Shallow Nitrogen-vacancy Centers Research Articles

Effect of low-damage inductively coupled plasma on shallow nitrogen-vacancy centers in diamond

Near-surface nitrogen-vacancy (NV) centers in diamond have been successfully employed as atomic-sized magnetic field sensors for external spins over the last years. A key challenge is still to develop a method to bring NV centers at nanometer proximity to the diamond surface while preserving their optical and spin properties. To that aim we present a method of controlled diamond etching with nanometric precision using an oxygen inductively coupled plasma process. Importantly, no traces of plasma-induced damages to the etched surface could be detected by X-ray photoelectron spectroscopy and confocal photoluminescence microscopy techniques. In addition, by profiling the depth of NV centers created by 5.0 keV of nitrogen implantation energy, no plasma-induced quenching in their fluorescence could be observed. Moreover, the developed etching process allowed even the channeling tail in their depth distribution to be resolved. Furthermore, treating a 12C isotopically purified diamond revealed a threefold increase in T2 times for NV centers with <4 nm of depth (measured by nuclear magnetic resonance signal from protons at the diamond surface) in comparison to the initial oxygen-terminated surface.

Nanoengineered diamond waveguide as a robust bright platform for nanomagnetometry using shallow nitrogen vacancy centers.

Photonic structures in diamond are key to most of its application in quantum technology. Here, we demonstrate tapered nanowaveguides structured directly onto the diamond substrate hosting shallow-implanted nitrogen vacancy (NV) centers. By optimization based on simulations and precise experimental control of the geometry of these pillar-shaped nanowaveguides, we achieve a net photon flux up to ∼ 1.7 × 10(6) s(-1). This presents the brightest monolithic bulk diamond structure based on single NV centers so far. We observe no impact on excited state lifetime and electronic spin dephasing time (T2) due to the nanofabrication process. Possessing such high brightness with low background in addition to preserved spin quality, this geometry can improve the current nanomagnetometry sensitivity ∼ 5 times. In addition, it facilitates a wide range of diamond defects-based magnetometry applications. As a demonstration, we measure the temperature dependency of T1 relaxation time of a single shallow NV center electronic spin. We observe the two-phonon Raman process to be negligible in comparison to the dominant two-phonon Orbach process.

Optical depth localization of nitrogen-vacancy centers in diamond with nanometer accuracy

Precise positioning of nitrogen-vacancy (NV) centers is crucial for their application in sensing and quantum information. Here we present a new purely optical technique enabling determination of the NV position with nanometer resolution. We use a confocal microscope to determine the position of individual emitters along the optical axis. Using two separate detection channels, it is possible to simultaneously measure reflected light from the diamond surface and fluorescent light from the NV center and statistically evaluate both signals. An accuracy of 2.6 nm for shallow NV centers was achieved and is consistent with other techniques for depth determination.

Effect of oxygen plasma and thermal oxidation on shallow nitrogen-vacancy centers in diamond

We investigate the effect of two different surface treatments on shallow nitrogen-vacancy (NV) centers in diamond. Short duration oxygen plasma exposure is found to damage near-surface NV centers, resulting in their disappearance in fluorescence images. Subsequent annealing creates large numbers of new NV centers, attributed to plasma-induced vacancy creation. By tracking individual NV centers during thermal oxidation, we show that oxidation at 550 °C results in modest improvement of spin coherence. Higher temperature oxidations correlate with gradual decline in spin coherence and eventual instability of NV centers before ultimate disappearance. This is indicative of a reduction of the NV-to-surface distance due to oxidative etching. Thermal oxidation can offer controlled access to near-surface NV spins at the nanometer scale, an important requirement for many applications of NV-based nanomagnetometry.

Investigation of surface magnetic noise by shallow spins in diamond.

We present measurements of spin relaxation times (T1, T1ρ, T2) on very shallow (≲5 nm) nitrogen-vacancy centers in high-purity diamond single crystals. We find a reduction of spin relaxation times up to 30 times compared to bulk values, indicating the presence of ubiquitous magnetic impurities associated with the surface. Our measurements yield a density of 0.01-0.1μB/nm2 and a characteristic correlation time of 0.28(3)ns of surface states, with little variation between samples and chemical surface terminations. A low temperature measurement further confirms that fluctuations are thermally activated. The data support the atomistic picture where impurities are associated with the top carbon layers, and not with terminating surface atoms or adsorbate molecules. The low spin density implies that the presence of a single surface impurity is sufficient to cause spin relaxation of a shallow nitrogen-vacancy center.

Increasing the creation yield of shallow single defects in diamond by surface plasma treatment

Single Nitrogen-Vacancy (NV) centers in diamond close to the crystal surface are very promising magnetic field sensors with very high sensitivity. Here, we report the enhanced creation of very shallow (less than 3 nm below the diamond surface) NV centers by using fluorine and oxygen plasma treatment. We observe a four fold increase—from 0.11% to about 0.45% in the production yield when the sample surface is terminated with fluorine or oxygen atoms. This effect is explained by the stabilization of the NV's negative charge state which is influenced by the various defects present on the diamond surface.

Engineering shallow spins in diamond with nitrogen delta-doping

We demonstrate nanometer-precision depth control of nitrogen-vacancy (NV) center creation near the surface of synthetic diamond using an in situ nitrogen delta-doping technique during plasma-enhanced chemical vapor deposition. Despite their proximity to the surface, doped NV centers with depths (d) ranging from 5 - 100 nm display long spin coherence times, T2 > 100 \mus at d = 5 nm and T2 > 600 \mus at d \geq 50 nm. The consistently long spin coherence observed in such shallow NV centers enables applications such as atomic-scale external spin sensing and hybrid quantum architectures.