Nucleation behavior in the presence of charge in the CVD diamond process

The CVD diamond process adopts gas activation by plasma or hot filament, which produce abundant charges. In the presence of these charges, the nuclei are expected to be multiply charged. The nucleation behavior in the presence of these charges is studied. The effect of charge is suggested to be twofold: one is the formation of an electrical double layer on the surface of the nuclei cluster and the other is to reduce the nucleation barrier by introducing a Coulomb energy term, which is known as charge-induced nucleation. By the electrical double layer, the surface energy of the dielectric diamond can be reduced more effectively than that of the conducting graphite. This reduction of the surface energy favors the stability of the diamond nuclei over that of the graphite nuclei and can result in the dominant nucleation of diamond over graphite, The reduction of the surface energy and the Coulomb energy term can reduce the nucleation barrier markedly when the nuclei are multiply charged. However, the estimated absolute nucleation rate can barely explain the experimentally observed nucleation rate especially for a gas mixture of low methane concentration.