SAMPLING DEPTH OF TIME-OF-FLIGHT ION-SCATTERING - PRIMARY ION TYPE AND ENERGY-DEPENDENCE

The sampling depth dependence on the type and energy of the primary ion used in time-of-flight scattering spectrometry has been investigated. Incident angle alpha-scans were made at various scattering angles-theta along the [11BAR0] and [001] azimuths of an Ir{110} surface using 4 keV Ar+, Ne+, and He+ and 2 keV Ne+ ion beams. The scattering patterns observed in the scans exhibit strong dependences on ion type and energy. The results show that surface-layer scattering dominates for 4 keV Ar+ and 2 keV Ne+, subsurface layer scattering dominates for 4 keV He+, and 4 keV Ne+ probes mainly the surface layer at low-alpha and subsurface layers at high-alpha. These differences are due mainly to variations in the size of the shadowing and blocking cones and the energy separation of quasi-single scattering with respect to multiple scattering events. Classical trajectory simulations are used to model selected interactions.