Nitrogen Partial Pressure Research Articles

Evolution of microstructure, mechanical and tribological properties of vanadium carbonitride coatings sputtered at different nitrogen partial pressures

Vanadium carbide coatings were deposited by R.F. reactive magnetron sputtering at different nitrogen partial pressures. The structures and the mechanical and tribological behaviour of these coatings were studied.By using a combined approach of EDS and WDS, it has been shown that increasing nitrogen concentration from 0 to 27 at.% led to decrease the carbon content from 48.50 to 30.50 at.%. All coatings exhibited a dominant fcc-VC structure with additional fractions of vanadium nitrides, as determined by XRD. Nanoindentation measurements showed that the highest hardness of 26.1 GPa was obtained for the coating with a (N + C) / (V) ratio equal to 1.44. The transition in brittleness-ductile failure mode was noticed with increasing nitrogen content. This adhesive feature can prevent phase separation and improves the wear resistance of the coatings. Moreover, the nitrogen partial pressure showed a significant influence on the friction coefficient because of film density and residual stress effects.

Formation of nanoscale structures in thin films deposited by reactive magnetron sputtering of binary metal targets in Ar+O2+N2 gas mixture

Bi-metal targets of ZnSn and SiAl were sputtered in A+O2+N2 gas mixtures at various N2/O2 ratios, and the deposited films were investigated by AFM and XPS. No nitrogen was detected in the films even at the highest nitrogen partial pressure in the gas, and the films were oxides. The concentration of the doping metal component in the deposited film increases with the increase of nitrogen partial pressure in the working gas. These experimental observations were supported by numerical calculations of the sputter-deposition process using a SRIM/SIMTRA+RSD software. It was shown that added nitrogen promotes sputtering of doping metal components of the targets, and the concentration of oxygen remains high enough to substitute the less active nitrogen in the growing film. The films consisted of nanograins with the average diameter, which decreased from 18 nm to 3 nm with increase of nitrogen content in the working gas. This effect was explained by the mechanism of abnormal grain growth: the film consisted of grains of oxides of two metals with different concentrations. The doping metal forms very fine nanograins of oxides, which suppress the growth of oxides of the main metal. With increase of nitrogen in the working gas mixture, the sputtering rate of doping metals from the cathodes and their respective concentration in the growing films increases, so the average diameter of oxide grains forming the coating decreases.

Correlating elemental distribution with mechanical properties of TiN/SiNx nanocomposite coatings

Detailed structural and chemical analyses reveal that Ti-Si-N coatings prepared with high nitrogen partial pressure and temperature are composed of nm-sized (nearly equiaxed) TiN crystallites encapsulated by ~1.0 nm thin Si-rich tissue phase. This nanocomposite structure allows for superior hardness (37.6 ± 1.5 GPa) and fracture toughness (4.5 ± 0.6 MPa√m). Contrary, deposition at lower nitrogen partial pressure and temperature does not allow for such a clear Si segregation during film growth, leading to nm-sized solid solution Ti1-xSixN crystallites. Although having the same Si content of 8.5 at.%, their hardness (32.1 ± 0.9 GPa) as well as fracture toughness (3.0 ± 0.2 MPa√m) is significantly lower.

Effect of altered nitrogen partial pressure on Chlorellaceae for spaceflight applications

Algal-based photobioreactors offer a promising bioregenerative technology that can perform the functions of air revitalization, water recycling, and food production in a human spacecraft life support system. In order to assess their performance in this context, this study exposed a non-axenic green algal culture (Chlorellacea) to an atmospheric pressure of 8.2psia [56.5 kPa] with an oxygen concentration of 34%, which are currently proposed cabin atmosphere conditions for future space exploration missions. Growth and metabolism of green algae were compared to a control experiment kept at 14.7psia [101.3 kPa] with oxygen and carbon dioxide partial pressure maintained at constant levels of 3.1 and 0.147psia [21.3 and 1.0 kPa], respectively, which represent concentrations of 21 and 1% at standard sea level pressure. To conduct the evaluation, a flow-through photobioreactor was developed that can precisely control atmospheric compositions such as partial pressures of oxygen and carbon dioxide and set the total pressure solely by altering the nitrogen partial pressure. Algal performance was measured by daily cell counts and optical density measurements. Additionally, continuous measurements of dissolved oxygen and pH in the liquid phase, as well as evolved oxygen and absorbed carbon dioxide in the gaseous phase, were collected. A metagenomic analysis was conducted on the algal culture to assure the composition of the algal culture remained consistent during the experimental phase, as well as to characterize the nature of coexisting contaminants in the non-axenic culture. The performance of the algal culture was compared to related, previously published literature values. The hypothesized increase in performance of the algal culture under reduced pressures was not verified, rather it was shown that the nitrogen partial pressure neither benefits nor inhibits algal growth under the tested conditions.

