dynamics around the remaining two strong axes. The reduced isotope effect of the lowest librational band is due to a special shape of the potential and not to changes of the hydrogen bond with deuteration.

The emperor penguin - Vulnerable to projected rates of warming and sea ice loss - Trathan, Philip N.; Wienecke, Barbara; Barbraud, Christophe; Jenouvrier, Stéphanie; Kooyman, Gerald; Le Bohec, Céline; Ainley, David G.; Ancel, André; Paranhos Zitterbart, Daniel; Chown, Steven L.; LaRue, Michelle; Cristofari, Robin; et al. (Biological Conservation, 2020)
We argue the need to improve climate change forecasting for ecology, and importantly, how to relate long-term projections to conservation. As an example, we discuss the need for effective management of one species, the emperor penguin, Aptenodytes forsteri. This species is unique amongst birds in that its breeding habit is critically dependent upon seasonal fast ice. Here, we review its vulnerability to ongoing and projected climate change, given that sea ice is susceptible to changes in winds and temperatures. We consider published projections of future emperor penguin population status in response to changing environments. Furthermore, we evaluate the current IUCN Red List status for the species, and recommend that its status be changed to Vulnerable, based on different modelling projections of population decrease of ≥50% over the current century, and the specific traits of the species. We conclude that current conservation measures are inadequate to protect the species under future projected scenarios. Only a reduction in anthropogenic greenhouse gas emissions will reduce threats to the emperor penguin from altered wind regimes, rising temperatures and melting sea ice; until such time, other conservation actions are necessary, including increased spatial protection at breeding sites and foraging locations. The designation of large-scale marine spatial protection across its range would benefit the species, particularly in areas that have a high probability of becoming future climate change refugia. We also recommend that the emperor penguin is listed by the Antarctic Treaty as an Antarctic Specially Protected Species, with development of a species Action Plan.
CRIS-Team Scopus Importer:2020-02-11
Keywords: Antarctic; Aptenodytes forsteri; Climate change; Conservation; IUCN Red List threat status; Protection

The evolution of crystalline ordering for ligand-ornamented zinc oxide nanoparticles - Zobel, Mirijam; Windmueller, Anna; Schmidt, Ella; Götz, Klaus; Milek, Theodor; Zahn, Dirk; Kimber, Simon A. J.; Hudspeth, Jessica M.; Neder, Reinhard (Crystengcomm, 2016)
Recent total scattering experiments have opened up the possibility to study nanoparticle formation in situ and to observe the structural transformation from precursor clusters to adult particles. Organic ligand molecules interact with precursors of metal oxide nanoparticles, yet their influence onto the evolution of crystallinity during particle formation has not been addressed in detail; nor have in situ total scattering experiments ventured into the field of low-concentration, room-temperature syntheses in organic solvents to date. In this report, we follow the crystallization of ZnO nanoparticles in ethanol in the presence of different organic ligands. Low coordinated zinc precursor clusters rapidly polymerize upon base addition to particles of ca. 1 nm in diameter. In situ SAXS experiments reveal that the overall particle size increases to 2 to 4 nm with advancing reaction time. Complementary in situ PDF experiments show smaller crystalline domain sizes, which are only one third to half as large as the particle diameter. The ZnO particles thus feature a crystalline core surrounded by a disordered shell. Both, the core and the shell diameter are influenced by the different surface-bound organic ligands, which prevent an immediate relaxation to fully crystalline particles. A slow crystallization takes place in solution. We assume a dynamic equilibrium of the ligand and solvent molecules at the particle surface, which enables gradual bond restructuring. With suitably adjusted synthesis conditions, in our case by a continuous base addition, we show how to bypass the disordered intermediates, allowing the spontaneous nucleation of fully crystalline nanoparticles.

The focal adhesion protein β-parvin controls cardiomyocyte shape and sarcomere assembly in response to mechanical load - Thievessen, Ingo; Suhr, Frank; Vergarajauregui, Silvia; Böttcher, Ralph T.; Brixius, Klara; Rosenberger, Georg; Fleischmann, Bernd K.; Ghanem, Alexander; Krüger, Marcus; Engel, Felix; Fabry, Ben; Bloch, Wilhelm; et al. (Current Biology, 2022)
Physiological and pathological cardiac stress induced by exercise and hypertension, respectively, increase the hemodynamic load for the heart and trigger specific hypertrophic signals in cardiomyocytes leading to adaptive or maladaptive cardiac hypertrophy responses involving a mechanosensitive remodeling of the contractile cytoskeleton. Integrins sense load and have been implicated in cardiac hypertrophy, but how they discriminate between the two types of cardiac stress and translate mechanical loads into specific cytoskeletal signaling pathways is not clear. Here, we report that the focal adhesion protein β-parvin is highly expressed in cardiomyocytes and facilitates the formation of cell protrusions, the serial assembly of newly synthesized sarcomeres, and the hypertrophic growth of neonatal rat ventricular cardiomyocytes (NRVCs) in vitro. In addition, physiological mechanical loading of NRVCs by either the application of cyclic, uni-axial stretch, or culture on physiologically stiff substrates promotes NRVC elongation in a β-parvin-dependent manner, which is achieved by binding of β-parvin to α/β-PIX, which in turn activates Rac1. Importantly, loss-of-function studies in mice also revealed that β-parvin is essential for the exercise-induced cardiac hypertrophy response in vivo. Our results identify β-parvin as a novel mechano-responsive signaling hub in hypertrophic cardiomyocytes that drives cell elongation in response to physiological mechanical loads.
CRIS-Team Scopus Importer:2022-08-05
Keywords: affixin; cardiac hypertrophy; integrin-linked kinase; mechanotransduction; Rac1; sarcomere assembly; β-parvin

The focal adhesion targeting domain of p130Cas confers a mechanosensing function - Bradbury, Peta; Turner, Kylie; Mitchell, Camilla; Griffin, Kaitlyn Rose; Middlemiss, Shiloh; Lau, Loretta; Dagg, Rebecca; Taran, Elena; Cooper-White, Justin; Fabry, Ben; O'Neill, Geraldine Margarete (Journal of Cell Science, 2017)

The formation and stability of sub-micron clusters in silane and argon plasmas - Hundhausen, Martin; Ley, Lothar (Journal of Non-Crystalline Solids, 1991)
We have studied the formation of small silicon clusters in the plasma of a capacitively coupled RF-glow discharge deposition system used for the preparation of a-Si:H. These particles were detected by light scattering and are found to grow from SiH4 in the gas phase only if the temperature during deposition is substantially lower than in plasmas normally used for the deposition of device-quality films. We find that the particles are confined to the inner plasma region. This is explained by the fact that the particles become negatively charged due to the higher mobility of electrons vs. the positive ions. On account of their charge the particles are confined to the positive plasma region. The influence of the negative charge on the defect density of the a-Si:H forming the small particles is discussed. © 1991 Elsevier Science Publishers B.V. All rights reserved.
UnivIS-Import:2015-03-05:Pub.1991.nat.dphy.IAP.exphys.thefor

The formation mechanism of secondary phases in Cu2ZnSnSe4 absorber layer - Yoo, Hye Sun; Wibowo, Rachmat Adhi; Manoharan, G.; Lechner, R.; Jost, S.; Verger, A.; Palm, J.; Hock, Rainer (ELSEVIER SCIENCE SA, 2015)
Secondary phase formation in a Cu2ZnSn(S,Se)(4) based p-type layer for photovoltaic applications is one of the major problems which must be overcome to improve solar cell efficiency. To better understand the crystallization mechanism of secondary phases in the material system Cu-Zn-Sn-Se, we investigated the selenization of binary metallic layers as a function of temperature. The sputtered thin film precursors comprise Cu-Zn, Cu-Sn, and Zn-Sn with different sequence. A total six precursors were studied by time-resolved X-ray diffraction while temperature increased from 30 degrees C to 550 degrees C. Selenium had been always deposited on top of the metallic precursors in a separate thermal evaporation step. The observed reaction sequences were shown different results depending on the metals which are in first contact with selenium. From these experimental results, the mutual affinities of metals are determined, and a way of reducing the ZnSe crystallization is presented. Preferable precursor composed of ternary metallic layers with Se is also suggested in conclusion with respect to a stacking order of the metals. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Secondary phase; Binding affinity; CZTSe; Stacking order; Sequence; Layer; Formation

The formation of CdS quantum dots and Au nanoparticles - Schiener, Andreas; Schmidt, Ella; Bergmann, Christoph; Seifert, Soenke; Zahn, Dirk; Krach, Alexander; Weihrich, Richard; Magerl, Andreas (Zeitschrift fur Kristallographie - Crystalline Materials, 2017)
We report on microsecond-resolved in-situ SAXS experiments of the early nucleation and growth behavior of both cadmium sulfide (CdS) quantum dots in aqueous solution including the temperature dependence and of gold (Au) nanoparticles. A novel free-jet setup was developped to access reaction times as early as 20 μs. As the signal in particular in the beginning of the reaction is weak the containment-free nature of this sample environment prooved crucial. The SAXS data reveal a two-step pathway with a surprising stability of a structurally relaxed cluster with a diameter of about 2 nm. While these develop rapidly by ionic assembly, a further slower growth is attributed to cluster attachment. WAXS diffraction confirms, that the particles at this early stage are not yet crystalline. This growth mode is confirmed for a temperature range from 25°C to 45°C. An energy barrier for the diffusion of primary clusters in water of 0.60 eV was experimentally observed in agreement with molecular simulations. To access reaction times beyond 100 ms, a stopped-drop setup -again contaiment- free is introduced. SAXS experiments on the growth of Au nanoparticles on an extended time scale provide a much slower growth with one population only. Further, the influence of ionizing X-ray radiation on the Au particle fromation and growth is discussed.
Keywords: Au nanoparticles; CdS quantum dots; Containment-free; In-situ SAXS; Nucleation and growth

The formation of CuInSe2 thin-film solar cell absorbers by laser annealing of electrodeposited precursors - Jost, Stefan Georg; Schurr, R.; Hergert, Frank; Hock, Rainer; Schulze, J.; Kirbs, A.; Voss, T.; Purwins, Michael; Palm, J.; Mys, I. (Solar Energy Materials and Solar Cells, 2008)
The formation of the compound semiconductor CuInSe2 by laser annealing of electroplated precursor films in inert gas atmosphere represents an entire non-vacuum production process of thin-film solar cell absorbers. Besides this technological aspect, the impact of extreme annealing rates on structural properties of the resulting semiconductor is interesting from a fundamental research point of view. For this reason, we compared absorbers processed by laser annealing with absorbers annealed with moderate heating rates in the range of 1 K/s by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). All absorbers processed with laser or furnace annealing consist of crystalline CuInSe2 in the chalcopyrite crystal structure with a high degree of cation disorder. We show that laser annealing does not lead to unintentional selenium loss during the semiconductor formation process. (c) 2007 Elsevier B.V. All rights reserved.
Keywords: CuInSe2; thin films; laser annealing; electrodeposition; non-vacuum processing

The formation of CuInSe2 thin film solar cell absorbers from electroplated precursors with varying selenium content - Hock, Rainer; et al. (Solar Energy Materials and Solar Cells, 2007)
We present results from real-time X-ray diffraction experiments on the formation of CuInSe2 solar cell absorbers by annealing precursors, produced by simultaneous electrodeposition of copper, indium and selenium. The investigations reveal, that a reduced amount of electrochemically deposited selenium is the decisive parameter in order to realise a chalcopyrite formation behaviour as observed for sputtered stacked elemental layer (SEL) precursors. A simultaneous electrodeposition of the elements copper, indium and selenium in the molar ratio 1: 1:2 of the chalcopyrite CuInSe2 leads to the formation of binary copper and indium selenides during the electrodeposition process. The existence of binary selenides besides the intermetallic phase Cu11In9 as initial phases leads to an unfavourable absorber morphology. This can be explained by the observed semiconductor formation mechanism. A reduction of the deposited amount of selenium favours the formation of the intermetallic compound Cu11In9 and reduces the amount of binary selenides. These precursors show a formation behaviour and resulting absorber morphology as known for sputtered SEL precursors. (C) 2007 Elsevier B.V. All rights reserved.
Keywords: CuInSe2; chalcopyrites; thin films; real-time x-ray diffraction; electrodeposition

The formation of the thin-film solar cell absorber CuInS2 by annealing of Cu-In-S stacked elemental layer precursors - A comparison of selenisation and sulfurisation - Jost, S.; Schurr, R.; Hölzing, Astrid; Hergert, Frank; Hock, Rainer; Purwins, Michael; Palm, J. (ELSEVIER SCIENCE SA, 2009)
We present results of in-situ X-ray diffraction experiments on the formation of CuInS2 thin film solar cell absorbers. The experiments have been performed while annealing Cu-In-S stacked elemental layer precursors produced by sputtering and thermal evaporation to investigate the crystallisation process of the chalcopyrite CuInS2. Rietveld refinement has been performed to obtain the quantitative phase evolution of crystalline phases while annealing. The annealing process is characterised by a rapid sulfurisation of the initially present intermetallic alloy Cu11In9 forming the sulfide phases CuS, Dg-Cu2-xS, InS and/or CuIn5S8. The chalcopyrite CuInS2 crystallises at elevated sample temperatures by the consumption of these sulfide phases as educts. Three different chalcopyrite formation reactions have been identified by an analysis of the quantitative phase evolution. A comparison to earlier investigations on the formation of CuInSe2 from Cu-In-Se precursors is presented to show similarities and differences of sulfurisation and selenisation processes. The chalcopyrite forms from chalcogenide educts in both cases. However, distinct differences concerning the chalcogenisation kinetics of sulfur and selenium containing Cu-In precursors have been revealed. The chalcogenisation of the intermetallic alloy phase Culling proceeds extremely fast for Cu-In-S precursors as compared to Cu-In-Se samples. (C) 2008 Elsevier B.V. All lights reserved.
Keywords: CuInS2; Chalcopyrite; Thin films; Real-time X-ray diffraction

The high-resolution time-of-flight spectrometer TOFTOF - Unruh, Tobias; Neuhaus, Jürgen; Petry, Winfried (Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007)
The TOFTOF spectrometer is a multi-disc chopper time-of-flight spectrometer for cold neutrons at the research neutron source Heinz Maier-Leibnitz (FRM II). After five reactor cycles of routine operation the characteristics of the instrument are reported in this article. The spectrometer features an excellent signal to background ratio due to its remote position in the neutron guide hall, an elaborated shielding concept and an s-shaped curved primary neutron guide which acts i.a. as a neutron velocity filter. The spectrometer is fed with neutrons from the undermoderated cold neutron source of the FRM II leading to a total neutron flux of similar to 10(10)n/cm(2)/s in the continuous white beam at the sample position distributed over a continuous and particularly broad wavelength spectrum. A high energy resolution is achieved by the use of high speed chopper discs made of carbon-fiber-reinforced plastic. In the combination of intensity, resolution and signal to background ratio the spectrometer offers new scientific prospects in the fields of inelastic and quasielastic neutron scattering. (C) 2007 Elsevier B.V. All rights reserved.
Keywords: neutron scattering; time-of-flight spectrometer; QENS; INS

