The use of refractive index as a measure of diamond-like carbon film quality

Diamond-like carbon (DLC) coatings can be divided into two main categories amorphous carbon (a-C) and amorphous carbon/hydrogen (a-C:H). Within these two categories the DLC films exhibit a wide range of mechanical and physical properties. This study evaluates the use of refractive index as an in situ technique to determine the quality of a wide range of coatings deposited using 13.56 MHz and 40 kHz plasmas (yielding a-C:H films) and from a saddle field atom source (yielding a-C films). Films with refractive index (at lambda=675 nm) between 1.6 and 2.3 were obtained for the a-C:H coatings, while the a-C coatings had indices in the range 1.7 to 2.6. A correlation was found between the coatings' refractive index and their extinction coefficient, which was independent of the conditions used to deposit the coatings. For both the a-C and a-C:H films, hardness and laser ablation resistance increased with refractive index. DLC films with similar indices had similar properties whether deposited at 13.56 MHz or 40 kHz plasmas or in the saddle field atom source. (C) 1998 Elsevier Science S.A.