Electron impact dissociations

Table 1. Electron Impact Dissociative Processes Operative in Silane Plasma ...

Table 2. Reactions Within Plasma During Transport of Species Produced by Electron Impact Dissociation of Silane...

Figure 14a-c shows the variation in the Fp, the and the of a CH4/CO/H2 plasma with [CO]. While the and increase with increasing [CO], the decreases with increasing [CO]. Figure 15a-c shows the EEDFs of a CH4/CO/H2 plasma as a function of [CO]. The hump at eV still appears with the addition of CO, and the spectrum shape retains almost the same feature. The inclinations below 6 eV become slow with increasing [CO], which means that the Tg increases with increasing [CO]. It is consistent with the result of Figure 14b. The electron impact dissociation of CO produces 0 (CO + e C + 0 )ina CH4/CO/H2 plasma. It is therefore assumed that the increase in negative ions reduces the relatively to satisfy the charge balance in a plasma, and that the decrease in leads to the increase in Fp and T. ...

High electron energies are required to optimize the production of N atoms by electron-impact dissociation of N2. Under conditions optimum for N2 dissociation, a large number of excited nitrogen atoms is produced, which can lead to undesired reactions in the presence of 02, namely rather than reducing NO, they would react with 02 to produce NO. 

With increasing the concentration of water vapor, NO and N02 removal efficiencies increased [26,27,29,30] as a result of generation of more OH and H02 radicals by electron impact dissociation of H20 molecules. 

When ammonia is injected, NH2, NH, N, and H radicals are formed in the region close to the nozzles by the following electron impact dissociation reactions [59,60] ... 

The particles are usually of extremely high kinetic energy and hence high temperature and are capable of breaking chemical bonds or ionising species by direct impact electron impact dissociation, ionisation and excitation (Equation 5.28) ... 

Haney, M.A. Franklin, J.T. Correlation of Excess Energies of Electron Impact Dissociations With the Translational Energies of the Products. J. Chem. Phys. 1968, 48, 4093-4097. 

High etch rates and selectivity can be achieved by judicious selection of feed gases to a plasma reactor. The atomic and radical species formed by electron impact dissociation depend largely on feed gas composition, and the intrinsic etch rates measured in the absence of a plasma (i.e., downstream etching) provide a useful indicator of chemical selectivity in the presence of a plasma. For example, the ratio of (100) silicon (34) to thermal oxide (Si02) (37) etching by F atoms is 41 1 at room temperature. As etch rates generally follow an Arrhenius type dependence on substrate temperature. 

Electron impact dissociation of DNA bases has been investigated in the gas [274] and the condensed phase [26,39,275]. In both phases, a large variety of stable anions is produced via DEA to the bases for electron energies below 30 eV. The anions O, CN, CH, OCN, ... 

Formulation of Equations. Discharge structure influences chemistry primarily through electron-impact dissociation and surface ion bombardment. To predict the rate of electron-impact dissociation, local electron number density and energy must be known. These quantities are obtained from equations for electron continuity and electron energy, respectively. 

In neutralization-reionization mass spectrometric experiments on CH2Si+ formed by electron-impact dissociative ionization of ClCH2SiH3, Srinivas, Stilzle and Schwarz found evidence for the formation of a viable neutral molecule whose fragmentation pattern and collisional activation mass spectrum were in accord with a H2C=Si structure422. These authors suggested that their experiments supported electron-capture by CH2Si+" as a mechanism for the formation of H2C=Si in interstellar space. Various models have predicted that H2C=Si is one of the most abundant forms of silicon in dense interstellar clouds423. 

The capillary plasma reactor consists of a Pyrex glass body and mounted electrodes which are not in direct contact with the gas flow in order to eliminate the influence of the cathode and anode region on CO2 decomposition. Analysis of downscaling effects on the plasma chemistry and discharge characteristics showed that the carbon dioxide conversion rate is mainly determined by electron impact dissociation and gas-phase reverse reactions in the capillary microreactor. The extremely high CO2 conversion rate was attributed to an increased current density rather than to surface reactions or an increased electric field. 

CF4 is widely used as a feed gas for plasma etching in the microelectronic industry dissociative electron collisions ultimately determine the constituents in the fragmentation of the parent molecule, producing the neutral etch-active species F and heavier molecular fragments which may cause surface damage and contamination. The electron impact dissociative ionization of CF4 has therefore been investigated thoroughly71. 

Figure 1 also shows an MBD for 8 eV electrons and the typical variation with energy of the total electron impact dissociation cross section for CHF3 [7], This points out that the fraction of the electron population which has enough energy to initiate gas phase chemistry is extremely dependent upon Te. 

LPCAT is a luminous CVD process with decoupled ionization process, i.e., the chemically reactive species are created by the neutral species-impact dissociation of molecules, but not by ion-impact or electron-impact dissociations. Because of this aspect, LPCAT provides important information pertinent to the nature of the creation of chemically reactive species in LCVD and will be discussed in some detail in the following chapters. 

Main reaction products from 308 nm photolysis of 92 naphthalene identified by mass spectrometry Emission cross-sections of excited fragments from the 493 electron impact dissociation of SiH4, SiD, Si2H, and GeH4... 

The balance of evidence thus appears to be that the conversion of electrolytic gas by uniform positive column reaction to water is explicable in terms of a mechanism of which the first step is the electron-impact dissociation of hydrogen to atoms. 

Fig. 12 shows a schematic of the steps typically involved in plasma etching [11]. Radicals generated in the plasma by electron impact dissociation of gas molecules (step 1) diffuse or are convected by gas flow (step 2) to the surface where they adsorb (step 3). The adsorbed species (adspecies) react with the surface to from products (step 4). The products then desorb (step 5) and diffuse back into the gas phase (step 6). The surface processes may be strongly influenced by energetic particle bombardment of the surface, including positive ions, electrons and photons. Of these, positive ion bombardment is though to be most important. Negative ions are excluded be-... 

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