Carbon nanotubes positional control

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-... 

Finally, significant amounts of single shell carbon nanotubes were obtained by adding metal catalysts such as Co, Fe, or Ni [15] [34] to the plasma arc process. The addition of metal catalysts seems to facilitate a controlled process by a VLS phase transformation. For example, the addition of cobalt was achieved with a modified positive carbon rod (electrode) into which a hole had been drilled that was filled with cobalt powder [34]. 

Figure 11.6 Overview of the lung section of (a) control rat and (b) rat exposed to 2.5 mgm MWCNT. (c) is a detail view of focal granulomatous inflammation observed in a rat exposed to 0.1 mg m MWCNT, and (d) in a rat exposed to 2.5 mg m" MWCNT. (e) Lung section of a rat exposed to 2.5 mg m showing intra-alveolar eosinophilic granular material which was diagnosed as lipoproteinosis. (f) This intra-alveolar eosinophilic granular material was PAS-positive. Reproduced from L. Ma-Hock et aL, Inhalation toxicity of multiwall carbon nanotubes in rats exposed for 3 months, Toxicol. Sci, 2009,112, 2, with permission from Oxford University Press. ...

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