Unraveling oxygen vacancy formation, dynamics and site distribution in MoO3-x thin films

Targeted oxygen vacancy creation in metal oxide film is a new approach to achieve innovative meta-materials. However, the precise dynamics of the formation, density distribution and site preference within the local lattice remains unclear. In this work, using several experimental and theoretical approaches, we try to untangle the O vacancy formation, dynamics and consequent electronic and structural modifications within MoO3-x via thermodynamical parameters. We demonstrate the tunability of the film's stoichiometry and the vacancy concentration within the bulk matrix from metallic to defective isolating material. Superficial and bulk ionic reconfiguration is discussed. For alpha-MoO3-x, our results show a high meta-stable equilibrium concentration of O vacancies (similar to 2.7%) at high temperatures and low oxygen pressure conditions. Our results suggest that O1 and O3 vacancies are formed during the thermal treatment, but only O3 vacancies persist upon air exposure. The structural effects of the vacancy formation and the resulting Mo redox mechanism are discussed.