A study of thin film Au–Al alloy oxidation in ambient air by X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES), and secondary ion mass spectrometry (SIMS)

The oxidation behavior of Al2Au and Au2Al alloys during a 3-month laboratory air exposure has been investigated using SIMS, XPS and XANES. The oxide growth on both alloys and Al metal were found to be remarkably similar in the whole exposure range. XPS studies showed a rapid initial growth of oxide over the first 10 days. The oxidation of the aluminum component caused phase transitions at the near-surface to alloys which were more Au-rich. SIMS depth profiling showed that the oxide thickness was considerably greater than that estimated by XPS using a simple overlayer model. Both alloy structures were shown to be epitaxically grown homologues to the base aluminum grain structures; by contrast, oxide structures showed no preferred growth on particular alloy grains. Oxidation of the Au2Al results in a major depletion in the aluminum in the immediately below the oxide. Al L2,3-edge XANES was used to probe the nature of the oxide formed on the alloys as compared to that on pure Al. The chemical characteristics of the oxide was found to be affected by the presence of the gold. This difference in oxide structure is detected at the interface and not through the oxide generally.