Heterogeneous interfaces in 3D interconnected networks of flower-like 1T/2H Molybdenum disulfide nanosheets and carbon-fibers boosts superior EM wave absorption.

With the wide application of electromagnetic waves in national defense, communication, navigation and home appliances, the electromagnetic pollution problem is becoming more and more prominent. Therefore, high-performance, and low-density composite wave-absorbing materials have attracted much attention. In this paper, three-dimensional (3D) network structures of flower-like 1T/2H Molybdenum disulfide nanosheets anchored to carbon fibers (1T/2H MoS2/CNFs) were prepared by electrostatic spinning technique and calcination process. The morphology and electromagnetic wave absorption properties were tuned by changing the content of flower-like MoS2. The optimized 1T/2H MoS2/CNFs composite exhibits superior electromagnetic wave absorption with minimum reflection (RLmin) of -42.26 dB and effective absorption bandwidth (EAB) of 6.48 GHz at 2.5 mm. Multi-facts contribute to the super performance. First, the uniquely designed nanosheet and 3D interconnected networks leads to multiple reflection and scattering of electromagnetic waves, which promotes the attenuation of electromagnetic waves. Second, the propriate content of CNFs and MoS2 with different phase regulates its impedance matching characteristic. Third, Numerous heterogeneous interfaces existed between CNFs and MoS2, 1T and 2H MoS2 phase results in interface polarization. Besides, the 1T/2H MoS2 rich in defects induces defect polarization, improving the dielectric loss. Furthermore, the electromagnetic wave absorption performance was proved via radar reflectance cross section simulation. This work illustrates 1T/2H MoS2/CNFs is a promising material for electromagnetic absorption with wide bandwidth, strong absorption, low density, and high thermal stability.

High-Resolution Quantum Dot Light-Emitting Diodes by Electrohydrodynamic Printing.

Quantum dot light-emitting diodes (QLEDs) have attracted increasing attention due to their excellent electroluminescent properties and compatibility with inkjet printing processes, which show great potential in applications of pixelated displays. However, the relatively low resolution of the inkjet printing technology limits its further development. In this paper, high-resolution QLEDs were successfully fabricated by electrohydrodynamic (EHD) printing. A pixelated quantum dot (QD) emission layer was formed by printing an insulating Teflon mesh on a spin-coated QD layer. The patterned QLEDs show a high resolution of 2540 pixels per inch (PPI), with a maximum external quantum efficiency (EQE) of 20.29% and brightness of 35816 cd/m2. To further demonstrate its potential in full-color display, the fabrication process for the QD layer was changed from spin-coating to EHD printing. The as-printed Teflon effectively blocked direct contact between the hole transport layer and the electron transport layer, thus preventing leakage currents. As a result, the device showed a resolution of 1692 PPI with a maximum EQE of 15.40%. To the best of our knowledge, these results represent the highest resolution and efficiency of pixelated QLEDs using inkjet printing or EHD printing, which demonstrates its huge potential in the application of high-resolution full-color displays.

Boosting the Efficiency of High-Resolution Quantum Dot Light-Emitting Devices Based on Localized Surface Plasmon Resonance.

With pixel miniaturization, the performance of high-resolution quantum dot light-emitting diodes (QLEDs) usually degrades. Considering the dimension of ultrasmall pixels, herein, a barrier architecture based on localized surface plasmon resonance (LSPR) that promotes the radiative recombination of neighboring quantum dots is rationally designed to improve the device performance. Au nanoparticles (NPs) are embedded in an insulating polymer to form a honeycomb-patterned barrier layer via the nanoimprint process. Each pixel fabricated in the void area (average diameter of 1.5 µm) of the barrier layer is surrounded by a number of LSPR-NPs to enhance the luminescence. The resultant green QLEDs with a resolution of 9027 pixels per inch show a maximum external quantum efficiency of 11.1%, a 42.8% enhancement compared to the control device. Additionally, the lifetime of high-resolution QLEDs is obviously improved by the LSPR effect.

Efficient CsPbBr3 Perovskite Light-Emitting Diodes via Novel Multi-Step Ligand Exchange Strategy Based on Zwitterionic Molecules.

