Nitrogen Impurities Research Articles

Solvent-Free Synthesis of Nickel Nanoparticles as Catalysts for CO2 Hydrogenation to Methane

The solid-state combustion method was used to prepare nickel-based catalysts for CO2 hydrogenation from [Ni(C3H4N2)6](NO3)2 and [Ni(C3H4N2)6](ClO4)2. These complexes were synthesized by adding nickel nitrate and perchlorate to melted imidazole. The composition and structure of the obtained complexes was confirmed by ATR FTIR, powder XRD, and elemental analysis. The stages of thermal decomposition of the complexes and their kinetic parameters were established. It was found that incomplete gasification of more thermostable Ni(C3H4N2)6](ClO4)2 led to the formation of carbon, nitrogen, and chlorine impurities. According to powder XRD and XPS, the solid products of gasification of both complexes consist of NiO and Ni0 covered with nickel hydroxide and/or a carbonate layer. In the case of the sample prepared from [Ni(C3H4N2)6](ClO4)2, this layer was pronounced. Therefore, it limits the nickel reduction in the reaction medium of CO2 hydrogenation, even at 450 °C. The surface of the sample prepared from [Ni(C3H4N2)6](NO3)2 contains nickel oxide, which is easily reduced. So, the catalyst active phase is already formed at 250 °C in the presence of CO2 and efficiently catalyzes CO2 hydrogenation as the temperature increases. Therefore, [Ni(C3H4N2)6](NO3)2 is a promising precursor for the CO2 hydrogenation catalyst, and its solvent-free synthesis follows Green Chemistry principles.

Hidden impurities in transparent conducting oxides: study of vacancies-related defects and impurities in (Cu–Ni) co-doped ZnO films

The effect of hydrogen and nitrogen impurities on the physical properties of transparent conductive oxides is investigated in this study. Therefore, 5 wt.% of copper and 5 wt.% of nickel co-doped zinc oxide ((Cu–Ni)/ZnO) films were prepared using the sol–gel method. The (Cu–Ni)/ZnO films were annealed in an oven at 500 °C for 2 h under air, vacuum, nitrogen, and argon atmospheres. The synthesized zinc hydroxide film was transformed to zinc oxide film during the annealing by evaporating {mathrm{H}}_{2}mathrm{O}. Films annealed under the mentioned atmosphere including as-prepared one were characterized by analyzing with UV–Vis and FTIR spectra in addition to the 2D mapping electrical conductivity of the surface measured by the 4-point probe. The annealed films under air, vacuum, and argon atmospheres led to generate H-related impurities bounded to the oxygen vacancy ({mathrm{H}}_{mathrm{O}}) which they act as shallow donor defects resulting in forming (Cu–Ni)/ZnO films into n-type materials. Whereas, the film annealed under a nitrogen atmosphere has N-related defects bounding to the zinc vacancy ({mathrm{N}}_{mathrm{Zn}}) which they act as shallow acceptor defects resulting in transforming the film from n-type to p-type. These defects affect the optical, electrical, and optoelectronic properties of the (Cu–Ni)/ZnO films.

Modeling the effect of nitrogen recycling on the erosion and leakage of tungsten impurities from the SAS-VW divertor in DIII-D during nitrogen gas injection

The new SAS-VW divertor in DIII-D has tungsten-coated components to enable the study of tungsten erosion and leakage from a closed, slot-like divertor. A proposed method of actively managing the tungsten impurities is to inject low-Z impurities, such as nitrogen, into the Scrape-off-Layer (SOL) to modify the conditions in the plasma boundary and in turn manipulate both the erosion and subsequent transport of tungsten. Nitrogen injection from the SOL crown has been modeled using SOLPS-ITER to calculate the background plasma including the intrinsic carbon and the injected nitrogen impurities, and subsequently DIVIMP has been used to calculate the tungsten erosion and transport on top of the background plasma solution. This workflow has been used to model scenarios at a variety of nitrogen injection rates with different assumptions about the nitrogen recycling at the target. In the scenario modeled here, an optimal nitrogen injection rate around 3–4 × 1 0 20 N/s is found to reduce the amount of tungsten reaching the core by a factor of about 2.4. However, when the nitrogen recycling rate at the divertor targets is high, the nitrogen redistributes within the slot leading to increased tungsten sputtering, and the range of injection rates resulting in tungsten mitigation becomes narrower. • Modeling shows N gas injection can be used to manipulate SOL force balance on W ions. • Optimal N gas injection rate may exist for W mitigation in new DIII-D divertor. • N recycling at divertor targets narrows operating window for W mitigation.

