Observation of Three-State Nematicity and Domain Evolution in Atomically Thin Antiferromagnetic NiPS3.

Nickel phosphorus trisulfide (NiPS3), a van der Waals 2D antiferromagnet, has received significant interest for its intriguing properties in recent years. However, despite its fundamental importance in the physics of low-dimensional magnetism and promising potential for technological applications, the study of magnetic domains in NiPS3 down to an atomically thin state is still lacking. Here, we report the layer-dependent magnetic characteristics and magnetic domains in NiPS3 by employing linear dichroism spectroscopy, polarized microscopy, spin-correlated photoluminescence, and Raman spectroscopy. Our results reveal the existence of the paramagnetic-to-antiferromagnetic phase transition in bulk to bilayer NiPS3 and provide evidence of the role of stronger spin fluctuations in thin NiPS3. Furthermore, our study identifies three distinct antiferromagnetic domains within atomically thin NiPS3 and captures the thermally activated domain evolution. Our findings provide crucial insights for the development of antiferromagnetic spintronics and related technologies.

Synthesis of 2D layered transition metal (Ni, Co) hydroxides via edge-on condensation.

Layered transition metal hydroxides (LTMHs) with transition metal centers sandwiched between layers of coordinating hydroxide anions have attracted considerable interest for their potential in developing clean energy sources and storage technologies. However, two-dimensional (2D) LTMHs remain largely understudied in terms of physical properties and applications in electronic devices. Here, for the first time we report > 20 µm α-Ni(OH)2 2D crystals, synthesized from hydrothermal reaction. And an edge-on condensation mechanism assisted with the crystal field geometry is proposed to understand the 2D intra-planar growth of the crystals, which is also testified through series of systematic comparative studies. We also report the successful synthesis of 2D Co(OH)2 crystals (> 40 µm) with more irregular shape due to the slightly distorted octahedral geometry of the crystal field. Moreover, the detailed structural characterization of synthesized α-Ni(OH)2 are performed. The optical band gap energy is extrapolated as 2.54 eV from optical absorption measurements and the electronic bandgap is measured as 2.52 eV from reflected electrons energy loss spectroscopy (REELS). We further demonstrate its potential as a wide bandgap (WBG) semiconductor for high voltage operation in 2D electronics with a high breakdown strength, 4.77 MV/cm with 4.9 nm thickness. The successful realization of the 2D LTMHs opens the door for future exploration of more fundamental physical properties and device applications.

Imaging Strain-Localized Single-Photon Emitters in Layered GaSe below the Diffraction Limit.

Nanoscale strain control of exciton funneling is an increasingly critical tool for the scalable production of single photon emitters (SPEs) in two-dimensional materials. However, conventional far-field optical microscopies remain constrained in spatial resolution by the diffraction limit and thus can provide only a limited description of nanoscale strain localization of SPEs. Here, we quantify the effects of nanoscale heterogeneous strain on the energy and brightness of GaSe SPEs on nanopillars with correlative cathodoluminescence, photoluminescence, and atomic force microscopy, supported by density functional theory simulations. We report the strain-localized SPEs have a broad range of emission wavelengths from 620 to 900 nm. We reveal substantial strain-controlled SPE wavelength tunability over a ∼100 nm spectral range and 2 orders of magnitude enhancement in the SPE brightness at the pillar center due to Type-I exciton funneling. In addition, we show that radiative biexciton cascade processes contribute to observed CL photon superbunching. Also, the GaSe SPEs show excellent stability, where their properties remain unchanged after electron beam exposure. We anticipate that this comprehensive study on the nanoscale strain control of two-dimensional SPEs will provide key insights to guide the development of truly deterministic quantum photonics.

Improving Strain-localized GaSe Single Photon Emitters with Electrical Doping.

Exciton localization through nanoscale strain has been used to create highly efficient single-photon emitters (SPEs) in 2D materials. However, the strong Coulomb interactions between excitons can lead to nonradiative recombination through exciton-exciton annihilation, negatively impacting SPE performance. Here, we investigate the effect of Coulomb interactions on the brightness, single photon purity, and operating temperatures of strain-localized GaSe SPEs by using electrostatic doping. By gating GaSe to the charge neutrality point, the exciton-exciton annihilation nonradiative pathway is suppressed, leading to ∼60% improvement of emission intensity and an enhancement of the single photon purity g(2)(0) from 0.55 to 0.28. The operating temperature also increased from 4.5 K to 85 K consequently. This research provides insight into many-body interactions in excitons confined by nanoscale strain and lays the groundwork for the optimization of SPEs for optoelectronics and quantum photonics.

