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|Figure 1. Scheme of determining chiral index and optical resonances of the same individual carbon nanotubes through combined electron diffraction and Rayleigh scattering techniques|
Led by Professor Wang Enge at Peking University (PKU) and Professor Wang Feng at the University of California, Berkeley, a joint research team recently reported their major progress on an atlas of carbon nanotube optical transitions, which was published in Nature Nanotechnology 7, 325 (2012).
Periodic table is one of the most important discoveries ever in science because it presents a systematic structure-property relation for each atom. A similar relation is equally important for nanostructures as the material properties of nanostructures depend sensitively on their structures. Single-walled carbon nanotubes (SWNTs), a model one-dimensional (1D) nanomaterial system, constitute a rich family of structures with distinctly different electrical and optical properties. The diversity of nanotube physical properties, together with their perfect structural integrity, makes SWNTs model systems to probe 1D physics and to promise materials for nanoscale electronics and photonics. However, a long-standing goal in nanotube research is how to establish the structure-property relation for hundreds of different SWNTs species with high accuracy.
The researchers illustrated the first comprehensive and accurate map between the structure and optical transitions in SWNTs through independent determination of chiral indices and optical transitions in over 200 individual nanotubes (Fig. 1). This map, effectively an "atlas" for SWNT optical transitions, has an uncertainty less than 20meV. It provides a valuable reference for nanotube spectroscopic identification, electronic and photonic applications. Once they know the optical resonances of a single-walled nanotube, they can identify its chiral index without any ambiguity, and vice versa.
In addition, this atlas opens the door for systematic understanding of fascinating 1D many-body effects in SWNTs of different types and diameters. By systematically investigating the electron-electron interaction induced optical resonance shifts in different nanotubes, they discovered surprisingly that the Fermi velocity renormalization is the same in metallic and semiconducting SWNTs, but increases monotonically with nanotube diameter towards the two-dimensional graphene limit (Fig. 2). This unusual behavior reveals an intriguing perfect cancellation of long-range electron-electron interaction effects and a diameter dependent short-range electron-electron interaction effects.
This study demonstrates the importance of a systematic approach in characterizing the property-structure relation in nanostructures. The atlas provides the prerequisite reference for the future energy-related applications. The revealed distinct behavior of long-range and short-range electron-electron interactions can be of general importance for differing low-dimensional materials.
The work was partly supported by the National Natural Science Foundation of China (NSFC) and the Ministry of Science and Technology (MOST).
Edited by: Zhang Jiang
Source: International Center for Quantum Materials
About Peking University
Peking University is a comprehensive and national key university. The campus, known as "Yan Yuan"（the garden of Yan）, is situated at Haidian District in the western suburb of Beijing, with a total area of 2,743,532 square metres (or 274 hectares). It stands near to the Yuanmingyuan Garden and the Summer Palace.
Peking University is proud of its outstanding faculty, including 53 members of the Chinese Academy of Sciences (CAS), 7 members of the Chinese Academy of Engineering (CAE), and 14 members of the Third World Academy of Sciences (TWAS).
The university has effectively combined research on important scientific subjects with the training of personnel with a high level of specialized knowledge and professional skill as demanded by the country's socialist modernization. It strives not only for improvements in teaching and research work, but also for the promotion of interaction and mutual promotion among various disciplines.
Thus Peking University has become a center for teaching and research and a university of a new type, embracing diverse branches of learning such as basic and applied sciences, social sciences and the humanities, and sciences of medicine, management, and education. Its aim is to rank among the world's best universities in the future.
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