Topological spin texture in the pseudogap phase of a high-Tc superconductor.

An outstanding challenge in condensed-matter-physics research over the past three decades has been to understand the pseudogap (PG) phenomenon of the high-transition-temperature (high-Tc) copper oxides. A variety of experiments have indicated a symmetry-broken state below the characteristic temperature T* (refs. 1-8). Among them, although the optical study5 indicated the mesoscopic domains to be small, all these experiments lack nanometre-scale spatial resolution, and the microscopic order parameter has so far remained elusive. Here we report, to our knowledge, the first direct observation of topological spin texture in an underdoped cuprate, YBa2Cu3O6.5, in the PG state, using Lorentz transmission electron microscopy (LTEM). The spin texture features vortex-like magnetization density in the CuO2 sheets, with a relatively large length scale of about 100 nm. We identify the phase-diagram region in which the topological spin texture exists and demonstrate the ortho-II oxygen order and suitable sample thickness to be crucial for its observation by our technique. We also discuss an intriguing interplay observed among the topological spin texture, PG state, charge order and superconductivity.

[Research on differential quality markers of medicine herbs for Danggui Buxue Decoction before and after processing based on fingerprint and network pharmacology].

The different quality markers of Danggui Buxue Decoction before and after processing were studied based on fingerprint and network pharmacological research, and the seven screened index components were quantitatively analyzed, so as to provide an experimental basis for the quality evaluation of Danggui Buxue Decoction before and after processing. HPLC method was used to establish fingerprints of Danggui Buxue Decoction before and after processing, and a multivariate statistical method was used to analyze the cha-racteristic maps and common peak areas of Danggui Buxue Decoction before and after processing. The different characteristic components before and after processing were screened out, and related targets and pathways of their different components were constructed based on network pharmacology. Their components were quantitatively analyzed. A total of 13 common peaks were identified in the fingerprint of the Danggui Buxue Decoction sample, and seven main chemical components were identified, with similarity > 0.911. Further cluster analysis, principal component analysis, and partial least squares discriminant analysis were used to distinguish raw and processed products. According to VIP value, the main difference components 1, 2, 6, 13, and 5 of Danggui Buxue Decoction before and after processing were screened. By combining the "five principles" of TCM Q-marker and network pharmacology, 5-hydroxymethylfurfural, ferulic acid, calycosin-7-O-ß-D-glucoside, calycosin, ligusticolide, formononetin, and ligusticolide I were selected as the signature components of quality difference before and after processing. The results of the quantitative analysis showed that the content of ligustrin I, calycosin, formononetin, and ligusticum decreased after the Danggui Buxue Decoction was processed. The content of calycosin-7-O-ß-D-glucoside and ferulic acid increased. At the same time, a new chemical compound, namely 5-hydroxymethylfurfural was produced. The established fingerprint analysis method is stable and reliable. Combined with network pharmacology and quantitative research, it screens out the differential Q-marker, which provides an experimental basis for further research on processed products of Danggui Buxue Decoction.

An Ion-Engineering Strategy to Design Hollow FeCo/CoFe2 O4 Microspheres for High-Performance Microwave Absorption.

Although assembled hollow architectures have received considerable attention as lightweight functional materials, their uncontrollable self-aggregation and tedious synthetic methods hinder precise construction and modulation. Therefore, this study proposes a bi-ion synergistic regulation strategy to design assembled hollow-shaped cobalt spinel oxide microspheres. Dominated by the coordination-etching effects of F- and the hydrolysis-complex contributions of NH4 + , the unique construction is formed attributed to the dynamic cycles between metal complexes and precipitates. Meanwhile, their basic structures are perfectly retained after reduction treatment, enabling FeCo/CoFe2 O4 bimagnetic system to be obtained. Subsequently, in-depth analyses are conducted. Investigations reveal that multiscale magnetic coupling networks and enriched air-material heterointerfaces contribute to the remarkable magnetic-dielectric behavior, supported by the advanced off-axis electron holography technique. Consequently, the obtained FeCo/CoFe2 O4 composites exhibit excellent microwave absorption performances with minimal reflection losses (RLmin ) as high as -51.6 dB, an effective absorption bandwidth (EAB) of 4.7 GHz, and a matched thickness of 1.4 mm. Thus, this work provides an informative guide for rationally assembling building blocks into hollow architectures as advanced microwave absorbers through bi-ion and even multi-ion synergistic engineering mechanisms.

