The influence of seed crystals on the quality of single-crystal diamond produced by a microwave plasma CVD method

Abstract

Natural diamonds from Liaoning and Shandong provinces, a HPHT diamond from Russia and a CVD diamond from the Element Six Company in America were selected as seed crystals for the growth of diamonds using the microwave plasma CVD method. The seeds and grown diamonds were characterized by FTIR, Raman spectroscopy, photoluminescence spectroscopy, XRD and AFM. Results indicate that the natural diamonds are type IaAB with a unique orientation and great differences in internal stress and crystalline quality. The HPHT and CVD diamonds are type Ib and type Ⅱa, respectively, with an angular deviation of 1-2.5 degrees and better crystal structure, and are more suitable for the CVD growth of single-crystal diamonds with little variation in internal stress and crystalline quality. The diamond layers grown on the natural IaAB seed crystals from Liaoning and Shandong provinces are polycrystalline with a serious lattice mismatch and impurities of microcrystalline graphite and amorphous carbon while the diamond layers grown on the HPHT type Ib seed crystal from Russia and the CVD type Ⅱa seed crystal from the Element Six Company are both of high quality. Moreover, the diamond layer grown on the CVD seed crystal has a narrower FWHM of the Raman peaks and a lower amount of non-diamond carbon impurity, indicating that it has a better crystalline quality than the diamond layer grown on the HPHT seed crystal.