Synthesis, Structure, and Properties of Single-Walled Carbon Nanotubes By Weiya Zhou, Xuedong Bai, Enge Wang, and Sishen Xie* 1. Introduction The observation of multiwalled carbon nanotubes (CNTs) was reported by Iijima in 1991. [1] Later, two independent groups, Iijima and Ichihashi [2] and Bethune et al., [3] reported the growth of single-walled CNTs in the same issue of Nature in 1993. The impact of these pioneer papers on the scientific community has been tremendous, leading to the birth of nanoscience and nanotechnology. The growth of CNTs was selected by ‘‘Materials Today’’ as one of the top ten advances in materials science over the last 50 years. [4] Indeed, as a kind of novel nanostructured material, CNTs have attracted intense attention because of their amazing mechanical, electrical, and thermal properties combined with their low density, promising a broad range of potential applications. In comparison to multiwalled CNTs (MWCNTs), single-walled carbon nanotubes (SWCNTs) have been shown to have much greater electrical conductivity, which will allow the miniaturization of electronics beyond the chip threshold as well as both nano- and macroscale applications for this outstanding structural material. The molecular structure of a SWCNT can be visualized as a graphene sheet of carbon atoms rolled into a seamless cylinder with a typical diameter of 1.5 nm and a length of up to tens of micrometers. As an ideal quasi-1D structure with an atomically monolayered surface and extended curved p-bonding configuration, an individual SWCNT can exhibit semiconducting or metallic or semimetallic behavior, depend- ing on its chirality and diameter. [5,6] The intriguing structure of a SWCNT is believed to give rise to its unique electrical, mechan- ical, optical, chemical, and thermal proper- ties, which have motivated worldwide efforts to understand their fundamental nature and explore their potential applica- tions. Various types of SWCNTs are pro- mising for advanced electrical intercon- nects, owing to their low resistivities, [7–10] high current-carrying capacities (up to 10 9 A cm 2 ), [11] and high thermal con- ductivities (up to 3500 W m 1 K 1 ). [12] The covalently bonded carbon network results in an extremely stable structure, arguably the strongest in nature. The axial Young’s modulus has been determined experimentally by several means, [13–19] in addition to theoretical calculations, [20] and is typically between 1 to 1.8 TPa. The fracture stress of SWCNT bundles can reach 50 GPa, [20,21] which corresponds to a density-normalized strength 50 times larger than that of steel wires. [17] Meanwhile, novel properties have been manifested by SWCNTs with a variety of geometric shapes, like rings, [22,23] X-, T-, and Y-junctions, [24,25] quantum dots, [26] and crossing objects, [27] which are desirable for the successful incorporation of SWCNTs into devices. In particular, their properties are very sensitive to chemical modification or atomic doping, and can give rise to brand-new quantum materials that promise remarkable application. To accelerate the fulfilment of these applications, it is of the utmost importance to be able to control the preparation of SWCNTs. Much progress has been achieved on this topic over the past decade, but many obstacles still remain that hamper further development in this field. To clarify the emerging problems and to provide a comprehensive understanding of this field, we review the recent progress in the synthesis, structure, and properties of SWCNTs, especially progress with respect to the SWCNT non-woven film, SWCNT rings, boron–nitrogen (B–N) co-doped SWCNTs (BCN-SWNTs), and individual SWCNTs. Finally, some long-standing problems and topics that warrant further investiga- tion in the near future are addressed. 2. SWCNT Non-Woven Films Thin films of SWCNTs represent an emerging class of materials; they are unlike the isolated tube and are suitable for scalable REVIEW www.advmat.de [*] Prof. S. S. Xie, Prof. W. Y. Zhou, Prof. X. D. Bai, Prof. E. G Wang Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing, 100190 (P.R. China) E-mail: ssxie@aphy.iphy.ac.cn DOI: 10.1002/adma.200901071 Great interest in single-walled carbon nanotubes (SWCNTs) derives from their remarkable electrical, thermal, optical, and mechanical properties together with their lower density, which promise extensive and unique applications. Much progress has been achieved in the fundamental and applied investigations of SWCNTs over the past decade. At the same time, many obstacles still remain, hampering further development in this field. To clarify the emerging problems and to provide a comprehensive understanding of the field, we review the recent progress of research on the synthesis, structure, and properties of SWCNTs, in particular the SWCNT non-woven film, SWCNT rings, boron–nitrogen (B–N) co-doped SWCNTs (BCN-SWNTs), and individual SWCNTs. Some long-standing problems and topics warranting further investigations in the near future are addressed. Adv. Mater. 2009, 21, 4565–4583 ß 2009 WILEY-VCH Verlag GmbH & Co. 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