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

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 VO and VO in disordered form, while the chemistry changed significantly after heat treatment, subject to the different gas environment. Forming gas (95% N + 5% H) annealing resulted in a VO composition, consisting mostly of the VO (B) phase with small amount of the VO (M) phase, whereas O annealing resulted in the VO 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 VO (V) with respect to the precursor used in the ALD (V). This implies that the prevalence of VO 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 VO structures.