N2 Gas Flow Research Articles

Influence of nitrogen gas flow ratio on gallium nitride film growth using high-density convergent plasma sputtering device at room temperature

The influence of the nitrogen gas ratio on the gallium nitride (GaN) film growth has been investigated using a high-density convergent plasma sputtering device at room temperature. To obtain a highly reactive environment for GaN film growth, the convergent magnetic field lines assist the high-density plasma transport near the target surface. An orthogonal array in the design of experiments was used to effectively investigate GaN film growth conditions. To optimize the GaN film growth conditions, we focus on four sputtering parameters: (1) the N2 gas flow ratio, (2) the inflowing ion current to the target, (3) the process gas pressure, and (4) the target-substrate distance. The N2 gas flow ratio mainly characterizes the growth condition of c-axis oriented wurtzite-structure GaN films on an unheated glass substrate. The full width at half maximum of the rocking curve for the GaN(0002) peak position decreases to 3.9° in the growth condition with 100% nitrogen at room temperature.

Bio-oil production from Moringa oleifera Lam. residue through fixed-bed pyrolysis

The thermal degradation of lignocellulosic materials is one of the most promising approaches for obtaining energy sources and chemical products. In this study, the chemical and thermochemical characterization of Moringa oleifera Lam. seeds and residues showed that biomass can potentially be used to produce energy through a thermochemical conversion process. The seeds and biomasses of Moringa oleifera Lam. were submitted to pyrolysis, the main method of thermochemical conversion. Pyrolysis reactions were conducted in a stainless steel fixed-bed reactor under atmospheric nitrogen pressure, temperatures of 500–600 °C and N2 gas flow of 1 and 3 mL min−1. The calorific value of the biomass ranged from 17 to 21 MJ/kg. The results obtained in the optimization of the pyrolysis conditions in a fixed-bed reactor, the temperature of 600 °C, and N2 flow of 1 mL min−1, were selected. The chromatographic analysis (GC/MS) of the bio-oil allowed the identification and semi-quantification of the different chemical classes present in the bio-oils (acids, phenols, oleonitriles, hydrocarbons, aromatics, ketones, aldehydes, ether, amines, amides, alcohol). High content of carboxylic acids (superior values 70%) was observed for the seeds and mechanical residue, and a high content of phenolic and nitrogen compounds, with 43% in both cases, for the Soxhlet residue. The moringa residues can be considered as a productive source of bioproducts, significantly reducing the harmful effects of chemicals originating from fossil fuels, while minimizing the disposal of waste into the environment.

Effects of substrate temperature on thermal stability of Al-doped ZnO thin films capped by AlOx

Effects of substrate temperature on the thermal stability of Al-doped ZnO (AZO) films have been studied. Degradation of electrical properties of AZO films by annealing under flowing N2 gas depends on their crystallinity controlled by the substrate temperature. A thin AlOx capping layer was employed to passivate the thermal degradation of the AZO layer. A strong correlation between Zn desorption and reduction in carrier concentration was observed. Thermal desorption of Zn was prevented by the AlOx layer, retaining carrier concentration. With the AlOx capping layer, the reduction in Hall mobility was prevented in samples with good c-axis orientation, while the reduction in Hall mobility was still observed in poor c-axis oriented films. However, the reduction was smaller than that in bare AZO films. The dependence of Hall mobility evolution on the substrate temperature, and therefore, on crystallinity, strongly suggests the impact of grain boundary scattering on thermal degradation. An increase in optical mobility, which was evaluated from optical spectra using the Drude model, with annealing temperatures, supports the conclusion that an increase in grain boundary scattering by annealing caused the degradation of Hall mobility. The increase in grain boundary scattering induced by Zn desorption was prevented by the capping layer, while contributions of domain alignment and other segregation of defects to the grain boundary scattering, which depend on the substrate temperature retained, leading to different evolutions of Hall mobility.

