Atomic-Scale Chemistry of Metal Surfaces

Abstract

The idea of pseudo-molecules is deduced from reviewing the results of scanning tunneling microscopy (STM) of metal surfaces. Ni(110), Cu(110), and Ag(110) surfaces exposed to H₂ or O₂ at room temperature reveal the formation of one-dimensional pseudo-molecules, which is essentially different from the phenomenon of adsorption. The pseudo-molecules produced on the surface are in an ordered arrangement on these metal surfaces, where the arrangement is influenced by their lateral interaction. The -Cu-O- chains oriented along the direction coalesce to form a p(2×1) arrangement on the Cu(110), but the added -Ag-O- rows on the Ag(110) surface may not prefer the p(2×1) structure, because the p(2×1) -Ag-O- added row induces a large distortion of the substrate Ag atoms. As a result, the added -Ag-O- rows undergo sequential change of the p(n×1) structures. When the p(2×1) -Cu-O- island is annealed at 550-640 K, the p(2×1) overlayer bunches into regular-sized in-phase p(2×1) -Cu-O- islands. In contrast, reordering of the (2×1) -Ag-O- overlayer to (4×1) at 500 K yields narrow out-of-phase (4×1) domains with the wavering domain boundaries. Based on these results, the influence of pseudomolecules on catalysis is predicted.