Electron Swarm Method Research Articles

Determination and assessment of a complete and self-consistent electron-neutral collision cross-section set for the C4F7N molecule

The perfluoronitrile C4F7N is considered a promising SF6-alternative in high-voltage gas-insulated apparatus, thanks to its high dielectric strength and low global warming potential. However, a complete and consistent set of electron-neutral collision cross-sections of C4F7N is still lacking, which hinders relevant plasma modeling. In this contribution, the available electron-neutral collision cross-sections of C4F7N are first compiled and assessed. The initial cross-sections are adjusted iteratively by the electron swarm method to determine a complete and self-consistent cross-section set of C4F7N for the first time. The set is validated by a systematic comparison of electron swarm parameters between Boltzmann equation analysis and experimental measurements in pure C4F7N as well as C4F7N/N2 and C4F7N/Ar mixtures. The proposed cross-section set of C4F7N will be made available to the community in the LXCat database. It will be of particular importance for applications with an emphasis on the discharge mechanisms of this novel gas.

Low-energy electron interactions with chlorotrimethylsilane (Si(CH3 )3 Cl), dichlorodimethylsilane (Si(CH3 )2 Cl2 ) and chloromethyldimethylsilane (SiH(CH3 )2 (CH2 Cl)).

Silane derivatives are widely used in industrial plasmas for manufacturing lighting devices, solar cells, displays, etc. Models of technological plasmas require quantitative data. The rate coefficients (k) and the activation energies (Ea ) of thermal electron attachment for chlorotrimethylsilane (Si(CH3 )3 Cl), dichlorodimethylsilane (Si(CH3 )2 Cl2 ) and chloromethyldimethylsilane (SiH(CH3 )2 (CH2 Cl)) are reported. This is important for understanding the basic processes occurring in plasmas. The pulsed Townsend technique (known as the electron swarm method) has been applied for the measurements. In this technique, electrons generated by a laser, under a uniform electric field, traverse to an anode and induce a charge on it. In the buffer gas charge grows linearly, but in the presence of a scavenger, electrons are captured, and thus the rate of charge increase slows down with time. From the shape of the pulse, the kinetic parameters are determined. Kinetic parameters from the study of thermal electron attachment by Si(CH3 )3 Cl, Si(CH3 )2 Cl2 and SiH(CH3 )2 (CH2 Cl) were determined for the first time. The corresponding rate coefficients at 298 K are equal to (9.56 ± 0.02) × 10-11 , (6.62 ± 0.02) × 10-11 and (1.24 ± 0.05) × 10-11 cm3 s-1 and Ea values are equal to 0.29 ± 0.01, 0.24 ± 0.01 and 0.31 ± 0.01eV for Si(CH3 )3 Cl, Si(CH3 )2 Cl2 and SiH(CH3 )2 (CH2 Cl), respectively. The experiment was performed in the 298-378K temperature range. The presented results provide important new information about fundamental quantities such as rate coefficients and activation energies for thermal electron capture by chlorinated derivatives of silane. These data can further advance our understanding of thermal electron interactions with chlorosilanes that can be used to control the important species in the plasmas of many modern technologies.

Electron Collision Cross Sections for the TRIES Molecule and Electron Transport Coefficients in TRIES-Ar and TRIES-O2 Mixtures

A reliable set of low-energy electron collision cross sections for the triethoxysilane (TRIES) molecule was derived based on the measured electron transport coefficients for a pure TRIES molecule by using an electron swarm method and a two-term approximation of the Boltzmann equation. The electron transport coefficients calculated using the derived set are in good agreement with experimental value over a wide range of E/N values (ratio of the electric field E to the neutral number density N). The present electron collision cross section set for the TRIES molecule, therefore, is the most reliable so far for plasma discharges and for materials processing using the TRIES molecule. Moreover, the electron transport coefficients for the TRIES-Ar and the TRIES-O2 mixtures were also calculated and analyzed over a wide range of E/N for the first time.

