Showing papers on "Chamber pressure published in 2017"

Integrated method for wafer outgassing reduction

Abstract: Implementations disclosed herein relate to methods for controlling substrate outgassing. In one implementation, the method includes removing oxides from an exposed surface of a substrate in an inductively coupled plasma chamber, forming an epitaxial layer on the exposed surface of the substrate in an epitaxial deposition chamber, and performing an outgassing control of the substrate by subjecting the substrate to a first plasma formed from a first etch precursor in the inductively coupled plasma chamber at a first chamber pressure, wherein the first etch precursor comprises a hydrogen-containing precursor, a chlorine-containing precursor, and an inert gas, and subjecting the substrate to a second plasma formed from a second etch precursor in the inductively coupled plasma chamber at a second chamber pressure that is higher than the first chamber pressure, wherein the second etch precursor comprises a hydrogen-containing precursor and an inert gas.

Effect of chamber pressure on defect generation and their influence on corrosion and tribological properties of HIPIMS deposited CrN/NbN Coatings

Abstract: It has been reported that compared to state-of-the-art technologies, High Power Impulse Magnetron Sputtering produces very dense and droplet free coatings due to the high plasma density and ionisation rate. However, thorough investigation of the coating morphology by Scanning Electron Microscopy, optical microscopy and other surface analysis methods revealed the existence of various types of coating defects. This study reports the influence of chamber pressure in particular on defect formation in CrN/NbN nanoscale multilayer coatings. The coating series was deposited using combined HIPIMS/UBM technique while varying the total chamber pressure from 0.2 Pa to 1 Pa. Four types of defects were identified, namely, nodular, open void, cone-like and pinhole. Defect density calculations showed that the coating produced at the lowest pressure, 0.2 Pa, had the lowest defect density of 0.84%. As expected coating corrosion properties improved linearly with decreasing defect density. Potentiodynamic polarisation corrosion studies revealed that in the potential range of - 300 mV to + 300 mV, the current density decreased with decreasing defect density (from 5.96% to 0.84%). In contrast, pin-on-disk tribology tests at room temperature demonstrated that the tribological properties of the coatings deposited at different chamber pressures were dependent on the crystallographic orientations and on the nature of the oxides formed at the tribological contact. Coatings with (200) crystallographic orientation had lower wear rates (  1.6×10-15 m3N-1m-1) whereas coating with (111) crystallographic orientation had the highest wear rate (2.6×10-15 m3N-1m-1). Friction properties were influenced by the tribolayer formed during the tribological tests. However, for the coatings deposited at same chamber pressure of 0.35 Pa but with different defect densities (due to the difference in chamber cleanliness), the friction behaviour was directly influenced by the coating defects. The friction co-efficient (μ) decreased by a factor of two from 0.48 to 0.25 when the defect density decreased from 3.18% to 1.37%.

Verification Firings of End-Burning Type Hybrid Rockets

Abstract: The authors have previously proposed the concept of end-burning-type hybrid rockets, which would use cylindrical fuel grains consisting of an array of many small ports running in the axial directio...

Kinetics of volatile impurity removal from silicon by electron beam melting for photovoltaic applications.

Abstract: A full domain control model is established for impurity transportation in the liquid phase, gas-liquid interface and gas phase of silicon to analyze the dynamic mechanics of impurity removal. The results show that the overall mass transfer coefficient mainly depends on the temperature and the chamber pressure. Its value increases with the increase of temperature or the decrease of chamber pressure. Under the same melting condition, the order of the overall mass transfer coefficients for P, Al and Ca is kP > kAl > kCa, indicating that P is easier to remove by evaporation. Mass transfer in the gas phase is the rate-controlling step for volatile impurity removal at the temperature above the melting point of silicon. The rate-controlling step transits to evaporation on the gas-liquid interface then to mass transfer in the liquid boundary layer as the temperature increases. During electron beam melting, the removal of P is controlled by both evaporation on the gas-liquid interface and mass transfer in the liquid boundary layer, and the removal of Al and Ca is controlled by evaporation on the gas-liquid interface.

