Strong mechanical anisotropy and an anisotropic Dirac state in 2D C5N3.

Two-dimensional (2D) carbon nitride materials have emerged as a versatile platform for the design of high-performance nanoelectronics, but strong anisotropy in 2D carbon nitrides has rarely been reported. In this work, a 2D carbon nitride with strong anisotropy composed of tetra-, penta-, and hexa-rings (named as TPH-C5N3) is proposed. This TPH-C5N3 exhibits both dynamical and mechanical stability. Furthermore, it also showcases remarkable thermal stability, reaching up to 2300 K, as evidenced by AIMD simulations conducted in an NVT environment utilizing the Nosé-Hoover thermostat. Significantly, TPH-C5N3 demonstrates high anisotropic ratios in its mechanical properties, positioning it as the frontrunner in the current carbon nitride systems. In addition, a Dirac cone with an anisotropic ratio of 55.8% and Fermi velocity of 7.26 × 105 m s-1 is revealed in TPH-C5N3. The nontrivial topological properties of TPH-C5N3 are demonstrated by a non-zero Z2 invariant and topologically protected edge states. Our study offers theoretical insights into an anisotropic 2D carbon nitride material, laying the groundwork for its design and synthesis.

High-Throughput Scanning Second-Harmonic-Generation Microscopy for Polar Materials.

The Materials Genome Initiative aims to discover, develop, manufacture, and deploy advanced materials at twice the speed of conventional approaches. To achieve this, high-throughput characterization is essential for the rapid screening of candidate materials. In this study, a high-throughput scanning second-harmonic-generation microscope with automatic partitioning, accurate positioning, and fast scanning is developed that can rapidly probe and screen polar materials. Using this technique, typical ferroelectrics, including periodically poled lithium niobate crystals and PbZr0.2 Ti0.8 O3 (PZT) thin films are first investigated, whereby the microscopic domain structures are clearly revealed. This technique is then applied to a compositional-gradient (100-x)%BaTiO3 -x%SrTiO3 film and a thickness-gradient PZT film to demonstrate its high-throughput capabilities. Since the second-harmonic-generation signal is correlated with the macroscopic remnant polarization over the probed region determined by the laser spot, it is free of artifacts arising from leakage current and electrostatic interference, while materials' symmetries and domain structures must be carefully considered in the data analysis. It is believed that this work can help promote the high-throughput development of polar materials and contribute to the Materials Genome Initiative.

Highly Flexible Freestanding BaTiO3 -CoFe2 O4 Heteroepitaxial Nanostructure Self-Assembled with Room-Temperature Multiferroicity.

Multiferroics with simultaneous electric and magnetic orderings are highly desirable for sensing, actuation, data storage, and bio-inspired systems, yet developing flexible materials with robust multiferroic properties at room temperature is a long-term challenge. Utilizing water-soluble Sr3 Al2 O6 as a sacrificial layer, the authors have successfully self-assembled a freestanding BaTiO3 -CoFe2 O4 heteroepitaxial nanostructure via pulse laser deposition, and confirmed its epitaxial growth in both out-of-plane and in-plane directions, with highly ordered CoFe2 O4 nanopillars embedded in a single crystalline BaTiO3 matrix free of substrate constraint. The freestanding nanostructure enjoys super flexibility and mechanical integrity, not only capable of spontaneously curving into a roll, but can also be bent with a radius as small as 4.23 µm. Moreover, piezoelectricity and ferromagnetism are demonstrated at both microscopic and macroscopic scales, confirming its robust multiferroicity at room temperature. This work establishes an effective route for flexible multiferroic materials, which have the potential for various practical applications.

Highly Ordered SnO2 Nanopillar Array as Binder-Free Anodes for Long-Life and High-Rate Li-Ion Batteries.

SnO2, a typical transition metal oxide, is a promising conversion-type electrode material with an ultrahigh theoretical specific capacity of 1494 mAh g-1. Nevertheless, the electrochemical performance of SnO2 electrode is limited by large volumetric changes (~300%) during the charge/discharge process, leading to rapid capacity decay, poor cyclic performance, and inferior rate capability. In order to overcome these bottlenecks, we develop highly ordered SnO2 nanopillar array as binder-free anodes for LIBs, which are realized by anodic aluminum oxide-assisted pulsed laser deposition. The as-synthesized SnO2 nanopillar exhibit an ultrahigh initial specific capacity of 1082 mAh g-1 and maintain a high specific capacity of 524/313 mAh g-1 after 1100/6500 cycles, outperforming SnO2 thin film-based anodes and other reported binder-free SnO2 anodes. Moreover, SnO2 nanopillar demonstrate excellent rate performance under high current density of 64 C (1 C = 782 mA g-1), delivering a specific capacity of 278 mAh g-1, which can be restored to 670 mAh g-1 after high-rate cycling. The superior electrochemical performance of SnO2 nanoarray can be attributed to the unique architecture of SnO2, where highly ordered SnO2 nanopillar array provided adequate room for volumetric expansion and ensured structural integrity during the lithiation/delithiation process. The current study presents an effective approach to mitigate the inferior cyclic performance of SnO2-based electrodes, offering a realistic prospect for its applications as next-generation energy storage devices.