Structural study of electrochemically induced adsorption and diffusion of metal surfaces

Sneddon, Douglas Dean

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https://hdl.handle.net/2142/21273 Copy

Description

Title

Structural study of electrochemically induced adsorption and diffusion of metal surfaces

Author(s)

Sneddon, Douglas Dean

Issue Date

1995

Doctoral Committee Chair(s)

Gewirth, Andrew A.

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Chemistry, Physical

Language

eng

Abstract

• In the first part of this thesis, the scanning tunneling microscopy (STM) was used to characterize adsorbates physisorbed onto conductive surfaces. The STM is ideal for this because it is capable of obtaining real space images of local electronic and topographic features with atomic resolution. It also has the ability to perform in many different environments, including electrolyte, air, cryogen, and vacuum. Unless the adsorbate is chemisorbed to the surface, the adsorbate diffuses across the surface due to thermal instability which causes difficulties in imaging. This problem can be overcome by lowering the temperature of the substrate. We have built a variable temperature STM, capable of operating at liquid helium temperatures. Initial results show the ability of the instrument to image benzene physisorbed onto a graphite substrate. Further work will focus on imaging other adsorbates on gold surfaces. Scanning tunneling spectroscopy (STS) will also be utilized in order to study the electronic properties of both the surface and the adsorbate.
• In the second part of this thesis, metal surfaces have been characterized through the use of scanning force microscopy. Scanning force microscopy is an ideal method for analyzing electrode surfaces in situ. In the first study, atomic force microscopy (AFM) was used to examine underpotentially deposited (upd) monolayers of Pb on Cu(111) in dilute acid solutions. Pb upd on Cu(111) forms a (111) close packed structure in both perchloric acid and acetic acid. In perchloric acid, the Pb overlayer is rotated $2\sp\circ\pm2\sp\circ$ with respect to the Cu(111) substrate. A rotation could not be determined in acetic acid due to the obscured images of the Cu(111) substrate before the Pb upd. In the second study, AFM and lateral force microscopy (LFM) were used to study the Ag(111) electrode surface in fluoride, sulfate, perchlorate, and chloride-containing electrolytes under potential control. Short range images reveal only the Ag(111) structure in each of these electrolytes. Long range images show step formation in both the perchlorate and chloride solutions. This effect is not seen with either sulfate or fluoride. In the third study, the structure of halide adlayers and Ag-halide growth on Ag(111) was studied by AFM as a function of electrode potential. For solutions containing F$\sp-$ and Cl$\sp-,$ only the underlying Ag(111) structure was observed while ordered overlayers were present for Br$\sp-$ and I$\sp-$-containing solutions. Long range images revealed a different electrode response for all four electrolytes. Lastly, AFM and LFM were utilized to study surface diffusion of a Ag(111) electrode surface in various electrolyte solutions under potential control. In I$\sp-$-containing solutions enhanced surface diffusion is observed. The rate of diffusion can be controlled by varying the potential in solutions containing Br$\sp-$ while in F$\sp-$-containing solution the rate of diffusion remains constant.

Type of Resource

text

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Copyright 1995 Sneddon, Douglas Dean

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