Observation of oscillating behavior in the reflectance difference spectra of oxidized Si(001) surfaces

Layer-by-layer oxidation of Si(001)-(2×1) surfaces was observed using the reflectance difference (RD) spectroscopy. Distinctive features in the RD spectra appeared near the E1 (3.3 eV) and E2 (4.2 eV) transition energies of Si. The polarity of these features was repeatedly reversed as the oxide thickness was increased to 4 monolayers (MLs). Oscillation of the RD amplitude near the E1 transition energy was observed in real time during the oxidation process. A half period of the oscillation corresponds to the oxidation of 1 ML. These results demonstrate the possibility of in situ counting and control of the number of oxidized layers.