Recently, the charged cluster model (CCM) was proposed as the nucleation and growth mechanism for low-pressure diamond, where the electric charges produced by gas activation are the nucleation sites for the supersaturated species in the gas phase. In this work, diamond is deposited using the hot filament chemical vapour technique on faceted alpha-(0 0 0 1) sapphire substrates. The unique combination of surface properties of sapphire such as the stable surface steps and the low charge transfer rate provides an excellent opportunity to investigate the formation of diamond within the framework of the CCM. (c) 2005 Elsevier B.V. All rights reserved.