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.

Two-dimensional (2D) materials have been a hot research topic in the last decade, due to novel fundamental physics in the reduced dimension and appealing applications. Systematic discovery of functional 2D materials has been the focus of many studies. Here, we present a large dataset of 2D materials, with more than 6,000 monolayer structures, obtained from both top-down and bottom-up discovery procedures. First, we screened all bulk materials in the database of Materials Project for layered structures by a topology-based algorithm and theoretically exfoliated them into monolayers. Then, we generated new 2D materials by chemical substitution of elements in known 2D materials by others from the same group in the periodic table. The structural, electronic and energetic properties of these 2D materials are consistently calculated, to provide a starting point for further material screening, data mining, data analysis and artificial intelligence applications. We present the details of computational methodology, data record and technical validation of our publicly available data ( http://www.2dmatpedia.org/ ).

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Transition metal dichalcogenide (TMD) quantum dots (QDs) are fundamentally interesting because of the stronger quantum size effect with decreased lateral dimensions relative to their larger 2D nanosheet counterparts. However, the preparation of a wide range of TMD QDs is still a continual challenge. Here we demonstrate a bottom-up strategy utilizing TM oxides or chlorides and chalcogen precursors to synthesize a small library of TMD QDs (MoS2, WS2, RuS2, MoTe2, MoSe2, WSe2 and RuSe2). The reaction reaches equilibrium almost instantaneously (~10–20 s) with mild aqueous and room temperature conditions. Tunable defect engineering can be achieved within the same reactions by deviating the precursors’ reaction stoichiometries from their fixed molecular stoichiometries. Using MoS2 QDs for proof-of-concept biomedical applications, we show that increasing sulfur defects enhanced oxidative stress generation, through the photodynamic effect, in cancer cells. This facile strategy will motivate future design of TMDs nanomaterials utilizing defect engineering for biomedical applications.

The demand for a new generation of flexible, portable, and high‐capacity power sources increases rapidly with the development of advanced wearable electronic devices. Here we report a simple process for large‐scale fabrication of self‐standing composite film electrodes composed of NiCo2O4@carbon nanotube (CNT) for supercapacitors. Among all composite electrodes prepared, the one fired in air displays the best electrochemical behavior, achieving a specific capacitance of 1,590 F g−1 at 0.5 A g−1 while maintaining excellent stability. The NiCo2O4@CNT/CNT film electrodes are fabricated via stacking NiCo2O4@CNT and CNT alternately through vacuum filtration. Lightweight, flexible, and self‐standing film electrodes (≈24.3 µm thick) exhibit high volumetric capacitance of 873 F cm−3 (with an areal mass of 2.5 mg cm−2) at 0.5 A g−1. An all‐solid‐state asymmetric supercapacitor consists of a composite film electrode and a treated carbon cloth electrode has not only high energy density (≈27.6 Wh kg−1) at 0.55 kW kg−1 (including the weight of the two electrodes) but also excellent cycling stability (retaining ≈95% of the initial capacitance after 5000 cycles), demonstrating the potential for practical application in wearable devices.

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As an effort to identify van der Waals heterostructures for efficient excitonic solar cell application, high-throughput computational screening was carried out to study the band alignments of 1540 vertical heterostructures formed by 56 two-dimensional semiconducting/insulating materials. More than 90 heterostructures with estimated power conversion efficiency (PCE) higher than 15% have been identified, of which 17 heterostructures are predicted to have PCE higher than the best value (20%) reported or proposed in the literature.