Confocal Raman spectroscopic observation of hexagonal diamond formation from dissolved carbon in nickel under chemical vapor deposition conditions

We have studied nucleation and growth of diamond on nickel substrate by microwave plasma assisted chemical vapor deposition followed by in situ carbon–hydrogen solution treatment. The Raman depth profiles of isolated diamond crystals on the (100) and (111) surfaces were measured by confocal Raman spectroscopy. In the case of the crystals having the [111] growth direction, the 1332 cm−1 diamond peak was observed near the diamond–nickel interface and it shifted 1323 cm−1 towards the surface. The 1323 cm−1 peak may be assigned to “hexagonal diamond.” The in-depth spectral change from cubic to hexagonal was observed in chemical vapor deposited diamond crystals. The chemical and/or structural effects of nickel substrate for dissolved carbon are essential for specific diamond crystallization.