Ordered arrays of gold nanoparticles crosslinked by dithioacetate linkers for molecular devices

The final performance of a molecular electronic device is determined by the chemical structure of the molecular wires used in its assembly. Molecular place-exchange was used to incorporate di-thioacetate terminated molecules into ordered arrays of dodecanethiol capped gold nanoparticles. X-Ray photoelectron spectroscopy confirmed successful molecular replacement. Room-temperature molecular conductance of a statistically large number of devices reveals that conductance is enhanced by up to two orders of magnitude for the di-thioacetate terminated molecules. Density functional theory transport calculations were performed on five different configurations of the di-thioacetate molecules between gold electrodes, and the calculated average conductance values are in good agreement with the experimentally-observed conductance trend. Our findings highlight important cooperative effects of bridging neighboring gold nanoparticles and choice of appropriate molecular wires when designing devices for efficient transport

Not So Innocent After All: Interfacial Chemistry Determines Charge-Transport Efficiency in Single-Molecule Junctions.

Most studies in molecular electronics focus on altering the molecular wire backbone to tune the electrical properties of the whole junction. However, it is often overlooked that the chemical structure of the groups anchoring the molecule to the metallic electrodes influences the electronic structure of the whole system and, therefore, its conductance. We synthesised electron-accepting dithienophosphole oxide derivatives and fabricated their single-molecule junctions. We found that the anchor group has a dramatic effect on charge-transport efficiency: in our case, electron-deficient 4-pyridyl contacts suppress conductance, while electron-rich 4-thioanisole termini promote efficient transport. Our calculations show that this is due to minute changes in charge distribution, probed at the electrode interface. Our findings provide a framework for efficient molecular junction design, especially valuable for compounds with strong electron withdrawing/donating backbones

Genomics of carbon atomic chains

To realise the technological potential of subnanometer graphene junctions, there is a need to understand how their electronic and spintronic properties are controlled by the carbon chains bridging their gaps. Motivated by the recent experimental efforts to form in-situ all-carbon junctions using graphene electrodes connected to carbon chains, here we systematically study a wide variety of such structures. We find that although a wide range of transport properties are possible, the junctions can be divided into a small number of categories, according to their qualitative transport properties. For example, we find that junctions bridged by even-numbered chains of carbon atoms tend to have a lower conductance than those bridged by odd-numbered atomic chains. We also find that junctions with ferromagnetically aligned electrode surface edges have a higher transmission than anti-ferromagnetically aligned ones, because ferromagnetic alignment tends to increase the transmission of one of the spin carriers. We also examine the effect of terminal rings, electrode terminal edges and the effect of saturation of edges with hydrogen on transport properties of all-carbon junctions. Just like genomics, our findings provide a complete set of information to construct junctions formed by carbon chains with desired properties for spintronic applications

Ordered arrays of gold nanoparticles crosslinked by dithioacetate linkers for molecular devices

Enhanced electrical conductance of the self-assembled monolayers upon molecular exchange with dithioacetate-terminating molecules.</jats:p

Selective anchoring groups for molecular electronic junctions with ITO electrodes

Indium tin oxide (ITO) is an attractive substrate for single-molecule electronics since it is transparent while maintaining electrical conductivity. Although it has been used before as a contacting electrode in single-molecule electrical studies, these studies have been limited to the use of carboxylic acid terminal groups for binding molecular wires to the ITO substrates. There is thus the need to investigate other anchoring groups with potential for binding effectively to ITO. With this aim, we have investigated the single-molecule conductance of a series of eight tolane or “tolane-like” molecular wires with a variety of surface binding groups. We first used gold-molecule- gold junctions to identify promising targets for ITO selectivity. We then assessed the propensity and selectivity of carboxylic acid, cyanoacrylic acid, and pyridinium-squarate to bind to ITO and promote the formation of molecular heterojunctions. We found that pyridinium squarate zwitterions display excellent selectivity for binding to ITO over gold surfaces, with contact resistivity comparable to that of carboxylic acids. These single-molecule experiments are complemented by surface chemical characterization with X-ray photoelectron spectroscopy, quartz crystal microbalance, contact angle determination, and nanolithography using an atomic force miscroscope. Finally, we report the first density-functional theory calculations involving ITO electrodes to model charge transport through ITO-molecule-gold heterojunctions

Not So Innocent After All: Interfacial Chemistry Determines Charge‐Transport Efficiency in Single‐Molecule Junctions

AbstractMost studies in molecular electronics focus on altering the molecular wire backbone to tune the electrical properties of the whole junction. However, it is often overlooked that the chemical structure of the groups anchoring the molecule to the metallic electrodes influences the electronic structure of the whole system and, therefore, its conductance. We synthesised electron‐accepting dithienophosphole oxide derivatives and fabricated their single‐molecule junctions. We found that the anchor group has a dramatic effect on charge‐transport efficiency: in our case, electron‐deficient 4‐pyridyl contacts suppress conductance, while electron‐rich 4‐thioanisole termini promote efficient transport. Our calculations show that this is due to minute changes in charge distribution, probed at the electrode interface. Our findings provide a framework for efficient molecular junction design, especially valuable for compounds with strong electron withdrawing/donating backbones.</jats:p

An Orthogonal Conductance Pathway in Spiropyrans for Well-Defined Electrosteric Switching Single-Molecule Junctions

While a multitude of studies have appeared touting the use of molecules as electronic components, the design of molecular switches is crucial for the next steps in molecular electronics. In this work, single-molecule devices incorporating spiropyrans, made using break junction techniques, are described. Linear spiropyrans with electrode-contacting groups linked by alkynyl spacers to both the indoline and chromenone moieties have previously provided very low conductance values, and removing the alkynyl spacer has resulted in a total loss of conductance. An orthogonal T-shaped approach to single-molecule junctions incorporating spiropyran moieties in which the conducting pathway lies orthogonal to the molecule backbone is described and characterized. This approach has provided singlemolecule conductance features with good correlation to molecular length. Additional higher conducting states are accessible using switching induced by UV light or protonation. Theoretical modeling demonstrates that upon (photo)chemical isomerization to the merocyanine, two cooperating phenomena increase conductance: release of steric hindrance allows the conductance pathway to become more planar (raising the mid-bandgap transmission) and a bound state introduces sharp interference near the Fermi level of the electrodes similarly responding to the change in state. This design step paves the way for future use of spiropyrans in single-molecule devices and electrosteric switches