An investigation of structures of thermal and anodic tantalum oxide films

Tantalum oxide films produced from anodic oxidation and thermal oxidation at 400 and 800°C have been investigated with respect to long- and short-range structure by X-ray diffraction and X-ray absorption spectroscopy, respectively. Films formed at 800°C show orthorhombic structure (β-Ta₂O₅) with greater disorder compared to the β-Ta₂O₅ powder reference, where six O atoms were observed at an avenge radial distances of 1.957 ± 0.014 (Ta₂O, powder) and 1.971 ± 0.007 Å (800°C Ta oxide film). Lower temperature films consist primarily of metastable TaO_x (Ta ₂O) and appear to be relatively stable for extended times of treatment with a first shell not unlike that of β-Ta₂O ₅, based on a linear combination analysis. Furthermore, using a linear combination of β-Ta₂O₅ and α-Ta metal, the amorphous anodic oxide films studied as a function of thickness were observed to exhibit a relatively ordered local structure consistent with the high-temperature (i.e., 800°C) phase. This work demonstrates that the nanoscale oxide films formed on tantalum exhibit an ordered local structure, reflecting the very compact nature that enhances its corrosion resistance.