Gold nanostructures created by highly charged ions

Abstract

Nanometer-sized structures produced by individual highly charged ion (HCI) impacts are now reported on a high-conductivity surface, and examined by scanning tunneling microscopy (STM). Highly charged ions, e.g., ${\mathrm{Bi}}^{81+}$, represent an exotic form of terrestrial matter with neutralization energies that can exceed $375\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ per ion, and velocities in excess of $1000\phantom{\rule{0.3em}{0ex}}\mathrm{km}∕\mathrm{s}$ from only moderate electrostatic potentials $(15\phantom{\rule{0.3em}{0ex}}\mathrm{kV})$. In the experiment presented here, a single-crystal $\mathrm{Au}(111)$ sample was irradiated with ${\mathrm{Xe}}^{25+}$ and ${\mathrm{Xe}}^{44+}$, which are vastly different in their neutralization energies. They have moderate velocities (slow compared to Bohr velocity) to maximize the likelihood of observing features and similar nuclear stopping powers. STM analysis indicates that the neutralization energy is less significant in forming features on gold than reported in low-free-electron-density systems. These results support the hypothesis that gold's high free-electron density enables efficient dissipation of the HCI's potential energy.