Intermixing in Cu/Ni(110) growth*

Using temperature accelerated dynamics simulations we have examined the intermixing process in the early stages of growth of Cu on Ni(110) and compared with experiments [1]. As in other (110) metal surfaces, the cross-channel hopping barrier is significantly larger than the in-channel barrier, while the barrier for a Cu-Ni exchange process - resulting in the embedding of a Cu atom in the Ni(110) substrate - is somewhat higher. However, this simple diffusion dynamics is significantly modified due to the presence of inherent metastable intermediate states as well as the complex dependence of exchange barriers on the local environment. This leads to relatively small barriers for Ni-Cu exchange as well as a novel exchange mechanism involving nearby islands which promotes intermixing. As a result we find that, while almost 90% of the Cu atoms are embedded in the substrate at coverage θ < 0.1 ML, at higher coverage the fraction of embedded Cu atoms decreases significantly due to reverse Ni-Cu exchange processes. Our results also resolve the apparent discrepancy found in experiment between the fraction of embedded Cu at low coverage and that found at higher coverage.

[1] T. Fukuda, K. Iwamoto, and H. Nakayama, Phys. Rev. B 78, 195422 (2008).