Synthesis, structure and properties of nanolayered DLC/DLC films

Abstract

Diamondlike carbon (DLC) films have been explored extensively in the past due to their highly attractive properties. However, the high level of internal stress developed during growth prevents deposition of thick films. Synthesis of DLC/DLC multilayers (DDM) presents a venue to overcome this drawback. In the present study, DLC films and DDM were deposited on Si substrate using dc plasma of CH4 and Ar gas mixture. FTIR was used to analyze the structure of the DLC films. Mechanical properties of the films were characterized by microhardness testing and nanoindentation. The tribological properties were studied by conducting pin-on-disc experiments in the laboratory environment (relative humidity 40-60%). Optical profilometry was used to analyze Intrinsic stress in the films and the wear profiles. A preliminary study was conducted utilizing different processing parameter (bias voltage, chamber pressure and ratio of Ar to CH4) to select the constituents of the DDM. Subsequently, DDM were synthesized consisting of alternating nanolayers of “soft” (high sp2content) and “hard” (low sp2 content) DLC by varying: (i) individual layer thickness while keeping the thickness ratio of soft/ hard DLC film, λ = 1 and; (ii) λ. The multilayered films found to exhibit low intrinsic stress ranging mostly below the average values of the two individual components. Nanoindentation behavior of DDM was comparable to the parent films and no significant variation was observed in different DDM films. DDM films with λ=1 exhibited better tribological properties compared to the films with λ other than unity. The 50 nm/50 nm DDM film exhibited the best tribological properties. It combined the low friction coefficient of the soft DLC component and low wear rate of the harder DLC component. The stress was found to be the average of the parent DLC films; hence it possesses the promise to be deposited as a thick coating, while maintaining desirable mechanical and tribological properties.