BISMUTH ADSORPTION ON PT(110) AND THE COADSORPTION OF CARBON-MONOXIDE

The adsorption of bismuth on Pt(110)-(1 x 2), and its coadsorption wit h CO, has been investigated using TPD, XPS, LEED and work function mea surements. Bismuth adsorption lifts the (1 x 2) surface reconstruction at coverages theta(Bi) > 0.3. The adsorbate induced lifting of the cl ean surface reconstruction is activated, and annealing the surface abo ve 350 K results in more complete ordering and the formation of. a ser ies of ordered bismuth overlayers on Pt(110)-(1 x 1). At theta(Bi) = 0 .5, a c(2 x 2) structure is observed. LEED measurements indicate that higher coverages are achieved by a uniaxial compression of this center ed overlayer structure, subsequently converting above theta(Bi) = 0.7 to a (3 x 1) and streaked (4 x 1) structure. Saturation coverage is es timated to be theta(Bi) = 0.75. Bismuth blocks CO adsorption through a local, short range interaction, resulting in a linear decrease in CO coverage with increasing bismuth coverage. CO adsorption is completely poisoned at the saturation coverage of theta(Bi) = 0.75. Coadsorption of low coverages of bismuth with CO produces a new, c(2 x 4) structur e which we associate with an ordered mixed phase of the adsorbates wit h theta(CO) = 0.5 and theta(Bi) = 0.25. At higher coverages of bismuth , the co-adsorbed CO phase does not disrupt the ordered bismuth layers observed in the absence of CO. Bismuth adsorption also favours the de sorption of CO from the low temperature (alpha) desorption peak, which we associate with repulsive interactions.