Title:	Scanning tunneling microscopy, fourier transform infrared spectroscopy, and electrochemical characterization of 2-naphthalenethiol self-assembled monolayers on the Au surface: A study of bridge-mediated electron transfer in ruthenium complex
Authors:	Ganesh, V. Lakshminarayanan, V.
Issue Date:	2005
Publisher:	American Chemical Society
Citation:	Journal of Physical Chemistry B, 2005, Vol.109, p16372-16381.
Abstract:	We have studied the structure, adsorption kinetics, and barrier properties of self-assembled monolayers of 2-naphthalenethiol on Au using electrochemical techniques, grazing-angle Fourier transform infrared (FTIR) spectroscopy, and scanning tunneling microscopy (STM). The results of cyclic voltammetric and impedance measurements using redox probes show that 2-naphthalenethiol on Au forms a stable and reproducible, but moderately blocking, monolayer. Annealing of the self-assembled monolayer (SAM)-modified surface at 72 ± 2 C remarkably improves the blocking property of the monolayer of 2-naphthalenethiol on Au. From the study of kinetics of SAM formation, we find that the self-assembly follows Langmuir adsorption isotherm. Our STM and FTIR results show that the molecules are adsorbed with the naphthalene ring tilted from the surface normal by forming a 3 × 3 R30 overlayer structure. From our studies, we conclude that the electron-transfer reaction of ferro/ferricyanide in the freshly formed monolayer occurs predominantly through the pinholes and defects present in the monolayer. However, in the case of thermally annealed specimen, although the ferro/ferricyanide reaction is almost completely blocked, the electron-transfer reaction of hexaammineruthenium(III) chloride is not significantly inhibited. It is proposed that the electron-transfer reaction in the case of the ruthenium redox couple takes place by a tunneling mechanism through the high-electron-density aromatic naphthalene ring acting as a bridge between the monolayer-modified electrode and the ruthenium complex.
Description:	Restricted Access.
URI:	http://hdl.handle.net/2289/2257
ISSN:	1520-6106 1520-5215 (Online)
Alternative Location:	http://dx.doi.org/10.1021/jp052489u
Copyright:	2005 American Chemical Society
Appears in Collections:	Research Papers (SCM)

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