ADSORPTION AND PHOTODECOMPOSITION OF MO(CO)(6) ON SI(111) 7X7 - AN INFRARED REFLECTION-ABSORPTION SPECTROSCOPY STUDY

The adsorption and photodecomposition of Mo(CO)(6) adsorbed on Si(111) 7X7 surfaces has been studied with Auger electron spectroscopy, tempe rature programmed desorption, low energy electron diffraction and infr ared reflection absorption spectroscopy in a single external reflectio n configuration. The external-reflection technique is demonstrated to have adequate sensitivity to characterize submonolayer coverages of ph otogenerated Mo(CO)(x) fragments. It is proposed that the first layer of Mo(CO)(6) adsorbs in ordered islands with a Mo(CO)(6) atop each ada tom of the 7X7 reconstructed Si surface. UV irradiation of these islan ds produces a carbonyl fragment, identified as chemisorbed Mo(CO)(5). The Mo(CO)(5) thermally decarbonylates via two subcarbonyl intermediat es with little CO dissociation. Photolysis of thicker layers results i n the formation of Mo-x(CO)(y) dimers/polymers, as evidenced by the ap pearance of bridging CO, which is attributed to a facile association r eaction. The dimer/polymer species correlate with deposition of C and O on the surface.