Zhang and co-workers developed a rational approach to growing a new family of semiconducting SWNTs: (n, n À 1) carbon nanotubes. Combined with catalyst design, both large-diameter (>2 nm) (n, n À 1) SWNTs and single-chirality (10, 9) SWNTs with abundances of 88% and >80%, respectively, were successfully realized. This strategy opens up a new route for the growth of SWNT families beyond catalyst design.

Direct growth of chirality-controlled single-walled carbon nanotubes (SWNTs) with metal catalyst free strategy, like cloning or epitaxial growth, has suffered from the low efficiency. The underlying problem is the activation of seed edge. Here an unexpectedly efficient microwave-assisted pathway to regenerate SWNTs from carbon fragments on SiO /Si substrate is demonstrated via Raman spectroscopy and atomic force microscope (AFM) characterization. In this attempt, microwave irradiation provides fast heating to remove polar groups bonded to carbon nanotubes and reduce the spontaneous closure of tubes' open ends. The survived SWNT and carbon fragments connected to it after plasma treatment are simply microwaved and then they serve as the template for regeneration. Scanning electron microscope and AFM characterizations indicate that the efficiency of the regeneration can reach 100%. And the regenerated SWNT has been proved without any change in chirality compared to the original SWNT. Electrical measurements on regenerated carbon nanotube films indicate 1 and 2 times increase in on/off ratio and on-state current respectively than original carbon nanotube films obtained from solution-phase separation, confirming the improvement of SWNT's quality. The microwave-assisted regeneration is found to be highly effective and would be applied to improve the cloning efficiency of carbon nanotubes potentially.

Single-walled carbon nanotubes (SWNTs), since reported in 1993, [1] have been regarded as a promising material owing to unique structure-dependent properties, especially in nanoelectronics applications. [2,3] Therefore, tremendous efforts have been made to pursue the specific-chirality growth of SWNTs, including designing various catalysts [4][5][6][7][8][9] and growth process con-trolling. [10][11][12] Despite of some progresses made in chirality selective synthesis of SWNTs, the mechanism for the experiment successes is far from clarification.Currently, epitaxial growth from well-defined seeds, such as solid catalysts [13][14][15][16][17] and segments of carbon nanotubes, [18][19][20][21] has been thought to be the most promising strategy to realize this goal. At present, mainly high temperature solid catalysts were developed to realize structure-controlled growth of SWNTs. For example, using Mo 2 C and WC solid catalysts, a few (2m, m) SWNTs, such as (12, 6) and (8, 4), have been Currently, designing solid catalysts at high temperature is the main strategy to realize single-walled carbon nanotubes (SWNTs) with specific chirality, meaning it is very hard and challenging to create new catalysts or faces to fit new chirality. However, low temperatures make most catalysts solid, and developing solid catalysts at low temperature is desired to realize chirality control of SWNTs. A rational approach to grow SWNTs array with different chiralities on same solid Co catalysts at low temperature (650 °C) is herein put forward. Using solid Co catalysts, near-armchair (10, 9) tubes horizontal array with ≈75% selectivity and (12, 6) tubes array with ≈82% are realized by adopting a small amount of ethanol and large amount of CO respectively. (10, 9) tubes are enriched for thermodynamic stability and (12, 6) tubes for kinetics growth rate. Both kinds of tubes show a similar symmetry to the Co (1 1 1) face with threefold symmetry for the symmetry matching nucleation mechanism proposed earlier. This method provides a new strategy to study the nucleation mechanism and more possibilities for preparing new solid catalysts to control the structure of SWNTs.

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