Integrated Lipidomics and Network Pharmacology Reveal Mechanism of Memory Impairment Improvement by Yuanzhi San.

Memory impairment (MI) is caused by a variety of causes, endangering human health. Yuanzhi San (YZS) is a common prescription used for the treatment of MI, but its mechanism of action needs further exploration. The purpose of this study was to investigate this mechanism through lipidomics and network pharmacology. Sprague Dawley (SD) rats were divided randomly into the normal, model, and YZS groups. The rats were gavaged with aluminum chloride (200 mg/kg) and intraperitoneally injected with D-galactose (400 mg/kg) every day for 60 days, except for the normal group. From the 30th day, YZS (13.34 g/kg) was gavaged once a day to the rats in the YZS group. Post-YZS treatment, ultra-high-performance liquid chromatography-mass spectrometry (UHPLC/MS) analysis was implemented to conduct a lipidomics study in the hippocampus of rats with memory impairment induced by aluminum chloride and D-galactose. Eight differential metabolites were identified between the normal group and the model group, whereas between the model group and the YZS group, 20 differential metabolites were established. Metabolic pathway analysis was performed on the aforementioned lipid metabolites, all of which were involved in sphingolipid and glycerophospholipid metabolism. Furthermore, serum pharmacochemistry analysis of YZS was carried out at the early stage of our research, which discovered 62 YZS prototype components. The results of the network pharmacology analysis showed that they were related to 1030 genes, and 451 disease genes were related to MI. There were 73 intersections between the YZS and MI targets. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that these targets were closely related to the sphingolipid metabolic, calcium signaling, and other pathways. The integrated approach of lipidomics and network pharmacology was then focused on four major targets, including PHK2, GBA, SPTLC1, and AChE, as well as their essential metabolites (glucosylceramide, N-acylsphingosine, phosphatidylserine, phosphatidylcholine, and phosphatidylcholine) and pathways (sphingolipid, glycerophospholipid, and arachidonic acid metabolism). The significant affinity of the primary target for YZS was confirmed by molecular docking. The obtained results revealed that the combination of lipidomics and network pharmacology could be used to determine the effect of YZS on the MI biological network and metabolic state, and evaluate the drug efficacy of YZS and its related mechanisms of action.

Current-Induced Magnetic Skyrmions with Controllable Polarities in the Helical Phase.

We report the current-induced creation of magnetic skyrmions in a chiral magnet FeGe nanostructure by using in situ Lorentz transmission electron microscopy. We show that magnetic skyrmions with controllable polarity can be transferred from the helical ground state simply by controlling the direction of the current flow at zero magnetic fields. The force analysis and symmetry consideration, backed up by micromagnetic simulations, well explain the experimental results, where magnetic skyrmions are created because of the edge instability of the helical state in the presence of spin-transfer torque. The on-demand generation of skyrmions and control of their polarity by electric current without the need for a magnetic field will enable novel purely electric-controlled skyrmion devices.

[Protective effect of Liujing Toutong Tablets on rats with permanent cerebral ischemia via NF-κB signaling pathway].

