UNDERPOTENTIAL DEPOSITION AND ELECTROCRYSTALLIZATION OF METALS - AN ATOMIC VIEW BY SCANNING TUNNELING MICROSCOPY

The formation of well-ordered 2-D metal adsorbate layers in the underpotential (UPD) range and 3-D metal deposits in the overpotential (OPD) range on foreign substrates was studied in the model system Ag(hkl)/Pb2+ by in situ STM under defined potential control with lateral atomic resolution. ''Real'' and ''quasi-perfect'' silver single-crystal faces served as substrates. The results are discussed in comparison with electrochemical and morphological studies, in situ extended x-ray absorption fine structure and grazing incidence x-ray scattering investigations. It is shown that in situ STM provides an excellent atomic view of the different stages of UPD and electrocrystallization of lead on silver. The influence of the substrate on the 2-D structure of UPD layers and on the kinetics of 3-D nucleation and crystal growth is demonstrated. The results indicate directly a Stranski-Krastanov mechanism of 3-D nucleation and growth in this system.