Stoichiometry control in molecular beam deposited nanocrystalline SnO2 and TiO2 thin films

Molecular beam deposition (MB) of thin film metal oxide is prospective for application in gas sensor technology due to the well-controlled oxide molecular fluxes during creation of multi-oxide structures with improved characteristics. However, the MB process leads to some oxygen deficiency in the oxide. Further application of the MB technology (and, in general, the e-beam oxide deposition in vacuum) for processing of sensor structures needs the control and correction of the oxygen stoichiometry by adding in-situ atomic oxygen to the growing material or via the thin film oxidation after deposition. Thin films (50 to 500 nm) of SnOx and TiOx were deposited on SiO2/(001)Si substrates at 100 degrees C by MB from SnO2 and TiO2 sources. The film stoichiometry in the as-deposited state and after annealing in vacuum and in oxygen is characterized by XRD, TEM and RES. Oxygen annealing transformed the strongly non-stoichiometric SnO (Romarchite) in the as-deposited state to Cassiterite, SnO2. Structure transformations in the TiO2 films during annealing are also discussed.