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Influence of applied potential on the impedance of alkanethiol SAMs
Harmonie Sahalov1, Brigid O'Brien, Kathleen J Stebe
1Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Abstract:
Self-assembled monolayers are generally considered to behave as dielectric layers with a capacitance that is dependent on the monolayer thickness and the relative permittivity that is determined by the hydrocarbon tail. We show that the impedance response of alkanethiol-modified gold surfaces can be modeled as a parallel network consisting of the capacitance and resistance of the monolayer over a wide potential range. At potentials positive to -0.3 V (Ag/AgCl), the monolayer resistance is greater than 10(6) Omega cm2; however, at more negative potentials, the monolayer resistance decreases exponentially with potential with an inverse slope of about 250 mV. Over the same potential range, the monolayer capacitance is independent of potential. Although the same behavior is observed on ultrasmooth, template-stripped gold, the resistance at any potential is larger than for evaporated gold. The progressive increase in permeability of the monolayer is associated with an increase in electric field at potentials negative to the potential of zero charge.
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In nature, compounds containing both carbon and hydrogen are known as "hydrocarbons". Aliphatic hydrocarbons are compounds whose molecules contain saturated single bonds (i.e., alkanes) or unsaturated double or triple bonds. Alkenes contain carbon–carbon double bonds and have a structural formula CnH2n. Unsaturated hydrocarbons containing carbon–carbon triple bonds are called "alkynes" and are structurally represented by the formula CnH2n-2.
The simplest alkyne is ethyne, or...

