Free-standing silicon nano-crystals were synthesized from silicon multi-crystals with high efficiency by induction plasma method. The particle morphology and distribution of nano powder were significantly influenced by powder feed rate, induction plasma power and the ratio of sheath gas. The average particle size monotonously increased with the increase of powder feed rate. The nano powder distribution became more and more concentrated as induction plasma power increased. The average size of nanopowder decreased obviously with the increase of H2 proportion. After the optimization of plasma parameters, mono-dispersed silicon nano-crystals were obtained with an average diameter of 20-85 nm and the mass yield reached a high level as 327 g/h. Meanwhile, the precursor utilization rate exceeded 81.8%. Under the TEM observation, all free-standing silicon nano-crystals had a uniform composition with a single crystal surrounded by a 1-2 nm thick amorphous silicon oxide shell. Although amorphous-like component was detected by Raman spectroscopy, the ensemble of silicon nano-crystals still showed a good crystallinity. The photoluminescence spectrum showed emission peaks in green region around 558 nm, which can be attributed to the oxide-related surface state of silicon nano-crystals.

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