Thickness-dependent oxygen chemisorption behaviors on (1 1 1) surfaces of two-dimensional FCC metals Al and Cu: First-principles study

Abstract

Oxygen chemisorption is one of the crucial factors to understand the performance of metal materials under special service environments. Here, we investigate the thickness-dependent O chemisorption behaviors on two-dimensional Al(111) and Cu(111) films based on first-principles calculations. It is found that the charge transfer from substrate to adsorbate O atom is mainly contributed by surface atoms in the Al system, but by surface associated with sub-surface atoms in the Cu system. Moreover, the thickness-dependent surface energy, work function, and O adsorption energy show an approximate three-monolayer oscillation for the Al surface, but not for the Cu surface. It results from quantum size effects (QSEs) in Al, which are related not only to z-direction size but also to wavevector: the QSEs reach their maximum at Γ¯ point resulting from strong interlayer coupling interaction between 3pz orbitals. The oscillations of Al_3pz PDOS mainly contribute to that of TDOS around EF, thus giving an oscillatory energy state contribution to periodic surface energies and reactivities. However, because d-band metals like Cu(111) have complex Fermi surfaces causing incremental Fermi wavelength anisotropy and larger-amplitude fluctuation of Cu_t2g at EF, QSEs will be generally canceled. Our findings may shed light on modeling the chemisorption and intrinsic physical properties, and thereby the distinct surface behaviors of low-dimensional metallic films.