Laser reflectance interferometry (LRI) was used as an in situ diagnostic tool to monitor the growth rate and surface roughness for a diamond film grown using a three-step chemical vapor deposition (CVD) process in which a multilayer (nanocrystalline/microcrystalline/ nanocrystalline) structure was produced. This multilayer structure was achieved by regulating the concentration of N2 in a H2/CH4 microwave plasma. The observed LRI interference fringes clearly show a decrease in surface roughness (i.e. an increase in reflectivity) for the nanocrystalline layer grown over the rough microcrystalline layer. Raman spectra of single and multilayer diamond films are compared. We find that high phase purity microcrystalline diamond can nucleate on a smooth nanocrystalline diamond layer and that, in turn, a smooth nanocrystalline layer can nucleate on the relatively rough microcrystalline layer. This results in a composite-like film whose toughness, hardness, and surface roughness properties can be tailored as desired. (C) 2000 Elsevier Science S.A. All rights reserved.