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Two-dimensional (2D) hybrid perovskites have been garnering increasing attention across various fields due to their rich optical, electrical, optoelectronic, and magnetic properties. Current growth techniques only offer millimeter-scale or polycrystalline perovskites, which present a major barrier to the practical large-scale applications of these materials. In this study, we successfully prepared a series of BA2CuCl4–xBrx perovskite single-crystalline nanosheets with centimeter size using a controlled cooling growth method. Characterization results suggest that the obtained single-crystalline nanosheets are of high quality and that Br is uniformly doped. Moreover, these single-crystalline nanosheets exhibit ferromagnetic ordering at low temperatures, with the Curie–Weiss temperature increasing from 14.2 to 16.5 K as Br-doping concentration increases. Our approach provides a potential solution for the scalable synthesis and application of hybrid perovskites. At the same time, this family of 2D magnetic perovskites with tunable optical properties holds great potential for future spintronics applications. [ABSTRACT FROM AUTHOR]

Unlike conventional thermotropicand lyotropic liquid crystals,nonamphiphilic lyotropic liquid crystals consist of hydrated assembliesof nonamphiphilic molecules that are aligned with a separation ofabout 6 nm between assemblies in an aqueous environment. This separationraises the question of how chirality, either from chiral mesogensor chiral dopants, would impact the phase as the assemblies that needto interact with each other are about 6 nm apart. Here, we reportthe synthesis of three stereoisomers of disodium chromonyl carboxylate,5′DSCG-diviol, and the correlation between the molecular structure,bulk assembly, and liquid crystal formation. We observed that thechiral isomers (enantiomers 5′DSCG-(R,R)-divioland 5′DSCG-(S,S)-diviol) formed liquid crystalswhile the achiral isomer 5′DSCG-meso-divioldid not. Circular dichroism indicated a chiral conformation with bisignatecotton effect. The nuclear Overhauser effect in proton NMR spectroscopyrevealed conformations that are responsible for liquid crystal formation.Cryogenic transmission electron microscopy showed that chiral 5′DSCG-diviolsform assemblies with crossings. Interestingly, only planar alignmentof the chiral nematic phase was observed in liquid crystal cells withthin spacers. The homeotropic alignment that permitted a fingerprinttexture was obtained only when the thickness of the liquid crystalcell was increase to above ∼500 μm. These studies suggestthat hydrated assemblies of chiral 5′DSCG-diviol can interactwith each other across a 6 nm separation in an aqueous environmentby having a twist angle of about 0.22° throughout the samplebetween the neighboring assemblies. [ABSTRACT FROM AUTHOR]

In-plane anisotropic two-dimensional (2D) materials, emerging as an intriguing type of 2D family, provide an ideal platform for designing and fabrication of optoelectronic devices. Exploring air-stable and strong in-plane anisotropic 2D materials is still challenging and promising for polarized photodetection. Herein, SiP 2 , a 2D IV-V semiconductor, is successfully prepared and introduced into an in-plane anisotropic 2D family. The basic characterizations combined with theoretical calculations reveal 2D SiP 2 to exhibit an intrinsically low-symmetry structure, the in-plane anisotropy of phonon vibrations, and an anisotropically dispersed band structure. Moreover, the photodetector based on 2D SiP 2 exhibits high performance with a high detectivity of 10 12 Jones, a large light on/off ratio of 10 3 , a low dark current of 10 -13 A, and a fast response speed of 3 ms. Furthermore, 2D SiP 2 demonstrates a high anisotropic photodetection with an anisotropic ratio up to 2. In addition, the polarization-sensitive photodetector presents a dichroic ratio of 1.6 due to the intrinsic linear dichroism. These good characteristics make 2D SiP 2 a promising candidate as an in-plane anisotropic semiconductor for high-sensitivity and polarized optoelectronic applications.

