Nucleation of Pb starfish clusters on the five-fold Al-Pd-Mn quasicrystal surface

Abstract

The nucleation of Pb clusters on the five-fold Al-Pd-Mn quasicrystal surface has been investigated using scanning tunneling microscopy (STM) and ab initio calculations based on density-functional theory (DFT). In the submonolayer regime, Pb atoms are highly mobile and adsorb preferentially within equatorially truncated pseudo-Mackay clusters present at the surface. The decoration of these unique adsorption sites leads to the formation of five-fold islands dubbed "starfish" and eventually to a quasiperiodic Pb monolayer. From a comparison of measured and calculated STM images it is concluded that most starfish clusters on all terraces are composed of ten Pb adatoms. A model of the structure of the starfish cluster has been proposed. Our total-energy calculations confirm its stability. The experimentally measured height profile of the starfish cluster is also reproduced by the DFT calculations. Disciplines Condensed Matter Physics | Metallurgy CommentsThis article is from Physical Review B 79 (2009) The nucleation of Pb clusters on the five-fold Al-Pd-Mn quasicrystal surface has been investigated using scanning tunneling microscopy ͑STM͒ and ab initio calculations based on density-functional theory ͑DFT͒. In the submonolayer regime, Pb atoms are highly mobile and adsorb preferentially within equatorially truncated pseudo-Mackay clusters present at the surface. The decoration of these unique adsorption sites leads to the formation of five-fold islands dubbed "starfish" and eventually to a quasiperiodic Pb monolayer. From a comparison of measured and calculated STM images it is concluded that most starfish clusters on all terraces are composed of ten Pb adatoms. A model of the structure of the starfish cluster has been proposed. Our total-energy calculations confirm its stability. The experimentally measured height profile of the starfish cluster is also reproduced by the DFT calculations.

Aperiodic and modulated Pb thin films on fivefold icosahedral Al-Cu-Fe and Al(111): Tailoring the structure of Pb

“…12,13 The size of the smallest pentagonal Pb feature observed in this study ͑edge length ϳ4.8 Å͒ is similar to what was observed on i-Al-Pd-Mn substrate ͑ϳ4.9 Å͒. The smallest pentagonal structural elements present on the clean substrate have an edge length of 3.0 Å, i.e., smaller than the smallest pentagon within the Pb structure.…”

“…Experiments suggest that these sites correspond to cut cluster sites, similar to previous report on Pb adsorption on the fivefold i-Al-Pd-Mn quasicrystalline substrate. 12 Because these two substrates are isostructural, the observed differences in the growth of the quasiperiodic monolayer must be a consequence of the different chemistry within the surface termination and the associated change in the surface electronic structure. As mentioned above, the quasicrystalline surface terminations consist of two planes separated by only 0.4 Å, the top plane being almost pure Al and the second one containing a higher content of transition metals.…”

“…43,44 The electronic structure of the quasiperiodic Pb monolayer formed on i-Al-Pd-Mn has been investigated by STS and a deep pseudogap in the electron density of states was found at the Fermi level. 12 The probability for electron-hole pair creation decreases exponentially with increasing binding energy and thus correlates with the density of states at E F . Therefore the existence of a pseudogap is consistent with a reduced sticking probability.…”

“…[8][9][10] A true two-dimensional ͑2D͒ quasiperiodic structure has been achieved only for specific elements, typically low melting point elements such as Pb, Bi, Sb, and Sn or rare gases such as Xe. [11][12][13][14][15] First, Franke et al 11 reported evidence for the formation of quasiperiodic Bi or Sb monolayers ͑MLs͒ deposited on either the fivefold surface of the i-Al-Pd-Mn or the tenfold surface of the d-Al-Ni-Co. The quasiperiodic structure of the monolayers was characterized using low-energy electron diffraction ͑LEED͒ and helium atom scattering.…”

“…12 In situ STM experiments clearly show how the quasiperiodic structure of the substrate propagates into the film. The growth proceeds via self-assembly of an interconnected network of small Pb islands with pentagonal shape.…”