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

TL;DR

This study uses scanning tunnelling microscopy to investigate how bismuth atoms form a quasicrystalline monolayer on a five-fold surface of an i-Al70Pd21Mn9 alloy, revealing nucleation on specific pseudo-Mackay clusters.

Contribution

It provides direct experimental evidence of Bi monolayer nucleation and growth mechanisms on a quasicrystalline surface, challenging previous theoretical models.

Findings

Bi forms pentagonal clusters with 4.9 Å edge length.

Clusters nucleate on pseudo-Mackay clusters with central Mn atoms.

The resulting film exhibits five-fold quasicrystalline symmetry.

Abstract

Scanning tunnelling microscopy has been used to study the formation of a Bi monolayer deposited on the five-fold surface of i-Al70Pd21Mn9. Upon deposition of low sub-monolayer coverages, the nucleation of pentagonal clusters of Bi adatoms of edge length 4.9 A is observed. The clusters have a common orientation leading to a film with five-fold symmetry. By inspection of images where both the underlying surface and the Bi atoms are resolved, the pentagonal clusters are found 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 initial nucleation site is different to that proposed on the basis of recent density functional theory calculations.