The vibrational and dielectric properties of diamond with N impurities: First principles study

The atomic and electronic structures as well as elastic and dielectric properties (including first simulations of loss tangent, tan δ) of diamond with nitrogen impurities are calculated using the first principles LCAO method and the hybrid functional B3LYP. The effect of the single nitrogen substitutional atom (C-center) on the Raman and IR absorbance spectra is analyzed and compared with other calculations. It is shown that nitrogen defects do not affect tan δ at far IR region used in diamond windows in fusion reactors for plasma heating and stabilization.

Oxidation kinetics and mechanism of nickel alloys

The study covers the effect of alloying elements on the kinetics and mechanism of oxidation at 1150 °С for 30 hours of heat-resistant nickel alloys obtained using such technologies as centrifugal SHS metallurgy (SHS(M)), vacuum induction melting (VIM), elemental synthesis (ES), hot isostatic pressing (HIP). A comparative analysis was carried out for alloys based on nickel monoaluminide and standard AZhK and EP741NP alloys. It was found that kinetic dependences are described mainly by parabolic approximation. The logarithmic law of oxidation with the rapid (within 3–4 hours) formation of the primary protective layer is typical for alloys doped with molybdenum and hafnium. In the case of AZhK and EP741NP, oxidation proceeds according to a parabolic law at the initial stage (2–3 hours), and then according to a linear mechanism with the voloxidation and complete destruction of samples. Oxygen and nitrogen diffusion proceeds predominantly along the nickel aluminide grain boundaries and it is limited by the Al2O3 + Cr2O3 + XnOm protective film formation. SHS(M) alloys feature by a positive effect of zirconium and tantalum added as dopants on heat resistance. The Ta2O5 phase is formed in the intergranular space, which reduces the rate and depth of oxidation. The zirconium-containing top layer Al2O3 + Zr5Al3O0.5 blocks the external diffusion of oxygen and nitrogen, thereby improving heat resistance. Doping with hafnium also has a positive effect on oxidation resistance and leads to the formation of submicron and nanosized HfO2 inclusions that suppress the grain boundary diffusion of oxygen. MoO3, Mo3O4, CoMoO4 volatile oxides are formed in alloys with a high content of molybdenum and compromise the protective layer integrity. A comparative analysis of the oxidation kinetics and mechanism for samples consisting of the base β-alloy with Cr + Co + Hf additives showed a significant effect on the heat resistance of the sample preparation method. As the proportion of impurity nitrogen decreases and the Cr2O3 sublayer is formed, the oxidation mechanism also changes.

A Molecular-Dynamics Study of the Influence of Carbon, Nitrogen, and Oxygen Impurities on the Edge Dislocation Slip in Aluminum and Nickel

A Molecular-Dynamics Study of the Influence of Carbon, Nitrogen, and Oxygen Impurities on the Edge Dislocation Slip in Aluminum and Nickel

Study of MIS structures based on CdHgTe and HfO2 applied by PEALD

We investigate the HfO2/Hg0.78Cd0.22Te interface fabricated by plasma-enhanced atomic layer deposition (PEALD) at 120 °C During the deposition of HfO2, no donor-like defects are introduced into mercury cadmium telluride. X-ray photoelectron spectroscopy and ellipsometry were used to establish the optimal process regime at 120 °C and to demonstrate how HfO2 layer composition and growth rate per cycle depend on post-plasma purge time; the optimum is achieved at 6 s. Increasing the post-plasma purge time decreases the carbon and nitrogen impurity concentration in the HfO2 layer. Measurements of the admittance of metal-insulator-semiconductor (MIS) structures over the surface of a sample show that the electro-physical properties are uniform. We discuss the method of measuring the admittance of MIS structures that allows us to minimize the contribution of slow states with trapped charge on shape and shift of the C–V curve. The results demonstrate that the densities of fixed charge, slow states, and fast interfacial traps at the HfO2/MCT interface are greater than that for Al2O3/MCT (also formed by PEALD). The interface trap density is estimated from a normalized parallel conductance map, and the HfO2 film adheres well.

