The introduction of new materials with unique properties, such as quasicrystals (QCs), opens up prospects for their application in various fields, including catalysis, thermoelectric devices, and protective coatings. Understanding the growth mechanisms of thin films on QC substrates is critical for the controlled creation of materials with desired characteristics.
In this paper, we present the results of kinetic Monte Carlo (KMC) simulations of the deposition of aluminum (Al) on the surface of Al–Cu–Fe QCs with 5-fold symmetry. The lattice gas model with a disordered bond network allows us to take into account the complex structure of the QC substrate, characterized by the absence of translational symmetry and the presence of a hierarchical structure.
The QMC modeling was performed taking into account the following elementary processes: adsorption of Al atoms from the gas phase, surface diffusion and desorption. The activation energies for these processes were estimated using density functional theory (DFT) methods for different positions of Al atoms on the QC surface.
Previous studies using scanning tunneling microscopy have shown the formation of pseudomorphic starfish-like structures during the early stages of aluminum deposition on the five-fold icosahedral surfaces of Al–Cu–Fe quasicrystals at the atomic level. To simulate this phenomenon, we first establish suitable five-fold surface terminations of Al–Cu–Fe based on a bulk structure model and generate corresponding potential energy surfaces for Al adsorption on these terminations.
We then construct a “disorganized bond network” (DBN) linking nearby local Al adsorption sites on Al–Cu–Fe and determine the binding energies of these sites as well as the energy barriers required for the movement of Al adatoms between neighboring sites. We take into account the adsorbate–adsorbate Al–Al interactions that contribute to the stabilization of the islands. Then, using the lattice gas model of the DBN, we simulate the deposition and diffusion of Al on Al–Cu–Fe. We analyze the competition between complete starfishes, incomplete starfishes (acting as deep potential well traps for diffusing Al), and isolated traps in the context of heterogeneous nucleation and aggregation of Al into islands.
The simulation results showed that the deposition of Al on the QC substrate leads to the formation of islands. The density, size and shape of the islands depend on the substrate temperature and the deposition rate. At low temperatures, numerous small islands are formed, while at high temperatures, large islands with a more complex morphology predominate. The disordered structure of the QC surface leads to the formation of islands with irregular boundaries and different orientations.
The obtained results allow us to better understand the mechanisms of thin film growth on QC substrates and can be used to optimize deposition conditions in order to obtain films with desired properties.
Author: C. Ghosh, Da-Jiang Liu, K. J. Schnitzenbaumer, C. J. Jenks, P. A. Thiel, J. W. Evans
Institute:
Departments of Chemistry and Mathematics, and Ames Laboratory – U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA