Crystal to Quasicrystal Surface Phase Transition: An Unlocking Mechanism for Templated Growth

In this experimental work we have studied and characterized a surface phase transition on a decagonal Al72Ni11Co17 sample between a crystalline phase, which is induced by sputtering with energetic noble gas ions, and the bulklike decagonal phase. The surface transition to the stable, quasicrystalline phase was followed as a function of temperature by two complementary techniques: high-resolution X-ray photoelectron spectroscopy (HR-XPS) and low-energy electron diffraction (LEED). The observation of shifts in the core-electron binding energies of the constituent atoms and of other photoemission line shape parameters as the surface undergoes the phase transition and the comparison with the structural information obtained from the LEED data enabled us to determine the evolution of the surface from 5 twinned cubic crystalline domains to the decagonal phase. A quasicrystalline chemical environment with some degree of long-range order is observed for Al before the quasicrystalline surface is fully recovered, pointing to a two-step reordering process, where two sublattices order separately at different temperatures. Strong modifications in the valence band are reflected in the core level binding energies, and the observed reduction in density of states at the Fermi energy for the decagonal phase is consistent with a Hume-Rothery stabilization mechanism