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Low-cost Prussian blue analogs (PBAs) have attracted great attentions as a group of promising cathodes for sodium-ion batteries (SIBs) due to their tailorable and open frameworks which endue the possibility of ultrahigh Na+ diffusion kinetics. Herein, a unique discharging plateau elevation was firstly determined in the iron hexacyanoferrate. The synergy between the crystal field and ligand field stabilization energy in the OH-coordinated Fe sites lowers the activation energy barrier of low-spin Fe, thus inducing the intercalation pseudocapacitance. Furthermore, we prove that the Na+ storage mechanism of high-spin Fe redox reaction features an ion–diffusion behavior while the low-spin Fe redox reaction shows a pseudocapacitance behavior. Benefitting from the improved ionic diffusivity in intercalation pseudocapacitance, the full cell achieves an outstanding rate performance and long-term cycling stability of over 3000 cycles at 500 mA g−1. It is expected that manipulating Fe redox kinetics of the PBAs through inducing special coordinated groups could be a new pathway towards the design of practical high-voltage SIBs.

Carbonaceous materials are the most promising candidates as the anode for sodium-ion batteries (SIBs), however, they still suffer from low electric conductivity and sluggish sodium ion (Na+) reaction kinetics. Appropriate composition modulation using heteroatoms doping and structure optimization is highly desired. A basic empirical understanding of the structure-capacity relationship is also urgent in tackling the above problems. Herein, multi-functional nitrogen (N) doped carbon micro-rods with enlarged interlayer spacing are synthesized and investigated as the anode in SIBs, showing an ultra-stable capacity of 161.5 mAh g−1 at 2 A g−1 for over 5000 cycles. Experimental investigations and first-principle calculations indicate that the enlarged interlayer spacing can facilitate Na+ intercalation and N doping can guarantee the high electric conductivity and favorable electrochemical active sites. Additionally, pyridinic N is theoretically proved to be more effective to enhance Na+ adsorption than pyrrolic N due to the lower adsorption energy and stronger binding energy with Na+. Full SIBs show a high capacity and cyclability, making the biomass-derived carbon micro-rods to be a promising anode for practical SIBs applications.

Generation of large strains upon Na+ intercalation is one of the prime concerns of the mechanical degradation of Prussian blue (PB) and its analogs. Structural construction from the atomic level is imperative to maintain structural stability and ameliorate the long-term stability of PB. Herein, an inter nickel hexacyanoferrate (NNiFCN) is successfully introduced at the out layer of iron hexacyanoferrate (NFFCN) through ion exchange to improve structural stability through compressive stress locking by forming NNiFCN shell. Furthermore, the kinetics of sodium ion diffusion is enhanced through the built-in electric pathway. The electrochemical performance is therefore significantly improved with a remarkable long-term cycling stability over 3,000 cycles at 500 mA·g−1 in the full sodium-ion batteries (SIBs) with a maximum energy density of 91.94 Wh·g−1, indicating that the core-shell structured NNiFCN/NFFCN could be the low-cost and high-performance cathode for full SIBs in large-scale EES applications.

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.

Metal solid-state batteries are regarded as the next-generation energy storage systems with high energy density and high safety. A robust and intimate solid-state interfacial contact between the sodium metal with the solid-state electrolyte (SSE) is vital to achieve good cyclic stability at high current density. However, inorganic SSEs suffer from poor stability when cycling at a current density below 2 mA cm−2. This can be ascribed to the dendrite formation through the SSE due to plating process or void formation during the stripping process. Furthermore, simply direct application of a sodium metal on SSE shows poor interfacial contact and low critical current density. In this review, the recent development of inorganic sodium-ion electrolytes, such as oxide-, sulphide-, and halide-based, are briefly discussed. More particularly, the dendrite formation through the SSE and the loss of solid-solid contact at the sodium/SSE interface are reviewed. Additionally, different engineering approaches to integrate the sodium metal with the solid-state electrolytes and its correlation with the electrochemical performance are discussed. Finally, perspectives in future researches are identified.

