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arXiv · 2505.04078

Differentiation of Distinct Single Atoms via Multi-Defocus Fusion Method

Yangfan Li·Yue Pan·Xincheng Lei·Weiwei Chen·Yang Shen·Mengshu Ge·Xiaozhi Liu·Dong Su
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Abstract

High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) is a vital tool for characterizing single-atom catalysts (SACs). However, reliable elemental identification of different atoms remains challenging because the signal intensity of HAADF depends strongly on defocus and other imaging parameters, potentially ruining the Z-contrast of atoms at different depths. In this work, we investigated the influence of the vertical position of atoms (defocus), support thickness, interatomic height, convergence and collection angles via multi-slice simulations on a model system of Fe/Pt atoms on amorphous carbon supports. Our calculation shows that at a convergence angle of 28 mrad, a defocus of 4.6 nm can cause Fe and Pt atoms indistinguishable. At a larger convergence angle, this critical indistinguishable defocus can be even shorter. To address this limitation, we propose a Multi-Defocus Fusion (MDF) method, retrieving the Z-contrast from serial images from multiple defocus. Experimental validation on a Fe/Pt SAC sample confirms the effectiveness of MDF, yielding clearly separated intensity histograms corresponding to Fe and Pt atoms. This work presents a robust, easy-to-implement strategy for accurate single-atom identification, offering valuable guidance for the accelerated screening and rational design of high-performance SACs.

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Yangfan Li, Yue Pan, Xincheng Lei, Weiwei Chen, Yang Shen, Mengshu Ge, Xiaozhi Liu, Dong Su. 2025-05-07. Differentiation of Distinct Single Atoms via Multi-Defocus Fusion Method. https://arxiv.org/abs/2505.04078

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