Infrared study of triruthenium dodecacarbonyl interactions with gold

We present here a study of the interaction of triruthenium dodecacarbonyl Ru ₃(CO) ₁₂ with gold surfaces using time-evolved and temperature-programmed infrared reflection absorption spectroscopy (IRAS) and STM. Ru ₃(CO) ₁₂ exhibits drastically different adsorption/desorption behavior on high-index surfaces of gold in comparison to the smooth Au(111) surface. On the smooth Au(111) surface, the adsorption of Ru ₃(CO) ₁₂ at 200 K is observed to be molecular and reversible with the molecule's Ru ₃-plane oriented essentially perpendicular to the surface in the first and second layer. In the multilayer (> 3 ML), the molecule is oriented parallel (or moderately inclined) to the surface. On high-index gold surfaces, prepared by partial annealing of rough gold films, the molecules dissociate. Vibrational spectra reveal dissociation of carbonyl to Ru and CO at elevated temperature (> 250 K) with the formation of CO covered Ru-islands and the subsequent desorption of CO from Ru-islands. Increasing amounts of CO observed with increasing surface roughness demonstrate that the rate of Ru ₃(CO) ₁₂ dissociation is related directly to the surface roughness of the gold surface. STM images reveal at low coverage the formation of 2-D islands of carbonyl fragments with lateral sizes of 1 to 1.5 nm and at higher coverage the formation of larger 3-D islands of 1 to 3 layers and lateral sizes above 10 nm.