Concentration Of Nitrogen Atoms Research Articles

Mechanically robust nitrogen-rich plasma polymers: Biofunctional interfaces for surface engineering of biomedical implants

Surface bio-functionalization through covalent attachment of bioactive molecules is a promising approach to facilitate rapid bone-implant integration. Radical-rich plasma polymer interlayers are highly attractive as platforms that enable covalent biofunctionalization in a single-step, reagent-free manner. However, fabrication of mechanically robust plasma polymer films, particularly for biomedical devices that operate in corrosive body fluids, is not trivial. Here we show a facile approach to tune the robustness of ion-assisted plasma polymer (IPP) films via simply varying the nitrogen atomic concentration incorporated into their structure. X-ray photoelectron spectroscopy data indicated that the total sp3/sp2 ratio of carbon atoms decreases in the films with increasing nitrogen atomic concentration. Electron recoil detection analysis data provided evidence that the hydrogen content decreases as the nitrogen atomic concentration increases. Nano-indentation and nano-scratch tests, together with long-term stability studies in simulated body fluid, showed a strong correlation between the nitrogen atomic concentration and the robustness and stability of the films. We confirmed the potential of the optimized, nitrogen-rich IPP film to regulate osseointegration by covalent attachment of fibronectin followed by quantifying primary osteoblast attachment and proliferation. The IPP films developed here hold great potential as robust interfaces for biomimetic surface engineering of implantable biomedical devices, in particular bone implants.

Effect of macronutrients and of anaerobic digestate on the heterotrophic cultivation of Chlorella vulgaris grown with glycerol.

The aim of this work was to investigate the kinetics of the heterotrophic growth of Chlorella vulgaris as a means of producing bio-oil for biodiesel production. Glycerol was used as the sole organic carbon substrate. Anaerobic digestate from a local plant was used to examine its effect on the kinetics and the protein and lipid content of the biomass. The effect of the initial carbon and nitrogen concentrations on the carbon uptake rate was studied independently. In the one set of five experiments, the organic carbon in the form of glycerol varied from 0.27 to 5.36g L-1, while the concentration of atomic nitrogen was held constant and equal to 45.4mg L-1. The Co/No ratio varied from 6 to 118.1. In the second set, also of five experiments, the organic carbon was held constant and equal to 3.3g L-1 and atomic nitrogen varied from 22.7 to 450mg L-1. The Co/No ratio varied from 7.3 to 145.4. In the third set of experiments, anaerobic digestate was added in increasing amounts into the culture media from 4 to 16%. It was found that the carbon uptake rate as well as the lipid and protein content depended on the Co/No ratio. Increasing ratios of Co/No led to higher carbon uptake rates, higher lipid content, and lower protein content. The initial nitrogen concentration was also found to affect the growth rate of C. vulgaris. The addition of anaerobic digestate did not affect appreciably the protein and lipid content of the biomass, while the addition of anaerobic digestate up to 16% in the culture medium increased the carbon uptake rate by about 24%.

Ti decorated heterocyclic rings for hydrogen storage

This study uses first-principles calculations to investigate and compare the hydrogen storage properties of Ti doped benzene (C6H6Ti) and Ti doped borazine (B3N3H6Ti) complexes. C6H6Ti and B3N3H6Ti complex each can adsorb four H2 molecules, but the former has a 0.11 wt% higher H2 uptake capacity than the latter. Ti atoms bind to C6H6 more strongly than B3N3H6. The hydrogen adsorption energies with Gibbs free energy correction for C6H6Ti and B3N3H6Ti complexes are 0.17 and 0.45 eV, respectively, indicating reversible hydrogen adsorption. The hydrogen adsorption properties of C6H6Ti have also been studied after boron (B) and nitrogen (N) atom substitutions. Several B and N substituted structures between C6H6Ti and B3N3H6Ti with different boron and nitrogen concentration and at different positions were considered. Initially, one boron and one nitrogen atom is substituted for two carbon atoms of benzene at three different positions and three different structures are obtained. Seven structures are possible when four carbon atoms of benzene are replaced by two boron and two nitrogen atoms at different positions. The hydrogen storage capacity of the C6H6Ti complex increases as boron and nitrogen atom concentrations increases. The positions of substituted boron and nitrogen atoms have less impact on H2 uptake capacity for the same B and N concentration. The position and concentration of B and N affects the H2 adsorption energy as well as the temperature and pressure range for thermodynamically favorable H2 adsorption. The H2 desorption temperature for all the complexes is found to be higher than 250 K indicates the stronger binding of H2 molecules with these complexes.

