Epitaxial Growth of 2 inch 3C-SiC on Si Substrates by Atmospheric Hot Wall CVD

2004 ◽  
Vol 815 ◽  
Author(s):  
Jiliang Zhu ◽  
Yi Chen ◽  
Yusuke Mukai ◽  
Akira Shoji ◽  
Taro Nishiguchi ◽  
...  
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Flow Direction ◽  
High Mobility ◽  
Ultra Violet ◽  
Optical Pyrometer ◽  
Great Promise ◽  
Flow Profile ◽  
Uniform Thickness ◽  
Si Substrates

AbstractAs a high mobility, wide bandgap semiconductor, 3C-SiC has great promise. In this paper, we examined to obtain 3C-SiC epilayer on Si substrates using hot-wall CVD furnace and report the use of hexamethyledisilane (HMDS) and propane as reaction gases to grow uniform thickness on 2 inch (100), (111), (110) and (211) orientation of Si substrates. A horizontal atmospheric pressure CVD reactor was used. A reaction zone was specially designed. To obtain uniform thickness of the epilayer, inside of the suscceptor hole was intentionally tapered along flow direction as follows; inlet of the square hole is 13 mm × 60 mm and outlet of the hole is 7 mm × 60 mm, and laminar channel for changing the gas flow profile was managed. The susceptor was surrounded by graphite foam. Temperature of the suscepotor was measured at inside wall of the susceptor by optical pyrometer. H2 flow rate for etching was 3 slm. An initial carbonization procedure was performed using 0.9 sccm propane at 1250 oC for 2-3 minutes. During the growth of SiC at 1300 °C, the flow rate of HMDS was 0.75-1.2 sccm and the flow rate of propane was 0.1 – 0.5 sccm. The hydrogen carrier gas flow rate was 3-10 slm. Typical growth rate was 4.5 micron /h. Uniform thick 3C-SiC was obtained. The samples were examined using ultra violet light spectrometer and RHEED.

Visualization Study on Two-Phase Flow Behaviors in the Gas-Liquid-Solid Microreactor for Hydrogenation of Nitrobenzene

2016 ◽  
Author(s):  
Hao Feng ◽  
Xun Zhu ◽  
Rong Chen ◽  
Qiang Liao
Keyword(s):  
Flow Rate ◽  
Liquid Flow ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Phase Flow ◽  
Microchannel Reactor ◽  
Two Phase ◽  
Modified Surface

In this study, visualization study on the gas-liquid two phase flow characteristics in a gas-liquid-solid microchannel reactor was carried out. Palladium nanocatalyst was coated onto the polydopamine functionalized surface of the microchannel through eletroless deposition. The materials characterization results indicated that palladium nanocatalyst were well dispersed on the modified surface. The effects of both the gas and liquid flow rates as well as inlet nitrobenzene concentration on the two-phase flow characteristics were studied. The experimental results revealed that owing to the chemical reaction inside the microreactor, the gas slug length gradually decreased along the flow direction. For a given inlet nitrobenzene concentration, increasing the liquid flow rate or decreasing the gas flow rate would make the variation of the gas slug length more obvious. High inlet nitrobenzene concentration would intensify both the nitrobenzene transfer efficiency and gas reactants consumption, and thereby the flow pattern in the microchannel was transferred from Taylor flow into bubble flow. Besides, the effect of both flow rate and original nitrobenzene concentration on the variation of nitrobenzene conversion and the desired product aniline yield were also discussed.

Heat Transfer Enhancement in Evaporating Mini-Layers: Effects of an Inert Gas Flow

2007 ◽  
Author(s):  
C. S. Iorio ◽  
O. A. Kabov
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Thermal Instability ◽  
Gas Flow ◽  
Flow Direction ◽  
Inert Gas ◽  
Transfer Enhancement ◽  
Capillary Stress ◽  
Volatile Liquid ◽  
Thermo Physical Properties

