The effect of the carbon matrix on the mechanical properties of nanocomposite filmscontaining nickel nanoparticles

Abstract

The correlation of structural electronic and mechanical properties of carbon–nickel compositethin films has been investigated. The films were deposited on oxidized silicon substrates by dcmagnetron sputtering of Ni and C targets in argon at different temperatures between 25 and800 °C. Composition variation was achieved by variation of the power of the Ni target withconstant power on the C target. Structural investigations were performed by transmissionelectron microscopy (including high resolution) both in plan view and cross section. Thenanocomposite films consisted of metallic nanocrystals embedded in a carbon matrix. Thecarbon matrix was disordered or graphite-like carbon; the crystalline phase consisted ofNi3C or Ni nanoparticles, depending on the deposition temperature. The temperature coefficientof resistivity measurements at low temperature confirmed the various structures of thecarbon matrix. The samples in which the prevailing matrix was disordered carbon show thetunneling effect and samples with graphite-like carbon matrix show metallic behavior. Thehardness of the films varies between 2 GPa (hardness of Ni) and 13 GPa depending on thedeposition temperature, but is independent of the Ni content. The highest hardness of∼11–13 GPa and modulusof elasticity of ∼120 GPa were obtained when the crystallineNi3C nanoparticles were separated by a 2–3 nm thin carbon matrix consisting of amorphous andgraphite-like carbon phases. In these films the hardness to modulus of elasticity ratio(H/E)is ∼0.1.