Formation and Microstructures of Anodic Alumina Films from Aluminum Sputtered on Glass Substrate

A transparent porous alumina nanostructure was formed on a glass covered tin-doped indium oxide (ITO) substrate by anodization of a highly pure sputtered aluminum layer. Details of the fabrication and microstructures of porous anodic alumina films are described and a possible mechanism of anodization is outlined. The variation of anodic current density reflects three processes, i.e. , ( i ) anodization of the sputtered aluminum layer, ( ii ) transition of electrolysis from aluminum to the underlying ITO film, and ( iii ) electrochemical reactions on the ITO film beneath the anodic alumina film. As all the aluminum is completely anodized, the resultant oxide films on the ITO/glass substrate possess a parallel porous structure (ϕ80-100 nm, cell size in ∼350 nm) with a thin arched barrier layer (∼80 nm) and exhibit a high transmittance in the ultraviolet-visible light range (75-100% transmittance 300-900 nm).