Ar-N2 Gas Mixture Research Articles

Laser powder bed fusion of molybdenum under various Ar[sbnd]N2 mixture build atmospheres

Laser powder bed fusion (LPBF) is a promising technology for the processing of refractory metals like molybdenum (Mo). Unfortunately, LPBF-processed Mo exhibits cracking when processed under typical conditions, limiting the application of the process. The influence of N content in a gas mixture used as the build atmosphere on the cracking tendency of LPBF processed Mo was studied. The effect of N partial pressure on grain structure, cracking characteristics and mechanical properties was evaluated under varying ArN2 gas mixtures. The microstructure analysis revealed that the increasing content of N in the build atmosphere caused a shift from columnar grain structure which is expected for pure metals fabricated under LPBF, to irregular grain structure. Also, a decrease in average crack length was observed with the increase in nitrogen content in the samples. A linked trend of decreasing oxide content was observed at grain boundaries from fracture surface investigation. The reduced embrittlement of GB from the suppression of GB oxide formation is believed to hinder GB cracking in LPBF processed Mo. While cracks were observed in some samples, crack-free samples could be fabricated under high N partial pressure conditions, resulting in N content equal to or higher than 580 ppm.

Characterisation of N2-GEM: a beam monitor based on Ar-N2 gas mixture

The gas recycle is nowadays an important issue for gaseous detectors operation under study and for this reason, scientists are testing new gas systems for GEM detectors. Since some gas purifier does not allow to use oxygen, the standard Ar-CO2 (70%–30%) cannot be used; thus, new gas mixtures are under investigation. This paper presents the study of a triple GEM detector filled with new gas mixture based on Argon and Nitrogen (Ar-N2) at different concentrations: 90%–10%, 80%–20% and 70%–30%. The GEM detector characterisation has provided the High Voltage working point for the gas mixtures and a comparison between the Ar-CO2 and the Ar-N2.

Influence of the Percentage of Argon in the Ar–N2 Gas Mixture on the Relative Number of Ar+, N2+, N, and N+ Particles in the Plasma of a Non-Self-Sustained Low-Pressure Glow Discharge With a Hollow Cathode

Influence of the Percentage of Argon in the Ar–N2 Gas Mixture on the Relative Number of Ar+, N2+, N, and N+ Particles in the Plasma of a Non-Self-Sustained Low-Pressure Glow Discharge With a Hollow Cathode

Investigation of admixed gas effect on plasma nitriding of AISI316L austenitic stainless steel

The influence of discharge gas composition on the plasma nitriding of AISI316L austenitic stainless steel was investigated using a laboratory-made apparatus consisting of a DC diode and a plasma monitoring system. H2-N2 and Ar-N2 gas mixtures with various mixture ratios were introduced in the apparatus, and nitriding was performed without auxiliary substrate heating. A >4 μm-thick surface layer, consisting of an expended austenitic phase, γN, was formed on the AISI316L substrate when the optimized H2-N2 plasma was used. The thickness and maximum nitrogen content of the surface layer increased with an increase in the population of N2+ species in the plasma; the N2+ population in the plasma is considered an underlying parameter for the optimization. Conversely, the penetration of nitrogen into the AISI316L surface was scarce when Ar-N2 plasma was used, irrespective of the gas mixture ratio. Such a phenomenon indicates that Ar-N2 plasma is ineffective for nitriding. However, the effects of H2-N2 plasma, which are not limited to the surface reaction, are beneficial to facilitate nitriding.

