Abstract
Potential energy barriers for dissociative chemisorption of O2 molecules on clean and H2O-preadsorbed Si(001) surfaces were verified using supersonic O2 molecular beams and synchrotron radiation photoemission spectroscopy. The saturated oxygen amount on both kinds of Si(001) surfaces were measured as a function of incident energy of O2 molecules. The saturated oxygen amount was dependent in both cases on the incident energy. Especially, two energy thresholds appeared in the H2O-preadsorbed Si(001) surface oxidation. An Si-2p photoemission spectrum for the oxygen-saturated Si(001) surface formed by O2 gas possessing incident energy below the first threshold on the clean surface revealed the oxygen insertion into backbond sites of Si dimers. The dimer backbonds, however, were not oxidized by O2 irradiation without incident energy larger than 1.0 eV in the H2O-preadsorbed surface. These facts indicate that a chemisorption reaction path of the oxygen insertion into dimer backbonds through bridge and dangling bond sites is open for the clean surface oxidation, and the path is cut by termination of dangling bonds by H and OH radicals.
