Characterization and Tribological Properties of Nanostructured Copper/Carbon Composite Films Prepared by Microwave Plasm
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Characterization and Tribological Properties of Nanostructured Copper/Carbon Composite Films Prepared by Microwave Plasma-Assisted Dual Deposition Processes
François Thiery, Yves Pauleau, and Jacques Pelletier, CNRS-LEMD, Grenoble, France Jean-Jacques Grob, CNRS-PHASE, Strasbourg, France ABSTRACT Nanocrystalline copper/hydrogenated amorphous carbon films have been deposited on Si substrates at the floating potential using a distributed electron cyclotron resonance microwave plasma reactor. In this deposition technique, the microwave plasma-enhanced chemical vapor deposition process of carbon from argon-methane or argon-acetylene mixtures of various compositions was associated with the sputter deposition of copper from a copper target. The total pressure was fixed at 0.13 Pa. For deposition, the substrates mounted on a water-cooled substrate holder were maintained at ambient temperature. The composition of films determined by Rutherford backscattering spectroscopy, energy recoil detection analyses and nuclear reaction analyses was investigated as a function of the gas phase composition. The structure of films was identified by X-ray diffraction (XRD) techniques and the size of copper crystallites incorporated in the amorphous carbon matrix was deduced from XRD data. The magnitude of residual stresses developed in these films was calculated from the radius of curvature of film/substrate samples determined by profilometry. The residual stress values were found to be nearly independent on the composition of films and deposition parameters.
INTRODUCTION Carbon films such as diamond-like carbon (DLC) and hydrogenated amorphous carbon (a-C:H) exhibit outstanding mechanical properties. These films providing low friction coefficients and reduced wear rates are very attractive for tribological applications [1]. However, the magnitude of compressive residual stresses developed in these films may reach very high values (several GPa); as a result, the adhesion of DLC films, in particular on stainless steel is not sufficient to ensure the reliability required for mechanical components in industrial applications. Recently, novel materials have been proposed to overcome these difficulties, in particular DLC nanocomposite films (DLN) composed of amorphous carbon (DLC or a-C:H) and a-Si:O vitreous phase [2,3]. The hardness of these DLN films (12-17 GPa) is less than the hardness of DLC films (15 to 25 GPa). However, the residual stresses are significantly lower (0.5 to 1 GPa) and these DLN films were found to be tightly adherent to various types of substrates. The objective of the present work is to prepare nanostructured metal-amorphous carbon films exhibiting tribological properties similar to those of DLC nanocomposite (DLN) films. Metals such as Cu, Ni or Ag not miscible with carbon and not convertible into carbide phases are very attractive candidates. In these metal-carbon composite films, nanocrystallites of metal would be wrapped in the matrix of amorphous carbon, which would act as a tissue surrounding the metal cr
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