An in situ scanning tunneling microscopy study of Ag electrodeposition on Au(111)

In situ structural study on underpotential deposition of Ag on Au(111) electrode using surface X-ray scattering technique

“…Three dominant cathodic peaks were observed at 520 mV (C1), 130 mV (C2), and 30 mV (C3). These peaks were also observed in most of the previous studies and the positions of these peaks are in good agreement with the ones reported before [14,15,[19][20][21]26]. In addition to these peaks, several small cathodic peaks were also observed at 500 mV (C1'), 330 mV (C4), 240 mV (C4'), and 100 mV (C2').…”

“…Peaks C4 and C4' were often missing in the CVs previously reported. Peaks C2 and C2' and peak C3 were considered as the second and third UPD peaks, respectively [19]. The charges corresponding to the first, second and third UPD peaks were 100 μC cm -2 , 60 μC cm -2 , and 220 μC cm -2 , respectively, and were exactly the same as those reported by Explandiu et al [19].…”

“…The UPD layer with the (1×1) structure was observed just before the bulk deposition was started [14,15,23]. Some groups also found compressed (3 × 3), (5 × 5), and/or (6 × 6) structures before the (1×1) structure was formed [19][20][21]23,24,26].…”

“…To clarify the details of each process, a wide variety of techniques such as STM [14][15][16][17][18][19], AFM [20,21], electrochemical quartz crystal microbalance (EQCM) [22], second harmonic generation (SHG) [23], UHV techniques such as low energy electron diffraction (LEED) [21,24], surface extended X-ray absorption fine structure 2 (EXAFS) using X-ray from a synchrotron radiation source [25], and X-ray diffraction (XRD) using a conventional laboratory X-ray source [26,27] have been applied. STM measurements in a sulfuric acid solution showed an ordered (bi)sulfate adlayer with the (√3 × √7)R19.1° structure [19] and the Ag UPD layer with the (√3 × √3)R30° structure [14,15,19] in the potential region more positive and negative, respectively, than the first UPD peak. The UPD layer with the (1×1) structure was observed just before the bulk deposition was started [14,15,23].…”

“…Recently, however, Explandiu et al proposed that the Ag UPD bilayer and not a monolayer is formed on Au(111) before the bulk deposition and the smaller charge originates from the difference in the potential of zero charge (pzc) between Au and Ag [19]. Most of the techniques mentioned above are not suitable to address the question whether a monolayer or a bilayer of Ag is formed.…”