Dynamic Variation of Rectification Observed in Supramolecular Mixed Mercaptoalkanoic Acid.

Functionality in molecular electronics relies on inclusion of molecular orbital energy level within a transmission window. This can be achieved by designing the active molecule with accessible energy levels or by widening the window. While many studies have adopted the first approach, the latter is challenging because defects in the active molecular component cause low breakdown voltages.

Uniform Silver Nanowire Patterned Electrode on Robust PEN Substrate Using Poly(2-hydroxyethyl methacrylate) Underlayer.

Silver nanowire (AgNW) electrodes are among the most essential flexible transparent electrodes (FTEs) emerging as promising alternatives to brittle indium tin oxide (ITO) electrodes. The polymer comprising the plastic substrate to which the AgNWs are applied must also satisfy the mechanical requirements of the final device and withstand the device processing conditions. However, AgNW-based FTEs have some limitations, such as poor adhesion to coated plastic substrates, surface roughness, and difficulty in patterning.

Li-Ion Intercalation, Rectification, and Solid Electrolyte Interphase in Molecular Tunnel Junctions.

This paper describes Li-ion intercalation into a pyrenyl-terminated self-assembled monolayer (SAM) on gold, inspired by the graphite anode in a Li-ion battery, and its effect on tunneling performance in a molecular junction incorporating the SAM. As the concentration of the Li-ion precursor ([LiPF]) increased from 0 to 10 M, the rectification ratio increased to ∼10. Further experiments revealed that the intercalation-induced changes in the orientation of PYR group and in the HOMO energy level account for the enhanced rectification.

Electronic Mechanism of Inversion of Rectification Polarity in Supramolecular Engineered Monolayer.

This Communication describes polarity inversion in molecular rectification and the related mechanism. Using a supramolecular engineered, ultrastable, binary-mixed self-assembled monolayer (SAM) composed of an organic molecular diode (SCBIPY) and an inert reinforcement molecule (SC), we probed a rectification ratio ()-voltage relationship over an unprecedentedly wide voltage range (up to |3.5 V|) with statistical significance.

Interstitially Mixed Self-Assembled Monolayers Enhance Electrical Stability of Molecular Junctions.

Electrical breakdown is a critical problem in electronics. In molecular electronics, it becomes more problematic because ultrathin molecular monolayers have delicate and defective structures and exhibit intrinsically low breakdown voltages, which limit device performances. Here, we show that interstitially mixed self-assembled monolayers (imSAMs) remarkably enhance electrical stability of molecular-scale electronic devices without deteriorating function and reliability.

Solid State Dilution Controls Marcus Inverted Transport in Rectifying Molecular Junctions.

Traditional Marcus theory accounts for electron transfer reactions in solutions, and the polarity of solvent molecule matters for them. How such an environment polarity affects electron transfer reactions in solid-state devices, however, remains uncertain. This paper describes how the Marcus inverted charge transport is influenced by solid-state molecular dilution in large-area tunneling junctions.

Superexchange Coupling-Induced Enhancements of Thermoelectric Performance in Saturated Molecules.

To develop thermoelectric devices, it is of the utmost importance to design organic building blocks to have efficient thermopower. Whereas conjugated and aromatic molecules with intrinsic narrow band gaps are attractive candidates to achieve efficient thermoelectric properties, saturated molecules are usually avoided owing to intrinsically poor thermopower. Here we demonstrate that thermopower of saturated molecules can be enhanced by superexchange coupling.

Interplay of Fermi Level Pinning, Marcus Inverted Transport, and Orbital Gating in Molecular Tunneling Junctions.

This Letter examines the interplay of important tunneling mechanisms-Fermi level pinning, Marcus inverted transport, and orbital gating-in a molecular rectifier. The temperature dependence of the rectifying molecular junction containing 2,2'-bipyridyl terminated -alkanethiolate was investigated. A bell-shaped trend of activation energy as a function of applied bias evidenced the dominant occurrence of unusual Marcus inverted transport, while retention of rectification at low temperatures implied that the rectification obeyed the resonant tunneling regime.

