Single Nitrogen-Vacancy-NMR of Amine-Functionalized Diamond Surfaces

Nuclear magnetic resonance (NMR) imaging with shallow nitrogen-vacancy (NV) centers in diamond offers an exciting route toward sensitive and localized chemical characterization at the nanoscale. Remarkable progress has been made to combat the degradation in coherence time and stability suffered by near-surface NV centers using suitable chemical surface termination. However, approaches that also enable robust control over adsorbed molecule density, orientation, and binding configuration are needed. We demonstrate a diamond surface preparation for mixed nitrogen- and oxygen-termination that simultaneously improves NV center coherence times for emitters <10-nm-deep and enables direct and recyclable chemical functionalization via amine-reactive crosslinking. Using this approach, we probe single NV centers embedded in nanopillar waveguides to perform $^{19}\mathrm{F}$ NMR sensing of covalently bound trifluoromethyl tags in the ca. 50-100 molecule regime. This work signifies an important step toward nuclear spin localization and structure interrogation at the single-molecule level.