FACTOR-ANALYSIS OF D(NE) DE AUGER-ELECTRON SPECTRA OF AUCU ALLOYS - SURFACE-COMPOSITION DURING AR+ ION-BOMBARDMENT AND OXIDATION

Factor analysis is applied to d(NE)/dE Auger electron spectra of a series of AuCu alloys (25% Au, 50% Au and 75% Au), including in the analysis the spectra of clean Au and Cu surfaces. Surface quantitation is obtained from the low‐energy Au NOO and Cu LMM spectra of the alloys. The overlap of these spectra is resolved with factor analysis. An accuracy of the derived, relative surface concentrations of 1:100 is possible with this method, with a similar sensitivity to changes in surface composition. During Ar+ ion bombardment the surfaces of 25% and 50% Au alloys show no difference from the bulk concentrations, within ±1:100, from 1 to 3 keV Ar+ ion energy. For the 75% Au alloy, a slight Au enrichment is produced, when the energy increases from 1 to 3 keV. However, at 500 eV Ar+ ion energy, the surfaces become strongly enriched in Au, probably due to threshold effects for Au. Thus, no evidence for such strongly varying processes are found in molecular dynamics simulations of the mass effect in the sputtering process from a 50%:50% alloy. Factor analysis is also used to detect the presence of chemically affected spectral features during oxygen exposure at room temperature of the alloys and of pure Cu. Oxidation of the copper component is observed, producing at saturation a cuprous oxide with a total copper enrichment of the surface. Copyright © 1990 John Wiley & Sons Ltd.