Partial Pressure Of Nitrogen Gas Research Articles

(Invited) Nitrogen Based Solid State Magneto-Ionics

Solid-state magneto-ionic (MI) effects have shown promise for energy-efficient nanoelectronics, where ionic migration may be used to achieve atomic-scale control of interfaces in magnetic nanostructures. To date, magneto-ionics have been mostly explored in oxygen-based systems [1-4], while there is a surge of interest in alternative ionic systems due to their different ionic migration mechanisms and characteristics [5-7].We have recently demonstrated effective MI control of magnetic functionalities using a variety of ionic species, particularly nitrogen. In nitride-based Ta/CoFe/MnN/Ta films, the chemically induced MI effect is combined with the electric field driving of nitrogen to electrically manipulate exchange bias [8]. Upon field-cooling the heterostructure, ionic diffusion of nitrogen from MnN into the Ta layers occurs. A significant exchange bias is observed, which can be further enhanced by ~ 20% after voltage conditioning (Figs. 1a-1e). This enhancement can be reversed by voltage conditioning with an opposite polarity. Nitrogen migration within the MnN layer and into the Ta capping layer causes the enhancement in exchange bias, which is observed in polarized neutron reflectometry studies.We have also achieved all-nitride-based magneto-ionic systems [9]. Thin films of (001)-ordered Mn4N are grown by sputtering Mn onto Mn3N2 seed layer on Si (100) substrate. Nitrogen ion migration across the Mn3N2 /Mn layers leads to a continuous evolution of the layers to Mn3N2 /Mn4N, Mn2N/Mn4N, and eventually Mn4N alone (Figs. 1f-1g). Furthermore, we have demonstrated MI control of the exchange bias effect in an all-nitride Mn4N/MnNx system, where the field-trained exchange field can be varied up to ten times by introducing or extracting nitrogen from the nitride system. This is achieved by adjusting the nitrogen gas partial pressure during deposition or varying annealing temperature after deposition.These effects demonstrate contrasts with oxygen-based MI effects in terms of operating principles, switching speed, and reversibility. Such MI systems are valuable platforms to gain quantitative understanding at buried interfaces. They also offer potentials for device applications based on electric modulation of magnetic functionalities.This work has been supported in part by the NSF (ECCS-2151809, DMR-2005108, DMR-1828420), SRC/NIST SMART Center, and KAUST.[1] U. Bauer et al., Nat. Mater. 14, 174 (2015).[2] C. Bi et al., Phys. Rev. Lett. 113, 267202 (2014).[3] D. A. Gilbert et al., Nat. Commun. 7, 11050 (2016).[4] G. Chen et al., Sci. Adv. 6, eaba4924 (2020).[5] A. J. Tan et al., Nat. Mater. 18, 35 (2019).[6] G. Chen et al., Phys. Rev. X 11, 021015 (2021).[7] J. de Rojas et al., Nat. Commun. 11, 5871 (2020).[8] C. J. Jensen et al., ACS Nano 17, 6745 (2023).[9] Z. J. Chen et al., Appl. Phys. Lett. 123, 082403 (2023). Figure 1

Production of Cyanide Using Thermal Plasma: Thermodynamic Analysis and Process-Specific Energy Consumption

A plasma process for making cyanide from nitrogen and hydrocarbon (methane and propane) has been successfully demonstrated, which can directly fix atmospheric nitrogen into hydrocarbons. Nitrogen serves as both the plasma gas and the primary reactant. The thermodynamic analysis as well as the experimental outcome indicates that it is feasible to achieve very high conversion of hydrocarbons into cyanide by increasing the partial pressure of nitrogen gas within the reaction mixture, but the high conversion comes at a cost of an increase in total energy consumption and was detrimental to process energy efficiency. Hence, the process was optimized based on specific energy consumption (SEC) instead of conversion. The conversion with respect to nitrogen and hydrocarbon ratio follows thermodynamic prediction. The primary byproducts obtained were hydrogen, acetylene, and soot. The laboratory system was stable and could be run for extended periods, achieving a minimal SEC of approximately 15.5 kW h/kg NaCN.

