Effect of Plasma-On Time on the Axial Distribution of Film Thickness in Internal Diamond-Like Carbon Coating with Microwave-Excited High-Density Plasma

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We demonstrated source gas depletion in our proposed method for internal diamond-like carbon (DLC) coating with microwaves by using high-speed camera imaging of the emission from Ar atoms and C<inf>2</inf>dimers during DLC coating. Then, we investigated the effect of the plasma-on time on the axial distribution of the film thickness, hardness, and other properties. The axial variation in DLC coated inside a 1/4-in. stainless steel tube 50 mm in length was greatly reduced from 14% with a plasma-on time T_{\text{on}} = 3.2 ms and a plasma-off time T_{\text{off}} = 96.8 ms in our previous work to 2% with T_{\text{on}} = 1.6 ms and T_{\text{off}} = 98.4 ms in this work. The coating conditions except for T_{\text{on}} and T_{\text{off}} were the same in both experiments. The decrease in the DLC film hardness with increasing plasma-on time was confirmed and is ascribed to a decrease in the film density and number of sp<sup>3</sup>carbons in the film.
2013-11-25