Nucleation of Pb electrodeposits on Ag and Cu

Initial stages in the electrocrystallization of Pb (up to 200A thick) from 1M NaClO4, 0.5 and 5 mM Pb (NO3)2, pH 3, on Ag(111) and Cu(111) have been investigated by ellipsometry and light scattering during cyclic voltammetry. Optical constants, thickness, valence, and free energy of adsorption of the underpotential deposit have been determined. An optical model which agrees with experimental data for fractional coverage by the underpotential deposit is based on the twodimensional spreading of islands of monolayer thickness. The bulk deposit immediately following formation of the underpotential monolayer involves three-dimensional growth from nucleation centers, even at the 20A level of deposit thickness, and results in a particulate, porous film on top of the underpotential deposit