J. A. Smerdon

Pseudomorphic Growth of a Single Element Quasiperiodic Ultrathin Film on a Quasicrystal Substrate

Surface Science Research Centre and Department of Physics,The University of Liverpool, Liverpool L69 3BX, UKWe have synthesised a thin film of copper with a quasi-periodic structure by the adsorption ofcopper atoms on the five-fold surface of the icosahedral quasicrystal Al-Pd-Mn at room temperature.The quasi-periodicity of the thin film is manifested in low energy electronic diffraction (LEED)measurements and in the existence of Fibonacci relationships between rows of copper atoms imagedusing scanning tunneling microscopy (STM). These findings demonstrate the feasibility of single-element quasi-periodic thin film formation using quasicrystals as templates.

Adsorption of cobalt on the tenfold surface of d-Al72Ni11Co17 and on the fivefold surface of i-Al70Pd21Mn9

The adsorption behaviour of Co on the tenfold surface of d-Al72Ni11Co17 and on the fivefold surface of i-Al70Pd21Mn9 has been studied using scanning tunnelling microscopy (STM), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). The analysis of a distinctive quasiperiodic LEED pattern for coverages from 3–30 ML of Co on d-Al72Ni11Co17 suggests that the Co forms in a pseudomorphic row structure composed of domains of Fibonacci spaced rows having a periodic lattice parameter along the rows of 2.5 ± 0.1 Å. The same structure, though less well-ordered and with a larger lattice parameter, is formed on the fivefold surface of i-Al70Pd21Mn9.

Templated quasicrystalline molecular ordering.

Quasicrystals are materials with long-range ordering but no periodicity. We report scanning tunneling microscopy (STM) observations of quasicrystalline molecular layers on 5-fold quasicrystal surfaces. The molecules adopt positions and orientations on the surface consistent with the quasicrystalline ordering of the substrate. Carbon-60 adsorbs atop sufficiently separated Fe atoms on icosahedral Al-Cu-Fe to form a unique quasicrystalline lattice, whereas further C60 molecules decorate remaining surface Fe atoms in a quasi-degenerate fashion. Pentacene (Pn) adsorbs at 10-fold symmetric points around surface-bisected rhombic triacontahedral clusters in icosahedral Ag-In-Yb. These systems constitute the first demonstrations of quasicrystalline molecular ordering on a template.

The surface science of quasicrystals

The surfaces of quasicrystals have been extensively studied since about 1990. In this paper we review work on the structure and morphology of clean surfaces, and their electronic and phonon structure. We also describe progress in adsorption and epitaxy studies. The paper is illustrated throughout with examples from the literature. We offer some reflections on the wider impact of this body of work and anticipate areas for future development.

Nucleation and growth of a quasicrystalline monolayer: Bi adsorption on the fivefold surface of i-Al70Pd21Mn9

Scanning tunneling microscopy has been used to study the formation of a Bi monolayer deposited on the fivefold surface of

Templated three-dimensional growth of quasicrystalline lead

i{\text{-Al}}_{70}{\text{Pd}}_{21}{\text{Mn}}_{9}

Structure and reactivity of Bi allotropes on the fivefold icosahedral Al-Pd-Mn quasicrystal surface.

. Upon deposition of low submonolayer coverages, the nucleation of pentagonal clusters of Bi adatoms of edge length

Ordering of adsorbed species on quasicrystal surfaces

4.9\text{ }\text{\AA{}}

Nucleation and growth of pseudomorphic monolayers on quasicrystal surfaces

is observed. The clusters have a common orientation leading to a film with fivefold symmetry. By inspection of images where both the underlying surface and the Bi atoms are resolved, the pentagonal clusters are proposed to nucleate on pseudo-Mackay clusters truncated such that a Mn atom lies centrally in the surface plane. The density of these sites is sufficient to form a quasiperiodic framework, and subsequent adsorption of Bi atoms ultimately leads to the formation of a quasicrystalline monolayer. The suggested nucleation site is different from that proposed on the basis of recent density-functional theory calculations.

The memory of surfaces: epitaxial growth on quasi-crystals

Quasicrystals, materials with aperiodic long-range order, have been found in intermetallics, soft materials such as colloids and supermolecules, and also in two-dimensional monolayer films. Here we present the first example of three-dimensional growth of a single-element quasicrystalline film. Using a hitherto unexplored template, the icosahedral Ag-In-Yb quasicrystal, and various experimental techniques combined with theoretical calculations of adsorption energies, we find that lead atoms deposited on the surface occupy the positions of atoms in the rhombic triacontahedral cluster, the building block of the substrate, and thus grow in layers with different heights and adsorption energies. We show that the adlayer-adlayer interaction is crucial for stabilizing this epitaxial quasicrystalline structure. The finding opens an avenue for further investigation of the impact of the aperiodic atomic order over periodic order on the physical and chemical properties of materials.