Vanadium dioxide (VO2) is one of promising materials for electrical/optical switches and sensors because of its temperature-driven metal–insulator transition (MIT) accompanied by significant changes in conductivity and optical properties at above room temperature. Because the MIT is accompanied by a structural phase change, the lattice dynamics and the rearrangement of atomic positions through the change have an impact on changes in electronic states that have to be controlled in device applications. Raman scattering spectroscopy is one of the most popular tools for investigating phonon modes. However, because of the lack of high-quality single crystals or epitaxial thin films of VO2, the symmetry of Raman-active phonon modes and their Raman tensors remain to be completely elucidated.
In this study, we have investigated the symmetries and the Raman tensors of the phonon modes of VO2 evaluated by the polarization angular dependence of Raman scattering for epitaxial VO2 films on MgF2 substrates. By comparing the tensor elements with a previous theoretical calculation, we identified the two characteristic phonon modes of the V–V dimers, which are believed to play an important role for opening a band gap at the Fermi level in the insulating phase. These findings provide clues to understanding the lattice dynamics of VO2 which are required for elucidating the mechanism of the MIT in VO2 and controlling the MIT in practical device applications.