In situ Real-time Monitoring of Electrochemical Ag Deposition on a Reconstructed Au(111) Surface Studied by Scanning Tunneling Microscopy

摘要

Electrochemical deposition of Ag on a 23 × √3 reconstructed surface of Au(111) electrode at various potentials was followed by scanning tunneling microscopy (STM) in situ in real time. At −0.2 V (vs Ag/AgCl), line shaped Ag deposits with the height of 0.46 ± 0.03 nm, which is equivalent to 2 atomic height, were observed. The center of each Ag line was located in the hcp domain of the reconstructed structure. They then grew two-dimensionally so that the other regions, i.e., bridge and fcc domains, of the reconstructed Au surface were gradually covered with the Ag bilayer. As the deposition proceeded, another Ag layer started to nucleate and grow on the Ag bilayer. This layer was one atomic height and grew not linearly but two-dimensionally from the beginning. At 0.3 V, the monatomic layer of Ag was formed preferentially in the hcp domain and the Ag growth stopped at ca. 1 ML. The potential dependent stabilities of the deposited bi- and mono-atomic Ag layers were confirmed by the potential step measurements. The structural conversion from the bi- to mono-atomic layer of Ag was observed when the potential was stepped from −0.2 to +0.3 V. At 0 V, an intermediate potential, both the bi- and mono-atomic Ag layers were observed at the initial stage of Ag deposition. These results revealed that the biatomic Ag layer was more favored at more negative potentials in the range of −0.2 to +0.3 V. The growth mode of the potentiostatic electrochemical deposition of Ag on the reconstructed Au (111) electrode surface observed in this study is quite different from those previously reported for the electrochemical deposition on the reconstruction-lifted Au(111) electrode surface and deposition under ultrahigh vacuum (UHV) condition on the reconstructed Au(111) surface, showing the importance of structure of substrate surface and electrode potential on the growth mode.