Study On Large-sized Diamond Crystals Synthesized By MPCVD

The unique physical and chemical properties of diamond make it an ideal material fora variety of applications that could revolutionize science and technology in the21st century.Chemical vapor deposition (CVD) diamond attracts many attentions of researches becausethe property of CVD diamond and nature diamond is very similar. The CVD large singlediamond will be larger and more useful than nature diamond in optical，thermal，electronicand mechanical tool. In this paper, we mainly studied how to improve the growth rate ofdiamond crystals by5kW microwave plasma CVD reactor. Effects of carbon concentrationand substrate’s temperature on homoepitaxial diamond were discussed when using theHTHP diamond as seed crystal. The results indicate that the (100) substrate presentsgrowth step which is caused by grain growth in high speed. After expending the depositedtime，the surface of diamond crystal becomes roughness without any regular shape.Therefore, the HTHP diamond could not replace the natural diamond as ideal seed crystal.According to spontaneous nucleation, large-sized diamond up to500μm is deposited on Sisubstrate by using edge effect and the deposition speed achieved50.0μm/h.The diamonds deposited on the edge region and the center region of the substrate andthe surface morphology of the grown diamond are characterized by scanning electronmicroscopy (SEM) and micro-Raman spectroscopy. The results show that the diameter andthe quality of diamonds deposited on the edge of substrate is larger and higher than thoseof diamonds deposited on the center of the substrate. And it can be concluded that the mainreason for the edge effect is that the temperature and the electric field intensity on the edgeregion are higher than the center of region the substrate after a series of analyses andexperiments.In this experiment，we investigated the effects of the twin appearing on the growth ofsingle crystal diamond deposition process which in gas source H2/CH4/O2plasma systemhad certain rules generated from the bottom to top. Two symmetrical twins peaks werecovered on every （111）plane of the octahedron. The crystal was divided into four sectorsby two gross grain boundaries. Under the different location, the symmetry of the twinpeaks was more and more obvious. Finally，the surface of grains morphology were not the same under different growth conditions. In a suitable growth conditions，a smooth surfaceand a single crystal size up to400μm was obtained. By analyzing the growth mechanism,we thought that the deposition condition reasonable control of α parameter will effectivelyinhibit the emergence of twins. This also provided a new way to synthetic large particles ofsingle crystal diamond.