4D-STEM Imaging of nanostructural heterogeneities in Ni-20Cr after corrosion in molten salt

Yang, Yang; Zhou, Weiyue; Yin, Sheng; Wang, Sarah; Qin, Yu; Ritchie, Robert O.; Asta, Mark; Ju, Li; Short, Michael P.; Minor, Andrew M.

doi:10.1017/s1431927621007698

Cited by 2 publications

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“…This offers the possibility of correlating defect content with microstructural features. 4D-STEM has been recently used to map stoichiometry 19 and compositional changes 20,21 , but has not been used to map primary vacancy concentrations where there is no change in chemical composition.…”

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Nanoscale mapping of point defects with 4D-STEM

Minor

Mills

Ercius

et al. 2022

Preprint

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Vacancies are missing atoms in a crystalline material, and occur both at equilibrium (varying with temperature) and out of equilibrium such as when crystalline materials are damaged with radiation or corrosion. While we know of their importance, particularly regarding diffusive mechanisms, it is not straightforward to experimentally measure their concentration or to visualize them directly. Traditionally, measurements such as positron annihilation spectroscopy and to some degree X-ray diffraction can measure average concentrations, but generally lack the ability to visualize or quantify a heterogenous concentration of vacancies that can occur at the level of individual defects and microstructural features. Here, we present a method to map vacancy concentrations and their distribution with 1 nm resolution. Our method utilizes a Au thin film as a model to demonstrate the method via four-dimensional scanning transmission electron microscopy (4D-STEM) by correlating the differences between changes in lattice parameter and the volumetric thermal expansion during in situ heating experiments. The vacancy mapping methodology is also applied to non-equilibrium defects accumulated in pure Al via knock-on electron beam irradiation. Our method demonstrates the ability to map point defect concentrations in heterogeneous systems in situ with nanometer spatial resolution. The result is a technique that can provide direct measurements of vacancy concentrations at the level of individual defects in studies of materials in and out of equilibrium.

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confidence: 99%