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 HF. 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 ∼520 cm−1 Raman phonon band of the small Si nanocrystals with respect to the bulk Si Raman band i…