Nitrogen Impurity Concentration Research Articles

Investigation of the dynamics of ionization induced injected electrons under the influence of beam loading effects

In laser-driven wakefield, ionization induced injection is an efficient way to inject electrons in the plasma wave. A detailed study on the beam dynamics under the influence of beam loading effects, which can be controlled by the concentration of nitrogen impurity introduced in the hydrogen gas was conducted. For a specific value of this percentage, the final energy of the high-energy electron bunch becomes nearly independent of the trapped positions, thus leading to a small energy dispersion. We also show that the final beam emittance is mainly determined by the injection process.

Creating nitrogen–vacancy ensembles in diamond for coupling with flux qubit**Project supported in part by the National Natural Science Foundation of China (Grant Nos. 91321208, 11574386, 11374344, and 11574380), the National Basic Research Program of China (Grant Nos. 2014CB921401 and 2016YFA0300601), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB07010300).

Hybrid quantum system of negatively charged nitrogen−vacancy (NV−) centers in diamond and superconducting qubits provide the possibility to extend the performances of both systems. In this work, we numerically simulate the coupling strength between NV− ensembles and superconducting flux qubits and obtain a lower bound of 1016 cm−3 for NV− concentration to achieve a sufficiently strong coupling of 10 MHz when the gap between NV-ensemble and flux qubit is 0. Moreover, we create NV− ensembles in different types of diamonds by 14N+ and 12C+ ion implantation, electron irradiation, and high temperature annealing. We obtain an NV− concentration of 1.05 × 1016 cm−3 in the diamond with 1-ppm nitrogen impurity, which is expected to have a long coherence time for the low nitrogen impurity concentration. This shows a step toward performance improvement of flux qubit-NV− hybrid system.

Spin coherence and 14N ESEEM effects of nitrogen-vacancy centers in diamond with X-band pulsed ESR

Pulsed ESR experiments are reported for ensembles of negatively-charged nitrogen-vacancy centers (NV−) in diamonds at X-band magnetic fields (280–400mT) and low temperatures (2–70K). The NV− centers in synthetic type IIa diamonds (nitrogen impurity concentration <1 ppm) are prepared with bulk concentrations of 2 ⋅ 1013 cm−3 to 4 ⋅ 1014 cm−3 by high-energy electron irradiation and subsequent annealing. We find that a proper post-radiation anneal (1000°C for 60min) is critically important to repair the radiation damage and to recover long electron spin coherence times for NV−s. After the annealing, spin coherence times of T2=0.74ms at 5K are achieved, being only limited by 13C nuclear spectral diffusion in natural abundance diamonds. By measuring the temperature dependence of T2 in the under-annealed diamonds (900°C) we directly extract the density (1014−16 cm−3) and activation energy (2.5meV) of unannealed defects responsible for the faster NV− decoherence. At X-band magnetic fields, strong electron spin echo envelope modulation (ESEEM) is observed originating from the central 14N nucleus, and we extract accurate 14N nuclear hypefine and quadrupole tensors. In addition, the ESEEM effects from two proximal 13C sites (second-nearest neighbor and fourth-nearest neighbor) are resolved and the respective 13C hyperfine coupling constants are extracted.

Diamond crystallization in a CO2-rich alkaline carbonate melt with a nitrogen additive

Diamond crystallization was experimentally studied in a CO2-bearing alkaline carbonate melt with an increased content of nitrogen at pressure of 6.3GPa and temperature of 1500°C. The growth rate, morphology, internal structure of overgrown layers, and defect-impurity composition of newly formed diamond were investigated. The type of growth patterns on faces, internal structure, and nitrogen content were found to be controlled by both the crystallographic orientation of the growth surfaces and the structure of the original faces of diamond seed crystals. An overgrown layer has a uniform structure on the {100} plane faces of synthetic diamond and a fibrillar (fibrous) structure on the faceted surfaces of a natural diamond cube. The {111} faces have a polycentric vicinal relief with numerous twin intergrowths and micro twin lamellae. The stable form of diamond growth under experimental conditions is a curved-face hexoctahedron with small cube faces. The nitrogen impurity concentration in overgrown layers varies depending on the growth direction and surface type, from 100 to 1100ppm.

