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Organic-inorganic hybrid perovskites (OIHPs) hold a great potential for scientific and technological endeavors in the field of ferroelectrics, solar cells, and electroluminescent devices, because of their structural diversity, low cost of manufacture, and ease of fabrication. However, lead iodide perovskite ferroelectrics with narrow band gap have rarely been reported. Here, we present a new two-dimensional (2D) layered lead iodide perovskite ferroelectric, (4,4-DFHHA)

Molecular ferroelectrics are attracting tremendous interest because of their easy and environmental-friendly processing, low acoustic impedance, and mechanical flexibility. Their ferroelectric mechanism is mainly ascribed to the order-disorder transition of molecules such as spherical 1,4-diazabicyclo[2.2.2] octane (DABCO) and quinuclidine. Here, we present two molecular ferroelectrics, [HDABCO][TFSA] and its deuterated one [DDABCO][TFSA] (TFSA = bis(trifluoromethylsulfonyl)ammonium), whose ferroelectricity is triggered by the proton ordering. This is the first time that the protons show a thermally fluctuated bistability with a double-well potential in DABCO-based ferroelectrics. A large deuterium isotope effect (ΔT = ∼53 K) not only proves that they are hydrogen-bonded ferroelectrics but also extends the ferroelectric working temperature range to room temperature. The superfast polarization switching of 100 kHz and ultralow coercive voltage of 1 V (far less than 5 V required for commercially available ferroelectric devices), benefiting from the low energy for proton transfer, allow [DDABCO][TFSA] a great potential for memory devices with low-voltage, high-speed operation. This work should inspire further exploration of hydrogen-bonded molecular ferroelectrics for flexible and wearable devices with the low-power information storage.

Molecular ferroelectrics have attracted considerable interests because of their easy and environmentally friendly processing, low acoustical impedance and mechanical flexibility. Herein, a molecular thermochromic ferroelectric, N,N'-dimethyl-1,4-diazoniabicyclo[2.2.2]octonium tetrachlorocuprate(II) ([DMe-DABCO]CuCl4 ) is reported, which shows both excellent ferroelectricity and intriguing thermochromism. [DMe-DABCO]CuCl4 undergoes a ferroelectric phase transition from Pca21 to Pbcm at a significantly high Curie temperature of 413 K, accompanied by a color change from yellow to red that is due to the remarkable deformation of [CuCl4 ]2- tetrahedron, where the ferroelectric and paraelectric phases correspond to yellow and red, respectively. Combined with multiple bistable physical properties, [DMe-DABCO]CuCl4 would be a promising candidate for next-generation smart devices, and should inspire further exploration of multifunctional molecular ferroelectrics.

Discovered in 1920 by Valasek, a molecular crystal of Rochelle salt (potassium sodium tartrate tetrahydrate) displayed abnormal electrical hysteresis, named as ferroelectric effect. After that, ferroelectrics became an important class of functional materials, due to their unique reversible spontaneous polarization characteristics and other fascinating dielectric, thermoelectric and piezoelectric properties. Although the first reported ferroelectric material is an organic material, the later discovered inorganic materials almost dominated the fields of ferroelectrics for both fundamental studies and practical applications. Among them, inorganic perovskite ceramics received rapid development and showed great application potential in a wide-range of applications such as non-volatile memories, capacitors, sensors, energy convertors, etc., due to their high phase transition temperature and excellent ferroelectric/piezoelectric properties. Comparing to inorganics, molecular materials possess advantages as low acoustic impedance, good flexibility of structure design and composition modification, simple solution synthesis and easy realization of functional properties. Thus, molecular ferroelectrics are expected to be an irreplaceable complement to conventional inorganics, especially in applications like flexible electronics and thin film devices. In the large family of molecular materials, some adapt a similar structure of perovskite with partial substitution of metal ions by organic molecules. These hybrid materials have attracted widespread attention because of their extraordinary optoelectronic and photovoltaic performance. Since last decade, the ferroelectric related properties of molecular perovskite materials were also largely improved. The combination of highly adaptive perovskite structures and variable composition attributes hybrid perovskites them unparalleled potential in rational design of ferroelectricity and piezoelectricity. In this review, we firstly introduced the structural characteristics and dimensionalities of different molecular perovskite ferroelectrics. The next part, we focused on the current design strategy toward rational synthesis of molecular perovskite ferroelectrics, especially on how to tune polarization performance and introducing multiple polar axial properties. In the third part, we briefly introduced the latest progress of molecular piezoelectrics and the role of perovskite structure, molecular design, halogen-bonding and morphotropic phase boundary (MPB) in dramatically improving the piezoelectric coefficient d 33. The fourth part of this review is an application-driven example of tuning band gap in molecular perovskite ferroelectrics, for better optoelectronic and photovoltaic performance. In the last part, a new class of perovskite materials, the metal-free perovskite, is introduced. Without the limitation of metal ions, the metal-free system is believed to have more potential with even better related properties. In summary, the ferroelectric, piezoelectric, and optoelectronic properties of perovskite molecular ferroelectric materials have been greatly developed. This article introduces several design strategies of perovskite molecular ferroelectrics, including “quasi-spherical” theory, H/F substitution and hydrogen bonding introduction method. Meanwhile, we combine comprehensive examples to introduce its recent application and the progress made in other functional characteristics such as band gap regulation and photo electricity. This review provides macroscopic view and general introduction of the evolution and recent progress in molecular perovskite ferroelectrics materials and is suitable for readers in a broad area of research.

