TY - JOUR A1 - Pietsch, Ullrich T1 - Reversible negative thermal expansion of polymer films Y1 - 2002 ER - TY - JOUR A1 - Pietsch, Ullrich T1 - Investigations of semiconductor surfaces and interfaces by X-ray grazing incidence diffraction Y1 - 2000 SN - 0011-3891 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Barberka, Thomas Andreas A1 - Geue, Thomas A1 - Stömmer, Ralph T1 - X-ray scattering from thin organic films and multilayers Y1 - 1997 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Bhattacharya, M. K. A1 - Mukherjee, M. A1 - Sanyal, M. K. A1 - Geue, Thomas A1 - Grenzer, Jörg T1 - Energy dispersive x-ray reflectivity technique to study thermal properties of polymer films Y1 - 2003 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Bhattacharya, M. K. A1 - Sanyal, M. K. A1 - Geue, Thomas T1 - Glass transition in Ultrathin Polymer Films : a Thermal Expansion Study N2 - The glass transition process gets affected in ultrathin films having thickness comparable to the size of the molecules. We observe systematic broadening of the glass transition temperature (T-g) as the thickness of an ultrathin polymer film reduces below the radius of gyration but the change in the average T-g was found to be very small. The existence of reversible negative and positive thermal expansion below and above T-g increased the sensitivity of our thickness measurements performed using energy-dispersive x-ray reflectivity. A simple model of the T-g variation as a function of depth expected from sliding motion could explain the results Y1 - 2005 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Bodenthin, Yves A1 - Grenzer, Jörg A1 - Geue, Thomas A1 - Möhwald, Helmuth A1 - Kurth, Dirk G. T1 - Structure and temperature behavior of metallo-supramolecular assemblies N2 - A detailed structural analysis of a Langmuir-Blodgett (LB) multilayer composed of a polyelectrolyte-amphiphile complex (PAC) is presented. The PAC is self-assembled from metal ions, ditopic bis-terpyridines, and amphiphiles. The vertical structure of the LB multilayer is investigated by X-ray reflectometry. The multilayer has a periodicity of 57 A, which corresponds to an architecture of flat lying metallo-supramolecular coordination polyelectrolyte (MEPE) rods and upright-standing amphiphiles (dihexadecyl phosphate, DHP). In-plane diffraction reveals hexagonal packing of the DHP molecules. Using extended X-ray absorption fine structure (EXAFS) experiments, we prove that the central metal ion is coordinated to the terpyridine moieties in a pseudo-octahedral coordination environment. The Fe-N bond distances are 1.82 and 2.0 angstrom, respectively. Temperature resolved measurements indicate a reversible phase transition in a temperature range up to 55 degrees C. EXAFS measurements indicate a lengthening of the average Fe-N bond distance from 1.91 to 1.95 angstrom. The widening of the coordination cage upon heating is expected to lower the ligand field stabilization, thus giving rise to spin transitions in these composite materials Y1 - 2005 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Bodenthin, Yves A1 - Möhwald, Helmuth A1 - Kurth, Dirk G. T1 - Inducing spin crossover in metallo-supramolecular polyelectrolytes through an amphiphilic phase transition N2 - A phase transition in an amphiphilic mesophase is explored to deliberately induce mechanical strain in an assembly of tightly coupled metal ion coordination centers. Melting of the alkyl chains in the amphiphilic mesophase causes distortion of the coordination geometry around the central transition metal ion. As a result, the crystal field splitting of the d-orbital subsets decreases resulting in a spin transition from a low-spin to a high-spin state. The diamagnetic-paramagnetic transition is reversible. This concept is demonstrated in a metallo-supramolecular coordination polyelectrolyte-amphiphile complex self-assembled from ditopic bis-terpyridines, Fe(II) as central transition metal, and dialkyl phosphates as amphiphiles. The magnetic properties are studied in a Langmuir-Blodgett