Electronic stopping of low-energy H and He in Cu and Au investigated by time-of-flight low-energy ion scattering

Electronic stopping has been investigated experimentally for slow ${\text{H}}^{+}$ and ${\text{He}}^{+}$ ions $\left(v<0.6\text{a}\text{.u}\text{.}\right)$ in polycrystalline Au and Cu, by means of time-of-flight low-energy ion scattering. Measurements were performed in backscattering geometry using polycrystalline films of several nanometers thickness; high-resolution Rutherford backscattering spectrometry was used for precise thickness calibration $\left(<4\%\right)$. Absolute stopping cross-section data for Cu and Au were obtained down to $v\sim 0.07\text{a}\text{.u}\text{.}$ Both Au and Cu exhibit a rather sharp, distinctive threshold velocity of $\sim 0.18\text{a}\text{.u}\text{.}$ for excitation of $d$ electrons by ${\text{H}}^{+}$ and ${\text{He}}^{+}$. Below this threshold, projectiles interact exclusively with $s$ electrons.

Figure 1

(Color online) Experimental TOF-LEIS spectra of 10 keV ${\text{He}}^{+}$ ions measured on Cu and Au samples. Also shown the results of TRBS simulations: as solid lines—spectra with optimized $\epsilon$; as dashed and dashed-dotted lines—spectra with 8% reduced and 8% increased $\epsilon$, respectively.

Figure 2

(Color online) Electronic stopping cross section of H and He ions in Au obtained via absolute measurements (see experiment). Also shown is the data from Refs. 10, 24. Dash-dotted and dashed lines represent DFT predictions for different density parameters $r_{\text{s}}$ based on (Refs. 4, 5) for H and He, respectively.

Figure 3

(Color online) Electronic stopping cross section of H and He ions in Cu obtained via absolute and relative measurements (see experiment). Dash-dotted and dashed lines represent DFT predictions for different density parameters $r_{\text{s}}$ based on (Refs. 4, 5) for H and He, respectively.