Grains and grain boundaries in single-layer graphene atomic patchwork quilts

Graphene patchwork analysed Single-atom-thick graphene sheets can now be produced at metre scales, bringing large-area applications in electronics and photovoltaics closer. But such large pieces can be expected to be polycrystalline, so it is important to determine the nature and size of the grains involved. Huang et al . use transmission electron microscopy to produce atomic-resolution images at grain boundaries, and map the location, orientation and shape of several hundred grains and boundaries using diffraction-filtered imaging. By correlating grain imaging with scanned probe and transport measurements, they show that the grain boundaries dramatically weaken the mechanical strength of graphene membranes, but do not as dramatically alter their electrical properties. Single-atom-thick graphene sheets can be produced at metre scales, bringing large-area applications in electronics and photovoltaics closer. However, such large pieces can be expected to be polycrystalline, so that it is important to determine the nature and size of grains in large-area graphene. This paper uses a combination of old and new transmission electron microscope techniques to carry out atomic-resolution imaging at grain boundaries as well as mapping of the location, orientation and shape of several hundred grains and boundaries with diffraction-filtered imaging. By correlating grain imaging with scanned probe and transport measurements, it is shown that the grain boundaries dramatically weaken the mechanical strength of graphene membranes, but do not as dramatically alter their electrical properties. The properties of polycrystalline materials are often dominated by the size of their grains and by the atomic structure of their grain boundaries. These effects should be especially pronounced in two-dimensional materials, where even a line defect can divide and disrupt a crystal. These issues take on practical significance in graphene, which is a hexagonal, two-dimensional crystal of carbon atoms. Single-atom-thick graphene sheets can now be produced by chemical vapour deposition 1 , 2 , 3 on scales of up to metres 4 , making their polycrystallinity almost unavoidable. Theoretically, graphene grain boundaries are predicted to have distinct electronic 5 , 6 , 7 , 8 , magnetic 9 , chemical 10 and mechanical 11 , 12 , 13 properties that strongly depend on their atomic arrangement. Yet because of the five-order-of-magnitude size difference between grains and the atoms at grain boundaries