STEM in an SEM: Towards high-throughput imaging and analysis of metal nanoclusters

Abstract

Accurately characterising metal nanoclusters is critical for advancing catalysis and energy conversion. While aberration-corrected scanning transmission electron microscopy (AC-STEM) achieves unmatched spatial resolution, its overall workflow throughput is often limited by instrument setup, alignment, and acquisition requirements. In contrast, scanning electron microscopy (SEM) offers higher throughput, but conventional SEM lacks sufficient spatial resolution for ultrasmall clusters of atoms. Here, we introduce a correlative imaging approach combining AC-STEM with high-angle annular dark-field (HAADF) STEM performed within an SEM (STEM-in-SEM), in particular using advanced in-lens field-emission SEM systems which offer the simplicity and ease-of-use of an SEM platform while retaining very high spatial resolution, to enable efficient and scalable metal nanocluster imaging and quantification workflows. Using platinum nanoclusters supported on graphene oxide as a model system for validation, identical-location imaging was employed to benchmark STEM-in-SEM against AC-STEM, eliminating the influence of sample polydispersity. Both techniques rely on the same incoherent HAADF imaging principle, and despite lower acceleration voltage and different detector geometry, STEM-in-SEM yields comparable intensity distributions. A comparison between STEM-in-SEM and AC-STEM demonstrated consistent intensity scaling. A reproducible and calibratable relationship between the number-of-atoms and image intensity can be established under STEM-in-SEM conditions. In this work, STEM-in-SEM is used to reliably quantify nanoclusters containing as few as ∼45 Pt atoms or nanoclusters with effective diameters down to ∼0.95 nm. Accordingly, a calibrated STEM-in-SEM image can be employed as a quantitative reference for other datasets imaged under the same conditions, provided that variations in specimen thickness and background contrast are sufficiently small to preserve consistent intensity scaling. By combining adequate spatial resolution and operational flexibility, STEM-in-SEM represents a practical and cost-effective complement to AC-STEM. Continued optimisation of imaging conditions, detectors, and automated analysis pipelines will further advance the broader applicability of this methodology in large-scale catalyst screening and nanomaterials discovery.