Dynamic surface composition changes in binary alloys under ion bombardment

Ion bombardment of single-phase binary alloys results generally in surface enrichment of one component. When investigating the surface composition with Auger Electron Spectroscopy (AES) as the energy of the bombarding ions (Ne, Ar or Xe) is changed from 0.5 to 5 keV and vice versa, a transition period is found where the surface composition shows rapid changes until a new equilibrium composition is reached. These dynamic surface composition changes were observed for Ag-Pd, Cu-Pt and Ag-Au alloys. This effect can be attributed to altered layers of different thickness, and to different ion doses needed to reach a new equilibrium for different ion energies. It is found that the altered layer thickness agrees well with calculated mean penetration depths of the primary ions at 0.5 and 5 keV, and, furthermore, the ion dose needed to reach equilibrium corresponds to the removal of one altered layer thickness. The results indicate that diffusion processes are of minor importance at room temperature. (orig.)