Gas Flow Rate Ratio Research Articles

Deposition of Cluster-Free B-doped Hydrogenated Amorphous Silicon Films Using SiH4+B10H14 Multi-Hollow Discharge Plasma Chemical Vapor Deposition

We have deposited cluster-free B-doped hydrogenated amorphous silicon (a-Si:H) films using a SiH4+B10H14 multi-hollow discharge plasma chemical vapor deposition (CVD) method. We have studied the dependence of the deposition rate, band gap, and conductivity of the films on the gas flow rate ratio R=[B10H14]/[SiH4]. The deposition rate for SiH4+B10H14 plasmas is 2–3 times as high as that for pure SiH4 plasmas. Optical emission spectroscopy (OES) measurements indicate that SiH3 radical generation rate remains nearly constant regardless of R. These results suggest that BxHy radicals enhance the surface reaction probability and/or sticking probability of SiH3, being the predominant deposition precursor. Cluster-free B-doped a-Si:H films have a wide band-gap energy of 1.8–2.0 eV and a conductivity as high as 5.0×10-6 S/cm. These results demonstrate that cluster-free B-doped a-Si:H films deposited using SiH4+B10H14 multi-hollow discharge plasma CVD are promising as a p-layer of pin a-Si:H solar cells.

Methods for evaluation of helium/oxygen delivery through non-rebreather facemasks

BackgroundInhalation of low-density helium/oxygen mixtures has been used both to lower the airway resistance and work of breathing of patients with obstructive lung disease and to transport pharmaceutical aerosols to obstructed lung regions. However, recent clinical investigations have highlighted the potential for entrainment of room air to dilute helium/oxygen mixtures delivered through non-rebreather facemasks, thereby increasing the density of the inhaled gas mixture and limiting intended therapeutic effects. This article describes the development of benchtop methods using face models for evaluating delivery of helium/oxygen mixtures through facemasks.MethodsFour face models were used: a flat plate, a glass head manikin, and two face manikins normally used in life support training. A mechanical test lung and ventilator were employed to simulate spontaneous breathing during delivery of 78/22 %vol helium/oxygen through non-rebreather facemasks. Based on comparison of inhaled helium concentrations with available clinical data, one face model was selected for measurements made during delivery of 78/22 or 65/35 %vol helium/oxygen through three different masks as tidal volume varied between 500 and 750 ml, respiratory rate between 14 and 30 breaths/min, the inspiratory/expiratory ratio between 1/2 and 1/1, and the supply gas flow rate between 4 and 15 l/min. Inhaled helium concentrations were measured both with a thermal conductivity analyzer and using a novel flow resistance method.ResultsFace models borrowed from life support training provided reasonably good agreement with available clinical data. After normalizing for the concentration of helium in the supply gas, no difference was noted in the extent of room air entrainment when delivering 78/22 versus 65/35 %vol helium/oxygen. For a given mask fitted to the face in a reproducible manner, delivered helium concentrations were primarily determined by the ratio of supply gas flow rate to simulated patient minute ventilation, with the inspiratory/expiratory ratio playing a secondary role. However, the functional dependence of helium concentration on these two ratios depended on the mask design.ConclusionsLarge differences in mask performance were identified. With continued refinement, the availability of reliable benchtop methods is expected to assist in the development and selection of patient interfaces for delivery of helium/oxygen and other medical gases.

ZnO:Al Thin Films with Buffer Layers Fabricated via Nitrogen Mediated Crystallization: Effects of N<sub>2</sub>/Ar Gas Flow Rate Ratio

ZnO:Al Thin Films with Buffer Layers Fabricated via Nitrogen Mediated Crystallization: Effects of N<sub>2</sub>/Ar Gas Flow Rate Ratio

Effects of Holding Time and Temperature on Sr Content of Mg-Sr Master Alloys Produced by Metallothermic Reduction of SrO