The hydrogenated and bare diamond (110) surface: a combined LEED-, XPS-, and ARPES study - Hammer, Lutz; Ristein, Jürgen; Ley, Lothar; et al. (Surface Science, 1999)
The atomic and electronic structures of the hydrogenated and hydrogen-free diamond (110) surface are investigated by low-energy electron diffraction (LEED), angle-resolved photoelectron spectroscopy (ARPES), and X-ray induced core-level spectroscopy (XPS). From the C 1s core-level spectra, different states of surface termination can be distinguished. The plasma-hydrogenated surface exhibits a surface C 1s component shifted by 0.8 eV towards a higher binding energy, which we attribute to coadsorbed hydrocarbons. During thermal annealing up to 900 °C, gradual desorption first of the hydrocarbons and then of hydrogen yields a clean surface with a surface C 1s component shifted by -1.1 eV and an increase in downward band bending of about 1.2 eV compared to the as-prepared surface. From the valence band spectra, we conclude that an essentially hydrogen-terminated surface is maintained at an annealing temperature of 600-800 °C. All states of the surface are unreconstructed. After the plasma treatment, the surface reveals monoatomic steps running parallel to the [11̄0] direction. From an analysis of the extinction of LEED reflexes, we conclude that within the chains of surface atoms running along [11̄0], the C-C bond length is uniformly altered in a way that keeps the chains undimerized. Finally, for the hydrogen-free surface, an occupied surface band is observed with a dispersion of 0.35 eV between Γ̄ and J̄ that lies entirely below the valence band maximum.
UnivIS-Import:2015-03-05:Pub.1999.nat.dphy.IAP.exphys.thehyd

The Impact of Ozone on the Surface Conductivity of Single Crystal Diamond - Ristein, Jürgen; Ley, Lothar; et al. (Diamond and Related Materials, 2004)
The electron affinity and thereby the ionisation energy of single crystal diamond (100) is changed between -1.3 and +1.7 eV and 4.2 and 7.2 eV, respectively, by stepwise oxidation of hydrogenated surfaces in ozone-rich atmospheres. Simultaneous measurements of the surface conductivity (SC) demonstrate that even for slight oxidation the SC disappears in air whereas SC is fully maintained in an ozone-rich atmosphere up to a partial oxygen coverage of ∼40%. These results constitute the first observation of electron transfer to the O3/O2 + OH- redox couple that extends on account of its lower electrochemical potential (compared to the H3O+/H2 couple active in normal air) the SC to samples with electron affinities higher than that of the hydrogenated surface. Thereby, the results confirm the basic tenet of the electrochemical transfer doping model in which the ionisation energy of diamond and the electrochemical potential of aqueous redox couples govern the charge exchange that leads to SC by a subcutaneous hole accumulation layer. In a second set of experiments, it is shown that for samples annealed in vacuum at temperatures between 250 and 700 °C SC is lost and does not recover upon air exposure despite an intact hydrogen coverage of the surface. However, after a brief exposure to ozone that does not result in any measurable oxidation, SC is recovered upon exposure to air. Explanations of this effect in terms of ozone-induced catalytic centers or passivation of donor-like surface defects are being offered. The relevance of these results for similar observations in connection with UV illumination is being alluded to. © 2003 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2004.nat.dphy.IAP.exphys.theimp
Keywords: Diamond properties and applications; Hydrogen terminated; Ozone; Surface conductivity

The influence of 2 kbar pressure on the global and internal dynamics of human hemoglobin observed by quasielastic neutron scattering - Appavou, Marie-Sousai; Busch, Sebastian; Doster, Wolfgang; Gaspar, A. M.; Unruh, Tobias (European Biophysics Journal, 2011)
Pressure is a ubiquitous physical parameter in life and is commonly used in the life sciences to study new protein folding pathways or association-dissociation phenomena. In this paper, an investigation of the influence of pressure on hemoglobin, a multimeric protein, at the picosecond time scale is presented using time-of-flight neutron scattering. The aim is to observe the influence of pressure on the translational diffusion and internal motions of hemoglobin in a concentrated solution and a possible dissociation of the subunits as suggested by Pin et al. (Biochemistry 29:9194, 1990) using fluorescence spectroscopy. A new flat 2 kbar pressure cell made of an aluminum alloy has been used, which allowed the effect of pressure to be studied with minimum background contribution. Within this range of pressure, the effect of this physical parameter on global diffusion can be explained in terms of the change in the water buffer viscosity and an oligomerization of hemoglobin subunits, whereas the internal motions were less affected.
Keywords: Pressure; Protein; Hemoglobin; Dynamics; Quasielastic neutron scattering

The influence of additives on the nanoscopic dynamics of the phospholipid dimyristoylphosphatidylcholine - Busch, Sebastian; Unruh, Tobias (Biochimica Et Biophysica Acta-Biomembranes, 2011)
The influence of additives on the molecular dynamics of the phospholipid dimyristoylphosphatidylcholine (DMPC) in its fully hydrated liquid crystalline phase was studied. Quasielastic neutron scattering (QENS) was used to detect motions with dimensions of some Angstroms on two different time scales, namely 60 ps and 900 Ps. The effects of myristic acid, farnesol, cholesterol, and sodium glycocholate could consistently be explained on the basis of collective, flow-like motions of the phospholipid molecules. The influence of the additives on these motions was explained by packing effects, corresponding to the reduction of free volume. Cholesterol was found to decrease the mobility of DMPC seen on the 900 ps time scale with increasing cholesterol content. In contrast, all other studied additives have no significant effect on the mobility. (C) 2010 Elsevier B.V. All rights reserved.
Keywords: DMPC; Dynamics; QENS; Myristic acid; Farnesol; Cholesterol; Sodium Glycocholate; Dynamic Heterogeneity

The influence of chemical annealing on the electronic properties of amorphous silicon - Ristein, Jürgen; Ley, Lothar; et al. (Solid State Phenomena, 1995)
UnivIS-Import:2015-04-16:Pub.1995.nat.dphy.IAP.exphys.theinf

The influence of gallium on phase transitions during the crystallisation of thin film absorber materials Cu(In,Ga)(S,Se)(2) investigated by in-situ X-ray diffraction - Hölzing, Astrid; Schurr, R.; Jost, S.; Palm, J.; Deseler, Klaus; Wellmann, Peter; Hock, Rainer (Thin Solid Films, 2011)
Chalcopyrite based photovoltaic materials Cu(InxGa1-x)(SySe1-y)(2) (CIGSSe) are substituted in the cation and anion lattice to adopt the semiconductor bandgap to the terrestrial solar spectrum. In-situ X-ray diffraction (XRD) investigations on the crystallisation of thin film absorber materials Cu(In,Ga)(S,Se)(2) while annealing stacked elemental layers (SEL) show phase transitions proceeding during the chalcopyrite synthesis. Thin layers of metals with elemental ratio Cu:In:Ga = 3:2:1 are deposited onto Mo-coated polyimide foil by DC-magnetron sputtering. The metal precursor is covered with S and subsequently Se by thermal evaporation of the elements in chalcogen excess (S + Se)/(Cu + In + Ga) = 23. Investigated chalcogen ratios reach from pure Se to pure S. Crystalline phases formed during the annealing of SEL are qualitatively determined. The results are compared to conclusions drawn from previous experiments on Ga-free CuIn(S,Se)(2) absorbers. The presence of Ga and S influences significantly the time-scale and the temperatures of phase transitions, i.e. the sulfoselenisation of precursor phases Cu-16(In,Ga)(9) and Cu-9(Ga,In)(4) proceeds faster with increasing S and is shifted to higher temperatures as compared to Ga-free Cu11In9/Cu16In9. (C) 2011 Elsevier BM. All rights reserved.
Keywords: Cu(In; Ga)(S; Se)2; Chalcopyrite; Chalcogenisation; Sulfoselenisation; Formation reaction; in-situ XRD

The influence of incorporated beta-carotene on the vibrational properties of single wall carbon nanotubes - Tschirner, Norman; Brose, Katharina; Maultzsch, Janina; Yanagi, Kazuhiro; Kataura, Hiromichi; Thomsen, Christian (physica status solidi (b), 2010)
Keywords: Raman; carontene; carbon nanotube; endohedral functionalization

The influence of n-hexanol on the morphology and composition of CTAB micelles - Schmutzler, Tilo; Schindler, Torben; Schmiele, Martin; Appavou, Marie-Sousai; Lages, Sebastian; Kriele, Armin; Gilles, Ralph; Unruh, Tobias (Colloids and Surfaces A-Physicochemical and Engineering Aspects, 2018)
The effect of the addition of n-hexanol as co-surfactant on the structure of cetyltrimethylammonium bromide (CTAB) micelles has been studied using small-angle X-ray and neutron scattering (SAXS, SANS). Contrast variation neutron scattering experiments were performed to determine the structure of both pure CTAB and n-hexanol modified CTAB micelles. The incorporation of n-hexanol leads to an elongation of the ellipsoidal CTAB micelles. The scattering length density of the micellar shell linearly depends on the degree of deuteration of the dispersion medium water and revealed the existence of substantial amounts of water in the micellar shell. The water content in the shell increased from 20 vol-% observed for pure CTAB micelles to 44 vol-% found for n-hexanol modified CTAB micelles. The amount of n-hexanol in the micellar shell was determined by varying the amount of fully deuterated and protonated n-hexanol. These experiments revealed a volume fraction of 26 vol-% of n-hexanol molecules in the micellar core which equals a molar fraction of 50% n-hexanol within the CTAB micelles. The total composition of micellar core and shell was estimated. The packing density of headgroups, water molecules and bromide ions turned out to drastically increase in n-hexanol modified CTAB micelles. These findings contribute to a fundamental understanding of the stabilization mechanism of micelles by alcoholic co-surfactants and the resulting alteration of the morphology and interface composition. These results will facilitate the optimization of processes where CTAB and other comparable surfactants are used as phase transfer catalysts, structure directing agents or stabilizers in colloidal dispersions or emulsions.
Keywords: CTAB micelles; Surfactants; Co-surfactants; SANS; SAXS

The influence of surface treatment on the electronic structure of CVD diamond films - Ristein, Jürgen; Hundhausen, Martin; Ley, Lothar; et al. (Diamond and Related Materials, 1994)
The electronic structure of CVD diamond surfaces has been studied by core level and valence band photoelectron spectroscopy. Upon annealing at 870 °C, a band of surface states appears within the top 6 eV of the valence bands which is accompanied by a decrease in spectral intensity around 9 eV and a band bending of 0.4 eV. Similar changes could be induced by Ar ion bombardment. Exposure to atomic hydrogen largely restored the original spectra. These observations are compared with corresponding data on single-crystalline diamond surfaces. Similarities and differences are discussed in terms of structural models of the CVD diamond surface. © 1994.
UnivIS-Import:2015-03-05:Pub.1994.nat.dphy.IAP.exphys.theinf

THE INVERSION OF AUTO-CONVOLUTION INTEGRALS - Fauster, Thomas; et al. (Journal of Computational Physics, 1981)

The IsoStretcher: An isotropic cell stretch device to study mechanical biosensor pathways in living cells. - Schürmann, Sebastian; Wagner, Sören; Herlitze, Simon; Fischer, C.; Gumbrecht, S.; Wirth-Hücking, Anette; Prölß, Gerhard; Lautscham, Lena; Fabry, Ben; Goldmann, Wolfgang; Nikolova-Krstevski, V.; Martinac, B.; et al. (Biosensors and Bioelectronics, 2016)
Mechanosensation in many organs (e.g. lungs, heart, gut) is mediated by biosensors (like mechanosensitive ion channels), which convert mechanical stimuli into electrical and/or biochemical signals. To study those pathways, technical devices are needed that apply strain profiles to cells, and ideally allow simultaneous live-cell microscopy analysis. Strain profiles in organs can be complex and multiaxial, e.g. in hollow organs. Most devices in mechanobiology apply longitudinal uniaxial stretch to adhered cells using elastomeric membranes to study mechanical biosensors. Recent approaches in biomedical engineering have employed intelligent systems to apply biaxial or multiaxial stretch to cells. Here, we present an isotropic cell stretch system (IsoStretcher) that overcomes some previous limitations. Our system uses a rotational swivel mechanism that translates into a radial displacement of hooks attached to small circular silicone membranes. Isotropicity and focus stability are demonstrated with fluorescent beads, and transmission efficiency of elastomer membrane stretch to cellular area change in HeLa/HEK cells. Applying our system to lamin-A overexpressing fibrosarcoma cells, we found a markedly reduced stretch of cell area, indicative of a stiffer cytoskeleton. We also investigated stretch-activated Ca(2+) entry into atrial HL-1 myocytes. 10% isotropic stretch induced robust oscillating increases in intracellular Fluo-4 Ca(2+) fluorescence. Store-operated Ca(2+) entry was not detected in these cells. The Isostretcher provides a useful versatile tool for mechanobiolog

The Magnetochiral Effect in Charge Transport in Carbon Nanotubes - Krstic, Vojislav; Roth, Siegmar; Burghard, Marko; Kern, Klaus; Rikken, Geert L.J.A. (Materials Research Society Symposium Proceedings: Nanotube-Based Devices, 2003)
Nanotubes forming carbon atoms arrange differently, resulting into three main types of carbon nanotubes: armchair, zigzag, chiral. Thus, depending on their type, nanotubes may be regarded as chiral, molecular electrical conductors. As a consequence of symmetry arguments, the magnetoresistance of such tubes depends on the relative orientation of the traversing current and the external magnetic field. Magnetotransport measurements on single walled carbon nanotubes have been performed showing the expected dependence on both the current and magnetic field. Further, the quantum-mechanical model of a free electron on a helix in an external magnetic field is discussed in order to provide indicators to possible microscopic mechanisms.

