Modelling of Gas-Phase and Surface Kinetics in Movpe of GaAs and AlxGal-xAs

1990 ◽  
Vol 204 ◽  
Author(s):  
T.J. Mountziaris ◽  
N.K. Ingle ◽  
S. Kalyanasundaram
Keyword(s):  
Gas Phase ◽  
Kinetic Models ◽  
Operating Conditions ◽  
Surface Kinetics ◽  
Tertiary Butyl ◽  
Gaas Films ◽  
Flow Heat ◽  
Chemical Reaction Mechanisms ◽  
Trimethyl Gallium ◽  
Trimethyl Aluminum

ABSTRACTWe present detailed chemical reaction mechanisms that describe the deposition of GaAs films from tertiary-butyl-arsine (TBA) and trimethyl-gallium (TMG) as well as the deposition of AlxGa1-xAs (0≤x≤1) films from trimethyl-aluminum (TMAl), TMG and arsine during metalorganic vapor phase epitaxy (MOVPE). The kinetic models include both gas-phase and surface reactions, whose rates are used to predict production or consumption of the participating species as well as the growth rate of the film. Two-dimensional simulations of flow, heat and mass transfer in horizontal MOVPE reactors have been coupled with the kinetic models to provide a realistic picture of the process. The predicted growth rates at different operating conditions as well as the predicted incorporation ratio, x, of Al in the AlxGal-xAs films are in good agreement with experimental observations.

Gas Phase and Surface Kinetics of Diamond-Like Carbon Films Growth in Pecvd Reactors

1998 ◽  
Vol 555 ◽  
Author(s):  
Maurizio Masi ◽  
Carlo Cavallotti ◽  
Sergio Carrà
Keyword(s):  
Gas Phase ◽  
Cross Sections ◽  
Kinetic Constant ◽  
Electron Distribution Function ◽  
Carbon Films ◽  
Operating Conditions ◽  
Kinetic Constants ◽  
Diamond Like Carbon ◽  
Plasma Reactors ◽  
Surface Kinetics

AbstractThe surface and gas-phase kinetic of deposition of diamond-like carbon films (DLC) obtained in plasma reactors using methane as precursor was here investigated. Kinetic constants of electronic reactions were evaluated using experimental ionization and neutral dissociation cross sections and the Druyvestein electron distribution function. Kinetic constants for ionic and neutral reactions were found in the literature. Surface reactions were divided into processes involving the impingement of gas-phase radicals or ions from the plasma and desorption or recombination reactions of adsorbed surface species. The kinetic constants of the former processes were evaluated.from the ambipolar theory or from the kinetic theory of gases, while the other kinetic constants were determined from analogy with hydrocarbon chemistry. The exception is the desorption of adsorbed methyl radicals, whose kinetic constant was fitted over experimental data. The predictivity of the model was tested through the simulation of three reactors described in the literature widely differing for operating conditions.

GAS-Phase Decomposition Kinetics of MOVPE Precursors in a Counterflow Jet Reactor

1992 ◽  
Vol 282 ◽  
Author(s):  
S. A. Safvi ◽  
T. J. Mountziaris
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Gas Phase ◽  
Experimental System ◽  
Operating Conditions ◽  
Tertiary Butyl ◽  
Carrier Gas ◽  
Hydride Elimination ◽  
Counterflow Jet Reactor ◽  
Stagnation Plane

