Ion irradiation induced modification in the electrical properties and the electronic structures of vanadium dioxide thin films

Ion irradiation modifies the physical properties of oxide materials. The present study focuses on the effect of 150 keV Fe and Ni ion irradiations in VO2 thin films. These films were deposited by pulsed laser on an r-cut sapphire substrate (1 1 02). The range of ion fluences was from 1 x 1014 to 1 x 1016 ions/cm2 and these samples were characterized by using grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, Temperature -dependent resistivity measurements (R-T), and Hall effect measurement. While the presence of monoclinic phases is confirmed by GIXRD and Raman measurements, the ion irradiation on VO2 modifies the metal to insulator transition temperature (MIT). The R-T measurement with supporting analysis of carrier concentration authenticates a decrease in transition temperature and an increase in conductivity with an increment of ion-fluences. Synchrotron-based X-ray photoemission spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) revealed that Vanadium ions are in mixed oxidation states of 4+ and 5+ after ion irradiation. Further, the Photo-Electron Spectroscopy (PES) measurement indicates the metallization of VO2 after ion irradiation consistent with R-T measurements.