PM-12Microstructure Analysis of Phase Separation in VO2 Thin Films

Vanadium dioxide (VO2) exhibits a metal-insulator phase transition which is accompanied by a change in the crystal structure, from the tetragonal lattice to the monoclinic lattice, upon cooling. Although the phase transition temperature in an unstrained bulk crystal is approximately 340 K, it can be manipulated by application of a mechanical pressure [1]. The aim of this study is to reveal the basic morphology of the phase separation in a strained VO2 film, in which the tetragonal phase can coexist with the monoclinic phase near room temperature. Transmission electron microscopy observations demonstrated that the tetragonal phase remained robust in the neighbourhood of the TiO2 substrate. The interface between the tetragonal and monoclinic phases was identified to be of {101} plane with reference to the tetragonal lattice. An intensive analysis using lattice images revealed that the residual tetragonal phase was subjected to a compressive strain along the [001] axis. 1. J Wu et al, Nano Lett., 6 (2006), 2313–2317.