Growth and morphology of aligned carbon nanotube layers

Abstract

The time dependence of the growth of aligned multi-walled carbon nanotubes (MWNT), obtained by bias-assisted microwave chemical vapour deposition (CVD), has been investigated. Short deposition times up to about 15 min favour the tubular tube structure being predominantly observed in the layers, whereas the bamboo-like structure was dominant after longer times (>60 min). It was clarified that this behaviour is related to the different growth rates of the structures, which are governed by the particles size and by the particle size distribution, respectively. Owe to an excess of large particles, the bamboo-like structure is dominant at long deposition time. The experimental findings confirm that both structures are formed by diffusion controlled processes. In the case of the tubular grown tubes, the diffusion coefficient of C in the Co particle was estimated to be about D≈1.8 10 −11 m 2/s, which is in agreement with the assumption of a liquid particle state. For the bamboo-like structure, bulk diffusion through solid particles is likely.