Improved corrosion resistance of reactive gas pulse sputtered (TiTaNbZrNi)N high entropy alloy coatings with a hybrid architecture of multilayered and compositionally graded structures

In an attempt to introduce a new coating structure design strategy to strengthen the high temperature water corrosion resistance or high temperature oxidation of the coating in the normal operation condition or event of a loss-of-coolant accident. (TiTaNbZrNi)N hybrid structure coatings with ν = 0.25, 0.5, 1, 2 sccm/min were prepared by the reactive gas pulse (RGP) sputtering technique. This hybrid structure consisted of a FCC (TiTaNbZrNi)N sublayer and an amorphous (TiTaNbZrNi)Nx sublayer with both N element concentration gradient, and .an amorphous TiTaNbZrNi sublayer. After autoclave test at a temperature of 360°C and a pressure of 18.6 MPa for 3, 14 and 50 days, the results indicated that the weight gain of the hybrid structure coating is approximately an order of magnitude lower than that of the uncoated N36 substrate, and it still has a stable FCC structure. The coating with ν = 2 sccm/min has a lower oxygen diffusion depth than the coating ν = 0.25, 2 sccm/min, which is due to the lower thickness of the (TiTaNbZrNi)Nx sublayer and the multilayer interface suppressing the diffusion of oxygen. Moreover, Corrosion resistance of the (TiTaNbZrNi)N hybrid coating can be well tuned by changing the undulation period number of N2 gas flow rate. Detailed analysis indicates that the corrosion resistance of hybrid structure coatings may be related to the combined effect of multilayer structure and composition gradient structures.

A Fast Response and CMOS Compatible Micro Gas Flow Sensor With Thermal Feedback

This letter presents a CMOS compatible micro flow sensor (MFS) that operates in a thermal feedback (TF) mode. The proposed MFS contains four parallel polysilicon resistors on the micro bridges. The gas flow induced temperature difference between two outlying thermistors is minimized and balanced through the negative thermal feedback, while the power distribution on two inlying microheaters is automatically adjusted. Accordingly, the measured voltage difference between two inlying microheaters is used as the sensor output signal. For the N2 gas flow, the proposed MFS works in TF mode achieve a prominent sensitivity of 1.74V/(m/s) and a bidirectional detection range of −6 ∼ 6 m/s, which shows an almost 2X enhanced flow range as compared to the counterpart works in a constant voltage mode. Moreover, the rise time of MFS under a suddenly generated gas flow is experimentally determined as 3.1 ms (error ±0.13 ms). The measured rise time is 43% faster than that of the micro flow sensor without thermal feedback, which proves the successful development of a fast response MFS.

A comparative analysis over different properties of TiN, TiAlN and TiAlSiN thin film coatings grown in nitrogen gas atmosphere

Titanium nitride (TiN), Titanium aluminum nitride (TiAlN), and Titanium aluminum silicon nitride (TiAlSiN) coatings were deposited over Silicon (Si) (100) substrates using chemical vapor deposition (CVD) process at a constant temperature under different N2 flow rate. Scanning electron microscopy (SEM) images reveal a smoother TiN coating surface compared to other coatings. Atomic force microscopy (AFM) indicates enhancement of particle size of TiN and TiAlN coatings with higher N2 gas flow rate. However, the particle size of TiAlSiN found to decrease with a higher N2 flow rate. X-ray diffraction (XRD) results confirm the diffraction phases of TiN, TiAlN and TiAlSiN at (111) and (200) crystal planes. The electrochemical test indicates higher corrosion resistance of TiAlSiN coating as compared to other coatings. Nano-indentation results reveal that TiAlSiN possesses higher hardness (H) and Young's modulus (E) as compared to other coatings.

Multi-objective optimization of Pulsed direct current magnetron sputtered titanium nitride thin film using Grey relational analysis

Titanium nitride coatings are extensively adopted as an intermediate adhesion layer in the cutting tools because of its superior mechanical properties. The interdependence of each process parameter during the deposition of such a coating process is nonlinear, and hence, it becomes a challenge to determine the output responses without carrying out a wide range of experiments. So to minimize the experiments, Taguchi-based L9 design of experiments were employed in this study with three factors and three levels such as Argon (Ar): Nitrogen (N2) gas mixture, Pulsed direct current power, and deposition time for depositing titanium nitride thin films on silicon (100) and tungsten carbide substrates using Pulsed direct current magnetron sputtering technique, where conventional direct current magnetron sputtering cannot be deployed using titanium nitride target. Multiple output responses such as average thickness, surface roughness, nano-hardness, Young’s modulus, wear track deformation, and coefficient of friction were measured by carrying out the systematic investigations, and a single optimum solution was obtained using Grey relational analysis. From the Grey relational analysis, the optimum Ar:N2 gas flow mixture, Pulsed direct current power, and deposition time for improved titanium nitride adhesion layer are 300 W, 10:5 sccm, and 5 min, respectively. Further, grazing incidence x-ray diffractometer profiles of deposited films exhibits (111) and (200) reflections corresponding to the titanium nitride phase, and the morphological analysis also revealed the existence of strongly faceted nano-grains with a triangular-shaped morphology.

