Size distribution of cobalt nanoclusters in an amorphous carbon matrix

Abstract

Results obtained in a study of electron micrographs of cobalt-doped amorphous hydrogenated carbon are presented. The micrographs were obtained by transmission electron microscopy, including high-resolution electron microscopy. Layers of amorphous carbon were grown by magnetron cosputtering of a graphite and a cobalt target in an atmosphere of argon-hydrogen plasma. It is shown that nanosize crystalline clusters are formed in the process. The influence exerted by 1-h thermal annealing at 800°C in an atmosphere of argon on the size distribution of nanoclusters was studied. It is shown that the distribution function is described by a Gaussian curve that is peaked at ∼7 nm for as-grown samples and is strongly broadened upon annealing, with the peak position shifted to larger sizes and the curve exhibiting deviations from the Gaussian shape. A characteristic structure, attributed to nanosize carbon capsules that envelop the clusters, is seen at cluster boundaries in the high-resolution mode.