Biocompatible Mn(II)-Enhanced N–S-Codoped Carbon Dots: A Versatile Fluorescence Sensor for Sensitive Hg²⁺ Detection in Coastal Seawater and Living Cells

Despite the promising potential of carbon dots (CDs) as a photoluminescent nanomaterial in advancing spectral analysis techniques for the detection of various harmful heavy metal ions such as Hg2+, Cu2+, Cd2+, and Pb2+, the fundamental challenge of effectively eliminating the interference of transition metal ions in multi-ion systems persists. In this study, we present straightforward, efficient, and versatile manganese(II)-enhanced nitrogen and sulfur codoped carbon dots (Mn(II)-N,SCDs) specifically designed for the highly selective and sensitive detection of Hg2+ ions. Mn(II)-N,SCDs exhibited uniform particle size (∼2.0 nm) and demonstrated excellent fluorescence performance, characterized by high fluorescence intensity and quantum yield (QY = 48.71%). The incorporation of Mn2+ not only enhances the fluorescence characteristics but also serves to effectively block the surplus transition metal ion binding sites on the surface of carbon dots, thereby leading to a heightened selective response to Hg2+. Furthermore, the synthesized Mn(II)-N,SCDs also exhibited low cytotoxicity and efficient cellular uptake, enabling fluorescence imaging of living cells. Importantly, the developed fluorescence sensor exhibited a highly specific response to Hg2+ ions even in the presence of other metal ions in phosphate-buffered solution (PBS), with a low detection limit of 0.29 nM (S/N = 3). The efficacy of the probe was successfully demonstrated through the determination of Hg2+ in live cells and natural coastal water samples

Nitrogen-Doped Mesoporous Graphene as a Synergistic Electrocatalyst Matrix for High-Performance Oxygen Reduction Reaction

To balance the anchoring sites and conductivity of the catalyst supports is a dilemma in electrocatalytic oxygen reduction reaction (ORR). Nitrogen-doped mesoporous graphene (N-MG) with large surface area, high porosity, and superior intrinsic conductivity has been developed to address this issue. Using N-MG as the backbone, a hybrid catalyst of Co₃O₄ nanocrystals embedded on N-MG (Co₃O₄/N-MG) was prepared for the electrocatalytic ORR in alkaline media. The Co₃O₄/N-MG showed high catalytic activity for the four-electron ORR, giving a more positive onset potential (0.93 V vs RHE) and a higher current density. The unique property of N-MG and the synergetic effect of Co₃O₄ and N-MG are prominent for ORR. With improved electrocatalytic activity and durability, the Co₃O₄/N-MG can be an efficient nonprecious metal catalyst and potentially used to substitute the platinum-based cathode catalysts in fuel cells and metal–air batteries

Self-Assembly of K_<i>x</i>WO₃ Nanowires into Nanosheets by an Oriented Attachment Mechanism

The K_<i>x</i>WO₃ nanosheets consisting of superfine nanowires were successfully synthesized in ambient air. The detailed electron microscopy and X-ray diffraction investigations imply that the nanosheets were obtained by self-assembly of the ordered nanowires with exposed {011̅0}_H facets. The sheet morphology is closely related with the growth conditions including temperature and time, etc. A possible mechanism based on the oriented attachment of neighboring nanowires for the formation of nanosheets is proposed. Our results shed light on the interfacial characteristics of self-assembled K_<i>x</i>WO₃ nanowires and can serve as guidance to the future design of relevant two-dimensional structures for various electrical and optical applications

Detection of Microplastics Based on a Liquid–Solid Triboelectric Nanogenerator and a Deep Learning Method

