A direct current glow discharge plasma source for inner surface modification of metallic tube

摘要

A dc glow discharge plasma source was developed for inner surface modification of metallic tubes with an inner diameter of 10 mm. A tungsten wire of 30 μm thick was stretched inside the tube to form coaxial electrodes. DC glow discharge plasma was generated inside the tube by applying a negative high dc voltage to the tube. It was found that the length of the cylindrical plasma bulk depends linearly on the applied voltage. The electron excitation temperature of Ar plasma was measured as 12830 ± 550 K by optical emission spectroscopy method. As a preliminary application, diamond-like carbon (DLC) films were deposited onto the inner surface of stainless steel tube of 100 mm in length and 10 mm in inner diameter by using CH_4/Ar mixture with 40% CH_4 at 40 Pa pressure. The chemical structure of the DLC film deposited on the substrate was analyzed by Raman spectroscopy. The integrated intensity ratio (I_D:I_G) was obtained as 1.62 from the Raman spectra. The thickness of the DLC film deposited on the substrate was estimated as 1.5 μm by scanning electron micros-copy (SEM) observation.