High resolution XPS studies of thin film gold–aluminum alloy structures

The surface oxidation behavior at room temperature of two thin films of the alloys Al2Au and Au2Al was investigated using X-ray photoelectron spectroscopy (XPS). Relatively large chemical shifts of both Au4f and Al2p photoelectron lines with the alloy composition assist the identification of additional alloy phases. The spectral resolution has been improved by the use of the Maximum Entropy Method which removes the external contributions to the photoelectron linewidth. In the case of Au2Al, as much as 80% of the surface phase is transformed into two new alloy phases. This is equivalent to a transformed layer thickness of 10 nm. For the Al2Au, oxidation also results in a partial phase transition to a gold-enriched alloy, but the transition region extends only to an estimated depth of 2 nm.