Tailoring carbon nanotips in the plasma-assisted chemical vapor deposition: Effect of the process parameters

Abstract

Carbon nanotips have been synthesized from a thin carbon film deposited on silicon by bias-enhanced hot filament chemical vapor deposition under different process parameters. The results of scanning electron microscopy indicate that high-quality carbon nanotips can only be obtained under conditions when the ion flux is effectively drawn from the plasma sustained in a CH4+NH3+H2 gas mixture. It is shown that the morphology of the carbon nanotips can be controlled by varying the process parameters such as the applied bias, gas pressure, and the NH3/H2 mass flow ratios. The nanotip formation process is examined through a model that accounts for surface diffusion, in addition to sputtering and deposition processes included in the existing models. This model makes it possible to explain the major difference in the morphologies of the carbon nanotips formed without and with the aid of the plasma as well as to interpret the changes of their aspect ratio caused by the variation in the ion/gas fluxes. Viable ways to optimize the plasma-based process parameters to synthesize high-quality carbon nanotips are suggested. The results are relevant to the development of advanced plasma-/ion-assisted methods of nanoscale synthesis and processing.

Enhancement of electron field emission of vertically aligned carbon nanotubes by nitrogen plasma treatment

“…The details of the deposition system and its operation can be found elsewhere [27]. Briefly, the reactor contains three coiled hot tungsten filaments for feedstock gas heating and pre-ionization.…”

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

“…When these ions bombard with the carbon film, the etching ions play a role in sputtering-etching of the carbon film deposited on silicon substrate, while the carbonaceous ions play a role in carbon deposition. In the previous work, we studied the formation of carbon nanotips from carbon film [16] and concluded that the formation of carbon nanotips resulted from the dynamic equilibrium of sputteringetching of etching ions and deposition of carbonaceous ions on the both sides of microhillocks formed on the carbon film. In this experiment, it was found that the different temperatures can result in the formation of carbon nanotips and nanotubes.…”

“…1 and 2 indicate that the carbon nanotips and nanotubes are grown from carbon film depending on temperature, which are related to the ion bombardment and diffusion at different temperatures. During the growth of carbon nanotips and nanotubes, the reactive gases are ionized by plasma into the carbonaceous ions (such as CH 3 + , CH 2 + ) and the etching ions including nitrogenous and hydrogen ions (such as N + , NH + , H + ) [4,16]. When these ions bombard with the carbon film, the etching ions play a role in sputtering-etching of the carbon film deposited on silicon substrate, while the carbonaceous ions play a role in carbon deposition.…”

“…As a result, the carbon film can not be separated from silicon substrate and still locates on it. Due to the micro-hillocks of the carbon film, the carbon nanotips are formed under the sputtering-etching of etching ions and the deposition of carbonaceous ions [16].…”

Enhanced electron field emission from plasma-nitrogenated carbon nanotips

“…Specifically, nitrogen-based ions N þ 2 , NH þ 2 , NH þ 3 , and NH þ 4 are produced in the plasma, and these ions can significantly sputter the surface of NCNTPs. 27,28 Moreover, the sputtering yield increases with the increase of the energy and mass of the impinging nitrogen-based ions. 29,30 As shown in Table I, the bias remained almost unchanged during the growth of samples B and C. However, the increase of nitrogen flow rate and the reduction of hydrogen flow rate result in the change in the partial pressure and the mean free path of the ions.…”