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We report on experiments and computations performed on a series of aromatic monothiol molecular junctions (AMMJs) to ascertain both the identity of the frontier molecular orbitals (FMOs) and their approximate energetic separation from the chemical potential. Joint transition voltage spectroscopy and thermoelectric measurements unambiguously show that the FMOs in all the studied junctions are the highest occupied molecular orbitals and that the energetic separation decreases with increasing molecular length. Our computational studies of energetic separations and Seebeck coefficients of these AMMJs are in agreement with the experimentally obtained values and elucidate the electronic structure origins of the observed length dependence. [ABSTRACT FROM AUTHOR]

We present a combined experimental and computational study that probes the thermoelectric and electrical transport properties of molecular junctions. Experiments were performed on junctions created by trapping aromatic molecules between gold electrodes. The end groups (-SH, -Nc) of the aromatic molecules were systematically varied to study the effect of contact coupling strength and contact chemistry. When the coupling of the molecule with one of the electrodes was reduced by switching the terminal chemistry from -SH to -H, the electrical conductance of molecular junctions decreased by an order of magnitude, whereas the thermopower varied by only a few percent. This has been predicted computationally in the past and is experimentally demonstrated for the first time. Further, our experiments and computational modeling indicate the prospect of tuning thermoelectric properties at the molecular scale. In particular, the thiol-terminated aromatic molecular junctions revealed a positive thermopower that increased linearly with length. This positive thermopower is associated with charge transport primarily through the highest occupied molecular orbital, as shown by our computational results. In contrast, a negative thermopower was observed for a corresponding molecular junction terminated by an isocyanide group due to charge transport primarily through the lowest unoccupied molecular orbital. [ABSTRACT FROM AUTHOR]

Abstract The energy-demanding nature of solid-state synthesis can be circumvented by using solvothermal synthesis routes involving milder heat treatment steps. Herein, we exploit one such route, ultrasonic sonochemical method, for the synthesis of Na 0.44 MnO 2 insertion material. Using simple oxide and carbonate precursors, the target compound can be successfully prepared by restricting the final annealing (at 900 °C) to within 2 h. Rietveld analysis confirms the purity of final product assuming an orthorhombic framework (s.g. Pbam). Involving a step-wise voltage profile with the average Mn4+/Mn3+ redox potential ∼3 V (vs. Na/Na+), it delivers reversible capacity over 110 mAh.g−1 at a rate of C/10 with decent rate kinetics and cycling stability. Ultrasonic sonochemical synthesis can be employed for synthesis and rapid screening of variety of insertion materials for sodium-ion batteries. Highlights • Ultrasonic sonochemical synthesis Na 0.44 MnO 2 Na-insertion material. • Quick synthesis involving restricted annealing duration of just 1–2 h. • Homogeneous morphology having reversible Mn4+/Mn3+ activity at 3 V. • Reversible capacity exceeding 110 mAh g−1 with good cycling stability. [ABSTRACT FROM AUTHOR]

The pursuit of more advanced electronics, and finding solutions to energy needs often hinges upon the discovery and optimization of new functional materials. However, the discovery rate of these materials is alarmingly low. Much of the information that could drive this rate higher is scattered across tens of thousands of papers in the extant literature published over several decades but is not in an indexed form, and cannot be used in entirety without substantial effort. Many of these limitations can be circumvented if the experimentalist has access to systematized collections of prior experimental procedures and results. Here, we investigate the property-processing relationship during growth of oxide films by pulsed laser deposition. To do so, we develop an enabling software tool to (1) mine the literature of relevant papers for synthesis parameters and functional properties of previously studied materials, (2) enhance the accuracy of this mining through crowd sourcing approaches, (3) create a searchable repository that will be a community-wide resource enabling material scientists to leverage this information, and (4) provide through the Jupyter notebook platform, simple machine-learning-based analysis to learn the complex interactions between growth parameters and functional properties (all data/codes available on https://github.com/ORNL-DataMatls). The results allow visualization of growth windows, trends and outliers, which can serve as a template for analyzing the distribution of growth conditions, provide starting points for related compounds and act as a feedback for first-principles calculations. Such tools will comprise an integral part of the materials design schema in the coming decade. [ABSTRACT FROM AUTHOR]