Innovative N2-selective metallic membranes for the potential use of CO2 capture

The permeability of nitrogen in Group V metal membranes having an approximate thickness of 40 μm was determined for the first time at conditions of relatively low temperature (400–600 °C) and pressure (300–600 kPa). Vanadium, niobium and tantalum membranes were investigated to evaluate the permeation characteristics towards nitrogen permeation. Analogous to the hydrogen transport mechanism through palladium-based membranes, the nitrogen permeating flux through the metallic membranes was determined to take place through a solution-diffusion mechanism. In particular, at 400 °C, the nitrogen permeability was found to be 1.15 × 10-12, 1.05 × 10-12, and 6.54 × 10-13 mol/(m s Pa0.5) for vanadium, niobium and tantalum, respectively.The optimal nitrogen partial pressure exponent value was found to be 0.5 for all the membranes investigated. The nitrogen permeability for the vanadium membrane was described by an Arrhenius-type relation where the pre-exponential factor and apparent activation energy for this correlation were 3.55 × 10-15 mol/(m s Pa0.5) and 31.8 kJ/mol, respectively. For niobium and tantalum membranes, it was not possible to perform any permeation tests due to cracks, which formed at temperatures higher than 500 °C.SEM and EDS analyses revealed the formation of metal oxides on the surface of V, Nb, Ta membranes, which may benefit the transport of nitrogen through the membrane as it may aid in preserving the structured nature of the bulk phase thereby preventing the formation of defects and/or grain migration at high temperature. Although the nitrogen permeability through metallic membranes is low and metal oxides form on the surface, this work describes the performance of metallic membranes toward nitrogen permeation, and it can be considered as the benchmark for future work related to this field.

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.

Chemical and structural characterization of tungsten nitride (WNx) thin films synthesized via Gas Injection Magnetron Sputtering technique

Tungsten nitride (WNx) thin films were synthesized on the silicon substrates by way of Gas Injection Magnetron Sputtering (GIMS) technique. Pulsed discharge conditions, generated in the GIMS method, were optimized to maintain the nitrogen partial pressure in the range of an order of 10−3 to 10−1 Pa by a periodical injection of gas doses. In this way, we could increase the mean free path of atomic species and preserve their kinetic energy, in comparison to the continuous sputtering techniques. Under these conditions we attempted to overcome the high nucleation barrier, common for β-W2N phase synthesis. Here, different nucleation mechanisms of tungsten nitride thin films were examined by the scanning electron microscopy (SEM) and the atomic force microscopy (AFM). In terms of chemical bonding state investigations of WNx films, we engaged the Raman spectroscopy measurements and the X-ray photoelectron spectroscopy (XPS). Furthermore, structural circumstances of tungsten nitrides were analyzed via X-ray diffraction (XRD) investigations. On a line of advanced applications issue, optical properties of these films were discussed on the basis of the spectroscopic ellipsometry results.

STRUCTURE AND MECHANICAL PROPERTIES OF MULTILAYER COATINGS (TiAlCrY)N/ZrN

Multiperiodic nitride coatings (TiAlCrY)N/ZrN with different layer thicknesses are formed by vacuum-arc evaporation in a nitrogen atmosphere (0.2…0.6 Pa) of two targets, TiAlCrY and Zr. The targets were located along one straight line at equal distances from the perpendicular axis on which the substrates were placed. The rotation of the axis with the substrates was carried out either continuously or with a fixed delay at the evaporators. The duration of the process was chosen so that the total thickness of the coating (total thickness of the bilayers) was 10…11 μm. The effect of nitrogen pressure and modulation period on the structural-phase state, elemental composition, and mechanical properties of multilayer coatings has been studied. An increase in the partial pressure of nitrogen and, consequently, its content in the coating leads to an increase in hardness. Reducing the thickness of the layers in the coatings increases the adhesive strength of the coatings and does not have a significant effect on the microstresses in the coating.

