Machine learning-aided 3D-AFM for identification of spatial heterogeneity in interfacial solvation structures

Interfacial solvation structures are crucial in wide-ranging applications, including lubrication and electrochemical energy storage. As the sole technique capable of in situ mapping of three-dimensional (3D) solvation structures, 3D atomic force microscopy (3D-AFM) resolves liquid-solid interfaces with angstrom precision. However, conventional analysis via global averaging or manual selection wastes the massive datasets generated by 3D-AFM, rendering the objective resolution of spatial heterogeneities and 3D features of the interfacial solvation structure unattainable. Here, leveraging the high-throughput capacity of unsupervised machine learning to handle massive datasets, we present a general method integrating 3D-AFM for the unbiased interpretation of interfacial force datasets. Applying this method to the graphite-water interface uncovers a previously obscured spatial heterogeneity, achieving a precise spatial partitioning of the interface into two distinct regimes with divergent mechanical responses. Molecular dynamics simulations attribute this heterogeneity to the non-uniform distribution of trace airborne hydrocarbon contaminants. This work not only elucidates the contaminant-mediated modulation of interfacial water structures but also provides a general paradigm for identifying chemical non-uniformities at diverse solid-liquid interfaces.