Changes in gold concentration at the surface of a AuCu alloy sputtered at low temperature

A series of depth profiles in Au_0.56Cu_0.44 produced by bombarding at ? 120°C with an argon ion beam of 2 keV energy and current densities of 4, 6, 12 and 24 μA/cm², respectively, are presented. Gold is enriched in the top layer but the concentration rapidly decreases to a minimum at an average depth of about 2 Å, then increases slowly and saturates at about 30 Å. The change in the composition at this point is called a dip. The magnitude of the dip depends on the ion current density, but the depth is nearly independent of it. Segregation and diffusion effects in establishing the surface composition are stressed.