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This paper describes tunneling junctions comprising self-assembled monolayers that can be converted between resistor and diode functionality in-place. The rectification ratio is affected by the hydration of densely packed carboxylic acid groups at the interface between the top-contact and the monolayer. We studied this process by treatment with water and a water scavenger using three different top-contacts, eutectic Ga–In (EGaIn), conducting-probe atomic force microscopy (CP-AFM), and reduced graphene oxide (rGO), demonstrating that the phenomena is molecular in nature and is not platform-speciffc. We propose a mechanism in which the tunneling junctions convert to diode behavior through the lowering of the LUMO, which is suffcient to bring it close to resonance at positive bias, potentially assisted by a Stark shift. This shift in energy is supported by calculations and a change in polarization observed by X-ray photoelectron spectroscopy and Kelvin probe measurements. We demonstrate light-driven modulation using spiropyran as a photoacid, suggesting that any chemical process that is coupled to the release of small molecules that can tightly bind carboxylic acid groups can be used as an external stimulus to modulate rectification. The ability to convert a tunneling junction reversibly between a diode and a resistor via an effect that is intrinsic to the molecules in the junction extends the possible applications of Molecular Electronics to reconfigurable circuits and other new functionalities that do not have direct analogs in conventional semiconductor devices.

Electron transport phenomena in molecular monolayers are complex and potentially different from those of single molecules because of, for example, molecule–molecule interactions. Unfortunately, access to detailed mechanistic investigations of molecular monolayer junctions at ultralow temperatures is typically hampered by the narrow range of operating temperatures for most large-area device platforms. Here, we present a highly optimized chemically derived graphene material with a near temperature-independent conductance profile. Using this material as a conducting interlayer electrode in solid-state molecular electronic devices, we show robust and reliable large-area molecular junction operation at temperatures ranging from room temperature to below 1 K, and we demonstrate the ability to measure inelastic electron tunneling spectroscopy of a conjugated molecular monolayer at cryogenic temperatures.

Vapor deposition of metals has long been the primary method for making contact with organic molecules in electronic devices in a fast and scalable manner. However, direct metal evaporation has proven to be the primary cause of device failure in solid-state molecular devices due to the degradation of the self-assembled molecular monolayers. The introduction of a protective interlayer between the molecular monolayer and the evaporated top electrode greatly improves the yield of working devices but at the cost of an increased internal contact resistance that depends on the nature of the interlayer and its interface with both organic molecules and metal top electrode. In the present work, we investigate the performance of a single layered graphene oxide as an atomically thin interlayer in solid-state molecular devices. We show that a single layered graphene oxide sheet is sufficient to protect an organic monolayer of alkane thiols from metal-induced degradation and short-circuiting. Remarkably, and despite graphene oxide being an insulating material, the contact resistance in our devices with a graphene oxide as a protective interlayer is similar to that of pure metal/molecule/metal junctions. We interpret this observation as graphene oxide effectively becoming part of the top electrode. The graphene oxide monolayer is thus a very promising candidate as a protective interlayer in solid-state molecular devices.