Abstract
The adsorption of CO on epitaxially grown Pt films of variable thickness has been studied using infrared-absorption spectroscopy, scanning tunnelling microscopy and thermal desorption spectroscopy. Depending on the number of pseudomorphic Pt layers ( N Pt = 1–4) the internal and external CO stretching modes ( ν C–O and ν Pt–CO, respectively) display characteristic frequency shifts due to the vanishing influence of the underlying Ru(0 0 0 1) substrate and Pt/Ru interface. For thicker layers ( N Pt ⩾ 5) when this influence has become negligible, the compressive stress within the Pt film is gradually relieved, leading to a dislocation network. The structural heterogeneity during the ongoing relaxation process of the Pt film is reflected in the ν C–O line shape; no line broadening is observed for either pseudomorphic or very thick films ( N Pt ⩾ 15). For N Pt ⩾ 3 the adsorption of CO on Pt/Ru(0 0 0 1) films closely resembles CO on Pt(1 1 1), with residual deviations in line position and desorption temperatures gradually converging to zero.
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