A procedure to determine electronic energy loss from relative measurements with TOF-LEIS

The electronic stopping cross section of protons in polycrystalline Ge is deduced from TOF-LEIS measurements using an amorphized Ge wafer and a thick Cu reference sample. The evaluation is based on the comparison of height ratios of backscattering spectra from both, experiment and Monte Carlo simulations, which allow for multiple scattering of the protons in the sample. This procedure yields the electronic stopping cross section of Ge for protons with a relative uncertainty of less than 10% per data point. In the velocity regime 0.07–0.56 a.u., corresponding to proton energies in the range 120 eV–8 keV, the electronic stopping cross section is linear in the ion velocity. Extrapolation of the data yields a velocity threshold of vth = 0.0274 a.u. ± 10%. At velocities below 0.18 a.u., i.e. at proton energies below 810 eV, electronic stopping in Ge is – compared to Cu – found to be more efficient by up to a factor of 2.6.