Oxygen diffusivity and reaction rate in spherical gel entrapping ammonia-oxidizing bacteria

Nitrifying biomass immobilized in a gel has been applied in wastewater treatment, as immobilization results in a high bacterial cell density in the reactor and facilitates easy solid–liquid separation in the settling tank. Herein, the diffusivity, reaction rate, and concentration profile of oxygen in a spherical gel entrapping ammonia-oxidizing bacteria (AOB) were investigated. Calcium alginate gel and 2,2-bis[4-(methacryloxy polyethoxy)phenyl] propane (BPE) gel were used as models to prepare millimeter-sized spherical gels. A novel method involving controlled oxygen transfer into/out of the spherical gel with alternative flow of air and N2 gas, measurement of oxygen concentration at the center of the spherical gel using an oxygen microsensor, and analysis using the Fickian diffusion equation was developed to determine oxygen diffusivity in the gel. Ammonia oxidation in the AOB-entrapping gel was also monitored by measuring the oxygen concentration at the center of the gel using an oxygen microsensor. The oxygen concentration profile in the gel was estimated based on the oxygen diffusivity and Michaelis–Menten model parameters determined for suspended AOB cells. The kinetic rate-determining step in the AOB-entrapping gel was identified using the effectiveness factor. The results would be useful for the development of aerobic bacteria-entrapping gels and the design of wastewater treatment processes using these gels.

Study on the thermal treatment conditions for fabricating open-cell structure Cu–Sn alloy foams

Cu–Sn alloy foams, with an open-cell structure, were fabricated by Cu/Sn coelectrodeposition onto a polyurethane (PU) template in an alkaline electrolyte with a citrate complexing agent before undergoing a subsequent thermal treatment for PU removal in a N2 gas environment. These foams were predominantly comprised of a Cu matrix along with Cu6Sn5 and Cu3Sn intermetallic compounds, which are known as active materials in Cu–Sn alloy electrodes used in rechargeable batteries. The chemical phase change of Cu–Sn alloy foams and its influence on the electrical resistance were studied according to the heating temperature and N2 gas flow rate. Assuming the thermal degradation of PU as a first-order reaction, the dependence of the PU removal process on the heating temperature was also theoretically investigated. In addition, a postannealing process of the Cu–Sn alloy foams was employed to reduce their electrical resistance by promoting grain growth.

Evaporation rate of molten copper in argon and nitrogen gas flow and characteristics of condensed particles

Copper has been levitation-melted in room temperature Ar and N2 gas flows to investigate the evaporation rate and characteristics of condensed particles. The evaporation measured experimentally increased with the increases of the temperature of the levitated Cu, and the gas flow rate. The site, the concentration and temperature at the vapor condensation in the gas film around the levitated Cu was analysed using the temperature distribution and the critical supersaturation concentration of Cu vapor. There was a linear relationship between the calculated and the experimentally obtained evaporation rates. The calculated evaporation rate was larger than the experimentally measured rate. The condensed particles were metallic Cu. When the temperature at the vapor condensation site was lower than the melting point of Cu, the vapor condensed as a solid phase, and the solid particles did not grow with collision-coalescence of the particles. Therefore, the size of them was not influenced by the temperature of levitated Cu and the gas flow rate. When the temperature at the condensation site was higher than the melting point, the size of them was increased by the distance which was the difference in the position at the melting point and the vapor condensation.

