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.

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.

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.

Light-Emitting Memristors for Optoelectronic Artificial Efferent Nerve.

The central nervous system sends a neural impulse through an efferent nerve system toward muscles to drive movement. In an electronically artificial neural system, the electronic neural devices and interconnections prevent achieving highly connected and long-distance artificial impulse transmission and exhibit a narrow bandwidth. Here we design and demonstrate light-emitting memristors (LEMs) for the realization of an optoelectronic artificial efferent nerve, in which the LEM combines the functions of a light receiver, a light emitter, and an optoelectronic synapse in a single device. The optical signal from the pre-LEM (presynaptic membrane) acts as the input signal for the post-LEM (postsynaptic membrane), leading to one-to-many transmission, dynamic adjustable transmission, and light-trained synaptic plasticity, thus removing the physical limitation in artificially electronic neural systems. Furthermore, we construct an optoelectronic artificial efferent nerve with LEMs to control manipulators intelligently. These results promote the construction of an artificial optoelectronic nerve for further development of sensorimotor functionalities.

Activation Entropy as a Key Factor Controlling the Memory Effect in Glasses.

As opposed to the common monotonic relaxation process of glasses, the Kovacs memory effect describes an isothermal annealing experiment, in which the enthalpy and volume of a preannealed glass first increases before finally decreasing toward equilibrium. This interesting behavior has been observed for many materials and is generally explained in terms of heterogeneous dynamics. In this Letter, the memory effect in a model Au-based metallic glass is studied using a high-precision high-rate calorimeter. The activation entropy (S^{*}) during isothermal annealing is determined according to the absolute reaction rate theory. We observe that the memory effect appears only when the second-annealing process has a large S^{*}. These results indicate that a large value of S^{*} is a key requirement for observation of the memory effect and this may provide a useful perspective for understanding the memory effect in both thermal and athermal systems.

Structural reconfiguration and stress relaxation in twisted epitaxial graphene by annealing.

The possibility to engineer the van der Waals interactions between graphene layers is crucial for controlling the electronic properties. Using epitaxial graphene with preferential orientations grown on the C-face 6H-SiC as a prototype, we have addressed the annealed structural reconfiguration of graphene layer in view of the evolutions of surface ripples and relative rotation angle (RRA) between lattices. It was found that the heat treatment of graphene layers under vacuum deformed the arcuate ripple surface and subsequently split one ripple into parallel twin pleats, which drastically increased the strains in the films. The originally oriented graphene layers, with small RRA between adjacent layers, were rearranged by the annealing resulting in disordered orientations and larger RRA. After a sufficient annealing, the compressive stress stored in the films was well released to give undistorted graphene lattices. The vacuum annealing is an effective treatment for irreversibly relaxing the graphene structure.

Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation.

Nuclear modifier gene(s) was proposed to modulate the phenotypic expression of mitochondrial DNA mutation(s). Our previous investigations revealed that a nuclear modifier allele (A10S) in TRMU (methylaminomethyl-2-thiouridylate-methyltransferase) related to tRNA modification interacts with 12S rRNA 1555A→G mutation to cause deafness. The A10S mutation resided at a highly conserved residue of the N-terminal sequence. It was hypothesized that the A10S mutation altered the structure and function of TRMU, thereby causing mitochondrial dysfunction. Using molecular dynamics simulations, we showed that the A10S mutation introduced the Ser10 dynamic electrostatic interaction with the Lys106 residue of helix 4 within the catalytic domain of TRMU. The Western blotting analysis displayed the reduced levels of TRMU in mutant cells carrying the A10S mutation. The thermal shift assay revealed the Tm value of mutant TRMU protein, lower than that of the wild-type counterpart. The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln However, the A10S mutation mildly increased the aminoacylated efficiency of tRNAs. The altered 2-thiouridine modification worsened the impairment of mitochondrial translation associated with the m.1555A→G mutation. The defective translation resulted in the reduced activities of mitochondrial respiration chains. The respiratory deficiency caused the reduction of mitochondrial ATP production and elevated the production of reactive oxidative species. As a result, mutated TRMU worsened mitochondrial dysfunctions associated with m.1555A→G mutation, exceeding the threshold for expressing a deafness phenotype. Our findings provided new insights into the pathophysiology of maternally inherited deafness that was manifested by interaction between mtDNA mutation and nuclear modifier gene.

[Research progress on exosomes in diagnosis and treatment of cardiovascular diseases].

Exosome is a specific subset of vesicles from intracellular origin vesicles containing varies of microRNAs, mRNAs, proteins and lipids. It has been demonstrated that contents of exosomes could be altered due to different physiological and pathological stress, which could be used as clinical biomarker to reveal the disease state. In addition, according to previous studies, exosomes could exert protective roles for cardiovascular diseases such as atherosclerosis, myocardial infarction and ischemia/reperfusion injury, etc. The aim of this review is to summarize current research progress on exosomes, related implications in diagnosis and treatment of cardiovascular diseases and corresponding mechanisms.

All-solution processed semi-transparent perovskite solar cells with silver nanowires electrode.

In this work, we report an all-solution route to produce semi-transparent high efficiency perovskite solar cells (PSCs). Instead of an energy-consuming vacuum process with metal deposition, the top electrode is simply deposited by spray-coating silver nanowires (AgNWs) under room temperature using fabrication conditions and solvents that do not damage or dissolve the underlying PSC. The as-fabricated semi-transparent perovskite solar cell shows a photovoltaic output with dual side illuminations due to the transparency of the AgNWs. With a back cover electrode, the open circuit voltage increases significantly from 1.01 to 1.16 V, yielding high power conversion efficiency from 7.98 to 10.64%.

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.

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.

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.

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.

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.

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%.

Resistive switching memory based on three-dimensionally confined Ag quantum dots embedded in ultra thin polyimide layers.

Resistive switching memory devices based on three-dimensionally confined Ag quantum dots (QDs) embedded in polyimide (PI) layers were fabricated by using spin-coating and thermal evaporation. The Ag QDs embedded in PI layer were distributed uniformly with sizes of approximately 4-6 nm and with surface density of approximately 1.25 x 10(11) cm(-2). The electrical properties of the Ag/PI (10 nm)/Ag QDs/PI (10 nm)/Ag devices were investigated at room temperature. Current-voltage (I-V) measurements on the devices showed a counterclockwise electrical hysteresis behavior with reliable and reproducible resistive switching to the existence of the Ag QDs. The memory device transformed from its original high-resistance state to low-resistance state under positive bias, and regained its original high-resistance state under negative bias. The maximum ON/OFF ratio of the current bistability was 1 x 10(4). The device also revealed excellent endurance ability at ambient conditions. The possible operating mechanisms concerning the interaction between Ag QDs and PI matrix for the resistance-transform phenomenon were analyzed on the basis of the I-V results.

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.

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.

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.

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.