Quantification of nitrogen impurity and estimated Orowan strengthening through secondary ion mass spectroscopy in aluminum cryomilled for extended durations

The strength of aluminum alloys and composites processed through powder metallurgy can be improved through the addition of nano-scale dispersoids introduced during the cryomilling process. Quantification of Orowan strengthening from these dispersoids requires a reliable measurement of the impurity concentration. Secondary ion mass spectrometry (SIMS) was used to quantify the nitrogen impurity concentration using a 14N ion implanted standard. An analytical approach is devised to determine the nitrogen concentration of an aluminum alloy and composite based on SIMS measurements. Results are compared to the measurements carried out by gas fusion analysis. An increase in nitrogen concentration was observed with an increase in cryomilling time up to 72h. The nitrogen concentration varied from 1.64±0.17at% (0.80±0.08wt%) to 19.12±1.10at% (13.17±0.71wt%) for the 8h and 72h cryomilled nanocrystalline AA5083, respectively. Assuming that all nitrogen reacts to form dispersoids, the nitrogen concentration determined was used to calculate the volume and weight fractions of dispersoids, which in turn was used to estimate the strengthening contribution via Orowan strengthening. Orowan strengthening was calculated using dispersoids of 3, 9 and 15nm. The range of Orowan strengthening contribution was estimated, in MPa, to be from 7.69±0.78 to 3.03±0.31 for the 8h nanocrystalline AA5083 sample, and 154.97±10.29 to 61.09±4.06 for the 72h nanocrystalline AA5083 sample.

Diamond crystallization from a tin–carbon system at HPHT conditions

Diamond crystallization from the tin–carbon system has been studied at 7GPa and temperatures ranging from 1600 to 1900°C with reaction times from 1 to 20h. Both diamond growth on the seed crystals and diamond spontaneous nucleation were established, providing evidence for the catalytic ability of tin. A distinctive feature of the Sn–C system is the existence of a significant induction period preceding diamond spontaneous nucleation. Temperature and kinetics are found to be the main factors governing diamond crystallization process. The minimum parameters of diamond spontaneous nucleation are determined to be 7GPa, 1700°C and 20h. The stable form of diamond growth is octahedron and it does not depend on temperature. Synthesized diamonds contain high concentrations of nitrogen impurities up to about 1600ppm.

Effect of nitrogen impurity on etching of synthetic diamond crystals

The etching rate and the morphology of dislocation etch pits on {111} faces of synthetic diamond crystals with nitrogen impurity content varying from 1ppm to 600ppm were studied. Etch pits on nitrogen-containing diamond crystals are found to be of triangular shape; their lateral walls are formed by planar faces. Etch pits on nitrogen-gettered diamonds have a shape of a convex triangle and the profile varying from the maximum inclination angle in the pit center to zero at a large distance from it. The rate of diamond etching (oxidation) rises as the content of nitrogen impurity in diamond crystals increases from 1ppm to 200ppm and subsequently decreases twice at nitrogen concentration of 600ppm. These regularities of etching agree well with the existing models of crystal dissolution in the presence of impurities. It is assumed that nitrogen atoms incorporated in the diamond lattice can be regarded on the crystal surface as atoms of a stable inhibiting impurity, which change the rate and character of etching of diamond crystals.

Diamond–tungsten based coating–copper composites with high thermal conductivity produced by Pulse Plasma Sintering

Abstract Diamond powder with an average particle size of 200 μm was coated with tungsten and tungsten carbide coatings of thickness 260 nm. Pulse Plasma Sintering (PPS) was then used to fabricate copper/diamond composites with a 1:1 volume ratio. The composition and structure of the composites, their components and interfacial phases were studied by XRD, SEM, X-ray, FTIR and Raman spectroscopy. The methods to assess the thermal conductivity of diamond based on nitrogen impurity content determined from FTIR spectrum were examined. The ITC was calculated from the measured composite conductivity using comparatively the Differential Effective Medium (DEM) model and the Hasselman–Johnson (H–J) equation. The composite with W coated diamond particles had the thermal conductivity of 690 W/(m K) and the ITC of 45 MW/(m2 K). The PPS process induced chemical reactions – carbidization of the coatings on diamond W → W2C → WC – when forming the filler/matrix interface within the composite. Raman spectroscopy was able to detect the formation of a thin (∼10–100 nm) restructured sublayer of carbon which is transitional from diamond to graphite in result of the deposition of the tungsten coating on the facets of the diamond particles, a sublayer of turbostratic carbon being formed in result of subsequent sintering.

