TECH FRONT
metallic properties at the nanoscale even though three-di- mensional, or bulk, boron is nonmetallic and semiconducting. “Borophenes are extremely intriguing because they are
quite different from previously studied two-dimensional mate- rials,” said Argonne nanoscientist Nathan Guisinger, who led the experiment. “And because they don’t appear in nature, the challenge involved designing an experiment to produce them synthetically in our lab.” One of boron’s most unusual features consists of its atomic
confi guration at the nanoscale. While other two-dimensional materials look more or less like perfectly smooth and even planes at the nanoscale, borophene looks like corrugated cardboard, buckling up and down depending on how the bo- ron atoms bind to one another, according to Andrew Mannix, a Northwestern graduate student and fi rst author of the study. The “ridges” of this cardboard-like structure result in a material phenomenon known as anisotropy, in which a mate- rial’s mechanical or electronic properties—like its electrical conductivity—become directionally dependent, Mannix said.
Based on theoretical predictions of borophene’s char- acteristics, the researchers also noticed that it likely has a higher tensile strength than any other known material—in- cluding graphene. 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,” researcher Nathan Guisinger said. As they grew the borophene monolayer, the researchers
discovered an 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 nontoxic technique called electron-beam evapora- tion, which essentially vaporizes a source material and then con- denses a thin fi lm on a substrate—in this case, boron on silver. The study will be published in the Dec. 18 issue of the
journal Science. Borophene thus joins graphene in a devel- opmental race of atom-thick miracle materials. We’ll watch to see which eventually takes a thin lead.
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