Hydrogen and oxygen mixed-termination for nitrogen-vacancy quantum sensors in hexagonal diamond

Controlling the chemical termination of hexagonal diamond surface opens up new possibilities for shallow nitrogen-vacancy (NV) centers in quantum sensing applications. In this work, the H/O/OH mixed terminations on hexagonal diamond (100) surfaces to host NV centers are investigated by first-principles calculations. Results indicate that H-O, O-OH, and H-O-OH mixed surfaces produce positive electron affinity with neither spin noise nor surface-related state. It is concluded that the surface-connected ether bonds should be maintained, and unconnected ether bonds should be avoided, preserving the shallow NV centers unaffected. Based on the surface stability analysis, we further confirm that the H-O surface has a higher possibility to be fabricated. Moreover, we make an intensive study by placing an NV center similar to 12 angstrom from the hexagonal (100) surface, and the results elucidate that the H-O surface has no obvious effect on the defect states of the NV center. Therefore, we identify a combination of surface terminators that is a prospective candidate for NV-based quantum sensors.