Molecular Junctions and Electron Transport Phenomena

Molecular junctions, comprising one or a few molecules bridged between conductive electrodes, represent the ultimate limit of electronic miniaturisation. Electron transport through these junctions is governed by a variety of quantum phenomena, including tunnelling, interference, Coulomb blockade and spin-selective effects. Charge carriers encounter discrete energy levels of the molecule, leading to rectification, switching and negative differential resistance under applied bias. Quantum interference arises when multiple molecular pathways combine constructively or destructively, profoundly affecting conductance. In chiral junctions, coupling between electron spin and molecular handedness can yield spin-polarised currents without magnetic elements. Advances in fabrication techniques—such as mechanically controlled break junctions and self-assembled monolayers—paired with theoretical modelling, have enabled detailed mapping of transmission functions and real-time probing of dynamic processes. These insights are guiding the design of molecular transistors, logic gates and spin filters for next‐generation low-power nanoscale devices.

Research from Nature Portfolio

Recent studies have demonstrated that tailored quantum interference within single-molecule transistors can markedly enhance device performance. In one example, a zinc-porphyrin core coupled to graphene electrodes realised a three-terminal junction exhibiting a conductance-switching ratio exceeding 10⁴ and a subthreshold swing at the thermionic limit. Detailed mapping of anti-resonance features confirmed that destructive interference between molecular orbitals and edge states underpins the high on/off contrast and stability over repeated cycles. In a foundational demonstration of interference design rules, oligo(phenyleneethynylene) junctions were shown to obey a quantum circuit rule dictating conductance ratios across para- and meta-connected core units. This finding established that the central aromatic ring dominates overall conductance independently of anchor connectivity, providing a predictive framework for molecular-scale circuit assembly.

Molecular Junctions and Electron Transport Phenomena publication trend

The graph below shows the total number of articles in molecular junctions and electron transport phenomena across all publications each year (not limited to Nature Index journals).

Technical terms

Molecular junction: A nanoscale bridge formed by one or a small number of molecules connecting two conductive electrodes, through which electrons can tunnel.

Quantum interference: The phenomenon by which electron wavefunctions traversing multiple pathways through a molecule combine to enhance (constructive) or suppress (destructive) conductance.

Coulomb blockade: Suppression of electron transport at low bias due to electrostatic charging energy required to add an extra electron to a small system.

Subthreshold swing: A measure of how effectively a transistor can switch off, defined as the voltage required to change the current by one order of magnitude.

Chiral induced spin selectivity (CISS): The effect whereby electron transmission through a chiral molecule becomes spin-polarised, with spin orientation correlated to molecular handedness.

References

1. Chiral Induced Spin Selectivity. Chemical Reviews (2024).
2. Quantum interference enhances the performance of single-molecule transistors. Nature Nanotechnology (2024).
3. A quantum circuit rule for interference effects in single-molecule electrical junctions. Nature Communications (2015).
4. Gating of Quantum Interference in Molecular Junctions by Heteroatom Substitution. Angewandte Chemie International Edition (2016).