Preparation of DLC films on inner surfaces of metal tubes by nanopulse plasma CVD

Abstract

A method of depositing diamond-like carbon (DLC) films on the inner surface of a circular tube by combining a nanopulse power source with chemical vapor deposition (CVD) was developed. Because a nanopulse power source can supply a high-voltage pulse with a narrow width, it is possible to generate a stable glow plasma even inside a narrow tube under a relatively high source gas pressure. As a result, DLC films were successfully formed on the inner surfaces of carbon steel pipes with an inner diameter of 40 mm and a length of 300 mm by using CH4 or C2H2 as a source gas. When CH4 was used, DLC films with a hardness of more than 9.3 GPa, a deposition rate of 0.7 μm/h, and a source gas yield of 42.3% were obtained. In contrast, when C2H2 was used, DLC films with a hardness of about 5 GPa, a much higher deposition rate of 14.5 μm/h, and a source gas yield of 42.1% were obtained. Wavelength- and time-resolved optical emission spectral measurements were conducted for the plasma generated inside the tubes under the nanopulse power source with various nanopulse repetition frequencies, which indicated the nanopulse-repetition-frequency-dependent behavior of the generated plasma.