Nitrogen In Diamond Research Articles

Nitrogen in Diamond

Nitrogen is ubiquitous in both natural and laboratory-grown diamond, but the number and nature of the nitrogen-containing defects can have a profound effect on the diamond material and its properties. An ever-growing fraction of the supply of diamond appearing on the world market is now lab-grown. Here, we survey recent progress in two complementary diamond synthesis methods-high pressure high temperature (HPHT) growth and chemical vapor deposition (CVD), how each is allowing ever more precise control of nitrogen incorporation in the resulting diamond, and how the diamond produced by either method can be further processed (e.g., by implantation or annealing) to achieve a particular outcome or property. The burgeoning availability of diamond samples grown under well-defined conditions has also enabled huge advances in the characterization and understanding of nitrogen-containing defects in diamond-alone and in association with vacancies, hydrogen, and transition metal atoms. Among these, the negatively charged nitrogen-vacancy (NV-) defect in diamond is attracting particular current interest in account of the many new and exciting opportunities it offers for, for example, quantum technologies, nanoscale magnetometry, and biosensing.

Research progress of large diamond single crystals under high pressure and high temperature

Diamond has a series of extreme characteristics superior to other materials, and also very wide application scope. The large diamond single crystal can play a role in its functional characteristics, which has become a research hotspot. In this paper, we introduce the principle and process of synthesizing large diamond single crystal by temperature gradient method (TGM) under high pressure and high temperature (HPHT), and summarizes the research status and research directions of different types of and additives-doped large diamond single crystals respectively. The principle of the temperature gradient method is that the carbon source, driven by the temperature gradient, diffuses from the high concentration region at the high temperature end to the low concentration region at the low temperature end, and diamonds are grown on the seed crystal. The growth rate of diamond crystal is controlled by adjusting the axial temperature gradient at synthesis cell, and the shape growth of Ib-type large diamond is controlled by the distribution in the V-shaped growth area. We introduce different kinds of diamond large single crystals from five aspects. Firstly, the Ia-type diamond large single crystal can be obtained by the annealing treatment of Ib-type diamond under HPHT. The conversion rate of C centre to A centre for nitrogen in diamond is improved by optimizing the conditions of HPHT. Secondly, the Ib-type larger diamond is studied very much in the following areas: the analysis of its surface characteristic, the control of inclusions and cracks, the precipitation mechanism and the elimination measures of regrown graphite and the mass production technology of multiseed method. Thirdly, IIa-type large diamond single crystal is introduced in which the nitrogen getter is selected due to the ability Al and Ti (Cu) to getter nitrogen, the catalyst is selected because of its effect on the nitrogen content in the diamond synthesized with Fe or Ni based catalyst, and the elimination method of microcrystalline graphite precipitation is presented by analyzing its mechanism. Fourthly, the boron elements exist in IIb-type diamond and have influence on the growth characteristics of synthetic diamond. Fifthly, introduced is the research status of diamond synthesized with B, N, S, P doping elements, in which its individual substance or their compound is used as a doping source or boron and other elements with small radius are used as co-doping agent. Then S or P with B co-doping is more conducive to the improvement of the performance of n-type diamond large single crystal semiconductor. Therefore, it is proposed that the large diamond single crystal need strengthening in mass production of IIa-type large diamond single crystal, superconducting characteristics of IIb-type large diamond single crystal, and doping of n-type semiconductors.

Effect of sulfur on diamond growth and morphology in metal–carbon systems

Sulfur additives inhibit diamond crystallization in the Fe–Ni–C system at 6 GPa and 1400 °C and affect the diamond crystal morphology and nitrogen impurity content.

