The effect of the crystalline structure transformation in VO$_2$/glass by inserting TiO$_2$ buffer layer and its application in smart windows

Vanadium dioxide (VO$_2$) undergoes a reversible metal–insulator transition at low temperature, which has wide range of applications in smart windows and infrared detectors. However, the preparation of VO$_2$ films with controllable phase on glass substrate is still limited. In this paper, it is shown that $B$-phase can be transformed into $M$-phase with monoclinic structure by inserting TiO$_2$ buffer layer on glass substrate at low temperature of 400$^\circ$ C. This crystalline transformation might be attributed to that Ti atoms diffuse and form oxygen deficient environments. Different thicknesses of buffer layers have different effect on characteristic of VO$_2$ film. With 50 nm TiO$_2$ buffer layer, the VO$_2$/TiO$_2$/glass film showed an abrupt resistance change with more than 2.5-order of magnitude across metal–insulator transition, and the visible-light transmittance value is as high as 55.5% with the solar modulation capability up to 8.6%. The current results are very important for the application in smart windows.