Comparative study on catalyst-free formation and electron field emission of carbon nanotips and nanotubes grown by chemical vapor deposition

The catalyst-free growth of carbon nanotips and nanotubes on silicon substrate pre-deposited with carbon film was realized under different temperatures in plasma-enhanced hot filament chemical vapor deposition system, in which methane, nitrogen and hydrogen were used as the reactive gases. The structure and composition of synthesized carbon nanotips and nanotubes were investigated using field emission scanning electron microscope, transmission electron microscope and micro-Raman spectroscopy, respectively. The results indicate that the carbon nanotips are formed at about 800 °C while the carbon nanotubes are formed about 900 °C. According to the ion bombardment effect and the diffusion at different temperatures, the catalyst-free formation of carbon nanotips and nanotubes was comparatively studied. The transformation from carbon film to spherical carbon particles at a high temperature results in the formation of carbon nanotubes depending on the diffusion of carbon. At a low temperature, the carbon film still locates at the substrate and leads to the formation of carbon nanotips relying on the sputtering-etching of etching ions and the deposition of carbonaceous ions. In addition, the electron field emission characteristics of carbon nanotips and nanotubes were investigated. The results indicate that there is much difference in the electron field emission properties for the carbon nanotips and nanotubes. According to the thermal effect produced by Joule heat during electron emission, the difference was interpreted.