Environmental Control of Shallow Nitrogen-Vacancy Sensors in Oxygenated (100) Diamond Surface

Quantum sensing with nitrogen vacancy (NV) center in diamond is an emerging technology to detect nuclear spins and chemical species with nearly atomistic resolution. This is achieved by translating the magnetic- and electric-field fluctuations from the respective sources directly to an optical signal, detected by a change in the fluorescence intensity of the NV center. In this work, we develop realistic models of the diamond-solvent interfaces to elucidate new sensing applications for the NV center, which are based on the reversible variations in the surface potential. More specifically, we show that aqueous diamagnetic electrolyte solutions such as sodium chloride can be sensed by an increase of the spin relaxation time of near-surface NV-center ensembles. Our first principles calculations combined with interface modeling identify a critical role of the interfacial band bending which leads to a stabilization of fluctuating charges at the interface of an oxygen-terminated diamond. In addition, we demonstrate that aqueous environment enables to recover a contrast in the optically detected magnetic resonance experiment for the shallow NV centers at cryogenic temperatures. Both predicted phenomena were directly confirmed in experiments by observing the optically detected magnetic resonance and spin relaxation times of the ensemble and single NV-centers.<br/><br/>This work was supported by the National Research, Development, and Innovation Office of Hungary (NKFIH) grant No. KKP129866 of the National Excellence Program of Quantum-coherent materials project and the Quantum Information National Laboratory supported by the Ministry of Innovation and Technology of Hungary, the QuantERA II MAESTRO project, and the Horizon Europe EIC Pathfinder QuMicro project (grant No. 101046911).