Dual-Vibration-Assisted Charge Transport Through Hexabenzocoronene in Single-Molecule Junctions.

Gaining deep understanding and effective regulation of the charge transport mechanism within molecular junctions is essential for the development of electronic devices. In this work, a series of hexabenzocoronene-based single-molecule junctions are successfully constructed, and their temperature-dependent charge transport properties are studied. It is found that rotational vibrations of both benzene and hexabenzocoronene rings are sequentially excited as the temperature increases, and the electron-vibration coupling enhances charge tunneling.

Understanding the Spin of Metal Complexes from a Single-Molecule Perspective.

Compared with aggregate spin behavior, single-molecule spin behavior can be accurately understood, controlled, and applied at the level of basic building blocks. The potential of single-molecule electronic and nuclear spins for monitoring and control represents a beacon of promise for the advancement of molecular spin devices, which are fabricated by connecting a single molecule between two electrodes. Metal complexes, celebrated for their superior magnetic attributes, are widely used in the devices to explore spin effects.

Full on-device manipulation of olefin metathesis for precise manufacturing.

Olefin metathesis, as a powerful metal-catalysed carbon-carbon bond-forming method, has achieved considerable progress in recent years. However, the complexity originating from multicomponent interactions has long impeded a complete mechanistic understanding of olefin metathesis, which hampers further optimization of the reaction. Here, we clarify both productive and hidden degenerate pathways of ring-closing metathesis by focusing on one individual catalyst, using a sensitive single-molecule electrical detection platform.

In Situ Detection of Interfacial Ions at the Single-Bond Level.

Detecting the ionic state at the solid-liquid interface is essential to reveal the various chemical and physical processes that occur at the interface. In this study, the adsorption states of the highly electronegative ions F and OH at the solid-liquid interface are detected by using the scanning tunneling microscopy break junction technique. With the active hydrogen atom of the amino group as a probe, the formed ionic hydrogen bonds are successfully detected, thereby enabling in situ monitoring of the ionic state at the solid-liquid interface.

Technologies for investigating single-molecule chemical reactions.

Single molecules, the smallest independently stable units in the material world, serve as the fundamental building blocks of matter. Among different branches of single-molecule sciences, single-molecule chemical reactions, by revealing the behavior and properties of individual molecules at the molecular scale, are particularly attractive because they can advance the understanding of chemical reaction mechanisms and help to address key scientific problems in broad fields such as physics, chemistry, biology and materials science. This review provides a timely, comprehensive overview of single-molecule chemical reactions based on various technical platforms such as scanning probe microscopy, single-molecule junction, single-molecule nanostructure, single-molecule fluorescence detection and crossed molecular beam.

Tracking Noncovalent Interactions of π, π-Hole, and Ion in Molecular Complexes at the Single-Molecule Level.

Noncovalent interactions involving aromatic rings, such as π-stacking and π-ion interactions, play an essential role in molecular recognition, assembly, catalysis, and electronics. However, the inherently weak and complex nature of these interactions has made it challenging to study them experimentally, especially with regard to elucidating their properties in solution. Herein, the noncovalent interactions between π and π-hole, π and cation, and π-hole and anion in molecular complexes in nonpolar solution are investigated in situ through single-molecule electrical measurements in combination with theoretical calculations.

Interfacial Stereoelectronic Effect Induced by Anchoring Orientation.

Heterogeneous interfaces in most devices play a key role in the material performance. Exploring the atomic structure and electronic properties of metal-molecule interfaces is critical for various potential applications, such as surface sensing, molecular recognition, and molecular electronic devices. This study unveils a ubiquitous interfacial stereoelectronic effect in conjugated molecular junctions by combining first-principles simulation and scanning tunneling microscopy break junction technology.

Electronic Devices Based on Heterostructures of 2D Materials and Self-Assembled Monolayers.

