IR laser-induced formation of amorphous Co-C films with crystalline Co, Co2C and Co3C nanograins in a graphitic shell

IR laser irradiation of Co in vacuum leads to deposition of Co films and when carried out in gaseous benzene or ethyne (0.5-50 Torr) it results in deposition of Co-C films, which was accounted for by concurrent laser-induced ablation of Co and dielectric breakdown in gaseous hydrocarbons. The laser-induced decomposition of the hydrocarbons was studied by FTIR spectroscopy and GC and GC/MS techniques and shown to yield a number of volatile unsaturated hydrocarbons and a solid carbonaceous material that resulted from dehydrogenation and carbonization reactions in the gas phase. The detailed analysis of the Co-C films by X-ray diffraction, FTIR, X-ray photoelectron, Auger and Raman spectroscopy and electron microscopy revealed that the Co-C films are amorphous and contain crystalline Co, Co2C and Co3C nanograins embedded in a shell of hexagonal graphite and amorphous sp(3)-hybridized carbonaceous matrix. The Co, Co2C and Co3C nanograins were identified by transmission electron microscopy as separate entities preferring, in the given order, a face-centered cubic, orthorhombic and hexagonal phase. The laser-induced process represents a novel approach to deposition of Co-C phases containing fcc-Co constituent. (C) 2010 Elsevier B.V. All rights reserved.