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  • 1995-1999  (4)
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  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A detailed structural determination of the Ni{111}–((square root of)7×(square root of)7)R19.1°–C6H6 overlayer has been performed using automated fully dynamical low energy electron diffraction I–V analysis. In the most likely geometry (RP = 0.26, total energy range: 1552 eV) benzene adsorbs with its center 1.91 A(ring) above an hcp site and with its C–C bonds oriented parallel to the close-packed rows of the substrate. The molecular radius is found to be slightly expanded relative to the gas phase (1.48 A(ring) and 1.50 A(ring) vs 1.40 A(ring)) and no significant vertical buckling can be seen (〈 0.04±0.05 A(ring)). The topmost Ni layer is strongly buckled (0.14 A(ring)) with the height of the Ni atoms decreasing with increasing lateral distance from the molecule (+0.08, 0.00, and –0.06 A(ring) with respect to the clean surface). A second similarly low RP factor minimum for adsorption on a bridge site was dismissed because of significantly higher R1 and R2 values and the extreme molecular distortions of this geometry. The resulting structure is fully consistent with recent UPS and PED studies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2454-2456 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Monomer solubility is identified as the primary factor determining network morphology in polymer stabilized cholesteric liquid crystal textures. Poorly soluble monomers form coarse structures composed of discrete, oblong grains, whereas soluble monomers yield smooth, continuous polymer networks. A crossover from smooth to grainy structure is observed as a function of monomer concentration. The grainy structure results from precipitation polymerization and the observed behavior is well described by the Flory–Huggins theory of polymer solubility. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have developed a video low-energy electron diffraction (LEED) system on the basis of a slow scan charge coupled device (CCD) camera which is capable of collecting LEED IV data at very low electron doses quickly and therefore enables us to study extremely beam sensitive surface structures which have not been accessible to LEED IV analysis before. The slow scan CCD camera allows separating the relatively short data acquisition process from the more lengthy digitizing, storage, and data analysis processes. Typical total effective exposure times can therefore be reduced to about 200–300 s (1 s per energy point) at a primary beam current of 100 nA which corresponds to a total dose of about 12 e per adsorbate particle; further decrease is possible. The total measurement time for collecting a complete set of LEED images is of the order of 30–40 min which assures the exclusion of contamination effects, even for sensitive layers. The IV curves are then extracted from the digitally stored images off-line which allows collecting the intensities of all visible spots simultaneously with a high reliability in tracing beams, even for very dense LEED patterns. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3007-3014 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electro-optical behavior of polymer stabilized cholesteric texture cells has been investigated for three different polymers. The switching process was studied with respect to the electric field dependence of the diffuse reflectivity, diffuse transmittance, and the dynamics of the reorientation process. For certain polymer concentrations, a two-stage reorientation process was observed. This behavior is consistent with the cholesteric liquid crystal being divided between two distinct environments. In the first, the liquid crystal is strongly dominated by the polymer network, while in the second a bulklike behavior, comparable to the unstabilized cholesteric material, is observed. Scanning electron micrographs of the polymer networks further support this model. Measurements of the diffuse scattering indicate that the polymer influenced regions contribute largely to the observed back scattering, whereas the bulklike material contributes primarily to forward scattering. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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