Figure 2
From: Metal–insulator transition tuned by oxygen vacancy migration across TiO2/VO2 interface
Structure and chemical states of TiO2/VO2 thin films. (a) HAADF-STEM image of TiO2/VO2 (LP) along the [100] axis of TiO2 substrate, which shows high crystal quality without observable extended defects. (b,c) Background subtracted EELS spectra of Ti L-edge (b) and V L-edge (c). While there are no appreciable differences between Ti L-edge spectra measured on the TiO2 capping layers of LP and HP samples, as well as the TiO2 substrate, a clear peak shift towards lower energy is observed in V L-edge spectrum of LP sample, compared with HP sample. (d,e) XPS spectra in V 2p (d) and Ti 2p (e) regions, which provides surface sensitive chemical information. While the Ti 2p peaks can be fitted with purely 4 + oxidation state, two components representing 4 + and 5 + oxidation states were needed to fit V 2p peaks. TiO2/VO2 sample showered higher V4+/V5+ relative concentration compared with pure VO2 sample, which indicates an increased oxygen vacancy concentration induced by the TiO2 capping layer.
