Differentiation of Distinct Single Atoms via Multi-Defocus Fusion Method

TL;DR

This paper introduces a Multi-Defocus Fusion method to reliably distinguish different single atoms in HAADF-STEM images by combining images taken at multiple defocus levels, overcoming limitations caused by imaging parameters.

Contribution

The study proposes and experimentally validates a novel Multi-Defocus Fusion technique for accurate atomic identification in electron microscopy, improving upon existing Z-contrast methods.

Findings

MDF effectively separates Fe and Pt atoms in HAADF-STEM images.

Defocus significantly affects atomic contrast, but MDF mitigates this issue.

Experimental results confirm MDF's robustness and practicality.

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.