The influence of adsorbed Bi on the chemisorption properties of Pt(111):H2, CO, and O2

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Abstract
The growth modes and interactions of vapor-deposited Bi on a clean Pt(111) surface and its effects on the chemisorption of H2, CO, and O2 have been monitored by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and thermal desorption mass spectroscopy (TDMS). For submonolayer Bi coverages, LEED patterns were observed to progress with increasing coverage through p(2×2), ( 7/8 × 7/8 )R30°, p(3×3), and p(4×4) structures. The Bi TDMS and AES data are consistent with proposed structural models giving absolute coverages of 0.25, 0.33, 0.44, and 0.56, respectively. For submonolayer coverages of this s2pn-type metal, Bi adatoms are strongly repulsive and maximize their spacing subject to the constraints of the Pt(111) sites. This is to be contrasted with dnsm-type metals such as Ag, Cu, and Au on Pt(111), which show attractive interactions and coalesce into 2d islands. In chemisorption of small molecules on Pt(111), each Bi adatom blocks about two Pt surface atoms. An ensemble of two adjacent Pt sites is required for both dissociative H2 and molecular O2 adsorption versus one site for CO adsorption; therefore, uptake of the former adsorbates is much more severely attenuated as θBi increases.

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