Epitaxial Growth of V₂O₃ Thin Films on c-Plane Al₂O₃ in Reactive Sputtering and Its Transformation to VO₂ Films by Post Annealing

Epitaxial growth of thin vanadium sesquioxide (V 2 O 3 ) films on c -plane sapphire ( c -Al 2 O 3 ) substrates was achieved with reactive magnetron sputtering under restricted oxygen flow. Even with a film thickness of approximately 12 nm, highly c -axis textured growth of corundum V 2 O 3 was realized because of the smaller mismatch of V 2 O 3 against corundum Al 2 O 3 . Post annealing in O 2 atmosphere for as-grown V 2 O 3 films caused phase transformation to oxidized crystalline phases. At a moderate annealing temperature of 450 °C, the V 2 O 3 thin films transformed to VO 2 films, which show a resistivity change of over three orders of magnitude. The X-ray photoelectron spectroscopy spectra for the annealed VO 2 film showed a single charge state of V 4+ , indicating a homogeneous crystalline structure, in contrast to the inhomogeneous feature with mixed charge states of V in addition to V 3+ for as-grown V 2 O 3 film. This method is promising to prepare thin VO 2 films with metal–insulator transition in productive reactive sputtering and to examine crystalline phase transformation mechanisms, including phase coexistence.