Diamond films were deposited on Si (100) substrates by a direct current and hot filaments-assisted CVD technique at different substrate-to-filaments distances and nucleation temperatures. The nucleation temperature in the range of 600-850 degrees C has negligible influence on the diamond nucleation density and the film quality. Conversely, the nucleation density is closely related to the distance between the filaments and the substrate during the nucleation step. This distance can be optimized to yield a high nucleation rate with good film quality. At too low distance, intense secondary nucleation takes place whereas at too high distance, poor nucleation occurs due to a decreasing ion-promoted nucleation process. The filaments-to-substrate distance governs through intense electron emission the concentration of ion species above the substrate and thus, to a certain extent, govems the nucleation rate, (c) 2005 Published by Elsevier B.V.