Interface effect on metal-insulator transition of strained vanadium dioxide ultrathin films

The interface effects on the metal-insulator transition (MIT) of strained VO2 ultrathin films grown epitaxially on TiO2 (001) single crystal substrate were investigated. Varying the surface conditions of TiO2 substrate, such as the roughness and the surface reconstructions, produced the remarkable changes in the MIT events of VO2 thin films, including the transition temperature and the abruptness. The presence of the surface reconstructions was found to be detrimental for applying effectively strain effects due to the strain relaxation in the c axis of VO2 thin films. The abrupt MIT in strained VO2 thin films, deposited on the substrate without such detrimental surface reconstructions, was successfully maintained down to around 5 nm film thickness.