Moleculeelectrode

Molecule-electrode junctions are nanoscale assemblies where a discrete molecule forms a conductive bridge between two metallic or semiconducting contacts. In typical setups, gold or other noble metals serve as electrodes, and the molecule is anchored by chemical groups such as thiols, amines, or phosphines. Junctions can be created using mechanically controllable break junctions, scanning tunneling microscope break junctions, or electromigration techniques to produce a gap bridged by a single molecule or a small number of molecules.

Electron transport through a molecule-electrode junction proceeds via molecular orbitals that couple to the electrode electronic states. The conductance depends on the alignment of the molecular levels with the electrode Fermi levels, the strength of electrode–molecule coupling, and the molecule’s conformation. Transport can show resonant tunneling, Coulomb blockade, or, in some cases with unpaired spins, the Kondo effect. Theoretical modeling commonly uses non-equilibrium Green’s function methods combined with density functional theory to predict I-V characteristics and transmission spectra.

Key measurements include current-voltage curves, differential conductance, and statistical conductance histograms across many breaking events. Variability arises from contact geometry, bonding chemistry, and molecular conformation, posing challenges for reproducibility.

Molecule-electrode systems underpin efforts in molecular electronics, aiming to realize single-molecule diodes, switches, and wires, potentially enabling ultra-dense circuits and novel energy conversion schemes. Ongoing work addresses stability, scalability, and integration with larger devices, as well as improving synthetic control over linker groups and junction geometry.