Hydrated Calcium Vanadate Nanoribbons with a Stable Structure and Fast Ion Diffusion as a Cathode for Quasi-Solid-State Zinc-Ion Batteries.

We demonstrated the use of hydrated calcium vanadate (CaV6O16·3H2O, denoted as CaVO-2) as a cathode for aqueous zinc-ion batteries (AZIBs). Nanoribbons of hydrated calcium vanadate facilitated shortening of the Zn2+ transport distance and accelerated zinc-ion insertion. The introduction of interlayer structure water increased the interlayer spacing of calcium vanadate and as a "lubricant". Ca2+ insertion also expanded the interlayer spacing and further stabilized the interlayer structure of vanadium-based oxide. The density functional theory results showed that the introduction of Ca2+ and structured water could effectively improve the diffusion kinetics, resulting in the rapid transport of zinc ions. As a result, AZIBs based on the CaVO-2 cathode offered high specific capacity (329.6 mAh g-1 at 200 mA g-1) and fast charge/discharge capability (147 mAh g-1 at 10 A g-1). Impressively, quasi-solid-state zinc-ion batteries based on the CaVO-2 cathode and polyacrylamide-cellulose nanofiber hydrogel electrolytes maintained an outstanding specific capacity and long cycle life (162 mAh g-1 over 10 000 cycles at 5 A g-1). This study provided a reliable strategy for metal-ion insertion and the structural water introduction of oxides to produce a high-quality cathode for ZIBs. Meanwhile, it provides ideas for the combination of vanadium-based materials and gel electrolytes to construct solid-state zinc-ion batteries.

Optical Modulation of MoTe2/Ferroelectric Heterostructure via Interface Doping.

Optical modulation through interface doping offers a convenient and efficient way to control ferroelectric polarization, thereby advancing the utilization of ferroelectric heterostructures in nanoelectronic and optoelectronic devices. In this work, we fabricated heterostructures of MoTe2/BaTiO3/La0.7Sr0.3MnO3 (MoTe2/BTO/LSMO) and demonstrated opposite ultraviolet (UV) light-induced polarization switching behaviors depending on the varied thicknesses of MoTe2. The thickness-dependent band structure of MoTe2 film results in interface doping with opposite polarity in the respective heterostructures. The polarization field of BTO interacts with the interface charges, and an enhanced effective built-in field (Ebi) can trigger the transfer of massive UV light-induced carriers in both MoTe2 and BTO films. As a result, the interplay among the contact field of MoTe2/BTO, the polarization field, and the optically excited carriers determines the UV light-induced polarization switching behavior of the heterostructures. In addition, the electric transport characteristics of MoTe2/BTO/LSMO heterostructures reveal the interface barrier height and Ebi under opposite polarization states, as well as the presence of inherent in-gap trap states in MoTe2 and BTO films. These findings represent a further step toward achieving multifield modulation of the ferroelectric polarization and promote the potential applications in optoelectronic, logic, memory, and synaptic ferroelectric devices.

Efficient filter-in-centrifuge separation of low-concentration bacteria from blood.

Separating bacteria from infected blood is an important step in preparing samples for downstream bacteria detection and analysis. However, the extremely low bacteria concentration and extremely high blood cell count make efficient separation challenging. In this study, we introduce a method for separating bacteria from blood in a single centrifugation step, which involves sedimentation velocity-based differentiation followed by size-based cross-flow filtration over an inclined filter. Starting from 1 mL spiked whole blood, we recovered 32 ± 4% of the bacteria (Escherichia coli, Klebsiella pneumonia, or Staphylococcus aureus) within one hour while removing 99.4 ± 0.1% of the red blood cells, 98.4 ± 1.4% of the white blood cells, and 90.0 ± 2.6% of the platelets. Changing the device material could further increase bacteria recovery to >50%. We demonstrated bacterial recovery from blood spiked with 10 CFU mL-1. Our simple hands-off efficient separation of low-abundant bacteria approaches clinical expectations, making the new method a promising candidate for future clinical use.

