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Publications (4)0 Total impact

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    ABSTRACT: Relative electron density profiles derived from high-resolution meridional x-ray diffraction data for ultrathin multilayers, fabricated by repeating from one to five bilayers of arachidic acid deposited on alkylated glass substrates via the Langmuir-Blodgett technique, have consistently displayed an asymmetry within each bilayer in the multilayer. Although the last bilayer deposited systematically displays the most significant asymmetry [V. Skita et al., J. Phys. (Paris) 47, 1849 (1986)], in fact each interior bilayer profile retained some residual asymmetry. This asymmetry in the interior bilayer profiles, which may depend upon the particular deposition conditions utilized, concerns the relatively electron dense feature associated with the apposed carboxyl end groups not being centered between the adjacent relatively electron deficient features associated with the apposed methyl end groups: the carboxyl peak is systematically shifted by 2.5-3.0 Å away from the substrate surface in each interior bilayer profile. We have shown via model calculations that this asymmetry in the interior bilayer profiles is indeed accurately manifest in the experimental intensity functions and the derived multilayer profiles, and therefore indicates a necessary difference in the configurations of the hydrocarbon chains of alternate monolayers. Hence, the Langmuir-Blodgett technique need not necessarily result in the intended formation of an N bilayer multilayer composed of a symmetric bilayer profile repeated N times for such ultrathin multilayers.
    Physical review. B, Condensed matter 04/1988; 37(9):4788-4791.
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    ABSTRACT: High-resolution, meridional x-ray diffraction data were recorded from ultrathin Langmuir-Blodgett multilayer films containing five bilayers of either arachidic acid (AA), pentacosa-10,12-diynoic acid (a disubstituted diacetylene monomer, DAM), the blue polymeric form of DAM (DAPb), or the red polymeric form (DAPr). In addition, periodic and nonperiodic three-bilayer multilayers containing various sequences of AA and DAPb or DAPr bilayers were similarly investigated at slightly lower resolution. A Patterson function deconvolution technique provided uniquely the relative electron density profiles for the average, symmetric bilayer within the five-bilayer multilayers. The average bilayer profiles were of sufficiently high spatial resolution (~=6Å) that one could distinguish the chain carboxyl and methyl end groups and a significant difference in the relative electron densities of the polymethylene groups in the carboxyl end and methyl end side chains of the polymer. These profile features established the average configurations of the polymer side chains. A refinement technique provided the relative electron density profile of the entire multilayer such that each individual monolayer in the multilayer was distinguished. The five-bilayer multilayer lattice exhibits long-range order for AA, DAM, and DAPb: This long-range order was effectively destroyed upon conversion of DAPb to DAPr. The relative electron density profiles for the three-bilayer multilayers allowed one to distinguish the different bilayer compositions within the multilayer. It was found that the incorporation of DAPb bilayers into a host AA multilayer preserved the long-range order of the multilayer lattice, while the incorporation of a single bilayer of DAPr was sufficient to effectively destroy the long-range order.
    Physical review. B, Condensed matter 04/1988; 37(9):4714-4726.
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    ABSTRACT: Meridional x-ray diffraction data from Langmuir-Blodgett multilayers containing two to ten molecular monolayers of arachidic acid were analyzed by two independent methods. A Patterson-function deconvolution technique uniquely provided the electron density profile (8 Å resolution) of the average, symmetric bilayer repeated in the multilayer. This average bilayer appeared to disorder as the number of bilayers in the multilayer decreased. A refinement technique uniquely provided the profile structure of the multilayer itself; in particular, it could distinguish the individual monolayers in the multilayer. The refinement demonstrated that only one of the monolayers (either the first or the last monolayer in the deposition sequence) in each multilayer was disordered.
    Physical review. B, Condensed matter 11/1986; 34(8):5826-5837.
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    ABSTRACT: X-ray scattering results from Langmuir-Blodgett thin films demonstrate that the surface monolayer at the multilayer-air interface is disordered and that ordering of the surface monolayer can be induced by the deposition of an additional monolayer. The data was analysed by a novel refinement technique which does not assume a centrosymmetric structure or the existence of a unit cell. On présente une expérience de diffusion des rayons X par des films de Langmuir-Blodgett. Les résultats montrent que la monocouche de surface à l'interface film multicouches/air est désordonnée, et qu'elle peut être réordonnée par dépôt d'une monocouche supplémentaire. Les données sont analysées au moyen d'une nouvelle technique qui calcule la fonction d'autocorrélation du profil du film sans supposer la structure centrosymétrique et sans postuler l'existence d'une cellule unité. 01/1986;