Self-Assembled Porous Tantalum Oxide Prepared in H[sub 2]SO[sub 4]/HF Electrolytes

The formation of porous Ta 2 O 5 on tantalum was investigated in H 2 SO 4 electrolytes containing low concentrations of HF (0.15 wt %). Under optimized electrochemical conditions, porous Ta 2 O 5 consisting of self-assembled pore arrays with single pore diameters of ∼ 20 nm and a pore spacing of ∼ 15 nm forms. The pore structure and the pore distribution depend on the concentration of HF, the anodization voltage, and the time for anodic oxidation. Porous layers ∼ 400 nm thick with a regular pore distribution can be formed. For thicker layers cracking and a tendency for delamination was observed.