Formation Of Nitrogen-vacancy Centers Research Articles

Effect of Nitrogen on Growth and Optical Properties of Single-Crystal Diamond Synthesized by Chemical Vapor Deposition.

Concurrently achieving high growth rate and high quality in single-crystal diamonds (SCDs) is significantly challenging. The growth rate of SCDs synthesized by microwave plasma chemical vapor deposition (MPCVD) was enhanced by introducing N2 into the typical CH4-H2 gas mixtures. The impact of nitrogen vacancy (NV) center concentration on growth rate, surface morphology, and lattice binding structure was investigated. The SCDs were characterized through Raman spectroscopy, photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy. It was found that the saturation growth rate was increased up to 45 μm/h by incorporating 0.8-1.2% N2 into the gas atmosphere, which is 4.5 times higher than the case without nitrogen addition. Nitrogen addition altered the growth mode from step-flow to bidimensional nucleation, leading to clustered steps and a rough surface morphology, followed by macroscopically pyramidal hillock formation. The elevation of nitrogen content results in a simultaneous escalation of internal stress and defects. XPS analysis confirmed chemical bonding between nitrogen and carbon, as well as non-diamond carbon phase formation at 0.8% of nitrogen doping. Furthermore, the emission intensity of NV-related defects from PL spectra changed synchronously with N2 concentrations (0-1.5%) during diamond growth, indicating that the formation of NV centers activated the diamond lattice and facilitated nitrogen incorporation into it, thereby accelerating chemical reaction rates for achieving high-growth-rate SCDs.

Effects of oxygen/nitrogen co-incorporation on regulation of growth and properties of boron-doped diamond films

Regulation with nitrogen and oxygen co-doping on growth and properties of boron doped diamond films is studied by using laughing gas as dopant. As the concentration of laughing gas (N2O/C) increases from 0 to 10%, the growth rate of diamond film decreases gradually, and the nitrogen-vacancy (NV) center luminescence intensity increases first and then weakens. The results show that oxygen in laughing gas has a strong inhibitory effect on formation of NV centers, and the inhibitory effect would be stronger as the concentration of laughing gas increases. As a result, the film growth rate and nitrogen-related compensation donor decrease, beneficial to increase the acceptor concentration (∼3.2 × 1019 cm−3) in the film. Moreover, it is found that the optimal regulation with the quality and electrical properties of boron doped diamond films could be realized by adding appropriate laughing gas, especially the hole mobility (∼700 cm2/V⋅s), which is beneficial to the realization of high-quality boron doped diamond films and high-level optoelectronic device applications in the future.

Optical and electronic spin properties of fluorescent micro- and nanodiamonds upon prolonged ultrahigh-temperature annealing.

High-temperature annealing is a promising but still mainly unexplored method for enhancing spin properties of negatively charged nitrogen-vacancy (NV) centers in diamond particles. After high-energy irradiation, the formation of NV centers in diamond particles is typically accomplished via annealing at temperatures in the range of 800-900 °C for 1-2 h to promote vacancy diffusion. Here, we investigate the effects of conventional annealing (900 °C for 2 h) against annealing at a much higher temperature of 1600 °C for the same annealing duration for particles ranging in size from 100 nm to 15 μm using electron paramagnetic resonance and optical characterization. At this high temperature, the vacancy-assisted diffusion of nitrogen can occur. Previously, the annealing of diamond particles at this temperature was performed over short time scales because of concerns of particle graphitization. Our results demonstrate that particles that survive this prolonged 1600 °C annealing show increased NV T1 and T2 electron spin relaxation times in 1 and 15 μm particles, due to the removal of fast relaxing spins. Additionally, this high-temperature annealing also boosts magnetically induced fluorescence contrast of NV centers for particle sizes ranging from 100 nm to 15 μm. At the same time, the content of NV centers is decreased fewfold and reaches a level of <0.5 ppm. The results provide guidance for future studies and the optimization of high-temperature annealing of fluorescent diamond particles for applications relying on the spin properties of NV centers in the host crystals.

The Study of the Efficiency of Nitrogen to Nitrogen‐Vacancy (NV)‐Center Conversion in High‐Nitrogen Content Samples

The nitrogen‐vacancy color center in diamond is one of the important systems in the fast‐growing field of sensing. This color center is used in both high‐resolution and high‐sensitivity sensors. However, techniques for the quick and efficient formation of NV centers are still in the development stage. Herein, a study on the influence of the electron irradiation dose on the conversion of substitutional nitrogen into NV− centers is presented. The study is done on diamonds that are highly enriched with nitrogen (≈100 ppm), which, on one hand, should maximize the effect of irradiation, and, on other hand, be of interest for high‐sensitivity magnetometers. The maximum achieved conversion efficiency is as high as 37% ± 3.7%, with no observed saturation on the electron dose even with the simplest annealing procedure. The measurements of the corresponding dephasing time made it possible to make a theoretical estimate for the shot‐noise‐limited magnetic field sensitivity per unit volume of diamond to be roughly .

Лазерно-индуцированные люминесцентные центры в алмазе: влияние экспозиции и длительности ультракоротких лазерных импульсов

The optical properties of point luminescent centers formed in the volume IaA-type natural diamond under the action of ultrashort laser pulses in the visible range (515 nm) with durations of 0.3–2.4 ps were investigated. The analysis using confocal Raman spectroscopy demonstrates the formation of nitrogen vacancy centers (NV) and there are no graphitization traces in processing areas. The luminescence amplitude of NV centers depends linearly on the exposure time at different durations of ultrashort laser pulses.