Piezoelectric sensors that can work under various conditions with superior performance are highly desirable with the arrival of the Internet of Things. For practical applications, a large piezoelectric voltage coefficient g and a high Curie temperature Tc are critical to the performance of piezoelectric sensors. Here, we report a two-dimensional perovskite ferroelectric (4-aminotetrahydropyran)2PbBr4 [(ATHP)2PbBr4] with a saturated polarization of 5.6 μC cm-2, high Tc of 503 K [above that of BaTiO3 (BTO, 393 K)], and extremely large g33 of 660.3 × 10-3 V m N-1 [much beyond that of Pb(Zr,Ti)O3 (PZT) ceramics (20 to 40 × 10-3 V m N-1), more than 2 times higher than that of poly(vinylidene fluoride) (PVDF, about 286.7 × 10-3 V m N-1)]. Combined with the advantages of molecular ferroelectrics, such as light weight, easy and environmentally friendly processing, and mechanical flexibility, (ATHP)2PbBr4 would be a competitive candidate for next-generation smart piezoelectric sensors in flexible devices, soft robotics, and biomedical devices.

The functional performance of food proteins can sometimes be enhanced by forming conjugates or complexes with other food-grade molecules. In this study, the impact of fabrication conditions (pH and mixing ratio) on the formation and properties of phytic acid (PA)-whey protein isolate (WPI) complexes was evaluated. In addition, the ability of the complexes to form and stabilize oil-in-water emulsions was characterized. Emulsions were formed using a high-shear mixer to simulate the production of commercial foods such as dressings and sauces. Most emulsions were highly unstable to creaming due to the relatively large size of the oil droplets they contained (d > 30 μm). Under acidic conditions, emulsions stabilized by PA-WPI complexes were more resistant to creaming and formed thicker cream layers than those stabilized by WPI alone, which was attributed to electrostatic bridging of the cationic protein-coated oil droplets by anionic phytic acid. Evidence for increased droplet-droplet attraction was confirmed by bulk rheology measurements: emulsions stabilized by PA-WPI complexes had a much higher viscosity than those stabilized by WPI. Interfacial tension measurements showed that the PA-WPI complexes adsorbed to an oil-water interface more rapidly than either PA or WPI molecules, as well as producing a greater reduction in interfacial tension. Surface rheology measurements indicated that the dilatational elastic modulus of the interfaces formed by the PA-WPI complexes was less than that formed by WPI alone, indicating that the PA inhibited interfacial protein cross-linking. Our results, indicate that even relatively low PA-to-WPI ratios (1:20) can be used to modulate the physicochemical properties and long-term stability of protein-coated oil droplets, thereby providing an effective strategy for designing food emulsions with improved functionality.

