Characterization and optical properties of diamondlike carbon prepared by electron cyclotron resonance plasma

Diamondlike carbon (DLC) films have been prepared on radio-frequency (rf) biased substrates maintained at low temperature using electron cyclotron resonance CH₄–Ar plasma. The effects of negative rf bias and reactant gas composition on the bonding structure, hardness, and resistivity of the films were systematically investigated. DLC films deposited on PMMA (polymethyl methacrylate) were examined by optical methods to determine the absorption coefficients and the optical band gap. It was found that DLC films synthesized at bias voltage of 2(80–100) V and F_{CH₄}/F_Ar of 0.075–0.086 exhibit extreme hardness of more than 3000 kgf mm⁻², high electrical resistivity up to 10¹⁴ Ω cm, band gap larger than 2.5 eV, and excellent optical transparency. The results indicate that ECR CH₄–Ar plasma with low negative rf bias and suitable CH₄/Ar gas ratio can process optically transparent and hard protective DLC films on PMMA plastics.