Surface characterization and electrochemical properties of tantalum nitride (TaN) nanostructured coatings produced by reactive DC magnetron sputtering

In this study, TaN nanostructured coatings were successfully produced on AISI 316 L stainless steel substrates using the reactive DC magnetron sputtering method. Among all of these coating processes, the only variable factor was the percentage of partial pressure of nitrogen gas (PN2) which was attended in the sputtering process. To do this, the percentage of partial pressure of nitrogen gas was chosen in different percentages of 5%, 10% and 15%. After the coatings formation, their microstructure, chemical composition and corrosion behavior were studied. The microstructure of the samples coated was studied by the scanning electron microscope (SEM), their elemental and phase composition by energy diffraction spectroscopy (EDS), X-ray diffraction (XRD) and elemental distribution was carried out by mapping (MAP) analysis. In order to study the corrosion behavior of coatings, the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests were carried out in a simulated body fluid (Ringer's solution). Immersion time of specimens was determined 1, 24, 48 h and 7 days in Ringer's solution. The results of different tests showed that coatings containing 15% nitrogen consisted of hard orthorhombic and hexagonal tantalum nitride phases, had free pores and denser microstructure. This coating exhibited better corrosion behavior than the other two ones in all of the immersion times. The corrosion resistance of this coating also increased by rising immersion time from 1 h to 7 days. In fact, the coating containing 15% of nitrogen being immersed for 7 days with a resistance of 118.68 (MΩ.cm2), had the highest corrosion resistance.

Nitrogen Solubility in Liquid Ni-V, Ni-Ta, Ni-Cr-V, and Ni-Cr-Ta Alloys

An investigation has been made concerning the solubility of nitrogen in liquid binary alloys (Ni-V and Ni-Ta) and ternary alloys (Ni-Cr-V and Ni-Cr-Ta) by sampling method. The experiments were carried out in the temperature range from 1773 K to 1873 K and under the nitrogen partial pressure up to 1.0 bar. A technique involving induction melting and a rapid quench device has been used in this study. It has been found that Sieverts’ law successfully describes the nitrogen dissolution in all these liquid alloys up to 1.0 bar of nitrogen gas partial pressure. The additions of vanadium, tantalum and chromium significantly increase the nitrogen solubility, especially vanadium-alloying addition. Furthermore, we have determined the interaction parameters, enthalpies and entropies of nitrogen dissolution in these liquid alloys.

Influence of nitrogen partial pressure on optical properties of magnetron sputtered Al-Si-N thin films

Al-Si-N thin films were deposited on glass substrates at varying nitrogen partial pressure through magnetron sputtering. The effect of partial pressure of nitrogen gas in the gaseous mixture (argon and nitrogen) on the optical properties such as absorption coefficient, band gap energy, refractive index, extinction coefficient, dielectric constant of the film was investigated and correlation with structure was carried out. Nitrogen partial pressure has a considerable effect on the film microstructure and consequently on their optical properties. The transformation of the film from opaque to transparent is dependent on the partial pressure of nitrogen. The crystallite size decreases from 27 to 19 nm with the rise in partial pressure of nitrogen from 3 × 10−1 Pa to 6 × 10−1 Pa but again increases as the pressure reaches 7.5 × 10−1 Pa. Refractive index of Al-Si-N coatings shows normal dispersive behaviour. The transmittance, band gap energy, optical conductivity and dielectric constant of the films were also studied as a function of nitrogen partial pressure.

HIGH TEMPERATURE GAS NITRIDING TREATMENT OF AISI 430 USING LOW AND HIGH PURITY NITROGEN GAS

The properties of stainless steels can be improved by high temperature gas nitriding (HTGN) treatment. The improving of their properties are obtained from nitrogen atom which diffuse into stainless steel. Nitrogen gas is the main source of nitrogen atom on the HTGN treatment. Generally, these treatment use high purity of nitrogen gas. The aim of this research is to investigate the effect of nitrogen gas purity on the HTGN treatment for AISI 430. Stainless steel AISI 430 plate 2 mm thick was processed by HTGN treatment. The specimens was exposed at nitrogen gas atmosphere at temperature 1200oC and held for 2 hours prior quenching in water. The treatment used industrial/welding grade (99.5%) as low nitrogen gas purity and ultra high purity (UHP) grade (99.999%) as high nitrogen gas purity. The vickers micro-hardness test was conducted to evaluate the hardness distribution from surface into middle section of the specimens before and after treatment. Light optical microscope was applied to examine the microstructure of specimens after treatment. Metallographic examination shows both treatments using low and high purity gas have the same grain size. However HTGN treatment using low purity of nitrogen gas produces hardness slightly lower than the high purity. This is due the high content of impurity of the low purity gas that reduces the partial pressure of nitrogen gas. Another effect of impurity is the reaction between nitrogen gas and its impurity especially oxygen gas. These reactions reduce the amount of free nitrogen atom which diffuses on the stainless steel.

