Spontaneous deposition of Sn on Au(1 1 1). An in situ STM study
Introduction
The deposition of metal monolayers onto a foreign metal surface is one of the most extensively studied subjects in surface electrochemistry because some of these modified surfaces have electrocatalytic or catalytic properties better than those of the pure components [1]. In some cases the metal overlayers can be generated onto the foreign metal substrate by underpotential deposition (UPD) [2], [3], namely, by deposition at potentials more positive than the Nernst equilibrium potential of the corresponding 3D metal bulk phase. In other cases the formation of such modified bimetallic surfaces can be achieved by “spontaneous deposition” using the so-called immersion technique [4], [5], [6], [7], which deals with the reduction as well as the oxidation of metal adspecies that has been introduced spontaneously onto the electrode surface at open-circuit from solutions containing the metal ions. The surface concentration of the deposited species depends on the immersion time and the bulk concentration of the adsorbing species.
The spontaneous adsorption of tin on polycrystalline and single-crystal gold surfaces was first analyzed by Rodes et al. [8], [9] and they concluded that this process could be explained by the adsorption of SnII species followed by a disproportionation reaction in which the product with the lower valency state is adsorbed. The formation of a Sn–Au surface alloy during this process was also suggested. More recently, Fonticelli et al. [10] studied the adsorbed tin species on evaporated gold films electrodes obtained by UPD and spontaneous deposition. They observed that Sn0 adatoms were generated on the surface either, by reducing SnII present in the solution through UPD or by first irreversibly adsorbing SnII and then reducing it in the supporting electrolyte.
In the present work, we present the first STM studies concerning the spontaneous deposition of Sn on Au(1 1 1). The possibility of surface alloying during this process is also discussed.
Section snippets
Experimental
A Au(1 1 1) single-crystal electrode (Φ = 4 mm) was used as working electrode. The substrate surface was first mechanically polished with diamond paste of decreasing grain size down to 0.25 μm and subsequently electrochemically polished in a cyanide bath [11].
Conventional electrochemical studies were performed in standard three-electrode electrochemical cells. The counter electrode was a platinum sheet (1 cm2) and the reference electrode was a Hg/Hg2SO4/K2SO4 saturated electrode (SSE). All potentials
Results and discussion
Fig. 1 shows the cyclic voltammogram of the Au(1 1 1)/Sn modified substrate (ti = 60 s) obtained in the test solution in the potential range −0.8 ⩽ E/V ⩽ 0.65. The cyclic voltammogram corresponding to the bare Au(1 1 1) surface is also included in the figure for comparison purpose. The potential was fixed at an initial value Estart = −0.70 V which is more negative than the stationary mixed potential of the system (E ≈ −0.27 V) and enables to consider that all the adsorbed tin is in its reduced form [8]. During
Conclusions
An adsorbed tin layer on the Au(1 1 1) surface was obtained by the immersion method in a solution containing Sn2+ ions. The presence of this layer was clearly evident from the voltammetric curves in sulphuric acid solutions. During the anodic scan characteristic peaks were recorded which can be ascribed to the dissolution of the Sn adlayer. The STM images of the Au(1 1 1)/Sn modified surface, showed flat terraces with rounded edges and two-dimensional islands. The anodic polarization of this
Acknowledgements
The authors wish to thank the Universidad Nacional del Sur, Argentina, and the Agencia de Promoción Científica (PICTO-UNS 2004 Cod. 614) for financial support of this work. L. Meier acknowledges a fellowship granted by CONICET.
References (13)
- et al.
Surf. Sci. Rep.
(2002) - et al.
J. Electroanal. Chem.
(1974) - et al.
Electrochim. Acta
(1976) - et al.
Electrochim. Acta
(2001) - et al.
J. Electroanal. Chem.
(2004) - et al.
J. Electroanal. Chem.
(1988)
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