@article{GorfmanTsirelsonPietsch2005, author = {Gorfman, S. V. and Tsirelson, Vladimir G. and Pietsch, Ullrich}, title = {X-ray diffraction by a crystal in a permanent external electric field : general considerations}, issn = {0108-7673}, year = {2005}, abstract = {The variations of X-ray diffraction intensities from a crystal in the presence of a permanent external electric field is modeled analytically using a first-order stationary perturbation theory. The change in a crystal, induced by an external electric field, is separated into two contributions. The first one is related to a pure polarization of an electron subsystem, while the second contribution can be reduced to the displacements of the rigid pseudoatoms from their equilibrium positions. It is shown that a change of the X-ray diffraction intensities mainly originates from the second contribution, while the influence of the pure polarization of a crystal electron subsystem is negligibly small. The quantities restored from an X-ray diffraction experiment in the presence of an external electric field were analyzed in detail in terms of a rigid pseudoatomic model of electron density and harmonic approximation for the atomic thermal motion. Explicit relationships are derived that link the properties of phonon spectra with E-field-induced variations of a structure factor, pseudoatomic displacements and piezoelectric strains. The displacements can be numerically estimated using a model of independent atomic motion if the Debye - Waller factors and pseudoatomic charges are known either from a previous single-crystal X-ray diffraction study or from density functional theory calculations. The above estimations can be used to develop an optimum strategy for a data collection that avoids the measurements of reflections insensitive to the electric-field-induced variations}, language = {en} } @article{GorfmanTsirelsonPucheretal.2006, author = {Gorfman, Semen and Tsirelson, Vladimir and Pucher, Andreas and Morgenroth, Wolfgang and Pietsch, Ullrich}, title = {X-ray diffraction by a crystal in a permanent external electric field : electric-field-induced structural response in alpha-GaPO4}, issn = {0108-7673}, doi = {10.1107/S0108767305036111}, year = {2006}, abstract = {For the first time, site-selective distortion has been investigated for two different structural units in the ternary compound alpha-GaPO4 under the influence of a permanent external electric field. Based on 54 measured reflection intensities, the electric-field-induced distortion of PO4 and GaO4 tetrahedra in alpha-GaPO4 crystals is evaluated using a model of pseudoatomic displacements introduced recently [Gorfman, Tsirelson \& Pietsch (2005). Acta Cryst. A61, 387- 396]. A stronger variation of the P-O bond lengths in the PO4 tetrahedron was found compared to the bonds in the GaO4 tetrahedron. The different distortions of the tetrahedra owing to the electric field were analysed in terms of the valence charge density of alpha-GaPO4 and its topological characteristics. The larger charge of the P pseudoatom compared to the Ga atom was recognized as the main reason for the higher sensitivity of the PO4 tetrahedron to a permanent external electric field}, language = {en} } @article{DarowskiPietschWangetal.1998, author = {Darowski, Nora and Pietsch, Ullrich and Wang, K. H. and Forchel, Alfred and Shen, W. and Kycia, S.}, title = {X-ray diffraction analysis of strain relaxation in free standing and buried GaAs/GaInAs/GaAs SQW lateral structures}, year = {1998}, language = {en} } @article{HennebergGeueSaphiannikovaetal.2003, author = {Henneberg, Oliver and Geue, Thomas and Saphiannikova, Marina and Pietsch, Ullrich and Rochon, Paul}, title = {X-ray and VIS light scattering from light-induced polymer gratings}, doi = {10.1088/0022-3727/36/10A/350}, year = {2003}, language = {en} } @article{HennebergPanznerPietschetal.2004, author = {Henneberg, Oliver and Panzner, Tobias and Pietsch, Ullrich and Geue, Thomas and Saphiannikova, Marina and Rochon, Paul and Finkelstein, Kenneth D.