9,616 research outputs found
Deep anisotropic dry etching of silicon microstructures by high-density plasmas
No full textThis thesis deals with the dry etching of deep anisotropic microstructures in monocrystalline silicon by high-density plasmas. High aspect ratio trenches are necessary in the fabrication of sensitive inertial devices such as accellerometers and gyroscopes. The etching of silicon in fluorine-based plasmas is isotropic. To obtain anisotropy the addition of sidewall passivation is necessary. This is achieved with both oxygen passivation at low temperatures and fluorocarbon passivation at room temperature. A quantitative approach was pursued to explain the etching mechanism. The etch results were analysed using the measured plasma species fluxes and the surface composition. Moreover, the transport of the plasma species in narrow anisotropic structures is a fundamental factor determining the etch rate and the profile evolution. The experimental methods such as the etching equipment, plasma diagnostics, surface analysis and sample preparation are described in chapter 2. Three etching processes were investigated: the cryogenic etching process with oxygen passivation at low temperatures, the Bosch process with fluorocarbon passivation at room temperature and the novel triple pulse process that was developed in our laboratory. The polymer deposition mechanism and the characteristic role of the ions are also explained. The cryogenic etching process is discussed in chapter 3. Fluorine radicals, oxygen radicals and ion bombardment are responsible for the three main sub-processes, that is, etching, sidewall passivation and depassivation of the trench bottom, respectively. Etching experiments with an extremely low ion-to-radical flux ratio were used to reveal the etching mechanism. Crystal orientation dependent etching leading to Si(111) crystal facets is observed in a surface kinetics controlled regime. By varying the plasma conditions it is possible to adjust the etching mechanism from fluorine-limited to ion-limited. Controlled etching is obtained because the etching is tuned from aspect ratio dependent in the fluorine-limited domain to aspect ratio independent in the ion-limited domain. The transport of radicals in high aspect ratio trenches is an important limiting factor and was investigated with special structures. The etch results are described by an analytic model that is based on the surface site balance of fluorine and oxygen radicals. The results are further explained with a Monte Carlo simulation model. The Bosch process is clarified in chapter 4. The anisotropy of the etched structures is controlled by balancing the etching and passivation pulse. However, the maximal obtainable aspect ratio is limited by convergence of the trench sidewalls due to excessive passivation. The maximal obtainable aspect ratio increases if the ion-to-radical flux ratio increases. The transport of ions is an important limiting factor in the depassivation of the bottom of the trench. Divergence of the ion beam leads to a reduction of the ion flux, so that the fluorocarbon passivation is insufficiently removed near the base of the sidewalls. The average ion angle was measured and correlated to the maximal obtainable aspect ratio. The Bosch process was improved at the depassivation side with the triple pulse process and at the passivation side with preferential sidewall deposition. The triple pulse process that is described in chapter 5 has the aim to improve the depassivation in deep trenches. The three main sub-processes are decoupled using a separate depassivation pulse directly after the etching and passivation pulses. The fluorocarbon passivation is efficiently removed with low-pressure, high-density, oxygen-based plasmas. The investigated plasma chemistries include O2, CO2 and SO2. The triple pulse process leads to better profile control with a straight trench bottom. However, the maximal obtainable aspect ratio is comparable to the Bosch process because a larger etch depth and a small lateral etch cancel out. The polymer deposition mechanism is treated in chapter 6 with the aim to understand the fluorocarbon passivation in deep trenches. The deposition on plane surfaces and on special structures was investigated to distinguish between the radical-induced and ion-enhanced components. A simple analytical model, which explains the main deposition characteristics, was developed. Preferential sidewall deposition is obtained for higher ion fluxes and higher bias voltages where sputtering plays an important role. In this case no fluorocarbon passivation has to be removed from the bottom of the trench. The trench profile was optimised in the Bosch process by tuning the bias voltage during etching and passivation independently. It resulted in perfectly anisotropic trenches but the maximal obtainable aspect ratio was still limited by a small lateral etch. The characteristic role of the ions in the etching mechanism is explained in chapter 7. Ion-induced etching of both SiC in a SF6-O2 plasma and Si in a Cl2 plasma