Deposition of Diamond-Like Carbon on Inner Surface by Hollow Cathode Discharge

A cylindrical hollow cathode discharge （HCD） in CH4/Ar gas mixture at pressure of 20-30 Pa was used to deposit diamond-like carbon （DLC） films on the inner surface of a stainless steel tube. The characteristics of the HCD including the voltage-current curves, the plasma im- ages and the optical emission spectrum （OES） were measured in Ar and CHn/Ar mixtures. The properties of DLC films prepared under different conditions were analyzed by means of Raman spectroscopy and scanning electron microscopy （SEM）. The results show that the electron exci- tation temperature of HCD plasma is about 2400 K. DLC films can be deposited on the inner surface of tubes. The ratio of sp3/sp2 bonds decreases with the applied voltage and the deposition time. The optimizing CH4 content was found to be around CH4/Ar =1/5 for good quality of DLC films in the present system.