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In recent years, potassium-ion batteries(KIBs)have received a lot of attention for their high energy density and low cost. However, a suitable anode is currently lacking. In this paper, to explore potential anode materials, PC3 monolayer was predicted using first-principles. The calculation results show that the PC3 monolayer is stiff and conductive after adsorbed K atoms. The adsorbed K atoms have small migration energy of 0.09 eV which provides a good charge/discharge rate. And the KIBs with PC3 monolayer anode shows high capacity (1200 mAh g−1) and low open-circuit voltage (OCV) (0.11 V) offering high energy density. At a maximum capacity of 1200 mAh g−1, the PC3 monolayer shows only small deformation and volume changes. The results predict PC3 monolayer would make a good material selection for potassium battery anodes.

Although the lithium-sulfur battery has a high theoretical specific capacity (1675 mAh g−1), its actual capacity is low, and the cycle stability is poor, because the active material undergoes the polarity and the nonpolarity transformation in the battery discharge/charge reaction. There are obvious limitations of using single polar or nonpolar binding, and it is needed to effectively combine the polar materials to the nonpolar matrix/sulfur. Here, we mechanically mixed 1-ethyl-3-methylimidazolium dicyanamide (Emim-dca)-based pore-making polar carbon (P-ILC) with nonpolar cotton carbon activated by KOH/sulfur (CKOH/S) to study the influence of the polar mixture on specific capacity and cycle stability of the battery. Comparing with the nonpolar cathode, the nonpolar-polar cathode has better electrochemical performance. The CKOH/S cathode with polar mixture of P-ILC shows a higher specific capacity (500 mAh g−1 at 100th 1C) and cyclic stability (average attenuation 0.34%). It is because the P-ILC+CKOH/S effectively combines the nonpolar physical binding and polar chemical anchoring by using the method of zonal binding of active materials.

Two-dimensional ferroelectric materials can maintain stable polarization with atomic layer thickness, and they have a wide range of technological applications in transistors, resistive memories, energy collectors and other multi-functional sensors for highly integrated flexible electronics. Domain evolution should be considered when 2d ferroelectric material-based devices are applied in a radiation environment, which may induce radiation damage and performance degradation. In this work, we investigate the domain evolution and photodetection performance degradation of α-In2Se3 nanoflakes induced by the total dose effect of 60Co γ-rays. The phonon modes change with an increase in total dose, while the domain structure changes in α-In2Se3 based transistors. Domain evolution may be one of the main reasons for the photoresponsivity degradation of these transistors. This investigation can provide a solid base for future research, and immediate applications in 2d ferroelectric material-based devices can be contemplated.

We present herein a modified cold sintering process (CSP) for BaTiO3 ceramics using a surface coating at the particle surface which could enhance the relative density of BaTiO3 up to ∼93.5% at 220 °C and 500 MPa. The surface coating greatly enhances the ceramic density, mainly because it facilitates the dissolution–precipitation process during CSP. Ba vacancies form at the surface of the coated powders, so Ba(OH)2 solution is used to compensate Ba ions in the as-cold-sintered ceramics, which increases the dielectric permittivity. Post-annealing at 700 and 900 °C increases the relative density to 97%, and the resulting relative dielectric permittivities are 810 and 1550, respectively, at room temperature and 1 kHz. This technique may also be extended to materials with very small, incongruent solubility in water or volatile solutions that use the cold sintering process.

The discovery of layered two-dimensional (2D) ferroelectric materials has promoted the development of miniaturized and highly integrated ferroelectric electronics. The 2D ferroelectric materials can be applied in a radiation environment, in which the effect of radiation on these materials should be considered. However, the effects of radiation on 2D ferroelectric materials may be entirely different from those on traditional ferroelectric materials. Ionization effect-induced domain switching can be recovered by applying an external electric field, whereas the displacement effect initiated by radiation particles produces crystal structure damage. The displacement damage that is extremely difficult to recover may have a negative impact on the application of 2D ferroelectric materials in a radiation environment. In this study, the effect of displacement induced by neutron irradiation on the promising α-In2Se3 nanoflakes was investigated. Neutron irradiation (1 MeV) with a fluence of 1014 cm-2 was used for avoiding ionization effects in a certain range. Although the topography of α-In2Se3 does not change underneutron irradiation, vacancies have been proved to be induced by neutron irradiation; furthermore, it has been identified that the vacancies mostly originate from the loss of In atoms. The out-of-plane (OOP) and in-plane (IP) domain structures of the α-In2Se3 nanoflakes with a few layers only slighlty change. In addition, the polarization of the irradiated nanoflakes could still be reversed. All these findings show that although the vacancies may influence the band structure and polarizaiton values of α-In2Se3, the ferroelectric performance may have a strong resistance to neutron irradiation. Therefore, our investigation implies that α-In2Se3 is an excellent 2D ferroelectric material for application in radiation-resistant electronic devices in the future.

The negative differential resistance (NDR) effect enables multilevel storage and gradual resistance modulation in resistive switching (RS) devices to be achieved. However, the poor reproducibility of NDR is the obstacle that restricts their application because the appearance of the NDR effect in RS devices is usually accidental or unstable at room temperature. In this report, we demonstrate a polarization and interfacial defect modulated NDR effect in h-LuFeO3/CoFe2O4 heterojunction-based RS devices; especially, the NDR is reproducible after hundreds of cycles at room temperature. This research provides an effective way for realizing the reproducible NDR effect in ferroelectric RS devices, and it may promote the development and application of RS devices with the NDR effect.

