Electronic properties of Cs layers adsorbed on Pt(111)

Abstract

ARUPS and LEED are combined to study Cs overlayers on Pt(111). The emphasis is given on the correlation of the Cs structures with the WF change, the variation of the sticking coefficient of Cs, and the analysis of the photoemission spectra. At T ≅ 90 K, the Cs sticking coefficient remains constant. At T = 300 K, it is constant only up to θ = 0,25 and subsequently decreases drastically up to monolayer (θ = 0.41). The ARUPS spectra show: (a) the absence of extra peak near E F, (b) a constant BE of the Cs5p levels up to the monolayer and after its completion a large shift (1 eV) for the incipient second layer (c) a flat K ∥ dispersion of the 5p levels and (d) the appearance of an Auger peak at the monolayer. The first effect is related to the low photoelectric cross section for Cs(6s) electrons. All other results derive from a relatively weak interaction between Cs and Pt substrate allowing the formation above θ = 0.33 of a highly compressed incommensurate layer which induces drastic reduction of the sticking coefficient. The correlated high density of free valence electrons explains the occurrence of an OVV Auger transition and the efficient screening of the 5p holes in the first layer.