IBM sees bright light with carbon nanotubes

By Stefanie Olsen
Staff Writer, CNET News.com

Published: November 18, 2005, 2:34 PM PST

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IBM Research said this week that it has discovered a miniscule light source from carbon nanotubes, one that's 1,000 times brighter than light-emitting diodes.

The discovery could mean a better understanding of interactions between electrons and holes (active carriers with a positive charge) on the conductor material--in this case nanotubes--or within tiny environments, according to Jia Chen, research staff member at IBM Research.

The light could also be used for optical probing at the level of single molecules--which previously was impossible because of the way light diffracts at a small scale.

"This is a new way to make bright light in low-dimensional materials, that people haven't demonstrated before. So in the future we can make them into a ray of tiny light, and we can use them to do optical probing on a nanoscale," said Chen, who has been working on the discovery over the last year.

IBM's research has its basis in creating efficiencies for the transmission between electronic and optical currents, and vice versa. Typically, incompatibilities between the semiconductor materials for electronics and optics have been a hurdle for chipmakers, but carbon nanotubes have proven an excellent current-carrying material for both types of information in recent years.

What IBM has purportedly turned on its ear is the central process of converting an electronic signal to an optical signal--which is converting an electron to a photon. In the past, researchers shot electrons and holes at each other, and when they met within a transmitter, they neutralized each other and made a photon--a fairly inefficient process, according to Chen. Now the researchers use only one type of carrier instead of two.

In other news:

"You just inject either an electron or hole into the transmitter. Then we still need to generate an electron in the hole to make a photon, because you still need both types of charges," she said.

"To do that, we introduce a local-high-electrical field along the lines of nanotubes. Then the injected carrier, when it comes to this field, will be energized or accelerated to energy high enough to generate the electron-hole pair."

The strong attraction between the pair will emit photons, without losing heat. That runs in stark contrast to what happens in bulk materials like graphite, in which the attraction is 10 to 100 times less, Chen said.

"The method doesn't waste energy," she said.

Big Blue's research arm published a 25-page paper on the subject this week. The journal Science highlights the paper in its current issue.