Dynamics of the Au (001) surface in electrolytes:In situcoherent x-ray scattering

Abstract

We studied the dynamics of the Au (001) surface in 0.1 M HClO 4 electrolyte solution using coherent surface x-ray scattering (CSXS). We find that edges of steps and islands on the Au (001) surface are highly dynamic in electrolyte and evolve continuously even at room temperature. The evolving speed increases nearly two orders of magnitude when the quasihexagonal reconstruction is lifted during slow potential sweep and is higher by more than four orders of magnitude than the speed measured previously in vacuum. In addition, we find that surface lattice dynamics appear when the reconstruction is lifted, and they are faster by two orders of magnitudes than the edge dynamics. Complementary scanning tunneling microscopy images are also presented for visual confirmation of the changes measured by the CSXS technique.

X‐ray Photon Correlation Spectroscopy Studies of Surfaces and Thin Films

“…These results were confirmed in other measurements made at room temperature on the Au (001) surface in an electrochemical cell in various electrolytes including pure water, and as a function of electrode potential. [77d]XPCS studies of domain wall fluc­tuations in magnetic films…”

“…Another area where it was realized that the dynamics was slow enough to be studied with XPCS at current synchrotron sources consists of metal surfaces in vacuum at elevated temper­atures, or in electrolytes as a function of electrode potential. Such studies have been carried out in the last few years on Au and Pt (001) surfaces by You and collaborators . Both these metals are fcc and their surfaces exhibit quasihexagonal reconstruction.…”

“…In the case of Pt (001) in vacuum,[77a] F( q ,t) could be fitted with a simple exponential and the measured values of τ showed interesting temperature dependence. At temperatures below 1620 K the authors state that τ is dominated by orientational fluctuations of the hexagonal domains, which tend to speed up so that τ −‐1 appears to diverge as (1‐ T / T 0 ) −1/2 ( Figure ), while above 1620 K, τ −‐1 increases again and appears to diverge at the roughening temperature T R .…”

“…At higher temperatures the behavior of τ −‐1 was well‐reproduced by the form , where f s is the free energy of the steps near the roughening transition, given by the theoretical expression (Figure ). Another interesting effect seen at high temperatures for Pt (001) surfaces, was oscillatory behavior observed in the speckle intensities as single steps flowed through the illuminated surface area of the sample,[77b] causing intensity to be transferred from one speckle to another and back again.…”

“…In the case of the Au (001) surfaces,[77c] which were carried out in an electrolytic cell with 0.1M HClO 4 solution, the hexagonal reconstruction of the Au (100) surface is lifted on application of an electrolytic potential. The surface of the gold is covered with islands and patches of local hexagonal symmetry which convert at higher potentials to local square symmetry.…”