Self-Assembled Fabrication of Vertically Oriented Ta₂O₅ Nanotube Arrays, and Membranes Thereof, by One-Step Tantalum Anodization

We report for the first time synthesis of high-aspect-ratio tantalum oxide nanotube arrays via one-step anodization of Ta foil. The use of aqueous electrolytes containing HF:H2SO4 in the volumetric ratios 1:9 and 2:8 results in formation of ordered nanodimpled surfaces with 40−55 nm pore diameters over the potential range 10−20 V. The addition of 5−10% of either ethylene glycol (EG) or dimethyl sulfoxide (DMSO) to the HF and H2SO4 aqueous electrolytes resulted in the formation of Ta oxide nanotube arrays up to ∼20 μm thick, either securely anchored to the underlying Ta film or as robust free-standing membranes, as dependent upon the anodization time and applied voltage.