DYNAMIC SURFACE-COMPOSITION CHANGES IN BINARY-ALLOYS UNDER ION-BOMBARDMENT

When investigating 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.