A Mechanism for Conductance Switching in Carbon-Based Molecular Electronic Junctions

Abstract

A molecular junction formed by a 10-15 Å organic monolayer between carbon and mercury contacts exhibited conductance switching for several monolayer structures. When the carbon potential was scanned to a sufficiently negative voltage relative to the mercury, the junction resistance suddenly decreased by at least an order of magnitude, and high resistance could be restored by a positive voltage scan. The high and low conductance states were persistent, and conductance switching was repeatable at least 100 cycles for the case of a terphenyl junction. The switching behavior is consistent with phenyl ring rotation and formation of a planar, quinoid structure as a consequence of electron injection into the monolayer. A unique feature of the junction structure is the strong electronic coupling between the monolayer system and the graphitic carbon through a quinoid double bond. Not only does this interaction lead to high conductivity and possible practical applications as a molecular switch, it also combines the electronic properties of the conjugated monolayer with those of the graphitic substrate. The switching mechanism reported here is an example of ''dry electrochemistry'' in which a redox process appears to occur under the influence of a high electric field in the absence of solvent or electrolyte.

A Comparative Study of Electrochemical Reduction of 4‐Nitrophenyl Covalently Grafted on Gold and Carbon

“…The current study is significant as, contrary to other studies performed that show the electrochemical reactivity of aryl diazonium salt derived layers is greater on gold than carbon [15,18], the electrochemical conversion of the 4-nitrophenyl to 4-aminophenyl proceeds more rapidly on carbon than on gold. This observation is rationalized by the unique quinoid structure that nitrobiphenol molecules have been shown to form on carbon surfaces [25,26], to demonstrate why this apparently contradictory observation is in fact consistent with previous observations.…”

“…Perhaps there is something specific about nitro moieties on carbon that enhances the electrochemical conversion of the nitro moiety on this surface. Solak et al [25] proposed that injecting an electron to ionize either nitrobiphenyl or biphenyl grafted on graphite electrodes could give rise to the rearrangement of the molecular structure to give a quinoid form (see Scheme 2). Through changes in the energetics and polarizability of the HOMO and LUMO, this quinoid structure greatly increases the conductance of the modified layer.…”

Progress with Molecular Electronic Junctions: Meeting Experimental Challenges in Design and Fabrication

“…2C). [69,[136][137][138] Related paradigms involve using eutectic Ga/In (eGaIn, melting point $16 8C) on SAMs at Ag, [139] Hg on adlayers bonded to flat carbon, [71,72,140] and Hg on a molecular layer at silicon. [141] A liquid metal top contact circumvents the use of vapor phase atoms, so metal incursion into the molecular layer is less likely.…”

Tuning of Organic Reversible Switching via Self‐Assembled Supramolecular Structures

“…[1] Amongst them, much research has been carried out on field-effect transistors, [2] light-emitting devices, [3] sensors, [4] and photovoltaic devices. [5] Another important property of organic molecules, namely voltage-induced conductance switching [6,7] can be applied in computational logic circuits. [8] In a memory-switching device, two conducting states are observed at the same applied voltage.…”