This study investigated the neuroprotective effects and underlying mechanism of Liujing Toutong Tablets(LJTT) on a rat model of permanent middle cerebral artery occlusion(pMCAO). The pMCAO model was established using the suture method. Eighty-four male SPF-grade SD rats were randomly divided into a sham operation group, a model group, a nimodipine group(0.020 g·kg~(-1)), and high-, medium-, and low-dose LJTT groups(2.8, 1.4, and 0.7 g·kg~(-1)). The Longa score, adhesive removal test and laser speckle contrast imaging technique were used to evaluate the degree of neurological functional impairment and changes in local cerebral blood flow. The survival and mortality of rats in each group were recorded daily. After seven days of continuous administration following the model induction, the rats in each group were euthanized, and brain tissue and blood samples were collected for corresponding parameter measurements. Nissl staining was used to examine pathological changes in brain tissue neurons. The levels of tumor necrosis factor-alpha(TNF-α), interleukin-6(IL-6), IL-1ß, vascular endothelial growth factor(VEGF), calcitonin gene-related peptide(CGRP), beta-endorphin(ß-EP), and endogenous nitric oxide(NO) in rat serum were measured using specific assay kits. The entropy weight method was used to analyze the weights of various indicators. The protein expression levels of nuclear factor kappa-B(NF-κB), inhibitor kappaB alpha(IκBα), phosphorylated IκBα(p-IκBα), and phosphorylated inhibitor of NF-κB kinase alpha(p-IKKα) in brain tissue were determined using Western blot. Immunohistochemistry was used to detect the protein expression of chemokine-like factor 1(CKLF1) and C-C chemokine receptor 5(CCR5) in rat brain tissue. Compared with the sham operation group, the model group showed significantly higher neurological functional impairment scores, prolonged adhesive removal time, decreased cerebral blood flow, increased neuronal damage, reduced survival rate, significantly increased levels of TNF-α, IL-1ß, IL-6, CGRP, and NO in serum, significantly decreased levels of VEGF and ß-EP, significantly increased expression levels of NF-κB p65, p-IκBα/IκBα, and p-IKKα in rat brain tissue, and significantly upregulated protein expression of CKLF1 and CCR5. Compared with the model group, the high-dose LJTT group significantly improved the neurological functional score of pMCAO rats after oral administration for 7 days. LJTT at all doses significantly reduced adhesive removal time and restored cerebral blood flow. The high-and medium-dose LJTT groups significantly improved neuronal damage. The LJTT groups at all doses showed reduced levels of TNF-α, IL-1ß, IL-6, CGRP, and NO in rat serum, increased VEGF and ß-EP levels, and significantly decreased expression levels of NF-κB p65, p-IκBα/IκBα, p-IKKα, and CCR5 protein in rat brain tissue. The entropy weight analysis revealed that CGRP and ß-EP were significantly affected during the model induction, and LJTT exhibited a strong effect in reducing the release of inflammatory factors such as TNF-α and IL-1ß. LJTT may exert a neuroprotective effect on rats with permanent cerebral ischemia by reducing neuroinflammatory damage, and its mechanism may be related to the inhibition of the NF-κB signaling pathway and the regulation of the CKLF1/CCR5 axis. Additionally, LJTT may exert certain analgesic effects by reducing CGRP and NO levels and increasing ß-EP levels.

Selectively Identifying Exposed-over-Unexposed C-C+ Pairs in Human Telomeric i-Motif Structures with Length-Dependent Polymorphism.

The i-motif structure (iM) has attracted much attention, because of its in vivo bioactivity and wide in vitro applications such as DNA-based switches. Herein, the length-dependent folding of cytosine-rich repeats of the human telomeric 5'-(CCCTAA)n-1CCC-3' (iM-n, where n = 2-8) was fully explored. We found that iM-4, iM-5, and iM-8 mainly form the intramolecular monomer iM structures, while a tetramolecular structure populates only for iM-3. However, iM-6 and iM-7 have the potential to fold as well into the dimeric iM structures besides the monomer ones. The natural hypericin (Hyp) was used as the polymorphism-selective probe to recognize the iM structures. Interestingly, only iM-3, iM-6, and iM-7 can efficiently switch on the Hyp fluorescence by specifically binding with the outmost C-C+ base pairs that are exposed directly to solution. However, other iM structures that fold in a way with a coverage of the outmost C-C+ pairs by loop sequences are totally unavailable for the Hyp binding. Theoretical modeling indicates that adaptive π-π and cation-π interactions contribute to the Hyp recognition toward the exposed C-C+ pairs. This specific iM recognition can be boosted by a photocatalytic DNAzyme construct. Our work provides a reliable fluorescence method to selectively explore the polymorphism of iM structures.

Magnetic Interacted Interaction Effect in MXene Skeleton: Enhanced Thermal-Generation for Electromagnetic Interference Shielding.

With the rapid advancements of portable and wearable equipment, high-efficiency electromagnetic interference (EMI) shielding materials are highly entailed to eliminate radiated electromagnetic pollution. Herein, by assembling hexagonal SrFe12 O19 flakes into a Ti3 C2 Tx MXene/MWCNT substrate, a magnetized Ti3 C2 Tx -based film is successfully fabricated by a facile filtration approach. Carbon nanotubes are used as isolation agents to realize the submicroscopic dispersion of MXene and SrFe12 O19 . The obtained MXene/MWCNTs/SrFe12 O19 film shows a high electrical conductivity of 438 S cm-1 and an excellent EMI shielding effectiveness of 62.9 dB in X-band at a thickness of only 40 µm. Benefiting from a strong magnetic response ability and an expanded magnetic coupling space, hexagonal SrFe12 O19 sheets can efficiently consume incident magnetic field energy by domain wall migration and the ferromagnetic resonance effect. Boosted EMI shielding performance can be achieved by improving the magnetic loss in the Ti3 C2 Tx MXene/MWCNTs/SrFe12 O19 film, preventing the secondary reflection of electromagnetic waves. Meanwhile, magnetized MXene-based films display the freestanding and flexible features and are suitable for installation in electric devices. It is anticipated that this strategy offers new ideas for designing EMI shielding films and in broadening potential utility of MXene-based materials.