Fluorescence XAFS study of local structures in high-k gate dielectrics HfSiON/SiON/Si annealed at various nitrogen gas partial pressure

Geometric structures for HfSiON/SiON/Si films annealed at various N2 gas partial pressures were investigated using fluorescence XAFS measurement at Hf LIII- and LI-edge. The XAFS analysis has revealed that the local structures around the Hf atoms strongly depend on the N2 gas partial pressure. For the sample annealed at the N2 gas partial pressure of 10 Torr HfN and HfSiON coexist, and for the samples annealed at the N2 gas partial pressure above 100 Torr Hf atoms form HfSiON only. These results indicate that the formation of HfN for HfSiON/SiON/Si films can be suppressed by annealing at proper partial pressure of N2 gas.

Metastable nitric acidhydrates—possible constituents of polar stratospheric clouds?

Crystallization kinetics of the metastable modifications of Nitric Acid Dihydrate (NAD) was investigated by time-dependent X-Ray Diffraction (XRD) measurements. Kinetic conversion curves were evaluated adopting the Avrami model. The growth and morphology of the respective crystallites and particles were monitored in situ on the cryo-stage of an Environmental Scanning Electron Microscope (ESEM) under a partial pressure of nitrogen gas (0.5 Torr, 67 Pa). The morphologies were used to adapt the InfraRed (IR) extinction spectra by T-matrix calculation using respective optical indices of NAD. The results show a significant dependence of the band shapes on different morphologies.

The crystallization kinetics and morphology of nitric acid trihydrate

Crystallization kinetics of stable and metastable nitric acid trihydrate (NAT) were investigated by time dependent X-ray powder diffraction (XRD) measurements. Kinetic conversion curves were evaluated adopting the Avrami model. The growth and morphology of the respective crystallites were monitored in situ on the cryo-stage of an environmental scanning electron microscope (ESEM) under a partial pressure of nitrogen gas (0.3 Torr, 40 Pa). The results show a close relationship between the presence of ice in the sample and the crystallization mechanism of NAT, which results in different shapes and sizes of NAT crystal particles.

Preparation and characterization of sputtered Fe1−xNx films

Iron nitride films have been prepared by reactive DC magnetron sputtering. The composition of Fe1−xNx was varied over a range of 0≤x≤0.5 by controlling the nitrogen flow rate during sputtering. These films were characterized using powder X-ray diffraction (XRD), thermogravimetric and electron microprobe analysis. We found that the nitrogen content in the films increased with nitrogen gas partial pressure. XRD experiments revealed an evolution through the α-Fe, γ′-Fe4N, ɛ-Fe2+zN, ζ-Fe2N, γ‴-FeN and γʺ-FeN phases, when the nitrogen gas mole percentage was increased from 0% up to 70%. Above 70%, only the γʺ-FeN phase was formed despite a measurable increase in the nitrogen content of the film with nitrogen gas partial pressure. Rietveld analysis of powder X-ray diffraction patterns revealed that this behavior is due to an increase in the nitrogen site occupation factor within the lattice.

Micro-Raman spectroscopic analysis of tetrahedral amorphous carbon films deposited under varying conditions

The structure of tetrahedral amorphous carbon (ta-C) films deposited by a filtered cathodic vacuum arc has been studied using micro-Raman spectroscopy in terms of substrate bias, nitrogen gas partial pressure (ta-C:N films) or aluminum content in a mixed aluminum/carbon target (ta-C:Al films) during deposition. The first-order Raman spectra generally show a broad feature overlaid by a disordered (D) peak and a graphitic (G) peak. The contribution of sp3 bonding to the Raman spectrum is not explicit, since the Raman phonon line is more sensitive to the sp2 carbon bonding due to its larger Raman scattering cross section. However by comparing the ratios of the intensities, the full widths at half maximum (FWHM), and the peak areas between the D and G peaks, the sp3 contribution may indirectly be reflected by the complex Raman features. The G peak position for the ta-C and ta-C:N films appears to not change significantly with the change of substrate bias voltage or N2 partial pressure, whereas the shift of the D peak is more appreciable. On the contrary, the G peak position for the ta-C:Al films shows a continuous decrease with increasing Al content. For the undoped ta-C films, the minimum intensity, area, and FWHM ratios between the D peak and the G peak are obtained at a bias around −100 V, which corresponds to the maximum sp3 content in the ta-C films. These ratios for the ta-C:N and ta-C:Al films, however, generally increase with increased N or Al content, which indicates the increase of sp2 bonded clusters.

