Diameter Dependence of Hydrogen Adsorption on Single-Walled Carbon Nanotubes

　

Akio Tokura1, Fumihiko Maeda1, Yuden Teraoka2, Akitaka Yoshigoe2, Daisuke Takagi3, Yoshikazu Homma3, Yoshio Watanabe4, and Yoshihiro Kobayashi1
1Materials Science Laboratory
2Synchrotron Radiation Research Center, Japan Atomic Energy Agency
3Department of Physics, Tokyo University of Science and CREST-JST
4Japan Synchrotron Radiation Research Institute

　Single-walled carbon nanotubes (SWNTs) are of great interest as a promising material for a new generation of electronics. Controlling their properties is an impotant challenge. Bacause the properties deeply depend on the SWNT structure, surface modification is suitable for such control. Additionally, selecting reactions in SWNTs is attractive as a way to extract nanotubes having desirable properties. It has been predicted theoretically that C-H bonds are stable for small-diameter SWNTs [1], and that the band-gap modulation depends on the coverage of hydrogen [2]. In this work, we investigated the adsorption of atomic hydrogen on SWNTs with the aim of controlling SWNT properties through surface modification.
　In situ core level photoelectron spectroscopy (PES) was used for the chemical analysis, and ex situ Raman spectroscopy was used for the structural deformation analysis. By fitting the C1s core level spectrum captured after atomic hydrogen irradiation, we found the C-H bonds in the nanotubes as shown in Fig. 1. Before and after PES measurement, Raman spectra were captured as shown in Fig. 2. The spectra demonstrate that, by the irradiation, the radial-breathing-mode (RBM) intensity of small-diameter SWNTs (less than about 1.2 nm in this work) is severely decreased compared to that of large-diameter SWNTs. Raman spectroscopy results indicate adsorption-induced bonding-structure deformation is generated more easily on small-diameter SWNTs. Taken together, these results indicate that hydrogen atoms adsorb more preferentially on SWNTs with small diameters [3]. Our results suggest that SWNT properties can be modified selectively by controlling hydrogen adsorption.

[1] T. Yildirim et al., Phys. Rev. B 64 (2001) 075404.
[2] K. A. Park et al., J. Phys. Chem. B 109 (2005) 8967.
[3] A. Tokura et al., Carbon 46 (2008) 1903.
　

Fig. 1. Peak fitting result of C1s spectrum of SWNT sample captured after hydrogen irradiation.
Fig. 2. Raman spectra in the RBM region of SWNT sample captured before and after hydrogen irradiation.
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