Formation of luminescent Si nanocrystals by ion irradiation

Intense red emission is achieved in silicon nanocrystals (SiNCs) grown by atom beam sputtering (ABS) followed by ion beam irradiation (IBI). The silicon rich silicon oxide thin films are grown by ABS technique with target consisting of 60% silicon-in-excess + SiO2. To precipitate the excess silicon in the form of nanocrystals, samples were processed under IBI post deposition treatment. IBI of the films is carried out using a 160 MeV Ni+ 11 ion beam at fluences 5 × 1012, 1 × 1013 and 5 × 1013 ions/cm2. The transmission electron microscopy (TEM) studies reveal that the size of the nanocrystals increases monotonically as the ion fluence is increased. The IBI treated samples show almost monodispersion at all fluences and the size of the particles can be controlled precisely by ion fluence. The photoluminescence (PL) studies support the TEM results and an intense emission with a red shift is observed as the particle size is increased with an increase in ion fluence. The asymmetry in transverse optical (TO) vibrational mode in Raman spectra also suggests the formation of SiNCs in the SiO2 films.