Perovskite nanocrystals have absorbed increasing interest, especially in the field of optoelectronics, owing to their unique characteristics, including their tunable luminescence range, robust solution processability, facile synthesis, and so on. However, in practice, due to the inherent instability of the traditional long-chain insulating ligands surrounding perovskite quantum dots (PeQDs), the performance of the as-fabricated QLED is relatively disappointing. Herein, the zwitterion 3-(decyldimethylammonio)propanesulfonate (DLPS) with the capability of double passivating perovskite quantum dots could effectively replace the original long-chain ligand simply through a multistep post-treatment strategy to finally inhibit the formation of defects. It was indicated from theexperimental results that the DLPS, as one type of ligand with the bimolecular ion, was very adavntageous in replacing long-chain ligands and further suppressing the formation of defects. Finally, the perovskite quantum dots with greatly enhanced PLQY as high as 98% were effectively achieved. Additionally, the colloidal stability of the corresponding PeQDs has been significantly enhanced, and a transparent colloidal solution was obtained after 45 days under ambient conditions. Finally, the as-fabricated QLEDs based on the ligand-exchanged PeQDs exhibited a maximum brightness of 9464 cd/m2 and an EQE of 12.17%.

Elimination of inhibitory effects of dodecyl dimethyl benzyl ammonium chloride on microalgae in wastewater by cocultivation with a newly screened microbial consortium.

As one of the most commonly used biocidal cationic surfactants, benzalkonium chlorides (BACs) have been an increasing concern as emerging contaminants. Wastewater has been claimed the main point for BACs to enter into the environment, but to date, it is still largely unknown how the BACs affect the microbes (especially microalgae) in the practical wastewater and how to cost-effectively remove them. In this study, the inhibitory effects of a typical BACs, dodecyl dimethyl benzyl ammonium chloride (DDBAC), on a green microalga Chlorella sp. in oxidation pond wastewater were investigated. The results showed that though a hermetic effect at the first 2 days was observed with the DDBAC at low concentration (<6 mg/L), the algal growth and photosynthesis were significantly inhibited by the DDBAC at all the tested concentrations (3 to 48 mg/L). Fortunately, a new microbial consortium (MC) capable of degrading DDBAC was screened through a gradient domestication method. The MC mainly composed of Wickerhamomyces sp., Purpureocillium sp., and Achromobacter sp., and its maximum removal efficiency and removal rate of DDBAC (48 mg/L) respectively reached 98.1 % and 46.32 mg/L/d. Interestingly, a microbial-microalgal system (MMS) was constructed using the MC and Chlorella sp., and a synergetic effect between the two kinds of microorganisms was proposed: microalga provided oxygen and extracellular polysaccharides as co-metabolic substrates to help the MC to degrade DDBAC, while the MC helped to eliminate the DDBAC-induced inhibition on the alga. Further, by observing the seven kinds of degradation products (mainly including CH5O3P, C6H5CH2-, and C8H11N), two possible chemical pathways of the DDBAC degradation were proposed. In addition, the metagenomic sequencing results showed that the main functional genes of the MMS included antibiotic-resistant genes, ABC transporter genes, quorum sensing genes, two-component regulatory system genes, etc. This study provided some theoretical and application findings for the cost-effective pollution prevention of BACs in wastewater.

Ligand-Nondestructive Direct Photolithography Assisted by Semiconductor Polymer Cross-Linking for High-Resolution Quantum Dot Light-Emitting Diodes.

The photolithographic patterning of fine quantum dot (QD) films is of great significance for the construction of QD optoelectronic device arrays. However, the photolithography methods reported so far either introduce insulating photoresist or manipulate the surface ligands of QDs, each of which has negative effects on device performance. Here, we report a direct photolithography strategy without photoresist and without engineering the QD surface ligands. Through cross-linking of the surrounding semiconductor polymer, QDs are spatially confined to the network frame of the polymer to form high-quality patterns. More importantly, the wrapped polymer incidentally regulates the energy levels of the emitting layer, which is conducive to improving the hole injection capacity while weakening the electron injection level, to achieve balanced injection of carriers. The patterned QD light-emitting diodes (with a pixel size of 1.5 µm) achieve a high external quantum efficiency of 16.25% and a brightness of >1.4 × 105 cd/m2. This work paves the way for efficient high-resolution QD light-emitting devices.

