CO adsorption on epitaxially grown Pt layers on Ru (0001)

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 (v(C-O) and v(Pl-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 v(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. (c) 2007 Elsevier B.V. All rights reserved.