Molecularly Controlled Stark Effect Induces Significant Rectification in Polycyclic-Aromatic-Hydrocarbon-Terminated n-Alkanethiolates.

The variation of the electronic structure of individual molecules as a function of the applied bias matters for the performance of molecular and organic electronic devices. Understanding the structure-electric-field relationship, however, remains a challenge because of the lack of in-operando spectroscopic technique and complexity arising from the ill-defined on-surface structure of molecules and organic-electrode interfaces within devices. We report that a reliable and reproducible molecular diode can be achieved by control of the conjugation length in polycyclic-aromatic-hydrocarbon (PAH)-terminated n-alkanethiolate (denoted as SCPAH), incorporated into liquid-metal-based large-area tunnel junctions in the form of a self-assembled monolayer.

Thermally Controlled Phase Transition of Low-Melting Electrode for Wetting-Based Spontaneous Top Contact in Molecular Tunnel Junction.

Top contacts for molecular-scale electronic devices should exhibit reliable and reproducible electronic performance. This goal is challenging and difficult to achieve because metals are usually evaporated under high-energy conditions that easily damage delicate organic surfaces, and complicated nanofabrication processes are needed for achieving geometrically defined small contact areas. Soft top contacts that are made by users under ambient conditions can circumvent this problem but often show user-dependence.

Elucidating the Role of Molecule-Electrode Interfacial Defects in Charge Tunneling Characteristics of Large-Area Junctions.

Interfacial chemistry at organic-inorganic contact critically determines the function of a wide range of molecular and organic electronic devices and other systems. The chemistry is, however, difficult to understand due to the lack of easily accessible in-operando spectroscopic techniques that permit access to interfacial structure on a molecular scale. Herein, we compare two analogous junctions formed with identical organic thin film and different liquid top-contacts (water droplet vs eutectic gallium indium alloy) and elucidate the puzzling interfacial characteristics.

Deconvolution of Tunneling Current in Large-Area Junctions Formed with Mixed Self-Assembled Monolayers.

Whereas single-component self-assembled monolayers (SAMs) have served widely as organic components in molecular and organic electronics, how the performance of the device is influenced by the heterogeneity of monolayers has been little understood. This paper describes charge transport by quantum tunneling across mixed SAMs of n-alkanethiolates of different lengths formed on ultraflat template-stripped gold substrate. Electrical characterization using liquid metal comprising eutectic gallium-indium alloy reveals that the surface topography of monolayer largely depends on the difference in length between the thiolates and is translated into distribution of tunneling current density.

Gradients of Rectification: Tuning Molecular Electronic Devices by the Controlled Use of Different-Sized Diluents in Heterogeneous Self-Assembled Monolayers.

Molecular electronics has received significant attention in the last decades. To hone performance of devices, eliminating structural defects in molecular components inside devices is usually needed. We herein demonstrate this problem can be turned into a strength for modulating the performance of devices.

Influence of halogen substitutions on rates of charge tunneling across SAM-based large-area junctions.

This paper examines the ability of structural modifications using halogen atoms (F, Cl, Br, and I) to influence tunneling rates across self-assembled monolayer (SAM)-based junctions having the structure Ag(TS)/S(CH2)n(p-C6H4X)//Ga2O3/EGaIn, where S(CH2)n(p-C6H4X) is a SAM of benzenethiol (n = 0) or benzyl mercaptan (n = 1) terminated in a hydrogen (X = H) or a halogen (X = F, Cl, Br, or I) at the para-position. The measured tunneling current densities (J(V); A cm(-2)) indicate that replacing a terminal hydrogen with a halogen atom at the X//Ga2O3 interface leads to a decrease in J(V) by ∼×13 for S(p-C6H4X) and by ∼×50 for SCH2(p-C6H4X). Values of J(V) for the series of halogenated SAMs were indistinguishable, indicating that changes in dipole moment and polarizability caused by introducing different halogen atoms at the interface between the SAM and the Ga2O3/EGaIn electrode do not significantly influence the rates of charge tunneling across the junctions.