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Graphene's Nature Controlled

Photonics.com
Jan 2009
TROY, N.Y., Jan. 21, 2009 – Researchers now can tune graphene’s electrical properties by growing it on different surfaces, a discovery that could bring the mass production of graphene-based nanoelectronics one step closer to realization.

Graphene, a one-atom-thick sheet of carbon, was discovered in 2004 and is considered a potential heir to copper and silicon as the fundamental building blocks of nanoelectronics.

With help from an underlying substrate, researchers at Rensselaer Polytechnic Institute have  demonstrated the ability to control the nature of graphene. Saroj Nayak, an associate professor in the department of physics, applied physics and astronomy, along with Philip Shemella, a postdoctoral research associate in the same department, determined that the chemistry of the surface on which graphene is deposited plays a key role in shaping the material’s conductive properties. The results are based on large-scale quantum mechanical simulations.

Results show that, when deposited on a surface treated with oxygen, graphene exhibits semiconductor properties. When deposited on a material treated with hydrogen, however, it exhibits metallic properties.
Graphene.jpg
Researchers at Rensselaer Polytechnic Institute have developed a method for controlling the conductive nature of graphene. Pictured is a rendering of two sheets of graphene, each with the thickness of just one carbon atom, resting atop a silicon dioxide substrate. (Image: Rensselaer/Shemella)
“Depending on the chemistry of the surface, we can control the nature of the graphene to be metallic or semiconductor,” Nayak said. “Essentially, we are ‘tuning’ the electrical properties of material to suit our needs.”

Conventionally, whenever a batch of graphene nanostructures is produced, some of the graphene is metallic, while the rest is semiconductor. It would be nearly impossible to separate the two on a large scale, Nayak said, yet realizing new graphene devices would require that they be composed solely of metallic or semiconductor graphene. The new method for “tuning” the nature of graphene is a key step to making this possible, he said.

Graphene’s excellent conductive properties make it attractive to researchers. Even at room temperature, electrons pass through the material effortlessly, near the speed of light and with little resistance. This means a graphene interconnect likely would stay much cooler than a copper interconnect of the same size. Cooler is better because heat produced by interconnects can have negative effects on both a computer chip’s speed and performance.

Results of the study were published this week in the paper “Electronic structure and band-gap modulation of graphene via substrate surface chemistry” in Applied Physics Letters and are featured on the cover of the journal’s Jan. 19 issue.

Large-scale quantum simulations for the study were run on Rensselaer’s supercomputing system, the Computational Center for Nanotechnology Innovations.

Funding for the project was from the New York State Interconnect Focus Center at Rensselaer.

For more information, visit: www.rpi.edu


GLOSSARY
modulation
In general, changes in one oscillation signal caused by another, such as amplitude or frequency modulation in radio which can be done mechanically or intrinsically with another signal. In optics the term generally is used as a synonym for contrast, particularly when applied to a series of parallel lines and spaces imaged by a lens, and is quantified by the equation: Modulation = (Imax – Imin)/ (Imax + Imin) where Imax and Imin are the maximum and minimum intensity levels of the image.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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