Surface Characteristics Of Quasicrystalline Materials: An Overview Of Work Conducted At Ames Laboratory

Abstract

AbstractOver the last few years, work in our laboratories in Ames has focussed on elucidating the surface characteristics of Al-based quasicrystalline materials, namely icosahedral (i-) Al-Cu-Fe and i-Al-Pd-Mn. Our work involves the study of the clean surfaces of these materials under ultrahigh vacuum conditions. We find that surfaces cleaned by Ar+ sputtering are depleted in Al relative to the bulk composition. Single grains, after sputtering, undergo a two-stage regrowth process as they are annealed. After heating to about 600 K, a crystalline overlayer is formed. This is rather abruptly replaced at about 750 K by a surface that appears quasicrystalline within the resolution of the experimental techniques used. Calculations based on low-energy electron diffraction (LEED) measurements of this higher temperature state indicate that the Al-rich layers in the bulk model of these materials are the favored surface terminations. Results of low-energy ion scattering (LEIS) corroborate this finding. Consistent with this, we find that the oxidation behavior and general reactivity of these materials are analogous to pure Al.