Direct Visualization of Metal–Insulator Transition Dynamics in VO₂ Thin Films

Abstract

The metal–insulator transition (MIT) in VO₂ is strongly governed by nanoscale morphology and structural defects. To elucidate the microscopic origin of this transition, we investigated the relationship between surface structure and MIT dynamics in VO₂ thin films epitaxially grown on TiO₂(110) via pulsed laser deposition. Operando X-ray diffraction confirmed a structural transformation from the monoclinic (insulating) to rutile (metallic) phase. Infrared scattering-type scanning near-field optical microscopy (s-SNOM) enabled direct visualization of individual anisotropic nanodomains with nanoscale resolution. The contrast in near-field amplitude allowed us to spatially resolve metallic and insulating phases across the surface. We observed that metallic domains nucleate and expand heterogeneously, influenced by local grain geometry and anisotropic strain along the [001] direction. These findings provide insight into the interplay between structural features and phase transition pathways in strongly correlated oxide systems.