Effect of plasma modulation on the nucleation and crystal evolution of nanodiamond seeds during CVD diamond growth

This study investigated the effect of plasma modulation on the nucleation and crystal evolution of nanodiamond seeds during chemical vapor deposition (CVD) diamond growth. To this end, secondary nucleation and growth of nanodiamond seeds on a mirror-polished silicon (100) substrate in nitrogen, oxygen, and nitrogen-oxygen codoping environments were investigated using a 5500-W microwave plasma-assisted CVD (MPCVD) reactor. Plasma diagnosis was performed to determine the impact of auxiliary gas addition on plasma modulation using optical emission spectroscopy (OES). The results demonstrate that although nitrogen doping can promote secondary nucleation and growth of nanocrystalline diamond (NCD), it leads to the formation of twinned crystal defects and NCD aggregates, which reduce the quality of diamond growth. Similarly, although a small amount of oxygen doping can promote the competitive growth of nanodiamond seed crystals and catalyze the transition of diamond from the (1 1 1) to (220), excessive oxygen can inhibit diamond nucleation and growth. However, controlled plasma modulation can be achieved through appropriate nitrogen and oxygen additions. This study provides theoretical and experimental data for diamond nucleation, grain size, and orientation regulation in CVD diamond growth, and it can serve as a reference for studies on NCD and coatings. Furthermore, this study provides new insights into the growth of nitrogen-oxygen co-doped diamond films.