Addition Of N2 Research Articles

The production mechanisms of OH radicals in a pulsed direct current plasma jet

The production mechanism of OH radicals in a pulsed DC plasma jet is studied by a two-dimensional (2-D) plasma jet model and a one-dimensional (1-D) discharge model. For the plasma jet in the open air, electron-impact dissociation of H2O, electron neutralization of H2O+, as well as dissociation of H2O by O(1D) are found to be the main reactions to generate the OH species. The contribution of the dissociation of H2O by electron is more than the others. The additions of N2, O2, air, and H2O into the working gas increase the OH density outside the tube slightly, which is attributed to more electrons produced by Penning ionization. On the other hand, the additions of O2 and H2O into the working gas increase the OH density inside the tube substantially, which is attributed to the increased O (1D) and H2O concentration, respectively. The gas flow will transport high density OH out of the tube during pulse off period. It is also shown that the plasma chemistry and reactivity can be effectively controlled by the pulse numbers. These results are supported by the laser induced fluorescence measurements and are relevant to several applications of atmospheric-pressure plasmas in health care, medicine, and materials processing.

Selective area deposition of diamond films on AlGaN/GaN heterostructures

Diamond‐on‐GaN heterostructure is a promising hybrid material system with a variety of applications such as heat spreaders, high‐temperature, and high‐power devices. From a practical point of view, polycrystalline diamond is shown to be an attractive solution to the limited use of the expensive monocrystalline diamond substrates. Here we present selective area diamond deposition on AlGaN/GaN layers focusing on the elimination of surface and metal contact damage (Ni, NiO, Ir, and IrO2) and suppressing the spontaneous nucleation of diamond. Metal contacts are important for further applications such as diamond‐coated GaN based electronic devices. The growth of diamond films was performed by microwave chemical vapor deposition in different gas mixtures with the addition of CO2 or N2 to CH4/H2. Adding CO2 resulted in polycrystalline (PCD), while adding N2 led to the formation of nanocrystalline diamond film (NCD). The diamond deposition was carried out using selective area nucleation in a three‐layer sandwich structure (polymer/seeding layer/polymer), which avoided damage to the electrode and GaN surfaces from ultrasonic seeding by diamond particles. No protective layer was used on the GaN surface before diamond deposition, i.e., diamond films were grown directly on the AlGaN/GaN heterostructures. In the case of NCD deposition, no surface damaging of GaN was observed. For both NCD and PCD films, increasing methane from 1% to 2% in H2 minimized the surface damage of GaN films.

Change of diamond film structure and morphology with N2 addition in MW PECVD apparatus with linear antenna delivery system

Deposition of nano‐crystalline diamond (NCD) over large areas is of high interest for industrial applications. For instance NCD is an excellent substrate for cell growth but it is also interesting for photonic applications associated with nitrogen‐vacancy (NV) centres. There have been many studies on the effect of nitrogen addition on the growth of diamond using conventional resonance cavity microwave plasmas (both H and Ar based) but none using MW PECVD apparatus with linear antenna delivery system (MW‐LA‐PECVD). In this work, we show that an ultra nano‐crystalline diamond (UNCD) type of morphology can be prepared upon N2 addition to H2CO2CH4 plasmas at low pressures (0.3 mbar) and low temperature (520 °C); however, these films despite their UNCD character show sp3 dominated Raman spectra and highly isolating behavior. The crystalline structure and morphology of the films were characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, grazing angle X‐ray diffraction, and transmission electron microscopy. Diamond films' composition was evaluated from thermal neutron depth profiling. Films were also characterized by photoluminescence spectroscopy to study the incorporation of luminescent NV centre. Addition of nitrogen increases deposition rate and dramatically changes surface morphology and crystalline structure from well faceted diamond crystals to UNCD like morphology.

Control of the area irradiated by the sheet-type plasma jet in atmospheric pressure

The sterilization effect has been investigated using the sheet-type plasma jet, which was generated between asymmetric electrodes with dielectric plates in gas flow released into the atmospheric air. In this paper, it is indicated there is a possibility that the plasma jet irradiation area can be controlled only by supplied gases without changing a generator structure. The irradiation area control was evaluated from both the sterilization area size and the oxidizing substances distribution. The oxidizing substance distribution was obtained using the chemical reagent prepared in our laboratory. The width of the sheet-type plasma jet was able to be controlled by N2 addition into He gas. As a result, the width of the sterilization area was able to be controlled within the range of 2 to 12 mm at a constant height without changing the generator structure. On the other hand, the evaluation from the oxidizing substances distribution indicated that the irradiation area cannot be controlled in one direction.