Mechanistic formulation of inorganic membranes at the air-liquid interface.

Freestanding functional inorganic membranes, beyond the limits of their organic and polymeric counterparts1, may unlock the potentials of advanced separation2, catalysis3, sensors4,5, memories6, optical filtering7 and ionic conductors8,9. However, the brittle nature of most inorganic materials, and the lack of surface unsaturated linkages10, mean that it is difficult to form continuous membranes through conventional top-down mouldings and/or bottom-up syntheses11. Up to now, only a few specific inorganic membranes have been fabricated from predeposited films by selective removal of sacrificial substrates4-6,8,9. Here we demonstrate a strategy to switch nucleation preferences in aqueous systems of inorganic precursors, resulting in the formation of various ultrathin inorganic membranes at the air-liquid interface. Mechanistic study shows that membrane growth depends on the kinematic evolution of floating building blocks, which helps to derive the phase diagram based on geometrical connectivity. This insight provides general synthetic guidance towards any unexplored membranes, as well as the principle of tuning membrane thickness and through-hole parameters. Beyond understanding  a complex dynamic system, this study comprehensively expands the traditional notion of membranes in terms of composition, structure and functionality.

Ferroelectric Engineered Electrode-Composite Polymer Electrolyte Interfaces for All-Solid-State Sodium Metal Battery.

To enhance the compatibility between the polymer-based electrolytes and electrodes, and promote the interfacial ion conduction, a novel approach to engineer the interfaces between all-solid-state composite polymer electrolyte and electrodes using thin layers of ferroelectrics is introduced. The well-designed and ferroelectric-engineered composite polymer electrolyte demonstrates an attractive ionic conductivity of 7.9 × 10-5 S cm-1 at room temperature. Furthermore, the ferroelectric engineering is able to effectively suppress the growth of solid electrolyte interphase (SEI) at the interface between polymer electrolytes and Na metal electrodes, and it can also enhance the ion diffusion across the electrolyte-ferroelectric-cathode/anode interfaces. Notably, an extraordinarily high discharge capacity of 160.3 mAh g-1 , with 97.4% in retention, is achieved in the ferroelectric-engineered all-solid-state Na metal cell after 165 cycles at room temperature. Moreover, outstanding stability is demonstrated that a high discharge capacity retention of 86.0% is achieved over 180 full charge/discharge cycles, even though the cell has been aged for 2 months. This work provides new insights in enhancing the long-cyclability and stability of solid-state rechargeable batteries.

Decomposing and analyzing contact resonance frequency in contact mode voltage modulated scanning probe microscopies.

Contact mode voltage modulated scanning probe microscopy (SPM) techniques, such as switching spectroscopy piezoresponse force microscopy (SS-PFM), are powerful tools for detecting local electromechanical behaviors. However, interpreting their signals, especially the contact resonance frequency (f0), is difficult due to the complexity of the tip-sample contact and the signal tracking system. In a previous study, an interesting phenomenon on the variation of f0 was observed, showing distinctions between ferroelectric and non-ferroelectric materials. Therefore, it is believed that f0 conveys important information about the tip-sample contact which is real-timely affected by charge accumulation or polarization switching. In this study, principal component analysis (PCA) and correlation analysis are applied to decompose the signal of f0. The first and second principal components successfully restore most information of the original data, and they describe different features which are related to the surface morphology and electromechanical behavior, respectively. In addition, a customized method based on the PCA and correlation analysis of f0 can well distinguish the responses from different materials of which the amplitude and phase signals show "ferroelectric like" phenomena during the SS-PFM measurements.

Breaking the Fundamental Limitations of Nanoscale Ferroelectric Characterization: Non-Contact Heterodyne Electrostrain Force Microscopy.