multilayer. The modularity of this concept provides extensive control of structure and function from molecular to macroscopic length scales and gives access to a wide range of new molecular magnetic architectures such as nanostructures, thin films, and liquid crystals Y1 - 2005 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Darowski, Nora A1 - Ulyanenkov, A. A1 - Grenzer, Jörg A1 - Wang, K. H. A1 - Forchel, Alfred T1 - Analysis of the strain distribution in lateral nanostructures for interpreting photoluminescence data Y1 - 2000 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Davaasambuu, Jav A1 - Kochin, V. A1 - Schwarz, K. H. A1 - Blaha, Pawel T1 - The atomistic origin of the inverse piezoelectric effect in a-quartz N2 - 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 Y1 - 2004 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Davaasambuu, Jav A1 - Pucher, Andreas A1 - Kochin, V. T1 - Atomistic origin of the inverse piezoelectric effect in alpha-SiO2 and alpha-GaPO4 Y1 - 2003 UR - http://www.edpsciences.org/articles/epl/pdf/2003/12/7666.pdf?access=ok SN - 0295-5075 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Geue, Thomas A1 - Henneberg, Oliver A1 - Saphiannikova, Marina T1 - X-ray investigations of formation efficiency of buried azobenzene polymer density gratings Y1 - 2003 UR - http://scitation.aip.org/journals/doc/JAPIAU-ft/vol_93/iss_6/3161_1.html U6 - https://doi.org/10.1063/1.1554753 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Grenzer, Jörg A1 - Bischoff, Lothar T1 - Grazing-incidence diffraction strain analysis of a laterally patterned Si wafer treated by focused Ge and An ion beam implantation N2 - Strain analysis of a laterally patterned Si-wafer was carried out utilizing X-ray grazing-incidence diffraction with synchrotron radiation. The lateral patterning was done by focused ion beam implantation using an ion source of liquid AuGeSi alloy. Samples were prepared by either 35 keV Au+ ions (dose: 0.2, 2 x 10(14) cm(-2)) or 70 keV Ge++ ions (dose: 8 X 10(14) cm(-1)). It was shown that due to implantation a periodical defect structure is created consisting of both implanted and not implanted stripes. The evaluated depth distribution of defects within the implanted stripes corresponds to that obtained by TRIM calculation. The induced strain distribution, however, shows no periodicity. This can be explained by an overlap of the strain fields created in each implanted stripe. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Y1 - 2005 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Grenzer, Jörg A1 - Geue, Thomas A1 - Neißendorfer, Frank A1 - Brezesinski, Gerald A1 - Symietz, Christian A1 - Möhwald, Helmuth A1 - Gudat, Wolfgang T1 - The energy dispersive reflectometer at BESSY II : a challenge for thin film analysis Y1 - 2001 SN - 0167- 5087 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Grenzer, Jörg A1 - Grigorian, Souren A. A1 - Weyers, Markus A1 - Zeimer, Ute A1 - Feranchuk, S. A1 - Fricke, J. A1 - Kissel, H. A1 - Knauer, A. A1 - Tränkle, G. T1 - Nanoengineering of lateral strain-modulation in quantum well heterostructures N2 - We have developed a method to design a lateral band-gap modulation in a quantum well heterostructure. The lateral strain variation is induced by patterning of a stressor layer grown on top of a single quantum well which itself is not patterned. The three-dimensional (3D) strain distribution within the lateral nanostructure is calculated using linear elasticity theory applying a finite element technique. Based on the deformation potential approach the calculated strain distribution is translated into a local variation of the band-gap energy. Using a given vertical layer structure we are able to optimize the geometrical parameters to provide a nanostructure with maximum lateral band-gap variation. Experimentally such a structure was realized by etching a surface grating into a tensile-strained InGaP stressor layer grown on top of a compressively strained InGaAs-single quantum well. The achieved 3D strain distribution