Plasma-Assisted Chemical Vapor Deposition of TiO<sub>2</sub> 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 400˚C, 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 TiO 2 layer without amorphous-phase could be formed above 340˚C 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 5˚ in dark and the quick conversion to super-hydrophilicity by UV-irradiation with a light-power density as low as 50 W/cm 2 were observed on the PCVDlayer grown at 380˚C, while the large initial contact angle was above 40˚ and the response for the UV-irradiation was gradual on the LPCVD-layer.

Atmospheric Pressure Plasma Deposition of TiO2: A Review

“…These methods have been also employed to deposit TiO 2 using APP; among them, the PECVD technique is used most commonly [48]. The wide use of this technique is attributable to its many advantages, primarily its relatively simple and low-cost experimental set-up and its ability to deposit thin films even at low temperatures [49][50][51][52][53][54][55][56][57]. The general process of the PECVD technique to deposit TiO 2 employs a Ti-based precursor-TTIP is used most often-which is transferred by a carrier gas, typically an inert gas, and then mixed with a feed gas.…”

“…Different types of discharges have been also applied. However, most researchers have used either an rf of 13.56 MHz [ 50 , 52 , 53 , 54 , 56 ] or microwave discharges [ 49 , 51 , 55 , 58 , 59 , 60 , 61 ] to ignite the plasma. Further, the thickness, morphology, crystallinity, and other properties of the grown films have been diverse in research findings as they depend largely on the deposition parameters.…”

Plasma-Assisted Chemical Vapor Deposition of Titanium Oxide Layer at Room-Temperature

“…Previously, it was reported by FTIR studies for TTIP dissociation that atomic oxygen radicals supplied from oxygen remote-plasma enhance the dissociation of TTIP and the dissociation energy is decreased to 27.3 kJ/mol [17]. In contrast, the energy for the dissociation in the PCVD was 4.5 kJ/mol as shown elsewhere [13]. The significantly low dissociation energy in the PCVD comparing to the remote-plasma assisted deposition suggested that charged particles such as electrons and ions were also contributed to the dissociation.…”

“…Schematic details of the apparatus was shown elsewhere [13]. DC-coil was settled around the bell-jar to induce DC-magnetic field during the deposition.…”

“…In the process, titanium tetra-iso-propoxide (TTIP) seems to be more sufficient as preliminary precursor than titanium tetrachloride (TiCl 4 ) in view of contamination in the layers [12]. Previously, we demonstrated the PCVD of anatase-TiO 2 for highly hydrophilic performance at 380˚C using TTIP and O 2 [13], in which the deposition was achieved in low pressure of 3 mtorr by the plasma-cracked precursors and the thermal dissociation of TTIP on the surface. However, the hydrophilic property was degraded with decreasing deposition temperature and not responsible to UV-irradiation on the amorphous layer deposited at low temperatures under 280˚C.…”