Effect of synthesis conditions on the properties of graphene doped with nitrogen atoms

Graphene doped with nitrogen atoms (N-graphene) was prepared by the template method. Magnesium oxide was subjected to carbonization in the 40% NH3–1% C2H2–C2H4 mixture at 650–750 °C. Then, the MgO core of the prepared N–С/MgO composite was dissolved by treatment in hydrochloric acid. The effects of temperature and synthesis time on the properties of the obtained N-graphene were studied by electron microscopy, Raman spectroscopy, XPS and XRD. The aggregates consisted of N-graphene particles with globular shape reflecting the template method used for their synthesis. The size of the carbon globules was about 30–50 nm. According to the chemical mapping data, C, O and N atoms were uniformly distributed in N-graphene within the analysis area. An increase of the synthesis temperature from 650 to 750 °C led to the decrease of the sample defectiveness, nitrogen atom concentration and surface area of N-graphene.

Analysis of the concentration of nitrogen and titanium ions simultaneously implanted into chromium-molybdenum low-alloy carbon steel

The concentration of nitrogen and titanium atoms that are introduced into the subsurface layers of chromium molybdenum low-alloy carbon steel exposed to the ion implantation surface modification method is estimated in this article using computational tools and the experimental parameters of the process; due to the difficulty of analyzing the trajectories and the distribution of the ions in the matter in an analytical or experimental way, simulation methods were used to effectuate this study. Additionally, experimental tests were carried out with implantation times of 5 minutes and 10 minutes and the behavior of both cases was compared. The results obtained made it possible to characterize the implantation processes through distribution profiles with respect to depth and showed that varying the exposure time did not reach greater depths. However, by increasing the discharge voltage parameter, it is estimated that the projected range increases and the region of greatest concentration are located deeper.

SURFACE CHEMICAL ANALYSIS OF C.I. LEUCO SULPHUR BLACK 1 DYED COTTON FABRIC AFTER-TREATED WITH PLANT-DERIVED TANNIN-BASED PROTECTIVE AGENT

In this investigation, the X-ray photoelectron spectroscopic technique has been used to examine the surface chemistry of C.I. Leuco Sulphur Black 1 dyed cotton fabric, which has been after-treated with a tannin-based commercial product, Bayprotect CL, and laundered in accordance with ISO 105 C06 and C09 washing protocols. The dyeings were evaluated for colour strength, wash fastness and colour loss. Surface chemical compositions of the dyeings were analysed to relate visual changes with surface chemical changes. Alterations in percentage atomic concentrations of carbon, nitrogen, oxygen and sulphur were compared for untreated, after-treated, unlaundered and laundered dyed samples. After-treated and laundered dyed samples exhibited higher content of surface sulphur and lower surface oxidation, as compared to the untreated counterparts. The S (2p) spectra of after-treated and laundered samples demonstrated reduced over-oxidised (S6+) species at 168 eV. There was 5% and 4% less surface oxidation for ISO 105 C06 and C09 washing systems, respectively.

Synergistic effect of Cu decoration and N doping in divacancy defected graphene nanoribbons on hydrogen gas sensing properties: DFT study

Density functional theory (DFT) calculations have been employed to analyze the molecular hydrogen interaction on Cu decorated nitrogen doped divacancy defected graphene nanoribbons (GNRs). In this study, 5-8-5 double vacancy has been specified as a functional defect in order to study their effect on the electronic properties of GNRs. Divacancies are considered to be thermodynamically more favorable than monovacancies because of low formation energy. Moreover, the introduction of nitrogen defects had a massive influence on adsorption properties. The adsorption capability of the complex systems improved as the concentration of nitrogen atoms increased, but when four nitrogen atoms were doped, the efficiency decreased significantly. Aside from adsorption energy, other parameters such as bonding distance, charge transfer; electronic properties were examined and found to be consistent with the previous findings. Our results suggested that simultaneous doping of nitrogen atoms and Cu decorated defected GNR could be a potential material for hydrogen sensing and could be utilized for future applications. Hence, it is worth noting that adding appropriate dopants and defects to the graphene-based gas sensors could greatly improve their sensitivity.

