Heteroepitaxial Growth Kinetics in a CVD Process Using Nickel Oxide on MgO as a Model System

Abstract

Three‐dimensional crysallites of NiO were grown on MgO substrates using a CVD process by reacting NiBr2 with oxygen in the presence of water vapor at 600°C. The vapor pressures of oxygen and water vapor were kept at 0.88 and 2.61 kPa, respectively. The growth rate of periodically spaced NiO nuclei was measured. The results, which show a peak in the average deposition rate when plotted against the nuclei spacing, are modeled in terms of an effective diffusion distance for the NiO molecules on the MgO surface, and assuming a negligibly small reaction rate of the precursors on the surface of NiO crystallites. The latter assumption results from the observation that the average growth rate on cleaved MgO surface dropped to a very low value once a continuous film of NiO was formed. An effective diffusion distance was manifested by the observation of characteristic denuded zones surrounding the NiO crystallites when the nucleation rate was increased by increasing the water vapor supersaturation on the surface. The comparison with model is used to estimate the effective diffusion distance.