Thesis Introduction

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Title

Time-Resolved Measurements of the Underpotential Deposition of Copper onto Platinum(111) in the Presence of Chloride

Abstract

We have studied in situ the ordering of a two-dimensional Cu-Cl crystal electrodeposited on a Pt(111) surface. We simultaneously measured high-resolution time-resolved x-ray scattering and chronoamperometric (current vs. time) transients. Both measurements were synchronized with the leading edge of an applied potential step that stimulated the desorption of Cu and subsequent ordering of the Cu-Cl crystal. In all cases, the current transient occurs on a shorter time-scale than the development of crystalline order. The time-dependent x-ray intensity data (2 × 10⁴ data points) are well fit by an Avrami-like function with only three parameters. By performing a series of voltage-step experiments, we demonstrate that the ordering time diverges with applied potential, consistent with the nucleation and growth of two-dimensional islands. Monitoring the time-dependent widths of the x-ray peak, we see a narrowing corresponding to the growing islands.