Modulated Structure and Rectification Properties of a Molecular Junction by a Mixed Self-Assembled Monolayer

The organization of the self-assembled monolayer (SAM) determines its electronic structure and so governs the charge transport process and device performance when adopted into a molecular device. We report a systematic study on the supramolecular structure and rectification performance of the ferrocene (11-ferrocenyl-1-undecanethiol, FUT) based SAM modulated by mixed SAM with inert 1-undecanethiol (C₁₁SH) as diluent. We compared mixed SAMs by two different post assembly strategies, i.e., post assembly of C₁₁SH on FUT SAM and post assembly of FUT on C₁₁SH SAM. The organization and structure of FUT in the mixed SAM were extensively studied by cyclic voltammetry (CV) using the Laviron model. Rectification properties of the mixed SAM obtained using eutectic indium gallium (EGaIn) as the top electrode revealed that the magnitude and stability of the rectification ratio (RR) strongly correlated to not only the amount but also the phase structure and orientation of the FUT in the monolayer, resulting in a tunable RR and increased stability. The mixed monolayer achieved an increased performance relative to pure FUT by post assembling FUT on C₁₁SH SAM, which formed an optimally dense and well-packed monolayer with the FUT head resting on the top of the alkane SAM.