Sputter-induced surface composition changes in alloys

Abstract

Radiation-induced redistribution of alloying elements in the near-surface region of dilute binary alloys during low-energy Ar + ion sputtering was calculated using a kinetic model that includes the effects of radiation-induced segregation and preferential sputtering. Changes in the alloy surface composition were calculated as functions of sputtering time, temperature, ion flux and initial alloy composition for Ni-based model alloys. In the temperature range 200–850°C, radiation-induced segregation is dominant initially and the surface is enriched with or depleted of solutes whose fluxes are coupled predominantly to interstitial or vacancy fluxes, respectively. As the bombardment time increases, the effects of preferential sputtering become dominant and the surface composition approaches a steady-state value determined by the sputtering coefficients of the alloy components. Below 200 and above 850°C, the surface composition is altered by preferential sputtering because radiation-induced segregation is insignificant. The time required to achieve steady state increases with increasing temperature and decreasing ion flux. The present calculations may be of importance in the areas of sputter depth-profiling, sputter etching, and plasma contamination in fusion reactors.