N. R. Arista

Electronic stopping of slow molecular ions in solids

Energy loss measurements were made for 12.5-130 keV per nucleon H+ and H2+ on carbon and aluminium foils. For incident H2+, both H+ and H2+ are transmitted; the energy per nucleon of the latter being lower than that of transmitted H+, at low energies. The theory shows this is due to interference effects in the binary excitation of target electrons by the spatially correlated protons and suggests that transmitted H2+ results from di-protons travelling inside the solid with the internuclear axis aligned close to the direction of motion.

Electron excitations by slow ions in metals

Abstract The energy and angular distribution of electrons excited by slow charged particles penetrating an electron gas, is analyzed using a representation of the particle by a general self-consistent potential. The number of excited electrons per unit path-length is also calculated. Oscillations with the nuclear charge of the ion, Z , are obtained for the spectra of electron excitations and the total excitation rate. These Z oscillations have the same origin as those found, both theoretically and experimentally, for the stopping power of low-velocity ions. The connection of electron excitation spectra with ion slowing down and with experiments on secondary electron emission is discussed.

Slow-ion-induced single excitations in an electron gas

Abstract We evaluate electron excitation spectra generated by slow ions in an electron gas. Energy and angular spectra, and total excitation rates, are given. Non-linear screening effects on the intruding charge Z result in Z oscillations in the spectra of electron excitations and in the total excitation rate. Predictions are given, for different electron gas densities, using phase shifts obtained from numerical self-consistent solutions of the Kohn-Sham density-functional formalism. The results are compared with those obtained in the linear dielectric response, and with the pseudopotential model of target response. The connection between electron excitation spectra and ion energy loss parameters (stopping power and straggling) is discussed.

Threshold effect in the energy-loss straggling of protons channeled in Au at very low velocities

The energy-loss straggling of protons channeled in gold crystals in the direction has been experimentally and theoretically studied at the low-velocity limit. The experimental results show a threshold effect in the straggling values, which is similar to that observed earlier in the energy loss. This effect is described by a theoretical model which explains the velocity dependence by considering the individual features of the contributions of free electrons in the conduction band and the nearly free (5d{sup 10}) electrons which generate a threshold effect at low energies due to their binding energy. The model predicts a deviation of proportionality with ion velocity of the energy-loss spread and yields a good description of the obtained experimental data.