Fine structural and carbon source analysis for diamond crystal growth using an Fe-Ni-C system at high pressure and high temperature

Diamond is synthesized in an Fe-Ni-C system at high pressure and high temperature, the Csp³ content profile through different thicknesses of interface between diamond and the catalyst film is measured by using electron energy loss spectroscopy. It is found that the Csp³ content varies from 87.33% to 78.15% when the measured position is located at the inner face near the diamond and then changes to 6 μm further away. Transmission electron microscope examinations show that there are different phases in the interface, such as Fe₃C, γ-(Fe,Ni), and graphite, but the graphite phase diminishes gradually towards the inner face of the interface. These results profoundly indicate that the carbon atoms, required for diamond growth, could only come from the carbon-rich phase, Fe₃C, but not directly from the graphite. It is possible that carbon atoms from the graphite in the interface first react with Fe atoms to produce carbide Fe₃C during diamond synthesis at high pressure and high temperature. The Fe₃C finally decomposes into carbon atoms with the sp³ electron state at the interface to form the diamond.