Nanotube engineering and science: Synthesis and properties of highly ordered carbon nanotube arrays and Y-junction carbon nanotubes

Highly ordered carbon nanotube arrays and Y-junction carbon nanotubes were synthesized and studied for the first time. These new nanostructures demonstrate the next step towards engineering carbon nanotubes into functional materials for nanoscale science and technology. Highly ordered arrays were fabricated by chemical vapour deposition involving the decomposition of acetylene within hexagonally-disposed nanochannel alumina templates. The nanotube arrays are characterized by a narrow size distribution, large scale periodicity and high densities. Y-junction tubes were grown similarly in high density arrays, using Y-branched template channels. These novel nanotube junctions consist of a large diameter tube branching into two smaller diameter ones. Electronic transport measurements on Y-junction nanotubes showed them to possess intrinsic and reproducible rectifying behaviour at room temperature. The results could be explained by considering the change in bandgap across the junction caused by joining together different diameter nanotubes and illustrate a new type of semiconductor heterojunction for nanoelectronics.