In-plane charged domain walls with memristive behaviour in a ferroelectric film.

Domain-wall nanoelectronics is considered to be a new paradigm for non-volatile memory and logic technologies in which domain walls, rather than domains, serve as an active element. Especially interesting are charged domain walls in ferroelectric structures, which have subnanometre thicknesses and exhibit non-trivial electronic and transport properties that are useful for various nanoelectronics applications1-3. The ability to deterministically create and manipulate charged domain walls is essential to realize their functional properties in electronic devices. Here we report a strategy for the controllable creation and manipulation of in-plane charged domain walls in BiFeO3 ferroelectric films a few nanometres thick. By using an in situ biasing technique within a scanning transmission electron microscope, an unconventional layer-by-layer switching mechanism is detected in which ferroelectric domain growth occurs in the direction parallel to an applied electric field. Based on atomically resolved electron energy-loss spectroscopy, in situ charge mapping by in-line electron holography and theoretical calculations, we show that oxygen vacancies accumulating at the charged domain walls are responsible for the domain-wall stability and motion. Voltage control of the in-plane domain-wall position within a BiFeO3 film gives rise to multiple non-volatile resistance states, thus demonstrating the key functional property of being a memristor a few unit cells thick. These results promote a better understanding of ferroelectric switching behaviour and provide a new strategy for creating unit-cell-scale devices.

Photocatalytic Overall Water Splitting over PbTiO3 Modulated by Oxygen Vacancy and Ferroelectric Polarization.

Ferroelectric materials hold great promise in the field of photocatalytic water splitting due to their spontaneous polarization that sets up an inherent internal field for the spatial separation of photogenerated charges. The ferroelectric polarization, however, is generally accompanied by some intrinsic defects, particularly oxygen vacancies, whose impact upon photocatalysis is far from being fully understood and modulated. Here, we have studied the role of oxygen vacancies over the photocatalytic behavior of single-domain PbTiO3 through a combination of theoretical and experimental viewpoints. Our results indicate that the oxygen vacancies in the negatively polarized facet (001) are active sites for water oxidation into O2, while the defect-free sites prefer H2O2 as the oxidation product. The apparent quantum yield at 435 nm for photocatalytic overall water splitting with PbTiO3/Rh/Cr2O3 is determined to be 0.025%, which is remarkable for single undoped metal oxide-based photocatalysts. Furthermore, the strong correlation among oxygen vacancies, polarization strength, and photocatalytic activity is properly reflected by charge separation conditions in the single-domain PbTiO3. This work clarifies the crucial role of oxygen vacancies during photocatalytic reactions of PbTiO3, which provides a useful guide to the design of efficient ferroelectric photocatalysts and their water redox reaction pathways.

Asymmetric Modulation on Exchange Field in a Graphene/BiFeO3 Heterostructure by External Magnetic Field.

Graphene, having all atoms on its surface, is favorable to extend the functions by introducing the spin-orbit coupling and magnetism through proximity effect. Here, we report the tunable interfacial exchange field produced by proximity coupling in graphene/BiFeO3 heterostructures. The exchange field has a notable dependence with external magnetic field, and it is much larger under negative magnetic field than that under positive magnetic field. For negative external magnetic field, interfacial exchange coupling gives rise to evident spin splitting for N ≠ 0 Landau levels and a quantum Hall metal state for N = 0 Landau level. Our findings suggest graphene/BiFeO3 heterostructures are promising for spintronics.

Multifunctional Electrospun Nanofibers for Enhancing Localized Cancer Treatment.

Localized cancer treatment is one of the most effective strategies in clinical destruction of solid tumors at early stages as it can minimize the side effects of cancer therapeutics. Electrospun nanofibers have been demonstrated as a promising implantable platform in localized cancer treatment, enabling the on-site delivery of therapeutic components and minimizing side effects to normal tissues. This Review discusses the recent cutting-edge research with regard to electrospun nanofibers used for various therapeutic approaches, including gene therapy, chemotherapy, photodynamic therapy, thermal therapy, and combination therapy, in enhancing localized cancer treatment. Furthermore, it extensively analyzes the current challenges and potential breakthroughs in utilizing this novel platform for clinical transition in localized cancer treatment.

Ultrathin Anatase TiO2 Nanosheets for High-Performance Photocatalytic Hydrogen Production.

