Energy Gaps in "Metallic" Single-Walled Carbon Nanotubes
Min Ouyang,1
Jin-Lin Huang,1
Chin Li Cheung,1
Charles M. Lieber12*
Metallic single-walled carbon nanotubes have been
proposed to be good one-dimensional conductors. However, the finite
curvature of the graphene sheet that forms the nanotubes and the broken symmetry due to the local environment may modify their electronic properties. We used low-temperature atomically resolved scanning tunneling microscopy to investigate zigzag and armchair nanotubes, both
thought to be metallic. "Metallic" zigzag nanotubes were found to
have energy gaps with magnitudes that depend inversely on the square of
the tube radius, whereas isolated armchair tubes do not have energy
gaps. Additionally, armchair nanotubes packed in bundles have
pseudogaps, which exhibit an inverse dependence on tube radius. These
observed energy gaps suggest that most "metallic" single-walled
nanotubes are not true metals, and they have implications for our
understanding of the electronic properties and potential applications
of carbon nanotubes.
1 Department of Chemistry and Chemical Biology,
2 Division of Engineering and Applied Sciences,
Harvard University, Cambridge, MA 02138, USA.
*
To whom correspondence should be addressed. E-mail:
cml{at}cmliris.harvard.edu
