Reactive Gas Flow Rate Research Articles

PEM fuel cells operated at 0% relative humidity in the temperature range of 23–120 °C

Operation of a proton exchange membrane (PEM) fuel cell without external humidification (or 0% relative humidity, abbreviated as 0% RH) of the reactant gases is highly desirable, because it can eliminate the gas humidification system and thus decrease the complexity of the PEM fuel cell system and increase the system volume power density (W/l) and weight power density (W/kg). In this investigation, a PEM fuel cell was operated in the temperature range of 23–120 °C, in particular in a high temperature PEM fuel cell operation range of 80–120 °C, with dry reactant gases, and the cell performance was examined according to varying operation parameters. An ac impedance method was used to compare the performance at 0% RH with that at 100% RH; the results suggested that the limited proton transfer process to the Pt catalysts, mainly in the inonomer within the membrane electrode assembly (MEA) could be responsible for the performance drop. It was demonstrated that operating a fuel cell using a commercially available membrane (Nafion ® 112) is feasible under certain conditions without external humidification. However, the cell performance at 0% RH decreased with increasing operation temperature and reactant gas flow rate and decreasing operation pressure.

Characteristics of Cobalt Thin Films Deposited by Remote Plasma ALD Method with Dicobalt Octacarbonyl

Cobalt thin films were deposited by a remote plasma atomic layer deposition (ALD) system with a metalorganic precursor of dicobalt octacarbonyl . To investigate the reaction kinetics and the characteristics of the Co films, we carried out experiments, varying parameters such as precursor flow rate and injection time, reactant gas flow rate, plasma power, and substrate temperature. The deposition rate of Co films was in the ALD window of . The extent of impurity content such as oxygen and carbon was highly affected by plasma power. Two Co films deposited with a plasma power of 50 and showed different compositional variations. The carbon content of the samples was about and , and oxygen content was about and , for deposition with plasma powers of 50 and , respectively. The incorporation of impurities was caused by the incomplete decomposition of and suppressed Co reaction on Si substrate, retarding silicide formation.

Hydrogen production from solar thermal dissociation of methane in a high-temperature fluid-wall chemical reactor

This study addresses the exploration of an unconventional route for potentially cost effective hydrogen production with solar thermal energy. The process co-produces hydrogen-rich gas and high-grade Carbon Black (CB) from concentrated solar energy and methane. The approach is based on a single-step thermal decomposition (pyrolysis) of methane to hydrogen and CB, without catalysts and without emitting carbon dioxide since solid carbon is sequestered as carbon black. A high temperature nozzle-type solar chemical reactor has been developed in which the solar radiation absorbed by a graphite nozzle is transferred to the flow of reactant (fluid-wall reactor). The conversion of methane dissociation depends strongly on the solar power input, on the geometry of the graphite nozzle, and on the inert and reactive gas flow rates, which determine both the residence time and the inlet CH 4 mole fraction. Maximum chemical conversion of methane was up to 99% (yield of hydrogen up to 90%). It was obtained with a vertical-axis solar furnace (2 m-diameter concentrator), with a given geometry of the nozzle determining the fluid-wall reaction surface area, and with the lowest flow rate of methane investigated (0.1 L n /min). For each target tested, the higher the inlet flow rate of methane or argon, the lower the gas residence time, thus the lower the chemical conversion.

