CRYSTAL STRUCTURAL CONTROL OF ULTRA-THIN ORGANIC FILMS BY MIXING LB TECHNIQUE INTRODUCING SPACER MOLECULES

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Lateral spacing of the molecules in the Langumuir-Blodgett (LB) films were controlled by introducing "Spacer Molecules" such as pyrrole or fullerene (C60) molecules into arachidic acid (C20) LB films. The transformation of the molecular arrangement of C20 LB film was studied with an increase of pyrrole (py) quantity or C60 quantity which we used as guest molecules to the host molecules, C20. The change of molecular occupation area of a C20 LB films was estimated by pressure-area curves, quartz crystal microbalance method and atomic force microscopy (AFM). It was found that that a C20 LB film can contain 1.5 times as large as C20 molecules. The observation by AFM showed that the enlargement of the occupation area of C20 upon addition of spacer molecules, however, the molecules of C20 maintained the highly ordered molecular arrangement. The change of the crystal structure observed by AFM agreed well with the results of computer simulation based on molecular mechanics. The experimental and computer simulation results showed that the lattice constant of a C20 LB film is easy to control by the quantity of spacer molecules contained in the LB film.Using these characteristics, several kinds of mixed LB films, composed of C20 and C60, were prepared and the adsorption characteristics of gas molecules to these films were studied using a quartz crystal microbalance. The dependence of the amount of the gas adsorbed on the number of layers reveal that the permeability of the gas molecules into the LB films remarkably increase with an increase of the intermolecular spacing of LB films. Gas molecules with different sizes or structure were sifted by using C60 containing LB films. This characteristic of the LB films containing C60 can be applied to a novel gas sensor with a molecular sifter function.