PREFERENTIAL SPUTTERING IN OXIDES AS METALS AND REVEALED BY X-RAY PHOTOELECTRON-SPECTROSCOPY

The surface film on an oxidized multicomponent alloy usually contains a number of metallic and oxidized phases. During depth-profile analysis, such metal and oxide phases can be differentiated by x-ray photoelectron spectroscopy (XPS), provided the surface oxides are sufficiently stable to withstand ion bombardment without decomposition. A quantitative analysis of the surface composition, however, is not possible without taking account of the effects of preferential sputtering of some phases. We have investigated the effects of 3-keV argon ion bombardment on the composition of oxide-free surfaces of iron-nickel and iron-nickel-chromium alloys. In addition, the effect of ion bombardment on metal-metal oxide surfaces has been studied using composite preparations of metal particles, 10-50 mu m diameter, in an oxide matrix. Quantitative XPS measurements of the sputtered alloy surfaces, using photoelectrons of 1. 0-2. 0 nm mean free path, do not reveal any significant change in the steady-state compositions (i. e. , greater than 10%) compared with the bulk compositions. In the composite metal-oxide mixtures studied, depletion of the metallic phase is significant in some cases and must be taken into consideration in a quantitative depth profile.