Nearly amorphous Mo-N gratings for ultimate resolution in extreme ultraviolet interference lithography

We present fabrication and characterization of high-resolution and nearly amorphous Mo1 − xNx transmission gratings and their use as masks for extreme ultraviolet (EUV) interference lithography. During sputter deposition of Mo, nitrogen is incorporated into the film by addition of N2 to the Ar sputter gas, leading to suppression of Mo grain growth and resulting in smooth and homogeneous thin films with a negligible grain size. The obtained Mo0.8N0.2 thin films, as determined by x-ray photoelectron spectroscopy, are characterized to be nearly amorphous using x-ray diffraction. We demonstrate a greatly reduced Mo0.8N0.2 grating line edge roughness compared with pure Mo grating structures after e-beam lithography and plasma dry etching. The amorphous Mo0.8N0.2 thin films retain, to a large extent, the benefits of Mo as a phase grating material for EUV wavelengths, providing great advantages for fabrication of highly efficient diffraction gratings with extremely low roughness. Using these grating masks, well-resolved dense lines down to 8 nm half-pitch are fabricated with EUV interference lithography.

The effect of surface reactions of O, O3 and N on film properties during the growth of silica-like films

The effect of surface reactions of O, O3 and N radicals during the growth of silica-like (SiOxCyHz) films on film properties is investigated. A SiOxCyHz film is deposited from a He/Hexamethyldisiloxan (HMDSO) cold atmospheric plasma on a rotating substrate. The surface of this film is, during the growth, treated on the opposite site of the substrate by a second cold atmospheric plasma with helium and an addition of O2 or N2. A reactor with four separated cells and gas curtains between them is used to avoid cross-contamination of the ambient atmosphere in each cell. The changes in film composition after the deposition with and without a treatment by O, O3 and N are investigated by Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy. Additionally, the effect of each species on the deposition rate is also presented and discussed.

CO2-/N2-Triggered Viscoelastic Fluid with N,N-Dimethyl Oleoaminde-Propylamine and Sodium p-Toluenesulfonate

In this article, a new type of CO2-triggered switchable wormlike micelles based on N,N-dimethyl oleoaminde-propylamine (DOAPA) and sodium p-toluene sulfonate (SPTS) mixed in a molar ratio of 1:1 is studied. With inlet of CO2, DOAPA molecules are protonated to form quaternary ammonium. The electrostatic attraction between quaternary ammonium and SPTS results in assembled structures and formation of a viscoelastic wormlike fluid. These results are proved by rheological methods in this study. Upon the release of CO2, the quaternary ammonium is deprotonated back to tertiary amines, the assemble structures are split, and water-like fluid is obtained. Such a reversible transition of viscosity between high and low can be repeated several times with or without CO2. This transition of the micromolecular structure is proved by 1H NMR and conductivity. As well, the process of viscosity reduction can be controlled by the flow rate of N2 addition.

Effects of diluents on NO x formation in coflow CH4/air diffusion flames

The effect of diluent addition on NO x formation in a laminar CH4/air coflow diffusion flame was investigated by numerical simulation with experimental verification. The hydrocarbon fuel stream was diluted with N2, CO2, and Ar. The volume fraction of diluents systematically changed from 0.0 to 0.5. The simulation data agree well with the experimental one. The computational results indicate that overall the three diluents reduce the formation of NO and the effects vary from weak to strong in the order: N2, Ar and CO2. Differences between the influences of the various diluents are discussed in terms of the thermal, the dilution and the direct chemical effects, respectively. Further, the addition of CO2 reduces the formation of NO2, while the addition of N2 or Ar has little effect on it. However, the formation rate of N2O increases by each of the added diluents.

Afterglow of Argon Plasmas with H2, O2, N2, and CO2Admixtures Observed by Thomson Scattering

This study assess the decay of a power-pulsed microwave plasma in argon mixtures using time resolved Thomson scattering. In argon at intermediate pressure, i.e. tens of mbar, the electron temperature decays very fast after power off and approaches the heavy particle temperature, while the electron density decays slower, in the order of tens of microseconds. Argon with small admixtures of O2 or H2 exhibits a similar behavior. However, strikingly different is the result for small additions of N2 or CO2. For up to 100 μs after the power is switched off, the electron temperature does not decrease to the gas temperature but remains at values as high as 0.8 eV. Nitrogen and carbon dioxide exhibit relatively large cross-sections to excite vibrational states by electron collisions. Knowing that, the observed post-heating can be attributed to super-elastic energy transfer from vibrational excited N2(X) and CO2(X) molecules to electrons.

