Paper SS1-ThA3
Far-From-Equilibrium Film Growth on Alloy Surfaces: Ni and Al on NiAl(110)

Thursday, November 12, 2009, 2:40 pm, Room M

We have analyzed the deposition of Ni and Al on NiAl(110) surfaces by STM and by KMC simulation of multi-site atomistic lattice-gas modeling incorporating DFT energetics. The goal is to elucidate far-from-equilibrium growth of metal films on alloy surfaces, including self-growth of alloys. Deposition of Ni produces reversible formation of monolayer islands which have some preference for diagonal steps at 300K and which are distorted-hexagons at 400K. Deposition of Al at 300K produces irreversible formation of irregular monolayer islands perhaps favoring steps in the [-110] direction. These features are recovered by the modeling, which elucidates the distinct nature of terrace diffusion of Ni versus Al on NiAl(110), the details of island nucleation, and the complexity of edge diffusion which controls island growth shapes. Additional studies of sequential co-deposition reveal “history-dependent” structures far from perfect equilibrium alloy ordering. Depositing Al first then Ni creates monolayer islands with a core of Al surrounded by a ring of Ni (although intermixing may occur at the interface). In contrast, depositing Ni first then Al creates monolayer Ni islands with significant second layer population by Al (reflecting stronger binding of Al on top of the Ni islands versus on NiAl(110) according to DFT).