Abstract
We have studied the initial growth of Pb on Ni(111) using low-energy 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 474 K 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.
Highlights
During growth, thereby revealing electronic growth-driven transitions of Pb islands
We find no indication of the locking-in of the previously reported (3 × 3) structure found at room temperature (RT) [16, 18, 19], at an in-plane lattice constant of 3.73 Å
We have studied the growth and properties of thin Pb films on Ni(111)
Summary
The experiments were performed in an Elmitec LEEM III instrument. A Ni(111) surface was cleaned by successive cycles of 1 keV Ar+ bombardment at room temperature (RT), followed by flash annealing to a temperature of 1150 K. The cleanness of the sample was monitored by Auger electron spectroscopy and LEEM. All sample temperatures are subject to an uncertainty of 5% and were calibrated using the uphill motion of steps over time at a temperature where sublimation is observed, as described in [14]. Lead was deposited from a Knudsen cell. According to the bulk phase diagram, lead and nickel are immiscible in the bulk [15]. The typical deposition rate used in the experiments was about 1 × 10−3 ML s−1, where a coverage of θPb/Ni = 1 ML corresponds to one Pb atom per Ni surface atom
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