INTERACTION OF MN WITH THE RU(001) SURFACE AND CHEMISORPTION OF CO ON THE MN/RU(001) INTERFACE

The interaction of vapor-deposited Mn with the Ru(001) surface and its effect on CO chemisorption were studied under ultrahigh vacuum by Auger electron spectroscopy (AES), thermal desorption spectroscopy (TDS), isotopic exchange, and low-energy electron diffraction (LEED). At room temperature, Mn grows layer by layer. The first three layers are pseudomorphic with respect to the Ru substrate. At higher coverages, manganese layers adopt a commensurate structure with a (√3×√3)R30° LEED pattern. At coverages of more than 10 layers, the growing layer of manganese becomes disordered. Disordered and √3 structures are thermally unstable, and annealing to 700 K leads to their transformation to a (1 × 1) pseudomorphic structure, together with a large decrease in the Mn/Ru AES ratio. A complete analysis of Mn thermal desorption data shows that there is a decrease of the heat of adsorption with increasing coverage within the first monolayer (69 to 55 kcal/mol) and zero-order desorption for higher coverages with desorption energy 54 kcal/mol. A new, higher temperature CO desorption state at 650-800 K appears at submonolayer coverages. The C-O bond of CO chemisorbed on Mn/Ru is severely weakened and probably dissociated as evidenced by a high CO desorption temperature and random isotope mixing of coadsorbed isotopes of carbon monoxide. © 1990 American Chemical Society.