Electrodeposited Ni and Ni-diamond composite layers were used as diffusion barriers for Fe to facilitate the diamond growth on stainless steel substrates. Raman spectroscopy and scanning electron microscopy show the formation of good quality diamond crystallites by chemical vapor deposition. X-ray diffraction results indicate that the expansion of Ni unit cell has taken place due to the formation of the Ni–C solid solution. This observation is also well supported by x-ray photoelectron spectroscopy studies. The lattice constant of the expanded Ni unit cell matches closely with the diamond, and this may be helpful in explaining the epitaxial growth of diamond on single-crystal Ni observed by others.