Optical, electrical, and electrochemical characteristics of ultrathin poly(phenylene oxide) films: organic dielectrics less than 10 nm thick

Abstract

Passive, ultra-thin dielectric films (5-7 nm) of poly(phenylene oxide), PPO, are formed by the anodic electropolymerization of tetramethylammonium phenoxide from acetonitrile onto Pt or Au electrodes. These films can have exceptionally low permeabilities to solution redox species, depending on electropolymerization potential, the time of deposition, and cross-linking reactions. The latter becomes evident at +0.4 V vs. SSCE and in the presence of electrogenerated mediator-oxidant. PPO blocks the cyclic voltammetry of ferrocene carboxylic acid and Cl − oxidations in acetonitrile by > 99% and 92%, respectively, and reduction of [Fe(CN) 6] −3 and oxidation of the sodium salt of ferrocene carboxylic acid in water by ⩾ 99%. By rotating disk voltammetry, the permeability PD S,POL of the film to FeCp 2 * in CH 3CN is as low as 8 × 10 −11 cm 2 s . Films prepared from alkyl substituted phenolates are thicker, more hydrophobic, but also more permeable owing to less efficient cross-linking. Film thicknesses were obtained by profilometry, ellipsometry, XPS, and high frequency electrical capacitance measurements, and physical and structural information by use of contact angle measurements and attenuated total reflectance FTIR.