Structure determination of the Cu(100)c(2x2)-Mn and Cu(100)c(2x2)-Au surface alloy phases by medium-energy ion scattering

The substitutional surface alloy phases Cu(100)c(2 x 2)-Mn and Cu(100)c(2 x 2)Au have been investigated by medium-energy ion scattering (MEIS) using 100 keV H+ ions. Blocking patterns in the scattered ion yield have been measured for [(111) over bar] [<(12)over bar0>] and [<(13)over bar0>] incidence geometries. Simulations of these blocking patterns have been performed for a range of trial structures and the optimum values of the structural parameters obtained are compared with those available from earlier low-energy electron diffraction (LEED) and photoelectron diffraction (PhD) investigations. The MEIS results confirm the presence of rumpling in the outermost alloy layer, with corrugation amplitudes of 0.37 +/- 0.06 Angstrom and 0.06 +/- 0.04 Angstrom for the CuMn and CuAu surface alloys respectively. This result supports the previously reported anomalously large corrugation for Cu(100)c(2 x 2)-Mn which has been attributed to the local high-spin state of the Mn atoms.