The effects of surface geometry and island formation on alkali-promoted surfaces: The coadsorption of CO and K on Ni(110)

The room temperature coadsorption of CO and low coverages of K on Ni(110) has been studied with LEED, thermal desorption spectroscopy, and high resolution electron energy loss spectroscopy (HREELS). The results indicate that two distinct CO species coexist on the surface. A strongly perturbed species is observed that exhibits behavior commonly attributed to alkali-promoted surfaces: a higher thermal desorption temperature and a lower C–O stretch frequency of 1660 cm−1. A very weakly perturbed species is observed that behaves in nearly identical fashion to CO adsorbed on the clean surface. We propose that the appearance of the distinct alkali-promoted species in HREELS is the result of the formation of ordered surface structures of fixed alkali:CO stoichiometry, and suggest that this relationship may be a general one.