Isolated diamond particles grown by chemical vapor deposition on a mirror‐polished Si substrate have been studied by cross‐sectional transmission electron microscopy. Focused ion beam micromachining enabled the cross‐sectional specimen to be carved out precisely at the center of the particle. Atomic scale observation of the diamond/Si interface revealed the presence of an ∼3 nm thick amorphous intermediate layer including a few pits around the nucleation site of the particle. Growth mechanism and relationship between growth orientation and internal defect structure of the diamond particle are discussed. ©1995 American Institute of Physics.