Near-Infrared Nanophosphors Based on CuInSe2 Quantum Dots with Near-Unity Photoluminescence Quantum Yield for Micro-LEDs Applications.

Highly efficient near-infrared (NIR) luminescent nanomaterials are urgently required for portable mini or micro phosphors-converted light-emitting diodes (pc-LEDs). However, most existing NIR-emitting phosphors are generally restricted by their low photoluminescence (PL) quantum yield (QY) or large particle size. Herein, a kind of highly efficient NIR nanophosphors is developed based on copper indium selenide quantum dots (CISe QDs). The PL peak of these QDs can be exquisitely manipulated from 750 to 1150 nm by altering the stoichiometry of Cu/In and doping with Zn2+ . Their absolute PLQY can be significantly improved from 28.6% to 92.8% via coating a ZnSe shell. By combining the phosphors with a commercial blue chip, an NIR pc-LED is fabricated with remarkable photostability and a record-high radiant flux of 88.7 mW@350 mA among the Pb/Cd-free QDs-based NIR pc-LEDs. Particularly, such QDs-based nanophosphors acted as excellent luminescence converter for NIR micro-LEDs with microarray diameters below 5 µm, which significantly exceeds the resolutions of current commercial inkjet display pixels. The findings may open new avenues for the exploration of highly efficient NIR micro-LEDs in a variety of applications.

Initiating Binary Metal Oxides Microcubes Electrsomagnetic Wave Absorber Toward Ultrabroad Absorption Bandwidth Through Interfacial and Defects Modulation.

Cobalt nickel bimetallic oxides (NiCo2O4) have received numerous attentions in terms of their controllable morphology, high temperature, corrosion resistance and strong electromagnetic wave (EMW) absorption capability. However, broadening the absorption bandwidth is still a huge challenge for NiCo2O4-based absorbers. Herein, the unique NiCo2O4@C core-shell microcubes with hollow structures were fabricated via a facile sacrificial template strategy. The concentration of oxygen vacancies and morphologies of the three-dimensional (3D) cubic hollow core-shell NiCo2O4@C framework were effectively optimized by adjusting the calcination temperature. The specially designed 3D framework structure facilitated the multiple reflections of incident electromagnetic waves and provided rich interfaces between multiple components, generating significant interfacial polarization losses. Dipole polarizations induced by oxygen vacancies could further enhance the attenuation ability for the incident EM waves. The optimized NiCo2O4@C hollow microcubes exhibit superior EMW absorption capability with minimum RL (RLmin) of -84.45 dB at 8.4 GHz for the thickness of 3.0 mm. Moreover, ultrabroad effective absorption bandwidth (EAB) as large as 12.48 GHz (5.52-18 GHz) is obtained. This work is believed to illuminate the path to synthesis of high-performance cobalt nickel bimetallic oxides for EMW absorbers with excellent EMW absorption capability, especially in broadening effective absorption bandwidth.

Interface-Induced Crystallinity Enhancement of Perovskite Quantum Dots for Highly Efficient Light-Emitting Diodes.

Perovskite quantum dot light-emitting diodes (QLEDs) with high color purity and wide color gamut have good application prospects in the next generation of display technology. However, colloidal perovskite quantum dots (PQDs) may introduce a large number of defects during the film-forming process, which is not conducive to the luminous efficiency of the device. Meanwhile, the disordered film formation of PQDs will form interfacial defects and reduce the device performance. Here, we report an interface-induced crystallinity enhancement (IICE) strategy to increase the crystallinity of PQDs at the hole transport layer (HTL)/PQD interface. As a result, both the Br- vacancies in the PQD film and the interfacial defects were well passivated and the leakage current was also suppressed. We achieved QLEDs with a maximum external quantum efficiency (EQE) of 16.45% and current efficiency (CE) of 61.77 cd/A, showing improved performance to more than twice that of the control devices. The IICE strategy paves a new way to enhance the crystallinity of PQD films, so as to improve the performance of QLEDs for application in the future display field.

