Energy-loss straggling of helium projectiles at low kinetic energies: Deconvolution of concentration depth profiles of inorganic salt solutes in aqueous solutions

Neutral impact collision ion scattering spectroscopy allows to determine concentration depth profiles. The method makes use of the energy loss of projectiles passing through matter to gain the depth information. The energy losses of the projectiles obey a statistical distribution, the energy-loss straggling. The energy-loss spectra are mainly given by the energy-loss straggling and the concentration depth profiles. Knowing the energy-loss straggling quantitatively makes it possible to deconvolute the energy-loss spectra. Here we use the Poisson distribution to describe the energy-loss straggling. The Poisson distribution and a previously developed method are used to deconvolute the energy-loss spectra of iodide of aqueous LiI solutions with concentrations between 5 and 7.2m. The iodide concentration depth profiles of these highly concentrated solutions are monotonous and do not show a local maximum near the surface.