Explosion characteristics of argon/nitrogen diluted natural gas–air mixtures

This work was initiated to address safety concerns related to natural gas (NG)–air mixtures. NG, being an alternative fuel for vehicles and a chemical feedstock in the manufacture of organic chemicals, has been widely used in the industrial process in the past decade. NG is a flammable, gaseous fuel and thus presents a fire and explosion hazard. In this study, an investigation of the explosion characteristics including flammability limits, maximum explosion pressure (pmax), maximum rate of pressure rise (dp/dt)max, and laminar burning velocity (SL) is carried out by systematically measuring the pressure histories in a standard 20-L spherical vessel. The dilution effects on the explosion characteristics are also explored through the addition of two diluents, i.e., argon (Ar) and nitrogen (N2), into the NG–air mixture. The experimental results indicate that the flammability region ranges from 5.5% to 15% NG by volume at ambient conditions. It is found that reducing the initial pressure decreases the interval width of flammability limits. This is due to the distance between the molecules of the gas being shorter as the initial pressure increases and therefore, resulting in a higher probability of effective collision between molecules. Consequently, this effect in turn promotes the initial and subsequent chemical reactions. The results also show that increasing diluent ratio results in a narrower flammability region and that the effect of N2 addition is more pronounced than Ar. The present results also confirm that the variation of pmax with the equivalence ratio of NG exhibits an inversely “U-shaped” behavior and pmax decreases with decreasing initial pressure. In general, the addition of Ar and N2 would decrease the value of pmax. However, it is observed in this study that the value of pmax fluctuates when argon is added, especially for those mixtures with φ<1. It is noted that increasing Ar dilution returns the mixture to an ignition condition and even reaches an optimal composition (i.e., close to the stoichiometric condition). On the other hand, the Ar dilution has a suppression effect on the explosion. These two competing effects with increasing Ar dilution therefore make pmax remain relatively constant within an interval of dilution percentage for fuel lean mixtures (e.g., with fuel concentration CNG equal to 5% and 6%). Finally, results also indicate that SL decreases with an increase of initial pressure and the rate of decrease of SL is faster when the mixture is diluted with N2 compared to the effect of Ar. This can be explained by the fact that the density dominates over the retarding effect for SL.

Optical Spectroscopic Investigation of Ar/CH3OH and Ar/N2/CH3OH Atmospheric Pressure Plasma Jets

Ar/CH3OH and Ar/N2/CH3OH plasma jets were generated at atmospheric pressure by dual-frequency excitations. Two different cases were studied with focus laid on the generation of CN radicals. In one case Ar gas passed through a bubbler with saturated methanol steam but without addition of N2 (Ar/CH3OH plasma). In the other case N2 passed through the bubbler with saturated methanol steam (Ar/N2/CH3OH plasma). The optical emission lines of CN radicals have been observed in these two cases of plasma discharges. The addition of N2 can significantly increase the optical emission intensity of CN bands.

Double-Position-Boundaries Free 3C-SiC Epitaxial Layers Grown on On-Axis 4H-SiC

High quality double-position-boundaries free 3C-SiC epilayers have been successfully grown on on-axis (0001) 4H-SiC by chemical vapor deposition at optimized conditions as observed with optical microscopy and X-ray diffraction. The effect of the growth parameters, including temperature, C/Si ratio, ramp-up condition, Si/H2 ratio, N2 addition and pressure, on the quality of the grown layers is investigated. Different techniques, including microscopic and spectroscopic techniques, are used to characterize the epilayers. High resolution X-ray diffraction shows 2θ-ω curve with full width at half maximum of only 16 arcsec for the (111) reflection detected from a 35 μm thick 3C-SiC layer, showing the good structural quality of the layer. Reciprocal space maps confirm the absence of double-position-boundaries in a large depth of the layers. Low temperature photoluminescence measurement shows clear near-bandgap emission with sharp and single peaks, which further verifies the high quality of the epilayers.

