Measurement of kinetic and potential energy deposition in highly charged ion collisions with surfaces

We measure craters in thin dielectric films formed by highly charged Xe$^{Q+}$ (26 $\leq Q \leq$ 44) projectiles [1]. Tunnel junction devices with ion-irradiated barriers were used to amplify the effect of charge-dependent cratering through the exponential dependence of tunneling conductance on barrier thickness. Electrical conductance of a crater $\sigma_{c}(Q)$ increased by 4 orders of magnitude ($7.9 \times 10^{-4}\mbox{ }\mu$S to \\6.1 $\mu$S) as $Q$ increased, corresponding to crater depths ranging from 2 to 11 \mbox{\AA}. By employing a heated spike model, we determine that the energy required to produce the craters spans from 8 to 25 keV over the investigated charge states where kinetic energies were $(8 \times Q)$ keV. We partition crater formation energy into potential and kinetic contributions to find that at least (27 $\pm$ 2) $\%$ of the available ion potential energy is required. Decreasing projectile kinetic energy at constant $Q$, provides a new test for charge-dependent kinetic energy loss theory.\\[4pt] [1] R.E. Lake, J.M. Pomeroy, H. Grube, C.E. Sosolik, Phys. Rev. Lett. \textbf{107}, 063202 (2011)