Two- to three-dimensional transition during growth and surface alloy formation of Mn on Pd(100)

摘要

We show that room temperature growth and alloying of Mn on Pd(100) undergoes 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 measurements 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 chemistry 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 surface uniformly is only found for the rather narrow coverage range between approximately 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 these islands have regions of c(2x2) and (1 x 1) symmetry, with the (1 x 1) areas terminated by pure Mn.