Scientists Create Atomically Thin Metallic Boron

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The “ridges” of this cardboard-like structure result in a material phenomenon known as anisotropy, in which a material’s mechanical or electronic properties – like its electrical conductivity – become directionally dependent. “This extreme anisotropy is rare in two-dimensional materials and has not been seen before in a two-dimensional metal,” Mannix said.

Based on theoretical predictions of borophene’s characteristics, the researchers also noticed that it likely has a higher tensile strength than any other known two-dimensional material. Tensile strength refers to the ability of a material to resist breaking when it is pulled apart. “Other two-dimensional materials have been known to have high tensile strength, but this could be the strongest material we’ve found yet,” Guisinger said.

The discovery and synthesis of borophene was aided by computer simulation work led by Stony Brook researchers Xiang-Feng Zhou and Artem Oganov, who is currently affiliated with the Moscow Institute of Physics and Technology and the Skolkovo Institute of Science and Technology. Oganov and Zhou used advanced simulation methods that showed the formation of the crinkles of the corrugated surface.

“Sometimes experimentalists find a material and they ask us to solve the structure, and sometimes we do predictions first and the experiment validates what we find,” Oganov said. “The two go hand-in-hand, and in this international collaboration we had a bit of both.”

“The connection we have between the institutions allows us to achieve things that we couldn’t do alone,” Hersam added. “We needed to combine scanning tunneling microscopy with X-ray photoelectron spectroscopy and transmission electron microscopy to both obtain a view of the surface of the material and verify its atomic-scale thickness and chemical properties.”

As they grew the borophene monolayer, the researchers discovered another advantage within their experimental technique. Unlike previous experiments that used highly toxic gases in the production of nanoscale boron-based materials, this experiment involved a non-toxic technique called electron-beam evaporation, which essentially vaporizes a source material and then condenses a thin film on a substrate – in this case, boron on silver.

“When we did our theoretical work, I had doubts as to feasibility of obtaining two-dimensional boron because boron likes to form clusters, and ironing it out into two-dimensions I thought would be challenging,” Oganov said. “It turned out that growing on the substrate was key, because the boron and silver turn out not to react with each other.”

The experimental work was funded by the DOE’s Office of Science and was performed at Argonne’s Center for Nanoscale Materials, a DOE Office of Science User Facility, and at the Northwestern University Materials Research Center.

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