Control of grain size and size effect on the dielectric constant of diamond films

This work reports that the optimum diamond grain size can be controlled by adjusting the flow rate of Ar/H-2 in the reaction chamber through orthogonal optimization. The dielectric properties of the diamond films were investigated using an RCL (resistance-capacitance-inductance) meter. It was found that (i) the dominating factors in controlling the grain size are in the following order: Ar/H-2 gas ratio, gas total pressure, plasma power and substrate temperature; (ii) increasing the Ar gas fraction reduces the grain size of synthetic diamond films; and (iii) reducing the grain size lowers the dielectric constant. The grain size effect on the dielectric behaviour can be explained by the change of the crystal field caused by surface bond contraction of the nanosized particles.