@article{GeueHennebergPietsch2002,
  author    = {Geue, Thomas and Henneberg, Oliver and Pietsch, Ullrich},
  title     = {X-ray reflectivity from sinusoidal surface relief gratings},
  issn      = {0023-4753},
  year      = {2002},
  language  = {en}
}
@article{GeuePietschHaferkornetal.1999,
  author    = {Geue, Thomas and Pietsch, Ullrich and Haferkorn, J. and Stumpe, Joachim and Date, R. W. and Fawcett, A. H.},
  title     = {Competition of alignment and aggregation? : Phenomena in constrained films of LC poly(olefin ulfone)s and maleic anhydride co- and terpolymers},
  year      = {1999},
  language  = {en}
}
@article{GeueSaphiannikovaHennebergetal.2002,
  author    = {Geue, Thomas and Saphiannikova, Marina and Henneberg, Oliver and Pietsch, Ullrich and Rochon, Paul and Natansohn, Almeria},
  title     = {Formation mechanism and dynamics in polymer surface gratings},
  year      = {2002},
  language  = {en}
}
@article{GeueSchultzEnglischetal.1999,
  author    = {Geue, Thomas and Schultz, M. and Englisch, Uwe and St{\"o}mmer, Ralph and Pietsch, Ullrich and Meine, Kerstin and Vollhard, D.},
  title     = {Investigation of pH-dependent domain structure of fatty acid salt Langmuir-Blodgett films by means of X-ray diffuse scattering and Atomic Force Microscopy},
  year      = {1999},
  language  = {en}
}
@article{GeueStumpePietschetal.1995,
  author    = {Geue, Thomas and Stumpe, Joachim and Pietsch, Ullrich and Haak, M. and Kaupp, G.},
  title     = {Photochemically induced changes of optical anisotropy and surface of LB-multilayers built up by an amphiphilic and liquid crystalline copolymer conating azobenzene moieties},
  year      = {1995},
  language  = {en}
}
@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{GrenzerDarowskiGeueetal.2001,
  author    = {Grenzer, J{\"o}rg and Darowski, Nora and Geue, Thomas and Pietsch, Ullrich and Daniel, A. and Rennon, Siegfried and Reithmaier, Johann-Peter and Forchel, Alfred},
  title     = {Strain analysis and quantum well intermixing of a laterally modulated multiquantum well system produced by focused ion beam implantation},
  year      = {2001},
  language  = {en}
}
@article{GrenzerDarowskiPietschetal.2000,
  author    = {Grenzer, J{\"o}rg and Darowski, Nora and Pietsch, Ullrich and Daniel, A. and Reithmaier, Johann-Peter and Rennon, Siegfried and Forchel, Alfred},
  title     = {Grazing-incidence diffraction strain analysis of a laterally-modulated multiquantum well system produced by focused-ion-beam implantation},
  year      = {2000},
  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{HaierHerrmannEsseretal.1998,
  author    = {Haier, P. and Herrmann, B. A. and Esser, N. and Pietsch, Ullrich and L{\"u}ders, K. and Richter, W.},
  title     = {Influence of the deposition rate on the structure of thin metal layers},
  year      = {1998},
  language  = {en}
}
@article{HennebergChiGeueetal.2001,
  author    = {Henneberg, Oliver and Chi, Li Feng and Geue, Thomas and Saphiannikova, Marina and Pietsch, Ullrich and Rochon, Paul and Natansohn, Almeria},
  title     = {Atomic force microscopy inspection of the early state of formation of polymer surface relief grating},
  year      = {2001},
  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{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{HennebergGeueSaphiannikovaetal.2001,
  author    = {Henneberg, Oliver and Geue, Thomas and Saphiannikova, Marina and Pietsch, Ullrich and Rochon, Paul and Natansohn, Almeria},
  title     = {Formation and dynamics of polymer surface relief gratings},
  issn      = {0378-5963},
  year      = {2001},
  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{HennebergPietschPanzneretal.2006,
  author    = {Henneberg, Oliver and Pietsch, Ullrich and Panzner, Tobias and Geue, Thomas and Finkelstein, Kenneth D.},
  title     = {Simultaneous X-ray and visible light diffraction for the investigation of surface relief and density grating formation in azobenzene containing polymer films},
  issn      = {1542-1406},
  doi       = {10.1080/15421400500383345},
  year      = {2006},
