The Effect Of Synthesis Technique On The Catalyst And Metallic Film And The Study Of Diamond/Film Interface

Synthetic diamonds under high temperature and high pressure (HTHP) is a very complex process, which concerns with many procedure parameters. These parameters are synthesis pressure, synthesis temperature and synthesis time. In this process, the procedure parameters have to achieve the best matching condition so as to obtain high-quality diamond single crystal. But the researches about the procedure parameters on the diamond single crystal growth and metallic film are few at home and abroad. The researches about the diamond/metallic film interface are also few. In view of this, the microstructures, morphologies and compositions of the metallic films and molten solvent formed by nickel-base and iron-base alloys under different procedure parameters were systematically investigated by means of optics microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscope (EDS), X-Ray diffraction (XRD) and electron probe microanalysis (EPMA). Transmission electron microscopy (TEM) and atom force microscopy (AFM) were used to investigate the phase structures and morphologies of diamond single crystal/metallic film interface. On the results obtained by the methods mentioned-above, the effects of the molten solvent and metallic film were analyzed. Abased on this, the synthetic mechanism of diamond single crystal under HTHP was discussed in this paper.The research on nickel-base molten solvent and metallic film under different procedure parameters shows that the graphite in the molten solvent is two forms: worm shape and globosity. When the synthesis pressure is smaller, globosity graphite mainly exist in the middle of the alloy flake, while the worm shape graphite mainly exist in the two sides of the alloy flake. Along with synthesis pressure and the time increasing, the globosity graphite increases, while the worm shape graphite decreases. The globosity graphite is formed by the worm shape graphite. So long as the time achieves 9 min, there is nearly no worm shape graphite in the nickel-base film, but there is an obvious fluctuation in carbon, nickel and manganese distributions in the film and some reticulations in the middle region of the film when synthesizing pressure and temperature are fit for diamond growth. The effect of synthesizing times on the morphologies of the film is not obvious. However, when the synthesizing pressure is not appropriate, a large amount of worm shape graphite appears in the whole film, while there are no reticulations in the middle region and the distributions of nickel and manganese are almost well-proportioned. The analysis suggests that the reticulations should be Ni-Mn-Co-C solid solutions (γ-phase). The different content of nickel, manganese, cobalt and carbon cause the different morphology with the substrate. This reticulation is a catalytic phase for diamond transformation in the film under HTHP.The research on iron-base molten solvent and metallic film under different procedure parameters shows that the molten solvent is composed with Fe3C, (Fe,Ni)23C6,γ-(Fe,Ni) and graphite. The primary Fe3C phase in the molten solvent exist two forms: stripe shape and cluster shape. The primary Fe3C phase in the catalyst structures under good synthesis conditions is stripe, while there is cluster Fe3C in the catalyst structures with bad synthesis conditions. This proposes that the Fe3C expresses different growth behaviors under different crystallization conditions. It occurs"facet growth—non-facet growth"transformation. There is less and less stripe Fe3C in the metallic film as prolonged the synthesis time, and no stripe Fe3C was found in the metallic film covering on super quality diamond. This indicates that a part of short-range order Fe3C decompose carbon groups as prolonged the synthesis time. This process consumes parts of Fe3C. The results support"the diamond growth depends on the decomposition of primary Fe3C".By TEM, The phase composition analysis shows that hexagonal Ni3C single crystal, nanometer scale particle diamond,γ-(Ni, Mn) and Mn23C6 exist in the nickel-base metallic film contacting the diamond, and graphite was not found on the diamond/film interface. The phase composition analysis shows that Fe3C,γ-(Ni, Mn), nanometer scale particle Mn23C6 exist in the iron-base metallic film contacting the diamond, but graphite and amorphous carbon were not found on the diamond/film interface. As for the nickel-base and iron-base catalysts, this proposes that the growth of diamond is not the transition of the graphite structure, but the decomposition of the carbides in the diamond/film interface at HTHP. When diamonds were synthesized by nickel-base and iron-base catalyst, the fine particles and terrace structures with homogeneous step height were found by AFM on the diamond (100) and (111) surfaces, respectively. AFM morphologies on diamond faces are similar to those of corresponding film, but not embossing each other. This is not produced by simple solidification relation. When the component super-cooling occur on the diamond/film interface, the morphology of diamond single crystal face concerns with the temperature gradient from the diamond/film interface to film. The temperature gradient is increasingly small, the crystal growth speed is accelerated, which is easy to form the rough surface. Otherwise, it is easy to form the flat surface.As for the nickel-base and iron-base catalysts, the results in this paper have provided the strong evidence for explaining the carbon atoms for diamond growth being from the decomposition of carbides or coordination compounds, which perfects the mechanism of synthesis diamond at HTHP.