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