Using accumulators for intercropping in agricultural production can change the heavy metal concentration in the target plants. This study aims to investigate how intercropping wheat (Triticum aestivum L.) and Solanum nigrum L. affects soil bacterial community and cadmium (Cd) absorption in response to Cd-contaminated soil. We compared the concentrations and accumulations of Cd by plants, the activities of soil enzymes and the bacterial community structures of rhizosphere soil in monoculture and intercropping system. Principal component analysis (PCA) ordinations showed that soil bacterial communities were significantly separated by MW and IW, which illustrated intercropping with Solanum nigrum L. impacted the bacterial community structure of wheat. Firstly, the results showed that the biomass of shoots and roots in intercropped wheat (IW) were significantly decreased by 16.19% and 29.38% compared with monoculture wheat (MW) after 60 days after transplanting (DAT). Secondly, the Cd concentration and accumulation of shoots in IW was higher than MW. The Cd accumulation of IW shoots and roots were increased 12.87% and 0.98%, respectively after 60 days DAT. Besides, the enzymes activity [catalase (CAT), urease (UA) and alkaline phosphatase (ALP)] of IW were decreased 35%, 6% and 21%, respectively after 60 days DAT. Finally, the diversity indexes [Abundance-based Coverage Estimator (ACE), Chao and InvSimpson] of IW were lower than MW. These results indicated that intercropping with Solanum nigrum L. inhibited the wheat growth and decreased the bacterial community diversity in wheat rhizosphere, increased the Cd concentration and accumulation in plant tissues of wheat. Therefore, intercropping Solanum nigrum L. and wheat with Cd-contaminated soil might increase the risk of excessive Cd in wheat.

49 samples of propolis from different regions in China were collected and analyzed for their chemical compositions, contents of total flavonoids (TFC), total phenolic acid (TPC) and antioxidant activity. High-performance liquid chromatography (HPLC) analysis identified 15 common components, including key marker compounds pinocembrin, 3-O-acetylpinobanksin, galangin, chrysin, benzyl p-coumarate, pinobanksin and caffeic acid phenethyl ester (CAPE). Cluster analysis (CA) and correlation coefficients (CC) analysis showed that these propolis could be divided into three distinct groups. Principal component analysis (PCA) and multiple linear regression analysis (MLRA) revealed that the contents of isoferulic acid, caffeic acid, CAPE, 3,4-dimethoxycinnamic acid, chrysin and apigenin are closely related to the antioxidant properties of propolis. In addition, eight peak areas decreased after reacting with 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radicals, indicating that these compounds have antioxidant activity. The results indicate that the grouping and spectrum&ndash, effect relationship of Chinese propolis are related to their chemical compositions, and several compounds may serve as a better marker for the antioxidant activity of Chinese propolis than TFC and TPC. The findings may help to develop better methods to evaluate the quality of propolis from different geographic origins.

Ferroelectric thin films are extensively attractive as next-generation nonvolatile memories. Recently, molecular ferroelectrics (MFe), as an emerging new class, have been a new research focus because of their desirable characteristics such as good solution processability, tunable chemical properties, and bio-friendly compositions. However, traditional uniaxial MFe only possess one polar axis which greatly limits their application, as it requires restricted orientational control in single crystal. To achieve macroscopic ferroelectricity and thus fully realize technological advantages of MFe, development of multiaxes is imperative to maximize effective polarization in specific crystallographic orientations. Herein, we present an early exploration on polycrystalline multiaxial MFe thin films of [Hdabco][ReO4] with a two-dimensional graphene hybrid nonvolatile memory device. The polarization switching of MFe is experimentally realized by the nonvolatile modulation of two current states in graphene. Such a hybrid device can exhibit large memory window ∼35 V implying its great potential in memory applications. Hence, by taking the advantages of multiple polarization axes of MFe, the low cost and large area MFe/graphene hybrid memory manifests new possibilities for the integration of these materials as flexible next generation memory devices.