A theoretical insight into excited-state decay and proton transfer of p-nitrophenylphenol in the gas phase and methanol solution.

The excited-state decay (ESD) and proton transfer (EPT) of p-nitrophenylphenol (NO2-Bp-OH), especially in the triplet states, were not characterized with high-level theoretical methods to date. Herein, the MS-CASPT2//CASSCF and QM(MS-CASPT2//CASSCF)/MM methods were employed to gain an atomic-level understanding of the ESD and EPT of NO2-Bp-OH in the gas phase and its hydrogen-bonded complex in methanol. Our calculation results revealed that the S1 and S2 states of NO2-Bp-OH are of 1ππ* and 1nπ* characters at the Franck-Condon (FC) point, which correspond to the ICT-EPT and intramolecular charge-transfer (ICT) states in spectroscopic experiments. The former state has a charge-transfer property that could facilitate the EPT reaction, while the latter one might be unfavorable for EPT. The vertical excitation energies of these states are almost degenerate at the FC region and the electronic configurations of 1ππ* and 1nπ* will exchange from the S1 FC region to the S1 minimum, which means that the 1nπ* state will participate in ESD once NO2-Bp-OH departs from the S1 FC region. Besides, we found that three triplets lie below the first bright state and will play very important roles in intersystem crossing processes. In terms of several pivotal surface crossings and relevant linearly interpolated internal coordinate (LIIC) paths, three feasible but competing ESD channels that could effectively lead the system to the ground state or the lowest triplet state were put forward. Once arrived at the T1 state, the system has enough time and internal energy to undergo the EPT reaction. The methanol solvent has a certain effect on the relative energies and spin-orbit couplings, but does not qualitatively change the ESD processes of NO2-Bp-OH. By contrast, the solvent effects will remarkably stabilize the proton-transferred product by the hydrogen bond networks and assist to form the triplet anion. Our present work would pave the road to properly understand the mechanistic photochemistry of similar hydroxyaromatic compounds.

Generalized Ab Initio Nonadiabatic Dynamics Simulation Methods from Molecular to Extended Systems.

Nonadiabatic dynamics simulation has become a powerful tool to describe nonadiabatic effects involved in photophysical processes and photochemical reactions. In the past decade, our group has developed generalized trajectory-based ab initio surface-hopping (GTSH) dynamics simulation methods, which can be used to describe a series of nonadiabatic processes, such as internal conversion, intersystem crossing, excitation energy transfer and charge transfer of molecular systems, and photoinduced nonadiabatic carrier dynamics of extended systems with and without spin-orbit couplings. In this contribution, we will first give a brief introduction to our recently developed methods and related numerical implementations at different computational levels. Later, we will present some of our latest applications in realistic systems, which cover organic molecules, biological proteins, organometallic compounds, periodic organic and inorganic materials, etc. Final discussion is given to challenges and outlooks of ab initio nonadiabatic dynamics simulations.

Effect of Strong Intermolecular Interaction in 2D Inorganic Molecular Crystals.

Strong intermolecular interactions in 2D organic molecular crystals arising from π-π stacking have been widely explored to achieve high thermal stability, high carrier mobility, and novel physical properties, which have already produced phenomenal progress. However, strong intermolecular interactions in 2D inorganic molecular crystals (2DIMCs) have rarely been investigated, severely limiting both the fundamental research in molecular physics and the potential applications of 2DIMCs for optoelectronics. Here, the effect of strong intermolecular interactions induced by unique short intermolecular Se-Se and P-Se contacts in 2D α-P4Se3 nanoflakes is reported. On the basis of theoretical calculations of the charge density distribution and an analysis of the thermal expansion and plastic-crystal transition, the physical picture of strong intermolecular interactions can be elucidated as a higher charge density between adjacent P4Se3 molecules, arising from an orderly and close packing of P4Se3 molecules. More importantly, encouraged by the strong intermolecular coupling, the in-plane mobility of α-P4Se3 nanoflakes is first calculated with a quantum nuclear tunneling model, and a competitive hole mobility of 0.4 cm2 V-1 s-1 is obtained. Our work sheds new light on the intermolecular interactions in 2D inorganic molecular crystals and is highly significant for promoting the development of molecular physics and optoelectronics.

