Materials Science

Graphene in Color

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Science  25 Jan 2013:
Vol. 339, Issue 6118, pp. 374
DOI: 10.1126/science.339.6118.374-a
CREDIT: J. T. ROBINSON

The properties of bilayer graphene films depend on the relative orientation or twist of the two layers. Robinson et al. grew single-layer graphene on copper surfaces and then performed two transfers of these films onto silica-coated silicon substrates to create bilayer regions. Because these films are polycrystalline, a variety of twist angles between the layers were created across the surface and resulted in a patchwork of colored regions that appeared red, yellow, or blue. Raman spectroscopy was used to characterize the twist angles; the enhancement of the G peak at ∼1600 cm−1 occurred at optical excitation wavelengths that differed for the red and yellow regions, and the extent of enhancement corresponded to the deviation of the orientation of the layers from a distinctive critical twist angle. The twist angles were also confirmed by low-energy electron diffraction studies. The coupling could be minimized by chemical functionalization: fluorination of the top graphene layers with XeF2 quenched the colors, which could be recovered by thermally desorbing the fluorine atoms.

ACS Nano 10.1021/nn304834p (2012).

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