Concentration Of Nitrogen Atoms Research Articles

Highly intensive emission of the NV− centers in synthetic HPHT microdiamonds at low nitrogen doping

Synthetic high-pressure high-temperature (HPHT) microdiamonds demonstrate strong resonant-like enhancement of the NV− photoluminescence (PL) at unexpectedly low concentration of the substitutional nitrogen atoms (NS) of 90 ppm, which is significantly smaller than the ∼250 ppm characteristic for conventional HPHT synthesis. The EPR, Raman, and luminescent spectroscopies, including time-resolved PL, provide evidence that this is due to competition between the increase in PL with increasing concentration of the NV− centers and nonradiative deactivation of these centers by defects induced by the NS in the diamond crystal lattice. It is suggested that the intensity of the NV− center emission can be optimized by the appropriate choice of nitrogen doping concentration which does not substantially disrupt the diamond crystal lattice.

The influence of sterilization on properties of polyurethane/polylactide blend

The biodegradable polyurethane/polylactide blend was treated with low temperature hydrogen peroxide plasma, ethylene oxide and immersing in ethanol combined with ultraviolet radiation. The samples sterilized by hydrogen peroxide and ethylene oxide stood practically unaffected, while UV/EtOH caused distinct changes in their mechanical properties. For example the signifficant reduction of tensile strength occured, elongation at break became twice lower, while the Young's modulus increased by 23%. The XPS measurements showed that after all types of treatment atomic carbon and nitrogen concentrations in the surface layer was slightly lower than in the bulk. Instead the surface layer was more enriched with oxygen. Ethylene oxide sterilization caused that both surfaces became more hydrophobic i.e. the contact angle increased about 15% for the top surface and 8% for the bottom surface, respectively. Sterilization with ethanol and UV radiation changed the nature of surface into more hydrophilic, the contact angle of the top surface was reduced about 6% and the bottom about 24%. The FT-IR spectra of all sterilized samples were recorded and discussed. From all used sterilization methods only hydrogen peroxide plasma is fully suitable for biodegradable PU/PLA blend.

Effects of lipid extraction and different collagen extraction methods on archaeological fish bones and its implications for fish bone diagenesis

Gelatin extracted from archaeological fish bones typically exhibits relatively high C/N ratios, presumed to be caused by contamination with lipids or humic substances. The effects of lipid extraction and different collagen extraction methods applied has been studied on modern fish bones but has never been studied systematically on archaeological specimens because of taphonomic and experimental reasons. In this study, the effects of lipid extraction and order of NaOH treatment in collagen extraction method on carbon and nitrogen stable isotope analysis of archaeological fish bone (n = 30) excavated from the Hamanaka 2 site, Hokkaido, Japan (approximately 8th BC–10th AD) is investigated. Gelatin extracted from the same fish bone subsamples with or without lipid extraction procedure indicates neither significant nor systematic differences in carbon and nitrogen stable isotope ratios, elemental concentrations, C/N ratios, and yield. However, reproducibility of stable isotope ratios and elemental concentrations decrease in gelatin extracted from poorly-preserved cod bones (<3.5% yield). Gelatin extracted from archaeological fish bones may contain humic contaminants, and its effect becomes greater in gelatin with lower extraction yield. Although there is no significant change in the stable isotope and C/N ratios, change in atomic concentration of carbon and nitrogen suggests that the purity of extracted gelatin increases when NaOH treatment is applied after decalcification. Because this is only a study from one archaeological site, further case studies that evaluate lipids and diagenesis in fish bones are required.

Investigation of thermal property of triangle vacancy nitrogen-doping graphene nanoribbons

ABSTRACTUnder different ratios of nitrogen atoms at 200 ~ 600K temperature range, we study thermal conductivity and heat rectification of NTGNs (Nitrogen-doping beside Triangle vacancy Graphene Nanoribbons) by using reverse non-equilibrium molecular dynamics simulation. The graphene nanoribbons are armchair graphene nanoribbons (AGNRs), and the length and width are 19.3nm and 3.7nm respectively. We find that thermal conductivity increases more than 30 when nitrogen atoms first replace 12 carbon atoms beside vacancy defect. Then as the proportion of nitrogen atoms increases from 0.85% to 7.2%, the thermal conductivity gradually decreases. Besides, the thermal conductivity of NTGNs becomes more and more insensitive to temperature with the increase of concentration of nitrogen atoms. In addition, we find that heat flow from left (L) to right (R) flows easily and the thermal rectification has a rising trend with the increase in the scale of nitrogen atoms at different temperatures. Moreover, phonon power spectra of the atoms are calculated to explain thermal rectification phenomenon. These findings will make a greater contribution to the design of heat transfer controlling and thermal rectifier.

