Structural and optical properties of surface-hydrogenated silicon nanocrystallites prepared by reactive pulsed laser ablation

Pulsed laser ablation (PLA) in an inert background gas is a promising technique for preparing Si nanoparticles. Although an inert gas is appropriate for preparing pure material, a reactive background gas can be used to prepare compound nanoparticles. We performed PLA in hydrogen gas to prepare hydrogenated silicon nanoparticles. The mean diameter of the primary particles measured using transmission electron microscopy was approximately 5 nm. The hydrogen content in the deposits was very high and estimated to be about 20%. The infrared absorption corresponding to Si-H, (n = 1, 2, 3) bonds on the surface were observed at around 2100 cm(-1). The Raman scattering peak corresponding to crystalline Si was observed, and that corresponding to amorphous Si was negligibly small. These results indicate that the Si nanoparticles were not an alloy of Si and hydrogen but Si nanocrystallite (nc-Si) covered by hydrogen or hydrogenated amorphous silicon. This means that PLA in reactive H-2 gas is a promising technique for preparing surface passivated nc-Si. The deposition mechanism and optical properties of the surface passivated silicon nanocrystallites are discussed.