Nanostructured Thin Film Photocatalyst
Enhanced surface reaction efficiency has been demonstrated in the photocatalysis of obliquely deposited TiO2 thin films with variously shaped columns such as zigzag, cylinder, and helix. The columnar thickness and spacing play an important role in the enhancement of the effective surface area, while the columnar shape is less important. The optimum morphology for a surface reaction has been obtained at the deposition angle α=70°, where the photocatalytic activity is 2.5 times larger than that at α=0°.
To understand the photocatalytic properties of obliquely deposited TiO2 thin films, we have developed a three-dimensional Monte Carlo simulator for thin film growth and applied it to understand the morphologies of thin films prepared by oblique deposition with a special emphasis on an effective surface area. The effective surface area is enhanced by oblique deposition owing to the columnar formation and becomes maximum at a deposition angle of 70°. On the contrary, no significant dependence of the effective surface area on the columnar shapes has been observed. Consequently, morphology-related quantities of obliquely deposited thin films such as the packing density and the effective surface area are understood in terms of the deposition angle and are insensitive to the motion of the azimuthal deposition direction.
In addition, the oblique angle deposition is one of the most powerful technique to realize light trapping nanostructures so-called perfect absorbers, which absorb nearly 100% of incident light with a designed wavelength. We have demonstrated that the photocatalysis is also enhanced for the columnar TiO2/SiO2/Al due to the efficient light trapping into the TiO2 layer.
Motofumi Suzuki is a professor at Kyoto University. He received his bachelor, master and doctor of engineering degrees from Kyoto University in 1986, 1988 and 1998, respectively. His current research interests include the optical properties of nanostructured thin films and the synthesis of novel nanostructures. He is a senior member of SPIE.