Direct current cathodic glow discharge polymerization of methane and butane

Abstract

The deposition of a polymeric material on the surface of the cathode of a direct current (dc) glow discharge was investigated for methane and butane. The cathode region of a dc glow discharge is not a plasma in a strict sense. Consequently, the deposition of a polymeric material to the cathode surface differs significantly from so-called plasma polymerization of the same monomer (starting gas or vapor) that deposits on a substrate placed in a glow discharge plasma. Using methane and n-butane, the influence of the molecular weight of the monomer (M), volume flow rate, and discharge power on the deposition rate in a dc glow discharge were investigated and compared with those in an audio frequency and a radio frequency glow discharge. It was found that the deposition rate expressed in (thickness growth rate)/(M) is linearly proportional to the current density, which implies that cathodic polymerization is controlled by the cathode region parameter (not plasma parameters). The refractive indices (632.8 nm) for the cathodic polymers are in the range of 2.2–2.4 while those for plasma polymers are in the range of 1.5–1.7. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 237–245, 1998