The measurement of self-diffusion coefficients in liquid germanium using quasielastic neutron scattering - Weiss, Henning; Unruh, Tobias; Meyer, Andreas (High Temperatures-High Pressures, 2013)
We measured dynamic structure factors using quasielastic neutron scattering for two liquid germanium samples, one in natural isotope abundance, and a second one with a Ge-nat/73 isotope mixture which exhibits an order of magnitude larger ratio of incoherent to coherent neutron scattering cross section. In an intermediate q range corresponding spectra exhibit similar quasielastic broadening. We show that the measured quasielastic line originates from incoherent scattering. Coherent contributions appear as an almost energy independent background. From the incoherent quasielastic neutron scattering signal self-diffusion coefficients can therefore accurately be derived.
Keywords: Liquid germanium; atomic self diffusion; thermal diffusion; phonon dispersion; neutron scattering; X-ray scattering; coherent and incoherent scattering; Rayleigh line; Brillouin lines

The moving photocarrier grating technique for the determination of transport parameters in thin film semiconductors - Hundhausen, Martin (Journal of Non-Crystalline Solids, 1996)
The moving-photocarrier-grating (MPG) technique for the determination of the photocarrier lifetime and the carrier mobilities in semiconductors is described. This method utilizes the moving interference pattern generated by the superposition of two frequency shifted laser beams for illumination of the sample. This moving intensity grating induces a short circuit current, jsc, and it is shown how the transport parameters of the sample are extracted from the grating-velocity dependence of jsc. Results for amorphous hydrogenated silicon are presented. The potential of the MPG technique to measure directly the drift velocity of electrons and holes in high electric fields is discussed.
UnivIS-Import:2015-03-05:Pub.1996.nat.dphy.IAP.exphys.themov

The nature of x-ray scattering from geo-nanoparticles: Practical considerations of the use of the Debye equation and the pair distribution function for structure analysis - Harrington, Richard; Neder, Reinhard; Parise, John B. (Chemical Geology, 2012)
Interpretation of elastic scattering from nanocrystals is critical to building and testing models of the short and medium range atomic arrangements in environmentally relevant nanoparticles. Along with information about atomic arrangements, the diffraction pattern arising from a collection of nanoparticles contains information on the grain size, shape and defect structure and cannot simply be treated as a broadened collection of Bragg peaks. The Debye equation, a sum over all pairs of atoms in the particle, calculates the scattering at each value of Q rather than at discrete values of hkl. Especially when atomic arrangements are well known, modeling using the Debye equation allows the refinement of particle shape, allowing the investigation of dominant growth axes. We show the example of 6-line ferrihydrite, fitting the diffraction pattern using a disc of 2.3(1) nm in the ab plane and 6(2) nm along the c axis. A powerful and intuitive way to help examine the diffraction pattern is to take the Fourier transform of the normalized total scattering (Bragg and diffuse), giving the pair distribution function (PDF). The PDF represents a bond length distribution of the material weighted by the respective scattering powers of the contributing atoms. Using examples from the literature, we show that by analyzing the medium range correlations (similar to 5-15 angstrom), the structure of a nanoparticle can be distinguished using PDFs generated from model structures. (c) 2011 Elsevier B.V. All rights reserved.
Keywords: X-ray diffraction; Debye equation; Nanoparticles; Pair distribution function; PDF; Ferrihydrite

The nipnip-THz-emitter: Photomixing based on ballistic transport - Malzer, Stefan; et al. (PHYSICS OF SEMICONDUCTORS: 27th International Conference on the Physics of Semiconductors, ICPS-27, 2005)
We report on a novel concept for THz-photomixers based on quasi-ballistic transport in an asymmetric nipnip-doping-superlattice. Due to tansport-optimized i-layers the emitted powers are not transit-time-limited up to 1 THz. Furthermore the capacitance and hence the RC-roll-off is minimized by increasing the number of pin-periods. The frequency-dependence of the nipnip-emitter proofs to be superior to corresponding pin-photomixers. © 2005 American Institute of Physics.

The Optical Properties of the Carbon Di-Vacancy-Antisite Complex in the Light of the TS Photoluminescence Center - Schober, M.; Jungwirth, N.; Kobayashi, Takuma; Lehmeyer, Johannes; Krieger, Michael; Weber, Heiko B.; Bockstedte, M. (Defect and Diffusion Forum, 2023)
The TS center is a promising temperature-stable photoluminescence center in 4H SiC. Here we investigate the carbon di-vacancy-antisite complex in the framework of ab initio theory as a tentative model for the TS center. We identify optical transitions of the basal complexes with the TS lines based on excitation energies, Stark shifts, and radiative characteristics. Charge-state-control of the TS center in p- and n-type Schottky contacts is demonstrated. Our experimental findings are consistent with the positively charged carbon di-vacancy-antisite complex.
CRIS-Team Scopus Importer:2023-09-01
Keywords: Ab Initio Theory; Charge-State Control; Color Center; Photoluminescence; Photophysics; Stark Effect

The origin of traveling waves in an emperor penguin huddle - Gerum, Richard; Fabry, Ben; Metzner, Claus; Beaulieu, Michaël; Ancel, André; Paranhos Zitterbart, Daniel (New Journal of Physics, 2013)

Theory of Rayleigh scattering from metallic carbon nanotubes - Malic, Ermin; Hirtschulz, Matthias; Milde, Frank; Wu, Yang; Maultzsch, Janina; Heinz, Tony F.; Knorr, Andreas; Reich, Stephanie (Physical Review B, 2008)
We present a microscopic calculation of the Rayleigh (elastic light) scattering spectra for single-walled carbon nanotubes. Combining density-matrix formalism and the tight-binding model, we obtain results for nanotubes of arbitrary chiral index. In agreement with experiment, the calculated Rayleigh spectra of metallic nanotubes show a double-peaked structure resulting from the trigonal warping effect, with the low-energy feature exhibiting greater intensity. We explain the intensity ratios by the wave-vector dependence of the optical matrix elements. Also in accord with experiment, the Rayleigh line shape of each peak is asymmetric, with an enhanced cross section for lower photon energies. This behavior arises from contributions of the nonresonant optical susceptibility to the Rayleigh scattering process.

The physics of hydrogen-terminated diamond surfaces - Ristein, Jürgen (AIP Conference Proceedings, 2005)
The termination of the surface dangling bonds of a semiconductor by chemical bonds is a key feature which determines the surface band diagram and the electronic properties related with it. In the case of diamond as the only representative of an elemental wide band gap semiconductor, the termination by monovalent hydrogen atoms leads to particularly interesting properties of its surfaces. Firstly it is ideal to remove (donor-like) surface states from the gap, secondly it creates a true negative electron affinity, and thirdly it makes the material susceptible to an unusual type of transfer doping where holes are injected by acceptors located at the surface instead of inside the host lattice. All of these effects are, directly or indirectly, brought about by the termination of the surface carbon atoms by the covalent but polar bonds with hydrogen. They can thus be tailored by gradually replacing the terminating hydrogen by oxygen bonds with opposite polarity. This makes diamond a material with a tremendous variability in its electronic surface properties. © 2005 American Institute of Physics.
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.IAP.exphys.thephy

The picosecond dynamics of the phospholipid dimyristoylphosphatidylcholine in mono- and bilayers - Busch, Sebastian; Pardo, Luis Carlos; Smuda, Christoph; Unruh, Tobias (Soft Matter, 2012)
The dynamics of the fully hydrated phospholipid dimyristoylphosphatidylcholine (DMPC) were studied on a time scale of about 60 picoseconds with quasielastic neutron scattering. Three types of samples were employed: multibilayers without solid support, single bilayers in vesicles, and monolayers in emulsions of perdeuterated hexadecane. The vesicles and emulsion droplets had diameters of about 130 nanometres; some of the emulsions also contained sodium glycocholate to enhance the stability. It could be shown that the mobility of the phospholipid molecules in the observed time regime increases from multibilayers over single bilayers to monolayers. Additionally, the high quality of the data of the multibilayer samples allows an evaluation of the molecular mechanism of the motions: while the interpretation in the frame of flow-like motions fits well at temperatures shortly above the main phase transition, the model of diffusive motions fits better at high temperatures of up to 80 degrees C.

The quasi-free-standing nature of graphene on H-saturated SiC(0001) - Speck, Florian; Jobst, Johannes; Fromm, Felix; Ostler, Markus; Waldmann, Daniel; Hundhausen, Martin; Weber, Heiko B.; Seyller, Thomas (Applied Physics Letters, 2011)
We report on an investigation of quasi-free-standing graphene on 6H-SiC(0001) which was prepared by intercalation of hydrogen under the buffer layer. Using infrared absorption spectroscopy, we prove that the SiC(0001) surface is saturated with hydrogen. Raman spectra demonstrate the conversion of the buffer layer into graphene which exhibits a slight tensile strain and short range defects. The layers are hole doped (p 5.0 - 6.5 1012 cm -2) with a carrier mobility of 3100 cm2/Vs at room temperature. Compared to graphene on the buffer layer, a strongly reduced temperature dependence of the mobility is observed for graphene on H-terminated SiC(0001) which justifies the term quasi-free-standing. © 2011 American Institute of Physics.
UnivIS-Import:2015-03-09:Pub.2011.nat.dphy.IAP.exphys.thequa

The radial breathing mode frequency in double-walled carbon nanotubes: an analytical approximation - Maultzsch, Janina; et al. (physica status solidi (b), 2003)
We study the breathing-like phonon modes of double-walled carbon nanotubes in a simple analytical model by considering the tube walls as coupled oscillators. The force constant of the oscillator coupling is found to be proportional to the inner tube diameter. Thus, only for small-diameter tubes, the shift of the breathing-like phonon mode frequencies (relative to the radial breathing modes of the isolated layers) scales with the tube diameter D. For tubes with larger diameter the in-phase breathing-like phonon mode frequency is inversely proportional to the diameter (like the radial breathing modes of the single wall carbon nanotubes), while the out-of-phase mode approaches asymptotically, as 1/D-2, the graphite B-2g phonon mode frequency.

Thermal evolution of cobalt deposits on Co3O4(111): Atomically dispersed cobalt, two-dimensional CoO islands, and metallic Co nanoparticles - Mehl, Sascha; Ferstl, Pascal; Schuler, Marina; Toghan, A.; Brummel, Olaf; Hammer, Lutz; Schneider, M. Alexander; Libuda, Jörg (Physical Chemistry Chemical Physics, 2015)
Cobalt oxide nanomaterials show high activity in several catalytic reactions thereby offering the potential to replace noble metals in some applications. We have developed a well-defined model system for partially reduced cobalt oxide materials aiming at a molecular level understanding of cobalt-oxide-based catalysis. Starting from a well-ordered Co3O4(111) film on Ir(100), we modified the surface by deposition of metallic cobalt. Growth, structure, and adsorption properties of the cobalt-modified surface were investigated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and infrared reflection absorption spectroscopy (IRAS) using CO as a probe molecule. The deposition of a submonolayer of cobalt at 300 K leads to the formation of atomically dispersed cobalt ions distorting the surface layer of the Co3O4 film. Upon annealing to 500 K the Co ions are incorporated into the surface layer forming ordered two-dimensional CoO islands on the Co3O4 grains. At 700 K, Co ions diffuse from the CoO islands into the bulk and the ordered Co3O4(111) surface is restored. Deposition of larger amounts of Co at 300 K leads to formation of metallic Co aggregates on the dispersed cobalt phase. The metallic particles sinter at 500 K and diffuse into the bulk at 700 K. Depending on the degree of bulk reduction, extended Co3O4 grains switch to the CoO(111) structure. All above structures show characteristic CO adsorption behavior and can therefore be identified by IR spectroscopy of adsorbed CO.

Thermal Expansion Coefficients of 6H Silicon Carbide - Stockmeier, Matthias; Sakwe, Aloysius; Hens, Philip; Wellmann, Peter; Hock, Rainer; Magerl, Andreas (Materials Science Forum, 2009)
The thermal expansion of 6H Silicon Carbide with different dopant concentrations of aluminum and nitrogen was determined by lattice parameter measurements at temperatures from 300 K to 1575 K. All samples have a volume of at least 6 x 6 x 6 mm(3) to ensure that bulk properties are measured. The measurements were performed with a triple axis diffractometer with high energy x-rays with a photon energy of 60 keV. The values for the thermal expansion coefficients along the a- and c-direction, alpha(11) and alpha(33), are in the range of 3.10(-6) K(-1) for 300 K and 6.10(-6) K(-1) for 1550 K. At high temperatures the coefficients for aluminum doped samples are approximately 0.5.10(-6) K(-1) lower than for the nitrogen doped crystal. alpha(11) and alpha(33) appear to be isotropi
Keywords: Bulk Characterization; High Energy X-Ray Diffraction; Thermal Expansion

Thermal expansion of colloidal CdSe/CdS core/shell quantum dots - Moses Badlyan, Narine; Biermann, Amelie; Aubert, Tangi; Hens, Zeger; Maultzsch, Janina (Physical Review B, 2019)

Thermal history effect on the nucleation of oxygen precipitates in germanium doped Cz-silicon studied by high-energy X-ray diffraction - Li, Zhen; Will, Johannes; Dong, Peng; Yang, Deren (Journal of Crystal Growth, 2017)
The oxygen (O) precipitate growth kinetics from moderate and high germanium (Ge) doped Czochralskigrowth silicon (Cz-Si) are in-situ investigated at 1000 degrees C utilizing high-energy X-ray diffraction and analyzed with respect to precipitate density within a diffusion-driven growth model. Distinct different precipitation kinetics are observed for high Ge doped specimens. From the comparison of three thermal treatments, it was found that even for a high Ge concentration the nucleation rate at 800 degrees C is not influenced, however it facilitates larger grown-in precipitates of smaller amount as compared to the precipitates in undoped and moderately Ge doped samples. However, those grown-in O precipitates can be erased either by a direct annealing at 1200 degrees C or 1000 degrees C, but on the other hand stabilized by an annealing step at 800 degrees C, which in this manner as a drift step of grown-in precipitates for the high Ge-doped samples. In comparison additional nuclei are formed at 800 degrees C in the moderate and undoped cases. (C) 2017 Elsevier B.V. All rights reserved.
Keywords: Doping; X-ray diffraction; Defects; Impurity; Czochralski method; Semiconducting silicon

Thermalization of excited carriers through band states studied by photoluminescence in As2Se3 single crystals - Ristein, Jürgen; et al. (Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties, 1987)
UnivIS-Import:2015-03-05:Pub.1987.nat.dphy.IAP.exphys.therma

THERMALLY INDUCED DISORDER ON A CU(110) SURFACE STUDIED BY LOW-ENERGY ION-SCATTERING AND INVERSE PHOTOEMISSION - Fauster, Thomas; et al. (Surface Science, 1987)

Thermally-induced evolution of codeposited Co-Si layers on Si(100) surfaces - Rangelov, Georgi; Fauster, Thomas (Surface Science, 1996)
The formation of ultrathin epitaxial layers of CoSi2 on Si(100) surfaces is studied by means of valence-band and core-level photoemission spectroscopy with synchrotron radiation, low-energy electron diffraction (LEED) and Auger electron spectroscopy. The CoSi2 films are prepared by the template method in which an amorphous layer with CoSi2 stoichiometry is coevaporated on top of a 2.6-3 monolayer thick Co overlayer at room temperature. The amorphous layer does not react to CoSi,. Annealing to 300 degrees C leads to the crystallization of the layer demonstrated by the formation of a (root 2x root 2)R45 degrees LEED pattern. This layer consists of disilicide in CaF2 structure with some contribution from another silicide phase. This surface is stable at least up to 460 degrees C. After further annealing above 460 degrees C the disilicide disappears, at least from the sub-surface layer, and the surface is covered by clean Si patches and patches of the second silicide phase. The new silicide phase is characterized by a (2 root 2x root 2)R45 degrees LEED pattern and has a different electronic structure and Si2p binding-energy shifts. A comparison with previous experimental results and existing theoretical electronic structure calculations suggests that the new silicide phase can be identified as adamantane disilicide.
Keywords: low-energy electron diffraction (LEED); metal-semiconductor interfaces; silicides; single-crystal epitaxy; soft X-ray photoelectron spectroscopy

Thermally stimulated Conductivity in a-Si:H Doping superlattices - Hundhausen, Martin (Journal of Non-Crystalline Solids, 1989)
Hydrogenated amorphous silicon doping superlattices are utilized to obtain a high metastable concentration of spatially separated electrons and holes trapped in their respective band tails. Thermally stimulated conductivity (TSC) experiments show that the thermal energy required to excite carriers to the transport path decreases with increasing concentration of metastable carriers (Nmeta). This is in contrast to IR-photoconductivity data which show a fixed threshold for the excitation of band tail carriers to the mobility edge which does not depend on Nmeta. A model is proposed in which the differences between thermal and optical excitation energies are due to potential fluctuations created by the trapped carriers themselves. © 1989.
UnivIS-Import:2015-03-05:Pub.1989.nat.dphy.IAP.exphys.therma

