Charge Transfer at Thin-Film Modified Solid -Liquid Interfaces in the Absence of Redox-Active Moieties
Gupta, Chaitanya
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https://hdl.handle.net/2142/82433
Description
Title
Charge Transfer at Thin-Film Modified Solid -Liquid Interfaces in the Absence of Redox-Active Moieties
Author(s)
Gupta, Chaitanya
Issue Date
2009
Doctoral Committee Chair(s)
Kenis, Paul J.A.
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Language
eng
Abstract
"The characterization of the flux of electrons (""leakage"" currents) crossing the electrified monolayer modified solid-liquid interface in the absence of redox active moieties in the electrolyte is the first step in the development of such a label free methodology. An analytical method is presented in this dissertation that enables the quantitative analysis of the leakage current in the absence of specific information about the species in the electrolyte that couples weakly and non-adiabatically to the electronic orbitals of the metallic electrode. Application of the analytical method enables the identification of the different mechanisms by which leakage current flows through the insulating monolayer film. The current density is limited by Ohmic transport and by space charge at low and intermediate anodic potentials respectively. At higher anodic potentials, quantum mechanical tunneling of the electron from the ground-state energy level of the electrolytic ionic species to the electrode Fermi level becomes rate-limiting. On the other hand, for cathodic potentials, the charge flux is limited by the thermal activation of either the transferring electron or the dielectric molecules over a free energy barrier. The terms anodic and cathodic are defined with respect to a characteristic potential where the electric field in the monolayer becomes zero. The electrolytic species that participates in the charge transfer process is also identified. Properties of the monolayer-electrolyte interface that describe physical and chemical interactions between the electrolyte species and the monolayer modified surface are obtained from the analysis, demonstrating the applicability of the electrode-monolayer-electrolyte system as a sensing platform. An extension of the analysis methodology yields a quantitative estimate of the surface charge density at the monolayer-electrolyte interface. A theoretical description of the evolution of surface charge density in the presence of leakage currents is also proposed here."
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