Nanomechanical properties are extremely critical to the applications of flexible electric devices and energy harvester; however, the direct mechanical measurement of composite nanofibers is challenging and rarely explored. In this work, we apply an effective method to obtain the elastic modulus distribution of lead zirconium titanate (PZT)-doped polyvinylidene fluoride (PVDF) nanofibers via bimodal amplitude modulated-frequency modulated scanning probe microscopy (AM-FM SPM). All the samples exhibit obvious piezoelectric properties, and the mechanical properties are clearly enhanced through doping of PZT. Compared with pure PVDF nanofibers, the composite nanofibers with PZT doping show higher elastic modulus which indicates superior stability under the same bending condition. The enhancement of mechanical properties in composite nanofibers via filler doping pave a way to the design of stable and flexible sustainable energy harvesters.

The scaling-up issue, mechanical instability, and possible packing capacity loss during pelletization remain as the major obstacles for the application of metal–organic frameworks (MOFs) in practic...

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.

Electrostatic energy-storage capacitors, with their ultrahigh storage density and high temperature stability, have been receiving increasing attention of late for their ability to meet the critical requirements of pulsed power devices in low-consumption systems. In such a context, this work reports on the successful production of anti-ferroelectric (AFE) thin films with excellent energy storage performance under a relatively low electric field. In particular, La-doped PbZrO3 thin films were fabricated using a sol-gel method, yielding a recoverable energy storage density of 34.87 J cm−3 with an efficiency of 59.23% at room temperature under the electric field of ~800 kV cm−1. The temperature dependence of the energy storage property was demonstrated from room temperature to 210°C, indicating a stable density variation between 34.87 and 27.98 J cm−3. The films also exhibited excellent anti-fatigue property (endurance of up to 3×109 cycles and the recoverable energy storage density varied from 39.78 to 29.32 J cm−3 combined with an efficiency of 61.03%–44.95% under the test frequencies from 10 to 5000 Hz). All results were obtained using compact films with a high polarization ( P max) of approximately 103.7 μC cm−2 and low remnant polarization ( P r~7 μC cm−2), which was owing to the combination of LaNiO3 buffer layers and vacancies at Pb sites. These results illustrate the great potential of pulsed power devices in low-consumption systems operating in a wide range of temperatures and long-term operations.

NASICON-type Na3V2(PO4)3 (NVP) has been regarded as one of the most promising cathode materials for high-voltage sodium-ion batteries (SIBs) because of its high theoretical energy density and stabl...

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.

The Garnet-type solid electrolyte Li7La3Zr2O12 (LLZO) showing high ionic conductivity and a wide electrochemical potential window is considered as one of the most promising candidates for solid-sta...

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.

In this study, the underlying physical mechanisms of imprint are addressed in order to obtain a better understanding of the imprint phenomenon of relaxor Pb(Zn1/3Nb2/3)O3-x%PbTiO3 (PZN-x%PT) ferroelectric single crystals. The local domain structure and imprint of Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZN-4.5%PT) single crystals are investigated by using Piezoresponse Force Microscopy (PFM) and Switching Spectroscopy PFM (SS-PFM) techniques, respectively. The results show that the imprint depends on polarization states. It is also found that surface charge accumulation shows no significant effects on the imprint behaviour of the PZN-4.5%PT single crystals. By studying the annealed samples in the oxygen and argon atmospheres respectively, it is found that the alignment of oxygen vacancy related defect dipoles is one of the origins for the occurrence of imprint. This study provides a better understanding of the imprint phenomenon in ferroelectric materials, which is crucial for the enhancement of the reliability and the advancement of ferroelectric relaxors into the application of ferroelectric devices.

Piezoresponse Force Spectroscopy (PFS) is a powerful method widely used for measuring the nanoscale ferroelectric responses of the materials. However, it is found that certain non-ferroelectric materials can also generate similar responses from the PFS measurements due to many other factors, hence, it is believed that PFS alone is not sufficient to differentiate the ferroelectric and non-ferroelectric materials. On the other hands, this work shows that there are distinct differences in contact resonance frequency variation during the PFS measurements for ferroelectric and non-ferroelectric materials. Therefore, a new, simple and effective method is proposed to differentiate the responses from the ferroelectric and non-ferroelectric materials, this new analysis uses contact resonance frequency responses during the PFS measurements as a new parameter to differentiate the PFS measured responses from different materials., 26 pages, 6 Figures

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.

