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Microwave plasma chemical vapor deposition was used to fabricate nanodiamond films. Nitrogen incorporation was achieved by the introduction of N2 gas along with H2 and CH4 gases in the plasma. SEM studies revealed a change in the microstructure with increase in the N2 flow rate, transitioning from a 'ridge'-like surface morphology to a more 'cauliflower'-like structure. X-ray photoelectron spectroscopy (XPS) analysis showed a general decrease in the sp3 hybridized carbon content while the sp2 hybridized carbon content increased with N2 flow rate (up to 28.7%) after which it declines. Deconvolution of the C1s XPS spectra indicates incorporation of nitrogen and existence of carbon-nitrogen bonding. Raman spectroscopy shows diamond peak at 1332 cm-1 and the graphite peak, which increases in intensity and shifts towards lower wave number with increase in the N2 flow rate. A diffuse band at 1140 cm-1 indicates presence of a nanocrystalline phase in the films.

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We report on the photoluminescence (PL) and transmission properties of 3 diamond film samples that were lightly doped with nitrogen at varying film growth rates and compare with a 4th diamond sample that had no nitrogen fed into the reactant gas during deposition. For the given film compositions, the PL spectra were qualitatively different, showing significant influence by the presence of nitrogen. Transmission data were collected in the UV-IR range and revealed that the non-nitrogenated sample is much brighter in the IR range than the other 3 doped films. The improved brightness is attributed to a lower number of free carriers, impurities, and lattice vibrations. Raman spectroscopy is used to identify the carbon and impurity bonding types. The effect of nitrogen on electrons is discussed further in terms of field emission turn-on field performance. These results may be used to develop diamond optical systems in the short wavelength infrared range.