Electronic structure of the K-(√3×√3)R30° on Al(1 1 1) at low and room temperature investigated by angular resolved EELS

The electronic excitations of a well ordered K-(√3×√3)R30° on Al(1 1 1) were investigated by using the angular resolved energy loss spectroscopy technique. Measurements were performed at low temperature (LT) where K atoms in the (√3×√3)R30° occupy the on-top sites and at room temperature (RT) where K atoms in (√3×√3)R30° are in substitutional sites. We found that the structural changes induce significant variation in the loss spectra. The excitation spectrum in the RT phase is ascribed to single-particle transitions involving states of the Al(1 1 1) surface with a (√3×√3)R30° vacancy structure; a new peak at 7.2 eV is interpreted as a multipole plasmon mode coming from the charge density profile predicted by calculations for the alloy surface phase. On the contrary, spectra in the LT exhibit single as well as collective excitations coming from states derived from the K adsorbate.