BBC NEWS Americas Africa Europe Middle East South Asia Asia Pacific Arabic Spanish Russian Chinese Welsh

 You are in: Sci/Tech
Front Page 
UK Politics 
Talking Point 
In Depth 

Commonwealth Games 2002

BBC Sport

BBC Weather

Thursday, 9 August, 2001, 17:16 GMT 18:16 UK
Tuning the tubes
Delft University
A predictable electronic signature seen in a carbon nanotube
By BBC News Online's Jonathan Amos

This colourful image is music to the ears of physicists.

It shows how the energy associated with electrons reverberates down a tube made of carbon atoms just 1.5 nanometres (billionths of a metre) in diameter.

Like an organ pipe that resonates to set up sound waves of a certain frequency and wavelength, this tiny cylinder is also playing a note - an electronic one.

And researchers believe that if they can learn how to "tune" such tubes they will be one step nearer to building fantastically small devices in which power is carried along even smaller wires.

Better control

Carbon nanotubes are sheets of graphite (carbon) that have rolled up on themselves. The molecules would look - if you could see something so small - like a soccer ball that had been stretched in one direction, or a roll of chicken wire (see bottom of page).

Interest in them stems from their remarkable electrical and mechanical properties, which come from the very precise way in which their atoms are arranged.

But if scientists are to exploit these properties to make new composite materials and ultra-small electronic circuits, they need to be able to better control their manufacture.

This means mass production of tubes, with the ability to make specific sizes to order.

It also means a better understanding of the tubes' properties and how they can be tuned - and here the work of Serge Lemay, of the Delft University of Technology in the Netherlands, and co-workers is significant.

'White puddles'

They probed very short tubes - less than 40 nanometres in length - with a scanning tunnelling microscope (STM), one of the few devices that can "see" detail at the atomic level.

The STM contains a fine metal tip, which feels for "bumps" and "grooves" in the electronic structure of the tube, producing images like the one above.

"We can see how each individual electron is distributed on the surface of the tube," Serge Lemay told BBC News Online. "The image corresponds to a distribution of the electron density for each electron - each family of white puddles corresponds to one electron that is delocalised on the surface of the nanotube."

Crucially, the patterns seen at different energies are predictable and reproducible.

The implication here is that if controlled synthesis of nanotubes does eventually become possible, scientists should be capable of tuning the tubes' properties.

Delicate interference

"If we can synthesise what we want then the electronic properties become important," Serge Lemay said. "What our work shows is that there are very delicate interference effects - quantum mechanical effects - that decide how the electrons move.

"Those effects are visible - they are not so subtle that they get lost in the noise. And they should be accessible to experiments and hopefully to technology.

"The dream is to be able to use these nanoscale effects to make new types of devices - new types of transistors that use principles that are entirely different to those that are currently used in electronics."

"Whether that turns out to be possible is still too early to say."

The Dutch research is published in the journal Nature.

Graphic BBC
Like chicken wire: The tube is a cage of carbon atoms and could form a minuscule wire in an electronic device
See also:

06 Nov 00 | Sci/Tech
Carbon tubes reach their limit
13 Dec 99 | Sci/Tech
World's smallest tweezers
Internet links:

The BBC is not responsible for the content of external internet sites

Links to more Sci/Tech stories are at the foot of the page.

E-mail this story to a friend

Links to more Sci/Tech stories