Carbon nanotubes (CNTs) are much heralded as the material of the 21st century because of their unique properties. Single walled carbon nanotubes (SWNTs, Figure 1) are unique one-dimensional conductors with dimensions of ~1 nanometer in diameter and several micrometers in length. Carbon nanotubes are made of hexagonally bonded carbon, like planar graphene. Physically, carbon nanotubes can be viewed as rolled sheets of graphene with a hollow core and round end caps.

Figure 1
  Figure 1: Artist’s rendition of a conductive carbon nanotube on a surface, courtesy of Simon Benjamin, Oxford University. Inset depicts a transmission electron micrograph of overlapping bundles of nanotubes.  

Individual CNTs exhibit exceptional electronic conduction properties. Semiconducting SWNTs have electron and hole mobilities of ca. 80,000 cm2/Vs. Long metallic nanotubes have been found have volume conductivities of ca. 700,000 S/cm, which is almost as conductive as pure copper. Because of their covalent bonding, carbon nanotubes do not suffer from electromigration, which is a common problem that leads to failure in thin metal wires and films. It is the covalent bonds of CNTs that make them thermally stable and highly resistant to chemical damage. Because individual nanotubes are several micrometers in length, macroscopic films can be made by depositing an ensemble of nanotubes onto a surface. The resulting coatings are uniform in optical and electronic properties on the macroscale. Nanotubes self-assemble into continuous networks (Figure 2) with volume conductivities from 1,000-10,000 S/cm, which is roughly equivalent to ITO and other metal oxides and substantially higher than conductive polymers like PEDOT:PSS.

  Figure 2: Left: AFM image of Invisicon® CNTs. Right: an image of a PET film coated with Invisicon, Sheet resistance of 233 Ω/□ at greater than 90% transparency.  




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