Hydrogen-terminated silicon nanoparticles were synthesized over a broad range of conditions in a continuous flow, nonthermal rf plasma. The effects of three operating parameters-rf power, reactor pressure, and hydrogen flow rate-were examined in terms of their effects on particle crystallinity, size, and surface composition. Silicon-hydrogen composition was characterized in situ by Fourier transform infrared spectrometry, and particle structural morphology was examined with a transmission electron microscope. Amorphous or crystalline particles could be synthesized by appropriately adjusting the operating parameters. Over the majority of settings examined, the minimum power required to produce discrete crystalline particles was similar to 20-30 W. Depending on the parameter settings, particles also exhibited hydrogen coverage ranging from predominantly monohydride (SiH) functional groups to more complex compositions of higher hydrides. Particles with the highest proportion of surface SiH bonds were consistently synthesized in the smallest diameter (4 mm i.d.) tube reactor. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3276451]