Optically Monitored Electric-Field-Induced Phase Transition in Vanadium Dioxide Crystal Film

Abstract

Vanadium dioxide (VO2), due to its electrically induced metal-to-insulator transition with dramatic changes in electrical and optical properties, is considered to be a powerful material for electro-optical devices. However, there are still some controversies about phase transition mechanism under voltage. Here, based on optical characterizations on VO2 crystal nanofilm during the whole process of phase transition, temporal evolution and spatial distribution of changes in electricity, optic and temperature are investigated simultaneously, to explore the mechanism. The variations of Raman spectrum and reflected spectrum, and changes in current and temperature are evidences for occurrence of phase transition, which exhibit different changing behaviors with time and space. These results offer a better understanding of the phase transition mechanism, implying that lattice structure of VO2 changes gradually after applying voltage until the structure is completely converted to metallic structure, which causes a rapid increase in carrier density, resulting in a rapid change in current, reflected spectrum and temperature. Temperature rise before phase transition and applied electric field alone are not enough for triggering metal-insulator transition, but these two factors can act synergistically on structural transformation to induce phase transition.