The Influence of Nitrogen Partial Pressure on the Composition, Microstructure, and Mechanical Characteristics of Ti1 –x–yAlxTаyN Coatings Obtained by Reactive Magnetron Sputtering

The evolution of the elemental composition, surface morphology, microstructure, and mechanical properties of Ti1 –x–yAlxTаyN coatings deposited by reactive magnetron sputtering has been studied when the ratio of the partial pressure of nitrogen to the total pressure of reactive gas mixture was increased from 0.1 to 0.5. It is established that most significant changes in the relative content of Ti, Al, and Ta in as-deposited coatings take place when this ratio is varied from 0.1 to 0.3. The observed changes in the elemental composition of Ti1 –x–yAlxTаyN coatings do not influence their phase composition, but lead to changes in the microstructure and mechanical characteristics.

Physical and electrical properties of nitrogen-doped hydrogenated amorphous carbon films

Nitrogen-doped hydrogenated amorphous carbon films (a-C:H:N) have been prepared by a plasma-activated chemical vapor deposition technique (PACVD) by using a plasma beam source (PBS). The properties of the a-C:H:N films were changed by varying the total pressure, the substrate temperature (100 °C, 300 °C) and nitrogen partial pressure p(N2) by adding nitrogen to the precursor acetylene (C2H2). For the investigations, a-C:H:N films have been deposited onto glass slides and doped silicon wafers. The deposition rate decreased with increasing nitrogen content in the N2/C2H2 gas mixture and with decreasing total pressure. The elemental composition of two sample series (300 °C) has been analyzed with Elastic Recoil Detection Analysis (ERDA). The highest N content and N/C ratio was estimated to be 16 at.% and 0.25 at the highest p(N2), respectively. Microhardness measurements showed that the hardness decreased with increasing p(N2). Electrical resistance of the a-C:H:N films was measured by 4-point probe. Electrically conductive coatings have been obtained by nitrogen-doped a-C:H films at higher substrate temperature (300 °C). The electrical resistance of the a-C:H:N films also decreases with decreasing total pressure, with the lowest value being about 1 Ohm cm. The film density was determined by means of X-ray reflectometry (XRR).

Experimental producing of Cu–Cr–N composite alloys and thermodynamic modeling of their phase composition

Composite Cu–Cr–N alloys were obtained in situ under vibration of “copper melt – chromium powder” compositions before their crystallization. Two types of alloys were prepared, where chromium powder was freely dispersed or compacted into a tablet. Atmospheric nitrogen was used as a source of chromium nitrides in the alloys. The microstructure of the alloys is represented by a copper matrix hardened with chromium particles and numerous inclusions of non-stoichiometric chromium nitrides Cr2N1–x. Thermodynamic modeling showed that the composition and quantities of chromium nitrides in the Cu–Cr–N alloy depend on the partial pressure of nitrogen above the melt.

Влияние парциального давления азота на состав, микроструктуру и механические характеристики покрытий Ti-=SUB=-1-x-y-=/SUB=-Al-=SUB=-x-=/SUB=-Tа-=SUB=-y-=/SUB=-N, полученных методом реактивного магнетронного распыления

AbstractThe evolution of the elemental composition, surface morphology, microstructure, and mechanical properties of Ti_1 –_ x _–_ y Al_ x Tа_ y N coatings deposited by reactive magnetron sputtering has been studied when the ratio of the partial pressure of nitrogen to the total pressure of reactive gas mixture was increased from 0.1 to 0.5. It is established that most significant changes in the relative content of Ti, Al, and Ta in as-deposited coatings take place when this ratio is varied from 0.1 to 0.3. The observed changes in the elemental composition of Ti_1 –_ x _–_ y Al_ x Tа_ y N coatings do not influence their phase composition, but lead to changes in the microstructure and mechanical characteristics.

Исследование оптических, механических и термических свойств свободновисящих пленок на основе нанокомпозитных материалов MoSi-=SUB=-2-=/SUB=-N-=SUB=-x-=/SUB=- и ZrSi-=SUB=-2-=/SUB=-N-=SUB=-y-=/SUB=-

The optical, mechanical, and thermal properties of freestanding films based on nitrided molybdenum and zirconium disilicides were investigated. It has been shown that nitriding of silicides leads to a significant increase in the thermal stability of the films. So, if crystallization of initially amorphous freestanding MoSi2 or ZrSi2 films is observed at temperatures of 330-370°C, the introduction of nitrogen into the film makes it possible to increase the temperature up to 600-700°С at which MoSi2Nx and ZrSi2Ny (at least for x ≥ 0.25, y ≥ 1.3) films can be used for many hours when heated under vacuum. The study of mechanical tensile strength showed that the ultimate strength is weakly dependent on the nitrogen content in MoSi2Nx films (0 ≤ x ≤ 0.55). Comparison of the properties of MoSi2Nx and ZrSi2Ny films obtained by the magnetron method at the same nitrogen partial pressure demonstrated that at similar values of the transmittance at 13.5 nm, nitrated ZrSi2 films are more effective as protective coatings (less susceptible to oxidation and more resistant to degradation at high temperatures).

