Influence of oxygen and nitrogen addition during growth of CVD diamond on pure cobalt substrates

It was shown that in MPCVD reactors the use of common H and CH4 flows, can lead to the formation of free-standing diamond films directly on pure cobalt substrates. The characteristic low adhesion of these films can be explained by the formation of a graphitic layer between the substrate and the film. Scanning electron microscopy analysis shows special areas at the film grain boundaries that were subsequently identified as cobalt inclusions by EDS.In this work we have studied the influence of oxygen and nitrogen addition on the film's growth morphology. Once again SEM and EDS were used to access respectively the films growth morphology and cobalt content. Our results clearly indicate that the addition of oxygen during the initial stages of diamond nucleation prevents diffusion of cobalt into the film. Further, we believed that this effect is likely due to the formation of a cobalt-oxide layer between the film and the substrate. Also, the addition of nitrogen and oxygen the later during nucleation or during growth leads to an increase in the film's growth rate. A preferential (111) surface morphology with clear octahedron facets and films with dominant (100) crystallographic planes are detected. A model is presented for the growth of CVD diamond on cobalt substrates with the addition of oxygen and nitrogen.