The usefulness of graphene for electronics has been limited because it does not have an energy bandgap. Although graphene nanoribbons have non-zero bandgaps, lithographic fabrication methods introduce defects that decouple the bandgap from electronic properties, compromising performance. Here we report direct measurements of a large intrinsic energy bandgap of ∼50 meV in nanoribbons (width, ∼100 nm) fabricated by high-temperature hydrogen-annealing of unzipped carbon nanotubes. The thermal energy required to promote a charge to the conduction band (the activation energy) is measured to be seven times greater than in lithographically defined nanoribbons, and is close to the width of the voltage range over which differential conductance is zero (the transport gap). This similarity suggests that the activation energy is in fact the intrinsic energy bandgap. High-resolution transmission electron and Raman microscopy, in combination with an absence of hopping conductance and stochastic charging effects, suggest a low defect density.
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The authors thank S. Tarucha, M. Yamamoto, T. Otsuka, Y. Iye, S. Katsumoto, T. Osada, H. Fukuyama, T. Ando, A. Endo, Y. Hashimoto, N. Miyazaki, Y. Yagi, H. Kodama, A. Sawabe, X.M. Jia, M.S. Dresselhaus, M.H. Han, J. Kohno and P. Kim for technical support, fruitful discussions and encouragement. The work at Aoyama Gakuin was partly supported by a Grant-in-aid for Scientific Research and a High-Technology Research Center Project for private universities in MEXT. The work at Rice University was supported by the AFOSR (FA9550-09-1-0581), the Alliance for Nanohealth, the AFRL through the University Technology Corporation (09-S568-064-01-C1) and the Office of Naval Research Multidisciplinary Research Program of the University Research Initiative (MURI) program.
The authors declare no competing financial interests.
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Shimizu, T., Haruyama, J., Marcano, D. et al. Large intrinsic energy bandgaps in annealed nanotube-derived graphene nanoribbons. Nature Nanotech 6, 45–50 (2011). https://doi.org/10.1038/nnano.2010.249
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