In the paper, the effects of the holding time and temperature on Sr content of the Mg-Sr master alloys produced by the metallothermic reduction of SrO into magnesium melt were investigated. The results preliminarily indicated that effects of the holding time and temperature on the Sr content of the Mg-Sr master alloys produced by the metallothermic reduction of SrO into magnesium melt were relatively obvious. For a given experimental conditions: magnesium melt of ~10 kg and powder flow rate to carrier gas flow rate ratio of 20 g SrO/min / 15 L Ar/min, with the increasing of holding time from 30min to 150 min at 800 °C or holding temperature from 700°C to 850 °C for 90 min, the Sr content of the Mg-Sr master alloy increased gradually. Obviously, the long holding time or high holding temperature was beneficial to produce Mg-Sr master alloys with high Sr content by the metallothermic reduction of SrO into magnesium melt.

Hydrodynamics of gas–liquid Taylor flow in rectangular microchannels

The effect of fluid properties and operating conditions on the generation of gas–liquid Taylor flow in microchannels has been investigated experimentally and numerically. Visualisation experiments and 2D numerical simulations have been performed to study bubble and slug lengths, liquid film hold-up and bubble velocities. The results show that the bubble and slug lengths increase as a function of the gas and liquid flow rate ratios. The bubble and slug lengths follow the model developed by Garstecki et al. (Lab chip 6:437–446, 2006) and van Steijn et al. (Chem Eng Sci 62:7505–7514, 2007), however, the model coefficients appear to be dependent on the liquid properties and flow conditions in some cases. The ratio of the bubble velocity to superficial two-phase velocity is close to unity, which confirms a thin liquid film under the assumption of a stagnant liquid film. Numerical simulations confirm the hypothesis of a stagnant liquid film and provide information on the thickness of the liquid film.

Experimental study of the effect of process parameters on plasma-enhanced chemical vapour deposition of silicon nitride film

The effect of plasma-enhanced chemical vapour deposition parameters on refractive index and deposition rate of silicon nitride films is investigated. Usually, this kind of study is performed in a laboratory system. In the present work, a horizontal batch system for the simultaneous coating of 100 silicon wafers is used. Using a gas mixture of silane and ammonia as the reactant-gas sources, the effects of the gas flow rate ratio ( R = NH3/SiH4 with the total flow rate constant), pressure, power and temperature on the refractive index and deposition rate were studied and the experimental results are presented and discussed.

Deposition of cluster‐free P‐doped a‐Si:H films using SiH4+PH3 multi‐hollow discharge plasma CVD

AbstractWe deposited cluster‐free P‐doped a‐Si:H films using a SiH4+PH3 multi‐hollow discharge plasma CVD method. The deposition rate sharply increased from 0.49 nm/s with an increasing gas flow rate ratio R = [PH3]/[SiH4] from 0% to 1.17 nm/s at R = 1.0%, then slightly increased to 1.27 nm/s for R = 10%. SiH* emission intensity monotonically increased with increasing R. The increase in deposition rate with increasing R was much higher than that of the SiHx generation rate. The surface reaction probability β of SiH3 increased from 0.33 for R = 0% to 0.62 for R = 0.6%, then remained nearly constant for R > 0.6%. The sticking probability s of SiH3 increased from 0.1 for R = 0% to 0.162 for R = 0.6%, then slightly increased to 0.181 for R = 10%. These results suggest that PHx radicals enhance the surface reaction probability and surface sticking probability of SiH3 radicals. We successfully deposited P‐doped a‐Si:H films with a low stabilized defect density of 2.9 × 1015 cm–3. This defect density is much lower than that of conventional doped a‐Si:H films (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Simultaneous removal of gaseous pollutants with a novel swirl wet scrubber

In recent years, researchers have put a considerable effort to decrease the emission of harmful gaseous pollutants to the atmosphere. Although conventional wet scrubbers are being widely used to remove harmful gases, they have low removal efficiencies. This study reports the effect of some operating conditions on simultaneous removal of NO, NO 2, SO 2, and CO 2, using a novel swirl wet scrubber system. The gaseous pollutants were absorbed into NaOH solution. As the absorbent media was circulated continuously for removal purpose, therefore the production of chemical wastes were minimized. The effect of absorbent concentration, gas flow rate, and liquid flow rate were investigated. The best efficiencies of NO, NO 2, SO 2, and CO 2 simultaneous removal were 77, 88, 100 and 80%, respectively, with 2%, w/v NaOH as the scrubber medium. A comparison between this study and literature data shows that the liquid–gas flow rate ratio ( F L/ F G) in the novel scrubber of this work is much smaller than other gaseous pollutant removal systems. Therefore higher removal efficiency is obtained based on the same liquid flow rates.

