Nitrogen Impurities Research Articles

DIAMONDS OF UKRAINE: RESULTS AND GOALS

Diamonds from Ukraine were studied in terms of their separation into their geological and genetic types, distribution and occurrence, the ages of their host rocks, and their nature in Proterozoic and Neogene age sediments. The diamonds are variable in morphology, internal structure, concentration and degree of aggregation of nitrogen centers, carbon isotopes and mineral inclusions. Placer diamonds, primarily from Neogene sands, are anomalous in many respects. They are mostly extremely small, polyhedral, and morphologically diverse showing octahedral, rhombic dodecahedral and cubic forms and they have various colors. In addition to the large heterogeneity in nitrogen concentrations, many diamonds are characterized by a low degree of aggregation of nitrogen centers, which indicates short mantle residence times. Depending on the nitrogen impurity content, the degree of aggregation of nitrogen centers and the possible temperatures of crystallization, several types of diamonds are distinguished in the studied sedimentary placers. According to new isotope-geochemical data, placer diamonds are characterized by a wide range of carbon isotopic composition. This may indicate isotopic inhomogeneity of diamond carbon, different modes of formation and chemical variability in their source regions. Impact diamonds from meteorite craters and Neogene sedimentary deposits of Ukraine are paramorphoses from graphite with similar morphological, isotopic and structural characteristics. The goals of future research of Ukrainian diamonds are discussed.

A review on forms and concentrations of nitrogen impurities in diamond

A review on forms and concentrations of nitrogen impurities in diamond

Ultrafast nonthermal NV center formation in diamond

NV color centers in diamond exhibit a variety of interesting properties which make them suitable for different technological applications, like quantum sensing, secure message encryption and biological imaging. They can also be used as qubits. In order to construct arrays of NV centers for quantum computing, it is necessary to maximize interqubit interactions and, at the same time, minimize all sources of decoherence. This could possibly be achieved by using femtosecond-laser pulses in the production process. In this work, we performed ab initio atomistic simulations to study ultrafast nonthermal NV center formation in diamond induced by excitation through femtosecond-laser pulses. Our results indicate that the interatomic bonding properties can be modified by the excitation in such a way that a vacancy and a nitrogen impurity, initially not nearest neighbors, attract themselves and form a NV center within 250 fs after the excitation. In contrast to the thermal behavior, here, the nitrogen atom starts to oscillate nonthermally between two grid points after the excitation. For comparison to the thermal case we performed a single run in which a NV center is thermally formed at T=1500 K in one of our supercells.

Effect of nitrogen or boron impurities on the mechanical and vibrational properties of graphene nanosheets: a molecular dynamics approach

Investigation of mechanical and vibrational properties of nano-structures using the analytical methods would be time-consuming. Therefore, using a semi-empirical method would reduce the time needed to investigate materials characterisation. One of the semi-empirical approaches is molecular dynamics. In this Letter, the large-scale atomic/molecular massively parallel simulator software is used to simulate the mechanical and vibrational behaviour of a nitrogen- and boron-doped 24.04 × 51.13 A graphene nano-sheet. The natural frequencies, Young's modulus, and ultimate tensile strength (UTS) are studied. By adding impurity to the nanosheet and increasing its density, Young's modulus, UTS, and natural frequencies were decreased. The decrease in tensile properties was more significant in the case of boron impurity. When the boron (nitrogen) impurity increased to about 20%, Young's modulus and the first natural frequency were decreased 7.1% (9%) and 16.8% (73%), respectively. This illustrates that Young's modulus and natural frequencies are directly related. Therefore, for the same dimensions and boundary conditions, it is obvious that the increase in impurity content has reduced the natural frequencies of the nanostructure.

Impact of impurity seeding on the electron energy distribution function in the COMPASS divertor region

In the COMPASS tokamak, series of experiments were performed aimed at studying the impact of nitrogen, neon, and argon impurity seeding on the electron energy distribution function (EEDF) in the divertor region. The experiments were conducted in D-shaped, L-mode, deuterium plasmas. In order to obtain the radial distribution of the floating potential, ion saturation current, electron temperatures, and densities, the current-voltage characteristics were measured by Langmuir probes embedded in the COMPASS tokamak divertor. The properties of the plasma in the divertor region were measured before and during impurity seeding. Before the N2 seeding, the EEDF was bi-Maxwellian with a low-energy electron fraction with temperatures 3.5–5 eV, and a higher-energy one with temperatures in the range of 10 eV to 23 eV. During seeding with an increasing number of molecules per second, the EEDF changed from bi-Maxwellian to Maxwellian and the electron temperature decreased. The time-evolution was studied of the change in the EEDF during N2 seeding. When the seeding was carried out by a valve in the private flux region, the duration of the transition from a bi-Maxwellian to a Maxwellian EEDF was about 10–15 ms. When the N2 seeding took place through a low-field side valve, the transition from a bi-Maxwellian to a Maxwellian EEDF took longer −25–45 ms. The temporal evolution was also analyzed of the plasma parameters’ radial profiles when neon and argon were puffed using a valve in the divertor low-field side. The application is discussed of the probe measurements’ results to calculating the parallel heat-flux densities in the divertor region of the COMPASS tokamak.

