Micro/nanomechanical and tribological characterization of ultrathin amorphous carbon coatings
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Micro/nanomechanical and tribological characterization of ultrathin amorphous carbon coatings Xiaodong Li and Bharat Bhushan Computer Microtribology and Contamination Laboratory, Department of Mechanical Engineering, The Ohio State University, Columbus, Ohio 43210-1107 (Received 1 September 1998; accepted 22 February 1999)
Micro/nanomechanical and tribological characterization of ultrathin amorphous carbon coatings, deposited by filtered cathodic arc (FCA), direct ion beam (IB), electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD), and sputter (SP) deposition processes on Si substrate have been conducted using a nanoindenter with a nanoscratch attachment and an accelerated ball-on-flat tribometer. Coating thicknesses of 20, 10, 5 nm and, for the first time, 3.5 nm coatings have been investigated. It was found the FCA coating exhibits the highest hardness and elastic modulus, followed by the ECR-CVD, IB, and SP coatings. In general, the thicker coatings exhibited better scratch/wear performance than the thinner coatings due to their better load-carrying capacity as compared to the thinner coatings. At 20 nm, the FCA and ECR-CVD coatings show the best scratch and wear resistance, while the IB and ECR-CVD coatings show the best scratch and wear resistance at 10 nm. Five nanometer thick coatings show reasonable scratch and wear resistance, while 3.5 nm thick coatings show extremely low load-carrying capacity and poor scratch and wear resistance. It appears that the 3.5 nm coatings studied are unfeasible for scratch and wear resistance applications as of now.
I. INTRODUCTION
With the emergence of a range of deposition technologies over the past two decades, considerable interest in the deposition and use of carbon coatings in tribological applications has been stimulated. Amorphous carbon coatings, often called diamondlike carbon (DLC) coatings, have been the center of attention due to their interesting properties such as very high hardness and elastic modulus, high electrical resistivity, high thermal conductivity, high optical transparency and chemical inertness, which are close to that of diamond. Thin DLC coatings reproduce substrate topography, not requiring any post-finishing. DLC coatings have wide range of uses including optical, electronic, thermal management (heat sinks), and biomedical and tribological applications.1 In certain applications, there is a need for ultrathin coatings to improve friction and wear performance. Two primary examples include overcoats for heads and magnetic media in hard disk and tape drive systems2–5 and the recently emerging field of microelectromechanical systems (MEMS).6,7 In both these cases, coatings of thicknesses ranging from 100 nm down to 10 nm are being employed. Intensive research is under way to develop DLC coatings as thin as possible— down to 5 nm and less. The important questions are, will these coatings possess the necessary properties that they were designed for, will they perform their role satisfact
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