Technical Description: The goal of this research project is to develop a novel method to place controlled amounts of substitutional impurities into graphene grown on SiC, to physically and electronically characterize the doped structures, and to evaluate the changes in the film's properties. Impurities are implanted into a SiC wafer prior to graphene formation. The wafer is annealed to bring the impurity distribution near the surface. Then graphene is grown by sublimation of Si, simultaneously driving the impurities into the graphene film. After this process, the impurity distribution is characterized by surface analytical techniques as well as by electrical transport measurements. If successful, the method can also be applied to other two-dimensional materials.
Non-technical Description: Graphene, a single layer of carbon atoms bound together in a honeycomb lattice structure, has unique electrical and mechanical properties. Effective use of these properties requires the inclusion of predetermined amounts of impurity atoms (doping) in the films. The project develops a new method to incorporate controlled amounts of atoms into a single atomic layer of graphene, and provides graduate student training in an interdisciplinary environment. In addition, undergraduate students at the University of Minnesota and at Rutgers University, as well as high school teachers working at Georgia Tech, obtain direct hands-on research experience in the project as well as study materials and new understanding resulting from the project in courses taught by the principal investigators.
Graphene is a unique form of carbon whose singular properties were first recognized in 2001 as a potential replacement for silicon in next generation electronics. While research in this new material exploded since 2003, the lack a way to make a semiconducting form of graphene has stymied its incorporation into mainstream electronics. Under this grant, we have developed a method to transform the metallic form of graphene to a semiconducting form suitable for electronics. Unlike most semiconducting material, graphene is a flat sheet. The physics of such a material is completely different than normal semiconductors like silicon. We showed that this material could become semiconducting by taking advantage of its single layer physics by bending it at the atomic scale using small amount of nitrogen that pin graphene to a surface (silicon carbide in this case). A schematic of how nitrogen bonds the graphene to the silicon carbide surface is shown in Figure 1. Besides demonstrating the concept of bending graphene to alter its electronic properties, we have invented new ways to control the quality of this new material. Rather than relying on random bending, we have altered how it grows on silicon carbide by growing it from thin stripes chemically edged into the silicon carbide. Using high-resolution microscopy and state of the art two-dimensional analytical tools, we have shown that large-scale bent graphene can be made with uniform structural and electronic properties. Figure 2 shows a cartoon of the bent nitrogen graphene and a high magnification image of the ribbons and the normal flat graphene. It is clear from Figure 2 that the graphene on the flat area is patchy (less uniform) compared to the graphene on the ribbons. The advances in graphene modification produced under this research program will play an important part in accelerating the development of carbon electronics. Because carbon based materials can operate at higher temperatures, in corrosive environments, and use less power, carbon electronics offers a significant advancement for the US electronics industry. This research represents an important step forward in the development of next generation electronics.