Positive ion pair production by electron impact dissociative ionization of CF4

Bruce, Mike; Ma, Ce; Bonham, R. A.

doi:10.1016/0009-2614(92)85340-g

Cited by 62 publications

(34 citation statements)

References 9 publications

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“…This indicates that the electronically excited (CF3~) * ions do not decay radiatively to the stable ground state of the CF~-ion, but rather to an unstable state which dissociates, perhaps into C F~-+ F and/or CF ÷ + 2 F (or F2). The combined double ion formation cross section for C F~-+ F + and C F + + F + from C F 4 was found [32,33] to be close the 1.8 x 10-iv cm 2 that we estimate for the cross section for (CF~-)* + F ÷ forma-tion. The b r o a d and largely unstructured shape of the emission is also indicative of a bound-free transition and thus supports the notion of a transition to a lower state of the C F~ ion that is unstable .…”

Section: Resultssupporting

confidence: 76%

“…Based on the excitation function shown in Fig. 4 and a reasonable estimate of the energy dependence of respectively the "neutral" and the "ionic" channel, we assign a value of approximately (1.8+0.5)x 10 -17 cm 2 to the cross section for double ion formation ( C F~) * + F + at 100eV which is roughly a factor of 5 larger [32,33] than the reported double ion formation cross section for CF~-+ F ÷ at the same energy. This indicates that the electronically excited (CF3~) * ions do not decay radiatively to the stable ground state of the CF~-ion, but rather to an unstable state which dissociates, perhaps into C F~-+ F and/or CF ÷ + 2 F (or F2).…”

Section: Resultsmentioning

confidence: 81%

“…[45,59]). It is interesting to compare the contribution to the absolute emission cross section due to the double ion formation (CF~-)* + F + above 40 eV to the cross section for the double ion formation C F~-+ F + as reported by Bonham and collaborators [32,33]. Based on the excitation function shown in Fig.…”

Section: Resultsmentioning

confidence: 94%

“…[29]. Furthermore, recent positive ion -positive ion coincidence studies of double-ion production cross sections following electron and photon impact on CF4 revealed that the fragmentation of CF 4 into CF~ and F + is among those double-ion production channels which was observed with an appreciable cross section [30][31][32][33]. Further evidence in support of the major rote of excited CF~-fragments was provided in the studies of dissociative excitation of CF 4 by Wang et at.…”

Section: Introductionmentioning

confidence: 99%

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Further studies of the continuous UV emission produced by electron impact on CF4

Müller

Bubel

Schulz

et al. 1992

Z Phys D - Atoms, Molecules and Clusters

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Abstract. The intense continuous UV emission which extends from 200 nm to beyond 500 nm produced by electron impact on carbontetrafluoride, CF4, has been investigated in a crossed electron-beam -gas-beam apparatus as well as in a gas-target apparatus under single collision conditions with special emphasis on the regime of impact energies below 50 eV. Systematic measurements of excitation functions (relative emission cross sections) at various wavelengths between 225 nm and 420 nm revealed the same onset of 23.5 + 2 eV and the same energy dependence for all excitation functions independent of the selected wavelength indicating that the continuous emission consists of a single fluorescence contribution. Evidence of a second onset around 40 eV, roughly 16 eV above the first onset which is an energy close to the ionization energy of atomic fluorine (17.4 eV), was foundmore or less prominent -in all excitation functions. The presence of the second onset lends strong support to the assignment of the excited (CF3 +)* fragment ion as the emitting source of the emission continuum. We identify the lower onset at 23.5 eV with the electron-impact induced breakup of the parent CF4 molecule into an excited (CF 3 +)* ion and a ground state fluorine atom ("neutral" channel), whereas the second onset around 40 eV indicates the presence of an "ionic" fragmentation channel in which an excited (CF 3 +)* fragment ion is produced together with a fluorine ion, F +. Wavelength scans taken at impact energies above and below the second onset revealed no significant difference in the envelope of the observed emission contiuum which further supports the notion that the emission continuum consists of a single fluorescence contribution.

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Section: Resultssupporting

confidence: 76%

Section: Resultsmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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Further studies of the continuous UV emission produced by electron impact on CF4

Müller

Bubel

Schulz

et al. 1992

Z Phys D - Atoms, Molecules and Clusters

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“…At the energies reported here, the majority of neutral fluorine production apparently comes from ionisation events. In fact, it is possible to construct upper and lower bounds for the gross fluorine production cross section (the gross cross section is weighted by the number of neutral fluorine atoms produced in a reaction; see Bruce et al 1992 for specific equations). To do this we adopt the following rules: (i) For the lower bound we assume contributions only from sources about which we are absolutely certain, and we choose branching ratios so that F production is minimised.…”

Section: Introductionmentioning

confidence: 99%

Dissociative Ionisation and Neutral Dissociation: CF4, a Case Study

Bonham¹,

Bruce²

1992

Aust. J. Phys.

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New results for the total neutral dissociation cross section and an estimate of the gross cross section for the production of neutral fluorine by electron impact on CF4 have been obtained by combining previously reported results for the total dissociation cross section and the counting cross section for the total dissociative ionisation. This advancement was made possible by recently reported results for multication formation obtained from coincidence experiments. The estimate of the neutral fluorine production cross section is of the same order of magnitude as the total dissociation cross section itself, a similarity which may explain why CF4 is such an effective etching gas. The available cross section data for electron impact energies between 5 and 200 e V are reviewed.

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