Energy Loss and charge exchange for medium energy ions in a large-angle collision

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Systematic understanding the charge exchange, inelastic energy loss and spectrum shape for medium energy ions scattered to a large-angle is indispensable to extract the quantitative information about the suiface structure and lattice dynamics from the energy spectra obseived for the ions scattered from solid surfaces. Unfortunately, however, it is impossible to measure directly the above physical quantities using gas targets, because of the extamely smali target densi and scattering cross sections. In this study, we measured the charge state distributions (CSDs), inelastic energy loss and spectrum shapes for He ions scattered to a large-angle at single ciystal surfaces using a toroidal electrostatic analyzer with an excellent energy resolution (Δ E =9 x 10^<-4>). The single ciystal targets used here are MgO(001), KI(001), BbI(001), B-type NiSi_2(111) and Si(111)-√<3> x√<3>-Sb. We also measured the elastic scattering cross sections with a solid state detector for He and Ne ions scattere … More d to a large-angle from Ni, Sb and Hf atoms. The present study has revealed the following points :(1) The CSDs for He ions scattered to a large-angle from the atoms on top of solid surfaces are not equilibrated and the smaller the Z-number of target atoms, the larger the average charge. The average charges for He ions scattered from high-Z atoms (z 【greater than or similar】20) observed agree with the semi-empirical formula proposed by Marion-Young [ii within experimental enors (±20%).(2) The observed avemge charges of He ions after a large-angle collision are scaled as a frmnction of ∫^∞_<r_<min>> P_e(r(t))dr/v(t), where P_e (r(t)) is the target electron density at r(t), R_<min> is the closest distance and v(t) is the He velocity.(3) The average charges of the He and Ne ions scattered from top most atoms are dependent on exit angle and the smaller the the exit angle (scaled from the surface plane), the smaller the average charges (reaching an equilibrium value).(4) The inelastic energy loss for he ions scattered from the Sb atoms were measured directly using the Si(111)-√<3> x√<3>-Sb. The result obtained agrees the theoretical calculation by Schiwietz using the coupled channel method.(5) In the case of a large-angle collision between a heavy ion such as Ne and a high-Z atom, the differential scattering cross sections are enhanced due to dynamical change of the target electron density distributions induced by formation of a molecular oitital during the collision Less