Observation of a first-order phase transition in Xe/Ta(110) by photoelectron spectroscopy

A photoemission study of submonolayer coverages of Xe on the Ta (110) surface, at temperatures around 20 and 80 K, is presented. We argue that at low coverages, less than {}15%, the Xe atoms occupy the ``deep'' sites on the surface, presumably in a disordered fashion. When the coverage is increased, the Xe atoms start forming islands at elevated positions above the Ta surface as the interaction between Xe forms a denser phase. Different local work functions in the two phases make it possible to study this first-order phase transition by photoelectron spectroscopy.