BBC: Whereas carbon nanotubes are superior to traditional circuitry materials for conducting electricity, it is not easy to place them on chips in a high-density arrangement. A team at IBM has taken the first step in making this possible, fitting thousands of carbon nanotube transistors onto a single chip. The team used traditional lithography on a hafnium-coated silicon wafer to etch the circuit pattern, then dipped the chip in a solution that bonded to the exposed hafnium channels. The chip was then dipped into a second solution of nanotubes coated in a chemical that bonded with the chemical filling the channels carved onto the wafer. The result was a density of a billion nanotube transistors per square centimeter. This density is a significant step in nanotube microcircuitry, but is still far from being an improvement on current traditional techniques. James Hannon, one of the team members, says that the technique holds promise for when traditional techniques can no longer increase transistor density. However, when the technique is refined, the maximum density attainable would be limited only by the size of the atoms involved.