Microplastics are sub-millimeter-sized fragments of plastics, which have been found in environments to a great extent. They are relatively new pollutants that are difficult to be degraded. They not only cause irreversible adverse effects on microorganisms, animals, and plants but also enter the human body through the food chain and affect human health. However, due to their small size, variety, and differences in physical and chemical properties of microplastics, traditional detection and identification still face challenges. This work provides a method for detecting and classifying microplastics in liquids using a liquid–solid triboelectric nanogenerator (LS-TENG) in combination with a deep learning model. The experiment showed that the type and content of microplastics in the liquid had a great effect on the contact electrification between the liquid and the perfluoroethylene-propylene copolymer. After adding polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, and polystyrene microplastics to the liquids, it was found that the type and content of different microplastics have a significant impact on the output voltage signal of the LS-TENG sensor. When the mass fraction of microplastics ranged from 0.025 to 0.25 wt %, the voltage output of the LS-TENG sensor had a linear relationship with the mass fraction of microplastics. Therefore, a method for quantitatively detecting the content of microplastics using the LS-TENG sensor has been established. Based on the LS-TENG output voltage signal, a convolutional neural network deep learning model was used to identify different types of labels, and high recognition accuracy was achieved. These are of great significance for expanding the application prospect of LS-TENG and realizing the detection of microplastics in liquids

Ferroelectricity in Epitaxial Perovskite Oxide Bi₂WO₆ Films with One-Unit-Cell Thickness

Retaining ferroelectricity in ultrathin films or nanostructures is crucial for miniaturizing ferroelectric devices, but it is a challenging task due to intrinsic depolarization and size effects. In this study, we have shown that it is possible to stably maintain in-plane polarization in an extremely thin, one-unit-cell thick epitaxial Bi2WO6 film. The use of a perfectly lattice-matched NdGaO3 (110) substrate for the Bi2WO6 film minimizes strain and enhances stability. We attribute the residual polarization in this ultrathin film to the crystal stability of the Bi–O octahedral framework against structural distortions. Our findings suggest that ferroelectricity can surpass the critical thickness limit through proper strain engineering, and the Bi2WO6/NdGaO3 (110) system presents a potential platform for designing low-energy consumption, nonvolatile ferroelectric memories

Scalable Fabrication of Self-Aligned Graphene Transistors and Circuits on Glass

Graphene transistors are of considerable interest for radio frequency (rf) applications. High-frequency graphene transistors with the intrinsic cutoff frequency up to 300 GHz have been demonstrated. However, the graphene transistors reported to date only exhibit a limited extrinsic cutoff frequency up to about 10 GHz, and functional graphene circuits demonstrated so far can merely operate in the tens of megahertz regime, far from the potential the graphene transistors could offer. Here we report a scalable approach to fabricate self-aligned graphene transistors with the extrinsic cutoff frequency exceeding 50 GHz and graphene circuits that can operate in the 1–10 GHz regime. The devices are fabricated on a glass substrate through a self-aligned process by using chemical vapor deposition (CVD) grown graphene and a dielectrophoretic assembled nanowire gate array. The self-aligned process allows the achievement of unprecedented performance in CVD graphene transistors with a highest transconductance of 0.36 mS/μm. The use of an insulating substrate minimizes the parasitic capacitance and has therefore enabled graphene transistors with a record-high extrinsic cutoff frequency (> 50 GHz) achieved to date. The excellent extrinsic cutoff frequency readily allows configuring the graphene transistors into frequency doubling or mixing circuits functioning in the 1–10 GHz regime, a significant advancement over previous reports (∼20 MHz). The studies open a pathway to scalable fabrication of high-speed graphene transistors and functional circuits and represent a significant step forward to graphene based radio frequency devices

van Hove Singularity Enhanced Photochemical Reactivity of Twisted Bilayer Graphene

Twisted bilayer graphene (tBLG) exhibits van Hove singularities (VHSs) in the density of states that can be tuned by changing the twist angle (θ), sparking various novel physical phenomena. Much effort has been devoted to investigate the θ-dependent physical properties of tBLG. Yet, the chemical properties of tBLG with VHSs, especially the chemical reactivity, remain unexplored. Here we report the first systematic study on the chemistry of tBLG through the photochemical reaction between graphene and benzoyl peroxide. Twisted bilayer graphene exhibits θ-dependent reactivity, and remarkably enhanced reactivity is obtained when the energy of incident laser matches with the energy interval of the VHSs of tBLG. This work provides an insight on the chemistry of tBLG, and the successful enhancement of chemical reactivity derived from VHS is highly beneficial for the controllable chemical modification of tBLG as well as the development of tBLG based devices