Thermal origin of light emission in nonresonant and resonant nanojunctions - Ott, Christian; Götzinger, Stephan; Weber, Heiko B. (Physical Review Research, 2020)
Electron tunneling is associated with light emission. In order to elucidate its generating mechanism, we provide an experimental ansatz that employs fixed-distance epitaxial graphene as metallic electrodes. In contrast to previous experiments, this open geometry permits an unobscured light spread from the tunnel junction, enabling both a reliable calibration of the visible to infrared emission spectrum and a detailed analysis of the dependence of the parameters involved. In a nonresonant geometry, the emitted light is perfectly characterized by a Planck spectrum. In an electromagnetically resonant environment, resonant radiation is added to the thermal spectrum, both being strictly proportional in intensity. In full agreement with a simple heat conduction model, we provide evidence that in both cases the light emission stems from a hot electronic subsystem in interaction with its linear electromagnetic environment. In a long-running discussion whether the light is of thermal or electromagnetic origin, these results on graphene nanojunctions clearly favor the thermal pictur

THERMAL VIBRATIONS AT COPPER SURFACES STUDIED BY LOW-ENERGY ION-SCATTERING - Fauster, Thomas; et al. (Vacuum, 1990)

Thermochemical and Structural Studies of New Chiral and Achiral Long Alkyl Chain Functionalized Imidazolinium Ionic Liquids - Seidl, Vera; Sternberg, Michelle; Heinemann, Frank Wilhelm; Schmiele, Martin; Unruh, Tobias; Wasserscheid, Peter; Meyer, Karsten (Crystal Growth and Design, 2021)
Adding to the versatile class of ionic liquids (ILs), an entirely new series of imidazolinium-based ionic liquids is reported herein, offering chirality and important thermal characteristics, such as polymorphism, glass transition, and plastic crystalline behavior. An efficient and general procedure for the preparation of long N,N′-alkyl chain-substituted compounds with either saturated (s) or chiral (c) cyclohexyl (cyC6)-substituted imidazolium (Im) backbones, namely, [C12C12RsIm][A] (A = Br-, [BF4]-, [ClO4]-, [PF6]- R = H, Me, iPr) and [C12C12cIm-cyC6][A] (A = Br-, I-, [I3]-, [BF4]-, [ClO4]-, [PF6]-, [SbF6]-, [BPh4]-), was developed, and the novel compounds were studied by thermochemical methods (DSC, TGA), X-ray diffraction in the small angle regime (SAXS), single-crystal X-ray diffraction (SC-XRD), and specific rotation analysis.
CRIS-Team Scopus Importer:2021-10-29

Thermoelectricity of near-resonant tunnel junctions and their relation to Carnot efficiency - Popp, Matthias Albert; Erpenbeck, André; Weber, Heiko B. (Scientific Reports, 2021)

The role of adsorbates and defects on diamond surfaces - Ristein, Jürgen; Ley, Lothar; et al. (New Diamond and Frontier Carbon Technology, 2000)
The influence of surface termination, defects, and adsorbates on the electronic properties of diamond surfaces is discussed. Hydrogen passivation leads to a negative electron affinity of diamond surfaces due to a dipole layer which is induced by the heteropolar carbon-hydrogen bonds of the surface atoms. This aspect is discussed quantitatively. Next, the role of surface defects is addressed and the correlation between the position of the surface Fermi level and the concentration of surface defects is discussed for p-type diamond. Finally, experiments combining total photoelectron yield spectroscopy and in situ conductivity measurements are reported which elucidate the phenomenon of surface conductivity of hydrogenated diamond. An electrochemical model is proposed to explain this unique feature of diamond surfaces.
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.IAP.exphys.therol_6
Keywords: Adsorbates; Diamond surface; Electronic properties

The role of connectivity in significant bandgap narrowing for fused-pyrene based non-fullerene acceptors toward high-efficiency organic solar cells - Liu, Shungang; Su, Wenyan; Zou, Xianshao; Du, Xiaoyan; Cao, Jiamin; Wang, Nong; Shen, Xingxing; Geng, Xinjian; Tang, Zilong; Yartsev, Arkady; Zhang, Maojie; Gruber, Wolfgang; et al. (Journal of Materials Chemistry A, 2020)

The role of focal adhesion anchoring domains of CAS in mechanotransduction - Braniš, Jaroslav; Pataki, Csilla; Spörrer, Marina; Gerum, Richard; Mainka, Astrid; Cermak, Vladimir; Goldmann, Wolfgang; Fabry, Ben; Brabek, Jan; Rosel, Daniel (Scientific Reports, 2017)

The role of focal adhesion anchoring domains of CAS in mechhttps://cris.fau.de/converis/mypages/edit/Publication/1080200/default#anotransduction - Braniš, Jaroslav; Pataki, Csilla; Spörrer, Marina; Gerum, Richard; Mainka, Astrid; Cermak, Vladimir; Goldmann, Wolfgang; Fabry, Ben; Brabek, Jan; Rosel, Daniel (Scientific Reports, 2017)

The role of hydrogen for field emission from chemical vapour deposited diamond and nanocrystaline diamond powder - Ley, Lothar; Ristein, Jürgen; Stammler, Martin; et al. (Journal of Applied Physics, 2000)
UnivIS-Import:2015-03-09:Pub.2000.nat.dphy.IAP.exphys.therol

The role of the tissue microenvironment in the regulation of cancer cell motility and invasion - Brabek, Jan; Mierke, Claudia; Roesel, Daniel; Vesely, Pavel; Fabry, Ben (Cell Communication and Signaling, 2010)

The role of vibrations in single-molecule charge transport: A case study of oligoynes with pyridine anchor groups - Ballmann, Stefan Dieter; Hieringer, Wolfgang; Härtle, Rainer; Brana Coto, Pedro; Bryce, Martin; Görling, Andreas; Thoss, Michael; Weber, Heiko B. (physica status solidi (b), 2013)
We report on measurements on molecular wires in single-molecule junctions. The target is to identify vibrational signatures in the differential conductance spectra, which cannot be resolved for most molecular wires in the resonant transport regime. For the given molecules, we find indeed vibrational sidepeaks, which can be assigned to the longitudinal modes of the string-like central motif of the molecule by comparison with density functional theory. These data corroborate that oligoyne wires are ideally suited for characterizing vibrational sidepeaks. A current increase as a consequence of vibrational decoherence observed for thiols is, however, not found due to the pyridine anchor group chosen in the present molecules. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The screened-exchange approximation as alternative method for DFT calculations on graphene structures - Gillen, Roland; Robertson, John (Physical Review B - Condensed Matter and Materials Physics, 2010)
Keywords: Density functional theory; Nanoribbons; Graphene; Screened-exchange approximation

The screening effects of the screened exchange hybrid functional in surface systems: A case study on the CO/Pt(111) problem - Li, Huanglong; Gillen, Roland; Robertson, John (AIP Advances, 2016)

The slow short-time motions of phospholipid molecules with a focus on the influence of multiple scattering and fitting artefacts - Busch, Sebastian; Unruh, Tobias (Journal of Physics: Condensed Matter, 2011)
Quasi-elastic neutron scattering is a powerful tool for the study of non-periodic motions in condensed matter, as a detailed line shape analysis can give information about the geometry and rate of the scatterers' displacements. Unfortunately, there are also a number of artefacts which can masquerade as signatures of motions and can therefore lead to erroneous results. Their influence on the evaluation of the motions of the phospholipid dimyristoylphosphatidylcholine (DMPC) is discussed. On a 60 ps timescale, the long-range motion of the molecules has a flow-like character with similar velocities above and below the main phase transition. It is proposed that the concepts of dynamical heterogeneities and 'floppy modes' developed in glass physics provide a framework for explaining the observed behaviour.

The Squeezable Nanojunction as a tuneable light-matter interface for studying photoluminescence of 2D materials - Popp, Matthias Albert; Kohring, Malte; Fuchs, Alexander; Korn, Sascha; Moses Badlyan, Narine; Maultzsch, Janina; Weber, Heiko B. (2D Materials, 2021)

The stopped-drop method: A novel setup for containment-free and time-resolved measurements - Magerl, Andreas; Schiener, Andreas; Seifert, Soenke (Journal of Synchrotron Radiation, 2016)
A novel setup for containment-free time-resolved experiments at a free-hanging drop is reported. Within a dead-time of 100 ms a drop of mixed reactant solutions is formed and the time evolution of a reaction can be followed from thereon by various techniques. As an example, a small-angle X-ray scattering study on the formation mechanism of EDTA-stabilized CdS both at a synchrotron and a laboratory X-ray source is presented here. While the volution can be followed with one drop only at a synchrotron source, a stroboscopic mode with many drops is preferable for the laboratory source.
Keywords: containment-free; in situ; millisecond time-resolved; sample environment; SAXS

The structure, methyl rotation reflected in inelastic and quasielastic neutron scattering and vibrational spectra of 1,2,3,5-tetramethoxybenzene and its 2:1 complex with 1,2,4,5-tetracyanobenzene - Pawlukojć, Andrzej; Prager, Michael; Dobrowolska, Wanda Sawka; Bator, Grażyna; Sobczyk, Lucjan; Ivanov, Alexander; Rols, Stephane; Grech, Eugeniusz; Nowicka-Scheibe, Joanna; Unruh, Tobias (Journal of Chemical Physics, 2008)
X-ray diffraction studies show that molecules of the 1,2,3,5-tetramethoxybenzene (TMOB)(2)center dot 1,2,4,5-tetracyanobenzene complex form center dot center dot center dot CCDCCDCC center dot center dot center dot columns with the short distances between molecular planes of C and D molecules equal to 3.186 angstrom. The vibrational spectra recorded by using the inelastic neutron scattering, Raman, IR, and quasielastic neutron scattering (QENS) techniques aided by density functional theory calculations for the isolated molecules and the crystalline state enabled all four inequivalent librational modes, ascribed to the methoxy groups, to be analyzed. A rather good consistency was found between the experimental frequencies and those calculated for the crystal. The consistency was also achieved between the experimental structure of molecules and the theoretically reproduced one. A close similarity of the structures of the TMOB molecule isolated and in the complex is taken as a sign of dominating intramolecular interaction. The QENS spectra contain three Lorentzians of relative intensities of 1:1:2. Thus the two most strongly hindered of the four inequivalent methoxy groups in the crystalline lattice are characterized by rather similar barrier heights in good agreement with the packing analysis. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.2990650]

The structure of diaminodurene and the dynamics of the methyl groups - Sobczyk, Lucjan; Prager, Michael; Sawka-Dobrowolska, Wanda; Bator, Grażyna; Pawlukojć, Andrzej; Grech, Eugeniusz; van Eijck, Lambert; Ivanov, Alexander; Rols, Stephane; Wuttke, Joachim; Unruh, Tobias (Journal of Chemical Physics, 2009)
Diaminodurene crystallizes in the orthorhombic space group Pbca, with eight molecules in the unit cell. Four inequivalent methyl groups with different environments exist in a molecule. The amino groups are also different, which is well reflected in infrared spectra. Two tunneling modes are resolved at 23.7 and 7.0 mu eV at 4.5 K. Their intensities are consistent with the presence of two further unresolved tunneling modes. Quasielastic spectra are composed of three Lorentzians of equal intensities. The two low activation energies and tunnel modes are modeled into consistent rotational potentials. The third activation energy and a librational band are used to guess the strength of the two stronger rotational potentials. The internal modes related to the torsional/librational vibrations mix with ring torsions in the range of 70-220 cm(-1). This way the tunnel modes couple to ring torsions whose energy determines the broadening of both tunnel bands. The calculations for free molecules yield mode frequencies a little bit lower than the experimental inelastic neutron scattering (INS) values. Application of theoretical methods elaborated for the crystalline state leads to a satisfactory consistency. It is also valid for bending modes of NH(2) groups, which in the solid state show much higher frequencies than in the gas phase, as expected. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3125629]

THE TEMPERATURE-DEPENDENCE OF THE INVERSE PHOTOEMISSION FROM COPPER SURFACES - Fauster, Thomas; et al. (Vacuum, 1990)

Thickness dependence of the integrated Bragg intensity for statistically disturbed silicon crystals - Will, Johannes; Gröschel, Alexander; Weißer, Matthias; Magerl, Andreas (Applied Physics Letters, 2011)
The thickness dependence of the integrated Bragg intensities for Czochralski-grown silicon was measured with the characteristic tungsten K(alpha 1)-line at 59.3 keV. In contrast to previous experiments the sample is wedge shaped, which allows to take data over a wide range of Pendellosung fringes in one exposure only and without any mechanical movement of the sample. The period length, the oscillation amplitude, and the mean value of the Bragg intensity can be explored to identify the presence of point defects, and the temperature dependence of the period length allows to quantify the thermal Debye-coefficient with high precision. (c) 2011 American Institute of Physics. [doi:10.1063/1.3531761]

Thin Film Diamond (part II) - Ristein, Jürgen; et al. (Elsevier, 2004)
UnivIS-Import:2015-05-08:Pub.2004.nat.dphy.IAP.exphys.struct

Three-Dimensional Electrostatic Field at an Electron Nano-Emitter Determined by Differential Phase Contrast in Scanning Transmission Electron Microscopy - Wu, Mingjian; Tafel, Alexander; Hommelhoff, Peter; Spiecker, Erdmann (Microscopy and Microanalysis, 2019)

Three-dimensional force microscopy of cells in biopolymer networks - Steinwachs, Julian; Metzner, Claus; Skodzek, Kai; Lang, Nadine; Thievessen, Ingo; Mark, Christoph; Münster, Stefan; Aifantis, Katerina E.; Fabry, Ben (Nature Methods, 2016)

THz collective oscillations of ballistic electrons in wide potential wells: Bridging classical transport with quantum dynamics - Malzer, Stefan; et al. (EPL - Europhysics Letters, 2005)
Parabolic shaped potential wells of a width between 120 nm and 250 nm are defined in a band gap engineered p -n-p heterostructure. After femtosecond photoinjection of carriers near the boundary of the well, electrons are found to coherently oscillate across the well with the classical harmonic-oscillator frequency of a few THz instead of performing the intuitively expected unidirectional relaxation towards the bottom of the well. Most strikingly, the coherence of this periodic electron motion is maintained despite multiple phonon scattering events. This novel transport regime is predicted by detailed Monte Carlo simulations and verified by analyzing the femtosecond transmission of the heterostructure as well as by directly detecting the THz radiation emitted by the oscillating electron-hole dipole. By decreasing the well width, this semi-classical ballistic transport regime is expected to converge towards a quantum-beat regime. © EDP Sciences.

THz-emitter based on ballistic transport in nano-pin diodes - Malzer, Stefan; et al. (physica status solidi (a), 2005)
Conventional semiconductor-based photomixers are limited by the carrier transit-time-roll-off and the RC-roll-off of the device-capacitance. We have developed a THz-photomixer which can overcome both limitations and proves far superior to a conventional pin-photomixer. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

THz-photomixer based on quasi-ballistic transport - Döhler, Gottfried; Renner, Frank; Klar, Oliver; Eckardt, Martin; Schwanhäußer, Axel; Malzer, Stefan; Driscoll, Dan; Hanson, Micah; Gossard, Art; Loata, gabriel; Löffler, Torsten; Roskos, Hartmut (Semiconductor Science and Technology, 2005)
We report on a novel concept for THz photomixers with high conversion efficiency up to several THz. In contrast to the conventional pin photomixer we can overcome the trade-off between either optimizing transit-time or RC-roll-off. Using quasi-ballistic transport in nano-pin-diodes the transport path can be optimized regarding both path length and transit time. Independently, the capacitance can be kept small by using a sufficiently large number of optimized nano-pin-diodes in series. The concept is presented in detail and first experimental results are reported which corroborate our theoretical expectations. © 2005 IOP Publishing Ltd.

