Intermediate Gas Flow Rate Research Articles

Effect of Gas Flow Rate in PECVD of Amorphous Silicon Thin Films for Interface Passivation of Silicon Heterojunction Solar Cells

Precursor gas flow rate variation (30–80 sccm) in the plasma‐enhanced chemical vapor deposition (PECVD) process of intrinsic a‐Si:H layer deposition using SiH4/H2 (equal ratio) plasma is explored and its effect on the i‐a‐Si:H/c‐Si interface passivation is investigated. A window of intermediate gas flow rates is determined for good quality surface passivation of n‐type c‐Si. Maximum effective minority carrier lifetime (τeff) above 1 ms, implied open‐circuit voltage (iVoc) ≈ 710 mV, and low interface defect density (Dit) ≈3.5 × 109 cm−2 eV−1 are obtained at an intermediate gas flow rate. The SiH4:H2 discharge emission characteristics, and the a‐Si:H film characteristics such as hydrogen concentration, film density, optical band gap, and refractive index, are also investigated. To examine the effect of the flow rate variation on the performance of the final device, front‐junction silicon heterojunction solar cells are fabricated on n‐type Si wafers, and ≈17% efficient cells are fabricated with an open‐circuit voltage (Voc) close to 690 mV at an optimized gas flow rate. This study provided information related to the transient plasma instability, SiH4 depletion, secondary reactions in the plasma, and flux of radicals toward the substrate for the film growth with a good level of surface passivation.

Study on the Large Area Diamond Film Deposition in a Self- built Overmoded Microwave Power Chemical Vapor Deposition Device

With a self-built overmoded microwave plasma chemical vapor deposition device, the effect of the gas flow rate variation on the uniform deposition of diamond films on molybdenum of 100 millimeter diameter was studied. The plasma density was 1.0×1019/m3 when the microwave power was 5.0 kW and the gas pressure was 10.0 kPa. The ovemoded MPCVD device presented good stability of the gas flow rate field distribution. The substrate surface can be well covered when the hydrogen flow rate varied from 50 to 800 sccm. The uniform diamond film with good quality was obtained at an intermediate gas flow rate, 300 sccm. The diamond film with good quality, 5.74 cm-1 as FWHM value and high growth rate, 5.8 μm/h was deposited when the gas flow rate was 300 sccm.

Direct injection high efficiency nebulizer-inductively coupled plasma mass spectrometry for analysis of petroleum samples

Direct injection high efficiency nebulizer (DIHEN)-inductively coupled plasma mass spectrometry (ICPMS) is investigated for analysis of petroleum samples dissolved in volatile organic solvents. To minimize solvent loading, the solution uptake rate is reduced to 10 μl/min, far less than the level (85 μl/min) commonly used for aqueous sample introduction with the DIHEN, and oxygen is added to the nebulizer gas flow and outer flow of the ICP. Factorial design is applied to investigate the effect of nebulizer tip position within the torch and the nebulizer and intermediate gas flow rates on the precision and the net signal intensity of the elements tested for multielemental analysis. Cluster analysis and principal component analysis are performed to distinguish the behavior of different isotopes, oxide species and doubly charged ions. The best operating conditions at a solution uptake rate of 10 μl/min are: RF power=1500 W, nebulizer gas flow rate=0.10–0.12 l/min, intermediate gas flow rate=1.5 l/min and DIHEN tip position=3–4 mm below the top of the torch intermediate tube. Acceptable recoveries (100±10%) and good precision (less than 3% relative standard deviation) are obtained for trace elemental analysis in organic matrices (a certified gas oil sample and a custom-made certified reference material) using flow injection analysis. Because of high blank levels, detection limits are 1–3 orders of magnitude higher for organic sample introduction than those acquired for aqueous solutions.

The influence of particle size on the flow of fluidised powders

Fluidised particles can form thin coherent flows that move swiftly over horizontal surfaces. When the particles are cohesionless, Eames and Gilbertson [J. Fluid Mech. 424 (2000) 169] demonstrated that the flow may be understood through vertically integrated momentum and mass balances, and good agreement was found between the model predictions and experimental observations. The behaviour of gas fluidised fine particles (diameter of the order of tens of micrometres) differs significantly from that of larger particles. This is true with respect to their flow which takes place through a series of episodic avalanches and waves rather than as a continuous flow. This behaviour can be explained in terms of a mild cohesive force between the particles. When cohesion is included in the vertically averaged momentum equation, the dynamics of fine particle flows can be reasonably predicted for low and high gas flow rates, when the cohesive forces are respectively weaker than internal frictional forces or drag forces generated by the gas flow. A quasi-static analysis of the combined effect of gas flow and cohesion shows that where cohesive sediments are thin they are not necessarily mobilised, even when fluidised, and this is supported by new experimental observations. A flow of cohesive particles thus has two distinct regions: a thin nose region where the material is not mobilised and a pile of mobile particles behind it. At intermediate gas flow rates comparable to the point of minimum fluidisation, the internal structure of the particle flow dominates how the pile flows along a horizontal surface, and continuum models fail to predict the pile dynamics.

