• Graphene-hBN breakthrough to spur new LE

    From ScienceDaily@1:317/3 to All on Thu Apr 14 22:30:46 2022
    Graphene-hBN breakthrough to spur new LEDs, quantum computing

    Date:
    April 14, 2022
    Source:
    University of Michigan
    Summary:
    In a discovery that could speed research into next-generation
    electronics and LED devices, a research team has developed a
    reliable, scalable method for growing single layers of hexagonal
    boron nitride on graphene.



    FULL STORY ==========================================================================
    In a discovery that could speed research into next-generation electronics
    and LED devices, a University of Michigan research team has developed the
    first reliable, scalable method for growing single layers of hexagonal
    boron nitride on graphene.


    ==========================================================================
    The process, which can produce large sheets of high-quality hBN with
    the widely used molecular-beam epitaxy process, is detailed in a study
    in Advanced Materials.

    Graphene-hBN structures can power LEDs that generate deep-UV light,
    which is impossible in today's LEDs, said Zetian Mi, U-M professor of electrical engineering and computer science and a corresponding author of
    the study. Deep- UV LEDs could drive smaller size and greater efficiency
    in a variety of devices including lasers and air purifiers.

    "The technology used to generate deep-UV light today is mercury-xenon
    lamps, which are hot, bulky, inefficient and contain toxic materials," Mi
    said. "If we can generate that light with LEDs, we could see an efficiency revolution in UV devices similar to what we saw when LED light bulbs
    replaced incandescents." Hexagonal boron nitride is the world's thinnest insulator while graphene is the thinnest of a class of materials called semimetals, which have highly malleable electrical properties and are
    important for their role in computers and other electronics.

    Bonding hBN and graphene together in smooth, single-atom-thick layers
    unleashes a treasure trove of exotic properties. In addition to deep-UV
    LEDs, graphene- hBN structures could enable quantum computing devices,
    smaller and more efficient electronics and optoelectronics and a variety
    of other applications.



    ========================================================================== "Researchers have known about the properties of hBN for years, but
    in the past, the only way to get the thin sheets needed for research
    was to physically exfoliate them from a larger boron nitride crystal,
    which is labor-intensive and only yields tiny flakes of the material,"
    Mi said. "Our process can grow atomic-scale-thin sheets of essentially
    any size, which opens a lot of exciting new research possibilities."
    Because graphene and hBN are so thin, they can be used to build
    electronic devices that are much smaller and more energy-efficient
    than those available today. Layered structures of hBN and graphene can
    also exhibit exotic properties that could store information in quantum computing devices, like the ability to switch from a conductor to an
    insulator or support unusual electron spins.

    While researchers have tried in the past to synthesize thin layers of
    hBN using methods like sputtering and chemical vapor deposition, they
    struggled to get the even, precisely ordered layers of atoms that are
    needed to bond correctly with the graphene layer.

    "To get a useful product, you need consistent, ordered rows of hBN atoms
    that align with the graphene underneath, and previous efforts weren't able
    to achieve that," said Ping Wang, a postdoctoral researcher in electrical engineering and computer science. "Some of the hBN went down neatly,
    but many areas were disordered and randomly aligned." The team, made up
    of electrical engineering and computer science, materials science and engineering, and physics researchers, discovered that neat rows of hBN
    atoms are more stable at high temperature than the undesirable jagged formations. Armed with that knowledge, Wang began experimenting with
    molecular- beam epitaxy, an industrial process that amounts to spraying individual atoms onto a substrate.



    ==========================================================================
    Wang used a terraced graphene substrate -- essentially an atomic-scale staircase -- and heated it to around 1600 degrees Celsius before spraying
    on individual boron and active nitrogen atoms.The result far exceeded
    the team's expectations, forming neatly ordered seams of hBN on the
    graphene's terraced edges, which expanded into wide ribbons of material.

    "Experimenting with large amounts of pristine hBN was a distant dream
    for many years, but this discovery changes that," Mi said. "This is a big
    step toward the commercialization of 2D quantum structures." This result
    would not have been possible without collaboration from a variety of disciplines. The mathematical theory that underpinned some of the work
    involved researchers in electrical engineering and computer science and materials science and engineering, from U-M and Yale University.

    Mi's lab developed the process, synthesized the material and characterized
    its interactions with light. Then, materials scientists and engineers
    at U-M and collaborators at Ohio State University studied its structural
    and electrical properties in detail.

    Emmanouil Kioupakis, associate professor of materials science and
    engineering at U-M, and Jay Gupta, professor of physics at OSU, are also corresponding authors of the paper.

    The research was supported by the Michigan Engineering Blue Sky
    Initiative, Army Research Office, National Science Foundation,
    U.S. Department of Energy and the W.M. Keck Foundation.


    ========================================================================== Story Source: Materials provided by University_of_Michigan. Original
    written by Gabe Cherry.

    Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Ping Wang, Woncheol Lee, Joseph P. Corbett, William H. Koll,
    Nguyen M.

    Vu, David Arto Laleyan, Qiannan Wen, Yuanpeng Wu, Ayush Pandey,
    Jiseok Gim, Ding Wang, Diana Y. Qiu, Robert Hovden, Mackillo Kira,
    John T.

    Heron, Jay A. Gupta, Emmanouil Kioupakis, Zetian Mi. Scalable
    Synthesis of Monolayer Hexagonal Boron Nitride on Graphene with
    Giant Bandgap Renormalization. Advanced Materials, 2022; 2201387
    DOI: 10.1002/ adma.202201387 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220414110726.htm

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