Large-area synthesis of carbon nanofibres at room temperature

Abstract

Carbon nanotubes, first identified by Iijima, require for their production a source of elemental carbon and a transfer of energy that is specific to the type of source and the growth environment. Methods developed so far involve arc discharge, and vaporization using laser, pyrolysis and chemical vapour deposition of hydrocarbons. Here, we show growth of carbon nanofibres from radio-frequency plasma-enhanced chemical vapour deposition at room temperature, which was made possible by substituting the thermal energy requirements for the growth with plasma decomposition of methane on the Ni catalyst. Electron microscopy analysis provides evidence for a 'tip' growth model, with the Ni catalyst particle attached to the tip of the nanofibre. Energy-filtered imaging shows the Ni catalyst has a surface layer rich in carbon, consistent with the formation of a eutectic Ni-C droplet as a nucleation site for the carbon nanofibres, so that the carbon diffuses across the surface. The reduced distortion of the catalyst particles at low temperatures leads to a more uniform growth of the carbon nanofibres over large areas. The lower growth temperature allows for the removal of the silicon dioxide barrier layer associated with catalytic growth, and should allow in situ growth of nanofibres on relatively large areas of temperature-sensitive substrates, such as plastics, organics and even paper.

Growth of carbon nanotubes at temperatures compatible with integrated circuit technologies

“…Progress has been reported recently in the lowering of the synthesis temperature, with reports of growth obtained using plasma-enhanced chemical vapour deposition (PECVD) [4][5][6][7] . However, in many cases demonstrating low temperature growth, the large area reproducibility and/or the quality of the nanotubes are not fully reported, or the growth results in carbon nanofibres (instead of nanotubes) [4][5][6][7] , with many internal material defects which affect their use as interconnects, requiring further annealing or opening up of inner-layer conduction channels via mechanical polishing 8,9 .…”

“…However, in many cases demonstrating low temperature growth, the large area reproducibility and/or the quality of the nanotubes are not fully reported, or the growth results in carbon nanofibres (instead of nanotubes) [4][5][6][7] , with many internal material defects which affect their use as interconnects, requiring further annealing or opening up of inner-layer conduction channels via mechanical polishing 8,9 . There has been a singular reporting of growth of SWNTs at low temperatures (below 400°C) 10 , non-uniform and over small areas, whilst follow-up attempts used temperatures in the region of 600°C 11 .…”

Photophysics of Individual Single-Walled Carbon Nanotubes

“…[22][23][24] Growth temperatures usually range between 500 and 1000 ºC, 2 but lower temperatures have been used to grow SWNTs on flexible or glass substrates. 25,26 Synthesis times vary from a few minutes to several hours, and SWNT growth ceases when the feedstock is discontinued or the catalyst becomes poisoned by amorphous carbon. 27,28 The catalyst lifetime can be extended by using carbon sources containing oxygen 18,24,28 or by introducing water, oxygen, or hydrogen gas during the synthesis.…”

Controlled Growth-Reversal of Catalytic Carbon Nanotubes under Electron-Beam Irradiation

“…At the core of this model is the observation that the activation energies, derived from the measured growth rates, relate directly to the bulk diffusion of carbon into the respective catalyst (Ni, Co, Fe). However, this also implies that the catalyst is at the eutectic temperature, which is unlikely when the growth results from an endothermic reaction 12 , and is also unlikely in recently observed growth at temperatures from room to 300ºC [13][14] . The group of surface diffusion models is based on the higher mobility of carbon atoms on the catalyst's surface, leading to carbon nanostructure growth.…”