Epitaxial Atomic Substitution for MoS2-MoN Heterostructure Synthesis.

Integrating different two-dimensional (2D) crystals is highly demanded for advancing their application in next-generation electronics. 2D transition metal carbides, nitrides, and carbonitrides (MXenes), as new members in the 2D family, are promising candidates for 2D electrodes because of their high conductivity and stability. However, integrating MXenes with other 2D semiconductors has been underdeveloped due to the limitation of top-down etching synthesis of MXenes. Our recent development of atomic substitution synthesis achieved ultrathin non-van der Waals (non-vdW) transition metal nitrides (TMNs) through the conversion of vdW transition metal dichalcogenides (TMDs), opening opportunities of combining TMDs with TMNs via controllable partial conversion. Here, we perform an in-depth study of the atomic substitution process from semiconducting MoS2 to metallic MoN and realize both lateral and vertical MoN-MoS2 heterostructures via edge and surface epitaxial conversion, respectively. The structural evolution investigation from MoS2 to MoN using high-resolution transmission electron microscopy suggests atomically bonded interface for lateral heterostructures and moiré pattern in vertical heterostructures. Moreover, mask-assisted atomic substitution is applied to create patterned MoN-MoS2-MoN lateral heterostructures. Electrical measurements reveal a Schottky barrier height of meV for a three-layer MoS2-MoN interface, showcasing the potential of atomically bonded lateral heterostructures for MoS2 electronics with MoN as contact electrodes.

Characteristics and distribution of microplastics in the surface water of the Songhua River in China.

This paper studied on the microplastics (MPs) pollution in the surface water of the Songhua River in China. MPs were detected in all sampling sites of the river, the abundance of MPs ranged from 1.09 to 15.97 items/L, and the average abundance was 5.72 ± 4.02 items/L. Human interference had a significant impact on the abundance of MPs, and abundance in the downstream were higher than those in the upstream in the urban area along the Songhua River. In this study, MPs with size <0.5 mm and size [0.5,1) mm were the main sizes; fiber and debris were the most common types; yellow was the dominant color. MPs in the Songhua River might have similar sources and degradation experiences, because the size, type, and color had no significant difference (P>0.05) in different sampling sections. PE, PET, and PS were the most common polymers of MPs, accounting for 33.55%, 29.68%, and 18.71%, respectively.

Flexible and high-performance electrochromic devices enabled by self-assembled 2D TiO2/MXene heterostructures.

Transition metal oxides (TMOs) are promising electrochromic (EC) materials for applications such as smart windows and displays, yet the challenge still exists to achieve good flexibility, high coloration efficiency and fast response simultaneously. MXenes (e.g. Ti3C2Tx) and their derived TMOs (e.g. 2D TiO2) are good candidates for high-performance and flexible EC devices because of their 2D nature and the possibility of assembling them into loosely networked structures. Here we demonstrate flexible, fast, and high-coloration-efficiency EC devices based on self-assembled 2D TiO2/Ti3C2Tx heterostructures, with the Ti3C2Tx layer as the transparent electrode, and the 2D TiO2 layer as the EC layer. Benefiting from the well-balanced porosity and connectivity of these assembled nanometer-thick heterostructures, they present fast and efficient ion and electron transport, as well as superior mechanical and electrochemical stability. We further demonstrate large-area flexible devices which could potentially be integrated onto curved and flexible surfaces for future ubiquitous electronics.

Microplastics pollution in China water ecosystems: a review of the abundance, characteristics, fate, risk and removal.

