Quantitative Measurement of Atomic Coordination at the Single-Atom Limit

Determining local atomic coordination with element specificity is central to linking structure and functionality in materials, yet quantitative coordination metrics (coordination number, bond length, and disorder) are typically obtained only from ensemble-averaged techniques such as extended X-ray absorption fine structure (EXAFS). This averaging obscures the resolving of structural heterogeneity at interfaces, defects, and dopant sites 1,2. Here we show that extended energy-loss fine structure (EXELFS) in an electron microscope, physically analogous to EXAFS but driven by an electron beam, can deliver quantitative coordination analysis with atomic resolution and single-atom sensitivity. By combining low-voltage scanning transmission electron microscopy (STEM) with dose-fractionated acquisition and direct electron detection, we achieve quantitative coordination analysis at the atomic scale for the first time. We resolve atomic-layer-by-atomic-layer coordination and bond-length disorder across the epitaxial graphene/SiC interface, and distinguish the coordination of individual Si impurities in graphene lattice. These results establish STEM-EXELFS as an atomic-scale coordination probe, enabling direct measurements of local order in complex materials beyond ensemble averaging.