Vanishing Electronic Energy Loss of Very Slow Light Ions in Insulators with Large Band Gaps

Electronic energy loss of light ions in nanometer films of materials with large band gaps has been studied for very low velocities. For LiF, a threshold velocity is observed at 0.1 a.u. ($250\mathrm{eV}/\mathrm{u}$), below which the ions move without transferring energy to the electronic system. For KCl, a lower (extrapolated) threshold velocity is found, identical for H and He ions. For ${\mathrm{SiO}}_2$, no clear velocity threshold is observed for He particles. For protons and deuterons, electronic stopping is found to perfectly fulfill velocity scaling, as expected for binary ion-electron interaction.

Figure 1

Experimental energy spectra $\mathrm{N}(E)$ for 500 eV deuterons backscattered from $\mathrm{Au}/\mathrm{Si}$ (open circles) and $\mathrm{LiF}/\mathrm{Au}/\mathrm{Si}$ (open squares). The corresponding simulated spectra (TRBS) are also shown as full and dashed lines, respectively. For details, see text.

Figure 2

Electronic stopping cross section $\epsilon$ of H, D, and He ions in LiF as a function of the projectile velocity $v$. Also shown are the data for H ions from [13] and for He ions from [24].

Figure 3

Electronic stopping cross section $\epsilon$ of H, D, and He ions in KCl as a function of the projectile velocity $v$.

Figure 4

Electronic stopping cross section $\epsilon$ of H, D, and He ions in ${\mathrm{SiO}}_2$ as a function of projectile velocity $v$.