Effect of Filler Content on the Morphology and Properties of Poly(n-Xylylene)–Sn Nanocomposite Films

Abstract

The effect of the filler content on the optical absorption spectra, electroconductivity, and surface morphology of thin nanoocomposite films based on poly(n-xylylene)–tin (PPX–Sn) has been studied. The films under study are prepared in vacuum by cryochemical synthesis on polished quartz, glass-ceramics, and silicon substrates. After completing the preparation, the samples are exposed to air for some time prior to measurements. With an increase in the filler content, a nonmonotonic change in both surface morphology of films (by atomic force microscopy) and adsorption spectra is found. An analysis of the spectra shows that, at the filler concentration C ≤ 9 vol %, tin in the composite is in the oxidized form of SnO2, while at C = 12 vol % it is in a metal state, respectively. With an increase in C from 4 to 12 vol %, the increase in conductivity of nanocomposites is more than 7 decimal orders, with a sharp change in the region of C ≈ 9–12 vol %. The conductivity of the film consisting of nanoparticles (C = 100 vol %) is found to be low and comparable with that for composites with C = 4–5 vol %. With a decrease in the temperature from 300 to 15 K, the resistance of the sample with C = 12 vol % is found to decrease, while that for all other samples increases by the activation law. The activation energy with an increase in the filler concentration to 9 vol % is found to decrease, while that for the sample with C = 100 vol % increases by almost an order of magnitude. The most significant changes in the properties and morphology of the surface of nanocomposites are observed at a concentration of ~9 vol %, which apparently is the percolation threshold.