When a layer of volatile liquid is subject to a flow of inert gas, a non-uniform distribution of the evaporation rate is generated all along the interface. Being evaporation stronger at the inlet boundary of the layer, because of the maximal efficiency of the inert gas flow in removing vapor from the interface, a thermal gradient along the interface is generated. Two opposite mechanisms regulate the movement of the interface: the shear stress of the gas that entrains the interface in the direction of the flow and the thermo-capillary stress that forces the interface to move against the flow direction. Moreover, because of the overall cooling of the interface due to the evaporative process, a gradient normal to the interface is also created. It results in a potentially unstable situation that is strongly influenced by the flow rate of inert gas, the layer thickness and the liquid thermo-physical properties. The goal of the present work is to study numerically if and how the dynamic evolution of the liquid layer is driven by the above-mentioned mechanisms. The main results concern the evaluation of the influence of the thermal instability patterns, eventually generated by the concurrent action of non-uniform evaporation and thermo-capillary motion, on the heat transfer at the bottom liquid. The distribution of temperature and velocity in the gas and liquid bulk phase for different mass flow rate of inert gas has also been of interest.

scholarly journals Microencapsulation of Copper(II) Sulfate in Ionically Cross-Linked Chitosan by Spray Drying for the Development of Irreversible Moisture Indicators in Paper Packaging

Polymers ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2039 ◽  
Author(s):  
Sandra Rojas-Lema ◽  
Jorge Terol ◽  
Eduardo Fages ◽  
Rafael Balart ◽  
Luis Quiles-Carrillo ◽  
...  
Keyword(s):  
Spray Drying ◽  
Flow Rate ◽  
Gas Flow ◽  
Sodium Tripolyphosphate ◽  
Great Promise ◽  
Cross Linking ◽  
Inlet Temperature ◽  
Chitosan Microparticles ◽  
Cellulose Substrates

Copper(II) sulfate-loaded chitosan microparticles were herein prepared using ionic cross-linking with sodium tripolyphosphate (STPP) followed by spray drying. The microencapsulation process was optimal using an inlet temperature of 180 °C, a liquid flow-rate of 290 mL/h, an aspiration rate of 90%, and an atomizing gas flow-rate of 667 nL/h. Chitosan particles containing copper(II) sulfate of approximately 4 µm with a shrunken-type morphology were efficiently attained and, thereafter, fixated on a paper substrate either via cross-linking with STPP or using a chitosan hydrogel. The latter method led to the most promising system since it was performed at milder conditions and the original paper quality was preserved. The developed cellulose substrates were reduced and then exposed to different humidity conditions and characterized using colorimetric measurements in order to ascertain their potential as irreversible indicators for moisture detection. The results showed that the papers coated with the copper(II) sulfate-containing chitosan microparticles were successfully able to detect ambient moisture shown by the color changes of the coatings from dark brown to blue, which can be easily seen with the naked eye. Furthermore, the chitosan microparticles yielded no cytotoxicity in an in vitro cell culture experiment. Therefore, the cellulose substrates herein developed hold great promise in paper packaging as on-package colorimetric indicators for monitoring moisture in real time.

High Carboxyhemoglobin Concentrations Occur in Swine during Desflurane Anesthesia in the Presence of Partially Dried Carbon Dioxide Absorbents 

1997 ◽  
Vol 87 (2) ◽  
pp. 308-316 ◽  
Author(s):  
Edward J. Frink ◽  
Wallace M. Nogami ◽  
Scott E. Morgan ◽  
Roger C. Salmon
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Water Content ◽  
Flow Rate ◽  
Gas Flow ◽  
Flow Direction ◽  
Anesthesia Machine ◽  
Oxygen Flow Rate ◽  
Oxygen Flow

