Electrodeposition of an ultrathin Ag-Cd bilayer on Au(111)

D.R. SALINAS; M.C. DEL BARRIO; S.G. GARCÍA

Benediktbeuern

Simposio; 10th International Fischer Symposium on Electrochemical Aspects of Biological and Nanoscopic Structures; 2006

Electrochemical processes become of great interest in modern thin layer technology, particularly for the development of heterostructures composed by more than one deposited metal to form metallic sandwich layers and/or surface alloys. The structure, thickness and composition of these films are controlled by the substrate, the electrolyte composition and the polarization routine used. In previous reports the formation of metal adlayers during the underpotential deposition process (UPD) in the systems Au(111)/Ag+, Ag(111)/Cd2+ and Au(111)/Cd2+ was analyzed. In the present work the formation of an ultrathin bilayer of Ag-Cd in the two-components system Au(111)/Ag+, Cd2+ was studied by conventional electrochemical techniques and in-situ Scanning Tunneling Microscopy (STM). In a first step a Ag monolayer (ML) was deposited on Au(111) at relatively high potentials, in the corresponding Ag OPD range. At lower potentials this Au(111)/1 ML Ag modified substrate exhibits UPD peaks that are in good agreement with those observed for the system Ag(111)/Cd2+. This result implies that the Au(111) substrate was practically screened by the Ag layer and a Cd ML is obtained on top of this silver layer reaching the equilibrium potential of Cd2+/Cdº. The complete sequence of deposition was followed by in situ STM and some of the images are shown below. The presence of monatomic islands and pits on the original Au(111) terraces after stripping of Cd and Ag deposits indicates a 3D Cd diffusion and the formation of surface alloys.