| Abstract
| - In this article, the underpotential deposition (UPD) of Sb on Au(111) and Au(100) over a wide potentialrange in a BMIBF4 ionic liquid containing SbCl3 is investigated by cyclic voltammetry and in situ scanningtunneling microscopy (STM). The cyclic voltammograms of the two surfaces show similar features of SbUPD, which is kinetically sluggish at high underpotential shift but rapid at low underpotential shift with alarge and broad reduction peak. The total charge flux associated with the UPD suggests an equivalent ofnearly 1 ML quantity of Sb deposit. In situ STM results showed precursor adsorption and several stages ofthe UPD. The prior UPD reversible adsorption of SbCl3 precursor occurs only on Au(111) with an orderedhexagonal array of six- and seven-membered clusters in (√31 × √31)R8.9° registration with the Au(111)surface. On both Au(111) and Au(100), the initial stage of Sb UPD (from −0.2 to −0.4 V) proceeds with theformation of similar short atomic strips of Sb atoms with a length of 2−2.5 nm and a width of two atoms.The average coverage of the Sb atoms is ca. 0.24 ML at −0.4 V with an electrosorption valency of close to3. In the later stage of Sb UPD (from −0.45 to −0.65 V), dramatically different behaviors were observed onAu(111) and Au(100). On Au(111), a multilevel feature of (√3 × √3)R30° structure was observed at afractional coverage with a small quantity of Sb aggregates at the top level. This was followed by a two-layersurface alloying at potentials close to that of Sb bulk deposition. On Au(100), however, the formation of adistinct second layer composed of islands of ∼4 nm was the sole characteristic at this stage. No surfacealloying appeared on Au(100). These features contrast those observed in aqueous solutions containingoxygeneous SbO+ species and display profound medium effects on the UPD of Sb. Discussions of theseobservations, especially the possible origin of the clusters on Au(111) and the structural invariance of theatomic strips on Au(111) and Au(100), is provided in view of mutual interactions at the interface that aremodified by the environment of the ionic liquid.
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