Effects of Ar gas dilution in methane plasma on the properties of diamond-like carbon films

Diamond-like carbon films have been deposited with different amounts of Ar gas dilution of a methane precursor by the radio frequency plasma enhanced chemical vapor deposition technique. The object of this work is to study the effects of Ar dilution on the film properties. Optical, IR and Raman spectroscopy, along with hardness tests, have been performed for this purpose. The optical bandgap, hardness and the integrated intensity ratio (I_D/I_G) of the Raman D-line and the G-line, respectively, tend to increase with increasing Ar fraction in the precursor gas mixture. FTIR spectra show that the amount of hydrogen in the films reduces with increasing Ar dilution. All these results show that the sp³ fraction in the films increases with increasing Ar fraction in the precursor. Results of different tests have been correlated with each other and possible explanations have been discussed.