Sublattice-selective inversion of dual- and multiple-scattering He + survival in binary collision approximation simulations of α − Al 2 O 3 : A comparative study with α − SiO 2 , GaN , and 3 C − SiC

The He + charge-state survival probability sets the absolute scale of quantitative low-energy ion scattering (LEIS), and a recent CaSiO 3 study [J. Brötzner , ] has shown that this probability depends on whether the backscattered trajectory involves one, two, or several collisions—suggesting that quantitative analysis ought to discriminate by collision history. How far this regime hierarchy generalizes is, however, an open question. This is addressed through scattering-regime-resolved binary collision approximation (BCA) simulations of He + at 1–3 keV under grazing incidence ( ψ = 22 ∘ ) for four crystallographically distinct targets: α -quartz SiO 2 , corundum α − Al 2 O 3 , wurtzite GaN, and zincblende 3C-SiC. The calculations combine pair-specific Nordlund-Lehtola-Hobler potentials, position-dependent electronic stopping, Debye thermal vibrations, and a velocity-dependent Hagstrum kernel; statistically converged trajectory ensembles were accumulated for the high-statistics analysis. For α − SiO 2 , GaN, and 3-SiC, the standard ordering 〈 P + 〉 s > 〈 P + 〉 d > 〈 P + 〉 m is recovered, with single-to-multiple contrast R s / m ≈ 1.5 – 2.2 . Corundum exhibits a qualitatively different behavior. When the backscattered ensemble is decomposed by the chemical identity of the final-collision atom, dual-scattering trajectories ending on the dominant Al sublattice show a charge survival that of multiple-scattering ones at all five investigated energies. The sublattice-resolved inversion is highly significant— 19.7 σ at 1 keV in the pooled three-seed ensemble, weakening monotonically to 3.7 σ at 3 keV—and reproduces across three independent random seeds (per-seed significance 10.9 − 11.7 σ at 1 keV). Because Al-ending trajectories make up 79 % – 83 % of the backscattered population, the inversion also persists in the integrated signal ( P d / P m = 0.59 – 0.80 ) despite the oppositely ordered minority O sublattice. The inversion is robust to a ± 30 % variation of the Hagstrum velocity parameter and survives detector-window selection. Tracking the recorded collision pairs reveals the cause: two Al atoms in the same atomic plane make up 52 % – 72 % of the dual events in α

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