Topologically nontrivial polar structures are not only attractive for high-density data storage, but also for ultralow power microelectronics thanks to their exotic negative capacitance. The vast majority of polar structures emerging naturally in ferroelectrics, however, are topologically trivial, and there are enormous interests in artificially engineered polar structures possessing nontrivial topology. Here we demonstrate reconstruction of topologically trivial strip-like domain architecture into arrays of polar vortex in (PbTiO3)10/(SrTiO3)10 superlattice, accomplished by fabricating a cross-sectional lamella from the superlattice film. Using a combination of techniques for polarization mapping, atomic imaging, and three-dimensional structure visualization supported by phase field simulations, we reveal that the reconstruction relieves biaxial epitaxial strain in thin film into a uniaxial one in lamella, changing the subtle electrostatic and elastostatic energetics and providing the driving force for the polar vortex formation. The work establishes a realistic strategy for engineering polar topologies in otherwise ordinary ferroelectric superlattices., The majority of polar structures emerging naturally in ferroelectrics are topologically trivial. Here, the authors demonstrate reconstruction of topologically trivial strip-like domain architecture into arrays of polar vortex in (PbTiO3)10/(SrTiO3)10 superlattice.

Non-polar porous carbon/doped polar carbon composite hosts have been proved effective for sulfur in lithium–sulfur (Li–S) battery. Pores in carbon can adsorb sulfur and Li2S, and nitrogen–doped surface shows a stronger affinity for polysulfides through additional chemisorptions. However, how the physical properties of doped carbon, e.g., surface area and porosity, affect the performance of the non-polar carbon/doped polar carbon composite hosts is unknown. Herein, we reported the cotton-derived carbon/porous 1-ethyl-3-methylimidazolium dicyanamide (Emim-dca) derived N-doped carbon, named C/PNC, and the cotton-derived carbon/imporous Emim-dca derived N-doped carbon, named C/NC. The surface area and porosity of the doped polar carbon in C/PNC and C/NC are controlled. The higher surface area of N-doped carbon makes more surface of cotton-derived carbon coated and more sulfur located on the surface of composite hosts. The micro-mesopores in the N-doped carbon can restrain sulfur but shows slow reactive kinetics at a higher current rate. The C/PNC cathode showed a higher discharge capacity of 1100 mAh g−1 than that of 1027 mAh g−1 for the C/NC cathode at 0.1 C and a lower capacity of 208.1 mAh g−1 than that of 349.2 mAh g−1 for C/NC cathode at 2 C.

Nontrivial topological structures offer a rich playground in condensed matters and promise alternative device configurations for post-Moore electronics. While recently a number of polar topologies have been discovered in confined ferroelectric PbTiO3 within artificially engineered PbTiO3/SrTiO3 superlattices, little attention was paid to possible topological polar structures in SrTiO3. Here we successfully create previously unrealized polar antivortices within the SrTiO3 of PbTiO3/SrTiO3 superlattices, accomplished by carefully engineering their thicknesses guided by phase-field simulation. Field- and thermal-induced Kosterlitz–Thouless-like topological phase transitions have also been demonstrated, and it was discovered that the driving force for antivortex formation is electrostatic instead of elastic. This work completes an important missing link in polar topologies, expands the reaches of topological structures, and offers insight into searching and manipulating polar textures. While the role of PbTiO3 in PbTiO3/SrTiO3 superlattices has been widely studied, little attention is paid to possible polar topologies in SrTiO3. Here, the authors create atomic-scale vortex–antivortex pairs in the superlattices, expanding the understanding of topological structures.

Perovskite solar cells (PSCs) have been developed rapidly in recent years, representing the most promising candidates for photovoltaics. Regarding their application in spacecraft, it is essential to exploring the space radiation tolerance of PSCs. In this paper, the mechanism of performance degradation of ternary cation (methylammonium (MA), formamidinium (FA) and cesium (Cs)) lead trihalide perovskite planar heterojunction (PHJ) solar cells under gamma-ray radiation was analyzed layer by layer. The results demonstrate that PSCs experience obvious performance degradation under gamma-ray irradiation, especially undergoing apparent recession of short-circuit current density (Jsc) and accordingly power conversion efficiency (PCE). They are mainly attributed to the phase transition of perovskite films and the color appearance of the glass substrate induced by the irradiation, deteriorating the perovskite film absorbance and the substrate transmittance. These results serve as a strong necessity to improve the stability of PSCs for the future application in aerospace.

Hierarchical polydomain nanostructures, usually formed in epitaxial films, serve to fully relax the misfits between the film and substrate, as well as the strains between the poly-twin variants of the film material. The minimization of the elastic energy endows this type of structure superior stability over other domain architectures. However, the existence of energetically degenerate polytwin variants and their intersecting domain boundaries often led to undesirable functional properties in non-engineered films. Here we show that such nanostructures in epitaxial perovskite ferroelectric films can be crystallographically engineered to eliminate intersecting domain boundaries, thereby achieving an improved ferroelectric performance. In addition to a reduced coercive field and increased dielectric and piezoelectric responses, this type of ferroelectric polydomain nanostructure shows an enhanced ferroelectric polarization with a substantially improved fatigue resistance, as opposed to non-engineered nanostructures with intersecting domain boundaries. These findings suggest an alternative route for the fabrication of highly-reliable nonvolatile ferroelectric memory devices, and may find broader applications in piezoelectrics and energy storage.

