Electron Dynamics in Transition Metal Granular Films

Near normal incidence reflectivity spectra of transition metal $\sim $500 nm thick cosputtered granular films on SiO$_{2}$ subtracts were measured from 30 to 11000 cm$^{-1}$ and at temperatures from 30 to 490 K. The reflectivity for Co$_{0.85}$(SO$_{2})_{0.15}$ has a frequency and temperature behavior according to conducting metal oxides. The electron scattering rate denotes an unique relaxation time characteristic of a single type of carriers and has a very strong temperature dependence due to strong electron-phonon interactions. Using small polaron fits we individualize these as related to glass stretching vibrational modes. The optical conductivity of Ni$_{0.61}$(SO$_{2})_{0.39}$, undergoing a metal-insulator transition at $\sim $77 K, has a Drude mode (freer carriers) and a mid-IR band (mid-infrared ``carriers''). This last disorder related strong resonance drives the phase transition by localization decreasing in magnitude as the temperature is lowered and points to a double relaxation process (two different scattering mechanisms). On the other hand, Co$_{0.51}$(SO$_{2})_{0.49}$ has an insulator reflectivity in which a distinctive band at $\sim $1450cm$^{-1}$ originates in electron promotion, localization, and defect induced quasiparticle formation.