Nitrogen vacancy (NV) center in diamond is expected as a magnetic sensor with high sensitivity at room temperature and single NV center succeeded in detecting ¹H spins out of the substrate. For improvement magnetic sensitivity, both shallow and aligned NV ensemble is required since the magnetic sensitivity is inversely proportional to the root of number of NV centers. N-terminated (111) surface was fabricated and thin layer (10 nm) of high purity (111) diamond film was epitaxially grown on the surface. We confirmed that N density in the high purity diamond film and the formation of NV ensemble with 2D concentration of about 1 x 10¹¹ cm^-2 using the confocal PL-intensity mapping.

Superconducting quantum interference devices (SQUIDs) are widely used as high-sensitive magnetometers in several fields. However, there is still a problem with material instability in scanning SQUID microscope or quantum bit in quantum computing application. Superconducting boron-doped diamond shows excellent robustness in SQUID characteristics. We have demonstrated a first single crystalline diamond SQUID, whose Josephson junctions (JJs) were formed by step-edge structure. However, it was operated at 2.6 K. In this work, we have demonstrated diamond SQUIDs operating at 8.0 K well above liquid helium temperature 4.2 K using only (111) growth layer with T_c=10 K by using trench JJs.