Vibrations give color to light, allowing local measurement of charges in a nano structure. (Image: IBM)

October 16, 2007 — IBM (NYSE: IBM) scientists say they have measured the distribution of electrical charges carbon nanotubes. The technique, which relies on the interactions between electrons and phonons (atomic vibrations), provides a detailed understanding of the electrical behavior of carbon nanotubes. Further, it enables a way to measure their suitability as wires and semiconductors inside of future computer chips.

“The success of nanoelectronics will largely depend on the ability to prepare well characterized and reproducible nano-structures, such as carbon nanotubes,” said Phaedon Avouris, IBM Fellow and lead researcher for IBM’s carbon nanotube efforts. “Using this technique, we are now able to see and understand the local electronic behavior of individual carbon nanotubes.”

To date, researchers have been able to build carbon nanotube transistors with superior performance, but have been challenged with reproducibility issues. Carbon nanotubes are sensitive to environmental influences. For example, their properties can be altered by foreign substances, affecting the flow of electrical current and changing device performance. These interactions are typically local and change the density of electrons in the various devices of an integrated circuit, and even along a single nanotube.

A better understanding of how the local environment affects the electrical charge of a carbon nanotube is needed to allow the fabrication of more reliable transistors. Therefore, the ability to measure local electron density changes in a nanotube is essential.

IBM’s achievement was published online October 14, 2007 in the journal Nature Nanotechnology. The team monitored the color of the light scattered from the nanotube (Raman Effect), and measured small changes in the color of the light corresponding to changes in the electron density in the nanotube. The technique takes advantage of the interaction between the motion of the atoms and the motion of the electrons, so that electron density changes can be reflected in changes of the frequency of the vibrational motion of the nanotube atoms.