Time-resolved Measurements of Loading Ratios and Heat Evolution in D2 (and H2)-Pd·Zr Mixed-oxide Systems

Using a twin system for hydrogen absorption, we have studied heat evolution and high-energy particle generation by D2 and H2 gas absorption into nano-sized mixed oxide powders of palladium and zirconium. We have found very large energy of hydrogen absorption by Pd·Zr oxide compounds exceeding 1.0 eV/D (or H) together with a very high D/Pd loading ratio, exceeding 1.0. The system has been improved to enable time-dependent measurements of the gas flow rate and loading ratio simultaneously with the output heat. It has been revealed that the first phase is divided into two sub-phases; the 1a-phase, where most of the anomalously large output energy is produced with a very high loading, D/Pd ≈ 1.2, and the 1b-phase, where much smaller power is produced as loading increases further by a ratio of about 0.5 with a difference in pressure between deuterium and hydrogen.

공기 중 메틸에틸케톤 제어를 위한 Pilot-Scale 흡수 시스템의 운영인자 분석

Unlike many laboratory-scale studies on absorption of organic compounds (VOCs), limited pilot-scale studies have been reported. Accordingly, the present study was carried out to examine operation parameters for the effective control of a hydrophilic VOC (methyl ethyl ketone, MEK) by applying a circular pilot-scale packed-absorption system (inside diameter 37 cm <TEX>${\times}$</TEX> height 167 cm). The absorption efficiencies of MEK were investigated for three major operation parameters: input concentration, water flow rate, and ratio of gas flow-rate to washing water amount (water-to-gas ratio). The experimental set-up comprised of the flow control system, generation system, recirculation system, packed-absorption system, and outlet system. For three MEK input concentrations (300, 350, and 750 ppm), absorption efficiencies approached near 95% and then, decreased gradually as the operation time increased, thereby suggesting a non-steady state condition. Under these conditions, higher absorption efficiencies were shown for lower input concentration conditions, which were consistent with those of laboratory-scale studies. However, a steady state condition occurred for two input concentration conditions (100 and 200 ppm), and the difference in absorption efficiencies between these two conditions were insignificant. As supported by an established gas-liquid absorption theory, a higher water flow rate exhibited a greater absorption efficiency. Moreover, as same with the laboratory-scale studies, the absorption efficiencies increased as water-to-gas ratios increased. Meanwhile, regardless of water flow rates or water-to-gas ratios, as the operation time of the absorption became longer, the pH of water increased, but the elevation extent was not substantial (maximum pH difference, 1.1).

The development of the structure of water – air bubble grid turbulence

The development of the turbulent flow field generated due to the interaction of grid turbulence with a swarm of bubbles is investigated experimentally, in a vertical channel of rectangular cross section. Void fraction and streamwise mean and rms velocity distributions have been measured at several distances from the grid, with an optical probe and Laser Doppler Velocimetry, in relation to the air flow rate ratio. The obtained results indicate that close to the grid the void fraction and velocity distributions are dictated by the bubble injectors’ location on the grid. Downstream the void fraction distribution changes to a double peak pattern. The velocity distribution is characterized by a shear layer between the wall area and the central area of the channel. The extend of this shear layer is increasing as the distance from the grid and the gas flow rate ratio are increasing, and is associated with a corresponding increase of the turbulence fluctuations. Autocorrelation and spectra measurements at the centre of the channel show a reduction of the flow scales for low void fraction. Consistently, power spectra distributions indicate that bubbles cause a redistribution of energy manifested by the relative enhancement of the intermediate scales’ energy content and a consequent reduction in the larger scales. These trends are gradually alleviated and reversed at large distances from the grid, as the air flow rate is increased.

