Nuclear magnetic resonance spectroscopy of nanoconfined water

Nanoscale interactions at the solid liquid boundary have been notoriously difficult to characterize, due to sensitivity, spatial, and temporal limitations of measurement techniques. Through dynamical decoupling sensing schema using shallow nitrogen vacancy (NV) centers we probe the molecular dynamics of water molecules confined within engineered ~5-nm-tall channels formed by a hexagonal boron nitride (hBN) structure on the diamond surface. The resulting nuclear magnetic resonance (NMR) proton spectrum shows evolving confinement effects as water slowly diffuses out of the chamber. Concurrent measurements show the evolution of satellite peaks within our NMR 1H water spectra, which we postulate arise from hyperfine interactions between charged clusters of water molecules produced by NV charge carrier generation. Correlation measurements show us long lasting nuclear spin coherences, indicative of molecular dynamics intermediate between bulk water and ice. We use molecular dynamics modeling and density functional theory calculations to understand how cluster formations may arise from accumulation of surface charge and carrier injection into the fluid under laser illumination. Further understanding of these dynamics has broad impacts in areas spanning geophysics, tribology, catalysis, polymer science, and biology.