Electron transport analysis in water vapor

A reliable set of electron collision cross sections for water vapor, including elastic, rotational, vibrational, and electronic excitation, electron attachment, and ionization cross sections, is estimated by the electron swarm method. In addition, anisotropic electron scattering for elastic and rotational excitation collisions is considered in the cross section set. Electron transport coefficients such as electron drift velocity, longitudinal diffusion coefficient, and effective ionization coefficient are calculated from the cross section set by Monte Carlo simulation in a wide range of E/N values, where E and N are the applied electric field and the number density of H2O molecules, respectively. The calculated transport coefficients are in good agreement with those measured. The obtained results confirm that the anisotropic electron scattering is important for the calculation at low E/N values. Furthermore, the cross section set assuming the isotropic electron scattering is proposed for practical use.

Electron collision cross sections of CHF3 and electron transport in CHF3 and CHF3–Ar mixtures

A set of electron collision cross sections for trifluoromethane (CHF3) is estimated by the electron swarm method. Electron transport coefficients in CHF3, such as the electron drift velocity, longitudinal diffusion coefficient, and effective ionisation coefficient, are calculated from the estimated cross section set by the Monte Carlo method, and the values are compared with the measured data. In the case of the transport coefficients, good agreement is obtained between the calculated and measured values in a wide range of reduced electric fields. Furthermore, the transport coefficients described above and the characteristic energy in CHF3–Ar mixtures are calculated, and the values are found to agree well with the measured data. This confirms the validity of the cross section set for CHF3 estimated here.

Determination of the electron collision cross-section set for the C4F6 molecule by using an electron swarm study

A set of electron collision cross-sections for the C4F6 molecule has been successfully determined for the first time by using an electron swarm method with a two-term approximation of the Boltzmann analysis. The set is evaluated by fitting the calculated electron drift velocities in pure C4F6 and in C4F6-Ar mixtures to the experimental data in the E/N range of 0.35 — 1200 Td (1 Td = 10−17 Vcm2), where E/N is the ratio of the electric field (E) to the neutral number density (N). The set is confirmed to be reliable due to our ability to reproduce satisfactorily the electron drift velocities in pure C4F6 and in 0.1, 0.5, 1, 5, and 10% C4F6-Ar mixtures with deviations of ±5%. The set may be the best available so far for use in the quantitative numerical modeling of a4 plasma discharge for various processing procedures with materials containing C4F6 molecules.

Determination of the electron collision cross sections for the C2H4 molecule by using the electron swarm method

A set of low-energy electron-collision cross sections for ethene (C2H4) is necessary for quantitative numerical modeling of plasma discharges for processing procedures with materials containing C2H4 molecules. The set was derived from the measured electron transport coefficients for a pure C2H4 molecule by using an electron swarm study and a two-term approximation to the Boltzmann equation for energy. The electron transport coefficients, which were calculated by using the derived set, are in good agreement with the experimental values over a wide range of E/N ratios in pure C2H4 molecule, where E is the electric field and N is the neutral number density. The validity of the present set of the C2H4 molecule was not only checked by using a Monte Carlo simulation but also evaluated by comparison with another set.

Electron transport in CF3I and CF3I-N2 mixtures

Electron collision cross sections for CF3I are estimated using the electron swarm method. Electron drift velocity, effective ionisation coefficient, and longitudinal diffusion coefficient in CF3I are calculated using Monte Carlo method, and the calculated electron transport coefficients are compared with those measured. Calculated electron drift velocity agrees with measured data within the difference of 6% below 1600 Td, and calculated effective ionisation coefficient agrees with measured data within the difference of 10% above 460 Td. Further, those swarm parameters in CF3I–N2 mixtures are calculated, and calculated values of electron drift velocity and effective ionisation coefficient agree well with measured data in CF3I–N2 mixtures. This confirms the validity of the estimated set.

Thermal electron capture by some halopropanes

Thermal electron attachment rate constants for CF 3CHClCH 3, CF 2ClCFClCF 3 and CBrF 2CH 2CH 2Br have been measured with electron swarm method. Corresponding rate constants are equal to 7.6×10 −11, 5.5×10 −9 and 1.5×10 −8 cm 3 molecule −1 s −1, respectively. The dissociative electron attachment (DEA) spectra for nine haloalkanes have been determined using negative ion mass spectrometry. The correlation between rate constants, position of the DEA peaks and vertical attachment energy (VAE) available in literature has been demonstrated.