Microplastics pollution has been a focus for researchers in recent years worldwide, for the large quantities of plastics in production and the resistance to degradation. China's microplastics pollution attracts much attention because of its long coastline, large population and rapid economic development. This review addresses the widespread microplastics pollution in China's water ecosystems through available research results from recent years and analyses the abundance, characteristics, fate and risk of microplastics. This paper also discusses the current treatment technology of microplastics. The conclusions show that estuaries are severely affected by microplastics pollution; the accumulation of microplastics and adsorption of contaminants by microplastics could also lead to serious risks besides ingestion; there are few technologies that can efficiently remove microplastics pollution in sewage treatment plants. Finally, this review suggests directions for future research trends.

Realization of 2D crystalline metal nitrides via selective atomic substitution.

Two-dimensional (2D) transition metal nitrides (TMNs) are new members in the 2D materials family with a wide range of applications. Particularly, highly crystalline and large area thin films of TMNs are desirable for applications in electronic and optoelectronic devices; however, the synthesis of these TMNs has not yet been achieved. Here, we report the synthesis of few-nanometer thin Mo5N6 crystals with large area and high quality via in situ chemical conversion of layered MoS2 crystals. The versatility of this general approach is demonstrated by expanding the method to synthesize W5N6 and TiN. Our strategy offers a new direction for preparing 2D TMNs with desirable characteristics, opening a door for studying fundamental physics and facilitating the development of next-generation electronics.

Theoretical investigations into the electronic structures and electron transport properties of fluorine and carbonyl end-functionalized quarterthiophenes.

In this work, we concentrate on systematic investigation on the fluorination and carbonylation effect on electron transport properties of thiophene-based materials with the aim of seeking and designing electron transport materials. Some relative factors, namely, frontier molecular orbital (FMO), vertical electron affinity (VEA), electron reorganization energy (λele), electron transfer integral (tele), electron drift mobility (µele) and band structures have been calculated and discussed based on density functional theory. The results show that the introduction of fluorine atoms and carbonyl group especially for the latter could effectively increase EA and reduce λele, which is beneficial to the improvement of electron transport performance. Furthermore, these introductions could also affect the tele by changing molecular packing manner and distribution of FMO. Finally, according to our calculation, the 3d system is considered to be a promising electron transport material with small λele, high electron transport ability and good ambient stability.

Theoretical study of isomerism/phase dependent charge transport properties in tris(8-hydroxyquinolinato)aluminum(III).

The charge carrier transporting ability in the polymorphism of tris(8-hydroxyquinolinato)aluminum(III) (Alq(3)) has been studied using density functional theory (DFT) and Marcus charge transport theory. α- and ß-Alq(3) composed of mer-Alq(3) molecules have stronger electron-transporting property (n-type materials) compared with their hole-transporting ability. In contrast, γ- and δ-Alq(3) formed by fac-Alq(3) molecules possess stronger hole-transporting character than their electron-transporting ability. The detailed theoretical calculations indicate the reason lies in the differences of HOMO and LUMO distribution states of the two kinds of isomers, and the different molecular packing modes of charge-transporting pathways for different phases.

Theoretical study on the electron transfer and phosphorescent properties of iridium(III) complexes with 2-phenylpyridyl and 8-hydroxyquinolate ligands.

The complexes AlQ(3) and Ir(ppy)(3) (Q = 8-hydroxyquinolate; ppy = 2-phenylpyridyl) are typical green emitting fluorescence and phosphorescence materials, respectively. Here we hybridize Ir(ppy)(3) with AlQ(3) to investigate the optoelectronic properties of the Ir(III)-centred derivatives including (ppy)(2)IrQ, (ppy)IrQ(2) and IrQ(3) by using density functional methods. Our calculations show that the derivative Ir(III) complexes are red emitting phosphorescence materials. The characters of the lowest triplet excited states for these Ir(III) complexes are mainly dominated by the 8-hydroxyquinolate ligand. IrQ(3) and (ppy)(2)IrQ possess good electron transfer performance, while (ppy)IrQ(2) might have hole transport properties.

Novel urea-functionalized quinacridone derivatives: ultrasound and thermo effects on supramolecular organogels.