Effect of carbon on microstructure of CrAlC xN 1- x coatings by hybrid coating system

A systematic investigation of the microstructure of CrAlC x N 1- x coatings as a function of carbon contents was conducted. Quaternary CrAlC x N 1- x coatings were deposited on Si wafers by a hybrid coating system combining an arc-ion plating technique and a DC reactive magnetron sputtering technique using Cr and Al targets in the Ar/N 2/CH 4 gaseous mixture. The effect of carbon content on microstructure of CrAlC x N 1- x coatings was investigated with instrumental analyses of X-ray diffraction, X-ray photoelectron, and high-resolution transmission electron microscopy. The results show that the carbon content of CrAlC x N 1- x coatings linearly increases with increasing CH 4/(CH 4/N 2) gas flow rate ratio. The surface roughness of the CrAlC x N 1- x coating layer decreases with the increase of carbon content.

Influence of Deposition Conditions on Silicon Nanoclusters in Silicon Nitride Films Grown by Laser-Assisted CVD Method

Crystalline-silicon-nanocluster-embedded silicon nitride films were deposited at low temperature using a laser-assisted CVD (LACVD) system with various reactant gas flow rates and assisting laser power densities. The photoluminescence (PL) performances of the resultant films were studied, showing a systematic spectra blue shift, and the enhancement of PL intensity with the increase of the reactant NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /SiH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> gas flow rate ratio and the assisting laser power density used in the film deposition. The spectra blue shift can be ascribed to the decrease of the size of the nanoclusters in the films. It is also deduced that both the reduction of the amount of nonradiative centers in the nanoclusters and the increase of the number density of the nanoclusters in the film are responsible for the enhancement of the PL intensity. The film growth process is also briefly discussed.

Local characteristics of the upward bubbly flow in an annular channel

Results of experimental investigation of the bubbly gas-liquid flow in a vertical annular channel are presented. The average and pulsation shear stresses and distributions of local void fraction were measured by the electrochemical method on both channel walls. It is shown that with a rise of gas flow rate ratio the value of wall shear stress increases significantly, and this effect becomes higher at a decrease in superficial liquid velocity. A presence of the gas phase effects significantly shear stress on the inner wall. Relative intensity of shear stress pulsations increases similarly on both channel walls.

Ultralow surface recombination in p-Si passivated by catalytic-chemical vapor deposited alumina films

The passivation effects of AlOx films were investigated for p-type crystalline Si (c-Si) solar cells. The AlOx films were deposited on 10 Ωcm c-Si substrates by catalytic chemical vapor deposition (Cat-CVD) using tri-methyl aluminum (TMA) and O 2 at a film temperature of 230 °C. The surface recombination velocity (S 0) at the AlOx/Si interface was measured to be below 0.5 cm/s for AlOx films deposited with O 2/TMA gas flow-rate ratios of 15–35. This ultra low S 0 was achieved primarily by band bending due to the negative interface fixed-charge density (N f) of an order of 10 12 charges/cm 2. The decrease in interface trapping density D it in the negative fixed charge region assists in decreasing S 0.

Multi-phase structured silicon carbon nitride thin films prepared by hot-wire chemical vapour deposition

In this work, Silicon Carbon Nitride (Si–C–N) thin films were deposited by Hot Wire Chemical Vapour Deposition (HWCVD) technique from a gas mixture of silane (SiH 4), methane (CH 4) and nitrogen (N 2). Six sets of Si–C–N thin films were produced and studied. The component gas flow rate ratio (SiH 4:CH 4:N 2) was kept constant for all film samples. The total gas flow-rate (SiH 4 + CH 4 + N 2) was changed for each set of films resulting in different total gas pressure which represented the deposition pressure for each of these films ranging from 40 to 100 Pa. The effects of deposition pressure on the chemical bonding, elemental composition and optical properties of the Si–C–N were studied using Fourier transform infrared (FTIR) spectroscopy, Auger Electron Spectroscopy (AES) and optical transmission spectroscopy respectively. This work shows that the films are silicon rich and multi-phase in structure showing significant presence of hydrogenated amorphous silicon (a-Si:H) phase, amorphous silicon carbide (a-SiC), and amorphous silicon nitride (a-SiN) phases with Si–C being the most dominant. Below 85 Pa, carbon content is low, and the films are more a-Si:H like. At 85 Pa and above, the films become more Si–C like as carbon content is much higher and carbon incorporation influences the optical properties of the films. The properties clearly indicated that the films underwent a transition between two dominant phases and were dependent on pressure.