As the next generation battery, the lithium-sulfur battery with high theoretical specific capacity and energy density needs to overcome the low practical discharge capacity and the poor cycle performance for the poor conductivity of sulfur and the shuttle effect of polysulfide. In this study, a hierarchical micro-mesoporous carbon (HPC) is designed and synthesized as a sulfur host from the cotton textile with KOH activation at 700 °C to combine the advantages of these two structures, where mesoporous structure can improve the infiltration of electrolyte to act as fast ionic channel and micropores have an excellent ability of binding sulfur. The HPC showed an excellent high specific surface area (2835.47 m2 g−1) and a high pore volume (2.82 cm3 g−1), and the ratio of the mesoporous reaches 57.85%. The sulfur in HPC/S was uniformly distributed in the host structure and no surface crystallization was observed by TEM characterization. Assembled in the lithium-sulfur battery, the cathode mixed with HPC/S and conductive agent delivers an initial discharge capacity of 1577 mAh g−1 at 0.1C, and a reversible capacity of 434.5 mAh g−1 after 300 cycles at the current rate of 1C.

Resistive switching devices based on ferroelectric two-dimensional (2D) van der Waals (vdW) nanomaterials may display simple structures, high density, high speed, and low power consumption, and can be used in flexible electronics and highly integrated devices. However, only a few studies about the in-plane (IP) resistive switching behavior of ferroelectric 2D vdW nanomaterials have been reported because it is very hard to achieve asymmetric barriers only by tuning the IP polarization directions when the electrodes of the planar device are all of the same type. In the current work, we developed a planar device based on an α-In2Se3 nanoflake, in which the IP/OOP (out-of-plane) polarization, free carriers and oxygen vacancies in SiO2 contribute to the resistive switching behavior of the device. This behavior of the device was shown to be affected by exposure to light, and the photoelectric performance was also investigated when the device was in the OFF state. The demonstration of this planar resistive switching device may promote the further development of resistive devices based on 2D vdW nanomaterials, and provide great inspiration for the development of new kinds of transistors.

In multiferroics, electromagnons have been recognized as a noticeable topic due to their indispensable role in magnetoelectric, magnetodielectric, and magnetocapacitance effects. Here, the electromagnons of Bi1−xNdxFeO3 (x = 0–0.2) nanoparticles are studied via terahertz time-domain spectroscopy, and the impacts of doping concentrations on electromagnons have been discussed. We found that the electromagnons in Bi1−xNdxFeO3 nanoparticles are associated with their phase transition. The total coupling weight of electromagnons is gradually increased in polar R3c structures and then reduces in the antipolar Pbam phase, and the weight in the antipolar phase is less than that of the pure R3c phase. Interestingly, a colossal electromagnon is observed at polar–antipolar and antiferromagnetic–ferromagnetic phase boundaries. Our work offers an avenue for designing and choosing materials with better magnetodielectric and magnetocapacitance properties.

Here, the Ag/amorphous Bi3.15Nd0.85Ti3O12/Pt resistive switching memories were designed and prepared, and the total ionizing dose (TID) effects of 60Co γ-ray on the Ag/amorphous Bi3.15Nd0.85Ti3O12/Pt resistive switching memories were investigated. The results show that the resistance in low resistance state (LRS), resistance in high resistance state (HRS), and set voltage are almost immune to a TID up to 1 Mrad(Si), whereas the reset voltage and forming voltage are impacted slightly. The good radiation immunity is related to the metallic conductive filaments and the amorphous Bi3.15Nd0.85Ti3O12 matrix. These results suggest that the Ag/amorphous Bi3.15Nd0.85Ti3O12/Pt devices show potential for radiation-hard electronics applications.

Transparent flexible electronics have captured tremendous attention as the next-generation of electronic devices. Recently, flexible devices for wearing are in high demand in practical applications under special circumstances, such as aeronautics and astronautics, which require highly-transparent and large-scale flexibility, as well as stability at elevated temperature. Here, highly transparent, epitaxial Pb(Zr0.1Ti0.9)O3 (PZT) ferroelectric thin films were fabricated on Sn-doped In2O3 (ITO) transparent electrodes on yttria-stabilized zirconia (YSZ) bufferred mica substrate using pulsed laser deposition. The structural, optical, mechanical, and electrical properties of these all-oxide heterostructures of the PZT/ITO/YSZ/mica were studied. The heteroepitaxy exhibit a high transmittance and an excellent remarkable mechanical properties with robust operation in bending cycle tests. Moreover, the electrical properties are examined to show the preservation of the primitive properties of PZT. Various bending tests are performed to show the tunability of functionalities and to confirm that the heterostructures retain the physical properties under repeated cycles at high temperature. These results demonstrated that these high-performance transparent flexible capacitors would open a route for the applications in transparent flexible devices under harsh conditions.