The synergized optimization of water flux and salt rejection by blending with inorganic fillers has been achieved for the polyamide (PA) thin film nanocomposite (TFN) membrane. However, it is difficult to characterize its mass transport properties due to the very thin and heterogeneous PA film. In this work, we select cellulose triacetate (CTA) as the base to prepare hybrid films and their transport properties were studied according to solution-diffusion theory. A series of inorganic fillers, such as reduced graphene oxide (RGO), zeolites, ZIF-8, SiO2 and graphene oxide (GO) were incorporated. The SEM and EDX results indicate a less than 1 wt% filler content for a uniform dispersion. The blending of inorganic fillers leads to enhanced glass transition temperature (Tg) and density, little effect on the water transport property but dramatically decreased salt permeability values, which are nearly ten-fold of that of the CTA film. The blending of GO can densify and hydrophilize CTA simultaneously, which is most promising for a desalination application. The increased water uptake should contribute to its increased water permeability, while the decreased free volume size and FFV value and various interactions between the ions (Na+, Cl-) and GO sheets account for salt permeability decrease.

Though dominating most of the practical applications, inorganic ferroelectric thin films usually suffer from the high processing temperatures, the substrate limitation, and the complicated fabrication techniques that are high-cost, energy-intensive, and time-consuming. By contrast, molecular ferroelectrics offer more opportunities for the next-generation flexible and wearable devices due to their inherent flexibility, tunability, environmental-friendliness, and easy processability. However, most of the discovered molecular ferroelectrics are uniaxial, one major obstacle for improving the thin-film performance and expanding the application potential. In this Perspective, we overview the recent advances on multiaxial molecular ferroelectric thin films, which is a solution to this issue. We describe the strategies for screening multiaxial molecular ferroelectrics and characterizations of the thin films, and highlight their advantages and future applications. Upon rational and precise design as well as optimizing ferroelectric performance, the family of multiaxial molecular ferroelectric thin films surely will get booming in the near future and inject vigor into the century-old ferroelectric field.

A fast and facile protocol is reported aiming at improving the antifouling property and hemocompatibility of poly(vinylidene fluoride) (PVDF) membranes by tethering PEG hydrogel and zwitterion immobilization. The coated PEG hydrogel was first prepared by interfacial polymerization and tethered on an alkali treated PVDF membrane (PVDFA) surface via a simultaneous thio-ene and thiol-epoxy reaction. Then, the thiol groups of cysteine reacted with the epoxy groups in PEG hydrogel to fabricate the PVDFA-g-Cys membrane. The membrane fabrication was complete within less than 20 min and was conducted in mild conditions. The successful preparation of PVDFA-g-Cys membrane was confirmed by ATR-FTIR and XPS. Raman spectroscopy showed that the hydrogels covalently bonded to the PVDF membrane surface. The membrane retained its mechanical strength after modification. The SEM measurements suggested that the membrane became denser after hydrogel coating, meanwhile, the EDX test verified that the functional species uniformly distributed in the membrane matrix. Water contact angle (WCA), protein adsorption and protein filtration tests showed significant improvements in hydrophilicity and antifouling properties for the modified membrane. The negativity of the membrane surface measured by the streaming potential method provides a basis for protein resistance and hemocompatibility. Moreover, the suppressed platelet adhesion and prolonged plasma coagulant time show that the PVDFA-g-Cys membrane has ultralow thrombotic potential and better hemocompatibility. The reported surface modification method combing thio-ene and thio-epoxy chemistry not only facilitates fabrication of hemocompatible PVDF membrane but also provide an universal chemical platform for multifunctionalization of porous membranes.

1T-TiSe 2 is a model transition metal dichalcogenide material that develops charge density waves (CDWs). Here we present variable-temperature Raman spectroscopy study on both CDW and optical phonon modes of 1T-TiSe 2 thin layers exfoliated onto SiO 2 substrate. Raman scattering intensities of all modes reach a maximum when the sample thickness is about 12 nm. This phenomenon can be explained by optical interference effect between the sample and the substrate. The CDW amplitude modes experience redshift and broadening as temperature increases. We extract CDW transition temperature ( T CDW ) from temperature dependence of the frequency of A 1 g CDW mode. We find that T CDW decreases in thinner flakes, which could be due to extrinsic effects.