Recent studies have shown that tellurium-based two-dimensional (2D) crystals undergo dramatic structural, physical, and chemical changes under ambient conditions, which adversely impact their much desired properties. Here, we introduce a diazonium molecule functionalization-based surface engineering route that greatly enhances their environmental stability without sacrificing their much desired properties. Spectroscopy and microscopy results show that diazonium groups significantly slow down the surface reactions, and consequently, gallium telluride (GaTe), zirconium telluride (ZrTe 3 ), and molybdenum ditelluride (MoTe 2 ) gain strong resistance to surface transformation in air or when immersed under water. Density functional theory calculations show that functionalizing molecules reduce surface reactivity of Te-containing 2D surfaces by chemical binding followed by an electron withdrawal process. While pristine surfaces structurally decompose because of strong reactivity of Te surface atoms, passivated functionalized surfaces retain their structural anisotropy, optical band gap, and emission characteristics as evidenced by our conductive atomic force microscopy, photoluminescence, and absorption spectroscopy measurements. Overall, our findings offer an effective method to increase the stability of these environmentally sensitive materials without impacting much of their physical properties.

Recent studies have shown that vapor phase synthesis of structurally isotropic two-dimensional (2D) MoS2 and WS2 produces well-defined domains with clean grain boundaries (GBs). This is anticipated to be vastly different for 2D anisotropic materials like ReS2 mainly due to large anisotropy in interfacial energy imposed by its distorted 1T crystal structure and formation of signature Re-chains along [010] b-axis direction. Here, we provide first insight on domain architecture on chemical vapor deposited (CVD) ReS2 domains using high-resolution scanning transmission electron microscopy, angle-resolved nano-Raman spectroscopy, reflectivity, and atomic force microscopy measurements. Results provide ways to achieve crystalline anisotropy in CVD ReS2, establish domain architecture of high symmetry ReS2 flakes, and determine Re-chain orientation within subdomains. Results also provide a first atomic resolution look at ReS2 GBs, and surprisingly we find that cluster and vacancy defects, formed by collusion of Re-chains at the GBs, dramatically impact the crystal structure by changing the Re-chain direction and rotating Re-chains 180° along their b-axis. Overall results not only shed first light on domain architecture and structure of anisotropic 2D systems but also allow one to attain much desired crystalline anisotropy in CVD grown ReS2 for the first time for tangible applications in photonics and optoelectronics where direction-dependent dichroic and linearly polarized material properties are required.

This work studies the phase separations between polymers and a small molecule in a common aqueous solution that do not have well-defined hydrophobic-hydrophilic separation. In addition to poly(acrylamide) (PAAm) and poly(vinyl alcohol) (PVA), poly(vinyl pyrrolidone) (PVP) also promotes liquid crystal (LC) droplet formation by disodium cromoglycate (5'DSCG) solvated in water. In the presence of these polymers, the concentration of 5'DSCG needed for forming LC droplets is substantially lower than that needed for forming an LC phase by 5'DSCG alone. To define the concentration ranges that 5'DSCG molecules form liquid crystals (either as droplets or as an isotropic-LC mixture), we constructed ternary phase diagrams for 5'DSCG, water, and a polymer - PVA, PVP, or PAAm. We discovered that PAAm with high molecular weight promotes LC droplet formation by 5'DSCG more effectively than PAAm with low molecular weight. At the same weight percentage, long-chain PAAm can cause 5'DSCG to form LC droplets in water, whereas short-chain PAAm does not. Poly(vinyl pyrrolidone) (PVP), which has functional groups that are more dissimilar to 5'DSCG than PVA and PAAm, promotes LC droplet formation by 5'DSCG more effectively than either of the other two polymers. Additionally, small angle neutron scattering data revealed that the assembly structure of 5'DSCG promoted by the presence of PVA is similar to the thread structure formed by 5'DSCG alone. Together, these results reveal how noncovalent polymerization can be promoted by mixing thermodynamically incompatible molecules and elucidate the basic knowledge of nonamphiphilic colloidal science.