In Situ Surface X-Ray Diffraction Studies of Homoepitaxial Electrochemical Growth on Au(100)

Direct in situ x-ray surface scattering studies of growth at a solid-liquid interface are demonstrated using the homoepitaxial electrodeposition on Au(100) as an example. With decreasing potential transitions from step-flow to layer-by-layer growth, manifested by layering oscillations in the x-ray intensity, then to multilayer growth, and finally back to layer-by-layer growth were observed. This complex growth behavior can be explained by the effect of anion coadsorbates and the potential-dependent Au surface reconstruction on the Au surface mobility.

Figure 1

In situ growth experiments on Au(100) in 0.1 M HCl solution containing (a) 0.05 mM, (b) 0.1 mM, (c) 0.2 mM, and (d) 0.5 mM ${\mathrm{HAuCl}}_4$ at a deposition potential of (a) 0 V, (b) 0.05 V (solid line) and 0.2 V (dashed line), (c) 0.10 V, and (d) 0.25 V. The panels show the background-corrected x-ray intensity $I(t)$ as a function of deposition time $t$, normalized with respect to the saturation value $I(0)$ directly before the potential step at $t=0$. The data were obtained at reciprocal space positions of (a),(d) $(1,1,0.1)$ and (b),(c) $(0,0,0.7)$; similar behavior was found at other positions along the CTRs.

Figure 2

Background-subtracted, normalized intensity as a function of deposition time $t$ after potential steps from 0.6 V to different potentials in 0.1 M $\mathrm{HCl}+0.5\mathrm{mM}$ ${\mathrm{HAuCl}}_4$. For clarity, the curves are shifted with respect to each other by a constant offset. The data were obtained at $(1,1,0.1)$ and show step-flow, layer-by-layer, multilayer, and reentrant layer-by-layer growth (for classification of each curve, see Fig. 3, topmost row of symbols) with decreasing potential. In the inset the steady-state intensity, measured 100 s after the potential step, is plotted as a function of potential.

Figure 3

Kinetic growth mode diagram for $\mathrm{Au}/\mathrm{Au}(100)$ in 0.1 M HCl, showing the occurrence of step-flow (filled circles), layer-by-layer (open triangles), and multilayer growth (filled squares) as a function of potential and deposition rate.