Large graphene crystals (10,000 times larger than the largest crystals of only four years ago) that possess exceptional electrical properties were recently created by researchers from the University of Texas at Austin. The new centimeter-size crystals were produced via the utilization of practically nothing but surface oxygen and thin sheets of copper.
The graphene crystals have quite a number of potential uses thanks to their impressively high electrical and thermal conductivity — potentially being used in anything from solar cells, to high-performance batteries, to aircraft wings, to flexible electronics, to high-speed transistors, etc.
Yufeng Hao, postdoctoral fellow at The University of Texas at Austin, demonstrates large, single graphene crystals grown on copper.
Image Credit: The Cockrell School of Engineering at The University of Texas at Austin
Talking about the creation process, researcher Rodney S. Ruoff, professor in the Cockrell School of Engineering, stated: “The game we play is that we want nucleation (the growth of tiny ‘crystal seeds’) to occur, but we also want to harness and control how many of these tiny nuclei there are, and which will grow larger. Oxygen at the right surface concentration means only a few nuclei grow, and winners can grow into very large crystals.”
The new research — and understanding of how graphene growth is influenced by differing amounts of surface oxygen — represents a significant step towards the manufacturing of high-quality graphene films on the industrial scale.
It’s “a fundamental breakthrough, which will lead to growth of high-quality and large area graphene film,” stated Sanjay Banerjee, the head of the Cockrell School’s South West Academy of Nanoelectronics. “By increasing the single-crystal domain sizes, the electronic transport properties will be dramatically improved and lead to new applications in flexible electronics.”
The University of Texas at Austin provides more:
Graphene has always been grown in a polycrystalline form, that is, it is composed of many crystals that are joined together with irregular chemical bonding at the boundaries between crystals (“grain boundaries”), something like a patch-work quilt. Large single-crystal graphene is of great interest because the grain boundaries in polycrystalline material have defects, and eliminating such defects makes for a better material.
By controlling the concentration of surface oxygen, the researchers could increase the crystal size from a millimeter to a centimeter. Rather than hexagon-shaped and smaller crystals, the addition of the right amount of surface oxygen produced much larger single crystals with multibranched edges, similar to a snowflake.
Another major finding by the team was that the “carrier mobility” of electrons (how fast the electrons move) in graphene films grown in the presence of surface oxygen is exceptionally high. This is important because the speed at which the charge carriers move is important for many electronic devices — the higher the speed, the faster the device can perform.
“In the long run it might be possible to achieve meter-length single crystals,” Ruoff noted. “This has been possible with other materials, such as silicon and quartz. Even a centimeter crystal size — if the grain boundaries are not too defective — is extremely significant. We can start to think of this material’s potential use in airplanes and in other structural applications — if it proves to be exceptionally strong at length scales like parts of an airplane wing, and so on.”