Generally, the diameter and length of carbon nanotubes were affec

Generally, the diameter and length of carbon nanotubes were affected by catalytic metal particle sizes in the early stage of growth. Since the average Fe particle size on Si(100) substrate is larger than that on Si(111) substrate, MWNTs grown on Si(100) have larger diameter and shorter length than those grown on Si(111) substrate. As the electrical

conductivity of Si(100) substrate increased, Fe particle size is increased, so carbon nanotubes with a short length and large diameter were grown. However, on the other hand, in the case of Si(111) substrate, as the electrical conductivity increased, smaller Fe particles were formed. Accordingly, MWNTs with small-diameter and long carbon nanotubes were synthesized. Conclusions In this study, we report MLN2238 mw the effects of the orientation and electrical conductivity of silicon substrates on the synthesis of MWNTs by thermal CVD. It was found that the size and distribution GANT61 of Fe particles on silicon substrate could be controlled by varying both orientation and σ. Accordingly, it is possible that the growth of MWNTs by thermal CVD could be also controlled by using the orientation and σ. In the case of Si(100) orientation, it was found that as the electrical conductivity

of Si(100) substrates increased, the vertical growth of MWNTs was restrained while the radial growth was enhanced. On the other hand, in the case of Si(111) orientation, the situation is reversed. In this case, it was found that as the electrical conductivity of Si(111) substrates increased, the vertical growth of MWNTs was enhanced while the radial growth

was restrained. More detailed investigation on this matter is in progress. As a result, a strong correlation exists between the growth modes of the MWNTs and the combination of σ and orientation of the silicon substrate. Our results suggest that the combination of σ and orientation of the silicon substrate can be considered as an important parameter for controlling the growth modes of CNTs fabricated by thermal CVD, without the need to alter other growth parameters. Acknowledgments This research was supported by the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (grant no. 20120482). The authors wish to thank Ms. Hyesoo Jeong for plotting the particle distribution. References 1. Takagi D, Kobayashi Y, Homma P-type ATPase Y: Carbon nanotube growth from diamond. J Am Chem Soc 2009, 131:6922–6923.CrossRef 2. Li C, Zhu H, Suenaga K, Wei J, Wang K, Wu E: Diameter dependent growth mode of carbon nanotubes on nanoporous SiO2 substrate. Mater Lett 2009, 63:1366–1369.CrossRef 3. Lee Y, Park J, Choi Y, Ryu H, Lee H: Temperature-dependent growth of vertically aligned carbon nanotubes in the range 800–1100°C. J Phys Chem 2002, 106:7614–7618. 4. Jang JW, Lee DK, Lee CE, Lee TJ, Lee CJ, Noh SJ: Metallic conductivity in bamboo-shaped multiwalled carbon nanotubes. Solid State Commun 2002, 122:619–622.CrossRef 5.

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