Dynamic metal depositiondissolution equilibrium

At reactive electrodes a dynamic equilibrium is established at the Nernst potential, where metal surface atoms and metal ions in solution are continuously exchanged by local dissolution and redeposition. The morphological rearrangement resulting from these processes is shown in Fig. 5 for Cu(100) electrodes in HC1 [29]. In the center of the STM image in Fig. 5(a) a straight monoatomic step is visible, which runs parallel to one of the close-packed directions of the c(2x2) superstructure formed by adsorbed CI. steps along preferred directions are the direct result of a rearrangement of surface atoms by exchange processes. In the absence of a CI adlayer, at very negative potentials, the steps are randomly oriented and appear frizzy, indicative of highly mobile Cu step atoms.

The dynamics of the rearrangement processes on the Cl-covered Cu(100) surface is illustrated in Fig. 5(b). In this image the upper terrace grows during the 90 s recording time by ten c(2x2) rows. The addition of each row proceeds by rapid growth along the step edge. Due to the fast growth, STM experiments merely probe when a growing row crosses the scanned area but cannot resolve the individual atomic processes. Apart from the dynamic effects caused by the growing rows, the step edges always appear straight in the STM images. This indicates that the creation of energetically unfavorable kink sites is largely avoided. The reverse process of local Cu dissolution proceeds in a completely analogous way by removal of atoms from kink sites.

Fig. 5. Local Cu deposition on Cu(100) in 10"3 M HC1 at -0.073 VSCE (140 x 140 A2) [29].
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