Structure of the Al_2Cu(001) and Al_9Co_2(001) surfaces: role of the covalent-like bonding network and off-stoichiometric effects

摘要

The Al_2Cu and Al_9Co_2 intermetallic compounds share structural similarities: they are both described 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 Al_2Cu and Al_9Co_2 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 Al_9Co_2 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 Al_2Cu and Al_9Co_2 are discussed.