An ethanol solvothermal route has been developed to prepare ultrathin anatase TiO2 nanosheets with dominant {001} facets (≈97%), a thickness of ≈2.5 nm, and a side length of ≈200 nm. The introduction of ethanol solvent significantly enhances the content of surface chemisorbed F- on the TiO2 nanosheet, which has a higher stability and further lowers the surface energy of {001} facets, giving rise to the large percentage of active {001} facets. Adopting well-defined morphology, such nanosheets loaded with 1 wt% Pt exhibit an H2 evolution rate as high as 17.86 mmol h-1 g-1 , and the corresponding apparent quantum efficiency has been determined to be 34.2%.

Constructing Implantable SrTiO3 :Yb,Ho Nanofibers for NIR-Triggered and Optically Monitored Chemotherapy.

Light-responsive and photoluminescent (PL) drug-delivery platforms have sparked fascinating advancements in personalized tumor chemotherapy due to their unique characteristics in biological imaging and manipulated release kinetics. Herein, implantable Yb3+ and Ho3+ co-doped strontium titanate (SrTiO3 :Yb,Ho) nanofibers were synthesized and decorated on the surface with polyacrylic acid (PAA) molecules. The preliminary in vitro assay confirmed that this implantable fibrous mesh presented sound cytocompatibility. The PAA surface decoration improved the loading capacity of an anticancer drug (doxorubicin (DOX)) and effectively prevented a daunting burst release in a neutral aqueous environment. Owing to the electrostatic bond between PAA and DOX molecules, low-pH microenvironments and NIR (λ=808 nm) irradiation both induced significantly accelerated DOX release and consequently enhanced the local cancer-cell-killing effect. Additionally, the ratio of green-to-red emission (I545 /I655 ) from the SrTiO3 :Yb,Ho-PAA fibers responded effectively to the DOX release progress and dosage due to a fluorescence resonance energy transfer (FRET) effect. This unique characteristic enabled optical monitoring of the delivery progress in a timely manner. These SrTiO3 :Yb,Ho-PAA nanofibers, with precise dual-triggering and optical monitoring of DOX release, are expected to serve as a new implantable drug delivery platform for personalized chemotherapy in the future.

Selective Deposition of Silver Oxide on Single-Domain Ferroelectric Nanoplates and Their Efficient Visible-Light Photoactivity.

In this work, single-crystal and single-domain PbTiO3 nanoplates are employed as substrates to prepare Ag2 O/PbTiO3 composite materials through a photodeposition method. It is revealed that silver oxide nanocrystals with an average size of 63 nm are selectively deposited on the positive polar surface of the ferroelectric substrate. The possible mechanism leading to the formation of silver oxide is that silver ions are first reduced to silver and then oxidized by oxygen generation. The composite shows an efficient photodegradation performance towards rhodamine B (RhB) and methyl orange (MO) under visible-light irradiation. Such highly efficient photoactivity can be attributed to the ferroelectric polarization effect of the substrate, which promotes the separation of photogenerated electrons and holes at the interface.

Optically Monitoring Mineralization and Demineralization on Photoluminescent Bioactive Nanofibers.

Bone regeneration and scaffold degradation do not usually follow the same rate, representing a daunting challenge in bone repair. Toward this end, we propose to use an external field such as light (in particular, a tissue-penetrating near-infrared light) to precisely monitor the degradation of the mineralized scaffold (demineralization) and the formation of apatite mineral (mineralization). Herein, CaTiO3:Yb(3+),Er(3+)@bioactive glass (CaTiO3:Yb(3+),Er(3+)@BG) nanofibers with upconversion (UC) photoluminescence (PL) were synthesized. Such nanofibers are biocompatible and can emit green and red light under 980 nm excitation. The UC PL intensity is quenched during the bone-like apatite formation on the surface of the nanofibers in simulated body fluid; more mineral formation on the nanofibers induces more rapid optical quenching of the UC PL. Furthermore, the quenched UC PL can recover back to its original magnitude when the apatite on the nanofibers is degraded. Our work suggests that it is possible to optically monitor the apatite mineralization and demineralization on the surface of nanofibers used in bone repair.

A Fibrous Localized Drug Delivery Platform with NIR-Triggered and Optically Monitored Drug Release.

