Effect of bias voltage on the formation of a-C:N nanostructures in ECR plasmas

Abstract

Amorphous carbon nitride (a-C:N) nanotubes and nanofibers on porous alumina templates were synthesized by an electron cyclotron resonance chemical vapor deposition system in which a variable negative d.c. bias was applied to the substrate holder of graphite to promote the flow of ionic fluxes through the nano-channels of the alumina template in microwave excited plasmas of C 2H 2 or N 2. The aligned structures of a-C:N nanotubes or nanofibers were verified by field emission scanning electron microscopy. Transmission electron microscopy micrographs showed that a-C:N nanotubes and nanofibers were the size with a diameter of ∼100–250 nm and a length of ∼50–80 μm. The amorphous nature of the nanostructures was confirmed by the absence of crystalline phases arising from selected area diffraction patterns. X-ray photoelectron spectroscopy spectra indicated that a-C:N nanotubes and nanofibers were composed of nitrogen and carbon, and the N/C ratios could reach as high as 72%. The absorption bands between 1250 and 1750 cm −1 in Fourier transform infrared spectroscopy provided direct evidence for the presence of nitrogen atoms in the amorphous carbon network. The well-aligned a-C:N nanotubes and nanofibers are expected to have potential applications in optical, electronic and optoelectronic devices.