Insect mitochondrial DNA (mtDNA) ranges from 14 to 19 kbp, and the size difference is attributed to the AT-rich control region. Jewel wasps have a parasitoid lifestyle, which may affect mitochondria function and evolution. We sequenced, assembled, and annotated mitochondrial genomes in Nasonia and outgroup species. Gene composition and order are conserved within Nasonia, but they differ from other parasitoids by two large inversion events that were not reported before. We observed a much higher substitution rate relative to the nuclear genome and mitochondrial introgression between N. giraulti and N. oneida, which is consistent with previous studies. Most strikingly, N. vitripennis mtDNA has an extremely long control region (7665 bp), containing twenty-nine 217 bp tandem repeats and can fold into a super-cruciform structure. In contrast to tandem repeats commonly found in other mitochondria, these high-copy repeats are highly conserved (98.7% sequence identity), much longer in length (approximately 8 Kb), extremely GC-rich (50.7%), and CpG-rich (percent CpG 19.4% vs. 1.1% in coding region), resulting in a 23 kbp mtDNA beyond the typical size range in insects. These N. vitripennis-specific mitochondrial repeats are not related to any known sequences in insect mitochondria. Their evolutionary origin and functional consequences warrant further investigations.

The ability to electrically write magnetic bits is highly desirable for future magnetic memories and spintronic devices, though fully deterministic, reversible, and nonvolatile switching of magnetic moments by electric field remains elusive despite extensive research. In this work, we develop a concept to electrically switch magnetization via polarization modulated oxygen vacancies, and we demonstrate the idea in a multiferroic epitaxial heterostructure of BaTiO3/Fe3O4 fabricated by pulsed laser deposition. The piezoelectricity and ferroelectricity of BaTiO3 have been confirmed by macro- and microscale measurements, for which Fe3O4 serves as the top electrode for switching the polarization. X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra indicate a mixture of Fe2+ and Fe3+ at O h sites and Fe3+ at T d sites in Fe3O4, while the room-temperature magnetic domains of Fe3O4 are revealed by microscopic magnetic force microscopy measurements. It is demonstrated that the magnetic domains of Fe3O4 can be switched by not only magnetic fields but also electric fields in a deterministic, reversible, and nonvolatile manner, wherein polarization reversal by electric field modulates the oxygen vacancy distribution in Fe3O4, and thus its magnetic state, making it attractive for electrically written magnetic memories.

Three-dimensional heterogeneous nanocomposites exhibit eminent cycling stability and rate capability as electrode materials for lithium-ion batteries. In this work, the composites of MoS2 nanosheets uniformly coated TiO2 nanowire arrays are fabricated by a glucose-assisted hydrothermal approach. The usage of glucose can be favorable to the uniform growth of MoS2 morphology. As anode materials for lithium ion batteries, the composites exhibit good specific capacity, cycling stability and rate capacity. The enhanced electrochemical properties are attributed to uniformity of composites since the uniform composites can effectively integrate the good cycling stability of TiO2 nanowire arrays and high capacity of MoS2 nanosheets. The gentle synthesis procedure and excellent electrochemical properties make TiO2 nanowire@MoS2 nanosheet arrays promising in high-performance lithium-ion batteries.

The toxicity and the instability of lead-based perovskites might eventually hamper the commercialization of perovskite solar cells. Here, we present the optoelectronic properties and stability of a two-dimensional layered (C6H5CH2NH3)2CuBr4 perovskite. This material has a low Eg of 1.81 eV and high absorption coefficient of ∼1 × 105 cm–1 at the most intensive absorption at 539 nm, implying that it is suitable for light-harvesting in thin film solar cells, especially in tandem solar cells. Furthermore, X-ray diffraction (XRD), ultraviolet–visible (UV–vis) absorption spectra, and thermogravimetric analysis (TGA) confirm the high stability toward humidity, heat, and ultraviolet light. Initial studies produce a mesoscopic solar cell with a power conversion efficiency of 0.2%. Our work may offer some useful inspiration for the further investigation of environment-friendly and stable organic–inorganic perovskite photovoltaic materials.

The three-dimensional heterostructured photoanode is considered to be an effective way to solve the problems of insufficient specific surface area and high electron recombination rate from one-dimensional nanomaterials. By combining the advantages of nanorods and nanosheets, we construct a novel TiO2 nanorod arrays/ZnO nanosheets (TNRAs/ZNSs) heterostructure as the photoanode in quantum-dot-sensitied solar cells (QDSSCs) by a controllable chemical bath deposition method at an appropriate temperature. The photoelectrochemical properties are measured by UV–Vis absorption spectra, current density–voltage (J-V), open-circuit voltage attenuation test (V-t) and electrochemical impedance spectroscopy (EIS). The results reveal that the TNRAs/ZNSs photoanode has larger specific surface area and slower electronic recombination rate, and its power conversion efficiency increases by 260% compared with TNRAs-based QDSSCs. This three-dimensional heterostructure exhibits distinct advantages and we believe that it can be used in other photoelectronic devices.

Here we demonstrate the synthesis of graphene directly on SiC substrates at 900 °C using ion beam mixing technique with energetic carbon cluster ions on Ni/SiC structures. The thickness of 7–8 nm Ni films was evaporated on the SiC substrates, followed by C cluster ion bombarding. Carbon cluster ions C4 were bombarded at 16 keV with the dosage of 4 × 1016 atoms/cm2. After thermal annealing process Ni silicides were formed, whereas C atoms either from the decomposition of the SiC substrates or the implanted contributes to the graphene synthesis by segregating and precipitating process. The limited solubility of carbon atoms in silicides, involving SiC, Ni2Si, Ni5Si2, Ni3Si, resulted in diffusion and precipitation of carbon atoms to form graphene on top of Ni and the interface of Ni/SiC. The ion beam mixing technique provides an attractive production method of a transfer-free graphene growth on SiC and be compatible with current device fabrication.