Yolk-Shell Nano ZnO@Co-Doped NiO with Efficient Polarization Adsorption and Catalysis Performance for Superior Lithium-Sulfur Batteries.

Achieving strong adsorption and catalytic ability toward polar lithium polysulfide species (LiPSs) of the sulfur host in lithium-sulfur (Li-S) batteries is essential for their electrochemical cyclic stability. Herein, a strategy of "self-termination of ion exchange" is put forward to synthesize the novel yolk-shell sulfur host composed of ZnO nanoparticles confined in Co-doped NiO (CDN) polyhedron (ZCCDN). After sulfur infiltration, the obtained S/ZCCDN cathode achieves excellent performance of 738.56 mAh g-1 after 500 cycles at 0.5 C with a very low capacity decay rate of only 0.048% per cycle. Even at 1 C, 501.05 mAh g-1 could be retained after 500 cycles, suggesting a capacity decay ratio of only 0.076% per cycle. The good cycle performance is attributed to the improved LiPSs' conversion kinetics, which originates from ZCCDN's sturdy chemical affinity and strong catalytic ability to polar LiPSs. For the first time, by electron holography, the local interfacial polarization electric field is clarified to be existed in the material which is conducive to the capture of LiPSs and the migration of electrons and Li+ from the mesopores. This work provides a rational way for the use of zeolitic imidazolate frameworks (ZIFs) and development of cathode materials for Li-S batteries.

A Polarization Boosted Strategy for the Modification of Transition Metal Dichalcogenides as Electrocatalysts for Water-Splitting.

The design and fabrication of transition metal dichalcogenides (TMDs) are of paramount significance for water-splitting process. However, the limited active sites and restricted conductivity prevent their further application. Herein, a polarization boosted strategy is put forward for the modification of TMDs to promote the absorption of the intermediates, leading to the improved catalytic performance. By the forced assembly of TMDs (WS2 as the example) and carbon nanotubes (CNTs) via spray-drying method, such frameworks can remarkably achieve low overpotentials and superior durability in alkaline media, which is superior to most of the TMDs-based catalysts. The two-electrode cell for water-splitting also exhibits perfect activity and stability. The enhanced catalytic performance of WS2 /CNTs composite is mainly owing to the strong polarized coupling between CNTs and WS2 nanosheets, which significantly promotes the charge redistribution on the interface of CNTs and WS2 . Density functional theory (DFT) calculations show that the CNTs enrich the electron content of WS2 , which favors electron transportation and accelerates the catalysis. Moreover, the size of WS2 is restricted caused by the confinement of CNTs, leading to the increased numbers of active sites, further improving the catalysis. This work opens a feasible route to achieve the optimized assembling of TMDs and CNTs for efficient water-splitting process.

Facile synthesis of AgNPs@SNCDs nanocomposites as a fluorescent 'turn on' sensor for detection of glutathione.

The present study illustrates the facile synthesis of silver nanoparticles capped with sulfur and nitrogen co-doped carbon dots (AgNPs@SNCDs) nanocomposites and their application towards the sensitive and selective detection of glutathione (GSH) using a spectrofluorimetry method. SNCDs were synthesized using solvothermal treatment of cysteamine hydrochloride and p-phenylenediamine. The as-fabricated SNCDs were then utilized as capping and stabilizing agents for the preparation of AgNPs@SNCDs nanocomposites using wet chemistry. The size of AgNPs@SNCDs nanocomposites was characterized to be ~37.58 nm or even larger aggregates. Particularly, the quenched fluorescence of AgNPs@SNCDs nanocomposites could be significantly restored upon addition of GSH, and the colour of its solution changed to some extent. The fluorescence intensity ratio of AgNPs@SNCDs nanocomposites at ~450 nm and 550 nm was directly proportional to the GSH concentration within the ranges 8.35-66.83 µM and 66.83-200.5 µM, and the detection limit was 0.52 µM. Furthermore various common organic molecules had no obvious interference in the detection mode. The proposed nanosensor was successfully applied for GSH assay in actual water samples.