Nitrogen concentration induced spin disorder in ε-iron nitrides

The magnetic and transport properties of ε-Fe3−xN (0 ≤ x ≤ 1) films were systematically characterized to identify the correlation among the nitrogen concentration x, magnetic structure, and electrical transport properties. It was found that increasing the nitrogen concentration x of ε-Fe3−xN not only resulted in a successive decrease in magnetization and Curie temperature, but also led to the contribution of magnetic scattering to the resistivity and magnetoresistance. All these experimental phenomena can be attributed to the distinctive exchange interaction in ε-Fe3−xN, which depends on the concentration and distribution of nitrogen atoms and causes the emergence of localized spin disorder. We believe this work would provide a new insight into the relationship between the magnetic and transport properties of iron nitrides.

Investigation of nitridation and oxidation reactions at SiC/SiO2 interfaces in NO annealing and modeling of their quantitative impacts on mobility of SiC MOSFETs

Nitridation and oxidation reactions at SiC/SiO2 interfaces during NO annealing were investigated and their quantitative impacts on the channel mobility were modeled. We evaluated the NO annealing condition dependence of nitrogen atom concentration at the SiC/SiO2 interfaces ([N]) and increased oxide thickness (ΔTOX), as indices of the nitridation and oxidation reactions, respectively. By using the obtained [N] and ΔTOX, the experimental mobility was well reproduced in an empirical formula. This empirical formula enables evaluation of the quantitative impact of the nitridation and oxidation reactions on the mobility. From the empirical formula, it was expected that the mobility would be further increased by lowering the annealing temperature from the investigated temperature range. However, an exponential increase in both NO gas consumption and processing time is also predicted, which leads to the conclusion that the further decrease in annealing temperature would be impracticable.

White Layer Control on AISI 316L Using Temperature and Gas Nitriding Diffusion Stage Process

The aim of the study was to compare the hardness properties resulting after the nitriding fluidized bed thermochemical treatments in different media and the diffuse temperature process, to evaluate the efficiency of the white layer formation on stainless steel substrats. The White layer is a layer with a high nitrogen atom concentration between the surface and the layer underneath. This concentration causes the layer to be hard and brittle. The use of diffusion stage after the boost stage (550°C) in a fluidized bed reactor aims at reducing the formation of the white layer. The results show that a reduction in white layer is followed by the increase of brittleness in the form of crack formation in the layer underneath. The imbalance reaction due to the exothermic reaction is the primary reason. An increase in the atmosphere temperature without nitrogen gas during the diffusion stage increases the supersaturated reaction. The optimal process is fixed diffusion at boost temperature of 550°C in the gas diffusion media without nitrogen. The use of atmosphere without nitrogen gas during diffusion increases the depth of diffusion of the nitrogen atom and reduces the white layer, thereby reducing brittleness. In addition, micro-cracks have been formed under white layers at the higher diffusion temperature of 650°C.

Characterization of Nitrogen-Rich Coating Films with Atmospheric-Pressure Plasma Generated by Re-Entrant Microwave Cavity

The deposition and characterization of nitrogen-rich coating films using atmospheric-pressure plasma generated with a re-entrant cylindrical microwave cavity is presented. This system enables simple matching, stable plasma, and free space under the orifice of plasma steam. Allylamine and acetonitrile are employed as monomers, whereas argon is used as the carrier gas. The effective area of the hydrophilic coating film is 55 mm in diameter and the deposition rate is 10 nm min–1. X-ray photoelectron spectroscopy measurements show that the surfaces of these films contain a high concentration of nitrogen atoms and primary amine groups. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry shows that the coating films have a large molecular weight (>200 kDa). The surface morphology is very flat (ca. 1 nm). The experimental results indicate that a highly cross-linked three-dimensional polymer matrix is formed and atmospheric-pressure plasma deposition is successfully achieved.

