Evaluating atomic counts in metal nanoclusters via scanning transmission electron microscopy

Nanoscale metal atom aggregates, metal nanoclusters (NCs), exhibit unique electronic properties that strongly depend on the number of constituent atoms. Precise control over atomic composition is highly anticipated to advance NC-based materials science, particularly for fine-tuning photonic responses, catalytic reactivity, and electronic spin characteristics. In this study, we employed high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) to observe platinum (Pt) NCs immobilized on a substrate, enabling direct visualization of their deposition states, densities, and structures. The Pt NCs, containing 19 to 70 atoms with single-atom precision, were deposited onto TEM grids. By analysing STEM images, structural information indicative of a spherical shape was revealed, demonstrating a clear correlation between the number of atoms in Pt NCs and their observed diameters in the STEM, comparable to mass spectrometry assessments. This approach highlights estimation of the number of constituent atoms in metal NCs based on diameter distributions observed by STEM, providing valuable insight for size-dependent structural analysis and the exploration of their functionalized metal NCs.