Adam C. Finnefrock

Anion and electrode surface structure effects on the deposition of metal monolayers: electrochemical and time-resolved surface diffraction studies

The effects of anions and electrode surface structure on the UPD of metal monolayers are illustrated with three different examples. In the first, we show that for Cu UPD on Pt[n(111)×(110)] (n=2, 3, 5, 9 and 19) stepped surfaces in sulfuric acid medium, submonolayer amounts of underpotentially deposited copper induce the adsorption of (bi)sulfate in the vicinity of copper adatoms deposited on (110) step sites. The induced anion adsorption increases with terrace width up to a three Pt atoms wide terrace, suggesting that this is the minimum width to accommodate the copper adatom and the coadsorbed anion. In the second case we present data from simultaneous time-resolved surface X-ray scattering and chronoamperometric measurements of Cu UPD on Pt(111) electrodes in the presence of chloride anions. These studies demonstrate that the kinetics of formation of the incommensurate CuCl adlayer from the commensurate (1×1) Cu layer takes place in a much longer time scale than the current response. This is a clear indication of the temporal separation (resolution) between electrochemical events and processes associated with surface reorganization to achieve long-range periodic ordering. Finally, we consider the UPD of Hg on Au(111) electrodes with emphasis on the relationship between the partial charge retained by the mercury and anion adsorption. At the early stages of Hg UPD, when mercury is still partially charged, an ordered mercurous–sulfate bilayer structure is formed on the electrode surface. At more negative potentials, where mercury is almost fully discharged, two additional ordered hexagonal mercury adlayers are formed with little, if any, interactions with the anions, suggesting that the interactions between them are largely electrostatic in nature.

Electrodeposition dynamics: electrochemical and X-ray scattering studies

Studies of the electrodeposition dynamics of underpotential deposition (UPD) processes based on electrochemical and in-situ surface X-ray scattering studies are presented. The studies focus on the UPD of Hg on Au(111) in sulfate media, and Cu UPD on Pt(111) in sulfate and chloride media. In the first case it is shown that Hg UPD on Au(111) in sulfuric acid follows a progressive nucleation mechanism which involves various surface structures. In the case of Cu UPD on Pt(111), the process appears to follow an instantaneous nucleation mechanism in both sulfate and chloride media. Time-resolved surface X-ray scattering studies of Cu UPD on Pt(111) in the presence of chloride demonstrate that the electrochemical relaxation and the achievement of long range order can take place on significantly different time scales. Analysis of time-resolved surface X-ray scattering data allows for the study of the dynamics of island growth.

X-ray-scattering measurements of the transient structure of a driven charge-density wave.

We report time-resolved x-ray scattering measurements of the transient structural response of the sliding {\bf Q}

Nucleation and Ordering of an Electrodeposited Two-Dimensional Crystal: Real-Time X-Ray Scattering and Electronic Measurements

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Time-Resolved Surface X-ray Scattering Study of Surface Ordering of Electrodeposited Layers

charge-density-wave (CDW) in NbSe

Scaling in Charge-Density-Wave Relaxation: Time-Resolved X-Ray Scattering Measurements

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Sliding charge-density waves as rough growth fronts

to a reversal of the driving electric field. The observed time scale characterizing this response at 70K varies from

Dynamic scaling during CDW relaxation from the sliding state

\sim

Sliding charge-density waves as rough growth surfaces

15 msec for driving fields near threshold to

Nucleation in Submonolayer Electrodeposition

\sim