Direct determination of arsenic in sea-water by reaction cell inductively coupled plasma mass spectrometry

A new procedure for the direct determination of total arsenic in sea-water has been developed. In order to remove the polyatomic interferences arising from the direct analysis of 15-fold diluted sea-water samples, the dynamic reaction cell (DRC) technique was applied. Different analytical strategies, such as reactive removal of the interfering species by ammonia, methane or hydrogen, as well as arsenic oxidation by oxygen or nitrogen protoxide, followed by detection of the AsO+ ion were explored. The use of DRC pressurized with ammonia, methane or hydrogen was not able to reduce the spectral interfering effects at m/z = 75. On the other hand, satisfactory results were obtained by using oxygen at 0.8 cm3 min−1 or nitrogen protoxide at 0.5 cm3 min−1 and detecting the analyte at m/z = 91. The relevant parameters, such as the reactive gas flow rate, the Mathieu stability parameters a and q of the DRC, and the rod offset voltages of both cell and mass analyzer quadrupole, were optimized for maximum ion transmission and selectivity. Following the optimization of the DRC conditions, a new analytical procedure for the direct determination of total arsenic concentration in sea-water was hence developed. The main analytical performance characteristics of the optimized method were evaluated, with special attention to the determination of the “procedural” and “field” blanks. A detection limit as low as 40 ng L−1 and instrumental precision of about 2% were achieved. The accuracy was verified by the analysis of certified reference materials (CRM) of sea-water (NASS-4, CASS-4) and estuarine water (SLEW-3). The analytical precision for replicated analyses of the CRMs ranged from 2.3% to 5.0% (n = 5). Finally, the developed procedure was applied to a number of sea-water samples from the Ross Sea (Southern Ocean, Antarctica). Arsenic concentration ranged from 0.88 to 1.03 μg L−1 (n = 12), which are typical values for the uncontaminated offshore waters.

熱 CVD 法による超微粒子コーティング装置を用いたSiC/Si3N4 複合粉体の作製

Si3N4 fine particles covered with deposited SiC ultrafine powder, denoted as SiC/Si3N4 composites, with excellent sinterability were prepared by an ultrafine powder coating reactor using thermal CVD technique. Reactant gases used were monosilane and ethylene. The CVD reactor was designed to accelerate homogeneous nucleation reaction. The effects of reactant gas flow rate ratio, C/Si, and reaction temperature on C2H4 conversion, C content in the deposited ultrafine powder and C selectivity were investigated. The CVD conditions were optimized to form stoichiometric ultrafine powder. The XPS results of ultrafine powder predict the synthesis of stoichiometric SiC. The required conditions for the sintering of the produced SiC/Si3N4 composites were drastically milder than that for a conventional sintering process for commercial Si3N4 fine particles. The application of our CVD reactor will be expected to the preparation of various composite particles with easy sinterability.

Influence of incidence angle and distance on the structure of aluminium nitride films prepared by reactive magnetron sputtering

Aluminum nitride (AlN) films were reactively deposited on (100) oriented silicon substrates by reactive radio frequency (RF) magnetron sputtering for different incidence angles and distances between substrate and target. X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to consider the influence of process parameters such as reactive gas flow rate, grazing incidence angle ( α), and distance ( d) between substrate and target surface on the property of AlN films. XRD results showed that AlN film prepared at a constant distance ( d) of 3 cm and an incidence angle of 45° revealed a mixture of AlN (002), (100), and (101) planes, while the film prepared at α = 0° revealed a strong AlN (002) orientation which has a perpendicular growth direction to the substrate surface. AFM results showed that AlN film prepared at α = 0° exhibited more flat surface morphology than that of film prepared at α = 45°.

Hot target sputtering: A new way for high-rate deposition of stoichiometric ceramic films

Titanium nitride or dioxide coatings have been reactively sputter-deposited under unstable sputtering conditions using a cold or hot target. We have shown that increasing the sputtered titanium flux in cold target sputtering (CTS), by increasing either the discharge current or the discharge voltage, increases the metalloid content in the coating deposited when the target operates at the higher reactive gas flow rate of the elemental sputtering mode. Using a hot target allows a perfect stabilisation of the process in the presence of an argon–nitrogen discharge, whereas only a slight stabilisation occurs when the sputtering stage takes place in argon–oxygen mixtures. It is shown that the stabilisation effect of hot target sputtering (HTS) is due to the strong increase of reactive species diffusion into the bulk target, which is more pronounced with nitrogen than with oxygen, as soon as the target heats up to the α-Ti→β-Ti transformation temperature.

