IMPEDANCE ANALYSIS OF SELF-ASSEMBLED NAPHTHALENE DISULFIDE MONOLAYER ON GOLD USING EXTERNAL REDOX PROBES

A self-assembled monolayer (SAM) of naphthalene disulfide (NDS) has be en formed on a polycrystalline gold surface. Techniques like cyclic vo ltammetry and impedance measurement with an external redox probe along with scanning tunnelling microscopy (STM) are used to investigate the monolayer structure and ion permeation through it. Impedance analysis shows that the rare constant or a fast redox couple like Fe(CN)(6)(4- /3-) has decreased from 2.3 x 10(-2) to 9.4 x 10(-4) cm s(-1) due to t he barrier provided by the monolayer. The STM image clearly shows the presence of defects (as pinholes) on the monolayer surface in agreemen t with the residual current observed in the voltammograms. (C) 1998 El sevier Science S.A. All rights reserved.