EFFECTIVE CONVERSION OF CO2 TO CARBONATE IN SURFACE OXIDATION PROCESSES AT SI(100)

It is found that effective carbonate formation occurs at a clean Si(10 0) surface between CO2 and surface oxidants: N2O and O-2. The reaction s of CO2 with N2O or O-2 are studied by temperature-programmed desorpt ion and X-ray photoelectron spectroscopy. CO2 physisorbed on Si(100) d esorbs exclusively at similar to 75 K. However, when CO2 is coadsorbed with N2O or O-2, CO2 is converted very effectively into surface carbo nate species below 140 K. The carbonate species are dissociated to pro duce desorbed species of CO or CO2 in the temperature range 200-600 K. By using (CO2)-O-18, it is confirmed that the carbonate is composed o f the adsorbate CO2 and one oxygen atom from the surface oxidant. In t he case of N2O/CO2 coadsorption, the carbonate formation is mainly ind uced by thermal dissociation of N2O adsorbates. In the case of O-2/CO2 coadsorption, the carbonate formation is not only induced by dissocia tive chemisorption of O-2, but also proceeded with chemisorbed dioxyge n that likely adsorbs in a peroxy bridging configuration.