전자군 방법에 의한 C3F8분자가스의 비탄성충돌단면적의 결정

The electron drift velocity W and the product of the longitudinal diffusion coefficient and the gas number density <TEX>$ND_{L}$</TEX> in the <TEX>$0.525\;\%$</TEX> and <TEX>$5.05\;\%$</TEX> <TEX>$C_{3}F_8-Ar$</TEX> mixtures were measured by using the double shutter drift tube with variable drift distance over the E/N range from 0.03 to 100 Td and gas pressure range from 1 to 915 torr. And we determined the electron collision cross sections set for the <TEX>$C_{3}F_8$</TEX> molecule by STEP 1 of electron swarm method using a multi-term Boltzmann equation analysis. Our special attention in the present study was focused upon the vibrational excitation and new excitations cross sections of the <TEX>$C_{3}F_8$</TEX> molecule.

Thermal electron capture by some chlorobromopropanes

Thermal electron attachment rate constants for CH2ClCHBrCH3 and CH2ClCH2CH2Br have been measured using electron swarm method. Corresponding rate constants are equal to 3.5×10-10 and 2.5×10-10 cm3 molec-1 s-1, respectively. Parallely, negative ion mass spectra of these compounds as well as CH2FCH2Br, CH2ClCH2Br, CH2BrCH2Br and CF3CHClBr has been measured with negative ion mass spectrometry method. The rate constants have been compared with the negative ion mass spectra.

Swarm derived electron collision cross section set for the perfluorocyclobutane molecule

The cross section set of perfluorocyclobutane (c-C4F8) is determined by the electron swarm method. The modification is applied to the vibrational excitation cross section and the elastic momentum transfer cross section. Our previously measured electron swarm parameters (drift velocities, longitudinal diffusion coefficients and effective ionization coefficients) in 0.468% and 4.910% c-C4F8/Ar mixtures are used for the determination of the vibrational excitation cross section. The measured drift velocity and longitudinal diffusion coefficient in pure c-C4F8 are used to determine the correct elastic momentum transfer cross section. The calculated electron transport coefficients were derived using the Monte Carlo simulation method.

Low energy electron attachment by bromoalkanes

Thermal electron attachment processes in the mixtures of CH3CH2CH2Br, CH3CHBrCH3, CH2BrCH2Br, CH2FCH2Br and CF3CH2Br with carbon dioxide have been investigated using an electron swarm method. It has been found that all the investigated compounds attach electrons only in a two-body process. Corresponding rate constants have been determined to be equal to 1.1×10−11, 1.4×10−12, 1.8×10−8, 5×10−11 and 1.4×10−9cm3molecule−1s−1, respectively. The dependence of the electron capture rate constants on electronic polarizability of the accepting center of the molecule has been demonstrated. The average rate constant for CH3Br, CH3CH2Br and CH3CH2CH2Br equal to (6±2)×10−12cm3molecule−1s−1 is recommended.

Low-Energy Electron Attachment by Chloroalkanes

Thermal electron attachment rate constants for 1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane, 1- and 2-chloropropanes, and 1,1-, 1,2-, 2,2-, and 1,3-dichloropropanes have been measured using an electron swarm method. It has been found that all the investigated compounds attach electrons only in a two-body process. Corresponding rate constants are equal to 1.4 × 10-10, 3.2 × 10-8, 2.7 × 10-13, 3.8 × 10-12, 5.7 × 10-11, 8.1 × 10-12, 6.3 × 10-12, and 1.2 × 10-11 cm3 molecule-1 s-1, respectively. The dependence of the electron capture rate constants on the electronic polarizability of the accepting center of the molecule and the vertical attachment energy has been demonstrated.

전자군 방법에 의한 전자충돌단면적 결정

The electron-atom collision studies have been essentially used for testing and developing suitable theories of the scattering and collision processes, and for providing a tool for obtaining detailed information on the structure of the target atoms and molecules and final collision products. And, the development of that has also been strongly motivated by the need for electron collision data in such fields as laser Physics and development, astrophysics, Plasma devices, upper atmospheric processes and radiation physics. The concept and the Principle of determination of the electron collision cross sections for atoms and molecules by using the present electron swarm method are explained.

