Deposition of Potential Energy in Solids by Slow, Highly Charged Ions

We have measured the deposition of potential energy of slow $(\sim 6\times {10}^5\mathrm{m}/\mathrm{s})$, highly charged ions in solids with an ion implanted silicon detector. A large fraction (about $35\%$ or 60 keV) of the potential energy dissipated by ${\mathrm{Au}}^{69+}$ ions can be traced in electronic excitations deep $(>50\mathrm{}\mathrm{nm})$ inside the solid. In contrast, only about $10\%$ of the potential energy has been accounted for in measurements of emitted secondary particles.