Hybrid Plasma-Liquid Treatment of Carbon Nanotubes for Application in Direct Absorption Solar Thermal Collectors

Covalent functionalization of carbon nanotubes (CNTs) with oxygen-based or nitrogen-based functional groups is one of the most popular techniques to modify the surface energy and inherent properties of the CNTs.1 This functionalization generates interest for a broad range of applications including mechanically superior advanced composites,2 more sensitive gas sensors,3 enhanced energy storage materials4 or ultra-conductive fibers.5 As an alternative to the harsh chemicals used by traditional chemical functionalization, plasma-based surface treatments can be used with great efficacy and reduced reaction times, providing an array of application-specific benefits.Awareness of the environmental pollution caused by fossil fuels and the ever-increasing demand for energy has driven research focussed on zero-carbon renewable energy sources. Conscious of this, direct absorption solar thermal collectors are gaining prominence, both for domestic heating and steam generation. CNTs have been investigated as an additive to take advantage of the near blackbody absorption and high thermal conductivity to improve system efficiency. Critical to the success of the additive nanoparticles is the stability in the fluid, however, due to their high surface energy CNTs tend to agglomerate which can limit the efficacy of their integration into real-world products.In this work, macroscopic ribbon-like assemblies of carbon nanotubes are functionalized by plasma-induced non-equilibrium electrochemistry (PiNE) implemented through a simple direct current-based plasma-liquid system. This system utilizes the plasma-generated species in an electrolyte of 10 %vol ethanol in water, with or without a nitrogen precursor, for the oxygen and/or nitrogen functionalization of the carbon nanotube assembly. For this treatment, a ribbon-like piece of CNT was used as the anode and a helium plasma discharge triggered by applying 10 mA and 1 - 1.6 kV to act as the cathode. The plasma-generated species are then expected to migrate towards the CNTs and functionalize the sidewalls.The oxygen content is shown to be increased by between 70 % and 300 % when the treatment solution of 10 %vol ethanol is used in the ribbon electrode configuration. When ethylenediamine is added as a nitrogen precursor, the atomic concentration of nitrogen reaches 23 %, with amine groups, pyrrolic groups and graphitic nitrogen observed in the x-ray photoelectron spectra. This nitrogen content is unmatched in quantity when compared to either a simple soaking procedure or an electrolysis process with a platinum foil replacing the plasma as the counter-electrode. This demonstrates that the plasma either directly or indirectly, through plasma-generated species, facilitates and enhances the availability of nitrogen from the ethylenediamine precursor. The potential plasma-induced chemical pathways which lead to the functionalization of the CNTs are also investigated and discussed.In the application of a direct absorption solar collector system, it is found that the covalent functionalization provided by the plasma-liquid system enhances the stability of the CNT-ethylene glycol nanofluid, with the oxygen-functionalized samples producing the most stable nanofluids. This is explained through the lower value for contact angle measurements, suggesting greater hydrophobicity of the CNTs.References(1) Mallakpour, S.; Soltanian, S. Surface Functionalization of Carbon Nanotubes: Fabrication and Applications. RSC Adv. 2016, 6 (111), 109916–109935. https://doi.org/10.1039/c6ra24522f.(2) Williams, J.; Broughton, W.; Koukoulas, T.; Rahatekar, S. S. Plasma Treatment as a Method for Functionalising and Improving Dispersion of Carbon Nanotubes in Epoxy Resins. J. Mater. Sci. 2013, 48 (3), 1005–1013. https://doi.org/10.1007/s10853-012-6830-3.(3) Ham, S. W.; Hong, H. P.; Kim, J. H.; Min, S. J.; Min, N. K. Effect of Oxygen Plasma Treatment on Carbon Nanotube-Based Sensors. J. Nanosci. Nanotechnol. 2014, 14 (11), 8476–8481. https://doi.org/10.1166/jnn.2014.10007.(4) Hulicova-Jurcakova, D.; Seredych, M.; Lu, G. Q.; Bandosz, T. J. Combined Effect of Nitrogen- and Oxygen-Containing Functional Groups of Microporous Activated Carbon on Its Electrochemical Performance in Supercapacitors. Adv. Funct. Mater. 2009, 19 (3), 438–447. https://doi.org/10.1002/adfm.200801236.(5) Li, L.; Liu, E.; Shen, H.; Yang, Y.; Huang, Z.; Xiang, X.; Tian, Y. Charge Storage Performance of Doped Carbons Prepared from Polyaniline for Supercapacitors. J. Solid State Electrochem. 2011, 15 (1), 175–182. https://doi.org/10.1007/s10008-010-1087-8. Figure 1