Tight-binding description of graphene - Maultzsch, Janina; et al. (Physical Review B, 2002)
We investigate the tight-binding approximation for the dispersion of the pi and pi* electronic bands in graphene and carbon nanotubes. The nearest-neighbor tight-binding approximation with a fixed gamma(0) applies only to a very limited range of wave vectors. We derive an analytic expression for the tight-binding dispersion including up to third-nearest neighbors. Interaction with more distant neighbors qualitatively improves the tight-binding picture, as we show for graphene and three selected carbon nanotubes.

Time constant/volume relationship of passive expiration in mechanically ventilated ARDS patients - Guttmann, Josef; Eberhard, Luc; Fabry, Ben; Bertschmann, W.; Zeravik, J.; Adolph, Michael; , Joachim Eckart; Wolff, G. (European Respiratory Journal, 1995)

Time course and heterogeneity of contractile responses in cultured human airway smooth muscle cells - Fabry, Ben; Maksym, Geoffrey N.; Shore, Stephanie A.; Moore, Paul E.; Panettieri, Reynold A.; Butler, James P.; Fredberg, Jeffrey (Journal of Applied Physiology, 2001)

Time-resolved coherent photoelectron spectroscopy of quantized electronic states on metal surfaces - Höfer, Ulrich; Shumay, Igor L.; Reuss, Christian; Thomann, Ulrich; Wallauer, Wolfgang; Fauster, Thomas (Science, 1997)
Time-resolved two-photon photoemission in combination with the coherent excitation of several quantum states was used to study the ultrafast electron dynamics of image-potential states on metal surfaces, For a (100) surface of copper, the spectroscopy of quantum beats made previously unresolved high-order states (quantum number n greater than or equal to 4) experimentally accessible, By exciting electrons close to the vacuum level, electron wave packets could be created and detected that described the quasi-classical periodic motion of weakly bound electrons, They traveled more than 200 Angstrom away from the surface and oscillated back and forth with a period of 800 femtoseconds.

Time-resolved photoemission at the Si(100)-Ga surface using a femtosecond higher-harmonic laser source - Melzer, Andrea Christine; Kampa, Daniel; Wang, Jinxiong; Fauster, Thomas (Physical Review B, 2009)
The Si(100)-(2x2)-Ga surface was used to investigate time-dependent Ga(3d) core-level shifts by pumping electrons from the valence to the conduction band. The pump-probe experiments were done by exciting carriers with 1.59 eV laser pulses and probing the Ga (3d) core level with higher harmonics. The higher harmonics were generated by focusing laser pulses with 1.4 mJ energy, 30 fs pulse duration, and 779 nm wavelength from a multipass amplifier at a repetition rate of 1 kHz into argon. For the 23rd harmonic, the time resolution of the experiment was similar to 400 fs after a grating monochromator. The band bending of about 110 meV of the p-doped Si(100)-(2x2)-Ga surface is completely lifted by illumination of the surface with the 1.59 eV laser pulses. The Ga(3d) core level shows a slow time-dependent shift attributed to the rise (similar to 1 ns) and decay (similar to 100 ns) of the photovoltage. The Ga(3d) core-level shift and broadening in the femtosecond range are determined to be < 15 meV at the used pump-pulse intensity of 19 mJ/cm(2). Experiments with pump pulses of 3.18 eV photon energy showed similar results.

Time-resolved photoemission from image-potential states - Fauster, Thomas; Weinelt, Martin (Journal of Electron Spectroscopy and Related Phenomena, 2001)
Electrons attracted by the image force to a metal surface are loosely bound and form a Rydberg-like series of states converging towards the vacuum level. Energies and lineshapes of these image-potential states are studied by two-photon photoelectron spectroscopy. The use of Ti-sapphire lasers as light sources has raised the count rates by several orders of magnitude and provided the opportunity to study the lifetime in the femtosecond range. Coherent excitation of several higher image-potential states of the Rydberg-like series leads to the observation of quantum beats in the time domain. The decay of the beat pattern and the lifetime are strongly influenced by adsorbates. The dependence on the quantum number of the image-potential states and the adsorbate will be discussed. The model system of image-potential states can be studied extremely well in present experiments and the results contribute to the understanding of photochemical processes and hot-electron dynamics at surfaces. (C) 2001 Elsevier Science B.V. All rights reserved.
Keywords: two-photon photoemission; image-potential states; femtosecond dynamics

Time-resolved Raman spectroscopy of optical phonons in graphite: Phonon anharmonic coupling and anomalous stiffening - Yan, Hugen; Song, Daohua; Mak, Kin Fai; Chatzakis, Ioannis; Maultzsch, Janina; Heinz, Tony F. (Physical Review B, 2009)
Time-resolved Raman spectroscopy has been applied to probe the anharmonic coupling and electron-phonon interaction of optical phonons in graphite. From the decay of the transient anti-Stokes scattering of the G-mode following ultrafast excitation, we measured a lifetime of 2.2 +/- 0.1 ps for zone-center optical phonons. We also observed a transient stiffening of G-mode phonons, an effect attributed to the reduction of the electron-phonon coupling for high electronic temperatures.

Time-resolved two-photon photoemission - Fauster, Thomas (Solid-State Photoemission and Related Methods, 2003)

Time-resolved x-ray diffraction study of laser-induced shock and acoustic waves in single crystalline silicon - Liss, K. -D.; D'Almeida, T.; Kaiser, M.; Hock, Rainer; Magerl, Andreas; Eloy, J. F. (Journal of Applied Physics, 2009)
A rod of single crystalline silicon has been subjected to high-power nanosecond laser pulses inducing ultrasonic and shock waves traveling into the bulk of the material. Stroboscopic time-resolved high-energy x-ray diffraction measurements were carried out in situ to probe for strain states in the bulk of the sample. First, a supersonic shock front is observed which moves faster than the longitudinal acoustic phonons. Following the shock front, a much slower bunch of waves travels along the crystal. The x-ray diffraction records obtained in different configurations reflect a strong dependence of the wave propagation on the sample geometry. These results offer an experimental approach for the investigation of coherent phonons, structural phase transformations, plastic deformations induced during shock peening, and for the development of x-ray free-electron-laser optics. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3204968]

Time scale and other invariants of integrative mechanical behavior in living cells - Fabry, Ben; Maksym, Geoffrey N.; Butler, James P.; Glogauer, Michael; Navajas, Daniel; Taback, Nathan A.; Millet, Emil J.; Fredberg, Jeffrey (Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2003)

Tip-based source of femtosecond electron pulses at 30 keV - Hoffrogge, Johannes; Stein, Jan Paul; Krüger, Michael; Förster, Michael; Hammer, Jakob; Ehberger, Dominik; Baum, Peter; Hommelhoff, Peter (Journal of Applied Physics, 2014)
We present a nano-scale photoelectron source, optimized for ultrashort pulse durations and well-suited for time-resolved diffraction and advanced laser acceleration experiments. A tungsten tip of several-ten-nanometers diameter mounted in a suppressor-extractor electrode configuration allows the generation of 30 keV electron pulses with an estimated pulse duration of 9 fs (standard deviation; 21 fs full width at half maximum) at the gun exit. We infer the pulse duration from particle tracking simulations, which are in excellent agreement with experimental measurements of the electron-optical properties of the source in the spatial domain. We also demonstrate femtosecond-laser triggered operation of the apparatus. The temporal broadening of the pulse upon propagation to a diffraction sample can be greatly reduced by collimating the beam. Besides the short electron pulse duration, a tip-based source is expected to feature a large transverse coherence and a nanometric emittance. © 2014 AIP Publishing LLC.
UnivIS-Import:2015-04-14:Pub.2014.nat.dphy.IAP.exphys.tipbas

Tip-enhanced Raman scattering along a single wall carbon nanotubes bundle - Peica, Niculina; Thomsen, Christian; Maultzsch, Janina (physica status solidi (b), 2010)
Raman scattering is a common technique for studying carbon nanotubes due to the possibility to observe the radial breathing mode (RBM), which is used for identification of single wall carbon nanotubes "SWCNT." Using tip-enhanced Raman scattering (TERS) we show along a small SWCNTs bundle that the RBMs are well visible in near-field, even if they are not observable in the far-field. Different Raman intensities in TERS for the D, G, and 2D modes at six different positions along a SWCNTs bundle were observed. We discuss this strong dependence of the TERS signal on the position of the tip on the sample and on the distance between the tip and the sample. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Keywords: bundle; Raman; single wall carbon nanotubes; TERS

Ti-Silicide Formation During Isochronal Annealing Followed by in situ Ellipsometry - Hundhausen, Martin; Ley, Lothar; et al. (Microelectronic Engineering, 2001)
Single-wavelength ellipsometry is employed to monitor in situ the reaction of titanium layers of different thickness (10-80 nm) with Si(100) to form titanium silicides during heating at constant rates up to 100 K/min. Previous studies performed on the platinum/silicon system showed that by the use of `Kissinger' plots the activation energy for the formation of the intermediate silicide phase Pt 2Si and that of the final PtSi can be determined with an accuracy of 50 meV. Additionally, by directly modelling the evolution of the ellipsometric data as they were obtained during the temperature ramp the pre-exponential growth factor of the two reactions was determined as well. In the present study the reaction of Ti with Si to the intermediate C49-TiSi 2 phase was followed and the activation energy of this reaction was determined to be 2.30 eV. The isomorphous C49-/C54-TiSi 2 phase transition can also be traced by ellipsometry. However, the change in the ellipsometric angles is less pronounced which might be ascribed to a TiO x overlayer. Complementary to the ellipsometric analysis of the silicidation, the chemical composition of the reaction products and the thicknesses of the formed layers were identified at crucial stages of the reaction by X-ray diffraction, Raman spectroscopy, and Rutherford backscattering spectroscopy.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.tisili

Towards a fully integrated accelerator on a chip: Dielectric Laser Acceleration (DLA) from the source to relativistic electrons - Wootton, K. P.; England, R. J.; Tantawi, S.; Aßmann, R. W.; Hartl, I.; Kärtner, F. X.; Kuropka, W.; Mayet, F.; Ruehl, A.; Rivkin, L.; Hommelhoff, Peter; Illmer, Johannes; et al. (IPAC 2017 - Proceedings of the 8th International Particle Accelerator Conference, 2017)
Dielectric laser acceleration of electrons has recently been demonstrated with significantly higher accelerating gradients than other structure-based linear accelerators. Towards the development of an integrated 1 MeV electron accelerator based on dielectric laser accelerator technologies, development in several relevant technologies is needed. In this work, recent developments on electron sources, bunching, accelerating, focussing, deflecting and laser coupling structures are reported. With an eye to the near future, components required for a 1 MeV kinetic energy tabletop accelerator producing sub-femtosecond electron bunches are outlined.
CRIS-Team Scopus Importer:2022-06-05

Towards quantitative treatment of electron pair distribution function - Gorelik, Tatiana E.; Neder, Reinhard; Terban, Maxwell W.; Lee, Zhongbo; Mu, Xiaoke; Jung, Christoph; Jacob, Timo; Kaiser, Ute (Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials, 2019)
The pair distribution function (PDF) is a versatile tool to describe the structure of disordered and amorphous materials. Electron PDF (ePDF) uses the advantage of strong scattering of electrons, thus allowing small volumes to be probed and providing unique information on structure variations at the nano-scale. The spectrum of ePDF applications is rather broad: from ceramic to metallic glasses and mineralogical to organic samples. The quantitative interpretation of ePDF relies on knowledge of how structural and instrumental effects contribute to the experimental data. Here, a broad overview is given on the development of ePDF as a structure analysis method and its applications to diverse materials. Then the physical meaning of the PDF is explained and its use is demonstrated with several examples. Special features of electron scattering regarding the PDF calculations are discussed. A quantitative approach to ePDF data treatment is demonstrated using different refinement software programs for a nanocrystalline anatase sample. Finally, a list of available software packages for ePDF calculation is provided.
CRIS-Team Scopus Importer:2019-08-23
Keywords: disordered material; electron crystallography; electron diffraction; PDF

Towards Super-resolution CEST MRI for Visualization of Small Structures - Folle, Lukas; Tkotz, Katharina; Gadjimuradov, Fasil; Kapsner, Lorenz; Fabian, Moritz; Bickelhaupt, Sebastian; Simon, David; Kleyer, Arnd; Krönke, Gerhard; Zaiß, Moritz; Nagel, Armin Michael; Maier, Andreas (Bildverarbeitung für die Medizin 2022, 2022)
The onset of rheumatic diseases such as rheumatoid arthritis is typically subclinical, which results in challenging early detection of the disease. However, characteristic changes in the anatomy can be detected using imaging techniques such as MRI or CT. Modern imaging techniques such as chemical exchange saturation transfer (CEST) MRI drive the hope to improve early detection even further through the imaging of metabolites in the body. To image small structures in the joints of patients, typically one of the first regions where changes due to the disease occur, a high resolution for the CEST MR imaging is necessary. Currently, however, CEST MR suffers from an inherently low resolution due to the underlying physical constraints of the acquisition. In this work we compared established up-sampling techniques to neural network-based super-resolution approaches. We could show, that neural networks are able to learn the mapping from low-resolution to high-resolution unsaturated CEST images considerably better than present methods. On the test set a PSNR of 32.29 dB (+10%), a NRMSE of 0.14 (+28%), and a SSIM of 0.85 (+15%) could be achieved using a ResNet neural network, improving the baseline considerably. This work paves the way for the prospective investigation of neural networks for super-resolution CEST MRI and, followingly, might lead to a earlier detection of the onset of rheumatic diseases.
Keywords: Deep Learning; Rheumatic diseases; Reconstruction

Towards wafer-size graphene layers by atmospheric pressure graphitization of silicon carbide - Emtsev, Konstantin; Bostwick, A.; Horn, Karsten; Jobst, Johannes; Kellogg, Gary L.; Ley, Lothar; McChesney, J.; Ohta, T.; Reshanov, Sergey; Röhrl, Jonas; Rotenberg, E.; Schmid, A.; et al. (Nature Materials, 2009)
Graphene, a single monolayer of graphite, has recently attracted considerable interest owing to its novel magneto-transport properties, high carrier mobility and ballistic transport up to room temperature. It has the potential for technological applications as a successor of silicon in the post Moore's law era, as a single-molecule gas sensor, in spintronics, in quantum computing or as a terahertz oscillator. For such applications, uniform ordered growth of graphene on an insulating substrate is necessary. The growth of graphene on insulating silicon carbide (SiC) surfaces by high-temperature annealing in vacuum was previously proposed to open a route for large-scale production of graphene-based devices. However, vacuum decomposition of SiC yields graphene layers with small grains (30-200 nm; refs 14-16). Here, we show that the ex situ graphitization of Si-terminated SiC(0001) in an argon atmosphere of about 1 bar produces monolayer graphene films with much larger domain sizes than previously attainable. Raman spectroscopy and Hall measurements confirm the improved quality of the films thus obtained. High electronic mobilities were found, which reach =2,000 cm 2 V 1 s 1 at T=27 K. The new growth process introduced here establishes a method for the synthesis of graphene films on a technologically viable basis.
UnivIS-Import:2015-04-14:Pub.2009.nat.dphy.IAP.LAP.towwar