Detecting the exponential relaxation spectrum in glasses by high-precision nanocalorimetry.

Nonexponential relaxations are universal characteristics for glassy materials. There is a well-known hypothesis that nonexponential relaxation peaks are composed of a series of exponential events, which have not been verified. In this Letter, we discover the exponential relaxation events during the recovery process using a high-precision nanocalorimetry, which are universal for metallic glasses and organic glasses. The relaxation peaks can be well fitted by the exponential Debye function with a single activation energy. The activation energy covers a broad range from α relaxation to ß relaxation and even the fast γ/ß' relaxation. We obtain the complete spectrum of the exponential relaxation peaks over a wide temperature range from 0.63Tg to 1.03Tg, which provides solid evidence that nonexponential relaxation peaks can be decomposed into exponential relaxation units. Furthermore, the contribution of different relaxation modes in the nonequilibrium enthalpy space is measured. These results open a door for developing the thermodynamics of nonequilibrium physics and for precisely modulating the properties of glasses by controlling the relaxation modes.

High sensitivity and wide response range artificial synapse based on polyimide with embedded graphene quantum dots.

Artificial electronic synapses are commonly used to simulate biological synapses to realize various learning functions, regarded as one of the key technologies in the next generation of neurological computation. This work used a simple spin coating technique to fabricate polyimide (PI):graphene quantum dots(GQDs) memristor structure. As a result, the devices exhibit remarkably stable exponentially decaying postsynaptic suppression current over time, as interpreted in the spike-timing-dependent plasticity phenomenon. Furthermore, with the increase of the applied electrical signal over time, the conductance of the electrical synapse gradually changes, and the electronic synapse also shows plasticity dependence on the amplitude and frequency of the pulse applied. In particular, the devices with the structure of Ag/PI:GQDs/ITO prepared in this study can produce a stable response to the stimulation of electrical signals between millivolt to volt, showing not only high sensitivity but also a wide range of "feelings", which makes the electronic synapses take a step forwards to emulate biological synapses. Meanwhile, the electronic conduction mechanisms of the device are also studied and expounded in detail. The findings in this work lay a foundation for developing brain-like neuromorphic modeling in artificial intelligence.

Flexible Quantum Dot Light-Emitting Device for Emerging Multifunctional and Smart Applications.

Quantum dot light-emitting diodes (QLEDs), owing to their exceptional performances in device efficiency, color purity/tunability in the visible region and solution-processing ability on various substrates, become a potential candidate for flexible and ultrathin electroluminescent (EL) lighting and display. Moreover, beyond the lighting and display, flexible QLEDs are enabled with endless possibilities in the era of the internet of things and artificial intelligence by acting as input/output ports in wearable integrated systems. Challenges remain in the development of flexible QLEDs with the goals for high performance, excellent flexibility/even stretchability, and emerging applications. In this paper, the recent developments of QLEDs including quantum dot materials, working mechanism, flexible/stretchable strategies and patterning strategies, and highlight its emerging multifunctional integrations and smart applications covering wearable optical medical devices, pressure-sensing EL devices, and neural smart EL devices, are reviewed. The remaining challenges are also summarized and an outlook on the future development of flexible QLEDs made. The review is expected to offer a systematic understanding and valuable inspiration for flexible QLEDs to simultaneously satisfy optoelectronic and flexible properties for emerging applications.

Buffer zone-based trace elements indicating the impact of human activities on karst urban groundwater.

