Outermost Surface Composition of Au-Cu Alloys Under Ion Bombardment of Different Current Densities of Ar+ Ions

Since the interacion of sputtered atoms with the outermost atomic layer of the alloy sample plays the most important role in the ionization and neutralization process, the exact knowledge of the surface composition of the outermost atomic layer under ion bombardment is needed. With respect to the surface composition of alloy samples under Ar+ ion bombardment, it is now well recognized that the ion-enhanced subsurface re-distribution results in a marked enrichment of constituent atoms of lower surface binding energy at the outermost atomic layer[l,2,3]. Furthermore, it has recently been suggested that the composition of the outermost atomic layer of Au-Cu alloys may change for different current densities of ion beam in the range below several tens of µA/cm2 [5],which corresponds to the current densities in usual SIMS measurement. If so, the outermost atomic layer leads to the change of secondary ion yield. The present work, therefore, aimed at examining whether or not such a density effect exists in usual operating conditions of SIMS. For this, surface composition of the outermost atomic layer of Ar-43at%Cu alloys was measured by ion scattering spectroscopy with the mixed He+ and Ar+ ions(mixed ion beam ISS).