Cross sections for electron collision with difluoroacetylene

Abstract

We report a detailed calculation of total elastic, differential elastic, momentum transfer and electronic excitation for electron impact on difluoroacetylene (C2F2) molecules using the R-matrix method at low energies. After testing many target models, the final results are reported for the target model that gave the best target properties and predicted the lowest value of the shape resonance. The shape resonance is detected at 5.86 eV and 6.49 eV with the close-coupling and static exchange models due to 2Πg (2B2g, 2B3g) states. We observed that the effect of polarization becomes prominent at low energies below 4 eV, decreasing the magnitude of the elastic cross section systematically as it increases for C2F2. We have also computed elastic cross sections for C2H2, C2F4 and C2H4 with a similar model and compared with the experimental data for these molecules along with C2F2. General agreement is found in terms of the shape and nature of the cross section. Such a comparison shows the reliability of the present method for obtaining the cross section for C2F2. The calculation of elastic scattering cross section is extended to higher energies up to 5 keV using the spherical complex optical potential method. The two methods are found to be consistent, merging at around 12 eV for the elastic scattering cross section. Finally we report the total ionization cross section using the binary encounter Bethe method for C2F2. The perfluorination effect in the shape and magnitude of the elastic, momentum transfer and ionization cross sections when compared with C2H2 showed a similar trend to that in the C2H4–C2F4 and C6H6–C6F6 systems. The cross-section data reported in this article could be an important input for the development of a C2F2 plasma model for selective etching of Si/SiO2 in the semiconductor industry.

Brief Review of Electron Collision Studies of Molecules Relevant to Plasma

“…This section discusses the recent results obtained by Gupta et al for C 2 F 2 [60], C 3 F 4 [61], and C 4 F 6 isomers [62] for elastic and inelastic scattering at low energies and C 2 F 6 [34] for ionization. Figure 1(a) shows the application of the R-matrix and SCOP methods at low, intermediate, and high energies to calculate the elastic cross section, as studied by Gupta et al [60]. The result is shown for C 2 F 2 .…”

“…The shifting of resonances to higher energies may be due to the shortening of the C-C bond in the case of C 2 F 2 and C 3 F 4 compared to C 2 H 2 and C 3 H 4 . A detailed explanation for such behavior is given in our previous articles [60,61]. It should be noted that there are no experimental or theoretical data available for such small fluorocarbon species.…”

“…Moreover, the dis- Figure 1. (a) Elastic scattering cross section for e-C2F2 from low (0.1 eV) to high (5 keV) energies calculated using the R-matrix and spherical complex optical potential (SCOP) methods [60] and comparison with experimental data of Gauf et al for C2H2 [136]. (b) Elastic and total cross section for C3F4 [61] calculated using the R-matrix method and comparison with the experimental data of Szmytkowski et al for C3H4 [137].…”

“…The low and intermediate energies cross-section calculations for various collision processes for several fluorocarbons have been theoretically predicted [54 59]. In recent years, the scarcity of cross-section data for simple fluorocarbons has led to studies on the low-energy cross section of fluorocarbons, such as C 2 F 2 [60], C 3 F 4 [61], and C 4 F 6 isomers [62], for various elastic and inelastic processes using the R-matrix method. At intermediate and high energies, differential and total cross sections have been computed using the single-center approach for C 4 F 6 isomers [63].…”

Electron scattering studies of BF and BF2

“…In the present work, we have used the spherical complex optical potential (SCOP) method to predict the elastic and MTCS at intermediate energies (up to 2000 eV). A detailed description of this method can be obtained from our previous articles [27,[48][49][50][51]. Here, we present an overview of the calculation.…”