The tanglesome allocation of landscape types at various spatial dimensions is an important component influencing the quality of groundwater environment in karst cities. Trace elements can be used as indicators of the extent of impact on groundwater which is an effective means of tracing groundwater contamination. In this study, we studied the influence of landscape patterns on trace elements in groundwater of typical karst cities in Southwest China (Guiyang City) on a multi-spatial scale by using multivariate statistical analysis. According to the sampling points, buffer zone scales with different radii (500 m, 1000 m, 1500 m, and 4000 m) were established to quantify the land use model. There are suburban and urban differences in trace element content. The city center has higher levels of trace elements compared to suburban areas, especially Li, Ni, Tl, Cu, Sr, Co, As, and Mn. In addition, the outcomes of the multiple linear regression had shown that the size effect of the association from landscape pattern to trace elements varies with different indicators and parameters. The results of redundancy analysis showed an overall change in trace elements was better interpreted by the landscape pattern of the 1500 m-scale buffer. At the same time, at the 1500 m scale, Ni, Tl, Cu, Co, As, Cr, Sr, Li, and Mn were positively correlated with the urban landscape index (4LPI, 4LSI), influenced by urban anthropogenic activities, while Cd, Zn, and Pb were positively correlated with the cropland landscape index (1AI, 1LPI), influenced by agricultural activities. This study indicates that trace elements are a reliable indicator for tracing groundwater contamination. The buffer zone can reflect the extent of urban impacts on groundwater and provide a new and effective analytical tool for groundwater management.

Dynamic Anti-Counterfeiting Labels with Enhanced Multi-Level Information Encryption.

Information encryption is an important means to improve the security of anti-counterfeiting labels. At present, it is still challenging to realize an anti-counterfeiting label with multi-function, high security factor, low production cost, and easy detection and identification. Herein, using inkjet and screen printing technology, we construct a multi-dimensional and multi-level dynamic optical anti-counterfeiting label based on instantaneously luminescent quantum dots and long afterglow phosphor, whose color and luminous intensity varied in response to time. Self-assembled quantum dot patterns with intrinsic fingerprint information endow the label with physical unclonable functions (PUFs), and the information encryption level of the label is significantly improved in view of the information variation in the temporal dimension. Furthermore, the convolutional residual neural networks are used to decode the massive information of PUFs, enabling fast and accurate identification of the anti-counterfeit labels.

Design of N-Type Textured Bi2 Te3 with Robust Mechanical Properties for Thermoelectric Micro-Refrigeration Application.

Thermoelectric refrigeration is one of the mature techniques used for cooling applications, with the great advantage of miniaturization over traditional compression refrigeration. Due to the anisotropic thermoelectric properties of n-type bismuth telluride (Bi2 Te3 ) alloys, these two common methods, including the liquid phase hot deformation (LPHD) and traditional hot forging (HF) methods, are of considerable importance for texture engineering to enhance performance. However, their effects on thermoelectric and mechanical properties are still controversial and not clear yet. Moreover, there has been little documentation of mechanical properties related to micro-refrigeration applications. In this work, the above-mentioned methods are separately employed to control the macroscopic grain orientation for bulk n-type Bi2 Te3 samples. The HF method enabled the stabilization of both composition and carrier concentration, therefore yielding a higher quality factor to compare with that of LPHD samples, supported by DFT calculations. In addition to superior thermoelectric performance, the HF sample also exhibited robust mechanical properties due to the presence of nano-scale distortion and dense dislocation, which is the prerequisite for realizing ultra-precision machining. This work helps to pave the way for the utilization of n-type Bi2 Te3 for commercial micro-refrigeration applications.

Enhanced Thermoelectric Performance of Yb-Filled Skutterudite with Bottom-Up Formed CoSi2 Nanoparticles.

It is known that Yb-filled skutterudite with excellent thermoelectric performance is promising for a power generation device in the intermediate temperature region. Here we created a new approach to obtain nanostructured materials by adding Si to Co-overstoichiometric Yb-filled skutterudite through high-energy ball milling, which embedded bottom-up formed CoSi2 nanoparticles into grain-refining Yb0.25Co4Sb12, synergistically resulting in the enhanced thermoelectric properties and room-temperature hardness. On one hand, the abundant grain boundaries and phase interfaces effectively blocked the propagation of medium-low frequency phonons, resulting in a lower lattice thermal conductivity. On the other hand, phase interfaces barrier nicely screened a portion of low-energy electrons, leading to an improved power factor. As a result, an enhanced peak ZT value of ∼1.43 at 823 K and a promising average ZT of ∼1.00 between 300 and 823 K were achieved in the Yb0.25Co4Sb12/0.05CoSi2 sample. Meanwhile, such nanostructures also enhanced the hardness through the collective contributions of second phase and fine grain strengthening, which made skutterudite more competitive in practical application.