The Condition of Machined Surface of Titanium Alloy in Dry Grinding

The Versa 3D twin-beam electron microscope was used to study the relief and chemical composition of the VT3-1 titanium alloy surface after grinding with the ceramic bonded silicon-carbide wheel without grinding fluid. The results show that the process of infeed grinding of titanium alloy is associated with adhesive and cohesive processes which lead to the formation of a multi-layer structure of the machined surface. The thickness of the multi-layer structure without adhered material amounts to 2-4 µm. The X-ray spectral microanalysis elicited the modification of the chemical composition. The experimental result indicated that the mass concentration of oxygen, nitrogen, and carbon atoms increases by more than 20 times. The concentration of carbon, nitrogen and silicon becomes lower as the analyzed layer thickness increases.

The Effect of Boron and Nitrogen Doping in Electronic, Magnetic, and Optical Properties of Graphyne

The electronic, magnetic, and optical properties of boron- and nitrogen-doped graphyne have been investigated with various doping positions and concentrations of boron and nitrogen atoms. We have explored how the presence of a single dopant atom changes the conductivity of doped graphyne from the semiconducting to metallic one. The boron atom at the chain site introduces spin polarization which is in the ferromagnetic (FM) ground state for minimal boron concentration and in the antiferromagnetic (AFM) ground state for an increasing number of boron atoms in the unit cell. We have examined the origin of spin polarization which increases with increasing dopant concentration. Our optical spectra show that the interband transition takes place in the low energy regime. Due to the presence of dopant atom, the absorption spectra extend from the infrared region to the UV region and exhibit a strong peak. The reflectivity and energy loss spectra derived the plasmon energy for these systems where the reflectivity di...

Optical band engineering of metal-oxynitride based on tantalum oxide thin film fabricated via reactive gas-timing RF magnetron sputtering

Abstract In this paper, we demonstrate a novel technique, as called reactive gas-timing (RGT) RF magnetron sputtering, to control and design an optical band engineering of TaON thin films without an external heating substrate temperature and post annealing treatment process. The influence of the oxygen intervals ranged from 5 to 60 s on deposition rate, chemical composition and optical properties of TaON thin films were investigated. The chemical composition was characterized by auger electron spectroscopy (AES). The optical properties were determined by UV–Vis spectrophotometer and spectroscopic ellipsometry. The nitrogen atomic concentration of the TaON thin films deposited by RGT decreased when the oxygen gas-timing intervals increased. In addition, the RGT sputtered TaON films could be demonstrated band gaps engineering from 1.90 to 2.15 eV.

On the Use of a Protic Ionic Liquid with a Novel Cation To Study Anion Basicity.

The need for reliable means of ordering and quantifying the Lewis basicity of anions is discussed and the currently available methods are reviewed. Concluding that there is need for a simple impurity-insensitive tool, we have sought, and here describe, a new method using NMR spectroscopy of a weak base, a substituted urea, 1,3-dimethyl-2-imidazolidinone (DMI), as it is protonated by Brønsted acids of different strengths and characters. In all cases studied the product of protonation is a liquid (hence a protic ionic liquid). NMR spectroscopy detects changes in the electronic structure of the base upon interaction with the proton donors. As the proton-donating ability, that is, acidity, increases, there is a smooth but distinct transition from a hydrogen-bonded system (with no net proton transfer) to full ionicity. The liquid state of the samples and high concentration of nitrogen atoms, despite the very low natural abundance of its preferred NMR-active isotope ((15) N), make possible the acquisition of (15) N spectra in a relatively short time. These (15) N, along with (13) C, chemical shifts of the carbonyl atom, and their relative responses to protonation of the carbonyl oxygen, can be used as a means, sensitive to anion basicity and relatively insensitive to impurities, to sort anions in order of increasing hydrogen bond basicity. The order is found to be as follows: SbF6 (-) <BF4 (-) <NTf2 (-) >ClO4 (-) >FSO3 (-) <TfO(-) <HSO4 (-) <Cl(-) <MsO(-) .