were investigated. The impact of the ions on the profile evolution can be examined more explicitly because spontaneous chemical reactions are absent for these plasma-material systems. The etching mechanism varies from fluorine-limited to ion-limited depending on the radical-to-ion flux ratio. Microtrenches are observed for an ion-limited etching mechanism. Fluorine-limited SiC etching is aspect ratio dependent in contrast to ion-limited SiC etching, which is aspect ratio independent. The etching of high aspect ratio SiC structures is limited by the positive sidewall taper. This is presumably caused by insufficient removal of the thin fluorocarbon layer on the surface. Si etching in a Cl2 plasma is always aspect ratio independent in contrast to SiC etching because of the low reaction probability. The conclusions and recommendations of this thesis are given in chapter 8.Applied Science
Design and commission of an experimental test rig to apply a full-scale pressure load on composite sandwich panels representative of aircraft secondary structure
No full textThis paper describes the design of a test rig, which is used to apply a representative pressure load to a full-scale composite sandwich secondary aircraft structure. A generic panel was designed with features to represent those in the composite sandwich secondary aircraft structure. To provide full-field strain data from the panels, the test rig was designed for use with optical measurement techniques such as thermoelastic stress analysis (TSA) and digital image correlation (DIC). TSA requires a cyclic load to be applied to a structure for the measurement of the strain state; therefore, the test rig has been designed to be mounted on a standard servo-hydraulic test machine. As both TSA and DIC require an uninterrupted view of the surface of the test panel, an important consideration in the design is facilitating the optical access for the two techniques. To aid the test rig design a finite element (FE) model was produced. The model provides information on the deflections that must be accommodated by the test rig, and ensures that the stress and strain levels developed in the panel when loaded in the test rig would be sufficient for measurement using TSA and DIC. Finally, initial tests using the test rig have shown it to be capable of achieving the required pressure and maintaining a cyclic load. It was also demonstrated that both TSA and DIC data can be collected from the panels under load, which are used to validate the stress and deflection derived from the FE model
Modelling and evaluation of pulsed and pulse phase thermography through application of composite and metallic case studies
No full textA transient thermal finite element model has been created of the pulsed thermography (PT) and pulse phase thermography (PPT) experimental procedure. The model has been experimentally validated through the application of four case studies of varying geometries and materials. Materials used include aluminium, carbon fibre reinforced plastic (CFRP) and adhesively bonded joints. The same four case studies have also formed a basis for comparison between three experimental techniques: PT, PPT and the more established ultrasonic (UT) c-scan.Results show PPT to be advantageous over PT due to its deeper probing as it is less influenced by surface features. Whilst UT is able to reveal all the defects in these case studies, the time consuming nature of the process is a significant disadvantage compared to the full field thermography methods.Overall, the model has achieved good correlation for the case studies considered and it was found that the main limiting factor of the PT model accuracy was knowledge of thermal material properties such as conductivity and specific heat. Where these properties were accurately known the model performed very well in comparison with experimental results. PPT modelling performed less well due to the method of processing the PT data which aims to emphasise small differences. Hence inaccuracies in inputted values such as material properties have a much greater influence on the modelled PPT data. The model enables a better understanding of PT and PPT and provides a means of establishing the experimental set-up parameters required for different components, allowing the experimental technique to be appropriately tailored to more complex situations including bonded joints or structures where several materials are present.The paper ends with a section on defect detectability based on thermal diffusivity contrast between the defect and the bulk material. It shows that in aluminium, because of its higher conductivity, greater thermal contrast is achieved for small differences in diffusivity. Regions where the diffusivity ratio between defect and bulk materials was insufficient to provide thermal contrast for defect identification were found. PPT phase data is shown to reduce the extent of such regions increasing the detectability of defects. Effusivity is introduced as a means of determining the thermal contrast between the defect and non-defective areas and hence establishing the defect detectability
