Plasma chemistry, modeling

ELECTRON COLLISION DATA FOR PLASMA CHEMISTRY MODELING... 

E. Verification, Validation, and Confirmation of Numerical Plasma Chemistry Models... 

Anyone who performs plasma chemistry modeling recognizes that cross sections and rate coefficients for an individual process are rarely used in isolation rather, they are generally used as part of a model involving a number of other processes. An example of this can be seen in the schematic model for C2F6 plasma chemistry shown in Fig. 1. While not much is known about C2F6 plasma... 

The first step in constructing a plasma chemistry model in which one might have some confidence is to assemble a set of electron collision cross sections that can be shown to yield transport coefficients that are in agreement with swarm measurements. Such a cross-section set was assembled for C2F6 by Hayashi and Niwa (1987) and is shown in Fig. 2. The origin of the various cross sections is described by Hayashi and Niwa as follows ... 

Dissociation, attachment, and ionization are among the most important inelastic electron collision processes that one needs to be able to treat in plasma chemistry modeling. The dissociation cross section is very difficult to measure directly but... 

Electron Collision Data for Plasma Chemistry Modeling, WL. Morgan... 

Collisional ionization can play an important role in plasmas, flames and atmospheric and interstellar physics and chemistry. Models of these phenomena depend critically on the accurate detennination of absolute cross sections and rate coefficients. The rate coefficient is the quantity closest to what an experiment actually measures and can be regarded as the cross section averaged over the collision velocity distribution. 

This section treats the plasma physics and plasma chemistry of the typical silane-hydrogen RF discharge, with occasional examples that employ a somewhat higher excitation frequency. Electrical characterization of the discharge is followed by an analysis of the silane chemistry. An appropriate set of gas phase species is presented, which are then used in the modeling of the plasma. A comparison is made between modeling results and experimental work in ASTER. Extension to 2D modeling is presented as well. 

Monomers were purchased from Polysciences, Inc. The liquid monomers (methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, methyl acrylate, n-butyl acrylate, methacrylic acid, acrylic acid, styrene and a-methylstyrene) were purified by vacuum distillation under nitrogen, poured into thin-walled ampules, degassed at 10 - 10 torr and subsequently frozen in liquid nitrogen. The partially filled ampules were then inserted between a pair of parallel plate electrodes connected to an International Plasma Corporation Model 3001 Radiofrequency Generator, which operates at 13.56 MHz and delivers up to 150 watts of power. In most of these experiments discussed in this work, the power input was limited to 40 - 80 watts. The ampules were allowed to warm up until droplets of liquids appeared. A glow discharge was then in-Current address Department of Chemistry, Ibaraki, University, Mito 310 Japan... 

A major obstacle to accurate numerical modeling of plasma chemistry has been the lack of reliable electron collision cross-section data. Electron collisions drive the entire processing plasma chemistry and, hence, are among the most important and critical processes that we need to consider. In addition to cross sections for elastic scattering and momentum transfer, to which the electrical and thermal conductivities are directly related, it is necessary to consider all important... 

The object of modeling plasma chemistry is to relate the external variables, such as discharge power or current, applied voltage, gas composition, pressure, temperature, discharge geometry, etc., which one can adjust in a laboratory device, to properties that are of interest, such as electron and ion densities, densities of excited or radical species, plasma radiation characteristics, etc. The electron impact processes in an ionized gas drive the plasma chemistry. In... 

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