Angular distributions of sputtered Mo and Ag during He + and Ar + ion bombardment

Abstract

Angular distributions of sputtered particles have been measured by collecting the particles on a semi-circular collector, and then analysed by the Rutherford backscattering (RBS) method. Mo and Ag targets were bombarded by He + and Ar + ions and the energy range was 15–80 keV. The ion beams were in all cases directed perpendicular to the bombarded surfaces. Deviations from a simple cosine distribution were observed and a significant energy dependence was found in the case of Ar + irradiations. For Ar + on an Ag target the measured angular distribution was close to a cos 2 function. For a reliable angular distribution measurement the sticking probability is an important factor. The RBS method, used for the analysis of the collector, gives quantitative results and makes it possible to measure the sticking probability which was found to be close to unity for an aluminium collector. Its dependence on the temperature of the collector was also investigated. The targets were mounted in an UHV target chamber (basic pressure 1 × 10 −9 Torr), and a movable shutter in front of the collector made it also possible to sputter-clean the targets before starting the measurements. Only relatively low beam doses were used in order to avoid topographical changes of the surface which might disturb the angular distribution of the sputtered material.