Diamond synthesis by microwave plasma assisted chemical vapour deposition (MPCVD) with a bias enhanced nucleation (BEN) step constitutes the most efficient method to obtain heteroepitaxy and is also useful to reach high nucleation densities. In this study, sequential reflection high-energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS) investigations enabled us to highlight the formation of amorphous carbon and crystalline silicon carbide on the surface before diamond growth. By varying the bias voltage, we underlined an optimized value corresponding to a higher quantity of amorphous carbon. This quantity is strongly correlated to the diamond nucleation density. As for the quality of the SiC texture, this seems to be directly linked to bias voltage too: low bias voltages enable us to obtain high oriented 3C-SiC whereas high bias voltages lead to a completely misoriented polycrystalline SiC film.