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We have measured the electronic energy-loss straggling of protons, helium, boron and silicon ions in silicon using a transmission time-of-flight approach. Ions with velocities between 0.25 and 1.6 times the Bohr velocity were transmitted through single-crystalline Si(100) nanomembranes in either channelling or random geometry to study the impact parameter dependence of energy-loss straggling. Nuclear and path length contributions to the straggling were determined with the help of Monte Carlo simulations. Our results exhibit an increase in straggling with increasing ion velocity for channelled trajectories for all projectiles as well as for protons and helium in random geometry. In contrast for heavier ions, electronic straggling at low velocities does not decrease further but plateaus and even seems to increase again. We compare our experimental results with transport cross section calculations. The satisfying agreement for helium shows that electronic stopping for light ions is dominated by electron-hole pair excitations, and that the previously observed trajectory dependence can indeed be attributed to a higher mean charge state for random trajectories. No agreement is found for boron and silicon indicating the breakdown of models based solely on electron-hole pair excitations, and that local electron-promotion and charge-exchange events significantly contribute to energy loss at low velocities.

We report measurements of $^{10}\mathrm{B}$ stopping powers in random and Si 〈100〉 directions. The measurements were carried out in the 500\char21{}9000 keV energy range for the channeling case and in the 300\char21{}800 keV for the random one. For the channeling measurements, the low energy data (500\char21{}800 keV) follow a ${\mathrm{v}}^{\mathrm{s}}$ regime with s=0.90\ifmmode\pm\else\textpm\fi{} 0.06 whereas, for the random data, dE/dx\ensuremath{\propto}${\mathrm{v}}^{\mathrm{s}}$ with s=1.1\ifmmode\pm\else\textpm\fi{}0.2. Both results are in good agreement with the prediction of current theories. On the other side, the experimental random $^{10}\mathrm{B}$ stopping power values (for energies up to 650 keV) are in fair agreement with the ones obtained from a scaling procedure by Ziegler, Biersack, and Littmark. However, for energies higher than 650 keV, slight but systematic differences are observed.

We present measurements of the stopping power of 800-keV $^{4}\mathrm{He}$ ions channeled along the Si〈100〉 axis, as a function of the incidence angle. We compare the experimental results with theoretical calculations by using the impact-parameter-dependent energy loss obtained from the solution of the time-dependent Schr\"odinger equation through the coupled-channel method. This nonperturbative calculation provides reliable energy-loss results which are in good agreement with the experimental results.

molecules. The results show small enhancements (about 5% and 15% for H + and H + molecules, respectively) of the stopping ratios. The values obtained by the simulation code SEICS indicate small vicinage effects as well and are in satisfactory agreement with the experimental data. Moreover, the same simulations carried out for carbon foils yield relatively higher stopping ratios. The differences between the vicinage effects obtained for C and Au are interpreted in terms of different excitation spectra of each material. Finally, our results obtained for Au are in clear disagreement with those reported in the seminal work of Brandt, Ratkowski, and Ritchie [Phys. Rev. Lett. 33, 1325 (1974)].

In the present work we report on the energy loss ratio Rn of fast H2 clusters in thin films 30‐50 A of LaScO3 and HfO2. The medium energy ion scattering technique was employed covering a broad energy range 40‐200 keV/amu. The energy loss ratio data showed no clear evidence of collective excitations in these materials. The experimental results were interpreted in terms of three different theoretical approaches: the dielectric formalism with the Brandt-Reinheimer theory for semiconductor materials; the detailed simulation of the molecular fragments dynamics through the target; and finally the unitary convolution approximation adapted for hydrogen molecules. Only the simulation agrees with the experimental results for both oxides. The unitary convolution approximation works quite well for HfO2 but overestimates slightly the LaScO3 data. The overall results indicate that the energy loss ratio depends critically on the description of the electronic properties of such oxides.

In the present work, we have explored the interference effects which arise when ${\mathrm{H}}_{2}^{+}$ and ${\mathrm{H}}_{3}^{+}$ cluster ions interact with a thin layer of $\mathrm{Si}{\mathrm{O}}_{2}$ in order to obtain a clear signature of plasmon excitations induced by these energetic projectiles. For this purpose, high-energy-resolution experiments were carried out as a function of the incoming projectile energy, covering an energy range between 40 and $200\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{amu}$. The ratio ${R}_{n}$ between the energy loss of the cluster and the sum of the energy loss of its constituents has a steep increase between 70 and $100\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{amu}$ for both cluster ions, which is associated with the plasmon excitation threshold.

The energy-loss spectrum associated with scattering of 100-keV H+ ions from K, Rb, and Cs atoms adsorbed on Al(111) has been investigated both experimentally and theoretically. Theoretical simulations were conducted based on calculations of the energy loss experienced in specific ion trajectories at the surface, using coupled-channel calculations to describe inner-shell ionization and excitation as a function of impact parameter. The energy losses can be attributed entirely to single atomic collisions from the alkali atoms, and the experiments reproduce the markedly increased asymmetry in scattering from Rb and Cs relative to K, attributable largely to the role of 3d and 4d excitations, respectively, and particularly the role of multiple excitations of these states. For Rb and Cs scattering, the data show excellent quantitative agreement between theory and experiment; for the K scattering, a discrepancy of a low-energy shoulder is attributed to a problem associated with the sample preparation.

The aim of this work is to investigate how the mean energy loss and straggling due to ${{\mathrm{H}}_{2}}^{+}$ molecules interacting with silicon are affected by the Coulomb explosion and vicinage effects. To that end, a SIMOX-type sample made up of $^{18}\mathrm{O}$ and with an appropriate $^{18}\mathrm{O}$ marker grown over the surface of crystalline Si was employed, allowing to carry out the measurements through the $^{18}\mathrm{O}(p,\ensuremath{\alpha})^{15}\mathrm{N}$ resonant reaction at $151.2\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ under channeling and random directions. The results show that the mean energy loss associated with the Coulomb explosion and vicinage effects are similar and amount each to about 2% of the total mean energy loss. The comparison of the energy straggling obtained for molecular beams at random and the well-aligned $⟨100⟩$ direction shows a larger value for the aligned case, which is interpreted as a result of the Coulomb explosion along the channel direction. The experimental results are also discussed in terms of Monte Carlo simulations.

$\text{Si-}K$ x-ray and backscattering yields have been measured as a function of the projectile entrance angle for atomic and molecular (${\mathrm{H}}_{2}^{+}$ and ${\mathrm{H}}_{3}^{+}$) hydrogen ions channeling at kinetic energies of $150\phantom{\rule{0.3em}{0ex}}\text{keV}$ per proton along the Si $⟨100⟩$ crystal direction. A large enhancement of the x-ray production has been observed for well-aligned ${\mathrm{H}}_{3}^{+}$ molecule beams. It is shown that this effect results from the Coulomb explosion of the molecule fragments during the channeling motion. Moreover, the shape and intensity of the measured angular distribution allows a quantitative determination of the corresponding heating of the transversal ion motion ($2.6\ifmmode\pm\else\textpm\fi{}0.6\phantom{\rule{0.3em}{0ex}}\text{eV}$ for ${\mathrm{H}}_{2}^{+}$ and $5.1\ifmmode\pm\else\textpm\fi{}0.8\phantom{\rule{0.3em}{0ex}}\text{eV}$ for ${\mathrm{H}}_{3}^{+}$ molecules) in the channel. These values are consistent with the stored potential energies per particle and they depend significantly on the collective wake forces and molecular alignment conditions.