Formation of Nano-Porous Structures on Oxide Semiconductor Surface by Photoetching Technique

光蚀刻是一种独特的半导体表面裁剪技术。研究了光蚀刻（光电化学蚀刻）对钛板热氧化制备的二氧化钛（TiO_2）膜电极光致亲水性转化的影响。我们发现光蚀刻TiO_2薄膜会导致纳米孔结构的形成，这取决于制备条件（氧化温度）、光蚀刻条件（电极电位）和TiO_2晶粒的晶体取向。在高于900℃的温度下对氧化膜进行光蚀刻，使TiO_2的纳米孔结构由金红石结构的（100）面组成，提高了光致亲水性转化性能。阳极极化下的光蚀刻提高了光致亲水性转化的速率，而弱阳极极化下的光蚀刻膜不表现出光致亲水性转化的特性。我们还研究了光蚀刻Cr， Sb掺杂可见光敏感TiO_2电极的光电化学性能。从太阳能利用的角度来看，提高TiO_2的可见光灵敏度具有重要意义。经紫外光刻蚀后，表面粗糙度增大，形成几十纳米大小的凹凸结构。而在紫外光照射下光刻后，台阶被选择性地不溶解，在其台阶表面观察到约100纳米大小的凹凸结构。UV光和VS光贴合后，VS光区的光响应增加到IPCE（入射光子到电流转换效率）的4%。相反，两种情况下紫外区的光响应都降低。

Photoetching is an unique technique for tailoring the semiconductor surface. The effect of photoetching (photoelectrochemical etching) on photoinduced hydrophilic conversion of titanium dioxide (TiO_2) film electrodes prepared by thermal oxidation of Ti plate has been studied. We have found that photoetching of TiO_2 film results in the formation of nano-porous structure depending upon preparation condition (oxidation temperature), photoetching condition (electrode potential) and crystallographic orientation of the TiO_2 grain. Photoetching of the film oxidized at temperature higher than 900℃ makes nano-porous structure consisting of (100) plane of rutile structure of TiO_2 and improves the photoinduced hydrophilic conversion property. Photoetching under anodic polarization increases the rate of photoinduced hydrophilic conversion, while the film photoetched under weak anodic polarization does not show the photoinduced hydrophilic conversion property. We have also examined the photoelectrochemical properties of photoetched Cr, Sb doped visible light sensitive TiO_2 electrode. It is important to increase visible-light sensitivity of TiO_2 from a viewpoint of solar energy utilization. After UV light photoetching, roughness of the surface increases and convexo-concave structures with several tens of nanometer size were observed. Whereas after photoetching of VS light illumination, the steps are selectively undissolved and convexo-concave structures with about one hundred nanometer size were observed on its terrace surface. After photetching with UV and VS light, the photoresponse for VS light region increases up to 4 % of IPCE (incident photon to current conversion efficiency). On the contrary the photoresponses for UV region decrease in both cases.