Characterization of GO2–GH2 Simulations of a Miniature Vortex Combustion Cold-Wall Chamber

Abstract: This study describes a numerical simulation of a miniature vortex combustion cold-wall chamber using a two-stage choked nozzle approach. Recognizing that the nozzle is choked at the throat under normal operation, the miniaturized vortex chamber is decomposed into two parts: The first segment extends from the headwall to the throat, whereas the second extends from the throat to the nozzle exit plane. In stage 1, an incompressible model is used leading up to the nozzle entrance. In stage 2, compressibility is superimposed, starting with the output from stage 1. This two-stage simulation reduces CPU time and helps to achieve convergence. Compressible simulations are then performed using a three-dimensional pressure-based, finite volume, unstructured solver. Furthermore, reaction mechanisms are simulated using a non-premixed combustion model with adiabatic probability density function lookup tables. Eight conventional chemical species are used, including O2, H2, H2O, HO2, H2O2, O, H, and OH. At the outset, th...

Overcharge and thermal destructive testing of lithium metal oxide and lithium metal phosphate batteries incorporating optical diagnostics

Abstract: Lithium batteries have a tendency to fail violently under adverse conditions leading to the rapid venting of gas. Overcharge, thermal heating, and a combination of the two conditions are applied here to investigate the gas venting process. A test chamber has been constructed with data recordings including chamber pressure and temperature, battery voltage, current, and surface temperature as functions of time throughout the charging and failure processes. High-speed imaging and schlieren flow visualization are used to visualize the gas venting process. A direct comparison between lithium iron phosphate based K2 26650 and lithium nickel manganese cobalt oxide LG 18650 cells is made through a test series of the three failure methods. Failure under thermal, overcharge, and thermal-overcharge conditions are generally similar in terms of the gas venting process, but are observed to have increasingly energetic failures. The thermal-overcharge abuse condition demonstrates an ability to reconnect via internal short circuit even after an initial electrical failure seen as the refusal to accept charge. This reconnection is associated with a secondary, more energetic failure which can produce weak shock pressure waves.

Spatial Variation of Pressure in the Lyophilization Product Chamber Part 2: Experimental Measurements and Implications for Scale-up and Batch Uniformity

Abstract: Product temperature during the primary drying step of freeze-drying is controlled by a set point chamber pressure and shelf temperature. However, recent computational modeling suggests a possible variation in local chamber pressure. The current work presents an experimental verification of the local chamber pressure gradients in a lab-scale freeze-dryer. Pressure differences between the center and the edges of a lab-scale freeze-dryer shelf were measured as a function of sublimation flux and clearance between the sublimation front and the shelf above. A modest 3-mTorr difference in pressure was observed as the sublimation flux was doubled from 0.5 to 1.0 kg·h−1·m−2 at a clearance of 2.6 cm. Further, at a constant sublimation flux of 1.0 kg·h−1·m−2, an 8-fold increase in the pressure drop was observed across the shelf as the clearance was decreased from 4 to 1.6 cm. Scale-up of the pressure variation from lab- to a manufacturing-scale freeze-dryer predicted an increased uniformity in drying rates across the batch for two frequently used pharmaceutical excipients (mannitol and sucrose at 5% w/w). However, at an atypical condition of shelf temperature of +10°C and chamber pressure of 50 mTorr, the product temperature in the center vials was calculated to be a degree higher than the edge vial for a low resistance product, thus reversing the typical edge and center vial behavior. Thus, the effect of local pressure variation is more significant at the manufacturing-scale than at a lab-scale and accounting for the contribution of variations in the local chamber pressures can improve success in scale-up.

Sub- and supercritical jet disintegration

Abstract: Shadowgraph visualization and Planar Laser Induced Fluorescence (PLIF) are applied to single orifice injection in the same facility and same fluid conditions to analyze sub- to supercritical jet disintegration and mixing. The comparison includes jet disintegration and lateral spreading angle. The results indicate that the shadowgraph data are in agreement with previous visualization studies but differ from the PLIF results that provided quantitative measurement of central jet plane density and density gradients. The study further evaluated the effect of thermodynamic conditions on droplet production and quantified droplet size and distribution. The results indicate an increase in the normalized drop diameter and a decrease in the droplet population with increasing chamber temperatures. Droplet size and distribution were found to be independent of chamber pressure.