Structure and dynamics of CO2and N2in a tetracyanoborate based ionic liquid

To gain insight into the transport behavior of gas molecules such as CO2versus N2 through ionic liquid membranes, we performed molecular dynamics simulations to investigate the structure and dynamics of CO2 and N2 gases in a tetracyanoborate based ionic liquid recently shown to exhibit high CO2/N2 permselectivity. We found that upon addition of CO2 or N2 the liquid structure does not change. CO2 or N2 molecules occupy the voids between ions and their local environments are found to be similar. Gas diffusivity is about one order of magnitude greater than that of the cation or anion. Dissolved N2 diffuses slightly faster than CO2. We hence conclude that the high permeability selectivity of CO2versus N2 observed experimentally is mainly due to the disparity in gas solubility. In other words, the much higher solubility of CO2 in tetracyanoborate-based ionic liquids such as 1-ethyl-3-methylimidazolium tetracyanoborate [emimB(CN)4] leads to their high CO2 permeability. Based on the experimental solubility and the simulated diffusivity, we obtained a permeability of 2830 barrer for CO2 in emimB(CN)4 at 300 K, in good agreement with the experimental value of 2040 barrer.

Rice Slurry Analysis Using Mixed-Gas Plasma and Axially Viewed ICP OES

This study deals with determination of essential and toxic elements in slurry of rice using axially viewed inductively coupled plasma optical emission spectrometry (ICP OES) and mixed gas plasma (N2-Ar ICP). Nitrogen was added (flow rate of 20 mL min−1) to the nebulizer gas through the spray chamber. It was observed that the addition of N2 increased the ICP robustness and mitigated the slurry matrix effects. Several parameters associated with the slurry preparation (extractant concentration, dispersant concentration, mass volume ratio of the slurry and sonication) were evaluated. The slurry was prepared in 10 % (m/v) HNO3 + 0.2 % (m/v) Triton X-100. Calibration was carried out with aqueous standards whereas Y(II) (371.029 nm) was used as internal standard (IS) in order to overcome matrix effects. The IS and sample solutions were mixed online. Accuracy was evaluated by the analysis of certified reference materials and by comparison with an independent method of sample preparation (acid digestion). The concentrations were consistent with those certified or found in digested rice sample. Calcium, Mg, K, Cd Cu, Fe, Mn, Mo, Cr, Zn, Co, Pb and Ni were investigated whose limits of detections were 0.080, 0.033, 0.050, 0.048, 0.050, 0.015, 0.005, 0.107, 0.036, 0.056, 0.040, 0.367 and 0.132 mg kg−1, respectively. The RSD (relative standard deviation) was typically lower than 10 %. Samples of parboiled, white, and brown rice were analysed and the concentrations found corroborate with those reported. It was concluded that calibration with aqueous standard is feasible, making the analysis simpler. The method is robust and can be routinely applied.

Ashing of photoresists using dielectric barrier discharge cryoplasmas

Plasma ashing of photoresists is a critical step in advanced microelectronics manufacturing as it often leads to extensive damage in porous organosilicate low-κ dielectrics and hinders the use of highly porous films in interconnects. To reduce plasma damage, the authors investigated the feasibility of ashing a 248-nm photoresist with cryoplasma. The authors ashed photoresist-coated silicon wafers with dielectric barrier discharge microplasma generated at temperatures of 170–291 K, a pressure of 100 Torr, applied voltages of Vappl=0.8−1.6 kV, and a frequency of f=20 kHz in both Ar/O2 and Ar/O2/N2 gas mixtures. While the ashing rates at 170 K in Ar/O2 decreased to about 20% of the ashing rates achieved at room temperature and 240 K, the addition of N2 to the plasma gas enhanced the ashing rates by a factor of 1.5–2. Optical emission spectroscopy measurements of the plasmas showed that, in the Ar/O2/N2 mixture, the main reactive species are N2 radicals; x-ray photoelectron spectra of the ashed photoresists i...

High efficiency chlorine removal from polyvinyl chloride (PVC) pyrolysis with a gas–liquid fluidized bed reactor

In this research a gas–liquid fluidized bed reactor was developed for removing chlorine (Cl) from polyvinyl chloride (PVC) to favor its pyrolysis treatment. In order to efficiently remove Cl within a limited time before extensive generation of hydrocarbon products, the gas–liquid fluidized bed reactor was running at 280–320°C, where hot N2 was used as fluidizing gas to fluidize the molten polymer, letting the molten polymer contact well with N2 to release Cl in form of HCl. Experimental results showed that dechlorination efficiency is mainly temperature dependent and 300°C is a proper reaction temperature for efficient dechlorination within a limited time duration and for prevention of extensive pyrolysis; under this temperature 99.5% of Cl removal efficiency can be obtained within reaction time around 1min after melting is completed as the flow rate of N2 gas was set around 0.47–0.85Nm3kg−1 for the molten PVC. Larger N2 flow rate and additives in PVC would enhance HCl release but did not change the final dechlorination efficiency; and excessive N2 flow rate should be avoided for prevention of polymer entrainment. HCl is emitted from PVC granules or scraps at the mean time they started to melt and the melting stage should be taken into consideration when design the gas–liquid fluidized bed reactor for dechlorination.

