We have studied nucleation and growth of diamond on nickel substrate by microwave plasma assisted chemical vapor deposition followed byin situcarbon–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, the1332 cm−1diamond peak was observed near the diamond–nickel interface and it shifted1323 cm−1towards the surface. The1323 cm−1peak 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. ©1998 American Institute of Physics.