[Roles of processing and compatibility in antidepression of Sini Powder:a metabonomics study].

The antidepressant mechanism of Sini Powder was investigated by metabonomics based on UHPLC-Q-TOF-MS, and the roles of processing and compatibility in the antidepression of Sini Powder were discussed in the present study. The chronic unpredictable mild stress(CUMS) model of depression was induced in the model group, the Bupleuri Radix group, the Paeoniae Radix Alba group, the herb-pair group(Bupleuri Radix-Paeoniae Radix Alba), the Sini Powder group, and the vinegar-processed Sini Powder group(Bupleuri Radix and Paeoniae Radix Alba were vinegar-processed). After the establishment of the model, the rats in each group were continuously administered with corresponding drugs(ig) at a dose of 9.6 g·kg~(-1) for eight days [the rats in the model group and the normal group(without model induction) received the same volume of normal saline at the same time]. Following the last administration, the differential metabolites were identified to analyze metabolic pathways based on the rat plasma samples collected from each group. A total of sixteen potential biomarkers were identified. The metabolites with significant changes were involved in many biological metabolic pathways, such as amino acid metabolism, pentose phosphate pathway, glycerol phospholipid metabolism, sphingolipid metabolism, and purine metabolism. After drug intervention, some biomarkers returned to normal levels. Further comparisons of processing and compatibility revealed that the vinegar-processed Sini Powder group had the most total metabolic pathways where differential metabolites were returned to normal. Compared with the individual herbs, the herb-pair significantly improved the recovery of differential metabolites in the pentose phosphate and purine metabolic pathways. Compared with the Sini Powder, the vinegar-processed Sini Powder facilitated the recovery of differential metabolites in the arginine biosynthesis, and pyrimidine and pentose phosphate metabolic pathways. As indicated by the results, Sini Powder may interfere with depression by regulating lipid and nucleotide metabolisms. The processing and compatibility of Chinese herbal medicines can potentiate the intervention on depression by regulating nucleotide, energy, and amino acid metabolisms to a certain extent.

Multidimension-Controllable Synthesis of MOF-Derived Co@N-Doped Carbon Composite with Magnetic-Dielectric Synergy toward Strong Microwave Absorption.

Metal-organic framework (MOF) is highly desirable as a functional material owing to its low density, tunable pore size, and diversity of coordination formation, but limited by the poor dielectric properties. Herein, by controlling the solvent and mole ratio of cobalt/linker, multidimension-controllable MOF-derived nitrogen-doped carbon materials exhibit tunable morphology from sheet-, flower-, cube-, dodecahedron- to octahedron-like. Tunable electromagnetic parameters of Co@N-doped carbon composites (Co@NC) can be obtained and the initial MOF precursor determines the distribution of carbon framework and magnetic cobalt nanoparticles. Carbonized Co@NC composites possess the following advantages: i) controllable dimension and morphology to balance the electromagnetic properties with evenly charged density distribution; ii) magnetic-carbon composites offer plenty of interfacial polarization and strong magnetic coupling network; iii) a MOF-derived dielectric carbon skeleton provides electronic transportation paths and enhances conductive dissipation. Surface-mediated magnetic coupling reflects the stray magnetic flux field, which is corroborated by the off-axis electron holography and micro-magnetic simulation. Optimized octadecahedral Co@NC sample exhibits the best microwave absorption (MA) of -53.0 dB at the thickness of 1.8 mm and broad effective frequency from 11.4 to 17.6 GHz (Ku-band). These results pave the way to fabricate high-performance MA materials with balanced electromagnetic distribution and controlled morphology.

Suppression of Persistent Photoconductivity of Rubrene Crystals using Gate-Tunable Rubrene/Bi2 Se3 Diodes with Photoinduced Negative Differential Resistance.

