We report on conductive changes caused by electric bias-driven insulator-to-metal transition in VO2 thin films on a TiO2(001) substrate and observe the evolution of giant metallic domains to reveal their microscopic origin. The metallic domains are anisotropically formed along the direction of applied current or voltage. This anisotropic formation of metallic states causes abrupt increase of conductivity when the fraction rate of metallic states is low, conforming with the directed percolation model. Our results illustrate the importance of spatially localized phase transitions to tune conductive behavior.

We observed micro-scale phase separation in VO2 thin films on TiO2(001) substrates and investigated the relationship between the appearance of metallic domains and the abrupt resistive changes around the phase transition. The resistive changes are interpreted using a combined resistance model of the two phases, and the conductance evaluated from the visualized domain behavior was consistent with the electronic properties. These results indicate the importance of modifying conductive behavior spatially using a partial phase transition.

We demonstrate control of spatial dimensionality of disordered configurations of giant electronic domains in systematically size-changed VO2 wires on TiO2 (001) substrates. One-dimensional alignment of the domains appears in wires narrower than 15 μm width, while two-dimensional configurations were observed for larger ones. The rearrangement of domains from two to one dimension causes modification of electronic properties.

We use bulk-sensitive hard X-ray core-level photoemission spectroscopy to investigate the electronic structure of 1 at. % W-doped VO2 (VWO) thin films exhibiting a high temperature coefficient of resistance, above -10%/K at room temperature. According to the W 4d core-level spectra, the chemical state of doped W takes only a 6+ valence state, which suggests the introduction of V3+. The satellite structure of the V 2p3/2 main peak, which corresponds to the metallic-coherent screened states, was enhanced for VWO compared with VO2 indicating that electron doping plays an important role in the control of metal–insulator transition.