Paper PS-TuP17
Effects of Ions and Radicals on the Growth of Single-Walled Carbon Nanotubes Produced by Diffusion-Plasma CVD

Tuesday, October 16, 2007, 6:00 pm, Room 4C

Individual single-walled carbon nanotubes (SWNTs) have attracted a great deal of attentions since the discoveries of their prominent electrical and optical characteristics. Recent progresses in a synthesis stage of the isolated SWNTs provide outstanding opportunities to efficiently study the basic science of ideal one-dimensional materials. A plasma CVD is well-known as a nanotube formation method including outstanding benefits in the vertical growth of individual multi-walled carbon nanotubes. Up to now, our group firstly demonstrated that those benefits in the plasma CVD can be also applied to the SWNT growth stage, and the freestanding individual SWNT growth on a flat substrate has been achieved with a diffusion plasma CVD method. These progresses of a plasma technology in the nanotube fabrication field can strongly accelerate industrial application of SWNTs. Unfortunately, however, any quantitative discussion about effects of plasmas on the growth of SWNT has not been realized at all so far, and it is one of inevitable issues to fully utilize potential abilities of plasmas for a realistic use of SWNT-device applications. These backgrounds motivate us to investigate the detailed effects of plasmas on the growth of SWNTs. In our study, the effects of ion energy and radicals are mainly focused with a precisely parameter- controlled diffusion plasma CVD system. Derived from the carefully investigated experimental results about the time evolution of SWNT growth, the simple equation is established to describe the growth kinetics of SWNTs during the plasma CVD. Based on the fitting of the experimental result with the equation, remarkable effects of ions and radicals are uncovered. There are clear threshold energies of ions for the destruction of the tube structure. It is conjectured that those threshold energies correspond to that of the bond breaking between carbon in the nanotube and the displacement of the carbon atom from a graphite network in the nanotube. In the case of the radicals, the etching rate during the SWNT growth is found to be strongly influenced by the amount of atomic hydrogen in the plasma. Furthermore, a unique correlation is also identified between the incubation time of the SWNT growth and density of ions in the plasma. These discoveries of the interesting correlations between the detailed growth parameters of SWNTs and key elements in plasmas could contribute to the further advance for the perfect structure control of SWNTs.