Resonance Light Scattering by Optical Phonons in Diamond Crystal with Nitogen-Vacancy Centres

Observation of the resonance enhancement of the intensity of light scattering by optical phonons in a diamond crystal with nitogen-vacancy centres is reported. It is established that the unusual resonance with electronic transitions for optically active nitrogen impurities with both zero-phonon-lines plays the determining role in the increase in intensity of such scattering: at 575.468 nm for a neutral NV0 center and at 637.874 nm for a negatively charged NV– center. The obtained experimental data indicate the detection of a strong resonant-intensity amplification in the input scattering channel for the NV0 center and in the output channel for the NV– center.

EPR of Radiation-Induced Nitrogen Centers in Hydroxyapatite: New Approaches to the Study of Electron-Nuclear Interactions

Radiation-induced impurity nitrogen centers ( $${\text{NO}}_{3}^{{2 - }}$$ ) in nanosized powders of synthetic hydroxyapatite are studied by pulse EPR and pulse double-frequency EPR, which is named the NMR detected by electron–electron double resonance (ELDOR detected NMR, EDNMR) method. The EPR signals caused by the interaction of the electron of $${\text{NO}}_{3}^{{2 - }}$$ with the environmental nuclei (1H, 14N, and 31P) are identified, and the parameters of the hyperfine and quadrupole interactions of the electron with the 14N nuclei are determined. The possibility of using the EDNMR method in the X-band of microwave frequencies (νmw ≈ 9 GHz) at room temperature to obtain a detailed information about peculiarities of electron-nuclear interactions in hydroxyapatite is demonstrated.

Deuterium retention in tungsten and tungsten alloys exposed to pure and impurities seeding deuterium plasma

Abstract Polycrystalline tungsten (W) and four kinds of tungsten alloys were exposed to pure and impurities seeding deuterium (D) plasma to investigate the deuterium retention behaviour. The results show that D retention in W increases with the increasing fluence and incident energy, and decreases with the increase of temperature. The doping of alloying element and compounds, such as Re, La2O3, and ZrC, suppress the D retention at lower fluence but has limited effect at fluence above 2.6 × 1025 D/m2, and D inventory in these W alloys is higher than in W at temperature of 800 K. Helium (He) and nitrogen (N) impurities seeding significantly reduce D retention in tungsten. And higher N content in plasma causes more obvious reduction of D inventory. But the argon (Ar) impurity seeding leads to the increase of D retention.

Revealing nitrogen-containing species in commercial catalysts used for ammonia electrosynthesis

Stimulated by the growing demand for sustainable and/or economical distributed ammonia synthesis, the electrochemical nitrogen reduction reaction has attracted considerable interest. The nitrogen-containing impurities in commercial metal-based nitrogen reduction reaction catalysts such as metal oxides and metallic irons have, however, been overlooked. Herein we report the presence of nitrogen-containing species in NOx− or nitrides at substantial levels revealed from many commercial catalysts. We call attention to the necessity to screen the NOx−/nitrides impurities in commercial catalysts, as the nitrogen impurities are not commonly listed in vendors’ assay documents. A simple two-step procedure (alkaline/acidic treatment followed by HPLC/UV–vis analysis) is recommended as a reliable protocol for screening NOx−/nitrides impurities in catalyst materials. A case analysis is also carried out on the previously reported H2O–NaOH–KOH system with both 15N-isotopic labelling and nitrogen elemental tracking, reassigning the true nitrogen source of the electrochemically produced NH3 from gaseous N2 to nitrogen-containing impurities in catalysts. The electrochemical nitrogen reduction reaction has recently attracted significant interest, but the true source of ammonia formation remains sometimes unclear. This Analysis reports a systematic investigation of the presence of nitrogen-containing species in a number of commercial catalysts, revealing substantial levels of NOx− and nitrides impurities for some of them.

