Giant tunnel resistance effect in (SrTiO3)2/(BaTiO3)4/(CaTiO3)2 asymmetric superlattice with enhanced polarization.

In this work, we report the effectively enhanced tunneling electroresistance effect in Au/(SrTiO3)2/(BaTiO3)4/(CaTiO3)2/Nb:SrTiO3 superlattice ferroelectric tunnel junction (FTJ). The stable polarization switching and enhanced ferroelectricity were achieved in the nanoscale thickness high-quality epitaxial superlattice. A high ON/OFF current ratio of more than 105 was obtained at room temperature, which is an order of magnitude larger than the BaTiO3 FTJ with the same structure. Nonvolatile resistance switching controlled by nonvolatile polarization switching was observed in the superlattice FTJ. Driven by increased polarization and intrinsic asymmetric ferroelectricity, a highly asymmetric depolarization field is generated compared with the Au/BaTiO3/Nb:SrTiO3 FTJ, resulting in an enhanced tunneling electroresistance effect. These results provide a potential way to construct FTJ memory devices by constructing asymmetric three-component ferroelectric superlattices.

Enhanced photoluminescence of double perovskite Cs2SnI6 nanocrystals via Na+ doping.

Double perovskites without lead element have attracted great attention in recent years. Further increasing the photoluminescence quantum yield of lead-free double perovskites is necessary for their potential applications. In this work, Na+ doped Cs2SnI6 nanocrystals were synthesized by hot injection method. It was displayed that all the NCs have uniform hexagonal shape with good crystallization. Energy dispersing spectroscopy and X-ray photoelectron spectroscopy proves the Na+ ions were doped in the lattice of perovskite structure. The photoluminescence intensity of doped NCs is increased by 2.7-fold than that of pure NCs. A maximum photoluminescence quantum yield of 72% is obtained. The luminous mechanism was investigated by femtosecond transient absorption spectrum and a self-trap emission was proved by the observation of ground state bleaching and photo-induced absorption signals.

W-doped VO2 for high-performance aqueous Zn-ion batteries.

Aqueous Zn-ion batteries (AZIBs) have become one of the most promising energy storage devices due to their high safety and low cost. However, the development of stable cathodes with fast kinetics and high energy density is the key to achieving large-scale application of AZIBs. In this work, W-doped VO2 (W-VO2) is developed by a one-step hydrothermal method. Benefiting from the pre-insertion of W6+ and the introduction of the W-O bond, accomplishing an expanded lattice spacing and a stable structure, both improved kinetics and long cycle life are achieved. The W-VO2 delivers a specific capacity of 340.2 mA h g-1 at 0.2 A g-1, an excellent high-rate capability with a discharge capacity of 186.9 mA h g-1 at 10 A g-1, and long-term cycling stability with a capacity retention of 76.5% after 2000 cycles. The electrochemical performance of the W-VO2 has been greatly improved, compared with the pure VO2. The W doping strategy proposed here also presents an encouraging pathway for developing other high-energy and stable cathodes.

Asymmetric liquid crystalline dibenzo[a,h]anthracenes for organic semiconductors with high mobility and thermal stability.

A series of asymmetric organic semiconductors based on N-shaped dibenzo[a,h]anthracene (DBA), Ph-DBA-Cn (n = 8, 10, 12), were developed. All Ph-DBA-Cn compounds had good chemical stability and smectic LC qualities, and thermally stable crystal phase can be maintained under 190 °C due to the suppressed molecular motions by the bent DBA core. High-quality crystalline films can be fabricated using a blade-coating technique. It was revealed that the average mobility of all Ph-DBA-Cn organic thin-film transistors (OTFTs) was estimated to be over 2.8 cm2 V-1 s-1, and a Ph-DBA-C8 device in particular afforded exceptional mobility of up to 11.8 cm2 V-1 s-1. The highly-ordered and uniaxially-oriented crystalline films composed of bilayer units were revealed to be responsible for their excellent electrical device performances. Furthermore, all Ph-DBA-Cn OTFTs can retain operational characteristics up to 160 °C over 1 cm2 V-1 s-1. These findings will be crucial for the development of high-mobility and thermally durable OSCs for practical electronics.

New Approach to Low-Power-Consumption, High-Performance Photodetectors Enabled by Nanowire Source-Gated Transistors.

