Redox Control of Charge Transport in Vertical Ferrocene Molecular Tunnel Junctions

Iain M Grace,Zipeng Zhao,Xiangfeng Duan,Ziying Feng,Zhihong Huang,Colin J Lambert,Yu Huang,Peng Chen,Laiyuan Wang,Chuancheng Jia,Yiliu Wang,Jingyuan Zhou,Abdelkareem Almeshal,Peiqi Wang

doi:10.1016/j.chempr.2020.02.018

Iain M Grace, Zipeng Zhao + Show 12 more

Open Access

https://doi.org/10.1016/j.chempr.2020.02.018

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Journal: Chem	Publication Date: Mar 19, 2020
Citations: 41	License type: publisher-specific-oa

Affiliation: Lancaster University, University of California, Los Angeles

Abstract

Summary Controlling charge transport through molecular tunnel junctions is of crucial importance for exploring basic physical and chemical mechanisms at the molecular level and realizing the applications of molecular devices. Here, through a combined experimental and theoretical investigation, we demonstrate redox control of cross-plane charge transport in a vertical gold/self-assembled monolayer (SAM)/graphene tunnel junction composed of a ferrocene-based SAM. When an oxidant/reductant or electrochemical control is applied to the outside surface of the neutral single-layer graphene top electrode, reversible redox reactions of ferrocene groups take place with charges crossing the graphene layer. This leads to counter anions on the outer surface of graphene, which balance the charges of ferrocene cations in the oxidized state. Correspondingly, the junctions switch between a high-conductance, neutral state with asymmetrical characteristics and a low-conductance, oxidized state with symmetrical characteristics, yielding a large on/off ratio (>100).

Highlights

A Ti/Au electrode is thermally deposited on the chip with one end around the graphene sheet, and a small amount of reactive solution or electrolyte solution is dropped on the top of Au/Fc-self-assembled monolayer (SAM)/single-layer graphene (SLG) channel
Working Mechanism of the Junction To understand the redox tunable charge transport behavior in the Fc-SAM devices, we have developed a theoretical model by using a combination of density functional theory (DFT)[45] and quantum transport theory.[46]
Due to the electronic transparency and ion impermeability of graphene in most cases, in the oxidized state, the counter anions remain separated on the top surface of the graphene layer and balance the oxidized Fc cations beneath graphene

Summary

SUMMARY

Controlling charge transport through molecular tunnel junctions is of crucial importance for exploring basic physical and chemical mechanisms at the molecular level and realizing the applications of molecular devices. Through a combined experimental and theoretical investigation, we demonstrate redox control of cross-plane charge transport in a vertical gold/self-assembled monolayer (SAM)/graphene tunnel junction composed of a ferrocene-based SAM. When an oxidant/reductant or electrochemical control is applied to the outside surface of the neutral single-layer graphene top electrode, reversible redox reactions of ferrocene groups take place with charges crossing the graphene layer. This leads to counter anions on the outer surface of graphene, which balance the charges of ferrocene cations in the oxidized state. The junctions switch between a high-conductance, neutral state with asymmetrical characteristics and a low-conductance, oxidized state with symmetrical characteristics, yielding a large on/off ratio (>100)

INTRODUCTION

RESULTS AND DISCUSSION

Conclusions