Island shapes and intermixing for submonolayer nickel on Au(111)

The growth of nickel on reconstructed Au(111) has been studied in the coverage range of 0.02 to 0.25 monolayers (ML) by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). As found in previous studies, submonolayer islands are two-dimensional, nucleating at the point dislocation elbows of the 22 x root 3 herringbone reconstruction, and with edges along close-packed directions. The present results show that the islands have a tendency towards threefold symmetry, and that the island shapes ape correlated with the underlying substrate reconstruction. It is found that the island orientations rotate by 180 degrees on alternate elbows, and that the island corners tend to lie on the partial dislocation lines of the herringbone. Noticeable structure exists within the islands, with topographic variations of approximately 0.3 Angstrom. due to intermixing of nickel and gold. Annealing the submonolayer growth at moderate temperatures (450-490 K) results in the formation of large, reconstructed gold islands via a ripening process, and is accompanied by an increase in the amount of gold in the surface layer, as determined by AES. Annealing at a sufficiently high temperature (510 K) results in nearly complete dissociation of the original islands and a disordered herringbone pattern on terraces. Deposition of nickel at 450 K is found to produce gold-rich islands via rapid exchange of nickel with substrate atoms, and subsequent binary (or higher-order) nucleation of gold adatom islands. (C) 1999 Elsevier Science B.V. All rights reserved.