and the induced band-gap variation are successfully probed by x-ray grazing incidence diffraction and low-temperature photoluminescence measurements, respectively Y1 - 2004 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Grigorian, Souren A. A1 - Grenzer, Jörg A1 - Feranchuk, S. A1 - Zeimer, Ute T1 - Grazing-incidence diffraction study of strain-modulated single quantum well nanostructures Y1 - 2003 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Grigorian, Souren A. A1 - Grenzer, Jörg A1 - Vartanyants, Ivan A. T1 - Thermal diffuse scattering in grazing incidence diffraction Y1 - 2003 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Gupta, Ajay A1 - Gupta, Mukul A1 - Ayachit, S. A1 - Rajagopalan, S. A1 - Balamurgan, A. K. A1 - Tyagi, A. K. T1 - Iron self-diffusion in nanocrystalline FeCr thin films N2 - Thin films of amorphous Fe85Zr15 alloy were deposited by ion-beam sputtering of a composite target. Analogous to the melt-spun amorphous alloys of similar composition, the crystallization of the amorphous film occurs in two steps, however, with a substantially reduced thermal stability. After completion of the first crystallization step which starts at 473 K, the microstructure consists of 12 nm nanocrystals of bcc-Fe embedded in a grain boundary region of the remaining amorphous phase. At 673 K, the remaining amorphous phase transforms into the Fe2Zr alloy. The self-diffusion measurements of iron in the nanocrystalline state and in the parent amorphous state has been carried out using secondary ion mass spectroscopy (SIMS) depth profiling and neutron reflectivity techniques. In contrast to the case of finemet Fe73.5Si13.5B9Nb3Cu1 alloy, where a significant enhancement of diffusivity takes place in the nanocrystalline state, in the present case the diffusivity in the nanocrystalline state is similar to that in the parent amorphous state. It is suggested that in this system the atomic diffusion occurs mainly via the grain boundary regions. The calculated values of the pre-exponential factor and the activation energy for the diffusion are D-0 = 1 x 10(-14+/-1) m(2)/s and E = (0.7 +/- 0.1) eV respectively. (C) 2004 Published by Elsevier B.V. Y1 - 2004 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Gupta, Amod A1 - Paul, A. A1 - Meneghini, C. A1 - Mibu, K. A1 - Maddalena, S. A1 - Dal Toe, S. A1 - Principi, G. T1 - Structural characterization of epitaxial Fe/Cr multilayers using anomalous x-ray scattering and neutron reflectivity N2 - 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 Y1 - 2004 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Hansen, N. K. T1 - A critical review of the valence charge density in GaAs Y1 - 1996 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Hazra, S. A1 - Chini, T. K. A1 - Sanyal, M. K. A1 - Grenzer, Jörg T1 - Ripple structure of crystalline layers in ion beam induced Si wafers N2 - 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 Y1 - 2004 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Hesse, A. A1 - Zhuang, Y. A1 - Holý, Vaclav A1 - Stangl, Jochen A1 - Zerlauth, S. A1 - Schaffler, F. A1 - Bauer, Günther T1 - X-ray grazing-incidence study of inhomogeneous strain relaxation in Si/SiGe wires Y1 - 2003 SN - 0168-583X 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 - BOOK A1 - Pietsch, Ullrich A1 - Holý, Václav A1 - Baumbach, Tilo T1 - High resolution X-ray scattering from thin films and lateral nanostructures T3 - Advanced texts in physics : physics and astronomy online library Y1 - 2004 SN - 0-387-40092-3 PB - Springer CY - New York ET - 2. ed. 