ABSTRACTA new reactor for studying the purely homogeneous thermal decomposition of organometallic precursors used in the Metalorganic Vapor Phase Epitaxy (MOVPE) of semiconductors is presented. The idea is based on the use of a counterflow jet configuration with one jet being heated and the other unheated. The heated jet contains pure carrier gas (typically hydrogen or nitrogen), while the unheated jet contains vapors of an organometallic species diluted in the same carrier gas. Under appropriate operating conditions, decomposition of the organometallic species takes place near the stagnation plane where the hot jet collides with the cool jet. Since the reactions occur in the gas phase and away from hot walls, purely homogeneous kinetics can be obtained. Such a counterflow jet reactor was designed for studying the thermal decomposition of tertiary-butyl-arsine (TBA), t-C4H9AsH2, a very promising precursor for MOVPE of GaAs films. Two-dimensional finite element simulations of transport phenomena and kinetics have been used to identify optimal operating conditions. An experimental system was constructed and capillary-sampled mass spectroscopy at the stagnation plane was used to study the thermal decomposition of TBA in nitrogen at a total pressure of 252 Torr. Gas-chromatography of the effluent gas stream was employed for positive identification of the hydrocarbon byproducts. The results indicate the existence of two major decomposition routes: (1) A low activation energy pathway producing isobutane AsH, and (2) a higher activation energy, β-hydride elimination pathway producing isobutene and arsine.

Reaction and Transport Models of the MOVPE of Ternary III-V Semiconductors

1992 ◽  
Vol 282 ◽  
Author(s):  
N. K. Ingle ◽  
T. J. Mountziaris
Keyword(s):  
Transport Model ◽  
Operating Conditions ◽  
Limited Growth ◽  
Transport Models ◽  
Group Iii ◽  
Diffusion Limited ◽  
Horizontal Reactor ◽  
Trimethyl Gallium ◽  
Trimethyl Aluminum ◽  
Deposited Films

ABSTRACTReaction and transport models describing the deposition of thin films of ternary compoundsemiconductors by Metalorganic Vapor Phase Epitaxy (MOVPE) are being developed. The growth of AlxGa1−x As (0≤x≤1) films from trimethyl-aluminum (TMA1), trimethyl-gallium (TMG) and arsine has been used as a typical example. A kinetic model of the process including both gas phase and surface reactions has been coupled to a two-dimensional transport model of a horizontal reactor with a flat susceptor. The model predicts reported experimental observations on growth rates and film compositions [1] using a single adjustable parameter, the activation energy of the the AlAs growth reaction. A parametric study was performed to identify operating conditions maximizing the thickness andcompositional uniformity of the deposited films. All inlet flow rates considered in this work were higher than the ones required to suppress transverse buoyancy-driven recirculations in the reactor [2,3]. Such conditions permit the growth of abrupt heterojunctions byrapidly switching various precursors on and off. Our results indicate that the most promising operating conditions coincide with the transition from kinetic limited to diffusion limited growth, which occurs at temperatures between 800 K and 850 K for typical experiments [1]. The optimal inlet mole fraction of the limiting group-III species was found to be about 6×10−4 for such cases.

scholarly journals High Pressure Photoreduction of CO2: Effect of Catalyst Formulation, Hole Scavenger Addition and Operating Conditions

Catalysts ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 430 ◽  
Author(s):  
Elnaz Bahadori ◽  
Antonio Tripodi ◽  
Alberto Villa ◽  
Carlo Pirola ◽  
Laura Prati ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Formic Acid ◽  
Gas Phase ◽  
Operating Conditions ◽  
Flame Spray ◽  
Co2 Solubility ◽  
Total Consumption ◽  
Solubility In Water ◽  
Hole Scavenger ◽  
Fuels And Chemicals

The photoreduction of CO2 is an intriguing process which allows the synthesis of fuels and chemicals. One of the limitations for CO2 photoreduction in the liquid phase is its low solubility in water. This point has been here addressed by designing a fully innovative pressurized photoreactor, allowing operation up to 20 bar and applied to improve the productivity of this very challenging process. The photoreduction of CO2 in the liquid phase was performed using commercial TiO2 (Evonink P25), TiO2 obtained by flame spray pyrolysis (FSP) and gold doped P25 (0.2 wt% Au-P25) in the presence of Na2SO3 as hole scavenger (HS). The different reaction parameters (catalyst concentration, pH and amount of HS) have been addressed. The products in liquid phase were mainly formic acid and formaldehyde. Moreover, for longer reaction time and with total consumption of HS, gas phase products formed (H2 and CO) after accumulation of significant number of organic compounds in the liquid phase, due to their consecutive photoreforming. Enhanced CO2 solubility in water was achieved by adding a base (pH = 12–14). In basic environment, CO2 formed carbonates which further reduced to formaldehyde and formic acid and consequently formed CO/CO2 + H2 in the gas phase through photoreforming. The deposition of small Au nanoparticles (3–5 nm) (NPs) onto TiO2 was found to quantitatively influence the products distribution and increase the selectivity towards gas phase products. Significant energy storage in form of different products has been achieved with respect to literature results.