Background Increased carboxyhemoglobin concentrations in patients receiving inhalation anesthetics (desflurane, enflurane, and isoflurane) have been reported. Recent in vitro studies suggest that dry carbon dioxide absorbents may allow the production of carbon monoxide. Methods The authors used high fresh oxygen flow (5 or 10 l/min) through a conventional circle breathing system of an anesthesia machine for 24 or 48 h to produce absorbent drying. Initial studies used 10 l/min oxygen flow with the reservoir bag removed or with the reservoir bag left in place during absorbent drying (this increases resistance to gas flow through the canister). A third investigation evaluated a lower flow rate (5 l/min) for absorbent drying. Water content of the absorbent and temperature were measured. Pigs received a 1.0 (human) minimum alveolar concentration desflurane anesthetic (7.5%) for 240 min using a 1 l/min oxygen flow rate with dried absorbent. Carbon monoxide concentrations in the circuit and carboxyhemoglobin concentrations in the pigs were measured. Results Pigs anesthetized with desflurane using Baralyme exposed to 48 h of 10 l/min oxygen flow (reservoir bag removed) had extremely high carboxyhemoglobin concentrations (more than 80%). Circuit carbon monoxide concentrations during desflurane anesthesia using absorbents exposed to 10 l/min oxygen flow (reservoir bag removed, 24 h) reached peak values of 8,800 to 13,600 ppm, depending on the absorbent used. Carboxyhemoglobin concentrations reached peak values of 73% (Baralyme) and 53% (soda lime). The water content of Baralyme decreased from 12.1 +/- 0.3% (mean +/- SEM) to as low as 1.9 +/- 0.4% at the bottom of the lower canister (oxygen flow direction during drying was from bottom to top). Absorbent temperatures in the bottom canister increased to temperatures as high as 50 degrees C. With the reservoir bag in place during drying (10 l/min oxygen flow), water removal from Baralyme was insufficient to produce carbon monoxide (lowest water content = 5.5%). Use of 5 l/min oxygen flow (reservoir bag removed) for 24 h did not reduce water content sufficiently to produce carbon dioxide with desflurane. Conclusions An oxygen flow rate of 10 l/min for 24 h in a conventional anesthesia circuit can dry carbon dioxide absorbents sufficiently to produce extremely high levels of carbon monoxide with high carboxyhemoglobin concentrations in desflurane-anesthetized pigs. When the reservoir bag is in place on the anesthesia machine or when a lower oxygen flow rate (5 l/min) is used, carbon dioxide absorbent drying still occurs, but 24-48-h exposure time is insufficient to allow for carbon monoxide production with desflurane.

scholarly journals Effect of Ar/CH4Mixture Ratio on Properties of Ag/C:H Nanocomposite Prepared by DC Sputtering

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
E. Mohsen Soltani ◽  
Z. Ghorannevis ◽  
M. Shirazi
Keyword(s):  
Structural Properties ◽  
Flow Rate ◽  
Gas Flow ◽  
Gas Mixture ◽  
Si Substrates ◽  
Dc Sputtering ◽  
Average Grain Size ◽  
Gas Flow Ratio ◽  
Afm Micrographs ◽  
Gas Ratio

Ag/C:H films were deposited by DC sputtering method on Si substrates with different Ar/CH4gas mixture ratios. Effect of Ar/CH4gas mixture ratios was investigated on optical and structural properties of Ag/C:H films by FTIR spectroscopy analysis, X-Ray diffractometry (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. In order to evaluate the effect of gas flow ratio on the optical and structural properties of Ag/C:H films, Ar/CH4gas ratio was changed by keeping the Ar flow rate constant while varying the CH4gas flow rate (2, 5, and 10 SCCM). From FTIR analysis it was observed that increase in the Ar/CH4gas ratio results in decreasing the sputtered Ag nanoparticles and increasing of C–H bonds. Also from XRD pattern it was found that intensity of Ag crystalline plane and average grain size decrease by adding CH4to working gas admixture. From SEM and AFM micrographs, size of the grains also became smaller on the surface of the films, which will lead to decreasing the roughness of the deposited thin films.

An Evaluation of Velocity Probes for Measuring Non-Uniform Gas Flow in Large Ducts

1979 ◽  
Vol 101 (4) ◽  
pp. 655-661 ◽  
Author(s):  
P. M. Gerhart ◽  
S. P. Nuspl ◽  
C. O. Wood ◽  
S. W. Lovejoy
Keyword(s):  
Flow Rate ◽  
Test Section ◽  
Gas Flow ◽  
Flow Direction ◽  
Venturi Tube ◽  
Centrifugal Fan ◽  
Nonuniform Flow ◽  
Flow Rates ◽  
Measuring Station ◽  
Downstream Section

