Adsorption of Methanol on Si(001): Reaction Channels and Energetics

Adsorption of methanol on Si(001) was studied by means of X-ray photoelectron spectroscopy (XPS), molecular beam techniques, and scanning tunneling microscopy (STM) at surface temperatures between 50 and 800 K. Even at lowest temperatures, only the final reaction products, i.e., a silicon bound methoxy group and a Si–H entity, were observed in the XPS and STM experiments. However, the initial sticking probability drops with increasing surface temperature, indicating that the reaction proceeds via an intermediate state. Two final configurations with the dissociation products adsorbed either on one or two silicon dimers were observed; their branching ratio does not change with temperature, indicating very similar, low conversion barriers for the two pathways.