ANHARMONICITY AND VIBRATIONAL-RELAXATION ON THE CU(110)-(2X1)-O SURFACE

The temperature-dependent energy shift and broadening of surface vibrations on the Cu(110)-(2 x 1)-O reconstructed surface have been studied between 100 and 600 K using high-resolution electron energy loss spectroscopy. Atomic motions involved in the observed vibrations were extracted from phonon slab calculations. The measured energy shifts are directly related to the anharmonicity of the potentials between the vibrating atoms and can be modeled with a simple Morse oscillator. By comparing to bulk phonon measurements, we find that both the oxygen-copper and copper-copper bonds at the surface have bulk-like anharmonicity. This is in contrast to the clean Cu(110) surface where strong anharmonicity is observed. Broadening observed in the oxygen-copper surface vibration can be explained by energy relaxation due to substrate anharmonicity.