Effect of pressure variation on acoustically perturbed swirling flames

Abstract: The current study aims to experimentally examine the effect of pressure variation on lean premixed low swirl flames, which were perturbed acoustically with three frequencies (61 Hz, 86 Hz, and 115 Hz). In the experiment, the hydroxyl (OH) chemiluminescence captured with a photomultiplier (PMT) indicated the global heat release. Furthermore, the phase-averaged flame surface density (FSD), which was calculated from the images of planar laser-induced fluorescence of the OH radical (OH-PLIF), was used to examine the local flame behavior. Global, local, and flame dynamics analyses were then used to investigate the flame oscillation. Results showed that when the perturbation level was sufficiently high, the fundamental oscillation tended to be amplified by the elevated pressure in the cases with perturbation frequencies of 61 Hz and 115 Hz. In contrast, in the cases with a frequency of 86 Hz, the fundamental oscillation was inhibited when the chamber pressure was elevated to 0.3 MPa. Analysis of flame dynamics and local flame response then showed that the effect of the pressure was affected by the phase delay between the pressure and the heat release oscillations. This was in turn dictated by the flame rollup process. Based on these analyses, it can be found that the general flame responses at different pressures showed similar trends when the perturbation frequency was the same. When the perturbation level and the pressure were sufficiently high, the fundamental mode oscillation was intensified by the elevated pressure when the heat release oscillation was in phase with the pressure fluctuation; otherwise, the fundamental oscillation tended to be inhibited. Moreover, both the strength and the distribution of the local heat release oscillations were affected by the elevated pressure.

Investigation and control of the - to -transition in a novel sub-atmospheric pressure dielectric barrier discharge

Abstract: A novel flow-driven dielectric barrier discharge concept is presented, which uses a Venturi pump to transfer plasma-generated reactive oxygen and nitrogen species from a sub-atmospheric pressure () discharge region to ambient pressure and can be operated with air. By adjusting the working pressure of the device, the plasma chemistry can be tuned continuously from an ozone ()-dominated mode to a nitrogen oxides ()-only mode. The plasma source is characterized focusing on the mechanisms effecting this mode change. The composition of the device's output gas was determined using Fourier-transform infrared spectroscopy. The results are correlated to measurements of discharge chamber pressure and temperature as well as of input power. It is found that the mode-change temperature can be controlled by the discharge chamber pressure. The source concept is capable of generating an -dominated plasma chemistry at gas temperatures distinctly below . Through mixing of the processed gas stream with a second flow of pressurized air required for the operation of the Venturi pump, the resulting product gas stream remains close to room temperature. A reduced zero-dimensional reaction kinetics model with only seven reactions is capable of describing the observed pressure- and temperature-dependence of the to mode-change.

A Cost-Effective Approach to Optimizing Microstructure and Magnetic Properties in Ce17Fe78B6 Alloys

Abstract: Optimizing fabrication parameters for rapid solidification of Re-Fe-B (Re = Rare earth) alloys can lead to nanocrystalline products with hard magnetic properties without any heat-treatment. In this work, we enhanced the magnetic properties of Ce17Fe78B6 ribbons by engineering both the microstructure and volume fraction of the Ce2Fe14B phase through optimization of the chamber pressure and the wheel speed necessary for quenching the liquid. We explored the relationship between these two parameters (chamber pressure and wheel speed), and proposed an approach to identifying the experimental conditions most likely to yield homogenous microstructure and reproducible magnetic properties. Optimized experimental conditions resulted in a microstructure with homogeneously dispersed Ce2Fe14B and CeFe2 nanocrystals. The best magnetic properties were obtained at a chamber pressure of 0.05 MPa and a wheel speed of 15 m·s−1. Without the conventional heat-treatment that is usually required, key magnetic properties were maximized by optimization processing parameters in rapid solidification of magnetic materials in a cost-effective manner.

