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In this work we study the vicinage effects that arise in the interaction of molecular projectiles with solids, considering, in particular, the effects produced by the excitation of inner shells. For this purpose, we use two different approaches. On one side we extend the use of the semiclassical impact-parameter model for the excitation of atomic shells, considering quantum corrections and the role of target screening in the vicinage effects. On the other hand, we adapt our extended wave-packet model, developed in a previous work to the calculation of stopping ratios and ionization cross sections for correlated ions. This model introduces modifications to the wave-packet method originally proposed by Kaneko, using the Levine and Louie technique to take into account the energy gaps corresponding to the different atomic levels of the target. Finally, we add the contribution of valence electrons calculated with the Lindhard free-electron-gas model and compare with experimental results of vicinage effects in the energy-loss and ionization cross sections for hydrogen molecules interacting with C, Al, Si, Al2O3, and SiO2 targets. Fil: Archubi, Claudio Darío. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Arista, Nestor Ricardo. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

We present a combined experimental-theoretical study of the energy loss of C and O ions in Zn in the energy range 50–1000 keV/amu. This contribution has a double purpose, experimental and theoretical. On the experimental side, we present stopping power measurements that fill a gap in the literature for these projectiletarget combinations and cover an extended energy range, including the stopping maximum. On the theoretical side, we make a quantitative test on the applicability of various theoretical approaches to calculate the energy loss of heavy swift ions in solids. The description is performed using different models for valence and inner-shell electrons: a nonperturbative scattering calculation based on the transport cross section formalism to describe the Zn valence electron contribution, and two different models for the inner-shell contribution: the shellwise local plasma approximation (SLPA) and the convolution approximation for swift particles (CasP). The experimental results indicate that C is the limit for the applicability of the SLPA approach, which previously was successfully applied to projectiles from H to B.We find that this model clearly overestimates the stopping data for O ions. The origin of these discrepancies is related to the perturbative approximation involved in the SLPA. This shortcoming has been solved by using the nonperturbative CasP results to describe the inner-shell contribution, which yields a very good agreement with the experiments for both C and O ions.

Energy-loss measurements and theoretical calculations for Be and B ions in Zn are presented. The experimental ion energies range from 40 keV/u to 1 MeV/u, which includes the energy-loss maximum and covers a lack of experimental data for these systems from intermediate to high energies. The measurements were performed using the Rutherford backscattering technique. The ab initio calculations are based on the extended Friedel sum rule–transport cross-section method for the valence electrons and the Shellwise local plasma approximation for the bound electrons. A comparison of these calculations to the present experimental data for Be and B and previous values for H, He, and Li ions on the same target is included. This confirms the applicability of the employed theoretical framework also for ions of intermediate atomic number.

The electronic stopping power, S, of HfO₂ films for proton and alpha particle beams has been measured and calculated. The experimental data have been obtained by the Rutherford backscattering technique and cover the range of 120–900 and 120–3000 keV for proton and alpha particle beams, respectively. Theoretical calculations of the energy loss for the same projectiles have been done by means of the dielectric formalism using the Mermin energy loss function—generalized oscillator strength (MELF-GOS) model for a proper description of the HfO₂ target on the whole momentum-energy excitation spectrum. At low projectile energies, a nonlinear theory based on the extended Friedel sum rule has been employed. The calculations and experimental measurements show good agreement for protons and a quite good one for alpha particles. In particular, the experimental maximums of both stopping curves (around 120 and 800 keV, respectively) are well reproduced. On the basis of this good agreement, we have also calculated the inelastic mean-free path IMFP and the stopping power for electrons in HfO₂ films. Our results predict a minimum value of the IMFP and a maximum value of the S for electrons with energies around 120 and 190 eV, respectively.

The energy loss of helium ions in zinc has been measured in the energy range from 37.5 to 1750 keV/amu using the transmission technique and the Rutherford backscattering method. In addition, calculations using the extended Friedel sum rule, the unitary convolution approximation, and the local plasma approximation have been performed. The contributions of the inner-shell and valence electrons to the total energy loss are separately evaluated. The measurements and calculations are in good agreement over an extended range of energies, and both of them yield stopping values higher than those provided by SRIM 2003.