Electrochemistry

Biography

Biography: Toshiaki Kondo

Abstract

Anodic porous TiO₂ has attracted attention due to its wide range of applications such as photonic crystals, solar cells and so on.  Performances of the devices depend on its geometrical structures of a nanohole array.  Therefore, for improvement of the performances, control of its geometrical structures is important.  Until now, improvement of an arrangement of nanoholes in an anodic porous TiO₂ by self-ordering anodization process has been achieved.  However, it is still difficult to obtain defect-free nanohole array structures in entire sample area.  In this presentation, fabrication processes of an anodic porous TiO₂ having ideally ordered nanoholes will be presented.  An ideally ordered anodic porous TiO₂ was obtained by anodizing a pretextured Ti plate.  Through a texturing process, an ordered array of concaves was formed on a surface of Ti.  In a subsequent anodization, each shallow concave acts as a starting point for generation of a nanohole at initial stage of the anodization and results in an ideally ordered structure.  We demonstrated two pretexturing processes.  One is a process to directly texture a surface of Ti.  The nanopattern was formed by pressing a metal (Ni) mold onto a surface of Ti.  The other is a process to texture a surface of Al layered on a Ti.  A two-layered sample composed of an Al top layer and a Ti underlying layer was prepared.  An ideally ordered array of concaves was formed on the surface of Al by pretexturing process using a Ni mold.  Owing to softness of Al, the nanopattern was easily formed.  By anodizing the sample, the arrangement of nanoholes was transferred to the surface of Ti substrate, resulting in the ideally ordered anodic porous TiO₂ as shown in Fig. 1.  These processes are expected to be applied to fabricate various functional devices, which require ideally ordered nanohole structures in TiO₂, such as photonic crystals.