Implantable localized drug delivery systems (LDDSs) with intelligent functionalities have emerged as a powerful chemotherapeutic platform in curing cancer. Developing LDDSs with rationally controlled drug release and real-time monitoring functionalities holds promise for personalized therapeutic protocols but suffers daunting challenges. To overcome such challenges, a series of porous Yb(3+)/Er(3+) codoped CaTiO3 (CTO:Yb,Er) nanofibers, with specifically designed surface functionalization, were synthesized for doxorubicin (DOX) delivery. The content of DOX released could be optically monitored by increase in the intensity ratio of green to red emission (I550/I660) of upconversion photoluminescent nanofibers under 980 nm near-infrared (NIR) excitation owing to the fluorescence resonance energy transfer (FRET) effect between DOX molecules and the nanofibers. More importantly, the 808 nm NIR irradiation enabled markedly accelerated DOX release, confirming representative NIR-triggered drug release properties. In consequence, such CTO:Yb,Er nanofibers presented significantly enhanced in vitro anticancer efficacy under NIR irradiation. This study has thus inspired another promising fibrous LDDS platform with NIR-triggered and optics-monitored DOX releasing for personalized tumor chemotherapy.

Synthesis of CaTiO3 Nanofibers with Controllable Drug-Release Kinetics.

Calcium titanate (CaTiO3) nanofibers with controlled microstructure were fabricated by a combination of sol-gel and electrospinning approaches. The fiber morphology has been found to rely significantly on the precursor composition. Altering the volume ratio of ethanol to acetic acid from 3.5 to 1.25 enables the morphology of the CaTiO3 nanofibers to be transformed from fibers with a circular cross section to curved ribbon-like structures. Ibuprofen (IBU) was used as a model drug to investigate the drug-loading capacity and drug-release profile of the nanofibers. It was found that the BET surface area and the pore volume decrease markedly with the utilization of F127 surfactant. The nanofibers synthesized without F127 surfactant present the highest drug-loading capacity and the most sustained release kinetics. This study suggests that calcium titanate nanofibers can offer a promising platform for localized drug delivery.

Preparation and sustained-release of chitosan-alginate bilayer microcapsules containing aromatic compounds with different functional groups.

This study investigated the release of aromatic compounds with distinct functional groups within bilayer microcapsules. Bilayer microcapsules of four distinctive core materials (benzyl alcohol, eugenol, cinnamaldehyde, and benzoic acid) were synthesized via freeze-drying. Chitosan (CS) and sodium alginate (ALG) were used as wall materials. CS concentration, using orthogonal experiments with the loading ratio as a metric. Under optimal conditions, three other types of microcapsules (cinnamic aldehyde, benzoic acid, and benzyl alcohol) were obtained. The four types of microcapsules were characterized using Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscope (TEM), and thermogravimetric analysis (TGA), and their sustained release characteristics were evaluated. The optimal conditions were: CS dosage, 1.2 %; CS-to-eugenol mass ratio, 1:2; and CS-to-ALG mass ratio, 1:1. By comparing the IR spectra of the four types of microcapsules, wall material, and core material, the core materials were revealed to be encapsulated within the wall material. SEM results revealed that the granular protuberances on the surface of the microcapsules were closely aligned and persistent when magnified 2000×. The TEM results indicated that all four microcapsules had a spherical and bilayer structure. The thermal stability and sustained release results showed that the four microcapsules were more resilient and less volatile than the four core materials. The release conformed to first-order kinetics, and the release ratios of the four microcapsules were as follows: benzyl alcohol microcapsules Ëƒ eugenol microcapsules Ëƒ cinnamaldehyde microcapsules Ëƒ benzoic acid microcapsules. The prepared bilayer microcapsules encapsulated four different core materials with good sustained release properties.

Novel Sandwich-Structured Flexible Composite Films with Enhanced Piezoelectric Performance.

Piezoelectric poly(vinylidene fluoride) (PVDF) and its copolymers have been widely investigated for applications in wearable electric devices and sensing systems, owing to their intrinsic piezoelectricity and superior flexibility. However, their weak piezoelectricity poses major challenges for practical applications. To overcome these challenges, we propose a two-step synthesis approach to fabricate sandwich-structured piezoelectric films (BaTiO3@PDA/PVDF/BaTiO3@PDA) with significantly enhanced ferroelectric and piezoelectric properties. As compared to pristine PVDF films or conventional 0-3 composite films, a maximum polarization (Pmax) of 11.24 µC/cm2, a remanent polarization (Pr) of 5.83 µC/cm2, and an enhanced piezoelectric coefficient (d33 ∼ 14.6 pC/N) were achieved. Simulation and experimental results have demonstrated that the sandwich structure enhances the ability of composite films to withstand higher poling electric fields in comparison with 0-3 composites. The sandwich-structured piezoelectric films are further integrated into a wireless sensor system with a high force sensitivity of 288 mV/N, demonstrating great potential for movement monitoring applications. This facile approach shows great promise for the large-scale production of composite films with remarkable flexibility, ferroelectricity, and piezoelectricity for wearable sensing devices.

