Among van der Waals layered ferromagnets, monolayer vanadium diselenide (VSe2) stands out due to its robust ferromagnetism. However, the exfoliation of monolayer VSe2 is challenging, not least because the monolayer flake is extremely unstable in air. Using an electrochemical exfoliation approach with organic cations as the intercalants, monolayer 1T‐VSe2 flakes are successfully obtained from the bulk crystal at high yield. Thiol molecules are further introduced onto the VSe2 surface to passivate the exfoliated flakes, which improves the air stability of the flakes for subsequent characterizations. Room‐temperature ferromagnetism is confirmed on the exfoliated 2D VSe2 flakes using a superconducting quantum interference device (SQUID), X‐ray magnetic circular dichroism (XMCD), and magnetic force microscopy (MFM), where the monolayer flake displays the strongest ferromagnetic properties. Se vacancies, which can be ubiquitous in such materials, also contribute to the ferromagnetism of VSe2, although density functional theory (DFT) calculations show that such effect can be minimized by physisorbed oxygen molecules or covalently bound thiol molecules.

We apply direct ink writing for the three-dimensional (3D) printing of polyaniline/reduced graphene oxide (PANI/RGO) composites with PANI/graphene oxide (PANI/GO) gel as printable inks. The PANI/GO gel inks for 3D printing are prepared via self-assembly of PANI and GO in a blend solvent of N-methyl-2-pyrrolidinone and water, and offer both shaping capability, self-sustainability, and electrical conductivity after reduction of GO. PANI/RGO interdigital electrodes are fabricated with 3D printing, and based on these electrodes, a planar solid-state supercapacitor is constructed, which exhibits high performance with an areal specific capacitance of 1329 mF cm. The approach developed in this work provides a simple, economic, and effective way to fabricate PANI-based 3D architectures, which leads to promising application in future energy and electric devices at micro-nano scale.

No abstract

No abstract

Recently, a class of thermoelectric (TE) materials with a FeOCl-type layered structure have been reported, such as GaOI, InOI, and TaCX (X = Cl, Br, I). These reports simulated further research on screening excellent TE monolayers with FeOCl-type structures. In this work, we carry out a comprehensive study on exploring the thermoelectric properties of Al2X2Se2 (X = Cl, Br, I) monolayers. The heat transport properties of the three monolayers are calculated and compared. Specifically, the thermal conductivities of 7.94 (16.98) W m–1 K–1 and 5.01 (16.15) W m–1 K–1 for the Al2Cl2Se2 and Al2Br2Se2 monolayers in the x direction (y direction) are obtained, respectively, which are more than that (0.29 (0.70) W m–1 K–1) for the Al2I2Se2 monolayer. The significant difference in the lattice thermal conductivity κl of Al2X2Se2 monolayers is attributed to their different phonon anharmonicity. It is also noted that strong anisotropy exists in the κl between the x and y directions. Additionally, the electronic transport parameters (the Seebeck coefficient and electrical conductivity) are figured out. Thus, the optimal ZT values of Al2X2Se2 monolayers from 200 to 700 K are obtained. It is found that the highest ZT value of the Al2I2Se2 monolayer (3.24) in the x direction is almost two times as higher as that (1.78) in the y direction at 700 K. The maximum ZT values of the Al2Cl2Se2 (0.59) and Al2Br2Se2 (0.95) monolayers in the y direction are higher than those of the Al2Cl2Se2 (0.34) and Al2Br2Se2 (0.77) monolayers in the x direction at 700 K, respectively, which are smaller than that of the Al2I2Se2 monolayer along with whether the x-axis (3.37) or the y-axis (1.75). This work reveals that the three monolayers exhibit anisotropies in the κl and ZT. The Al2I2Se2 monolayer has better TE performance than the Al2Cl2Se2 and Al2Br2Se2 monolayers.

Heteroatom-doped carbon-based materials are of significance for clean energy conversion and storage because of their fascinating electronic properties, low cost, high durability, and environmental friendliness. Atomically precise fabrication of carbon-based materials with well-defined heteroatom-dopant positions and atomic-scale understanding of their atomic-level electronic properties is a challenge. Herein, we demonstrate the bottom-up on-surface synthesis of 1D and 2D monolayer carbon nitride nanostructures with precise control of the nitrogen-atom doping sites and pore sizes. We also observe an electronic band offset at the C−N heterojunction. Using highresolution scanning tunneling microscopy, the atomic structure of the as-prepared carbon nitride nanoporous monolayers are revealed, indicating successful and precise control of the structures and N atom doping sites. Furthermore, corroborated by theoretical calculations, scanning tunneling spectroscopy measurements reveal a valence band shift of 140 meV that results in an electric field of 2.9 × 10 8 V m −1 at the C−N heterojunction, indicating efficient separation of the electron−hole pair at the N doping site. Our finding offers direct atomic-level insights into the local electronic structure of the heteroatom-doped carbon-based materials.

Chemical exfoliation has been used for the fast and large‐scale production of 2D nanosheets from graphene and transition metal dichalcogenides; however, it is rarely used for domain engineering of exfoliated nanosheets. Herein, it is found that the use of large sized molecular intercalants during electrochemical intercalation induce atomic row dislocation and parallel mirror twin boundaries (MTBs) on an otherwise pristine rhenium disulfide (ReS2) crystal, such that the exfoliated flakes possess a parallel, multi‐domain structure. These domains can be distinguished under a polarized microscope owing to the intrinsic in‐plane optical dichroic properties of ReS2, thereby affording a way to track the number of domains introduced versus the size of the molecular intercalant during electrochemical exfoliation. Ferromagnetism is detected on the intercalated sample using large sized molecular intercalants. Density function theory suggests that these may be due to the coupled effects of lattice strain and S vacancies in the MTBs.

Ansamycins are a class of macrolactams with diverse bioactivities, characterized by the unique 3-amino-5-hydroxybenzoic acid moiety. In this study, the ansamycin gene cluster aas in Streptomyces sp. S35 was activated by the constitutive coexpression of two pathway-specific regulator genes aas1 and aas10, and seven novel pentaketide ansamycin aminoansamycins A–G (1–7) were identified. Compound 4 with better antiproliferative activity indicated that the anthranilate analogues are probably promising building blocks for the production of unnatural ansamycins with improved activity.