Via photoemission from discrete quantum-well valence states and the Li 1s core level, three different types of atom rearrangements are observed for Cu͑111͒/Li. In the monolayer coverage range gradual energy shifts for the core-level as well as a quantum-well state reflect a gradual lateral compression of the Li overlayer as more atoms are adsorbed. The onset of Li substitution and formation of a (2ϫ2) structure when, at RT, monolayer Li coverage is exceeded, is monitored via the disappearance

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... d appearance of quantum-well states characteristic of the adsorbed full monolayer of Li and the part substitutional (2ϫ2) structure, respectively. A splitting of the Li 1s emission peak into a doublet reflects the two different Li sites characteristic of the (2ϫ2) phase. A small energy shift of the quantum-well state ͑25 meV͒ indicates that, if it is cooled ͑170 K͒, the substitutional structure is unstable with respect to Li adsorption.