Stimulated Emission Depletion Microscopy with Diamond Silicon Vacancy Centers

The spatial resolution and fluorescence signal amplitude in stimulated emission depletion (STED) microscopy is limited by the photostability of available fluorophores. Here, we show that negatively-charged silicon vacancy (SiV) centers in diamond are promising fluorophores for STED microscopy, owing to their photostable, near-infrared emission and favorable photophysical properties. A home-built pulsed STED microscope was used to image shallow implanted SiV centers in bulk diamond at room temperature. The SiV stimulated emission cross section for 765-800 nm light is found to be (4.0 +/- 0.3) x 10^(-17) cm^2, which is approximately 2-4 times larger than that of the negatively-charged diamond nitrogen vacancy center and approaches that of commonly-used organic dye molecules. We performed STED microscopy on isolated SiV centers and observed a lateral full-width-at-half-maximum spot size of 89 +/- 2 nm, limited by the low available STED laser pulse energy (0.4 nJ). For a pulse energy of 5 nJ, the resolution is expected to be ~20 nm. We show that the present microscope can resolve SiV centers separated by <150 nm that cannot be resolved by confocal microscopy.

Absorption-free superluminal light propagation in a diamond nitrogen vacancy center

We investigate the dispersion and absorption properties of a weak probe field in a four-level tripod system in a diamond nitrogen vacancy (NV) center. We apply a static magnetic field to the system and it is shown that the slope of dispersion changes from positive to negative only by varying either the intensity or relative phase of applied fields. Then, the transparent subluminal light propagation switches to the transparent superluminal light propagation. It is demonstrated that the group velocity of light pulse can be also controlled by a static magnetic field. Additionally, it is shown that the static magnetic field induces the amplification without inversion in the NV center. Unlike the atomic gas system, the obtained results in the NV center can be experimentally observed at room temperature.

Adiabatic population transfer of dressed spin states with quantum optimal control

We report theoretical studies of adiabatic population transfer using dressed spin states. Quantum optimal control using the algorithm of Chopped Random Basis (CRAB) has been implemented in a negatively charged diamond nitrogen vacancy center that is coupled to a strong and resonant microwave field. We show that the dressed spin states are highly effective in suppressing effects of spin dephasing on adiabatic population transfer. The numerical simulation also demonstrates that CRAB-based quantum optimal control can enable an efficient and robust adiabatic population transfer.

Selective Decoupling and Hamiltonian Engineering in Dipolar Spin Networks.

We present a protocol to selectively decouple, recouple, and engineer effective interactions in mesoscopic dipolar spin networks. In particular, we develop a versatile protocol that relies upon magic angle spinning to perform Hamiltonian engineering. By using global control fields in conjunction with a local actuator, such as a diamond nitrogen vacancy center located in the vicinity of a nuclear spin network, both global and local control over the effective couplings can be achieved. We show that the resulting effective Hamiltonian can be well understood within a simple, intuitive geometric picture, and corroborate its validity by performing exact numerical simulations in few-body systems. Applications of our method are in the emerging fields of two-dimensional room temperature quantum simulators in diamond platforms, as well as in molecular magnet systems.

Spontaneous parametric four wave mixing and fluorescence lifetime manipulation in the diamond nitrogen vacancy center

We report the lifetime of spontaneous parametric four wave mixing (SP-FWM) and multiorder fluorescence in two-, three-, and four-level systems of negatively charged nitrogen vacancy (NV−) in diamond. The lifetime of SP-FWM is enhanced at high power by the induced dark state from coupling fields. The reduction and enhancement in fluorescence lifetime are attributed to destructive and constructive quantum interference, respectively. The quantum interference is induced by interaction among different decay pathways of spontaneous emission by closely spaced energy levels, which can be controlled by dipole–dipole interaction and the mutual orientations of dipole moments. The lifetime is observed to be longer in two-level as compared to three-level and four-level systems. The different measured lifetimes suggest the sensitivity of these NV systems to quantum interference and the dressing effect. These outcomes may provide new insights in development of all-optical communication devices and quantum storage on photonic chips.

Integrated waveguides and deterministically positioned nitrogen vacancy centers in diamond created by femtosecond laser writing.

