z-Piezo Pulse-Modulated STM Break Junction: Toward Single-Molecule Rectifiers with Dissimilar Metal Electrodes

A Robust Molecular Rectifier Based on Ferrocene-Functionalized Bis(diarylcarbene) on Gold

While thiol-based adsorbates have achieved significant success in surface modification and molecular electronics, their thermal and storage instability has hindered long-term commercial viability. Carbene-based thin films offer a promising alternative due to their enhanced stability; however, their molecular electronic properties after postfunctionalization remain to be investigated. In this study, by attaching a ferrocene (Fc) unit to a bis(diarylcarbene)-modified gold surface via carbodiimide coupling, the system exhibits diode behavior with a current rectification ratio of ∼100. This diode behavior is highly temperature-dependent, indicating that hopping is the dominant mechanism for current rectification. Notably, the system demonstrated excellent electrical stability under ambient storage conditions for over 6 months. Our work highlights the potential for designing carbene-based molecular junctions through postmodification and for developing durable functional molecular electronic devices.

Supramolecular Diodes with Donor-Acceptor Interactions

Inspired by the initial proposal of σ-bridged donor-acceptor (D-σ-A) single-molecule diodes in 1974, extensive studies over the past 50 years have explored various designs for π-conjugated D-π-A single-molecule diodes due to their feasible chemical synthesis and effective charge transfer. However, the rectification ratio of π-conjugated single-molecule diodes has been long-term limited by the challenge of asymmetric electronic coupling to induce the rectification effect. Here, we present a supramolecular diode constructed through an intramolecular π-π interaction-driven assembly strategy. The asymmetric transmission in this system is tunable via subangström mechanical control, resulting in a rectification ratio of up to 16. Electron transport studies reveal that this through-space D-π-π-A system constructed by the π-π stacking between pyrene (Py) and naphthalenediimide (NDI) is crucial for achieving asymmetric currents under different bias polarization. Theoretical calculations suggest that the intermolecular destructive quantum interference not only enables a sharp variation in electron transmission but also facilitates asymmetric electronic energy shifts through mechanical stretching, significantly improving the rectification ratio. Our work provides a general approach to fabricating and modulating asymmetric molecular architectures through noncovalent supramolecular interactions, showcasing the potential of high-performance single-molecule rectifiers.

Electromechanics of the Molecule-Electrode Interface and Interface-Mediated Effects in Single-Molecule Junctions

The molecule-electrode interface can regulate both the efficiency and pathways of electron transport through single-molecule junctions (SMJs). The electromechanics of the interface has proven crucial in exposing the underlying mechanisms of electron transmission through SMJs, providing a theoretical base and practical guidance for designing and constructing functional molecular devices. Here we encompass several currently developed methodologies for investigating the electromechanics of molecule-electrode interface and provide an account of their application in elucidating the effects of the molecule-electrode interface on electron transport properties of SMJs. This review will offer a comprehensive picture and new insights into developing single-molecule electromechanical devices and the progression of devices' mechanical stability toward large-scale integration.

Boron-Doped Single-Molecule van der Waals Diode

Single-molecule diode was the first proposed device in molecular electronics. Despite the great efforts and advances over 50 years, the reported rectification ratios, the most critical parameter of a diode, remain moderate for the single-molecule diode. Herein, we report an approach to achieve a larger rectification ratio by adopting the combined strategies of p-type boron doping, the single-layer graphene nodes, and the van der Waals layer-by-layer architecture. Measured current-voltage curves showed one of the as-fabricated single-molecule diodes hit an unprecedented large rectification ratio of 457 at ±1 V. Break junction operations and spectroscopic measurements revealed the three-atom-thick configuration of the single-molecule diodes. With the experimental and theoretical calculation results, we demonstrated the doped boron atoms induced holes to redistribute the electron density, making the asymmetric coupling at positive and negative biases, and the van der Waals interaction promoted asymmetric coupling and significantly boosted diode performance.

