Graphene Grains Make Atom-thick Patchwork Quilts
Using Diffraction Imaging Electron Microscopy
Cornell University researchers have unveiled striking, atomic-resolution details of what graphene "quilts" look like at the boundaries between patches, and have uncovered key insights into graphene's electrical and mechanical properties. Researchers focused on graphene - a one atom-thick sheet of carbon atoms bonded in a crystal lattice like a honeycomb or chicken wire - because of its electrical properties and potential to improve everything from solar cells to cell phone screens. But graphene doesn't grow in perfect sheets. Rather, it develops in pieces that resemble patchwork quilts, where the honeycomb lattice meets up imperfectly. These "patches" meet at grain boundaries, and scientists had wondered whether these boundaries would allow the special properties of a perfect graphene crystal to transfer to the much larger quilt-like structures.
To study the material, the researchers grew graphene membranes on a copper substrate (a method devised by another group) but then conceived a novel way to peel them off as free-standing, atom-thick films.
Then with diffraction imaging electron microscopy, they imaged the graphene by seeing how electrons bounced off at certain angles, and using a color to represent that angle. By overlaying different colors according to how the electrons bounced, they created an easy, efficient method of imaging the graphene grain boundaries according to their orientation. And as a bonus, their pictures took an artistic turn, reminding the scientists of patchwork quilts.
David Muller, professor of applied and engineering physics and co-director of the Kavli Institute at Cornell for Nanoscale Science, conducted the work with Paul McEuen, professor of physics and director of the Kavli Institute, and Kavli member Jiwoong Park, assistant professor of chemistry and chemical biology. The paper's other contributors were: Pinshane Huang, Carlos Ruiz-Vargas, Arend van der Zande, William Whitney, Mark Levendorf, Shivank Garg, JonathanAlden and Ye Zhu, all from Cornell; Joshua Kevek, Oregon State University and Caleb Hustedt, Brigham Young University.
Huang P.Y. et al.: Grains and grain boundaries in single-layer graphene atomic patchwork quilts.
Nature (5 January 2011) doi:10.1038/nature09718 Letter