Nano-tendril bundles behavior under plasma-relevant electric fields

The appearance of unipolar arcs is a negative phenomenon that occurs among plasma-wall interaction processes in thermonuclear devices. Nano-tendril bundles (NTBs) can be formed on a plasma-facing surface of tungsten after irradiation by helium plasma that contains impurities of neon or nitrogen. These structures can increase the probability of unipolar arcing because of significant electron emission under a relatively small applied electric field of several kV/mm. The electron emission can appear due to sufficient field enhancement factor that can be up to several thousand. Furthermore, NTBs can be easily overheated, which leads to initiation of the thermofield emission, consequently triggering explosive emission because of intensive heating by Joule source, even without any additional external power load. This paper shows the results of the field enhancement factor estimations, as well as the critical field strength for NTBs when they can collapse because of explosive electron emission caused by Joule heating. The results were obtained by numerical simulations in COMSOL Multiphysics© and experimentally in a vacuum diode.

Visible-Light Activation of Photocatalytic for Reduction of Nitrogen to Ammonia by Introducing Impurity Defect Levels into Nanocrystalline Diamond.

Nitrogen impurity has been introduced in diamond film to produce a nitrogen vacancy center (NV center) toward the solvated electron-initiated reduction of N2 to NH3 in liquids, giving rise to extend the wavelength region beyond the diamond’s band. Scanning electron microscopy and X-ray diffraction demonstrate the formation of the nanocrystalline nitrogen-doped diamond with an average diameter of ten nanometers. Raman spectroscopy and PhotoLuminescence (PL) spectrum show characteristics of the NV0 and NV− charge states. Measurements of photocatalytic activity using supraband (λ < 225 nm) gap and sub-band gap (λ > 225 nm) excitation show the nitrogen-doped diamond significantly enhanced the ability to reduce N2 to NH3 compared to the polycrystalline diamond and single crystal diamond (SCD). Our results suggest an important process of internal photoemission, in which electrons are excited from negative charge states into conduction band edges, presenting remarkable photoinitiated electrons under ultraviolet and visible light. Other factors, including transitions between defect levels and processes of reaction, are also discussed. This approach can be especially advantageous to such as N2 and CO2 that bind only weakly to most surfaces and high energy conditions.

Ion beam modification of the Ni-Si solid-phase reaction: The influence of substrate damage and nitrogen impurities introduced by ion implantation

We report on the growth of thin NiSi films via the thermal reaction of Ni layers (13–35 nm) with Si(100) substrates modified by ion implantation. By introducing substrate damage or nitrogen impurities prior to the solid-phase reaction, several properties of the NiSi films can be modified: the formation temperature, texture, diffusion-limited growth rate and morphological stability. As some of the modifications to the NiSi films are rooted in the early silicide phases preceding the NiSi phase, particularly its formation temperature, special attention is devoted to the growth of the amorphous Ni-Si alloy and the crystalline δ-Ni2Si and θ-Ni2Si phases.We employed a number of experimental techniques, including in situ synchrotron x-ray diffraction (XRD), in situ Rutherford backscattering spectrometry (RBS), in situ sheet resistance measurements, ex situ ion beam channelling and ex situ pole figure measurements. We show that both the formation temperature of the NiSi films and the intensity of epitaxial and axiotaxial components of the NiSi texture can be either lowered or raised by selecting appropriate implantation conditions. Agglomeration of the NiSi films at high temperature (> 700 °C) can be slowed down, either by slowing down the mobility of the Ni and Si atoms, or by removing the morphologically destabilizing axiotaxial texture. Our results emphasize the strong interwoven nature of phase formation, texture and morphological degradation. We illustrate that the kinetics of the early stages of thin film reactions consist of more than just diffusion, i.e. nucleation can also play a crucial role.