Influence of the cold plasma treatment on the Al2O3/ZrO2 nanocomposites surfaces

In the present work, Al2O3/ZrO2 nanocomposite surfaces were treated with cold plasma using N2,H2, andO2 gaseous atmospheres. For this, Al2O3/ZrO2 samples were shaped and sintered at 1500 °C for 2 h. Then, the surfaces were treated with cold plasma using different N2 and O2 gas flow proportions. The H2 gas flow was maintained at 50%. The treatment conditions were a total gas flow rate of 20 sccm, total pressure of 2.0 mbar, square pulses of voltage with duration of the 50 µs repeated every 100 µs, and a temperature of 400 °C. The surface treatment, regardless of the gaseous atmospheres, affected the functional groups attributed to ZrO2 significantly more than those of Al2O3. In general, it was observed that the surfaces treated in gaseous atmospheres with a higher proportion of N2 gas flow had a more hydrophilic character due to the greater amount of active species coming from this gas. Although active N2 gas species are predominant, active O2 gas species can also affect ZrO2 functional groups. Thus, the pre-treatment contributes both to increasing hydrophilic character as well as promoting chemical changes in the functional groups present on the nanocomposite surfaces.

Enhancement of p-type conductivity of monolayer hexagonal boron nitride by driving Mg incorporation through low-energy path with N-rich condition

We report a low-energy path to enhance the incorporation of Mg on the VB site in monolayer hexagonal boron nitride (h-BN) by an N-rich condition for effective p-type conductivity. Density functional theory calculations reveal that VB and MgB both behave as a shallow acceptor for p-type conduction of h-BN. The N-rich condition is found to promote the formation of VB as a low-barrier site for MgB incorporation. Experimentally, Mg p-type doping is achieved in a h-BN monolayer under N2 (or NH3) gas flow through a chemical vapor deposition method. The surface current of Mg-doped h-BN has been enhanced by three times up to 32 μA under a 8 V external voltage. This approach provides excellent p-type conductivity in monolayer h-BN for future applications in two-dimensional optoelectronic devices.

Gate leakage current reduction and improved reliability with an ultra-thin Ti layer for low-power applications

This study analyzed the physical and electrical characteristics of the interface reactions between hafnium-based high-k gate dielectrics and a TiN-based metal gate. Decreasing the N2 gas flow ratio (RN2 = N2/Ar+N2) from the physical-vapor-deposited TiN decreased the gate leakage current (JG) and the effective work function (EWF) of the metal gate. X-ray photoelectron spectroscopy analysis confirmed that TiN deposited with a lower RN2 condition can be easily oxidized to form TiOx at the gate oxide and metal gate interface after annealing at 1050 °C. This newly created oxide layer can prevent oxygen diffusion from the gate oxide through TiN to the TiN/poly-silicon interface, resulting in improved gate oxide quality. Inserting a thin Ti layer (< 1 nm) on the gate oxide formed a TiOx layer without a change in EWF, indicating that TiN composition variation followed the same trend as capacitance equivalent thickness (CET) versus JG. Therefore, an oxygen-blocking layer can have the same effect as gate oxide quality improvement for both scenarios—low RN2 of TiN and the thin Ti insertion—due to decreased oxide charge density. The Ti insertion process was associated with improved gate oxide leakage, negligible CET increase (0.2 Å), and gate oxide reliability, including time-dependent dielectric breakdown characteristics due to the blockage of oxygen up-diffusion.

The core-shell structural and optical stability of SiNWs:Ce3+@SiO2

Based on high temperature solid-state method, SiNWs:Ce3+@SiO2 core-shell fluorescent nanomaterials are prepared, CeO2 powders are used as rare earth dopant under doping temperature 1200 ℃, and N2 gas flow rate is 1000 sccm and doping time is 60 min. The morphology, structure, composition and distribution of elements as well as the luminescent properties and stability of the material are tested and characterized by transmission electron microscopy, X-ray energy spectrum elemental image analysis technology and fluorescence spectrophotometer. The results show that there are a large number of SiO2 with thickness of 5−30 nm coating rare earth nanoparticles on Si nanowires (SiNWs) surface. At room temperature, SiNWs:Ce3+@SiO2 has a strong blue luminescence with the emission peak at 405 nm(5D→2F5/2) and the full width at half maxim (FWHM) of 36.7 nm. The fluorescence quantum efficiency is 90.57%. They have good properties such as temperature, acid and alkali and anti-light bleaching stability.

