“This is the first measurement of the intrinsic conduction properties of semiconducting nanotubes,” said Michael Fuhrer of Maryland University. “It is an important step forward in efforts to develop nanotubes into the building blocks of a new generation of smaller, more powerful electronics.”

To measure the properties of the nanotubes the researchers grew tubes at least 300 microns long onto catalyst iron nanoparticles on a silicon substrate. The technique resulted in about 5 to 10 nanotubes more than 100 microns long per square millimetre, and around 30 short (about 5 microns long) nanotubes over an area of 100 square microns. The scientists contacted some of the long nanotubes with chromium/gold contacts deposited by electron-beam lithography. Then they carried out electrical measurements by applying drain and gate voltages relative to the source electrode.

The nanotubes exhibited p-type behaviour, and one of the devices had a field-effect mobility of 79,000 sq. cm/Vs at 300 K, a value 70 times that of silicon. The scientists estimated the intrinsic mobility of the nanotubes at more than 100,000 sq. cm/Vs at room temperature - almost 25% higher than any previous semiconducting material.

“Many challenges remain before nanotubes can be used instead of silicon in computer chips,” said Fuhrer. “The contact resistance between nanotube and metal electrodes must be controlled, nanotube batches must be prepared that contain only semiconducting nanotubes, and nanotubes must be placed with precision on substrates.” That said, Fuhrer believes that significant progress is taking place in all these areas and the challenges do not seem insurmountable.

The researchers reported their work in Nano Letters.