Here we report the room-temperature and low-temperature absorption spectroscopy (UV-VIS-NIR), and electron paramagnetic resonance spectroscopy (EPR) conducted over a range of chemical vapour deposition (CVD) grown diamond samples. Room temperature absorption and fluorescence studies are shown. We also compared the room-temperature spectra with the experimental results conducted at 80 K. Finally, we used these data to calculate the density of NV in these samples that is responsible for the maser action. The number of NV defect centres is crucial since the total available number of NVs that are useful for maser are limited by the hyperfme coupling with nitrogen. From our previous studies, an NV concentration that lies between 0.2 to 2 ppm will offer the best solution in terms of pumping efficiency and uniform pumping rate for maser.
Here we report the room-temperature and low-temperature absorption spectroscopy (UV-VIS-NIR), and electron paramagnetic resonance spectroscopy (EPR) conducted over a range of chemical vapour deposition (CVD) grown diamond samples. Room temperature absorption and fluorescence studies are shown. We also compared the room-temperature spectra with the experimental results conducted at 80 K. Finally, we used these data to calculate the density of NV in these samples that is responsible for the maser action. The number of NV defect centres is crucial since the total available number of NVs that are useful for maser are limited by the hyperfme coupling with nitrogen. From our previous studies, an NV concentration that lies between 0.2 to 2 ppm will offer the best solution in terms of pumping efficiency and uniform pumping rate for maser.
Electron spin resonance (ESR) in polycrystalline diamond films grown by dc arc-jet and microwave plasma chemical vapour deposition is studied. The films with nitrogen impurity concentration up to 8 × 10 18 cm −3 are also characterized by Raman, cathodoluminescence and optical absorption spectra. The ESR signal from P1 centre with g -factor of 2.0024 (nitrogen impurity atom occupying C site in diamond lattice) is found to exhibit an inversion with increasing the microwave power in an H 102 resonator. The spin inversion effect could be of interest for further consideration of N-doped diamonds as a medium for masers operated at room temperature.
Single substitutional nitrogen atoms Ns0 are the prerequisite to create nitrogen-vacancy (NV) centers in diamonds. They not only serve as the electron donors to create the desired NV− center and provide charge stability against photo-ionisation but also are the main source of decoherence. Therefore, precise and quick determination of Ns0 concentration is a key advantage to a multitude of NV-related research in terms of material improvement as well as applications. Here, we present a method to determine the Ns0 concentration based on absorption spectroscopy in the UV-Visible range and fitting the 270 nm absorption band. UV-Visible spectroscopy has experimental simplicity and widespread availability that bear advantages over established methods. It allows a rapid determination of Ns0 densities, even for large numbers of samples. Our method shows further advantages in determining low concentrations as well as the ability to measure locally, which is highly relevant for diamonds with largely varying Ns0 concentrations in a single crystal. A cross-check with electron paramagnetic resonance shows high reliability of our method and yields the absorption cross section of the 270 nm absorption band σ=1.96±0.15 cm−1 ppm−1 (in common logarithm) or σe=4.51±0.35 cm−1 ppm−1 (in natural logarithm), which serves as a reference to determine Ns0 concentrations and makes our method applicable for others without the need for a known Ns0-reference sample and calibration. We provide a rapid, practical, and replicable pathway that is independent of the machine used and can be widely implemented as a standard characterization method for the determination of Ns0 concentrations.
In this paper, we analyse the prospects for using nitrogen-vacancy centre (NV) containing diamond as a laser gain material by measuring its key laser related parameters. Synthetic chemical vapour deposition grown diamond samples with an NV concentration of ~1 ppm have been selected because of their relatively high NV concentration and low background absorption in comparison to other samples available to us. For the samples measured, the luminescence lifetimes of the NV- and NV0 centres were measured to be 8±1 ns and 20±1 ns respectively. The respective peak stimulated emission cross-sections were (3.6±0.1)×10-17 cm2 and (1.7±0.1)×10-17 cm2. These measurements were combined with absorption measurements to calculate the gain spectra for NV- and NV0 for differing inversion levels. Such calculations indicate that gains approaching those required for laser operation may be possible with one of the samples tested and for the NV- centre.
