Precision measurements of energy losses of He-ions in thin carbon foils

Abstract

Energy loss measurements have been performed with 301 and 610 keV He-ions and 620 keV H-ions in carbon foils for a thickness range of 100–1000 Å. The relative foil thicknesses were calibrated by Rutherford backscattering (RBS) with 1.5 MeV H-ions. For all runs a linear relationship between energy loss and foil thickness was found. An extrapolation to zero foil thickness results in nonzero intercepts for the energy loss of +0.6 keV for 610 keV He + +0.6keV for 610 keV He 2+ and +0.5 keV for 301 keV He + with an experimental error of ± 0.2 keV. For protons, a value of zero for the energy loss intercept lies within the experimental uncertainty. However, SIMS and NRA revealed surface layers of hydrogen accounting for 50% of the intercept for He. The residual intercept which might be due to charge equilibration, surface plasmons or other effects was measured to be 0.37 ± 0.19 keV for 610 keV He, 0.25 ± 0.20 keV for 301 keV He, 0.34 ± 0.37 keV for the mean and 0.02 ± 0.37 keV for the most probable energy loss for 620 keV protons. For the individual targets the difference between mean and most probable energy loss is in good agreement with calculations of Sigmund and Winterbon.