Organic single-crystalline semiconductors show great potential in high-performance photodetectors. However, they suffer from persistent photoconductivity (PPC) due to the charge trapping, which has severely hindered high-speed imaging applications. Here, a universal strategy of solving the PPC by integrating with topological insulator Bi2 Se3 is provided. The rubrene/Bi2 Se3 heterojunctions are selected as an example for general demonstration due to the reproducibly high mobility and broad optoelectronic applications of rubrene crystals. By virtue of high carrier concentration on Bi2 Se3 surface and the strong built-in electrical field, the photoresponse of the heterotransistor is significantly reduced for more than two orders (from over 10 s to 54 ms), meanwhile the photoresponsivity can reach 124 A W-1 . To the best of knowledge, this operating speed is among the fastest responses in organic-inorganic heterojunctions. The heterotransistor also shows unique negative differential resistance under positive gate bias, which can be explained by photoinduced de-trapping of electron trap states in the bulk rubrene crystals. Besides, the rubrene/Bi2 Se3 heterojunction behaves as a gate-tunable backward-like diode due to the inhomogenous carrier distribution in the thick rubrene crystal and inversion of relative Fermi level positions. The findings demonstrate versatile functionalities of the rubrene/Bi2 Se3 heterojunctions for various emerging optoelectronic applications.

Atomically Thin Oxyhalide Solar-Blind Photodetectors.

2D wide-bandgap semiconductors demonstrate great potential in fabricating solar-blind ultraviolet (SBUV) photodetectors. However, the low responsivity of 2D solar-blind photodetectors still limits their practical applications. Here, high-responsivity solar-blind photodetectors are achieved based on 2D bismuth oxychloride (BiOCl) flakes. The 2D BiOCl photodetectors exhibit a responsivity up to 35.7 A W-1 and a specific detectivity of 2.2 × 1010 Jones under 250 nm illumination with 17.8 µW cm-2 power density. In particular, the enhanced photodetective performances are demonstrated in BiOCl photodetectors with increasing ambient temperature. Surprisingly, their responsivity can reach 2060 A W-1 at 450 K under solar-blind light illumination, maybe owing to the formation of defective BiOCl grains evidenced by in situ transmission electron microscopy. The high responsivity throughout the solar-blind range indicates that 2D BiOCl is a promising candidate for SBUV detection.

Understanding molecular surface doping of large bandgap organic semiconductors and overcoming the contact/access resistance in organic field-effect transistors.

The contact resistance (Rc) and the effective carrier mobility (µeff) are considered as the important indicators of the performance of organic field-effect transistors (OFETs). Conventionally, the contact resistance is regarded as the interface effect between the metal electrodes and the organic semiconductors, while the carrier mobility is correlated to the crystallinity and π-π stacking of the organic molecules. In the staggered OFETs, Rc is actually closely correlated to µeff through the channel sheet resistance. Besides, the accuracy of the carrier mobility directly extracted from the non-ideal transfer curves with significant contact effect is always questionable. Herein, a diffusion-lead surface doping approach is employed to improve the contact resistance and mobility issues simultaneously. By suppressing the trap states in the sublimated 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic semiconductor with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), we observed a 3-fold increase in the carrier mobility from 0.5 to 1.6 cm2 V-1 s-1, and the Rc also drops remarkably from 25.7 kΩ cm to 5.2 kΩ cm. Moreover, the threshold voltage (VTH), subthreshold swing (SS) and the bias stability of the OFETs are also significantly improved. Based on the detailed characterization of the C8-BTBT film upon surface doping, including X-ray diffraction (XRD) for the film crystallinity, Kelvin probe force microscopy (KPFM) for the surface potential, trap state investigation by density of states (DOS) measurement and electrical circuit modeling for partial doping analysis, we confirmed that the spontaneous charge transfer process due to the diffusion of the F4-TCNQ dopants in the C8-BTBT matrix can lead to an effective trap filling. This technique and findings can be potentially developed into a general approach for the improvement of different performance parameters of OFETs.

Cell-Membrane-Anchored DNA Nanoplatform for Programming Cellular Interactions.

Cell-cell interactions are mediated through compositions expressed on the membrane. Engineering the cell surface to display functional modules with high biocompatibility, high controllability, and high stability would offer great opportunities for studying and manipulating these intercellular reactions. However, it remains a technical challenge because of the complex and dynamic nature of the cell membrane. Herein, by using three-dimensional (3D) amphiphilic pyramidal DNA as the scaffold, we develop a biocompatible, effective, and versatile strategy for engineering the cell surface with DNA probes. Compared with linear DNA constructs, these pyramidal probes show higher (nearly 100-fold) membrane-anchoring stability and higher (about 2.5-fold) target accessibility. They enable specific, effective, and tunable connections between cells. Meanwhile, our results indicate that connecting cells in close proximity are critical to initiate intercellular communication. By combining high programmability and high diversity of DNA probes, this strategy is expected to provide a powerful and designable membrane-anchored nanoplatform for studying multicellular communication networks.