Graphene Sheets ... And Transistors

Two new reports on graphene show that the electronically promising supermolecule, composed of a single layer of carbon atoms linked like chicken wire, can be prepared in large, uniform films and can be doped with electrons to make transistors. Graphene, which has taken the field of materials research by storm in the past couple of years, is usually synthesized in micrometer-sized bits by peeling off slices of three-dimensional graphite. Rodney S. Ruoff and colleagues of the University of Texas, Austin, now demonstrate the ability to grow centimeter-sized monolayer graphene films on copper substrates from methane via chemical vapor deposition (Science, DOI: 10.1126/science.1171245). The graphene films can be transferred to different substrates. As for graphene's electronic properties, scientists have prepared graphene field-effect transistors with hole doping that confers positive charges. But electron doping of graphene transistors has not been done until now. Stanford University's Hongjie Dai and colleagues worked around the impasse by heating ribbons of graphene in ammonia gas, which caused nitrogen species to bond with the carbon atoms at the edges and reactive defect sites in the plane of the ribbons, injecting negative charges into the graphene (Science 2009, 324, 768). From the material, the group produced a field-effect transistor, which operates at room temperature.