Template design based on molecular and crystal structure similarity to regulate conformational polymorphism nucleation: the case of α,ω-alkanedicarboxylic acids

Template design on polymorph control, especially conformational polymorphs, is still in its infancy and the result of polymorph control is often accidental. A method of regulating the crystallization of conformational polymorphs based on the crystal structure similarity of templates and the target crystal form has been developed. Crystal structure similarity was considered to be able to introduce lattice matching (geometric term) with chemical interactions to regulate conformational polymorph nucleation. The method was successfully applied to induce the crystallization of DA7-II [HOOC–(CH2) n −2–COOH (diacids), named DAn, where n = 7, 9, 15, 17 and II represents the metastable polymorph] on the surface of DA15-II. An analogous two-dimensional plane – the (002) face of both DA15-II and DA7-II – was firstly predicted as the epitaxially attached face with similar lattice parameters and the strongest adsorption energy. The powder DA15-II template with the preferred orientation face in (002) presented much stronger inducing DA7-II ability than the template with other preferred orientation faces. The epitaxial growth of DA7-II on DA15-II through an identical (002) face was clearly observed and verified by the single-crystal inducing experiments. The molecular dynamics simulation results demonstrated that the strong interactions occurred between DA7 molecules and the (002) face of DA15-II. This method has been verified and further applied to the crystallization of DA7-II on the surface of DA17-II and DA9-II on the surface of DA15-II. This study developed a strategy based on structure similarity to regulate the conformational polymorph and verified the significant role of lattice matching and chemical effects on the design and preparation of templates.

Structural and Electric Properties of Epitaxial Na0.5Bi0.5TiO3-Based Thin Films

Substantial efforts are dedicated worldwide to use lead-free materials for environmentally friendly processes in electrocaloric cooling. Whereas investigations on bulk materials showed that Na0.5Bi0.5TiO3 (NBT)-based compounds might be suitable for such applications, our aim is to clarify the feasibility of epitaxial NBT-based thin films for more detailed investigations on the correlation between the composition, microstructure, and functional properties. Therefore, NBT-based thin films were grown by pulsed laser deposition on different single crystalline substrates using a thin epitaxial La0.5Sr0.5CoO3 layer as the bottom electrode for subsequent electric measurements. Structural characterization revealed an undisturbed epitaxial growth of NBT on lattice-matching substrates with a columnar microstructure, but high roughness and increasing grain size with larger film thickness. Dielectric measurements indicate a shift of the phase transition to lower temperatures compared to bulk samples as well as a reduced permittivity and increased losses at higher temperatures. Whereas polarization loops taken at −100 °C revealed a distinct ferroelectric behavior, room temperature data showed a significant resistive contribution in these measurements. Leakage current studies confirmed a non-negligible conductivity between the electrodes, thus preventing an indirect characterization of the electrocaloric properties of these films.

Parity-preserving and magnetic field–resilient superconductivity in InSb nanowires with Sn shells

Improving materials used to make qubits is crucial to further progress in quantum information processing. Of particular interest are semiconductor-superconductor heterostructures that are expected to form the basis of topological quantum computing. We grow semiconductor indium antimonide nanowires that are coated with shells of tin of uniform thickness. No interdiffusion is observed at the interface between Sn and InSb. Tunnel junctions are prepared by in-situ shadowing. Despite the lack of lattice matching between Sn and InSb a 15 nm thick shell of tin is found to induce a hard superconducting gap, with superconductivity persisting in magnetic field up to 4T. A small island of Sn-InSb exhibits the two-electron charging effect. These findings suggest a less restrictive approach to fabricating superconducting and topological quantum circuits.