Compositional and structural changes in i-AlPdMn quasicrystals induced by sputtering and annealing: A medium energy ion scattering study

The five-fold surface of an Al70Pd21Mn9 quasicrystal has been studied under a variety of surface preparation conditions using medium energy ion scattering. Argon ion sputtering of the surface was seen to give rise to Mn depletion and the formation of a thick five-domain AlPd(1 1 0) layer with 〈1 0 0〉 azimuths oriented close to, but not exactly on the five-fold symmetric directions of the substrate. Annealing to just 450 °C was sufficient to restore the Mn content and the icosahedral structure in the surface and near-surface region. Annealing to increasingly higher temperatures was seen to cause Mn enrichment in the surface region above the ideal composition for icosahedral structure and this was accompanied by increased amounts of disorder in the sample. For the highest temperature anneals the surface showed low apparent roughness and exhibited blocking patterns consistent with a contraction of the outermost layer of atoms in line with previous studies of this material.