  abstract  = {The development of surface relief and density patterns in azobenzene polymer films was studied by diffraction at two different wavelengths. We used x-ray diffraction of synchrotron radiation at 0.124 nm in combination with visible light diffraction at a wavelength of 633 nm. In contrast to visible light scattering x-ray diffraction allows the separation of a surface relief and a density grating contribution due to the different functional dependence of the scattering power. Additionally, the x-ray probe is most sensitive for the onset of the surface grating formation},
  language  = {en}
}
@article{HennebergRochonPanzneretal.2004,
  author    = {Henneberg, Oliver and Rochon, Paul and Panzner, Tobias and Finkelstein, Kenneth D. and Geue, Thomas and Saphiannikova, Marina and Pietsch, Ullrich},
  title     = {In-situ Investigation of Surface Relief Grating Formation in Photosensitive Polymers},
  year      = {2004},
  language  = {en}
}
@article{HerrmannKauppGeueetal.1997,
  author    = {Herrmann, A. and Kaupp, G. and Geue, Thomas and Pietsch, Ullrich},
  title     = {AFM and GID investigations of the gas-solid diazotation of 4-sulfanil-acid-monohydrat single crystals},
  year      = {1997},
  language  = {en}
}
@article{HolyDarhuberStangletal.1999,
  author    = {Hol{\´y}, V{\´a}clav and Darhuber, A. and Stangl, Jochen and Zerlauth, S. and Sch{\"a}ffler, F. and Bauer, G{\"u}nther and Darowski, Nora and L{\"u}bbert, Daniel and Pietsch, Ullrich and Vavra, I.},
  title     = {HRXRD and GID investigations of a self-organized SiGe quantum dot multilayer},
  year      = {1999},
  language  = {en}
}
@book{HolyPietschBaumbach1999,
  author    = {Hol{\´y}, V{\´a}clav and Pietsch, Ullrich and Baumbach, Tilo},
  title     = {High-resolution x-ray scattering from thin films and multilayers},
  series = {Springer tracts in modern physics},
  volume    = {149},
  journal   = {Springer tracts in modern physics},
  publisher = {Springer},
  address   = {Berlin, Heidelberg},
  isbn      = {3-540-62029-X},
  doi       = {10.1007/BFb0109385},
  pages     = {256 S.},
  year      = {1999},
  language  = {en}
}
@article{HolyStanglZerlauthetal.1999,
  author    = {Hol{\´y}, V{\´a}clav and Stangl, Jochen and Zerlauth, S. and Bauer, G{\"u}nther and Darowski, Nora and L{\"u}bbert, Daniel and Pietsch, Ullrich},
  title     = {Lateral arrangement of self-assembled quantum dots in an SiGe/Si superlattice},
  year      = {1999},
  language  = {en}
}
@article{JoshiPingelGrigorianetal.2009,
  author    = {Joshi, Siddharth and Pingel, Patrick and Grigorian, Souren and Panzner, Tobias and Pietsch, Ullrich and Neher, Dieter and Forster, Michael and Scherf, Ullrich},
  title     = {Bimodal temperature behavior of structure and mobility in high molecular weight p3ht thin films},
  issn      = {0024-9297},
  doi       = {10.1021/Ma900021w},
  year      = {2009},
  abstract  = {We report a temperature dependent crystalline structure of spin-coated thin films of high molecular weight regioregular poly(3-hexylthiophene) (P3HT) (M-n similar to 30000 g/mol) and its correlation with charge carrier mobility. These investigations show a reversible change of the crystalline structure, where the interlayer lattice spacing (100)along the alkyl side chains continuously increases up to a temperature of about 220 degrees C; in contrast, the in-plane pi-pi distance reduces with increasing temperature. These changes in structure are reversible and can be repeated several times. The temperature-induced structural properties differ for thick and thin films, pointing to a surface/interface role in stabilization of the layer morphology. In contrast to the structural changes, the carrier mobility is rather constant in the temperature range from room temperature up to 100-120 degrees C, followed by a continuous decrease. For thick layers this drop is significant and the transistor performance almost vanishes at high temperature, however, it completely recovers upon cooling back to roorn temperature. The drop of the charge carrier mobility at higher temperatures is in contrast with expectations front the structural studies, considering the increase of crystalline fraction of the polycrystalline layer. our electrical measurements Underscore that the reduction of the macroscopic mobility is mostly caused by it pronounced decrease of the intergrain transport. The thermally induced crystallization along(100) direction and the creation of numerous small crystallites at the film-substrate interface reduce the number of long polymer chain, bridging crystalline domains, which ultimately limits the macroscopic charge transport.},
