Abstract

We report the infrared specular reflectivity of Cox(SiO2)1-x (x ∼ 0.85, 0.55, 0.38) films on SiO2 glass spanning from a metal-like to insulating behavior. While films for x ∼ 0.85 show carrier metallic shielding and hopping conductivity, for x ∼ 0.65 and lower concentrations, the nanoparticles' number and size promote a localization edge near the highest longitudinal optical frequency. Such an edge is associated with a reflectivity minimum and a higher frequency band connoting strong electron-phonon interactions, carrier phonon assisted hopping, and polaron formation. Optical conductivity fits with current polaron models provide grounds toward a microscopic understanding of transport properties in these as-prepared granular films. © 2007 Elsevier Ltd. All rights reserved.