In a radio frequency or high frequency discharge, electrons are accelerated toward the central plasma region by oscillating sheath electric fields. In a dc discharge, a cathode sheath field provides steady electron acceleration into the plasma. These accelerations provide the energy deposition to the discharge, and the same (time averaged) sheath fields drift positive ions toward the rf electrodes or dc cathode. In a dc discharge, a much smaller but important field also accelerates electrons away form the anode, or any insulating walls, into the central plasma. This provides current continuity at the anode and ambipolar diffusion to insulators, as electrons back diffuse against this field. Discharge electrons can attach to silicon-bearing gases, and since sheath fields accelerate electrons toward the plasma, they also trap these negative ions in the plasma. Since the negative ions have the vapor thermal energy, while sheath voltages are several volts (dc) to 100 V (rf), negative ions are very effectively trapped in the central plasma regions of discharges. This provides time for negative ions to grow in size, by reacting with radicals and cations in the same manner as the growing film. The net effect is that silicon-based particles are produced in discharges that include silane (SiH4), and similarly for discharges in hydrocarbons or germanes. This can be viewed as an inevitable consequence of the deposition character of the plasma conditions, and the relatively large electron affinity of C, Si, and Ge.