We have studied the formation of Si nanoparticles in a SiH4-Ar plasma discharge generated in a helical resonator type inductively coupled plasma reactor. It is observed that Si particles vary in sizes from 5 to 15 nm under different conditions. The particles were mostly spherical and made up of a crystalline core with a 1-2 nm thick amorphous shell. The size distribution was narrow for particles formed at a pressure of 200 mTorr, plasma power of 400 W acid silane flow rate of 20 seem (+980 seem Ar). The effect of a de bias applied to the particle collecting grids has also been studied. It is found that a negative bias (-25 to -100 V) applied to the grids used for particle collection results in a large increase in the number of Si nanoparticles collected, while a positive bias does not change the collection efficiency considerably, suggesting that the particles are positively charged. Under very low flow rates and under high plasma powers, the Si particle density decreases considerably and a film like deposition occurs on transmission electron microscopy grids placed in the reactor for collecting the particles. We have also studied the formation of Ge particles (50-200 nm) in a GeH4-Ar plasma generated in the same reactor. These particles are crystalline with a spherical morphology.