Fivefold i-Al-Pd-Mn surface as template for growing monatomic quasiperiodic layers: First-principles simulations for adatoms from groups one to three

By using ab initio density-functional calculations, we have explored the conditions for the formation of quasiperiodic overlayers on top of a fivefold surface of an icosahedral Al-Pd-Mn quasicrystal. We calculate binding energies of single adatoms at special sites of the surface, with the aim to construct the potential-energy landscape of the quasiperiodic surface. We show that the energetically favorable adsorption sites are located at the vertices of a DHBS tiling [consisting of decagons (D), hexagons (H), boats (B), and stars (S)] describing the quasiperiodic ordering of the surface. An idealized structural model for the adlayer is constructed by decorating the interior of these tiles such that atoms are placed again in energetically favorable locations and that the local arrangement does not break the fivefold symmetry of the underlying substrate. The stability of this idealized structure is probed for elements from groups one to three of the Periodic Table by performing a conjugate-gradient relaxation under the action of the ab initio calculated forces. We demonstrate that in addition to a strong binding of the adatoms to the substrate, the size of the adatoms and the achievement of a dense surface coverage are the most important factors influencing the stability of quasiperiodic ordering in the adsorbed monolayer. From the analysis of the geometrical distribution of the adsorption sites, we conclude that a dense quasiperiodic overlayer with a density of 0.066atoms/Å2 (corresponding to a coverage Θ≈0.50 monolayers) can be formed by adatoms with an atomic size of 3.7ű0.4Å. Atoms with this size are Na, Ca, Y, and La. We suggest that these elements and presumably also most rare-earth elements are good candidates for the formation of highly regular quasiperiodic adlayers with a structure described by a decagonal DHBS tiling consisting of decagons, hexagons, boats, and pentagonal stars.