Scientists at Argonne National Laboratory have developed a new X-ray technique to see inside continuously packed nanoparticles, also known as grains, to examine deformations and dislocations that affect their properties.
In a new study, researchers described an X-ray scattering technique called Bragg coherent diffraction imaging to reconstruct in 3-D, the size and shape of grain defects. These defects create imperfections in the lattice of atoms inside a grain that can give rise to interesting material properties and effects.
The technique provides the ability to study materials under a number of different realistic conditions, such as high temperatures.
For the past ten years, scientists had looked at the defect structure of separated nanoparticles. But they didn't have a way of looking at the distortions in the crystal lattice in grains that formed continuous films of material, like those found in some solar cells or certain catalytic materials.
In Bragg coherent diffraction imaging, scientists shine X-rays at a sample, which scatter off the atoms in the material's structure. By observing the scattering patterns, they can reconstruct the material's composition in 3-D. With small isolated nanoparticles, this information is relatively easy to gather, but for thin films there are additional complications. The research focused on a specific area between particles known as the grain boundary, a region that causes most of the interesting material phenomena.
Thin-film solar cells, a promising photovoltaic technology, are a notable example of a type of material that could benefit from the study. “These are usually pretty complicated materials whose behavior is largely determined by the atoms that are on the ‘front lines,’ near the grain boundaries,” said Argonne materials scientist Andrew Ulvestad. The dislocations near grain boundaries are controlled by the defect structure in the material, and Ulvestad hopes that as scientists gain the ability to control the synthesis and positioning of defects, they will ultimately also be able to control the behavior of materials near the grain boundary.
By using the especially penetrative high-energy X-rays produced by Argonne's Advanced Photon Source, the researchers were able to watch the deformation of the crystal lattice in real time.
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