Polysilicon RTCVD process optimization for environmentally-conscious manufacturing

In 2021, estimation shows that the worldwide annual hydrogen production is around 94 Mt. Exploitation of native hydrogen being not mature, it is obtained by its separation from other elements by different methods such as steam methane reforming, and electrolysis of water. The latter supplied by a renewable power source will take part in the development of a green hydrogen economy [1]. In this context, Proton Exchange Membrane (PEM) Electrolyzer is a promising technology due to its flexibility and very quick adaptation to load variations. However, its current development still confronts some limitations at a large industrial scale. For instance, efficiency and durability are directly impacted by the mass transport and electrical transfer within the porous materials at the anode side. Limitation of the water supply to the catalyst layer happens once there is a poor oxygen evacuation which decreases the performance of the device by inducing high overpotential. Furthermore, the PTL has an important role as an electrical conductor for charge transfer from the catalyst layer [1]. The efficiency of all the transport phenomena through the PTL and porous electrode assembly depends on their transport properties which are related to their microstructure and operating conditions. For instance, PTL with a large pore size allows good water and gas transport, while produced electrons choose a long-distance path generating an electrical resistance higher than that in the case of PTL with a small pore size [1]. So, controlled and optimum porosity and pore size could contribute to efficient water, gas, and electron transport. To define the best porous layers morphologies, a deep and accurate understanding of the phenomena is developed in this work by combining modeling and experiments.The magnetic resonance imaging (MRI) technique was used to quantify the water content within the porous layer during the two-phase flow. Instead of the real PTL made of titanium which is paramagnetic and cannot be used in the MRI, borosilicate filters with thickness, porosity, and pore size similar to the PTL were used. After positioning the sample in the 600 MHz vertical imager (Figure 1-A), a constant water flow rate is introduced while the gas flow rate is varied. The saturation profiles measured through the porous material depend on the gas flow rate and a semi-dryness of the sample occurs (Figure 1-B) with a residual quantity trapped between pores (minimum stable water content). The water flow rate variation in the channel does not affect saturation, but a higher gas flow rate is needed to reach a minimum stable water content for higher water flow rate.The gas pressure drop through the porous medium was measured and bubble formation in the channel was also analyzed. The results show that the pressure drops and types of flow (slug, annular, and bubble flow) depend on orientation of the water channel (horizontally and vertically) and flow direction (up or downward), and on the water and gas flow rates.To reach a better understanding of the dynamic characteristics of water and oxygen transport over the PTL, the phase-field model based on the Cahn-Hilliard theory was used to simulate the two-phase flow through a porous medium [2]. In this model, the modified Navier-Stokes equations for two phases are coupled with a phase-field equation for describing the diffuse interface. Numerical simulations performed in the COMSOL® multiphysics software were carried on 2D geometries composed of spherical solid grains of different sizes, having properties similar to the PTL used in the MRI experiments. Gas is injected on one side of the sample and flows through the porous medium initially saturated and evacuated on another side in contact with the water channel (Figure 1-C). Gas flow in the porous medium and bubble formation in the water channel are studied while varying the gas and water flow rates. The simulation results give information about the gas pathways within the porous medium and the saturation profiles over time, depending on the gas/water flow rates, which will be compared with experimental results.[1] J. Parra-Restrepo, “Caractérisation des hétérogénéités de fonctionnement et de dégradation au sein d’un électrolyseur à membrane échangeuse de protons (PEM),” Université de Lorraine, 2020.[2] J. W. Cahn and J. E. Hilliard, “Free Energy of a Nonuniform System. I. Interfacial Free Energy,” The Journal of Chemical Physics, vol. 28, no. 2, pp. 258–267, Feb. 1958. Figure 1

