A study of an interfacial layers between freestanding diamond films and substrate diamond film growth was performed. Polycrystalline diamond films were grown on molybdenum substrates by dc arc jet plasma methods. A molybdenum carbide layer epitaxially was formed on the substrates used several times later, and its structure and composition were analyzed by different characterization techniques. The concentration of carbon decreased with an increase of distance from the substrate surface. Thicker and better-defined interfacial layers were found in diamond films grown on substrates used several times. This interface efficiently avoided carbon and hydrogen diffusion and also improved the chemical bond between diamond film and substrate during diamond growth. Characterization by X-ray diffraction, Raman spectroscopy and SEM analysis were also carried out. (c) 2004 Elsevier B.V. All rights reserved.