Nucleation and growth of Au overlayers on Pt(100)-hex-R0.7° studied by STM and photoelectron spectroscopy

The nucleation and growth of Au overlayers on the hexagonally reconstructed Pt(100) surface have been studied by scanning tunneling microscopy (STM) and photoelectron spectroscopy. Adsorption of Au atoms on Pt(100)-hex-R0.7 degrees induces a local lifting of the surface reconstruction of Pt, in units of reconstruction rows. The anisotropy of the Pt reconstruction leads to anisotropy in Au surface diffusion, as well as in growth of the Au overlayer. Au forms rectangular (1 x 1) islands of monolayer height, with the long axis of the islands being parallel to the rows of the Pt(100) hexagonal reconstruction. Nucleation occurs at both flat terraces and step edges, preferably at step edges intersecting the reconstruction rows. Islands also nucleate at structural defects in the surface. The STM images show that Pt atoms are incorporated into the first monolayer Au islands, contributing to about 20% of the island area. Growth of the second monolayer islands starts well before completion of the first monolayer. The first and second monolayers grow simultaneously until the first monolayer is nearly completed, without any nucleation of third monolayer islands. Further growth proceeds in a quasi-layer-by-layer mode. After deposition of more than 4 ML of Au, a (1 x 7) surface reconstruction is seen to emerge. High-resolution photoelectron spectroscopy measurements show contributions to the Au 4f(7/2) core level spectrum from Au atoms in four different local environments in the surface: Au atoms at the Pt interface at (83.32 +/- 0.02) eV binding energy, surface Au atoms with (1 x 1) symmetry at (83.50 +/- 0.02)eV binding energy, surface Au atoms with a (1 x 7) symmetry at (83.63 +/- 0.02) eV and bulk-like Au atoms at (83.87 +/- 0.02) eV. (C) 1998 Elsevier Science B.V. All rights reserved.