Abstract: Optical emission spectra were applied to detect the chemical radicals in the system. It is shown that
the additional nitrogen makes the chemical radicals and surface activity of diamond films change tremendously. Nitrogenous species
abstract the atomic hydrogen on the diamond surface and speed up the desorption rate of H, so as to promote the diamond films deposition.
Further more, the selective absorption of nitrogenous species causes the (100) facets chemical roughening, which makes the growth rate of
(100) facet higher than that of other facets and leads to the presence of (100) textured diamond films. The effects of nitrogen
addition in CH₄/H₂ gas mixtures on morphology, quality and growth rate of polycrystalline diamond films prepared by hot filament chemical
vapor deposition (HFCVD) were also studied. The results agree with the analysis of the optical emission spectra.

Key words: hot filament CVD, optical emission spectra, nitrogenous radicals, diamond growth