A practical guide to interpreting low energy ion scattering (LEIS) spectra

Low-Energy Ion Scattering (LEIS) spectrometry is extraordinarily sensitive and specific to the outermost atomic layers of materials. It is a powerful tool for surface science. Here, we present a practical guide on LEIS spectral interpretation that is based on actual LEIS spectra of a variety of materials. While this article covers some of the theory of LEIS, it is not an exhaustive description of this aspect of the technique. Rather, it is intended for the broad community of scientists who, while not necessarily active users of LEIS instruments, need LEIS in their research, perhaps obtaining LEIS spectra by collaboration or encountering it in the scientific literature. The spectra/experimental results we present reflect both basic and advanced features of LEIS. We believe this guide is quite comprehensive. Most of the spectra shown herein were obtained on a modern high sensitivity (HS)-LEIS instrument. The analyser of this instrument defines and fixes a scattering angle of 145 degrees. However, these results are representative of other widely used geometries. The features of these spectra are quite general. Key concepts covered in this work include surface peaks, elements that promote reionization, double and multiple scattering/ collisions, quantification with reference materials, the effect of contamination, differences between particulate and crystalline materials/surfaces, direct scattering from the second atomic layer of a material, and the use and effects of different primary ions, e.g., He+, Ne+, and Ar+. The LEIS spectra shown and discussed in this work come from different materials, including as-received, clean, and oxidized Cu, silicone rubber, Ca evaporated onto SiO2, Al, graphene on Cu, Fe, Rh, FeRh, CaF2, native silicon oxide (SiO2) on silicon, BeO, B2O3, Bi2Se3, Teflon (polytetrafluoroethylene), LiF, SrTiO3, an alloy with five elements (Cr, Mn, Fe, Co and Ni), and Au. Many of these materials are of substantial technological interest.