Structural investigation and C ₆₀ adsorption on the (100) surface of a 1/1 pseudo-Tsai-type Au–Si–Ho quasicrystalline approximant

Tsai-type 1/1 quasicrystalline approximants in the Au-Si-RE (RE = Ho, Tb) system are body-centered cubic phases decorated by clusters having their inner part occupied by either a disordered tetrahedron (IT) or a single rare-earth atom (CC). The system investigated in the present study is the Au-Si-Ho(CC) compound having full occupation of the cluster centers by single Ho atoms. We present a detailed study of the structure and reactivity of its (100) surface using scanning tunneling microscopy and X-ray photoelectron spectroscopy. After annealing Au-Si-Ho(CC) between 725 K and 880 K, the surface exhibits a (2 × 2) surface reconstruction. The surface appears to terminate at specific bulk planes intersecting Tsai-type cluster centers. Adsorption of C₆₀ molecules on this surface leads to a film with a hexagonal structure corresponding to a (111) plane of the C₆₀ bulk structure. Compared with a previous report on the (100) surface of the Au-Si-Ho 1/1 approximant having a mixed IT and CC decoration, it appears that cluster center decoration does not affect the surface plane selection rule in Tsai-type approximants. However, the inner decoration affects the atomic structure within the selected surface termination and the structure of C₆₀ thin films formed on these surfaces.