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1. Ion velocity effect governs damage annealing process in defective KTaO ₃

   https://doi.org/10.1088/1361-6463/ad53da  

   Velişa, G.; Iancu, D.; Zarkadoula, E.; Tong, Y.; Zhang, Y.; Weber, W_J (June 2024, Journal of Physics D: Applied Physics)

   Abstract Effects of electronic to nuclear energy losses (S_e/S_n) ratio on damage evolution in defective KTaO₃have been investigated by irradiating pre-damaged single crystal KTaO₃with intermediate energy O ions (6 MeV, 8 MeV and 12 MeV) at 300 K. By exploring these processes in pre-damaged KTaO₃containing a fractional disorder level of 0.35, the results demonstrate the occurrence of a precursory stage of damage production before the onset of damage annealing process in defective KTaO₃that decreases with O ion energy. The observed ionization-induced annealing process by ion channeling analysis has been further mirrored by high resolution transmission electron microscopy analysis. In addition, the reduction of disorder level is accompanied by the broadening of the disorder profiles to greater depth with increasing ion fluence, and enhanced migration is observed with decreasing O ion energy. SinceS_e(∼3.0 keV nm⁻¹) is nearly constant for all 3 ion energies across the pre-damaged depth, the difference in behavior is due to the so-called ‘velocity effect’: the lower ion velocity below the Bragg peak yields a confined spread of the electron cascade and hence an increased energy deposition density. The inelastic thermal spike calculation has further confirmed the existence of a velocity effect, not previously reported in KTaO₃or very scarcely reported in other materials for which the existence of ionization-induced annealing has been reported. In other words, understanding of ionization-induced annealing has been advanced by pointing out that ion velocity effect governs the healing of pre-existing defects, which may have significant implication for the creation of new functionalities in KTaO₃through atomic-level control of microstructural modifications, but may not be limited to KTaO₃. 

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2. New Ionization Processes for Ionizing Nonvolatile Compounds in Mass Spectrometry: The Road of Discovery to Current State-of-the-Art

   https://doi.org/10.1021/jasms.0c00312  

   Trimpin, Sarah; Moreno-Pedraza, Abigail; Yenchick, Frank S.; Hoang, Khoa; Pophristic, Milan; Karki, Santosh; Marshall, Darrell D.; Lee, Chuping; Lu, I-Chung; El-Baba, Tarick J.; et al (January 2020, Journal of the American Society for Mass Spectrometry)

   null (Ed.)

   This Perspective covers discovery and mechanistic aspects as well as initial applications of novel ioni-zation processes for use in mass spectrometry that guided us in a series of subsequent discoveries, in-strument developments, and commercialization. With all likelihood, vacuum matrix-assisted ionization on an intermediate pressure matrix-assisted laser desorption/ionization source without the use of a laser, high voltages, or any other added energy was the defining turning point from which key developments grew that were at the time unimaginable, and continue to surprise us in its simplistic preeminence, and is therefore a special focus here. We, and others, have demonstrated exceptional analytical utility with-out a complete understanding of the underlying mechanism. Our current research is focused on how best to understand, improve, and use these novel ionization processes through dedicated platform and source developments which convert volatile and nonvolatile compounds from solid or liquid matrices into gas-phase ions for analysis by mass spectrometry using e.g., mass-selected fragmentation and ion mobility spectrometry to provide reproducible, accurate, and sometimes improved mass and drift time resolution. The combination of research and discoveries demonstrated multiple advantages of the new ionization processes and established the basis of the successes that lead to the Biemann Medal and this Perspective. How the new ionization processes relate to traditional ionization is also presented, as well as how these technologies can be utilized in tandem through instrument modification and implementa-tion to increase coverage of complex materials through complementary strengths. 

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3. Infrared spectroscopy of cations in helium nanodroplets

   https://doi.org/10.1063/5.0163390  

   Singh, Amandeep; Bergmeister, Stefan; Azhagesan, Andrew; Scheier, Paul; Vilesov, Andrey F (September 2023, Review of Scientific Instruments)

   Here, we describe our pulsed helium droplet apparatus for spectroscopy of molecular ions. Our approach involves the doping of the droplets of about 10 nm in diameter with precursor molecules, such as ethylene, followed by electron impact ionization. Droplets containing ions are irradiated by the pulsed infrared laser beam. Vibrational excitation of the embedded cations leads to the evaporation of the helium atoms in the droplets and the release of the free ions, which are detected by the quadrupole mass spectrometer. In this work, we upgraded the experimental setup by introducing an octupole RF collision cell downstream from the electron impact ionizer. The implementation of the RF ion guide increases the transmission efficiency of the ions. Filling the collision cell with additional He gas leads to a decrease in the droplet size, enhancing sensitivity to the laser excitation. We show that the spectroscopic signal depends linearly on the laser pulse energy, and the number of ions generated per laser pulse is about 100 times greater than in our previous experiments. These improvements facilitate faster and more reproducible measurements of the spectra, yielding a handy laboratory technique for the spectroscopic study of diverse molecular ions and ionic clusters at low temperature (0.4 K) in He droplets. 

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4. Effects of Multiple Pulses on Nanosecond Discharges

   https://doi.org/10.2514/6.2023-0569  

   Duarte, Alfredo J.; Deak, Nicholas E.; Bisetti, Fabrizio (April 2023, AIAA SciTech Forum, 23-27 January 2023, National Harbor, MD & Online)

   Numerical simulations of axisymmetric nanosecond pulsed discharges at atmospheric pressure and temperature are performed with a novel fully implicit time integration approach. The plasma fluid equations with a drift-diffusion model and local-field approximation are made dimensionless and solved using a preconditioned Jacobian Free Newton-Krylov method. A simplified kinetics model is employed, including electrons, one positive ion, and one negative ion. The chemical processes of ionization, attachment, detachment, and recombination are considered along with photoionization. The newly developed fully-implicit integration scheme with physics-based preconditioning allows for the efficient simulations capable of describing the cathode sheath over time-scales of O(10 us). The implicit solver overcomes the limiting time scales related to electron drift, diffusion, dielectric relaxation, and ionization. 

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5. The Contribution of N ⁺ Ions to Earth's Polar Wind

   https://doi.org/10.1029/2020GL089321  

   Lin, Mei‐Yun; Ilie, Raluca; Glocer, Alex (September 2020, Geophysical Research Letters)

   Abstract The escape of heavy ions from the Earth atmosphere is a consequence of energization and transport mechanisms, including photoionization, electron precipitation, ion‐electron‐neutral chemistry, and collisions. Numerous studies considered the outflow of O⁺ions only, but ignored the observational record of outflowing N⁺. In spite of 12% mass difference, N⁺and O⁺ions have different ionization potentials, ionospheric chemistry, and scale heights. We expanded the Polar Wind Outflow Model (PWOM) to include N⁺and key molecular ions in the polar wind. We refer to this model expansion as the Seven Ion Polar Wind Outflow Model (7iPWOM), which involves expanded schemes for suprathermal electron production and ion‐electron‐neutral chemistry and collisions. Numerical experiments, designed to probe the influence of season, as well as that of solar conditions, suggest that N⁺is a significant ion species in the polar ionosphere and its presence largely improves the polar wind solution, as compared to observations. 

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