Feng Wang (left) and Yuanbo Zhang at an optics bench in Birge Hall, where they conduct their experiments on graphene.
Now, University of California, Berkeley, researchers have shown that a form of carbon called graphene has an electronic structure that can be controlled by an electrical field, an effect that can be exploited to make tunable electronic and photonic devices. While such properties were predicted for a double layer of graphene, this is the first demonstration that bilayer graphene exhibits an electric field-induced, broadly tunable bandgap, according to principal author Feng Wang, UC Berkeley assistant professor of physics. The bandgap of a material is the energy difference between electrons residing in the two most important states of a material - valence band states and conduction band states - and it determines the electrical and optical properties of the material. "The real breakthrough in materials science is that for the first time you can use an electric field to close the bandgap and open the bandgap. No other material can do this, only bilayer graphene," Wang said. Because tuning the bandgap of bilayer graphene can turn it from a metal into a semiconductor, a single millimeter-square sheet of bilayer graphene could potentially hold millions of differently tuned electronic devices that can be reconfigured at will, he said. Wang, post-doctoral fellow Yuanbo Zhang, graduate student Tsung-Ta Tang and their UC Berkeley and Lawrence Berkeley National Laboratory (LBNL) colleagues report their success in the June 11 issue of Nature.
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