Power consumption makes next-generation large-scale photodetection challenging. In this work, the source-gated transistor (SGT) is adopted first as a photodetector, demonstrating the expected low power consumption and high photodetection performance. The SGT is constructed by the functional sulfur-rich shelled GeS nanowire (NW) and low-function metal, displaying a low saturated voltage of 0.61 V ± 0.29 V and an extremely low power consumption of 7.06 pW. When the as-constructed NW SGT is used as a photodetector, the maximum value of the power consumption is as low as 11.96 nW, which is far below that of the reported phototransistors working in the saturated region. Furthermore, benefiting from the adopted SGT device, the photodetector shows a high photovoltage of 6.6 × 10-1 V, a responsivity of 7.86 × 1012 V W-1, and a detectivity of 5.87 × 1013 Jones. Obviously, the low power consumption and excellent responsivity and detectivity enabled by NW SGT promise a new approach to next-generation, high-performance photodetection technology.

Enhanced upconversion red light emission of TiO2:Yb,Er thin film via Mn doping.

TiO2:Yb,Er films with different concentrations of Mn2+ are grown on SiO2 glass substrates by pulsed laser deposition. It is found that the introduction of Mn2+ enhanced the intensity of upconversion emission. In particular, TiO2:Yb,Er thin film with 5% Mn2+ ions exhibits the brightest upconversion emission. The upconversion red emission intensity is increased by 2.5-fold than that of a TiO2:Yb,Er thin film without Mn2+ ions, which is ascribed to the multi-photon absorption and efficient exchange-energy transfer process between Er3+ and Mn2+. The high transmittance and good conductivity of the films made them possible to act as electron transport layer in solar cells.

Enhanced photoluminescence of CsPbBr3-xIx nanocrystals via plasmonic Au nanoarrays.

Large scale ordered Au nanoarrays are fabricated by nanosphere lithography technique. The photoluminescence improvement of CsPbBr3-xIx nanocrystals by more than three times is realized in the CsPbBr3-xIx nanocrystal/Au nanoarray/Si structure. Time-resolved photoluminescence decay curves indicate that the lifetime is decreased by introducing the Au nanoarrays, which results in a increasing radiation recombination rate. The reflection spectra with two major valleys (the dip in the curve) located at ∼325 nm and 545 nm of Au nanoarray/Si structure, which illustrates two plasmonic resonance absorption peaks of the Au nanoarrays. The enhancement of photoluminescence is ascribed to a well match between the excitation/emission of CsPbBr3-xIx nanocrystals and localized surface plasmon/gap plasmon resonance absorption of the ordered Au nanoarrays, as also revealed from the finite-difference time-domain simulation analysis. Our work offers an effective strategy to improve the fluorescence of perovskite nanocrystals and provide the potential for further applications.

Enhancing the bulk photovoltaic effect by tuning domain walls in epitaxial BiFeO3films.

In this letter, the role of domain wall (DW) on bulk photovoltaic effect (BPV) effect in BiFeO3(BFO) films was studied by x-ray reciprocal space mapping and conductive atomic force microscope. It was found that the domain structure and DW can be tuned by controlling the epitaxial orientation of BFO film. Remarkably, under 1 sun AM 1.5 G illumination, the 109° DW enhances the transport of photogenerated carriers and simultaneously improves the conductivity and power conversion efficiency (PCE). The short-circuit current density and PCE can reach 171.15µA cm-2and 0.1127%, respectively. Therefore, our study reveals the correlation between the DW and the BPV effect in BFO film and provides a new pathway to improve the PCE of BFO-based photovoltaic device.

Ultrastable Laurionite Spontaneously Encapsulates Reduced-dimensional Lead Halide Perovskites.

Reduced dimensional lead halide perovskites (RDPs) have attracted great research interest in diverse optical and optoelectronic fields. However, their poor stability is one of the most challenging obstacles prohibiting them from practical applications. Here, we reveal that ultrastable laurionite-type Pb(OH)Br can spontaneously encapsulate the RDPs in their formation solution without introducing any additional chemicals, forming RDP@Pb(OH)Br core-shell microparticles. Interestingly, the number of the perovskite layers within the RDPs can be conveniently and precisely controlled by varying the amount of CsBr introduced into the reaction solution. A single RDP@Pb(OH)Br core-shell microparticle composed of RDP nanocrystals with different numbers of perovskite layers can be also prepared, showing different colors under different light excitations. More interestingly, barcoded RDP@Pb(OH)Br microparticles with different parts emitting different lights can also be prepared. The morphology of the emitting microstructures can be conveniently manipulated. The RDP@Pb(OH)Br microparticles demonstrate outstanding environmental, chemical, thermal, and optical stability, as well as strong resistance to anion exchange processes. This study not only deepens our understanding of the reaction processes in the extensively used saturation recrystallization method but also points out that it is highly possible to dramatically improve the performance of the optoelectronic devices through manipulating the spontaneous formation process of Pb(OH)Br.

