Irreversible metal-insulator transition in thin film VO 2 induced by soft X-ray irradiation
In this study, we show the ability of soft x-ray irradiation to induce room temperature metal-insulator transitions (MITs) in VO 2 thin films grown on R-plane sapphire. The ability of soft x-rays to induce MIT in VO 2 thin films is confirmed by photoemission spectroscopy and soft x-ray spectroscopy measurements. When irradiation was discontinued, the systems do not return to the insulating phase. Analysis of valence band photoemission spectra revealed that the density of states (DOSs) of the V 3d band increased with irradiation time, while the DOS of the O 2p band decreased. We use these results to propose a model in which the MIT is driven by oxygen desorption from thin films during irradiation. As a strongly correlated transition metal oxide, VO 2 is an interesting and valuable material both for expanding our understanding of fundamental physics and for potential applications due to its particular metal-insulator transition (MIT). At 340 K, the resistance of bulk VO 2 exhibits a large jump (up to 5 orders of magnitude), accompanied by first order crystal phase transition from a room temperature monoclinic phase to a high temperature tetragonal phase.1,2 The origin of the MIT has been widely discussed since electron–phonon interaction (Peierls type) or electron–electron interaction (Mott–Hubbard type) could play a key role in inducing the occurrence of the MIT.3–7 Furthermore, these characteristics of the VO 2 .