Gas Phase and Surface Reactions in Mocvd of GaAs from Triethylgallium, Trimethylgallium, and Organometallic Arsenic Precursors

1988 ◽  
Vol 131 ◽  
Author(s):  
Thomas R. Omstead ◽  
Penny M. Van Sickle ◽  
Klavs F. Jensen
Keyword(s):  
Gas Phase ◽  
Low Temperatures ◽  
Surface Reactions ◽  
Rate Data ◽  
Gas Phase Reactions ◽  
Heated Zone ◽  
Model Predictions ◽  
First Time ◽  
Good Agreement

ABSTRACTThe growth of GaAs from triethylgallium (TEG) and trimethylgallium (TMG) with tertiarybutylarsine (tBAs), triethylarsenic (TEAs), and trimethylarsenic (TMAs), has been investigated by using a reactor equipped with a recording microbalance for in situ rate measurements. Rate data show that the growth with these precursors is dominated by the formation of adduct compounds in the gas lines, by adduct related parasitic gas phase reactions in the heated zone, and by the surface reactions. A model is proposed for the competition between deposition reactions and the parasitic gas phase reactions. Model predictions are in very good agreement with experimental data for all combinations of precursors except for TEG/TMAs where extensive gallium droplet formation is observed at low temperatures. Growth of reasonable quality GaAs with Hall mobilities of 7600 cm2/Vs at 77 K using TEG and tBAs is reported for the first time.

Models and Mechanisms of III-V Compound Semiconductor Growth by Movpe

1989 ◽  
Vol 145 ◽  
Author(s):  
Klavs F. Jensen ◽  
Triantafillos J. Mountziaris ◽  
Dimitrios I. Fotiadis
Keyword(s):  
Gas Phase ◽  
Surface Reactions ◽  
Transport Phenomena ◽  
Reaction Model ◽  
Reactor Performance ◽  
Gas Phase Reactions ◽  
Carbon Incorporation ◽  
Transport Reaction ◽  
Model Predictions ◽  
Good Agreement

AbstractA kinetic model for metalorganic vapor phase epitaxy (MOVPE) of GaAs from trimethylgallium and arsine is imbedded into two-dimensional transport phenomena descriptions of horizontal and vertical MOVPE reactors. The mechanism involves 15 gas-phase species, 17 gas-phase reactions, 9 surface species and 26 surface reactions. The surface reactions take into account different crystallographic orientations of the GaAs substrate. Carbon incorporation is predicted to occur via carbene containing species. A sensitivity analysis shows that only a few reactions are needed to simulate observed growth rates while the full mechanism is important in computing carbon levels in GaAs. The model predictions are in good agreement with data for trimethylgallium decomposition in hot isothermal tubes, with GaAs growth in horizontal reactors, and with carbon incorporation in vertical reactors. The transport-reaction model demonstrates that both gas-phase and surface reactions as well as transport phenomena are important in predicting MOVPE reactor performance.

Effects of Various Parameters on Nanofluid Thermal Conductivity

2006 ◽  
Vol 129 (5) ◽  
pp. 617-623 ◽  
Author(s):  
Seok Pil Jang ◽  
Stephen U. S. Choi
Keyword(s):  
Thermal Conductivity ◽  
Thermal Behavior ◽  
Volume Fraction ◽  
Heat Transfer Fluids ◽  
New Concepts ◽  
Model Predictions ◽  
Simplifying Assumptions ◽  
Thermal Phenomena ◽  
First Time ◽  
Good Agreement

The addition of a small amount of nanoparticles in heat transfer fluids results in the new thermal phenomena of nanofluids (nanoparticle-fluid suspensions) reported in many investigations. However, traditional conductivity theories such as the Maxwell or other macroscale approaches cannot explain the thermal behavior of nanofluids. Recently, Jang and Choi proposed and modeled for the first time the Brownian-motion-induced nanoconvection as a key nanoscale mechanism governing the thermal behavior of nanofluids, but did not clearly explain this and other new concepts used in the model. This paper explains in detail the new concepts and simplifying assumptions and reports the effects of various parameters such as the ratio of the thermal conductivity of nanoparticles to that of a base fluid, volume fraction, nanoparticle size, and temperature on the effective thermal conductivity of nanofluids. Comparison of model predictions with published experimental data shows good agreement for nanofluids containing oxide, metallic, and carbon nanotubes.

