Oral: Gate-Voltage Dependent Charge Transport in Large-Area Redox-Active Molecular Transistors

The field of molecular electronics presents an important frontier in nanotechnology, where single molecules or molecular monolayers are used as active electronic components. In particular, molecular transistors have emerged as key devices for studying molecular orbital gating and charge transport mechanisms at the quantum level [1]. The transport properties of redox-active molecules through their frontier orbitals have been extensively studied. Furthermore, the use of electrolytes as gate material has enabled vertical electrostatic gating, allowing for the implementation of molecular transistors in large-area molecular devices [2]. In this study, we fabricated molecular vertical transistors and experimentally validated a new transport theory that integrates the tunneling mechanisms and Marcus theory, represented by so-called Lifetime-Broadened Marcus theory [3]. Specifically, we fabricated large-area vertical molecular transistors using redox-active ferrocenyl alkanethiolate (FcC11) molecules, Au and monolayer graphene films, and an ion-gel, as the channel, bottom and top electrodes, and gate, respectively. The monolayer graphene acts as a transparent medium for the electric field created by the electric double layer (EDL) of the ion-gel, facilitating effective gating while also serving as an electrode. We conducted temperature-variable experiments to investigate the dominant charge transport mechanisms within the molecular devices. The results demonstrate that the activation energy for charge transport is sensitive to the gate voltage, which influences the position of the HOMO. Importantly, the experimental data could not be fully explained by either Landauer theory or Marcus theory alone. However, the Lifetime-Broadened Marcus theory, which combines the two, provides a comprehensive description of the data across all gate voltage regimes.

References

[1] D. Xiang et al., Chem. Rev. 116, 4318 (2016).

[2] C. Jia et al., Sci. Adv. 4, eaat8237 (2018).

[3] J. Sowa et al., J. Chem. Phys. 149, 154112 (2018).