Dual Properties of Carbon Nanotubes Revealed

April 28, 2006
Dual Properties of Carbon Nanotubes Revealed
Tobias Beetz (left) and Matt Sfeir review data in the electron microscopy lab at Brookhaven.

For the first time, researchers have directly measured the electronic structure of individual carbon nanotubes whose physical properties had already been determined. This new study, pioneered by researchers at the U.S. Department of Energy’s Brookhaven National Laboratory working with their colleagues at Columbia University, may help scientists determine the usefulness of carbon nanotubes in various applications, from microelectronics to mechanical, thermal, and photovoltaic devices.

The researchers report on their work in the April 28 issue of Science.

“This combined study technique allows us -- for the first time -- to test some fundamental predictions about nanotube behavior,” said Matt Sfeir, a physicist in Brookhaven’s Condensed Matter Physics and Materials Sciences Division and lead author of the study. “Understanding how these materials function on a basic level is key to controlling and manipulating them for future successful commercial applications.”

Carbon nanotubes are capsule-shaped molecules only a few billionths of a meter (nanometers) in width. In nanotube form, many materials take on useful, unique properties, such as physical strength and excellent conductivity. Single-walled carbon nanotubes are the most widely investigated variety, but what makes them so interesting also makes them very difficult to study -- several hundred distinct species exist, and each has dramatically different electronic properties thought to be linked to their unique individual structure.

Sfeir and his colleagues sought to look at both the structure of carbon nanotubes and their corresponding electronic properties using two existing techniques. The twist is that the two techniques would be used on each of the nanotubes studied, giving the researchers a complete picture of their unique structure and behavior as well as greater knowledge about how they “transition” from semi-conducting to metallic in terms of their electronic properties.

The work started at Columbia, where the single-walled carbon nanotubes were grown freely suspended over a slit etched into a silicon substrate. The researchers then identified usable individual nanotubes, labeled them, and studied them with a technique known as resonance Rayleigh scattering. This method allows researchers to detect the optical spectrum of light scattered from the nanotubes and use that scattered light to determine their electronic structure.

“The optical spectra alone, however, does not give us sufficient information to absolutely assign electronic transitions to the nanotubes’ physical structure,” said Sfeir. “We needed a technique that could provide independent structural verification. Fortunately, our colleagues in the electron microscopy group at Brookhaven were interested in this problem as well and were able to provide a solution - electron diffraction.”

The labeled nanotubes were brought to Brookhaven, where physicist Tobias Beetz subjected them to electron diffraction studies using an electron microscope. This gave the researchers complementary data on the nanotubes’ physical structure.

“Electron diffraction is an ideal tool for determining the exact structure of metallic and semiconducting nanotubes,” said Beetz. “We can use this tool to easily see if we are dealing with single-walled or double-walled nanotubes, and we are not limited to studying a certain nanotube diameter range as we would be using other methods.”

After collecting these two sets of information from many different nanotube structures, researchers were then able, for the first time, to test theories of nanotube electronic transitions and confirm several assumptions made in previous models.

“One aspect we have verified is how small changes in the pitch of the hexagons on the nanotube sidewall, determined by how the nanotube grows, lead to systematic deviations in the electronic behavior in both semi-conducting and metallic structures,” said Sfeir. “This predicted behavior, known as the “family pattern,” had never before been directly tested, and our experimental results place it on a solid foundation that was previously lacking.”

Source: BNL

Explore further: Engineers create prototype chip just three atoms thick

Related Stories

Engineers create prototype chip just three atoms thick

November 29, 2016

For more than 50 years, silicon chipmakers have devised inventive ways to switch electricity on and off, generating the digital ones and zeroes that encode words, pictures, movies and other forms of data.

Deep insights from surface reactions

November 30, 2016

Things that happen on the surface are often given short shrift compared to what goes on inside. But when it comes to chemical reactions, what occurs on the surface can mean the difference between a working material and one ...

'Pressure-welding' nanotubes creates ultrastrong material

November 8, 2016

Researchers from the Moscow Institute of Physics and Technology (MIPT), Technological Institute for Superhard and Novel Carbon Materials (TISNCM), Lomonosov Moscow State University (MSU), and the National University of Science ...

Recommended for you

Particles self-assemble into Archimedean tilings

December 8, 2016

(Phys.org)—For the first time, researchers have simulated particles that can spontaneously self-assemble into networks that form geometrical arrangements called Archimedean tilings. The key to realizing these structures ...

Nano-calligraphy on graphene

December 8, 2016

Scientists at The University of Manchester and Karlsruhe Institute of Technology have demonstrated a method to chemically modify small regions of graphene with high precision, leading to extreme miniaturisation of chemical ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.