Stoichiometric gallium ferrite (GFO) is a promising single-phase multiferroic material at room temperature. Nevertheless, simultaneous magnetism and ferroelectricity in a single GFO at room temperature has not been demonstrated yet. In this work, single-phase GFO thin films with different amount of excessive Fe have been successfully grown using a dual target pulsed laser deposition (PLD) process, and the magnetic transition temperature is found to be above room temperature with excessive Fe distributed among the available cation sites of GFO unit cell. Ferroelectricity of GFO films have been confirmed by second harmonic generation (SHG), polarization hysteresis, pyroelectric reversal, and piezoresponse force microscopy (PFM), and magnetoelectric (ME) coupling has been demonstrated by increase in piezoresponse induced via external magnetic field applied in-plane, all measured at room temperature. From the data, it is theorized that the magnetic properties of GFO originate from the superexchange interaction mediated via the Fe1-O-Fe2 bond, and an additional Fe1-O-Fe* bond can form from excess Fe atoms. Under a magnetic field applied along c axis, the magnetic moment of Fe2 and Fe* increase while that of Fe1 decreases, and these changes in magnetic moment result in larger distortion of Fe2 and Fe* octahedrons along the b-axis, and thus enhanced polarization and piezoresponse. This series of studies thus confirm single-phase GFO with excessive Fe as a multiferroic material at room temperature with ME coupling, paving way for its potential functional applications in microelectronic and spintronic devices.

Ferroelectric films epitaxially grown on vicinal substrates have been widely researched in recent decades for their unprecedented performance tuned by the surface-step-terrace (SST) induced strains of substrates. Here, BaTiO3 films are epitaxially grown on miscut (001) SrTiO3 substrates with different miscut angles of 0°, 0.2°, 1°, and 2°, and the impacts of SST-induced strains on the second-order nonlinear optical coefficients are discussed by fitting the measured second harmonic generation (SHG) signals from the films. The results show that different miscut angles of the substrates can bring about different SST strain states in the BTO films, which make different contributions on the second-order nonlinear optical coefficients. These results disclose that the second-order nonlinear optical coefficients can be effectively controlled by SST induced strains, which provides a new way to tune the optical properties of functional oxide thin films.

Magnetic nanopillars are promising for a variety of technological applications, though the template-free fabrication of magnetic nanopillar arrays with good crystallinity and uniform distribution remains a substantial challenge. Herein, we report successful fabrication of a regular array of CoFe2O4 (CFO) nanopillars using an elaborately designed dual-target pulsed laser deposition (PLD) process, which exhibit a truncated pyramid surface with consistent size and orientation as well as uniform distribution. Detailed X-ray diffraction, scanning transmission electron microscopy and X-ray photoelectron spectroscopy demonstrate the high quality nature of the CFO nanopillars, while vibrating sample magnetometer and magnetic force microscopy studies confirm their room temperature magnetism. This dual-target PLD process takes advantage of BiFeO3 decomposition, and the subsequent formation of CFO nanopillars requires no template, giving us a powerful technique to prepare oxide nanopillars with desired composition and functional properties.

Flexible electronics have attracted long-standing attention in today's energy-conscious world. Among the flexible electronics, the flexible ferroelectric tunnel junction can realize non-destructive readout and consume less energy, and it may be a very promising device owing to the advantages of excellent portability, bendability and being lightweight. However, few flexible ferroelectric tunnel junctions with good performance have been reported because the inorganic materials with good ferroelectric properties always have a high crystallization temperature, which restricts the flexible substrate selection. In this report, we report a flexible ferroelectric tunnel junction that is based on PbZr0.52Ti0.48O3 film grown on mica with a bottom electrode of SrRuO3 film. The flexible ferroelectric tunnel junction of asymmetric structure not only can achieve nondestructive readout, but it also has good bendability. Especially, the on/off ratio of the junction averages about 1.08 × 104%. The application of flexible ultrathin ferroelectric film is beneficial to realize flexible ferroelectric electronic devices that are integrated with flexible circuit systems in modern microelectronics.

Recently, Sn-based two-dimensional layered halide perovskites(Sn-2DLHP) with fine light-harvesting performances and longstanding stabilities have attracted considerable interests. However, the impact of thickness on the optoelectronic properties of Sn-2DLHP is still insufficiently known. In this work, we take BA2SnI4(BA=C4H9NH3+) as a representative to present theoretical studies of electronic structure, carrier mobilities, optical absorption, and exciton-binding energy to reveal the effect of thickness on the optoelectronic properties of Sn-2DLHP. Results show that the 2D-layered BA2SnI4 are direct bandgap semiconductors with absorption coefficients of up to 105 cm−1 and appreciable carrier mobilities, which all can be significantly modified by tuning thickness. Notably, the 2D-layered BA2SnI4 have large and thickness-dependent exciton-binding energies, indicating the 2D-layered BA2SnI4 may have more application potential in optoelectronic devices. Our theoretical work paves a theoretical foundation of potential applications for other Sn-2DLHP in optoelectronic devices.