The classical organic ferroelectric, poly(vinylidene fluoride) (PVDF), has attracted much attention as a promising candidate for data storage applications compatible with all-organic electronics. However, it is the low crystallinity, the large coercive field, and the limited thermal stability of remanent polarization that severely hinder large-scale integration. In light of that, we show a molecular ferroelectric thin film of [Hdabco][ReO4] (dabco = 1,4-diazabicyclo[2.2.2]octane) (1), belonging to another class of typical organic ferroelectrics. Remarkably, it displays not only the highest Curie temperature of 499.6 K but also the fastest polarization switching of 100k Hz among all reported molecular ferroelectrics. Combined with the large remanent polarization values (∼9 μC/cm2), the low coercive voltages (∼10 V), and the unique multiaxial ferroelectric nature, 1 becomes a promising and viable alternative to PVDF for data storage applications in next-generation flexible devices, wearable devices, and bio...

Ferroelectric thin-films are highly desirable for their applications on energy conversion, data storage and so on. Molecular ferroelectrics had been expected to be a better candidate compared to conventional ferroelectric ceramics, due to its simple and low-cost film-processability. However, most molecular ferroelectrics are mono-polar-axial, and the polar axes of the entire thin-film must be well oriented to a specific direction to realize the macroscopic ferroelectricity. To align the polar axes, an orientation-controlled single-crystalline thin-film growth method must be employed, which is complicated, high-cost and is extremely substrate-dependent. In this work, we discover a new molecular ferroelectric of quinuclidinium periodate, which possesses six-fold rotational polar axes. The multi-axes nature allows the thin-film of quinuclidinium periodate to be simply prepared on various substrates including flexible polymer, transparent glasses and amorphous metal plates, without considering the crystallinity and crystal orientation. With those benefits and excellent ferroelectric properties, quinuclidinium periodate shows great potential in applications like wearable devices, flexible materials, bio-machines and so on., Molecular ferroelectric crystals hold promise in data storage applications, yet their preparations by maximizing molecular polarization are challenging. Here, You et al. report quinuclidinium periodate with six rotation axes and grow them in macroscopic ferroelectric thin films via a solution process.

It is known that CH3NH3PbI3 is particularly promising for next-generation solar devices; therefore, molecular perovskite structures have recently received extraordinary attention from the academic community because of their potential in producing unique physical properties. However, although great efforts have been made, molecular ferroelectrics with three-dimensional (3D) perovskite structures are still rare. So far, reported perovskite-like molecular ferroelectrics are basically one- or two-dimensional, significantly deviating from the inorganic perovskite ferroelectrics. Thus, their ferroelectric properties have to be greatly improved to meet the requirements of practical applications. Here, we report a 3D molecular perovskite ferroelectric: (3-ammoniopyrrolidinium)RbBr3 [(AP)RbBr3], with a high Curie temperature (Tc = 440 K) beyond that of BaTiO3. To the best of our knowledge, such above-room-temperature ferroelectricity in the 3D molecular perovskite compound is unprecedented. Furthermore, (AP)RbBr3 ...

Ferroelectrics with luminescent properties are promising candidates for the next generation of optical waveguides and displays. However, reports on ferroelectrics with triboluminescence properties have been very scarce so far. In this study, we demonstrate a potential hybrid molecular ferroelectric, (Ph3PO)2MnBr2, which exhibits intense green triboluminescence. Using piezoresponse force microscopy, the presence of ferroelectric domains in (Ph3PO)2MnBr2 thin films is confirmed. We also show evidence for the reversible switching of the ferroelectric domains by poling with DC biases. We believe that this combination of ferroelectricity and triboluminescence will bring about potential multifunctional optoelectronic device applications.

Molecular ferroelectrics are attracting much attention as valuable complements to conventional ceramic ferroelectrics owing to their solution processability and nontoxicity. Encouragingly, the recent discovery of a multiaxial molecular ferroelectric, tetraethylammonium perchlorate, is expected to be able to solve the problem that in the technologically relevant thin-film form uniaxial molecular ferroelectrics have been found to perform considerably more poorly than in bulk. However, it can show good polarization–electric field (P–E) hysteresis loops only at very low frequency, severely hampering practical applications such as ferroelectric random access memory. Here, we present a biaxial molecular ferroelectric thin film of [Hdabco]ClO4 (dabco = 1,4-diazabicyclo[2.2.2]octane) (1), where a perfect ferroelectric hysteresis loop can be observed even at 10 kHz. It is the first example of a molecular ferroelectric thin film whose polarization can be switched at such a high frequency. Moreover, using piezorespo...

