@article{PanznerGleberSantetal.2007, author = {Panzner, Tobias and Gleber, Gudrun and Sant, Tushar and Leitenberger, Wolfram and Pietsch, Ullrich}, title = {Coherence experiments at the white-beam beamline of BESSYI}, doi = {10.1016/j.tsf.2006.12.002}, year = {2007}, abstract = {The third-generation X-ray source BESSYII (Berlin, Germany) provides coherent X-ray radiation which can be used for static and dynamic speckle analysis. Recently we have demonstrated that one can perform experiments with coherent white radiation provided by a bending magnet (5 < E < 20 keV). In this paper we show that the diffraction figure of the initial pinhole must be considered for the interpretation of coherent experiments. The reflectivity spectrum of a sample results from the Fresnel diffraction of the incident pinhole deformed by the static speckle features of the sample surface. For dynamical experiments all speckle like features alter with time whereas the pure Fresnel fringes remain constant. (c) 2007 Published by Elsevier B.V.}, language = {en} } @article{PietschPanznerLeitenbergeretal.2003, author = {Pietsch, Ullrich and Panzner, Tobias and Leitenberger, Wolfram and Grenzer, J{\"o}rg and Bodenthin, Th. and Geue, Thomas and M{\"o}hwald, Helmuth}, title = {Coherence experiments at the energy-dispersive reflectometry beamline at BESSY II}, year = {2003}, language = {en} } @article{PietschPanznerLeitenbergeretal.2005, author = {Pietsch, Ullrich and Panzner, Tobias and Leitenberger, Wolfram and Vartanyants, Ivan A.}, title = {Coherence experiments at the EDR-beamline of BESSY II}, year = {2005}, language = {en} } @article{StruthDecherSchmittetal.1999, author = {Struth, Bernd and Decher, Gero and Schmitt, J. and Hofmeister, Wolfgang and Neißendorfer, Frank and Pietsch, Ullrich and Brezesinski, Gerald and M{\"o}hwald, Helmuth}, title = {Chemical modification of Topaz surfaces}, issn = {0928-4931}, year = {1999}, language = {en} } @article{PaschkeGeueBarberkaetal.1997, author = {Paschke, K. and Geue, Thomas and Barberka, Thomas Andreas and Bolm, A. and Pietsch, Ullrich and R{\"o}sch, M. and Batke, Edwin and Faller, F. and Kerkel, K. and Oshiniwo, J. and Forchel, Alfred}, title = {Characterization of lateral semiconductor nano structures by means of x-ray grazing-incidence diffraction}, year = {1997}, language = {en} } @article{RosePietschZeimer1997, author = {Rose, Dirk and Pietsch, Ullrich and Zeimer, Ute}, title = {Characterization of InGaAs single quantum wells buried in GaAs[001] by grazing incidence diffraction}, year = {1997}, language = {en} } @article{SendAbboudHartmannetal.2013, author = {Send, Sebastian and Abboud, Ali and Hartmann, Robert and Huth, M. and Leitenberger, Wolfram and Pashniak, N. and Schmidt, J. and Str{\"u}der, Lothar and Pietsch, Ullrich}, title = {Characterization of a pnCCD for applications with synchrotron radiation}, series = {Nuclear instruments \& methods in physics research : a journal on accelerators, instrumentation and techniques applied to research in nuclear and atomic physics, materials science and related fields in physics ; A, Accelerators, spectrometers, detectors and associated equipment}, volume = {711}, journal = {Nuclear instruments \& methods in physics research : a journal on accelerators, instrumentation and techniques applied to research in nuclear and atomic physics, materials science and related fields in physics ; A, Accelerators, spectrometers, detectors and associated equipment}, number = {5}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0168-9002}, doi = {10.1016/j.nima.2013.01.044}, pages = {132 -- 142}, year = {2013}, abstract = {In this work we study the response of a pnCCD by means of X-ray spectroscopy in the energy range between 6 key and 20 key and by Laue diffraction techniques. The analyses include measurements of characteristic detector parameters like energy resolution, count rate capability and effects of different gain settings. The limit of a single photon counting operation in white beam X-ray diffraction experiments is discussed with regard to the occurrence of pile-up events, for which the energy information about individual photons is lost. In case of monochromatic illumination the pnCCD can be used as a fast conventional CCD with a charge handling capacity (CHC) of about 300,000 electrons per pixel. If the CHC is exceeded, any surplus charge will spill to neighboring pixels perpendicular to the transfer direction due to electrostatic repulsion. The possibilities of increasing the number of storable electrons are investigated for different voltage settings by exposing a single pixel with X-rays generated by a microfocus X-ray source. The pixel binning mode is tested as an alternative approach that enables a pnCCD operation with significantly shorter readout times.