Metal-Molecule Contacts and Charge Transport across Monomolecular Layers: Measurement and Theory

Abstract

Charge transport studies across molecular length scales under symmetric and asymmetric metal-molecule contact conditions using a simple crossed-wire tunnel junction technique are presented. It is demonstrated that oligo(phenylene ethynylene), a conjugated organic molecule, acts like a molecular wire under symmetric contact conditions, but exhibits characteristics of a molecular diode when the connections are asymmetric. To understand this behavior, we have calculated current-voltage ($I\mathrm{\text{−}}V$) characteristics using extended Huckel theory coupled with a Green’s function approach. The experimentally observed $I\mathrm{\text{−}}V$ characteristics are in excellent qualitative agreement with the theory.