Tracing attosecond electron emission from a nanometric metal tip - Dienstbier, Philip; Seiffert, Lennart; Paschen, Timo; Liehl, Andreas; Leitensdorfer, Alfred; Fennel, Thomas; Hommelhoff, Peter (Nature, 2023)
Solids exposed to intense electric fields release electrons through tunnelling. This fundamental quantum process lies at the heart of various applications, ranging from high brightness electron sources in d.c. operation to petahertz vacuum electronics in laser-driven operation. In the latter process, the electron wavepacket undergoes semiclassical dynamics in the strong oscillating laser field, similar to strong-field and attosecond physics in the gas phase. There, the subcycle electron dynamics has been determined with a stunning precision of tens of attoseconds, but at solids the quantum dynamics including the emission time window has so far not been measured. Here we show that two-colour modulation spectroscopy of backscattering electrons uncovers the suboptical-cycle strong-field emission dynamics from nanostructures, with attosecond precision. In our experiment, photoelectron spectra of electrons emitted from a sharp metallic tip are measured as function of the relative phase between the two colours. Projecting the solution of the time-dependent Schrödinger equation onto classical trajectories relates phase-dependent signatures in the spectra to the emission dynamics and yields an emission duration of 710 ± 30 attoseconds by matching the quantum model to the experiment. Our results open the door to the quantitative timing and precise active control of strong-field photoemission from solid state and other systems and have direct ramifications for diverse fields such as ultrafast electron sources, quantum degeneracy studies and sub-Poissonian electron beams, nanoplasmonics and petahertz electronics.
Keywords: Nanophotonics and plasmonics; Quantum mechanics; Ultrafast photonics

Tracing the phase of focused broadband laser pulses - Hoff, Dominik; Krüger, Michael; Maisenbacher, Lothar; Sayler A, M; Paulus, Gerhard G.; Hommelhoff, Peter (Nature Physics, 2017)
Precise knowledge of the behaviour of the phase of light in a focused beam is fundamental to understanding and controlling laser-driven processes. More than a hundred years ago, an axial phase anomaly for focused monochromatic light beams was discovered and is now commonly known as the Gouy phase1,<a href="https://www.nature.com/articles/nphys4185#ref2" title="Born, M. & Wolf, E. Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light (Cambridge Univ. Press, 1890).">2,3,4. Recent theoretical work has brought into question the validity of applying this monochromatic phase formulation to the broadband pulses becoming ubiquitous today5,<a href="https://www.nature.com/articles/nphys4185#ref6" title="Porras, M. A. Characterization of the electric field of focused pulsed Gaussian beams for phase-sensitive interactions with matter. Opt. Lett. 34, 1546–1548 (2009).">6. Based on electron backscattering at sharp nanometre-scale metal tips, a method is available to measure light fields with sub-wavelength spatial resolution and sub-optical-cycle time resolution7,8,<a href="https://www.nature.com/articles/nphys4185#ref9" title="Piglosiewicz, B. et al. Carrier-envelope phase effects on the strong-field photoemission of electrons from metallic nanostructures. Nat. Photon. 8, 37–42 (2014).">9. Here we report such a direct, three-dimensional measurement of the spatial dependence of the optical phase of a focused, 4-fs, near-infrared pulsed laser beam. The observed optical phase deviates substantially from the monochromatic Gouy phase—exhibiting a much more complex spatial dependence, both along the propagation axis and in the radial direction. In our measurements, these significant deviations are the rule and not the exception for focused, broadband laser pulses. Therefore, we expect wide ramifications for all broadband laser–matter interactions, such as in high-harmonic and attosecond pulse generation, femtochemistry10, ophthalmological optical coherence tomography<a href="https://www.nature.com/articles/nphys4185#ref11" title="Johnson, J. L., Dorney, T. D. & Mittleman, D. M. Enhanced depth resolution in terahertz imaging using phase-shift interferometry. Appl. Phys. Lett. 78, 835–837 (2001).">11,12 and light-wave electronics13</sup

Tracing the phase of focused broadband laser pulses - Hoff, Dominik; Krüger, Michael; Maisenbacher, Lothar; Sayler, A. Max; Paulus, Gerhard G.; Hommelhoff, Peter (2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019, 2019)
Precise knowledge of the behavior of the phase of light in the focus of a laser beam is fundamental to understand and control laser-driven processes. More than a hundred years ago the axial phase evolution for focused monochromatic light beams was described and is now commonly known as the Gouy phase [1]. Recent theoretical work has brought into question the validity of applying this monochromatic phase formulation to the broadband laser pulses becoming ubiquitous today [2]. The need for investigation of the spatial behavior of the local carrier-envelope phase (CEP) is also underscored by experimental studies, which suggest deviations from the monochromatic Gouy phase (see for instance [3]).
CRIS-Team Scopus Importer:2019-11-15

Traction fields, moments, and strain energy that cells exert on their surroundings - Butler, James P.; Tolić-Nørrelykke, Iva Marija; Fabry, Ben; Fredberg, Jeffrey (American Journal of Physiology-Cell Physiology, 2002)

Traction Force Microscopy in 3-Dimensional Extracellular Matrix Networks. - Cóndor, Mar; Steinwachs, Julian; Mark, Christoph; Garcia-Aznar, Jose M.; Fabry, Ben (Current protocols in cell biology, 2017)
Cell migration through a three-dimensional (3-D) matrix depends strongly on the ability of cells to generate traction forces. To overcome the steric hindrance of the matrix, cells need to generate sufficiently high traction forces but also need to distribute these forces spatially in a migration-promoting way. This unit describes a protocol to measure spatial maps of cell traction forces in 3-D biopolymer networks such as collagen, fibrin, or Matrigel. Traction forces are computed from the relationship between measured force-induced matrix deformations surrounding the cell and the known mechanical properties of the matrix. The method does not rely on knowledge of the cell surface coordinates and takes nonlinear mechanical properties of the matrix into account. © 2017 by John Wiley & Sons, Inc.

Trans-1,2-bis(N-methylimidazol-2-yl)ethylene: Towards building blocks for 2D fabrics and MML-type 1D molecular strands - Fischer, Nina; Alam, Sahabul; Jum'H, Inshad; Stocker, Michael; Fritsch, Nico; Dremov, Viatcheslav; Heinemann, Frank Wilhelm; Burzlaff, Nicolai; Müller, Paul (Chemistry - A European Journal, 2011)
Find the thread: Copper acetate and trans-bis(N-methylimidazol-2-yl) ethylene-derived 1D coordination polymers were investigated on mica and highly oriented pyrolytic graphite (HOPG) substrates by using AFM/STM. On HOPG, single isolated strands were mapped by STM and their electronic properties were subsequently characterized by current imaging tunneling spectroscopy. On mica the material shows a tendency to form bundles of strands. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Translational diffusion of water and its dependence on temperature in charged and uncharged clays: A neutron scattering study - González Sánchez, Fátima; Juranyi, Fanni; Gimmi, Thomas; Van Loon, Luc R.; Unruh, Tobias; Diamond, Larryn W. (Journal of Chemical Physics, 2008)
The water diffusion in four different, highly compacted clays [montmorillonite in the Na- and Ca-forms, illite in the Na- and Ca-forms, kaolinite, and pyrophyllite (bulk dry density rho(b)=1.85 +/- 0.05 g/cm(3))] was studied at the atomic level by means of quasielastic neutron scattering. The experiments were performed on two time-of-flight spectrometers and at three different energy resolutions [FOCUS at SINQ, PSI (3.65 and 5.75 A), and TOFTOF at FRM II (10 A)] for reliable data analysis and at temperatures between 27 and 95 degrees C. Two different jump diffusion models were used to describe the translational motion. Both models describe the data equally well and give the following ranking of diffusion coefficients: Na-montmorillonite <= Ca-montmorillonite < Ca-illite < Na-illite < water <= pyrophyllite <= kaolinite. Uncharged clays had slightly larger diffusion coefficients than that of bulk water due to their hydrophobic surfaces. The time between jumps, tau(t), follows the sequence: Ca-montmorillonite >= Na-montmorillonite>Ca-illite>Na-illite >= kaolinite>pyrophyllite >= water, in both jump diffusion models. For clays with a permanent layer charge (montmorillonite and illite) a reduction in the water content by a factor of 2 resulted in a decrease in the self-diffusion coefficients and an increase in the time between jumps as compared to the full saturation. The uncharged clay kaolinite exhibited no change in the water mobility between the two hydration states. The rotational relaxation time of water was affected by the charged clay surfaces, especially in the case of montmorillonite; the uncharged clays presented a waterlike behavior. The activation energies for translational diffusion were calculated from the Arrhenius law, which adequately describes the systems in the studied temperature range. Na- and Ca-montmorillonite (similar to 11-12 kJ/mol), Na-illite (similar to 13 kJ/mol), kaolinite and pyrophyllite (similar to 14 kJ/mol), and Ca-illite (similar to 15 kJ/mol) all had lower activation energies than bulk water (similar to 17 kJ/mol in this study). This may originate from the reduced number and strength of the H-bonds between water and the clay surfaces, or ions, as compared to those in bulk water. Our comparative study suggests that the compensating cations in swelling clays have only a minor effect on the water diffusion rates at these high densities, whereas these cations influence the water motion in non-swelling clays.
Keywords: clay; hydrogen bonds; neutron diffraction; self-diffusion; swelling; water

Transmission-Electron-Microscopy-Generated Atomic Defects in Two-Dimensional Nanosheets and Their Integration in Devices for Electronic and Optical Sensing - Quincke, Moritz; Lehnert, Tibor; Keren, Itai; Moses Badlyan, Narine; Port, Fabian; Goncalves, Manuel; Mohn, Michael J.; Maultzsch, Janina; Steinberg, Hadar; Kaiser, Ute (ACS Applied Nano Materials, 2022)
For electronic and optical applications of two-dimensional (2D) materials and their vertical heterostructures, it is important to know the positions, densities, and atomic structures of crystallographic defects. Thus, to understand the role of these well-defined defects on the properties of 2D heterostructure devices, it is desirable to combine device measurements with atomically resolved transmission electron microscopy (TEM) experiments. Here, the electron beam is used not only to image atomic defects but also to create and manipulate them. However, TEM poses special requirements to sample preparation because it needs freestanding samples. Our presented generic sample platform enables TEM imaging of freestanding 2D materials, followed by experiments on the same sample area placed on an arbitrary substrate or embedded into a heterostructure device. A sacrificial copper layer and a hydrophobic polystyrene film enable the transfer of a strongly adhered 2D material flake from a TEM grid to the substrate. Proof-of-principle experiments show that signatures of electron-beam-induced defects can be measured in electric tunneling measurements and photoluminescence. Our transfer procedure works reliably for monolayer and few-layer transition-metal dichalcogenides such as MoS2, MoSe2, WSe2, MoTe2, hBN, and graphene. It can also be suitable for the assembly of defect-based sensors and photon sources.
CRIS-Team Scopus Importer:2022-09-09
Keywords: defects; deterministic transfer; molybdenum disulfide; photoluminescence; transmission electron microscopy; tunneling

Transporting, splitting and merging of atomic ensembles in a chip trap - Hommelhoff, Peter; Hänsel, Wolfgang; Steinmetz, Tilo; Hänsch, Theodor; Reichel, Jakob (New Journal of Physics, 2005)
We present a toolbox for cold atom manipulation with time-dependent magnetic fields generated by an atom chip. Wire layouts, detailed experimental procedures and results are presented for the following experiments: use of a magnetic conveyor belt for positioning of cold atoms and Bose-Einstein condensates (BECs) with a potential resolution of 2 nm; splitting of thermal clouds and BECs in adjustable magnetic double-well potentials; and controlled splitting of a cold reservoir. The devices that enable these manipulations can be combined with each other. We demonstrate this by combining reservoir splitter and conveyor belt to obtain a cold atom dispenser. We discuss the importance of these devices for quantum information processing, atom interferometry and Josephson junction physics on the chip. For all devices, absorption-image video sequences are provided to demonstrate their time-dependent behaviour.
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.IAP.exphys.transp

Transport properties of high-quality epitaxial graphene on 6H-SiC(0001) - Jobst, Johannes; Waldmann, Daniel; Speck, Florian; Hirner, R.; Maude, Duncan; Seyller, Thomas; Weber, Heiko B. (Solid State Communications, 2011)
We have extensively studied the electronic properties of epitaxial graphene grown on the Si face of a 6H silicon carbide substrate by thermal decomposition in an argon atmosphere. Using e-beam lithography, large van der Pauw structures as well as Hall bars were patterned. Their size ranged from millimeters down to submicrometer-sized Hall bars, the latter entirely placed on atomically flat substrate terraces. We found reproducible electronic properties, independent of the sample size and orientation, over a broad temperature range. A comparison of the mobility values indicated no enhanced scattering at the macroscopic step edges of the SiC substrate and due to adsorbed molecules. However, the strong coupling to the substrate results in an elevated charge carrier density n and a reduced mobility mu compared to exfoliated graphene. If n is decreased the mobility rises substantially (up to 29 000 cm(2)/V s at 25 K), and Shubnikov-de Haas oscillations and the graphene-like quantum Hall effect become visible. This leads to the conclusion that the electrons in epitaxial graphene have the same quasi-relativistic properties previously shown in exfoliated graphene and expected from theory. (C) 2011 Elsevier Ltd. All rights reserved.

Transverse and longitudinal characterization of electron beams using interaction with optical near-fields - Kozak, Martin; McNeur, Joshua; Leedle, Kenneth; Deng, Hudan; Schönenberger, Norbert; Ruehl, Axel; Hartl, Ingmar; Hoogland, Heinar; Holzwarth, Ronald; Harris, James; Byer, Robert L.; Hommelhoff, Peter (Optics Letters, 2016)
We demonstrate an experimental technique for both transverse and longitudinal characterization of bunched femtosecond free electron beams. The operation principle is based on monitoring of the current of electrons that obtained an energy gain during the interaction with the synchronized optical near-field wave excited by femtosecond laser pulses. The synchronous accelerating/decelerating fields confined to the surface of a silicon nanostructure are characterized using a highly focused sub-relativistic electron beam. Here the transverse spatial resolution of 450 nm and femtosecond temporal resolution of 480 fs (sub-optical-cycle temporal regime is briefly discussed) achievable by this technique are demonstrated. (C) 2016 Optical Society of Ameri

Trapped-atom interferometer in a magnetic microtrap - Hänsel, Wolfgang; Reichel, Jakob; Hommelhoff, Peter; Haensch, Theodor W. (Physical Review A, 2001)
A dynamic potential interferometer working with three-dimensionally trapped atoms was studied. A time-dependent interaction picture was used to describe the quantum-state evolution. Probabilities for nonadiabatic transitions were compared to neighboring levels. For a realistic magnetic microtrap, parameters that suggest an experimental implementation in the near future were established. Based on the theoretical results, an optimization scheme for the reduction of vibrational excitations was developed.
UnivIS-Import:2015-03-09:Pub.2001.nat.dphy.IAP.exphys.trappe

Trapping field assisted backscattering in strong-field photoemission from dielectric nanospheres - Seiffert, Lennart; Henning, Philipp; Rupp, Philipp; Zherebtsov, Sergey; Hommelhoff, Peter; Kling, Matthias Friedrich; Fennel, Thomas (Journal of Modern Optics, 2017)
We study strong-field ionization of dielectric nanospheres and focus on the enhancement of the cut-off energies for backscattering electrons resulting from charge interaction. Though recent studies clearly demonstrated the decisive impact of a surface trapping field on the electron backscattering process, a clear picture of the underlying mechanism is lacking. Here, we provide this picture and present a simple and transparent extension of the famous three-step model of strong-field science by adding a triangular surface trapping potential. We justify this model for the case of dielectric nanospheres based on high-level transport simulations. The analysis of the trapping field assisted backscattering provides a universal scaling of the maximal recollision and backscattering energies as 9 Up and 14.5 Up, respectively, where Up the local ponderomotive potential. The universal nature of the enhancement over the conventional three-step model is of particular interest for the generation of attosecond electron bunches via near-field induced photoemission and high harmonic generation at nanostructures.
UnivIS-Import:2017-12-18:Pub.2017.nat.dphy.IAP.exphys.trappi
Keywords: Strong-field ionization; electron backscattering; nanostructures; near-fields; dielectric nanospheres

Trapping surface electrons on graphene layers and islands - Niesner, Daniel; Fauster, Thomas; Dadap, J. I.; Zaki, N.; Knox, K. R.; Yeh, P. -C.; Bhandari, R.; Osgood, R. M.; Petrovic, Marin; Kralj, Marko (Physical Review B, 2012)
We report the use of time-and angle-resolved two-photon photoemission to map the bound, unoccupied electronic structure of the weakly coupled graphene/Ir(111) system. The energy, dispersion, and lifetime of the lowest three image-potential states are measured. In addition, the weak interaction between Ir and graphene permits observation of resonant transitions from an unquenched Shockley-type surface state of the Ir substrate to graphene/Ir image-potential states. The image-potential-state lifetimes are comparable to those of midgap clean metal surfaces. Evidence of localization of the excited electrons on single-atom-layer graphene islands is provided by coverage-dependent measurements.