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 - Pietsch, Ullrich A1 - Kubowicz, Stephan A1 - Thünemann, Andreas F. A1 - Geue, Thomas A1 - Watson, M. D. A1 - Tchebotareva, N. A1 - Müllen, K. T1 - X-ray reflectivity study of an amphiphilic hex-peri-hexabenzocoronene at a structured silicon wafer surface Y1 - 2003 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Leitenberger, Wolfram A1 - Wendrock, Horst A1 - Bischoff, Lothar A1 - Panzner, Tobias A1 - Grenzer, Jörg A1 - Pucher, Andreas T1 - Double pinhole diffraction of white synchrotron radiation Y1 - 2003 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Mukhopadhyay, M. K. A1 - Sanyal, M. K. A1 - Datta, A. A1 - Mukherjee, M. A1 - Geue, Thomas A1 - Grenzer, Jörg T1 - Transition from two-dimensional to three-dimensional melting in Langmuir-Blodgett films N2 - 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 Y1 - 2004 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Panzner, Tobias A1 - Leitenberger, Wolfram A1 - Grenzer, Jörg A1 - Bodenthin, Th. A1 - Geue, Thomas A1 - Möhwald, Helmuth T1 - Coherence experiments at the energy-dispersive reflectometry beamline at BESSY II Y1 - 2003 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Panzner, Tobias A1 - Leitenberger, Wolfram A1 - Vartanyants, Ivan A. T1 - Coherence experiments using white synchrotron radiation N2 - Experiments at the bending magnet beamline at BESSY II (EDR beamline) profit from the excellent coherence properties of third generation synchrotron sources. Considering the exponentially decaying incident spectrum, and because no optical elements are installed except slits and vacuum windows, coherence experiments can be performed between 5 keV < E < 15 keV. First, the energy dependence of spatial coherence properties were determined measuring diffraction at single and double pinholes. Next, the coherent white radiation was used to probe the morphology of thin films in reflection geometry. The recorded intensity maps (reflectivity versus sample position) provide speckle patterns which reveal the locally varying sample morphology. Setting the incident angle, alpha(i), smaller or larger than the critical angle of total external reflection, alpha(c), one should be able to separate the surface height profile from the subsurface density modulation of a sample. The validity of this approach is verified at the example of reciprocal space maps taken from a polymer surface where we could reconstruct the lateral height profile from speckle data. (C) 2004 Elsevier B.V. All rights reserved Y1 - 2005 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Panzner, Tobias A1 - Leitenberger, Wolfram A1 - Vartanyants, Ivan A. T1 - Coherence experiments at the EDR-beamline of BESSY II Y1 - 2005 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Panzner, Tobias A1 - Pfeiffer, Franz A1 - Robinson, Ian K. T1 - Substrate morphology repetition in "thick" polymer films N2 - Using Grazing-incidence small-angle scattering (GISAXS) technique we investigated the surface morphology of polymer films spin-coated on different silicon substrates. As substrates we used either technologically smooth silicon wafers or the same silicon wafer coated with thin aluminium or gold films which show a granular structure at the surface. Although the polymer thickness exceeds 300 nm the GISAXS pattern of the film shows the same in-plane angle distribution Delta2theta as the underlying substrate. Annealing the polymer films at a temperature above its glass transition temperature Delta2theta changed from a broad to a narrow distribution as it is typically for films on pure silicon. The experiment can be interpreted by roughness replication and density fluctuation within the polymer film created while spin-coating at room temperature. Due to the low segment mobility there are density fluctuations which repeat the surface morphology of the substrate. Above the glass temperature the polymer density can be homogenized independently from the morphology of the substrate. (C) 2004 Elsevier B.V. All rights reserved Y1 - 2005 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Rochon, Paul A1 - Natansohn, Almeria T1 - Formation of a buried lateral density grating in azopenzene polymer films Y1 - 2000 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Saphiannikova, Marina A1 - Henneberg, Oliver A1 - Geue, Thomas T1 - Non-linear effects during inscription of azobenzene surface relief gratings Y1 - 2004 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Stahn, Jochen A1 - Davaasambuu, Jav A1 - Pucher, Andreas T1 - Electric field induced charge density variations in partially-ionic compounds Y1 - 2001 SN - 0022-3697 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Tsirelson, Vladimir G. A1 - Gorfan, S. V. T1 - X-ray scattering amplitude of an atom in a permanent external electric field Y1 - 2003 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Zeimer, Ute A1 - Grenzer, Jörg A1 - Grigorian, Souren A. A1 - Fricke, J. A1 - Gramlich, S. A1 - Bugge, F. A1 - Weyers, Markus A1 - Trankle, G. T1 - Influence of lateral patterning geometry on lateral carrier confinement in strain-modulated InGaAs- nanostructures Y1 - 2003 ER - TY - JOUR A1 - Pietsch, Ullrich A1 - Zeimer, Ute A1 - Hofmann, L. A1 - Grenzer, Jörg A1 - Gramlich, S. T1 - Strain induced compositional modulations in AlGaAs overlayers induced by lateral surface gratings Y1 - 2001 SN - 0272-9172 ER - TY - JOUR A1 - Poloucek, P. A1 - Pietsch, Ullrich A1 - Geue, Thomas A1 - Symietz, Christian A1 - Brezesinski, Gerald T1 - X-ray reflectivity analysis of thin complex Langmuir-Blodgett films Y1 - 2001 ER - TY - JOUR A1 - Reddy, Raghavendra V. A1 - Gupta, Ajay A1 - Gome, Anil A1 - Leitenberger, Wolfram A1 - Pietsch, Ullrich T1 - In situ x-ray reflectivity and grazing incidence x-ray diffraction study of L1(0) ordering in Fe-57/Pt multilayers N2 - In situ high temperature x-ray reflectivity and grazing incidence x-ray diffraction measurements in the energy dispersive mode are used to study the ordered face-centered tetragonal (fct) L1(0) phase formation in [Fe(19 angstrom)/ Pt(25 angstrom)](x10) multilayers prepared by ion beam sputtering. With the in situ x-ray measurements it is observed that (i) the multilayer structure first transforms to a disordered FePt and subsequently to an ordered fct L1(0) phase, (ii) the ordered fct L1(0) FePt peaks start to appear at 320°C annealing, (iii) the activation energy of the interdiffusion is 0.8 eV and (iv) ordered fct FePt grains have preferential out-of-plane texture. The magneto-optical Kerr effect and conversion electron Mossbauer spectroscopies are used to study the magnetic properties of the as- deposited and 400°C annealed multilayers. The magnetic data for the 400°C annealed sample indicate that the magnetization is at an angle of ~50° from the plane of the film. Y1 - 2009 UR - http://iopscience.iop.org/0953-8984 U6 - https://doi.org/10.1088/0953-8984/21/18/186002 SN - 0953-8984 ER - TY - JOUR A1 - Reiche, Jürgen A1 - Barberka, Thomas Andreas A1 - Janietz, Dietmar A1 - Hofmann, Dieter A1 - Pietsch, Ullrich A1 - Brehmer, Ludwig T1 - X-ray structure investigation and computer modelling of Langmuir-Blodgett films formed from disc-shaped pentaalkines Y1 - 1994 ER - TY - JOUR A1 - Reiche, Jürgen A1 - Barberka, Thomas Andreas A1 - Knochenhauer, Gerald A1 - Woolley, Martin A1 - Pietsch, Ullrich T1 - Comprehensive structure investigation and computer modelling of perfluorododecanoic acid multilayers formed by in-vacuo thermal evaporation Y1 - 1994 ER - TY - JOUR A1 - Reiche, Jürgen A1 - Dietzel, Birgit A1 - Freydank, Anke-Christine A1 - Geue, Thomas A1 - Pietsch, Ullrich A1 - Brehmer, Ludwig T1 - Lateral structure of thermally treated oxadiazole Langmuir-Blodgett films Y1 - 1995 ER - TY - JOUR A1 - Reiche, Jürgen A1 - Knochenhauer, Gerald A1 - Barberka, Thomas Andreas A1 - Geue, Thomas A1 - Pietsch, Ullrich A1 - Brehmer, Ludwig A1 - Hodge, P. A1 - Tredgold, Richard H. T1 - In-plane structure of perfluorotetra decanoic acid Langmuir-Blodgett films and films formed by vacuum deposition Y1 - 1995 ER - TY - JOUR A1 - Reiche, Jürgen A1 - Knochenhauer, Gerald A1 - Dietel, Reinhard A1 - Freydank, Anke-Christine A1 - Zetzsche, Thomas A1 - Pietsch, Ullrich A1 - Brehmer, Ludwig A1 - Barberka, Thomas Andreas A1 - Geue, Thomas T1 - Structure of thermally treated oxadiazoleamide Langmuir-Blodgett films N2 - The thermal treatment of Y-type Langmuir-Blodgett (LB) films formed from the amphiphilic derivative of 2,5- diphenyl-1,3,4-oxadiazole 1 results in changes of the molecular packing. These changes have been