Phase identification of vanadium oxide thin films prepared by atomic layer deposition using X-ray absorption...

The chemical and local structures of vanadium oxide (VO ) thin films prepared by atomic layer deposition (ALD) were investigated by soft X-ray absorption spectroscopy. It is shown that the as-deposited film was a mixture of VO₂ and V₂O₅ in disordered form, while the chemistry changed significantly after heat treatment, subject to the different gas environment. Forming gas (95% N₂ + 5% H₂) annealing resulted in a VO₂ composition, consisting mostly of the VO₂ (B) phase with small amount of the VO₂ (M) phase, whereas O₂ annealing resulted in the V₂O₅ phase. An X-ray circular magnetic dichroism study further revealed the absence of ferromagnetic ordering, confirming the absence of oxygen vacancies despite the reduction of V ions in VO₂ (V⁴⁺) with respect to the precursor used in the ALD (V⁵⁺). This implies that the prevalence of VO₂ in the ALD films cannot be attributed to a simple oxygen-deficiency-related reduction scheme but should be explained by the metastability of the local VO₂ structures.