A novel form of carbon nitrides: Well-aligned carbon nitride nanotubes and their characterization

Well-aligned carbon nitride nanotubes were prepared with a porous alumina membrane as a template when using electron cyclotron resonance (ECR) plasma in a mixture of C₂H₂ and N₂ as the precursor with an applied negative bias to the graphite sample holder. The hollow structure and good alignment of the nanotubes were verified by field-emission scanning electron microscopy. Carbon nitride nanotubes were transparent when viewed by transmission electron microscopy, which showed that the nanotubes were hollow with a diameter of about 250 nm and a length of about 50–80 μm. The amorphous nature of the nanotubes was confirmed by the absence of crystalline phases arising from selected-area diffraction patterns. Both Auger electron microscopy and x-ray photoelectron spectroscopy spectra indicated that these nanotubes are composed of nitrogen and carbon. The total N/C ratio is 0.72, which is considerably higher than other forms of carbon nitrides. No free-carbon phase was observed in the amorphous carbon nitride nanotubes. The absorption bands between 1250 and 1750 cm⁻¹ in Fourier transform infrared spectroscopy provided direct evidence for nitrogen atoms, effectively incorporated within the amorphous carbon network. Such growth of well-aligned carbon nitride nanotubes can be controlled by tuning the ECR plasma conditions and the applied negative voltage to the alumina template.