Perceiving nanoscale ferroelectric phenomena from real space is of great importance for elucidating underlying ferroelectric physics. During the past decades, nanoscale ferroelectric characterization has mainly relied on the Piezoresponse Force Microscopy (PFM) invented in 1992, however, the fundamental limitations of PFM have made the nanoscale ferroelectric studies encounter significant bottlenecks. In this study, a high-resolution non-contact ferroelectric measurement, named Non-Contact Heterodyne Electrostrain Force Microscopy (NC-HEsFM), is introduced. It is demonstrated that NC-HEsFM can operate on multiple eigenmodes to perform ideal high-resolution ferroelectric domain mapping, standard ferroelectric hysteresis loop measurement, and controllable domain manipulation. By using a quartz tuning fork (QTF) sensor, multi-frequency operation, and heterodyne detection schemes, NC-HEsFM achieves a real non-contact yet non-destructive ferroelectric characterization with negligible electrostatic force effect and hence breaks the fundamental limitations of the conventional PFM. It is believed that NC-HEsFM can be extensively used in various ferroelectric or piezoelectric studies with providing substantially improved characterization performance. Meanwhile, the QTF-based force detection makes NC-HEsFM highly compatible for high-vacuum and low-temperature environments, providing ideal conditions for investigating the intrinsic ferroelectric phenomena with the possibility of achieving an atomically resolved ferroelectric characterization.

Response and Implication of NASICON Solid-State Electrolytes to Local Electrical Stimulation: From Surface Engineering to Interfacial Manipulation.

The surface feature of solid electrolytes fundamentally governs their own physical properties and significantly affects the interaction with the electrode materials. The evaluation of interfacial contact between the electrolyte and the metallic anode is largely relied on the macroscopic contact angle measurement, which is influenced by the intrinsic wettability and the microstructure of the electrolyte. In this work, the surface chemistry of the solid electrolyte is first regulated via facile thermal treatments. Then, scanning probe microscopy (SPM)-based techniques are comprehensively adopted to study the interaction between the electrolyte and metallic anode at the nanoscale. By manipulating the overpotential applied on the SPM tip, the mobile sodium ions at the subsurface of the solid electrolyte can be extracted toward the surface, and the eventual topography of the products is deliberately correlated with the sodium wettability. In this context, the impact of surface treatment on the sodium wettability of the surface layer is systematically evaluated based on the topographic evolution at the nanoscale. Furthermore, the local electrochemical reaction dynamics is revealed by correlating the surface ionic activity and current-voltage (I-V) curves. This work presents a new methodology to effectively evaluate the sodium wettability of the solid electrolyte, and these findings can provide meaningful implications to the surface engineering of ceramic electrolytes for high-performance solid-state batteries.

Humidity Effects on Domain Structure and Polarization Switching of Pb(Zn1/3Nb2/3)O3-x%PbTiO3 (PZN-x%PT) Single Crystals.

The effect of relative humidity on the domain structure imaging and polarization switching process of Pb(Zn1/3Nb2/3)O3-x%PbTiO3 (PZN-x%PT) ferroelectric single crystals has been investigated by means of the piezoresponse force microscopy (PFM) and piezoresponse force spectroscopy (PFS) techniques. It was found that the PFM amplitude increases with the relative humidity, and that the ferroelectric hysteresis loops at different relative humidity levels show that the coercive bias decreases with the increase in relative humidity. These observed phenomena are attributed to the existence of the water layer between the probe tip and the sample surface in a humid atmosphere, which could affect the effect of the electric field distribution and screening properties at the ferroelectric sample surface. These results provide a better understanding of the water adsorption phenomena at the nanoscale in regard to the fundamental understanding of ferroelectrics' properties.

Intrinsic low sodium/NASICON interfacial resistance paving the way for room temperature sodium-metal battery.