Diamond's nitrogen vacancy (NV) center is an optically active defect with long spin coherence times, showing great potential for both efficient nanoscale magnetometry and quantum information processing schemes. Recently, both the formation of buried 3D optical waveguides and high-quality single NVs in diamond were demonstrated using the versatile femtosecond laser-writing technique. However, until now, combining these technologies has been an outstanding challenge. In this Letter, we fabricate laser-written photonic waveguides in quantum grade diamond which are aligned to within micron resolution to single laser-written NVs, enabling an integrated platform providing deterministically positioned waveguide-coupled NVs. This fabrication technology opens the way toward on-chip optical routing of single photons between NVs and optically integrated spin-based sensing.

P31 NMR study of discrete time-crystalline signatures in an ordered crystal of ammonium dihydrogen phosphate

The rich dynamics and phase structure of driven systems includes the recently described phenomenon of the "discrete time crystal" (DTC), a robust phase which spontaneously breaks the discrete time translation symmetry of its driving Hamiltonian. Experiments in trapped ions and diamond nitrogen vacancy centers have recently shown evidence for this DTC order. Here, we show nuclear magnetic resonance (NMR) data of DTC behavior in a third, strikingly different system: a highly ordered spatial crystal in three dimensions. We devise a DTC echo experiment to probe the coherence of the driven system. We examine potential decay mechanisms for the DTC oscillations, and demonstrate the important effect of the internal Hamiltonian during nonzero duration pulses.

Three‐Photon Polarization‐Spatial Hyperparallel Quantum Fredkin Gate Assisted by Diamond Nitrogen Vacancy Center in Optical Cavity

AbstractThe construction of a near‐deterministic photonic hyperparallel quantum Fredkin (hyper‐Fredkin) gate is investigated for a three‐photon system with the optical property of a diamond nitrogen vacancy center embedded in an optical cavity (cavity‐NV center system). This hyper‐Fredkin gate can be used to perform double Fredkin gate operations on both the polarization and spatial‐mode degrees of freedom (DOFs) of a three‐photon system with a near‐unit success probability, compared with those on the double three‐photon systems in one DOF. In this proposal, the hybrid quantum logic gate operations are the key elements of the hyper‐Fredkin gate, and only two cavity‐NV center systems are required. Moreover, the possibility of constructing a high‐fidelity and high‐efficiency hyper‐Fredkin gate in the experimental environment of a cavity‐NV center system is discussed, which may be used to implement high‐fidelity photonic computational tasks in two DOFs with a high efficiency.

Substitutional nitrogen in diamond: A quantum mechanical investigation of the electronic and spectroscopic properties

This paper reports the fully-relaxed lattice and electronic structures, vibrational spectra, and hyperfine coupling constants of the substitutional Ns defect in diamond, derived from B3LYP calculations constructed from all-electron Gaussian basis sets and based on periodic supercells. Mulliken analyses of the charge and spin distributions indicate that the defect comprises a single unpaired electron distributed very largely over both the negatively-charged substituted site and one of the four nearest-neighbour carbon sites, which relaxes away from the impurity. This leads to a local C3v symmetry, with the nitrogen ‘lone pair’ lying along the C3 axis and pointed towards the ‘dangling’ bond of the shifted carbon neighbour. The calculated band gap is 5.85 eV, within which a singly-occupied, majority spin donor band is found ∼2.9 eV above the valence band, and an unoccupied, minority spin acceptor band ∼0.9 eV below the conduction band. Atom-projected densities of states of the donor and acceptor levels show that, contrary to a widespread description, ∼30% only of the donor band derives from nitrogen states per se, with the majority weight corresponding to states associated with the shifted carbon atom. The defect formation energy is estimated to be ∼3.6 eV. The calculated IR spectrum of the impurity centre shows several features between 800 and 1400 cm−1, all of which are absent in the perfect crystal, for symmetry reasons. These show substantial agreement with recent experimental observations. The calculated hyperfine constants related to the coupling of the unpaired electron spin to the N and C nuclei, for which the Fermi contact terms vary from over 200 MHz to less than 3 MHz, are generally in good agreement with the largest experimental values, both in terms of absolute magnitudes and site assignments. The agreement is less good for the smallest two values, for which the experimental assignments are less certain. The results lend support to previous suggestions that some of the weaker lines in the observed spectra, notably those below ∼7 MHz, which are difficult to assign unambiguously, might result from the overlap of lines from different sites.

