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In spite of the immiscibility of Pb in bulk Cu, atomically resolved scanning tunneling microscopy reveals surface alloy formation of Pb deposited on Cu(111) even at 300 K. Due to kinetic limitations at room temperature, the incorporation of Pb is restricted to advance from step edges, while after annealing to 470 K or higher embedded Pb atoms are found to be randomly distributed at terraces. At low tunneling voltages, standing waves of scattered surface state electrons scattered by embedded Pb atoms could be observed. The maximum packing density of the surface alloy is about 40 % (=0.4 ML) of a close packed Pb overlayer. Thus, deposition above 0.4 ML results in hexagonal close-packed Pb regions, whereas on the non-annealed surface hexagonal close-packed Pb islands are already found at 0.2 ML. Eventually, at 1 ML the surface alloy is entirely replaced by a Pb overlayer.
Corresponding author: M. Schmid (schmid).
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