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Fig. 3. Stress-voltage curve for UPD of silver onto a gold (111) coated cantilever.

The second possibility is based on electrochemical quartz crystal microbalance results. Uchida et al. [44] suggest that following the first silver monolayer deposition process, there is a gradual deposition of more Ag atoms and that the monolayer coverage increases from around 1/3 to around 2/3, at which point the final epitaxial monolayer is formed at a potential near the bulk deposition region. This gradual filling of the first open monolayer does not, they claim, alter the extent of anion adsorption, so this process could be responsible for the slow increase in compressive stress in this region, particularly if the silver atoms retain a partial charge as has been suggested.

Finally, the observed decrease in the surface stress could arise from an electrocapillary-type effect. In this case the gradual increase in compressive stress occurs as the potential moves further away from the pzc, just as was seen for the electrocapillary curve of gold. This clearly depends on the value of the pzc of a gold (111) surface covered with a partial silver monolayer, which is not known. Electrocapillary curves of this type of system have been calculated from coulometric data [12] but the agreement between these calculations and experimental measurements [30] is not very good.

Fig. 4. Derivative of the stress with respect to voltage of Ag on Au(lll).

Potential vs. Ag/Ag+ N

Fig. 4. Derivative of the stress with respect to voltage of Ag on Au(lll).

It is clear that the electrocapillary curve exhibits gradual stress changes with changes in potential, whereas the gradient of the stress changes associated with the silver monolayer deposition process is much greater. Taking the derivative of the stressvoltage curve for the silver UPD process illustrates this (Fig. 4). This effectively diminishes the contribution from the potential region between the first monolayer and bulk deposition. There is a very clear correlation between the peaks in this derivative curve and those in the cyclic voltammogram in both scan directions. This derivative curve is less affected by the gradual electrocapillary-type

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