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Development of Modelling Techniques for Pulsed Pressure Chemical Vapour Deposition (PP-CVD)Cave, Hadley Mervyn January 2008 (has links)
In this thesis, a numerical and theoretical investigation of the Pulsed Pressure Chemical
Vapour Deposition (PP-CVD) progress is presented. This process is a novel method for the
deposition of thin films of materials from either liquid or gaseous precursors. PP-CVD
operates in an unsteady manner whereby timed pulsed of the precursor are injected into a
continuously evacuated reactor volume.
A non-dimensional parameter indicating the extent of continuum breakdown under strong
temporal gradients is developed. Experimental measurements, supplemented by basic
continuum simulations, reveal that spatio-temporal breakdown of the continuum condition
occurs within the reactor volume. This means that the use of continuum equation based
solvers for modelling the flow field is inappropriate. In this thesis, appropriate methods are
developed for modelling unsteady non-continuum flows, centred on the particle-based Direct
Simulation Monte Carlo (DSMC) method.
As a first step, a basic particle tracking method and single processor DSMC code are used to
investigate the physical mechanisms for the high precursor conversion efficiency and
deposition uniformity observed in experimental reactors. This investigation reveals that at
soon after the completion of the PP-CVD injection phase, the precursor particles have an
approximately uniform distribution within the reactor volume. The particles then simply
diffuse to the substrate during the pump-down phase, during which the rate of diffusion
greatly exceeds the rate at which particles can be removed from the reactor. Higher precursor
conversion efficiency was found to correlate with smaller size carrier gas molecules and
moderate reactor peak pressure.
An unsteady sampling routine for a general parallel DSMC method called PDSC, allowing the
simulation of time-dependent flow problems in the near continuum range, is then developed
in detail. Nearest neighbour collision routines are also implemented and verified for this code.
A post-processing procedure called DSMC Rapid Ensemble Averaging Method (DREAM) is
developed to improve the statistical scatter in the results while minimising both memory and
simulation time. This method builds an ensemble average of repeated runs over small number
of sampling intervals prior to the sampling point of interest by restarting the flow using either
xi
a Maxwellian distribution based on macroscopic properties for near equilibrium flows
(DREAM-I) or output instantaneous particle data obtained by the original unsteady sampling
of PDSC for strongly non-equilibrium flows (DREAM-II). The method is validated by
simulating shock tube flow and the development of simple Couette flow. Unsteady PDSC is
found to accurately predict the flow field in both cases with significantly reduced run-times
over single processor code and DREAM greatly reduces the statistical scatter in the results
while maintaining accurate particle velocity distributions. Verification simulations are
conducted involving the interaction of shocks over wedges and a benchmark study against
other DSMC code is conducted.
The unsteady PDSC routines are then used to simulate the PP-CVD injection phase. These
simulations reveal the complex flow phenomena present during this stage. The initial
expansion is highly unsteady; however a quasi-steady jet structure forms within the reactor
after this initial stage. The simulations give additional evidence that the collapse of the jet at
the end of the injection phase results in an approximately uniform distribution of precursor
throughout the reactor volume.
Advanced modelling methods and the future work required for development of the PP-CVD
method are then proposed. These methods will allow all configurations of reactor to be
modelled while reducing the computational expense of the simulations.
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OPTIMIZING GROWTH CONDITIONS FOR CHEMICAL VAPOR DEPOSITION OF SINGLE-WALLED CARBON NANOTUBESMcVay, Stanton W 01 January 2004 (has links)
Carbon nanotubes present enormous potential for future nanoelectronic applications. This study details one method for producing such nanotubes via chemical vapor deposition (CVD) of methane gas at high temperatures. This method represents the best known way to selectively place nanotubes, as will be needed for complex electronic structures. Various growth conditions are manipulated and the effects on the resulting nanotubes are recorded.
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Low Temperature Chemical Vapor Deposition of Zirconium Nitride in a Fluidized BedArrieta, Marie 2012 August 1900 (has links)
The objective of this research was to design, assemble, and demonstrate the initial performance of a fluidized bed chemical vapor deposition (FB-CVD) system capable of producing thin, uniform zirconium nitride (ZrN) coatings (1 to 10 micrometers thick) on uranium-molybdenum (UMo) particulate fuel. Plate-type fuel with U-xMo (x = 3 to 10 wt.%) particle fuel dispersed in an aluminum matrix is under development at Idaho National Laboratory (INL) for the Reduced Enrichment for Research and Test Reactors (RERTR) program. Initial irradiation tests performed at INL in the Advanced Test Reactor (ATR) indicate an interaction layer forms between the fuel microspheres and the matrix at relatively high power levels. These power levels induce higher temperatures which enables uranium diffusion into the aluminum during irradiation, eventually causing fuel plate failure. The objective of this work was to create a process to mitigate the fuel/matrix interaction by forming a thin barrier coating on the surface of the U-xMo microspheres before incorporation into the dispersion fuel plate matrix.
One of the main challenges in performance of the FB-CVD system was the effective fluidization of a powder whose physical characteristics (size, density) are continuously changing. To address this, two types of fluidized bed reaction vessels were designed and improved over the course of this research: a spouted fluidized bed and an inverted fluidized bed. Both reaction vessels utilized tetrakis(dimethylamino)zirconium (TDMAZ) and ammonia gas as precursors at atmospheric pressure. Tungsten wires and zirconia-silica (ZrO2-SiO2) microspheres were used as the substrates for the coating experiments. The substrate temperature and precursor gas flow were manipulated as the process variables.
The FB-CVD system was successful in forming zirconium based coatings on surrogate microspheres with elevated levels of chemical impurities. At atmospheric pressure, coatings of thicknesses ranging from 0.5 micrometers to 1.5 micrometers were produced between temperatures of 250 degrees C and 350 degrees C. The deposited coatings were characterized using scanning electron microscopy, energy dispersive spectroscopy and wavelength dispersive spectroscopy.
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Untersuchungen zum Bandsägen mit diamantbeschichteten WerkzeugenGleim, Patrick. January 2006 (has links)
Zugl.: Kassel, Universiẗat, Diss., 2006. / Download lizenzpflichtig.
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Particle coating by chemical vapor deposition in the fluidized bedCzok, Gregor Sebastian January 2005 (has links)
Zugl.: Hamburg, Techn. Univ., Diss., 2005
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CVD and ALD of group IV- and V-Oxides for dielectric application /Forsgren, Katarina, January 1900 (has links)
Diss. (sammanfattning) Uppsala : Univ., 2001. / Härtill 8 uppsatser.
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Self-assembled (Al)GaInN quantum dots grown by metalorganic vapor phase epitaxyPérez-Solórzano Borragán, Victoria January 2008 (has links)
Zugl.: Stuttgart, Univ., Diss., 2008
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Die optische Selektivität von W/Altn2O3-Schichten nach Auslagerungen bei 500C mittels spektraler Ellipsometrie zwischen 0,25 und 25 63mmǦahānbakhsh, Mohammad. Unknown Date (has links)
Techn. Universiẗat, Diss., 1998--Berlin.
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Strukturelle Charakterisierung und Optimierung der Beugungseigenschaften von Si1-xGex-Gradientenkristallen, die aus der Gasphase gezogen wurdenLiß, Klaus-Dieter. Unknown Date (has links) (PDF)
Techn. Hochsch., Diss., 1994--Aachen.
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Niedertemperaturepitaxie zur Herstellung von SiGe/Si-HBTsWolansky, Dirk. Unknown Date (has links) (PDF)
Brandenburgische Techn. Universiẗat, Diss., 2003--Cottbus.
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