Nanostructural and Optical Features of nc-Si:H Thin Films Prepared by Plasma Enhanced Chemical Vapor Deposition Techniques

The nanostructural and optical features of hydrogenated nanocrystalline silicon (nc-Si:H) thin films, which were prepared by plasma enhanced chemical vapor deposition (PECVD), were investigated as a function of deposition conditions. It was found that the crystallite size varied with the relative fraction of Si-H3 bonds in the films, [ ] eger n n n H Si H Si int 3 1 3 / ] [ = = ∑ − − , which was sensitively related with the flow rate of SiH4 reaction gas. The silicon nanocrystallites in the films enlarged from ~2.0 to ~8.0 nm in their size with increasing gas flow rate, while the PL emission energy varied from 2.5 to 1.8 eV; the relative fractions of the Si-H3, Si-H2, and Si-H bonds in the amorphous matrix were also varied sensitively with the SiH4 flow rate. A model for the nanostructure of the nc-Si:H films was suggested to discribe the variations in the size and chemical bonds of the nanocrystallites as well as the amorphous matrix depending on the deposition conditions.

Reactor Studies of Supported Ionic Liquids: Rhodium-catalysed Hydrogenation of Propene

Rhodium-based catalysts in ionic liquids have been used for the hydrogenation of propene in a reactor composed of thin layers of catalyst solution supported on or in corrugated polymer sheets operated in a cross-corrugated configuration. The effect of the number of corrugated sheets and of reactant gas flow rate is described. Conversions to propane of up to 95% have been demonstrated and reactor performance has been maintained over hundreds of hours of operation. The catalyst-membrane system based on rhodium(I)-[bmim]PF6-PESC was found to be remarkably robust, retaining high levels of activity after removal from the reactor, storage in air for 3 months and re-introduction into the reactor.

Endurance and Data Retention Improvement of Silicon–Oxide–Nitride–Oxide–Silicon Nonvolatile Semiconductor Memory Devices with Partially Bottom-Silicon-Rich Nitride Structure

A significant reliability improvement in silicon–oxide–nitride–oxide–silicon (SONOS) flash memory devices by band-gap engineering of the nitride layer has been attained. The gradually varied reaction gas flow rate during deposition has generated special nitride films with non uniform composition profiles and band gaps. As a result, SONOS devices with partially Si-rich nitride structures have exhibited superior cycling endurance, radiation hardness, and data retention compared with devices with a uniform standard nitride. The marked improvement can be attributed to the increased charge-trapping/detrapping efficiency of the nitride layer since a significant number of highly accessible trapping levels have been created in the nitride that has a graded band gap. In addition, the deepened barrier heights between the nitride and its surrounding oxides may also reduce undesirable charge-loss probability and assist in charge storage. Because the dimension of flash memory cells is continuously shrinking, the proposed technique will be valuable for mass storage applications.

Properties of MoN xO y thin films as a function of the N/O ratio

The main purpose of this work is the preparation of single layer films of molybdenum oxynitride, MoN x O y . The films were deposited on steel substrates by dc reactive magnetron sputtering. The depositions were carried out from a pure Mo target and varying the flow rate of reactive gases. This allowed tuning of the crystallographic structure between insulating oxides and metallic nitrides and consequently changes in the electronic, mechanical and optical properties of the material. X-ray diffraction (XRD) results revealed the presence of molybdenum nitride for the films with low oxygen fraction: face-centered cubic phases (γ-Mo 2N) for low nitrogen flow rate or cubic MoN x and hexagonal phase (δ-MoN) for high nitrogen flow rate. The increase of oxygen content induces an amorphization of the nitride phases and the appearance of MoO 3 phases. The increase of the oxygen fraction in the films induces also a high decrease in the film's hardness. Residual stresses were compressive, in the range of very few tenths of GPa to − 2 GPa. These results will be presented as a function of the deposition parameters, the chemical composition and the structure of the films.

