The mechanisms involved in the early stages of bias enhanced nucleation (BEN) of diamond have been investigated on thinned Si (1 1 1) areas using several TEM techniques (high resolution, selected area diffraction and nanodiffraction). A comparison with a hot filament chemical vapour deposition synthesis (HFCVD) performed without BEN emphasizes the helpful role of BEN in diamond nucleation: besides the speeding up of the nucleation kinetic and the great increase of the nucleation density,. a significant part of the diamond nuclei are oriented with respect to the Si substrate. (C) 2003 Elsevier Science B.V. All rights reserved.