Zirconium nitride as a highly efficient nitrogen source to synthesize the metal nitride clusterfullerenes

Metal nitride clusterfullerenes (NCFs) have significant applications in molecular electronics, biomedical imaging, and nonlinear optical devices due to their unique structures. However, their wide applications are limited by the production quantity. In this work, the yields of metal nitride clusterfullerenes M3N@C80 (M=Y, Sc, Gd) were greatly enhanced by utilizing zirconium nitride (ZrN) as an efficient nitrogen source for the arc-discharge method. Compared with the traditional synthetic route using N2 gas as nitrogen source, the ZrN inside graphite tube can be vaporized simultaneously with metal and graphite, and then afford the high concentration of nitrogen atoms in the arc region, which will promote the formation of metal nitride clusterfullerenes finally. The ZrN can promote the yields of Y3N@C80, Sc3N@C80 and Gd3N@C80, revealing the universal applicability of ZrN as a highly efficient nitrogen source. Specifically, the yield of Sc3N@C80 was greatly improved when adding ZrN, and it shows over double yield compared to traditional synthetic route using N2 gas. In addition, ZrN can also enhance the yields of paramagnetic azametallofullerene M2@C79N due to the high concentration of nitrogen atoms in the arc region. This new method enhances the production quantity of metal nitride clusterfullerenes and azametallofullerenes, and it will greatly promote the research and application of these molecular carbon materials.

Theoretical investigation of electronic and optical properties of nitrogen doped triangular shaped graphene quantum dots

The electronic and optical properties of graphene quantum dots can be significantly tailored by doping it with heteroatoms, thus extending its potential applications. In this work, we have employed time-dependent density functional theory to systematically explore the effect of introduction of nitrogen atoms in varying concentration at pyridinic and graphitic configuration in armchair and zigzag-edged triangular shaped graphene quantum dots (TQDs) of different sizes. Our results indicate that the electronic band-gap in these N-doped systems can be effectively tuned by varying the configuration as well as concentration of dopants and nature of edge-termination. The variation of electronic band-gap is critically determined by the localized/delocalized nature of molecular orbitals and presence of additional energy levels due to dopant nitrogen atoms. However, the significance of these extra energy levels in modulating the optical properties (appearance of characteristic N-dopant absorption peaks) becomes conspicuous only for specific configuration and concentration of nitrogen atoms. In addition, our studies have attributed the strong dependence of blue/red-shift of absorption spectra and variation in the peak profile to position as well as concentration of dopant atoms and edge-termination pattern. Further, it is observed that the effect of increasing size of TQDs on the strength of most intense absorption peak of pyridinic N-doped TQDs is remarkably different from graphitic N-doped systems. This selective manipulation of optical properties in TQDs due to different N-doping pattern can open up new frontiers for rational design of novel optoelectronic devices.

Investigation on the Threading Dislocations Formed by Lattice Misfits during Initial Stage of Sublimation Growth of 4H-SiC

We investigated the relation between the nucleation of dislocations and the lattice misfits by nitrogen concentration difference between seed and grown crystal during the initial stage of growth. 4H-SiC single crystals were grown with various nitrogen gas flow rates introduced into the crystal growing chamber under the same temperature and pressure to minimize the effect of thermal stress on the nucleation of dislocations. The nitrogen atomic concentrations of grown crystals depended on the introduced nitrogen gas ratios and they highly increased at the very early stage of growth. The generation of new threading dislocations at the interface also was affected by the nitrogen atomic concentrations differences between seed and grown crystals. Very few generated threading dislocations were observed in low nitrogen atomic concentration samples, however nucleation of threading dislocations at the interface were found in high nitrogen atomic concentrations samples. At initial stages of PVT growth process, the generation of threading dislocations induced by lattice misfits originated from nitrogen concentration difference between seed and grown crystals were investigated and found the appropriate nitrogen gas flow rates and profile at the heating and depressurized stage.

