Electron Transport in Graphene

Graphene, a one-atom thick sheet of carbon, shows great promise as a material for building nanometer-scale electronic devices that would help to continue the trend toward smaller and more capable integrated circuits. This project, a collaboration with university researchers, is measuring the properties that underlie the high-speed transport of electrons in graphene. The researchers are also observing how defects in graphene's atomic structure influence the movement of electrons, including defects that arise at interfaces with other materials and those within the graphene atomic lattice.  With a state-of-the-art scanning tunneling microscope operated at low temperatures, the team can obtain atomic-resolution images of the graphene surface while simultaneously measuring local electronic properties with high energy resolution.

Although its existence was thought not possible on theoretical grounds, graphene -- a honeycomb-patterned sheet of carbon atoms -- was experimentally isolated only in 2004. (Carbon nanotubes, discovered earlier, are essentially graphene sheets rolled into a cylinder.) Since its discovery, graphene has become a leading contender to be a key building-block material for future generations of extraordinarily fast electronic devices. Electrons travel through this novel material like light waves, with the least amount of disturbance at room temperature than any other known substance.    

This project is applying NISTs unique nanoscale measurement instrumentation and expertise to realizing future electronics based on this form of carbon. One aim is to determine the properties that underlie the high-speed movement of electrons in graphene and how that movement might be affected by structural defects that arise within single sheets of graphene and at boundaries with other materials. The project is also evaluating a promising “wafer scale” method for making high-quality graphene, an achievement that will be critical to commercialization of graphene-based devices.

The research effort includes work on refining a promising method for manufacturing graphene on a commercial scale.  Large sheets of graphene are prepared by evaporating silicon from wafers of silicon carbide (SiC). (Graphene on silicon carbide is a leading candidate for graphene-based nanoelectronics.) As the silicon evaporates, it leaves behind atom-thick layers of carbon that are stacked atop the SiC that remains. Project scientists use a custom-built scanning tunneling microscope (STM) in the NIST Center for Nanoscale Science and Technology to measure both physical surface features and the behavior of electrons scattering from atoms in the crystal. With the unique STM, it is possible to image both the surface of the graphene sheet and its interface with the underlying SiC.  

The team has found that higher-energy electrons moving through graphene interact strongly with the irregular SiC-graphene interface, but that lower-energy electrons, which are most important for graphene-based electronics, are barely affected by the interface. Therefore, prospects are good that high-performance graphene electronics can be manufactured on SiC, even if the interface is not perfect.

Project researchers are pushing ahead with work to determine in more detail how the structure of graphene and its interface with SiC influences the flow of electricity, heat, and other forms of energy. Understanding the energy dynamics at this fundamental level will help to guide the design and manufacture of electronic devices that exploit the superlative properties of graphene.