All 23,000 atoms mapped in a nanoparticle


Rebecca Pool

Thursday, February 2, 2017 - 14:30
Image: Atomic composition of iron-platinum nanoparticle revealed, red; iron atoms, blue; platinum atoms.
A team of US- and UK-based researchers have mapped the complex atomic-scale structure of a FePt nanoparticle containing some 23,000 atoms, using one of the world’s most powerful electron microscopes.
The 3D coordinates and chemical species of each atom were recorded to an incredible 22 picometre precision with results then used in density functional theory calculations to determine material properties.
Insight into atomic spin, local magnetocrystalline anisotropy and more, at the single-atom level, is set to drive the design of high density data storage forward.
"We can now take a snapshot that shows the positions of all the atoms in a nanoparticle at a specific point in its growth," highlights Professor Mary Scott from The Molecular Foundry, Lawrence Berkeley National Laboratory.
"This will help us to learn how nanoparticles grow atom by atom, and set the stage for a materials-design approach starting from the smallest building blocks," she adds.
Mary Scott (left) and Peter Ercius at the controls of the TEAM microscope at the Molecular Foundry’s National Center for Electron Microscopy. [Marilyn Chung]
To decipher the chemical order and disorder, and material properties at the single-atom level, the researchers first synthesized FePt nanoparticles, annealing these to induce partial chemical ordering.
Then using 'TEAM1' at the National Center for Electron Microscopy in the Molecular Foundry, Berkeley Lab, they acquired tomographic tilt series from several nanoparticles.
The aberration-corrected STEM was operated in annular dark-field mode at 300 kV with Scott and colleagues selecting a high quality tilt-series, comprising 68 images.
They then used reconstruction algorithms - GENeralized Fourier Iterative Reconstruction, GENFIRE - developed by Professor John Miao and colleagues at University of California, Los Angeles, to produce the 3D structure of the nanoparticle to 22 picometre precision.
As Scott highlights, the structure contains 6569 iron atoms and 16627 platinum atoms, with each atom's coordinates precise plotted to less than the width of a hydrogen atom.
"We correlated the chemical order/disorder and crystal defects with material properties at the single-atom level," she says. "We could identify rich structural variety with unprecedented 3D detail, including atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects."
Video provides overview of the 3D positions of individual atoms, with iron atoms in red and platinum atoms in blue. It then splits apart into the large and small grains that compose the nanoparticle. [Colin Ophus and Florian Niekiel, Berkeley Lab]
Feeding results into density functional theory models, the researchers calculated material properties including atomic spin, orbital magnetic moments and local magnetocrystalline anisotropy.
They also observed abrupt changes in magentic properties at grain boundaries.
“This work makes significant advances in characterization capabilities and expands our fundamental understanding of structure-property relationships, which is expected to find broad applications in physics, chemistry, materials science, nanoscience and nanotechnology,” explains Miao.
"[The results] could help scientists learn how to steer the growth of iron-platinum nanoparticles so they develop more highly magnetic patterns of atoms," says Scott's colleague Peter Ercius.
"More broadly, the imaging technique will shed light on the nucleation and growth of ordered phases within nanoparticles, which isn't fully theoretically understood but is critically important to several scientific disciplines and technologies," adds Scott.
Research is published in Nature.
  • Team 1 is a modified FEI Titan 80-300 TEM equipped with a special high-brightness Schottky-field emission electron source, a source monochromator, a high-resolution GIF Tridiem energy-filter, and CEOS hexapole-type spherical aberration correctors and a chromatic aberration corrector.
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