HEXAGONAL COBALT CARBIDE FORMED BY CARBON ION-IMPLANTATION

Thin films of ferromagnetic metals, i.e., bcc Fe, hcp Co, and fcc Ni, were subjected to 50-keV carbon ion implantation at room temperature. At the dose of 2.5 x 10(17) ions/cm2, the formation of hexagonal Fe3C and Ni3C phases was confirmed by transmission electron microscopy selected area electron diffraction patterns; and more interestingly a similar pattern for Co was also observed for the first time. The phase was identified as hexagonal Co3C with a = 2.685 angstrom and c = 4.335 angstrom based on the spacings and intensities of the diffraction rings. The carbide formation was also confirmed by Auger electron spectra. The stoichiometry of the hexagonal structure may be extended in the range of Co3-2C as estimated from the experiments performed up to the dose of 9 x 10(17) ions/cm2.