Education

Ph.D. 1988, University of Texas—Austin

Research

Electroanalytical chemistry using chemically modified electrodes and interfaces. Specific projects involve the electrosynthesis of semiconductor nano films, bipolar electrochemistry, bio/chemical sensor development, surface chemistry of polyoxometalates, nanoporous thin films for separations, and surface enhance Raman spectroscopy of bio/chemical interfaces.

The central theme of our research is controlling the chemical behavior of electrode surfaces at the atomic/molecular level. A wide range of analytical tools, including scanning probe microscopy (AFM and STM), surface plasmon resonance, quartz microbalance, Raman spectroscopy, and surface IR spectroscopy, are available in our laboratory.

1. Synthesis and screening of solid-state material libraries. We use bipolar electrodeposition to generate one-dimensional material libraries rapidly and without direct electrical contact. An electric field applied across an electrically floating conductor in a bipolar electrochemical cell generates a position-dependent potential gradient along the conductor, which, in turn, induces variations of chemical composition within electrodeposited films. These films are continuous one-dimensional solid-state material libraries and can be screened using conventional techniques such as Raman microscopy and Auger spectroscopy. The technique is experimentally simple, scalable, amenable to a wide variety of materials.

2. Electrosynthesis of semiconductor thin films. The advantages of electrodeposition include growth at ambient temperature and pressure, deposition onto surfaces with complex topographies, and low cost. The widespread application of electrosynthesis hinges on overcoming two limitations: polycrystalline growth and contaminated deposits. We are attempting to address these two issues through achieving atomic-level control of the deposition process. We are currently investigating approaches based on the electrochemical analogs of atomic layer deposition and atomic layer epitaxy. 

3. Polyoxometalate monolayers as model oxide surfaces. Polyoxometalates (POMs) are highly symmetric, stable, nanometer scale clusters with characteristic sizes and shapes that resemble discrete fragments of bulk metal oxide phases. POMs adsorbed on metal substrates are good models of metal oxide surfaces and excellent catalysts in their own right. Our interest stems from their use as electrocatalysts, with potential applications as general oxidation catalysts, and components of fuel cells and dye-sensitized solar cells.

4. Analytical applications of imprinted polymers. We use self assembled monolayer techniques and 'click' chemistry to graft ultrathin layers of molecularly imprinted polymers onto electrode surfaces for selective and sensitive detection of chiral analytes.

5. Surface Enhanced Raman Spectroscopy. Recent advances in the growth of size monodisperse metal nanoparticles and nanoparticle arrays with well-defined optical properties has lead to renewed interest SERS as an analytical technique. We are investigating the use of SERS to probe chemical and biological interactions relevant in analytical chemistry, such as the interaction between bacteriophages and pathogenic bacteria.

Selected Publications

S. Ramakrishnan; C. Shannon, “Display of Solid-State Materials Using Bipolar Electrochemistry”, Langmuir 2010, 26, 4602-4606.

C. Gu, H. Xu, M. Park, C. Shannon “Synthesis of Metal-Semiconductor Core-Shell Nanoparticles Using Electrochemical Surface-Limited Reactions” Langmuir 2009, 25(1),  410-414.

K. Jiang, H. Zhang, C. Shannon, W. Zhan, “Preparation and Characterization of Polyoxometalate/Protein Ultrathin Films Grown on Electrode Surfaces Using Layer-by-Layer Assembly”, Langmuir, 2008, 24, 3584-3589.

A. V. Sankarraj, S. Ramakrishnan, C. Shannon, “Improved Oxygen Reduction Cathodes Using Polyoxometalate Co-catalysts”, Langmuir, 2008, 24, 632-634.

C. Gu and C. Shannon, “Investigation of the Photocatalytic Activity of TiO₂-polyoxometalate Systems for the Oxidation of Methanol”, J. Mol. Cat. A: Chemical, 2007, 262, 185.

A. R. Howells, A. Sankarraj and C. Shannon, “A di-Ruthenium-substituted Polyoxometalate as an Electrocatalyst for Oxygen Generation”, J. Am. Chem. Soc. 2004, 126, 12258-12259.