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 22 nm/s. The deposition rate under atmospheric pressure was faster than that of low-pressure plasma CVD (~ 5-16 nm/s). Ultraviolet transmittance of 2 μm thick a-C:H film synthesized at the C2H2 mixing rate of 10% on 100 μm thick PET substrates ranged from 0 to 3% as the UV wavelength ranged from 310 to 400 nm, 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.