Adsorption of lithium on Mo(110): an EELS study of the adsorbate vibrations and substrate phonons

Electron energy loss spectroscopy (EELS) was used to investigate the vibrat ions of lithium adsorbed on Mo(110) at T=110 K. The frequency of the perpen dicular Li vibration was found to be 312 cm(-1) at low coverage, reaches a maximum of 342 cm(-1) at a coverage of 1/3, then drops to 307 cm(-1) at 1 M L coverage. With the completion of the second monolayer the frequency shift s upwards to about 350 cm(-1). The loss intensity (relative to the elastic peak) was found to have a maximum at 0.2 ML. At 1 ML coverage, the loss pea k shows an asymmetric Langreth line shape indicative of a strong coupling t o electron-hole pair excitations. For the same coverage range the dispersio n curve of the Rayleigh wave along the direction displays an anomalous, bro ad dip. The dip is possibly a Kohn anomaly due to Fermi surface nesting, as found for the hydrogen-covered Mo(110) surface. (C) 2000 Elsevier Science B.V. All rights reserved.