Transition from Tunneling to Schottky Barriers in Molecular Junctions Based on Polyoxometalate Monolayers

Schottky barriers are typically observed in mesoscale materials but are challenging to form at the molecular scale due to the discrete energy levels of molecules and the limited length of the transport channel, which hinder the development of an effective depletion region. In this study, we present the development of a molecular-scale Schottky diode within a monolayer junction by utilizing self-assembled monolayers (SAMs) of polyoxometalate (POM) nanoclusters. The high electron affinity and multiple redox states of POMs facilitate band bending at the molecule/EGaIn (Ga and In alloy) electrode interface, promoting the formation of a Schottky-like band structure. This molecular monolayer junction demonstrates an exceptional rectification ratio exceeding 3000, and temperature-dependent measurements reveal a transition in the charge transport mechanism from direct tunneling at low bias to thermionic emission at high bias. POM-based molecular junctions offer promising potential for molecular-scale Schottky devices, introducing novel mechanisms for high-performance molecular diodes. With their low power consumption, molecular diversity, and potential for integration into nanoscale circuits, molecular Schottky diodes are well-positioned to become key components in functional molecular devices.