Rational Hydrogenation for Enhanced Mobility and High Reliability on ZnO-based Thin Film Transistors: From Simulation to Experiment

Hydrogenation is one of the effective methods for improving the performance of ZnO thin film transistors (TFTs), which originate from the fact that hydrogen (H) acts as a defect passivator and a shallow <i>n</i>-type dopant in ZnO materials. However, passivation accompanied by an excessive H doping of the channel region of a ZnO TFT is undesirable because high carrier density leads to negative threshold voltages. Herein, we report that Mg/H codoping could overcome the trade-off between performance and reliability in the ZnO TFTs. The theoretical calculation suggests that the incorporation of Mg in hydrogenated ZnO decrease the formation energy of interstitial H and increase formation energy of O-vacancy (<i>V</i>_O). The experimental results demonstrate that the existence of the diluted Mg in hydrogenated ZnO TFTs could be sufficient to boost up mobility from 10 to 32.2 cm²/(V s) at a low carrier density (∼2.0 × 10¹⁸ cm^–3), which can be attributed to the decreased electron effective mass by surface band bending. The all results verified that the Mg/H codoping can significantly passivate the <i>V</i>_O to improve device reliability and enhance mobility. Thus, this finding clearly points the way to realize high-performance metal oxide TFTs for low-cost, large-volume, flexible electronics

Rational Design of Amorphous Indium Zinc Oxide/Carbon Nanotube Hybrid Film for Unique Performance Transistors

Here we report unique performance transistors based on sol–gel processed indium zinc oxide/single-walled carbon nanotube (SWNT) composite thin films. In the composite, SWNTs provide fast tracks for carrier transport to significantly improve the apparent field effect mobility. Specifically, the composite thin film transistors with SWNT weight concentrations in the range of 0–2 wt % have been investigated with the field effect mobility reaching as high as 140 cm²/V·s at 1 wt % SWNTs while maintaining a high on/off ratio ∼10⁷. Furthermore, the introduction SWNTs into the composite thin film render excellent mechanical flexibility for flexible electronics. The dynamic loading test presents evidently superior mechanical stability with only 17% variation at a bending radius as small as 700 μm, and the repeated bending test shows only 8% normalized resistance variation after 300 cycles of folding and unfolding, demonstrating enormous improvement over the basic amorphous indium zinc oxide thin film. The results provide an important advance toward high-performance flexible electronics applications

High-Resolution Tracking Asymmetric Lithium Insertion and Extraction and Local Structure Ordering in SnS₂

In the rechargeable lithium ion batteries, the rate capability and energy efficiency are largely governed by the lithium ion transport dynamics and phase transition pathways in electrodes. Real-time and atomic-scale tracking of fully reversible lithium insertion and extraction processes in electrodes, which would ultimately lead to mechanistic understanding of how the electrodes function and why they fail, is highly desirable but very challenging. Here, we track lithium insertion and extraction in the van der Waals interactions dominated SnS₂ by in situ high-resolution TEM method. We find that the lithium insertion occurs via a fast two-phase reaction to form expanded and defective LiSnS₂, while the lithium extraction initially involves heterogeneous nucleation of intermediate superstructure Li_0.5SnS₂ domains with a 1–4 nm size. Density functional theory calculations indicate that the Li_0.5SnS₂ is kinetically favored and structurally stable. The asymmetric reaction pathways may supply enlightening insights into the mechanistic understanding of the underlying electrochemistry in the layered electrode materials and also suggest possible alternatives to the accepted explanation of the origins of voltage hysteresis in the intercalation electrode materials