Decoherence of nitrogen-vacancy spin ensembles in a nitrogen electron-nuclear spin bath in diamond

Nitrogen-vacancy (NV) centers in diamond have been developed into essential hardware units for a wide range of solid-state-based quantum technology applications. While such applications require the long spin coherence times of the NV centers, they are often limited due to decoherence. In this study, we theoretically investigate the decoherence of NV-spin ensembles induced by nitrogen impurities (P1 centers), which are one of the most dominant and inevitable magnetic field noise sources in diamond. We combined cluster correlation expansion and density functional theory to compute the Hahn-echo spin-coherence time of the NV centers for a broad range of P1 concentrations. Results indicate a clear linear dependence of T2 on P1 concentrations on a log scale with a slope of −1.06, which is in excellent agreement with previous experimental results. The interplay between the Jahn–Teller effect and the hyperfine interaction in the P1 center plays a critical role in determining the bath dynamics and the resulting NV decoherence. Our results provide a theoretical upper bound for the NV-spin T2 over a wide range of P1 densities, serving as a key reference for materials optimization and spin bath characterization to develop highly coherent NV-based devices for quantum information technology.

(Digital Presentation) Tuning Oxygen Reduction on Monoclinic and Tetragonal Zirconia Surfaces Using Oxygen Vacancy and Nitrogen Doping: A Density-Functional Study

The proton exchange membrane fuel cell (PEMFC) shows the interesting properties,1 where oxygen reduction reaction (ORR) is rate-determining.2 For the PEMFC, Pt-based materials are effective to be its ORR catalyst but their expensive cost and the limited availability are unavoidable,3 motivating to searching non-Pt materials. Zirconia (ZrO2) becomes a considerable candidate for the ORR catalyst since it has a higher chemical stability than that of Pt in an acidic environment,4 where tetragonal ZrO2 (t-ZrO2) (101) and monoclinic ZrO2 (m-ZrO2) (-111) surfaces have been observed to be the most stable.5 In this study, oxygen reduction reaction (ORR) on m-ZrO2 (-111), (-101), (110) and t-ZrO2 (101) surfaces is investigated using the density-functional theory. Each surface is divided into two regimes, that are pristine and defective surfaces, containing defects as two nitrogen impurities and an oxygen vacancy (2NO + VO). Then, the effect of the defects on free energy diagrams and bonding characteristics of an adsorbed oxygen (O*) is investigated. The free energy diagrams correspond to elementary ORR steps involving four intermediates, that are O2*, O2H*, O*, and OH*.As the results, the free energy diagrams show that the first electron transfer, corresponding to the formation of O2H*, is rate-determining on the pristine surfaces. It is modified to the third and fourth electron transfers, corresponding to the formation and removal of OH*, on the defective t-ZrO2 and m-ZrO2 surfaces, respectively. Furthermore, the defects provide a significant effect on the bonding of O*, leading to a slight improvement of ORR catalytic activity on t-ZrO2 but an apparent decrease on m-ZrO2 surfaces. Moreover, due to the defects, adsorption free energies for the defective m-ZrO2 surfaces, ΔG O, ΔG OH, and ΔG OOH, are moving away from the universal scaling curve and the ideal catalyst point. On the other hand, for the defective t-ZrO2 surface, ΔG O, ΔG OH, and ΔG OOH are off the universal scaling curve, heading to the ideal catalyst point. Our result presents the significant effect of the defects, providing a new insight into the oxide-based catalysts. References E. Brightman et al., J. of Power Sources, 242, 244–254 (2013)M. Beltrán-Gastélum et al., Energy, 181, 1225–1234 (2019)X. Sun et al., Electrochim. Acta, 332, 135474 (2020)A. Ishihara et al., J. Phys. Chem. C, 123(30), 18150–18159 (2019)C. Morterra et al., Mater. Chem. Phys., 37(3), 243–257 (1994)

초임계 조건에서 이산화탄소 혼합물의 점성 측정

The purpose of this study was to experimentally investigate the viscosity for carbon dioxide with nitrogen and methane impurities under supercritical conditions. The experimental setup was comprised of a test section, a condensation section for the liquefaction of carbon dioxide before entering the pump, and a heating section for controlling the temperature of the entrance of the test section. The test section was comprised of a capillary tube with a length of 300 mm and a ⅛ inch diameter. The experiment was performed under a mass flux of 200~400 kg/(m²s) at a impurities concentration of 1.0~5.0 mol%. The viscosity of nitrogen mixture was lower by 0.5% for 1% mole fraction, 4.9% for 3% mole fraction, and 23.5% for 5% mole fraction compared with that of pure CO₂. The viscosity of methane mixture was lower by 7.3% for 1% mole fraction, 11.2% for 3% mole fraction, and 24.4% for 5% mole fraction compared with that of pure CO₂. A model for predicting the viscosity of CO₂ mixtures under the supercritical condition was developed by the multi-variable regression analysis. The model included the non-dimensional parameters for temperature, pressure, and density.

