Gradual transitions in morphology of diamond films grown by using N2 admixtures of CH4+H2 gas in a hot filament assisted chemical vapour deposition system

A study of the evolution of morphology of diamond films grown as a function of N2 gas additions to the CH4+H2 precursor in an HF-CVD system is presented. With the increase of admixture of N2 fraction, in contrast to earlier studies, the morphology was observed first to gradually change from {111}-faceted crystallites texture to that of an intermediate cubo-octahedral crystallite texture and then gradually but finally to transform completely into that of {100}-faceted crystallites. The threshold nitrogen concentration, [N2]thr, required to bring about the said transition in morphology was much larger than it was reported previously. Moreover, the morphology transition required a larger [N2]thr when a large fraction of methane was employed. Further additions of nitrogen, that just exceeded the [N2]thr, resulted in growth of films containing slightly bigger {100}-multi-layered grains or isolated planar {100}-platelets. For extremely large nitrogen additions, the growth of nanocrystalline or amorphous carbon films was observed. The N2 additions more than 50 vol.% did not yield any deposition. Raman scattering and photoluminescence measurements were used respectively for characterizing the quality and nitrogen doping in the films. These results are attributed to the possible catalytic role of atomic nitrogen at the growing surface.