Doping Nitrogen into Q-Graphene by Plasma Treatment toward Peroxidase Mimics with Enhanced Catalysis.

A facile and efficient plasma treatment strategy has been applied for the first time to dope heteroatom nitrogen (N) into Q-graphene (QG) under ambient temperature toward a carbon-based green nanozyme. It was discovered that the resulting N doped QG (N-QG) nanozyme can present the greatly enhanced catalysis activity, which is nearly 5-fold higher than that of pristine QG, as comparably revealed by the kinetic studies. Herein, the plasma treatment-assisted N doping could improve the conductivity (hydrophilicity) and create the surface defects of QG so as to promote the electron transferring toward the enhanced catalytic activities of N-QG. Furthermore, the catalase, superoxide dismutase, and oxidase-like catalysis activities of N-QG were explored, indicating the N doping could endow the obtained nanozyme with a high specificity of peroxidase-like catalysis. The application feasibility of the developed N-QG nanozyme was demonstrated subsequently by the catalysis-based colorimetric assays for H2O2 in milk samples, with the linear range from 2.00 to 1500 µM. Importantly, such a plasma-assisted heteroatom doping route may open a door toward the large-scale applications for the rational designs of various enzyme mimics with improved catalysis performances.

Efficient Laser-Induced Construction of Oxygen-Vacancy Abundant Nano-ZnCo2 O4 /Porous Reduced Graphene Oxide Hybrids toward Exceptional Capacitive Lithium Storage.

Recently, binary ZnCo2 O4 has drawn enormous attention for lithium-ion batteries (LIBs) as attractive anode owing to its large theoretical capacity and good environmental benignity. However, the modest electrical conductivity and serious volumetric effect/particle agglomeration over cycling hinder its extensive applications. To address the concerns, herein, a rapid laser-irradiation methodology is firstly devised toward efficient synthesis of oxygen-vacancy abundant nano-ZnCo2 O4 /porous reduced graphene oxide (rGO) hybrids as anodes for LIBs. The synergistic contributions from nano-dimensional ZnCo2 O4 with rich oxygen vacancies and flexible rGO guarantee abundant active sites, fast electron/ion transport, and robust structural stability, and inhibit the agglomeration of nanoscale ZnCo2 O4 , favoring for superb electrochemical lithium-storage performance. More encouragingly, the optimal L-ZCO@rGO-30 anode exhibits a large reversible capacity of ≈1053 mAh g-1 at 0.05 A g-1 , excellent cycling stability (≈746 mAh g-1 at 1.0 A g-1 after 250 cycles), and preeminent rate capability (≈686 mAh g-1 at 3.2 A g-1 ). Further kinetic analysis corroborates that the capacitive-controlled process dominates the involved electrochemical reactions of hybrid anodes. More significantly, this rational design holds the promise of being extended for smart fabrication of other oxygen-vacancy abundant metal oxide/porous rGO hybrids toward advanced LIBs and beyond.

Study on organic-inorganic hybrid perovskite nanocrystals with regular morphologies and their effect on photoluminescence properties.

Organic-inorganic hybrid perovskite nanocrystals have been widely studied for their excellent photoelectric properties. However, the irregular morphologies of organic-inorganic hybrid perovskite nanocrystals have limited application in the field of lighting and display. From this, the regular morphologies of nanospheres, nanorods, nanoplatelets and MAPbBr3 (MA = CH3NH3 +) nanocrystals have been synthesized by regulating the type and proportion of auxiliary ligands. The phase evolution, morphology and fluorescent properties were systematically studied by the various instruments of XRD, TEM, PL/UV-vis spectroscopy and fluorescence decay analysis. With the morphologies changing from nanospheres to nanoplatelets, the emission peaks of MAPbBr3 nanocrystals red-shifted, and the lifetimes have increased gradually. The underlying mechanisms were thoroughly investigated and elucidated. On this basis, the role of acid and amine in the synthesis of MAPbBr3 nanocrystals was systematically studied by regulating the ratio of oleic acid and N-octylamine. The fluorescence kinetics of MAPbBr3 nanocrystals were studied by femtosecond transient absorption spectroscopy, and the charge carrier relaxation mechanism was clarified. Furthermore, the effect of temperature on the fluorescence properties of the nanocrystal was investigated in detail. Organic-inorganic hybrid perovskite nanocrystals with morphologies-controlled and excellent fluorescence properties are expected to be widely used in lighting and display fields.

