A SCANNING-TUNNELING-MICROSCOPY STUDY OF THE ADSORPTION OF XE ON PT(111) UP TO ONE MONOLAYER

The adsorption of Xe on Pt(111) has been investigated from the arrival of the very first atoms up to completion of the monolayer using a var iable-temperature Scanning Tunneling Microscope (STM). Surprisingly, i n the initial stages of the adsorption Xe preferentially binds to a lo w coordination site, the upper edge of the platinum steps. The strong binding to these sites leads to a local repulsive interaction with fur ther Xe atoms. Therefore, the Xe atoms located at the upper edge of th e steps do not serve as nuclei for 2D Xe islands, which, instead, form on the terraces and at the lower edges of the platinum steps. Only du ring completion of the monolayer do these islands make contact with th e atoms adsorbed at the beginning in the upper-edge positions. The ful l monolayer exhibits the Hexagonal Incommensurate Rotated (HIR) phase already known from earlier helium-diffraction experiments.