Hysteresis-free deposition of TiOxNy thin films: Effect of the reactive gas mixture and oxidation of the TiN layers on process control

This paper investigates the effect of the reactive gas mixture (N2 + O2 + Ar) and oxidation of the nitride layers on the system stability during the reactive sputter deposition of TiOxNy thin films. The present research is an extension of previous investigations conducted by Severin et al. (Appl. Phys. Lett., 88 (2006) 161504) and Duarte et al. (Appl. Surf. Sci., 269 (2013) 55–59) in which the Berg's model was used to study reactive deposition of oxynitrides. The results show that the addition of N2 to the process avoids the formation of a hysteresis loop and facilitates the deposition of films with fractions of TiO2 at any value. These achievements are not possible without this procedure. In contrast, despite eliminating plasma instabilities, the addition of N2 decreases the mass deposition rate due to the modifications in the sputtering yield. Other results show that the oxidation of TiN also plays a key role in the mass deposition rate and in the hysteresis loop.

Nucleophilic Addition of Nitrogen to Aryl Cations: Mimicking Titan Chemistry

The reactivity of aryl cations toward molecular nitrogen is studied systematically in an ion trap mass spectrometer at 10(2) Pascal of nitrogen, the pressure of the Titan main haze layer. Nucleophilic addition of dinitrogen occurs and the nature of aryl group has a significant influence on the reactivity, through inductive effects and by changing the ground state spin multiplicity. The products of nitrogen activation, aryldiazonium ions, react with typical nitriles, aromatic amines, and alkynes (compounds that are relevant as possible Titan atmosphere constituents) to form covalently bonded heterocyclic products. Theoretical calculations at the level [DFT(B3LYP)/6-311++G(d,p)] indicate that the N2 addition reaction is exothermic for the singlet aryl cations but endothermic for their triplet spin isomers. The -OH and -NH2 substituted aryl ions are calculated to have triplet ground states, which is consistent with their decreased nitrogen addition reactivity. The energy needed for the generation of the aryl cations from their protonated precursors (ca. 340kJ/mol starting with protonated aniline) is far less than that required to directly activate the nitrogen triple bond (the lowest energy excited state of N2 lies ca. 600kJ/mol above the ground state). The formation of aza-aromatics via arene ionization and subsequent reactions provide a conceivable route to the genesis of nitrogen-containing organic molecules in the interstellar medium and Titan haze layers.

Theoretical and experimental study of the influence of nitrogen admixture on characteristics of dc diffuse glow discharge in rare gases at intermediate pressures

An effect of nitrogen admixture on the electric field in positive column of diffuse glow discharge in various rare gases at intermediate pressures is studied both experimentally and theoretically. The discharge is maintained in a cylindrical glass tube. Earlier it was observed and reproduced in calculations that addition of N2 (1%) to Ar at pressure 40 Torr led to noticeable decrease in the electric field strength at a fixed discharge current. In the present work there are results for pure Ne and Ne + 1%N2 gas mixtures at pressure 40 Torr. It is found that the addition of N2 to Ne leads to the increase in the electric field strength; the observed effect is reproduced in calculations. The explanation of differences in the impact of N2 addition on the electric field strength in Ar and Ne discharges is given. On the basis of the performed analysis it is predicted that the addition of N2 to He leads to the increase in the electric field in the discharge and the addition of N2 to Xe leads to the decrease in the electric field. For the case of He, the prediction is experimentally confirmed in this work, while for the case of Xe, it is corroborated by literature data.

Highly-enhanced reflow characteristics of sputter deposited Cu interconnections of large scale integrated devices by optimizing sputtering conditions

Improving the reflow characteristics of sputtered Cu films was attempted by optimizing the sputtering conditions. The reflow characteristics of films deposited under various sputtering conditions were evaluated by measuring their filling level in via holes. It was found that the reflow characteristics of the Cu films are strongly influenced by the deposition parameters. Deposition at low temperatures and the addition of H2 or N2 to the Ar sputtering gas had a significant influence on the reflow characteristics. Imperfections in the Cu films before and after the high-temperature, high-pressure treatments were investigated by positron annihilation spectroscopy. The results showed that low temperature and the addition of H2 or N2 led to films containing a large number of mono-vacancies, which accelerate atomic diffusion creep and dislocation core diffusion creep, improving the reflow characteristics of the Cu films.