Physical and optical properties of room temperature microwave plasma anodically grown TiO2

Abstract

A dense, amorphous form of TiO2 produced by plasma assisted anodic oxidation of Ti was identified using infrared absorption, x-ray diffraction, x-ray reflectivity, atomic force microscopy, and ellipsometry. The films were grown by nominally room temperature processing. Comparison of the physical properties of the material is made with respect to existing data on plasma enhanced chemical vapor deposited TiO2 and new data obtained on electron beam evaporated TiO2. Anodic TiO2 is found to be amorphous with a refractive index of the order of 2.33 as compared to 2.2 for plasma enhanced chemical vapor deposited films and 1.89 for electron beam evaporated TiO2 films. The density is measured to be 4.1g∕cm3. Samples annealed up to 600°C in a N2 atmosphere for 1h remained amorphous, the refractive index increasing to 2.38 and the density to 4.25g∕cm3. The surface roughness remained almost unchanged consistent with the amorphicity. No evidence for the presence of crystalline rutile or anatase phases was detected. Furthermore, unlike plasma assisted chemical vapor deposited and electron beam evaporated TiO2 films, annealed anodic TiO2 showed no observable interaction with the Si substrate either during growth or following annealing.