An investigation into the suitability of several types of velocity probes in current use for measurement of nonuniform flow in large ducts is described. An experimental duct was fabricated with a test section near the discharge of a centrifugal fan. Different flow rates were obtained by using an adjustable throttle plate at the duct outlet. The flow rate in the duct was also measured at a downstream section located nine diameters from the fan. A flow straightener was located between the fan and this measuring station; the flow rate measured at this section was assumed to be the true flow rate in the duct. Six different velocity probes of five different designs were used to measure the flow at the fan discharge. The probes were 1) Pitot-static tube, 2) Kiel (Pitot-venturi) tube, 3) Forward-reverse tube (2 tubes), 4) Fechheimer (three hole yaw probe), and 5) turbine meter probe. Of these, only the Fechheimer is capable of measuring the direction of the flow. The best results were produced by the Fechheimer probe. This is felt to be due to this probe’s ability to measure direction as well as speed. It is recommended that only probes which are capable of sensing flow direction be used in highly nonuniform flows.

Effects of Different CH4-H2 Gas Compositions on the Morphology and Growth of Diamond Grown by Hot Filament CVD

1989 ◽  
Vol 162 ◽  
Author(s):  
Edward N. Farabaugh ◽  
Albert Feldman
Keyword(s):  
Flow Rate ◽  
Growth Rates ◽  
Gas Flow ◽  
Particle Nucleation ◽  
Cross Sectional ◽  
Average Growth ◽  
Sem Micrographs ◽  
Si Substrates ◽  
Diffraction Patterns ◽  
Hot Filament

ABSTRACTDiamond films have been grown on single crystal Si and polycrystalline mullite substrates by hot filament chemical vapor deposition. Both substrates offer a good thermal expansion match with diamond. Gas mixture ratios of CH4 :H2 ranged from 0.1–1.0%. The remaining deposition parameters were: substrate temperature, 750°C; filament temperature, 1800°C; gas pressure, 5×103 Pa; gas flow rate, 52 seem except for the 0.1% CH4 :H2 ratio deposition in which the flow rate was 120 seem. Film thicknesses were determined from cross sectional SEM micrographs. The average growth rates on the mullite increased nearly linearly with increasing CH4 gas fraction, ranging from 0.05 μm/hr to 0.21 μm/hr. Growth rates on the Si substrates were slightly lower for identical growth conditions. Surface SEM micrographs revealed that the roughness of the films decreased with increasing CH4 gas fraction during deposition. X-ray diffraction patterns showed that crystalline grain size in the films decreased with increasing CH4 gas fraction. No preferred crystallographic orientation was seen in the diffraction patterns. Isolated particles were also grown on Si substrates under the same deposition conditions as the film growth. As the CH4 gas fraction increased, the particle growth displayed increasing rates of secondary particle nucleation resulting in a less well faceted morphology.

Deposition Mechanism of Tungsten Silicide Films by Low Pressure CVD

1990 ◽  
Vol 181 ◽  
Author(s):  
Jae H. Sone ◽  
Hyeong J. Kim
Keyword(s):  
Mass Transfer ◽  
Deposition Rate ◽  
Flow Rate ◽  
Deposition Temperature ◽  
Gas Flow ◽  
Chemical Vapor ◽  
Low Pressure ◽  
Deposition Mechanism ◽  
Si Substrates ◽  
Si Content

ABSTRACTWSix thin films were deposited on SiO2/Si substrates by Low Pressure Chemical Vapor Deposition (LPCVD) using WF6 and SiH4 gases. The deposition mechanism has been studied by measuring the thickness, resistivity and composition of the films by varying deposition temperature and gas flow rate at a constant total reactant gas pressure. Below 300°C, the surface chemical reaction was the rate-limiting process and the deposition rate increased exponentially with temperature having a thermal activation energy of 3.2 kcal/mol. Meanwhile, above 300°C the reaction was governed by the mass transfer step in the gas. The deposition rate in this range is insensitive to the deposition temperature but shows dependence of the flow rate of reactant gases. AES and RBS analyses were performed to determine the stoichiometry of WSix thin film. The Si content in film gradually increased as the deposition temperature increased. The resistivity of as-deposited WSix film has dependence on both deposition temperature and Si/W ratio, and exponentially increased with a moderate slope. However, temperature insensitive behavior of resistivity appeared in the mass transfer controlled region. Such resistivity changes with temperature were discussed with the Si/W ratio and the microstructure of films.

