Large Single Diamond Crystals Were Synthesized From {111} Seed Crystals Of Different Shapes Under High Temperature And Pressure

Diamond has good physical and chemical properties,Its excellent performance in the great mechanical hardness,high thermal conductivity and low thermal expansion coefficient,the widest light transmission band and resistance to strong acid and alkali corrosion.Diamond is a potential candidate material for high and new devices to work under extreme conditions,so it is widely used in defense,medical,science and technology,industry,biology,electronics and many other fields.Compared with natural diamond,synthetic diamond has gradually replaced natural diamond in many aspects because it usually contains less impurities,has lower cost and is suitable for mass production.There are two main methods of synthetic diamond: chemical vapor deposition(CVD)and high temperature and high pressure(HPHT).CVD method is easy to synthesize large diamond single crystals in a short time with less impurities,but CVD method can only achieve the two-dimensional growth of crystals,and the requirements for seed crystals are very strict,most of which are limited to the pretreated {100} surface,and other crystal directions are not allowed.At the same time,the quality of the CVD growing crystals will decrease at the edge of the seed crystal growth surface with the extension of time,which results in the shrinkage of the effective growth surface and affects the growth size of the crystals.The HPHT methodcan not only realize the three-dimensional growth of seed crystal and obtain high-quality gem-grade diamond with complete morphology,but also simulate the formation process of natural diamond in the mantle to some extent,which is beneficial to the research on the genesis of natural diamond.At the same time,HPHT method has a low requirement for seed crystal synthesis and will not affect crystal synthesis.Although HPHT method has advantages over CVD method in some aspects,the seed whiskers used are selected industrial grade diamonds with complete crystal faces,which will lead to the waste of manpower and resources.Moreover,the research on the synthesis of diamond by seed crystals is not completely clear.Most researchers use complete seed crystals with crystal faces of {100} and {111},without paying attention to the effect of the shape of seed crystals themselves on the growth of diamond.Moreover,compared with {100} crystals,{111} crystals have a wider temperature range and fewer surface hanging bonds,which is the preferred object for HPHT method and industrial synthesis of high-quality diamond single crystals.Based on the above problems,this paper carried out the research on the heteromorphic seed crystals with {111} crystal plane as the initial growth plane.Seed crystals of various shapes were obtained by laser cutting on the same exponential surface of {111}.FeNi alloy was used as catalyst and temperature gradient method was used as the diamond synthesis method.Specific research contents are as follows:Diamond monocrystals were successfully synthesized from seed crystals at different cutting angles based on the original crystal plane.The relationships between different seed crystals and synthetic crystals were investigated,and the morphology and quality of seed crystals and diamond were studied in detail by means of Optical Microscope(OM),Scanning Electron Microscope(SEM),Raman Spectroscopy(Raman)and Fourier Transform Infrared Spectroscopy(FTIR).The results showed that the seed crystal orientation was different due to the different initial cutting angles,and the seed crystal growth patterns in different crystal orientation were also different.Seed crystal orientation determined the growth trend of diamond,but some seed crystal cutting orientation would lead to growth defects.In addition,the results ofRaman spectroscopy and infrared spectroscopy showed that the seed crystals of type Ib diamond cut into different shapes were still of type Ib crystal type,which did not affect the crystal type.Several crystals were obtained by keeping the cutting Angle of seed crystal unchanged and adopting different synthesis time.The growth law of the crystal was observed according to the time of synthesis.The results showed that the shape of seed crystal affected the epitaxial growth rate at different positions of the crystal,had a greater effect on the morphology of the initial growth stage,and had a smaller effect on the morphology of the late growth stage.At the initial stage of crystal growth,the time is not long enough to reverse the crystal morphology,so the shape of seed crystal at the initial stage of growth has a great impact on the morphology of diamond.With the extension of growth time,the crystal morphology gradually tends to the conventional crystal morphology due to the difference of growth rate in different positions of the crystal.That is to say,although the seed crystal shape is different,but this difference in growth rate makes the heteromorphy {111} seed crystal eventually synthesized into the regular {111} crystal.