“Nanowires are really the major building blocks of future nano-devices,” said postdoctoral researcher Parsian Mohseni, first author of the study. “Nanowires are components that can be used, based on what material you grow them out of, for any functional electronics application.” Li’s group uses a method called van der Waals epitaxy to grow nanowires from the bottom up on a flat substrate of semiconductor materials, such as silicon. The nanowires are made of a class of materials called III-V (three-five), compound semiconductors that hold particular promise for applications involving light, such as solar cells or lasers.
Thanks to its thinness, graphene is flexible, while silicon is rigid and brittle. It also conducts like a metal, allowing for direct electrical contact to the nanowires. Furthermore, it is inexpensive, flaked off from a block of graphite or grown from carbon gases. “One of the reasons we want to grow on graphene is to stay away from thick and expensive substrates,” Mohseni said. “About 80 percent of the manufacturing cost of a conventional solar cell comes from the substrate itself. We’ve done away with that by just using graphene. Not only are there inherent cost benefits, we’re also introducing functionality that a typical substrate doesn’t have.”