Plasma parameters internal

FIG. 46. Plasma parameters as deduced from the lEDs and material properties as a function of process pressure of a SiH4-Hi discharge at an excitation frequency of 50 MHz and a power of 10 W (a) the plasma potential Vp] (circles) and dc self-bias (triangles), (b) the sheath thickness r/.v, (c) the maximum ion flux fmax- growth rate rj. (e) the hydrogen content, (f) the microstructure parameter R. (g) the internal stress a. and (h) the refractive index tin cV- (Compiled from E. A. G. Hamers, Ph.D. Thesis. Universiteit Utrecht. Utrecht, the Netherlands. 1998.)... 

The effectiveness of a given plasma-assisted surface treatment depends primarily on the nature of the feed gas, and on a number of externally controllable parameters pressure, power, gas flow rate, frequency of the electrical energy used to excite the discharge, reactor geometry, etc. These "external variables, in turn, affect the "internal" plasma parameters which control the overall processes, namely the electron density ne, the average electron energy , the electron energy distribution function f(E), and the plasma potential... 

From Figure 11.6c it can also be noted that the internal stress in CAT polymers deceased with increasing VpMDSO monomer feed rate. In plasma deposition process, when the other plasma parameters are kept the same, the increase of monomer feed rate indicates that the same amount of energy input is consumed by a larger number of monomer molecules. In other words, when the other plasma parameters are kept constant, the increase of monomer feed rate will actually reduce the relative energy input in plasma polymerization process. 

The apphcation of microwave power to gaseous plasmas is also of interest (see Plasma technology). The basic microwave engineering procedure is first to calculate the microwave fields internal to the plasma and then calculate the internal power absorption given the externally appHed fields. The constitutive dielectric parameters are useful in such calculations. In the absence of d-c magnetic fields, the dielectric permittivity, S, of a plasma is given by equation 10 ... 

The interindividual variability reflects differences in the extent of exposure, in toxicokinetics as well as in toxicodynamics. The variability due to factors which influence the extent of exposure (physiological differences in the intake, e.g., inhalation rates) can be considered by means of suitable parameters for the internal exposure (absorbed dose, area under the curve AUC, plasma concentration) if sufficient information is available. With respect to toxicokinetic factors, interindi-vidual differences in the metabolism of chemicals are generally considered as the most significant explanatory factor. Hardly any knowledge is available with respect to the factors that influence toxicodynamics. In the following, a brief overview of the factors playing a role for the toxicokinetic and toxicodynamic differences is presented. 

Taking advantage of advances in computational atomic and plasma physics and of the availability of powerful supercomputers, a collaborative effort - the international Opacity Project - has been made to compute accurate atomic data required for opacity calculations. The work includes computation of energy levels, oscillator strengths, photoionization cross-sections and parameters for pressure broadening of spectral lines. Several... 

The internal stress of plasma polymers is dependent not only on the chemical nature of monomer but also on the conditions of plasma polymerization. In the plasma polymerizations of acetylene and acrylonitrile, apparent correlations are found between and the rate at which the plasma polymer is deposited on the substrate [2], as depicted in Figure 11.3. The effect of copolymerization of N2 and water with acetylene on the internal stress is shown in Figures 11.4 and 11.5. The copolymerization with a non-polymer-forming gas decreases the deposition rate. These figures merely indicate that the internal stress in plasma polymers prepared by radio frequency discharge varies with many factors. The apparent correlation to the parameter plotted could be misleading because these parameters do not necessarily represent the key operational parameter. 

Thus, recognition of the characteristic internal stress buildup in a plasma polymer is important for estimating the upper limit of thickness of a plasma polymer for a practical application. Poor results with respect to such parameters as adhesion and barrier characteristics are often due to the application of too thick a plasma polymer layer. The tighter the network of plasma polymer, the higher is the internal stress. Consequently, the tighter the structure, the thinner is the maximal thickness... 

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