Thickness-dependent evolution of structure, electronic structure, and metal-insulator transition in ultrathin V2O3(0001) films on Ag(001)

Abstract

Epitaxial hexagonal V2O3(0001) films were grown on cubic Ag(001) substrate for coverages ranging from 1-20 monolayers equivalent (MLE) and have studied their structure, electronic structure and the metal-insulator transition (MIT) using Low Energy Electron Diffraction (LEED), X-ray Photoelectron Spectroscopy (XPS) and Angle-Resolved Photoemission Spectroscopy (ARPES) techniques. Detailed LEED and XPS study reveal that, for the lower film coverages (∼1 MLE), a complex (coexisting phase of) vanadium oxide is formed while from 3 MLE coverage onwards, three-dimensional crystallites of V2O3 grows epitaxially. Our LEED results also show that the hexagonal surface of V2O3(0001) is stabilizing on top of square symmetry substrate by the formation of twin-domain structure, where each domain is rotated by 90o. Our photoemission results show that the surface of V2O3 is more insulating than its bulk, similar to the case of many strongly correlated oxide surfaces which is discussed based on the valence band electronic structure with varying probing depth. Evolution of the surface electronic structure was also studied as a function of the film thickness. Further, the effect of lattice strain, film thickness and the domain formation on the metal-insulator transition (MIT) are discussed. The change in the orbital occupancy of (a1g, egπ) and (egπ, egπ) orbitals of V 3 d, a vanishing of quasiparticle (QP) peak and opening an energy gap at the Fermi level is observed below a critical temperature as a consequence of the MIT.