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Fabrication and Properties of TiO2Thin Films by DC Facing-target Magnetron Sputtering

Author: ChenPi
Tutor: TanXin
School: Tianjin University
Course: Environmental Science
Keywords: TiO2thin films DC facing-target magnetron sputtering sputteringpower total pressure Ar/O2flow ratios IPA degradation photocurrent
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Type: PhD thesis
Year: 2012
Downloads: 44
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Abstract


TiO2have been widely used in many environmental applications due to its highphotocatalytic activity, non-toxicity and chemical stability. Compared to powders,TiO2thin films could be easily separated from the reaction system and thus attracted agreat deal of attention. Here we proposed a new physical deposition technique,namely DC facing target magnetron sputtering for TiO2thin film preparation with theaim of prevention of high energetic ions bombardment and increase of targetutilization during the sputtering process. The prepared films coule be stably coated onvarious kinds of substrates with strong adhesion.TiO2thin film was deposited on FTO substrates using a pair of facing Ti targetsas sputtering targets. Pure Ar gas and O2gas were selected as the working gas andreactive gas respectively. A series of TiO2thin films deposited under differentsputtering times were characterized by Field Emission Scanning Electron Microscopy（FE-SEM） and Atomic Forece Microscope （AFM）, which proved TiO2thin filmsforming in Stranski-Krastanow growth on FTO substrates.The effects of sputtering parameters on the crystal structure, surface morphologyand opitical property of TiO2thin films were investigated by the characterizationincluding surface roughness tester, X-Ray diffraction, FE-SEM, AFM and UV-VisibleSpectrophotometer （UV-Vis）. Firstly, sputtering power mainly affected the depositionrate of TiO2thin film and the film thickness increased linearly with the sputteringpower. The amorphous films transform to anatase with the higher sputtering powerthan280W. Sencondly, annealing treatment could improve the crystallinity of TiO2thin films by providing free energy which promoted the surface migration andreunification of grains. Thirdly, Ar/O2flow ratio played an important role in thesputtering and oxidation reaction on the target surface. Both of deposition rates andcrystallinity of TiO2thin films reduced with lower Ar/O2flow ratio than1:1due to“the oxidation mode”. When Ar/O2flow ratio was higher than1:1, the phase of TiO2thin films change from pure anatase into mixed-phase as the O2flow increased.Fourthly, high pressure inhibited the growth of rutile phase. When the sputteringpressure was lower than2.5Pa, the crystallinity of deposited films increased with theincreasing sputtering pressure. However, the followed increasing pressure caused anapparently derease of the crystallinity of deposited films.The photocatalytic activities of TiO2thin films were evaluated by thedecomposition of gaseous iso-propanol （IPA） under UV light irradiation. And the photoelectric performances of the deposited films were analyzed by measuringtransient photocurrent of TiO2electrodes. The optimized sputtering parameters suchas350W,550centigrade,1:1and2.5Pa were determined by the above measurments.Under UV irradiation, IPA degradation rate of the optimized TiO2thin film whichkept high stability constant during the repetitive experiments, could reach to100%in120min with the IPA inicial concentration of90ppm. Simultaneously, the highesttransient photocurrent with the value of1.02mA/cm2was obtained by the samesample.

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