Ferroelectric semiconductors splitting water reactions have presented a new paradigm in improving conversion efficient of solar energy into electricity or fuel. Here, we show the switchable photoelectrochemical response controlled by ferroelectric polarization in (101)-oriented Pb(Zr0.2Ti0.8)O3 (PZT) epitaxial films prepared on the (110) SrTiO3 substrate with SrRuO3 as bottom electrodes. Photoelectrochemical (PEC) measurements exhibit that the switchable photocurrent response can be observed in the PZT/SRO heterostructures photo-electrode. Moreover, under illumination, the switchable photocurrents of the PZT/SRO electrode present high repeatability and non-volatility, which only depend in the ferroelectric polarization direction of the PZT film. The result indicates that the PZT/SRO electrode may be as a photoanode or photocathode only through poling treatment with the external electric field. We suggest that the internal electric field and depletion region by ferroelectric polarization at the PZT film is mainly responsible for the switchable PEC effect. The study indicates that this ferroelectric photo-electrode material may have potential applications in solar water splitting, and specially in the PEC sensing and any other smart photo-responsive systems. Keywords: Switchable PEC effect, Ferroelectric polarization, Poling treatment, PZT thin film, Photo-electrode, Water splitting

In this paper, the epitaxial hexagonal LuFeO3 (h-LuFeO3) thin films with c-axis-oriented single phase, smooth surface were grown on YSZ (111) substrates by pulsed laser deposition method. Furthermore, a structural distortion of increased lattice constant of c is found in the epitaxial h-LuFeO3 thin films. Moreover, the epitaxial h-LuFeO3 thin films show room-temperature ferromagnetism. The coercive field and remnant magnetization of the epitaxial h-LuFeO3 thin film decrease with the increase in the test temperature from 50 to 300 K. The study would be of benefit to the room-temperature single-phase multiferroic materials.

Organic/inorganic hybrid materials can be promising thermoelectric materials due to the possibilities of achieving high electrical conductivity and low thermal conductivity, which are necessary for their potential application in heat–electricity conversion. In this work, we show that the new n-type organic/inorganic hybrid C6H4NH2CuBr2I can simultaneously exhibit a high electrical conductivity of ∼3.6 × 103 S cm−1 and a Seebeck coefficient of ∼−70 μV K−1 at room temperature in a thin-film design, presenting the highest power factor reaching 1740 μW mK−2. The temperature dependence of both the electrical conductivity and Seebeck coefficient in this C6H4NH2CuBr2I film illustrates that this organic/inorganic hybrid film behaves like a metallic material. The high electrical conductivity of the C6H4NH2CuBr2I film can be attributed to the defect-related heavy doping caused by CuI in this semiconductor, while the relatively large Seebeck coefficient is due to the coexisting entropy difference and polarization difference. The temperature-dependent polarization difference between the hot and the cold side of the film can function as an additional driving force besides the entropy difference and contribute to the Seebeck effect development in C6H4NH2CuBr2I. When applying a temperature difference of 4.8 °C along the in-plane direction, the C6H4NH2CuBr2I film with gold contacts generates a thermoelectric voltage of −0.31 mV and a thermoelectric current of −0.022 mA, suggesting a promising n-type thermoelectric material for heat–electricity conversion in thermoelectric power generators.

In this work, hollow structured V2O5 microspheres were fabricated from solid vanadium precursor microspheres which were prepared by microwave-assisted, solvothermal approach. In the annealing process, the spherical precursor microspheres can be converted into hollow microspheres, serving as a sacrificial template. The synthesis approach is quite different from the previously reported approaches for the preparation of hollow structured V2O5 microspheres. As cathode materials for lithium ion batteries, the hollow-structured V2O5 microspheres exhibit high capacity and good rate capability. The electrodes deliver specific discharge capacities of 132 and 113 mA h g−1 at the current densities of 1 C and 8 C, respectively.

Multilevel data ferroelectric storage memory is a breakthrough for addressing low density in ferroelectric random access memories. However, the application of the multilevel data ferroelectric storage memory is limited by high cost and difficulty to prepare high quality epitaxial films. Herein, we create a multilevel data ferroelectric storage memory with a non-epitaxial ferroelectric ultrathin film to overcome these issues. Through controlling the polarization switching and oxygen vacancy migration with the voltage pulses, we demonstrated that voltage-controlled barrier heights yield a memristive behavior with resistance variations. Moreover, we achieved eight logic states, which are written and read easily. Our results suggest new opportunities for ferroelectrics as high density non-volatile memories.

Ferroelectric resistive switching memory is a non-destructive and easy to achieve multilevel storage, which is a breakthrough for further improving the density in the random access memory. However, the application of ferroelectric resistive switching memory is limited by the high operating voltage, the low switching ratio or slow write/read speed. Herein, we show a type of memristor with a thin ferroelectric film, the device can switch its resistance states by controlling the oxygen vacancy migration in the effect of an external electric field. The device still exhibits stable resistive switching phenomena after an endurance test of about 100 cycles and has high switch ratio about 108% and good retention about 1.7 × 105 s. Furthermore, the device has the potential of being a multi-states memory with a low write voltage below 2 V and a fast write/read speed of about 5 μs. Our results suggest new opportunities for the development of high storage density nonvolatile memory.

