Cross-section measurements for electron-impact ionization of atoms

Freund, Robert M.; Wetzel, Robert C.; Shul, R. J.; Hayes, Todd R.

doi:10.1103/physreva.41.3575

Cited by 370 publications

(361 citation statements)

References 79 publications

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“…Given the differing efficiencies with which the various radicals can be ionized ͑electron ionization cross sections͒, normalization of the background-corrected data is necessary to determine their relative abundance. The cross section for Si comes from the measurements by Freund et al 14 For the other SiH x , cross section measurements by Tarnovsky et al 15 were used. After subtracting the background contributions to the raw data, the cross section normalization was applied.…”

Section: Methodsmentioning

confidence: 99%

The aging of tungsten filaments and its effect on wire surface kinetics in hot-wire chemical vapor deposition

Holt

Swiatek

Goodwin

et al. 2002

Journal of Applied Physics

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Wire-desorbed radicals present during hot-wire chemical vapor deposition growth have been measured by quadrupole mass spectrometry. New wires produce Si as the predominant radical for temperatures above 1500 K, with a minor contribution from SiH 3 , consistent with previous measurements; the activation energy for the SiH 3 signal suggests its formation is catalyzed. Aged wires also produce Si as the predominant radical ͑above 2100 K͒, but show profoundly different radical desorption kinetics. In particular, the Si signal exhibits a high temperature activation energy consistent with evaporation from liquid silicon. The relative abundance of the other SiH x species suggests that heterogeneous pyrolysis of SiH 4 on the wire may be occurring to some extent. Chemical analysis of aged wires by Auger electron spectroscopy suggests that the aging process is related to the formation of a silicide at the surface, with silicon surface concentrations as high as 15 at. %. A limited amount ͑2 at. %͒ of silicon is observed in the interior as well, suggesting that diffusion into the wire occurs. Calculation of the relative rates for the various wire kinetic processes, coupled with experimental observations, reveals that silicon diffusion through the silicide is the slowest process, followed by Si evaporation, with SiH 4 decomposition being the fastest.

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Section: Methodsmentioning

confidence: 99%

The aging of tungsten filaments and its effect on wire surface kinetics in hot-wire chemical vapor deposition

Holt

Swiatek

Goodwin

et al. 2002

Journal of Applied Physics

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“…We assume that metal ions are created by electron impact ionization, by Penning ionization, by collisions of metal atoms with electronically excited argon atoms (Ar m + M → M + + Ar + e) with a rate coefficient k P = 5.9 × 10 −16 m 3 s −1 [39], and through charge exchange Ar + + M → M + + Ar with a rate coefficient k chexc = 1 × 10 −15 m 3 s −1 [39]. The rate coefficient for the electron impact ionization of aluminum is calculated from the electron impact ionization cross sections given by Freund et al [40]. The collision energy loss E m,ci per electron-ion pair created for the aluminum atom is calculated using the electron impact excitation (to levels 4s, 3d and 4p only) and elastic cross sections calculated by Wells and Miller [41].…”

Section: Appendix B Sputtering Yields Cross Sections and Rate Coeffmentioning

confidence: 99%

An ionization region model for high-power impulse magnetron sputtering discharges

Raadu¹,

Axnäs²,

Guðmundsson³

et al. 2011

Plasma Sources Sci. Technol.

113

176

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A time-dependent plasma discharge model has been developed for the ionization region in a high-power impulse magnetron sputtering (HiPIMS) discharge. It provides a flexible modeling tool to explore, e.g., the temporal variations of the ionized fractions of the working gas and the sputtered vapor, the electron density and temperature, and the gas rarefaction and refill processes. A separation is made between aspects that can be followed with a certain precision, based on known data, such as excitation rates, sputtering and secondary emission yield, and aspects that need to be treated as uncertain and defined by assumptions. The input parameters in the model can be changed to fit different specific applications. Examples of such changes are the gas and target material, the electric pulse forms of current and voltage, and the device geometry. A basic version, ionization region model I, using a thermal electron population, singly charged ions, and ion losses by isotropic diffusion is described here. It is fitted to the experimental data from a HiPIMS discharge in argon operated with 100 µs long pulses and a 15 cm diameter aluminum target. Already this basic version gives a close fit to the experimentally observed current waveform, and values of electron density n e , the electron temperature T e , the degree of gas rarefaction, and the degree of ionization of the sputtered metal that are consistent with experimental data. We take some selected examples to illustrate how the model can be used to throw light on the internal workings of these discharges: the effect of varying power efficiency, the gas rarefaction and refill during a HiPIMS pulse, and the mechanisms determining the electron temperature.

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“…[4,16,17]), but for this rough estimate the classical formula is assumed to hold in the azimuthal direction. The ionization coefficient k ion is evaluated using the following expressions [18,19] for the rate coefficients As concerns the excitation de-excitation term neglected in (4), a crude estimate of the rate coefficient (−k exc + k dexc n Ar * /n Ar ) can be carried out using a simple steady state balance for Ar* dn Ar * dt = 0 = k exc n e n Ar − k iz,Ar * n e n Ar * − k dexc n e n Ar * − k p n e n Ar * n Ar * = k exc k dexc + k p + k ion,Ar * that plugged into the neglected term in the first line of (4) gives…”

Section: Appendix a Determination Of The Physical Parametersmentioning

confidence: 99%

A phenomenological model for the description of rotating spokes in HiPIMS discharges

Gallian

Hitchon

Eremin

et al. 2013

Plasma Sources Sci. Technol.

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Abstract. In the ionization region above circular planar magnetrons, well defined regions of high emissivity are observed, when the discharge is driven in the HiPIMS regime. These regions are characterized by high plasma density and are often referred to as "spokes". Once their mode is stabilized, these structures rotate in the E × B direction with a constant rotation frequency in the hundreds of kHz range. A phenomenological model of the phenomenon is developed, in the form of a system of nonlinear coupled partial differential equations. The system is solved analytically in a frame co-moving with the structure, and its solution gives the neutral density and the plasma density once the electron density shape is imposed. From the balance of ionization, electron loss and constant neutral refilling, a steady state configuration in the rotating frame is achieved for the electron and neutral densities. Therefore, the spoke experimentally observed can be sustained simply by the combination of this highly reduced number of phenomena. Finally, a study of the sensitivity of neutral and plasma densities to the physical parameters is also given.

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Cross-section measurements for electron-impact ionization of atoms

Cited by 370 publications

References 79 publications

The aging of tungsten filaments and its effect on wire surface kinetics in hot-wire chemical vapor deposition

The aging of tungsten filaments and its effect on wire surface kinetics in hot-wire chemical vapor deposition

An ionization region model for high-power impulse magnetron sputtering discharges

A phenomenological model for the description of rotating spokes in HiPIMS discharges

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