Poroelastic Model of Trabecular Bone in Uniaxial Strain Conditions

1998 ◽  
Vol 02 (02) ◽  
pp. 167-180 ◽  
Author(s):  
Tae-Hong Lim ◽  
Jung Hwa Hong
Keyword(s):  
Mechanical Behavior ◽  
Trabecular Bone ◽  
Uniaxial Strain ◽  
Deformation Model ◽  
Total Stress ◽  
Model Predictions ◽  
Poroelastic Model ◽  
Good Agreement ◽  
The Continuum

A one-dimensional poroelastic model of trabecular bone was developed to investigate the fluid effect on the mechanical behavior at the continuum level. The poroelastic properties were determined based upon an assumed drained Poisson's ratio of 0.3 and experimental results reported in the literature. Even though the free escape of the fluid through the loading end was allowed during deformation, model predictions showed that the pore pressure generated within trabecular bone would cause significant variations in total stress. The total stress increase resulted in a stiffening of trabecular bone, which supports the concept of hydraulic stiffening that has been advocated by several investigators. Model predictions showed a good agreement to the mechanical behaviors of trabecular bone specimens with marrow in situ in a uniaxial strain condition observed in previous studies. These results support the hypothesis that trabecular bone is poroelastic and the fluid effect on the mechanical behavior at the continnum level is significant. Thus, the incorporation of the fluid effect in future studies is recommended to improve our understanding of mechanical behavior of trabecular bone.

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.

ChemInform Abstract: Experimental Studies of Gas-Phase Reactions at Extremely Low Temperatures

ChemInform ◽  
2010 ◽  
Vol 26 (28) ◽  
pp. no-no
Author(s):  
B. R. ROWE ◽  
I. R. SIMS ◽  
P. BOCHEREL ◽  
I. W. M. SMITH
Keyword(s):  
Gas Phase ◽  
Low Temperatures ◽  
Experimental Studies ◽  
Gas Phase Reactions

Metallic Fe nanoparticles trapped in self-adapting nanoreactors: a novel high-capacity anode for aqueous Ni–Fe batteries

2017 ◽  
Vol 53 (94) ◽  
pp. 12661-12664 ◽  
Author(s):  
Linpo Li ◽  
Jianhui Zhu ◽  
Yanli Niu ◽  
Zuhong Xiong ◽  
Jian Jiang
Keyword(s):  
Gas Phase ◽  
Single Phase ◽  
High Capacity ◽  
Gas Phase Reactions ◽  
Cyclic Durability ◽  
Fe Nanoparticles

An in situ evolution method via gas-phase reactions is developed to make single-phase Fe nanoparticles confined in thick C nanoreactors for Ni–Fe cells. Such smart hybrids exhibit prominent anodic performance on both stored capacity and cyclic durability.

scholarly journals Estimation of ship emission rates at a major shipping lane by long path DOAS measurements

2021 ◽  
Author(s):  
Kai Krause ◽  
Folkard Wittrock ◽  
Andreas Richter ◽  
Stefan Schmitt ◽  
Denis Pöhler ◽  
...  
Keyword(s):  
Emission Factors ◽  
Emission Rates ◽  
River Elbe ◽  
Gaussian Plume ◽  
Remote Sensing Techniques ◽  
One Year ◽  
First Time ◽  
Good Agreement ◽  
Ship Emission

