Surface alloying of Pb as a surfactant during epitaxial growth on Cu(1 1 1)

As an important surfactant, Pb surface alloying in surfactant-assisted epitaxy growth was studied by synchrotron radiation photoemission. As annealing causes the submonolayer Pb, distributed as two-dimensional islands on Cu(1 1 1), to form Pb–Cu surface alloy, Cu growth is also found to activate the Pb–Cu surface alloy formation on submonolayer Pb covered Cu(1 1 1). Whereas, different from the fact that the Pb–Cu surface alloy is replaced by a Pb overlayer when the Pb coverage increases up to 1.0 ML, Co deposition gives rise to the Pb–Co surface alloy even on the 1.0 ML Pb covered Cu(1 1 1) surface. In the Pb–Cu surface alloy the Pb 5d core level is shifted toward Fermi level by about 20 meV. Heating de-alloys the Pb–Co surface alloy, while the interface intermixture between Co film and Cu substrate is also enhanced at the same time.