XPS Studies of Silicon Nanoclusters/Nanocrystals Embedded in SiO2 Matrix

In this study, the analysis of the XPS Si 2p peaks shows the existence of the five chemical structures corresponding to the Si oxidation states Si n+ (n =0, 1, 2, 3, and 4) in Si-implanted SiO2 films, and the concentration of each oxidation states is determined quantitatively. The evolution of the five Si oxidation states as a function of thermal annealing is studied. On the other hand, Si 2p core levels of Si nanocrystals (corresponding to the Si oxidation state Si 0 ) embedded in SiO2 matrix have been determined also. After the correction of the charging effect, the core level of Si nanocrystals (nc-Si) is found to shift towards a lower binding energy, which is contrary to the prediction of the existing theories that the core level of Si nanocrystals should shift towards a higher binding energy due to the quantum size effect. It is suspected that the corelevel shift of the nc-Si towards a lower binding energy is due to the influence of the differential charging between the SiO2 surface layer and the nc-Si underneath.