The first level plasmons of Si in the pure Si state （corresponding to bonding energy （BE） of 116.95 eV） and in the SiO2 state （corresponding to BE of 122.0 eV） of Si-SiO2 prepared by irradiation hard and soft processing were studied with XPS before and after 60Co radiation. The experimental results indicate that there was an interface consisting of the two plasmons, this interface was extended by 60Co radiation, the fractions of the plasmon for Si in the Si-SiO2 were changed with the variation of radiation dosage, the difference of the change in fraction of plasmons for the two kinds of samples was that the soft varied faster than hard, the change of concentrations in plasmons for both hard and soft Si-SiO2 irradiated in positive bias field were greater than that in bias-free field. The experimental results are explained from the view point of energy absorbed in form of quantization.
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