The Comparison of Nitrogen Atom Solubility in the Formation of Surface Layer on Stainless Steel and Alloy Steel

The chrome alloy has better affinity with nitrogen atom in nitriding process than any other alloy elements in steel. The higher content of chrome element binds larger number of nitrogen atoms. However, the higher concentration of nitrogen atom on the surface of the steel does not often make thicker case depth. This study clarified the phenomenon. The nitriding process was performed in two stages, namely the boost stage in the fluidized bed with the composition of 80 % NH3 and 20 % of N2 in 4 hours at 550 °C. Subsequently, the diffusion process was carried out in fluidized bed with the gas composition of 100 % N2 HP (high purity) in 2 hours. The chemical composition was measured by spectrometry and EDAX. The case depth was identified by micro-Vickers, and metallography was observed by SEM. The concentration of nitrogen atom on the surface of AISI 316 L is twice higher than that on the AISI 4140. The result shows that 0.1 to 1 wt % of nitrogen atom creates diffusion layer, 1 to 5 wt % of nitrogen atom produces nitride layer of γꞌ and ε, and nitrogen atom above 5 wt % forms white layer. The layer strongly depends on the percentage of nitrogen atom concentration. The nitrogen atom concentration is determined by the concentration of chromium element within the steel (AISI 316 L). Meanwhile, the depth of nitrogen atom diffusion is highly determined by the alloy element of Fe (AISI 4140).

Hybrid Plasma-Liquid Treatment of Carbon Nanotubes for Application in Direct Absorption Solar Thermal Collectors

Awareness of the environmental pollution caused by fossil fuels and the ever-increasing demand for energy has driven research focussed on zero-carbon renewable energy sources. Conscious of this, direct absorption solar thermal collectors are gaining prominence, both for domestic heating and steam generation. Carbon nanotubes (CNTs) have been investigated as an additive to take advantage of the near blackbody absorption and high thermal conductivity to improve system efficiency. Critical to the success of the additive nanoparticles is the stability in the fluid, however, due to their high surface energy CNTs tend to agglomerate which can limit the efficacy of their integration into real-world products. Covalent functionalization of the CNT sidewalls with oxygen-based or nitrogen-based functional groups is one of the most popular techniques to modify the surface energy of the CNTs.1 As an alternative to the harsh chemicals used by traditional chemical functionalisation, plasma-based surface treatments can be used with great efficacy and reduced reaction times.In this work, macroscopic ribbon-like assemblies of carbon nanotubes are functionalized using a simple direct current-based plasma-liquid system. This system utilizes the plasma-generated species in a fluid of 10 %vol ethanol in water, with or without a nitrogen precursor, for the oxygen and/or nitrogen functionalisation of the carbon nanotube assembly. For this treatment, a ribbon-like piece of CNT was used as the anode and a helium plasma discharge triggered by applying 10 mA and 1 - 1.6 kV to act as the cathode. The plasma-generated species are then expected to migrate towards the CNTs and functionalisation the sidewalls.The oxygen content is shown to be increased by between 50 % and 200 % when the treatment solution of 10 %vol ethanol is used in the ribbon electrode configuration. When ethylenediamine is added as a nitrogen precursor, the atomic concentration of nitrogen reaches 23 % in the ribbon electrode configuration, with amine groups, pyrrolic groups and graphitic nitrogen observed in the x-ray photoelectron spectra. This nitrogen content is unmatched in quantity when compared to either a simple soaking procedure or an electrolysis process with a platinum foil replacing the plasma as the counter-electrode. This demonstrates that the plasma either directly or indirectly, by means of plasma-generated species, facilitates and enhances the availability of nitrogen from the ethylenediamine precursor. The potential plasma-induced chemical pathways which lead to the functionalization of the CNTs are also investigated and discussed.In the application of a DASC system, it is found that the covalent functionalisation provided by the plasma-liquid system enhances the stability of the CNT-EG nanofluid, with the oxygen-functionalized samples producing the most stable nanofluids. This functionalization method generates interest for a broader range of applications including mechanically superior advanced composites,2 more sensitive gas sensors,3 enhanced energy storage materials4 or ultra-conductive fibres.5 References (1) Mallakpour, S.; Soltanian, S. Surface Functionalization of Carbon Nanotubes: Fabrication and Applications. RSC Adv. 2016, 6 (111), 109916–109935.(2) Williams, J.; Broughton, W.; Koukoulas, T.; Rahatekar, S. S. Plasma Treatment as a Method for Functionalising and Improving Dispersion of Carbon Nanotubes in Epoxy Resins. J. Mater. Sci. 2013, 48 (3), 1005–1013.(3) Ham, S. W.; Hong, H. P.; Kim, J. H.; Min, S. J.; Min, N. K. Effect of Oxygen Plasma Treatment on Carbon Nanotube-Based Sensors. J. Nanosci. Nanotechnol. 2014, 14 (11), 8476–8481.(4) Hulicova-Jurcakova, D.; Seredych, M.; Lu, G. Q.; Bandosz, T. J. Combined Effect of Nitrogen- and Oxygen-Containing Functional Groups of Microporous Activated Carbon on Its Electrochemical Performance in Supercapacitors. Adv. Funct. Mater. 2009, 19 (3), 438–447.(5) Li, L.; Liu, E.; Shen, H.; Yang, Y.; Huang, Z.; Xiang, X.; Tian, Y. Charge Storage Performance of Doped Carbons Prepared from Polyaniline for Supercapacitors. J. Solid State Electrochem. 2011, 15 (1), 175–182. Figure 1

