US Patent 7125534 - Double Walled Carbon Nanotube Fabrication

http://www.freepatentsonline.com/7125534.pdf

Usually carbon nanotubes are characterized in terms of single walled and multiwalled types. The single walled nanotubes can be conductive or semiconductive depending on their chirality, while multiwalled tubes are conductive. However, their is also some interest in a subcategory of multiwalled tubes which include only two carbon layers. These double walled carbon nanotubes (DWNTs) may be more pristine then large multiwall tubes and more conducive to ballistic electron transport which would produce less heat in electronics applications. This patent from Rice University teaches a method of producing such DWNTs. Claim 1 reads:


1. A method for producing carbon nanotubes comprising: contacting metal catalyst particles in a reaction zone maintained at an elevated temperature with a carbon-containing compound to produce carbon nanotubes, wherein the carbon nanotubes predominately have no more than two walls and wherein at least about 30% of the carbon nanotubes are double-wall carbon nanotubes.