THE WIDTH OF AN RBS SPECTRUM - INFLUENCE OF PLURAL AND MULTIPLE-SCATTERING

The width of RBS spectra from thin films depends on film thickness and stopping power, hence it is possible to determine one of these quantities when the other is known. For low ion energies or large film thicknesses, however, the spectrum shape significantly differs from that obtained by the single scattering calculation normally used. In this contribution, we determine quantitatively the influence of plural and multiple scattering on the width of RBS spectra: we calculate RBS spectra for protons and He ions by Monte Carlo simulation and by an analytical single scattering model using the same stopping power and interaction potential. As a result, quantitative agreement of the Monte Carlo spectra with measurements is found, while the single scattering model fails, especially near the low energy edge and below. Not only the spectrum shape but also the position of the low energy edge is affected by plural and multiple scattering. We determine this shift by varying projectile and target parameters and we find it is mostly governed by the angular width alpha(1/2) of the multiple scattering distribution. In bad cases, the shift may be as large as 3-4% for alpha(1/2) congruent-to 20-degrees.