Controlled Hysteresis of Conductance in Molecular Tunneling Junctions

• Published in: ACS nano 2022-03, Vol.16 (3)
• Main Authors: Park, Junwoo, Kodaimati, Mohamad S., Belding, Lee, Root, Samuel E., Schatz, George C., Whitesides, George M.
• Format: Article
• Language: English
• Subjects: charge transport; charge transport, hysteresis in conductance, quantum tunneling, molecular tunneling junctions, self-assembled monolayers (SAMs), EGaIn junction, molecular electronics; EGaIn junction; electrical conductivity; electrodes; gold; hysteresis; hysteresis in conductance; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; molecular electronics; molecular tunneling junctions; quantum tunneling; self-assembled monolayers (SAMs); tunneling
• ISSN: 1936-0851; 1936-086X

The problem this paper addresses is the origin of the hysteretic behavior in two-terminal molecular junctions made from an EGaIn electrode and self-assembled monolayers of alkanethiolates terminated in chelates (transition metal dichlorides complexed with 2,2'-bipyridine; BIPY-MCl2). The hysteresis of conductance displayed by these BIPY-MCl2 junctions changes in magnitude depending on the identity of the metal ion (M) and the window of the applied voltage across the junction. The hysteretic behavior of conductance in these junctions appears only in an incoherent (Fowler–Nordheim) tunneling regime. When the complexed metal ion is Mn(II), Fe(II), Co(II), or Ni(II), both incoherent tunneling and hysteresis are observed for a voltage range between +1.0 V and –1.0 V. When the metal ion is Cr(II) or Cu(II), however, only resonant (one-step) tunneling is observed, and the junctions exhibit no hysteresis and do not enter the incoherent tunneling regime. Using this correlation, the conductance characteristics of BIPY-MCl2 junctions can be controlled. Furthermore, this voltage-induced change of conductance demonstrates a simple, fast, and reversible way (i.e., by changing the applied voltage) to modulate conductance in molecular tunneling junctions.