Properties of SnO2 and SnO2−xNx grown on the boat walls using vapor transport method

The aim of the study was to examine the properties of SnO2 and SnO2−xNx nanowires (NWs) grown on the walls of the boat of the vapor transport system. Nanowires of SnO2 and SnO2−xNx were synthesized using Ar plus O2 and N2 plus O2 gas mixtures, respectively. The obtained chemical compositions were SnO2 and SnO1.71N0.18. In both cases, tetragonal single-phase SnO2 with nanowires morphologies were obtained by X-ray diffraction and scanning electron microscopy examinations, respectively. The NWs diameters were ranged from 150 nm to 1.6 µm, and the lengths extended to more than 400 µm for the sample grown with Ar plus O2, whereas the diameters of the NWs ranged from 30 nm to 2.1 µm and the lengths exceeded to 1 mm for the sample grown with N2 plus O2. The calculated optical band gap values were 3.54 and 3.27 eV for samples grown with Ar plus O2 and N2 plus O2, respectively. Higher photoluminescence spectrum intensity was observed for SnO2−xNx NWs. The room-temperature resistivity of SnO2−xNx was one order lower than that for SnO2 NWs and decreased upon increasing temperature, indicating a semiconducting behavior. Two activation energies were recorded for each sample.

Electrochemical characteristics of NixN thin films deposited by DC and HiPIMS reactive magnetron sputtering

This study deals with the DC and HiPIMS reactive magnetron deposition process using a pure nickel target (99.995%) in an Ar-N2 gas mixture with varied nitrogen gas flow and bias voltage (floating or -100 V). The characterization of the NiN films has been carried out by X-ray diffraction (XRD), X-ray photoelectrons spectroscopy (XPS) and Energy dispersive X-ray Spectroscopy (EDXS). XRD measurements have highlighted the deformation of the Ni cubic cell as a function of nitrogen content, and a mixture of nitrided phases (Ni4N, Ni3N and Ni2N) appears for 20% N2 in the discharge. XPS and EDX are well correlated and permit us to determine three zones: metallic between 0 and 20% N2, Ni4N between 20% and 42% N2 and finally Ni3N for N2 above 50%. These three zones are in good agreement with deposition rates and optical emission spectroscopy measurements. Cyclic voltammetry has been performed in a conventional three-electrode cell using neutral, alkaline and acidic aqueous electrolytes. The NixN electrochemical behavior shows a pseudocapacitive charge storage mechanism in LiNO3 and KOH electrolytes using an appropriate voltage window, suitable for supercapacitors, whereas NixN exhibits reversible faradaic redox peaks beyond one potential in KOH, depicting NixN film as a battery-type electrode.

Influence of Nitrogen Partial Pressure on Microstructure and Tribological Properties of Mo-Cu-V-N Composite Coatings with High Cu Content

In this study, Mo-Cu-V-N composite coatings with high Cu content of ~18 at.% were deposited on 316L stainless steel and YT14 cemented carbide substrates by high power impulse magnetron sputtering in Ar–N2 gas mixtures. The influence of N2 partial pressure was investigated with respect to the microstructure and tribological properties of the coatings. The results indicated that the Mo-Cu-V-N composite coatings exhibited FCC B1-MoN phase with a strong (200) preferred orientation, and Cu phase was found to exist as metallic species. As the N2 partial pressure increased from 0.11 to 0.35 Pa, the peak intensity of (200) plane decreased gradually and simultaneous peak broadening was observed, which was typical for grain refinement. With increasing the N2 partial pressure, the columnar microstructure became much coarser, which led to the decrease of residual stress and hardness. The Mo-Cu-V-N composite coatings with high Cu content exhibited a relatively low wear rate of 10−8 mm3/N·m at 25 °C, which was believed to be attributed to the mixed lubricious oxides of MoO2, CuO and V2O5 formed during tribo-oxidation, which cannot be formed in the coatings with low Cu content. When the wear temperature was increased up to 400 °C, the wear rate increased sharply up to 10−6 mm3/N·m despite the formation of lubricious oxides of MoO3/CuMoO4 and V2O5. This could be due to the loss of nitrogen and pronounced oxidation at high temperatures, which led the wear mechanism to be transformed from mild oxidation wear to severe oxidation wear.