Sodium-metal batteries have strong potential to be utilized as stationary high energy density storage devices. Owing to its high ionic conductivity, low electronic conductivity and relatively easy fabrication, NASICON-structure electrolyte (Na3Zr2Si2PO12) is one of the potential candidates to be considered in the solid-state sodium-metal batteries at room temperature. However, the large interfacial resistance between the solid-state electrolyte and the metallic sodium is known to limit the critical current density (CCD) of the cell. In this study, a simple and cost-effective annealing process is introduced to the electrolyte preparation to improves its interface with metallic sodium. X-ray photoelectron spectroscopy and scanning probe microscopy show that Si forms bonds with the surface functional groups when exposed to the ambient condition. With the removal of surface contamination as well as a partially reduced electrolyte surface, the annealed electrolyte shows an extremely small interfacial resistance of 11 Ω cm2 and a high CCD of 0.9 mA cm-2. This study provides an insight on the electrolyte surface preparation and its significant in a sodium-metal solid-state battery.

Nanoscale Ferroelectric Characterization with Heterodyne Megasonic Piezoresponse Force Microscopy.

Piezoresponse force microscopy (PFM), as a powerful nanoscale characterization technique, has been extensively utilized to elucidate diverse underlying physics of ferroelectricity. However, intensive studies of conventional PFM have revealed a growing number of concerns and limitations which are largely challenging its validity and applications. In this study, an advanced PFM technique is reported, namely heterodyne megasonic piezoresponse force microscopy (HM-PFM), which uses 106 to 108 Hz high-frequency excitation and heterodyne method to measure the piezoelectric strain at nanoscale. It is found that HM-PFM can unambiguously provide standard ferroelectric domain and hysteresis loop measurements, and an effective domain characterization with excitation frequency up to ≈110 MHz is demonstrated. Most importantly, owing to the high-frequency and heterodyne scheme, the contributions from both electrostatic force and electrochemical strain can be significantly minimized in HM-PFM. Furthermore, a special measurement of difference-frequency piezoresponse frequency spectrum (DFPFS) is developed on HM-PFM and a distinct DFPFS characteristic is observed on the materials with piezoelectricity. By performing DFPFS measurement, a truly existed but very weak electromechanical coupling in CH3NH3PbI3 perovskite is revealed. It is believed that HM-PFM can be an excellent candidate for the ferroelectric or piezoelectric studies where conventional PFM results are highly controversial.

Temperature-Induced Phase Transition Characteristics of [001]-Oriented 0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3 (PZN-7%PT) Single Crystal by Using Piezoresponse Force Microscopy.

The evolution of the domain structures of [001]-oriented relaxor ferroelectric 0.93PbZn1/3Nb2/3O3-0.07PbTiO3 (PZN-7%PT) single crystals as a function of temperature was investigated in situ by using piezoresponse force microscopy (PFM). It was found that the local domain structure of PZN-7%PT single crystals at room temperature is rhombohedral with nanoscale twins. Temperature-dependent domain structures showed that the phase transition process is a collective process and that the sample underwent a sequence of rhombohedral (R) → monoclinic (Mc) → tetragonal (T) → cubic (C) phase transformations when the temperature increased from 25 °C to 170 °C. The results provide direct observation of the phase transition evolution of PZN-7%PT single crystals as a function of temperature, which is of great significance to fully understand the relationships between the domain structure and phase structure of PZN-7%PT single crystals.

Prediction of cross section fracture path of cortical bone through nanoindentation array.

Although great progresses in the fracture mechanisms and deformation behaviors of cortical bones have been achieved, the effective methods to predict the surface fracture path of cortical bones are still difficult. By using depth-sensing nanoindentation measurement technique, the hardness distribution map of cortical bones was obtained through nanoindentation array. Combined with the compressive tests under approximate in vivo environment and micro computed tomography (CT) analysis, the correlation between hardness distribution map and compressive fracture path on the cross section of cortical bone was established. Through extracting the high hardness regions from the hardness distribution map and connecting the high hardness regions combined with the minimum directional derivative principle, the fracture path on cross section under compressive stress was accurately predicted. The feasibility of the prediction method was verified through the comparison between the fitted and actual fracture paths of specimens with sampling orientations of 90° and 45°. The relation between the regions where the fracture propagation path passed through and distribution of Haversian canals were also analyzed.