Identification of a Novel Selective CDK9 Inhibitor for the Treatment of CRC: Design, Synthesis, and Biological Activity Evaluation.

Cyclin-dependent kinase 9 (CDK9) is a member of the transcription CDK subfamily. In this work, we preliminarily demonstrated the feasibility of CDK9 as a potent target of treatment for colorectal cancer, and a series of novel CDK9 inhibitors were rationally designed and synthesized based on the structure of AZD5438 (a pan CDKs inhibitor reported by AstraZeneca). A novel selective CDK9 inhibitor named CLZX-205, which possessed significant CDK9 inhibitory activity (IC50 = 2.9 nM) with acceptable pharmacokinetic properties and antitumor efficacy in vitro and in vivo, was developed. Research on the mechanism indicated that CLZX-205 could induce apoptosis in the HCT116 cell line by inhibiting phosphorylation of RNA polymerase II at Ser2, which resulted in the inhibition of apoptosis-related genes and proteins expression, and these results were validated at the cellular and tumor tissue levels. Currently, CLZX-205 is undergoing further research as a promising candidate for CRC treatment.

Solution epitaxy of polarization-gradient ferroelectric oxide films with colossal photovoltaic current.

Solution growth of single-crystal ferroelectric oxide films has long been pursued for the low-cost development of high-performance electronic and optoelectronic devices. However, the established principles of vapor-phase epitaxy cannot be directly applied to solution epitaxy, as the interactions between the substrates and the grown materials in solution are quite different. Here, we report the successful epitaxy of single-domain ferroelectric oxide films on Nb-doped SrTiO3 single-crystal substrates by solution reaction at a low temperature of ~200 oC. The epitaxy is mainly driven by an electronic polarization screening effect at the interface between the substrates and the as-grown ferroelectric oxide films, which is realized by the electrons from the doped substrates. Atomic-level characterization reveals a nontrivial polarization gradient throughout the films in a long range up to ~500 nm because of a possible structural transition from the monoclinic phase to the tetragonal phase. This polarization gradient generates an extremely high photovoltaic short-circuit current density of ~2.153 mA/cm2 and open-circuit voltage of ~1.15 V under 375 nm light illumination with power intensity of 500 mW/cm2, corresponding to the highest photoresponsivity of ~4.306×10-3 A/W among all known ferroelectrics. Our results establish a general low-temperature solution route to produce single-crystal gradient films of ferroelectric oxides and thus open the avenue for their broad applications in self-powered photo-detectors, photovoltaic and optoelectronic devices.

Lattice-Gradient Perovskite KTaO3 Films for an Ultrastable and Low-Dose X-Ray Detector.

Conventional indirect X-ray detectors employ scintillating phosphors to convert X-ray photons into photodiode-detectable visible photons, leading to low conversion efficiencies, low spatial resolutions, and optical crosstalk. Consequently, X-ray detectors that directly convert photons into electric signals have long been desired for high-performance medical imaging and industrial inspection. Although emerging hybrid inorganic-organic halide perovskites, such as CH3 NH3 PbI3 and CH3 NH3 PbBr3 , exhibit high sensitivity, they have salient drawbacks including structural instability, ion motion, and the use of toxic Pb. Here, this work reports an ultrastable, low-dose X-ray detector comprising KTaO3 perovskite films epitaxially grown on a Nb-doped strontium titanate substrate using a low-cost solution method. The detector exhibits a stable photocurrent under high-dose irradiation, high-temperature (200 °C), and aqueous conditions. Moreover, the prototype KTaO3 -film-based detector exhibits a 150-fold higher sensitivity (3150 µC Gyair -1 cm-2 ) and 150-fold lower detection limit (<40 nGyair s-1 ) than those of commercial α-Se-based direct detectors. Systematic investigations reveal that the high stability of the detector originates from the strong covalent bonds within the KTaO3 film, whereas the low detection limit is due to a lattice-gradient-driven built-in electric field and the high insulating property of KTaO3 film. This study unveils a new path toward the fabrication of green, stable, and low-dose X-ray detectors using oxide perovskite films, which have significant application potential in medical imaging and security operations.

Surface Oxygen Vacancies Confined by Ferroelectric Polarization for Tunable CO Oxidation Kinetics.

