IBM moves carbon nanotubes closer to semi use with measurement technique

By Ann Steffora Mutschler, Senior Editor -- 10/15/2007

Giving a detailed understanding of the electrical behavior of carbon nanotubes, a team of researchers at IBM Corp.’s T.J. Watson Research Center in Yorktown Heights, N.Y. reported today that they have measured the distribution of electrical charges in tubes of carbon measuring smaller than 2-nm in diameter – which is 50,000 times thinner than a human hair – a development which moves carbon nanotubes closer to implementation in semiconductor chips.

Carbon in a nanotube structure is a material that shows promise as a building block for smaller, faster and lower power computer chips compared to today's conventional silicon transistors.

IBM’s technique relies on the interactions between electrons and phonons. Phonons are the atomic vibrations that occur inside material, which can determine the material's thermal and electrical conductivity, whereas electrons carry and produce the current: both are important features of materials that can be used to carry electrical signals and perform computations.

This development is important since the interaction between electrons and phonons can release heat and impede electrical flow inside computer chips and by understanding the interaction of electrons and phonons in carbon nanotubes, the researchers have a better way to measure their suitability as wires and semiconductors inside of future computer chips.

However, in order to make carbon nanotubes useable in building logic circuitry, scientists are pushing to demonstrate their high speed, high packing density and low power consumption capabilities as well as the ability to make them viable for potential mass production, IBM noted.

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

IBM noted that to date, researchers have been able to build carbon nanotube transistors with superior performance, but have been challenged with reproducibility issues as 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; with these interactions, typically local, changing the density of electrons in the various devices of an IC and even along a single nanotube, Big Blue explained.

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

IBM’s development was published in the journal Nature Nanotechnology.

During development, IBM noted that its 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, which 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.

In March 2006, IBM researchers built what the company believes is the first complete IC around a single carbon nanotube molecule.

Source: IBM

In the image above, vibrations give color to light allowing for local measurement charges in a nanoscale electronic device.

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