Self-Assembled Monolayers for Interfacial Engineering in Solution-Processed Thin-Film Electronic Devices: Design, Fabrication, and Applications

Interfacial engineering has long been a vital means of improving thin-film device performance, especially for organic electronics, perovskites, and hybrid devices. It greatly facilitates the fabrication and performance of solution-processed thin-film devices, including organic field effect transistors (OFETs), organic solar cells (OSCs), perovskite solar cells (PVSCs), and organic light-emitting diodes (OLEDs). However, due to the limitation of traditional interfacial materials, further progress of these thin-film devices is hampered particularly in terms of stability, flexibility, and sensitivity. The deadlock has gradually been broken through the development of self-assembled monolayers (SAMs), which possess distinct benefits in transparency, diversity, stability, sensitivity, selectivity, and surface passivation ability. In this review, we first showed the evolution of SAMs, elucidating their working mechanisms and structure-property relationships by assessing a wide range of SAM materials reported to date. A comprehensive comparison of various SAM growth, fabrication, and characterization methods was presented to help readers interested in applying SAM to their works. Moreover, the recent progress of the SAM design and applications in mainstream thin-film electronic devices, including OFETs, OSCs, PVSCs and OLEDs, was summarized. Finally, an outlook and prospects section summarizes the major challenges for the further development of SAMs used in thin-film devices.

Characterization and Application of Supramolecular Junctions

The convergence of supramolecular chemistry and single-molecule electronics offers a new perspective on supramolecular electronics, and provides a new avenue toward understanding and application of intermolecular charge transport at the molecular level. In this review, we will provide an overview of the advances in the characterization technique for the investigation of intermolecular charge transport, and summarize the experimental investigation of several non-covalent interactions, including π-π stacking interactions, hydrogen bonding, host-guest interactions and σ-σ interactions at the single-molecule level. We will also provide a perspective on supramolecular electronics and discuss the potential applications and future challenges.

Smart Eutectic Gallium-Indium: From Properties to Applications

Eutectic gallium-indium (EGaIn), a liquid metal with a melting point close to or below room temperature, has attracted extensive attention in recent years due to its excellent properties such as fluidity, high conductivity, thermal conductivity, stretchability, self-healing capability, biocompatibility, and recyclability. These features of EGaIn can be adjusted by changing the experimental condition, and various composite materials with extended properties can be further obtained by mixing EGaIn with other materials. In this review, not only the are unique properties of EGaIn introduced, but also the working principles for the EGaIn-based devices are illustrated and the developments of EGaIn-related techniques are summarized. The applications of EGaIn in various fields, such as flexible electronics (sensors, antennas, electronic circuits), molecular electronics (molecular memory, opto-electronic switches, or reconfigurable junctions), energy catalysis (heat management, motors, generators, batteries), biomedical science (drug delivery, tumor therapy, bioimaging and neural interfaces) are reviewed. Finally, a critical discussion of the main challenges for the development of EGaIn-based techniques are discussed, and the potential applications in new fields are prospected.

Recent Advances in Single-Molecule Sensors Based on STM Break Junction Measurements

Single-molecule recognition and detection with the highest resolution measurement has been one of the ultimate goals in science and engineering. Break junction techniques, originally developed to measure single-molecule conductance, recently have also been proven to have the capacity for the label-free exploration of single-molecule physics and chemistry, which paves a new way for single-molecule detection with high temporal resolution. In this review, we outline the primary advances and potential of the STM break junction technique for qualitative identification and quantitative detection at a single-molecule level. The principles of operation of these single-molecule electrical sensing mainly in three regimes, ion, environmental pH and genetic material detection, are summarized. It clearly proves that the single-molecule electrical measurements with break junction techniques show a promising perspective for designing a simple, label-free and nondestructive electrical sensor with ultrahigh sensitivity and excellent selectivity.

Gating the Conductance of Single - Molecule Junction with Ion-π Interaction

The single molecular conductance of viologen derivative VSMe and supramolecular compound VSMe-PA[5] (pillararene[5]) was investigated. The difference of their conductance demonstrated the gating effect of cation-π interaction. Theoretical calculations showed...

Substituent-mediated quantum interference toward a giant single-molecule conductance variation

Quantum interference (QI) in single molecular junctions shows a promising perspective for realizing conceptual nanoelectronics. However, controlling and modulating the QI remains a big challenge. Herein, two-type substituents at different positions ofmeta-linked benzene, namely electron-donating methoxy (-OMe) and electron-withdrawing nitryl (-NO₂), are designed and synthesized to investigate the substituent effects on QI. The calculated transmission coefficientsT(E) indicates that -OMe and -NO₂could remove the antiresonance and destructive quantum interference (DQI)-induced transmission dips at position 2. -OMe could raise the antiresonance energy at position 4 while -NO₂groups removes the DQI features. For substituents at position 5, both of them are nonactive for tuning QI. The conductance measurements by scanning tunneling microscopy break junction show a good agreement with the theoretical prediction. More than two order of magnitude single-molecule conductance on/off ratio could be achieved at the different positions of -NO₂substituent groups at room temperature. The present work proves chemical substituents can be used for tuning QI features in single molecular junctions, which provides a feasible way toward realization of high-performance molecular devices.