Surface NMR Using Quantum Sensors in Diamond

Characterization of the molecular properties of surfaces under ambient or chemically reactive conditions is a fundamental scientific challenge. Nuclear magnetic resonance (NMR) spectroscopy would be the ideal technique, however it lacks the sen-sitivity to probe the small number of spins at interfaces. Here we use nitrogen vacancy (NV) centers in diamond as quantum sensors to optically detect NMR signals from chemically modified thin films. Aluminum oxide (Al2O3) layers, common supports in catalysis and materials science, are prepared by atomic layer deposition and are subsequently functionalized by phosphonate chemistry to form self-assembled monolayers (SAMs). The surface NV-NMR technique detects NMR signals from the monolayer, indicates chemical binding, and quantifies molecular coverage. In addition, it can monitor in real-time the formation kinetics at the solid-liquid interface. This work demonstrates the capability of NV quantum sensors as a sur-face-sensitive (femtomole) NMR tool for in-situ analysis in catalysis, materials and biological research.