Anomalous behaviour in resonant Auger emission of SiO x thin films

Abstract

Silicon oxide (SiO x , x≈1.3) films ∼100 Å thick were prepared by evaporation from a silicon monoxide source. The stoichiometry and chemical state of the samples were characterised by X-ray photoemission spectroscopy showing that they can be described as a mixture of Si + and Si 3+ species. Further characterisation was done by X-ray absorption spectroscopy at the Si K edge. Resonant Auger effects were studied by tuning the photon energy across the Si K edge and measuring the corresponding excited Auger spectra. A strong and ‘anomalous’ dispersion is found for the resonant Si KLL Auger peak, probably associated to Si + species: in this case, the energy of the Si KLL signal decreases when the photon energy is increased across the Si K edge. This behaviour is the opposite of that observed for Si 4+ species in SiO 2 and for similar Auger resonant phenomena studied for many materials. It is also in apparent contradiction with the prediction of the available theories of resonant Auger emission. Resonant Auger spectroscopy appears to be an adequate technique to distinguish between different electronic environments in SiO x interfaces or compounds. Moreover, for the range of compositions studied here, it is proposed as a mean to establish whether the different Si n+ species are distributed through a common SiO network or are segregated into separated phases.