Some aspects of diamond crystal growth at high temperature and high pressure by TEM and SEM

Abstract

Diamond crystal growth process at high temperature–high pressure (HPHT) from Fe–Ni–C system was investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Parallel growth cellular interfaces in the growing diamond crystals were directly observed by transmission electron microscopy (TEM) for the first time. The presence of the cellular growth interface indicates that the diamond crystal grows from solution of graphite in molten catalyst and there exists a narrow constitutional supercooling zone in front of the growth interface during the diamond crystal growth. The formation of the cellular interface may be related to the solubility difference between diamond and graphite in molten catalyst. The successive parallel arrays of layers with cellular interface by TEM suggest that the diamond grows from solution layer by layer, which can be further confirmed by morphologies on the surface of growing diamonds and as-grown diamonds obtained by SEM. Some particle clusters were found on the growing parallel layers and diamond surface by TEM and SEM, which may be the diamond atom clusters transmitted to the growing diamond through diffusion. This study provides direct evidence that the diamond is formed at HPHT through graphite continuous dissolution in the molten catalyst to form a colloidal solution, transition of graphite to diamond under the action of the catalyst, diffusion of the diamond atom clusters to the growing diamond, and collection or unification of the diamond subcritical atom clusters on the growing diamond crystal.