April 15, 2009

Getting Graphene Edges to Atomic Precision and Real Time Atom Observation

Foresight highlighted two important research developments.

MIT can use to heat to get the edges of Graphene to Atomic Precision and scientists at the University of California at Berkeley and the Lawrence Berkeley National Laboratory were able to observe carbon atoms moving around the edges of a hole punched in a graphene crystal.

Live Action Movies of Carbon Atoms Around Graphene

Researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), working with TEAM 0.5, the world’s most powerful transmission electron microscope, have made a movie that shows in real-time carbon atoms repositioning themselves around the edge of a hole that was punched into a graphene sheet. Viewers can observe how chemical bonds break and form as the suddenly volatile atoms are driven to find a stable configuration. This is the first ever live recording of the dynamics of carbon atoms in graphene.

Two years ago, co-authors Cohen and Louie, theorists who hold joint appointments with Berkeley Lab’s Materials Sciences Division and UC Berkeley, calculated that nanoribbons of graphene can conduct a spin current and could therefore serve as the basis for nanosized spintronic devices. Spin, a quantum mechanical property arising from the magnetic field of a spinning electron, carries a directional value of either “up” or “down” that can be used to encode data in the 0s and 1s of the binary system. Spintronic devices promise to be smaller, faster and far more versatile than today’s devices because — among other advantages — data storage does not disappear when the electric current stops.

Said Cohen, “Our calculations showed that zigzag graphene nanoribbons are magnetic and can carry a spin current in the presence of a sufficiently large electric field. By carefully controlling the electric field, it should be possible to generate, manipulate, and detect electron spins and spin currents in spintronics applications.”

Said Louie, “If electric fields can be made to produce and manipulate a 100-percent spin-polarized carrier system through a chosen geometric structure, it will revolutionize spintronics technology.”…

Action movie of individual atoms.

Simulation of individual atoms

Controlling the Edges of Graphene Nanoribbons

Controlled Formation of Sharp Zigzag and Armchair Edges in Graphitic Nanoribbons

Graphene nanoribbons can exhibit either quasi-metallic or semiconducting behavior, depending on the atomic structure of their edges. Thus, it is important to control the morphology and crystallinity of these edges for practical purposes. MIT researchers demonstrated an efficient edge-reconstruction process, at the atomic scale, for graphitic nanoribbons by Joule heating. During Joule heating and electron beam irradiation, carbon atoms are vaporized, and subsequently sharp edges and step-edge arrays are stabilized, mostly with either zigzag- or armchair-edge configurations. Model calculations show that the dominant annealing mechanisms involve point defect annealing and edge reconstruction.

9 pages of supporting material on the research work.

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