Band gap engineering in carbon nanotubes

"Carbon nanotubes have been successfully used for nanometer-sized devices such as diodes, transistors and random access memory cells. Despite these achievements, efforts to integrate these unit devices into functional systems have not yet succeeded. We report a method for constructing self-assembled, multiple quantum dots in a semiconducting carbon nanotube and demonstrate a spatial modulation of the band gap using a low-temperature scanning tunneling microscope (LTSTM). When we imaged topographies of the semiconducting SWNTs at bias voltages of ?.8V to +1.0V, parts of the nanotubes appeared brighter than other areas, suggesting that the diameter may be greater there than at other areas or that the local electronic structure is modified by the inserted fullerene. In the dI/dV spectra, strong VHS peaks corresponding to conduction and valence band edges are clearly observed. The original band gap of ~ 0.5 eV is narrowed down to ~0.2 eV where the fullerene is expected to be located. There are two possible senarios to explain the observation: 1) Elastic strain can change the band gap significantly. For example, a strain of 4% in the tube axis direction can induce a gap reduction of 60% for the (15,1) tube. 2) Charge transfer from the nanotube to the metallofullerenes or the Au(111) substrate may also induce a change in the electronic structure. We have demonstrated that we can synthesize this band gap-engineered system by self-assembly instead of epitaxial growth.



[1] J. Lee, H. Kim, S.-J. Kahng, G. Kim, Y.-W. Son, J. Ihm, H. Kato, Z.W. Wang, T. Okazaki, H. Shinohara, & Y. Kuk, Nature, 415, 1005 (2002)

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