Abstract A platform for heteroepitaxial (111) chemical vapor deposition (CVD) diamond quantum sensors with preferentially aligned nitrogen vacancy (NV) centers on a large substrate is developed, and its operation as an electric vehicle (EV) battery monitor is demonstrated. A self‐standing heteroepitaxial CVD diamond film with a (111) orientation and a thickness of 150 µm is grown on a non‐diamond substrate and subsequently separated from it. The high uniformity and crystallinity of the (111)‐oriented diamond is confirmed. A 150‐µm thick NV‐diamond layer is then deposited on the heteroepitaxial diamond. The T 2 value measured by confocal microscopy is 20 µs, which corresponds to substitutional nitrogen defect concentration of 8 ppm. The nitrogen‐vacancy concentration and T 2 * are estimated to be 0.05 ppm and 0.05 µs by continuous wave optically detected magnetic resonance (CW‐ODMR) spectroscopy in a fiber‐top sensor configuration. In a gradiometer, where two sensors are placed on both sides of the busbar, the noise floor is 17 nT/Hz 0.5 in the frequency range of 10–40 Hz without magnetic shielding. The Allan deviation of the magnetic field noise in the laboratory is below 0.3 µT, which corresponds to a busbar current of 10 mA, in the accumulation time range of 10 ms to 100 s.
Abstract A platform for heteroepitaxial (111) chemical vapor deposition (CVD) diamond quantum sensors with preferentially aligned nitrogen vacancy (NV) centers on a large substrate is developed, and its operation as an electric vehicle (EV) battery monitor is demonstrated. A self‐standing heteroepitaxial CVD diamond film with a (111) orientation and a thickness of 150 µm is grown on a non‐diamond substrate and subsequently separated from it. The high uniformity and crystallinity of the (111)‐oriented diamond is confirmed. A 150‐µm thick NV‐diamond layer is then deposited on the heteroepitaxial diamond. The T 2 value measured by confocal microscopy is 20 µs, which corresponds to substitutional nitrogen defect concentration of 8 ppm. The nitrogen‐vacancy concentration and T 2 * are estimated to be 0.05 ppm and 0.05 µs by continuous wave optically detected magnetic resonance (CW‐ODMR) spectroscopy in a fiber‐top sensor configuration. In a gradiometer, where two sensors are placed on both sides of the busbar, the noise floor is 17 nT/Hz 0.5 in the frequency range of 10–40 Hz without magnetic shielding. The Allan deviation of the magnetic field noise in the laboratory is below 0.3 µT, which corresponds to a busbar current of 10 mA, in the accumulation time range of 10 ms to 100 s.
Taking advantage of the wide dynamic range feature of diamond quantum sensor, a prototype battery monitor for electric vehicles (EVs) with a measurement range of ±1000 A and an accuracy of 10 mA has been developed1 using HPHT-Ib diamond irradiated with 3✕1018 cm-2 electron beam (EB). A battery monitor prototyped with a 150 μm thick 2✕1018 cm-3 nitrogen doped layer grown on a 150 μm thick heteroepitaxial (111) CVD substrate, has also confirmed 10 mA accuracy2,3. In this presentation, we demonstrate that these battery monitors can track the current in actual EV. The current was measured as the resonance frequency difference (RH-RL) on the ODMR spectrum . The current from the battery to the motor was supplied to the busbar. Electronics and optics were within cooler-box size and could be placed on the rear seat of the EV enabling the measurement during driving. The EV was driven in the WLTC (World-wide Light vehicle Test Cycle) mode on a chassis dynamometer and the whole mode could be correctly tracked by both sensors. For more abrupt current changes than in WLTC mode, HPHT-Ib monitor showed better trackability. Improving the trackability of the heteroepitaxial monitor, increasing the NV concentration and enhancing fluorescence intensity should certainly be effective.
Considering the rising popularity of electric vehicles (EVs), it is essential to enhance the cruising mileage and extend the lifetime of batteries. To accomplish this, accurate monitoring of the charge and discharge current of the battery over a wide temperature range is essential. We developed a compact diamond quantum sensor head with a size of 1 × 1 × 0.5 cm3, consisting of a (111) high-pressure and high-temperature synthesized diamond with nitrogen-vacancy centers, by electron beam irradiation, which was adhered to the top of the multimode fiber and surrounded by the microwave antenna, for EV battery monitoring. We demonstrated that our quantum sensor achieved the current measurement accuracy of 10 mA in the −150 to 150 °C temperature range with a bandwidth of 500 Hz under atmospheric pressure and confirmed that the diamond quantum sensor meets the performance requirements of EV current sensors. Moreover, the temperature dependence of shot noise and external magnetic field noise were investigated, and their relation to the linewidth and contrast of the optically detected magnetic resonance spectrum were analyzed. At high temperatures, the contrast decreased because shortening of the singlet lifetime, which accelerate the initialization. At low temperatures, the contrast was slightly decreased. This is possibly a result of increased losses due to condensation on the microwave antenna.
