Adsorption of Oxygen on HF-Etched Si(111) Surfaces: XPS Study

X-ray photoelectron spectroscopy studies of the Si(111) surfaces, after dilute HF etching and methanol rinse, are reported. These included a detailed analysis of the main core-levels (Si 2p, O 1s) and the valence band spectra. The observed asymmetry of the O 1s lines was attributed to two contributing subpeaks: the main (1) and the minor one (2), shifted ≈ 1.5 eV to higher binding energies. Their relative intensity was found to depend on the air exposure time and on the take-off angle. The peaks were assigned to two different positions of surface oxygen: (1) O chemisorbed with methoxy group, (2) bridging O atom. The valence band X-ray photoelectron spectroscopy spectra reveal the influence of surface states induced by the "chemisorbed O"-Si bond.