Resonant transport in a highly conducting single molecular junction via metal-metal covalent bond

TL;DR

This study demonstrates a highly conductive, air-stable molecular junction using Ferrocene, revealing resonant transport facilitated by covalent-like metal-metal bonding, with implications for low-power molecular electronics.

Contribution

It provides direct experimental evidence and theoretical analysis of resonant transport in a Ferrocene-based junction with covalent-like metal-metal bonding at ambient conditions.

Findings

Conductance peak at ~0.2 G0 observed in Ferrocene junctions.

Strong hybridization between Au electrodes and Fe atom enables near-perfect transmission.

Covalent-like bonding with bond energies around 660 meV confirmed by calculations.

Abstract

Achieving highly transmitting molecular junctions through resonant transport at low bias is key to the next-generation low-power molecular devices. Although, resonant transport in molecular junctions was observed by connecting a molecule between the metal electrodes via chemical anchors by applying a high source-drain bias (> 1V), the conductance was limited to < 0.1 G$_0$, G$_0$ being the quantum of conductance. Here, we report electronic transport measurements by directly connecting a Ferrocene molecule between Au electrodes at the ambient condition in a mechanically controllable break junction setup (MCBJ), revealing a conductance peak at ~ 0.2 G$_0$ in the conductance histogram. A similar experiment was repeated for Ferrocene terminated with amine (-NH2) and cyano (-CN) anchors, where conductance histograms exhibit an extended low conductance feature including the sharp high conductance peak, similar to pristine ferrocene. Statistical analysis of the data along with density functional theory-based transport calculation suggests the possible molecular conformation with a strong hybridization between the Au electrodes and Fe atom of Ferrocene molecule is responsible for a near-perfect transmission in the vicinity of the Fermi energy, leading to the resonant transport at a small applied bias (< 0.5V). Moreover, calculations including Van der Waals/dispersion corrections reveal a covalent like organometallic bonding between Au and the central Fe atom of Ferrocene, having bond energies of ~ 660 meV. Overall, our study not only demonstrates the realization of an air-stable highly transmitting molecular junction, but also provides an important insight about the nature of chemical bonding at the metal/organo-metallic interface.