CNx thin films grown by pulsed laser deposition: Raman, infrared and X-ray photoelectron spectroscopy study

Carbon nitride films have been deposited by pulsed laser ablation of graphite targets in a controlled nitrogen atmosphere. The samples composition was determined by means of X-ray photoelectron spectroscopy. A study of the C 1s and N 1s core level photoemission bands evidenced, upon increasing nitrogen gas partial pressure, the continuous increase of the nitrogen content, along with a systematic modification of the components related to both trigonal and tetrahedral CN bonding configuration. Nitrogen atomic contents up to 30%, with respect to carbon, were estimated. Raman and infrared spectroscopy results showed broad and featureless structures typical of an amorphous carbon phase. On the whole they confirm a progressive raise of the number of N atoms bonded to sp2-hybridized C when increasing the nitrogen partial pressure.

Densification of TiN-Ni cermets by improving wettability of liquid nickel on TiN grain surface with addition of Mo 2C

A new fabrication method for full density TiN-base cermets by conventional liquid phase sintering in vacuum has been developed in the present study. Poor wettability of liquid Ni on a TiN grain surface was greatly improved with addition of Mo 2C into the TiN-Ni alloys and thus a wetting angle changed from about 90 to nearly 0°. The TiN-Mo 2C-Ni compacts were able to be sintered to almost full density by a conventional vacuum sintering without controlling the partial pressure of nitrogen gas. Pore formation and pore growth occurring during the sintering of TiN-Ni compacts was attributed to evolution of nitrogen gas due to thermal dissociation of TiN from an uncovered TiN grain surface being directly exposed to pores. Vanadium carbide (VC) appeared to suppress significantly the growth of TiN grains during liquid phase sintering and to improve greatly the mechanical properties of sintered TiN-Mo 2C-Ni compacts.

Investigation of titanium nitride films deposited at room temperature by energetic cluster impact

Energetic cluster impact (ECI) deposition was applied to grow titanium nitride films on silicon (100) substrate at room temperature. Proton elastic scattering (PES), X-ray diffraction (XRD) and atomic force microscopy (AFM) were employed to characterize the composition, structure and morphology of TiN x films, respectively. The PES results reveal that the films are N-deficient and there exists a certain amount of oxygen impurity in the films. It is found from the XRD results that the structure of TiN x films is sensitive to experimental conditions such as nitrogen gas partial pressure, sputtering current and substrate bias voltage and that TiN x films are (220) preferred orientation within some range of experimental conditions. The AFM observation indicates that the films become more uniform and compact with increasing substrate bias voltage. The root mean square roughness also decreases with increasing bias voltage. Some interpretation for the above results are also given in this paper.

Formation of titanium nitride films by energetic cluster impact deposition

Titanium nitride (TiN) films were formed on silicon (100) substrates at room temperature by energetic cluster impact deposition (ECID). The films show a gold-like color. The influence of deposition conditions, such as nitrogen partial pressure (P N2) and sputter current (I s), on the properties of the films, was investigated by Rutherford backscattering spectrometry (RBS), proton elastic scattering (PES) and X-ray diffraction (XRD). The RBS results show the film thickness is typically 360 nm. It is found using PES spectra that the relative content of nitrogen in the films increases first fast then slowly with the increase of nitrogen gas partial pressure (P N2). XRD results show the films appear to be (220) preferential orientation. Additionally, a certain amount of oxygen impurity was incorporated into the films. Some explanations for the above results are also given in this paper.

Direct current magnetron sputtered W–AlN cermet solar absorber films

W–AlN cermet selective surfaces have been investigated using a special direct current (dc) magnetron sputtering technology. During the deposition of the W–AlN cermet layer, both Al and W targets were run simultaneously in a gas mixture of argon and nitrogen. The total sputtering gas pressure was 1 Pa and the reactive nitrogen gas partial pressure was chosen at 2.5×10−2 Pa, which is beyond the transition point from metal phase to dielectric phase in the deposited material. The ceramic AlN component was deposited by dc reactive sputtering and the metallic W component by dc sputtering due to the excellent nitriding resistance of metallic tungsten. By substrate movement a multi-sublayer system, consisting of alternating W and AlN sublayers, was deposited. This deposited multi-sublayer system can be considered as a macro-homogeneous W–AlN cermet layer with metal volume fraction determined by controlling the thickness of the sublayers. W–AlN cermet selective surfaces with a double cermet layer film structure were deposited. The typical film structure from surface to bottom substrate is an AlN anti-reflection layer on a double W–AlN cermet layer on an Al metal infrared reflection layer. A solar absorptance of 0.92–0.94 with emittance of 0.03–0.05 at room temperature and 0.08–0.10 at 350°C has been achieved for such W–AlN cermet selective surfaces. The W–AlN cermet has excellent thermal stability in vacuum at high operating temperature.

