On the structure of dense CO overlayers

Abstract

A series of dense CO structures formed on the Ni(100), Cu(100) and Pd(100) surfaces have been investigated using high resolution electron energy loss spectroscopy (EELS). The structures were monitored by low energy electron diffraction (LEED). The simple half-monolayer structures i.e. the c(2×2) CO on Ni and Cu and the p(2 2 × 2 ) R45° CO on Pd are fully compatible with on-top site (Ni, Cu) and bridge site (Pd) adsorption, respectively. The denser structures form in a somewhat different manner on the three surfaces, with the common factor that the CO molecules bend in order to accommodate the increasing CO-CO repulsion while still retaining simple coordinations with respect to the substrate surface atoms.