Synthesis of hydrogenated amorphous carbon films with a line type atmospheric-pressure plasma CVD apparatus

In this study, hydrogenated amorphous carbon (a-C:H) films were synthesized on polyethylene terephthalate (PET) substrates with a line type atmospheric-pressure plasma chemical vapor deposition (CVD) apparatus. Acetylene and nitrogen mixture gas was used for process gas and a-C:H films having two different thickness were synthesized with varying the C₂H₂ mixing rates. We investigated the effect of chemical bonding structure on the ultraviolet ray shielding property of the films. The deposition rate increased as a function of the C₂H₂ mixing rates. Increasing the C₂H₂ mixing rate from 2.5 to 10% caused an increase in the deposition rates from 13 to 22nm/s. The deposition rate under atmospheric pressure was faster than that of low-pressure plasma CVD (~5-16nm/s). Ultraviolet transmittance of 2-m thick a-C:H film synthesized at the C₂H₂ mixing rate of 10% on 100-m thick PET substrates ranged from 0 to 3% as the UV wavelength ranged from 310 to 400nm, while that of uncoated PET substrates ranged from 0 to 80%. From the result of X-ray photoelectron spectroscopy (XPS) analysis, the component of sp²-hybridized C, such as CC and CO bonds increased as the C₂H₂ mixing rate and thickness of a-C:H films increased. A decrease of sp³-hybridized C, such as CC and CO bonds and an increase of sp²-hybridized C bonds lead to an improvement of ultraviolet ray shielding property.