Control of stoichiometry and morphology in polycrystalline V2O3 thin films using oxygen buffers

In this work, we investigate the influence of low temperature reduction conditions (873 K) by different oxygen buffers on the off-stoichiometry of polycrystalline V2O3 thin films. Vanadium oxide thin films (thickness 300 nm and 100 nm) have been grown by reactive sputtering and have been annealed in a buffered atmosphere subsequently. Buffer couples were chosen throughout the stability range of V2−yO3 (y ≤ 0.03) by the use of different oxygen buffer combinations, namely Ni/NiO, Fe/Fe3O4, Cr/Cr2O3 and Mn/MnO. Thin films have been characterized by scanning electron microscopy, X-ray diffractometry and low temperature electrical transport measurements. Upon decreasing the oxygen partial pressure, the mean grain size of V2O3 decreases systematically from 45 ± 20 nm with a high porosity to 27 ± 10 nm without porosity. The most favourable reduction conditions have been identified for Fe- and Cr-based couples. Moreover, all thin films reduced by the four buffer couples exhibit high insulator-to-metal transition temperatures (110–155 K) close to the value of ideally stoichiometric V2−yO3 (y < 0.005) (155 K) as well as large changes in resistance at the transition (three to five orders of magnitude). This oxygen buffer method hence provides a valuable synthesis method of highly stoichiometric polycrystalline V2O3 thin films with technological relevance.