The synthesis of single-crystal silicon nanocrystals we present is performed in the gas phase of a radio frequency (rf) discharge. The plasma is produced in a discharge box, enclosed in a vacuum vessel, containing an Ar/SiH4 mixture (92:8). The typical pressure is 0.12 mbar while typical rf injected power is 10 W. Gas temperature can be decreased to -40 °C. Dust particle formation and growth is monitored thanks to an electrical diagnostics based on the time evolution of the discharge current third harmonic amplitude (3H). Size, density and crystallinity of dust particles are determined thanks to microscopy (SEM, TEM, AFM).