High energy ERDA with very heavy ions using mass and energy dispersive spectrometry

Abstract

The capabilities of the elastic recoil detection analysis (ERDA) method for depth profiling are investigated using high energy very heavy ion beams with energies close to the Coulomb barrier from the VICKSI accelerator and mass and energy dispersive recoil spectrometry by means of a time-of-flight energy detector telescope. Due to the unusually high beam energies of the 129Xe and 127I beams of 260 to 420 MeV, which nevertheless remain safely within the Coulomb scattering regime, the high velocities even of heavy recoil ions allow us their detection with unambiguous mass and adequate energy resolution for depth profiling up to depths of e.g. 3–4 μm in Si and 2 μm in GaAs. The concentration profiles of all target elements are measured simultaneously, uniquely resolved, since their isotopic masses are separated at least up to the Ga/As mass range. Typical depth resolutions obtained are comparable with values for RBS. The kinematical shifts between the separate depth profile spectra of the different isotopes of a probed atomic element clearly demonstrate that the depth resolution is reduced if only charges but no masses are resolved unless one isotope dominates.