TY - JOUR A1 - Henneberg, Oliver A1 - Rochon, Paul A1 - Panzner, Tobias A1 - Finkelstein, Kenneth D. A1 - Geue, Thomas A1 - Saphiannikova, Marina A1 - Pietsch, Ullrich T1 - In-situ Investigation of Surface Relief Grating Formation in Photosensitive Polymers Y1 - 2004 UR - http://www.chess.cornell.edu/pubs/csnm2004/research/insitu.pdf 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 - 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 - Saphiannikova, Marina A1 - Henneberg, Oliver A1 - Gene, T. M. A1 - Pietsch, Ullrich A1 - Rochon, Paul T1 - Nonlinear effects during inscription of azobenzene surface relief gratings N2 - Surface relief gratings were inscribed on azobenzene polymer films using a pulselike exposure of an Ar+ laser. The inscription process was initiated by a sequence of short pulses followed by much longer relaxation pauses. The development of the surface relief grating was probed by a He-Ne laser measuring the scattering intensity of the first- order grating peak. The growth time of the surface relief grating was found to be larger than the length of the pulses used. This unusual behavior can be considered as a nonlinear material response associated with the trans-cis isomerization of azobenzene moieties. In this study the polymer stress was assumed to be proportional to the number of cis-isomers. One-dimensional viscoelastic analysis was used to derive the polymer deformation. The rate of trans-cis isomerization increases with the intensity of the inscribing light; in the dark it is equal to the rate of thermal cis- trans isomerization. The respective relaxation times were estimated by fitting theoretical deformation curves to experimental data Y1 - 2004 SN - 1520-6106 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 - 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 - 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 - 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 - Henneberg, Oliver A1 - Geue, Thomas A1 - Pietsch, Ullrich A1 - Winter, Bernd T1 - Investigation of azobenzene side group orientation in polymer surface relief gratings by means of photoelectron spectroscopy N2 - 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 Y1 - 2004 UR - http://scitation.aip.org/journals/doc/APPLAB-ft/vol_84/iss_9/1561_1.html 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 -