Plasma regions

The relative abundance of neutral SiH and H2 species have been measured as a function of power, pressure, flow rate, and dilution. For low power levels, eg, 5 W, up to 50% of the SiH gas is dissociated and the percentage increases to 80% for a power of 50 W. The decomposition of SiH gas proceeds more readily with lower flow rates. These observations, coupled with infrared (ir) measurements performed on the films, suggest that deposition under conditions in which the silane gas is not entirely decomposed leads to a majority of SiH units, whereas those deposited under conditions in which silane is strongly dissociated contain a majority of dihydride units leading to a deterioration of the semiconductor. Also, when the dwell time of SiH in the plasma region increases, the resultant film exhibits a pronounced peak at 2090 cm from the ir spectra corresponding to S1H2 inclusion. 

By tire coiTect choice of the metal oxide/carbon ratio in the ingoing burden for the furnace, the alloy which is produced can have a controlled content of carbon, which does not lead to the separation of solid carbides during the reduction reaction. The combination of the carbon electrode, tire gaseous oxides and the foamed slag probably causes tire formation of a plasma region between the electrode aird the slag, and this is responsible for the reduction of elecU ical and audible noise which is found in this operation, in comparison with tire arc melting of scrap iron which is extremely noisy, and which injects unwanted electrical noise into the local electrical distribution network. 

Two-dimensional distributions of ground-state NO were detected by planar laser-induced fluorescence during the process of NO removal in a corona radical shower system in NO/dry air mixtures [57,58], The authors observed that the density of NO molecules decreased not only in the plasma region formed by the corona streamers and the downstream region of the reactor, but also in the upstream region of the reactor. They explained this behaviour by oxidation with ozone, which is transported upstream by electrohydrodynamic flow. 

Dors et al. [49] investigated NOx removal in a hybrid system consisting in a d.c. corona discharge and a molecular sieve placed inside the plasma region. In the corona discharge, all NO converted was oxidized to N02, so the removal rate of NOx was zero. 

Cook (Ref 2) detected the production of a highly ionized plasma region. It was found to originate more directly from the explosive than from thermal ionization associated with the accompanying shock wave, and to be of the same nature as current flow in a metal... 

The extension of the shock tube to the plasma region where particle collision s become infrequent and other dissipative mechanisms must be explored, opens an exciting area for study... 

The ionization of focal volume, or formation of plasma, is expected to alter the usual photochemical material modihcation pathway, as has been recently demonstrated in photopolymerization of SU-8 resist by femtosecond pulses [57]. In addition, nanometric-sized plasma regions created by the ionization, e.g., at defect sites, have spatio-temporal dynamics of their own. Recently, a model of nanosheet formation from plasma nanospheres in glass has been proposed [60]. Similar conditions are expected in polymers as well. Let us discuss here held enhancement by a metalhc nanoparticle (similar arguments are also valid for surfaces containing nanometric features). 

The presence of a catalyst in plasma regions will not only increase the reaction surface area and provide catalytic sites, but also maintain and most likely increase... 

Metallurgical waste powders containing iron and zinc oxides and hydroxides can be reduced to metals in RF thermal plasma in the presence of hydrogen. However, if the particles are agglomerated they cannot be reduced due to the short residence time in the hot plasma region. Thus, to achieve... 

The model which is considered now assumes the optimum and simplest case the silicon tetrachloride molecules passing the tube are activated on entering the plasma region and diffuse in all directions, ready for deposition on the tube walls. This is somewhat oversimplified but the consequences should show where the model holds. The term activate is used in ignorance of the true mechanisms, but for our purpose of a phenomenological description this knowledge is not necessary. Since we have laminar flow the equations that describe the deposition are... 

The solution for (17.29) in a semi-infinite plasma region x > 0, assuming for the sake of simplicity that only fast electrons are present (i.e., n0c = 0), is [88]... 

Properties of the plasma are often characterized by expansions in (nA )-1. Figure 2 shows n 3D plotted versus number densities for various plasma temperatures, T. The upper region in the figure, above the dashed line for nAjp = 1, is the classical plasma region, characterized by... 

Experiments with trapped a cryogenic plasma of electrons at temperatures as low as 50K and densities as high as 1010/cm3 have begun to probe plasma behavior below the classical plasma region in Fig. 2. Experiments with laser-cooled trapped ions have been underway to probe the liquid region.33 Very recently crystalization was observed with only a few ions34 35 and with more than 100 ions.36 A very nice feature of the measurements is that one can learn the positions of shells of ions and even individual ions by imaging the fluorescence from the ions. A numerical simulation produced crystalization very similar to what was observed.37... 

Fig. 3.5. Plasma electron temperature before and after a Type I ELM in JET versus the major radius of the torus, showing the collapse of the plasma temperature in the peripheral plasma region caused by the ELMs [16]...

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