Carbon Nanotube Synthesis from Diamond


Daisuke Takagi and Yoshihiro Kobayashi*
Materials Science Laboratory, *Osaka University

 We have succeeded in growing carbon nanotubes (CNTs) from diamond. CNTs are promising as future base components in many industrial fields due to their various superior properties, such as low weight, high mechanical strength, and good electrical/thermal conductivities. So far, Fe, rare metals like Co and Ni, and noble metals like Au, Ag, and Pt have been used as effective catalysts for CNT synthesis. However, because these metal catalyst particles easily lose their catalytic activities due to aggregation/fusion and reaction with substrates, they are not suitable for high-density CNT growth. Furthermore, because these metal catalyst particles are in a liquid phase at the single-wall CNT (SWCNT) growth temperatures, they cannot be used to precisely control the CNT structure, especially the chirality. Diamond is free from aggregation/fusion and is in a solid phase at the growth temperatures. Therefore, we hope diamond will make it possible to grow CNTs with a precisely controlled structure.
 In this work, we clarified that the CNT syntehsis from diamond by chemical vapor deposition (CVD) requires (1) the use of nanodiamond particles with a diameter smaller than 5 nm [1]; (2) removal of the graphite formed on the nanoparticle surface; and (3) the use of gases that thermally decomposed easily, such as ethanol vapor and acetylene, as the carbon feed stock [2]. Transmission electron microscopy (TEM) images [Figs. 1(a) and 1(b)] and the Fourier transform pattern [Fig. 1(c)] obtained from Fig. 1(b) indicate that SWCNTs are grown from nanodiamond particles. Scanning electron microscopy (SEM) image in Fig. 1(d) indicates that SWCNTs can be grown from three-dimensionally accumulated nanodiamond particles. This means that the nanodiamond particles were in the solid phase at the CVD ambient conditions and did not aggregate. It is known that, in metal-catalyzed CNT growth, carbon atoms are supplied to the CNT through bulk diffusion of carbon atoms in the particle. On the other hand, CNT growth from nanodiamond particles must be promoted by surface diffusion of carbon atoms.
 Nanodiamond particles are produced at low cost and have catalyst activities as high as metal nanoparticles. The nanodiamond particles offer the possibility of not only low-cost, high-density growth of SWCNT but also precise control of the structure of SWCNT.

[1] E. O()sawa, Diamond Relat. Mater. 16 (2007) 2018.
[2] D. Takagi et al., J. Am. Chem. Soc. 131 (2009) 6922.

Fig. 1. (a) TEM image of SWCNTs and (b) TEM image of a SWCNT and nanodiamond particle. (c) Fourier
transform pattern obtained from (b). (d) SEM image of SWCNTs grown from three-dimensionally
accumulated nanodiamond particles on graphite substrate.

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