The energy evolution of surface plasmons on an oxidized aluminum surface: the role of the atomic polarizability of oxygen adsorbates and the thickness of the oxide layer
The energy evolution of surface plasmons on an aluminum surface during the oxidation process is investigated using electron energy loss spectroscopy (EELS) and x-ray photoemission spectroscopy (XPS). The surface plasmon energy is determined from the location of the surface plasmon loss peak in the EELS spectra; at the same time, the total oxygen coverage (in the submonolayer regime) and the oxide layer thickness (in the multilayer regime) are obtained from the peak profiles of O 1s and Al 2p photoemission lines in the XPS spectra. In the submonolayer regime, the surface plasmon energy slightly decreases with the total oxygen coverage θ when θ ≪ 1, and the rate of decrease becomes larger as θ increases. This behaviour can be explained by a frequency-dependent polarizability model adopted in this work. In the multilayer regime, the surface plasmon energy decreases with the oxide layer thickness dox, and the rate of decrease becomes smaller as dox increases. The behaviour can be interpreted using a classical electromagnetic model. Based on this model, the relative dielectric constant of the oxide layer should be 3.9 ± 0.1 in the energy range of 7-8.5 eV.