MARLOWE simulations of He and Ne ion scattering on CuAu(100) and comparison with TOF-ISS experiments

We investigated the CuAu(100) surface structure with TOF-ISS [1-3]. This provided evidence for a bulk truncated structure, with a first layer containing Cu and Au in equal proportions and a second layer containing only Cu. The topmost layer is rippled, with Au atoms lying 0.12 Å above the Cu atoms. A better understanding of the signal origin requires the use of the MARLOWE simulation code. The spectra are first simulated and then decomposed into their layer contributions. The agreement between experimental and simulated spectra is pretty good. The large differences in the 1 keV He spectrum shape along the 〈100〉 and the 〈110〉 directions are reproduced by simulation. With 2 keV Ne the simulations clearly demonstrate that the second layer is directly reached by the beam along the 〈110〉 direction but not along the 〈100〉 direction. The surface model proposed from the experiments is then fully confirmed by the simulations.