Structural evolution of SnO2TiO2 nanocrystalline films for gas sensors

Thin films (50–200 nm) of SnO2TiO2 were deposited on SiO2/(001)Si substrates by RF-sputtering and by molecular beam before they were annealed in vacuum at 200–900°C. In-situ TEM, XRD, SEM, Raman and IR-spectroscopy were used to analyze the structure transformations in the SnO2TiO2 films. In the as-deposited state, the films are amorphous. They crystallize at higher temperatures (starting at about 500°C) forming nanosized grains. The problem of the spinodal decomposition in the SnO2TiO2 system observed earlier at high temperatures is discussed also for low-temperature processing. The stoichiometry of the films of both groups (reactive ion sputtered and high-vacuum e-gun sputtered) is being compared.