2D materials (2DMs), known for their atomically ultrathin structure, exhibit remarkable electrical and optical properties. Similarly, molecular self-assembled monolayers (SAMs) with comparable atomic thickness show an abundance of designable structures and properties. The strategy of constructing electronic devices through unique heterostructures formed by van der Waals assembly between 2DMs and molecular SAMs not only enables device miniaturization, but also allows for convenient adjustment of their structures and functions.

Toward Practical Single-Molecule/Atom Switches.

Electronic switches have been considered to be one of the most important components of contemporary electronic circuits for processing and storing digital information. Fabricating functional devices with building blocks of atomic/molecular switches can greatly promote the minimization of the devices and meet the requirement of high integration. This review highlights key developments in the fabrication and application of molecular switching devices.

Single-Molecule Electrical Profiling of Peptides and Proteins.

In recent decades, there has been a significant increase in the application of single-molecule electrical analysis platforms in studying proteins and peptides. These advanced analysis methods have the potential for deep investigation of enzymatic working mechanisms and accurate monitoring of dynamic changes in protein configurations, which are often challenging to achieve in ensemble measurements. In this work, the prominent research progress in peptide and protein-related studies are surveyed using electronic devices with single-molecule/single-event sensitivity, including single-molecule junctions, single-molecule field-effect transistors, and nanopores.

Unveiling the Properties of Sulfhydryl Groups in a Single-Molecule Junction.

The metal-thiol interface is ubiquitous in nanotechnology and surface chemistry. It is not only used to construct nanocomposites but also plays a decisive role in the properties of these materials. When organothiol molecules bind to the gold surface, there is still controversy over whether sulfhydryl groups can form disulfide bonds and whether these disulfide bonds can remain stable on the gold surface.

Breakdown of Ohm's Law in Molecular Junctions with Electrodes of Single-Layer Graphene.

For sufficiently low biases, Ohm's law, the cornerstone of electricity, stating that current and voltage are proportional, is satisfied at low biases for all known systems ranging from macroscopic conductors to nanojunctions. In this study, we predict theoretically and demonstrate experimentally that in single-molecule junctions fabricated with single-layer graphene as electrodes the current at low scales as the cube of , thereby invalidating Ohm's law. The absence of the ohmic regime is a direct consequence of the unique band structure of the single-layer graphene, whose vanishing density of states at the Dirac points precludes electron transfer from and to the electrodes at low biases.

The role of halogens in Au-S bond cleavage for energy-differentiated catalysis at the single-bond limit.

The transformation from one compound to another involves the breaking and formation of chemical bonds at the single-bond level, especially during catalytic reactions that are of great significance in broad fields such as energy conversion, environmental science, life science and chemical synthesis. The study of the reaction process at the single-bond limit is the key to understanding the catalytic reaction mechanism and further rationally designing catalysts. Here, we develop a method to monitor the catalytic process from the perspective of the single-bond energy using high-resolution scanning tunneling microscopy single-molecule junctions.

Graphene: Preparation, tailoring, and modification.

Graphene is a 2D material with fruitful electrical properties, which can be efficiently prepared, tailored, and modified for a variety of applications, particularly in the field of optoelectronic devices thanks to its planar hexagonal lattice structure. To date, graphene has been prepared using a variety of bottom-up growth and top-down exfoliation techniques. To prepare high-quality graphene with high yield, a variety of physical exfoliation methods, such as mechanical exfoliation, anode bonding exfoliation, and metal-assisted exfoliation, have been developed.

Transferred Polymer-Encapsulated Metal Electrodes for Electrical Transport Measurements on Ultrathin Air-Sensitive Crystals.

Owing to rapid property degradation after ambient exposure and incompatibility with conventional device fabrication process, electrical transport measurements on air-sensitive 2D materials have always been a big issue. Here, for the first time, a facile one-step polymer-encapsulated electrode transfer (PEET) method applicable for fragile 2D materials is developed, which showed great advantages of damage-free electrodes patterning and in situ polymer encapsulation preventing from H O/O exposure during the whole electrical measurements process. The ultrathin SmTe metals grown by chemical vapor deposition (CVD) are chosen as the prototypical air-sensitive 2D crystals for their poor air-stability, which will become highly insulating when fabricated by conventional lithographic techniques.

