Development of stacked porous tantalum oxide layers by anodization

Interest in nanoporous tantalum oxide (Ta2O5) has been increasing due to its high variety of applications, from protective coatings, photocatalysts to biomedical devices. Anodization is a surface modification technique, which is inexpensive, versatile, easily scalable and widely used to produce these nanostructures. In this study, Ta2O5 nanoporous surfaces were produced by anodization in HF-free electrolyte composed of ethylene glycol, water and ammonium fluoride (NH4F) with different anodization parameters (electrolyte concentration, applied potential and time). The surface morphology of each sample was investigated by scanning electron microscopy (SEM) and the sample with the more uniform porous nanostructure was characterized in terms of cross-section morphology, chemical composition and crystalline structure. The concentration of NH4F and applied potential demonstrated a significant impact on current-density-time curve, and thereafter in surface morphology. Multiple thin porous nanolayers were formed under strong electrochemical conditions (very high current density and electrolyte temperature). Through chemical analysis, it was possible to detect the presence of fluoride, which is consistent with an amorphous Ta2O5 layer with fluoride ions incorporation. Thereby, managing the electrochemical conditions is crucial to control the morphology of an anodic Ta2O5 layer.