Zeolitic imidazolate framework derived Fe-N/C for efficient microwave absorbers

Abstract Three main strategies for designing efficient microwave absorber includes the intrinsic dielectric/magnetic properties, the novel structure and the single atom doping. The Fe-N/C nanocomposites integrate the advantages of above three strategies into one system. In this work, the method for preparing Fe-N/C nanocomposite by calcining the FePc@ZIF-8 precursor under a flowing N2 gas is described. Fe-N/C nanocomposites, displaying respectable dodecahedron-like morphology, have the merits of strong absorption ability, wide effective absorption bandwidth, thin thickness, and excellent microwave absorption efficiency, which are attributed to the synergistic effect of good electromagnetic loss capacity and proper impedance matching originating from intrinsic dielectric/magnetic properties, the novel structure and the single atoms (Fe and N) doping. Fe-N/C-24 composite delivers an optimal reflection loss of −30.98 dB, an effective absorption bandwidth of 5.04 GHz, the microwave absorption capacity of 87.61 dB GHz the absorption efficiency of 51.53 dB GHz/mm at 1.7 mm.

Fabrication of tungsten nitride thin films by superimposed HiPIMS and MF system: Effects of nitrogen flow rate

The high-power impulse magnetron sputtering (HiPIMS) technology starts a new era in the thin film fabrication, which already attracts researchers and industries' interest on its further application in many fields. For improving the low deposition rate of HiPIMS, the superimposition concept by introducing mid-frequency (MF) pulses during the off-time of HiPIMS pulsing was adopted for the fabrication of transition metal nitride hard coatings. Tungsten nitride coating is characterized by its high hardness, good thermal stability and low electrical resistivity. In this study, tungsten nitride coatings were fabricated using five different N2 gas flow rate ratios by a superimposed HiPIMS-MF power system. The W target showed a hysteresis-free behavior during the reactive sputtering process of WNx coating, where x indicated the chemical composition ratio between W and N elements. The peak current and peak power density values of both HiPIMS and MF powers decreased with increasing N2 flow rate ratio. The nitrogen content of WNx coating increased with increasing nitrogen flow rate ratio, whereas the tungsten concentration shows a decreasing tendency. The x value and the nitrogen content of WNx coating increased from 0.05 to 0.60 and from 5.1 to 36.7 at.%, respectively, when the nitrogen flow rate increased from 13 to 37 sccm. The crystalline structure of WNx coatings changed from a pure BCC-W phase to a mixture of BCC-W and FCC β-W2N phases when the x value increased from 0.05 to 0.12. A pure FCC β-W2N phase structure was obtained when the x values of WNx coating reached 0.36, 0.43 and 0.60. The hardness values of WNx coatings were ranging from 26.7 to 31.6 GPa. The WN0.12 coating with a low coefficient of frictions of 0.33, a high hardness of 31.5 GPa and high H/E and H3/E2 ratios were achieved due to the solution hardening and smoother microstructure induced by the substrate bias and the higher energy of superimposed HiPIMS-MF system.

Energy Level Alignment at Interfaces in Metal Halide Perovskite Solar Cells

Adv. Mater. Interfaces 2018, 5, 1800260 In the initially published version of this article, one word on the second page was wrong, the positions of the symbols “HOMO” and “LUMO” were misplaced in Figure 2 and the subparts in caption of figure 20 weren't identified correctly. Please find the correct sentence, Figure 2 and the caption of figure 20 below. The authors apologize for any inconvenience or misunderstanding this may have caused. The third sentence in paragraph 2 on page 2 is corrected as follows: When an organic layer contacts with metal, if vacuum level aligns, one can estimate the energy offsets at the organic/metal interface (e.g., the energy offset between the HOMO of spiro-OMeTAD and the Fermi level of Au) by simply comparing the ionization potential of bulk organic material and the work function (WF) of metal (as shown in the subpanel (i) of Figure 2b). Figure 20. UPS results of the as-prepared doped spiro-MeOTAD films and the films exposed to a) only H2O vapor (a relative humidity of 90%; which is generated by letting a stream of dry N2 gas flow through an H2O bubbler), b) only O2 (>99.5 of purity), and c) ambient air (a relative humidity of 50%) for 0, 3, 6, 18, and 39 h. The UPS spectra are shown in (i) and the corresponding energy level diagrams of them are shown in (ii), respectively. The substrate for UPS measurements is Si/Au. a,b) Reproduced with permission.[54] Copyright 2016, Wiley-VCH Verlag GmbH & Co. KGaA (c) Reproduced with permission.[88] Copyright 2015, Royal Society of Chemistry.

