INFIQC   05475
INSTITUTO DE INVESTIGACIONES EN FISICO- QUIMICA DE CORDOBA
Unidad Ejecutora - UE
artículos
Título:
Electrochemical STM investigation of 1,8-octanedithiol monolayers on Au(111). Experimental and theoretical study
Autor/es:
M.J. ESPLANDIU; M.L. CAROT; F.P. COMETTO; V.A. MACAGNO; E.M. PATRITO
Revista:
SURFACE SCIENCE
Editorial:
ELSEVIER
Referencias:
Año: 2006 vol. 600 p. 155 - 172
ISSN:
0039-6028
Resumen:
The surface structure of Au(111) electrodes covered by 1,8-octanedithiol self-assembled monolayers (SAMs) was
studied with in situ scanning tunnelling microscopy (STM) as a function of the electrode potential in acidic and alkaline
electrolytes. We investigated the correlation between the dynamics of the SAM and the underlying gold atoms during the
reductive desorption and oxidative readsorption processes. The reductive desorption of 1,8-octanedithiol is characterized
by a transition from a compact monolayer with an upright molecular con.guration to a striped phase with .at lying
dithiol molecules, whereas during the oxidative readsorption process the surface .rst becomes increasingly covered by
the striped phase until the transition to the compact phase occurs. We also considered under equivalent conditions
1-octanethiol/Au(111) SAMs which were used as a reference to evaluate the in.uence of the SH terminal group on
the structure and stability of dithiol SAMs. The desorption and readsorption of both the dithiol and the monothiol have
a considerable in.uence on the substrate morphology which is manifested in the dynamics of vacancy islands, gold islands
and indentation of step edges. Quantum mechanical calculations in the framework of density functional theory (DFT)
show that adsorbed thiols greatly facilitate the detachment of gold atoms from step edges. The high mobility of gold
atoms observed experimentally is compatible with the presence of a defected layer of gold atoms. The DFT results suggest
that the formation of a monolayer may involve the di.usion and self assembly of thiolateAu moieties rather than the
di.usion of the bare thiolates across the surface. This mechanism explains the formation of a defected layer of gold atoms.
2005 Elsevier B.V. All rights reserved.2005 Elsevier B.V. All rights reserved.