Molecular dynamics results on the diffusive properties of Au and Cu adatoms on the ordered Cu3Au(001) surface were presented. It was found that for both adatoms there were two available equilibrium positions: one over the fourfold cite and another one on top of a Cu surface atom. It turns out that although this second position was rather a stopover than a stable adatom cite, it played an important role in adatom diffusive behavior. The Cu adatom diffused via a variety of Arrhenius type mechanisms, among which was an exchange mechanism, occurring at temperatures higher than Ts = 500K, involving second layer Cu atoms. In addition, some interlayer Cu diffusion events were observed, induced by the Cu adatom when localized at the on top Cu position. Moreover, it was found that the Cu adatom stimulates the creation of diffusive vacancies that contributed in the rearrangement of the surface atoms. Concerning the Au adatom, it was found that its diffusive behavior was substantially different from the Cu adatom case. Although the Cu and Au adatoms had similar reaction paths for diffusion, the Au adatom behavior was affected by an exchange mechanism that took place exclusively with the participation of Cu surface atoms. This mechanism, occurring more often above Ts, resulted in a local disorder of the surface layer, rendering the Au adatom unstable. Therefore, it appeared that above Ts, the presence of Cu or Au adatoms on the Cu3Au(001) face stimulates segregation and diffusive phenomena that could be related with the order-disorder transition occurring at higher temperatures.

Diffusion Processes of Au and Cu Adatoms on the Cu3Au(001) Surface. Lekka, C.E., Evangelakis G.A.: Surface Science, 2001, 473[1-2], 39-49