Effect of solvents on the self-assembly of long chain alkylphosphonic acids on indium tin oxide surface - In situ studies on the adsorption kinetics and electron transfer process

Abstract

The spontaneous self-assembly process of phosphonic acids (PAs) onto indium tin oxide (ITO) surface has been studied in this work. We have carried out in situ adsorption kinetics studies of phosphonic acids in ethanol as a solvent using electrochemical impedance spectroscopy (EIS). Further, the effect of different solvents like ethanol, water, toluene and hexane on the structural integrity of the alkylphosphonic acid (CH3 (CH2)n PO3H2, n=15,17) thin films on ITO surface has been investigated by using [Fe(CN)6]3‐/4‐ as a redox probe. From the study of formation kinetics, it is concluded that molecular self-assembly process follows two adsorption steps, a fast first step followed by a slower second step. The results of cyclic voltammetric (CV) and impedance measurements show that phosphonic acids form a highly impermeable surface film on ITO when polar solvents like ethanol and water are used.