Material and Device Properties of 3” Diameter GaAs-on-Si with Buried P-type Layers

1988 ◽  
Vol 144 ◽  
Author(s):  
S. J. Pearton ◽  
K. M. Lee ◽  
N. M. Haegel ◽  
C.-J. Huang ◽  
S. Nakahara ◽  
...  
Keyword(s):  
Gas Flow ◽  
Flow Direction ◽  
Scale Up ◽  
Buffer Layers ◽  
Photoluminescence Intensity ◽  
Doping Density ◽  
High Background ◽  
Si Substrates ◽  
Gaas On Si ◽  
P Type

ABSTRACTTwo problems facing MOCVD grown GaAs-on-Si are firstly, scale up to 3” and greater wafer diameter with acceptably uniform layer thicknesses and electrical and optical properties, and secondly the achievement of adequate device isolation through the use of buffer layers of low doping density (≤1014 cm−3). We have investigated the thickness uniformity and 300K photoluminescence intensity of 3” Ø, MOCVD grown GaAs layers on Si substrates by whole wafer mapping of these parameters, and correlate the variations found with the gas flow direction during deposition of the GaAs. We have overcome the high background doping densities (n =5−20 × 1015 cm2) in the material by a buried Be implant (1−5 × 1012 at 120 keV) followed by 850°C, 3 sec annealing. This provides adequate isolation for MESFETS and we fabricated such devices with gm's of 160-175 mS mm−1 using our standard process. These values are similar to homoepitaxial MESFETS fabricated in the same way.

SCIENTIFIC AND ENGINEERING PRINCIPLES OF EFFICIENT FUEL USE AND ENVIRONMENTALLY FRIENDLY GAS COMBUSTION IN STOVE PLATES. PART 1. MODERN STATE-OF-THE-ART AND DIRECTIONS FOR IMPROVEMENT THE GAS BURNING IN DOMESTIC GAS COOKERS

2017 ◽  
pp. 3-18 ◽  
Author(s):  
B.S. Soroka ◽  
V.V. Horupa
Keyword(s):  
Natural Gas ◽  
Flow Rate ◽  
Gas Flow ◽  
Renewable Energy Sources ◽  
Combustion Process ◽  
Orifice Diameter ◽  
Firing Process ◽  
Gas Flow Rate ◽  
Gas Combustion ◽  
Gas Stoves

Natural gas NG consumption in industry and energy of Ukraine, in recent years falls down as a result of the crisis in the country’s economy, to a certain extent due to the introduction of renewable energy sources along with alternative technologies, while in the utility sector the consumption of fuel gas flow rate enhancing because of an increase the number of consumers. The natural gas is mostly using by domestic purpose for heating of premises and for cooking. These items of the gas utilization in Ukraine are already exceeding the NG consumption in industry. Cooking is proceeding directly in the living quarters, those usually do not meet the requirements of the Ukrainian norms DBN for the ventilation procedures. NG use in household gas stoves is of great importance from the standpoint of controlling the emissions of harmful components of combustion products along with maintenance the satisfactory energy efficiency characteristics of NG using. The main environment pollutants when burning the natural gas in gas stoves are including the nitrogen oxides NOx (to a greater extent — highly toxic NO2 component), carbon oxide CO, formaldehyde CH2O as well as hydrocarbons (unburned UHC and polyaromatic PAH). An overview of environmental documents to control CO and NOx emissions in comparison with the proper norms by USA, EU, Russian Federation, Australia and China, has been completed. The modern designs of the burners for gas stoves are considered along with defining the main characteristics: heat power, the natural gas flow rate, diameter of gas orifice, diameter and spacing the firing openings and other parameters. The modern physical and chemical principles of gas combustion by means of atmospheric ejection burners of gas cookers have been analyzed from the standpoints of combustion process stabilization and of ensuring the stability of flares. Among the factors of the firing process destabilization within the framework of analysis above mentioned, the following forms of unstable combustion/flame unstabilities have been considered: flashback, blow out or flame lifting, and the appearance of flame yellow tips. Bibl. 37, Fig. 11, Tab. 7.

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