X-ray absorption spectroscopy studies of Vanadium dioxide thin films across the metal-insulator phase transition boundary

X-ray absorption (XAS) and photoemission (XPS) spectroscopy of the V 2p edges and O 1s edge was performed on VO$_{2}$ thin films synthesized by RF sputtering at various conditions. Distinct changes of the electronic structure depending on the film quality, whether the sample is above or below the metal insulator transition (MIT) temperature, and thermal history of the sample are observed. The spacing between 3d$_{\pi }$ and 3d$_{\sigma }$ band peaks probed by O- edge XAS decreases by 0.8eV with concurrent peak broadening for the sample sputtered at lower substrate temperature and consequently having more polycrystalline and disordered character. There is a similar tendency in the V 2p$_{3/2}$ and 2p$_{1/2}$ edges, i.e. the convergence of the doublets for the disordered sample. The temperature dependence of the XAS V and O edges including repeated crossing of the MIT has been studied. The reversible switches of the 3d$_{\pi }$ and 3d$_{\sigma }$ band peak widths in the O-edge on different sides of the MIT are measured while the peak separation remains the same. The abruptness of the band structure transformation at MIT suggests that the band width changes are determined by the VO$_{2}$ MIT phase rather than gradual evolution with temperature.