Extending Spin Dephasing Time of Perfectly Aligned Nitrogen-Vacancy Centers by Mitigating Stress Distribution on Highly Misoriented Chemical-Vapor-Deposition Diamond

Extending the spin-dephasing time (T-2(*)) of perfectly aligned nitrogen-vacancy (NV) centers in large-volume chemical vapor deposition (CVD) diamonds leads to enhanced DC magnetic sensitivity. However, T-2(*) of the NV centers is significantly reduced by the stress distribution in the diamond film as its thickness increases. To overcome this issue, we developed a method to mitigate the stress distribution in the CVD diamond films, leading to a T-2(*) extension of the ensemble NV centers. CVD diamond films of approximate to 60 mu m thickness with perfectly aligned NV centers are formed on (111) diamond substrates with misorientation angles of 2.0 degrees, 3.7 degrees, 5.0 degrees, and 10.0 degrees. The study found that T-2(*) of the ensemble of NV centers increased to approach its value limited only by the electron and nuclear spin bath with increasing the misorientation angle. Microscopic stress imaging revealed that the stress distribution was highly inhomogeneous along the depth direction in the CVD diamond film at low misorientation angles, whereas the inhomogeneity was largely suppressed on highly misoriented substrates. The reduced stress distribution possibly originates from the reduction of the dislocation density in the CVD diamond. This study provides an important method for synthesizing high-quality diamond materials for use in highly sensitive quantum sensors.