Multi-state storage memory is a breakthrough for further improving the density in random access memory. However, the low switching ratio and high operating voltage limit the application of multibit-storage. Herein, we report a kind of four state memory with low operating voltage, in which the four states are caused by polarization switching and filament forming/rupture. In the switching of the four states, the electronic transport mechanisms of the device switch between thermionic injection and electron tunneling. Especially, the four states can be written/erased feasibly and distinguished clearly in the reading processes. It shows strong promise for the application of high storage density nonvolatile memory.

Neuromorphic computing has the potential to accelerate high performance parallel and low power in-memory computation, artificial intelligence, and adaptive learning. Despite emulating the basic functions of biological synapses well, the existing artificial electronic synaptic devices have yet to match the softness, robustness, and ultralow power consumption of the brain. Here, we demonstrate an all-inorganic flexible artificial synapse enabled by a ferroelectric field effect transistor based on mica. The device not only exhibits excellent electrical pulse modulated conductance updating for synaptic functions but also shows remarkable mechanical flexibility and high temperature reliability, making robust neuromorphic computation possible under external disturbances such as stress and heating. Based on its linear, repeatable, and stable long-term plasticity, we simulate an artificial neural network for the Modified National Institute of Standards and Technology handwritten digit recognition with an accuracy of 94.4%. This work provides a promising way to enable flexible, low-power, robust, and highly efficient neuromorphic computation that mimics the brain.

With the energy density of intercalation electrodes approaching the ceiling, there are tremendous interests in developing metal oxide conversion type electrodes for lithium ion batteries, which involve more lithium ions in electrochemical reactions. Nevertheless, the cyclic and rate performances of conversion electrodes are rather poor, due to their large volume changes during charging and discharging, poor contact with current collector, and accumulated internal passivation over cycling. Here by carefully designing epitaxial array of Fe3O4 nanodots as a binder-free conversion electrode, we accomplish excellent rate performance under current density as high as 60C with long cycling life and good capacity, and the detailed scanning transmission electron microscopy in combination with comprehensive electrochemical analysis suggest that the success can be attributed to the synergic effects of released internal stress, slowed internal passivation, and good structure integrity all rendered by the nanodot array architecture of Fe3O4. Our study thus overcome materials breakdown, contact failure, and internal passivation of conventional conversion electrodes, providing new insight into optimizing conversion electrodes for practical applications.

In this work, high pressure effect on the structure, mechanical and electronic properties of Mo2ScAlC2 has been investigated with first-principles method. Results show that Mo2ScAlC2 is much more compressible along a axis than along c axis. Besides, mechanical properties are explored. Elastic constants and moduli creep up with the increasing pressure. Especially, the sharp increment of C33 also predicts a strong resistance to the compression strain along c axis. With the increasing of pressure, Mo2ScAlC2 change from brittle to ductile. Furthermore, the electronic analysis indicates that Mo2ScAlC2 is predicted to be metallic and the metallicity of Mo2ScAlC2 reduces gradually with the increase of pressure. Finally, the deformation charge density distribution indicates that Sc-atom provides more electrons to C-atom obtains with increasing pressure.

We report accurates and informative measurement with subunit cell resolution for local polarization distribution in ferroelectrics., Recently, several captivating topological structures of electric dipole moments (e.g., vortex, flux closure) have been reported in ferroelectrics with reduced size/dimensions. However, accurate polarization distribution of these topological ferroelectric structures has never been experimentally obtained. We precisely measure the polarization distribution of an individual ferroelectric vortex in PbTiO3/SrTiO3 superlattices at the subunit cell level by using the atomically resolved integrated differential phase contrast imaging in an aberration-corrected scanning transmission electron microscope. We find, in vortices, that out-of-plane polarization is larger than in-plane polarization, and that downward polarization is larger than upward polarization. The polarization magnitude is closely related to tetragonality. Moreover, the contribution of the Pb─O bond to total polarization is highly inhomogeneous in vortices. Our precise measurement at the subunit cell scale provides a sound foundation for mechanistic understanding of the structure and properties of a ferroelectric vortex and lattice-charge coupling phenomena in these topological ferroelectric structures.

Domain orientations and their volume ratios in ferroelectrics are recognized as a compelling topic recently for domain switching dynamics and domain stability in devices application. Here, an optimized second harmonic generation method has been explored for ferroelectric domain characterization. Combing a unique theoretical model with azimuth-polarization-dependent second harmonic generation response, the complex domain components and their distributions can be rigidly determined in ferroelectric thin films. Using the proposed model, the domain structures of rhombohedral BiFeO3 films with 71° and 109° domain wall, and, tetragonal BiFeO3, Pb(Zr0.2Ti0.8)O3, and BaTiO3 ferroelectric thin films are analyzed and the corresponding polarization variants are determined. This work could provide a powerful and all-optical method to track and evaluate the evolution of ferroelectric domains in the ferroelectric-based devices. An optimized optical method is developed to determine the ferroelectric domain structure and their distributions in several ferroelectric films. A team led by Xiangli Zhong and Yichun Zhou from Xiangtan University, and Jianmin Yuan from National University of Defense Technology in China, combined optimized second harmonic generation (SHG) measurements and theoretical analysis to determine the polarization components of domains and their distribution in rhobohedral BiFeO3, tetragonal BiFeO3, Pb(Zr0.2Ti0.8)O3 and BaTiO3 thin films. They first collect azimuth-polarization-dependent SHG signals with respect to both the polarization angle of the incident beam and the azimuth angle of sample relative to the beam. Then they fit the SHG signals with a theoretical model with good agreement. This work provides an effective and all-optical method to determine the domain structures and distributions for ferroelectric thin films.

