Study On The Characteristics Of Polycrystalline Frame Of CVD Synthetic Diamond And Coating On SiC

This study combed and summarized the growth principles of chemical vapor deposition（CVD）grown synthetic diamonds,and used 3D digital microscope,gemological microscope,laser confocal microscope and scanning electron microscope to analyze the black polycrystalline borders of CVD synthetic diamonds.The structure and morphology of the synthetic moissanite coated with nano-diamond film were observed and characterized in a comprehensive microscopic techniques.The composition characteristics and crystal orientation of the black polycrystalline diamond frame were investigated by electron backscatter diffraction（EBSD）and X-ray diffraction（XRD）techniques,The gemological properties in the different micro areas of the CVD synthetic diamond,were also investigate using Diamond View ^TM,Fourier infrared spectrometer,Raman spectroscopy and photoluminescence spectroscopy.It was found that the composition of the black polycrystalline diamond frame is different.The black polycrystalline frame consists of mainly diamond phase.Both graphite phase and amorphous carbon phase were coexisted in most of investigated sample.Different CVD synthetic diamond producers show different features which is related to the crystal growth condition.The polycrystalline frame also displays the layered structure of the main monocrystalline diamond,and a large number of microscopic characteristics of the{100}growth surface can be seen,and there are deformed grains,dislocations and impurity elements（especially nitrogen）etc.The microscopic study of the moissanite shows that the optimal thickness of the diamond film is about 200～500 nanometers,Where the transparency of the moissanite can be maintained and the surface scratch resistance of the synthetic moissanite can be maximized.If the diamond film is too thick,the tiny diamond crystals with a cubic and octahedral morphology could be formed.The spectroscopic characteristics of nano-diamond coated moissanite samples are basically the same as ordinary moissanite,but the film characteristics observed by Diamond View ^TMimaging system can be used as an important basis for identifying this type of coated moissanite.According to the microscopic test results,the growth and distribution mechanism of the black polycrystalline diamond frame and the formation mechanism of moissanite diamond grains covered with nano-diamond film are discussed.The boundary effect leads to the formation of non-diamond phases at the edges of CVD synthetic diamonds.The morphology varies with the growth stage.However,the polycrystalline frame gradually expands and affects the lateral epitaxy of the single crystal diamond;the nucleation of the diamond grains covered with nano-diamond film moissanite and the generation of the non-diamond phase in the black polycrystalline diamond frame are different mechanisms,but it is not ruled out The boundary effect has an influence on diamond nucleation.It was the first time to systematic investigate the on black polycrystalline frame of CVD growth synthetic diamonds.At the same time,a systematic gemological study was carried out on the nano-diamond coated synthetic moissanite,and the detection identification features and techniques for this material are summaries.