Vanadium dioxide (VO2), a strongly correlated electron and metal-insulator transition (MIT) material, is an extremely interesting material suitable for many technological applications including the memory devices and smart window. However, the critical MIT temperature of VO2 is about 68º C, which unfortunately is still too high for practical applications. Thus decreasing the phase transition temperature to room temperature is always one of the hottest topics for VO2 study. It has been proved that tuning the metal insulator transition (MIT) behavior of VO2 film through the interfacial strain is effective for decreasing the MIT temperature. However, the mechanism for strain modulated MIT is still under debate. Here the researchers from the functional oxide film group directly record the strain dynamics of ultrathin VO2 film on TiO2 substrate and reveal the intrinsic modulation process by means of synchrotron radiation based X-ray diffraction and the related reciprocal space mapping (RSM) technique. It is observed that the MIT process of the obtained VO2 films can be modulated continuously via the interfacial strain. The relationship between the phase transition temperature and the strain evolution is established from the initial film growth. From the interfacial strain dynamics and theoretical calculations, we claim that the electronic orbital occupancy is strongly affected by the interfacial strain, which changes also the electron−electron correlation and controls the phase transition temperature. These findings open the possibility of an active tuning of phase transition for the thin VO2 film through the interfacial lattice engineering. [Nano Letters 2014，14，4036]

(Left) The synchrotron X-ray diffraction and reciprocal space mapping for the epitaxial VO2 films with different thickness; (Right) the thickness dependent R-T curves for VO2 films