Dual-function perovskite light-emitting/sensing devices for optical interactive display.

Interactive display devices integrating multiple functions have become a development trend of display technology. The excellent luminescence properties of perovskite quantum dots (PQDs) make it an ideal luminescent material for the next generation of wide-color gamut displays. Here we design and fabricate dual-function light-sensing/displaying light-emitting devices based on PQDs. The devices can display information as an output port, and simultaneously sense outside light signals as an input port and modulate the display information in a non-contact mode. The dual functions were attributed to the device designs: (1) the hole transport layer in the devices also acts as the light-sensing layer to absorb outside light signals; (2) the introduced hole trapping layer interface can trap holes originating from the light-sensing layer, and thus tune the charge transport properties and the light-emitting intensities. The sensing and display behavior of the device can be further modulated by light signals with different time and space information. This fusion of sensing and display functions has broad prospects in non-contact interactive screens and communication ports.

Research progress of full electroluminescent white light-emitting diodes based on a single emissive layer.

Carbon neutrality, energy savings, and lighting costs and quality have always led to urgent demand for lighting technology innovation. White light-emitting diodes (WLEDs) based on a single emissive layer (SEL) fabricated by the solution method have been continuously researched in recent years; they are advantageous because they have a low cost and are ultrathin and flexible. Here, we reviewed the history and development of SEL-WLEDs over recent years to provide inspiration and promote their progress in lighting applications. We first introduced the emitters and analysed the advantages of these emitters in creating SEL-WLEDs and then reviewed some cases that involve the above emitters, which were formed via vacuum thermal evaporation or solution processes. Some notable developments that deserve attention are highlighted in this review due to their potential use in SEL-WLEDs, such as perovskite materials. Finally, we looked at future development trends of SEL-WLEDs and proposed potential research directions.

Mixed-Halide Perovskite Film-Based Neuromorphic Phototransistors for Mimicking Experience-History-Dependent Sensory Adaptation.

Sensory adaptation is an essential function for humans to live on the earth. Herein, a hybrid synaptic phototransistor based on the mixed-halide perovskite/organic semiconductor film is reported. This hybrid phototransistor achieves photosensitive performance including a high photoresponsivity over 4 × 103 A/W and an excellent specific detectivity of 2.8 × 1016 Jones. Due to the photoinduced halide-ion segregation of the mixed-halide perovskites and their slow recovery properties, the experience-history-dependent sensory adaptation behavior can be mimicked. Moreover, the light pulse width, intensity, light wavelength, and gate bias can be used to regulate the adaptation processes to improve its adaptability and perceptibility in different environments. The CsPbBrxI3-x/organic semiconductor hybrid films produced by spin coating are beneficial to large-scale fabrication. This study fabricates a novel solution-processable light-stimulated synapse based on inorganic perovskites for mimicking the human sensory adaptation that makes it possible to approach artificial neural sensory systems.

Quantum Dot Self-Assembly Deposition in Physically Confined Microscale Space by Using an Inkjet Printing Technique.

Inkjet printing technique is susceptible to form coffer-ring patterns and inhomogeneous films owing to the evaporation and its accompanying hydrodynamics of microscale quantum dot droplet. Pioneer efforts are usually confined to two-dimensional flat substrates and inks with mixed solvents/additives. Herein we demonstrate that physically confined space offers an additional parameter in tailoring such processes of droplets and the following quantum-dot self-assembly deposition, without extra modification of quantum dots or solvent chemistry. Owing to the boundary of physically confined space, two three-phase border lines in both the bottom center (horizontal direction) and the barrier of the bank substrate (vertical direction) arise, inducing dual capillary flows and Marangoni backflows. The evaporation, fluid flow, and film-forming process in physically confined space are studied by introducing well-prepared single-solvent quantum dots inks. The systematical analysis offers valuable instructions including ink preparation, surface modification, and postprocessing evaporation technique for inkjet-printed patterning applications, especially for pixelated display, polychrome patterning, and sensor array.