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E. Bodewits, R. Hoeckstra, K. Dobes, F. Aumayr:
"Electron-emission processes in highly charged Ar and Xe ions impinging on highly ordered pyrolytic graphite at energies just above the kinetic threshold";
Physical Review A, 90 (2014), 0527031 - 0527039.

At keV energies, many electronic processes contribute to the emission of secondary electrons in the interaction
of highly charged ions on surfaces. To unravel contributions resulting from isolated hollow atoms in front of
the surface or embedded in the electron gas of the target, heavy highly charged Ar and Xe ions are collided on
highly ordered pyrolytic graphite (HOPG). A light target material as HOPG assures straight-line trajectories in
the subsurface range. By a systematic change of incidence angle and energy of low-charged Ar and Xe ions, the
kinetic electron emission component is determined. Separating out the kinetic energy contribution for the highly
charged ions yields pure potential-energy-driven secondary-electron yields. From these yields it is concluded that
in contrast to metallic targets, only a small fraction of the secondary electrons stem from above the surface. The
lack of above-surface emission is likely due to the semimetallic electronic structure of HOPG. The subsurface
emission is found to scale with the increase in binding energy of the inner-shell hole when incrementing the
charge state of the projectile Ar or Xe ions.