Formation of High-Pressure Phase of Titanium Dioxide (TiO_2-Ⅱ) Thin Films by Vapor-Liquid-Solid Growth Process on GaAs Substrate

摘要

In this work, the high pressure phase of titanium dioxide (TiO2-II) film is grown with vapor-liquid-solid (VLS) method on -GaAs substrate by utilizing the natural process-induced-strain, originating from the thermo-elastic mismatch between TiO2 and GaAs in VLS process. The mismatches in thermal expansion coefficient and elastic constant of TiO2 and GaAs are Delta alpha approximate to 55% and Delta Y approximate to 170% which incorporate a substantial amount of stress (approximate to GPa) during cooling from the growth temperature (500 degrees C). SEM imaging suggests the formation of a continuous film and cross-sectional TEM image confirmed its high crystalline quality. XRD peaks at 2 theta = 31.30(0) and 58.67(0) confirm the formation of [111] and [212]-planes of TiO2-II phase and its chemical states are analyzed from X-ray photoelectron spectroscopy (XPS) measurements. The bandgap of TiO2-II phase is estimated to be 2.88 eV from cathodoluminescence study for the first time which agrees satisfactorily with the theoretical predictions reported.