Switching in Nanoscale Molecular Junctions due to Contact Reconfiguration

Abstract

Switching effects are key elements in the design and characterization of nanoscale molecular electronics systems. They are used to achieve functionality through the transition between different conducting states. In this study, we analyze the presence of switching events in reference molecular systems, which are not designed to have switching behavior, such as oligo(phenylene ethynylene)s and alkanes, using the mechanically controllable break junction technique. These events can be classified in two groups, depending on whether the breaking trace shows exponential decay or plateau-like features before the switch happens. We argue that the former correspond to junctions forming after rupture of the gold atomic point contact, while the latter can be related to a change in the contact geometry of the junction. These results highlight how a proper choice of anchoring group and careful comparison with reference compounds are essential to understanding the origin of switching in molecular break junctions.

Exploring the impact of select anchor groups for norbornadiene/quadricyclane single-molecule switches

“…In the case of NBD-3, Class 1 exhibits a conductance of 2 Â 10 À4 G 0 , which is twice as low as the thioacetate counterpart, consistent with observations in the literature for similar systems. 29,30,33,40 Notably, the plateau length for NBD-3 is 0.7 nm, corresponding to a molecular length of 1.3 nm, which is consistent with the SCXRD result. The observed difference of 0.5 nm is considerably higher than the expected 0.1-0.2 nm often reported in the literature.…”

“…The observed difference of 0.5 nm is considerably higher than the expected 0.1–0.2 nm often reported in the literature. 29,30,40,41…”

“…In previous studies on similar NBD/QC derivatives, 25 the transition was proven to be possible at low yields even at a small voltage bias. However, the presence of other mechanisms, such as the formation of junctions in which the molecule binds with different coordination to the gold surface, 29 cannot be excluded.…”

“…The measurements were performed at room temperature, utilizing a voltage bias of 0.1 V and a piezoelectric element actuation speed of 50 V s À1 , corresponding to about 1 nm s À1 in electrode displacement speed. A deviation from the typically employed molecular solution concentrations of 100 mM 29,37,38 was necessary for stability during the experiment. Specifically, at a 100 mM concentration with NBD-2 as the target molecule, stable measurements were unattainable, yielding only a few consecutive breaking traces.…”

“…Given the considerable influence that experimental setup, molecular length, and anchor groups can exert on conductance properties, 29–33 this study embarks on investigating a novel series of thioether- and thioester-capped NBD molecules, characterized by reduced lengths and encompassing three distinct anchor groups: tert -butyl thioether ( NBD-1 ), thioacetate ( NBD-2 ), and methyl thioether ( NBD-3 ). To achieve this, a modified synthetic strategy was employed, capitalizing on palladium-catalyzed cross-coupling reactions to construct the molecular systems.…”