Two- to three-dimensional transition during growth and surface alloy formation of Mn on Pd(100) - art. no. 125401

We show that room temperature growth and alloying of Mn on Pd(100) undergoe s a two- to three-dimensional transition. We have correlated the mesoscopic and atomic-scale structures seen in scanning tunneling microscopy to core- level photoemission and Fourier-transform infrared spectroscopy measurement s which use CO adsorption as a probe of the surface chemical stoichiometry. In this way we have derived a detailed description of the structure and ch emistry of the surface as a function of the Mn coverage. At low coverages, islands of a c(2x2) Mn-Pd surface alloy grow on unreconstructed 1x1 Pd(100) terraces. An epitaxial c(2x2) reconstruction which covers the whole surfac e uniformly is only found for the rather narrow coverage range between appr oximately 0.7 and 1 ML. Above 1 ML, we observe large, three dimensional Pd- Mn ahoy islands situated on a c(2x2) wetting layer. The top surfaces of the se islands have regions of c(2x2) and (1 x 1) symmetry, with the (1 x 1) ar eas terminated by pure Mn.