Structural transitions at the surface of the decagonal quasicrystal Al–Co–Ni

At the 2- and 10-fold-symmetry surfaces of the two-dimensional quasicrystal Al–Co–Ni an epitaxial cubic layer is induced by preferential sputtering of Al using Ar+ ions. Annealing the sample at 760 K restores the Al concentration at the surface and, thereby, the quasicrystalline structure. Simultaneous observations of the surface chemistry by Auger electron spectroscopy and of its atomic structure by secondary-electron imaging reveal that the transition is a two-step process. The replenishment of Al at the surface is limited by high-temperature mediated diffusion of Al from bulk, while the assembly kinetics of the quasicrystalline structure proceeds at lower temperatures. Thus, the underlying bulk Al–Co–Ni quasicrystal acts as an Al reservoir and as a structural template for the recovery of the quasicrystal. The paper also presents a discussion of different cubic orientations of the surface phase formed by different sputtering conditions.