Thursday, June 01, 2006

US Patent 7052666 - Untangling Single Walled Nanotubes By Cutting

Single Walled Carbon Nanotubes (SWNTs) are basically carbon atoms in a hexagonal lattice formed in a cylindrical shape of nanometer scale diameter. Generally carbon has four electrons for bonding but in the case of SWNTs only three of these electrons are used per carbon atom. The extra electrons cause a stickiness between SWNTs when a large concentration of the SWNTs are produced resulting in a tangled web of the SWNTs. In order to isolate individual SWNTs, this patent proposes a cutting technique (using for example a focused ion beam or oxidative etching). Claim 1 reads

1. A method for untangling single-wall carbon nanotubes comprising: a) providing tangled single-wall carbon nanotubes; b) cutting at least a portion of the single-wall carbon nanotubes to un-tangle at least some of the single-wall carbon nanotubes; and c) recovering a material comprising the single-wall carbon nanotubes un-tangled by the cutting step.

This patent is yet another in a long line of recently issued SWNT patents from Smalley's group at Rice University claiming priority from many years ago, in this case from 1996. The Examiner initially applied prior art dealing with the purification of tangled SWNTs and arguing inherency of cutting based on purification but the patent attorney successfully convinced the Examiner that the inherency was incorrect by noting that the cited purification would require a different energy input and application time to achieve the claimed cutting.