  language  = {en}
}
@article{KarageorgievNeherSchulzetal.2005,
  author    = {Karageorgiev, Peter and Neher, Dieter and Schulz, Burkhard and Stiller, Burkhard and Pietsch, Ullrich and Giersig, Michael and Brehmer, Ludwig},
  title     = {From anisotropic photo-fluidity towards nanomanipulation in the optical near-field},
  issn      = {1476-1122},
  year      = {2005},
  abstract  = {An increase in random molecular vibrations of a solid owing to heating above the melting point leads to a decrease in its long-range order and a loss of structural symmetry. Therefore conventional liquids are isotropic media. Here we report on a light-induced isothermal transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. Whereas during irradiation by circular polarized light the film behaves as an isotropic viscoelastic fluid, it shows considerable fluidity only in the direction parallel to the light field vector under linear polarized light. The fluidization phenomenon is related to photoinduced motion of azobenzene-functionalized molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization. We also describe here how the photofluidization allows nanoscopic elements of matter to be precisely manipulated},
  language  = {en}
}
@article{KarcenkoEnglischGrenzeretal.2000,
  author    = {Karcenko, Anatolij V. and Englisch, Uwe and Grenzer, J{\"o}rg and Geue, Thomas and Pietsch, Ullrich and Siebrecht, R.},
  title     = {Investigation of partially deuterated multilayers by means of X-ray and polarized neutron reflectometry},
  issn      = {1044-8632},
  year      = {2000},
  language  = {en}
}
@article{LeitenbergerHartmannPietschetal.2008,
  author    = {Leitenberger, Wolfram and Hartmann, Robert and Pietsch, Ullrich and Andritschke, Robert and Starke, Ines and Str{\"u}der, Lothar},
  title     = {Application of a pnCCD in X-ray diffraction : a three-dimensional X-ray detector},
  doi       = {10.1107/S0909049508018931},
  year      = {2008},
  abstract  = {The first application of a pnCCD detector for X-ray scattering experiments using white synchrotron radiation at BESSY II is presented. A Cd arachidate multilayer was investigated in reflection geometry within the energy range 7 keV < E < 35 keV. At fixed angle of incidence the two-dimensional diffraction pattern containing several multilayer Bragg peaks and respective diffuse-resonant Bragg sheets were observed. Since every pixel of the detector is able to determine the energy of every incoming photon with a resolution Delta E/E similar or equal to 10(-2). a three-dimensional dataset is finally obtained. In order to achieve this energy resolution the detector was operated in the so-called single-photon- counting mode. A full dataset was evaluated taking into account all photons recorded within 10(5) detector frames at a readout rate of 200 Hz. By representing the data in reciprocal-space coordinates, it becomes obvious that this experiment with the pnCCD detector provides the same information as that obtained by combining a large number of monochromatic scattering experiments using conventional area detectors.},
  language  = {en}
}
@article{LeitenbergerPietsch2007,
  author    = {Leitenberger, Wolfram and Pietsch, Ullrich},
  title     = {A monolithic Fresnel bimirror for hard X-rays and its application for coherence measurements},
  issn      = {0909-0495},
  doi       = {10.1107/S0909049507003846},
  year      = {2007},
