Engineers create double layer of borophene
New material maintains borophene's electronic properties, offers new advantages

Date:
August 26, 2021
Source:
Northwestern University
Summary:
Engineers have created a double layer of atomically flat borophene,
a feat that defies the natural tendency of boron to form non-planar
clusters beyond the single-atomic-layer limit.



FULL STORY ==========================================================================
For the first time, Northwestern University engineers have created
a double layer of atomically flat borophene, a feat that defies the
natural tendency of boron to form non-planar clusters beyond the single-atomic-layer limit.


========================================================================== Although known for its promising electronic properties, borophene
-- a single- atom-layer-thick sheet of boron -- is challenging to
synthesize. Unlike its analog two-dimensional material graphene, which
can be peeled away from innately layered graphite using something as
simple as scotch tape, borophene cannot merely be peeled away from bulk
boron. Instead, borophene must be grown directly onto a substrate.

And if growing one layer was difficult, growing multiple layers of
atomically flat borophene seemed impossible. Because bulk boron is not
layered like graphite, growing boron beyond single atomic layers leads
to clustering rather than planar films.

"When you try to grow a thicker layer, the boron wants to adopt its
bulk structure," said Northwestern's Mark C. Hersam, co-senior author
of the study.

"Rather than remaining atomically flat, thicker boron films form particles
and clusters. The key was to find growth conditions that prevented the
clusters from forming. Until now, we didn't think you could go beyond
one layer. Now we have moved into unexplored territory between the single atomic layer and the bulk, resulting in a new playground for discovery."
The research will be published Aug. 26 in the journal Nature Materials.

Hersam is the Walter P. Murphy Professor of Materials Science and
Engineering at the McCormick School of Engineeringand director of the
Materials Research Science and Engineering Center. He also is a member
of Northwestern's International Institute for Nanotechnologyand the
Simpson Querrey Institute.

Hersam co-led the work with Boris Yakobson, the Karl F. Hasselmann Chair
in Engineering at Rice University.



==========================================================================
Five years ago, Hersam and his collaborators created borophene for
the first time. Stronger, lighter and more flexible than graphene,
borophene has the potential to revolutionize batteries, electronics,
sensors, solar cells and quantum computing. Although theoretical research predicted that a double layer of borophene was possible, many researchers, including Hersam, were not convinced.

"It is challenging to make a new material, even when theoretical work
predicts its existence," Hersam said. "Theory rarely tells you the
synthetic conditions needed to achieve that new structure." The key
to the correct conditions, Hersam's team discovered, was the substrate
used for growing the material. In the study, Hersam and his colleagues
grew borophene on a flat, silver substrate. When exposed to very high temperatures, the silver bunched to form exceptionally flat, large
terraces between bunches of atomic-scale steps.

"When we grew borophene on these large, flat terraces, we saw a second
layer forming," Hersam said. "Following that serendipitous observation,
we intentionally focused our effort in that direction. We weren't looking
for the second layer when we found it. Many materials discoveries occur
in this manner, but you have to realize the opportunity when you stumble
upon something unexpected." The double-layered material maintained
all of borophene's desirable electronic properties, while offering new advantages. For example, the material comprises two atomic-layer-thick
sheets bonded together with space between, which could be used for energy
or chemical storage.

"There have been theoretical predictions that bilayer borophene is a
promising material for batteries," Hersam said. "Having space between
the layers provides a place to hold lithium ions." Hersam's team hopes
other researchers now are inspired to keep growing even thicker layers
of borophene or create double layers with different atomic geometries.

"Diamonds, graphite, graphene and carbon nanotubes are all
based on one element (carbon) with different geometries,"
Hersam said. "Boron appears to be just as rich in its
possibilities, if not more so, than carbon. We believe that we
are still in the early chapters of the two-dimensional boron saga." ========================================================================== Story Source: Materials provided by Northwestern_University. Original
written by Amanda Morris. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Xiaolong Liu, Qiucheng Li, Qiyuan Ruan, Matthew S. Rahn, Boris I.

Yakobson & Mark C. Hersam. Borophene synthesis beyond the
single-atomic- layer limit. Nature Materials, 2021 DOI:
10.1038/s41563-021-01084-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210826111646.htm

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