Structural characterization of Fe–C coatings prepared by reactive triode-magnetron sputtering

Fe_1–xC_x coatings were synthesized by triode magnetron sputtering of an iron target in a methane/argon atmosphere with a large range of composition (x = 0.3 to 0.6 ± 0.06). Film surfaces were characterized by grazing incidence x-ray diffraction, scanning and transmission electron microscopies, and electron energy loss spectroscopy, to study effects of the variation of the methane gas flow rate on their structural properties. The coatings were constituted of the ε-Fe₃C carbide (x = 0.3 and 0.36), in which carbon atoms are in octahedral sites, and of nanocomposite structure constituted of disordered and crystalline carbide nanograins embedded in a carbon matrix made of an amorphous and poorly crystallized graphenelike material (x = 0.55 and 0.60). In situ annealing of the nanocomposite Fe_0.45C_0.55 coating led to the formation of carbides θ-Fe₃C and Fe₇C₃ (with carbon atoms in prismatic sites) and C-rich cubic carbide possibly related to the τ₂-Fe₂C₇ compound.