IV Latin American Symposium on Scanning Probe Microscopy - Formation of a Ag/Cd bilayer onto Au(100) by sequential underpotential deposition

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Summary *

Modification and structuring of surfaces by electrochemical deposition of metals to form defined heterostructured metal films are of future importance for the application in micro- and nano-technology. The formation of epitaxial metal adlayers previously reported in the systems Au(100)/Ag+, Ag(100)/Cd2+ and Au(100)/Cd2+, constitutes an excellent possibility to form sandwich metal films using multicomponent electrolytes and a defined polarization routine. In this work, the formation of an ultrathin bilayer of Ag-Cd in the two-components system Au(100)/Ag+,Cd2+ was studied using electrochemical techniques together with in-situ Scanning Tunneling Microscopy (STM). One or more Ag monolayers (ML) were obtained on the Au(100) surface by polarizing the substrate during different polarization times, in the Ag OPD range, at a potential where no Cd UPD occurs. Afterwards, the Au(100)/Ag modified substrate was polarized to a potential close to the equilibrium potential of the Cd2+/Cd0 system in order to obtained a Cd ML. The cyclic voltammogram obtained with the system Au(100)/3 ML Ag/Cd2+ corresponds very well with that reported in the literature for Ag(100)/Cd2+, indicating that the Au(100) surface was completely screened by the epitaxially deposited Ag layers. The STM images shown that the deposition of 3 Ag ML on Au(100) occurs by a multinuclear multilayer mechanism, with growth of steps and nucleation of 2D islands. When the potential was stepped to a value near to the Cd equilibrium potential, a relatively fast growth of steps together with nucleation of new 2D islands were observed. Once the first monolayer was completed, the Cd deposition continues with the formation of new 2D islands with polygonized features, according to the (100) structure. The formation of a second and a third Cd ML is also observed. This behavior is in good agreement with that obtained in the system Ag(100)/Cd. Information provided by the agent in SIGEVA