Thermoelectric (TE) polymers have unique advantages in converting heat into electricity. But their Seebeck coefficient is lower than that of inorganic TE materials by about one order of magnitude. Here, surface energy filtering is proposed to significantly enhance the Seebeck coefficient of TE polymers. The as-prepared poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, the most popular TE polymer) films from aqueous solution have a low Seebeck coefficient of 15–18 μV K−1 and a power factor of ∼0.008 μW m−1 K−2. Depositing Rhodamine 101, a zwitterion, on PEDOT:PSS films can enhance the Seebeck coefficient to 47.2 μV K−1 and the power factor to 401.2 μW m−1 K−2. The Rhodamine 101 effect on the Seebeck coefficient is consistent with its effect on the work function of PEDOT:PSS. The enhancement in the Seebeck coefficient is ascribed to the dipole moment of Rhodamine 101 and the interfacial dipole moment formed at the surface of the PEDOT:PSS films. This is confirmed by theoretical simulations. We call this mechanism surface energy filtering. Surface energy filtering can increase the mean energy of the transporting carriers and thus the Seebeck coefficient of the PEDOT:PSS films while only slightly affecting the electrical conductivity. It can thus significantly enhance the Seebeck coefficient and the power factor simultaneously.

This paper presents multiple-modes Scanning Probe Microscopy (SPM) studies on characterize the correlation of resistance switching (RS) and polarization rotation (PR) in copper doped ZnO (ZnO:Cu) thin films. Firstly, the bipolar RS behavior is confirmed by conductive Atomic Force Microscopy (c-AFM). The PR with almost 180° phase angle is confirmed by using the Piezoresponse Force Microscopy (PFM) on the same location. In addition, it elucidates that obvious PR behavior can be observed in the sample with increasing Cu concentration by combining Kelvin Probe Force Microscopy (KPFM). Furthermore, it is found that the region with downward polarization has low resistance state (LRS), whereas the region with upward polarization has high resistance state (HRS). Moreover, the Piezoresponse Force Spectroscopy (PFS) and Switching Spectroscopy PFM (SS-PFM) measurements further confirm that the existence of the built-in voltage, Vbuilt-in is largest in the ZnO:Cu (8 at.%) film deposited at the oxygen partial pressure of 2 × 10−4 Torr. The schematic diagrams of energy band diagram with varied built-in field, Ebuilt-in, polarization directions and redistributed charges are presented to explain the correlation between RS and PR behavior. Keywords: Resistive switching, Polarization rotation, Built-in voltage, ZnO:Cu thin film, Next generation memory

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.

Integrating multiple properties in a single system is crucial for the continuous developments in electronic devices. However, some physical properties are mutually exclusive in nature. Here, we report the coexistence of two seemingly mutually exclusive properties-polarity and two-dimensional conductivity-in ferroelectric Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ thin films at the LaAlO$_3$/Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ interface at room temperature. The polarity of a ~3.2 nm Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ thin film is preserved with a two-dimensional mobile carrier density of ~0.05 electron per unit cell. We show that the electronic reconstruction resulting from the competition between the built-in electric field of LaAlO$_3$ and the polarization of Ba$_{0.2}$Sr$_{0.8}$TiO$_3$ is responsible for this unusual two-dimensional conducting polar phase. The general concept of exploiting mutually exclusive properties at oxide interfaces via electronic reconstruction may be applicable to other strongly-correlated oxide interfaces, thus opening windows to new functional nanoscale materials for applications in novel nanoelectronics., Comment: Main text: 25 pages, 4 figures Supplementary note: 19 pages, 11 figures

Two-dimensional-layered materials (TDLMs) have gained enormous attention because of their open layered structures and high specific capacities in sodium ion batteries (SIBs). However, effectively s...

All-solid-state lithium metal batteries (ASSLiMB) have been considered as one of the most promising next-generation high-energy storage systems that replace liquid organic electrolytes by solid-state electrolytes (SSE). Among many different types of SSE, NASICON-structured Li1+ xAl xGe2- x(PO3)4 (LAGP) shows high a ionic conductivity, high stability against moisture, and wide working electrochemical windows. However, it is unstable when it is in contact with molten Li, hence largely limiting its applications in ASSLiMB. To solve this issue, we have studied reaction processes and mechanisms between LAGP and molten Li, based on which a failure mechanism is hence proposed. With better understanding the failure mechanism, a thin thermosetting Li salt polymer, P(AA- co-MA)Li, layer is coated on the bare LAGP pellet before contacting with molten Li. To further increase the ionic conductivity of P(AA- co-MA)Li, LiCl is added in P(AA- co-MA)Li. A symmetric cell of Li/interface/LAGP/interface/Li is prepared using molten Li-Sn alloy and galvanically cycled at current densities of 15, 30, and 70 μA cm-2 for 100 cycles, showing stable low overpotentials of 0.036, 0.105, and 0.257 V, respectively. These electrochemical results demonstrate that the interface coating of P(AA- co-MA)Li can be an effective method to avoid an interfacial reaction between the LAGP electrolyte and molten Li.

