XPS Study of Thin Thermal Oxide Films on PbIn Alloys

Properties of the thermal oxide films of PbIn alloys have been studied by means of XPS. Prior to the oxidation, Ar sputtering and subsequent storage in UHV were carried out in order to relax the sputtering effect. The oxide films were then formed by exposing the alloys to O2 for 30 minutes. Pb oxide and In oxide were determined to be PbO x and In2O3 according to their XPS chemical shifts. By using angle resolved-XPS, PbO x was found to exist in a small oxide layer. On the assumption that an oxide layer consists of an overlying PbO x , layer and an underlying In2O3 layer, the thickness for each layer was also measured by XPS. The total oxide thickness has a maximum at In ∼12 wt.% in alloy. The In2O3 volume fraction in oxide layer increases monotonically with an increase of In concentration in alloys, and PbO x is formed only in the region below In ∼30 wt.%.