}, language = {en} } @article{TalalaevTommElsaesseretal.2005, author = {Talalaev, V and Tomm, JW and Elsaesser, T and Zeimer, Ute and Fricke, J and Knauer, A and Kissel, H and Weyers, Markus and Tarasov, GG and Grenzer, J{\"o}rg and Pietsch, Ullrich}, title = {Carrier dynamics in laterally strain-modulated InGaAs quantum wells}, year = {2005}, abstract = {We investigate the transient recombination and transfer properties of nonequilibrium carriers in an In0.16Ga0.84As/GaAs quantum well (QW) with an additional lateral confinement implemented by a patterned stressor layer. The structure thus contains QW- and quantum-wire-like areas. At low excitation densities, photoluminescence (PL) transients from both areas are well described by a rate equation model for a three-level system with a saturable interlevel carrier transfer representing the lateral drift of carriers from the QW regions into the wires. Small-signal carrier lifetimes for QW, wires, and transfer time from QW to wire are 180, 190, and 28 ps, respectively. For high excitation densities the time constants of the observed transients increase, in agreement with the model. In addition, QW and wire PL lines merge indicating a smoothening of the potential difference, i.e., the effective carrier confinement caused by the stressor structure becomes weaker with increasing excitation. (c) 2005 American Institute of Physics}, language = {en} } @article{JoshiPingelGrigorianetal.2009, author = {Joshi, Siddharth and Pingel, Patrick and Grigorian, Souren and Panzner, Tobias and Pietsch, Ullrich and Neher, Dieter and Forster, Michael and Scherf, Ullrich}, title = {Bimodal temperature behavior of structure and mobility in high molecular weight p3ht thin films}, issn = {0024-9297}, doi = {10.1021/Ma900021w}, year = {2009}, abstract = {We report a temperature dependent crystalline structure of spin-coated thin films of high molecular weight regioregular poly(3-hexylthiophene) (P3HT) (M-n similar to 30000 g/mol) and its correlation with charge carrier mobility. These investigations show a reversible change of the crystalline structure, where the interlayer lattice spacing (100)along the alkyl side chains continuously increases up to a temperature of about 220 degrees C; in contrast, the in-plane pi-pi distance reduces with increasing temperature. These changes in structure are reversible and can be repeated several times. The temperature-induced structural properties differ for thick and thin films, pointing to a surface/interface role in stabilization of the layer morphology. In contrast to the structural changes, the carrier mobility is rather constant in the temperature range from room temperature up to 100-120 degrees C, followed by a continuous decrease. For thick layers this drop is significant and the transistor performance almost vanishes at high temperature, however, it completely recovers upon cooling back to roorn temperature. The drop of the charge carrier mobility at higher temperatures is in contrast with expectations front the structural studies, considering the increase of crystalline fraction of the polycrystalline layer. our electrical measurements Underscore that the reduction of the macroscopic mobility is mostly caused by it pronounced decrease of the intergrain transport. The thermally induced crystallization along(100) direction and the creation of numerous small crystallites at the film-substrate interface reduce the number of long polymer chain, bridging crystalline domains, which ultimately limits the macroscopic charge transport.}, language = {en} } @article{PietschDavaasambuuPucheretal.2003, author = {Pietsch, Ullrich and Davaasambuu, Jav and Pucher, Andreas and Kochin, V.}, title = {Atomistic origin of the inverse piezoelectric effect in alpha-SiO2 and alpha-GaPO4}, issn = {0295-5075}, year = {2003}, language = {en} } @article{HennebergChiGeueetal.2001, author = {Henneberg, Oliver and Chi, Li Feng and Geue, Thomas and Saphiannikova, Marina and Pietsch, Ullrich and Rochon, Paul and Natansohn, Almeria}, title = {Atomic force microscopy inspection of the early state of formation of polymer surface relief grating}, year = {2001}, language = {en} } @article{LeitenbergerHartmannPietschetal.2008, author = {Leitenberger, Wolfram and Hartmann, Robert and Pietsch, Ullrich and Andritschke, Robert and Starke, Ines and Str{\"u}der, Lothar}, title = {Application of a pnCCD in X-ray diffraction : a three-dimensional X-ray detector}, doi = {10.1107/S0909049508018931}, year = {2008}, abstract = {The first application of a pnCCD detector for X-ray scattering experiments using white synchrotron radiation at BESSY II is presented. A Cd arachidate multilayer was investigated in reflection geometry within the energy range 7 keV < E < 35 keV. At fixed angle of incidence the two-dimensional diffraction pattern containing several multilayer Bragg peaks and respective diffuse-resonant Bragg sheets were observed. Since every pixel of the detector is able to determine the energy of every incoming photon with a resolution Delta E/E similar or equal to 10(-2). a three-dimensional dataset is finally obtained. In order to achieve this energy resolution the detector was operated in the so-called single-photon- counting mode. A full dataset was evaluated taking into account all photons recorded within 10(5) detector frames at a readout rate of 200 Hz. By representing the data in reciprocal-space coordinates, it becomes obvious that this experiment with the pnCCD detector provides the same information as that obtained by combining a large number of monochromatic scattering experiments using conventional area detectors.