Observation of Whispering-Gallery Modes in a Diamond Microsphere

We demonstrate a Type Ib diamond (nitrogen impurity of >5 ppm) microsphere whispering-gallery mode resonator in the near-infrared wavelengths between 1426.10 nm and 1427.42 nm in the 90° elastic-light-scattering for both transverse magnetic (TM) and transverse electric (TE) polarizations. The highest measured whispering-gallery mode quality-factor is in the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> , and the mode spacing is 0.332 nm both for TM and TE polarizations. The coupling of the continuous-wave tunable infrared excitation laser to the diamond microsphere is achieved by a single-mode silica optical-fiber half-coupler. Such a diamond resonator can further be used as stable optical-frequency-comb generating or lasing microcavities by exploiting the nitrogen-vacancy centers present within the diamond.

A method of measuring micro-displacement based on spin magnetic resonance effect of diamond color center

As one of the excellent piezoelectric materials, piezoelectric ceramic has been widely used to develop a highly precise displacement measurement system, which is the key part of the scanning probe system of the high-precision measuring instrument.Based on the high-precision scanning probe system, the micro/nano structures can be easily and accurately detected by the instrument system.However, due to the limitations caused by the character of hysteresis and nonlinearity, it is difficult to further improve the precision of highly precise displacement measurement system.In this work, we present a novel method to develop the highly precise displacement measurement system based on the quantum spin effect.The nitrogen vacancy (NV) color center of single crystal diamond as a sensitive element senses the change of the micro-displacement.Based on the electron spin magnetic resonance effect of diamond nitrogen vacancy color center, the variation of the magnetic field generated from the magnetic steel can be detected with high precision by the electron spin.The relative relation between the displacement and the magnetic gradient field can be used to establish the correlation model between the displacement and the electron spin resonance peak.In the experiment, a corresponding micro-displacement measurement system is established based on the cylindrical permanent magnet, according to the correlation model between the electron spin resonance effect and micro-displacement.The linear region of magnetic field gradient is designed to detect the micro-displacement.Firstly, the intensity distribution of magnetic field gradient is measured by the gauss meter.As the measurement results show, the gradient value is -7.77 Gauss/mm along the core axis of cylindrical permanent magnet, and the intensity of magnetic field gradient distribution region is linear in the millimeter range.Meanwhile, the electron spin magnetic resonance peak of diamond nitrogen vacancy color center is achieved by the optically detected magnetic resonance technology.The electron spin magnetic resonance peak is approximately 2.79 MHz/Gauss in the magnetic field achieved by the fluorescence spectrum of diamond nitrogen vacancy color center, attributed to the relation model between Zeeman splitting effect and magnetic field. In the experiment, the electron spin magnetic resonance signal of diamond nitrogen vacancy color center is lockedin by the demodulation method to achieve the change of micro-displacement.As the results show, the sensitivity is about 16.67 V/mm at the corresponding demodulation frequency of 3000.56 MHz.By the calculation, the resolution of micro-displacement measurement system is about 60 nm based on our method.It proves out a high precision and well reliability method to detect the micro-displacement.By the further theoretical calculation, based on the electron spin effect, the detection resolution of our method can be enhanced up to sub-nanometer scale by reducing the distance between the NV color center and the magnet.It presents a new research direction and field for the micro-displacement detection system.