Because of their high sensitivity, quantum materials are extremely promising for new technologies. The main challenge lies in maintaining a sufficiently quantum coherence times for quantum computation or quantum sensing systems. NV centers in diamond which are point defects consisting of a substitutional nitrogen atom neighboring an atomic vacancy, where an electron pair can reside in a triplet state – are ideal candidates for the development of industrial-scale quantum systems. These spin states exhibit ms-long coherence times at room temperature and can be manipulated optically, hence opening interesting perspectives for sending magnetic fields with high sensitivity1.At HiQuTe Diamond, we take up the challenge of mastering the entire nitrogen-doped diamond production chain synthesized by Microwave Plasma-Assisted Chemical Vapor Deposition (MPACVD). We aim at creating affordable diamonds specially engineered to achieve long coherence times with high NV density and high doping uniformity. This quest require to overcome the impact of several external factors that contribute to electron spin decoherence. First, the chemical composition of the diamond, specifically the types and concentrations of impurities within the diamond matrix (such as substitutional nitrogen NS, NV centres, mono-vacancies and clusters, hydrogen, etc.), as well as their electrical charge states (NS⁰, NS⁺, NV⁰, NV⁻) should be carefully controlled. Thanks to extensive scientific research conducted over the past decade, combined with our own R&D efforts, we are now able to quantify these parameters using experimental techniques compatible with industrial applications (Raman and UV-Vis spectroscopy) and compare our results with key performance indicators2. Second, we study the relationship between coherence (T2*) and strain inhomogeneities in our diamond layers, which we analyse using birefringence measurements. Our findings demonstrate our capability to produce CVD diamond layers with reduced strain and extended defect and confirm that strain could be a critical limiting factor for T2*.In this poster, I will review the efforts carried out at HiQuTe Diamond to develop specific material that is well suited for quantum sensing applications.References1.Barry, J. F., Schloss, J. M., Bauch, E., Turner, M. J., Hart, C. A., Pham, L. M., & Walsworth, R. L. (2020). Sensitivity optimization for NV-diamond magnetometry. Reviews of Modern Physics, 92(1), 015004.2.Langer, J. (2022). Quantum-grade diamond for cavity-based solutions. Fraunhofer Verlag.
Masers, the microwave analog of lasers, are an important class of devices that can be used to generate highly coherent and stable microwave signals as well as quantum-limited amplification of microwave photons. Recently, the interest in such devices has increased, probably owing to experiments demonstrating the successful operation at room temperature of solid-state maser employing defects in diamond. These defects, called nitrogen vacancy (NV) centers, are comprised of a negatively charged substitutional nitrogen that replaces one of the diamond crystal lattice’s carbons and a vacancy adjacent to the excluded carbon atom. The performance of diamond-based masers, in terms of gain, noise, bandwidth, frequency of operation, and saturation, greatly depends upon the specific diamond crystal composition and its geometry in the respective microwave device. The currently available data on these issues are scarce and sometimes conflicting. It is, therefore, important to provide additional experimental data, complemented by theoretical analysis, to further optimize the required diamond material and thus enhance the capabilities of diamond-based maser technology. The latter is currently limited to operate only as an oscillator at very small bandwidths, with low saturation power. Here, we provide experimental results on a set of important parameters affecting diamond maser operation, such as the population and linewidth of the electron spin energy levels of the NVs under light illumination, as well as their relaxation times for several different diamond material compositions. These results are then used to point out which diamond material compositions and crystal geometry may be best suitable for maser-type applications.
This thesis reports research conducted on point defects in single crystal diamond utilising the complementary techniques of electron paramagnetic resonance (EPR), optical absorption and photoluminescence (PL) spectroscopy. Intentional silicon-doping of chemical vapour deposition (CVD) diamond allowed the production of samples grown on differently oriented substrates and containing distinct silicon isotopic abundances. The EPR spectrum of the neutral charge state of the silicon split-vacancy centre in diamond, (Si-V)0, has been characterised in the literature. Evidence for the assignment of the 1.31 eV zero phonon line (ZPL) seen in absorption and PL to the 3A2g -> 3A1u transition arising at (Si-V)0 is presented. Reversible charge transfer between the negatively charged centre, (Si-V)− (ZPL at 1.68 eV), and (Si-V)0 enabled the determination of calibration factors relating defect concentrations to their respective ZPL intensities. Preferential alignment of trigonal centres, such as (Si-V), in CVD material grown on {110}-substrates has been observed. The formation of (Si-V) centres during CVD synthesis and via irradiation and annealing of silicon-doped diamond was studied. Variable temperature EPR spectroscopy under illumination was used to investigate the optical spin polarisation (SP) of the (Si-V)0 3A2g ground state. Two different mechanisms for the SP are considered; selective intersystem crossing of (Si-V)0, and photoionisation of (Si-V)−. The properties of (Si-V)0 are compared to those of the extensively studied negatively charged nitrogen vacancy centre, (N-V)−. The effective spin-lattice relaxation and spin polarisation rates for both centres during continuous illumination are explored using pulsed EPR methods. A new defect, labelledWAR3, with spin S = 1 2 was observed in silicon-doped diamond and characterised using multifrequency EPR. Analysis of the data revealed that WAR3 is the neutral charge state of a silicon divacancy complex decorated by a hydrogen atom, (Si-V2:H)0. The experimentally derived 29Si and 1H hyperfine parameters are in good agreement with the values calculated using the spindensity- functional technique, confirming this model and ruling out a non-planar structure.