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- Tackling the nanostructure problem
- The curious depletion of helium and neon in Jupiter's atmosphere
Now in Focus
Swimming Microbes Change Fluid Viscosity
March 15, 2010
Experiments show that swimming microorganisms can change a fluid’s viscosity. Not all of the effects can be explained by current theories.
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Graphene gets the hole thing
Metal to Insulator Transition in Epitaxial Graphene Induced by Molecular Doping
S. Y. Zhou, D. A. Siegel, A. V. Fedorov, and A. Lanzara
Phys. Rev. Lett. 101, 086402 (Published August 20, 2008)
The applicability of a new material for microelectronics depends on how well one can fine-tune the transport properties of its charge carriers. In a paper appearing in Physical Review Letters, Shuyun Zhou and colleagues from the University of California, Berkeley and Lawrence Berkeley National Laboratory use the tools of angle-resolved photoemission spectroscopy to demonstrate they can induce a reversible metal-insulator transition in epitaxial graphene with chemical doping.
The authors study single- and bilayer graphene grown on silicon carbide substrates, since this type of epitaxially grown graphene may have superior device performance compared to graphene sheets that are “peeled” from bulk graphite. The graphene layers are exposed to NO2 gas, which dopes the graphene layers with holes and pushes the Fermi energy within the gap between the conductance and valence bands, turning the graphene from a metal into an insulator [1]. With sufficient photon flux, the NO2 will desorb and the graphene will revert to being a metal.
This sort of control over transport properties opens possibilities to use expitaxially grown graphene for sensitive microelectronics, while also addressing the physics of hole-doping. – Sami Mitra
[1] K. Novoselov, Nature Mater. 6, 720 (2007).