Electrocompression of the Au(111) Surface Layer during Au Electrodeposition

In situ grazing-incidence x-ray diffraction studies of reconstructed Au(111) electrodes in aqueous electrolyte solutions are presented, which reveal a significantly increased compression of the Au surface layer during Au electrodeposition as compared to Au(111) surfaces under ultrahigh vacuum conditions or in the Au-free electrolyte. The compression increases towards more negative potentials, reaching 5.3% at the most negative potentials studied. It may be explained within a simple thermodynamic model by a release of potential-induced surface stress.

Figure 1

X-ray scattering profiles along the ${\overrightarrow{q}}_r$ direction ($L=0.15$) recorded in 0.1 M HCl at $-0.3$ (a) and $0.7{\mathrm{V}}_{\mathrm{A}\mathrm{g}/\mathrm{A}\mathrm{g}\mathrm{C}\mathrm{l}}$ (b) as well as after the exchange with $0.1\mathrm{M}\mathrm{H}\mathrm{C}\mathrm{l}+50\mu \mathrm{M}$ ${\mathrm{H}\mathrm{A}\mathrm{u}\mathrm{C}\mathrm{l}}_4$ at 0.81 (c) and $-0.3{\mathrm{V}}_{\mathrm{A}\mathrm{g}/\mathrm{A}\mathrm{g}\mathrm{C}\mathrm{l}}$ (d). Solid lines are fits of the data with two Lorentzians convoluted by a Gaussian resolution function. The inset shows a schematic diffraction pattern of the ($p\times \sqrt{3}$) reconstruction (peak intensities are indicated by the symbol size).

Figure 2

Potential dependence of the stripe separation $p$ in Au-free (open symbols) and Au-containing (filled symbols) electrolyte solution, calculated from the reconstruction peak positions. The data were obtained during stepwise potential increase (○) and subsequent decrease (□) in 0.1 M HCl, potential increase (●) and decrease (■) in $0.1\mathrm{M}\mathrm{H}\mathrm{C}\mathrm{l}+50\mu \mathrm{M}$ ${\mathrm{H}\mathrm{A}\mathrm{u}\mathrm{C}\mathrm{l}}_4$, potential increase (▽) and decrease (△) in 0.1 M KCl, potential decrease (▲) in $0.1\mathrm{M}\mathrm{K}\mathrm{C}\mathrm{l}+50\mu \mathrm{M}$ ${\mathrm{H}\mathrm{A}\mathrm{u}\mathrm{C}\mathrm{l}}_4$, and by potential steps from the $\mathrm{A}\mathrm{u}/{\mathrm{A}\mathrm{u}\mathrm{C}\mathrm{l}}_4^{-}$ equilibrium potential in $0.1\mathrm{M}\mathrm{H}\mathrm{C}\mathrm{l}+200\mu \mathrm{M}$ ${\mathrm{H}\mathrm{A}\mathrm{u}\mathrm{C}\mathrm{l}}_4$ (★). The inset shows the change in $p$ as a function of the time $t$ after the potential step from the $\mathrm{A}\mathrm{u}/{\mathrm{A}\mathrm{u}\mathrm{C}\mathrm{l}}_4^{-}$ equilibrium potential to $-0.4{\mathrm{V}}_{\mathrm{A}\mathrm{g}/\mathrm{A}\mathrm{g}\mathrm{C}\mathrm{l}}$.