Colorimetric determination of the activity of alkaline phosphatase by exploiting the oxidase-like activity of palladium cube@CeO2 core-shell nanoparticles.

Core-shell palladium cube@CeO2 (Pd cube@CeO2) nanoparticles are shown to display oxidase-like activity. This is exploited in a method for determination of the activity of alkaline phosphatase (ALP). The Pd cube@CeO2 nanoparticles were thermally synthesized from Ce(NO3)3, L-arginine and preformed Pd cube seeds in water. The Pd cube@CeO2 nanoparticles catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by oxygen. This results in the formation of oxidized TMB (oxTMB) with an absorption peak at 652 nm. Ascorbic acid (AA) is generated from the hydrolysis of L-ascorbic acid 2-phosphate (AAP) catalyzed by ALP. It can reduce oxTMB to TMB, and this results in a decrease of the absorbance. The method allows for quantitative determination of the activity of ALP in the range from 0.1 to 4.0 U·L-1 and with a detection limit down to 0.07 U·L-1. Endowed with high sensitivity and selectivity, the assay can quantify ALP activity in biological system with satisfactory results. Graphical abstractSchematic illustration of Pd cube@CeO2 core-shell nanoparticles for colorimetric determination of alkaline phosphatase.

Fe3O4 Nanozymes with Aptamer-Tuned Catalysis for Selective Colorimetric Analysis of ATP in Blood.

In this work, a simple and highly selective colorimetric method has been developed for quantifying trace-level ATP using Fe3O4 nanoparticles (Fe3O4 NPs). It was discovered that Fe3O4 NPs could present the dramatically enhanced catalysis once anchored with ATP-specific aptamers (Apts), which is about 6-fold larger than that of bare Fe3O4 NPs. In the presence of ATP, however, the Apts would be desorbed from Fe3O4 NPs due to the Apts-target binding event, leading to the decrease of catalysis rationally depending on ATP concentrations. A colorimetric strategy was thereby developed to facilitate the highly selective detection of ATP, showing the linear concentrations ranging from 0.50 to 100 µM. Subsequently, the developed ATP sensor was employed for the evaluation of ATP in blood with the analysis performances comparably better than those of the documented detection methods, showing the potential applications in the clinical laboratory for the detective diagnosis of some ATP-indicative diseases. Importantly, such a catalysis-based detection strategy should be extended to other kinds of nanozymes with intrinsic catalysis properties (i.e., peroxidase and oxidase-like activities), promising as a universal candidate for monitoring various biological species simply by using target-specific recognition elements like Apts and antibodies.

Laser irradiation-induced laminated graphene/MoS2 composites with synergistically improved tribological properties.

Engineering lubricant additives that have extraordinary friction reduction and anti-wear performance is critical to almost any modern mechanical machines. Here, we demonstrate the fabrication of laminated lubricant additives that can combine the advantages of zero-dimensional nanospheres and two-dimensional nanosheets. A simple in situ laser irradiation method is developed to prepare the laminated composite structure composed of ideally ultrasmooth MoS2 sub-microspheres embedded within multiple layers of graphene. These ultrasmooth MoS2 spheres within the laminated structure can change sliding friction into rolling friction under strong shear force created by moving contact surfaces to significantly reduce the friction. Meantime, the graphene layers can behave as 'protection pads' to efficiently avoid the formation of scars on the metal-to-metal contact surfaces. Overall, the laminated composites as lubricant additives synergistically improve the friction reduction and anti-wear properties. Additionally, due to the unique loosely packed laminated structure, the composites can stably disperse in the lubricant for more than 15 d and work under high temperatures without being oxidized. Such constructed laminated composites with outstanding tribological properties by an in situ laser irradiation method supply a new concept in designing lubricant additives that can combine the advantages of 0D and 2D structures.

Reversible Band Gap Narrowing of Sn-Based Hybrid Perovskite Single Crystal with Excellent Phase Stability.

