Ionoluminescence induced by low-energy proton excitation of Si nanocrystals embedded in silica

Silicon nanocrystals (Si-nc) can be synthesized into a silica matrix by ion implantation of silicon excess, followed by thermal annealing in N2 or Ar atmosphere. In this work, ionoluminescence (IL) measurements have been performed on fused silica samples containing Si-nc using a 18 keV proton beam for the IL excitation. This low energy irradiation has allowed us to reduce the IL probing range to the first 300 nm of the studied materials, thus enhancing the contribution to the IL signal of the sample region where the Si-nc are located. A transmission optical detection set-up has been developed to ensure the collection of a strong IL signal. Comparison of the data recorded between 300 and 800 nm shows that the IL intensity decreases for long excitation times in Si-nc samples, whereas the IL signal intensity remains remarkably stable in pure SiO2 sample. The variations observed for samples with Si-nc are attributed to the damaging effects induced by the impinging protons. The sample annealed under N2 exhibits a stronger IL emission than the sample annealed under Ar, where both the concentration of residual defects and the excitation efficiency of the radiative centers could be lower. The results make the IL measurements a promising tool for in situ monitoring of ion implantation with pure fused silica samples, as well as a promising technique for novel characterizations of Si-nc embedded within SiO2.