Plasma assisted growth of nanotubes and nanowires

Plasma enhanced chemical vapour deposition (PECVD) growth of carbon nanotubes and silicon nanowires has been studied in an Oxford Instruments Plasma Technology reactor. Typical growth regimes involve a catalyst pre-treatment step and a growth step where a precursor gas is decomposed to form the desired nanostructure. For both catalyst pre-treatment and nanostructure growth, utilising plasma gives advantages over other growth methods. During catalyst pre-treatment, a plasma step can promote formation of nanoparticles from a thin metal film, while also increasing the catalytic activity compared with thermal pre-treatment. In the case of carbon nanotube growth, PECVD can result in vertically aligned nanotubes where thermal CVD gave randomly ordered structures. Further, gas composition is seen to strongly affect the morphology and dimensions of the nanotubes grown. For Si nanowire growth PECVD can reduce the growth temperature, and enable the use of catalysts more compatible for fabrication of Si-based devices. In both cases catalyst particles are observed at the tips of the grown nanostructures, indicating a tip-growth mechanism.