Enhanced anharmonicity in the interaction of low-Zadsorbates with metal-surfaces

Abstract
Temperature-dependent surface extended x-ray-absorption fine-structure (SEXAFS) measurements on half a monolayer of O and N atoms on Ni(100) and Cu(100) surfaces indicate enhanced anharmonic contributions in the adsorbate-substrate pair potential, with respect to bulk values. From the temperature dependence of the SEXAFS amplitude and phase we calculate the thermal expansion coefficients. These coefficients are found to be enhanced independent of the system, establishing the observed anharmonicity as a general surface-related property. The implications of these findings for surface reconstructions are discussed.