Imanishi Akihito, Suzuki Hidenori, Murakoshi Kei, Nakato Yoshihiro
Division of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
J Phys Chem B. 2006 Oct 26;110(42):21050-4. doi: 10.1021/jp057538h.
Dye-sensitized photocurrents at (100)-, (001)-, and (110)-cut TiO(2) rutile surfaces were increased by photoetching of TiO(2), but the increasing ratio strongly depended on the cut crystal faces and the illumination intensity for the photoetching. For the (110)-cut surface, the photocurrent increase was moderately large and in proportion to the increase in the surface area of TiO(2) induced by the photoetching, irrespective of the illumination intensity for the photoetching. On the other hand, the photocurrent increases for the (001)- and (100)-cut surfaces, especially that for the (001)-cut surface, were prominent and largely exceeded the increases in the surface area. The results were explained by taking into account the following factors: (1) The (001)- and (100)-cut surfaces were thermodynamically unstable in contrast to the (110)-cut surface and had thicker inactive surface layers (or higher densities of surface defects), produced by surface reconstruction during heat treatment of TiO(2) at 550 degrees C in a hydrogen atmosphere for getting n-type semiconductivity. (2) Photoetching not only increased the surface area through formation of nanoholes and grooves at the surface but also effectively removed the thin inactive surface layers (or surface defects).
通过对TiO₂进行光蚀刻，（100）面、（001）面和（110）面切割的TiO₂金红石表面的染料敏化光电流有所增加，但增加的比例强烈依赖于切割的晶面以及光蚀刻的光照强度。对于（110）面切割的表面，光电流的增加幅度适中，且与光蚀刻引起的TiO₂表面积增加成比例，与光蚀刻的光照强度无关。另一方面，（001）面和（100）面切割表面的光电流增加，尤其是（001）面切割表面的光电流增加显著，且大大超过了表面积的增加。考虑以下因素可以解释这些结果：（1）与（110）面切割表面相比，（001）面和（100）面切割表面在热力学上不稳定，并且具有较厚的非活性表面层（或较高密度的表面缺陷），这是在550℃氢气气氛中对TiO₂进行热处理以获得n型半导体时通过表面重构产生的。（2）光蚀刻不仅通过在表面形成纳米孔和凹槽增加了表面积，而且有效地去除了薄的非活性表面层（或表面缺陷）。