The effect of interscholastic volleyball competition on the self-esteem of juvenile delinquent females in a residential child care facility
No full textThere is no abstract available for this research paper.Thesis (M.A.)School of Physical Educatio
Role of technology in small college public affairs offices : a study of 10 institutions
No full textThere is no abstract available for this research paper.Thesis (M.A.)Department of Journalis
Barton Sensenig : M.A., 1894
No full textOral teacher, Mt. Airy, Pennsylvania ; Retired in 1936https://ida.gallaudet.edu/alumni-cards/1387/thumbnail.jp
Predicting implant UHMWPE wear in-silico: A robust, adaptable computational-numerical framework for future theoretical models
No full textComputational methods for the pre-clinical wear prediction for devices such as hip, knee or spinal implants are valuable both to industry and academia. Archard’s wear model laid the basis for the first generation of theoretical wear estimation algorithms, and this has been adapted to account for the importance of multi-directional sliding. These second-generation cross-shear algorithms are useful, but they leave room for improvement.In this paper, we outline a generalised framework for a ‘third generation’ wear model. The essential feature of this proposed approach is that it removes the acausality and scale-independence of current second-generation algorithms. The methodology is presented in such a way that any existing second-generation model could be adapted using this framework. Using this approach, the predictive power against pin-on-disc and implant tests is shown to be improved; however, the model is still essentially a purely adhesive-abrasive wear predictor, accounting for only a limited number of factors as part of the tribological process. Further ongoing work is needed to expand and improve upon the current capabilities of in-silico UHMWPE wear prediction capabilities.<br/
Assessment of Models for Near Wall Behavior and Swirling Flows in Nuclear Reactor Sub-system Simulations
No full textAccurate simulation of turbulence remains one of the most challenging problems in nuclear reactor analysis and design. Due to limitations in computing resources, Reynolds averaged Navier Stokes models (RANS) continue to play an important role in reactor simulations. The Consortium for advanced simulations of light water reactors (CASL) is a Department of Energy technology hub that is investing in research and developmentof a state-of-the-art computational fluid dynamics capabilityto meet the challenges of turbulent simulation of nuclear reactors. In this presentation, we assess several RANS eddy viscosity models appropriate for single-phase incompressible turbulent flows. Specifically, we compare the single equation Splalart-Allmaras to several variations of the model. The assessment takes into consideration elements of full system reactor cores such as complex geometries, heterogeneous meshes, swirling flow, near wall flow behavior, heat transfer and robustness issues. The goal of this strategically oriented assessment is to provide an accurate and robust turbulent simulation capability for the CASL community. Metrics of performance will be constructed by comparing different models on a strategically chosen set of problems that represent reactor core sub-systems
O zarubežnoj dejatel'nosti professora M.A. Kumaxova
No full textOn professor M.A. Kumakhov's work and research abroad (in Russian)
Professor Mukhadin A. Kumakhov and the author collaborated in the area of Northwest Caucasian languages under a period from 1991 to 2008. The fruitful collaboration at Lund and Malmö universities resulted in three joint monographs and a number of articles, which is outlined in the article. Mukhadin A. Kumakhov became Honorary Doctor of the Philosophical Faculty of Lund University in 1998
Bringing clouds into our lab!: The influence of turbulence on early stage rain droplets
No full textWe are investigating a droplet-laden flow in an air-filled turbulence chamber, forced by speaker-driven air jets. The speakers are running in a random manner; yet they allow us to control and define the statistics of the turbulence. We study the motion of droplets with tunable size in a turbulent flow, mimicking the early stages of raindrop formation. 3D Particle Tracking Velocimetry (PTV) is chosen as the experimental method to track the droplets and collect data for statistical analysis. Thereby it is possible to study the spatial distribution of the droplets in turbulence using the so-called Radial Distribution Function (RDF), a statistical measure to quantify the clustering of particles. Additionally, this technique allows us to measure velocity statistics of the droplets and the influence of the turbulence on droplet trajectories, both individually and collectively. In this contribution, we will present velocity statistics of the droplets and quantify their clustering using the RDF for different turbulence conditions
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