Silicon Nanocrystals Produced by Nanosecond Laser Ablation in an Organic Liquid

Small (3-5 nm in diameter following HRTEM images) Si nanocrystals were produced in a two-stage process including (1) nanosecond laser ablation of a Si target in an organic liquid (chloroform) that results in formation of big composite polycrystalline particles (about 20-100 nm average diameter) and (2) ultrasonic post-treatment of Si nanoparticles in the presence of HP. The post-treatment is responsible for disintegration of the composite Si particles, release of small individual nanocrystals, and reduction of their size due to HF-induced etching of Si oxide. The downshift and broadening of the similar to S20 cm(-1) Raman phonon band of the small Si nanocrystals with respect to the bulk Si Raman band is consistent with the presence of similar to 4.5 nm Si nanocrystals. The photoluminescence spectra (450-900 nm) and decay kinetics of small Si nanocrystals were detected, and the possible origin of the luminescence is discussed.