Comprehensive suppression of single-molecule conductance using destructive σ-interference

Abstract

The tunnelling of electrons through molecules (and through any nanoscale insulating and dielectric material ) shows exponential attenuation with increasing length , a length dependence that is reflected in the ability of the electrons to carry an electrical current. It was recently demonstrated that coherent tunnelling through a molecular junction can also be suppressed by destructive quantum interference , a mechanism that is not length-dependent. For the carbon-based molecules studied previously, cancelling all transmission channels would involve the suppression of contributions to the current from both the π-orbital and σ-orbital systems. Previous reports of destructive interference have demonstrated a decrease in transmission only through the π-channel. Here we report a saturated silicon-based molecule with a functionalized bicyclo[2.2.2]octasilane moiety that exhibits destructive quantum interference in its σ-system. Although molecular silicon typically forms conducting wires , we use a combination of conductance measurements and ab initio calculations to show that destructive σ-interference, achieved here by locking the silicon-silicon bonds into eclipsed conformations within a bicyclic molecular framework, can yield extremely insulating molecules less than a nanometre in length. Our molecules also exhibit an unusually high thermopower (0.97 millivolts per kelvin), which is a further experimental signature of the suppression of all tunnelling paths by destructive interference: calculations indicate that the central bicyclo[2.2.2]octasilane unit is rendered less conductive than the empty space it occupies. The molecular design presented here provides a proof-of-concept for a quantum-interference-based approach to single-molecule insulators.

Multicenter‐Bond‐Based Quantum Interference in Charge Transport Through Single‐Molecule Carborane Junctions

“…Quantum interference (QI) offers the unique opportunity to tune charge transport through molecular devices and materials, [1] which leads to various applications such as QIbased thermoelectrics, [2] molecular memory, [3] molecular transistors, [4] and sensors. [5] Them olecular building blocks play avital role in investigating QI-based molecular junctions.…”

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Molecular components are vital to introduce and manipulate quantum interference (QI) in charge transport through molecular electronic devices.Uptonow,the functional molecular units that show QI are mostly found in conventional p-a nd s-bond-based systems;i ti st hus intriguing to study QI in multicenter bonding systems without both p-a nd sconjugations.N ow the presence of QI in multicenter-bondbased systems is demonstrated for the first time,t hrough the single-molecule conductance investigation of carborane junctions.W ef ind that all the three connectivities in carborane frameworks showdifferent levels of destructive QI, which leads to highly suppressed single-molecule conductance in para-and meta-connected carboranes.T he investigation of QI into carboranes provides ap romising platform to fabricate molecular electronic devices based on multicenter bonds.Quantum interference (QI) offers the unique opportunity to tune charge transport through molecular devices and materials, [1] which leads to various applications such as QIbased thermoelectrics, [2] molecular memory, [3] molecular transistors, [4] and sensors. [5] Them olecular building blocks play avital role in investigating QI-based molecular junctions.

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Thermal and Thermoelectric Properties of Molecular Junctions

“…This enhancement is mainly because the meta configuration of the central ring of the OPE molecule induces destructive π‐interference which leads to a steeper slope of the transmission function at the Fermi energy. Similarly, a recent study by Garner et al reports that this concept can also be applied to destructive σ‐interference in a σ‐orbital system (Figure c). Specifically, they demonstrate that a saturated silicon‐based molecule with a functionalized bicyclo[2.2.2]octasilane moiety (Si2‐Si222‐Si2) can exhibit strong destructive QI in its σ‐system.…”

Nanoscale Organic Thermoelectric Materials: Measurement, Theoretical Models, and Optimization Strategies

“…Utilizing the destructive quantum interference effect, Garner et al achieved the single molecule insulator in a space with a length of less than 1 nm. As showed in Figure a, its conductance was even smaller than that obtained by occupying the vacuum barrier energy of the same sized space, and an unusually large thermoelectric potential (up to 0.97 mV K −1 ) was obtained (Figure b,c).…”

“…c) Measured conductance of Si2‐Si222‐Si2, Si222, and Si4. Reproduced with permission . Copyright 2018, Springer Nature.…”