Coriolis devices are continuously evolving to meet the demands of different conditions, such as wet gas flow. However, their application in wet gas flow has not yet been thoroughly explored. The impact of steady flow disturbances on Coriolis flow meters is well-documented, and empirical compensation or correction methods can be implemented accordingly. However, there has been inadequate investigation into the response of Coriolis meters under transient flow conditions and their comparison with steady flow in a wet gas. In this study, a Coriolis device was horizontally installed in a 50 mm pipe diameter. The experimental fluids consisted of air and water, with Lockhart-Martinelli (XLM) values ranging from 0.02 to 0.40. Steady and transient flow conditions at different gas and liquid flow rates were studied. The findings demonstrate the capability of standard deviation (STD) in distinguishing transient flow from steady one. Additionally, a strong correlation was observed between XLM and gas Over-Reading (OR) across various gas flow rates and XLM values. This correlation is particularly evident for XLM < 0.1. At extremely low liquid loading (XLM < 0.05), the average percentage error remains below 7 % even without the utilization of any correction models. Furthermore, the impact of different sensor installations, which had been largely overlooked in previous studies, was investigated.

Chemical vapor deposition (CVD) of graphene has attracted high interest in the electronics industry due to its potential scalability for large-scale production. However, producing a homogeneous thin-film graphene with minimal defects remains a challenge. Studies of processing parameters, such as gas precursors, flow rates, pressures, temperatures, and substrate types, focus on improving the chemical aspect of the deposition. Despite the many reports on such parameters, studies on fluid dynamic aspects also need to be considered since they are crucial factors in scaling up the system for homogenous deposition. Once the deposition kinetics is thoroughly understood, the next vital step is fluid dynamics optimization to design a large-scale system that could deliver the gas uniformly and ensure maximum deposition rate with the desired property. In this review, the influence of fluid dynamics in graphene CVD process was highlighted. The basics and importance of CVD fluid dynamics was introduced. It is understood that the fluid dynamics of gases can be controlled in two ways: via reactor modification and gas composition. This paper begins first with discussions on horizontal tubular reactor modifications. This is followed by mechanical properties of the reactant gasses especially in terms of dimensionless Reynolds number which provides information on gas flow regime for graphene CVD process at atmospheric pressure. Data from the previous literature provide the Reynolds number for various gas compositions and its relation to graphene quality. It has been revealed that hydrogen has a major influence on the fluid dynamic conditions within the CVD, hence affecting the quality of the graphene produced. Focusing on atmospheric pressure CVD, suggestions for up-scaling into larger CVD reactors while maintaining similar fluid properties were also provided.

HfO 2 growth by low-pressure chemical vapor deposition using the Hf(N(C 2H 5) 2) 4/O 2 gas system

Hydrodynamics characteristics of HDS trickle bed test reactor

Analytical aspects of different adjustment of parameters of an inductively coupled plasma atomic emission spectrometer (ICP‐AES) were investigated. The ICP‐AES was a LABTAM 8440M (now called GBC) spectrometer. Since at many times, the elemental concentration of the analyte is near to the detection limit, the lowest possible detection limit has to be reached. When the signal‐to‐background ratio (SBR) is maximized, the detection limit is the smallest. This is the reason why the effects of each adjustable parameters on the signal‐to‐background ratios were investigated. Seven adjustable parameters can be analyzed in this equipment: (i) viewing height, (ii) forward power, (iii) sample gas, (iv) coolant gas, (v) auxiliary gas, (vi) flushing gas, and (vii) sample uptake flow rates. Furthermore aerosol distribution by droplet size and nebulization efficiency were also examined applying three different sample gas flow rates and four elements [iron (Fe), magnesium (Mg), manganese (Mn), and nickel (Ni)]. The alkali metals with low excitation energy [potassium (K), lithium (Li), and sodium (Na)] were detectable in higher regions of the plasma, some alkali‐earth and transition metals with medium excitation energy [calcium (Ca), srontium (Sr), and copper (Cu)] were well detectable in medium height, whereas the maximum signal‐to‐background ratios of the other elements with relatively high excitation energy [e.g. cadmium (Cd), Ni, and phosphorus (P)] reached in lower regions of the plasma. On the basis of results the compromised viewing height for all the elements is found 5 mm, the optimum sample gas flow rate 1.14 dm3 min‐1 and the forward power 1200 W. Change of coolant and auxiliary gas flow rates has not changed the signal‐to‐background ratios significantly. Consequently the optimum argon flow rates in aspect of consumption of argon are the possible lowest flow rates, where plasma remains stable. For coolant and auxiliary gas flow rates these values are 10 dm3 min‐1 and 0.1 dm3 min‐1, respectively. Changing the rate of peristaltic pump (i.e. sample uptake rate) the signal‐to‐background ratios increase to 4‐ or 5‐fold of the original values, therefore the optimum sample uptake rate is considered 4 cm3min‐1. Increase of flushing gas flow rate has not changed the signal‐to‐background ratios significantly, except in case of sulfur (S) and P, because of oxygen (O2) absorption from the air. When analysis of S and P content is necessary, 0.13 dm3min‐1 and 0.2 dm3 min‐1, respectively, of flushing gas flow rate is recommended to use.

