Resonant Hard X-ray Emission Spectroscopy of VO₂ Thin Films in Metallic and Insulating Phases

Resonant X-ray emission spectroscopy (XES) was carried out to study the metal-insulator transition (MIT) of vanadium dioxide. The Vanadium K-beta emission spectra including k_β2,5 and k_β1,3 both in the metallic and insulating phase were monitored with an x-ray energy resolution of about 1.6 eV at the 3rd generation Pohang Accelerator Laboratory using a highly oriented pyrolytic graphite (HOPG) spectrometer in von-Hamos geometry. The K-beta emission intensities were monitored as the excitation x-ray energy was scanned through the Vandium K-edge to obtain the X-ray absorption near edge structure (XANES) profile. In both the emission spectra and the XANES profile, the difference between the insulating and metallic phase was clearly observed. We also observed distinct resonant behavior in the elastic/inelastic scattering intensity. The physical interpretation of the resonant behavior will be discussed in relation with the energy band structure of the insulating and metallic phase of VO_2.