Bright off-axis directional emission with plasmonic corrugations.

In this work, a new plasmonic bulls-eye structure is introduced to efficiently harvest the emitted light from diamond nitrogen vacancy (NV) centers. We show that the presence of a simple metal sub-layer underneath of a conventional bulls-eye antenna, separated by a dielectric layer, results in the spontaneous emission enhancement and increment in out-coupled light intensity. High Purcell factor is accessible in such a structure, which consequently boosts efficiency of the radiated light intensity from the structure. The structure shows considerable enhancement in far-field intensity, about three times higher than that of a one-side corrugated (conventional) optimized structure. In addition, we study for the first time asymmetric structures to steer emitted beams in two-axis. Our results show that spatial off-axial steering over a cone is approachable by introducing optimal asymmetries to grooves and ridges of the structure. The steered light retains a level of intensity even higher than conventional symmetric structures. A high value of directivity of 16 for off-axis steering is reported.

Tracking sources of selected diamonds from Southern Africa based on carbon isotopic and chemical impurities

AbstractThe morphological, chemical impurities and carbon isotope properties of diamonds may reveal subtle details of their mantle source and growth characteristics, supporting efforts towards identifying their original place of harvesting. Here we investigate the mantle carbon and nitrogen sources and growth patterns from selected diamonds mined from four kimberlites: macro-sized diamonds from River Ranch kimberlite in Zimbabwe and the Swartruggens and Klipspringer kimberlitic deposits from South Africa, and micro-sized diamonds from the Klipspringer and Premier kimberlite intrusions in South Africa. Type IaAB diamonds are found in all the samples; Type IaB diamonds only occur in samples from the Swartruggens, River Ranch and Premier kimberlites. A single Type II diamond (nitrogen below the detection limit) was also observed in the River Ranch and Premier kimberlites. Both the micro- and macro-sized diamonds from Klipspringer have similar nitrogen contents. Based on the % B-defect, the diamonds from Klipspringer are grouped into low- and high-nitrogen aggregates (i.e. % of B-defect &lt;40% and &gt;56%, respectively) that likely represent two different diamond forming episodes. Time averaged mantle storage temperatures for Type IaAB diamonds are calculated to have been: 1060°C for Swartruggens; 1190°C for River Ranch; 1100°C (low aggregated); and 1170°C (highly aggregated) for Klipspringer, and 1210°C for Premier diamonds. The CL-images of the River Ranch, Klipspringer and Premier diamonds reveal multi-oscillatory growth zones. The carbon isotopic analyses on the diamonds reveal an average δ13CVPDB value of: -4.5‰ for Swartruggens; -4.7‰ for River Ranch; -4.5‰ for Klipspringer; and -3‰ for Premier. With the exception of the diamond from Premier, the average δ13C value of the diamonds are similar to the average δ13C value of the mantle (-5‰), which is similar to the occurrence of diamonds in the other kimberlites. The internal carbon isotopic variation of individual diamonds from Swartruggens, Klipspringer and Premier are less than 4‰, which is similar to the variability of most other diamond occurrences reported from elsewhere in the world. Up to 6.7‰ internal carbon isotopic variation was observed in a single diamond from River Ranch. The internal carbon isotopic studies of the diamonds reveal that the primary carbon in the Swartruggens and Klipspringer was derived from an oxidation of CH4-bearing fluid, whereas in the River Ranch the primary carbon was derived from the reduction of carbonate-or CO2-bearing fluids. The Swartruggens diamonds also reveal a secondary carbon sourced from a reduction of CO2- or carbonate-rich fluid or melt. Diamonds from Klipspringer exhibit a cyclic change in δ13C values that reflects fluctuation in a complex mantle perturbation system or periodic change in fugacity of the mantle. Based on this study, we conclude that, in principle, a selected range of diamond signatures might be used to fingerprint their origins; especially when linked to their other physical properties such as a low temperature magnetic signature.

