THE numerous extraordinary properties of carbon nanotubes are now well known and it is clear that nanotubes differ from ordinary molecules and solids in many respects. In fact, nanotubes have an ambiguous identity: they have reasonably well defined structures - albeit a large variety of them - like molecules, but their relatively large length and width means that they also resemble solids. Indeed, nanotubes can be extended to macroscopic lengths and widths to ultimately merge with bulk graphite, which has a familiar layered structure.
The bond that connects every atom to its three neighbours in the graphite plane is one of the strongest found in nature. This strength is reflected in the hardness of diamond, although the graphitic bond is even stronger. This property gives carbon nanotubes exceptional strength. In stark contrast, the bonding between the graphite planes is very weak, which means that the layers can easily slide over each other -- a property that makes graphite a good lubricator.
We are only beginning to understand the uniqueness of the electrical properties of carbon nanotubes, which can be semiconductors or metals depending on the way the graphene sheets are rolled up into a cylinder. In their metallic form, nanotubes have exceptional current-carrying capabilities, which may be related to "ballistic transport". This form of electrical transport had previously only been observed at very low temperatures, but may occur at room temperature in carbon nanotubes, albeit in a modified form. Meanwhile, the hollow interiors of carbon nanotubes and the high chemical inertness of the graphite suggest that nanotubes could be used as containers for gasses and chemicals.
There is no doubt that carbon nanotubes have unique and important properties, and for this reason industry has taken notice - but no applications have reached the marketplace so far.
In the June issue of Physics World magazine, Walt de Heer from Georgia Tech and Richard Martel from IBM write about the technological hurdles that need to be overcome before large-scale applications of nanotubes reach the market.