X-ray photoelectron studies of near surface oxidation and plasmon excitation in spatially confined bi- and tri- layers periodic multilayer mirrors

Highlights: • X-ray photoelectron excited plasmon of Si and Be in bi- and tri- layers structure • Confinement of plasmon oscillation in spatially confined layers • Plasmon excitation of conduction electron in Be and valence electron in Si layers • Near surface oxidation of periodic multilayer structures The alternate bi- and tri- layers nanoscale periodic multilayers of Mo/Si, Mo/Be and Mo/Be/Si are useful for the high reflectivity mirrors, operating effectively around 13.5 nm of wavelength. In X-ray photoelectron spectroscopy (XPS), binding energy shift of BeO was observed in the Mo/Be structures. However, the chemical shifts of BeO and SiO₂ was observed in the Mo/Be/Si multilayer structures. These evidences have indicated the near surface oxidation of multilayers. In the spatially confined layers, the plasmon was excited by the inelastic scattering of Mo4p photoelectrons, generated by the AlK_α X-ray radiation of XPS. In the periodic multilayers, the plasmon was excited at higher energy as compared to the bulk counterpart, which was associated to quantum confinement of the condensed Si and Be nanolayers. In the bi- and tri- layers, the quantum confinement of plasmon in the Si nanolayer was fundamentally described by the density of valence electron and energy width of the band gap. However, in the bi- layer of Mo/Be, the plasmon shift of metallic Be layer was associated to confinement of the conduction electron density.