Trajectory-dependent electronic excitations by light and heavy ions around and below the Bohr velocity

Abstract

We present experiments demonstrating trajectory-dependent electronic excitations at low ion velocities, where ions are expected to primarily interact with delocalized valence electrons. The energy loss of H${}^{+}$, H${}_2^{+}$, He${}^{+}$, B${}^{+}$, N${}^{+}$, Ne${}^{+}$, ${}^{28/29}$Si${}^{+}$ and Ar${}^{+}$ in self-supporting silicon membranes was analysed along channelled and random trajectories in a transmission approach. For all ions, we observe a difference in electronic stopping dependent on crystal orientation. For heavier ions, the energy-loss difference between channelling and random geometry is generally found more pronounced, and, in contrast to protons, increases for decreasing ion energy. Due to the inefficiency of core-electron excitations at employed ion velocities, we explain these results by reionization events occurring in close collisions of ions with target atoms, which are heavily suppressed for channelled trajectories. These processes result in trajectory-dependent mean charge states, which strongly affects the energy loss. The strength of the effect seems to exhibit a Z${}_1$ oscillation with an observed minimum for Ne. We, furthermore, demonstrate that the simplicity of our experimental geometry leads to results that can serve as excellent benchmark systems for dynamic calculations of the electronic systems of solids using time-dependent density functional theory.

References in corpus (8)

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• Examining real-time TDDFT non-equilibrium simulations for the calculation of electronic stopping power
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• Disparate energy scaling of trajectory-dependent electronic excitations for slow protons and He ions
• Multi-scale simulations of electron and ion dynamics in self-irradiated silicon
• Anisotropy of electronic stopping power in graphite

Cited by in corpus (5)

• Trajectory dependence of electronic energy-loss straggling at keV ion energies
• On the effect of electronic stopping in molecular dynamics simulations of collision cascades in Gallium Arsenide
• On the correlation of angular distributions of keV ions and trajectory-dependent electronic excitations in transmission channelling geometry
• Simultaneous assessment of energy, charge state and angular distribution for medium energy ions interacting with ultra-thin self-supporting targets: a time-of-flight approach
• Molecular Dynamics Simulations on Nuclear Recoils in Silicon Crystals towards Single Electron-Hole Pair Ionization Yields