Temperature dependence of the Raman line width in diamond: Revisited

Despite more than 60‐year history of Raman scattering studies of diamond, considerable discrepancies between values of the Raman linewidth and its temperature dependence reported by different authors still exist. In this paper we report on the Raman scattering measurements performed for synthetic diamond crystals with nitrogen impurity content below 1 ppm (type IIa) and dislocation density 102–103 cm−2 over the temperature range of 50–1000 K. The spectra were recorded with a high spectral resolution (~0.3 cm−1) and thoroughly analyzed to account for the instrumental response. The results demonstrate unequivocally that the temperature dependence of the Raman line width is well described by a model which assumes both three‐phonon and four‐phonon anharmonic processes. Elimination of the discrepancies in the line width description advances the Raman scattering technique in the characterization of diamonds with different crystalline quality, defect and/or impurity concentration. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Photoluminescence studies of growth-sector dependence of nitrogen distribution in synthetic Ib diamond

The photoluminescence technology previously employed to investigate the boron distribution of type IIb diamond has now been applied to study the nitrogen distribution of type Ib diamond. All growth sectors were clearly distinguished by the characteristic colors and the brightness of the synthetic Ib diamond's cathodoluminescence topography. As a measure of the concentration of nitrogen impurity, the nitrogen-vacancy luminescence gave relative concentrations in different growth sectors as: the {111} sector was the highest, followed by the {311}, {100} and {511} sectors. The results were reconfirmed by the evidence of the broadened and strengthened zero phonon lines of nitrogen-vacancy center with the increase of nitrogen concentration of type Ib diamond.

Mantle–slab interaction and redox mechanism of diamond formation

Subduction tectonics imposes an important role in the evolution of the interior of the Earth and its global carbon cycle; however, the mechanism of the mantle-slab interaction remains unclear. Here, we demonstrate the results of high-pressure redox-gradient experiments on the interactions between Mg-Ca-carbonate and metallic iron, modeling the processes at the mantle-slab boundary; thereby, we present mechanisms of diamond formation both ahead of and behind the redox front. It is determined that, at oxidized conditions, a low-temperature Ca-rich carbonate melt is generated. This melt acts as both the carbon source and crystallization medium for diamond, whereas at reduced conditions, diamond crystallizes only from the Fe-C melt. The redox mechanism revealed in this study is used to explain the contrasting heterogeneity of natural diamonds, as seen in the composition of inclusions, carbon isotopic composition, and nitrogen impurity content.

Effect of nitrogen impurity on the dislocation structure of large HPHT synthetic diamond crystals

The real structure of the {111} sectors of large single synthetic diamond crystals with different nitrogen contents has been studied by the selective etching method: (1) nitrogen-gettered diamonds with nitrogen impurity content at a level of 1–2ppm, (2) diamond crystals grown without additives with nitrogen impurity of 180–220ppm and (3) diamonds nitrogen alloyed during growth up to the concentrations of 550–600ppm. All diamond crystals have been grown by the temperature gradient method using the high pressure apparatus of “split-sphere” type (BARS) at T=1350°C, P=5.7GPa and (100) seed crystal. It is found that the density of dislocations increases from 85cm−2 to 4.0×103cm−2 and the total length of planar defects increases from 30 to 300μm/cm2 as the nitrogen content in the crystals increases up to 600ppm. It is shown that partial dislocations are the dominant dislocations (60–90%) in all the crystals studied. A proportion of perfect dislocations increases as the nitrogen content in crystals, and correspondingly, the dislocation density increase. Possible causes for the increase of the extended defects density in the synthetic diamond crystals with the nitrogen impurity concentration rise are discussed.

Suppression of Al Memory-Effect on Growing 4H-SiC Epilayers by Hot-Wall Chemical Vapor Deposition

Al memory-effect during the growth of p-type 4H-SiC by hot-wall chemical vapor deposition method was investigated. A technique of suppressing the unintentional Al impurities incorporating into succeeding growth was developed by utilizing “site-competition” growth technology. Lowering C/Si ratio from 1 to 0.4 effectively reduced the level of incorporated Al-impurity almost 3 orders, and a high abrupt Al distribution between Al-doped layer and undoped layer was obtained at a reduction factor about 1/17000 with Al-impurity concentration in the undoped layer decreased to the range of 1015 cm-3. In addition, it is found that, due to low C/Si ratio, the nitrogen impurity concentration increases about one order of magnitude up to the order of 1016 cm-3. Combining with site-competition growth technology, the influences of growth temperature and pressure on Al-impurity concentration were examined.