Highly Reliable Amorphous In-Ga-Zn-O Thin-Film Transistors Through the Addition of Nitrogen Doping

The electrical properties and the device reliability under positive/negative bias stress with/without illumination regarding amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) are evaluated as a function of the nitrogen partial pressure in the sputter deposition. Interestingly, it is easy to control the carrier concentration through the incorporation of nitrogen into IGZO, whereby the device performance is changed. In addition, when nitrogen is introduced during the conventional IGZO deposition, the device reliability of N-doped IGZO TFTs is considerably improved compared to that of undoped-IGZO TFTs due to the reduced amount of defects. It is also interesting that such an improvement of the device reliability regarding IGZO is easily obtainable through the simple addition of nitrogen to the conventional deposition process. It is, therefore, strongly believed that this simple nitrogen-doping process for IGZO is very effective regarding the achievement of highly durable devices, and it can be immediately applied to the current mass production of the high-performance displays for which the oxide semiconductor is used.

Reactive sputtered TixNbyN coatings. II. Effect of common deposition parameters

Abstract TiNbN coatings are being applied to orthopaedic hip and knee implants for the purpose of improved wear resistance and reduced friction during application. However, the performance of these coatings is not always satisfactory and improvements in reliability in particular, are needed. Fundamentally, this stems from a lack of materials processing knowledge. In the present investigation, TixNbyNz coatings have been processed using reactive magnetron sputtering. The aim has been to establish the fundamental relationships that exist between several common sputtering parameters and the material properties exhibited by the resulting coatings. The sputtering parameters include deposition pressure, nitrogen partial pressure, applied substrate heating, and applied substrate bias, and the materials properties include composition, structure, microstructure and surface roughness. The present investigation is the second of a two component investigation on the processing of TixNbyNz coatings.

Nitrogen passivation formation on Cu surface by Ar–N2 plasma for Cu-to-Cu wafer stacking application

Wafer stacking technology provides reduced interconnect delay, improved bandwidth, reduced form factor, and decreased cost. Solder-based metallic die bonding is presently utilized in high-volume manufacturing, but Cu-based metallic wafer bonding is quickly becoming a key bonding technique for next generation 3D IC and heterogeneous stacking applications. In this study, Ar–N2 plasma treatment on Cu surface was investigated to passivate Cu surface with nitrogen and to enhance the bonding quality of Cu-to-Cu wafer bonding. The Ar–N2 plasma treatment was performed by conventional DC sputtering under 5 mTorr working pressure with different Ar–N2 partial pressures. Then, the effect of Ar–N2 plasma treatment on Cu surface was evaluated structurally and electrically. It was observed that the Ar–N2 plasma treatment with high nitrogen partial pressure over a sufficient plasma treatment time provided activated Cu surface, reduction of copper oxide and chemisorbed nitrogen, and copper nitride passivation. The Ar–N2 plasma treatment of Cu surface was found to be a potential pretreatment method for Cu-to-Cu bonding.

CrAlSiN barrier layer to improve the thermal stability of W/CrAlSiNx/CrAlSiOyNx/SiAlOx solar thermal absorber

