Slow charge relaxation in ionizable alkanethiols and its role in modulating electric characteristics of molecules and passivated gold nanoparticles

Abstract

This work addresses the electric characteristics associated with the slow ionization relaxation in ionizable alkylthiols which are widely used as passivation ligands for gold nanoparticles (NPs). It is observed that reversible ionic motion under a cycling voltage induces highly transient current with strong hysteresis loop. The ionization and relaxation of alkanethiols is responsible for the buildup and reversal of an internal bias, and thus leads to capacitive and charge memory effect in the electric conduction of the molecules. The role of ligand ionization in the electric behavior of passivated gold NPs is also demonstrated. The slow ionic process allows for both capacitive and resistive conduction and can be used to regulate the charge transport through the Au NP film. Our results represent a novel charge conduction mechanism governed by ligands in the NP/molecule binary system and would find new applications in molecular electronics and NP-based memory and sensor devices. © 2009 American Chemical Society.