Oxygen chemisorption and oxide formation on Si(111) and Si(100) surfaces

We have used photoemission techniques with synchrotron radiation to study the adsorption of oxygen on the Si(111)–(7 × 7) and Si( 100)–(2 × 1) surfaces at room temperature in the submonolayer and monolayer regimes. High resolution Si 2p core-level spectra, valence-band spectra, workfunction, and Fermi-level pinning positions have been measured for exposures between 1 and 1000 L and after annealing at 700 °C. Four oxidation states have been detected for the silicon surface atoms with Si 2p core-level shifts of 0.9, 1.9, 2.6, and 3.4 eV which are assigned to silicon atoms bonded to 1, 2, 3, and 4 oxygen atoms. Both (111) and (100) surfaces are characterized by about the same sticking coefficient, a simple adsorption process for 1-L exposures, the quenching of the surface states after 15 L and a saturation of the amount of oxygen after 100 L. Significant differences exist in the initial bonding geometries for the (111) and (100) surfaces. After 15-L exposure, oxygen atoms are incorporated below the Si (l11 )-(7 × 7) surface to form SiO4 units. © 1983, American Vacuum Society. All rights reserved.