NUCLEATION AND GROWTH OF AU OVERLAYERS ON PT(100)-HEX-R0.7-DEGREES STUDIED BY STM AND PHOTOELECTRON-SPECTROSCOPY

The nucleation and growth of Au overlayers on the hexagonally reconstr ucted Pt(100) surface have been studied by scanning tunneling microsco py (STM) and photoelectron spectroscopy. Adsorption of Au atoms on Pt( 100)-hex-R0.7 degrees induces a local lifting of the surface reconstru ction of Pt, in units of reconstruction rows. The anisotropy of the Pt reconstruction leads to anisotropy in Au surface diffusion, as well a s 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 inters ecting the reconstruction rows. Islands also nucleate at structural de fects in the surface. The STM images show that Pt atoms are incorporat ed into the first monolayer Au islands, contributing to about 20% of t he island area. Growth of the second monolayer islands starts well bef ore completion of the first monolayer. The first and second monolayers grow simultaneously until the first monolayer is nearly completed, wi thout any nucleation of third monolayer islands. Further growth procee ds 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-resolu tion 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) symm etry 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.