Nanometer scaled single-crystal particles of Si have been prepared by heating of amorphous SiO in an inert atmosphere. X-ray powder diffraction data on the quenched specimens have revealed that the Si crystallization in cooperation with the disproportionation reaction of SiO to Si and SiO2 starts around 850degreesC and becomes very rapid above 1000degreesC. High-resolution electron diffraction observations show that below 1000degreesC, fine Si particles precipitate in a single crystal form with a diameter of 4-5 nm, and the amount, rather than the size, of the precipitated particles gradually increases with the annealing time. It is suggested that Si atoms of about 2 x 10(3) gather together between 850degreesC and 950degreesC to make a single particle and migration of Si atoms proceeds with a maximum diffusion length of < 7 nm in the amorphous medium of Si and O. (C) 2002 Published by Elsevier Science B.V.