Experimental Demonstration of the Vacuum Specific Impulse of a Hybrid Rocket Engine

Abstract: This paper presents the experimental results of a hybrid rocket engine fired both at ambient pressure and under low-pressure conditions. The hybrid engine includes a catalyst bed and a vortex injector, and it is fitted with ultrasound sensors to measure the instantaneous fuel regression rate. These tests have enabled demonstration of the experimentally achievable specific impulse of the hybrid rocket technology under low-pressure conditions and validated the extrapolation of experimental results at ambient pressure to vacuum pressure conditions. The demonstrated combustion efficiency is above 98%, and the specific impulse is experimentally proven to be above 270 s for a conical nozzle with an expansion ratio of 50.

A large ion beam device for laboratory solar wind studies.

Abstract: The Colorado Solar Wind Experiment is a new device constructed at the Institute for Modeling Plasma, Atmospheres, and Cosmic Dust at the University of Colorado. A large cross-sectional Kaufman ion source is used to create steady state plasma flow to model the solar wind in an experimental vacuum chamber. The plasma beam has a diameter of 12 cm at the source, ion energies of up to 1 keV, and ion flows of up to 0.1 mA/cm2. Chamber pressure can be reduced to 4 × 10-5 Torr under operating conditions to suppress ion-neutral collisions and create a monoenergetic ion beam. The beam profile has been characterized by a Langmuir probe and an ion energy analyzer mounted on a two-dimensional translation stage. The beam profile meets the requirements for planned experiments that will study solar wind interaction with lunar magnetic anomalies, the charging and dynamics of dust in the solar wind, plasma wakes and refilling, and the wakes of topographic features such as craters or boulders. This article describes the technical details of the device, initial operation and beam characterization, and the planned experiments.

Effect of gas generator pressure on the physicochemical, oxidation and combustion characteristics of boron-based propellant primary combustion products

Abstract: To clarify the effect of gas generator pressure on the physicochemical, oxidation and combustion characteristics of the condensed primary combustion products of boron-based propellants, the elemental, composition and morphology of the primary combustion products collected under chamber pressure of 0.2–8 MPa were investigated by energy-dispersive (EDS), X-ray photoelectron spectroscopy and scanning electron microscopy with energy-dispersive (SEM–EDS) individually. The oxidation, ignition and combustion behaviors of these products were further studied by laser ignition system and thermogravimetry–differential scanning calorimetry. We found out that high-pressure condition lowered the content of elementary boron and elementary carbon while raised the content of boron carbide. Numerous spherical carbon particles with a diameter around 100 nm were observed in the products. Boron lumps were partially or almost fully covered with carbon particles on the surface. The reaction mechanisms of thermal oxidation of primary combustion products were given. The onset temperature of boron in the products kept at 500 °C when pressure ranged from 3 to 8 MPa but increased to 583 °C at 0.2 MPa. As the pressure increased from 0.2 to 8 MPa, the emission spectrum intensity of both boron and carbon got enhanced by ~25%, and the ignition delay of boron was significantly shortened by 515 ms. In conclusion, high gas generator pressure is favorable to the secondary ignition and combustion of primary combustion products.

Multiphysics Model for Radio-Frequency Gridded Ion Thruster Performance

Abstract: A multiphysics radio-frequency gridded-ion thruster performance model is presented. The model is composed of various submodels to account for different physics phenomena. A two-dimensional axisymme...

Combustion Dynamics of an Extreme Fuel-Rich Throttleable Rocket Engine During Continuously Throttling Process

Abstract: An experimental study has been conducted to investigate the dynamics of an extreme fuel-rich throttleable rocket engine during continuously throttling process. The rocket engine burned kerosene (RP-1) and oxygen and it was continuously throttled in fire tests by adjusting the flow rate of kerosene. Dynamic response of chamber pressure was analyzed. Results show two phenomena named hysteresis of characteristic velocity and anti-regulation of chamber pressure during the throttling process. When characteristic velocity hysteresis occurs, transient characteristic velocity is higher in condition of increasing mixture ratio (MR) and lower in condition of decreasing MR than steady value during throttling process. The anti-regulation can be induced by throttling or purging process. In addition, both throttling method and throttling rate influence the amplitude and duration of anti-regulation. Finally, the response of chamber pressure to the throttling was divided into two periods, namely ramp response and...