Electrochemical and in-situ stm study of the surface alloy formation in the system Au(100)/Cd

•The Cd UPD process is characterized by three adsorption/desorption current density peaks pairs before the Cd bulk deposition.•A Au-Cd surface alloy, generated by a turnover mechanism, takes place at low underpotentials.•The appearance of new peaks in the anodic stripping curves, can be attributed to the formation of other phases of a CdzAux alloy. The Cd UPD process in the system Au(100)/Cd2+, SO42− and the involved Au-Cd surface alloy formation have been investigated, using conventional electrochemical techniques and in-situ STM analysis. The voltammetric experiences have shown three adsorption/desorption steps in the extended UPD range 0≤ΔE/mV≤800. The obtained desorption spectra indicate the formation of a surface alloy at low underpotentials and long polarization times. STM images have shown that the Cd deposition becomes evident at low underpotentials, with the nucleation of two-dimensional islands of monatomic height, which grow and coalesce up to a complete monolayer. At lower underpotentials, new islands nucleate on the monolayer previously formed, and grow acquiring a quadratic structure. The subsequent stripping of this film promotes morphological changes that are related to the dissolution of a Cd-Au surface alloy, which is consistent with the electrochemical experiences.