CARDEQ develops nano scales

European researchers have built a device that uses carbon nanotubes to measure the mass of the smallest atoms, and could in future be used to weigh protons and neutrons.

The CARDEQ project, a collaboration between seven European universities, exploits the combined physical and semiconductor properties of the nanotubes using the fact that, like guitar strings, heavier nanotubes vibrate slower than lighter ones. It may ultimately allow scientists to study the progress of a chemical reaction.

The scientists built a semiconducting nanotube into a transistor so that the vibration modulates the current passing through it, making a single nanotube both the vibrating element and the readout element. To get a single atom on the nanotube, metal is evaporated and by chance one will impinge on the string.

Project coordinator, Prof Pertti Hakonen from Helsinki University of Technology, explained that there are two ways to detect this occurring. ‘The most straightforward is that you map out the response curve then detect the frequency shift. The other way is you vibrate the string at a fixed frequency and see how the response changes. When the frequency moves, then the response fixed frequency will change.’

Hakonen said that the CARDEQ research is getting more accurate results than other attempts using similar techniques because the technology detects the change across the entire response curve and can actually see the change rather than just the change from a fixed frequency.

So far the device has been able to detect the mass of single chromium atoms alighting on the nanotube. Even smaller atoms such as argon can be sensed, but the device is not yet stable enough for this to be accurately repeated.

‘The plan is to go for smaller and smaller atomic weights, and in the other direction, to try to use it to detect reactions involving large molecules during chemical processes,’ added Hakonen. This would allow scientists studying molecular biology, for example, to achieve a deeper understanding of the processes that happen in living organisms. In the longer term, the device could even detect protons and neutrons.

At the moment, the project aims more towards producing better tools for research than to satisfy any particular industrial application. But Hakonen foresees that the principle could be applied to the small-scale fabrication of research instruments for use in a variety of fields.

The biggest problem the researchers have had to deal with is the inconsistency of nanotubes grown for this purpose. ‘Every sample is different; every nanotube is like an individual,’ said Hakonen. ‘So far the only solution is to make many samples and select the best.’

CARDEQ began in March 2006 and is due to finish in August. By this time, the collaborators aim to have achieved a resolution where single chromium atoms can be detected consistently and expect to detect increasingly smaller atoms.

They are also attempting to measure vibrations at very-low temperatures. ‘One of the goals people have at the moment is to see quantum vibrations, so if we could kill the thermal vibration we would be left with only the quantum mechanical vibration,’ said Hakonen.

Berenice Baker