A relation between a metallic film covering on diamond and diamond nucleation and growth at high-temperature-high-pressure in a Ni-Mn-C system

There exists a thin metallic film covering on a growing diamond during diamond synthesis at high-pressure and high-temperature (HPHT). Through the film the graphite carbon is catalyzed into diamond structure and transferred to the surface of growing diamond. Study on the chemical composition and structure of the metallic film is of great importance to study the diamond nucleation and growth mechanism and to prepare high-quality single-crystalline diamond. In this paper, a thin metallic film covering on diamond crystals grown from a Ni-Mn-C system was investigated by scanning Raman spectroscopy, scanning auger microprobe, electron probe microanalysis and transmission electron microscopy. It was found that diamond structure was not found in the film, the state of carbon atoms does not significantly change and the fine structures of carbon atoms almost do not transform within the whole metallic film. However, diamond structure was observed on the surface of the film contacting directly with the as-grown diamond, while crystalline graphite and amorphous carbon were not found on the surface. Based on the systemic study of microstructures on the metallic film, it could be reasonably suggested that graphite could not be directly catalyzed into diamond structure in the molten film at HPHT, and the diamond formation should be finished on the diamond-film interface.