Bulk and surface structure of the clean and adsorbate-covered decagonal Al–Co–Niquasicrystal

Abstract

We review our Al adsorption experiments on the tenfold-symmetry surface of the decagonalAl–Co–Ni quasicrystal and present computational simulations of adsorption on a structuralmodel based on a fundamental Al–Co cluster with 20 Å diameter, symmetry , and 8 Å periodicity. This cluster is the building unit ofτ2-Al13Co4, from which, by a sequence of minor changes, the structures of the phases in the stabilityregion of decagonal Al–Co–Ni can be derived. The model used for the decagonalAl70Co15Ni15 is an idealized model with a two-layer periodicity (4 Å) and no chemical or structuraldisorder. We find that the bulk and surface properties of this model are in good agreementwith experiments. Our molecular-dynamics simulations of Al adsorption reproduce theexperimental results and show that by varying the thermal relaxation rates of the adsorbedlayer, a variety of different surface morphologies can be achieved. We also present ourrecent experiments on dissociative adsorption of oxygen on the decagonal surface.