Unraveling oxygen vacancy formation, dynamics and site distribution in MoO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si440.svg" display="inline" id="d1e3035"><mml:msub><mml:mrow/><mml:mrow><mml:mtext>3-x</mml:mtext></mml:mrow></mml:msub></mml:math> thin films
Francesco Paparoni, Georghii Tchoudinov, Andrea Di Cicco, Emiliano Fonda, Andrea Zitolo, Zeinab Ebrahimpour, R. Gunnella, N. Lockwood, S.J. Rezvani
Abstract
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 MoO 3-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 α -MoO 3-x , our results show a high meta-stable equilibrium concentration of O vacancies ( ∼ 2.7%) at high temperatures and low oxygen pressure conditions. Our results suggest that O 1 and O 3 vacancies are formed during the thermal treatment, but only O 3 vacancies persist upon air exposure. The structural effects of the vacancy formation and the resulting Mo redox mechanism are discussed. • The vacancy formation mainly occurs in O 1 and O 3 sites. • The vacancy site preference can be controlled via thermodynamical parameters. • MoO 3 redox shows interchangeable multistep dynamics including Mo 4 O 11 formation. • The surface-to-bulk O vacancy diffusion is affected by the oxygen partial pressure.