In this paper, a detailed study is presented for the growth kinetics of rapid thermal chemical vapor deposition (RTCVD) of nitrogen-doped polysilicon using silane and ammonia chemistry. It is found that nitrogen doping has reduced the surface roughness and grain size of the RTCVD polysilicon film. Both the deposition rate and the incubation time of film growth depend strongly on the ammonia to silane flow ratio. We have proposed a novel structure of NICER (Nitrogen Incorporation into CMOS Gate Electrode by in-situ RTCVD). High performance and highly reliable dual gate CMOS can be formed by combining rapid thermal oxidation (RTO) with RTCVD.

The effects of ratio of draft tube to reactor diameter (Dd/D), liquid nozzle diameter (dN), aeration tube diameter (dG) and immersion height of the two‐fluid nozzle into the draft tube (HN) on overall and annulus gas holdups for the air‐water system were evaluated experimentally in a reversed flow jet loop reactor over wide ranges of gas and liquid flow rates. Both the gas holdups increased with increasing gas and liquid flow rates and with decreasing dN and HN. The influence of dG on gas holdups is found to vary with gas flow rates. Correlations are proposed to predict gas holdups.

The most of past studies in foaming trickle bed reactors aimed at the improvement of efficiency and operational parameters leads to high economic advantages. Conventionally most of the industries rely on frequently used gas continuous flow (GCF) where operational output is satisfactory but not yields efficiently as in pulsing flow (PF) and foaming pulsing flow (FPF). Hydrodynamic characteristics like regime transitions are significantly influenced by foaming nature of liquid as well as gas and liquid flow rates. This study?s aim was to demonstrate experimentally the effects of liquid flow rate, gas flow rates and liquid surface tension on regime transition. These parameters were analyzed for the air-aqueous Sodium Lauryl Sulphate and air-water systems. More than 240 experiments were done to obtain the transition boundary for trickle flow (GCF) to foaming pulsing flow (PF/FPF) by use excessive foaming 15-60 ppm surfactant compositions. The trickle to pulse flow transition appeared at lower gas and liquid flow rates with decrease in liquid surface tension. All experimental data had been collected and drawn in the form of four different transitional plots which are compared and drawn by using flow coordinates proposed by different researchers. A prominent decrease in dynamic liquid saturation was observed especially during regime transitional change. The reactor two phase pressure evident a sharp rise to verify the regime transition shift from GCF to PF/FPF. Present study reveals, the regime transition boundary significantly influenced by any change in hydrodynamic as well as physiochemical properties including surface tension.

