Oxidation processes for Si(1 1 1)-7×7 surfaces analyzed in situ by synchrotron-radiation-induced photoemission and medium energy ion scattering

Initial oxidation processes for Si(1 1 1)-7×7 surfaces were analyzed in situ at the Beamline 8 named SORIS connected to a compact superconducting storage ring, which allows photoelectron spectroscopy (PES) and medium energy ion scattering(MEIS). Oxidation was performed at room temperature (RT) under O2 pressure of 1×10− 8 Torr. The MEIS measurement using 60 keV H+ ions determined the absolute amounts of O as a function of O2 exposure and the PES analysis with 40 and 134 eV photons gave the information about the molecular states and the coverage of each oxidation state ( Si+, Si2+, Si3+ and Si4+). The oxidation is saturated with O coverage of 1.7 ML (1 ML: 0.783×1015 atoms/cm2) at O2 exposure of 5 L (1 L: 1×10−6 Torr s). At this stage, the backbonds of the adatoms and rest atoms are almost oxidized. This situation supports the recent prediction based on the density functional theory.