@article{PietschZeimerGrenzeretal.2003, author = {Pietsch, Ullrich and Zeimer, Ute and Grenzer, J{\"o}rg and Grigorian, Souren A. and Fricke, J. and Gramlich, S. and Bugge, F. and Weyers, Markus and Trankle, G.}, title = {Influence of lateral patterning geometry on lateral carrier confinement in strain-modulated InGaAs- nanostructures}, year = {2003}, language = {en} } @article{PietschBhattacharyaMukherjeeetal.2003, author = {Pietsch, Ullrich and Bhattacharya, M. K. and Mukherjee, M. and Sanyal, M. K. and Geue, Thomas and Grenzer, J{\"o}rg}, title = {Energy dispersive x-ray reflectivity technique to study thermal properties of polymer films}, year = {2003}, language = {en} } @article{PietschGrigorianGrenzeretal.2003, author = {Pietsch, Ullrich and Grigorian, Souren A. and Grenzer, J{\"o}rg and Feranchuk, S. and Zeimer, Ute}, title = {Grazing-incidence diffraction study of strain-modulated single quantum well nanostructures}, year = {2003}, 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{PietschGeueHennebergetal.2003, author = {Pietsch, Ullrich and Geue, Thomas and Henneberg, Oliver and Saphiannikova, Marina}, title = {X-ray investigations of formation efficiency of buried azobenzene polymer density gratings}, doi = {10.1063/1.1554753}, year = {2003}, language = {en} } @article{Pietsch2003, author = {Pietsch, Ullrich}, title = {Evidence of a density grating under light induced formation of surface relief gratings at polymers containing azobenzene moieties}, year = {2003}, 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{PietschTsirelsonGorfan2003, author = {Pietsch, Ullrich and Tsirelson, Vladimir G. and Gorfan, S. V.}, title = {X-ray scattering amplitude of an atom in a permanent external electric field}, year = {2003}, 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{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{PietschLeitenbergerWendrocketal.2003, author = {Pietsch, Ullrich and Leitenberger, Wolfram and Wendrock, Horst and Bischoff, Lothar and Panzner, Tobias and Grenzer, J{\"o}rg and Pucher, Andreas}, title = {Double pinhole diffraction of white synchrotron radiation}, year = {2003}, 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{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{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{SaphiannikovaGeueHennebergetal.2004, author = {Saphiannikova, Marina and Geue, Thomas and Henneberg, Oliver and Morawetz, Knut and Pietsch, Ullrich}, title = {Linear viscoelastic analysis of formation and relaxation of azobenzene polymer gratings}, doi = {10.1063/1.1642606}, year = {2004}, abstract = {Surface relief gratings on azobenzene containing polymer films were prepared under irradiation by actinic light. Finite element modeling of the inscription process was carried out using linear viscoelastic analysis. It was assumed that under illumination the polymer film undergoes considerable plastification, which reduces its original Young's modulus by at least three orders of magnitude. Force densities of about 10(11) N/m(3) were necessary to reproduce the growth of the surface relief grating. It was shown that at large deformations the force of surface tension becomes comparable to the inscription force and therefore plays an essential role in the retardation of the inscription process. In addition to surface profiling the gradual development of an accompanying density grating was predicted for the regime of continuous exposure. Surface grating development under pulselike exposure cannot be explained in the frame of an incompressible fluid model. However, it was easily reproduced using the viscoelastic model with finite compressibility. (C) 2004 American Institute of Physics}, 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{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{HennebergGeuePietschetal.2004, author = {Henneberg, Oliver and Geue, Thomas and Pietsch, Ullrich and Winter, Bernd}, title = {Investigation of azobenzene side group orientation in polymer surface relief gratings by means of photoelectron spectroscopy}, year = {2004}, abstract = {The molecular orientation of azobenzene side groups in polymer films before (nonpatterned) and after (patterned) development of a surface relief grating has been investigated by photoelectron spectroscopy using synchrotron radiation. The photoemission spectra obtained for 60-100 eV photons of a patterned and a nonpatterned surface are similar when the polarization vector of the synchrotron light is parallel to the grating vector. However, for perpendicular excitation, considerable spectral intensity differences can be observed for 9-14 eV electron binding energy. The observed changes are attributed to the formation of well-oriented azobenzenes at the surface. (C) 2004 American Institute of Physics}, language = {en} } @article{PietschHazraChinietal.2004, author = {Pietsch, Ullrich and Hazra, S. and Chini, T. K. and Sanyal, M. K. and Grenzer, J{\"o}rg}, title = {Ripple structure of crystalline layers in ion beam induced Si wafers}, year = {2004}, abstract = {Ion-beam-induced ripple formation in Si wafers was studied by two complementary surface sensitive techniques, namely atomic force microscopy (AFM) and depth-resolved x-ray grazing incidence diffraction (GID). The formation of ripple structure at high doses (similar to7x10(17) ions/cm(2)), starting from initiation at low doses (similar to1x10(17) ions/cm(2)) of ion beam, is evident from AFM, while that in the buried crystalline region below a partially crystalline top layer is evident from GID study. Such ripple structure of crystalline layers in a large area formed in the subsurface region of Si wafers is probed through a nondestructive technique. The GID technique reveals that these periodically modulated wavelike buried crystalline features become highly regular and strongly correlated as one increases the Ar ion-beam energy from 60 to 100 keV. The vertical density profile obtained from the analysis of a Vineyard profile shows that the density in the upper top part of ripples is decreased to about 15\% of the crystalline density. The partially crystalline top layer at low dose transforms to a completely amorphous layer for high doses, and the top morphology was found to be conformal with the underlying crystalline ripple}, language = {en} } @article{PietschGuptaPauletal.2004, author = {Pietsch, Ullrich and Gupta, Amod and Paul, A. and Meneghini, C. and Mibu, K. and Maddalena, S. and Dal Toe, S. and Principi, G.}, title = {Structural characterization of epitaxial Fe/Cr multilayers using anomalous x-ray scattering and neutron reflectivity}, year = {2004}, abstract = {The interface structure of epitaxial Fe/Cr multilayers was studied using anomalous X-ray and neutron reflectivity. The analysis of X-ray reflectivity at three different energies provided a reliable information about the interface roughnesses. It is found that the Cr-on-Fc interface is more diffused as compared to the Fe-on-Cr interface and that the roughness exhibits a significant increase with increasing depth. The magnetic roughness, as determined from neutron reflectivity, is lower than the geometrical roughness, in conformity with the behavior of a number of magnetic thin films and multilayers. (C) 2004 Elsevier B.V. All rights reserved}, language = {en} }