Abstract. Ships are an important source of SO2 and NOx, which are key parameters of air quality. Monitoring of ship emissions is usually carried out using in situ instruments on land, which depend on favourable wind conditions to transport the emitted substances to the measurement site. Remote sensing techniques such as long path DOAS (LP-DOAS) measurements can supplement those measurements, especially in unfavourable meteorological conditions. In this study one year of LP-DOAS measurements made across the river Elbe close to Hamburg (Germany) have been evaluated. Peaks (i.e. elevated concentrations) in the NO2 and SO2 time series were assigned to passing ships and a method to derive emission rates of SO2, NO2 and NOx from those measurements using a Gaussian plume model is presented. 7402 individual ship passages have been monitored and their respective NOx, SO2 and NO2 emission rates have been derived. The emission rates, coupled with the knowledge of the ship type, ship size and ship speed have been analysed. Emission rates are compared to emission factors from previous studies and show good agreement. In contrast to emission factors (in gram per kilogram fuel) the derived emission rates (in gram per second) do not need further knowledge about the fuel consumption of the ship. To our knowledge this is the first time emission rates of air pollutants from individual ships have been derived from LP-DOAS measurements.

scholarly journals A method for monitoring hydrological conditions beneath herbaceous wetlands using multi-temporal ALOS PALSAR coherence data

2015 ◽  
Vol XL-7/W4 ◽  
pp. 221-226 ◽  
Author(s):  
M. Zhang ◽  
Z. Li ◽  
B. Tian ◽  
J. Zhou ◽  
J. Zeng
Keyword(s):  
Effective Area ◽  
Interferometric Synthetic Aperture Radar ◽  
Alos Palsar ◽  
Hydrological Conditions ◽  
In Situ Data ◽  
Key Indicator ◽  
Multi Temporal ◽  
First Time ◽  
Good Agreement

Reed marshes, the world’s most widespread type of wetland vegetation, are undergoing major changes as a result of climate changes and human activities. The presence or absence of water in reed marshes has a significant impact on the whole ecosystem and remains a key indicator to identify the effective area of a wetland and help estimate the degree of degeneration. Past studies have demonstrated the use of interferometric synthetic aperture radar (InSAR) to map water-level changes for flooded reeds. However, the identification of the different hydrological states of reed marshes is often poorly understood. The analysis given in this paper shows that L-band interferometric coherence is very sensitive to the water surface conditions beneath reed marshes and so can be used as classifier. A method based on a statistical analysis of the coherence distributions for wet and dry reeds using InSAR pairs was, therefore, investigated in this study. The experimental results were validated by in-situ data and showed very good agreement. This is the first time that information about the water cover under herbaceous wetlands has been derived using interferometric coherence values. This method can also effectively and easily be applied to monitor the hydrological conditions beneath other herbaceous wetlands.

scholarly journals Estimation of ship emission rates at a major shipping lane by long-path DOAS measurements

2021 ◽  
Vol 14 (8) ◽  
pp. 5791-5807
Author(s):  
Kai Krause ◽  
Folkard Wittrock ◽  
Andreas Richter ◽  
Stefan Schmitt ◽  
Denis Pöhler ◽  
...  
Keyword(s):  
Emission Factors ◽  
Optical Absorption Spectroscopy ◽  
Emission Rates ◽  
River Elbe ◽  
Gaussian Plume ◽  
Remote Sensing Techniques ◽  
First Time ◽  
Good Agreement ◽  
Ship Emission

Abstract. Ships are an important source of SO2 and NOx, which are key parameters of air quality. Monitoring of ship emissions is usually carried out using in situ instruments on land, which depend on favourable wind conditions to transport the emitted substances to the measurement site. Remote sensing techniques such as long-path differential optical absorption spectroscopy (LP-DOAS) measurements can supplement those measurements, especially in unfavourable meteorological conditions. In this study 1 year of LP-DOAS measurements made across the river Elbe close to Hamburg (Germany) have been evaluated. Peaks (i.e. elevated concentrations) in the NO2 and SO2 time series were assigned to passing ships, and a method to derive emission rates of SO2, NO2 and NOx from those measurements using a Gaussian plume model is presented. A total of 7402 individual ship passages have been monitored, and their respective NOx, SO2 and NO2 emission rates have been derived. The emission rates, coupled with the knowledge of the ship type, ship size and ship speed, have been analysed. Emission rates are compared to emission factors from previous studies and show good agreement. In contrast to emission factors (in grams per kilogram fuel), the derived emission rates (in grams per second) do not need further knowledge about the fuel consumption of the ship. To our knowledge this is the first time emission rates of air pollutants from individual ships have been derived from LP-DOAS measurements.

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