Directional dependency of electronic stopping in nickel, projectile’s excited charge state and momentum transfer

We studied the directional dependency of electronic stopping power of swift light ions in nickel using real-time time-dependent density functional theory. We report a variation of electronic stopping for moving ions as the projectile probes different electronic densities of the host material. These results show that while the predicted magnitude stays in reasonable agreement with experiment, for $$v > 2$$ v > 2 . a.u. simulating only low index crystallographic directions is not enough to sample the experimental average values. The ab initio simulations give us access to microscopic quantities, such as non-adiabatic forces, momentum transfer and transient excited state charges of the projectile and host ions, which are not available through other methods. We report these quantities for the first time.

Infrared analysis of Glycine dissociation by MeV ions and keV electrons

Knowledge on amino acid's dissociation rates by solar wind is relevant for the study of biomaterial resistance in space. The radiolysis and sputtering of glycine by 1 keV electron beam and by 1.8 MeV H+, 1.5 MeV He+ and 1.5 MeV N+ ion beams are studied in laboratory, at room temperature. The column density decrease rates due to each beam are measured via infrared spectroscopy and destruction cross sections are determined. Present results stand in good agreement with those found in the literature and show that over five orders of magnitude, apparent destruction cross sections (which includes sputtering), σdap, are approximately proportional to the electronic stopping power, Se, that is (σdap ≈ a Se), where 1/a ≈ 120 eV/nm3. This value corresponds to the mean absorbed energy density necessary to dissociate (and/or eject) glycine; it also suggests that the stopping power threshold for molecular destruction is 23 keV μm−1. Assuming σdap = a Se for electron and ion projectiles, the half-life of pure α-glycine is estimated for the solar wind processing at 1 AU: about 10 days for protons or electrons and 40 days for He ions.

Ab initio electronic stopping power for protons in Ga 0.5 In 0.5 P/GaAs/Ge triple-junction solar cells for space applications

Motivated by the radiation damage of solar panels in space, firstly, the results of Monte Carlo particle transport simulations are presented for proton impact on triple-junction Ga 0.5 In 0.5 P/GaAs/Ge solar cells, showing the proton projectile penetration in the cells as a function of energy. It is followed by a systematic ab initio investigation of the electronic stopping power (ESP) for protons in different layers of the cell at the relevant velocities via real-time time-dependent density functional theory calculations. The ESP is found to depend significantly on different channelling conditions, which should affect the low-velocity damage predictions, and which are understood in terms of impact parameter and electron density along the path. Additionally, we explore the effect of the interface between the layers of the multilayer structure on the energy loss of a proton, along with the effect of strain in the lattice-matched solar cell. Both effects are found to be small compared with the main bulk effect. The interface energy loss has been found to increase with decreasing proton velocity, and in one case, there is an effective interface energy gain.

Radiolysis of NH3:CO ice mixtures – implications for Solar system and interstellar ices

ABSTRACT Experimental results on the processing of NH3:CO ice mixtures of astrophysical relevance by energetic (538 MeV 64Ni24+) projectiles are presented. NH3 and CO are two molecules relatively common in interstellar medium and Solar system; they may be precursors of amino acids. 64Ni ions may be considered as representative of heavy cosmic ray analogues. Laboratory data were collected using mid-infrared Fourier transform spectroscopy and revealed the formation of ammonium cation (NH$_4^+$), cyanate (OCN−), molecular nitrogen (N2), and CO2. Tentative assignments of carbamic acid (NH2COOH), formate ion (HCOO−), zwitterionic glycine (NH$_3^+$CH2COO−), and ammonium carbamate (NH$_4^+$NH2COO−) are proposed. Despite the confirmation on the synthesis of several complex species bearing C, H, O, and N atoms, no N–O-bearing species was detected. Moreover, parameters relevant for computational astrophysics, such as destruction and formation cross-sections, are determined for the precursor and the main detected species. Those values scale with the electronic stopping power (Se) roughly as σ ∼ a S$_\mathrm{ e}^n$, where n ∼ 3/2. The power law is helpful for predicting the CO and NH3 dissociation and CO2 formation cross-sections for other ions and energies; these predictions allow estimating the effects of the entire cosmic ray radiation field.

Computational investigation of the valid valence state contribution in calculating the electronic stopping power of a proton in bulk Al within the linear response approach

The electronic stopping power is a fundamental quantity to many technological fields that use ion irradiation. Here we investigate the validity of using a fully ab initio computational scheme based on linear response time-dependent density functional theory to predict the random electronic stopping power (RESP) of a proton in bulk aluminum. We verify the power of using the extrapolation scheme to overcome the expected convergence issue of the RESP calculations. We show that the calculated RESP of valence electrons compares well with experimental data for low proton velocity only when at full convergence and including the exchange-correlation effect. We demonstrate that the inclusion of valence states only is sufficient for calculating the electronic stopping power up to the stopping maximum.