Effects of bonding structure on the properties of plasma immersion ion processed diamondlike carbon films

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Abstract
Hydrogenated diamondlike carbon (a-C:H DLC) films were prepared on different substrates by using C2H2–Ar plasma immersion ion processing (PIIP), and their bonding structure was modified by changing deposition parameters of the chamber pressure and the gas composition. The influence of the bonding structure on the properties of the DLC films was investigated by using ion-beam analysis techniques and Raman, infrared, and ultraviolet/visible spectroscopies and by analyzing the measured properties. The increases in density, hardness, and refractive index were found to correlate with the increase of the sp3-bonded structure and the concurrent decrease of both the C–H bonds and the average size of sp2-bonded domains in the films. An optimal combination of optical and mechanical properties was highly dependent on the hydrogen status existing in DLC films that can be adjusted by means of modulation of the synthesis parameters. The prepared DLC films exhibited desirable properties, which included a hardness above 28 GPa, a density above 2.3 g cm−3, a refractive index above 1.94, and band gap energies in the range of 1.8–1.85 eV.