Reflection high‐energy electron diffraction (RHEED) technique, with the possibility to shift, rotate, and tilt the sample with respect to the electron beam, has been used to investigate the structure of the transition layers formed at the interface between titanium substrate and diamond films. The diamond films were deposited on partially masked titanium sheets by means of the chemical vapor deposition technique, using CH4/H2mixtures activated by hot filament. Deposition experiments have been performed at 650 and 730 °C. The RHEED analysis has been carried out in selected area conditions on the boundary between coated and uncoated regions; it enabled us to detect and characterise the inhomogeneous and complex structural configuration of the diamond/titanium interface. For the samples deposited at 650 °C we identified, starting from the titanium surface: a mixed phase constituted by titanium hydride and carbide precipitates, graphitic clusters embedded into a titanium hydride/carbide phase, TiC layers, and finally diamond films. At 730 °C both growth location and formation sequence of the various structures were found to be similar to those detected at 650 °C, resulting, however, in the complete absence of the Ti hydride phase. A first indication about the time scale of the process has been determined from structural investigations of deposits grown by runs lasting from 3 up to 20 min. A schematic model is presented which describes the growth sequence of the various species inside the intermediate reaction layers. ©1996 American Institute of Physics.