Effect of Nb content on the microstructure and corrosion resistance of the sputtered Cr-Nb-N coatings

Thin Cr-Nb-N films with Nb content ranging from 5.1 to 19.5 at.% were prepared onto the AISI 440C substrates by reactive magnetron sputtering of the Cr and Nb in Ar-N2 gas mixture. The effects of the Nb content on the microstructure and the corrosion behavior in 3.5 wt% NaCl solution were investigated. All the deposited films showed a typical surface feature of granular structure. The Cr-Nb-N films with 5.1 at.% and 10.9 at.% Nb showed a duplex layers consisting of a dense and coherent layer near film-substrate interface, followed by a columnar layer differed from the uniform columnar structure for pure CrN. While for Cr-Nb-N films with higher Nb content, there was no obvious dense layer but a columnar structure. The low Nb content Cr-Nb-N coated samples showed a positive shift of both corrosion potential and the pitting potential compared to the pure CrN coated sample while the pitting potential decreased for high Nb content Cr-Nb-N coated samples. The Cr-Nb-N film with Nb content of 10.9 at.% possesses the best corrosion resistance due to the high polarization resistance resulted from the modification of the microstructure by the Nb incorporation.

Microstructure and mechanical properties of magnetron sputtered Ti-Si-N coatings with different silicon content

This work deals with the deposition and characterization of (Ti-Si-N) coatings. A series of Ti-Si-N thin films with different silicon content were deposited on Si (100) substrate by RF magnetron sputtering in an Ar-N2 gas mixture. The influence of Si content on the microstructural and mechanical properties of the as deposited. The as deposited films were studied by using different characterization techniques such as SEM equipped with Energy Dispersive X-ray spectroscopy (EDS) for determining the composition of the films, XRD was used to determine microstructural composition and nano-indentation with MTS XP system for mechanical properties. Scherer’s formula was used to determine the grain size, from the full width at half maximum of (111) experimental peaks, residual stresses of the films were measured by an optical interference apparatus using Newton’s ring method            Results reveal that the film deposited with Si content of 20 at. % has a dense nanostructure and the surface morphology of the Ti-Si-N coatings show neither holes nor column headings. The film deposited with Si content of 33 at. % shows a surface morphology of damaged surface. The X-ray spectra show that Ti-Si-N coatings deposited with Si content of 0 at.%, 27 at.%, 33 at.%, 40 at.% possess a preferential orientation in the direction of (111) and this orientation peak disappears for films with low of Si content. The residual stress built in the coating is compressive and they increase with increase in Si content and reach a maximum of 2.22 GPa. The hardness of the Ti-Si-N films also increases to a maximum with increase in Si content beyond which further addition of the Si decrease the hardness. The TiN grain size as calculated from the XRD diffraction peak decreases with increase in the Si content to saturation value of around 12.8nm for films without addition of silicon to 3.8nm for films with 40at. % of Si   Keywords:   hard coating, magnetron sputtering, residual stress; grain size, Ti-Si-N

Effect of the carrier gas on morphological, optical and electrical properties of SnO2 nanostructures prepared by vapor transport

The aim of the study was to explore the effects of carrier gas on the properties of SnO2 nanostructures grown by vapor transport method for possible optoelectronic applications. Nanostructures of SnO2 were synthesized via vapor transport method using Ar plus O2 and N2 plus O2 gas mixtures. It was found that the carrier gas (Ar or N2) has great influences on the properties of the resulting SnO2 nanostructures. Tetragonal single phase SnO2 with nanowires (NWs) morphologies was obtained for Ar/O2. The diameters of the NWs ranged from 10 to 162 nm and the lengths exceed 5 µm. While tetragonal single phase SnO2 with nanoparticles morphologies (diameters of 42–173 nm) was obtained for N2/O2. The calculated optical band gap values were 3.81 and 2.95 eV for samples prepared with Ar/O2 and N2/O2, respectively. The conduction mechanism in the samples was found to be thermally activated. Single activation energy of 0.49 eV was evaluated for the sample prepared in Ar/O2, while two activation energies (EAL = 1.48 eV and EAh = 0.83 eV) were obtained for the sample prepared with N2/O2. The photoluminescence emission (intensity and shape) depended on the carrier gas. The observed emission peaks were assigned to the oxygen vacancies and the oxygen related defects. The obtained results may find applications in optoelectronics such as light emitting diodes.