analysed by a combination of X-ray specular reflectivity data, X-ray grazing incidence diffraction data and scanning force microscopy images, On the basis of these experimental data we have simulated possible supramolecular structures, These simulations provide insight into the intermolecular interactions giving rise to the observed structural transitions. The crystalline structure induced by thermal treatment of the LB films is characterized by a uniaxial texture, which is correlated with the dipping direction during deposition of the LB film. Y1 - 1997 ER - TY - JOUR A1 - Reiche, Jürgen A1 - Penacorada, Florencio A1 - Geue, Thomas A1 - Pietsch, Ullrich A1 - Brehmer, Ludwig T1 - In-plane structure of uranylarachidate multilayers Y1 - 1995 ER - TY - JOUR A1 - Reiche, Jürgen A1 - Penacorada, Florencio A1 - Geue, Thomas A1 - Pietsch, Ullrich A1 - Brehmer, Ludwig T1 - Monolayers and multilayers of uranyl arachidate : in-plane structure of uranyl arachidate multilayers N2 - The molecular in-plane structure of uranyl arachidate Langmuir-Blodgett (LB) films formed at different subphase pH values was analysed by means of X-ray grazing-incidence diffraction. For multilayers formed at low subphase pH a reorganisation of the arachidic acid film structure is confirmed. At appropriate subphase pH values, reorganisation of the film structure, e.g. via the formation of three-dimensional crystallites, is prevented by the presence of the uranyl ions and by the subsequent introduction of conformational disorder (gauche defects) in the alkyl chains. The observation of a macroscopic flow-induced in-plane texture in these uranyl arachidate LB films has profound implications for the design of ordered, supramolecular structures by the Langmuir-Blodgett technique. Y1 - 1997 ER - TY - JOUR A1 - Reiche, Jürgen A1 - Pietsch, Ullrich A1 - Fink, Hans-Peter A1 - Lemmetyinen, Helge T1 - A comparison fo x-ray methods for structure refinement of Langmuir-Blodgett multilayers N2 - 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. Y1 - 1992 ER - TY - JOUR A1 - Reinhold, Beate A1 - Geue, Thomas A1 - Huber, Patrick A1 - Sant, Tushar A1 - Pietsch, Ullrich A1 - Sztucki, Michael T1 - In situ and ex situ SAXS investigation of colloidal sedimentation onto laterally patterned support N2 - We report on in situ investigations of colloidal ordering during gravity sedimentation from a colloidal suspension onto a prepatterned support using a polymeric surface relief grating (SRG) as the support. The ordering of colloids with a diameter of 420 nm was investigated by means of grazing-incidence small-angle X-ray scattering (GISAXS) and transmission SAXS using a preparation cell guaranteeing stable temperature and humidity. GISAXS was used for in situ monitoring of the time evolution of colloidal ordering within the whole illuminated sample area. The onset of ordering was indicated by the increase of integrated intensity within a small time frame shortly before complete evaporation of the dispersant. Single domains of coated samples were investigated ex situ by SAXS in transmission geometry where the irradiated sample area was 200 x 200 mu m(2) only. Domains with the typical size of a few millimeters were observed varying in orientation and crystallographic structure for various positions at the sample. They were mainly oriented along the grooves of the grating, confirming the influence of the underlying grating on colloidal ordering. Y1 - 2009 UR - http://pubs.acs.org/journal/langd5 U6 - https://doi.org/10.1021/La803078b SN - 0743-7463 ER - TY - JOUR A1 - Rose, Dirk A1 - Pietsch, Ullrich A1 - Zeimer, Ute T1 - Characterization of InGaAs single quantum wells buried in GaAs[001] by grazing incidence diffraction Y1 - 1997 ER - TY - JOUR A1 - Saphiannikova, Marina A1 - Geue, Thomas A1 - Henneberg, Oliver A1 - Morawetz, Knut A1 - Pietsch, Ullrich T1 - Linear viscoelastic analysis of formation and relaxation of azobenzene polymer gratings N2 - 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 Y1 - 2004 U6 - https://doi.org/10.1063/1.1642606 ER -