Thermodynamic analysis of chemical processes in Ni/Cr/Si structure for carbon nanotubes growing by CVD

Abstract

This paper presents results of the thermodynamic analysis of chemical processes in the Ni/Cr/Si structure during the formation of catalytic centers and the growth of carbon nanotubes on them. It is shown that before starting CVD process Ni/Cr/Si structure is oxidized in atmosphere, and the Cr underlayer oxidation occurs due to an exchange reaction between Cr and NiO, with the formation of chromium oxide. Argon is supplied during the heating displaces residual atmospheric gases, and ammonia due to decomposition under the action of temperature allows to bind the free oxygen in the water vapor. The activation step may be accompanied by a reduction reaction of the oxide of catalyst material up to full reduction of nickel. It was revealed that under nickel CC formed the complex composition underlayer Cr/CrxOy/CrSi2, which is a diffusion barrier, which prevents the interaction of nickel with a silicon substrate. It is shown that in the growth stage decomposition of acetylene occurs on nickel CC with the release of free carbon, however in the underlayer may be formed a solid solution of Cr2O3 and Cr3C2.