Electron Impact Ionization of Metastable States of Diatomic Molecules

The Binary-Encounter Bethe approach was applied to the estimation of total ionization induced by electron impact in metastable states of diatomic molecules. The cross sections recently obtained for N2 and CO are reviewed and the new results for H2 are presented, discussing their reliability through the comparison with other theoretical methods.

A Binary-Encounter-Bethe approach to compute electron-impact partial ionization cross sections of plasma relevant molecules like Hexamethyldisiloxane and Silane

The electron-impact partial ionization cross sections (PICS) of the fragments are reported from threshold to 5~keV energy using the modified form of the binary-encounter-Bethe model. The scaling using mass spectrometry data ensures that the cross sections are of correct order of magnitude. The total ionization cross sections (TICS) were obtained by summing the PICS of fragments. The PICS and TICS obtained from the modified-binary-encounter-Bethe model are in excellent agreement with the experimental results and theoretical results. The molecules investigated are hexamethyldisiloxane (HMDSO) and silane. Both these species are highly relevant in plasma processing where the PICS are required over an extended energy range. The study of ionization process in conjunction with mass spectrometry provides correct estimates of the contribution that each charged ion makes to the TICS. The present approach can be easily extended to any species provided ion energetics, and relative cation abundances data are available.

Electron-Impact Ionization of Heavy Atoms Using the Time-Dependent Close-Coupling Method

The time-dependent close-coupling method has been recently applied to calculate electron-impact direct ionization cross sections for the Kr, W, and Pb atoms. An overview is presented for these three heavy neutral atom systems. When the direct ionization cross sections are combined with excitation-autoionization cross sections, the total ionization cross sections were found to be in reasonable agreement with crossed-beams measurements for Kr and Pb.

Chlorine-bearing species and the 37Cl/35Cl isotope ratio in the coma of comet 67P/Churyumov-Gerasimenko

<p>A full-mission analysis of Cl-bearing species in the coma of comet 67P/Churyumov-Gerasimenko has been conducted using data from the Rosetta ROSINA/DFMS mass spectrometer. This contribution will focus on the challenges encountered to relate DFMS data on Cl-bearing species to the neutral abundances at the comet.</p><p>DFMS was operated in neutral mode, in which electron impact ionizes a fraction of the incoming neutral gas in the ion source. Only ions in a narrow range around a certain commanded mass-over-charge ratio (m/z) pass through the mass analyser at a time and impact on a micro-channel plate (MCP), creating an electron avalanche that is recorded by a Linear Electron Detector Array chip with two rows of 512 pixels each (LEDA A and LEDA B). Data are obtained as Analog-to-Digital Converter (ADC) counts as a function of LEDA pixel number. The instrument scans over a sequence of m/z values.</p><p>A well-defined approach exists to convert ADC counts as a function of pixel number to the number of ions that were detected on the MCP. However, to relate the number of ions detected this way to the abundance of neutrals in the coma gas, the sensitivity for each neutral needs to be known. The sensitivity for a certain neutral takes into account the total ionization cross section for the neutral and product ion fraction, instrument transmission and secondary electron yield for each product ion. Sensitivities can be determined experimentally by introducing the neutrals in the DFMS instrument copy in the laboratory, but such data are not available for Cl-bearing species and an alternative approach needs to be used. Fortunately, the use of ratios cancels out some of the factors that play a role in the sensitivity. As an example, for the <sup>37</sup>Cl/<sup>35</sup>Cl ratio, total ionization cross sections and product ion fractions can be considered identical. In the case of <sup>37</sup>Cl/<sup>35</sup>Cl, taking into account the sensitivity results in a correction of more than 15%, mainly due to the secondary electron yield.</p><p>The<sup> 37</sup>Cl/<sup>35</sup>Cl ratio does not appear to change appreciably throughout the mission and is compared with known values from other solar system objects. The Cl/HCl ratio obtained with DFMS indicates that there must be at least one additional chlorine-bearing species on the comet next to HCl, CH<sub>3</sub>Cl and NH<sub>4</sub>Cl, the identity of which is unknown at this time.</p>

Radiation tolerance of the PNI RM3100 magnetometer for a Europa lander mission

The results of two radiation test campaigns on a low-cost commercial off-the-shelf magnetometer are presented. The test setup and the total ionization dose (TID) levels studied were designed to meet the requirements of a mission to land on Europa. Based on the Europa Lander Science Definition Team report, instruments inside an aluminum vault at the surface of Europa would need to withstand TID of up to 300 krad(SI). In order to evaluate the performance of the PNI RM3100 magnetometer, nine separate sensors were irradiated at two different facilities during two separate campaigns and under different configurations, including passive and active tests. Of the nine sensors, seven survived the TID of 300 krad(SI) while the other two sensors started presenting failures after reaching 150 krad(SI). Post-irradiation tests showed that eight of the nine sensors continued to work without appreciable degradation after stopping exposure, while one sensor stopped working altogether.

Electron-ion dynamics of hydroperoxyl radical under intense femtosecond laser pulses

The electron-ion dynamics of hydroperoxyl radical in intense femtosecond laser pulses is studied by using time-dependent density functional theory combined with molecular dynamics approach. We calculate the optimized structure, the ionization energy, and the optical absorption strength. The results are in good agreement with experiments. The irradiation dynamics of HO2 including the ionization, the dipole moment, the bond lengths, the kinetic energies, and the level depletion is explored by varying the laser frequency. Computational results indicate that the excitation behaviors are distinct due to different frequencies. Furthermore, the angular dependence of the total ionization and the orbital ionization yields of HO2 are explored. The calculated result predicts a maximum around [Formula: see text] and [Formula: see text] for the total ionization and the angular dependence of the total ionization reflects the symmetry of the HOMO.

A Novel SRAM PUF Stability Improvement Method Using Ionization Irradiation

As one of the fundamental elements of the fingerprints of integrated circuit chips, static random-access memory based physical unclonable function (SRAM PUF) has been regarded as an attractive option for hardware security circuits. Commercial SRAM chips could be used as PUF chips for low cost systems. However, the mismatches existing in most commercial SRAM chips are quite small, which could result in poor stability of SRAM PUF. To address this issue, this paper proposes a novel SRAM PUF stability improvement method using total ionization dose (TID) effect for commercial SRAM chips. The principles of this new method are presented in detail and verified by simulations. Thereafter, the TID experiments are carried out on one kind of commercial SRAM chips and validate that this novel method could reduce the intra-chip hamming distance (??_?????) by two orders of magnitude within the ionizing dose range of 40–100 Krad (SiO2), which is a significant stability improvement. Furthermore, considering the trade-offs of other performance factors, 40 Krad (SiO2) has been regarded as the recommended ionizing dose, which not only makes the stability and uniformity of SRAM PUF attain almost ideal values but also keeps the radiation-induced damage within a limited level.