In a hot‐filament reactor diamond films were deposited on various substrates without pretreatment. A nickel wire placed at a short distance above the substrate yields an increase of the nucleation density by five orders of magnitude. Closed diamond films were obtained for different substrate materials. The deposits were characterized by scanning electron microscopy, Raman spectroscopy, and x‐ray photoelectron spectroscopy. The presence of Ni in the diamond films indicates that Ni containing species are transported through the gas phase during the reaction to the substrate surface thus forming nucleation centers. Replacing the Ni wire by a diamond membrane nucleation enhancement is reduced by about three orders of magnitude. The pronounced distance dependence observed suggests that volatile unstable species are produced which form nucleation centers upon impact on the substrate surface. ©1995 American Institute of Physics.