Angular-dependent Ne+-ion scattering from a solid Au target

Abstract

Ion-scattering spectroscopy (ISS) is a technique used for composition analysis of solid surfaces. The angular dependence of low-energy ion scattering has been investigated in order to assess the possibility of using large scattering angles in ISS. The equipment used for these experiments is described. It allows for measurements of the angular dependence of the scattering process between 0° and 150°. A detailed discussion of the special ion optical design of the primary beam train and the analyzing system for the scattered ions, comprising a retarding system and a 127° cylindrical analyzer, is given. Results are presented for 2-keV-Ne+ scattering from Au. It is found that increasing the scattering angle beyond 60° has little effect on the intensity of the scattered ions. However, it does increase the mass resolution, thus favoring large angle scattering for surface analytical studies. From a comparison of the measured scattered ion current with computed charge-independent scattering cross sections, the ion fractions P+ of the scattered particles have been determined as a function of scattering angle. Scattering cross sections have been calculated using a Firsov, Molière, and two different Born–Mayer interaction potentials. It was found that the neutralization of the ions is mainly governed by a direct interaction with the target atom and to a smaller extent by interaction with the neighboring surface.

Ion Scattering Spectrometry

“…In general it is not possible to separate these contributions except by a process of fitting experimental results to theoretical equations. For example, Brongersma et al (1976) suggested the neutralization factor could be written Verheij et al (1976) have analysed a similar situation in considerably more detail. An overall variation of ion yield with a parameter such as energy, angle of incidence or angle of exit is then fitted by an equation similar to or more complex than equation (lO).…”