Trap States in Lead Iodide Perovskites - Wu, Xiaoxi; Trinh, M. Tuan; Niesner, Daniel; Zhu, Haiming; Norman, Zachariah; Owen, Jonathan S.; Yaffe, Omer; Kudisch, Bryan J.; Zhu, X. -Y. (Journal of the American Chemical Society, 2015)
Recent discoveries of highly efficient solar cells based on lead iodide perovskites have led to a surge in research activity on understanding photo carrier generation in these materials, but little is known about trap states that may be detrimental to solar cell performance. Here we provide direct evidence for hole traps on the surfaces of three-dimensional (3D) CH3NH3PbI3 perovskite thin films and excitonic traps below the optical gaps in these materials. The excitonic traps possess weak optical transition strengths, can be populated from the relaxation of above gap excitations, and become more significant as dimensionality decreases from 3D CH3NH3PbI3 to two-dimensional (2D) (C4H9NH3I)(2)(CH3NH3I)(n-1)(PbI2)(n) (n = 1, 2, 3) perovskites and, within the 2D family, as n decreases from 3 to 1. We also show that the density of excitonic traps in CH3NH3PbI3 perovskite thin films grown in the presence of chloride is at least one-order of magnitude lower than that grown in the absence of chloride, thus explaining a widely known mystery on the much better solar cell performance of the former. The trap states are likely caused by electronphonon coupling and are enhanced at surfaces/interfaces where the perovskite crystal structure is most susceptible to deformation.

Treatment of hydrogen background in bulk and nanocrystalline neutron total scattering experiments - Page, Katharine; White, Claire E.; Estell, Eben G.; Neder, Reinhard; Llobet, Anna; Proffen, Thomas (Journal of Applied Crystallography, 2011)
Nuclear incoherent neutron scattering contributions present a challenge in the structural characterization of many classes of materials. This article introduces methods for the correction of nanoparticle, bulk crystalline and amorphous powder neutron scattering data with significant incoherent contributions from hydrogen, and describes the effects the corrections have on the resulting atomic pair distribution function data sets. The approach is presented in the context of the PDFgetN data-reduction program [Peterson, Gutmann, Proffen & Billinge (2000). J. Appl. Cryst. 33, 1192].

Treatment of keratinocytes with 4-phenylbutyrate in epidermolysis bullosa: Lessons for therapies in keratin disorders - Spörrer, Marina; Prochnicki, Ania; Tölle, Regine C.; Nyström, Alexander; Esser, Philipp R.; Homberg, Melanie; Athanasiou, Ioannis; Zingkou, Eleni; Schilling, Achim; Gerum, Richard; Thievessen, Ingo; Winter, Lilli; et al. (EBioMedicine, 2019)
Background: Missense mutations in keratin 5 and 14 genes cause the severe skin fragility disorder epidermolysis bullosa simplex (EBS)by collapsing of the keratin cytoskeleton into cytoplasmic protein aggregates. Despite intense efforts, no molecular therapies are available, mostly due to the complex phenotype of EBS, comprising cell fragility, diminished adhesion, skin inflammation and itch. Methods: We extensively characterized KRT5 and KRT14 mutant keratinocytes from patients with severe generalized EBS following exposure to the chemical chaperone 4-phenylbutyrate (4-PBA). Findings: 4-PBA diminished keratin aggregates within EBS cells and ameliorated their inflammatory phenotype. Chemoproteomics of 4-PBA-treated and untreated EBS cells revealed reduced IL1β expression- but also showed activation of Wnt/β-catenin and NF-kB pathways. The abundance of extracellular matrix and cytoskeletal proteins was significantly altered, coinciding with diminished keratinocyte adhesion and migration in a 4-PBA dose-dependent manner. Interpretation: Together, our study reveals a complex interplay of benefits and disadvantages that challenge the use of 4-PBA in skin fragility disorders.
CRIS-Team Scopus Importer:2019-05-17
Keywords: 4-PBA; Epidermolysis bullosa; Keratinocyte; Keratins; Skin blistering

Triethynylmethanol Derivatives: Stable Acetylenic Building Blocks for Surface Chemistry - Prenzel, Dominik; Sander, Tim; Gebhardt, Julian; Soni, Himadriben; Hampel, Frank; Görling, Andreas; Maier, Sabine; Tykwinski, Rik (Chemistry - A European Journal, 2017)
The synthesis of non-conjugated, carbon-rich building blocks is described, based on a basic scaffold of triethynylmethanol (TEtM). The substitution of the ethynyl groups can be easily varied (including R3Si, H, Br), and this allows structural tuning for stabilization, synthetic derivatization, and adsorption on Ag(111) or Au(111). X-ray crystallography helps to explain the surprising stability of the selected derivatives in the solid state, and an unusual form of hydrogen bonding is identified from these analyses. Preliminary efforts to achieve surface-based reactions on Ag(111) and Au(111) are outlined experimentally and computationally.
Keywords: alkynes; carbon allotropes; graphdiyne; graphyne; surface chemistry

Tunable, Continuos-Wave Photomixer Sources and Applications - Malzer, Stefan; Wang, Lijun; Gossard, Art; Döhler, Gottfried; Preu, Sascha (Journal of Applied Physics, 2011)
UnivIS-Import:2015-03-09:Pub.2011.nat.dphy.IAP.LAP.tunabl
Keywords: Terahertz; Photomixing

Tunable infrared light emission from MoS2/WSe2 heterostructures - Karni, Ouri; Barré, Elyse; Lau, Sze Cheung; Gillen, Roland; Ma, Eric Yue; Gal, Lior; Yaffe, Tzach; Kim, Bumho; Watanabe, Kenji; Taniguchi, Takashi; Orenstein, Meir; Maultzsch, Janina; et al. (Optics InfoBase Conference Papers, 2020)
We report light emission around 1200 nm from a vertical heterostructure consisting of MoS2 and WSe2 monolayers. The emission, arising from the fundamental interlayer exciton, can be tuned by nearly 100 nm by electrical gating.
CRIS-Team Scopus Importer:2020-11-13

Tunable quantum interference in bilayer graphene in double-resonant Raman scattering - Herziger, Felix; Tyborski, Christoph; Ochedowski, Oliver; Schleberger, Marika; Maultzsch, Janina (Carbon, 2018)
The line shape of the double-resonant 2D Raman mode in bilayer graphene is often considered to be characteristic for a certain laser excitation energy. Here, in a joint experimental and theoretical study, we analyze the dependence of the double-resonant Raman scattering processes in bilayer graphene on the electronic broadening parameter g. We demonstrate that the ratio between symmetric and antisymmetric scattering processes sensitively depends on the lifetime of the electronic states, explaining the experimentally observed variation of the complex 2D-mode line shap
Keywords: graphene; Raman scattering

Tuning of phase diffusion in small Josephson junctions by magnetic field - Koval, Yury; Fistul, Mikhail; Ustinov, Alexey (Physical Review B, 2006)
We report experimental and theoretical study of low-voltage resistive states in submicrometer Josephson tunnel junctions placed in an external magnetic field H. The junctions display a low-voltage Josephson phase diffusion branch characterized by small but finite resistance and hysteretic switching to higher voltages. Depending on the junction area, we observe two different effects of the external magnetic field on the low-voltage part of current-voltage characteristics. In the first case, the maximum voltage Vm of the phase-diffusion branch increases with magnetic field. In the second case, we find Vm to be nearly independent of magnetic field. These resistive states depend on the ratio between the Josephson energy EJ (H) and energy of thermal fluctuations kB T. A theoretical analysis based on a diffusion of the "center mass" of the Josephson phase is in good accord with experimental observations. © 2006 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.pephys.tuning

Tuning superconductivity by carrier injection - Koval, Yury; Jin, Xiaoyue; C, Bergmann; Simsek, Yilmaz; Özyüzer, Lütfi; Müller, Paul; Wang, Huabing; Behr, Günter; Büchner, Bernd (Applied Physics Letters, 2010)
We have found that by extensive current injection along the c-axis, the superconducting properties of BiSrCaCu O can be changed effectively. We show that critical temperature, c-axis resistivity, and critical current of intrinsic Josephson junctions can be tuned in a large range from underdoping to extreme overdoping. This effect is reversible and persistent. Our results can be explained by trapping charges in the insulating layers, which induce a change of carrier concentration in superconducting planes. This floating gate concept can be a general property of layered materials where the insulating charge reservoir layers are separated from the conducting planes. © 2010 American Institute of Physics.

Tuning the molecular order of C60-based self-assembled monolayers in field-effect transistors - Schmaltz, Thomas; Khassanov, Artöm; Steinrück, Hans-Peter; Magerl, Andreas; Hirsch, Andreas; Halik, Marcus (Nanoscale, 2014)
The control of order in organic semiconductor systems is crucial to achieve desired properties in electronic devices. We have studied the order in fullerene functionalized self-assembled monolayers by mixing the active molecules with supporting alkyl phosphonic acids of different chain length. By adjusting the length of the molecules, structural modifications of the alignment of the C60 head groups within the SAM can be tuned in a controlled way. These changes on the sub-nanometre scale were analysed by grazing incidence X-ray diffraction and X-ray reflectivity. To study the electron transport properties across these layers, self-assembled monolayer field-effect transistors (SAMFETs) were fabricated containing only the single fullerene monolayer as semiconductor. Electrical measurements revealed that a high 2D crystalline order is not the only important aspect. If the fullerene head groups are too confined by the supporting alkyl phosphonic acid molecules, defects in the crystalline C60 film, such as grain boundaries, start to strongly limit the charge transport properties. By close interpretation of the results of structural investigations and correlating them to the results of electrical characterization, an optimum chain length of the supporting alkyl phosphonic acids in the range of C10 was determined. With this study we show that minor changes in the order on the sub-nanometre scale, can strongly influence electronic properties of functional self-assembled monolayers.

Twice-refocused stimulated echo diffusion imaging: Measuring diffusion time dependence at constant T-1 weighting - Martin, Jan; Endt, Sebastian; Wetscherek, Andreas; Kuder, Tristan Anselm; Dörfler, Arnd; Uder, Michael; Hensel, Bernhard; Laun, Frederik Bernd (Magnetic Resonance in Medicine, 2019)
Purpose Diffusion times longer than 50 ms are typically probed with stimulated-echo sequences. Varying the diffusion time in stimulated-echo sequences affects the T-1 weighting of subcompartments, complicating the analysis of diffusion time dependence. Although inversion recovery preparation could be used to change the T-1 weighting, it cannot ensure equal T-1 weighting at arbitrary mixing times. In this article, a sequence that ensures constant T-1 weighting over a wide range of diffusion times is presented. Methods The proposed sequence features 2 independent longitudinal storage periods: TM1 and TM2. Diffusion encoding is performed during TM1, effectively coupling the diffusion time and TM1. Equal T-1 weighting at arbitrary diffusion times is realized by keeping the total mixing time TM1 + TM2 constant. The sequence was compared with conventional stimulated-echo measurements of diffusion in a 2-compartment phantom consisting of distilled water and paraffinum perliquidum. Additionally, in vivo DTI of the brain was carried out for 8 healthy volunteers with diffusion times ranging from 50 to 500 ms. Results Diffusion time dependence of the axial and radial diffusivity was detected in the brain. Both sequences resulted in almost identical diffusivities in white matter. In regions containing partial volumes of gray and white matter, a dependency on T-1 weighting was observed. Conclusion In accordance with previous studies, little variance of T-1 values appeared to be present in healthy white matter. However, this is likely different in diseased tissue. Here, the proposed sequence can be effective in differentiating between diffusion time dependence and T-1 weighting effects.
CRIS-Team WoS Importer:2019-11-12

Twisting integrin receptors increases endothelin-1 gene expression in endothelial cells - Fabry, Ben; et al. (American Journal of Physiology-Cell Physiology, 2001)

Twist-tailoring Coulomb correlations in van der Waals homobilayers - Merkl, Philipp; Mooshammer, Fabian; Brem, Samuel; Girnghuber, Anna; Lin, Kai Qiang; Weigl, Leonard; Liebich, Marlene; Yong, Chaw Keong; Gillen, Roland; Maultzsch, Janina; Lupton, John M.; Malic, Ermin; et al. (Nature Communications, 2020)
The recent discovery of artificial phase transitions induced by stacking monolayer materials at magic twist angles represents a paradigm shift for solid state physics. Twist-induced changes of the single-particle band structure have been studied extensively, yet a precise understanding of the underlying Coulomb correlations has remained challenging. Here we reveal in experiment and theory, how the twist angle alone affects the Coulomb-induced internal structure and mutual interactions of excitons. In homobilayers of WSe2, we trace the internal 1s–2p resonance of excitons with phase-locked mid-infrared pulses as a function of the twist angle. Remarkably, the exciton binding energy is renormalized by up to a factor of two, their lifetime exhibits an enhancement by more than an order of magnitude, and the exciton-exciton interaction is widely tunable. Our work opens the possibility of tailoring quasiparticles in search of unexplored phases of matter in a broad range of van der Waals heterostructures.
CRIS-Team Scopus Importer:2020-05-08

Twist-Tailoring Hybrid Excitons in Van der Waals Homobilayers - Mooshammer, Fabian; Merkl, Philipp; Ovesen, Simon; Brem, Samuel; Girnghuber, Anna; Lin, Kai Qiang; Liebich, Marlene; Yong, Chaw Keong; Gillen, Roland; Maultzsch, Janina; Lupton, John M.; Malic, Ermin; et al. (2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021, 2021)
In homobilayer systems, the twist angle θ has emerged as a powerful tuning knob for tailoring novel phase transitions in atomically thin layers stacked at magic twist angles [1] - a paradigm shift for condensed-matter physics. For twisted bilayers of transition metal dichalcogenides, topological phases [2] and even potential signatures of a superconducting state [3] have been discussed. Yet, a precise understanding of the underlying Coulomb correlations has remained challenging.
CRIS-Team Scopus Importer:2021-10-29

