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Chemkin 4.1.1 Chapter 4: Materials Problems 4.1.4.3 Project Results Figure 4-11 shows the axial, radial and circumferential velocity components for the rotating disk reactor as a function of height above the surface. The deposition surface is at the origin, and the gas enters at x = 6.2 cm with an axial velocity of -12.4 cm/sec and zero radial and circumferential velocity components. As the gas approaches the rotating surface, the axial velocity initially increases slightly then decreases while the radial and circumferential velocity components increase. At the surface, the axial and radial velocity components are zero, and the circumferential velocity matches that of the disk (in radians/sec), as expected. Figure 4-11 Deposition in a Rotating Disk—Gas Velocity Components Figure 4-12 shows predicted mole fractions for the various silicon hydrogen species as a function of distance above the surface (the helium carrier gas is not included), again for the first simulation in the project. The composition at the grid point with largest x value is constrained to that of the inlet gas (silane and helium only). The other grid points show varying amounts of product and reactive intermediate species that are formed by gas-phase and surface reactions. Si atoms are present in very low amounts (mole fractions ~10 -12 ), but can easily be detected by laser-induced fluorescence techniques, so they are kept in the mechanism. You can choose concentration units for species composition in the Species/Variables tab of the Select Results to Load panel when the Post-Processor is first launched. This yields the results shown in Figure 4-13, illustrating that Si atom concentrations increase with increasing silane concentration, as expected. The profiles of the Si atom concentrations are shown as a function of distance above the surface for different starting silane partial pressures: #1 = 0.11 Torr, #2 = 0.34 Torr, #3 = 0.67 Torr. The curves in this figure suggest that the profiles might also be changing shape. This is confirmed in Figure 4-14, which was made by exporting the simulation results, normalizing and plotting experimental results from Ho, Coltrin and Breiland (see © 2007 Reaction Design 128 RD0411-C20-000-001
Chapter 4: Materials Problems <strong>Tutorials</strong> <strong>Manual</strong> Figure 4 of referenced paper) 34 (p. 155) in third party software. It shows that: a) Si atom profiles are experimentally observed to be narrower for higher silane concentrations, and b) this reaction mechanism reproduces this observation. Comparisons between the model and this experimental data set shown that the original reaction proposed for Si atom formation, the collisionally-induced decomposition of SiH 2 , could not account for the experimental observations. Two other reactions, H 3 SiSiH ↔ Si + SiH 4 and Si + Si 2 H 6 ↔ H 3 SiSiH + SiH 2 , are instead the primary reactions involving Si atoms. Figure 4-12 Deposition in a Rotating Disk—Mole Fractions RD0411-C20-000-001 129 © 2007 Reaction Design
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Chemkin 4.1.1 Contents Table of Con
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Chemkin 4.1.1 Tables List of Tables
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Tutorials Manual 4.1.1 Figures List
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List of Figures Tutorials Manual 2-
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Chemkin 4.1.1 1 1 Introduction The
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Chemkin 4.1.1 2 2 Combustion in Gas
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Chapter 2: Combustion in Gas-phase
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