전자군 방법에 이용되는 2항근사와 다항근사 볼츠만 방정식의 적용

An accurate cross sections set is necessary for the quantitatively understanding and modeling of plasma phenomena. By using the electron swarm method, we determine an accurate electron cross sections set for objective atoms or molecule at low electron energy range. It is general calculation that used in this method to an two-term approximation of Boltzmann equation. But it may give erroneous transport coefficients for CF<TEX>$_4$</TEX> molecule treated in this paper having \`C2v symmetry\`, therefore, multi-term approximation of the Boltzmann equation analysis which can consider anisotropic scattering exactly is carried out. It is necessary to require understanding of the fundamental principle of analysis method. Therefore, in this paper, we compared the electron transport coefficients(W and ND<TEX>$\_$</TEX>L/) in pure Ar, O<TEX>$_2$</TEX>, and CF<TEX>$_4$</TEX> gas calculated by using two-term approximation of the Boltzmann equation analysis code uses the algorithm proposed by Tagashira et al. with those by multi-term approximation by Rubson and Ness which was developed at James-Cook university, and discussed an application and/or validity of the calculation method by comparing these calculated results.

Electron capture by haloethanes in a carbon dioxide buffer gas

An electron swarm method for investigation of the electron capture reaction has been modified. It is based on the registration of the temporal evolution of a single electron pulse. The method gives straightforward results on electron drift velocities in any mixture and allows calculating the rate constants for the electron capture. The thermal electron capture kinetics for eight haloethanes has been investigated. Only two-body attachment processes have been found in their mixtures with carbon dioxide. All corresponding rate constants have been determined. A link between the two-body rate constant and an electron polarizability of the attaching center has been demonstrated.

Effect of temperature on electron attachment to and negative ion states of CCl2F2

The effect of temperature on electron attachment to dichlorodifluoromethane (CCl2F2) has been investigated for temperatures up to 500 K and for mean-electron energies from thermal to 1.0 eV using an electron swarm method. The measurements were made in mixtures of CCl2F2 with nitrogen. The electron attachment rate constant increases with temperature over the entire temperature and mean-electron energy range investigated. The variation of the thermal value of the electron attachment rate constant with temperature compares well with earlier measurements of this quantity and shows an increase by a factor of 10 when the temperature is raised from 300 to 500 K. From a comparison of published data on the electron affinity, electron attachment using the swarm method, electron attachment using the electron beam method, electron scattering, electron transmission, indirect electron scattering, and related calculations, the lowest negative ion states of CCl2F2 have been identified with average positions as follows: a1(C–Clσ*) at +0.4 eV and −0.9 eV, b2(C–Clσ*) at −2.5 eV, a1(C–Fσ*) at −3.5 eV, and b1(C–Fσ*) at −6.2 eV; an electron-excited Feshbach resonance is also indicated at −8.9 eV.

Electron attachment processes in halomethanes

We have investigated thermal electron capture processes in the mixtures of halomethanes and carbon dioxide (in excess) using the electron swarm method. We have found that except the very slow second order reactions (single collision) there occur processes involving homo-(RX)2 or heterogeniouos (RX·CO2) van der Waals complexes (multi-body pressure dependent processes) which are at least a few times faster at atmospheric pressures. The mechanism and the kinetics of some of these processes are presented.

Thermal electron attachment to CHF 2CL in mixtures with CO 2 and N 2

Electron attachment to CHF 2Cl in mixtures with nitrogen and carbon dioxide has been investigated using an electron swarm method. The attachment mechanism involving both two-body process and electron capture by van der Waals complexes (CHF 2Cl × N 2) and (CHF 2Cl) 2 was found. The corresponding rate constants are equal to (1.1 ± 0.1) × 10 −13 cm 3 molec −1 s −1, (2.0 ± 0.1) × 10 −33 cm 6 molec −2 s −1 and (1.1 ± 0.1) × 10 −50 cm 9 molec −3 s −1, respectively.