Measurement of the electron density and the attachment rate coefficient in silane/helium discharges

Measurements of the electron density in dc and pulsed silane/helium discharges show that the addition of silane to the gas mixture causes a large reduction in the electron density. By monitoring the electron decay time in the afterglow, it is found that the dominant electron loss mechanism in silane/helium is not ambipolar diffusion to the walls, but instead is a volumetric loss process, most likely dissociative attachment of electrons to a product of the silane dissociation. A lower bound for the rate coefficient for this loss process has been determined to be 2.65×10−10 cm3/sec.