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Layer-by-layer design of nanostructured thermoelectrics: First-principles study of ZnO:organic superlattices fabricated by ALD/MLD
Source:Nano Energy, Volume 22
Author(s): Antti J. Karttunen, Tommi Tynell, Maarit Karppinen
Crystalline atomic/molecular layer deposited ZnO:organic superlattices form a fundamentally new exciting family of coherent multilayered thermoelectric materials. They retain the n-type electrical transport properties derived from the parent ZnO lattice, while the organic molecular layers reduce the thermal conductivity. The controlled nanostructuring opens up the possibility of improving the thermoelectric characteristics of the parent oxide. Here we employ quantum chemical methods to rationalize our experimental results on the ZnO:organic superlattices and determine the thermoelectric structure–property relationships arising from the nanoscale layer-by-layer engineering of ZnO. Our results reveal the importance of systematic tailoring of the organic superlattice component and provide us with atomic-level guidelines for the rational design of novel hybrid inorganic–organic thermoelectrics.
Graphical abstract
Pressure-Tuned Structure and Property of Optically Active Nanocrystals
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Enhancement of Magnetic Resonance Imaging with Metasurfaces
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It is revealed that the unique properties of ultrathin metasurface resonators can improve magnetic resonance imaging dramatically. A metasurface formed when an array of metallic wires is placed inside a scanner under the studied object and a substantial enhancement of the radiofrequency magnetic field is achieved by means of subwavelength manipulation with the metasurface, also allowing improved image resolution.
Thin-finger growth and droplet pinch-off in miscible and immiscible displacements in a periodic network of microfluidic channels
We report the results of experimental and numerical studies of two-phase flow in a periodic, rectangular network of microfluidic channels. This geometry promotes the formation of anisotropic, dendrite-like structures during viscous fingering experiments. The dendrites then compete with each other for the available flow, which leads to the appearance of hierarchical growth pattern. Combining experiments and numerical simulations, we analyze different growth regimes in such a system, depending on the network geometry and fluid properties. For immiscible fluids, a high degree of screening is present which results in a power-law distribution of finger lengths. Contrastingly, for miscible fluids, strong lateral currents of displaced fluid lead to the detachment of the heads of the longest fingers from their roots, thus preventing their further growth.