Novel [111] oriented γ-Mo2N thin films deposited by magnetron sputtering as an anode for aqueous micro-supercapacitors

The γ-Mo2N thin films were deposited using reactive dc magnetron sputtering, and tested as an electrode material in an aqueous solution of Li2SO4 with a working potential window of 0.05V∼-0.85V versus SCE. The morphology, structure and electrochemical properties were systematically studied for the films of different deposition conditions. It was found that the electrochemical property of the γ-Mo2N film depends not only on the deposition temperature but also on the nitrogen concentration in Ar-N2 gas mixture. The sample deposited for 1h at 400°C with nitrogen concentration x=0.35 shows a dense microstructure and strong (111) texture. It exhibits the best electrochemical property, with a high volumetric capacitance of 722Fcm−3 at 5mVs−1, moderate rate capability with a relaxation time constant of 220ms, and excellent cycling stability of 100% capacitance retention after 2000 cycles. The (111)-oriented γ-Mo2N film is suggested to be a promising candidate of anode materials for micro-electrochemical-capacitors.

Characterization of a Microwave-Induced Atmospheric-Pressure Ar–N2Plasma Pencil

A microwave-induced atmospheric-pressure plasma pencil was developed with an Ar–N2 gas mixture supplied to a coaxial transmission line. High-frequency simulation showed sufficient high electric field at the tip of the inner conductor, which resulted to automatic plasma ignition and a stable operation. The dependence of the characteristics of the plasma pencil from Ar and N2 gas flow rates was extensively studied. At moderate Ar gas flow rates, the plasma pencil can be operated at several tens of watts to achieve a near room-temperature and centimeter-long Ar–N2 plasma plume with OH and NO radicals as active species. Optical emission spectroscopy was also used to determine the vibrational and rotational temperatures of the plasma pencil. The vibrational temperature of N2 from the second positive system (2PS) can be obtained at moderate gas flow rates, since there was a good linear fitting with the Boltzmann distribution. At these gas flow rates, the vibrational and rotational temperatures of N2 from 2PS were found to be 0.42 and 0.29 eV, respectively.

Transition temperatures and upper critical fields of NbN thin films fabricated at room temperature

NbN thin films were deposited on thermally oxidized Si substrate at room temperature by using reactive magnetron sputtering in an Ar-N2 gas mixture. Total sputtering gas pressure was fixed while varying N2 flow rate from 1.4 sccm to 2.9 sccm. X-ray diffraction pattern analysis revealed dominant NbN(200) orientation in the low N2 flow rate but emerging of (111) orientation with diminishing (200) orientation at higher flow rate. The dependences of the superconducting properties on the N2 gas flow rate were investigated. All the NbN thin films showed a small negative temperature coefficient of resistance with resistivity ratio between 300 K and 20 K in the range from 0.98 to 0.89 as the N2 flow rate is increased. Transition temperature showed non-monotonic dependence on N2 flow rate reaching as high as 11.12 K determined by the mid-point temperature of the transition with transition width of 0.3 K. On the other hand, the upper critical field showed roughly linear increase with N2 flow rate up to 2.7 sccm. The highest upper critical field extrapolated to 0 K was 17.4 T with corresponding coherence length of 4.3 nm. Our results are discussed with the granular nature of NbN thin films.

Influence of modulation period and modulation ratio on structure and mechanical properties of TiBN/CrN coatings deposited by multi-arc ion plating