The Nature and Compositional Peculiarities of Volcanogenic Diamonds

Abstract —We have studied volcanogenic diamonds in the context of a discussion of their genesis, including some assumption on their artificial origin. The carbon isotope composition of diamonds collected from the eruption products of Tolbachik volcano (δ13CVPDB from –22 to –29‰) is within the range of the δ13CVPDB values of natural diamonds, including those from kimberlites. The δ15NAir values of the Tolbachik diamonds, measured for the first time (–2.58 and –2.32‰), correspond to δ15NAir of volcanic gases and differ from that of atmospheric nitrogen (δ15NAir = 0‰), which may be expected in synthetic diamonds. In the studied volcanogenic diamonds, as in synthetic ones, the nitrogen impurity is unaggregated. However, such an unaggregated form of nitrogen is specific to many natural diamonds (e.g., variety II diamonds, according to Orlov’s classification). Impurity elements (Cl, F, O, S, Si, Al, Ca, and Na) are locally concentrated in volcanogenic diamonds; they are a constituent of micro- and nanoinclusions in them. The high contents of F and Cl in the studied diamonds are correlated with the composition of volcanic gases; there is no reason to expect a similar correlation in synthetic diamonds. Moreover, the studied cube-octahedral Tolbachik diamonds have a number of accessory forms, some of which are not observed in synthetic diamonds. Their surfaces are frequently covered with films composed of Mg–Fe and Ca–Mg silicates, aluminosilicates, sulfates, metal alloys, and native Al. Mineral inclusions in the studied diamonds are Mn–Ni–Si alloys and silicides varying in composition from (Mn,Ni)4Si to (Mn,Ni)5Si2, Mn5Si2, and pure Mn silicide MnSi. Summing up the obtained data, we conclude that volcanogenic diamonds form in a strongly reducing environment, in which silicides and native metals and their alloys are stable. The predominant cube-octahedral morphology of these diamonds and the unaggregated nitrogen impurity point to their short-term residence under high-temperature conditions. This makes them similar, to some extent, to synthetic diamonds. There are, however, clear differences as well. Volcanogenic diamonds are similar in compositional peculiarities, including isotope compositions, to natural diamonds that form under most unfavorable conditions, such as cuboids, balases, carbonado, and some diamonds of the eclogite paragenesis. They also resemble diamonds found in situ in harzburgite and chromitite of ophiolites. This suggests a specific mechanism of formation of both volcanogenic and ophiolitic diamonds in the oceanic lithosphere.

Effects of nitrogen impurity on the atmospheric pressure helium plasma jets exposed to a nitrogen environment

In this study, the effects of small nitrogen impurity on the behaviors of helium APPJs propagating into nitrogen surrounding gas are investigated numerically based on a two-dimensional fluid model. The results show that the addition of N2 impurity can change the APPJ length and there exists an optimal N2–helium ratio which enables the plasma jet to reach the maximum length. This is attributed to the variation of helium mole fraction and the ionization rate in the helium flow channel resulting from N2 impurity. Like the APPJ propagating into ambient air, with the addition of nitrogen, the profile of APPJ exposed to a nitrogen environment varies from an annular shape to a nearly uniform structure, though their reaction chemistries inside the jet effluent differ remarkably. Also, under different impurity concentrations, the density distribution and evolution of active species throughout the effluent of APPJ, as well as their dominant reaction pathways, behave differently. The physics mechanisms underlying these behaviors are discussed in detail.

Decoration of growth sector boundaries with nitrogen vacancy centers in as-grown single crystal high-pressure high-temperature synthetic diamond

Large (> 100 mm$^3$), relatively pure (type II) and low birefringence single crystal diamond can be produced by high pressure high temperature (HPHT) synthesis. In this study we examine a HPHT sample of good crystalline perfection, containing less than 1 ppb (part per billion carbon atoms) of boron impurity atoms in the {001} growth sector and only tens of ppb of nitrogen impurity atoms. It is shown that the boundaries between {111} and {113} growth sectors are decorated by negatively charged nitrogen vacancy centres (NV$^-$): no decoration is observed at any other type of growth sector interface. This decoration can be used to calculated the relative {111} and {113} growth rates. The bulk (001) sector contains concentrations of luminescent point defects (excited with 488 and 532 nm wavelengths) below 10$^{11}$ cm$^{-3}$ (10$^{-3}$ ppb). We observe the negatively charged silicon-vacancy (SiV$^-$) defect in the bulk {111} sectors along with a zero phonon line emission associated with a nickel defect at 884 nm (1.40 eV). No preferential orientation is seen for either NV$^-$ or SiV$^-$ defects, but the nickel related defect is oriented with its trigonal axis along the <111> sector growth direction. Since the NV$^-$ defect is expected to readily re-orientate at HPHT diamond growth temperatures, no preferential orientation is expected for this defect but the lack of preferential orientation of SiV$^-$ in {111} sectors is not explained.

Co-doping with boron and nitrogen impurities in T-carbon

Previously, Ren et al. [Chem. Phys. 518, 69–73, 2019] reported the failure of Boron-Nitrogen (B-N) co-doping as inter B-N bond in T-carbon. In present work, a B-N atom pair is introduced in T-carbon as p-n co-dopant to substitute two carbon atoms in the same carbon tetrahedron and form an intra B-N bond. The stability of this doping system is verified from energy, lattice dynamic, and thermodynamic aspects. According to our B3PW calculations, B-N impurities in this situation can reduce the band gap of T-carbon from 2.95 eV to 2.55 eV, making this material to be a promising photocatalyst. Through the study of its transport properties, we can also conclude that B-N co-doping cannot improve the thermoelectric performance of T-carbon.