Photocatalytic degradation of 2-propanol over TiO2-based thin films in a simulated pilot microreactor

2021 ◽  
Vol 02 ◽  
Author(s):  
Corrado Garlisi ◽  
Ahmed Yusuf ◽  
Giovanni Palmisano
Keyword(s):  
Thin Films ◽  
Gas Phase ◽  
Continuous Flow ◽  
Molecular Diffusion ◽  
Batch Reactor ◽  
High Surface ◽  
Operating Conditions ◽  
Flow Mode ◽  
Doped Tio2 ◽  
Kinetics Of

Background: Microreactor devices have attracted increasing attention over the last years due to their high surface-to-volume ratio which ensures a high heat and mass transfer, short molecular diffusion distance and greater spatial illumination homogeneity compared to traditional reactors. Objective: The aim of this study was to model the kinetics of photodegradation of 2-propanol over TiO2-based thin films in a gas-phase batch-reactor and simulate their performance in a microreactor device. Methods: The reaction was carried out in a gas-phase batch-reactor assessing the reactivity of a single-layer nitrogen (N)-doped TiO2 and a bilayer consisting of N-doped TiO2 as a bottom layer and copper (Cu)-doped TiO2 as a top layer. The kinetics of the photocatalytic process was modelled by Langmuir–Hinshelwood (LH) model. The constants obtained from LH model were used to simulate the performance of the photocatalysts in a microreactor operating in a continuous flow mode and investigating the effect of the volumetric flow rate (Q), initial concentration of pollutant (Co), number of microchannels (n) and microchannel length (l) on the photodegradation of 2-propanol. Results: N-Cu-TiO2 exhibited a higher reactivity but a lower to adsorption ability towards the target pollutant compared to N-TiO2. To maximize and leverage the advantages of microreactor, optimal operating conditions for a continuous flow mode, at steady state, should be moderately low Q and Co, long l and moderate n that minimizes flow maldistribution in parallel. Conclusion: The findings in this work could serve as a basis to design and fabricate efficient microreactors for the removal of VOC in air purification applications.

An Evaluation of Simplified Models for Surface Kinetics in Movpe Processes

1988 ◽  
Vol 131 ◽  
Author(s):  
Max Tirtowidjojo ◽  
Richard Pollard
Keyword(s):  
Gas Flow ◽  
Equilibrium Constants ◽  
Operating Conditions ◽  
Surface Kinetics ◽  
Partial Pressures ◽  
Alternative Approach ◽  
Process Behavior ◽  
Parameter Values ◽  
Rate Limiting ◽  
Reactor Pressure

ABSTRACTA general MOVPE model has been used to assess the applicability of simplified representations for surface kinetics. With the general model, predictions for GaAs deposition on (111 )Ga using trimethylgallium and arsine show excellent agreement with observed growth rates. However, if Langmuir-Hinshelwood kinetics is assumed, the model only matches the deposition rates over a narrow range of operating conditions, even when several rate-limiting steps are included. This limitation arises because combinations of equilibrium constants and local partial pressures often do not give reasonable approximations for the surface concentrations of reactive intermediates. The form of the Langmuir-Hinshelwood relation(s) and the parameter values can be fitted empirically to experimental data, but this could lead to erroneous conclusions concerning process behavior and the model would have limited predictive capabilities. An alternative approach is to use surface reaction probabilities, but they can only be applied in an empirical fashion and their magnitudes depend on gas flow rate, inlet composition, and reactor pressure as well as surface temperature.

