Si (111) 7 × 7 clean surface and oxygen chemisorbed stage valence band density of states from L23VV Auger spectra

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Abstract
Valence band density of states of clean, oxygen chemisorbed and initial oxidation stages of Si (111) 7 × 7 surface are presented. The transition densities were obtained by self-deconvolution of L23 VV Auger spectra. The results are correlated directly with the 25% vacancies theoretical model for the clean surface, with molecular state calculations in the case of an oxygen chemisorbed layer and with the band calculations for the silicon oxide. A quantitative method for the Auger intensities analysis is presented, allowing the authors to characterise the oxygen chemisorbed stage for oxygen coverages lower than 0.6 monolayers (1 Å of O2 equivalent to 0.8 ml) and the initial oxidation stage for SiO2 coverages approximately=0.2 ml (1 Å SiO2 equivalent to 0.31 ml). The surface states of clean Si (111) 7 × 7 were observed directly on the self-deconvoluted spectrum. The oxygen chemisorbed stage is characterised by the attenuation of the surface state corresponding to normal surface dangling bonds and the appearance of two sub-bands at 4 and 10 eV which are characteristic of the molecular configuration of the chemisorbed oxygen. The initial oxidation stage shows a significant reduction in the vacancy dangling bond surface states and the appearance of the characteristic peak at 5.6 eV previously observed in UPS experiments.