Si Doping Effects on the Growth of Large Single-Crystal Diamond in a Ni-Based Metal Catalyst System under High Pressure and High Temperature

Si powder was added to Ni-based metal catalysts under high pressure and high temperature conditions to investigate its effects on the growth of large single-crystal diamonds. As the Si content increased, the internal inclusions of the diamonds showed a trend in the distribution of point-like → sheet-like → string-like, illustrating that it is ultimately difficult to grow intact crystals. The results show that the first-order Raman peak shifted from 1331.71 to 1329.76 cm –1, and its full width at half-maximum increased from 3.945 to 4.976 cm –1 . These results indicate that the Si doping caused an increase in the stresses inside the crystal and that the crystalline quality of the diamond became worse. The Raman and X-ray photoelectron spectroscopy results confirm that the inclusion impurities (graphite, amorphous carbon, and Si 3 N 4 ) in diamond increase with the Si content. There are significant interactions between silicon and nitrogen in the synthesis process. The addition of Si reduces the nitrogen concentration in diamond. Meanwhile, the presence of nitrogen also reduces the effectiveness of Si doping into diamond.