Influence of analyser transmission and detection efficiency on the energy dependence of low-energy ion scattering signals

The signal intensity in low-energy ion scattering depends, among others, on the kinetic energy of the scattered ions. The measured energy dependence is a combination of the intrinsic energy dependence, determined by the ion– sample interaction, and the energy dependence of the instrumental response function. The intrinsic energy dependence is often exploited to obtain information on the charge transfer processes taking place between the ions and the sample surface. The resulting information is of relevance both for quantitative surface analysis as well as for obtaining a fundamental understanding of charge transfer processes. For a correct determination of the intrinsic energy dependence it is crucial that the energy dependencies of the analyser transmission and the ion detection efficiency of the instrument are accurately known. In this paper we outline how these energy dependencies may be obtained, and we present the results for the cylindrical mirror analyser and microchannelplate-based detector in our apparatus. The discussions about the energy dependencies are not specific for our apparatus, but can be applied directly to other cylindrical mirror analysers and channelplate-based detectors. Therefore, the similarities and differences with other types of analysers are briefly discussed. The implications of uncertainties in these energy dependencies for charge-exchange studies and quantitative compositional surface analysis are treated in detail.