Scientists construct carbon nanotube device that can detect colors of the rainbow

Friday, May 1, 2009

WASHINGTON - Researchers at Sandia National Laboratories, US, have constructed a carbon nanotube device that can detect the colours of the rainbow, by identifying the entire visible spectrum of light, a feat that could soon allow scientists to probe single molecule transformations.

Carbon nanotubes are long thin cylinders composed entirely of carbon atoms. While their diameters are in the nanometer range (1-10), they can be very long, up to centimeters in length.

The carbon-carbon bond is very strong, making carbon nanotubes very robust and resistant to any kind of deformation.

Zhou and his Sandia colleagues Francois Leonard, Andy Vance, Karen Krafcik, Tom Zifer, and Bryan Wong created the device.

To construct a nanoscale color detector, Sandia researchers took inspiration from the human eye, and in a sense, improved on the model.

When light strikes the retina, it initiates a cascade of chemical and electrical impulses that ultimately trigger nerve impulses.

In the nanoscale color detector, light strikes a chromophore and causes a conformational change in the molecule, which in turn causes a threshold shift on a transistor made from a single-walled carbon nanotube.

“In our eyes the neuron is in front of the retinal molecule, so the light has to transmit through the neuron to hit the molecule,” said Sandia researcher Xinjian Zhou. “We placed the nanotube transistor behind the molecule-a more efficient design,” he added.

The idea of carbon nanotubes being light sensitive has been around for a long time, but earlier efforts using an individual nanotube were only able to detect light in narrow wavelength ranges at laser intensities.

The Sandia team found that their nanodetector was orders of magnitude more sensitive, down to about 40 W/m2-about 3 percent of the density of sunshine reaching the ground.

“Because the dye is so close to the nanotube, a little change turns into a big signal on the device,” said Zhou.

To construct the device, Zhou and Krafcik first had to create a tiny transistor made from a single carbon nanotube.

They deposited carbon nanotubes on a silicon wafer and then used photolithography to define electrical patterns to make contacts.

This research eventually could be used for a number of exciting applications, such as an optical detector with nanometer scale resolution, ultra-tiny digital cameras, solar cells with more light absorption capability, or even genome sequencing.

“A large part of why we are doing this is not to invent a photo detector, but to understand the processes involved in controlling carbon nanotube devices,” said Leonard. (ANI)

Filed under: Nano Tech

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