  Characterization of the molecular properties of surfaces under ambient or
chemically reactive conditions is a fundamental scientific challenge. Moreover,
many traditional analytical techniques used for probing surfaces often lack
dynamic or molecular selectivity, which limits their applicability for
mechanistic and kinetic studies under realistic chemical conditions. Nuclear
magnetic resonance spectroscopy (NMR) is a widely used technique and would be
ideal for probing interfaces due to the molecular information it provides
noninvasively. However, it lacks the sensitivity to probe the small number of
spins at surfaces. Here, we use nitrogen vacancy (NV) centers in diamond as
quantum sensors to optically detect nuclear magnetic resonance signals from
chemically modified aluminum oxide surfaces, prepared with atomic layer
deposition (ALD). With the surface NV-NMR technique, we are able to monitor in
real-time the formation kinetics of a self assembled monolayer (SAM) based on
phosphonate anchoring chemistry to the surface. This demonstrates the
capability of quantum sensors as a new surface-sensitive tool with
sub-monolayer sensitivity for in-situ NMR analysis with the additional
advantage of a strongly reduced technical complexity.
