M.M. García, O. Sánchez, C. Gómez Alexandre and J.M. Albella. Instituto de Ciencia de los Materiales de Madrid (CSIC), Cantoblanco 28049 Madrid, Spain.

In this work we study the bias-enhanced nucleation process in the deposition of diamond films by Microwave Plasma Assisted Chemical Vapor Deposition Process (MWCVD). Nucleation was enhanced applying a negative DC voltage, 250 V, to the silicon substrate immersed in a CH₄/H₂ plasma, previously to the deposition process. This pre-treatment presents many advantages versus other pre-treatment process such as the mechanical abrasion with diamond paste. The morphology of the films was studied by Atomic Force Microscopy (AFM) and the chemical composition of the films were analyzed by X-ray Absorption Near-Edge Spectroscopy. We have found that the nuclei formation occurs after the development of intermediate species called active sites and germs. The evolution of the active sites and germs to diamond nuclei takes place by capturing of the adatoms, species which are diffusing over the surface, instead by the capture of plasma species. The application of the nucleation pre-treatment led to large deposition rates, even for low treatment times. It is a clear dependence between the nucleation time and the surface morphology of the polycrystalline diamond films, so very long bias enhanced nucleation time and the surface morphology of the polycrystalline diamond films, so very long bias enhanced nucleation times are required to obtain very smooth surface diamond films.