DIRECT-CURRENT CATHODIC GLOW-DISCHARGE POLYMERIZATION OF METHANE AND BUTANE

The deposition of a polymeric material on the surface of the cathode o f a direct current (dc) glow discharge was investigated for methane an d butane. The cathode region of a de 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 pol ymerization 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), volu me flow rate, and discharge power on the deposition rate in a de glow discharge were investigated and compared with those in an audio freque ncy and a radio frequency glow discharge. It was found that the deposi tion rate expressed in (thickness growth rate)/(M) is linearly proport ional to the current density, which implies that cathodic polymerizati on is controlled by the cathode region parameter (not plasma parameter s). 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. (C) 1998 John Wiley & Sons, Inc.