Image credit: Colin Ophus and Florian NickelResearchers have mapped the coordinates of more than 23 000 individual atoms in an iron-platinum nanoparticle to show the defects, the missing atoms, the substitutions and the deviations from the lattice. The work hints at what might be possible with high-resolution imaging but also feeds data into quantum mechanics models to reveal correlations between material defects and properties at the single-atom level. [Miao et al., Nature (2017) 542, 75-79; DOI: 10.1038/nature21042]
Jianwei (John) Miao of the University of California Los Angeles and his international colleagues explain the relevance of the new work: "No one has seen this kind of three-dimensional structural complexity with such detail before," he says. The focus of their work, an iron-platinum alloy with promise in the area of next-generation magnetic storage media and permanent magnet applications make it particularly poignant - defects mean disruption and data loss in storage media after all. The team reports in Nature that, "The experimentally measured coordinates and chemical species with 22 picometer precision can be used as direct input for density functional theory (DFT) calculations of material properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy."
The team obtained multiple images of an iron-platinum nanoparticle using advanced electron microscopy at Lawrence Berkeley National Laboratory. They then applied a powerful reconstruction algorithm developed by the scientists at UCLA and known as GENFIRE for GENeralized Fourier Iterative Reconstruction - to build an accurate three-dimensional model of the thousands of atoms in this nanoparticle. "For the first time, we can see individual atoms and chemical composition in three dimensions. Everything we look at, it's new," Miao adds.
The study located more than 6,500 iron atoms and some 16,600 platinum atoms revealing them to lie in nine grains each containing different ratios of iron to platinum atoms. Atomic arrangements at the grain surface were more irregular than those closer to the center of the grain, Miao and his colleagues demonstrated. They also defined the grain boundaries, the interfaces between grains. "Understanding the three-dimensional structures of grain boundaries is a major challenge in materials science because they strongly influence the properties of materials," Miao adds. The calculations suggest that there are abrupt changes to magnetic properties at these grain boundaries in the iron-platinum nanoparticle.
The team hopes to use GENFIRE to analyze data from other materials in a similar way. With this tool, they hope to build a databank for materials that would be akin to the protein databank used by life scientists and others but with applications in materials science, engineering and beyond. "For our next step, we want to map out the 3D individual atoms at surfaces and interfaces, which play a very important role in material properties and functionality," Miao told Materials Today. He also suggests that the same method might itself be applied to biological and medical imaging that could be carried out with lower doses of radiation on sensitive objects.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".