An investigation of structures of thermal and anodic tantalum oxide films

Tantalum oxide films produced from anodic oxidation and thermal oxidation at 400 and 800degreesC have been investigated with respect to long- and short-range structure by X-ray diffraction and X-ray absorption spectroscopy, respectively. Films formed at 800degreesC show orthorhombic structure (beta-Ta2O5) with greater disorder compared to the beta-Ta2O5 powder reference, where six O atoms were observed at an average radial distances of 1.957 +/- 0.014 (Ta2O5 powder) and 1.971 +/- 0.007 Angstrom (800degreesC Ta oxide film). Lower temperature films consist primarily of metastable TaOx (Ta2O) and appear to be relatively stable for extended times of treatment with a first shell not unlike that of beta-Ta2O5, based on a linear combination analysis. Furthermore, using a linear combination of beta-Ta2O5 and alpha-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., 800degreesC) 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. (C) 2005 The Electrochemical Society. All rights reserved.