Distinct armchair and zigzag charge transport through single polycyclic aromatics.

In aromatic systems with large π-conjugated structures, armchair and zigzag configurations can affect each material's electronic properties, determining their performance and generating certain quantum effects. Here, we explore the intrinsic effect of armchair and zigzag pathways on charge transport through single hexabenzocoronene molecules. Theoretical calculations and systematic experimental results from static carbon-based single-molecule junctions and dynamic scanning tunneling microscope break junctions show that charge carriers are preferentially transported along the hexabenzocoronene armchair pathway, and thus, the corresponding current through this pathway is approximately one order of magnitude higher than that through the zigzag pathway.

Real-time monitoring of reaction stereochemistry through single-molecule observations of chirality-induced spin selectivity.

Stereochemistry has an essential role in organic synthesis, biological catalysis and physical processes. In situ chirality identification and asymmetric synthesis are non-trivial tasks, especially for single-molecule systems. However, going beyond the chiral characterization of a large number of molecules (which inevitably leads to ensemble averaging) is crucial for elucidating the different properties induced by the chiral nature of the molecules.

Exploring Electronic Characteristics of Acceptor-Donor-Acceptor-Type Molecules by Single-Molecule Charge Transport.

The electronic characteristics of organic optoelectronic materials determine the performance of corresponding devices. Clarifying the relationship between molecular structure and electronic characteristics at the single-molecule level can help to achieve high performance for organic optoelectronic materials and devices, especially for organic photovoltaics. In this work, a typical acceptor-donor-acceptor (A-D-A)-type molecule is explored by combining theoretical and experimental studies to reveal the intrinsic electronic characteristics at the single-molecule level.

Potassium Titanate Supported Atomically Dispersed Palladium for Catalytic Oxidation.

Single-atom catalysts based on noble metals provide efficient atomic utilization along with enhanced reactivity. Herein, a convenient strategy to construct atomically dispersed palladium catalyst on layered potassium titanate (KTO), which has enhanced interaction between the TiO layer and the palladium atoms, is presented. Due to the presence of K ions in the interlayers of KTO, the TiO octahedron layers have negative charge, which increases the interaction between Pd atoms and the substrate, thus preventing their agglomeration.

Dipole-Modulated Charge Transport through PNP-Type Single-Molecule Junctions.

The PNP structure realized by energy band engineering is widely used in various electronic and optoelectronic devices. In this work, we succeed in constructing a PNP-type single-molecule junction and explore the intrinsic characteristics of the PNP structure at the single-molecule level. A back-to-back azulene molecule is designed with opposite ∼1.

A general one-step plug-and-probe approach to top-gated transistors for rapidly probing delicate electronic materials.

The miniaturization of silicon-based electronics has motivated considerable efforts in exploring new electronic materials, including two-dimensional semiconductors and halide perovskites, which are usually too delicate to maintain their intrinsic properties during the harsh device fabrication steps. Here we report a convenient plug-and-probe approach for one-step simultaneous van der Waals integration of high-k dielectrics and contacts to enable top-gated transistors with atomically clean and electronically sharp dielectric and contact interfaces. By applying the plug-and-probe top-gate transistor stacks on two-dimensional semiconductors, we demonstrate an ideal subthreshold swing of 60 mV per decade.

Vibration-Assisted Charge Transport through Positively Charged Dimer Junctions.

Intermolecular charge transport plays a vital role in the fields of electronics, as well as biochemical systems. Here, we design supramolecular dimer junctions and investigate the effects of charge state and energy level alignment on charge transport under nanoconfinement. Incoherent tunneling caused by thermally-induced vibrations is enhanced in positively charged systems.