Energy-loss straggling of helium projectiles at low kinetic energies

Abstract

Concentration depth profiles at liquid surfaces can be determined by means of neutral impact collision ion scattering spectroscopy. The energy resolution of the spectra is influenced by the energy loss straggling of the projectiles. Energy loss straggling is a measure of the width of the energy loss distribution of particles passing through matter. Knowledge of the energy loss straggling is especially important for determining concentration depth profiles of aqueous surfaces. Here it is shown that the energy loss in the gas phase and the energy loss distribution can be determined with a series of spectra taken at different vapor pressures of the aqueous solution. The projectiles used are $3\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ helium ions. The gas phase causes a shift of the spectra to lower energies and a broadening of the structure due to energy loss straggling. Both the energy loss in the gas phase and the energy loss straggling must be gauged in order to determine concentration depth profiles quantitatively. Knowledge of the energy loss distribution can be used to determine accurate concentration depth profiles by means of deconvolution.