The enhancement effect and kinetics of rare earth assisted salt bath nitriding

A rapid salt bath nitriding technology was primarily developed by adding rare earth lanthanum (RE La) in the salt bath media on the basis of normal salt bath nitriding technique (NT). Characterization of the modified surface layers was made by means of optical microscopy, X-ray diffraction, energy dispersive spectroscopy (EDS) and micro-hardness tester. The results showed that the nitriding efficiency could be significantly enhanced assisted by RE La, and the enhancement effect was RE La concentration dependent. The thickness of compound layer was increased from 13.3 μm up to 18.5 μm with 5% La addition at the temperature of 833 K for 2 h. Higher surface hardness, modestly higher sub-surface hardness and superior micro-hardness profile were obtained due to the solution of RE La atoms and consequent lattice expansion in the surface layer. Meanwhile, kinetics analysis showed that the diffusion coefficient was increased and activation energy was decreased with enhancement effect of RE La, the following kinetics formulas were obtained, dNT=0.1exp−21990/Tt and dRE=4.3×10−3exp−16319/Tt for NT and RE treatment, respectively. And the confidence level of the kinetics is examined to be perfectly agreed with the data. The main enhancement mechanism is that RE La can accelerate the decomposition rate of CNO− and thus increase the concentration of active nitrogen atoms in the salt bath medium, and especially increase the number of nitrogen atoms that meet the requirements for diffusing toward the substrate by reducing the energy barrier.

Mechanical properties and corrosion behavior of the nitriding surface layer of Ti[sbnd]6Al[sbnd]7Nb using large pulsed electron beam (LPEB)

Large pulsed electron beam (LPEB) irradiation was used as a single surface finishing process for TiAl7Nb. Nitrogen plasma gas and cathodic apparatus have been adopted to induce nitriding effect of Ti6Al7Nb during the electron beam irradiation. The atomic concentration of nitrogen atoms at the re-solidified layer could be achieved up to ∼18% by LPEB nitriding. Nano-hardness in the re-solidified layer was improved by ∼75% following the irradiation process, as a result of a phase transformation and the formation of TiN. The re-solidified layer induced by the LPEB nitriding, consisted of TiN, TiO2, and TiOxNy, indicated significantly modified corrosion resistance showing a nobler corrosion potential, decreased corrosion current density, and improved charge transfer resistance. The increasing fraction of TiN at the re-solidified layer, induced by LPEB nitriding, was suggested as being responsible for remarkable improvement of mechanical properties and corrosion resistance, embedding uniformly noble and stable characteristics at the top surface. The corrosion-resistant surface layer with superior mechanical properties on Ti6Al7Nb has been successfully demonstrated by LPEB nitriding technique.

Minimizing &lt;em&gt;Pseudomonas aeruginosa&lt;/em&gt; adhesion to titanium surfaces by a plasma nitriding process

The research of the interaction between bacteria-surface has great importance for titanium biomedical applications once microorganisms offer risks because promoting implant loss. Therefore, study bacterial adhesion and colonization on titanium is interesting because are principal factors infections pathogeny on biomaterials. In this study, commercial grade II titanium was submitted to nitriding treatment to plasma at 2.2 mbar, using gas mixtures of 80% hydrogen (H2) and 20% nitrogen (N2) during 1 hour and 3 hour. The surfaces were physically and chemically characterized. In order to evaluate bacterial response, the surfaces were exposed to <em>Pseudomonas aeruginosa</em>. The titanium surface modified in nitriding plasma, although exposes a higher roughness as compared with untreated samples, exhibited lower bacterial growth. The nitrided sample for 3 hour exhibited the higher amount of TiN phase and the higher concentration of atomic nitrogen on surface and lower bacterial adhered count. These results were confirmed by scanning electron microscopy. Based on these results can be said to the thermochemical treatment of plasma nitriding on titanium samples results a significant reduction of adherence of <em>Pseudomonas aeruginosa</em>. It was found that the Ti surface nitrided offers significant reduction of bacterial adherence which prevent biofilm formation and offersing lower risk of infection and implant remotion.

Upward Shift in Conduction Band of Ta2O5 Due to Surface Dipoles Induced by N-Doping

Density functional theory calculations were executed to clarify the mechanism of the experimentally observed upward shift in conduction band minimum (CBM) and valence band maximum (VBM) of N-doped Ta2O5, which is used as a photosensitizer in CO2 reduction. Calculations reproduce well the experimental energy levels (with respect to vacuum) of nondoped Ta2O5 and N-doped Ta2O5. Detailed analyses indicate that N-doping induces formations of defects of oxygenated species, such as oxygen atom and surface hydroxyl group, in the Ta2O5, and the defect formations induce charge redistributions to generate excess negative charges near the doped nitrogen atoms and excess positive charges near the defect sites. When the concentration of the doped nitrogen atoms at the surface is not high enough to compensate positive charges induced at the surface defects, the remaining positive charges are compensated by the nitrogen atoms in inner layers. Dipole moments normal to the surface generated in this situation raise the CBM ...

