Some considerations on the microwave electrodeless discharge

Avni, R.; Winefordner, J. D.

doi:10.1016/0584-8547(75)80027-9

Cited by 33 publications

(15 citation statements)

References 17 publications

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“…The conclusion can be summarized as follows: (i) The formation of various kinds of polymer radicals (up to C,3) was confirmed experimentally and may be characteristic of plasma in general; (ii) the formations of the polymer hydrocarbon radicals can be achieved with a simple apparatus; and (iii) the present results not only contribute to enhancing our understanding of the chemical component of the plasma, but also provide fresh evidence that the radical-molecule reactions are involved in the polymerization process of the CH4 plasma [10].…”

supporting

confidence: 65%

Identification of intermediate radicals in theCH4microwave plasma by theLi+
Fujii
¹
,
Syouji
²

1992
Phys. Rev. A
22
1
11
0
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We (i) describe the complete Li -adduct mass spectrum of the CH4 microwave discharge plasma, obtained by ion attachment techniques, (ii) give evidence that many radicals are produced in the plasma, and (iii) present a preliminary spectral identification analysis. The identified species are C"Hz" (n =2-13), C"Hz"+l (n =2-13), C"H"(n =2,4, 5, 6), and so on. PACS number(s): 52.80.s, 35.20.WgIn order to demonstrate that a recent development of the Li+ ion attachment and quadrupole mass spectrometer technique for the sensitive detection of intermediate radicals will yield important data for various radical reactions, we have investigated the identi6cation of the principal radical species produced by the CH4 microwave (MW) discharge. We have succeeded in detecting various kinds of hydrocarbon polymer radicals, which were C"H2", (n =2-13), C"H2"+, (n =2-13), C"H"(n=2, 4, 5,6), and so on. The concurrent formation of these types of radials is experimental evidence on radical involvement in plasma-induced polymerization and may be characteristic of plasma, suggesting the importance of radical-molecule reactions in the plasma environment. Intermediate radicals have short lifetimes. Furthermore, their steady-state concentration in a reacting gas phase is sometimes low. The combination of small concentrations and short lifetimes has ofFered a real challenge to scientists [1].On the other hand, it has been widely recognized that neutral radical species are responsible for the plasma treatment [2-4], such as the deposition of hydrogenerated amorphous carbon thin films as well as crystal diamond films, the etching of highly integrated circuits, and surface graft polymerization.However, the difficulties of radical detection have hampered the development of insights into the process mechanisms.We believe that the present study concerns one of the most important problems that had to be resolved before the radical contribution to the total reaction schemes could be determined in plasma chemistry.The apparatus is shown in Fig. 1. A Shimadzu atmospheric pressure ionization quadrupole mass spectrometer with a Li+ ion attachment reaction chamber (RC) was used [5,6]. A stream of reaction products from a quartz discharge flow tube is directed into the alkali-metal ion attachment reaction chamber.The RC has a glass bead (Li+ emitter) which contains the alkali-metal oxide (lithium oxide in the present study) in an aluminosilicate matrix. By heating this bead, lithium ions are produced [7]. These parent ions, in turn, ionize the radical products (R ) by adduct formation (R+Li)+. (R+Li)+ complexes are formed by termolecular association reactions [8,9]. Parent-daughter ion cavity skimmer GH4 U 0 (R+Li) 0 0 lens glass lead (Li emitter) J I quadrupoles INW generator DP DP FIG.

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supporting

confidence: 65%

Identification of intermediate radicals in theCH4microwave plasma by theLi+
Fujii
¹
,
Syouji
²

1992
Phys. Rev. A
22
1
11
0
View full text Add to dashboard Cite

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“…The discharge parameters used in our calculations are listed in Table I. These values were obtained from a paper by Avni and Winefordner (20) which describes electrical double probe measurements in a microwave-induced discharge (2.450 GHz, 120 W) in helium (1 Torr). Although the experimental emission radiant powers with which we have compared our calculated results were obtained with different apparatus (5, 21), the conditions were very similar and it is reasonable to expect that values of the electron mean free path, electron density, and electric field would be at least approximately equal.…”

Section: Resultsmentioning

confidence: 99%

“…49, NO. Table I. Discharge Parameters (20) Electric field (E°) 18.0 V at 1 Torr Helium Electron mean free path ( ) 7.24 X 10-2 cm at 1 Torr Helium °These values were obtained by fitting the data (13) with Equation 14.…”

Section: Theorymentioning

confidence: 99%

“…On the other hand, spectroscopic studies of the pressure-dependent loss rate of 3XD and 33D states of helium (19) suggest associative ionization rate constants of 9.5 X 10~n and 4.3 X 10"10 cm3/s, respectively. The values of adopted for our treatment are thus as follows: The population densities of various excited states in helium are then obtained by inserting appropriate values into the modified form of Equation 7, namely (kj)nen + k^n (20) ~£o j ( 18)…”

Section: Jomentioning

confidence: 99%

“…The population densities of various excited states in helium are then obtained by inserting appropriate values into the modified form of Equation 7, namely (20) (kj nj = rj-' kAn RESULTS AND DISCUSSIONS The discharge parameters used in our calculations are listed in Table I. These values were obtained from a paper by Avni and Winefordner (20) which describes electrical double probe measurements in a microwave-induced discharge (2.450 GHz, 120 W) in helium (1 Torr).…”

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confidence: 99%

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Steady-state kinetic treatment of the emission from reduced pressure microwave induced discharges in helium

Lampe¹,

Risby²,

Serravallo³

1977

Anal. Chem.

