Electron energy loss spectroscopy investigation of volume and surface plasmons at the Al-Pd-Mn fivefold surface

We have measured the electron energy losses on different Al-Pd-Mn quasicrystal surface states established by low energy electron diffraction. X-ray photoelectron spectroscopy and Auger electron spectroscopy. On the well characterized and ordered Al-Pd-Mn quasicrystalline surfaces, the energy loss signal with an energy of incident electrons at 2 keV shows a strong peak at 16 eV and a satellite at about 33 eV. As the electron primary energy is decreased to 260 eV, an energy loss at 10.5 eV is clearly observed. A short ion bombardment (1 mu A at 500 eV during 1 min) erases this loss at 10.5 eV which can be recovered by annealing at 800 K. All these observations are simply attributed to the existence of a bulk plasmon at about 16 eV and a surface plasmon at 10.5 eV. The ratio between these two energies is 1.52. This is quite close to the expected root 2 from the classical plasmon model. On the crystalline partially annealed surface, a bulk plasmon is observed at about 16.5 eV. Oxygen-contaminated surface presents a bulk plasmon shifted towards higher energy of about 20 eV.