Electronic interaction of slow hydrogen and helium ions with nickel-silicon systems

Abstract

Paper accepted for publication by Physical Review A Link to the abstract: https://journals.aps.org/pra/accepted/af070N0aRc31281619294920dc695c1c385658bbf Electronic stopping cross sections (SCS) of nickel, silicon and nickel-silicon alloys for protons and helium (He) ions are studied in the regime of medium and low energy ion scattering, i.e., for ion energies in the range from 500 eV to 200 keV. For protons, at velocities below the Bohr velocity the deduced SCS is proportional to the ion velocity for all investigated materials. In contrast, for He ions non-linear velocity scaling is observed in all investigated materials. Static calculations using density functional theory (DFT) available from literature accurately predict the SCS of Ni and Ni-Si alloy in the regime with observed velocity proportionality. At higher energies, the energy dependence of the deduced SCS of Ni for protons and He ions agrees with the prediction by recent timedependent DFT calculations. The measured SCS of the Ni-Si alloy was compared to the SCS obtained from Bragg's rule based on SCS for Ni and Si deduced in this study, yielding good agreement for protons, but systematic deviations for He projectiles, by almost 20%. Overall, the obtained data indicate the importance of non-adiabatic processes such as charge-exchange for proper modelling of electronic stopping of in particular medium-energy ions heavier than protons in solids.

Two-channel approach to the average retarding force of metals for slow singly ionized projectiles

“…This curve signals a two-slope behavior with linearities in the projectile velocity. Remarkably, a quite similar, i.e., two-slope, behavior was found in [16] for Ni (r s 1.8) with a singly ionized He + intruder. There a comparison with TDDFT results [31] was made by using 1.15 as a multiplying factor for the simulation-based results.…”

“…Neither the screening treatment nor the scattering description of RPA is correct for a nonlinear situation. For protons, where reasonable agreement [15,16,21] between nonlinear Q (1) (v F ) and data was found, Eq. (10) with Z 1 = 1 would give a serious underestimation [19].…”

“…Our Q (2) = 0 values for Z 1 = 1 are in accord with a screened-proton picture without a bound state, where there is no charge-changing cycle; thus q = 0 during the motion of the projectile. Since the experimental data, obtained with low-velocity proton projectiles for Al and Ni targets, are in reasonable harmony [15,16,21] with nonlinear theory [18][19][20] based solely on Q (1) (v F ), we have transferable knowledge in this case. A desired convergence between the two sides of understanding is achieved.…”

“…( 7) an a priori unit-weight assumption. In reality, i.e., for channelinglike conditions in metals, the impact parameterdependent closest approach of intruders and lattice ions [7,[14][15][16] may influence that assumption. In more simple terms, our present weighting would refer to random-collision situations.…”

Experimental electronic stopping cross section of transition metals for light ions: Systematics around the stopping maximum

“…For V, we employed data from [47]. For Ti, Cr, and Ni, we used values (and trends) based on recent experimental works [65][66][67][68] and intercomparisons [69]. Finally, for Zr, Mo, and W, we relied on the available data in IAEA that, unfortunately for these elements, are limited and show a significant scatter of up to 5%-10% around the Bragg peak.…”