Membrane evaporation of amine solution for energy saving in post-combustion carbon capture: Performance evaluation

The synthesis of SiC (and/or Si3N4) in an inductive thermal plasma from liquid disilane precursor is described in this paper. One goal of the process presented hereafter is the valorization of a liquid disilane fraction, which is a by‐product of the silicone industry. The liquid precursor is atomized in the core of the thermal inductive plasma and decomposed in the high‐temperature zone. The coating grows on the substrate according to the thermal plasma chemical vapor deposition (CVD) process. The resulting synthesized materials are investigated by means of X‐ray diffraction, scanning and transmission electron microscopy, and nuclear magnetic resonance. The composition of the material synthesized is studied as a function of process parameters, such as the plasma gas nature and its composition, the atomization gas flow rate and the plasma reactor pressure. Control over the composition of the synthesized material composition, as well as the coating microstructure, can be achieved by an appropriate adjustment of the experimental parameters. Nanostructured α/β‐SiC and α/β‐Si3N4can be synthesized successfully with such a thermal plasma process. The deposition rate reached with such a technology is more than 20 μm min−1, which is two to three orders of magnitude higher than that of the conventional CVD method. Copyright © 2001 John Wiley & Sons, Ltd.

Dielectric Barrier Discharges (DBD) have been used for more than a century, especially for ozone production. Research conducted within the last twenty years has investigated the discharge mechanisms involved and the different discharge regimes observable (filamentary, glow, Townsned and multi-peaks). These studies highlight the fundamental role of metastable species to establish and maintain a homogeneous discharge. These recent improvements in understanding the physics of DBD's open perspectives for new applications and new interests in atmospheric pressure surface treatment. Working at atmospheric pressure for silicon oxide deposition is of great interest : the possibility of continuous process, no vacuum component costs and maintenance, no loading/unloading time. However, in comparison with a classical plasma enhanced chemical vapor deposition (PECVD) process, the high pressure and thus the high gas density may result in a gas phase chemistry and a larger formation of dust particles. Exploring a new pressure range from 10 to 1000 mbar could be an alternative for this process. In the first part of this work the effect of the pressure on a DBD in non-reactive gases (helium, argon and nitrogen), then in neutral gas/oxygen mixture has been investigated with electrical measurements (discharge current and applied voltage), with high-speed imaging and with time-resolved optical emission spectroscopy. The second part of this work is dedicated to SiOx barrier coating characterization (FTIR-ATR, XPS, AFM and SEM) as a function of pressure in oxygen/hexamethyldisiloxane (HMDSO) gas mixture highly diluted in nitrogen. The exploration of discharge regimes as a function of pressure shows, in nitrogen, a progressive transition from Townsend to multi-peaks regime between 320 and 160 mbar. A detailed study of this regime in helium and nitrogen with high-speed imaging shows that each multi-peak corresponds to a new spatially homogeneous discharge. However, the discharge is not completely extinguished between each pulse and the remaining light emission reveals the metastable activity (excitation transfer or Penning effect). Paschen's curves obtained from electrical characterization of the discharge show an inversion (compared to standard cuves) of argon and helium cuves. This inversion shows the importance of metastable energies and capabilities to ionize almost all impurities, in the case of helium. This explains why in helium a breakdown under a lower electric field than in argon is possible. A detailed study of a glow discharge in helium as a function of pressure and impurities with time-resolved spectroscopy showed the metastables evolution within a discharge and the role of impurities in quenching or creation rate of metastables. This study also shows a 4 minutes time for thermal stabilization of the discharge (electrode heating and thermosdesorption). In helium and nitrogen, the very first microseconds of discharge are filamentary and change after 2-3 periods (∼ 200 µs) to the glow or Townsend regime respectively. Adding oxygen, an electronegative and metastable quencher gas, make the discharge change to filamentary when a proportion of more than 1500 ppm is added at atmospheric pressure. This rate is increased until 2 % in nitrogen at 350 mbar. The presence of a polymer substrate reduced this Townsend working domain due to the increase of impurities in the discharge caused by polymer etching. However, this process in pure nitrogen is very efficient for implanting nitrogen functional groups on the surface of polymer films. An incorporation of 23 % of nitrogen onto a PET surface has been reached. Regarding SiOx thin film deposition, adding HMDSO, even for ∼ 100 ppm make the discharge change to filamentary. A pressure below 40 mbar must be reached to obtain a multi-peak regime. This high pressure process is fast and deposition rate of 17 nm/s could be obtain at 500 mbar. FTIR, AFM and SEM characterisation of the coatings showed an inhomogeneous composition and structure of the layer between entrance and exit of the discharge along the gas flow. These conditions could explain that the best oxygen barrier obtained was 40.5 cm3/(m2· atm · day). Depending on the discharge parameters (frequency, residence time, power and pressure) the coatings are more or less organic. A progressive decarbonification of the layer due to progressive monomer depletion explains this behavior. A higher oxygen rate allows a better film composition homogeneity along the discharge, while a longer deposition time results in a rougher coating but has no effect on the layer composition. The particular geometry of the discharge cell (6 cm by 6 cm electrodes and 2 mm gap) with gas injection from one side, leads to a different chemistry along the gas flow. At the entrance, the coating is smooth (Ra ∼ 5 nm) and dense but organic whereas at the exit it is rough (Ra ∼ 15 nm) but has a quasi-stoechiometric composition. These differences are explained by heterogeneous reactions, comparable to PECVD process (surface chemistry) close to the gas input and a progressive transition to homogeneous reactions at the exit of the discharge (volume chemistry) which result in particle formation of nanometric size. Analysis of these particles by laser light scattering (LLS) shows a pressure threshold of 200 mbar with a constant gas mixture and flow within all the pressure range. At this pressure, the first detectable particles appear at the end of the discharge. From 200 to 1000 mbar, this threshold becomes closer and closer to the discharge entrance, but it always corresponds to a residence time of the gas in the discharge of around 30 ms. Thus this time corresponds to the characteristic formation time of detectable particles in the discharge. We also showed that this threshold varies linearly with the power injected in the discharge, the higher the power the faster the particles appear. Spatio-temporal LLS measurements show a cyclic (Τ ∼ 1-2 s) formation of particles. This behavior is linked to a rapid growth and a trapping of the particle in the discharge when they reach a 200 nm size. Then, when their size or density increases (∼ 240 nm) they are collected on the electrodes or expelled by the flow drag force which becomes preponderant in comparison with the electrostatic trapping force. Finally, they agglomerate at the exit of the discharge up to ∼ 300 nm size. Then a new cycle starts. This global approach of SiOx deposition process by DBD opens new perspectives of applications in a new pressure range and show the key parameters to be adjusted for an industrial application.

