Deposition phenomena of diamond-like carbon coating on inner surface of circular metal tube by nanopulse plasma chemical vapor deposition

Abstract

A method of depositing a diamond-like carbon (DLC) film on the inner surface of a circular metal tube by chemical vapor deposition using a nanopulse power source was developed. Because the nanopulse power source can supply rapidly rising and falling high-voltage nanopulses of nanosecond order, a stable plasma can be obtained even in small-diameter tubes by applying a high gas pressure of more than 100 Pa. DLC films were successfully deposited on the inner surfaces of metal tubes of 14 mm diameter and 300 mm length (21% aspect ratio), and of 40 mm diameter and 300 mm length. To understand the plasma state inside the tubes to determine appropriate DLC film deposition conditions, wavelength- and time-resolved optical emission spectroscopy of the plasma generated inside the tubes and numerical simulation were performed. Results of these investigations and characterization clarified that one nanopulse power source introduced to tubes generates glow and after-glow discharges at μs time intervals. It was further clarified that these discharges in combination with high-repetition pulses, suggested together contribute to the effective ionization of gas. Thus, the high speed and high source gas yield of DLC film deposition inside the tubes were confirmed.