Channels of Potential Energy Dissipation during Multiply Charged Argon-Ion Bombardment of Copper

The dissipation of potential energy of multiply charged Ar ions incident on Cu has been studied by complementary electron spectroscopy and calorimetry at charge states between 2 and 10 and kinetic energies between 100 eV and 1 keV. The emitted and deposited fractions of potential energy increase at increasing charge state, showing a significant jump for charge states $q>8$ due to the presence of $L$-shell vacancies in the ion. Both fractions balance the total potential energy, thus rendering former hypotheses of a significant deficit of potential energy obsolete. The experimental data are reproduced by computer simulations based on the extended dynamic classical-over-the-barrier model.

Figure 1

Energy dispersive emitted amount of kinetic energy of secondary electrons for different charge states of argon ions impinging on a copper surface. The kinetic energy of the ions was fixed to 720 eV for all charge states.

Figure 2

Total amount of emitted electron energy $E^{\mathrm{em}}$ (circles) and potential energy deposited in the bulk $E^{\mathrm{dep}}$ (squares) per incident ion versus the charge state $q$ of the incident argon ions. The data are compared to the potential energies $E^{\mathrm{pot}}$ as obtained from atomic structure codes [14, 15] (open triangles).

Figure 3

Fractions of the potential energy dissipated into electron emission (circles, solid line) and deposited in the surface (squares, dashed line) versus charge state $q$. The symbols denote the experimental data. The lines have been obtained from numerical simulations using the extended dynamic classical-over-the-barrier model at a kinetic ion energy of 720 eV, as described in the text. The dotted line denotes the deposited fraction with the contribution from image charge acceleration being neglected.