Wear behavior of DC unbalanced magnetron sputter deposited ZrCN films

For many years, TiN has been the most generally used film in every field of applications Another transition metal Zr, which belongs to the same periodic element group as Ti, is also an attractive material. There have been a lot of research reports discussing ZrN. However, knowledge on ZrCN is still limited. This paper presents initial experimental results on ZrCN films obtained with a DC unbalanced magnetron sputtering machine. The main purpose of this study is to understand the effects of variations in the ratio of C2H2/N2 reactive gas flow rates and the additions of Ti and W on the hardness and wear performance of ZrCN series of films, while keeping the total of C2H2 and N2 flow rates constant at 15 sccm. The results showed that the hardness and wear behavior of ZrCN films were strongly dependent on the variations in the ratio of C2H2/N2 reactive gas flow rates. The addition of Ti and W led to a significant enhancement in wear performance of ZrCN films, as well as in their hardness. The enhancement by Ti addition was greater than that by W addition. ZrCN, with and without Ti/W additions, showed much better wear behavior than TiN.

SONOS Device With Tapered Bandgap Nitride Layer

A unique, band-engineered, configuration of the charge-trapping layer in silicon-oxide-nitride-oxide-silicon (SONOS) devices is proposed for high-density Flash memory applications. In this paper, a varying Si-N ratio in modified silicon nitride is obtained by controlling reaction gas flow-rate during deposition. This generates a graded composition profile from Si-rich at the bottom to N-rich at the top in a nitride film. The nonuniform composition profile of the silicon nitride layer corresponds to a tapered bandgap and results in significant improvement in device performance and reliability characteristics including operation window, cycling endurance and data retention. The dramatic improvement can be attributed to increased charge-trapping efficiency of the nitride layer since a significant number of highly accessible trapping levels are created in the tapered bandgap. In addition, the increased barrier height between the nitride and tunnel oxide layers also reduces back-tunneling probability and assists charge trapping. The SONOS device designed in this paper is suitable for next-generation Flash memory applications.

Reactive sputtering of iron in Ar–N2 and Ar–O2 mixtures

This paper reports on the preparation of iron nitride and iron oxide films by DC reactive magnetron sputtering. The reactivity of the Fe–N2 and Fe–O2 systems is compared by the measurement of the total pressure in the deposition chamber, the iron target voltage and the films' growth rate as a function of the reactive gas flow rate. The Fe–N2 system does not exhibit an instability phenomenon and the total pressure is quite proportional to the nitrogen flow rate. This system exhibits a low reactivity as confirmed by the effect of the nitrogen flow rate on the films' growth rate. On the other hand, a hysteresis loop occurs for the Fe–O2 system, indicating a higher reactivity for this last system.

Unit capacitance distribution of a silicon nitride MIM capacitor in silicon wafer

In this paper, a silicon nitride (SiNx) metal–insulator–metal (MIM) capacitor was prepared with the plasma-enhanced chemical vapour deposition (PECVD) method. Slight variation of unit capacitance from the edge to the centre of the wafer was found. From our experimental results, it was shown that this variation was relative to reaction conditions (RF power and reaction gas flow rate). The reason for this phenomenon was proposed.

Reactive magnetron sputtering of copper, silver, and gold

Copper, silver, and gold targets were sputtered in various reactive gas mixtures (Ar–N2, Ar–O2, and Ar–CH4) to compare the reactivity of noble metal atoms during the sputtering process. The evolution of the film's growth rate and the variation of the reactive gas partial pressure vs. the reactive gas flow rate were investigated for each kind of metal. The structure of the deposited films was characterised by X-ray diffraction. Electrical resistivity of the coatings was determined at room temperature. The optical band gap of oxides and nitrides films were deduced from UV–visible transmission measurements. The reactive sputtering of copper target leads to the synthesis of Cu3N, Cu2O, Cu4O3, or CuO films. No copper carbide films were deposited. Depending on the methane flow rate, Cu/C films were either nanocomposite coatings (nc-Cu/a-C:H) or amorphous. Silver oxide (Ag2O) films were formed by reactive sputtering of a silver target in Ar–O2 mixtures. On the other hand, the reactive sputtering method did not allow the synthesis of silver nitride nor gold oxide films.

