Abstract
Abstract Determining the precise atomic structure of materials’ surfaces, defects, and interfaces is important to help provide the connection between structure and important materials’ properties. Modern scanning transmission electron microscopy (STEM) techniques now allow for atomic resolution STEM images to have down to sub-picometer precision in locating positions of atoms, but these high-precision techniques generally require large electron doses, making them less useful for beam-sensitive materials. Here, we show that 1- to 2-pm image precision is possible by non-rigidly registering and averaging a high-angle dark field image series of a 5- to 6-nm Au nanoparticle even though a very coarsely sampled image and decreased exposure time was used to minimize the electron dose. These imaging conditions minimize the damage to the nanoparticle and capture the whole nanoparticle in the same image. The high-precision STEM image reveals bond length contraction around the entire nanoparticle surface, and no bond length variation along a twin boundary that separates the nanoparticle into two grains. Surface atoms at the edges and corners exhibit larger bond length contraction than atoms near the center of surface facets.
Highlights
Many materials science problems require relating materials’ properties to the atomic structure near the materials’ surfaces, interfaces, extended defects, point defects, and other types of strain fields
Transmission electron microscopy (TEM) and scanning TEM (STEM) allow for the imaging of these atomic structures, helping us understand property-structure relationships
high-angle annular dark field (HAADF) STEM images were collected using a detector range of 54 to 270 mrad creating Z-contrast images where the atomic column intensity is approximately proportional to Z1.7, where Z is the atomic number of the atoms under the electron beam
Summary
Many materials science problems require relating materials’ properties to the atomic structure near the materials’ surfaces, interfaces, extended defects, point defects, and other types of strain fields. The serial acquisition of pixels in STEM puts it at a disadvantage compared to the parallel acquisition of pixels in TEM because serial acquisition translates position instabilities of the probe and sample into displacements of the imaged atoms. Despite these disadvantages, high-angle annular dark field (HAADF) STEM imaging has the advantage of giving a faithful representation of the sample structure over a wide range of thickness and defocus, making it more interpretable and quantifiable than TEM imaging.
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