Structure of the Al2Cu(001) and Al9Co2(001) surfaces: role of the covalent-like bonding network and off-stoichiometric effects

Abstract

ABSTRACTThe Al2Cu and Al9Co2 intermetallic compounds share structural similarities: they are bothdescribed in terms of coordination polyedra with a tetragonal symmetry and covalent-like bonding occur in both compounds. In this paper, the (001) surface structure of Al2Cu and Al9Co2 is described based on a combined scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), X-ray and ultraviolet photoemission spectroscopy (XPS and UPS) and density functional theory (DFT) study. Surface models are elaborated from stoichiometric ideal compounds, leading to a pure aluminium plane as the surface termination in both cases. The nature of the constitutional defect in Al9Co2 is determined using density functional theory calculations. The influence of the surface atomic density, of the surface composition and of off-stoichiometric effects on the (001) surface structures of Al2Cu and Al9Co2 are discussed.