Electrochemical formation of ultra-thin Ag/Cd films onto Au(111) substrates

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

Río de Janeiro

Congreso; 2nd Mercosur Congress on Chemical Engineering . 4th Mercosur Congress on Process Systems Engineering; 2005

The formation of ultra-thin metal films on foreign substrates (metals, superconductors and semiconductors) plays an important role in modern fields of technology such as micro- and nano-electronics, sensors, electrocatalysis, etc. Electrochemical processes become of great interest in modern thin layer technology, specially for the development of heterostructures formed 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 the Ag/Cd and Au/Cd surface alloys in the systems Ag(111)/Cd2+ and Au(111)/Cd2+ was studied during the underpotential deposition process (UPD). In the present work the formation of an ultrathin bilayer of Ag/Cd in the system Au(111)/Ag/Cd2+,SO42- was studied by conventional electrochemical techniques and in-situ Scanning Tunneling Microscopy (STM). Different amounts of Ag, from several monolayers to 1-2 monolayers (ML), were electrodeposited on a Au(111) single crystal substrate and the behaviour of this modified substrate surface was analyzed in a solution containing Cd2+ ions. Cyclic voltammetric measurements indicated that the deposition of Cd onto the Au(111) surface modified with only 2 ML of Ag originates adsorption/desorption UPD peaks which are in good agreement with those obtained in the system Ag(111)/Cd2+. These results indicate that only 2 ML of Ag are enough to transform the Au(111) surface in a Ag(111) surface. In addition, this effect was also observed in chronoamperometric experiences, which reveal that the formation of the 3D Au-Cd alloy is also affected by this Ag film. Moreover, the morphological surface changes during the Cd UPD on the modified substrate were followed with STM analysis.