Low temperature reduction in Ta–O and Nb–O thin films

Abstract

The effect of thermal reduction in ultra-high vacuum was studied in films of tantalum and niobium oxides obtained by oxidation of deposited metallic layers. The obtained films appeared to be amorphous and their stoichiometry was not uniform. For the Ta based film the main component was Ta2O5 while for the oxidized Nb film the pentoxide was present in the topmost part of the film and the thickest layer had the electron density assigned to NbO2. Thermal reduction was studied with the use of in situ photoelectron spectroscopy which revealed for the Nb–O film a strong effect for temperature as low as 300 °C. The Nb–O film reduced at 600 °C exhibited dominating metallic-like electronic states assigned to NbO. For the Ta–O film the significant reduction process started above 600 °C. At 900 °C the film showed metallic-like states which can be attributed to Ta2O. A single crystal of Nb2O5 showed no effect of reduction for temperatures up to 500 °C. A test performed with the use of local conductivity atomic force microscopy showed the most interesting bipolar-like resistive switching properties for the films reduced at temperatures up to 300 °C.