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A steady-state kinetic treatment of the number density of excited atoms in a helium dlscharge has shown these populations to be consistent wlth electron impact excitation. This study was initiated since it has been well establlshed that the electrons are the activating species In discharges. The calculated number densitles of exclted atoms were obtained by conslderation of the processes which cause excltatlon and deactivation. The processes whlch produce the population of a particular state are the followlng: electron Impact and radlative cascading from higher levels. The processes which reduce the population of a particular state are radiative and nonradiative deactivation. The results of this klnetlc treatment compare remarkably well wlth experlmental number densities obtained from emission studies.In a number of recent studies of light emission from electrical discharges, it has been reported that the population densities n, of the emitting states depend exponentially on the energy level of the state, i.e., n, CE e-PtJ where 6 is the slope of a plot of In n, us. e, . A consequence of this rather familiar dependence has been to identify this slope p with (kT)-', where k is Boltzmann's constant, and T is the excitation temperature (1-11). While it may be useful to characterize the excited state population densities of electrical discharges in this way, the attendant implication that the species present are in thermal equilibrium can be misleading.The process of excitation in electrical discharges is definitely not the result of collisions between particles in thermal equilibrium. Rather, excitation in such systems is brought about principally by the impact of energetic electrons on the gas atoms or molecules (12). The population densities of atoms in the various electronic states are then determined by a dynamic balance between formation via electron impact and decay via emission of radiation and nonradiative decay processes. In this paper, we treat this balance for reduced pressure microwave-induced discharges in helium by the method of steady-state kinetics. (4)in which the subscript i denotes optically accessible states of lower energy than j and the subscript k denotes optically accessible states of higher energy than j, kj is the rate constant (cm3/s) for excitation of the j t h state, A;i and Ak, are transition probabilities (s-l) for the emission processes j -i and k -j, respectively, and kA is the rate constant (cm3/s) for associative ionization. At the pressure of interest, it is easily shown that an emitting state will decay by Reaction 3 or 4 before it reaches a wall.On the basis of this mechanistic scheme, the change in number density of the j t h state with respect to time is:where ne is the density (~m -~) of electrons and n is the density (cm-3) of ground state helium atoms. The rate of population of the j t h state by radiative decay from higher states, Le., Reaction 3, is most probably only a few percent (23) of the rate of electron-impact excitation, Reaction 1. Therefore, as a reasonable appro...

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The dependence of coating in inductive R.F. plasmas on gas flow velocity, pressure and R.F. power

Khait¹,

Inspektor²,

Avni³

1980

Thin Solid Films

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Some considerations on the microwave electrodeless discharge

Cited by 33 publications

References 17 publications

Identification of intermediate radicals in theCH4microwave plasma by theLi+
Fujii
¹
,
Syouji
²

1992
Phys. Rev. A
22
1
11
0
View full text Add to dashboard Cite

Identification of intermediate radicals in theCH4microwave plasma by theLi+
Fujii
¹
,
Syouji
²

1992
Phys. Rev. A
22
1
11
0
View full text Add to dashboard Cite

Steady-state kinetic treatment of the emission from reduced pressure microwave induced discharges in helium

The dependence of coating in inductive R.F. plasmas on gas flow velocity, pressure and R.F. power

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Some considerations on the microwave electrodeless discharge

Cited by 33 publications

References 17 publications

Identification of intermediate radicals in theCH4microwave plasma by theLi+Fujii1, Syouji2 1992Phys. Rev. A221110View full textAdd to dashboardCite

Identification of intermediate radicals in theCH4microwave plasma by theLi+Fujii1, Syouji2 1992Phys. Rev. A221110View full textAdd to dashboardCite

Steady-state kinetic treatment of the emission from reduced pressure microwave induced discharges in helium

The dependence of coating in inductive R.F. plasmas on gas flow velocity, pressure and R.F. power

Contact Info

Product

Resources

About

Identification of intermediate radicals in theCH4microwave plasma by theLi+
Fujii
¹
,
Syouji
²

1992
Phys. Rev. A
22
1
11
0
View full text Add to dashboard Cite

Identification of intermediate radicals in theCH4microwave plasma by theLi+
Fujii
¹
,
Syouji
²

1992
Phys. Rev. A
22
1
11
0
View full text Add to dashboard Cite