Electronic structure of the K-(root 3 x root 3)R30 degrees on Al(111) at low and room temperature investigated by angular resolved EELS

The electronic excitations of a well ordered K-(root3 x root3)R30 degrees 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 (root3 x root3)R30 degrees occupy the on-top sites and at room temperature (RT) where K atoms in (root3 x root3)R30 degrees 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(I 1 1) surface with a (root3 x root3)R30 degrees 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, (C) 2001 Elsevier Science B.V. All rights reserved.