Sputtering pressure dependent photocatalytic properties of TiO2 thin films

The TiO2 films were deposited on glass substrate by direct current reactive magnetron sputtering under various total sputtering gas pressures (P-Tot) of 0.2, 0.5, 0.8, and 5 Pa, and at the target to substrate distances (DT-S) of 40 and 70 mm. Argon and oxygen gas mixtures (Ar: O-2 = 80: 20) were used to deposit the films. The optimum conditions to deposit the films with high photocatalytic activities were investigated in detail using in situ Fourier transform infrared spectra in relation to the sputter deposition processes. The band gap energy was found to decrease from 3.25 to 3.13 eV for the TiO2 films deposited at PTot of 5 - 0.2 Pa and DT-S of 40 mm. For the films deposited at DT-S of 70 mm, the band gap varied between 3.3 and 3.2 eV. The, rate of decomposition of methanol is rapid for the films deposited at P-Tot of 0.2 Pa and DT-S of 40 mm and as the DT-S and P-Tot increase, the photo-oxidation of methanol by TiO2 decreases. The formaldehyde and CO species are the main intermediates by increasing the irradiation time and CO2 is produced after the complete decomposition. (c) 2006 American Vacuum Society.