CHAOS ANALYSIS OF BUBBLE FORMATION TRANSITION PHENOMENA ON A MULTI-HOLE SIEVE PLATE

Bubble formation on a sieve plate with multiple holes is a very complicated process. At low to intermediate gas flow rates, not all holes are actively bubbling all the time. Furthermore, the interval between bubbling events may be highly variable These phenomena are types of bubble formation transitions, and they involve both active hole location and event interruption. In this investigation, nonlinear analysis was applied to the experimental time series data obtained from light scattering, which was sensitive to active hole location. The correlation dimensions and the largest Lyapunov exponent were estimated from the delay coordinates. These findings, along with the result of the surrogate data testing suggest that active hole location transitions can be regarded as low dimensional, deterministic chaos. Effects of gas chamber volume below the sieve plate and elevated viscosity of the liquid phase upon both the transition frequency and the chaotic invariants were studied, it was found that either increased gas chamber volume or elevated liquid viscosity may lead to less frequent active hole location transitions.

Application of tertiary amines for arsenic and selenium signal enhancement and polyatomic interference reduction in ICP-MS analysis of biological samples

Water soluble tertiary amines enhance signals and decrease polyatomic chloride interferences in the direct inductively coupled plasma – mass spectrometric (ICP-MS) determination of As and Se in biological samples. Preliminary experiments with amine concentrations and nebulizer flow rates produced element and interference signal intensity changes. Arsenic and Se ICP-MS determination parameters have been optimized by a simplex procedure with amines in an argon plasma or without amines but with addition of N2 to the Ar. Variables include RF (radio frequency) power, nebulizer gas flow rate, intermediate gas flow rate, and amine concentration or nitrogen gas flow rate. Detection limit, minimization of polyatomic ion intensities, and reproducibility have been evaluated as reponse factors. The signal enhancement and element-to-molecular interference ratios differ to some extent with analyte intensity optimum operating conditions. The detection limits with addition of nitrogen (16 pg mL–1 for As and 180 pg mL–1 for Se) or of amines (8 pg mL–1 for As and 120 pg mL–1 for Se) and the extent of chloride interference minimization were compared. Amines addition was more beneficial. Biological standard reference materials and food and fecal samples were analyzed following different sample dissolution procedures.

Influence of operating conditions on the effects of acids in inductively coupled plasma atomic emission spectrometry

The influence of the operating conditions on interferences from HCl, HNO3 and H2SO4 in inductively coupled plasma atomic emission spectrometry was studied. The acid concentration was in the 0–2 mol l–1 range. It was found that the acid interferences were strongly dependent on the operating conditions. Several different plasma excitation conditions were obtained by modifying the aerosol carrier gas and the intermediate gas flow rates. The test element was vanadium. Plasma diagnostics were performed by measuring the excitation temperature, the electron number density and the ionic-to-atomic line intensity ratio. In each instance, it was found that the excitation temperature was not modified as a function of the acid concentration. For long residence time and efficient energy transfer, the electron number density and the ionic-to-atomic line intensity ratio were not modified. Only a minor depressing effect was observed for ionic lines, which was attributed to the aerosol formation and transport. In contrast, for short residence time and inefficient energy transfer, both the electron number density and the ionic-to-atomic line intensity ratio were depressed. The significant depressing effect for ionic lines was attributed to a change in the excitation conditions. It is, therefore, possible to separate the acid effects originating from the sample introduction system from those originating in the plasma by carefully selecting the operating conditions of the plasma.

The characteristics of water and bubbling jets in a cylindrical vessel with bottom blowing.

Experimental conditions of bubbling jets were chosen in the intermediate gas flow rate regime where the size and the shape of bubbles are mainly determined by nozzle size and gas flow rate. The velocity of liquid in bubbling jets were measured by making use of LDV (Laser Doppler Velocimeter). The radial and axial distributions of them were related to the behaviour of rising bubbles. The empirical expressions for the mean velocity and root mean square value of velocity fluctuation on the center-line were presented as functions of gas flow rate. Also, water jets in the same vessel were measured to confirm the applicability of LDV system and to clarify the effect of side wall on the confined jets.

Application of an argon-nitrogen inductively-coupled radiofrequency plasma (ICP) to the analysis of geological and related materials for their rare earth contents

An account is given of the development of a procedure for the determination of the rare earth (RE) elements in a large variety of geological materials employing a medium power argon-nitrogen ICP coupled with a 3.4m Ebert spectrograph. The effects of the carrier and intermediate gas flow rates, height of observation and power on RE spectral line intensities have been studied. The line-to-background ratio of the RE analyte was found to increase with observation height and passed through a maximum at 12–14 mm above the top of the work coil. The method eventually developed allows the direct determination of the lanthanides and yttrium at the 50–200 μg g −1 levels using a single solution prepared by fusing 0.2–1 g samples with Na 2O 2 or LiBO 2 and dissolving the melt in 4–10% (v/v) HNO 3, or by treating the samples with HF-HClO 4-HNO 3 mixtures. For lower contents of the RE elements, they can be separated from matrix concomitants by ion exchange employing AG50W-X8 resin. A large variety of silicate and phosphate reference materials was analysed using scandium as the internal standard. The relative standard deviations vary from about 1.5–15%. No matrix effects were observed despite the large compositional variation of the samples analysed.