TiBN/CrN multilayered superlattice coatings with modulation periods Λ (bilayer thickness) ranging from 22.5 to 4.2nm and modulation ratio R (the thickness ratio of CrN and TiBN layers) ranging from 6:1 to 3:1 were synthesized using an industrial-scale cathodic arc ion plating system in an Ar–N2 gas mixture. X-ray diffraction (XRD), transmission electron microscopy (TEM) and nanoindention were employed to investigate the influence of modulation period and ratio on microstructure and mechanical properties of the multilayers. The sharp interfaces and nanoscale multilayered modulation were confirmed by TEM. TiBN/CrN multilayer coatings were crystallized with orientations at the (111), (200) and (220) crystallographic planes and the microstructure was strengthened at (200) preferred orientation. The maximum hardness of 38.6GPa and elastic modulus of 477GPa were obtained at Λ=11.7nm and R=5:1. The lowest value of the friction coefficient at 0.32 sliding against a WC-Co ball was obtained at a bilayer period of 11.7nm, compared to those of the coatings with other modulation periods and monolithic coatings. The wear rate of the multilayered coatings was also lower than those of the monolithic CrN and TiBN coatings.

Silicon Nitride Thin Films Deposited By Reactive Gas-timing Magnetron Sputtering For Protective Coating Applications

Silicon nitride is a promising alternative to carbon based materials for protective coatings, owing to its compatibility with existing silicon-based microfabrication. The complexity of the fabrication processes and contaminations hamper fine-tuning to obtain desirable coating properties. We have explored the reactive gas-timing rf plasma sputtering technique for silicon nitride thin film deposition as an alternative method to fine-tune the film properties. The gas-timing technique controls the on-off sequence of the sputtering gas (Ar) and the reactive gas (N2) during deposition. We focus this investigation to the effect of the Ar:N2 gas timing ratio (10:0, 10:1, 10:3, 10:5, 10:7 and 10:10) on the composition, the morphology, the corrosion resistance, and the hardness properties of the films, in comparison to the films deposited by conventional reactive sputtering with Ar-N2 gas mixture. These deposited silicon nitride films were characterized by Auger electron spectroscopy, Raman spectroscopy, and atomic force microscopy. The chemical resistance was measured by the electrochemical corrosion test in sulfuric acid, while the hardness properties were obtained by nanoindentation. The results reveal that although the nitrogen content in the films increases only slightly when the N2 timing is prolonged, the corrosive current of the films decreases abruptly. A thin passivating oxidized layer is found to play a major role in the corrosion resistance. In contrast, the hardness properties exhibit a uniform variation with the N2 timing. The gas-timing sequence may induce morphological changes the underlying silicon nitride films. The highest hardness obtained by the gas-timing technique almost doubles that produced by the conventional mixed gas sputtering. Thus the reactive gas-timing technique suggests a new route to selectively control the properties of silicon nitride films with minor modification to existing microfabrication processes. Copyright © 2015 VBRI Press.

Structure and Microstructure of Binary Nitride TiN Thin Films Deposited by DC Reactive Sputtering

Titanium nitride (TiN) thin films were deposited on to unheated silicon (100) and stainless steel substrates by home-made direct current (DC) reactive magnetron sputtering method at a deposition of 60 min in an Ar-N2 gas mixture. The effects of sputtering power on structure and microstructure of these films have been studied. The films were analyzed by X-ray diffraction (XRD), Atomic Force Microscope (AFM) and Field-Emission Scanning Electron Microscope (FE-SEM). The films colors were influenced by sputtering parameter which altered from green purple to light gold and dark gold, respectively. By XRD, the polycrystalline structure of the as-deposited films was face center cubic (fcc) of TiN structure with (111), (200), (220), and (311), planes. The increasing of sputtering power transformed film from amorphous phase to crystal phase with crystal size were enhanced from 21.9 nm to 39.8 nm. The AFM scans revealed that sputtering power significantly affected surface morphologies and thicknesses of the TiN films. With increase in sputtering power, the roughness and films thickness were increased from 0.5 nm to 25.1 nm and 331 nm to 1113 μm, respectively. The microstructure combined with cross-section analysis FE-SEM revealed that the grain refinement with columnar structure were obtained for the film deposited at sputtering power of 270 W.

