We investigated the gate bias stress effects of multilayered MoS2 field effect transistors (FETs) with a back-gated configuration. The electrical stability of the MoS2 FETs can be significantly influenced by the electrical stress type, relative sweep rate, and stress time in an ambient environment. Specifically, when a positive gate bias stress was applied to the MoS2 FET, the current of the device decreased and its threshold shifted in the positive gate bias direction. In contrast, with a negative gate bias stress, the current of the device increased and the threshold shifted in the negative gate bias direction. The gate bias stress effects were enhanced when a gate bias was applied for a longer time or when a slower sweep rate was used. These phenomena can be explained by the charge trapping due to the adsorption or desorption of oxygen and/or water on the MoS2 surface with a positive or negative gate bias, respectively, under an ambient environment. This study will be helpful in understanding the electrical-stress-induced instability of the MoS2-based electronic devices and will also give insight into the design of desirable devices for electronics applications.

We investigated the physical properties of molybdenum disulfide (MoS2) atomic crystals with a sulfur vacancy passivation after treatment with alkanethiol molecules including their electrical, Raman, and photoluminescence (PL) characteristics. MoS2, one of the transition metal dichalcogenide materials, is a promising two-dimensional semiconductor material with good physical properties. It is known that sulfur vacancies exist in MoS2, resulting in the n-type behavior of MoS2. The sulfur vacancies on the MoS2 surface tend to form covalent bonds with sulfur-containing groups. In this study, we deposited alkanethiol molecules on MoS2 field effect transistors (FETs) and then characterized the electrical properties of the devices before and after the alkanethiol treatment. We observed that the electrical characteristics of MoS2 FETs dramatically changed after the alkanethiol treatment. We also observed that the Raman and PL spectra of MoS2 films changed after the alkanethiol treatment. These effects are attributed to the thiol (-SH) end groups in alkanethiols bonding at sulfur vacancy sites, thus altering the physical properties of the MoS2. This study will help us better understand the electrical and optical properties of MoS2 and suggest a way of tailoring the properties of MoS2 by passivating a sulfur vacancy with thiol molecules.

A mechanically controllable break junction (MCBJ) represents a fundamental technique for the investigation of molecular electronic junctions, especially for the study of the electronic properties of single molecules. With unique advantages, the MCBJ technique has provided substantial insight into charge transport processes in molecules. In this review, the techniques for sample fabrication, operation and the various applications of MCBJs are introduced and the history, challenges and future of MCBJs are discussed.

We investigated the effects of passivation on the electrical characteristics of molybdenum disulfide (MoS(2)) field effect transistors (FETs) under nitrogen, vacuum, and oxygen environments. When the MoS(2) FETs were exposed to oxygen, the on-current decreased and the threshold voltage shifted in the positive gate bias direction as a result of electrons being trapped by the adsorbed oxygen at the MoS(2) surface. In contrast, the electrical properties of the MoS(2) FETs changed only slightly in the different environments when a passivation layer was created using polymethyl methacrylate (PMMA). Specifically, the carrier concentration of unpassivated devices was reduced to 6.5 × 10(15) cm(-2) in oxygen from 16.3 × 10(15) cm(-2) in nitrogen environment. However, in PMMA-passivated devices, the carrier concentration remained nearly unchanged in the range of 1-3 × 10(15) cm(-2) regardless of the environment. Our study suggests that surface passivation is important for MoS(2)-based electronic devices.

An ultimate goal of molecular electronics, which seeks to incorporate molecular components into electronic circuit units, is to generate functional molecular electronic devices using individual or ensemble molecules to fulfill the increasing technical demands of the miniaturization of traditional silicon-based electronics. This review article presents a summary of recent efforts to pursue this ultimate aim, covering the development of reliable device platforms for high-yield ensemble molecular junctions and their utilization in functional molecular electronic devices, in which distinctive electronic functionalities are observed due to the functional molecules. In addition, other aspects pertaining to the practical application of molecular devices such as manufacturing compatibility with existing complementary metal-oxide-semiconductor technology, their integration, and flexible device applications are also discussed. These advances may contribute to a deeper understanding of charge transport characteristics through functional molecular junctions and provide a desirable roadmap for future practical molecular electronics applications.

Molecules are promising candidates for electronic device components because of their small size, chemical tunability, and ability to self-assemble. A major challenge when building molecule-based electronic devices is forming reliable molecular junctions and controlling the electrical current through the junctions. Here, we report a three-terminal junction that combines both the ability to form a stable single-molecule junction via the mechanically controllable break junction (MCBJ) technique and the ability to shift the energy levels of the molecule by gating. Using a noncontact side-gate electrode located a few nanometers away from the molecular junction, the conductance of the molecule could be dramatically modulated because the electrical field applied to the molecular junction from the side gate changed the molecular electronic structure, as confirmed by the ab initio calculations. Our study will provide a new design for mechanically stable single-molecule transistor junctions fabricated by the MCBJ method.

The electrical properties of diarylethene photoswitching molecular devices on flexible substrates are studied. When exposed to UV or visible light, diarylethene molecular devices show two electrical states (a high and a low conductance state) with a discrepancy of an order of magnitude in the level of current between the two states. The diarylethene flexible molecular devices exhibit excellent long‐time stability and reliable electrical characteristics in both conductance states when subjected to various mechanical stresses.

The electrical properties of ferrocene-alkanethiolate self-assembled monolayers (SAMs) on a high yield solid-state device structure are investigated. The devices are fabricated using a conductive polymer interlayer between the top electrode and the SAM on both silicon-based rigid substrates and plasticbased fl exible substrates. Asymmetric electrical transport characteristics that originate from the ferrocene moieties are observed. In particular, a distinctive temperature dependence of the current (i.e., a decrease in current density as temperature increases) at a large reverse bias, which is associated with the redox reaction of ferrocene groups in the molecular junction, is found. It is further demonstrated that the molecular devices can function on fl exible substrates under various mechanical stress confi gurations with consistent electrical characteristics. This study enhances the understanding of asymmetric molecules and may lead to the development of functional molecular electronic devices on both rigid and fl exible substrates.