The mechanism of film deposition by particle-beam induced polymerization

Deposition of polymer films from the vapor phase by an electron beam has been studied using a variety of siloxanes and aromatic compounds. Octamethyltrisiloxane and vinylaphthalene have been studied in detail. Applying a simple kinetic model we have discussed single grafting as well as chain reactions as possible mechanisms for the deposition. It is shown that a convenient way to decide between the mechanisms is to study the dependence of the growth efficiency as a function of the flux of incident monomer molecules and to combine these results with measurements of the time constants. Experiments of this kind have been performed using pulsed beams and a gas friction pressure gauge to determine the molecular flux. Results indicate that chain reaction is the predominant process, but the number of centers from which further chain reactions can start is low in the already deposited film thus leading to low deposition rates. (IAF)