Plasma electron impact

This change in E/N as methane is replaced with acetylene strongly influences the EVDF, as shown in figure 12. As a result of this, kinetics of electron impact plasma chemical reactions is not the same at different precursors as well as at different region along the axis of tubes. 

Chemical kinetics of methane and acetylene dissociation and other gas phase reactions are studied for him coating applications under atmospheric pressure plasma conditions. In order to determine the plasma parameters, OES, V-I measurement, micro-photography and numerical simulations are used. From the determined EVDF and n, electron impact plasma chemical reaction rates are determined. On the basis of rate of different possible reaction. 

The probability for a particular electron collision process to occur is expressed in tenns of the corresponding electron-impact cross section n which is a function of the energy of the colliding electron. All inelastic electron collision processes have a minimum energy (tlireshold) below which the process cannot occur for reasons of energy conservation. In plasmas, the electrons are not mono-energetic, but have an energy or velocity distribution,/(v). In those cases, it is often convenient to define a rate coefficient /cfor each two-body collision process ... 

Veprek S and Sarott F A 1982 Electron-impact-induced anisotropic etching of silicon by hydrogen Plasma Chem. Plasma Proc. 2 233-46... 

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...

In two other implementations of electron impact SNMS, a plasma is generated in the ionizer volume to provide an electron gas sufFiciendy dense and energetic for efficient postionization (Figure 2c). In one instrument, the electrons are a component of a low-pressure radiofrequency (RF) plasma in Ar, and in the second, the plasma is an electron beam excited plasma, also in Ar. The latter type of electron-gas SNMS is still in the developmental stages, while the former has been incorporated into commercial instmmentation. 

Several ion sources are particularly suited for SSIMS. The first produces positive noble gas ions (usually argon) either by electron impact (El) or in a plasma created by a discharge (see Fig. 3.18 in Sect. 3.2.2.). The ions are then extracted from the source region, accelerated to the chosen energy, and focused in an electrostatic ion-optical column. More recently it has been shown that the use of primary polyatomic ions, e. g. SF5, created in FI sources, can enhance the molecular secondary ion yield by several magnitudes [3.4, 3.5]. 

SNMS sensitivity depends on the efficiency of the ionization process. SNs are post-ionized (to SN" ) either hy electron impact (El) with electrons from a hroad electron (e-)heam or a high-frequency (HF-) plasma (i.e. an e-gas), or, most efficiently, hy photons from a laser. In particular, the photoionization process enables adjustment of the fragmentation rate of sputtered molecules by varying the laser intensity, pulse width, and/or wavelength. 

Fig. 3.31. Distributions (i)/(Ee) dEe of electron energy (E ) for a low-pressure HF-plasma (suffix pi, Maxwellian with temperature = 80000 K) and an electron beam (suffix eb, simplified to Gaussian shape with 40 eV half-width) (ii) rTx (Ej) ofthe Ej dependent electron impact ionization cross-section for X=Ti...

Typical ion sources employ a noble gas (usually Ar). The ionization process works either by electron impact or within a plasma created by a discharge the ions are then extracted from the region in which they are created. The ions are then accelerated and focused with two or more electrostatic lenses. These ion guns are normally operated to produce ions of 0.5-10 keV energy at currents between 1 and 10 pA (or, for a duoplasmatron, up to 20 pA). The chosen spot size varies between 100 pm and 5 mm in diameter. 

Due to the high mass, low volatility, and thermal instability of chlorophylls and derivatives, molecular weight determination by electron impact (El) MS is not recommended. Desorption-ionization MS techniques such as chemical ionization, secondary ion MS, fast-atom bombardment (FAB), field, plasma- and matrix-assisted laser desorption have been very effective for molecular ion detection in the characterization of tetrapyrroles. These techniques do not require sample vaporization prior to ionization and they are effective tools for allomerization studies. 

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. ...

In general, the substrate temperature will remain unchanged, while pressure, power, and gas flow rates have to be adjusted so that the plasma chemistry is not affected significantly. Grill [117] conceptualizes plasma processing as two consecutive processes the formation of reactive species, and the mass transport of these species to surfaces to be processed. If the dissociation of precursor molecules can be described by a single electron collision process, the electron impact reaction rates depend only on the ratio of electric field to pressure, E/p, because the electron temperature is determined mainly by this ratio. 

Atmospheric pressure spray with electron impact ionisation Atomic plasma emission spectrometry... 

The high-energy electrons generated in the plasma mainly initiate the chemical reactions by reactions with the background gas molecules (see Table 12.1). Direct electron impact reactions with NO are usually not important for NO decomposition, as in real flue gas, as well as in experiments in simulated gas, the concentrations of NO are very low (some hundreds of ppm), and therefore, the probability of electron collisions is also low. 

Plasma sources are expected to see production use in the early 1990 s and synchrotron sources are not expected to make an impact on commercial device fabrication in the United States until the mid 1990 s (5). It appears that the first use of XRL for high-volume device fabrication will rely on electron impact sources. 

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