Furan and Pyran Functional Groups Driven the Surface of Nitrogen‐Doped Nanofiber Sponges

AbstractHighly surface oxidized, nitrogen‐doped, and nitrogen functionalized carbon nanotube sponge (N‐CFS) were produced at 1020 °C using two sprayers approach in an aerosol‐assisted chemical vapor deposition (AACVD) experiment. The structure of N‐CFS consisted of entangled and corrugated carbon nanofibers of ∼200 nm diameter, also showing junctions and knots. TEM characterizations revealed that the carbon nanofiber exhibits stacked graphitic layers in a transversal way with positive curvature. Superficial chemical analysis by XPS showed that the N‐CFSs contain an atomic concentration of oxygen and nitrogen of 9.2% and 2.9%, respectively. The high‐resolution XPS scans deconvolution‐analysis revealed high percentages for C−O bonds, pyrrolic nitrogen doping, NH3 functionalization, and Si−C interactions. The cyclic voltammetry measurements did not display a redox process despite the high oxygen concentration at the surface. Hydrophobic functional groups containing C−O bonds do not participate in a redox process (furan, pyran, epoxy, methoxy, ethoxy, among others) could mostly determine the electroactivity of N‐CFS. Based on density functional theory calculations, we determine that the furans transfer a high amount of electron and promote a positive curvature in thin carbon nanotubes. Graphitic materials with furans, pyrans, and epoxy functional groups could be used as an anode in lithium‐ion batteries.

Theoretical study of electronic properties of nitrogen doped carbon nanotubes

In this work, we have studied the effects of nitrogen (N) substitutional doping on the electronical properties of single wall carbon nanotube (SWCNT). The electronic density of states (eDOS) of these nanosystems has been calculated in the framework of tight-binding calculations method. The obtained results show that the semiconducting SWCNT could be a quasi-metallic one after N-substitution. We conclude that electronic properties of the N-doped nanotubes (SWCNNT) are sensitive not only to the concentration of nitrogen atoms but also to their distribution on the nanotube surface. Our main results are discussed in the light of the experimental data.

Optical investigation of as-grown NV centers in heavily nitrogen doped delta layers in CVD diamond

In this paper, we realize growth of the delta doped layer (3 nm thick) with high concentration of nitrogen atoms (about 1.4 × 1019 cm−3) during CVD diamond growth process. We experimentally investigate the distribution of the nitrogen inside the grown layer and formation of the NV centers during such growth. Using confocal microscopy, we analyze the spatial distribution of the NV centers and investigate the formation efficiency of the NV centers in delta doped layers. The spatial distribution is measured by two methods, using second-order correlation function and emission volume analysis, and NV center concentration is found to be 3.9 ± 0.6 and 2.7 ± 0.2 μm-2 consequently. The divergence between the methods is discussed. As-grown NV centers formation efficiency was found to be 30 times lower than in the case of uniform doped diamond growth. Nevertheless, coherence time of an electron spin for a single NV center inside the delta layer was found to be around 1 μs which is quite reasonable given the concentration of the nitrogen in the sample.

Evolution of N(4S) atoms produced under nitrogen streamer conditions: time-resolved TALIF study at reduced pressures

The evolution of N(4S) species produced by filamentary streamer discharge was investigated by two-photon absorption laser-induced fluorescence technique. A triggered single streamer filament was periodically produced in pure nitrogen at pressures of 20, 50, 100 and 200 Torr, and N(4S) species were monitored in the center of the discharge gap during the streamer formation, decay and afterglow. Under all of the investigated pressures, the population maxima of nitrogen atoms were observed in a microsecond timescale; i.e. well after the extinction of the streamer event. The concentration of nitrogen atoms increased with pressure. The maximum N(4S) concentration measured at 20 Torr was about 1013 cm−3, while it exceeded 1015 cm−3 at 200 Torr. After reaching maxima, atomic densities exhibit hyperbolic decay, which was followed up to the post-discharge time of 0.5 ms. Our results show that only a small part of N(4S) is produced during the streamer transit or within 200 ns after the transit (20%–25% increase with respect to the background density), while most of the nitrogen N(4S) atoms are produced during the streamer channel decay in timescales from units to several tens of microseconds.

