Experimental Evidence for Nucleation and Growth Mechanism of Diamond by Seed-Assisted Method at High Pressure and High Temperature

In this paper, the diamond growth mechanism at high-pressure and high-temperature (HPHT) conditions from solvent-graphite system was investigated by growing diamond on different seeds and tracking the particular shapes of the seeds before and after treated under HPHT conditions. According to the results, we established a direct correlation between the morphology of the diamond and the original shape of the seeds. The crystallization of carbon phases (diamond-graphite) in the Fe-Ni-C system is depicted in detail in the P-T diagram. Experimental results show the synthetic pressure obviously decreases when diamond seed crystals arc added into the original synthetic system, which confirms that the energy barrier of the diamond nucleation is higher than that of growth. In addition, we detected in our experiments that the diamond growth at HPHT conditions belongs to two-dimensional growth. Furthermore, we also found crystal direction and original shape of seed play important roles in the formation of diamond morphology in the early growth stage and the synthetic temperature will further affect the crystal shape in the following growth process.