The transition zone as a host for recycled volatiles: Evidence from nitrogen and carbon isotopes in ultra-deep diamonds from Monastery and Jagersfontein (South Africa)

Sublithospheric (ultra-deep) diamonds provide a unique window into the deepest parts of Earth's mantle, which otherwise remain inaccessible. Here, we report the first combined C- and N-isotopic data for diamonds from the Monastery and Jagersfontein kimberlites that sample the deep asthenosphere and transition zone beneath the Kaapvaal Craton, in the mid Cretaceous, to investigate the nature of mantle fluids at these depths and the constraints they provide on the deep volatile cycle.Both diamond suites exhibit very light δ13C values (down to −26‰) and heavy δ15N (up to +10.3‰), with nitrogen abundances generally below 70at.ppm but varying up to very high concentrations (2520at.ppm) in rare cases. Combined, these signatures are consistent with derivation from subducted crustal materials. Both suites exhibit variable nitrogen aggregation states from 25 to 100% B defects. Internal growth structures, revealed in cathodoluminescence (CL) images, vary from faintly layered, through distinct cores to concentric growth patterns with intermittent evidence for dissolution and regular octahedral growth layers in places.Modelling the internal co-variations in δ13C-δ15N-N revealed that diamonds grew from diverse C-H-O-N fluids involving both oxidised and reduced carbon species. The diversity of the modelled diamond-forming fluids highlights the complexity of the volatile sources and the likely heterogeneity of the deep asthenosphere and transition zone. We propose that the Monastery and Jagersfontein diamonds form in subducted slabs, where carbon is converted into either oxidised or reduced species during fluid-aided dissolution of subducted carbon before being re-precipitated as diamond. The common occurrence of recycled C and N isotopic signatures in super-deep diamonds world-wide indicates that a significant amount of carbon and nitrogen is recycled back to the deep asthenosphere and transition zone via subducting slabs, and that the transition zone may be dominated by recycled C and N.

Robust hyperparallel photonic quantum entangling gate with cavity QED.

Under the balance condition of the diamond nitrogen vacancy center embedded in an optical cavity as a result of cavity quantum electrodynamics, we present a robust hyperparallel photonic controlled-phase-flip gate for a two-photon system in both the polarization and spatial-mode degrees of freedom (DOFs), in which the noise caused by the inequality of two reflection coefficients can be depressed efficiently. This gate doubles the quantum entangling operation synchronously on a photon system and can reduce the quantum resources consumed largely and depress the photonic dissipation efficiently, compared with the two cascade quantum entangling gates in one DOF. It has a near unit fidelity. Moreover, we show that the balance condition can be obtained in both the weak coupling regime and the strong coupling regime, and the high-fidelity quantum gate operation is easier to be realized in the balance condition than the ones in the ideal condition in experiment.

Secondary Ion Mass Spectrometry Analyses of Diamond and Moissanite in Ophiolite

The Cameca 1280‐HR large geometry SIMS instrument is a highly versatile analytical tool which can support a broad range of geochemical applications. Research using the Potsdam 1280 instrument focuses primarily on isotope ratio determinations in geomaterials. Optimized measurement protocols have already been established for δ18O determinations in zircon, and we are also working towards routine oxygen isotope determinations for quartz, calcite, mica, apatite and titanite. The primary challenge in developing such measurement systems are the identification and characterization of suitable reference materials (RMs), and this is made particularly challenging due to the matrix dependent ion yields of the SIMS ion source.Here we wish to report our progress towards establishing new analytical protocols for the determination of δ13C in both diamond and moissanite. In the case of diamond, our facility possesses three natural RMs with which we are able to produce data with a typical analytical repeatability of ∼0.15 ‰ (1sd). An inter‐comparison of our three diamond RMs demonstrates an overall data quality of better than 0.5‰ in terms of systematic offset between the various materials characterized using gas source mass spectrometry (Palot et al., 2012). A single such δ13C determination in diamond requires 80 s of data acquisition and involves a test portion mass of ∼400 pg of material. In‐house diamond reference materials for δ15N calibration allow us to measure this isotopic system to a total analytical uncertainty of ± 1.6 ‰ (1sd) at nitrogen concentrations reaching down to 250 μg/g. Due to the relatively low abundance of nitrogen in diamonds, such isotope ratio determinations require around 9 minutes of data collection.With respect to δ13C determinations in moissanite, we use a kimberlitic SiC as calibrant (Mathez et al., 1995), on which we achieve a repeatability of ∼0.2 ‰ (1sd) on a ∼350 pg test portion mass. Total data acquisition time for such measurements is 80 s. We are currently in the process of developing a second moissanite RM based on a synthetic, coarse‐grained powder. We will also investigate this new material for its δ30Si characteristics.

