Quantitative ion beam analysis of ultra thin films with magnetic spectrometers using heavy MeV ions

The aim of a combination of magnetic spectrometers with ion beam analysis techniques is to measure concentration profiles in thin layers with sub-nanometer depth resolution. For these measurements heavy ions from a MV-ion accelerator are directed to the sample. Scattered primary ions or ejected recoil atoms are detected and energy analysed under forward angles. The depth resolution depends directly on the energy resolution of the spectrometer. High energy resolution can only be obtained using magnetic particle spectrometers, where the energy measurement is transformed into a position measurement at the focal plane.
The depth scale is provided by the stopping power of energetic heavy ions moving in matter. The yet produced data are only valid for dynamic charge state equilibrium due to electron loss and capture along the ion trajectory. In the case of ultra thin layers the path length of the particles are too short to achieve this equilibrium. Since magnetic spectrometers separate particles with identical energy but different charge states, it is necessary to consider charge state dependent stopping cross sections for quantitative data analysis. Here only very few data are available in the literature.
In this work, we introduce quantitative ion beam analysis of ultra thin films with magnetic spectrometers.
1. the Quadruple-Quadrupole-Dipole-Sextupole spectrometer “Little John” to measure concentration profiles and charge state distribution of light ions.
2. The Browne-Buechner spectrometer, which is designed to measure samples with heavy atoms.