VAPOR ADSORPTION IN THIN SILICALITE-1 FILMS STUDIED BY SPECTROSCOPIC ELLIPSOMETRY

Thin films of silicalite-1 grown on silicon substrates were studied by spectroscopic ellipsometry. Analysis of spectra using an optical mode l consisting of a single porous layer on silicon yielded average film thicknesses of 84 and 223 nm for films synthesized for 10 and 30 h. Vo id fraction for the films was 0.32-0.33. Vapor adsorption from a nitro gen carrier gas at room temperature was monitored by ellipsometry. Iso therms for different adsorbates were obtained by analysis of spectra t aken at different Vapor concentrations using an optical model where th e void volume was filled with both nitrogen and condensed vapors. Quan tification of the condensed vapor amount was based on the changes in r efractive index when adsorbates replaced nitrogen in the pores. Adsorb ate volumes for water, toluene, 1-propanol, and hexane were 0.13, 0.12 , 0.15, and 0.17 cm(3) liquid g(-1) film, respectively.