Laser-induced luminescent centers in diamond: influence of exposure and duration of short laser pulses

The optical properties of point luminescent centers formed in the volume IaA-type natural diamond under the action of ultrashort laser pulses in the visible range (515 nm) with durations of 0.3-2.4 ps were investigated. The analysis using confocal Raman spectroscopy demonstrates the formation of nitrogen vacancy centers (NV) and there are no graphitization traces in processing areas. The luminescence amplitude of NV centers depends linearly on the exposure time at different durations of ultrashort laser pulses. Keywords: ultrashort laser pulses, luminescence, luminescent centers in diamond, NV centers.

Formation of nitrogen-vacancy centers in 4H-SiC and their near infrared photoluminescence properties

NCVSi− centers in SiC [nitrogen-vacancy (NV) centers], which produce near-infrared (NIR) photoluminescence (PL) at room temperature, is expected to have applications as quantum sensors for in vivo imaging and sensing. To realize quantum sensing using NV centers, clarification of the formation mechanism as well as control of the high-density formation is necessary. This paper reports a comprehensive investigation on the NIR-PL properties originating from NV centers in high purity semi-insulating and nitrogen (N) contained 4H-SiC substrates formed by ion beam irradiation and subsequent thermal annealing. It is shown that NV centers are exclusively formed by the contained N as impurities rather than the implanted N, and also the heavier ion irradiations induce the NV center formation effectively than the lighter ion irradiations. The study on thermal annealing at different temperatures reveals that the optimal temperature is 1000 °C. From the results of temperature dependence on the PL intensity, it is shown that little thermal quenching of the PL intensity appears at room temperature and the PL signal is collected even at 783 K. The formation mechanism of NV centers is also discussed based on the obtained results.

Photothermal effects during nanodiamond synthesis from a carbon aerogel in a laser-heated diamond anvil cell

Nanodiamonds have emerged as promising materials for quantum computing, biolabeling, and sensing due to their ability to host color centers with remarkable photostability and long spin-coherence times at room temperature. Recently, a bottom-up, high-pressure, high-temperature (HPHT) approach was demonstrated for growing nanodiamonds with color centers from amorphous carbon precursors in a laser-heated diamond anvil cell (LH-DAC) that was supported by a near-hydrostatic noble gas pressure medium. However, a detailed understanding of the photothermal heating and its effect on diamond growth, including the phase conversion conditions and the temperature-dependence of color center formation, has not been reported. In this work, we measure blackbody radiation during LH-DAC synthesis of nanodiamond from carbon aerogel to examine these temperature-dependent effects. Blackbody temperature measurements suggest that nanodiamond growth can occur at 16.3 GPa and 1800 K. We use Mie theory and analytical heat transport to develop a predictive photothermal heating model. This model demonstrates that melting the noble gas pressure medium during laser heating decreases the local thermal conductivity to drive a high spatial resolution of phase conversion to diamond. Finally, we observe a temperature-dependent formation of nitrogen vacancy centers and interpret this phenomenon in the context of HPHT carbon vacancy diffusion.

Generation of ensembles of individually resolvable nitrogen vacancies using nanometer-scale apertures in ultrahigh-aspect ratio planar implantation masks.

A central challenge in developing magnetically coupled quantum registers in diamond is the fabrication of nitrogen vacancy (NV) centers with localization below ∼20 nm to enable fast dipolar interaction compared to the NV decoherence rate. Here, we demonstrate the targeted, high throughput formation of NV centers using masks with a thickness of 270 nm and feature sizes down to ∼1 nm. Super-resolution imaging resolves NVs with a full-width maximum distribution of 26 ± 7 nm and a distribution of NV-NV separations of 16 ± 5 nm.

Microscopic origin for the orientation dependence of NV centers in chemical-vapor-deposited diamond

First-principles calculation reveals that hydrogen, which is abundant in chemical vapor deposition (CVD), can significantly improve the uniformity of nitrogen-vacancy (NV) centers in diamond. It shows that the formation of NV centers can be described as a multi-step process: first, a substitutional N (NC) is preferentially formed at the surface layer over that of either a carbon vacancy (VC) or an in-pane nitrogen-vacancy-hydrogen (NVH) complex. Second, with the help of H, a VC is preferentially incorporated in the newly formed topmost layer as a nearest neighbor to the NC (now buried in the first sublayer). This NVH complex is even more stable than NC on the same layer. Third, H protects the already formed NV centers by forming low-energy NVHX complexes. These NV centers with their axes pointing along the directions of surface C–H bonds during their incorporation explain the experimental observations by CVD growth on (1 0 0) and (1 1 0) surfaces. Based on the model, we predict that CVD growth on (1 1 1) surface could eliminate the orientation domains to significantly improve the performance of NV centers.

Depletion of nitrogen-vacancy color centers in diamond via hydrogen passivation

We show reduction in the emission from nitrogen-vacancy (NV) centers in single crystal diamond due to exposure to hydrogen plasmas ranging from 700 °C to 1000 °C. Significant fluorescence reduction was observed beneath the exposed surface to 80 μm depth after ∼10 min and did not recover after post-annealing in vacuum for 7 h at 1100 °C. We attribute the fluorescence reduction to the formation of nitrogen-vacancy-hydrogen centers by the plasma-induced diffusion of hydrogen. These results have important implications for the formation of NV centers for quantum applications, whilst also providing experimental evidence of long range hydrogen diffusion through intrinsic high-purity diamond.