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arXiv:2006.07763 · Journal of Applied Physics

Spin coherence and depths of single nitrogen-vacancy centers created by ion implantation into diamond via screening masks

Shuntaro Ishizu, Kento Sasaki, Daiki Misonou, Tokuyuki Teraji, Kohei M. Itoh, Eisuke Abe

Published Jun 24, 2020• 8 citations
arXivHTMLPDF

Abstract

We characterize single nitrogen-vacancy (NV) centers created by 10-keVN+ ion implantation into diamond via thin SiO2 layers working as screening masks. Despite the relatively high acceleration energy compared with standard ones (<5keV) used to create near-surface NV centers, the screening masks modify the distribution of N+ ions to be peaked at the diamond surface [Ito et al., Appl. Phys. Lett. 110, 213105 (2017)]. We examine the relation between coherence times of the NV electronic spins and their depths, demonstrating that a large portion of NV centers are located within 10 nm from the surface, consistent with Monte Carlo simulations. The effect of the surface on the NV spin coherence time is evaluated through noise spectroscopy, surface topography, and x-ray photoelectron spectroscopy.

DOI
10.1063/5.0012187

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We characterize single nitrogen-vacancy (NV) centers created by 10-keVN+ ion implantation into diamond via thin SiO2 layers working as screening masks. Despite the relatively high acceleration energy compared with standard ones (<5keV) used to create near-surface NV centers, the screening masks modify the distribution of N+ ions to be peaked at the diamond surface [Ito et al., Appl. Phys. Lett. 110, 213105 (2017)]. We examine the relation between coherence times of the NV electronic spins and their depths, demonstrating that a large portion of NV centers are located within 10 nm from the surface, consistent with Monte Carlo simulations. The effect of the surface on the NV spin coherence time is evaluated through noise spectroscopy, surface topography, and x-ray photoelectron spectroscopy.
We report on an ion implantation technique utilizing a screening mask made of SiO2 to control both the depth profile and the dose. By appropriately selecting the thickness of the screening layer, this method fully suppresses the ion channeling, brings the location of the highest nitrogen-vacancy (NV) density to the surface, and effectively reduces the dose by more than three orders of magnitude. With a standard ion implantation system operating at the energy of 10 keV and the dose of 1011 cm2 and without an additional etching process, we create single NV centers close to the surface with coherence times of a few tens of μs.
Efficient creation of shallow NV−^-− ensembles by high-angle ion implantation
Negatively charged nitrogen-vacancy (NV−^-−) centers located a few nanometers below the diamond surface are key quantum defects for nanoscale sensing of external spins. However, the creation of shallow NV−^-− centers with high yield remains a materials challenge. Here, we demonstrate that high-angle ion implantation enhances the creation efficiency of shallow NV−^-− centers. By implanting 15^{15}15N ions at angles exceeding 60∘^\circ∘, we achieve high NV−^-− yields approaching 10% with effective NV−^-− depths below 10 nm. These yields are significantly higher than those typically reported for shallow NV−^-− creation. The enhanced NV−^-− yield is consistent with an increased vacancy-to-nitrogen ratio in the near-surface region, which is expected to promote NV formation during annealing. The created NV−^-− ensembles show coherence properties comparable to those of single shallow NV−^-− centers at similar depths, and allow detection of nuclear spins in van der Waals materials attached to the diamond surface. Our results establish geometric control of ion implantation as a simple and broadly applicable approach to engineer shallow vacancy-related quantum defects.
Scalable realizations of quantum network technologies utilizing the nitrogen vacancy center in diamond require creation of optically coherent NV centers in close proximity to a surface for coupling to optical structures. We create single NV centers by 15^{15}15N ion implantation and high-temperature vacuum annealing. Origin of the NV centers is established by optically detected magnetic resonance spectroscopy for nitrogen isotope identification. Near lifetime-limited optical linewidths (<<< 60 MHz) are observed for the majority of the normal-implant (7∘^\circ∘, ≈\approx≈ 100 nm deep) 15^{15}15NV centers. Long-term stability of the NV−^-− charge state and emission frequency is demonstrated. The effect of NV-surface interaction is investigated by varying the implantation angle for a fixed ion-energy, and thus lattice damage profile. In contrast to the normal implant condition, NVs from an oblique-implant (85∘^\circ∘, ≈\approx≈ 20 nm deep) exhibit substantially reduced optical coherence. Our results imply that the surface is a larger source of perturbation than implantation damage for shallow implanted NVs. This work supports the viability of ion implantation for formation of optically stable NV centers. However, careful surface preparation will be necessary for scalable defect engineering.
Scalable realizations of quantum network technologies utilizing the nitrogen-vacancy (NV) center in diamond require creation of optically coherent NV centers in close proximity to a surface for coupling to optical structures. We create single NV centers by 15N^{15}\mathrm{N}15N ion implantation and high-temperature vacuum annealing. The origin of the NV centers is established by optically detected magnetic resonance spectroscopy for nitrogen isotope identification. Near-lifetime-limited optical linewidths (<60MHz)(<60 \mathrm{MHz})(<60MHz) are observed for the majority of the normal-implant (${7}^{\ensuremath{\circ}}$, $\ensuremath{\approx}100$ nm deep) 15NV^{15}\mathrm{NV}15NV centers. Long-term stability of the ${\mathrm{NV}}^{\ensuremath{-}}$ charge state and emission frequency is demonstrated. The effect of NV-surface interaction is investigated by varying the implantation angle for a fixed ion energy, and thus lattice damage profile. In contrast to the normal-implant condition, NVs from an oblique implant (${85}^{\ensuremath{\circ}}$, $\ensuremath{\approx}20$ nm deep) exhibit substantially reduced optical coherence. Our results imply that the surface is a larger source of perturbation than implantation damage for shallow implanted NVs. This work supports the viability of ion implantation for formation of optically stable NV centers. However, careful surface preparation will be necessary for scalable defect engineering.
We investigated the depth dependence of coherence times of nitrogen-vacancy (NV) centers through precise depth control using oxidative etching at 580 °C in air. By successive nanoscale etching, NV centers could be brought close to the diamond surface step by step, which enabled us to track the evolution of the number of NV centers remaining in the chip and to study the depth dependence of coherence times of NV centers with diamond etching. Our results showed that the coherence times of NV centers declined rapidly with the depth reduction in the last about 22 nm before they finally disappeared, which revealed a critical depth for the influence of a rapid fluctuating surface spin bath. Moreover, by using the slow etching method combined with low-energy nitrogen implantation, NV centers with depths shallower than the initially implanted depths can be generated, which are preferred for detecting external spins with higher sensitivity.
We have studied optical and spin properties of near-surface nitrogen-vacancy (NV) centers incorporated during chemical vapor phase growth of isotopically purified (12)C single-crystal diamond layers. The spectral diffusion-limited line width of zero-phonon luminescence from the NV centers is 1.2 ± 0.5 GHz, a considerable improvement over that of NV centers formed by ion implantation and annealing. Enhanced spin dephasing times (T(2)* ≈ 90 μs, T(2) ≈ 1.7 ms) due to the reduction of (13)C nuclear spins persist even for NV centers placed within 100 nm of the surface.