Revealing the atomic surface structure of the (100) Y-Al-Ni-Co approximant by low-energy electron diffraction and scanning tunneling microscopy
Physical Review B 81(6): 064201
In this paper we present an investigation of the (100) Y-Al75.8Ni2.1Co22.1 surface, which is structurally and chemically related to the (10000) twofold symmetric surface of the decagonal Al-Ni-Co quasicrystal. The atomic surface structure was probed by low-energy electron diffraction (LEED) and by scanning tunneling microscopy (STM), revealing three different surface terminations and three different types of surface reconstructions. All three terminations were successfully assigned to the densest bulk layers and the origin of the surface reconstructions revealed by LEED could be identified locally by STM. The (100) Y-Al-Ni-Co surface shares with the related (10000) d-AlNiCo quasicrystal surface the strong tendency of reconstruction, which in the former case is occurring along the b axis and in the later along the periodic  direction. Gaining a theoretical understanding of the reconstructions of the (100)Y-Al-Ni-Co surface might therefore help to understand the stability of bulk and surface atomic structures in decagonal quasicrystals. Furthermore, due to the strong relation to the quasicrystalline (10000) d-AlNiCo surface, the crystalline (100) Y-Al75.8Ni2.1Co22.1 surface is now a very promising candidate to study directional anisotropies in epitaxial thin film growth, friction, or the electronic structure, with the advantage of representing a much simpler structure (32 atoms/unit cell) which can be theoretically addressed with less effort compared to its quasicrystalline counter part.