Designing optical elements from isotropic materials by using transformation optics

International audienceBy taking advantage of a conformal mapping technique, we propose designs for various optical elements such as directional antennas, flat lenses, or bends. In contrast to most of the existing design approaches, the elements can be implemented with isotropic materials, thus strongly facilitating their fabrication. We furthermore generalize the concept and show that under certain conditions previously suggested devices consisting of anisotropic materials may be replaced by isotropic ones using an appropriate transformation. The designs are double-checked by full-wave simulations. A comparison with their anisotropic counterparts reveals a similar performance

Analysis of the structure of nanocomposites of triglyceride platelets and DNA

DNA-complexes with platelet-like, cationically modified lipid nanoparticles (cLNPs) are studied with regard to the formation of nanocomposite structures with a sandwich-like arrangement of the DNA and platelets. For this purpose suspensions of platelet-like triglyceride nanocrystals, stabilized by a mixture of two nonionic (lecithin plus polysorbate 80 or poloxamer 188) and one cationic stabilizer dimethyldioctadecylammonium (DODAB), are used. The structure of the platelets in the native suspensions and their DNA-complexes, ranging from the sub-nano to the micron scale, is investigated with small- and wide-angle scattering (SAXS, SANS, WAXS), calorimetry, photon correlation spectroscopy, transmission electron microscopy and computer simulations. The appearance of strong, lamellarly ordered peaks in the SAXS patterns of the DNA-complexes suggests a stacked arrangement of the nanocrystals, with the DNA being partially condensed between the platelets. This finding is supported with computer simulated small-angle scattering patterns of nanocrystal stacks, which can reproduce the measured small-angle scattering patterns on an absolute scale. The influence of the choice of the nonionic stabilizers and the amount of the cationic stabilizer DODAB on the structure of the native suspensions and the inner structure of their DNA-complexes is studied, too. Using high amounts of DODAB, lecithins with saturated acyl chains and polysorbate 80 instead of poloxamer 188 produces thinner nanocrystals, and thus decreases their repeat distances in the nanocomposites. Such nanocomposites could be of interest as DNA carriers, where the triglyceride platelets protect the sandwiched DNA from degradation

Structural Changes during the Growth of Atomically Precise Metal Oxido Nanoclusters from Combined Pair Distribution Function and Small‐Angle X‐ray Scattering Analysis

The combination of in situ pair distribution function (PDF) analysis and small-angle X-ray scattering (SAXS) enables analysis of the formation mechanism of metal oxido nanoclusters and cluster–solvent interactions as they take place. Herein, we demonstrate the method for the formation of clusters with a [Bi38O45] core. Upon dissolution of crystalline [Bi$_6$O$_5$(OH)$_3$(NO$_3$)$_5$]⋅3 H$_2$O in DMSO, an intermediate rapidly forms, which slowly grows to stable [Bi$_{38}$O$_{45}$] clusters. To identify the intermediate, we developed an automated modeling method, where smaller [BixOy] structures based on the [Bi$_{38}$O$_{45}$] framework are tested against the data. [Bi$_{22}$O$_{26}$] was identified as the main intermediate species, illustrating how combined PDF and SAXS analysis is a powerful tool to gain insight into nucleation on an atomic scale. PDF also provides information on the interaction between nanoclusters and solvent, which is shown to depend on the nature of the ligands on the cluster surface

Structural Changes during the Growth of Atomically Precise Metal Oxido Nanoclusters from Combined Pair Distribution Function and Small‐Angle X‐ray Scattering Analysis

The combination of in situ pair distribution function (PDF) analysis and small-angle X-ray scattering (SAXS) enables analysis of the formation mechanism of metal oxido nanoclusters and cluster–solvent interactions as they take place. Herein, we demonstrate the method for the formation of clusters with a [Bi38O45] core. Upon dissolution of crystalline [Bi$_6$O$_5$(OH)$_3$(NO$_3$)$_5$]⋅3 H$_2$O in DMSO, an intermediate rapidly forms, which slowly grows to stable [Bi$_{38}$O$_{45}$] clusters. To identify the intermediate, we developed an automated modeling method, where smaller [BixOy] structures based on the [Bi$_{38}$O$_{45}$] framework are tested against the data. [Bi$_{22}$O$_{26}$] was identified as the main intermediate species, illustrating how combined PDF and SAXS analysis is a powerful tool to gain insight into nucleation on an atomic scale. PDF also provides information on the interaction between nanoclusters and solvent, which is shown to depend on the nature of the ligands on the cluster surface