}, title = {X-ray and VIS light scattering from light-induced polymer gratings}, issn = {0044-2968}, year = {2004}, abstract = {Sinusoidally shaped surface relief gratings made of polymer films containing, azobenzene moieties can be created by holographic illumination with laser light of about lambda approximate to 500 nm. The remarkable material transport takes place at temperatures far (100 K) below the glass transition temperature of the material. As probed by visible light scattering the efficiency of grating formation crucially depends on the polarization state of the laser light and is maximal when circular polarization is used. In contrast to VIS light scattering X-ray diffraction is most sensitive for periodic surface undulations with amplitudes below 10 nm. Thus, combined in-situ X-ray and visible light scattering at CHESS were used to investigate the dynamics of surface relief grating formations upon laser illumination. The time development of grating peaks up to 9th order at laser power of P = 20 mW/cm(2) could be investigated, even the onset of grating formation as a function of light polarization. A linear growth of grating amplitude was observed for all polarizations. The growth velocity is maximal using circularly polarized light but very small for s-polarized light}, language = {en} } @article{GrenzerSchomburgLingottetal.1998, author = {Grenzer, J{\"o}rg and Schomburg, E. and Lingott, I. and Ignotov, A. a. and Renk, K. F. and Pietsch, Ullrich and Rose, Dirk and Zeimer, Ute and Melzer, B. J. and Ivanov, S. and Schaposchnikov, S. and Kop'ev, P. S. and Pavel'ev, D. G. and Koschurinov, Yu.}, title = {X-ray and transport characterization of an Esaki-Tsu superlattice device}, year = {1998}, language = {en} } @article{EnglischPenacoradaBrehmeretal.1999, author = {Englisch, Uwe and Penacorada, Florencio and Brehmer, Ludwig and Pietsch, Ullrich}, title = {X-ray and neutron reflection analysis of the structure and the molecular exchange process in simple and complex fatty acid salt Langmuir-Blodgett multilayers}, year = {1999}, language = {en} } @article{PietschHolyStroemmeretal.1995, author = {Pietsch, Ullrich and Hol{\´y}, Vaclav and Str{\"o}mmer, R. and Englisch, Uwe}, title = {X-ray and neutron diffuse scattering from multilayers of fatty acid salt molecules}, year = {1995}, language = {en} } @article{PietschJarreSaldittetal.2004, author = {Pietsch, Ullrich and Jarre, A. and Salditt, T. and Panzner, Tobias and Pfeiffer, F.}, title = {White beam x-ray waveguide optics}, year = {2004}, abstract = {We report a white beam x-ray waveguide (WG) experiment. A resonant beam coupler x-ray waveguide (RBC) is used simultaneously as a broad bandpass (or multibandpass) monochromator and as a beam compressor. We show that, depending on the geometrical properties of the WG, the exiting beam consists of a defined number of wavelengths which can be shifted by changing the angle of incidence of the white x-ray synchrotron beam. The characteristic far-field pattern is recorded as a function of exit angle and energy. This x-ray optical setup may be used to enhance the intensity of coherent x-ray WG beams since the full energetic acceptance of the WG mode is transmitted. (C) 2004 American Institute of Physics}, language = {en} } @article{ThuenemannKubowiczPietsch2000, author = {Th{\"u}nemann, Andreas F. and Kubowicz, Stephan and Pietsch, Ullrich}, title = {Ultra-thin solid polyelectrolyte-surfactant complex films : structure and wetting}, year = {2000}, language = {en} } @article{PietschMukhopadhyaySanyaletal.2004, author = {Pietsch, Ullrich and Mukhopadhyay, M. K. and Sanyal, M. K. and Datta, A. and Mukherjee, M. and Geue, Thomas and Grenzer, J{\"o}rg}, title = {Transition from two-dimensional to three-dimensional melting in Langmuir-Blodgett films}, year = {2004}, abstract = {Results of energy-dispersive x-ray reflectivity and grazing incidence diffraction studies of Langmuir-Blodgett films exhibited evolution of conventional three-dimensional melting from continuous melting, characteristic of two- dimensional systems, as a function of deposited monolayers. Continuous expansion followed by a sharp phase transition of the in-plane lattice was observed before the melting point and found to be independent of number of deposited layers. Evolution of conventional melting with an increase in the number of monolayers could be quantified by measuring stiffness against tilting of the vertical stack of molecules, which are kept together by an internal field. The internal field as defined in this model reduces as the in-plane lattice expands and the sample temperature approaches melting point. The sharpness of the melting transition, which has been approximated by a Langevin function, increases with the number of deposited monolayers}, language = {en} } @article{Pietsch2003, author = {Pietsch, Ullrich}, title = {Thin Layers of columns of an amphiphilic hexa-peri-hexabenzocoronene at silicon wafer surfaces}, year = {2003}, language = {en} } @article{EnglischGutberletSeitzetal.1997, author = {Englisch, Uwe and Gutberlet, T. and Seitz, R. and Oeser, R. and Pietsch, Ullrich}, title = {Thermally induced rearrangement of fatty acid salt molecules in Langmuir-Blodgett multilayers}, year = {1997}, language = {en} } @article{PietschGrigorianGrenzeretal.2003, author = {Pietsch, Ullrich and Grigorian, Souren A. and Grenzer, J{\"o}rg and Vartanyants, Ivan A.