Characterization of Growth Hillocks on the Surface of High-Pressure Synthetic Diamonds

Diamond crystals, with dimensions of about 0.5-0.6 mm, were synthesized in the presence of Fe-Ni and Fe-Ni-Si catalyst solvents under high-pressure-high-temperature (HPHT) conditions. The as-known dendritic pattern was clearly seen on the (111) or (100) planes of diamond single crystals grown using Fe-Ni as a catalyst solvent. However, the conventional dendritic pattern was not observed in diamonds grown in the presence of Fe-Ni-Si alloy catalyst. Trigonal-type, pyramid-type, polygonal-type, and rectangular-type growth hillocks were clearly observed on the (111) and (100) surfaces of diamonds grown from the Fe-Ni-Si-C system, and the density of the hillocks is very higher at some position. Clear successive growth layers can also be found on the (111) planes of the high-pressure diamond single crystals grown in the presence of Fe-Ni Si alloy catalyst. The growth hillocks distributing on the (111) and (100) planes of the diamonds generally occur on or near growth steps, and some of the hillocks terminate at certain solid inclusions and voids. Growth hillocks on the (111) and (100) surfaces directly indicate the spiral growth mechanism under high temperature-high pressure (HPHT). A possible formation process for growth hillocks is proposed.