Comparative Investigation of Mo(CO)₆ Adsorption on Clean and Oxidized Si(111) Surfaces

Mo(CO)₆ adsorption on the clean, oxygen-precovered and deeply oxidized Si(111) surfaces was comparatively investigated by high-resolution electron energy loss spectroscopy. The downward vibrational frequency shift of the C-O stretching mode in adsorbed Mo(CO)₆ illustrates that different interactions of adsorbed Mo(CO)₆ occur on clean Si(111) and SiO₂/Si(111) surfaces, weak on the former and strong on the latter. The strong interac-tion on SiO₂/Si(111) might lead to the partial dissociation of Mo(CO)₆, consequently the formation of molybdenum subcarbonyls. Therefore, employing Mo(CO)₆ as the precursor, metallic molybdenum could be successfully deposited on the SiO₂/Si(111) surface but not on the clean Si(111) surface. A portion of the deposited metallic molybdenum is transformed into the MoO₃ on the SiO₂/Si(111) surface upon heating, and the evolved MoO₃ finally desorbs from the substrate upon annealing at elevated temperatures.