Fractal Nature of Metallic and Insulating Domain Configurations in a VO2 Thin Film Revealed by Kelvin Probe Force Microscopy

Abstract

We investigated the surface work function (W-S) and its spatial distribution for epitaxial VO2/TiO2 thin films using Kelvin probe force microscopy (KPFM). Nearly grain-boundary-free samples allowed observation of metallic and insulating domains with distinct W-S values, throughout the metal-insulator transition. The metallic fraction, estimated from W-S maps, describes the evolution of the resistance based on a two-dimensional percolation model. The KPFM measurements also revealed the fractal nature of the domain configuration.