}, language = {en} } @article{PietschDarowskiUlyanenkovetal.2000, author = {Pietsch, Ullrich and Darowski, Nora and Ulyanenkov, A. and Grenzer, J{\"o}rg and Wang, K. H. and Forchel, Alfred}, title = {Analysis of the strain distribution in lateral nanostructures for interpreting photoluminescence data}, year = {2000}, language = {en} } @article{SendAbboudLeitenbergeretal.2012, author = {Send, Sebastian and Abboud, Ali and Leitenberger, Wolfram and Weiss, Manfred S. and Hartmann, Robert and Str{\"u}der, Lothar and Pietsch, Ullrich}, title = {Analysis of polycrystallinity in hen egg-white lysozyme using a pnCCD}, series = {Journal of applied crystallography}, volume = {45}, journal = {Journal of applied crystallography}, number = {6}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0021-8898}, doi = {10.1107/S0021889812015038}, pages = {517 -- 522}, year = {2012}, abstract = {A crystal of hen egg-white lysozyme was analyzed by means of energy-dispersive X-ray Laue diffraction with white synchrotron radiation at 2.7 angstrom resolution using a pnCCD detector. From Laue spots measured in a single exposure of the arbitrarily oriented crystal, the lattice constants of the tetragonal unit cell could be extracted with an accuracy of about 2.5\%. Scanning across the sample surface, Laue images with split reflections were recorded at various positions. The corresponding diffraction patterns were generated by two crystalline domains with a tilt of about 1 degrees relative to each other. The obtained results demonstrate the potential of the pnCCD for fast X-ray screening of crystals of macromolecules or proteins prior to conventional X-ray structure analysis. The described experiment can be automatized to quantitatively characterize imperfect single crystals or polycrystals.}, language = {en} } @article{HerrmannKauppGeueetal.1997, author = {Herrmann, A. and Kaupp, G. and Geue, Thomas and Pietsch, Ullrich}, title = {AFM and GID investigations of the gas-solid diazotation of 4-sulfanil-acid-monohydrat single crystals}, year = {1997}, language = {en} } @article{StahnMoehlePietsch1996, author = {Stahn, Jochen and M{\"o}hle, Marcus and Pietsch, Ullrich}, title = {Accurate structure determination for GaAs using Pendell{\"o}sung oscillation}, year = {1996}, language = {en} } @article{LichanotAzavantPietsch1996, author = {Lichanot, Albert and Azavant, P. and Pietsch, Ullrich}, title = {Ab-initio Hartree-Fock study of the electronic charge density of the cubic boron nitride and its comparison with the experiment}, year = {1996}, language = {en} } @article{LeitenbergerPietsch2007, author = {Leitenberger, Wolfram and Pietsch, Ullrich}, title = {A monolithic Fresnel bimirror for hard X-rays and its application for coherence measurements}, issn = {0909-0495}, doi = {10.1107/S0909049507003846}, year = {2007}, abstract = {Experiments using a simple X-ray interferometer to measure the degree of spatial coherence of hard X-rays are reported. A monolithic Fresnel bimirror is used at small incidence angles to investigate synchrotron radiation in the energy interval 5-50 keV with monochromatic and white beam. The experimental setup was equivalent to a Young's double-slit experiment for hard X-rays with slit dimensions in the micrometre range. From the high-contrast interference pattern the degree of coherence was determined.}, language = {en} } @article{PietschHansen1996, author = {Pietsch, Ullrich and Hansen, N. K.}, title = {A critical review of the valence charge density in GaAs}, year = {1996}, language = {en} } @article{ReichePietschFinketal.1992, author = {Reiche, J{\"u}rgen and Pietsch, Ullrich and Fink, Hans-Peter and Lemmetyinen, Helge}, title = {A comparison fo x-ray methods for structure refinement of Langmuir-Blodgett multilayers}, year = {1992}, abstract = {The possibilities and limits of structure refinement of Langmuir-Blodgett films by means of symmetrical reflection of X- rays are described using the example of a stearic acid multilayer. Three different techniques for the determiantion of the electron density profile from reflectivity data are compared; a Fourier method, a Patterson method, and model calculations. The important role of the a priori information for finding the besft structure model is outlined.}, language = {en} }