Electronic structure of quasicrystalline surfaces: Effects of surface preparation and bulk structure

We elucidate the nature of the surface electronic properties of quasicrysta lline Al-Pd-Mn. We do this by using photoelectron and Auger electron spectr oscopies, and by making a variety of comparisons-across types of bulk sampl es, and across methods of surface preparation. The main conclusions are the se: (i) The narrow Mn 2P(3/2) core-level line observed in the icosahedral p hase is a fingerprint of a suppression in the density of states (a pseudoga p) at the Fermi level and is Pot unique to the quasicrystalline phase. It i s also independent of the symmetry of the quasicrystalline surface. The Aug er line shape is also affected and may be used as a fingerprint of a pseudo gap. (ii) A similarly narrow Fe 2P3/2 core-level line characterizes the ico sahedral Al-Cu-Fe quasicrystal, consistent with the expectation that the el ectronic structure is of general importance in the stabilization of icosahe dral phases. (iii) In icosahedral AI-Pd-Mn, the pseudogap of the bulk is no t retained up to the surface immediately after fracture, but can be restore d by annealing, or by sputter annealing to sufficiently high temperatures. Assuming that the pseudogap reflects an electronic stabilization of the ato mic structure, these results suggest that the heat-treated surfaces are mor e stable than the surface obtained by fracturing at room temperature.