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 vibra tions on the Ag(110) and the Ag(110)(2 x 1)O surfaces have been studie d by high resolution electron energy loss spectroscopy (HREELS). For A g(110) the energy of the surface phonon resonance around 13 meV decrea ses by 3.4 meV and the intrinsic width increases from 1.1 to 3.4 meV i n 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 eff ects are related to the anharmonicity of the potentials between the vi brating atoms. Our results indicate that on the Ag(110) clean surface the anharmonicity is larger by about a factor of two as compared to th e 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 Spectro sc. Relat. Phenom. 64/65 (1993) 691].