Corrosion resistance of ZrN xO y thin films obtained by rf reactive magnetron sputtering

The main aim of this work is the investigation of the corrosion resistance of single layered zirconium oxynitride, ZrN x O y , thin films in artificial sweat solution at ambient temperature. The films were produced by rf reactive magnetron sputtering, using a pure Zr target at a constant temperature of 300 °C. Two different sets of samples were produced. In the first set of films, the substrate bias voltage was the main variable, whereas in the second set, the flow rate of reactive gases (oxygen/nitrogen ratio) was varied. The control of the amount of oxygen allowed the film properties to be tailored from those of covalent zirconium nitride to those of the correspondent ionic oxide. The corrosion behaviour was evaluated by potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) tests. The analysis of EIS data provided detailed information of the corrosion processes occurring at the surface of the system throughout the immersion time. The modifications of the coating microstructure and/or chemical composition induced by the variation of the deposition parameters were also evaluated and correlated with the corrosion mechanisms occurring in each system.

THICK GaN LAYER GROWN BY Ga VAPOR TRANSPORT TECHNIQUE

Using a novel Ga vapor transport technique, thick gallium nitride layers have been deposited on a 3-6 μm GaN film grown on sapphire substrate via hydride vapor phase epitaxy (HVPE). GaN powder was successfully used as a stable Ga source material for the growth. A growth rate of greater than 200 μm/hr was achieved by optimizing the growth temperature and the reactant gas flow rates. This growth rate is as high as that achieved by HVPE. The GaN layers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Atomic Force Microscopy (AFM).

Physical and Barrier Properties of Amorphous Silicon-Oxycarbide Deposited by PECVD from Octamethylcyclotetrasiloxane

This work investigates the thermal stability and physical and barrier properties for three species of amorphous silicon-oxycarbide (α-SiCO) dielectric barrier films, deposited by plasma-enhanced chemical vapor deposition (PECVD), to copper (Cu) diffusion using octamethylcyclotetrasiloxane precursor and helium (He) carrier gas with and without oxygen reaction gas. The α-SiCO dielectric barrier film deposited by PECVD without reaction gas exhibits a low k-value of 2.8, thermally stable at temperatures up to 550°C, excellent moisture resistance, and superb Cu barrier property until 400°C. With the addition of reaction gas during the dielectric deposition process, the dielectric constant of the α-SiCO dielectric barrier films increases with increasing flow rate of reaction gas. Increasing flow rate of reaction gas during the deposition of the α-SiCO dielectric barrier films also degrades the thermal stability and moisture resistance of the dielectric barrier films. Moreover, the addition of reaction gas also results in a degraded Cu barrier property of dielectric films. © 2004 The Electrochemical Society. All rights reserved.

Performance studies of PEM fuel cells with interdigitated flow fields

Efforts in developing various models for PEM fuel cells have been increasing in recent years, and thus creating an urgent need for systematic experimental data on fuel cells with commercially available components. Such systematic experimental data is also needed by new fuel cell developers to accelerate their system development and optimization. To meet these needs, we present in this paper systematic experimental data on the performance of a proton exchange membrane fuel cell with interdigitated flow fields. The experiments concentrate on the effects of cell temperature, gas humidification, cell operating pressure and reactant gas flow rate. The experimental results are presented in the form of polarization curves. In addition, a three-dimensional fuel cell mathematical model is used to simulate the cell performance with the interdigitated flow fields. The comparison of the modeling results and experimental data shows a good agreement.