Theoretical analysis of the NH3, NO, and NO2 adsorption on boron-nitrogen and boron-phosphorous co-doped monolayer graphene - A comparative study

In this work, a density functional theory (DFT) based detailed theoretical study has been performed on the Boron/Nitrogen (B/N) and Boron/Phosphorous (B/P) codoped monolayer Graphene for molecular adsorptions and co-adsorptions of three Nitrogen-based environmental pollutant gasses, namely Ammonia (NH3), Nitrogen Di-Oxide (NO2) and Nitric Oxide (NO). The B acts as a localized electron deficit site in the codoped lattice and subsequently offers a suitable adsorption site for electron-enriched gas molecules like NH3 and NOx. The work systematically explores the influence of introducing Nitrogen or Phosphorus impurities in the same and different sub-lattice sites of boron-doped Graphene in the context of molecular adsorption. In this context, six doping configurations are identified that demonstrate distinct electronic properties and characteristic responses towards individual gas molecule adsorption. The molecular adsorption strongly influences the spatial distribution of electronic states near the band edges due to orbital overlaps from the adsorbed gas molecules, which leads to significant modulations in the energy band gaps and effective masses of the codoped lattices. The co-doping strategies appear highly advantageous for electrochemical gas sensing as it leads to appreciable semiconducting bandgap opening while retaining the intrinsic nature of the Graphene. The subsequent molecular adsorptions and co-adsorptions result in notable charge transfer between the gas molecules and the host lattice and considerably enhance the density of electronic states around the Fermi-level for codoped lattices.

Hydrogen-terminated diamond MOSFETs on (0 0 1) single crystal diamond with state of the art high RF power density

Diamond field-effect transistor (FET) has great application potential for high frequency and high power electronic devices. In this work, diamond FETs were fabricated on (0 0 1) single crystal diamond with homoepitaxial layer. The nitrogen impurity content in the homoepitaxial layer is greatly decreased as measured by the Raman and photoluminescence spectra. The diamond field effect transistor with 100 nm Al2O3 as gate dielectric shows ohomic contact resistance of 35 Ω . mm, maximum drain saturation current density of 500 mA/mm, and maximum transconductance of 20.1 mS/mm. Due to the high quality of Al2O3 gate dielectric and single crystal diamond substrate, the drain work voltage of −58 V is achieved for the diamond FETs. A continuous wave output power density of 4.2 W/mm at 2 GHz is obtained. The output power densities at 4 and 10 GHz are also improved and achieve 3.1 and 1.7 W/mm, respectively. This work shows the application potential of single crystal diamond for high frequency and high power electronic devices.

Nitrogen Investigation by SIMS in Two Wide Band-Gap Semiconductors: Diamond and Silicon Carbide

Diamond and Silicon Carbide (SiC) are promising wide band-gap semiconductors for power electronics, SiC being more mature especially in term of large wafer size (200 mm). Nitrogen impurities are often used in both materials for different purpose: increase the diamond growth rate or induce n-type conductivity in SiC. The determination of the nitrogen content by secondary ion mass spectrometry (SIMS) is a difficult task mainly because nitrogen is an atmospheric element for which direct monitoring of N± ions give no or a weak signal. With our standard diamond SIMS conditions, we investigate 12C14N- secondary ions under cesium primary ions by applying high mass resolution settings. Nitrogen depth-profiling of diamond and SiC (multi-) layers is then possible over several micrometer thick over reasonable time analysis duration. In a simple way and without notably modifying our usual analysis process, we found a nitrogen detection limit of 2x1017 at/cm3 in diamond and 5x1015 at/cm3 in SiC.