Effect of H2O on Diamond Crystal Growth in Metal–Carbon Systems

In this paper, we report on the influence of the H2O additive in the metal melt on the growth processes, morphology, and defect-and-impurity structure of diamond crystals. As a source of water, a mixture of Mg(OH)2 and SiO2 was used, which reacted under the experimental conditions following the reaction 2Mg(OH)2 + SiO2 = Mg2SiO4 + 2H2O. The main experiments were performed in the Ni0.7Fe0.3–C system at a pressure of 6 GPa, a temperature of 1370 °C, a duration of 15 h, and a H2O concentration (CH2O) ranging from 0 to 0.5 wt %. It is found that, as the H2O content increases from 0 to 0.2 wt %, the diamond morphology changes from bulky octahedra to {111} platelike crystals and then to {111} dendrites. Further increases in CH2O in the range of 0.22–0.4 wt % result in crystallization of bulky rhombic dodecahedra and then {110} dendrites. At a CH2O higher than approximately 0.43 wt %, nucleation and growth of diamond are completely terminated and only graphite crystallizes. The systematic changes in diamond growth and morphology are accompanied by a decrease in nitrogen impurity concentration in diamond from 220–230 to 40–50 ppm, an increase in the density of microinclusions, and the appearance in the IR spectra of a peak at 2840 cm–1, related to hydrocarbons.

Enhanced solid-state multispin metrology using dynamical decoupling

We use multipulse dynamical decoupling to increase the coherence lifetime (${T}_{2}$) of large numbers of nitrogen-vacancy (NV) electronic spins in room temperature diamond, thus enabling scalable applications of multispin quantum information processing and metrology. We realize an order-of-magnitude extension of the NV multispin ${T}_{2}$ in three diamond samples with widely differing spin impurity environments. In particular, for samples with nitrogen impurity concentration $\ensuremath{\lesssim}$1 ppm, we extend ${T}_{2}$ to $&gt;$2 ms, comparable to the longest coherence time reported for single NV centers, and demonstrate a tenfold enhancement in NV multispin sensing of ac magnetic fields.

Small-Angle X-ray and neutron scattering from diamond single crystals

Results of Small-Angle Scattering study of diamonds with various types of point and extended defects and different degrees of annealing are presented. It is shown that thermal annealing and/or mechanical deformation cause formation of nanosized planar and three-dimensional defects giving rise to Small-Angle Scattering. The defects are often facetted by crystallographic planes 111, 100, 110, 311, 211 common for diamond. The scattering defects likely consist of clusters of intrinsic and impurity-related defects; boundaries of mechanical twins also contribute to the SAS signal. There is no clear correlation between concentration of nitrogen impurity and intensity of the scattering.

Theoretical Investigation on Single‐Wall Carbon Nanotubes Doped with Nitrogen, Pyridine‐Like Nitrogen Defects, and Transition Metal Atoms

This study addresses the inherent difficulty in synthesizing single‐walled carbon nanotubes (SWCNTs) with uniform chirality and well‐defined electronic properties through the introduction of dopants, topological defects, and intercalation of metals. Depending on the desired application, one can modify the electronic and magnetic properties of SWCNTs through an appropriate introduction of imperfections. This scheme broadens the application areas of SWCNTs. Under this motivation, we present our ongoing investigations of the following models: (i) (10, 0) and (5, 5) SWCNT doped with nitrogen (CNxNT), (ii) (10, 0) and (5, 5) SWCNT with pyridine‐like defects (3NV‐CNxNT), (iii) (10, 0) SWCNT with porphyrine‐like defects (4ND‐CNxNT). Models (ii) and (iii) were chemically functionalized with 14 transition metals (TMs): Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag, Pt and Au. Using the spin‐unrestricted density functional theory (DFT), stable configurations, deformations, formation and binding energies, the effects of the doping concentration of nitrogen, pyridine‐like and porphyrine‐like defects on the electronic properties were all examined. Results reveal that the electronic properties of SWCNTs show strong dependence on the concentration and configuration of nitrogen impurities, its defects, and the TMs adsorbed.

