FIVEFOLD SURFACE OF QUASI-CRYSTALLINE ALPDMN - STRUCTURE DETERMINATION USING LOW-ENERGY-ELECTRON DIFFRACTION

The atomic structure of the fivefold symmetric quasicrystal surface of icosahedral AlPdMn has been investigated by means of a dynamical low- energy-electron diffraction (LEED) analysis. Approximations were devel oped to make the structure of an aperiodic, quasicrystalline surface r egion accessible to LEED theory. A mix of several closely similar, rel axed, bulklike lattice terminations is favored, all of which have a de nse Al-rich layer on top followed by a layer with a composition of abo ut 50% Al and 50% Pd. The interlayer spacing between these two topmost layers is contracted from the bulk value by 0.1 Angstrom, to a final value of 0.38 Angstrom, and the lateral density of the two topmost lay ers taken together is similar to that of an Al(111) surface. The LEED structural result is qualitatively consistent with data from ion scatt ering spectroscopy, which supports an Al-rich termination.