Aluminum–nitrogen co‐doping improves the blue emission of ZnO films: A combined theoretical–experimental study

AbstractThe investigation on visible emission of ZnO is necessary due its potential application in electrochemical communication, biosensor, and white light diodes, and so forth. Previous report indicates that the visible light of ZnO is related to the defect type and concentration. It can be regulated by various methods. However, quenching of light emission occurs if too many defects are introduced. In this work, combined with theoretical calculation about energy band structure, aluminum–nitrogen co‐doped ZnO is conducive to form p‐type semiconductor, but aluminum doped ZnO films tend to form a deep n‐type semiconductors. Therefore, in the experiment, aluminum–nitrogen co‐doped ZnO films are prepared using radio frequency magnetron sputtering. The substitution of oxygen using nitrogen impurity is expected to introduce more oxygen vacancies and interstitial zinc defects related to visible light emission. At the same time, annealing in vacuum is also a highly non‐equilibrium processes with low oxygen and high zinc contents. Results indicate that combined with aluminum–nitrogen co‐doping and an appropriate annealing temperature, the blue and blue‐green emission of ZnO films can be greatly improved.

Spectroscopic features of electron-irradiated diamond crystals from the Mir kimberlite pipe, Yakutia

The behavior of characteristic centers in diamond crystals from the Mir pipe (Yakutia) was investigated upon electron irradiation. A series of diamond crystals of different types was chosen for experiments based on the nitrogen content and aggregation parameters. In electron-irradiated diamonds of the IaAB type, a new characteristic photoluminescence system was found with a zero-phonon line (ZPL) at 615 nm together with phonon replicas of 41 and 90 meV. The phonons' energies pointed to multiphonon interactions with a quasilocal vibration of a vacancy. According to our data, the nitrogen-related defect responsible for this phenomenon contains a vacancy and may be accompanied by some other impurity. Conversely, in an almost nitrogen-free crystal, a specific system with the ZPL at 558 nm was noted. The center in question is known to be vacancy-related and was formed in type IIa crystals from the Mir pipe not only by electron irradiation but also by high-pressure high-temperature annealing when vacancies were released as a result of motion or annihilation of dislocations. Regardless of the nitrogen impurity, specific systems with the ZPL at 454, 491, and 492 nm were registered in the irradiated diamond crystals from the Mir pipe. To examine the generated defects, the irradiated diamond crystals were subjected to low-temperature annealing at ≤600 °C. Although the 454 and 491 nm systems persisted, the annealing of the 492 nm system along with well-known 523.6, 489.0, and 503.4 nm (3H) centers indicated the interstitial-vacancy nature of the defect.

Participation of nitrogen impurities in the growth of grown-in oxide precipitates in nitrogen-doped Czochralski silicon

For nitrogen-doped Czochralski (NCZ) silicon, it is well known that nitrogen (N) and oxygen (O) impurities can interact to form nitrogen–oxygen shallow thermal donors (N–O STDs); moreover, the N impurities can be involved into heterogeneous nucleation to facilitate the formation of grown-in oxide precipitates. However, how the N impurities participate in the growth of grown-in oxide precipitates during the post-anneal remains unclear. Besides, the correlation between the formation of N–O STDs and the growth of grown-in oxide precipitates is yet to be revealed. In this work, the effects of pre-anneals at temperatures of 900–1200 °C on the formation of N–O STDs at 650 °C in NCZ silicon have been first investigated. Thus, it has been found that the more significant growth of grown-in oxide precipitates during the pre-anneal, which consumes much more N impurities, leads to forming much fewer N–O STDs. This finding stimulates us to explore the mechanism for the participation of N impurities in the growth of grown-in oxide precipitates. To this end, the capture of N impurities by the oxide precipitates, on the one hand, and the release of N impurities from the oxide precipitates, on the other hand, have been investigated by two systematically constructed experiments. The obtained results enable us to reasonably propose that the N impurities participating in the growth of grown-in oxide precipitates predominately reside at the oxide precipitate/Si interfaces, which reduces the interfacial energies, thus favoring the growth of grown-in oxide precipitates. Such a viewpoint is well supported by the density functional theory calculations. In a word, this work has gained an insight into the mechanism for the participation of N impurities in the growth of grown-in oxide precipitates, starting from exploring the correlation between the formation of N–O STDs and the growth of grown-in oxide precipitates.