}, title = {Thermal diffuse scattering in grazing incidence diffraction}, year = {2003}, language = {en} } @article{SiebrechtSchreyerEnglischetal.1997, author = {Siebrecht, R. and Schreyer, A. and Englisch, Uwe and Pietsch, Ullrich and Zabel, Hartmut}, title = {The new reflectometer ADAM at the ILL}, year = {1997}, language = {en} } @article{PietschGrenzerGeueetal.2001, author = {Pietsch, Ullrich and Grenzer, J{\"o}rg and Geue, Thomas and Neißendorfer, Frank and Brezesinski, Gerald and Symietz, Christian and M{\"o}hwald, Helmuth and Gudat, Wolfgang}, title = {The energy dispersive reflectometer at BESSY II : a challenge for thin film analysis}, issn = {0167- 5087}, year = {2001}, language = {en} } @article{PietschDavaasambuuKochinetal.2004, author = {Pietsch, Ullrich and Davaasambuu, Jav and Kochin, V. and Schwarz, K. H. and Blaha, Pawel}, title = {The atomistic origin of the inverse piezoelectric effect in a-quartz}, year = {2004}, abstract = {Ab initio calculations have been carried out using the FP-APW+lo method in order to understand the atomic origin of the inverse piezoelectric effect in x-quartz. The external electric field was modelled by a saw-like potential V-ext in order to achieve translational symmetry within a supercell (SC) containing 72 atoms. The original trigonal quartz structure was repeated along the [110] direction, which corresponds to the direction of the external field. An electric field with 550 kV/mm was applied and the atomic positions of the SC were relaxed until the forces acting on the atoms vanished. In parts of the SC, V-ext changes almost linearly and thus the relaxed atomic positions can be used to determine the structural response due to the external electric field. The calculations provide the piezoelectric modulus of the correct order of magnitude. In contrast to previous models and in agreement with recent experimental results, the atomic origin of the piezoelectric effect can be described by a rotation of slightly deformed SiO4 tetrahedra against each other. The change of the Si-O bond lengths and the tetrahedral O-Si-O angles is one order of magnitude smaller than that of the Si-O-Si angles between neighbouring tetrahedra. The calculated changes of X-ray structure factors are in agreement with experiment when the theoretical data are extrapolated down to the much smaller field strength that is applied in the experiment (E < 10 kV/mm). (C) 2004 Elsevier Ltd. All rights reserved}, language = {en} } @article{MukherjeeBhattacharyaSanyaletal.2000, author = {Mukherjee, M. and Bhattacharya, M. K. and Sanyal, M. K. and Geue, Thomas and Grenzer, J{\"o}rg and Pietsch, Ullrich}, title = {Temperature dependent thickness and surface tension of polymer films}, isbn = {81-7371295-6}, year = {2000}, language = {en} } @article{BrajpuriyaTripathiSharmaetal.2007, author = {Brajpuriya, Ranjeet and Tripathi, Sumit and Sharma, Abhishek and Chaudhari, S.M. and Phase, D.M. and Gupta, Ajay and Shripathi, Thoudinja and Leitenberger, Wolfram and Pietsch, Ullrich and Laxmi, N.}, title = {Temperature dependent energy-dispersive X-ray diffraction and magnetic study of Fe/Al interface}, issn = {0169-4332}, doi = {10.1016/j.apsusc.2007.04.069}, year = {2007}, abstract = {In situ temperature dependent energy-dispersive structural and magnetic study of electron beam evaporated Fe/Al multilayer sample (MLS) has been investigated. The structural studies show the formation of an intermixed FeAl transition layer of a few nanometers thick at the interface during deposition, which on annealing at 300 degrees C transforms to B2FeAl intermetallic phase. Magnetization decreases with increase in temperature and drops to minimum above 300 degrees C due to increase in anti-ferromagnetic interlayer coupling and formation of nonmagnetic FeAl phase at the interface. The Curie temperature (T-c) is found to be 288 degrees C and is much less than that of bulk bcc Fe.}, language = {en} } @article{BodenthinGrenzerLauteretal.2002, author = {Bodenthin, Yves and Grenzer, J{\"o}rg and Lauter, Robert and Pietsch, Ullrich and Lehmann, Pit and Kurth, Dirk G. and M{\"o}hwald, Helmuth}, title = {Temperature and time resolved x-ray scattering at thin organic films}, year = {2002}, language = {en} }