An intriguing reversible band gap narrowing behavior of the lead-free hybrid perovskite single crystal DMASnI3 (DMA=CH3 NH2 CH3 + ) from yellow to black is observed without phase transformation. We discuss the transformation mechanism in detail. More interestingly, the transformed samples in black can rapidly self-heal into yellow ones when exposed to deionized water (DI water). Contrary to other hybrid perovskites, DMASnI3 crystals exhibit excellent water phase stability. For example, DMASnI3 was immersed in DI water for 16 h and no decomposition was observed. Inspired by its excellent water phase stability, we demonstrate a potential eco-friendly application of DMASnI3 in photo-catalysis for H2 evolution in DI water. We present the first H2 evolution rate of 0.64 µmol h-1 with good recycling properties for pure DMASnI3 crystals. After the narrowing process, the optical band gap of DMASnI3 can be lowered from 2.48 eV to 1.32 eV. Systematical characterizations are applied to investigate their structures and optoelectronic properties. The reversible band gap narrowing behavior and outstanding electrical properties, such as higher carrier mobility and long carrier lifetime show that DMASnI3 has a great potential for optoelectronic applications.

Simultaneous Defect Passivation and Electric Level Regulation with Rubidium Fluoride for High-Efficiency CsPbI2Br Perovskite Solar Cells.

Due to the good balance of efficiency and stability, CsPbI2Br perovskite solar cells (PSCs) recently have attracted widespread attention. However, the improvement in photovoltaic performance for CsPbI2Br PSCs was mainly limited by massive defects and unmatched energy levels. Surface modification is the most convenient and effective strategy to decrease defect densities of perovskite films. Herein, we deposited rubidium fluoride (RbF) onto the surface of CsPbI2Br perovskite films by spin-coating. The numerous defects could be significantly passivated by RbF, resulting in suppressed nonradiative recombination. Furthermore, the CsPbI2Br perovskite film after RbF treatment exhibits a deeper Fermi level, and an additional built-in electric field forms to promote charge transport. Consequently, the champion device achieves a high efficiency of 10.82% with an improved VOC of 1.14 V, and it also exhibits excellent stability after long-term storage. This work offers a simple and effective approach to enhance the photovoltaic performance and stability of PSCs for broader applications in the future.

Novel Strategy for High Efficient and Stable Perovskite Solar Cells through Atomic Layer Deposition.

The perovskite material has demonstrated conceivable potential as an absorbing material of solar cells. Although the power conversion efficiency of the device based on perovskite has rapidly come to 26%, there are still many factors that affect the further improvement of the photoelectric conversion efficiency. Interface defects are the dominating concern that influence carrier transportation and stability. Here, we report a novel strategy where B2O3 is deposited on the fresh perovskite film by atomic layer deposition technology. The organic atmosphere during atomic layer deposition can effectively regulate the crystallization kinetics of perovskites and promote crystal growth. The B2O3 adsorbed on the perovskite light-absorption layer can effectively reduce the electropositive defects on the surface of the perovskite, such as uncoordinated Pb2+ and I vacancies due to the electron-donating properties of the side O atoms in B2O3. Consequently, the power conversion efficiency of the perovskite solar cell after B2O3 treatment increases to 21.78% from 18.89%. Simultaneously, B2O3 can improve the stability of devices.

Large-Scale Fabrication of Three-Dimensional Surface Patterns Using Template-Defined Electrochemical Deposition.

A new strategy to achieve large-scale, three-dimensional (3D) micro- and nanostructured surface patterns through selective electrochemical growth on monolayer colloidal crystal (MCC) templates is reported. This method can effectively create large-area (>1 cm2), 3D surface patterns with well-defined structures in a cost-effective and time-saving manner (<30 min). A variety of 3D surface patterns, including semishells, Janus particles, microcups, and mushroom-like clusters, is generated. Most importantly, our method can be used to prepare surface patterns with prescribed compositions, such as metals, metal oxides, organic materials, or composites (e.g., metal/metal oxide, metal/polymer). The 3D surface patterns produced by our method can be valuable in a wide range of applications, such as biosensing, data storage, and plasmonics. In a proof-of-concept study, we investigated, both experimentally and theoretically, the surface-enhanced Raman scattering (SERS) performance of the fabricated silver 3D semishell arrays.

Reactive template synthesis of polypyrrole nanotubes for fabricating metal/conducting polymer nanocomposites.

Unique nanocomposites of polypyrrole/Au and polypyrrole/Pt hybrid nanotubes are synthesized employing polypyrrole (PPy) nanotubes as an advanced support by solution reduction. The conducting polymer PPy nanotubes are fabricated by using pre-prepared MnO2 nanowires as the reactive templates. MnO2 nanowires induce the 1D polymerization of pyrrole monomers and the simultaneous dissolution of the templates affords the hollow tube-like structure. The loading content of metal nanoparticles in the nanocomposites could be adjusted by simply changing the amount of metal precursors. This work provides an efficient approach to fabricate an important kind of metal/conducting polymer hybrid nanotubes that are potentially useful for electrocatalyst and sensor materials.