Disparate energy scaling of trajectory-dependent electronic excitations for slow protons and He ions

Abstract

We have simultaneously measured angular distributions and electronic energy loss of helium ions and protons directly transmitted through self-supporting, single-crystalline silicon foils. We have compared the energy loss along channelled and random trajectories for incident ion energies between 50 keV and 200 keV. For all studied cases the energy loss in channelling geometry is found lower than in random geometry. In the case of protons, this difference increases with initial ion energy. This behaviour can be explained by the increasing contribution of excitations of core electrons, which are more likely to happen at small impact parameters accessible only in random geometry. For helium ions we observe a reverse trend - a decrease of the difference between channelled and random energy loss for increasing ion energy. Due to the inefficiency of core-electron excitations even at small impact parameters at such low energies, another mechanism has to be the cause for the observed difference. We provide evidence that the observation originates from reionisation events induced by close collisions of helium ions occurring only along random trajectories.

References in corpus (6)

• Core electrons in the electronic stopping of heavy ions
• The electron elevator: excitations across the band gap via a dynamical gap state?
• Examining real-time TDDFT non-equilibrium simulations for the calculation of electronic stopping power
• Electronic stopping power in a narrow band gap semiconductor from first principles
• Anisotropy of electronic stopping power in graphite
• Electronic interaction of slow hydrogen and helium ions in the nickel-silicon system

Cited by in corpus (7)

• Trajectory-dependent electronic excitations by light and heavy ions around and below the Bohr velocity
• Experimental electronic stopping cross section of tungsten for light ions in a large energy interval
• Trajectory dependence of electronic energy-loss straggling at keV ion energies
• Impact of the experimental approach on the observed electronic energy loss for light keV ions in thin self-supporting films
• 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
• Contrast modes in a 3D ion transmission approach at keV energies