TY - JOUR A1 - Gorfman, S. V. A1 - Tsirelson, Vladimir G. A1 - Pietsch, Ullrich T1 - X-ray diffraction by a crystal in a permanent external electric field : general considerations N2 - 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 Y1 - 2005 SN - 0108-7673 ER - TY - JOUR A1 - Gorfman, Semen A1 - Tsirelson, Vladimir A1 - Pucher, Andreas A1 - Morgenroth, Wolfgang A1 - Pietsch, Ullrich T1 - X-ray diffraction by a crystal in a permanent external electric field : electric-field-induced structural response in alpha-GaPO4 N2 - 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 Y1 - 2006 UR - http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1600-5724 U6 - https://doi.org/10.1107/S0108767305036111 SN - 0108-7673 ER - TY - JOUR A1 - Darowski, Nora A1 - Pietsch, Ullrich A1 - Wang, K. H. A1 - Forchel, Alfred A1 - Shen, W. A1 - Kycia, S. T1 - X-ray diffraction analysis of strain relaxation in free standing and buried GaAs/GaInAs/GaAs SQW lateral structures Y1 - 1998 ER - TY - JOUR A1 - Henneberg, Oliver A1 - Geue, Thomas A1 - Saphiannikova, Marina A1 - Pietsch, Ullrich A1 - Rochon, Paul T1 - X-ray and VIS light scattering from light-induced polymer gratings Y1 - 2003 UR - http://stacks.iop.org/0022-3727/36/A241 U6 - https://doi.org/10.1088/0022-3727/36/10A/350 ER - TY - JOUR A1 - Henneberg, Oliver A1 - Panzner, Tobias A1 - Pietsch, Ullrich A1 - Geue, Thomas A1 - Saphiannikova, Marina A1 - Rochon, Paul A1 - Finkelstein, Kenneth D. T1 - X-ray and VIS light scattering from light-induced polymer gratings N2 - 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 Y1 - 2004 UR - 1960 = doi:10.1524/zkri.219.4.218.30438 SN - 0044-2968 ER - TY - JOUR A1 - Grenzer, Jörg A1 - Schomburg, E. A1 - Lingott, I. A1 - Ignotov, A. a. A1 - Renk, K. F. A1 - Pietsch, Ullrich A1 - Rose, Dirk A1 - Zeimer, Ute A1 - Melzer, B. J. A1 - Ivanov, S. A1 - Schaposchnikov, S. A1 - Kop'ev, P. S. A1 - Pavel'ev, D. G. A1 - Koschurinov, Yu. T1 - X-ray and transport characterization of an Esaki-Tsu superlattice device Y1 - 1998 ER - TY - JOUR A1 - Englisch, Uwe A1 - Penacorada, Florencio A1 - Brehmer, Ludwig A1 - Pietsch, Ullrich T1 - X-ray and neutron reflection analysis of the structure and the molecular exchange process in simple and complex fatty acid salt Langmuir-Blodgett multilayers Y1 - 1999 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Holý, Vaclav A1 - Strömmer, R. A1 - Englisch, Uwe T1 - X-ray and neutron diffuse scattering from multilayers of fatty acid salt molecules Y1 - 1995 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Jarre, A. A1 - Salditt, T. A1 - Panzner, Tobias A1 - Pfeiffer, F. T1 - White beam x-ray waveguide optics N2 - 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 Y1 - 2004 ER - TY - JOUR A1 - Thünemann, Andreas F. A1 - Kubowicz, Stephan A1 - Pietsch, Ullrich T1 - Ultra-thin solid polyelectrolyte-surfactant complex films : structure and wetting Y1 - 2000 ER -