STRUCTURE CHANGES FOR CU(111) LI OBSERVED VIA DISCRETE QUANTUM-WELL STATES/

Via photoemission in the near UV from discrete quantum well states, fo ur different types of atom rearrangements are observed for Cu(111)/Li. In the monolayer range a gradual energy shift reflects a gradual comp ression of the Li layer as more atoms are adsorbed. The onset of Li su bstitution and formation of a (2 x 2) structure when, at RT, monolayer Li coverage is exceeded is monitored via the appearance of a quantum well state characteristic of the new phase. A small energy shift indic ates that, if it is cooled (170 K), the new structure is unstable with respect to Li adsorption. Finally, an energy downshift with increasin g coverage observed for a state characteristic of 2 ML Li is ascribed to an increasing area for one-atomic-layer-high islands formed by Li a toms on top of the first full layer.