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Berkeley Lab Scientists Control Light Scattering in Graphene

A flake of graphene was grown on copper and transferred onto an insulating substrate of silicon dioxide. The Fermi energy in the graphene was adjusted by varying the gate voltage on the overlying ion gel, which confines a strongly conducting liquid in a polymer matrix.

Led by the Materials Sciences Division's Feng Wang, researchers have made the first direct observation of quantum interference in graphene, a 'chicken wire'-like sheet of carbon just one atom thick. These findings illuminate controls for quantum pathways in light scattering devices for material characterization or biological tagging.

By investigating a form of scattering in which waves of light from different quantum pathways interfere constructively or destructively with one another, the researchers gleaned insight into how light emission can be controlled in graphene. Blocking or opening different interference paths served as a control for increasing or decreasing the brightness of light.

In this study, graphene placed on a silicon dioxide substrate was coated with an ion gel, a strongly conducting liquid in a polymer matrix. By varying the voltage applied across this device, the team could examine the contribution of each quantum pathway when lit up with an infrared laser. The scattered light grew brighter as excitation pathways were reduced – a surprising result. This unusual phenomenon could serve as a valuable research tool for scientists studying ultrafast electron dynamics, an important characteristic of graphene.

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C.-F. Chen, C.H. Park, B.W. Boudouris, J. Horng, B. Geng, C. Girit, A. Zettl, M.F. Crommie, R.A. Segalman, S.G. Louie, and F. Wang, "Controlling Inelastic Light Scattering Quantum Pathways in Graphene," Nature 471, 617–620 (31 March 2011).