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

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 A of O2 equivalent to 0.8 ml) and the initial oxidation stage for SiO2 coverages approximately=0.2 ml (1 A 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.