In this study, cadmium sulfide (CdS) and antimony sulfide (Sb2S3) quantum dot (QD) co-sensitized solar cells were fabricated using iodine-based gel polymer electrolytes. It was noticed that in comparison with TiO2/Sb2S3 QDs, the short-circuit current (Jsc) and the photoconversion efficiency (η) of the fabricated photovoltaic device based on TiO2/CdS/Sb2S3 QDs increased from 5.61 to 8.35 mA/cm2 and 1.06–1.61%, respectively. The presence of a CdS buffer layer between TiO2 and Sb2S3 was attributed to the enhancement of Jsc and η. The CdS buffer layer promoted the growth of Sb2S3 and facilitated the transfer of electrons from Sb2S3 to TiO2 through the reorganization of band levels between CdS and Sb2S3. It was also observed that the polymer electrolytes effectively prevented the corrosion of Sb2S3 QDs. Therefore, it can be concluded that the outcomes of this research could expedite future work on novel Sb2S3 quantum dot sensitized solar cells (QDSCs) based on polymer electrolytes with improved performance.

Multilevel data ferroelectric tunnel junction is a breakthrough for further improving the storage density of ferroelectric random access memories. However, the application of these ferroelectric tunnel junctions is limited by high cost of epitaxial perovskite heterostructures, unsatisfactory retention and difficulty of exactly controlling the middle polarization states. In order to overcome the issues, we develop a ferroelectric tunnel junction with smooth ultrathin polycrystalline BiFeO3 (BFO) film. Through controlling the polarization state and oxygen vacancy migration using voltage pulses, we demonstrate that voltage-controlled barrier yields a memristive behavior in the device, in which the resistance variations exceed over two orders of magnitude. And we achieve multi logic states written and read easily using voltage pulses in the device. Especially the device is integrated with the silicon technology in modern microelectronics. Our results suggest new opportunity for ferroelectrics as high storage density nonvolatile memories.

Lead halide perovskite solar cells have recently emerged as a very promising photovoltaic technology due to their excellent power conversion efficiencies; however, the toxicity of lead and the poor stability of perovskite materials remain two main challenges that need to be addressed. Here, for the first time, we report a lead-free, highly stable C6H4NH2CuBr2I compound. The C6H4NH2CuBr2I films exhibit extraordinary hydrophobic behavior with a contact angle of ∼90°, and their X-ray diffraction patterns remain unchanged even after 4 h of water immersion. UV/vis absorption spectrum shows that C6H4NH2CuBr2I compound has an excellent optical absorption over the entire visible spectrum. We applied this copper-based light absorber in printable mesoscopic solar cell for the initial trial and achieved a power conversion efficiency of ∼0.5%. Our study represents an alternative pathway to develop low-toxic and highly stable organic–inorganic hybrid materials for photovoltaic application.

A phase field method was used to investigate the influence of charge accumulation at the grain boundary on the electrical behavior of a ferroelectric field-effect transistor containing a polycrystalline gate. Both the domain structure and the electrical behavior of the ferroelectric field-effect transistor were found to depend on the coefficient χ, which represents the charge accumulation at the grain boundary. With increasing χ, both the width of the memory window of the capacitance–voltage curves and the on-state source–drain current decreased, while the off-state source–drain current increased. This can be explained in terms of the weakening polarization effect in the grain interior owing to the presence of a built-in electric field caused by the accumulated charge at the grain boundary.A phase field method was used to investigate the influence of charge accumulation at the grain boundary on the electrical behavior of a ferroelectric field-effect transistor containing a polycrystalline gate. Both the domain structure and the electrical behavior of the ferroelectric field-effect transistor were found to depend on the coefficient χ, which represents the charge accumulation at the grain boundary. With increasing χ, both the width of the memory window of the capacitance–voltage curves and the on-state source–drain current decreased, while the off-state source–drain current increased. This can be explained in terms of the weakening polarization effect in the grain interior owing to the presence of a built-in electric field caused by the accumulated charge at the grain boundary.

Resistive random access memory (RRAM) is recognized as a promising candidate for the next generation of non-volatile memory devices. In this work, the effect of γ-rays irradiation on WO x -based RRAM devices is investigated. The basic device parameters including high resistance, low resistance, set voltage, and reset voltage show high uniformity with a total dose as high as 500 krad(Si). Furthermore, the retention of 104 s can be achieved after irradiation, and the static resistances are also tested and compared. The highly uniformity after γ-rays irradiation provides the WO x -based RRAM devices with great potential for applications.

Ferroelectric tunnel junction (FTJ) is a breakthrough for addressing the nondestructive read in the ferroelectric random access memories. However, FTJs with nearly ideal characteristics have only been demonstrated on perovskite heterostructures that are deposited on closely lattice-matched and non-silicon substrates, or silicon substrates with epitaxial multilayer. In order to promote the application of FTJs, we develop a polycrystalline FTJ with ultrathin bottom electrode, in which the resistance variations exceed two orders of magnitude. And we achieve two stable logic states written and read easily using voltage pulses. Especially the device integrates with the silicon technology in modern microelectronics. Our results suggest new opportunities for ferroelectrics as nonvolatile resistive switching memory.