Two-color coherent control in photoemission from gold needle tips - Dienstbier, Philip; Paschen, Timo; Hommelhoff, Peter (Journal of Physics B: Atomic, Molecular and Optical Physics, 2021)
We demonstrate coherent control of photoemission from a gold needle tip using a two-color laser field. The relative phase between a fundamental field and its second harmonic imprints a strong modulation on the emitted photocurrent with up to 96.5% visibility. The visibility as a function of the second harmonic intensity can be described by three interfering quantum pathways. Increasing the bias voltage applied to the tip reduces the maximum achievable visibility and modifies the weights of the involved pathways. Simulations based on the time-dependent Schrödinger equation reproduce the characteristic cooperative signal and its dependence on the second harmonic intensity, which further confirms the involvement of three emission pathway
Keywords: Coheren control; gold needle tips; photoemission; quantum-pathway interference

Two-color coherent control of femtosecond above-threshold photoemission from a Tungsten nanotip - Förster, Michael; Paschen, Timo; Krüger, Michael; Lemell, Christoph; Wachter, Georg; Libisch, Florian; Madlener, Thomas; Burgdoerfer, Joachim; Hommelhoff, Peter (Physical Review Letters, 2016)
We demonstrate coherent control of multiphoton and above-threshold photoemission from a single solid-state nanoemitter driven by a fundamental and a weak second harmonic laser pulse. Depending on the relative phase of the two pulses, electron emission is modulated with a contrast of the oscillating current signal of up to 94%. Electron spectra reveal that all observed photon orders are affected simultaneously and similarly. We confirm that photoemission takes place within 10 fs. Accompanying simulations indicate that the current modulation with its large contrast results from two interfering quantum pathways leading to electron emissio

Two-color phase-controlled photoemission from a zero-dimensional nanostructure - Paschen, Timo; Förster, Michael; Krüger, Michael; Lemell, Christoph; Wachter, Georg; Libisch, Florian; Madlener, Thomas; Burgdoerfer, Joachim; Hommelhoff, Peter (205, 2019)
We demonstrate that multi-photon photoemission including above-threshold multiphoton orders from a nanotip can be coherently controlled with the optical phase between two light fields. By focusing 74 fs drive pulses at 1560 nm and their second harmonic at 780 nm onto the tip and changing the optical phase between the two colors, we observe an emission current modulation of up to 97.5 %. Additionally, electron energy spectra reveal a homogeneous modulation of all multiphoton orders. Hence, the electron current can be strongly increased (by a factor of 3.7) or almost completely turned off due to interference between two different quantum channels in the material. We argue that the extremely high degree of coherence evidenced by this near-unity current modulation depth is due to the confinement of the local field enhancement at the nanotip. The nano-rod effect allows to apply large DC fields, adding a further degree of freedom to investigate the modulation contrast of the photoemitted electron yield. We show that for an increasing DC electric field a non-cooperative distribution of electron emission leads to a decrease in modulation contras

Two-Dimensional Analysis of the Double-Resonant 2D Raman Mode in Bilayer Graphene - Herziger, Felix; Calandra, Matteo; Gava, Paola; May, Patrick; Lazzeri, Michele; Mauri, Francesco; Maultzsch, Janina (Physical Review Letters, 2014)
By computing the double-resonant Raman scattering cross section completely from first principles and including the electron-electron interaction at the GW level, we unravel the dominant contributions for the double-resonant 2D mode in bilayer graphene. We show that, in contrast to previous works, the so-called inner processes are dominant and that the 2D-mode line shape is described by three dominant resonances around the K point. We show that the splitting of the transversal optical (TO) phonon branch in the Gamma-K direction, as large as 12 cm(-1) in the GW approximation, is of great importance for a thorough description of the 2D-mode line shape. Finally, we present a method to extract the TO phonon splitting and the splitting of the electronic bands from experimental data.

Two-Dimensional Antimony Oxide - Wolff, Stefan; Gillen, Roland; Assebban, Mhamed; Abellan Saez, Gonzalo; Maultzsch, Janina (Physical Review Letters, 2020)

Two-dimensional delocalized states in organometallic bis-acetylide networks on Ag(111) - Yang, Zechao; Gebhardt, Julian; Schaub, Tobias; Sander, Tim; Schönamsgruber, Jörg; Soni, Himadriben; Görling, Andreas; Kivala, Milan; Maier, Sabine (Nanoscale, 2018)

Two-dimensional electronic and vibrational band structure of uniaxially strained graphene from ab initio calculations - Mohr, Marcel; Papagelis, Konstantinos; Maultzsch, Janina; Thomsen, Christian (Physical Review B, 2009)
We present an in-depth analysis of the electronic and vibrational band structure of uniaxially strained graphene by ab initio calculations. Depending on the direction and amount of strain, the Fermi crossing moves away from the K point. However, graphene remains semimetallic under small strains. The deformation of the Dirac cone near the K point gives rise to a broadening of the 2D Raman mode. In spite of specific changes in the electronic and vibrational band structure the strain-induced frequency shifts of the Raman active E(2g) and 2D modes are independent of the direction of strain. Thus, the amount of strain can be directly determined from a single Raman measurement.

Two-dimensional simulation of superlubricity on NaCl and highly oriented pyrolytic graphite - Pascal, Steiner; Roth, Raphael; Gnecco, Enrico; Baratoff, Alexis; Maier, Sabine; Glatzel, Thilo; Meyer, Ernst (Physical Review B, 2009)
The friction between an atomically sharp tip and a solid surface (NaCl and highly oriented pyrolytic graphite) is analyzed theoretically in the framework of a modified Tomlinson model in two dimensions. Lateral forces are studied as a function of temperature, load, and magnitude of actuation. The actuation leads to a reduction in friction and allows one to enter a dynamic superlubricity regime. In addition, our model is able to describe other ultralow friction states as static superlubricity and thermolubricity. We find a good agreement between the calculations and the experimental results.
Keywords: friction; graphite; lubrication; sodium compounds

Two-photon excitation processes and linewidths of surface and image states on Cu(111) - Wallauer, Wolfgang; Fauster, Thomas (Surface Science, 1997)
The occupied surface state and the first image state on Cu(111) have been observed by high-resolution, two-photon photoemission as a function of photon energy. A pronounced narrowing of the linewidth is found for the resonant excitation from the occupied surface state into the first image state. The product of two Lorentzians convoluted with a Gaussian leads to a satisfactory description of the complete series of spectra. The intrinsic linewidth of the first image state on Cu(111) is obtained as 85 +/- 10 meV, in agreement with recent time-resolved measurements. The occupied surface state has an intrinsic linewidth of 65 +/- 15 meV, as also observed in one-photon photoemission experiments. (C) 1997 Elsevier Science B.V.
Keywords: copper; low-index single crystal surfaces; surface electronic phenomena; two-photon photoelectron spectroscopy

Two-photon photoelectron spectroscopy - Fauster, Thomas (Surface and Interface Science, 2012)

Two-photon photoemission from CoO layers on Ir(1 0 0) - Otto, Sebastian; Fauster, Thomas (Journal of Physics: Condensed Matter, 2016)
Two-photon photoelectron spectroscopy is used to study the unoccupied electronic states of cobalt oxide layers on Ir(1 0 0). For thicker layers of (1 0 0) orientation the conduction band minimum is found 2 eV above the Fermi level. Layers with (1 1 1) orientation and thickness ⩽ 4 bilayers show a peak around 3.4 eV energy and no evidence for the conduction band minimum. This is attributed to the metallic character of thin CoO(1 1 1) layers.
Keywords: cobalt oxide; electronic states; work function; two-photon photoemission

Two-photon photoemission from image-potential states of epitaxial graphene - Gugel, Dieter; Niesner, Daniel; Eickhoff, Christian; Wagner, Stefanie; Weinelt, Martin; Fauster, Thomas (2D Materials, 2015)

Ultrafast dynamics in photoexcited valence-band states of Si studied by time- and angle-resolved photoemission spectroscopy of bulk direct transitions - Kanasaki, Junichi; Tanimura, Hiroshi; Tanimura, Katsumi; Ries, Philip; Heckel, Wolfgang; Biedermann, Kerstin; Fauster, Thomas (Physical Review B - Condensed Matter and Materials Physics, 2018)

Ultrafast Dynamics of the Topological Semimetal GdSbxTe2-x-δ in the Presence and Absence of a Charge Density Wave - Kirby, Robert J.; Montanaro, Angela; Giusti, Francesca; Koch-Liston, Andre; Lei, Shiming; Petrides, Ioannis; Narang, Prineha; Burch, Kenneth S.; Fausti, Daniele; Scholes, Gregory D.; Schoop, Leslie M. (Journal of Physical Chemistry C, 2023)
Time-resolved dynamics in charge-density-wave materials have revealed interesting out-of-equilibrium electronic responses. However, these are typically only performed in a single material possessing a CDW. As such, it is challenging to separate subtle effects originating from the CDW. Here, we report on the ultrafast dynamics of the GdSbxTe2-x-δ series of materials where EF can be tuned, resulting in a change from an undistorted tetraganal phase to a CDW with a wavevector that depends on x. Using mid-infrared, near-infrared, and visible excitation, we find the dynamics are sensitive to both EF and the presence of the CDW. Specifically, as the Sb content of the compounds increases, transient spectral features shift to higher probe energies. In addition, we observe an enhanced lifetime and change in the sign of the transient signal upon removing the CDW with high Sb concentrations. Finally, we reveal fluence- and temperature-dependent photoinduced responses of the differential reflectivity, which provide evidence of transient charge density wave suppression in related telluride materials. Taken together our results provide a blueprint for future ultrafast studies of CDW systems.
CRIS-Team Scopus Importer:2023-01-27

Ultrafast electron control with various means: from multiphoton physics at needle tips to nanophotonic particle acceleration - Shiloh, Roy; Chlouba, Tomas; Li, Ang; Dienstbier, Philip; Tafel, Alexander; Illmer, Johannes; Schönenberger, Norbert; Yousefi, Peyman; Kraus, Stefanie; Brückner, Leon; Litzel, Julian; Loehrl, Bastian; et al. (2021 34TH INTERNATIONAL VACUUM NANOELECTRONICS CONFERENCE (IVNC), 2021)
CRIS-Team WoS Importer:2022-02-04

Ultrafast Electron Phase-space Control in a Nanophotonic Structure - Chlouba, Tomas; Shiloh, Roy; Illmer, Johannes; Kraus, Stefanie; Yousefi, Peyman; Schönenberger, Norbert; Niedermayer, U.; Mittelbach, Anna; Hommelhoff, Peter (Optics InfoBase Conference Papers, 2022)
We demonstrate ultrafast electron beam phase space control in a silicon-based nanostructure. With this we guide the electron beam through a 225 nm wide and 77 μm channel. This scheme can be applied in chip-based nanophotonic accelerators.
CRIS-Team Scopus Importer:2023-03-07

Ultrafast electron pulses from a tungsten tip triggered by low power femtosecond laser pulses - Hommelhoff, Peter; Kealhofer, Catherine; Kasevich, Mark A. (Physical Review Letters, 2006)
We present an experimental and numerical study of electron emission from a sharp tungsten tip triggered by sub-8-fs low-power laser pulses. This process is nonlinear in the laser electric field, and the nonlinearity can be tuned via the dc voltage applied to the tip. Numerical simulations of this system show that electron emission takes place within less than one optical period of the exciting laser pulse, so that an 8fs 800 nm laser pulse is capable of producing a single electron pulse of less than 1 fs duration. Furthermore, we find that the carrier-envelope phase dependence of the emission process is smaller than 0.1% for an 8 fs pulse but is steeply increasing with decreasing laser pulse duration. © 2006 The American Physical Society.
UnivIS-Import:2015-03-09:Pub.2006.nat.dphy.IAP.exphys.ultraf

Ultra-fast intramolecular singlet fission to persistent multiexcitons by molecular design - Pun, Andrew B.; Asadpoordarvish, Amir; Kumarasamy, Elango; Tayebjee, Murad J. Y.; Niesner, Daniel; Mccamey, Dane R.; Sanders, Samuel N.; Campos, Luis M.; Sfeir, Matthew Y. (Nature Chemistry, 2019)
Singlet fission-that is, the generation of two triplets from a lone singlet state-has recently resurfaced as a promising process for the generation of multiexcitons in organic systems. Although advances in this area have led to the discovery of modular classes of chromophores, controlling the fate of the multiexciton states has been a major challenge; for example, promoting fast multiexciton generation while maintaining long triplet lifetimes. Unravelling the dynamical evolution of the spin- and energy conversion processes from the transition of singlet excitons to correlated triplet pairs and individual triplet excitons is necessary to design materials that are optimized for translational technologies. Here, we engineer molecules featuring a discrete energy gradient that promotes the migration of strongly coupled triplet pairs to a spatially separated, weakly coupled state that readily dissociates into free triplets. This 'energy cleft' concept allows us to combine the amplification and migration processes within a single molecule, with rapid dissociation of tightly bound triplet pairs into individual triplets that exhibit lifetimes of similar to 20 mu s.

Ultrafast laser-induced electron emission from field emission tips - Foreman, Seth M.; Kealhofer, Catherine; Kasevich, Mark A.; Hommelhoff, Peter (Ultrafast Phenomena XVI, 2009)
We describe a laser-triggered electron source based on a field emission tip. Numerical results indicate that the electron emission times can be sub-femtosecond. We are exploring applications of this source to ultrafast SEM, and have begun characterization of emission mechanisms in an alternate tip material, hafnium carbide. Here we observe a higher efficiency in laser emission and, at high power, non-additive scaling as the number of incident laser pulses per second is doubled.
UnivIS-Import:2015-04-16:Pub.2009.nat.dphy.IAP.exphys.ultraf

Ultrafast phenomena on the nanoscale - Hommelhoff, Peter; Kling, Matthias Friedrich; Stockman, Mark I. (Annalen Der Physik, 2013)
UnivIS-Import:2015-03-09:Pub.2013.nat.dphy.IAP.exphys.ultraf

Ultrafast Relaxation Dynamics via Acoustic Phonons in Carbon Nanotubes - Dyatloya, Olga A.; Koehler, Christopher; Malic, Ermin; Gomis-Bresco, Jordi; Maultzsch, Janina; Tsagan-Mandzhiev, Andrey; Watermann, Tobias; Knorr, Andreas; Woggon, Ulrike (Nano Letters, 2012)
Carbon nanotubes as one-dimensional nanostructures are ideal model systems to study relaxation channels of excited charged carriers. The understanding of the ultrafast scattering processes is the key for exploiting the huge application potential that nanotubes offer, e.g., for light-emitting and detecting nanoscale electronic devices. In a joint study of two-color pump-probe experiments and microscopic calculations based on the density matrix formalism, we extract, both experimentally and theoretically, a picosecond carrier relaxation dynamics, and ascribe it to the intraband scattering of excited carriers with acoustic phonons. The calculated picosecond relaxation times show a decrease for smaller tube diameters. The best agreement between experiment and theory is obtained for the (8,7) nanotubes with the largest investigated diameter and chiral angle for which the applied zone-folded tight-binding wave functions are a good approximation.
Keywords: Carbon nanotubes; acoustic phonons; pump-probe spectroscopy; intraband scattering