Investigation on the swirlmeter performance in low pressure wet gas flow

Large‐scale animal cell operation is costly both in terms of facilities and consumables. Hence developmental studies with animal cells normally start at laboratory scale, often using small stirred tanks. In order to better optimise cell performance, it is necessary to know the physical conditions under which the cells are grown. In this study a laboratory‐scale vessel (2 dm3 working volume) with two large‐bladed paddle impellers was characterised hydrodynamically. Three different aeration methods (surface, sparging and membrane aeration) were investigated and compared. Power input and oxygen transfer rates to culture medium were determined as a function of agitation and gas flow rates. Non‐dimensional correlations were established for each case, which can be useful for scale‐up purposes. The results obtained indicate that power input is quite dependent on the vessel accessories: for the same agitation rate, the maximum power is required for the membrane structure and the minimum for surface aeration, with the addition of the sparger leading to an intermediate situation. Predictions found in the literature can be used for simple vessels, but may not be applicable when accessories are added to the vessel structure; in such cases, the use of experimental relationships are required. Oxygen transfer rate was dependent on the aeration method and working conditions (agitation and gas flow rates), particularly for sparger aeration. Membrane aeration gave larger oxygen transfer but higher gas pressure and flow rates were required. Surface aeration was the least effective method, nevertheless requiring gas flow rates similar to those used for membrane aeration. The aeration method of choice depends upon the culture and work specificities: surface aeration is limited to small cell concentrations and low oxygen consumption rates. For higher cell concentrations and oxygen consumption rates, both membrane and sparger aeration methods can be applied: the use of the sparger is limited to cells that are not affected by the presence of bubbles or the addition of surfactants, whereas the membrane aeration basket should not be used when a hydrodynamically controlled stirred tank is required.

Gas–liquid two-phase flow distributions in parallel channels for fuel cells