Chemical, structural and electronic properties of ultrathin V2O3 films on Al2O3 substrate: Implications in Mott-like transitions

VO presents a complex interrelationship between the metal-insulator transition and the structural rhombohedral-monoclinic one in temperature, as a function of sample thickness. Whilst in bulk VO the two transitions coincide on the temperature scale, at 15 nm thickness a fully independent Mott-like transition occurs at lower temperature, with no corresponding structural changes perhaps related to epitaxial strain. It is therefore of relevance to investigate the thin and ultrathin film growth to pinpoint the chemical, electronic and structural phase phenomenology and the role of the interface with the substrate. Here we present results on the thickness dependent properties of VO from 1 nm up to 40 nm thick as grown on c-plane AlO substrates by exploiting variable sampling depth probes. The surface morphology of stoichiometric ultra-thin VO layers evolves from islands-like to continuous flat film with thickness, with implications on the overall properties.