Christian Nijhuis: "Electrochemistry" inside Molecular Tunnel Junctions

Speaker: Prof. Dr. Christian A. Nijhuis

Address: National University of Singapore

Title: “Electrochemistry” inside Molecular Tunnel Junctions

Date: Friday, May 17th, 2019 Time: 14.00 hrs

Place: Room 5115.0020, Nijenborgh 4, Groningen

Host: Ryan Chiechi

Tel.: +31 50 36 37664 / 38750 (secr)

ABSTRACT Charge transport phenomena across solid-state molecular tunnel junctions are usually assumed to proceed via activationless coherent tunnelling processes which can be described by the Landauer theory [1]. On the other extreme, thermally-activated charge transfer processes frequently encountered in wet electrochemical environments are incoherent and can be described by the Marcus theory [2]. In redox- active molecular junctions, the mechanism of charge transport may be in between these two extremes [3]. We have been studying the mechanisms of charge transport across molecular diodes inside EGaIn junctions based on self-assembled monolayers of with redox-active ferrocenyl (Fc) groups [4]. This system has been well-characterized and yields molecular diodes with exceptionally large rectification ratios [5]. We used this system to demonstrate experimentally the transition from the Marcus to the inverted Marcus region via intra-molecular orbital gating [6]. In the inverted Marcus region, charge transport is incoherent yet virtually independent of temperature; these findings fit well to a theoretical model that combines Landauer and Marcus theories [3]. Recently, we have been studying other types of redox-groups which show interesting phenome including molecular memory. As a group, these findings demonstrate that molecular junctions can operate in the grey zone in between pure electrochemical and tunnelling extremes which can be used in the future design of molecular junctions.

References 1) Vilan, A., Aswal, D. & Cahen, D. Chem. Rev. 2017, 117, 4248-428. 2) Joachim, C. & Ratner, M. A. Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 8801-8808. 3) Migliore, A., Schiff, P. & Nitzan, A. Phys. Chem. Chem. Phys. 2012, 14, 13746-13753. 4) Thompson, D.; Nijhuis, C. A. Acc. Chem. Res. 2016, 49, 2061–2069 5) Chen, X.; Roemer, M.; Yuan, L.; Du, W.; Thompson, D.; del Barco, E.; Nijhuis, C. A. Nat. Nanotech. 2017, 12, 797–803. 6) Yuan, L.; Wang, L.; Garrigues, A. R.; Jian, L.; Annadata, H. V.; del Barco, E.; Nijhuis, C. A. Nat. Nanotech. 2018, accepted.