SURFACE ANHARMONICITY - TEMPERATURE-DEPENDENCE OF DIPOLE ACTIVE VIBRATIONS ON AG(110) AND AG(110)(2X1)O

The temperature dependent energy shifts of dipole active surface vibrations on the Ag(110) and the Ag(110)(2 x 1)O surfaces have been studied by high resolution electron energy loss spectroscopy (HREELS). For Ag(110) the energy of the surface phonon resonance around 13 meV decreases by 3.4 meV and the intrinsic width increases from 1.1 to 3.4 meV in the temperature range between 160 and 550 K. For Ag(110)(2 x 1)O the energy of the oxygen stretching vibration around 41 meV decreases by 0.9 meV and that of the surface resonance by 0.8 meV. The measured effects are related to the anharmonicity of the potentials between the vibrating atoms. Our results indicate that on the Ag(110) clean surface the anharmonicity is larger by about a factor of two as compared to the bulk, while bulk-like anharmonicity is observed after completion of the (2 x 1)O reconstruction. These values are in agreement with those observed on Cu(110) by Baddorf and Plummer [Phys. Rev. Lett. 66 (1991) 2770] and on Cu(110)(2 x 1)O by Durr and Baddorf [J. Electron Spectrosc. Relat. Phenom. 64/65 (1993) 691].