Abstract
The heat of adsorption of CO on Pd overlayers on a Ta(110) single crystal substrate has been measured using temperature programmed desorption (TPD). We find that the Pd monolayer film has a dramatically altered chemistry, weakly chemisorbing CO with an adsorption energy of only 14.4 kcal/mol. This can be contrasted with the value of 34 kcal/mol for the heat of adsorption of CO on the bulk Pd(111) surface. The CO adsorption energy increases with Pd film thickness, returning to the value for bulk Pd for a 3 ML Pd film. The Pd adlayers were characterized using AES, LEED, and Pd TPD to accurately determine the Pd coverage on Ta(110). Pd was shown to grow in a layer-by-layer mechanism at 775 K. The first monolayer adopts a pseudomorphic structure with the Ta(110) surface. Pd films annealed to 1075 K resulted in extensive alloy formation. However, the alloy is capped by a Pd monolayer that has a structure and surface chemistry identical to the as-deposited 1 ML Pd film formed at lower temperatures.
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