Constructing quantum devices comprises various challenging tasks, especially when concerning their nanoscale geometry. For quantum color centers, the traditional approach is to fabricate the device structure after the nondeterministic placement of the centers. Reversing this approach, we present the controlled generation of quantum centers in silicon carbide (SiC) by focused proton beam in a noncomplex manner without need for pre- or postirradiation treatment. The generation depth and resolution can be predicted by matching the proton energy to the material's stopping power, and the amount of quantum centers at one specific sample volume is tunable from ensembles of millions to discernible single photon emitters. We identify the generated centers as silicon vacancies through their characteristic magnetic resonance signatures and demonstrate that they possess a long spin-echo coherence time of 42 ± 20 μs at room temperature. Our approach hence enables the fabrication of quantum hybrid nanodevices based on SiC platform, where spin centers are integrated into p-i-n diodes, photonic cavities, and mechanical resonators.

We investigated the charge state stability and coherence properties of near-surface single nitrogen vacancy (NV) centers in 12 C-enriched diamond for potential use in nanoscale magnetic field sensing applications. The stability of charge states in negatively charged NV centers (NV % ) was evaluated using one of the pulsed optically detected magnetic resonance measurements, Rabi oscillation measurements. During the accumulation of Rabi oscillations, an unstable shallow NV % was converted to a neutral state. As a result, the contrast of Rabi oscillations degraded, depending on charge state stability. We stabilized the NV % state of very shallow NV centers (>2.6 + 1.1 nm from the surface) created by 1.2 keV nitrogen ion implantation by diamond surface modification, UV/ozone exposure, and oxygen annealing. This improvement indicates that we can suppress the upward surface band bending and surface potential fluctuations through Fermi level pinning originating from oxygen-terminated diamond surfaces.

The nitrogen-vacancy (NV) center in diamond is the most promising candidate for quantum sensing because of its beneficial properties. For quantum-sensing applications, a shallow NV center is critical for approximating the sensing target on a diamond surface. Such shallow NV centers are strongly affected by the diamond surface termination. The properties of shallow NV centers in hydrogen-, oxygen-, and fluorine-terminated diamond have been well studied. In recent years, silicon-terminated diamond has also been investigated; however, the effect of silicon-terminated diamond on the properties of shallow NV centers remains unclear. Recently, the suitability of nitrogen-terminated diamond for shallow NV centers has been theoretically and experimentally examined; however, quantum sensing has not yet been performed. In this work, we evaluated the effect of silicon and nitrogen termination on shallow NV centers. The negatively charged state of shallow NV centers was unstable below silicon termination. In contrast, the properties of shallow NV centers in nitrogen-terminated diamond were satisfactory for quantum sensing and enabled 1H NMR detection. Our results are in good agreement with previous reports on silicon and nitrogen terminations and provide the perspective that the stability of shallow NV centers highly depends on the polarity of electron affinity of the diamond surface.

The simultaneous control of the number and position of negatively charged nitrogen-vacancy (NV) centers in diamond was achieved. While single near-surface NV centers are known to exhibit outstanding capabilities in external spin sensing, trade-off relationships among the accuracy of the number and position, and the coherence of NV centers have made the use of such engineered NV centers difficult. Namely, low-energy nitrogen implantation with lithographic techniques enables the nanoscale position control but results in degradation of the creation yield and the coherence property. In this paper, we show that low-energy nitrogen ion implantation to a 12 C(99.95%)-enriched homoepitaxial diamond layer using nanomask is applicable to create shallow NV centers with a sufficiently long coherence time for external spin sensing, at a high creation yield. Furthermore, the NV centers were arranged in a regular array so that 40% lattice sites contain single NV centers. The XY8-k measurements using the individual NV centers reveal that the created NV centers have depths from 2 to 12nm, which is comparable to the stopping range of nitrogen ions implanted at 2.5keV. We show that the position-controlled NV centers are capable of external spin sensing with a ultra-high spatial resolution.