Nitrogen- and Boron-Doped Double-Walled Carbon Nanotubes

Nitrogen- and Boron-Doped Double-Walled Carbon Nanotubes 

Chemistry and Physics of Materials Unit, CS1R Center of Excellence in Chemistry and DST Unit on Nanoscience, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 064, India 

KEYWORDS carbon nanotubes doped nanotubes double-walled nanotubes Raman spectroscopy transmission electron microscopy 

Double-walled carbon nanotubes (DWNTs), first observed in 1996, constitute a unique family of carbon nanotubes (CNTs). -2 DWNTs occupy a position between the single-walled carbon nanotubes (SWNTs) and the multiwalled carbon nanotubes (MWNTs), as they consist of two concentric cylinders of rolled graphene. DWNTs possess useful electrical and mechanical properties with potential applications. Thus, DWNTs and SWNTs have similar threshold voltages in field electron emission, but the DWNTs exhibit longer lifetimes.3 Unlike SWNTs, which get modified structurally and electronically upon functionalization, chemical functionalization of DWNTs surfaces would lead to novel carbon nanotube materials where the inner tubes are intact. The stability of DWNTs is controlled by the spacing of the inner and outer layers but not by the chirality of the tubes 4 therefore, one obtains a mixture of DWNTs with varying diameters and chirality indices of the inner and outer tubes. DWNTs have been prepared by several techniques, such as arc discharge5 and chemical vapor depo- 

Applications of CNTs based on their electrical properties strongly depend on the diameter and helicity as well as parity.2 3 Doping of CNTs by boron and nitrogen renders them p-type and retype, respectively. MWNTs and SWNTs doped with nitrogen 4 17 and boron 1 9 have been reported. Boron-doped carbon nanotubes appear to exhibit enhanced electron field emission due to the presence of the boron atom at the nanotube edges.20 2 N-doped CNTs show retype behavior regardless of tube chirality.22 

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