A 2D-SnSe film with ferroelectricity and its bio-realistic synapse application.

Catering to the general trend of artificial intelligence development, simulating humans' learning and thinking behavior has become the research focus. Second-order memristors, which are more analogous to biological synapses, are the most promising devices currently used in neuromorphic/brain-like computing. However, few second-order memristors based on two-dimensional (2D) materials have been reported, and the inherent bionic physics needs to be explored. In this work, a second-order memristor based on 2D SnSe films was fabricated by the pulsed laser deposition technique. The continuously adjustable conductance of Au/SnSe/NSTO structures was achieved by gradually switching the polarization of a ferroelectric SnSe layer. The experimental results show that the bio-synaptic functions, including spike-timing-dependent plasticity, short-term plasticity and long-term plasticity, can be simulated using this two-terminal devices. Moreover, stimulus pulses with nanosecond pulse duration were applied to the device to emulate rapid learning and long-term memory in the human brain. The observed memristive behavior is mainly attributed to the modulation of the width of the depletion layer and barrier height is affected, at the SnSe/NSTO interface, by the reversal of ferroelectric polarization of SnSe materials. The device energy consumption is as low as 66 fJ, being expected to be applied to miniaturized, high-density, low-power neuromorphic computing.

Study of the Freeze Casting Process by Artificial Neural Networks.

Freeze casting technology has experienced vast development since the early 2000s due to its versatility and simplicity for producing porous materials. A linear relationship between the final porosity and the initial solid material fraction in the suspension was reported by many researchers. However, the linear relationship cannot well describe the freeze casting for various samples. Here, we proposed an artificial neural network (ANN) to analyze the influence of critical parameters on freeze-cast porous materials. After well training the ANN model on experimental data, a porosity value can be predicted from four inputs, which describe the most influential process conditions. Based on the constructed model, two improvements are also successfully added on to infer more information. By involving big data from real experiments, this method effectively summarizes a general rule for diverse materials in one model, which gives a new insight into the freeze casting process. The good convergence and accuracy prove that our ANN model has the potential to be developed for solving more complicated issues of freeze casting. Finally, a user-friendly mini-program based on a well-trained ANN model is also provided to predict the porosity for customized freeze-casting experiments.

Probing the Coexistence of Ferroelectric and Relaxor States in Bi0.5Na0.5TiO3-Based Ceramics for Enhanced Piezoelectric Performance.

To tackle the global restriction on the use of lead-based materials, a feasible strategy of developing a piezoelectric ceramic with a ferroelectric- and relaxor-coexisted hybrid state is proposed in order to reduce the energy barrier as well as to assist polarization rotation. A significantly enhanced piezoelectric coefficient, d33, of 173 pC/N along with a broadened high-temperature stability above 300 °C has been obtained. Further probing via piezoresponse force microscopy unveils the grain boundary-governed domain structures with complicated configurations, suggesting close correlations with the coexistence of ferroelectric and relaxor states. This work demonstrates a recipe for establishing a novel grain-based ferroelectric-relaxor hybrid state with improved piezoelectric performance, which can further be beneficial for realistic applications.

Sustainable Fuel Production from Ambient Moisture via Ferroelectrically Driven MoS2 Nanosheets.

Unlike traditional water splitting in an aqueous medium, direct decomposition of atmospheric water is a promising way to simultaneously dehumidify the living space and generate power. Here, a tailored superhygroscopic hydrogel, a catalyst, and a solar cell are integrated into a humidity digester that can break down ambient moisture into hydrogen and oxygen, creating an efficient electrochemical cell. The function of the hydrogel is to harvest moisture from ambient humidity and transfer the collected water to the catalyst. Barium titanate and vertical 2D MoS2 nanosheets are integrated as the catalyst: the negatively polarized cathode can enhance the electron transport and attract H+ to the MoS2 surface for water reduction, while water oxidation takes place at the positively polarized anode. By employing this mechanism, it is possible to maintain the relative humidity in a medium-sized room at <60% without any additional energy input, and a stable current of 12.5 mA cm-2 is generated by the humidity digester when exposed to ambient light.

