Bi adsorption and poisoning on Ni(100) surface as probed by CO chemisorption

CO chemisorption on Bi-modified Ni(100) surfaces, along with the structure and growth of vapor-deposited Bi adlayers on Ni(100), was characterized by Auger electron spectroscopy (AES), temperature-programmed desorption (TPD), low-energy electron diffraction (LEED), energy loss spectroscopy (ELS), UV photoelectron spectroscopy (UPS), work function measurements, and high-res olution electron energy loss spectroscopy (HREELS). Bi growth on Ni(100) at 500 K proceeds via a layer-plus-island (Stranski - Krastanov) growth mode and the gradual formation of a c(2 x 2) structure near monolayer coverage. Desorption of Bi from the first monolayer on Ni(100) occurs with an activat ion energy E-d = 290 = 240 kJ mol(-1). Bi desorption from Bi multilayers ha s E-d = 200 kJ mol(-1). Adsorbed Bi changed the work function of the Ni(100 ) surface only slightly, indicating an initial dipole moment of only -0.5 D and thus relatively little charge transfer between Bi and Ni compared to o ther modifier adlayers. CO chemisorption was used to probe the reactivity o f Ni(100) surfaces modified by preadsorbed Bi adlayers, denoted as Bi/Ni(10 0). Only a small decrease (4 kJ mol(-1)) occurs for the CO adsorption energ y as determined by CO TPD. Site-blocking effects dominate over electronic ( ligand) effects on the surface chemistry of CO on Bi/Ni(100). A comparison of these results to those on Bi/Pt(111), where Bi has been used as a model inert site-blocking agent, indicates that Bi modifies the electronic struct ure of Ni(100) even less than on Pt(111). Therefore. Bi adatoms may allow u seful probing of adsorption and reaction ensemble requirements on Ni surfac es that contain modifiers as adatoms.