An AES study of the surface composition of ion-etched iron–chromium alloys: effect of adsorbed CO

The surface composition of a series of iron–chromium alloys was analyzed by Auger electron spectroscopy as a function of Ar and Ne ion etching conditions. The relative sensitivity factor was determined from iron and chromium and from an Fe–25%Cr alloy and was found to be independent of composition. No preferential sputtering of either alloy component was observed as long as the surface was free from any impurities. When small quantities of CO are adsorbed onto the alloys’ surfaces, the Cr content appeared to decrease markedly, much more than when H2O adsorbed. It is suggested that the preferential adsorption of CO onto Cr atoms of the alloy surface can account for this effect. Similar effects are likely during ion etching of other alloy systems.