Abstract
We report the infrared specular reflectivity of Co
x
(SiO
2)
1−
x
(
x
∼
0.85
, 0.55, 0.38) films on SiO
2 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.