Mechanism of strain relaxation: key to control of structural and electronic transitions in VO2 thin-films

Abstract

VO2 is a smart transition-metal oxide, which exhibits a tetragonal-to-monoclinic phase transition at ∼ 68°C. We report a case where both tetragonal and monoclinic phases exist in relaxed and strained domains, respectively, above the transition temperature. The epitaxial nucleation of these relaxed domains of VO2 over the strained one occurs when the critical thickness criterion is met through the emergence of interfacial dislocations under domain-matching epitaxy paradigm. Below this critical thickness, the film isostructurally (across the transition temperature range) adopts a strained-monoclinic phase. Above the critical thickness, domains are structurally free to transform from tetragonal to monoclinic.