Pd/Pt(111) surface structure and metal epitaxy by time-of-flight impact-collision ion scattering spectroscopy and scanning tunneling microscopy: Does lattice mismatch really determine the growth mode?

We have investigated the growth of 3 NIL of Pd on Pt(1 1 1) at substrate temperature of around 300 K using TOF-ICISS. Also a series of STM topographs were taken as a function of coverage of Pd atoms. The Pd-Pt(1 1 1) combination does not have lattice mismatch (less than 1%); the nearest neighbor distance of bulk Pd(1 1 1) and Pt(1 1 1) are 2.75 angstrom and 2.77 angstrom, respectively. Experimental data and computer simulations result clearly show the growth mode of Pd(1 1 1) [(2) over bar 1 1 ]/Pt(1 1 1) [(2) over bar 1 1] hetero epitaxy at the coverage of the Pd deposition less than 3 ML. The growth mode of Pd(1 1 1) [(1) over bar (1) over bar 2]/Pt(1 1 1) [(2) over bar 1 1] could not be observed at all. One would expect that the growth mode of Pd atoms on Pt(l 11) surfaces is like homo epitaxy (layer-by-layer growth), because of no lattice mismatch (less than 1%). However, it was not. The calculated surface and interface energies and STM results show 2D or 3D dimensional island growth. I'd atoms is mainly form dense islands at the steps on Pt(1 1 1) surfaces at the coverage of 0.13 ML. (c) 2008 Elsevier B.V. All rights reserved.