IR laser-induced formation of amorphous Co–C films with crystalline Co, Co 2C and Co 3C nanograins in a graphitic shell

Abstract

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, Co 2C and Co 3C nanograins embedded in a shell of hexagonal graphite and amorphous sp 3-hybridized carbonaceous matrix. The Co, Co 2C and Co 3C 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.