Gas barrier properties of carbon films synthesized by atmospheric pressure glow plasma

High gas barrier carbon films were successfully synthesized on top of polymer substrates using an atmospheric-pressure glow (APG) plasma CVD equipment by reducing the discharge area and by changing the size of the electrodes of the equipment. Homogeneous and highly stable plasma was constantly generated under an atmosphere of acetylene gas (C₂H₂) without using any other dilution gases such as He, Ar and N₂ that are generally used in order to stabilize the plasma. The absence of the dilution gases led to form rigid carbon-to-carbon bonds. The rigid C bonds constructed dense carbon films at the very surface of the coated films with high gas barrier properties. The oxygen transmission rates of the polyethylene terephthalate (PET) film coated with this amorphous carbon (a-C:H) material was therefore dramatically improved (23 times less in transmission rate) compared with that of an uncoated PET film. The microstructures of the films were investigated by Fourier transform infrared spectroscopy (FT-IR) and the surface morphology was observed by a scanning electron microscope (SEM).