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 of the mesa, characterized by the appearance of populous monatomic-layer-high Pb nano-islands on top of the mesa. The edges of the Pb nano-islands are decorated with Cs adatoms, and the nano-islands 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 nano-islands 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.