5 August 2014

Researchers uncover groundbreaking properties of promising material

MagLab scientists working with graphene — a stronger-than steel, but feathery light material with a myriad of intriguing attributes — have observed new properties that bring this high-tech super material closer to everyday use.

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TALLAHASSEE, Fla. – MagLab scientists working with graphene — a stronger-than steel, but feathery light material with a myriad of intriguing attributes — have observed new properties that bring this high-tech super material closer to everyday use. Their findings were recently published in Nature Communications, in the paper "Observation of an intrinsic bandgap and Landau level renormalization in graphene/boron-nitride heterostructures".

Energy spectrum of graphene with a bandgap.Energy spectrum of graphene with a bandgap.When the scientists layered the one-atom thick graphene with boron nitride, they found several exciting results that could lead to new, unexplored uses for this wonder material.

In the future, graphene may make new products possible - from thin, flexible computer screens that can be rolled up like a sheet of paper to quantum computers that can process complex calculations using quantum-mechanical phenomena. Working with collaborators in both Beijing, China and Berkeley, Calif., MagLab researchers Zhi-Guo Chen, You Lai and Zhiqiang Li spent more than one year experimenting with small samples of graphene layered with boron nitride — a synthetic, inorganic compound used in cosmetics and personal care products to increase adherence and absorb oil.

"Our research reveals the largest bandgap yet observed in graphene on boron nitride," said Zhi-Guo Chen, a postdoc working at the MagLab. "We were so surprised, we had to check our results many times."

A material's bandgap is an energy region that electrons are not allowed to occupy. It's what determines whether a material's electrical current can be turned on and off, a critical component of modern electronic devices.

Earlier research with graphene alone showed that the material is an excellent conductor of electricity, but has no naturally occurring bandgap, limiting its electronic applications. MagLab researchers, however, found a bandgap of 440 Kelvin (or 332 degrees Fahrenheit) — larger than room temperature — in their graphene on boron nitride.

"This huge bandgap means that our graphene/boron-nitride structure could have many exciting practical applications," said Zhiqiang "Jason" Li, who has been studying graphene for a decade
beyond the bandgap, how the MagLab team's graphene/boron-nitride samples were produced is also important to possible practical use of this material.

When graphene is laid atop boron-nitride.When graphene is laid atop boron-nitride, a new, larger pattern called a moire pattern emerges, as shown above.Graphene was discovered when researchers used Scotch tape to peel off layers of graphite until they ended up with a new one-atom thick material. Since then, research teams often create their own samples of graphene with tape in a similar way. The MagLab team's new graphene/boron-nitride sample is unique because it is not made with tape, but rather grown by a method called chemical vapor deposition, making it "scalable," or able to be manufactured on a larger scale and in larger quantities. This ability to process graphene/boron-nitride in a way that can meet growing demand is a critical step to the material's potential practical application.

The director of the MagLab's DC Field Facility, Tim Murphy, noted: "It is very exciting to witness the evolution of graphene from an interesting new material to one that holds the promise of fundamentally changing the landscape of how electronics will be made in the future."

The lab's scientists also made a critical observation regarding graphene's Landau levels, or the discrete energy levels occupied by electrons in a magnetic field. By combining optics with the strong magnetic fields available at the MagLab, their study showed that the Landau levels in graphene/boron-nitride are strongly influenced by electronic interactions.

MagLab collaborators on this paper include Zhiwen Shi, from the University of California's physics department; Wei Yang, Xiaobo Lu and Guangyu Zhang from the Beijing National Laboratory for Condensed Matter Physics and Chinese Academy of Sciences; Hugen Yan, from the Watson Research Center in New York; and Feng Wang, from UC Berkeley and Lawrence Berkeley National Laboratory.

The National High Magnetic Field Laboratory is the world’s largest and highest-powered magnet facility. Located at Florida State University, the University of Florida and Los Alamos National Laboratory, the interdisciplinary National MagLab hosts scientists from around the world to perform basic research in high magnetic fields, advancing our understanding of materials, energy and life. The lab is funded by the National Science Foundation (DMR-1157490) and the state of Florida. For more information, visit us online at nationalmaglab.org or follow us on Facebook, Twitter, Instagram and Pinterest at NationalMagLab.