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.

We investigated the photoconductive characteristics of molybdenum disulfide (MoS2) field-effect transistors (FETs) that were fabricated with mechanically exfoliated multi-layer MoS2 flakes. Upon exposure to UV light, we observed an increase in the MoS2 FET current because of electron-hole pair generation. The MoS2 FET current decayed after the UV light was turned off. The current decay processes were fitted using exponential functions with different decay characteristics. Specifically, a fast decay was used at the early stages immediately after turning off the light to account for the exciton relaxation, and a slow decay was used at later stages long after turning off the light due to charge trapping at the oxygen-related defect sites on the MoS2 surface. This photocurrent decay phenomenon of the MoS2 FET was influenced by the measurement environment (i.e., vacuum or oxygen environment) and the electrical gate-bias stress conditions (positive or negative gate biases). The results of this study will enhance the understanding of the influence of environmental and measurement conditions on the optical and electrical properties of MoS2 FETs.