REVERSAL OF AN ADSORPTION-SUBSTITUTION STRUCTURE CHANGE FOR LI CU(111) INDUCED BY O-2 OR H2O EXPOSURE/

Previous work shows that alkali-metal atoms may change position on a m etal substrate from adsorptional to substitutional sites if a critical coverage is exceeded, one case being Li/Cu(111) at room temperature. For this system we observe also the reversed change, which occurs upon a small exposure to oxygen or water vapor. The observations, made by low-energy electron diffraction and photoemission, suggest that the st ructure preferred is reversibly dependent on the surface content of ne utral Li atoms. [S0163-1829(98)05604-5].