Energy Gaps in "Metallic" Single-Walled Carbon Nanotubes

Abstract

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.

Chemistry of Single-Walled Carbon Nanotubes

“…[22][23][24][25] It is now known that SWNTs can behave as metals, semiconductors, or small band-gap semiconductors, [26][27][28] depending upon their diameter and chirality. 29 Electronic transitions between the energy bands of SWNTs ( Figure 2) can be observed by standard spectroscopic techniques.…”

Effects of suspended multi-walled carbon nanotubes on daphnid growth and reproduction

“…Depending on the diameter and chirality, the tubes may have electrochemical properties similar to metals (Ouyang et al 2001), or as semiconductors (Itkis et al 2002). Their variability in electrochemical behavior makes them attractive to microelectronic applications (Avouris 2007).…”

Intertube effects on one-dimensional correlated state of metallic single-wall carbon nanotubes probed by C13 NMR

“…The obtained C-C bond length is 1.34Å, which shows reasonable agreement with our recent XRD result. 36 Thus, 13 C enriched NMR can be applied for the determination of the C-C bond length of SWCNTs.…”

“…The SQUID measurements indicated that the amount of ferromagnetic impurities in the purified sample was two orders of magnitude smaller than in pristine material. 13 C NMR measurements were performed under a magnetic field of 9.4 Tesla. The nuclear spin-lattice relaxation rate T −1 1 was determined by a saturation recovery method.…”

“…[8][9][10] It is well known that SWCNTs pack together closely and form a triangular lattice called a bundle structure, 11,12 which can also give rise to environmental effects. [13][14][15][16][17] For example, bundling of SWCNTs produces a redshift of the optical transition energy, and has been understood as the consequence of the mutual dielectric screening provided by adjacent SWCNTs in a bundle, which reduces the electron-electron repulsion in each SWCNT. 18,19 Thus, effective Coulomb interactions between adjacent metallic SWCNTs within a bundle of metallic SWCNTs may be largely screened out, leading to a significant deviation from the proposed TLL state.…”