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.
"In the long run it might be possible to achieve meter-length single crystals," Ruoff said. "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," he said.
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.
Yufeng Hao says he thinks the knowledge gained in this study could prove useful to industry.
"The high quality of the graphene grown by our method will likely be developed further by indus
|Contact: Sandra Zaragoza|
University of Texas at Austin