STRUCTURE OF CLEAN CU85PD15(110) AND SURFACE RESTRUCTURING INDUCED BY CS ADSORPTION

The equilibrated clean surface of a Cu85Pd15{110} alloy single crystal exhibits a (2 × 1) superstructure. The superstructure may be attributed to an outermost two-layer slab consisting of a pure Cu and a mixed Cu-Pd layer, the (2 × 1) periodicity arising from a double-spaced Pd superstructure in the [110] direction in the mixed layer. The surface does not chemisorb CO at 300 K, suggesting an outermost layer of pure Cu or alternatively implying an unusually low heat of desorption for CO bonded on Pd "on-top" sites (< 80 kJ mol-1). Cs adsorption drives a (1 × 2) reconstruction of this surface to produce a LEED pattern of (2 × 2) symmetry. The alkali-metal coverage dependence, kinetics of the transition and thermal stability of the (2 × 2) phase have been studied. The optimal Cs coverage required to drive the phase transition to completion, 0.14 monolayers, lies between those coverages required to reconstruct the {110} surfaces of Pd and Cu. Conflicting with these observations are the results of Li adsorption. Submonolayer coverages of Li do not drive a (1 × 2) reconstruction of the Cu85Pd15{110} surface. © 1990 Elsevier Science Publishers B.V. (North-Holland).