Diamond (111) is grown heteroepitaxially on 2″ Ir/YSZ/Si (111) wafers (YSZ=yttria‐stabilized zirconia) with a diameter of 50 mm and off‐cuts of up to 6, applying plasma‐enhanced chemical vapor deposition supported by bias‐enhanced nucleation and epitaxial lateral overgrowth. In the final growth step, a nitrogen‐doped layer (N‐Cap) is superimposed. In the N‐Cap, a preferential orientation of nitrogen vacancy (NV) centers along the surface normal is observed, which has a T coherence time of 9.3 μs, which is the highest value ever reported for heteroepitaxial diamond (111). In the meantime, the T dephasing time is 95 ns, which means that the T / T ratio is almost 100, while published ratios for homoepitaxial diamond are in the range 5–20. The total nitrogen concentration as measured by Time‐of‐Flight Secondary Ion Mass Spectrometry is determined to be 7.3 ppm, which, in combination with photoluminescence analysis, yields an NV incorporation efficiency of .
Ensembles of nitrogen-vacancy (NV) centers in diamond are versatile quantum sensors with broad applications in the physical and life sciences. The concentration of neutral substitutional nitrogen ( [ N s 0 ]) strongly influences NV electronic spin coherence times, sensitivity, and optimal sensing strategies. Diamonds with [ N s 0 ] ∼ 1–10 ppm are a focus of recent material engineering efforts, with higher concentrations being favorable for continuous-wave optically detected magnetic resonance (CW-ODMR) and lower concentrations expected to benefit pulsed magnetometry techniques through extended NV spin coherence times and improved sensing duty cycles. In this work, we synthesize and characterize low- [ N s 0 ] ( ∼ 0.8 ppm), NV-enriched diamond material, engineered through low-strain chemical vapor deposition (CVD) growth on high-quality substrates, 12 C isotopic purification, and controlled electron irradiation and annealing. Our results demonstrate good strain homogeneity in diamonds grown on CVD substrates and spin-bath-limited NV dephasing times. By measuring NV spin and charge properties across a wide range of optical NV excitation intensity, we provide direct comparisons of photon-shot-noise-limited magnetic field sensitivity between the current low- [ N s 0 ] and previously studied higher- [ N s 0 ] ( ∼ 14 ppm) NV-diamond sensors. We show that low- [ N s 0 ] diamond can outperform higher- [ N s 0 ] diamond at moderate and low optical NV excitation intensity. Our results provide practical benchmarks and guidance for selecting NV-diamond sensors tailored to specific experimental constraints and sensing requirements.
The negatively charged nitrogen-vacancy (${\mathrm{NV}}^{\ensuremath{-}}$) center in diamond is an attractive candidate for applications that range from magnetometry to quantum information processing. Here we show that only a fraction of the nitrogen (typically <0.5%) incorporated during homoepitaxial diamond growth by chemical vapor deposition (CVD) is in the form of undecorated ${\mathrm{NV}}^{\ensuremath{-}}$ centers. Furthermore, studies on CVD diamond grown on (110)-oriented substrates show a near 100% preferential orientation of NV centers along only the [111] and [111] directions, rather than the four possible orientations. The results indicate that NV centers grow in as units, as the diamond is deposited, rather than by migration and association of their components. The NV unit of the ${\mathrm{NVH}}^{\ensuremath{-}}$ is similarly preferentially oriented, but it is not possible to determine whether this defect was formed by H capture at a preferentially aligned NV center or as a complete unit. Reducing the number of NV orientations from four orientations to two orientations should lead to increased optically detected magnetic resonance contrast and thus improved magnetic sensitivity in ensemble-based magnetometry.
Heteroepitaxial chemical vapor deposition is the most promising option to fabricate wafer-scale monocrystalline diamonds for quantum applications. Previously, we demonstrated the feasibility to manufacture functional micrometer-sized pyramids on as-grown heteroepitaxial diamond as well as their quantum optical characteristics. Due to high background signals and microfabrication challenges, these pyramids could not compete with homoepitaxially grown structures. In this study, we overcame these problems with a nominally undoped buffer layer between the heteroepitaxial substrate and the pyramidal microstructure to reduce the signal-to-noise ratio from the substrate on the spin measurements of the nitrogen-vacancy (NV) center. Moreover, the microfabrication was improved to reach a higher angle of the pyramidal side plane, corresponding to the {111} facets. These improvements lead to pyramids on which each facet contains almost purely only one of the four possible NV orientations as shown by optically detected magnetic resonance (ODMR). ODMR shows a very high contrast of 19% without an external magnet and of 13% for a single spin resonance in the presence of a magnetic field. The contrast is more than doubled compared to our previous study. The T2* dephasing time of the NV centers of the samples ranges from 0.02 to 0.16 μs. The P1 center is a single substitutional nitrogen center, and the P1 densities range from 1.8 to 5 ppm.