The influence of adding CrAlSiN barrier layer between the back-reflector tungsten (W) and stainless-steel substrate on thermal stability has been investigated. In previous work, after the annealing in vacuum at 600 °C, tungsten diffusion from the back-reflection layer towards the stainless-steel substrate was found. In this study, a barrier layer was added and its influence upon the W diffusion was studied. Several designs of multilayer solar selective absorber for high temperature applications were used to test the thermal and chemical stability and oxidation resistance after vacuum annealing. These samples were characterized by Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS), X-ray diffraction (XRD), Fourier-transform Infrared Spectroscopy (FTIR) and UV–VIS–NIR spectroscopy. All absorber tandems show good thermal stability after vacuum annealing at 600 °C and the changes in optical constants solar absorptance (α) and thermal emittance (ε) are negligible. In some cases, small changes in the reflectance curves after the first step of annealing were seen. Some changes were found in the oxide layer, due to the incomplete oxidized Si atoms, as confirmed by FTIR analyses. This cannot justify the increase of NIR reflectance observed in the optical stacks after annealing, which can be due to the phase changes of the back-reflector tungsten layer. All layers of stacks are amorphous, except the tungsten layer, which is polycrystalline and shows a columnar growth. The addition of a CrAlSiNP = 0.11 Pa barrier layer between tungsten and stainless-steel substrate proved to be a good solution to control the diffusion of W atoms towards the substrate, whereas using higher nitrogen partial pressure in the high and the low absorption layers reduce the diffusion of Cr from those layers to surface.

Effect of transition layer on the performance of hydroxyapatite/titanium nitride coating developed on Ti-6Al-4V alloy by magnetron sputtering

A gradient transition multilayer hydroxyapatite/titanium nitride (HA/TiN) coating was prepared on the Ti-6Al-4V alloy by magnetron sputtering. The composition, surface topography, microstructure, adhesion strength and electrochemical properties of the as-deposited coatings were characterized by SEM/EDS, AFM, XRD, FT-IR and electrochemical workstation. The experimental results showed that the single TiN coating deposited at a partial pressure of nitrogen (N2) of 0.08 Pa had the best internal stress and tribological performance, and its volume loss was only 0.89% of that of Ti-6Al-4V alloy. The introduction of the TiN transition layer greatly improved the wear resistance of the Ti-6Al-4V alloy, and the adhesion strength of the HA layer to the substrate increased from 6.50 ± 0.5 N to 11.70 ± 1.2 N, an increase of 56%. The HA/TiN coating surface consisted of uniform hemispherical particles with dense structure and invisible defects (micro-cracks and pores). For the HA surface layer, the crystal structure and active hydroxyl (-OH) group was restored after heat treatment. Potentiodynamic polarization experiments indicated that the HA/TiN coating achieved the lowest corrosion current density and the most positive corrosion potential compared to the single TiN layer and Ti-6Al-4V alloy. In summary, it can be conclude that the gradient transition layer can well improve the mechanical properties and electrochemical behavior of the titanium alloy, and largely ensuring the stability of the surface bioactive coating.

Challenges in Pressureless Sintering of Interstitially Alloyed TRIP Steel and Resulting Mechanical Properties

The focus of the current study is to investigate the challenges encountered in processing an interstitially alloyed stainless steel powder by means of an extrusion process derived from the manufacture of ceramics with subsequent pressureless sintering. Previous investigations reveal a distinct loss of nitrogen during conventional sintering in pure argon atmospheres due to the temperature/time regimes applied and the absence of a suitable partial pressure of nitrogen. Consequently, different flushing gases (consisting of argon and nitrogen) are used to keep the nitrogen content in the pre‐alloyed steel powder constant during consolidation. The resulting chemical compositions of the manufactured compacts are determined, as are the microstructures and the mechanical properties, which are recorded under quasi‐static compressive loading. A detailed analysis is conducted to determine the reasons for the loss of interstitial elements in the materials studied, a phenomenon caused by oxidation and reduction reactions throughout the processing chain. In addition, the differences between the materials in their work‐hardening behavior and in the kinetics of the TRansformation Induced Plasticity (TRIP) effect are discussed as a function of the amount of interstitial elements remaining in the sintered materials.

Experimental and computational analysis of PSZ 10- and PSZ 20-derived Si-C-N ceramics

A Si-C-N ceramic was synthesized by pyrolysis of the polysilazane Ceraset® PSZ 10 and PSZ 20. The preceramic polymer was crosslinked by gradual heating up to 300 °C and pyrolyzed at temperatures from 1000 °C to 1500 °C in flowing Ar- and N2-containing atmospheres, respectively. The influence of the pyrolysis temperature and the nitrogen partial pressure (pN2) on the high-temperature stability, phase reactions and crystallization behavior was investigated by STA, XRD and SEM/EDX. Additionally, gaseous pyrolysis- and reaction products were analyzed by on-line mass spectrometry. The CALPHAD (CALculation of PHAse Diagrams) method was used to calculate pyrolysis products and high-temperature phase stabilities as a function of temperature and pAr/pN2. It is shown that the observed experimental findings are quantitatively confirmed and explained by the modelling.