Formation and phase transition of VO_2 precipitates embedded in sapphire

摘要

Crystallographically coherent precipitates of vanadium dioxide (VO2) have been formed in the near-surface region of single crystals of sapphire (Al2O3) using a combination of ion implantation and thermal treatments. As in the case of either bulk VO_2 single crystals or thin films of VO_2, the thermally induced semiconductor-to-metal phase transition of the embedded VO_2 precipitates is accompanied by a large hysteretic change in the infrared optical transmission. The VO_2 precipitate transition temperature (Tc = 72 to 85 deg. C) is higher than that of bulk VO_2 (T. = 68 deg C) and is sensitive to the implantation conditions. The present results show that the damage resulting from the coimplantation of vanadium and oxygen into an Al2O3 host lattice dictates the final microstructure of the VO_2 precipitates and consequently, affects the transition temperature, as well as the optical quality of the VO,/Al,O, surface-nanocomposite precipitate system.