Pb electrodeposition on polycrystalline Cu in the presence and absence of Cl^-: A combined oblique incidence reflectivity difference and in situ AFM study

Oblique incidence reflectivity difference (OI-RD) measurements reveal differences in the earliest stages of overpotential-deposited (OPD) growth between Pb electrodeposition on polycrystalline Cu surfaces in the presence and absence of Cl^-. At moderate overpotentials, when only 100 mM ClO₄^- is present, the magnitude of the real part of the OI-RD signal continues to increase after completion of the first underpotential-deposited (UPD) Pb monolayer, but with the addition of 20 mM KCl the magnitude decreases after the UPD monolayer forms. In situ atomic force microscopy (AFM) shows that in the former case the island density is much greater than in the latter. Using OI-RD as a probe, we show additionally that when the substrate potential is returned to a more positive potential in the presence of Cl^-, the UPD Pb monolayer dissolves after the Pb islands disappear.