Graphene, wonder material though it may be, is horribly difficult to grow in the clean, perfect sheets that electronics engineers need to build the successors to today’s silicon chips. But new research from scientists at Cornell will make it easier to see where the defects are in a sheet of graphene, leading eventually to better fabrication processes.
Although the text book picture of graphene is of a sheet of cleanly intersecting hexagons, in the real world graphene grows in pieces that join together oddly, creating imperfections in the lattice. At the joins, the hexagons have five or seven carbon atoms, rather than the perfect six.
The new imaging technique reveals the surface of a sheet to be something like a patchwork-quilt, with patches coloured differently according to the alignment of the atoms.
From Cornell’s press announcement: "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."
The research has revealed that, contrary to expectations, the size of the patches doesn’t affect the electrical properties of graphene. It is impurities that get into the monolayers as they form that cause problems with conductivity. This insight, Cornell says, will help researchers in their quest for the best way to grow graphene.
The work is published in Nature, here.