Investigation of short-term, high-temperature oxidation of AlCrN coating on WC substrate

A surface analysis was performed on an aluminum chromium nitride (AlCrN) coating formed on a tungsten carbide (WC) substrate subjected to short-term (in minutes) oxidation at an elevated temperature (900 °C) using focused ion beam (FIB), X-ray photoelectron spectroscopy (XPS), grazing incidence X-ray diffraction (GI-XRD), and laser-induced breakdown spectroscopy (LIBS). To separately analyze a coating with a thickness of several micrometers, the GI-XRD method was used. For cross-sectional imaging, the samples were milled using an FIB system, and chemical bonding states and surface elemental concentrations were analyzed by XPS. Within just a few seconds, the color of the AlCrN coating surface changed irregularly and, after 10 min, the entire coating layer surface changed. The entire coating surface oxidation as discoloration progressed in partial areas after 30 min. Based on the GI-XRD and XPS results, after 1 min, alumina and chromium oxides formed on the outermost surface, and after 10 min, Cr-W and Co-W oxide phases appeared, resulting from a reaction with WC near the interface. The atomic concentration of nitrogen in the AlCrN coating decreased after few seconds on the outermost surface and was almost eliminated after 10 min; oxygen showed the opposite trend. Finally, the FIB and LIBS results showed that voids formed within the coating layer and interface at high temperatures, and diffusion of Al and Cr in subsequent reactions was identified. This work demonstrates interesting results from various analyses that differ from previously reported AlCrN coating oxidation behaviors, and could provide a better understanding of long-term reactions for the surface oxidation of AlCrN coatings at high temperatures.

In Situ Monitoring of Surface Reactions during Atomic Layer Etching of Silicon Nitride Using Hydrogen Plasma and Fluorine Radicals.

The atomic layer etching (ALE) of silicon nitride (SiN) via a hydrogen plasma followed by exposure to fluorine radicals was investigated by using in situ spectroscopic ellipsometry and attenuated total reflectance Fourier transform infrared (FTIR) spectroscopy to examine the surface reactions and etching mechanism. FTIR spectra of the surface following exposure to the hydrogen plasma showed an increase in the concentration of Si-H and N-H bonds, although the N-H bond concentration plateaued more quickly. In contrast, during fluorine radical exposure, the Si-H bond concentration decreased more rapidly. Secondary ion mass spectrometry demonstrated that the nitrogen atom concentration was decreased to a depth of 4 nm from the surface after the hydrogen plasma treatment and indicated a structure consisting of N-H rich, Si-H rich, and mixed layers. This indicated that Si-H bonds were primarily present near the surface, while N-H bonds were mainly located deeper into the film. The formations of the N-H and Si-H rich layers are important phenomena associated with modification by hydrogen plasma and fluorine radical etching, respectively.

N-doped graphene catalysts with high nitrogen concentration for the oxygen reduction reaction

Nitrogen doped reduced graphene oxide (NrGO) catalysts and composites of these with carbon nitride (CN) with nitrogen content as high as 19.8 wt% and 35.8 wt%, respectively, have been synthesized by thermal annealing of multilayer graphene oxide and urea at different temperatures. Nitrogen has been effectively introduced as a mix of pyridinic, pyrrolic, pyridonic and quaternary bonding configurations into the carbon lattice of graphene upon removal of CN phase over 650 °C. The electrocatalytic activity towards oxygen reduction reaction (ORR) in 0.1 M NaOH has been investigated. NrGO catalysts with less nitrogen content show better performance than composites. NrGO produced at 800 °C presents the best activity with half-wave potential of 0.76 V vs. RHE and a mean number of electrons of 3.7, which are close to a commercial Pt/C catalyst. This study concludes that a high concentration of nitrogen atoms in multilayer reduced graphene oxide does not necessarily produce a highly active electrocatalyst, suggesting that carbon in the neighbourhood of nitrogen atoms are the active sites for ORR in alkaline medium.