Abstract
Several theories have been proposed to synthesize diamond particles from graphite using a metal solvent（also called a catalyst, flux or dissolver）under high-pressure and high-temperature（HPHT）conditions. Many researchers support the “dissolution-precipitation” theory, by which graphitic carbon dissolves in molten metal and subsequently precipitates in diamond form. An alternative is Hosomi's theory: solid state nucleation occurs to form diamond crystals. This study uses confocal Raman spectroscopy to examine the crystallinity of cubic boron nitride （c-BN）contained in a single-crystal diamond matrix synthesized using HPHT method according to Hosomi's theory. We also observed theheterointerface between c-BN and the diamond matrix using transmission electron microscopy to assess the type of bonding present. Constituent elements and the local chemical bonding state were examined using electron energy loss spectroscopy. Results demonstrated that the c-BN and diamond were not bonded directly, but revealed an approx. 5-nm-thick boron-based compound（or amorphous）layer at the interface. The respective concentrations of boron in diamond and carbon in c-BN were below the detection limits, indicating no effect on the crystallinity of either material under the HPHT conditions.
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