Scanning tunneling microscopy (STM)/local tunnneling barrier height (LBH) studies on Cs adsorption on a Pt(111) surface

The initial stage of Cs adsorption and the formation process of a Cs monolayer on a Pt(111) surface, as well as the variations of the local work function, are investigated by scanning tunneling microscopy (STM) and local tunneling barrier height (LBH) imaging. The STM/LBH images of the surface with a small amount of Cs adsorbate indicate increases in local density of states (LDOS) and LBH near the Cs adsorption sites, which are considered to provide a long-range effect of the Cs adsorption. At the Cs coverage of about 0.1, small (2 x 2) patches are seen throughout the surface, but they are so unstable that the Cs atoms in the patches diffuse to form stabilized patches at room temperature. With increasing Cs coverage, the area covered by the stabilized (2 x 2) patches increases. The stabilized (2 x 2) structure gives low LBH values and large atomic corrugations. The charge density in this structure is considered to be strongly localized due to the bond formation between Cs and Pt. This induces a strong surface dipole, resulting in a large work function reduction.