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

Abstract

Using scanning tunneling microscopy (STM) and first-principles calculations within density functional theory (DFT), we study the effect of Cs adsorption on the energy landscape of ultrathin Pb films on vicinal Si(111) substrates in the quantum growth regime. As the Cs coverage increases, a dramatic morphological evolution takes place on the initially flat-top nanomesas, characterized by the emergence of monolayer-high Pb islands predominately in the quantum mechanically unstable regions. The STM observations can be rationalized within a model rooted in DFT results, showing that the Cs adatoms repel each other, prefer to adsorb on the stable regions of the mesa top, and reduce the step formation energy of the emerging Pb islands. PACS number: 68.43.Hn, 73.21.Fg, 68.37.Ef, 68.43.Bc