Formation of Co filled carbon nanocapsules by metal-template graphitization of diamond nanoparticles

Co filled carbon nanocapsules, which are formed by a heat treatment of the mixture of Co and diamond nanoparticles, have been studied by in situ trans mission electron microscopy (TEM), x-ray diffraction, and Raman spectroscop y. Raman studies show that the heat treatment reduces the surface native ox ide (Co3O4) of Co nanoparticles. The reduction is accompanied by graphitiza tion of diamond nanoparticles, indicating that diamond nanoparticles being in contact with the metallic Co are transformed into graphitic coating. The in situ TEM studies show that the graphitic coating is formed in the heati ng process, not in the cooling process. Furthermore, once the coating is co mpleted, the number of the graphitic layers is almost constant on further h eating and cooling. These results allow us to conclude that metallic Co par ticles simply act as templates for graphitic coating. (C) 2000 American Ins titute of Physics. [S0021-8979(00)07522-8].