Nitrogen Vacancy Centers as a Source of Solvated Charges Across the Diamond-Water Interface*

Injection of charges from solid state materials into water is a poorly understood field due to the complexity of the surace chemistry, ultrafast time scales for charge injection and instability of the solvated charges. Diamond, being chemically inert in aqueous conditions, has been shown to generate solvated electrons with ultraviolet light illumination and subsequent chemical transformations have been confirmed. Now there is strong evidence that near-surface nitrogen vacancy (NV) centers in diamond can inject both electrons and holes into ultrapure water at the diamond-water interface through a process of photoionization and charge migration. Oxygen-terminated diamond members in a spectroelectrochemical cell configuration allows photocurrents to be collected as a function of bias voltage and green laser excitation. Photocurrent can be modulated by laser power and bias voltage and there is evidence that wavelength-dependent characteristics support a charge cycling mechanism with the NV center. Discovery that the NV center is a viable source of solvated electrons  expands NV diamond as a substrate for chemical reactions. Theoretical calculations also elucidate the mechanism of charge injection/solvation and reinforce the experimental observations. These results lays the ground work for future investigations that demonstrate in-situ carrier sensing across the diamond-water interface using the NV center's quantum sensing abilities.