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.

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.

Sepsis-related bone diseases are rarely reported although many ICU patients are diagnosed with bone damage after prolonged immobility. In this work, cortical bone of femurs from Sprague-Dawley rats under mild sepsis condition are investigated by using Scanning Probe Microscopy (SPM) to study the influence of sepsis on the changes of structure, chemistry, and elastic modulus of bone microconstituents, i.e., collagen fibers and mineral. The results show that there are significant changes on elastic modulus, shape, and chemical composition of collagen fibers 24 h after the sepsis insult, but all of the changes are recovered to almost normal 96 h after the insult. These phenomena are found to be associated with demineralization of the collagen fiber. For the mineral constituents in bone, the elastic modulus decreases significantly 96 h after the insult, showing slower responses compared with those in the collagen fibers. Particle analysis reveals that the size of the mineral particles decreases continuously and significantly with the time after the sepsis insulting. This work reveals the responding processes of bone microconstituents to sepsis in rat mode and, hence, can provide an insight into the pathogenesis of sepsis related human bone damage.

Parametrically tuning the oscillation dynamics of coupled micro/nano-mechanical resonators through a mechanical pump scheme has recently attracted great attentions from fundamental physics to various applications. However, the special design of the coupled resonators and low dissipation operation conditions significantly restrict the wide application of this tuning technique. In this study, we will show that, under ambient conditions, mechanical pump can parametrically control the oscillation dynamics in a single commercial microcantilever resonator. A strong phonon-cavity coupling with cooperativity up to ~398 and normal-mode splitting are observed in the microcantilever. The strong parametric interaction of the phonon-cavity coupling enables using mechanical pump to achieve a 43 dB (3 dB) parametric amplification (cooling). By utilizing mechanical pump, the force sensitivity and signal-to-noise ratio of the frequency-modulation Kelvin Probe Force Microscopy can be significantly improved in the ambient environment. Furthermore, both single-mode and two-mode thermomechanical noise squeezing states can be created in the microcantilever via applying mechanical pump., Main Text includes 25 pages, 5 figures and SI includes 8 pages, 4 figures

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.

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., A heterodyne megasonic piezoresponse force microscopy (HM‐PFM) is introduced for nanoscale ferro/piezoelectric characterization. HM‐PFM specially uses 106 to 108 Hz high‐frequency excitation and heterodyne method to measure piezoelectric strain, providing a substantial improvement for the signal source issue of conventional PFM. It is believed that HM‐PFM is an excellent candidate for ferro/piezoelectric studies where conventional PFM measurements are highly controversial.

Metal–organic framework (MOF) UiO-66 nanocrystals were previously believed to be piezo-/ferroelectrically inactive because of their centrosymmetric lattice symmetries [Fm3m (225)] revealed by Powd...

Although different metal–organic framework (MOF) membranes have been widely studied for gas separation, their application for water treatment is still in its infancy. MOF membranes with improved hydrophilicity and stability are particularly essential for water/wastewater treatment. Herein, we have successfully developed heterogeneous membranes (Zn/Co-ZIF-L) composed of vertically standing leaf-like crystals of Zn-ZIF-L grown in situ onto porous ceramic supports, followed by the subsequent heterogeneous growth of Co-ZIF-L. The heterogeneous membranes show improved hydrophilicity (WCA = 13.6 ± 1.6°) and enhanced anti-bacterial adhesion. Significantly, they simultaneously deliver a relative high water flux and much improved anti-bacterial adhesion when compared with the homogeneous membranes (Co-ZIF-L and Zn-ZIF-L). The improvements are attributed to the intrinsic hydrophilic nature of Co-ZIF-L, their epitaxial growth onto Zn-ZIF-L as well as the increased surface roughness. The success of constructing a heterogeneous MOF structure shows an effective strategy to achieve the hydrophilic MOF membranes with considerably enhanced stability for water treatment.

