Real-space and nanoscopic observation of phase transition behaviors of VO$_{2}$ thin films using Kelvin probe force microscopy

VO$_{2}$ undergoes a metal-insulator transition (MIT) and a tetragonal-monoclinic structural phase transition (SPT) near room temperatureWe carry out transport and KPFM (Kelvin probe force microscopy) measurements on epitaxial VO$_{2}$/TiO$_{2}$ thin films simultaneously in the temperature range of 285-330 K. The samples have large grains due to very small lattice mismatch, which allows us to study inherent nature of the phase transition in quasi-2D VO$_{2}$ system. The sample's work function decreases from 5.1 eV to 4.9 eV, while spanning the transition temperature. The work function maps can clearly reveal coexistence of the two distinct states at the intermediate temperate range, well explained by the 2D percolation theory.