XPS analysis for cubic boron nitride crystal synthesized under high pressure and high temperature using Li3N as catalysis

Cubic boron nitride (cBN) single crystals are synthesized with lithium nitride (Li3N) as catalyst under high pressure and high temperature. The variation of electronic structures from boron nitride of different layers in coating film on the cBN single crystal has been investigated by X-ray photoelectron spectroscopy. Combining the atomic concentration analysis, it was shown that from the film/cBN crystal interface to the inner, the sp2 fractions are decreasing, and the sp3 fractions are increasing in the film at the same time. Moreover, by transmission electron microscopy, a lot of cBN microparticles are found in the interface. For there is no Li3N in the film, it is possible that Li3N first reacts with hexagonal boron nitride to produce Li3BN2 during cBN crystals synthesis under high pressure and high temperature (HPHT). Boron and nitrogen atoms, required for cBN crystals growth, could come from the direct conversion from hexagonal boron nitride with the catalysis of Li3BN2 under high pressure and high temperature, but not directly from the decomposition of Li3BN2.