MXenes as 2D materials have attracted great attention due to their high electrical conductivity, high surface area, high transparency in the visible range and high hydrophilicity. They have been investigated in devices and systems including batteries, supercapacitors, and sensors as well as in catalysis but not in optoelectronic devices. In this work, we studied the application of Ti3C2Tx for electron and hole collection in organic solar cells (OSCs). The work function of Ti3C2Tx can be increased by a UV–ozone treatment and decreased through a treatment with N2H4. It can be thus tuned in a range from 4.08 to 4.95 eV. MXene films with different work functions are studied as electron and hole collection buffer materials for non-fullerene organic solar cells (OSCs) with poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))] (PBDB-T) and 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC) as the active materials. The OSCs with MXenes for electron or hole collection layers can exhibit a power conversion efficiency of 9.06% or 9.02%. These efficiencies are comparable to those obtained using conventional charge-collection buffer 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.

Vanadium dioxide (VO2) undergoes an insulator to metal transition (MIT) and an accompanied phase transition from a monoclinic (M) structure to rutile (R) structure near room temperature, forming the basis for many VO2-based functional devices. The MIT transition of VO2 and the functionality of VO2-based devices can be controlled by a variety of chemical and physical stimuli. With these external stimuli, defects, such as oxygen vacancies, are often inevitably introduced. However, due to the VO system-induced challenge to synthesize stable VO2 with different oxygen vacancy concentrations, the impact of oxygen vacancies on the resistance and transition of the VO2 is not fully understood. Oxygen vacancy, as one of the typical defects in VO2, is expected to concentrate at grain boundaries, and hence a concentration gradient of oxygen vacancies may exist between the grains interior and the boundaries, and this suggests a possibility to study the effects of oxygen vacancies on the transition of VO2 by probing local phenomena at the grain boundaries. For investigating local phenomena at the grain boundaries, Scanning Probe Microscopy (SPM) techniques are effective, which allows probing the structure and various properties at the nanoscale. In this work, a series of SPM techniques, including Atomic Force Microscopy (AFM), conductive-AFM (c-AFM), Electrochemical Strain Microscopy (ESM), and Kelvin Probe Force Microscopy (KPFM), are employed to measure variations of the surface structure, the resistance, the oxygen vacancy concentration, and the work function between the grain interior and the grain boundary. It has been demonstrated that, for most cases, both the resistance and the work function are lower at the grain boundaries as a result of the accumulation of oxygen vacancies at those positions. In addition, the resistance change induced by the electric field has been observed in the deposited VO2 thin films, which may be associated with the generation/annihilation of the oxygen vacancies, rather than charge injection. This work has demonstrated the effects of oxygen vacancies in the transition of VO2 by probing the local phenomena at grain boundaries, also provided a new insight into the resistance change of VO2 under an electric field. Keywords: Fermi level, VO2 thin film, c-AFM, KPFM, ESM

Current-voltage (I-V) characteristics well reveal the resistive switching performance of materials promising for the next-generation memory-resistance random access memory (ReRAM). It has been observed that the atmospheric environment can affect the resistive switching performance, but the origin of this effect is still under debate. Conductive Atomic Force Microscopy (c-AFM) is widely used to study the resistive switching performance because of its capability to realize the resistive switching at the nanoscale that is becoming attractive as the miniaturization of memory devices. This study therefore aims to understand the effects of oxygen and moisture on the I-V characteristics of the TiO2 thin film by performing c-AFM measurements in ambient air, synthetic air, and argon gas. It is found that the oxygen in the environment can reduce the set and the reset voltages for the resistive switching, and it can also reduce the resistance at the low resistance state (LRS). Where the moisture in the environment can increase the set and reset voltages, and increase the resistance at LRS. These effects of oxygen and moisture in the environment can be attributed to the modification of the effective electric field during the resistive switching processes, which have been further confirmed by Kelvin Probe Force Microscopy (KPFM) measurements. In addition, it is found that the local ionic dynamics of TiO2 during the resistive switching are strongly dependent of the environments by performing the FORC-IV (First Order Reversal Curve-Current-Voltage) measurements in the three gas environments. Results in this work can provide a new perspective on the effect of environments on the resistive switching of materials, that is, the modulation of the effective electric field due to the adsorption of oxygen and moisture under the c-AFM tip. Keywords: Resistive switching, Environmental control, c-AFM, KPFM, FORC-IV

In this study, dopamine@BaTiO3 whiskers/P(VDF-HFP) nanocomposite films with high charge energy density were successfully prepared by a simple solution casting method. The BaTiO3 whiskers has been o...

