Quantum size effects on surfaces without a projected bandgap: Pb/Ni(111)

Abstract

We have studied the initial growth of Pb on Ni(111) using lowenergy electron microscopy (LEEM) and selective area low-energy electron diffraction (μLEED). First, a one-layer-high wetting layer develops that consists of small (7×7) and (4×4) domains. For larger coverages, Pb mesas are formed that are embedded in the wetting layer. In spite of the absence of a projected bandgap on clean Ni(111), we observe distinct quantum size effect (QSE)-driven preferred heights. These are apparent from a variety of frequently occurring island height transitions during growth, both on wide terraces and across substrate steps. Also, the average island heights that evolve during deposition at 422 and 474K show a clear signature of QSE-driven preferred heights. These distinctly include five, seven and nine layers and thus correspond nicely to the values obtained in the key examples of QSE: Pb films on Si(111) and Ge(111). We suggest that the Pb-induced surface modification of Ni(111) shifts the Fermi level into the gap of the interface projected Ni bulk bands, thereby effectively causing decoupling of the Pb states with the bulk Ni states. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.