Probing the Effect of the Density of Active Molecules in Large-Area Molecular Junctions.

The effect of the density of active molecules in molecular junctions (MJs) has been investigated by using a host/guest strategy. Mixed layers consisting of oligothiophene (BTB) encapsulated by β-cyclodextrin (BTB@β-CD) were generated. Cyclodextrins were then removed, and the pinholes generated were filled with BTB to obtain BTB@BTB films.

Chemical Conformation Induced Transport Carrier Switching in Molecular Junction based on Carboxylic-Terminated Thiol Molecules.

The paper demonstrates the effect of the chemical conformation of the -COOH group on the transport characteristic including conductance, rectification, and length effect in molecular junctions (MJs) formed by self-assembled monolayers of carboxylic-terminated thiol molecules. For an alkyl chain shorter than C, the transport mechanism was attributed to a direct off-resonant tunneling of a hole carrier, located at the Au-S interface, whereas a hopping mechanism was assigned to the alkyl chain longer than the C chain located at the -COOH group. The hopping mechanism may be operated by electron transport associated with the breaking of the -OH bonding likely driven by a voltage.

Quantifying Image Charge Effects in Molecular Tunnel Junctions Based on Self-Assembled Monolayers of Substituted Oligophenylene Ethynylene Dithiols.

A number of factors contribute to orbital energy alignment with respect to the Fermi level in molecular tunnel junctions. Here, we report a combined experimental and theoretical effort to quantify the effect of metal image potentials on the highest occupied molecular orbital to Fermi level offset, ε, for molecular junctions based on self-assembled monolayers (SAMs) of oligophenylene ethynylene dithiols (OPX) on Au. Our experimental approach involves the use of both transport and photoelectron spectroscopy to extract the offsets, ε and ε, respectively.

Quantitative analysis of weak current rectification in molecular tunnel junctions subject to mechanical deformation reveals two different rectification mechanisms for oligophenylene thiols alkane thiols.

Metal-molecule-metal junctions based on alkane thiol (CT) and oligophenylene thiol (OPT) self-assembled monolayers (SAMs) and Au electrodes are expected to exhibit similar electrical asymmetry, as both junctions have one chemisorbed Au-S contact and one physisorbed, van der Waals contact. Asymmetry is quantified by the current rectification ratio RR apparent in the current-voltage (-) characteristics. Here we show that RR 1 for CT and RR 1 for OPT junctions, in contrast to expectation, and further, that RR behaves very differently for CT and OPT junctions under mechanical extension using the conducting probe atomic force microscopy (CP-AFM) testbed.

Looking Through the COVID-19 Window of Opportunity: Future Scenarios Arising From the COVID-19 Pandemic Across Five Case Study Sites.

The COVID-19 pandemic has caused (and continues to cause) severe disruption in global and local economies and has forced countries, societies, and individuals to adapt quickly to the unprecedented and unpredictable situations. Despite the obvious negative consequences of the pandemic, many have called for efforts to identify transformative opportunities for sustainable development throughout this disorderly time. In the present paper, we explore such potential opportunities in the context of an interdisciplinary, international research project, which is focusing on sustainable marine management in biosphere reserves and marine parks in Southeast Asia.

Hopping Conductance in Molecular Wires Exhibits a Large Heavy-Atom Kinetic Isotope Effect.

We report a large kinetic isotope effect (KIE) for intramolecular charge transport in π-conjugated oligophenyleneimine (OPI) molecules connected to Au electrodes. C and N substitution on the imine bonds produces a conductance KIE of ∼2.7 per labeled atom in long OPI wires >4 nm in length, far larger than typical heavy-atom KIEs for chemical reactions.

Charge injection and transport properties of large area organic junctions based on aryl thin films covalently attached to a multilayer graphene electrode.

The quantum interaction between molecules and electrode materials at molecule/electrode interfaces is a major ingredient in the electron transport properties of organic junctions. Driven by the coupling strength between the two materials, it results mainly in the broadening and energy shift of the interacting molecular orbitals. Using new electrode materials, such as the recently developed semi-conducting two-dimensional nanomaterials, has become a significant advancement in the field of molecular/organic electronics that opens new possibilities for controlling the interfacial electronic properties and thus the charge injection properties.

Highly Efficient Long-Range Electron Transport in a Viologen-Based Molecular Junction.

Thin layers of viologen-based oligomers with thicknesses between 3 and 14 nm were deposited on gold electrodes by electrochemical reduction of a diazonium salt, and then a Ti/Au top contact was applied to complete a solid-state molecular junction (MJ). MJs show symmetric J- V curves and highly efficient long-range transport, with an attenuation factor as small as 0.25 nm.

Control of Rectification in Molecular Junctions: Contact Effects and Molecular Signature.

Thin layers of oligomers with thickness between 7 and 9 nm were deposited on flat gold electrode surfaces by electrochemical reduction of diazonium reagents, then a Ti(2 nm)/Au top contact was applied to complete a solid-state molecular junction. The molecular layers investigated included donor molecules with relatively high energy HOMO, molecules with high HOMO-LUMO gaps and acceptor molecules with low energy LUMO and terminal alkyl chain. Using an oligo(bisthienylbenzene) based layer, a molecule whose HOMO energy level in a vacuum is close to the Fermi level of the gold bottom electrode, the devices exhibit robust and highly reproducible rectification ratios above 1000 at low voltage (2.

Robust Bipolar Light Emission and Charge Transport in Symmetric Molecular Junctions.

Molecular junctions consisting of a Ru(bpy) oligomer between conducting carbon contacts exhibit an exponential dependence of junction current on molecular layer thickness (d) similar to that observed for other aromatic devices when d < 4 nm. However, when d > 4 nm, a change in transport mechanism occurs which coincides with light emission in the range of 600-900 nm. Unlike light emission from electrochemical cells or solid-state films containing Ru(bpy), emission is bipolar, occurs in vacuum, has rapid rise time (<5 ms), and persists for >10 h.