Recent advances in Na-ion battery have made it more attractive and promising for large-scale energy storage. Emerging of Na-ion battery technology is closely associated to recent achievements in di...

Different from the signals of amplitude and phase lag in piezoresponse force microscopy (PFM) and piezoresponse force spectroscopy (PFS), the signals of the contact resonance frequency (f0) have not been clearly interpreted. Due to the complexity of the tip–sample system at the nanoscale, the relevant models and mechanisms were continuously improved in the past decades. The variation of f0 has been reported in a few previous studies, but the physical meaning of the unique variation in ferroelectric materials still needs to be investigated. Due to the imperfect tip–sample contact, the existence of a dielectric gap and screening charges causes the discontinuity in the conduction band. The evolution of the electrostatic force during the PFS measurements is significantly affected by the tip-induced ferroelectric domain evolution, resulting in the variation of the effective contact stiffness (k*) and f0. By involving the screening effect and tunneling effect in this model, the anomalies of the on-field f0 and off-field f0 can be well explained, respectively.

Ferroelectricity has been reported in organic–inorganic perovskites, and it can enhance the power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) because ferroelectricity can facilitate charge carrier separation and charge transport through the perovskite layer. However, the existence of ferroelectricity in perovskites has been in hot debate, particularly at room temperature. Here, we report the ferroelectric polarization switching of MAPb(I1−xBrx)3 which showed a high dependence on its composition. The ferroelectric behavior of MAPbI3-50% PbBr2 is confirmed with domain switching by Piezoelectric Force Microscopy (PFM) imaging and bias-off “butterfly-like” amplitude loops and piezoresponse hysteresis loops at room temperature. The possible factors, such as film electrical properties attributed to the enhanced room-temperature ferroelectricity in MAPb(I1−xBrx)3 films are clarified by using conductive atomic force microscopy (C-AFM). In addition, the charge separation and charge transport in the perovskite MAPb(I1−xBrx)3 films are further investigated by Kelvin probe force microscopy (KPFM). Finally, the possible influences of polarization orientations, trapping effects and ion migrations within the MAPb(I1−xBrx)3 films on the J–V characteristics of PSC devices are discussed in detail. It discovers that the polarization switching under the positive tip biased condition in the PSCs with 50% PbBr2, which could hinder the photovoltaic performance. These findings help better understand the electronic structure of hybrid organic–inorganic perovskites and provide guidance for the improvement of the PSC performance and other electronic applications of perovskites.

The recent epitaxial growth of monolayer PtSe2 has raised hope for its novel applications in valleytronic, spintronic, and energy-harvesting devices. Compared with 2H-phase transition-metal dichalcogenides, the 1T-phase PtSe2 is much less studied and this is especially true for its defects behaviors and their influence on electronic properties. In this article, we systemically explore the structure, stability, and kinetics of both Pt and Se vacancies in monolayer PtSe2 using first-principles calculations. By examining the relative energies of these vacancies, we identify the most stable Se/Pt single and double vacancies. In particular, we reveal a new type of Se double vacancy structure with the lowest energy. Energetically, both Se and Pt single vacancies prefer to combine to form double vacancies. All Se and Pt vacancies have remarkable influence on the electronic properties. Moreover, Pt single and double vacancies can introduce strong spin polarization in PtSe2, which may be promising for spintronic applications. These findings not only enrich the fundamental understanding of 1T-phase PtSe2 but also provide useful guidance to design PtSe2 for its optoelectronic and spintronic applications.

Formamidinium lead halide perovskite nanoparticles (FAPbBr3 NPs), because of their prominent piezoelectric properties, have drawn increasing attention in the fields of piezoelectric applications. Remarkable enhancement of piezoelectric power output is achieved from a piezoelectric composite nanogenerator by combining the FAPbBr3 NPs with poly(vinylidene fluoride) (PVDF) polymer. The FAPbBr3 NPs @ PVDF composite based piezoelectric nanogenerators show the highest outstanding outputs with voltage of 30 V and current density of 6.2 μA cm−2 for organic-inorganic lead halide perovskite material based devices. The improved performance can be ascribed to the using of PVDF, piezoelectric polymer as matrix, as well as the homogeneous distribution of FAPbBr3 NPs with enhanced stress on piezoelectric nanoparticles. The alternating energy generated from the nanogenerator can be utilized to charge a capacitor through a bridge rectifier and light up a commercial light-emitting diode (LED). Our obtained results open the feasibility of organic-inorganic lead halide perovskite materials for the design and development of high-efficiency energy harvesting applications.