  abstract  = {Experiments using a simple X-ray interferometer to measure the degree of spatial coherence of hard X-rays are reported. A monolithic Fresnel bimirror is used at small incidence angles to investigate synchrotron radiation in the energy interval 5-50 keV with monochromatic and white beam. The experimental setup was equivalent to a Young's double-slit experiment for hard X-rays with slit dimensions in the micrometre range. From the high-contrast interference pattern the degree of coherence was determined.},
  language  = {en}
}
@article{LichanotAzavantPietsch1996,
  author    = {Lichanot, Albert and Azavant, P. and Pietsch, Ullrich},
  title     = {Ab-initio Hartree-Fock study of the electronic charge density of the cubic boron nitride and its comparison with the experiment},
  year      = {1996},
  language  = {en}
}
@article{LuebbertBaumbachPontietal.1999,
  author    = {L{\"u}bbert, Daniel and Baumbach, Tilo and Ponti, S. and Pietsch, Ullrich and Leprince, L. and Schneck, J. and Talneau, A.},
  title     = {Strain investigation of low strained buried gratings by grazing incidence X-Ray diffraction and the theory of elasticity},
  year      = {1999},
  language  = {en}
}
@article{MahlerBodensteinPietsch1995,
  author    = {Mahler, Willy and Bodenstein, G. and Pietsch, Ullrich},
  title     = {Phasentransformationen in Cd-Stearat-Multischichten bei unterschiedlichen Metallionenkonzentrationen},
  year      = {1995},
  language  = {de}
}
@article{MetzgerPietschGarstein1999,
  author    = {Metzger, T. H. and Pietsch, Ullrich and Garstein, E.},
  title     = {High-resolution lattice parameter measurement by x-ray grazing incidence diffraction: Application to the interface of silicon on sapphire},
  year      = {1999},
  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{MukhopadhyayDattaSanyaletal.2001,
  author    = {Mukhopadhyay, M. K. and Datta, A. and Sanyal, M. K. and Geue, Thomas and Pietsch, Ullrich},
  title     = {Synchrotron Studies of Melting of Langmuir-Blodgett Films},
  year      = {2001},
  language  = {en}
}
@article{NeissendorferBolmPietsch1997,
  author    = {Neißendorfer, Frank and Bolm, A. and Pietsch, Ullrich},
  title     = {Energy dispersive X-ray reflectometry and X-ray grazing incidence diffraction from organic multilayers},
  year      = {1997},
  language  = {en}
}
@article{NeissendorferPietschBreszisinskietal.1999,
  author    = {Neißendorfer, Frank and Pietsch, Ullrich and Breszisinski, G. and M{\"o}hwald, Helmuth},
  title     = {Energy-dispersive reflectometry and diffractometry at the WLS of BESSY-I},
  year      = {1999},
  language  = {en}
}
@article{NeumannBuchsteinerMahleretal.2000,
  author    = {Neumann, Werner and Buchsteiner, Alexandra and Mahler, Willy and Geue, Thomas and Pietsch, Ullrich},
  title     = {Dielectric loss spectroscopy at fatty acid salt multilayers},
  year      = {2000},
  abstract  = {Dielectric loss spectroscopy (DLS) was performed at compact samples and lamellary organized Langmuir-Blodgett (LB) films from various fatty acid salts. Previous thermoanalytical measurements at compact samples revealed the appearance of two different phase transition temperatures; the lower one is related to the acid the second one to the acid salt molecules. In spite of ill defined electrical contacts with the film the characteristic DLS frequencies obtained from about 100nm thick multilayer films are similar to those recorded from bulk samples. No significant variations of frequencies were found changing the counter ions. Besides conductivity influence at low frequncies we found two relaxations related to the mobility of the dipolar carboxylat-metal group at about 100 and 10000Hz. One of these frequencies is related to the rotation around the chain axis. The strength of this relaxation increases significantly with increasing the sample temperature above 105°C. This temperature is connected with a structural phase transition observed by X-ray reflectometry. In case of Pb-stearate the results of the dielectric measurements help to interprete this structural change as a transition from an orthorhombic into a free-rotator phase. The uncorrelated rotation of molecules around their molecular axes initiates a much increased relaxation strength at the carboxylat-metal sites.},
  language  = {en}
}
