UCLA: 3D imaging study shows how atoms are packaged in amorphous materials

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UCLA-led research could revise a 70-year-old model of how the basic building blocks of substances are composed. Many substances around us, from table salt and sugar to most metals, are arranged in crystals. Because their molecules are arranged in an ordered, repeating pattern, much is known about their structure. Many substances around us, from table salt and sugar to most metals, are arranged in crystals. Because their molecules are arranged in an ordered, repeating pattern, much is known about their structure. However, a much larger number of substances – including rubber, glass, and most liquids – lack this basic order, making it difficult to determine their molecular structure. To date, the understanding of these amorphous substances is based almost exclusively on theoretical models and indirect experiments. However, a much larger number of substances – including rubber, glass, and most liquids – lack this basic order, making it difficult to determine their molecular structure. To date, the understanding of these amorphous substances is based almost exclusively on theoretical models and indirect experiments. A UCLA-led research team is changing that. Using a method they developed for mapping atomic structures in three dimensions, the scientists observed directly how atoms are packed in samples of amorphous materials. The results, published today in Nature Materials, force a rewrite of the traditional model and influence the design of future materials and devices that use these substances. A UCLA-led research team is changing that. Using a method they developed for mapping atomic structures in three dimensions, the scientists observed directly how atoms are packed in samples of amorphous materials. The results, published today in Nature Materials, force a rewrite of the traditional model and influence the design of future materials and devices that use these substances. “We believe this study will have a very important impact on our future understanding of amorphous solids and liquids – some of the most abundant substances on earth,” said lead author of the study, Jianwei “John” Miao UCLA Professor of Physics and Astronomy and member of the California NanoSystems Institute at UCLA. “Understanding the basic structures can lead to dramatic technological advances.” “We believe this study will have a very important impact on our future understanding of amorphous solids and liquids – some of the most abundant substances on earth,” said lead author of the study, Jianwei “John” Miao UCLA professor of physics and astronomy and member of the From 1952 with a work by British physicist Frederick Charles Frank, the prevailing scientific knowledge was that atoms and molecules in a liquid or an amorphous solid generally fit together in groups of 13. The model says it is configured with a central atom or molecule surrounded by the other 12 – two rings of five around the central particle, with one other covering the top and one covering the bottom. Beginning in 1952 with work by British physicist Frederick Charles Frank, the prevailing scientific understanding was that atoms and molecules in a liquid or amorphous solid generally fit together in groups of 13. The model says that they are surrounded by a central atom or molecule by the other 12 – two rings of five around the central particle, with another covering the top and one covering the bottom. To model how clumps of atoms or molecules might fit together on a larger scale, scientists are conceiving this group of 13 as a 3D shape, treating each outer particle as a corner and connecting the points, resulting in a body with 20 triangular faces, one so-called icosahedron, a shape known to every Dungeons & Dragons player in the form of a 20-sided cube. To model how clumps of atoms or molecules might fit together on a larger scale, scientists are conceiving this group of 13 as a 3D shape, treating each outer particle as a corner and connecting the points, resulting in a body with 20 triangular faces, one so-called icosahedron, a shape known to every Dungeons & Dragons player in the form of a 20-sided cube. However, Miao and his colleagues found something else. However, Miao and his colleagues found something else. The team analyzed three amorphous metallic objects using atom-electron tomography. This powerful imaging method beams electrons at a sample and measures the electrons as they pass, capturing the data multiple times as the sample is rotated so that computer algorithms can create a 3D image. The team analyzed three amorphous metallic objects using atom-electron tomography. This powerful imaging method beams electrons at a sample and measures the electrons as they pass, capturing the data multiple times as the sample is rotated so that computer algorithms can create a 3D image. The researchers found that only a very small fraction of the atoms formed icosahedral groups of 13. The most common arrangement seen was groups of seven, with five in a central layer, one above, one below, and no central atom – a shape the researchers describe as a pentagonal bipyramid with 10 triangular faces. They also observed that these pentagonal bipyramids formed into networks in which edges were often divided. The researchers discovered that only a very small fraction of the atoms formed icosahedral groups of 13. The most common arrangement seen was groups of seven, with five in a central layer, one above, one below, and no central atom – a shape the researchers describe as a pentagonal bipyramid with 10 triangular faces. “Since Frank’s article, the scientific community has believed that the icosahedral order is the most important structural motif in liquids or amorphous solids,” Miao said. “But so far nobody has been able to determine and verify the position of all atoms. We have found that the pentagonal bipyramid is the most common motif. Nature seems to prefer to combine in sevens.” “Since Frank’s article, the scientific community has believed that the icosahedral order is the most important structural motif in liquids or amorphous solids,” Miao said. “But so far nobody has been able to determine and verify the position of all atoms. We have found that the pentagonal bipyramid is the most common motif. Nature seems to prefer combining in sevens.” The dominance of this combination was consistent across the samples examined by the researchers, who, for the sake of simplicity, selected materials that exist as individual atoms on their fundamental scale. The materials studied were a thin film of tantalum, a rare metal used for electronic components, and two nanoparticles made of palladium, a metal that is important for the catalytic converters that make car exhausts less toxic. The dominance of this combination was consistent across the samples examined by the researchers, who, for the sake of simplicity, selected materials that exist as individual atoms on their fundamental scale. The materials studied were a thin film of tantalum, a rare metal used for electronic components, and two nanoparticles made of palladium, a metal that is important for the catalytic converters that make car exhausts less toxic. The team also used their experimental data as a basis for a computer simulation of what happens when tantalum is melted and then rapidly cooled so that crystals do not form, resulting in what is known as a metallic glass. In the simulation, the tantalum atoms are packed in networks of pentagonal bipyramids with a similar frequency than any other form, both as a liquid and as a glass. The team also used their experimental data as a basis for a computer simulation of what happens when tantalum is melted and then rapidly cooled so that crystals do not form, resulting in what is known as a metallic glass. In the simulation, the tantalum atoms are packed in networks of pentagonal bipyramids with a similar frequency than any other form, both as a liquid and as a glass. These results can lead to a re-evaluation of certain aspects of the physical model of science for the world around us. And since amorphous materials are built into certain semiconductors and numerous devices, including solar panels, this research could be an early step to replace trial-and-error with deliberate design when those materials are involved. These results can lead to a re-evaluation of certain aspects of the physical model of science for the world around us. And since amorphous materials are built into certain semiconductors and numerous devices, including solar panels, this research could be an early step to replace trial-and-error with deliberate design when those materials are involved. “This work, along with our recent Nature paper on noncrystalline materials, could be comparable in impact to the first time science revealed the 3-D atomic structure of salt crystals over a century ago,” said Miao. “This work, along with our current Nature Paper â–º Related: Centuries-old problem solved with the first atomic 3D imaging of an amorphous solid The study’s co-first-time authors were former UCLA postdocs Yakun Yuan, Dennis Kim, and Jihan Zhou. Other co-authors were Dillan Chang, Fan Zhu, Yao Yang, Minh Pham, and Stanley Osher from UCLA; Yasutaka Nagaoka and Ou Chen from Brown University; and Peter Ercius and Andreas Schmid of the Molecular Foundry at Lawrence Berkeley National Laboratory, where the experiment was conducted. The study was co-first-time authors. The study was primarily supported by the Department of Energy. Support also came from the STROBE National Science Foundation science and technology centerof which Miao is the deputy director; the National Science Foundation; and the Army Research Office. The study was supported primarily by the Department of Energy. Support also came from the


This press release was prepared by UCLA. The views expressed here are your own.

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