The impedance of a Au(111) electrode modified by
three different self-assembled monolayers has been studied
over a wide frequency range in aqueous NaClO4 solutions.
The impedance characteristics of the bare electrode
are compared with those of the same electrode modified with
decanethiol, ω-hydroxydecanethiol, and 4‘-hydroxy-4-mercaptobiphenyl. In the case of the decanethiol system
the interfacial impedance can be represented
as a capacitor due to the self-assembled monolayer in series with the
solution resistance. However, for the
latter two systems, the impedance behavior is more complex with a high
resistance in the monolayer parallel
to the expected capacitance. This behavior is quite different than
that discussed to date in the literature and
assumed in the interpretation of voltammetric data for modified
electrodes. The parameters for these systems
are reported here as a function of electrolyte concentration at the
point of zero charge on the bare Au(111).
The consequences of the present observations are discussed with
respect to the phenomena observed for
these systems.
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