Adsorbate-induced restructuring of Pb mesas grown on vicinal Si(111) in the quantum regime

Using scanning tunneling microscopy and spectroscopy, we demonstrate that the adsorption of a minute amount of Cs on a Pb mesa grown in the quantum regime can induce dramatic morphological changes in the mesa, characterized by the appearance of populous monatomic-layer-high Pb nanoislands on top of the mesa. The edges of the Pb nanoislands are decorated with Cs adatoms, and the nanoislands preferentially nucleate and grow on the quantum mechanically unstable regions of the mesa. Furthermore, first-principles calculations within density-functional theory show that the Pb atoms forming these nanoislands were expelled by the adsorbed Cs atoms via a kinetically accessible place-exchange process when the Cs atoms alloyed into the top layer of the Pb mesa.