Experimental study and computer simulations of the energy loss straggling of slow ions in thin foils: Results for H+ and D+ in C, Si, Cu, Ag and Bi

We present an experimental and computer simulation study of the energy loss straggling of low energy (2-10 keV) proton and deuteron beams in C, Si, Cu, Ag and Bi. The measurements were done using the transmission technique with several self-supporting foils with thicknesses in the range of 13-25 nm. The computer simulations were based on a Monte Carlo code which provides a method to analyze in detail the influence of various effects, such as foil roughness and slowing down of the ions in the medium. The theoretical model for the stopping and straggling coefficients is based on the Density Functional Theory. The results of the simulations yield a good agreement with the experimental values for the total straggling, taking into account the target roughness which significantly increases the measured energy widths. Within the experimental uncertainties the results show a linear dependence of the energy loss straggling with the projectile velocity and no isotopic effects. The results clearly indicate that a quantitative analysis of the energy loss straggling in this energy range requires a careful evaluation of the foil roughness effect.