Surface oxygen vacancies have been widely discussed to be crucial for tailoring the activity of various chemical reactions from CO, NO, to water oxidation by using oxide-supported catalysts. However, the real role and potential function of surface oxygen vacancies in the reaction remains unclear because of their very short lifetime. Here, it is reported that surface oxygen vacancies can be well confined electrostatically for a polarization screening near the perimeter interface between Pt {111} nanocrystals and the negative polar surface (001) of ferroelectric PbTiO3. Strikingly, such a catalyst demonstrates a tunable catalytic CO oxidation kinetics from 200 °C to near room temperature by increasing the O2 gas pressure, accompanied by the conversion curve from a hysteresis-free loop to one with hysteresis. The combination of reaction kinetics, electronic energy loss spectroscopy (EELS) analysis, and density functional theory (DFT) calculations, indicates that the oxygen vacancies stabilized by the negative polar surface are the active sites for O2 adsorption as a rate-determining step, and then dissociated O moves to the surface of the Pt nanocrystals for oxidizing adsorbed CO. The results open a new pathway for tunable catalytic activity of CO oxidation.

Bright blue photoluminescence from the amorphous carbon via surface plasmon enhancement.

Blue photoluminescence (PL) from hydrogenated amorphous carbon (a-C:H) films has been successfully enhanced via surface plasmons (SPs). a-C:H films with different thickness were deposited on Ag interlayers, of which the nanostructure was tuned from nanoparticles (NPs) to continuous films via processing conditions control. The PL enhancement factor was found to increase with the Ag NP growth and the surface roughness of the continuous Ag interlayer. A PL enhancement factor of more than 9 times has been successfully achieved when the 43 nm-thick a-C:H film coupled to an Ag interlayer with the peak surface roughness. a-C:H films with SP-enhanced PL have therefore been demonstrated to be promising for light-emitting applications.

Octahedral Shaped PbTiO3-TiO2 Nanocomposites for High-Efficiency Photocatalytic Hydrogen Production.

In this work, octahedral shaped PbTiO3-TiO2 nanocomposites have been synthesized by a facile hydrothermal method, where perovskite ferroelectric PbTiO3 nanooctahedra were employed as substrate. The microstructures of the composites were investigated systemically by using XRD, SEM, TEM and UV-Vis spectroscopy. It was revealed that anantase TiO2 nanocrystals with a size of about 5 nm are dispersed on the surface of the {111} facets of the nanooctahedron crystals. Photocatalytic hydrogen production of the nanocomposites has been evaluated in a methanol alcohol-water solution under UV light enhanced irradiation. The H2 evolution rate of the nanocomposites increased with an increased loading of TiO2 on the nanooctahedra. The highest H2 evolution rate was 630.51 µmol/h with the highest concentration of TiO2 prepared with 2 mL tetrabutyl titanate, which was about 36 times higher than that of the octahedron substrate. The enhanced photocatalytic reactivity of the nanocomposites is possibly ascribed to the UV light absorption of the nanooctahedral substrates, efficient separation of photo-generated carriers via the interface and the reaction on the surface of the TiO2 nanocrystals.

Pattern-Potential-Guided Growth of Textured Macromolecular Films on Graphene/High-Index Copper.

Macromolecular films are crucial functional materials widely used in the fields of mechanics, electronics, optoelectronics, and biology, due to their superior properties of chemical stability, small density, high flexibility, and solution-processing ability. Their electronic and mechanical properties, however, are typically much lower than those of crystalline materials, as the macromolecular films have no long-range structural ordering. The state-of-the-art for producing highly ordered macromolecular films is still facing a great challenge due to the complex interactions between adjacent macromolecules. Here, the growth of textured macromolecular films on a designed graphene/high-index copper (Cu) surface is demonstrated. This successful growth is driven by a patterned potential that originates from the different amounts of charge transfer between the graphene and Cu surfaces with, alternately, terraces and step edges. The textured films exhibit a remarkable improvement in remnant ferroelectric polarization and fracture strength. It is also demonstrated that this growth mechanism is universal for different macromolecules. As meter-scale graphene/high-index Cu substrates have recently become available, the results open a new regime for the production and applications of highly ordered macromolecular films with obvious merits of high production and low cost.

PbTiO3 nanofibers with edge-shared TiO6 octahedra.

A new tetragonal phase of PbTiO(3) was discovered, in which each TiO(6) octahedron pair shares an edge and stacks over following pairs in an interlaced manner to form a one-dimensional (1D) columned structure along the c-axis. This new tetragonal phase of PbTiO(3) transforms into a normal perovskite phase in air at elevated temperature.