Jul 10, 2019 | |
Giving nanowires a DNA-like twist(Nanowerk News) We see crystals all around us: snowflakes, ice cubes, table salt, gemstones, to name a few. Invisible to the naked eye, but of special interest to scientists, are crystalline “nanowires” — wires with a diameter of a mere few nanometers and a typical length of a micrometer. |
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Normally in a rod-like shape, these wires are an interesting area of worldwide research because of their many potential applications, including semiconductors and miniaturized optical and optoelectronic devices. | |
As reported in a recent Nature paper ("Helical van der Waals crystals with discretized Eshelby twist"), scientists at the Center for Nanoscale Materials (CNM), a U.S. Department of Energy (DOE) Office of Science User Facility located at Argonne National Laboratory, played a critical role in the discovery of a DNA-like twisted crystal structure created with a germanium sulfide nanowire, also known as a “van der Waals material.” The research was conducted in collaboration with the University of California at Berkeley and Lawrence Berkeley National Laboratory. | |
Helical structure of stacked bricks (right, Shutterstock image) is similar to that produced by giving nanowires an Eshelby twist (left, Lawrence Berkeley National Laboratory image). | |
The helical DNA-like structure forms spontaneously by giving the nanowire an “Eshelby twist.” Co-first author Jie Wang, a former materials scientist in CNM (now at Thorlabs, Inc.), explained that the term “Eshelby twist” refers to its discoverer, John Eshelby. | |
While a research associate working at the University of Illinois at Urbana-Champaign in the 1950s, Eshelby conducted an important theoretical analysis of “screw dislocation” in a thin rod. Relating the effect to crystals, Wang noted that the “screw dislocation occurs when stress is applied to a rod shape in which the atoms become rearranged in a helical pattern.” | |
When applied to a germanium sulfide nanowire, this twisting causes it to elongate and widen into a helical structure. | |
“It is amazing that these inorganic germanium sulfide nanowires so closely resemble the organic DNA structure,” said co-author Jianguo Wen, a CNM materials scientist. “Nature creates remarkable structures beyond our imagination.” | |
Also important, added CNM scientist and co-author Dafei Jin, was the finding that the nanostructure automatically divides into segments that resemble helically stacked bricks. These brick-like segments arise from the release of energy as the wire diameter grows from tens of nanometers to micrometers. | |
Micrograph of nanowire with Eshelby twist (inset) spontaneously grown into microscale DNA-like structure. (Image: Lawrence Berkeley National Laboratory) | |
“The discovered Eshelby twist here offers a new way to engineer nanomaterials,” said Wang. “We can tailor these nanowires in many different ways — twist periods from two to twenty micrometers, lengths up to hundreds of micrometers, and radial dimensions from several hundred nanometers to about ten micrometers.” | |
By this means, researchers can adjust the electrical and optical properties of the nanowires to optimize performance for different applications. | |
“This is an important materials discovery,” Wen said. “We are excited to have figured out, using CNM’s high-resolution transmission electron microscope, the dislocation structures that drive the nanowires to have an Eshelby twist.” |
Source: Argonne National Laboratory | |
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