Lithium ion intercalation and de-intercalation at electrodes are critically issues for development of the high performance Li-ion batteries. However, the changes of the surface morphologies, electrical and mechanical properties during the charge/discharge cycles are still not well understood. In this study, by using Atomic Force Microscopy (AFM), Electrochemical Strain Microscopy (ESM), AM-FM (Amplitude Modulation - Frequency Modulation), and conductive AFM (c-AFM) techniques, we have studied the significant changes, with nanoscale resolution, on the surface topography, electrochemical deformation, stiffness/elastic modulus, and electronic conductivity of Li-rich layered oxide cathode under the first cycle of galvonostatic charging/discharging process. This study has established the relationship between the nanoscale morphology and properties variations and the macroscopic charge/discharge processes for the Li-rich layered oxide cathode material, and the results also prove the feasibility of combining various Scanning Probe Microscopy (SPM) based techniques on the studies of lithium ion battery materials.

The bipolar resistive switching (RS) behavior of Cu doped ZnO (ZnO:Cu) thin film samples is studied by using the conductive Atomic Force Microscopy (c-AFM) technique without an electroforming process. It is found that, comparing with the undoped ZnO, both “set” and “reset” voltages are increased in the ZnO:Cu (8 at.%) thin film. The “set” and “reset” voltage are slightly increased with the significantly increased built-in voltage. It is also found that the electroforming process has no influence on the retaining of the RS behavior. In addition, the results indicate that the RS behavior can only be retained on the control of scan rate and scan time. Furthermore, in the endurance tests by using the Piezoresponse Force Microscopy (PFM) in spectroscopy mode, the results suggest that the fatigue of polarization switching has a severely influence on the film endurance performance. The correlation of polarization switching and RS is further investigated by conducting PFM measurement on the same area where c-AFM measurement was performed. The results suggest that the polarization reversal occurs when samples are in the high resistance state (HRS). Hence, the coupling mechanisms between the polarization and RS behavior in ZnO:Cu thin film are studied.

This paper presents the in situ mapping of temperature-dependent lithium-ion diffusion at the nanometer level in thin film Li1.2Co0.13Ni0.13Mn0.54O2 cathode using electrochemical strain microscopy. The thin-film Li1.2Co0.13Ni0.13Mn0.54O2 cathode exhibits higher lithium-ion diffusivities with increasing temperature, which explains the higher capacity observed in the lithium-ion batteries with a Li-rich cathode at elevated temperature. In addition, the activation energy for lithium-ion diffusion can be extracted in an Arrhenius-type plot at the level of grain structure with the assumption that the ionic movement is diffusion controlled. Compared with the grain interiors, the grain boundaries show relatively lower activation energy; hence, it is the preferred diffusion path for lithium ions. This study has bridged the gap between atomistic calculations and traditional macroscopic experiments, showing direct evidence as well as mechanisms for ionic diffusion for Li-rich cathode material.

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.

Though plasmonic effect is making some headway in the energy harvesting realm, its fundamental charge transfer mechanism to a large extent is attributed to the hot-carrier generation at the contact interface. Herein this work attempts to elucidate the physical origin of light induced plasmo-pyroelectric enhancement based on charge density manipulation on surface state in the vicinity of the metal-ferroelectric contact interface. More importantly, by tuning the band bending, it is shown that the charge density on the surface state of a hybrid plasmo-pyroelectric (BaTiO3 -Ag) nanosystem can be manipulated and largely increased under the resonant blue light illumination (363 nm). It is also demonstrated that owing to this effect, the spatial pyroelectric activity of a hybrid plasmo-pyroelectric nanosystem governs 46% enhancement in pyroelectric coefficient. This research highlights the optically regulated charge density in plasmo-pyroelectric nanosystems, which could pave a new avenue for energy harvesting/conversion devices with distinguished advantages in wireless, photonic-controlled, localized, and dynamic stimulation.

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.