The emission of fast secondary atoms from ionically bombarded copper “reflections”

Abstract

Abstract A study was made of the production of fast secondary atoms from copper poly-crystalline and single-crystalline targets. The “reflected” atoms were measured with a secondary emission detector. The targets were bombarded with Ar + ions, mainly at an energy of 15 keV. We found, by application of pulsed ion beam techniques that the energy distribution of the measured atoms has a sharp maximum at the mean value expected for single elastic biparticle collisions. The total yield of these “reflections” was measured as a function of the angle of incidence of the ion beam. It increases much faster than the sputtering ratio and reaches a value of more than 1% of the primary ion beam for very oblique incidence. Experiments on a single crystal show the influence of crystal orientation on the “reflections”. The influence of crystal order is much smaller than the analogous one for sputtering. This shows that the process of sputtering of neutral copper atoms takes place deeper inside the crystal than the emission of fast particles. Most “reflected” atoms were found at a “reflection angle” of 70° with the normal, independent of the angle of incidence of the primary iom. The maximum “reflection” angle will be determined by the surface roughness, which is not strongly dependent on the angle of incidence for polycrystalline targets. An estimate of secondary sputtering due to the “reflections” and the surface roughness gives a yield in the order of 10% of primary sputtering.