Submonolayer growth of Pb on Cu(111): surface alloying and de-alloying

C. Nagl, O. Haller, E. Platzgummer, M. Schmid and P. Varga

Institut für Allgemeine Physik, Technische Universität Wien, A-1040 Wien, Austria

Surf. Sci. 321 (1994) 237-248

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< encoded email address >).

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Part of this work is on display in the IAP/TU Wien STM Gallery (see the Pb on Cu and electron waves) pages.