Posted: May 18th, 2012 Scientists illustrate an atlas of carbon nanotube opticaltransitions ( Nanowerk News ) Led by Professor Wang Enge at Peking University (PKU) andProfessor Wang Feng at the University of California, Berkeley, ajoint research team recently reported their major progress on anatlas of carbon nanotube optical transitions, which was publishedin Nature Nanotechnology ( "An atlas of carbon nanotube optical transitions" ). Figure 1. Scheme of determining chiral index and optical resonancesof the same individual carbon nanotubes through combined electrondiffraction and Rayleigh scattering techniques Periodic table is one of the most important discoveries ever inscience because it presents a systematic structure-propertyrelation for each atom. A similar relation is equally important fornanostructures as the material properties of nanostructures dependsensitively on their structures. Single-walled carbon nanotubes(SWNTs), a model one-dimensional (1D) nanomaterial system,constitute a rich family of structures with distinctly differentelectrical and optical properties. |
The diversity of nanotubephysical properties, together with their perfect structuralintegrity, makes SWNTs model systems to probe 1D physics and topromise materials for nanoscale electronics and photonics. However,a long-standing goal in nanotube research is how to establish thestructure-property relation for hundreds of different SWNTs specieswith high accuracy. The researchers illustrated the first comprehensive and accuratemap between the structure and optical transitions in SWNTs throughindependent determination of chiral indices and optical transitionsin over 200 individual nanotubes (Fig. 1). This map, effectively an"atlas" for SWNT optical transitions, has an uncertainty less than20meV.
It provides a valuable reference for nanotube spectroscopicidentification, electronic and photonic applications. Once theyknow the optical resonances of a single-walled nanotube, they canidentify its chiral index without any ambiguity, and vice versa. Figure 2. (a) The momentum-resolved optical transition energydispersion Ep(k) for p="5" (or S44 transition) in the grapheneBrillouin zone. (b) Renormalized effective Fermi velocity vF as afunction of transition index p (or mean diameter d in the toppanel).
In addition, this atlas opens the door for systematic understandingof fascinating 1D many-body effects in SWNTs of different types anddiameters. By systematically investigating the electron-electroninteraction induced optical resonance shifts in differentnanotubes, they discovered surprisingly that the Fermi velocityrenormalization is the same in metallic and semiconducting SWNTs,but increases monotonically with nanotube diameter towards thetwo-dimensional graphene limit (Fig. 2). This unusual behaviorreveals an intriguing perfect cancellation of long-rangeelectron-electron interaction effects and a diameter dependentshort-range electron-electron interaction effects. This study demonstrates the importance of a systematic approach incharacterizing the property-structure relation in nanostructures.The atlas provides the prerequisite reference for the futureenergy-related applications.
The revealed distinct behavior oflong-range and short-range electron-electron interactions can be ofgeneral importance for differing low-dimensional materials.
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