OXIDATION OF A AU +4 AT-PERCENT TI ALLOY

The gold alloy (Au + 4 at % Ti) was subjected to oxygen exposures at different temperatures in uhv. The surface concentration was monitored by AES and XPS. The solute Ti, segregated to the surface at temperatures above 300-degrees-C to form mixed oxides. The almost 1:1 ratio of Ti and O was a prominent feature at all temperatures. Carbon always appeared to be in the bound or carbidic form, its segregation to the surface enhancing that of Ti. The appearance of an Auger peak at 293 eV correlates with the presence of C and O in the surface region and is interpreted as due to a KVd transition where V represents valence states of the CO molecule and d a screening electron transferred from adjacent Au atoms to the C atom site. In contrast to pure gold that does not oxidise, the Au in this alloy oxidises between 500 and 600-degrees-C, forming an unstable oxide, probably Au2O. The appearance of an Auger peak at 80 eV during this oxidation process, is interpreted as an interband transition between Au and O while the shift of the 69 eV Au peak to 65 eV is the result of the chemical bonding between Au and O.