Spectroscopic investigation of a neon-operated DBD at atmospheric and intermediate pressure

A sinusoidally-excited Venturi-DBD operating in neon has been investigated. The Ne(1s5) metastable density has been quantified spatially resolved using laser atomic absorption spectroscopy for different pressure levels. Density values of up to 7 · 1016 m−3 could be determined at atmospheric pressure and up to 3 · 1016 m−3 at 100 mbar. For all investigated parameters, the Ne(1s5) density was found to be distinctly higher in the proximity of the cathode than in the anode region. Complementary investigations of the discharge development using phase-resolved optical emission spectroscopy complete the characterization of the device. The discharge was found to show typical properties of a glow-like discharge regarding current waveform and luminosity distribution. In addition, the influence of nitrogen and oxygen impurities and admixtures in the process gas has been determined. A substantial impact was found on both the Ne(1s5) concentration and the current waveform.

Express-analysis of nitrogen content in CVD-diamonds by FTIR-spectrometry

Natural and synthetic diamonds most often contain nitrogen impurities, which can form tens of impurity and impurity-vacancy centers in the crystal structure of diamond. At the same time, crystals properties of and possibility of their use in specific application strongly depend on the diamonds impurity composition. In this work, we investigated by the method of Fourier-transform infrared spectrometry (FTIR) the impurity composition of HPHT-diamond substrates and changes in it after the deposition of diamond layers by the CVD-method. We used Ardis 300 for deposition of diamond layers from methane-hydrogen plasma with 3% methane at a temperature of 1100 °C, a pressure of 26.7 kPa and a power of 3800 W on diamond HPHT-substrates containing from 70 to 200 ppm of nitrogen. The proposed technique makes possible to study the integral content of impurities in diamond, which will make it possible to quickly evaluate the result of the diamond layers synthesis and conclude about the possibility of their application in various fields of science and technology, as well as use in jewelry industry.

Enhanced interfacial reaction of precursor and low temperature substrate in HfO2 atomic layer deposition with highly Ar diluted O2 plasma

The internal energy of metastable oxygen atoms in highly Ar diluted oxygen plasma was utilized in the initial stage of the atomic layer deposition of HfO2 on SiO2/Si(100) at low temperature of 150 °C. The highly Ar dilute oxygen plasma enhanced the oxidation of the incomplete chemisorption state of the precursor at low temperature, successfully formed Hf silicate interface, and decreased the impurity nitrogen atoms in the HfO2 film compared to the pure oxygen plasma ALD. Residual nitrogen atoms in the film were found to cause excessive precursor adsorption. The results of plasma emission spectroscopy and ion saturation current measurements show that the highly Ar-diluted O2 plasma can increase the O radical formation rate for ion fluxes at pressures above 100 Pa. The relatively high metastable oxygen atom irradiation is thought to be responsible for the removal of HfN bonds and enable ALD on low temperature substrates. Atomic force microscopy showed that the root mean square roughness in the high Ar dilution sample was 0.093 nm, indicating high flatness.

On influence of various substances dissolved in water on hematological parameters

Content of marine animaIs in captivity Ieads to the accumuIation of waste products in the artificiaI habitat, as weII as funds used for the handIing of pooIs in different concentrations. WideIy used disinfectants containing chIorine Iead to the formation of chIorinated acid in the water pooIs and subsequentIy the emergence of mono- and trichIoramines, as weII as a Iarge number of nitrates and nitrites are determined in it. These substances have a strong enough impact on bioIogicaI objects: toxic, mutagenic, etc. They affect different systems: centraI nervous system, cardiovascuIar, reduces the oxygen capacity of the bIood, impaired function of the Iiver and kidneys. In the intestine of bottIenose doIphins, depending on the IeveI of urea, various forms of chIorine in the water, there are changes in the ratio of normaI microflora, which Ieads to dysbiosis. To determine the effect of these groups of substances, studies were conducted to determine the parameters in the bIood of bottIenose doIphins: aIanine transaminase, aspartate transaminase, gamma-gIutamyItranspeptidase, Iactate dehydrogenase and aIkaIine phosphotase. The conducted researches on two groups of experimentaI bottIenose doIphins aIIowed to estabIish certain reference points for an assessment of admissibIe indicators of the contents in sea water of pooIs of impurity chIorine and nitrogen containing and connections, IeveI of nitrites in water - no more than 0,2 mg/I, ammonium - 0,6 mg/I and urea - 1,5 mg/I.