Silicon powders produced in a low pressure silane plasma show varying structural properties depending on the location of collection of the powders in the reactor. This is revealed by high resolution transmission electron microscopy, infrared and Raman spectroscopy. The particulates are found to consist either of heterogeneously distributed amorphous and crystalline phases or of nanoscale particles with amorphous and molecular like spectral features as found from the Raman spectroscopic studies. Infrared spectra show clustered silicon‐hydrogen phases and the presence of oxidized phases in the powder, upon exposure to atmosphere. Phonon confinement effects due to the nanometer size and expansive strain is observed in the vibrational Raman spectra. The average particle size estimated from the observed phonon quantum confinement corresponds with the particle sizes observed by high resolution electron microscopy if strain contributions are included. Annealing at temperatures as low as 300 °C leads to Raman vibrational band similar to crystalline silicon. ©1995 American Institute of Physics.