Surface NMR using quantum sensors in diamond

Significance

Many of the functions and applications of materials in catalysis, energy conversion, drug delivery, bioanalysis, and electronics are based on their interfacial properties and structures. The characterization of their molecular properties under ambient or chemically reactive conditions is a fundamental scientific challenge. Here, we develop a surface-sensitive magnetic resonance technique that combines the nanoscale-sensing capabilities of defects in diamond with a high precision and versatile protocol for diamond surface modification. We demonstrate the functionality of this method for probing the molecular properties and kinetics at surfaces and interfaces under ambient conditions.

Abstract

NMR is a noninvasive, molecular-level spectroscopic technique widely used for chemical characterization. However, it lacks the sensitivity to probe the small number of spins at surfaces and interfaces. Here, we use nitrogen vacancy (NV) centers in diamond as quantum sensors to optically detect NMR signals from chemically modified thin films. To demonstrate the method’s capabilities, aluminum oxide 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. The surface NV-NMR technique detects spatially resolved 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. With our approach, we show that NV quantum sensors are a surface-sensitive NMR tool with femtomole sensitivity for in situ analysis in catalysis, materials, and biological research.