Deposition and Thermal Stability of DLC/Si-N Composite Films Synthesized Using a Sputtering-PBII Hybrid System

Abstract

Diamond-like carbon (DLC) is a metastable amorphous material that exhibits unique properties. However, there are many limitations regarding the use of this material due to factors such as its tribological characteristics at high temperature and limited thermal stability. In this study, the thermal stability and tribological properties of DLC/silicon-nitrogen (DLC/Si-N) composite films were investigated and compared to those of pure DLC films. All the films were synthesized using a combination of radio frequency (RF) magnetron sputtering and plasma-based ion implantation (PBII) (a so-called sputtering-PBII hybrid system) which is newly developed by us. A high purity silicon nitride (99.9%) disk was used as the target, applying an RF power in the range of 500 - 700 W and a negative pulsed bias voltage of 5 kV to the substrate. An Ar-CH4 mixture was used as the reactive gas. The CH4 partial pressure was varied between 0 and 0.15 Pa, while the total gas pressure and total gas flow were fixed at 0.30 Pa and 30 sccm, respectively. The structures of the resulting films were characterized using Raman spectroscopy, while the thermal stabilities were assessed using thermogravimetric-differential thermal analysis (TG-DTA) and friction coefficients were obtained via ball-on-disk friction tests. The results indicate that the DLC/Si-N composite films produced in this work exhibit improved thermal stability relative to that of pure DLC owing to the presence of thermally stable atomic-scale Si-N compound in the carbon main flame networks. A DLC/Si-N film containing approximately 11 at.%Si and 18.5 at.%N shows good thermal stability in air over 800°C up to 1100°C, together with excellent tribological performance at 500°C in air. Overall, the data demonstrate that DLC/Si-N composite films offer improved thermal stability and superior tribological performance at high temperatures.