Preparation and properties of reactive-sputtered amorphous CN x films

We prepared amorphous CN x films by a rf reactive magnetron sputtering using ArN 2 mixed gas and a graphite target. The nitrogen-carbon ratio x = N C in films determined by the XPS increased from 0.48 to 0.62 as increasing the nitrogen gas partial pressure ratio r = p N 2 (p N 2 + p Ar ) . Optical energy gap E 0 obtained by the Tauc's plots increased from 1.4 to 1.6 eV with the nitrogen-carbon ratio x. Dangling bonds density of a-CN x was 10 18 to 10 19 cm −3 from ESR measurement. Dc conductivity of a-CN x is very small. As irradiated Xe lamp, photoconductivity was observed. The hydrogenation of a-CN x was tried by a hydrogen-plasma treatment.

High Nitrogen Steels. Dissolution and Reprecipitation of Nitrides in an Austenitic Stainless Steel Produced by Powder Metallurgy.

Production of nitrogen-alloyed AISI 316 steel containing titanium has been studied using a powder metallurgy route. The material is prepared by nitriding titanium-free 316 powder in an ammonia/nitrogen gas mixture at temperatures below 900°C and then blending with the titanium alloyed steel to give the required total nitrogen content in the alloy. Alloys with sufficient nitrogen for precipitation of titanium nitride (TiN) and an excess of 0.2%N in solid solution were prepared. The blend powders were cold isostatically pressed into cylindrical samples and sintered at temperatures between 1100 and 1350°C. Samples were also extruded at 1200°C without prior sintering. The results show that the titanium alloyed powder is not fully austenitic in the as-sprayed form but the austenite phase is stabilised by the presence of nitrogen. The as-nitrided powder contains a considerable amount of chromium nitride and the microstructure of the sintered or extruded steel is controlled by the behaviour of that phase. The best conditions for densification are found to be at 1350°C in a vacuum furnace with a partial pressure of nitrogen gas applied as the temperature approaches the sintering maximum, followed by a hold for one hour. This gives a material of relatively high density with a controlled nitrogen distribution, high hardness and a fully austenitic structure. During the heating cycle and while the pore structure remains open the vacuum results in the decomposition of some chromium nitride and redistribution of nitrogen into solid solution, but as this is above the atmospheric solubility limit some of it is lost to the atmosphere. The process is limited by the onset of pore closure at maximum sintering temperature. The rate of decomposition of the nitride in the solid state is slow and if the sintering temperature is low then the process of decomposition of the nitrides is incomplete, residual (coarse) chromium nitride remains and the properties are poor. This is also the case in extruded samples which contain remains of the original nitrided particles even after heat treatment. However, when the sintering regime involves liquid phase sintering, the process of dissolution of the original chromium nitride goes to completion, fine titanium nitride remains and a high-density strengthened component is achieved.

Thermal stability of WNx/n-GaAs Schottky contacts formed by reactive sputtering

The electrical properties and thermal stability of WNx/GaAs contacts where WNx is formed by reactive sputtering of W are investigated. The results show that contacts have good electrical properties and thermal stability provided that the partial pressure of nitrogen gas during sputtering does not exceed certain limits. Excess nitrogen in WNx film degrades contact properties, The formation of W and W2N phases, trapping of excess nitrogen atoms at the interface and the possible formation of GaAsxN1-x, compound at the interface, with x being a function of annealing temperature, were used to explain the observation.

Magnetron sputtered carbon nitride films

Carbon nitride (CN x ) thin film deposition was undertaken in a closed-field, unbalanced magnetron system. Reactive deposition utilised a graphite target in an argon/nitrogen plasma. The main deposition parameters investigated were magnetron current, total gas pressure and nitrogen gas partial pressure. The films deposited were examined using IR spectroscopy, ellipsometry, and X-ray diffraction (XRD). Analysis of the results yielded the following characteristics: refractive index of nitrogen-containing films was reduced below that for pure carbon films but had little dependence on substrate bias and total gas pressure. It was, however, strongly dependent on the magnetron current at which the film was deposited. IR spectroscopy showed the transmittance of the films for given deposition conditions to be a monotonic function of nitrogen content. The deposition conditions themselves also had a significant effect, in particular the magnetron current. In addition, C N bonding was evident from the absorption bands observed. Structural analysis by means of XRD showed that the amorphous nature of the films with some degree of graphitic content depended more on the deposition parameters than on the nitrogen concentration. Increased graphitic-type structure was observed at low magnetron currents, high system pressure and large (negative) substrate bias.