Comparison of the structural properties and residual stress of AlN films deposited by dc magnetron sputtering and high power impulse magnetron sputtering at different working pressures

Aluminium nitride (AlN) films were deposited by dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) on (100) oriented silicon (Si) substrates, in Ar–N2 gas mixture, at different working pressures. The films were characterized using X-ray diffraction (XRD), profilometer and transmission electron microscopy (TEM). The effect of the sputtering pressure on the structure, the residual stress and the deposition rate of AlN films deposited by the two processes (dcMS and HiPIMS) was investigated. It was found that the deposition rate is always lower in HiPIMS compared to dcMS. The AlN films are textured along (002) direction in both cases of dcMS and HiPIMS as it is indicated by XRD measurements, with residual stresses which are more important in the case of films deposited by HiMIPS. These residual stresses decrease with the sputtering pressure increase, especially in the case of the films deposited by HiPIMS. TEM analyses have shown a local epitaxial growth of AlN on the Si substrate which would favour thermal evacuation improvement of AlN as thermal interface material.

Time-resolved temperature study in a high-power impulse magnetron sputtering discharge

The gas heating dynamics is studied in a high-power impulse magnetron sputtering discharge operating in Ar-N2 gas mixtures. The time-resolved rotational temperature analysis based on the spectral transition between the B2Σu+-X2Σg+ energy levels in molecular nitrogen ion (N2+ First Negative Band) is undertaken for this purpose. The rotational temperature in the discharge is found to increase linearly during the plasma pulse being roughly independent on the nitrogen content in the examined range. Such a temperature increase is attributed to the bulk gas heating which is the result of collisions with the sputtered species. Two sputtered materials, Ti and W, are examined during the study. In the case of W sputtering, the gas heating is found to be more pronounced than in the Ti case, which is explained by more efficient energy exchange between the sputtered W atoms and the bulk gas atoms during the plasma on-time. The obtained temperature data are compared to the laser-induced fluorescence study of Ar metastable atoms performed recently in the same discharge in our group. The particularities related to gas thermalization as well as to validity of the utilized approach for characterization of the pulsed sputtering discharges are discussed.

Microstructure, surface morphology and optical properties of N-incorporated Ga2O3 thin films on sapphire substrates

Abstract N-incorporated Ga2O3 films were successfully prepared on sapphire substrates in Ar–N2 gas mixtures by radio frequency magnetron sputtering. The influence of N2 gas flux on microstructure, surface morphology and optical properties of N-incorporated Ga2O3 films was analyzed in detail. The films have better crystalline quality after nitrogen incorporating properly, while keeping their original β-Ga2O3 crystalline structure. The surface morphology of the N-incorporated Ga2O3 films was investigated by atomic force microscopy (AFM). The photoluminescence spectra consisted of ultraviolet emission peak and green emission band were also observed and discussed. The optical transmittance of the as-deposited N-incorporated Ga2O3 films exceeds 80% in the visible range. The optical band gap decreases with increasing the N2 gas flux, resulting from the formation of Ga–N bonds.

Microstructure Evolution of nc-TiN/a-(C, CNX) Nanocomposite Films with Different Amorphous Phase Amounts

The microstructure evolution of two-phase nanocomposite Ti-C-N thin films grown by reactive close-field unbalanced magnetron sputtering in an Ar-N2 gas mixture with microstructures comprising of nanocrystalline (nc-) Ti(N,C) phase surrounded by amorphous (a-) (C,CNx) matrix under different a-phase amounts have been investigated by using high-resolution transmission electron microscopy and Monte Carlo simulation. The results show that with the a-phase amounts increasing, the grain size decreasing and a size-dependent lognormal grain size distribution have been found in nanocomposite films. The formation mechanism of this microstructure evolution is attributed to the transformation of grain growth mode from the nc/nc-boundary-curvature-driven growth to the a/nc-boundary-curvature-driven growth accompanied with a convergence of energy on per grain boundary with grain size decreasing (i.e. a-phase amount increasing), leading to the tendency from the off-lognormal size distribution to the lognormal one. When a-phase amount increases to about 28% with grain size reducing to let per grain boundary covered by one monolayer a-phase, the uniform diffusion-controlled growth is dominant, resulting in the lognormal grain size distribution. This study suggests an important implication to prepare the nanocomposite films with a well-controlled nanostructure.