Understanding of the shape-controlled synthesis of strip shape diamond under high pressure and high temperature conditions

We present the shape-controlled synthesis of strip shape diamond with stretched crystal faces along {100} or {111} direction and larger length-to-radius ratio than the conventional diamond in the designed NiFe–C system at high pressures and high temperatures (HPHT). A series of synthetic experimental results on the strip shape diamonds were obtained at different pressures and temperatures. Under the constant pressure condition, the morphology of the strip shape diamond varied with the increase of temperature obviously. Fourier transform infrared (FTIR) micro spectroscopy and Raman spectroscopy revealed that the various locations of crystal face have different nitrogen impurity concentration, and internal strain and defects in these strip shape crystals. According to these results, it can be concluded that the difference of growth rates at various crystal faces results in different crystal morphologies. Based on the growth characteristics, we suggest that composition segregation of the metal film around the growing crystal induces the formation of strip shape diamond.

Optically stimulated luminescence (OSL) and laser excited photo luminescence of electron beam treated (EBT) diamonds: Radiation sensitization and potential for tissue equivalent dosimetry

We report the first optically stimulated luminescence (OSL; blue light stimulated luminescence (BLSL) and infrared light stimulated luminescence (IRSL)) results on colored diamonds and present experimental evidence that electron beam treatment (EBT) increases the radiation sensitivity of diamonds to a level that makes them suitable for low level radiation dosimetry. A suite of seven samples was examined. These comprise a white, three brown and three yellow diamond pieces. The FT-IR spectra of these diamonds revealed the nature and concentration of nitrogen impurity. The white diamond was kept as a control. The brown and yellow (with varied saturation) diamonds were irradiated by a 1.7 MeV electron beam. These turned blue/dark green; three of them were then heated in vacuum in the temperature range of 850–900 °C for two hours. Heating turned the irradiated diamonds to lemon yellow, pink, and purple colors. The irradiated and unheated blue samples were designated as 2C and 2D. The control sample, an un-irradiated white type Ia diamond, did not yield any significant IRSL/BLSL with doses up to 100 Gy. The BLSL/IRSL sensitivity of irradiated and heat treated diamonds was very poor, and depended on the heat cycle and hence were not pursued. Sample 2C exhibited significant BLSL and negligible IRSL sensitivity. Sample 2D gave an intense orange red emission under IR excitation as also responded to BLSL. The dose response of the BLSL signal in 2C suggested a minimum detectable dose of ~ 0.1 Gy and its use as a tissue equivalent dosimeter. Based on supporting experiments such as laser excited photoluminescence, we suggest that the BLSL process in 2C is primarily driven by carbon vacancies, which release a mobile hole when excited by GR2 band in the blue region. BLSL intensity exhibited a maximum around 285 °C. Given that TL glow peak also occurs near this temperature and that the nitrogen–interstitial carbon (N–Ci) complex also forms at this temperature (as reported in the literature), and it appears that the e–h recombination at sites with N–Ci complex could be involved in BLSL production. Laser excited photoluminescence (PL) at wavelengths 325, 514 and 785 nm and absorption spectra in UV–Visible range gave insights into the contrasting BLSL/IRSL responses of 2C and 2D. These differences were due to differences in nitrogen impurity complexes and the concentration of carbon vacancies produced by EBT in 2C and 2D. In 2D, the presence of Ni as NE8 center (four nitrogens coordinated to Ni) giving 800 nm emission on 785 nm excitation, appeared to suppress BLSL and sensitize IRSL in the orange window.

Assessment of different mechanisms of C-14 production in irradiated graphite of RBMK-1500 reactors

Abstract Two RBMK-1500 water-cooled graphite-moderated channel-type power reactors at the Ignalina Nuclear Power Plant (INPP) are under decommissioning now. The total mass of irradiated graphite in the cores of both units is more than 3600 tons. The main source of uncertainty in the numerical assessment of graphite activity is the uncertainty of the initial impurities content in graphite. Nitrogen is one of the most important impurities, having a large neutron capture cross-section. This impurity may become the dominant source of C-14 production. RBMK reactors graphite stacks operate in the cooling mixture of helium-nitrogen gases and this may additionally increase the quantity of the nitrogen impurity. In this paper the results of the numerical modelling of graphite activation for the INPP Unit 1 reactor are presented. In order to evaluate the C-14 activity dependence on the nitrogen impurity content, several cases with different nitrogen content were modelled taking into account initial nitrogen impurity quantities in the graphite matrix and possible nitrogen quantities entrapped in the graphite pores from cooling gases.