Tribological characterization of smooth diamond films grown in Ar-C-60 and Ar-CH4 plasmas

Abstract

In this paper, we describe the fundamental tribological mechanisms of smooth, nanocrystalline diamond films grown in Ar-C-60 and Ar-CH4 plasmas. These films can provide very low friction coefficients (approximate to 0.04 to 0.15) to sliding SiC and Si3N4 surfaces in air or dry N-2. To understand the mechanisms of friction and wear behavior in relation to the chemical and physical states of the diamond films, we used a variety of analytical techniques (electron diffraction, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, atomic resolution transmission electron microscopy, near-edge X-ray absorption fine structure, and atomic force microscopy) both before and after sliding tests. The results of these studies verified that the films were made of sp(3)-bonded diamond nanocrystals (100-300 Angstrom) and that their surfaces were exceptionally smooth (i.e., 20-40 nm, root mean square). Additionally, pin-on-disk experiments verified that these films provided very low friction coefficients (0.04, in dry N-2) and wear rates, essentially comparable to those of natural diamond. Undoubtedly, such diamond films with smooth surface finish can have significant impact in a wide range of tribological applications.