The validity of Cls charge referencing in the XPS of oxidised AlSi alloys

During a XPS study of oxide growth and segregation on commercial aluminium-silicon alloys, problems were encountered in the application of Cls charge referencing. Using the Cls peak maximum as a reference, shifts were observed in the aluminium and magnesium peak positions, particularly after high temperature oxidation, which could not be accounted for. Referencing against the native oxide Ols peak corrected the shifts. A consequent analysis of the Cls spectra revealed that the hydrocarbon contamination was reacting under the conditions used to oxidise the alloys. From the XPS results it is deduced that active sites on the oxidised alloy surface are responsible for catalytic cracking and oxidation of the adventitious hydrocarbon. Parallel studies on other heat treated oxidic systems have produced similar results. It is recommended that an alternative to Cls charge referencing should be used when performing XPS studies on heat treated oxidic systems.