Lithospheric diamond formation as a consequence of methane-rich volatile flooding: An example from diamondiferous eclogite xenoliths of the Karelian craton (Finland)

A collection of 61 xenocrystic and 12 eclogite xenolith-derived diamonds from the 600Ma Lahtojoki kimberlite in central Finland has been investigated. Calculated pressure and temperature conditions for the diamondiferous eclogites are in excess of 5.5GPa and 1300°C, suggesting residence depths greater than 180km, near the base of the Karelian cratonic mantle lithosphere. Geochemically, the eclogite xenoliths have gabbroic compositions showing positive Eu and Sr anomalies, relatively low ΣREE and elevated Al2O3 contents, yet garnets have ambiguous δ18O values of 5.7‰ and 5.9‰. Gabbroic eclogite formation could therefore be linked to either subduction processes during the 1.9Ga Svecofennian orogeny or to cumulate processes during 2.1Ga rift-induced magmatism. Determination of the oxygen fugacity of Lahtojoki eclogite xenoliths from both this work and previous studies suggests that diamond-bearing eclogites may be more reduced (ΔFMQ-3.5) compared to barren eclogites (ΔFMQ-1.7).While recycled oceanic crust protoliths for the eclogites remain a possibility, the carbon isotopic compositions and nitrogen abundances of the Lahtojoki diamonds indicate mantle-derived volatile sources. All diamonds (i.e., loose and eclogite xenolith-derived) display a restricted range of δ13C values from −7.8‰ to −3.7‰ that overlaps with the carbon isotopic composition of Earth’s mantle. The Lahtojoki diamond δ13C values form a negatively skewed distribution, indicating diamond growth from reduced mantle-derived carbon sources such as methane- (CH4) bearing fluids. Nitrogen contents of the Lahtojoki diamonds range from 40 to 1830atomic ppm with a mean of ∼670atomic ppm; these elevated nitrogen contents combined with the close association to eclogites suggest an eclogitic or crustal volatile source. However, the Karelian craton was periodically intruded by ultramafic alkaline magmas since at least 1.8Ga, noting in particular the occurrence of phlogopite-rich kimberlites and olivine lamproites between 1200 and 700Ma. We argue that this punctuated volatile-rich magmatism simultaneously metasomatised the cratonic mantle lithosphere, forming nitrogen enriched phlogopite-bearing metasomes. We propose that reduced, carbon-bearing and nitrogen-rich fluids were remobilized to form the Lahtojoki diamonds. The diamond-forming event(s) most probably occurred during or shortly prior to the entraining kimberlite magmatism as indicated by the diamond nitrogen aggregation systematics. Involvement of reduced diamond-forming fluids is supported by both the negative skewness of Lahtojoki diamond δ13C values and the more reduced nature of the diamondiferous Lahtojoki eclogites compared with their more oxidized barren counterparts. Our results from the diamondiferous eclogites derived from the deepest parts of the Karelian cratonic mantle root are in support of methane being the stable carbon volatile species at the base of thick continental lithosphere.