@article{PanznerGleberSantetal.2007,
  author    = {Panzner, Tobias and Gleber, Gudrun and Sant, Tushar and Leitenberger, Wolfram and Pietsch, Ullrich},
  title     = {Coherence experiments at the white-beam beamline of BESSYI},
  doi       = {10.1016/j.tsf.2006.12.002},
  year      = {2007},
  abstract  = {The third-generation X-ray source BESSYII (Berlin, Germany) provides coherent X-ray radiation which can be used for static and dynamic speckle analysis. Recently we have demonstrated that one can perform experiments with coherent white radiation provided by a bending magnet (5 < E < 20 keV). In this paper we show that the diffraction figure of the initial pinhole must be considered for the interpretation of coherent experiments. The reflectivity spectrum of a sample results from the Fresnel diffraction of the incident pinhole deformed by the static speckle features of the sample surface. For dynamical experiments all speckle like features alter with time whereas the pure Fresnel fringes remain constant. (c) 2007 Published by Elsevier B.V.},
  language  = {en}
}
@article{PaschkeGeueBarberkaetal.1997,
  author    = {Paschke, K. and Geue, Thomas and Barberka, Thomas Andreas and Bolm, A. and Pietsch, Ullrich and R{\"o}sch, M. and Batke, Edwin and Faller, F. and Kerkel, K. and Oshiniwo, J. and Forchel, Alfred},
  title     = {Characterization of lateral semiconductor nano structures by means of x-ray grazing-incidence diffraction},
  year      = {1997},
  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{Pietsch2003,
  author    = {Pietsch, Ullrich},
  title     = {Thin Layers of columns of an amphiphilic hexa-peri-hexabenzocoronene at silicon wafer surfaces},
  year      = {2003},
  language  = {en}
}
@article{Pietsch2002,
  author    = {Pietsch, Ullrich},
  title     = {X-ray reflectivity from sinusoidal surface relief gratings},
  year      = {2002},
  language  = {en}
}
@article{Pietsch2002,
  author    = {Pietsch, Ullrich},
  title     = {Reversible negative thermal expansion of polymer films},
  year      = {2002},
  language  = {en}
}
@article{Pietsch2000,
  author    = {Pietsch, Ullrich},
  title     = {Investigations of semiconductor surfaces and interfaces by X-ray grazing incidence diffraction},
  issn      = {0011-3891},
  year      = {2000},
  language  = {en}
}
@article{PietschBarberkaGeueetal.1997,
  author    = {Pietsch, Ullrich and Barberka, Thomas Andreas and Geue, Thomas and St{\"o}mmer, Ralph},
  title     = {X-ray scattering from thin organic films and multilayers},
  year      = {1997},
  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{PietschBhattacharyaSanyaletal.2005,
  author    = {Pietsch, Ullrich and Bhattacharya, M. K. and Sanyal, M. K. and Geue, Thomas},
  title     = {Glass transition in Ultrathin Polymer Films : a Thermal Expansion Study},
  year      = {2005},
  abstract  = {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},
  language  = {en}
}
@article{PietschBodenthinGrenzeretal.2005,
  author    = {Pietsch, Ullrich and Bodenthin, Yves and Grenzer, J{\"o}rg and Geue, Thomas and M{\"o}hwald, Helmuth and Kurth, Dirk G.},
  title     = {Structure and temperature behavior of metallo-supramolecular assemblies},
  year      = {2005},
  abstract  = {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},
  language  = {en}
}
@article{PietschBodenthinMoehwaldetal.2005,
  author    = {Pietsch, Ullrich and Bodenthin, Yves and M{\"o}hwald, Helmuth and Kurth, Dirk G.},
  title     = {Inducing spin crossover in metallo-supramolecular polyelectrolytes through an amphiphilic phase transition},
  year      = {2005},
  abstract  = {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},
  language  = {en}
}
@article{PietschDarowskiUlyanenkovetal.2000,
  author    = {Pietsch, Ullrich and Darowski, Nora and Ulyanenkov, A. and Grenzer, J{\"o}rg and Wang, K. H. and Forchel, Alfred},
  title     = {Analysis of the strain distribution in lateral nanostructures for interpreting photoluminescence data},
  year      = {2000},
  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{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}
}