Radiation-stimulated photoluminescence in electron irradiated 4H-SiC

The photoluminescence (PL) arising in low doped CVD grown n- and p-type 4H-SiC upon electron irradiation (0,9 MeV) has been studied. After each doze of irradiation spectrum of PL was measured. The PL spectrum was dominated by a band peaked at hv ≈ 2,45 eV, commonly observed upon irradiation of SiC. The experiments demonstrated that, for samples with both types of conduction, the PL intensity approaches a constant value with increasing irradiation dose. A model was suggested, describing the PL characteristics in terms of the radiative recombination via a donor-acceptor pair constituted by nitrogen and a structural defect formed in the course of irradiation. Also, the concentration of nitrogen atoms was measured by the SIMS method. The experimental data were used to calculate in terms of the suggested model the dependence of the PL intensity on the irradiation dose. A good agreement between the calculated and experimental dependences was observed. A conclusion is made that the PL is activated by donor—acceptor pairs constituted by a nitrogen atom and a structural defect.

Structure and element composition of the nitride layer of AlN/Al2O3 templates obtained by the thermochemical nitridation of sapphire

Aluminum-nitride layers on sapphire (AlN/sapphire templates) are obtained by the thermochemical nitridation (TCN) of sapphire substrates. According to X-ray diffraction data, AlN layers have a singlecomponent texture with the axis [0001] and high structural perfection (the rocking curve half-width β is 15′–30′). The nitride-layer depth reaches 1 μm. The structure and element composition of the nitride layer were studied via the step-by-step removal of the nitride layer while polishing the AlN/sapphire templates. The study of the element composition of the nitride surface by X-ray photoelectron spectroscopy during the process of the step-by-step removal of the nitride layer reveals a gradual decrease in the concentration of nitrogen atoms confirming the diffusion mechanism of sapphire nitridation. Characterization of the surface morphology of the polished AlN/sapphire templates by means of atomic-force microscopy shows the presence of pores in it. The formation of these pores can be caused by the dissociative decomposition of sapphire in reducing-gas media upon TCN followed by the formation of gaseous products which form the pores upon reaching the surface.

Heat transfer regulation of hole defect graphene by nitrogen doping

Using classical molecular dynamics simulation, we investigate the thermal transport properties of hole defect graphene nanoribbons (HD-GNRs) possing various doping concentration of nitrogen atoms. By changing the concentration of nitrogen atoms, we try to find an effective method to adjust the heat transfer of HD-GNRs. The results show that the existence of hole defect in graphene destroys the structural integrity of the GNRs, which causes great decrease in thermal conductivity. We detect that nitrogen doping is a very sensitive mode for hole defect graphene nanoribbons. The thermal conductivity of HD-GNRs can be greatly improved by decreasing the N doping concentration from 7 to 0.87 %.

Characterization of the charge trapping properties in p-channel silicon–oxide–nitride–oxide–silicon memory devices including SiO2/Si3N4 interfacial transition layer

The role of SiO2/Si3N4 interfacial transition (IFT) layer in the oxide–nitride–oxide (ONO) tri-layer is quantitatively analyzed for the first time by simulating the temperature and stress-accelerated retention characteristics of p-channel silicon–oxide–nitride–oxide–silicon (SONOS) devices. The ONO tri-layer is modeled as an alloy-dielectric by changing the atomic concentration of silicon, oxygen and nitrogen. It is revealed that simulated results including the IFT layer are more consistent with the experimental data than those neglecting the IFT layer. In addition, the results show that the trapped charge density in IFT layer is two times larger than in the bulk Si3N4 film, due to the oxygen atoms penetrated from SiO2 cause the extrinsic defects in the IFT layer. The energy levels of the trapped charge are continuously distributed, and the peak value is ∼1.6 eV below the conduction band of the ONO tri-layer with a full width at half maximum of 0.45 eV.