In investigations into the effects of environmental factors on organogels, two urea-functionalized quinacridone derivatives 1a and 1b have been designed and synthesized. These two compounds can respond to ultrasound and thermal stimuli in the organic test solvents, and exhibit pronounced aggregation properties. The field-effect (FE)-SEM images of xerogels show the characteristic gelation morphologies of 3D fibrous network structures. The concentration- and temperature-dependent (1)H NMR spectra suggest that the intermolecular π-π and hydrogen-bonding interactions of gelators are the main driving forces for the supramolecular assembly process. X-ray diffraction (XRD), UV/Vis absorption, and photoluminescent spectroscopy studies have been carried out and provide more information to define the molecular packing model in gelation states.

Carbazolyl-contained phenol-pyridyl boron complexes: syntheses, structures, photoluminescent and electroluminescent properties.

A series of phenol-pyridyl boron complexes 1-4 bearing carbazolyl-containing groups on boron centres have been designed and synthesized. The single crystals of complexes 1, 2 and 4 were grown, and the crystal structures were determined by X-ray diffraction analysis. All complexes possess very high melting points (346-385 °C) and decomposition temperatures (Td5: 397-423 °C), indicative of their high thermal stabilities. The electrochemical and photophysical properties as well as theoretical calculations were also investigated. Typical three-layer electroluminescent (EL) devices based on these organoboron complexes exhibited white electroluminescence.

Sonication-induced molecular gels based on mono-cholesterol substituted quinacridone derivatives.

A series of monocholesterol substituted quinacridone derivatives MCC(n) (n = 4, 6, 8) has been designed and synthesized. Compounds MCC(6) and MCC(8) can gelate a wide range of organic solvents upon ultrasound irradiation and afford intriguing well-defined nanostructures composed of three-dimensional sponge-like superstructures or fibrous networks. Interestingly, the gel produced from MCC(6) is sensitive to thermo-, aniline, and formic acid stimulus, giving obviously different aggregation behaviors as well as physical properties. Time-dependent spectroscopic data and theoretical calculation results provided explanation for the possible molecular aggregation mode during the formation of the gels.

Luminescent boron-contained ladder-type pi-conjugated compounds.

Four diboron-contained ladder-type pi-conjugated compounds 1-4 were designed and synthesized. Their thermal, photophysical, electrochemical properties, as well as density functional theory calculations, were fully investigated. The single crystals of compounds 1 and 3 were grown, and their crystal structures were determined by X-ray diffraction analysis. Both compounds have a ladder-type pi-conjugated framework. Compounds 1 and 2 possess high thermal stabilities, moderate solid-state fluorescence quantum yields, as well as stable redox properties, indicating that they are possible candidates for emitters and charge-transporting materials in electroluminescent (EL) devices. The double-layer device with the configuration of [ITO/NPB (40 nm)/1 or 2 (70 nm)/LiF (0.5 nm)/Al (200 nm)] exhibited good EL performance with the maximum brightness exceeding 8000 cd/m(2).

Theoretical characterization of a typical hole/exciton-blocking material bathocuproine and its analogues.

The structural, electronic, and carrier transport properties of bathocuproine (BCP), which is a typical hole/exciton-blocking material applied in organic light-emitting diodes (OLEDs), have been investigated based on density functional theory (DFT) and ab initio HF method. The detail characterizations of frontier electronic structure and lowest-energy optical transitions have been studied by means of time-dependent density functional theory (TD-DFT). Five BCP analogues, o-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2), 2,9-diphenyl-1,10-phenanthroline (3), 4,7-diphenyl-1,10-phenanthroline (4), and 2,9-bis(trifluoromethyl)-1,10-phenanthroline (5) have also been studied in order to select more suitable candidates of efficient hole-blocking materials. The calculated results showed that rigid planar structures, conjugate degrees, and substitute groups play crucial roles in the hole/exciton-blocking and electron-transport properties of these materials. The calculated geometries, ionization energies (IP), and energy gap between the singlet ground state and triplet excited state (E(T1)) were well in agreement with the experimental results. On the basis of the incoherent transport model, the calculated electron mobility of BCP is 1.79 x 10(-2) cm(2)/(V s), which is comparable to experimental results of 1.1 x 10(-3) cm(2)/(V s). The electron mobilities for compounds 1, 4, and 5 are 3.45 x 10(-2), 2.90 x 10(-2), and 1.40 x 10(-2) cm(2)/(V s), respectively. The calculated results indicated that compounds 1, 4, and 5 may be more effective hole/exciton-blocking materials than BCP.