Rensselaer Research Review Fall 2010
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Water Could Hold Answer to Graphene Nanoelectronics
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* Water Could Hold Answer to Graphene Nanoelectronics

Professor Nikhil Koratkar,
Department of Mechanical,
Aerospace, and Nuclear Engineering

Researchers at Rensselaer have developed a new method for using water to tune the band gap of the nanomaterial graphene, opening the door to new graphene-based transistors and nanoelectronics.

By exposing a graphene film to humidity, Rensselaer Professor Nikhil Koratkar and his research team were able to create a band gap in graphene — a critical prerequisite to creating graphene transistors. At the heart of modern electronics, transistors are devices that can be switched “on” or “off” to alter an electrical signal. Computer microprocessors are comprised of millions of transistors made from the semiconducting material silicon, for which the industry is actively seeking a successor.

Graphene, an atom-thick sheet of carbon atoms arranged like a nanoscale chain-link fence, has no band gap. Koratkar’s team demonstrated how to open a band gap in graphene based on the amount of water they adsorbed to one side of the material, precisely tuning the band gap to any value from 0 to 0.2 electron volts. This effect was fully reversible and the band gap reduced back to zero under vacuum. The technique does not involve any complicated engineering or modification of the graphene, but requires an enclosure where humidity can be precisely controlled.

Opening a Bandgap

“Graphene is prized for its unique and attractive mechanical properties. But if you were to build a transistor using graphene, it simply wouldn’t work as graphene acts like a semi-metal and has zero band gap,” said Koratkar, a professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer. “In this study, we demonstrated a relatively easy method for giving graphene a band gap. This could open the door to using graphene for a new generation of transistors, diodes, nanoelectronics, nanophotonics, and other applications.”

Results of the study were detailed in the paper “Tunable Band Gap in Graphene by the Controlled Adsorbtion of Water Molecules,” published by the journal Small. See the full paper at: http://dx.doi.org/10.1002/smll.201001384

In its natural state, graphene has a peculiar structure but no band gap. It behaves as a metal and is known as a good conductor. This is compared to rubber or most plastics, which are insulators and do not conduct electricity. Insulators have a large band gap — an energy gap between the valence and conduction bands — which prevents electrons from conducting freely in the material.  

Between the two are semiconductors, which can function as both a conductor and an insulator. Semiconductors have a narrow band gap, and application of an electric field can provoke electrons to jump across the gap. The ability to quickly switch between the two states — “on” and “off” — is why semiconductors are so valuable in microelectronics.

Splash Photo Credit: Fir0002/Flagstaffotos. Reprinted under GFDL license.

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“Water Could Hold Answer to
Graphene Nanoelectronics”
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