Abnormal Ionic Conductivities in Halide NaBi3 O4 Cl2 Induced by Absorbing Water and a Derived Oxhydryl Group.

In hunting for safe and cost-effective materials for post-Li-ion energy storage, the design and synthesis of high-performance solid electrolytes (SEs) for all-solid-state batteries are bottlenecks. Many issues associated with chemical stability during processing and storage and use of the SEs in ambient conditions need to be addressed. Now, the effect of water as well as oxyhdryl group (. OH) on NaBi3 O4 Cl2 are investigated by evaluating ionic conductivity. The presence of water and . OH results in an increase in ionic conductivity of NaBi3 O4 Cl2 owing to diffusion of H2 O into NaBi3 O4 Cl2 , partially forming binding . OH through oxygen vacancy repairing. Ab initio calculations reveal that the electrons significantly accumulate around . OH and induce a more negative charge center, which can promote Na+ hopping. This finding is fundamental for understanding the essential role of H2 O in halide-based SEs and provides possible roles in designing water-insensitive SEs through control of defects.

High-Speed Piezoresponse Force Microscopy and Machine Learning Approaches for Dynamic Domain Growth in Ferroelectric Materials.

Domain dynamics has been one of the hottest research topics for ferroelectric materials in order to understand the ferroelectric mechanisms and to develop the related applications. By using high-speed piezoresponse force microscopy (HSPFM), it is possible to observe the dynamic domain evolution in an ultrashort time increment. This paper combines the HSPFM experiments and machine learning to study the domain growth under a weak AC field in ferroelectric materials. Here, the Bayesian optimized support vector machine is employed to classify the switching domain and stable domain. The results indicate that the machine learning classifier is capable of discerning the switching area. In addition, the domain associated characteristics, such as domain pinning and domain wall pinning, can also be observed and analyzed by combining experiments and machine learning. The machine learning approach can fast and deeply extract the complicated features related to free energy from the multidimensional signals obtained by HSPFM.

Composite NASICON (Na3Zr2Si2PO12) Solid-State Electrolyte with Enhanced Na+ Ionic Conductivity: Effect of Liquid Phase Sintering.

NASICON-type of solid-state electrolyte, Na3Zr2Si2PO12 (NZSP), is one of the potential solid-state electrolytes for all-solid-state Na battery and Na-air battery. However, in solid-state synthesis, high sintering temperature above 1200 °C and long duration are required, which led to loss of volatile materials and formation of impurities at the grain boundaries. This hampers the total ionic conductivity of NZSP to be in the range of 10-4 S cm-1. Herein, we have reduced both the sintering temperature and time of the NZSP electrolyte by sintering the NZSP powders with different amounts of Na2SiO3 additive, which provides the liquid phase for the sintering process. The addition of 5 wt % Na2SiO3 has shown the highest total ionic conductivity of 1.45 mS cm-1 at room temperature. A systematic study of the effect of Na2SiO3 on the microstructure and electrical properties of the NZSP electrolyte is conducted by the structural study with the help of morphological and chemical observations using X-ray diffraction (XRD), scanning electron microscopy, and using focused ion-beam-time of flight-secondary ion mass spectroscopy. The XRD results revealed that cations from Na2SiO3 diffused into the bulk change the stoichiometry of NZSP, leading to an enlarged bottleneck area and hence lowering activation energy in the bulk, which contributes to the increment of the bulk ion conductivity, as indicated by the electrochemical impedance spectroscopy result. In addition, higher density and better microstructure contribute to improved grain boundary conductivity. More importantly, this study has achieved a highly ionic conductive NZSP only by facile addition of Na2SiO3 into the NZSP powder prior to the sintering stage.