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Imaging Electron Clouds on the Surface of Graphene

By imaging electron clouds on the surface of graphene, Molecular Foundry scientists, in collaboration with researchers at the University of Buffalo and SEMATECH, discovered surface folds, ripples and other distortions can impair graphene's ability to conduct electrons. Here, dotted lines show distinct regions in graphene sloped at different angles (a and b) with differences in peak height ratios of each region (c) interpreted as effective angles by comparison with first-principles simulations (d).

Guided by the Molecular Foundry's David Prendergast, researchers at the University of Buffalo and SEMATECH have imaged electron clouds on the surface of graphene. These clouds reveal surface folds, ripples and other distortions that can impair graphene's ability to conduct electrons.

The promise of graphene lies in the simplicity of its structure---a 'chicken wire' lattice of carbon atoms just one layer thick. This sheet confines electrons in one dimension, forcing them to race across a plane. Such quantum confinement results in stellar electronic, mechanical and optical properties far beyond what silicon and other traditional semiconductor materials can offer.

In this study, Prendergast used simulations to interpret experimental x-ray spectroscopy results to predict how subtle changes in the structure of graphene affect its electronic properties. His findings showed regions of graphene sloped at different angles, much like looking down onto the slanted roofs of many houses packed close together.

The researchers also found contaminants that cling to graphene during processing linger in valleys where the material is uneven. Such contaminants uniquely distort the electron cloud, and emphasize the need to keep graphene straight and flat if it is to be successfully employed in electronic devices.

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B. J. Schultz, C.J. Patridge, V. Lee, C. Jaye, P.S. Lysaght, C. Smith, J. Barnett, D.A. Fischer, D. Prendergast and S. Banerjee, "Imaging local electronic corrugations and doped regions in graphene,"Nature Communications 2, 372 (2011). DOI: 10.1038/ncomms1376