Correlation between ferroelectricity and nitrogen incorporation of undoped hafnium dioxide thin films

The ferroelectric characteristics of undoped hafnium oxide (HfO2) in titanium nitride (TiN)/HfO2/TiN stacks exhibited improved remanent polarization by controlling the nitrogen gas flow during TiN deposition in this work. Electrical measurements revealed that samples with a higher N2/(Ar + N2) ratio obtained a higher remanent polarization of approximately 10 μC/cm2 at 2.5 V but exhibited a larger leakage current and less reliability. Among all the samples, the sample with a N2/(Ar + N2) ratio of 33% exhibited a relatively high remanent polarization of 12 μC/cm2 and excellent endurance over 108 cycles. Through X-ray photoelectron spectroscopy (XPS) analysis, it was observed that increasing the N2 gas flow during TiN electrode deposition contributed to excessive N-diffusion, leading to the creation of more oxygen vacancies and subsequently to device failure. Therefore, controlling the appropriate N2 gas flow during TiN deposition is crucial to enhance the ferroelectric characteristics of undoped HfO2. The results of this study may be applicable to future work on nonvolatile memory applications.

&lt;i&gt;In Situ&lt;/i&gt; Pyrolysis of Pine Flowers to Produce Bio-Oil: Effect of Temperature and Catalyst Treatment

Nowadays, the demand for renewable energy increases dramatically which is caused by the crisis of fossil fuel. Bio-oil is one of the environmental renewable energy since it can be produced from biomass. Pine flowers as biomass mostly still become waste so that it has the potential to become a source of energy production. The purpose of this study is to investigate the effect of temperature and catalyst treatment on the characterization of bio-oil obtained. This research was using Zeolit catalyst activated by HCl 4N for six hours and impregnated by Fe2(NO3)3.9H2O. The experiment was carried out at different temperature treatment (450 °C, 500 °C, 550 °C) and different catalyst treatment (non-catalyst, non-impregnated catalyst, and impregnated catalyst). The catalyst and the biomass with size of (-100+120) mesh and (-30+40) mesh, respectively, were mixed where the catalyst used was 5% of the total weight of the biomass. The mixed catalyst-biomass was then put into the reactor to be pyrolyzed. The pyrolysis process was carried out by flowing N2 gas to prevent the presence of oxygen in the reactor. The result showed that optimum bio-oil production, 33.73%, was obtained from the sample with 550 °C with non-impregnated catalyst. The resulting bio-oil has the following properties : dark brown, yield of bio-oil 17.58%-33.73%, pH 2.95-3.56, density 1.055 gr/mL-1.068 gr/mL, and heating value 2,065.07-2,490.40 cal/gr. Finally, the GCMS results with the effect of temperature and catalyst treatment show the difference in the percentage of the phenolic-aromatic compound, acid, hydrocarbon, and ketone.

Optimization of carbon-supported Ir–Ru alloys for polymer electrolyte fuel cell anodes under cell reversal

Cell reversal (CR) caused by fuel starvation can significantly affect the performance of the polymer electrolyte membrane fuel cells (PEMFCs). To mitigate this issue, carbon-supported Ir–Ru alloys are considered as one of the most promising PEMFC anode materials. Herein, carbon-supported Ir–Ru alloys were prepared via a simple wet impregnation method followed by solid-state reduction at temperatures of 200, 250, and 300°C under H2 gas flow and 300, 600, and 900 °C under N2 gas flow. The size, stoichiometric composition, and structural information of the prepared IrRu4/C were investigated using transmission electron microscopy, scanning electron microscopy–energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray absorption fine structure, the results of which exhibited different electrochemical properties in terms of hydrogen oxidation reaction and oxygen evolution reaction (OER). The electrochemical results showed the enhanced OER activities of IrRu4/C formed at 200 °C under H2. Furthermore, IrRu4/C can be formed under N2 with a change in the reduction temperature. This study provides fundamental properties for optimizing synthetic parameters of Ir–Ru-based catalysts to alleviate the degradation of conventional carbon-supported Pt owing to CR issues.