The effect of nitrogen addition to Ar/CH₄ gas mixture on microstructural characterization of nanocrystalline diamond

In the present study, nanocrystalline diamond (NCD) nanowire films were synthesized on silicon substrates, using microwave plasma-enhanced chemical vapor deposition (PECVD) with a CH₄/Ar/N₂ gas mixture at moderate temperatures. The influence of nitrogen concentration on the formation of NCD was investigated. The characteristics of NCD films were evaluated using scanning electron microscopy (SEM), Raman spectroscopy, optical emission spectroscopy (OES), and a contact angle meter. NCD nanowire films with 300-500 nm length were grown with the incorporation of nitrogen. Heterostructures of sp³-bonded diamond nanowires and sp²-bonded graphite were synthesized by adding small amounts of nitrogen to the CH₄/Ar gas mixture. Surface roughness became smooth and the grain size decreased as the nitrogen was introduced into the CH₄/Ar gas mixture. With the increase of nitrogen concentration, the sp²/sp³ ratio of carbon bonds increased. The wettability of the NCD nanowire films was sensitive to the bonding structure. The hydrophobic and non-reactive properties of NCD nanowire films make them highly applicable for biomedical implants.