Surface-Only Nuclear Magnetic Resonance Spectroscopy by Dynamic Nuclear Polarization and 2H-Dephasing.

Understanding and controlling surface structure at the atomic scale is essential in functional materials, yet direct and selective surface characterization in such systems remains a challenge. Here a broadly applicable strategy for surface-only solid-state NMR enabled by dynamic nuclear polarization (DNP) is introduced. The method exploits partially deuterated vitrified solvents as proximity "probe" molecules and 2H-based dipolar dephasing to filter out signals from the bulk, thereby providing clear detection of nuclei located exclusively in the first one or two atomic layers at the surface (without 1H-2H exchange). Implemented through a 1H-X{2H} CP-REDOR scheme, this approach allows the detection of X through the 2H-X dipolar couplings, which are almost an order of magnitude lower than their 1H-X counterparts, thus providing unprecedented surface selectivity. The applicability of the new method is demonstrated on several compounds including core-shell nanocrystalline hydroxyapatite, tin dioxide, silica, as well as a passivated hybrid perovskite, and surface sites are resolved that would otherwise have been obscured by the bulk signals. Quantitative analysis of the dephasing curves allows interfacial distance measurements to the solvent. This 2H-dephasing DNP approach establishes a versatile platform for the atomic-scale characterization of functional surfaces in both inorganic materials and proton-rich nanomaterials.