Effect of Surface Morphology of a SiO2/Si Reference Electrode Modified by ODMS on the Responses to pH and Ionic Strength

Abstract

The purpose of this work was to study the effect of surface morphology on the responses to pH and ionic strength of a SiO2/Si reference electrode (RE) modified by octadecyltrimethoxysilane (ODMS). Representative REs with contact angles (CA) of 60o, 80o and 106o were studied in various solutions: those with combined effects of pH and ionic strength, those with ionic strength variation and constant pH, and those with pH variation and constant ionic strength. REs with the flat surface shows response to ionic strength, while REs with the rough surface shows response to pH. The reason may be that total ionic strength determines the charge and potential distribution in the electrolyte-insulator-semiconductor structure for REs with flat surfaces, but that the combined effects of uncovered binding sites, penetration of H+ into pinholes, and the special adsorption of H+ dictate the charge and potential distribution for REs with rough surfaces.