Field-assisted assembly and alignment of carbon-nanofibres

It is essential to find a technique for assembling carbon nanotubes into a desired functional structure if we are to realize advanced functions. This paper describes large-area synthesis of wire-like building blocks consisting of carbon nanofibres by electric field-assisted growth on a substrate. The wire-like building blocks with diameters of a few micrometres are synthesized by using chemical vapour deposition (CVD) on a substrate on which interdigitated finger electrodes are formed by photolithography in order to enable electrical control of the growth. The metal electrodes are buried in silicon dioxide in order to electrically isolate each electrode, and then nickel thin film, a catalyst for the growth, is deposited on the top surface. It is found that the electric field enhances the growth of carbon nanofibres only on negatively biased electrodes. As carbon fibres grow, compressive stress is induced in the nanofibre film due to the congestion; this causes the film to lift from the substrate and leads to a rounded shape, and finally free-standing wire-shaped building blocks are formed along the narrow electrodes. In contrast, carbon nanofibres formed by CVD using an iron catalyst tend to align perpendicular to the finger electrodes due to the electrostatic force.