Thermal Stability of Perfectly Aligned Nitrogen-Vacancy Centers for High Sensitive Magnetometers

A large sensor volume based on a chemical-vapor-deposited diamond film containing perfectly aligned ensemble nitrogen-vacancy (NV) centers is a promising route to achieve high sensitive quantum magnetometers. To synthesize a thick NV film by chemical vapor deposition (CVD), the thermal stability of the N-V axis becomes an important issue. In this study, the thermal stability of the N-V orientation has been investigated and its activation energy is estimated as 4.7 eV. It is found that the perfect alignment of the NV centers to the [111] direction can be maintained during a long-time CVD growth at temperature 900 degrees C and lower. In contrast, the alignment ratio gradually decreases with increasing the growth time at 1050 degrees C. The mechanism of the reorientation of the N-V axis has been discussed. The observations presented here provide important insight to achieve highly sensitive macro-scale sensors.