Plasma-Assisted Chemical Vapor Deposition of TiO 2 Thin Films for Highly Hydrophilic Performance

Abstract

Titanium-oxide layer was grown on glass substrate by plasma-assisted chemical vapor deposition (PCVD) using oxygen gas plasma excited by radio-frequency power at 13.56 MHz in the pressure as low as 3mtorr at relatively low temperature below 400oC, and studied on the crystallographic properties with the hydrophilic behavior comparing to the layer deposited by low-pressure chemical vapor deposition (LPCVD). Raman spectra indicated anatase-phase TiO2 layer without amorphous-phase could be formed above 340oC by simultaneous supply of plasma-cracked and non-cracked titanium-tetra-iso-propoxide (TTIP) used as preliminary precursor. Surface Scanning Electron Microscope images indicated the PCVD-layer consists of distinct nanometer-size plate-like columnar grains, in contrast to rugged micrometer-size grains in the LPCVD-layer. Extremely small water contact angle about 5o in dark and the quick conversion to super-hydrophilicity by UV-irradiation with a light-power density as low as 50 W/cm2 were observed on the PCVD- layer grown at 380oC, while the large initial contact angle was above 40o and the response for the UV-irradiation was gradual on the LPCVD-layer.