Abstract
The negatively charged nitrogen-vacancy (hbox {NV}^{-}) center shows excellent spin properties and sensing capabilities on the nanoscale even at room temperature. Shallow implanted hbox {NV}^{-} centers can effectively be protected from surface noise by chemical vapor deposition (CVD) diamond overgrowth, i.e. burying them homogeneously deeper in the crystal. However, the origin of the substantial losses in hbox {NV}^{-} centers after overgrowth remains an open question. Here, we use shallow hbox {NV}^{-} centers to exclude surface etching and identify the passivation reaction of NV to NVH centers during the growth as the most likely reason. Indirect overgrowth featuring low energy (2.5–5 keV) nitrogen ion implantation and CVD diamond growth before the essential annealing step reduces this passivation phenomenon significantly. Furthermore, we find higher nitrogen doses to slow down the NV–NVH conversion kinetics, which gives insight into the sub-surface diffusion of hydrogen in diamond during growth. Finally, nano sensors fabricated by indirect overgrowth combine tremendously enhanced T_2 and T_2^* times with an outstanding degree of depth-confinement which is not possible by implanting with higher energies alone. Our results improve the understanding of CVD diamond overgrowth and pave the way towards reliable and advanced engineering of shallow hbox {NV}^{-} centers for future quantum sensing devices.
Highlights
The negatively charged nitrogen-vacancy (N V− ) center shows excellent spin properties and sensing capabilities on the nanoscale even at room temperature
Our results improve the understanding of chemical vapor deposition (CVD) diamond overgrowth and pave the way towards reliable and advanced engineering of shallow NV− centers for future quantum sensing devices
The sequence of NV− production via the so-called direct overgrowth procedure is depicted in Fig. 1(a): nitrogen ion implantation with subsequent annealing and overgrowth
Summary
The negatively charged nitrogen-vacancy (N V− ) center shows excellent spin properties and sensing capabilities on the nanoscale even at room temperature. To achieve a high sensitivity to external spins the NV− center has to be positioned a few nanometers below the diamond’s surface[6,20,22,25,26,27], since the measurable signal decays with the third power of the distance. Long coherence times are favorable for applications involving quantum registers where the NV–NV dipole detection limit strongly depends on T232 In our opinion, this trade-off finds an optimum in the so-called intermediate-regime (depths of 10–30 nm) which is characterized by significantly extended spin lifetimes while still preserving sufficient sensitivity to external spins on the surface. The tailored fabrication of NV− centers with a narrow depth distribution combined with the possibility of increasing their coherence times by slightly enlarging the average depth to the surface is key for several applications mentioned above
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