A comparison of helium ion and fast atom scattering from copper surfaces

Abstract

Low energy ion scattering from surfaces is an established technique, which gives unique information from the first two atomic layers of a surface. A high flux of ions employed in such technique will change the nature of the surface in a number of ways, such as preferential sputtering, chemical damage and charging effects, particularly in insulating and semiconducting samples. A time-of-flight fast atom spectrometer with a pulsed ion/fast atom source (energy range of 100–5000 eV) has been developed to overcome these disadvantages. In this study, spectra of He scattered from both ‘ion-cleaned’ and ‘ion-cleaned and heated’ polycrystalline copper surfaces, bombarded with either ions or fast atoms were monitored for incident angles ranging from 5°–80° with a constant scattering angle of 90°. For the ‘ion-cleaned’ surfaces, spectra of both ion and neutral projectiles show that the technique is sensitive to the outermost surface atomic layer, but that fast atom bombardment seems the more surface specific. For the ‘ion-cleaned and heated’ surface, spectra of both projectiles are qualitatively identical. But small differences of peak energy were observed and may be explained in terms of an electronic stopping process.