Adsorption of CO on, and S poisoning of, a perfect Ni(111) single crystal and a Ni(111) crystal with small angle boundaries

A Ni(111) crystal with small angle boundaries was used to examine the adsorption of CO. The adsorption of CO on a perfect Ni(111) single crystal was used for reference. Auger spectra show that the boundary lines on the sample surface provide favorable sites for the adsorbed CO to dissociate at temperatures as low as 25°C. The post-dissociation carbon appears mostly in the form of a nickel carbide on the surface. After heating the crystal to 850°C, sulfur diffused to the surface and blocked the surface adsorption sites uniformly. The boundary-enhanced dissociation of absorbed CO is no longer observed after the diffusion of sulfur to the crystal surface. AES depth profiling of sulfur concentration at different positions on the crystal with respect to the boundary lines show no evidence that the boundary lines provide an enhanced path for sulfur diffusion.