Computer Construction of Detailed Chemical Kinetic Models for Gas-Phase Reactors

2001 ◽  
Vol 40 (23) ◽  
pp. 5362-5370 ◽  
Author(s):  
W. H. Green ◽  
P. I. Barton ◽  
B. Bhattacharjee ◽  
D. M. Matheu ◽  
D. A. Schwer ◽  
...  
Keyword(s):  
Gas Phase ◽  
Kinetic Models ◽  
Chemical Kinetic ◽  
Detailed Chemical

An Experimental Study of Controlled Gas-Phase Combustion in Porous Media for Enhanced Recovery of Oil and Gas

2001 ◽  
Author(s):  
Javier E. Sanmiguel ◽  
S. A. (Raj) Mehta ◽  
R. Gordon Moore
Keyword(s):  
Experimental Study ◽  
Porous Media ◽  
Gas Phase ◽  
Oil Recovery ◽  
Gas Flow ◽  
Oil And Gas ◽  
Enhanced Recovery ◽  
Gas Production ◽  
Operating Conditions ◽  
Operating Pressure

Abstract Gas-phase combustion in porous media has many potential applications in the oil and gas industry. Some of these applications are associated with: air injection based improved oil recovery (IOR) processes, formation heat treatment for remediation of near well-bore formation damage, downhole steam generation for heavy oil recovery, in situ preheating of bitumen for improved pumping, increased temperatures in gas condensate reservoirs, and improved gas production from hydrate reservoirs. The available literature on gas-phase flame propagation in porous media is limited to applications at atmospheric pressure and ambient temperature, where the main application is in designing burners for combustion of gaseous fuels having low calorific value. The effect of pressure on gas-phase combustion in porous media is not well understood. Accordingly, this paper will describe an experimental study aimed at establishing fundamental information on the various processes and relevant controlling mechanisms associated with gas-phase combustion in porous media, especially at elevated pressures. A novel apparatus has been designed, constructed and commissioned in order to evaluate the effects of controlling parameters such as operating pressure, gas flow rate, type and size of porous media, and equivalence ratio on combustion characteristics. The results of this study, concerned with lean mixtures of natural gas and air and operational pressures from atmospheric (88.5 kPa or 12.8 psia) to 433.0 kPa (62.8 psia), will be presented. It will be shown that the velocity of the combustion front decreases as the operating pressure of the system increases, and during some test operating conditions, the apparent burning velocities are over 40 times higher than the open flame laminar burning velocities.

Homogeneous Oxidation of Hydrogen in Catalytic Mini/Microchannels

2011 ◽  
Author(s):  
Azad Qazi Zade ◽  
Metin Renksizbulut ◽  
Jacob Friedman
Keyword(s):  
Gas Phase ◽  
Surface Reactions ◽  
Operating Conditions ◽  
Planar Geometry ◽  
Channel Height ◽  
Phase Reaction ◽  
Gas Phase Reactions ◽  
Radical Chain ◽  
Oxidation Of Hydrogen ◽  
Volume Method

Gas phase reaction effects in the catalytic oxidation of hydrogen on platinum-coated minichannels and microchannels are investigated numerically in planar geometry. The main objective of this work is to identify the relative importance of the gas phase and surface reactions under different operating conditions. A collocated finite-volume method is used to solve the governing equations. Detailed gas phase and surface reaction mechanisms along with a multi-component diffusion model are used. As the channel size is reduced, heat and radical losses to the walls can significantly alter the combustion behavior. While catalytic walls help in sustaining the gas phase reactions at very small length scales by reducing the heat losses to the walls owing to heat release associated with the surface reactions, they may inhibit homogeneous reactions by extracting radicals due to typically high absorption rates of such species at the walls. Thus, the radical chain mechanisms can be significantly altered by the presence of wall reactions, and the build-up of radical pools in the gas phase, which lead to homogeneous ignition, can be suppressed as a consequence. In the present study, the effects of two key parameters, i.e. channel height and the inlet mass flux on the interaction of gas phase and surface reactions will be explored. In each case, the limiting values beyond which the gas-phase reactions become relatively negligible compared to surface reactions will be identified for hydrogen/air mixtures.

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