Probing Single-Molecule Electrochemistry with Tip-Enhanced Raman Spectroscopy

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The thermodynamics and kinetics of electron transfer reactions in catalysis, energy conversion and storage, and plasmon-driven chemistry depend strongly on nanoscale electrode surface structure. To elucidate the structure-function relationships that determine nanoscale electrochemical reactivity, it is necessary to observe electron transfer reactions one molecule at a time. Over the past three decades, single-molecule sensitivity has been achieved using several optical spectroscopy methods. Most notable among these are fluorescence microscopy and surface-enhanced Raman spectroscopy (SERS), which can achieve < 50 nm spatial resolution when paired with super-resolution techniques. However, probing chemistry at the single-molecule, single-surface site limit requires spatial resolution on the scale of a few nanometers or smaller. Tip-enhanced Raman spectroscopy (TERS), which combines the sensitivity and rich chemical information of SERS with the nanoscale imaging capability of scanning probe microscopy (SPM), has recently been demonstrated to provide remarkable Ã…ngstrom-scale resolution. The ability to simultaneously obtain spectroscopic information with TERS and surface topography with SPM with sub-nm resolution makes TERS the most promising available method for investigating single-molecule electrochemistry on heterogeneous electrode surfaces.', '\tThis work details the development of electrochemical tip-enhanced Raman spectroscopy (EC-TERS) and its use in single-molecule electrochemistry experiments. A general overview of methods previously used to study nanoscale and single-molecule electrochemistry is discussed in Chapter 1. Chapter 2 details a Monte Carlo model of single-molecule spectroelectrochemistry in order to develop a fundamental understanding of EC-TERS data. In Chapter 3, the development of EC-TERS on an atomic force microscopy (AFM) platform, and a quantitative description of TERS cyclic voltammetry is explored. Chapter 4 covers the development of tip-enhanced Raman excitation spectroscopy (TERES) toward a fundamental understanding of the tip-sample junction in EC-TERS. Last, Chapter 5 details the design and construction of a combined scanning electrochemical microscopy (SECM) Raman instrument for correlated structure-activity investigations of electrode surfaces at the nanoscale. Taken together, this suite of new electrochemical and optical nanoscopy techniques offers an exciting new window into nanoscale and single-molecule electrochemistry with the potential to fundamentally transform our understanding of electron transfer processes.

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  • 10/08/2019
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