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

Abstract

The correlation of structural electronic and mechanical properties of carbon–nickel composite thin films has been investigated. The films were deposited on oxidized silicon substrates by dc magnetron sputtering of Ni and C targets in argon at different temperatures between 25 and 800 °C. Composition variation was achieved by variation of the power of the Ni target with constant power on the C target. Structural investigations were performed by transmission electron microscopy (including high resolution) both in plan view and cross section. The nanocomposite films consisted of metallic nanocrystals embedded in a carbon matrix. The carbon matrix was disordered or graphite-like carbon; the crystalline phase consisted of Ni3C or Ni nanoparticles, depending on the deposition temperature. The temperature coefficient of resistivity measurements at low temperature confirmed the various structures of the carbon matrix. The samples in which the prevailing matrix was disordered carbon show the tunneling effect and samples with graphite-like carbon matrix show metallic behavior. The hardness of the films varies between 2 GPa (hardness of Ni) and 13 GPa depending on the deposition temperature, but is independent of the Ni content. The highest hardness of ~11–13 GPa and modulus of elasticity of ~120 GPa were obtained when the crystalline Ni3C nanoparticles were separated by a 2–3 nm thin carbon matrix consisting of amorphous and graphite-like carbon phases. In these films the hardness to modulus of elasticity ratio (H/E) is ~0.1.