Plasma-produced species

As noted earlier, electron impact reactions in the plasma produce a variety of species owing to processes such as... 

Further designs of ion sources applied in plasma spectroscopy such as electrodeless microwave induced plasmas (MIPs) operating in a noble gas atmosphere at low power (mostly below 200 W) or capacitively coupled microwave plasma using Ar, He or N2 the as plasma gas (at 400-800 W) were described in detail by Broekaert.33 Microwave plasmas produced by a magnetron are operated at 1-5 GHz. Their special application fields for selected elements and/or element species are based (due to the low power applied) in atomic emission spectrometry.33... 

Fluorocarbon plasmas produce two different kinds of reactive species in the glow, namely, CF and F atoms. The density of CF ... 

It has been stated (12) that in contrast to hydrocarbon based plasmas, fluorocarbon plasmas produce a high yield of gaseous products as well as polymer. This has been confirmed in this work by the observation of both low molecular weight species and higher molecular weight oligomers. Clearly any reaction scheme invoked must allow for homogeneous (gas phase) reactions as well as polymer production at a surface. 

Multicharged ions coexist with neutral species in plasmas produced by high-frequency photons, or when a current of neutral atoms is injected into a magnetically confined plasma. The degree of penetration of a neutral hydrogen beam is very dependent upon charge-transfer processes of the type... 

With DART, an electric potential is applied to a gas forming a high-energy plasma containing ions, electrons, and excited-state (metastable) atoms and molecules. This plasma interacts with the sample, causing desorption and ionization of compounds. Some ionization of analytes may occur via proton transfer as the plasma produces ionized water species. In DESI, a charged solvent spray hits the sample surface. Large molecules are desorbed... 

The plasma-generated gaseous species are typically in electronically excited states. Figme 2a shows a typical optical emission spectrum of the Ar plasma produced in air (10). The characteristic emission peaks from the excited Ar molecules are clearly seen in the region from 696 nm to 812 tun. The peaks at 337 nm and 674 nm originate from the excited N2 molecule (11). The peak at 309 nm is due to the OH radical produced by dissociation of water vapor in the plasma (11). The peaks at 111 nm and 845 nm are due to the excited atomic oxygen. 

In addition to the complexity arising from gas composition, the frequency used to excite the plasma also has a major effect on the plasma. Visible and VUV spectral emission data from microwave and RF (13.56 MHz) plasmas have been compared to show the differences in ion and excited species concentrations that result from these two types of excitation. Essentially, the data show that an RF plasma produces a large amount of O ions where few are observed in a microwave plasma. Also, the RF plasma produces more O than the microwave plasma. However, a microwave plasma produces a larger amount of O than an RF plasma. 

Polyatomic Ion Interferences. An interference problem that is usually more serious than that caused by iso-baric elements occurs when polyatomic species form from interactions between species in the plasma and species in the matrix or the atmosphere. These species may then produce several molecular ions that interfere. This type of interference is found usually at m/z values of below about 82. The presence of several of these species is shown in bigure Il-I5b. Among the potential interferentsarc Ar", ArH, " O,. " OH ,... 

FT Raman studies showed that N4 (Ta) could be detected at levels of 34 ppm in liquid N2 and 80 ppm in solid N2. The calculated wavenumbers of N4 are 728,939 and 1322 cm . Matrix-IR spectra obtained by cooling an N2 plasma produced by microwave or electric discharge included a band at 936.7 cm , assigned to a tetrahedral N4 species, consistent with ab initio calculations. ... 

In a plasma-enhanced chemical vapor deposition (PECVD) process, a substrate is exposed to one or more volatile precursors whose atoms or molecules react and/or decompose on the substrate surface, typically using hydrogen in a thermal activation to produce the required deposition. Compounds, such as oxides and nitrides, are produced in reaction with the plasma gas species, usually at lower temperature. A plasma polymerization can occur on a surface when a precursor vapor is not completely decomposed within the plasma. 

A microwave-induced plasma produces a much higher degree of Ionisation and disassoclatlon. This, 1n turn, provides a field of active species some 10 times higher than obtained with other types of electrically-excited plasma. 

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