Influence Assessment of Supply Gas Condition and Separator Structure on In-Plane Temperature Distribution and Power Generation Performance of Single Cell of PEFC

To clarify the mechanism of coupling phenomena such as heat, mass and electric charge transfer in a single-cell polymer electrolyte fuel cell (PEFC), we have measured in-plane temperature distribution in a single-cell PEFC by thermograph under power generation. We have investigated the influence of relative humidity and flow rate of supply gas and gas channel pitch of separator on in-plane temperature distribution and power generation performance. As a result, when the stoichiometric ratio of gas flow rate is set over 1.00 regardless of relative humidity of supply gas, the lower and higher temperature region is observed near the inlet and outlet of cell, respectively. This is caused by the convention heat transfer by excess oxygen flow in gas channel at the cathode. Total voltage is increased and the temperature in observation area is decreased with decreasing the gas channel pitch of separator regardless of relative humidity of supply gas under the experimental condition in this study.

Material removal function of the capacitive coupled hollow cathode plasma source for plasma polishing

A novel plasma polishing process has been developed. In the process, highly stable SF6 and Ar/O2 plasmas were generated by using capacitive coupled hollow cathode (CCHC) RF discharge method. The influences of the plasma source operational parameters such as gas flow rate, gas flow rate ratio of the mixed gases, pressure and discharge power on the material removal function of the plasma polishing process were investigated. Material used in the polishing process was fused silica, which was pre-polished to an initial surface roughness of about 1.4nm rms.

Performance comparison of an adiabatic and an internally cooled structured packed-bed dehumidifier

Abstract Liquid desiccant dehumidifiers are used to improve the indoor air quality and achieve lower humidity levels in conditioned spaces. The performance of these dehumidifiers can be enhanced by providing simultaneous cooling in them. This paper presents the performance comparison of an adiabatic and an internally cooled structured packed-bed dehumidifier. The non-adiabatic structured packed-bed absorber consists of rigid media pads with cooling water flowing through the tubes embedded in the packing. The desiccant (CaCl2 in this study) falls by gravity while air flows in the cross flow configuration. The performance of this absorber has been evaluated at varying desiccant flow rates. The moisture removal from the air, the effectiveness of the dehumidifier and the mass transfer coefficients between air and solution have been compared for the dehumidifier operation with and without internal cooling. It is found that the optimum liquid to gas flow rate ratio for maximum effectiveness is about 1.0.

Synthesis and Its Characteristic of Silicon Nitride Film Deposited by ECR-PECVD at Low Temperature

The silicon nitride films have been deposited by Electron Cyclotron Resonance-plasma enhanced chemical vapor deposition (ECR-PECVD) method at low temperature, and the pure nitrogen is introduced into the ECR chamber as the plasma gas, the silane(Ar diluted, Ar:SiH4=19:1) is used as precursor gas. The optimum deposition parameters of SiN films for photovoltaic application as an efficient antireflection coating(ARC) have been investigated. The actual composition of the films will be varied with the deposition conditions, such as gas flow rate ratio(N2/SiH4), substrate temperature, and microwave power. The effect of deposition parameters on the optical performance of SiN films was determined by Ellipsometry. The Si-N and N-H stretching characteristic peaks of SiN films have been observed by FTIR spectroscopy. Results shown that uniform silicon nitride films with low hydrogen content can be deposited at high deposition rate(10.7nm/min), and the refractive index increased with the increasing of substrate temperature and microwave power. The film shows good optical properties (refractive index is 2.0 or so) and satisfied surface quality (average roughness is 1.45nm) when the deposition parameter is 350oC and microwave power is 650W.