The study of metal adsorption and growth processes on quasicrystalline (QC) surfaces is an exciting area of materials science that combines fundamental issues of crystal growth and the unique properties of QC materials. Unlike traditional crystalline substrates, QC surfaces, lacking translational symmetry, provide unusual conditions for the nucleation and formation of metallic nanostructures.
The presented work is devoted to the study of the initial stages of metal film growth on QC substrates, in particular, using the example of the nucleation of metal atoms that form pseudomorphic structures resembling a starfish. The use of scanning tunneling microscopy (STM) and atomic force microscopy (AFM) methods made it possible to visualize the formation of these structures with atomic resolution.
Direct examination of the surface atoms of aluminum on the five-fold face of the icosahedral Al–Cu–Fe alloy demonstrates the formation of pseudomorphic structures resembling starfish in shape. These “starfish” are located in strictly defined places on the quasi-crystalline surface, namely, on areas with lateral faces.
It is assumed that the primary stage of formation begins when an aluminum atom, moving along the surface, enters a vacant area located in the center of the substrate pentagon. Then the structure grows by successively adding five aluminum atoms, which tend to occupy the nodes of the crystal lattice.
A characteristic feature is that these six-atom starfish-like structures do not expand as the coating increases, resulting in the formation of uniformly sized islands and premature surface roughening.
It was observed that metal atoms deposited on the QC surface do not tend to form traditional crystalline islands. Instead, they show a tendency to self-organize, forming radially diverging “rays” emanating from the center of the seed cluster. These “rays” consist of individual chains of atoms arranged along specific directions related to the local atomic structure of the QC surface.
The formation of the pseudomorphic “starfish” structure is probably due to the interaction between the metal atoms and the CC substrate, as well as the lateral interaction between the metal atoms. The CC surface, with its complex atomic structure and lack of translational symmetry, provides many potential adsorption sites with different binding energies. This leads to the metal atoms being selectively adsorbed on certain sites, forming preferred growth directions.
Author: T. Caia1, J. Ledieu, R. McGrath, V. Fournée, T. Lograsso, A. Ross, P. Thiel
Institute: Ames Department of Chemistry and Laboratory, Iowa State University, Ames, IA 50011, USA, Surface Science Research Centre, University of Liverpool, Liverpool, L69 3BX, UK, Department of Chemistry, Department of Metallurgy and Ceramics, and Ames Laboratory, Iowa State University, Gilman Hall, 1605, Ames, IA 50011, USA