K adsorption on Ag(110), effect on surface structure and surface electronic excitations

The growth of K adlayers on Ag(110) was studied by energy loss spectroscopy -low energy electron diffraction (ELS-LEED) which allows the analysis of bo th elastically and inelastically scattered electrons. Ordered (1 x n) missi ng row reconstructions and disordered adsorption were investigated. We find that extended surface reconstruction takes place already at 3% K coverage generating a (1 x 3) missing row structure. Elastic spot profile analysis s hows that a long range correlation between K adatoms is present along the [ <1(1)over bar>0] direction on the reconstructed surface, implying the stabi lization of the reconstruction also at long distances from the K adatoms. W ith increasing coverage [(1 x 2) and (1 x 3) structures] the distance betwe en the K adatoms along [<1(1)over bar>0] decreases and the adsorption sites become correlated also along [001] in contrast with the behaviour of K on Ni, Cu and Pd. For disordered K adsorption we observe that a weak correlati on between the adatoms along both directions is already present in the back ground. The inelastic intensity shows only one marked loss at the surface p lasmon frequency, indicating that in the investigated coverage range both K -induced s and p levels are empty. Ag surface plasmon dispersion and dampin g are affected by the presence of K in accord with the electronic mechanism generating the reconstruction. For the ordered (1 x n) reconstructions the structural anisotropy is enhanced, while the anisotropy of Ag surface plas mon dispersion is reduced. K adsorption strongly affects in particular the quadratic term of the dispersion along [001], which drops by 60% already at 3% K coverage while the linear term remains initially unaffected independe ntly of surface reconstruction. Above 30% K coverage also the linear term d ecreases and the anisotropy present for the surface plasmon dispersion of t he bare Ag(110) is removed. (C) 1999 Published by Eisevier Science B.V. All rights reserved.