Far-from-equilibrium film growth on alloy surfaces: Ni and Al on NiAl(110)

STM analysis reveals diverse nonequilibrium island structures formed by deposition of Ni and Al on NiAl(110) at around 300 K. Epitaxial growth in this complex alloy system is described by multisite lattice-gas modeling incorporating DFT energetics for adatoms both at adsorption sites and transition states. This approach accounts for multiple adsorption sites and diffusion paths, and accurately describes diffusion and detachment kinetics for a vast number of step-edge configurations. This is key for realistic description of island growth shapes, structure, and partial alloy ordering.

Figure 1

STM images for deposition at 300 K: (a) 0.19 ML Ni ($F=0.003$ ML/s); (b) 0.12 ML Ni ($F=0.0003$ ML/s); (c) 0.10 ML Al ($F=0.003$ ML/s); (d) 0.27 ML Al ($F=0.009$ ML/s). The [001] direction is vertical.

Figure 2

Scaled island size distributions (ISD) at 0.2 ML for the density $N_s$ of islands of $s$ atoms, where $s_{\mathrm{av}}$ denotes the average size and $N_{\mathrm{isl}}$ the overall density.

Figure 3

(a) Ni-br and Al-br adsorption site and TS binding energies in eV for isolated Ni (Al) on NiAl(110) in green (yellow); diffusion paths: solid green (dashed yellow) arrows for Ni (Al); sites 1, 3,...$=$ Ni-br; 2, 4,...$=$ Al-br; $t$ $=$ Ni-top; $b$ $=$ Ni-Al bridge. (b) Ni diffusion along a diagonal Ni-Al island edge: solid (dashed) lines denote interactions of the diffusing Ni at adsorption sites (TS) with nearby adatoms. (c) Ni-Ni (Al-Al); (d) Ni-Al interaction energies in eV (attraction $>0$). Dots denote adatoms or adsorption sites. [100] direction is vertical.

Figure 4

Simulated islands (sizes in atoms). Ni at 300 K: (a)–(c) $F=0.003$ ML/s; (d) $F=0.0003$ ML/s. Al at 300 K: (e), (f) $F=0.003$ ML/s; (g), (h) $F=0.009$ ML/s. Simultaneous stoichiometric codeposition of Ni and Al ($F=0.03$ ML/s) at (i) 300 K, (j) 400 K, (k) 500 K, (l) 600 K.