Surface dynamics of Mo(110)-H and Mo(110)-Li

We compare the surface dynamics of the adsorbate systems Mo(110)-H and Mo(110)-Li. In both cases electron energy loss spectroscopy measurements revealed strong substrate surface phonon anomalies. Whereas the phonon anomaly of the hydrogen-covered surface was unequivocally assigned to be of the Kohn type, the anomalous behavior of the surface phonons of the lithium-covered surface remained obscure. In this paper we develop an experimental criterion based on the dispersion of adsorbate phonons, which allows to decide whether the observed substrate surface phonon anomaly is of the Kohn type or not. Employing this criterion we now definitely rule out that the anomaly on Mo(110)-Li is due to the Kohn effect. (C) 2003 Elsevier Science B.V. All rights reserved.