Synthesis of cobalt nanoparticles by ion implantation and effects of postimplantation annealing
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abstract
A study of the synthesis of Co nanoparticles by ion implantation and the effects of postimplantation annealing was carried out. Silica was implanted with 35keVCo+ ion beams to doses ranging from 81015to11017atomscm2. Nanoparticle size, distribution, and structure were ascertained via transmission electron microscopy measurements, which reveal the presence of spherical nanoparticles in both as-implanted and annealed samples. X-ray photoelectron spectroscopy show the chemical state of the nanoparticles in both as-implanted and annealed samples to be metallic. Temperature-dependent field-cooled and zero-field-cooled, susceptibility measurements indicated superparamagnetic behavior, which is analyzed by accounting for the size dispersion of the nanoparticles. Results showed that the magnetic properties of the specimen can be tailored by implantation conditions. Annealing in vacuum at 900C for up to 10h leads to an increase of the average nanoparticle size and a broader size distribution. Mie scattering and magnetic force microscopy measurements provide evidence of a strong interaction among the nanoparticles in the annealed samples. The feasibility of obtaining small-dispersion size-controlled synthesis of Co nanoparticles at room temperature is illustrated.
