Effect of Metallic Film in Diamond Growth from an Fe-Ni-C System at High Temperature and High Pressure

The metallic film surrounding a diamond single crystal, which plays an important role in the diamond growth from an Fe-Ni-C system, has been successfully investigated by using transmission electron microscopy (TEM), Raman spectroscopy and x-ray photo-electron spectroscopy (XPS). Diamond and graphite were not found in surface layer (near diamond) of the film by TEM and Raman spectroscopy, but a parallel relationship exists between the (1ī ī) plane of γ-(Fe,Ni) and the (100) plane of (Fe,Ni)₃C in this region. Compared to that of solvent metal (catalyst) near diamond, the binding energy in the valence bands of iron, nickel and carbon atoms of the film has an increase of 0.9 eV. According to the microstructures on the film obtained by the TEM, Raman spectra, and XPS, the catalytic mechanism of the film may be assumed as follows. In the surface layer of the film, iron and nickel atoms in the γ-(Fe,Ni) lattice can absorb carbon atoms in the (Fe,Ni)₃C lattice and make them transform to an sp³-like state. Then carbon atoms with the sp³-like structure are separated from the (Fe,Ni)₃C and stack on the growing diamond crystal. This study provides a direct evidence for the diamond growth from a metallic catalyst-graphite system under high temperature and high pressure.