Inelastic energy loss and charge exchange in low-energy heavy ions scattered from Cu and Cu-alloy surfaces.

Abstract

Inelastic energy loss and charge exchange processes in low-energy (1--9 keV) ${\mathrm{Ne}}^{+}$ ions scattered from the Cu atoms in Cu(100), ${\mathrm{Cu}}_{3}$Au(100), and polycrystalline Cu surfaces have been studied at large scattering angles. The experiments reveal that significant inelastic energy losses (up to 300 eV) occur in these scattering systems. The inelastic energy loss observed is independent of the Cu target matrix. It shows a sharp increase with increasing incident energy at a threshold energy dependent on the scattering angle. The scattered ${\mathrm{Ne}}^{+}$ ion yield, the ${\mathrm{Ne}}^{2+}$ ion yield, and the ${\mathrm{Cu}}^{+}$ recoil yield all show a similar threshold-type behavior as a function of incident energy. The threshold energies vary as a function of scattering angle. Various theoretical models of inelastic energy loss are discussed but the experimental results in general do not agree with these models. A model is suggested in which the total inelastic energy loss is proposed to be composed of two parts: the energy lost in continuous electron excitation along the incoming and outgoing trajectories and the energy lost in the inner-shell electron promotion during close atomic encounters. Good agreement between experiments and the model is obtained. The inelastic energy loss in ${\mathrm{Na}}^{+}$-Cu and ${\mathrm{Ne}}^{+}$-Au collisions was also studied and compared with that of ${\mathrm{Ne}}^{+}$-Cu collisions. Charge exchange in these inelastic energy-loss processes is discussed.