Methods for the analysis, interpretation, and prediction of single-molecule junction conductance behaviour.

This article offers a broad overview of measurement methods in the field of molecular electronics, with a particular focus on the most common single-molecule junction fabrication techniques, the challenges in data analysis and interpretation of single-molecule junction current-distance traces, and a summary of simulations and predictive models aimed at establishing robust structure-property relationships of use in the further development of molecular electronics.

Exploring relationships between chemical structure and molecular conductance: from α,ω-functionalised oligoynes to molecular circuits.

The quantum circuit rule (QCR) allows estimation of the conductance of molecular junctions, electrode|X-bridge-Y|electrode, by considering the molecule as a series of independent scattering regions associated with the anchor groups (X, Y) and bridge, provided the numerical parameters that characterise the anchor groups (aX, aY) and molecular backbones (bB) are known. Single-molecule conductance measurements made with a series of α,ω-substituted oligoynes (X-{(CC)N}-X, N = 1, 2, 3, 4), functionalised by terminal groups, X (4-thioanisole (C6H4SMe), 5-(3,3-dimethyl-2,3-dihydrobenzo[b]thiophene) (DMBT), 4-aniline (C6H4NH2), 4-pyridine (Py), capable of serving as 'anchor groups' to contact the oligoyne fragment within a molecular junction, have shown the expected exponential dependence of molecular conductance, G, with the number of alkyne repeating units. In turn, this allows estimation of the anchor (ai) and backbone (bi) parameters. Using these values, together with previously determined parameters for other molecular fragments, the QCR is found to accurately estimate the junction conductance of more complex molecular circuits formed from smaller components assembled in series.

Redox-Addressable Single-Molecule Junctions Incorporating a Persistent Organic Radical.

Integrating radical (open-shell) species into non-cryogenic nanodevices is key to unlocking the potential of molecular electronics. While many efforts have been devoted to this issue, in the absence of a chemical/electrochemical potential the open-shell character is generally lost in contact with the metallic electrodes. Herein, single-molecule devices incorporating a 6-oxo-verdazyl persistent radical have been fabricated using break-junction techniques. The open-shell character is retained at room temperature, and electrochemical gating permits in situ reduction to a closed-shell anionic state in a single-molecule transistor configuration. Furthermore, electronically driven rectification arises from bias-dependent alignment of the open-shell resonances. The integration of radical character, transistor-like switching, and rectification in a single molecular component paves the way to further studies of the electronic, magnetic, and thermoelectric properties of open-shell species.

Fabrication of metallic and non-metallic top electrodes for large-area molecular junctions.

Molecular junctions have proven invaluable tools through which to explore the electronic properties of molecules and molecular monolayers. In seeking to develop a viable molecular electronics based technology it becomes essential to be able to reliably create larger area molecular junctions by contacting molecular monolayers to both bottom and top electrodes. The assembly of monolayers onto a conducting substrate by self-assembly, Langmuir-Blodgett and other methods is well established. However, the deposition of top-contact electrodes without film penetration or damage from the growing electrode material has proven problematic. This Review highlights the challenges of this area, and presents a selective overview of methods that have been used to solve these issues.

Hydrothermal Synthesis of N-Doped Graphene for Supercapacitor Electrodes.

N-doped graphene based on graphene oxide and 3,3',4,4'-tetraaminodiphenyl oxide (TADPO) was obtained using a one-step hydrothermal process. The resulting materials were fully characterized using elemental analysis, infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron micrographs, and transmission electron microscopy. The findings reveal that benzimidazole rings were formed during the reaction, and the mass content of nitrogen in the obtained material varied from 12.3% to 14.7%, depending on the initial concentration of TADPO. Owing to the redox activity of benzimidazole rings, the new N-doped graphene materials demonstrated a high specific capacitance, reaching 340 F g-1 at 0.1 A g-1, which was significantly higher than that of the sample of reduced graphene oxide obtained under similar conditions without the use of TADPO (169 F g-1 at 0.1 A g-1). The resulting material also exhibited good cyclic stability after 5000 cycles.