Electronic and Ionic Impact Phenomena

Massey, H. S. W.; Burhop, E. H. S.; McDaniel, E. W.

doi:10.1119/1.1976400

Cited by 55 publications

(63 citation statements)

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“…Although there is naturally some correlation between ionization threshold energy and ionization efficiency, the range of first ionization thresholds in typical gases is small compared with the kinetic energy distribution of the cascading electrons (Massey & Burhop, 1969). In fact, our simulations indicate that even under maximum amplifying conditions, energies of the ionizing collisions tend to be well in excess of the threshold.…”

Section: Ionization Efficiency Of Gasesmentioning

confidence: 83%

“…This can be attributed to the fact that the maximum in a molecular ionization cross-section tends to occur at some energy several electronvolts beyond the threshold, as is the case with H 2 O (see Fig. 3) (Massey & Burhop, 1969).…”

Section: Ionization Efficiency Of Gasesmentioning

confidence: 99%

“…The nonionizing inelastic scattering cross-section of a molecule is directly related to its molecular complexity (Massey & Burhop, 1969). Additional atoms in a molecule provide an increased number of normal modes (e.g.…”

Section: Ionization Efficiency Of Gasesmentioning

confidence: 99%

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An improved model for gaseous amplification in the environmental SEM

Thiel

Bache

Fletcher

et al. 1997

Journal of Microscopy

103

150

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SummaryWe present a new model for the gas amplification effect used in many environmental scanning electron microscopes, wherein molecular complexity is shown to be the critical factor. Monte Carlo simulations, based on experimental electron scattering cross-sections, are used to deduce a predictive model for the amplification process that is superior to the Townsend gas capacitor model. These predictions are compared with experimentally obtained amplification curves. Significantly, it is shown that the ionization efficiency of the electrons changes dramatically over the gap distance, and a constant value cannot be assumed. Atomic and molecular excitations affect the amplification process in two ways: first, they serve to lower the average kinetic energy of the imaging electrons, thereby keeping a greater fraction near the ionization threshold energy. Second, molecular normal modes determine the effectiveness of positive gas ions in producing additional secondaries upon surface impact. Practical implications such as signal gain and fraction of useful signal as a function of operating conditions are discussed in the light of the new model. Finally, we speculate on potential new contrast mechanisms brought about by the presence of an imaging gas.

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Section: Ionization Efficiency Of Gasesmentioning

confidence: 83%

Section: Ionization Efficiency Of Gasesmentioning

confidence: 99%

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An improved model for gaseous amplification in the environmental SEM

Thiel

Bache

Fletcher

et al. 1997

Journal of Microscopy

103

150

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show abstract

“…In the He* system the quantum number S is well conserved during ionization and the application of Wigner's spin conservation rule [29] tells us that 5 P (ion) is very small [30], while Müller et al [31] report ionization probabilities of 0.975 for other spin states; we thus set 5 P (ion) = 0 and 1 P (ion) = 3 P (ion) = 1 in Eq. (2).…”

Section: A Ionization Rate Coefficientsmentioning

confidence: 99%

Heteronuclear ionizing collisions between laser-cooled metastable helium atoms

et al. 2007

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We have investigated cold ionizing heteronuclear collisions in dilute mixtures of metastable (2 3 S1) 3 He and 4 He atoms, extending our previous work on the analogous homonuclear collisions [R. J. W. Stas et al., PRA 73, 032713 (2006)]. A simple theoretical model of such collisions enables us to calculate the heteronuclear ionization rate coefficient, for our quasi-unpolarized gas, in the absence of resonant light (T = 1.2 mK): K (th) 34 = 2.4×10 −10 cm 3 /s. This calculation is supported by a measurement of K34 using magneto-optically trapped mixtures containing about 1×10 8 atoms of each species, K (exp) 34 = 2.5(8)×10 −10 cm 3 /s. Theory and experiment show good agreement.

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“…Uma seção de choque aproximada para a captura de elétrons de velocidade v por uma partícula carregada de número atômico Z pode ser dada por [91] [92]…”

Section: Estados De Ionização De Strangeletsunclassified

Matéria de quarks (strangelets) de origem astrofísica e sua detecção por experimentos terrestres

Paulucci¹

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Electronic and Ionic Impact Phenomena

Cited by 55 publications

References 0 publications

An improved model for gaseous amplification in the environmental SEM

An improved model for gaseous amplification in the environmental SEM

Heteronuclear ionizing collisions between laser-cooled metastable helium atoms

Matéria de quarks (strangelets) de origem astrofísica e sua detecção por experimentos terrestres

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