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

光刻是一种用于裁剪半导体表面的独特技术。研究了光刻(光电化学刻蚀)对钛板热氧化制备的二氧化钛薄膜电极光诱导亲水转化的影响。我们发现，光刻蚀会导致纳米孔结构的形成，这取决于制备条件(氧化温度)、光刻条件(电极电位)和二氧化钛颗粒的晶体取向。当氧化温度高于90 0℃时，薄膜表面形成了金红石型(10 0)晶面的纳米孔结构，提高了薄膜的光诱导亲水转化性能。阳极极化下的光刻提高了薄膜的光致亲水转化率，而弱阳极下光刻后的薄膜没有表现出光致亲水转化特性。我们还研究了光刻铬、锑掺杂可见光敏感的二氧化钛电极的光电化学性能。从太阳能利用的角度来看，提高二氧化钛的可见光灵敏度具有重要意义。紫外光刻蚀后，表面粗糙度增加，并观察到几十纳米的凹凸结构。而VS光刻后，台阶选择性地不溶解，在其平台表面观察到约100纳米的凸凹结构。在紫外光和VS光的光刻后，VS光区的光响应提高到IPCE(入射光子到电流的转换效率)的4%。相反，在这两种情况下，紫外区的光响应都降低了。

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.