Influence of Surface Hydrophilicity on the Charge Dynamics of Nitrogen Vacancy Centers

Nitrogen-vacancy (NV) centers in diamonds are emerging material platforms for spin qubits. They possess exceptional spin coherence at room temperature and sensitivity to external stimuli like magnetic and electric fields. These properties allow NV centers to be quantum sensors for single-molecule detection, medical diagnostics, and chemical detection. However, achieving reliable quantum sensing performance in aqueous environments remains challenging. Remarkably, the effects of solvent and surface-related noise on the charge stability and the charge transfer mechanisms remain poorly understood. Here, we explore the chemical and electronic processes of NV centers near aqueous interfaces using first-principles molecular dynamics and constrained density functional theory calculations. We examine diamond surfaces with varying hydrophilicity and electron donors, such as solvated ions and solid-state dopants. Three key factors that influence charge stability are found: (i) surface hydrophilicity, (ii) charge transfer dynamics between the liquid and near-surface defects, and (iii) temperature-induced fluctuations in defect electronic states. These insights provide essential descriptors for designing and optimizing spin defects for quantum sensing applications in complex environments.