Investigation of diamond-like carbon formed on PET film by plasma-source ion implantation using C 2 H 2 and CH 4

The characteristics of amorphous carbon films deposited on polyethylene terepthalate (PET) film by plasma-source ion implantation (PSII) using C 2 H 2 and CH 4 gases are examined. PSII is performed using a pulsed, high negative bias (∼9 kV, ∼10 μs pulse width, 300 pulses/s) to form the self-excited discharge for processing. The use of CH 4 at lower gas pressure modified the PET film by direct implantation of carbon atoms to form a mixing layer with high C–H bond density, in contrast to formation using C 2 H 2 which forms a surface coating of amorphous carbon. At higher gas pressure, CH 4 was found also to produce a surface layer of amorphous carbon. The films produced using CH 4 were found to consist primarily of hydrogenated graphite crystal with C–H, C–H 2 and C–H 3 components. The oxygen transmission rates (OTR) of PET treated with CH 4 were reduced by a factor of 50–70 from that of untreated PET at a carbon film thickness of only ∼50 nm, however the transmission rate reduction per unit thickness of film was lower than for films formed using C 2 H 2. The surface modification with CH 4 is a viable alternative method for reducing the OTR. The relationships between the gas conditions and the properties of the carbon films are discussed.