Enhancement of the creation yield of NV ensembles in a chemically vapour deposited diamond

In this work we investigate the properties of negatively charged nitrogen-vacancy (NV−) centres created during single crystal diamond growth by chemical vapour deposition (CVD) on [113]-oriented substrates and with N2O as a dopant gas. The use of spin echo and double electron-electron resonance (DEER) allows us to assess NV− ratio with respect to substitutional nitrogen impurities (Ns0) incorporated during growth, a critical figure of merit for quantum technologies. We demonstrate that, at moderate growth temperatures (800 °C), dense NV− ensembles of several hundreds of ppb (800 ppb for 50 ppm of added N2O) and with exceptionally high NV−/ Ns0 ratios of up to 25% can be achieved. This NV− creation yield is higher by at least an order of magnitude to that typically obtained on standard [100]-grown diamonds and comparable to the best values reported for electron-irradiated diamonds. The material obtained here thus advantageously combines a high NV− density, high creation yield, long coherence times of several tens of μs together with a partial preferential orientation. These are highly desirable requirements for diamond-based quantum sensors that may spur new developments with this crystalline orientation leading to improved performance and sensitivity.

Accumulation of Inert Impurities in a Polymer Electrolyte Fuel Cell System with Anode Recirculation and Periodic Purge: A Simple Analytical Model

Anode recirculation with periodic purge is commonly used in polymer electrolyte fuel cell systems to control the accumulation of nitrogen, water, and other impurities that are present in the fuel or diffuse through the membrane from the cathode compartment. In this work, we develop a simple, generalized analytical model that simulates the time dependence of the accumulation of inert impurities in the anode compartment of such a system. It is shown that, when there is transport out of the anode chamber, the inert species is expected to accumulate exponentially until equilibrium is reached when the rate of inert entering the anode in the fuel supply and/or via crossover from the cathode is balanced by the rate of leakage and/or crossover to the cathode. The model is validated using recently published experimental data for the accumulation of N2, CH4, and CO2 in a recirculated system. The results show that nitrogen accumulation needs to be taken into account to properly adjust system parameters such as purge rate, purge volume, and recirculation rate. The use of this generalized analytical model is intended to aid the selection of these system parameters to optimize performance in the presence of inerts.

Proximal nitrogen reduces the fluorescence quantum yield of nitrogen-vacancy centres in diamond

The nitrogen-vacancy colour centre in diamond is emerging as one of the most important solid-state quantum systems. It has applications to fields including high-precision sensing, quantum computing, single photon communication, metrology, nanoscale magnetic imaging and biosensing. For all of these applications, a high quantum yield of emitted photons is desirable. However, diamond samples engineered to have high densities of nitrogen-vacancy centres show levels of brightness varying significantly within single batches, or even within the same sample. Here we show that nearby nitrogen impurities quench emission of nitrogen-vacancy centres via non-radiative transitions, resulting in a reduced fluorescence quantum yield. We monitored the emission properties of nitrogen-vacancy centre ensembles from synthetic diamond samples with different concentrations of nitrogen impurities. All samples were irradiated with high energy electrons to create high densities of nitrogen-vacancy centres relative to the concentration of nitrogen impurities. While at low nitrogen densities of 1.81 ppm we measured a lifetime of 13.9 ns, we observed a strong reduction in lifetime with increasing nitrogen density. We measure a lifetime as low as 4.4 ns at a nitrogen density of 380 ppm. The change in lifetime matches a reduction in relative fluorescence quantum yield from 77.4% to 32% with an increase in nitrogen density from 88 ppm to 380 ppm, respectively. These results will inform the conditions required to optimise the properties of diamond crystals devices based on the fluorescence of nitrogen-vacancy centres. Furthermore, this work provides insights into the origin of inhomogeneities observed in high-density nitrogen-vacancy ensembles within diamonds and nanodiamonds.

Influence of nitrogen impurities on the characteristics of helium discharge at high pressure

In this paper, a helium model with nitrogen impurities was established by COMSOL Multiphysics. In order to validate the model, the results of this model were compared with those of the pure helium model and the experimental data. A concept named “reaction chain” was applied to investigate the effects of the nitrogen impurities and elucidate the underlying mechanisms. In terms of discharge mechanisms, the Penning ionization of the He* and N2 can consume He* constantly and directly, which can shorten the reaction chain for the production of dominant ions. The direct ionization of ground state nitrogen molecules can produce more electrons to strengthen the effects of electron avalanche, which will further intensify the reactions. Therefore, the presence of nitrogen impurities can simplify the reaction pathways and intensify the reactions. As a result, the presence of nitrogen impurities can decrease the breakdown voltage remarkably.