Closest Look Ever At Graphene
Hailed as the world’s most powerful transmission electron microscope, TEAM 0.5 is living up to expectations. Using TEAM 0.5 (TEAM stands for Transmission Electron Aberration-corrected Microscope), researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have produced stunning images of individual carbon atoms in graphene, the two-dimensional crystalline form of carbon that is highly prized by the electronics industry. These first time ever images were recorded at Berkeley Lab’s National Center for Electron Microscopy (NCEM), a DOE national user facility that is a premier center for electron microscopy and microcharacterization. TEAM 0.5, its newest instrument, is capable of producing images with half-angstrom resolution, which is less than the diameter of a single hydrogen atom. “Simply put, TEAM 0.5 is the best transmission electron microscope in the world, representing a quantum leap forward in instrumentation,” said physicist Alex Zettl who led this research. “Having the ability to see, basically in real time, each and every individual atom in a sample is unbelievably useful and the images we can now see have been jaw-dropping for even the most seasoned electron microscopists. TEAM 0.5 is pushing transmission electron microscopy to a new level.” Zettl holds joint appointments with Berkeley Lab’s Materials Sciences Division (MSD) and the Physics Department at the University of California’s Berkeley campus, where he is the director of the Center of Integrated Nanomechanical Systems. Collaborating with him on this graphene imaging project were Jannik Meyer, also with Berkeley Lab’s Materials Sciences Division, and Christian Kisielowski, Rolf Erni and Marta Rossell of NCEM. Their results were published in the journal Nanoletters, in a paper entitled: “Direct imaging of lattice atoms and topological defects in graphene membranes.” The properties of solid materials stem from the arrangement of their constituent atoms in the solid’s crystal structure. While technologies such as electron and x-ray crystallography can reveal the atomic geometry of a crystal, they do not identify the precise location and position of each individual atom. When the dimensions of a material shrink to the nanoscale, the location and position of each individual atom becomes critically important, as Zettl explains. “Think of the steel re-bars on a three-dimensional structure, like a jungle gym,” he said. “If a small piece of re-bar is rusted out somewhere in the center of the gym, it won’t likely have much affect on the overall properties of the structure. In a two-dimensional structure, however, a rusted out segment becomes a much bigger problem, and in a one-dimensional structure, i.e., a single re-bar, a rusted out segment can be catastrophic, causing the entire structure to fail.
On a nanoscale crystal, one missing atom or some other defect in the arrangement can result in catastrophic failure.” Graphene is especially sensitive to defects in its atomic structure. Consisting of a single-layered sheet of carbon atoms arranged in hexagons, like a sheet of chicken wire with an atom at each nexus, graphene features extraordinary electrical, mechanical and thermal properties that could enable it to serve in a broad array of carbon-based electronic devices. For the enormous promises of graphene to be fulfilled, however, scientists need a much better understanding of how specific types of defects in the crystal structure, including those that change location over time, affect its properties.