Molecular ferroelectrics are currently an active research topic in the field of ferroelectric materials. As complements or alternatives of conventional inorganic ferroelectrics, they have been designed to realize various novel properties, ranging from multiferroicity and semiconductive ferroelectricity to ferroelectric photovoltaics and ferroelectric luminescence. The stabilizing of ferroelectricity in various systems is owing to the flexible tailorability of the organic components. Here we describe the construction of optically active molecular ferroelectrics by introducing homochiral molecules as polar groups. We find that the ferroelectricity in (R)-(−)-3-hydroxlyquinuclidinium halides is due to the alignment of the homochiral molecules. We observe that both the specific optical rotation and rotatory direction change upon paraelectric-ferroelectric phase transitions, due to the existence of two origins from the molecular chirality and spatial arrangement, whose contributions vary upon the transitions. The optical rotation switching effect may find applications in electro-optical elements., Ferroelectric phase transitions are normally accompanied by structural changes in the materials. Here, Li et al. synthesize homochiral molecular crystals and utilize their ferroelectric transitions to achieve optical switches with different refractive indices for left- and right-handed polarizations.

Current MOF composite membranes usually suffer from unduly thick MOF layers and poor adhesion with the polymer substrate. We prepared a thin MOF film (440 nm) on a polymer support with 2-D MOF nanosheets as seeds via a layer-by-layer growth. These 2-D MOF seeds not only provided bonding between the MOF film and the polymer substrate but also facilitated the formation of a continuous and defect-free MOF membrane, which demonstrated excellent performance in gas separation.

The X-site ion in organic-inorganic hybrid ABX3 perovskites (OHPs) varies from halide ion to bridging linkers like HCOO- , N3- , NO2- , and CN- . However, no nitrite-based OHP ferroelectrics have been reported so far. Now, based on non-ferroelectric [(CH3 )4 N][Ni(NO2 )3 ], through the combined methodologies of quasi-spherical shape, hydrogen bonding functionality, and H/F substitution, we have successfully synthesized an OHP ferroelectric, [FMeTP][Ni(NO2 )3 ] (FMeTP=N-fluoromethyl tropine). As an unprecedented nitrite-based OHP ferroelectric, the well-designed [FMeTP][Ni(NO2 )3 ] undergoes the ferroelectric phase transition at 400 K with an Aizu notation of 6/mmmFm, showing multiaxial ferroelectric characteristics. This work is a great step towards not only enriching the molecular ferroelectric families but also accelerating the potential practical applications.

Ferroelectrics are attractive due to their great application potential in information storage, optoelectronics, spintronics and sensing. As an important characteristic affecting semiconducting applications, the energy band structure is important for the development of light-emitting devices. Although it is a tremendous challenge to tune the bandgap in inorganic ferroelectric materials due to the strict requirement of structural symmetry for the fragile ferroelectricity, hybrid organic–inorganic perovskite (HOIP) ferroelectrics, which have a flexible structure, provide a new method to optimize the ferroelectric performance and bandgap. Based on the overview of methods for designing ferroelectrics, this Perspective systematically provides in-depth insight into the relationships between the structure–property and bandgap of HOIP ferroelectrics. In addition, we discussed the challenges and directions of HOIP ferroelectrics in semiconducting applications for the future.

The relationship between desalting membrane and its water/salt transport properties remain largely unknown. This is especially true for polyamide thin film nanocomposite (TFN) membranes which have shown excellent desalination performance and attracted booming attention in recent years. Considering cellulose triacetate (CTA) can be made into dense membranes whose transport properties can be measured based on the solution-diffusion theory, we systematically study the water/salt transport property of the CTA nanocomposite membranes blended with reduced graphene oxide (rGO) of varying reduction degrees, with multilayer graphene oxide (MGO) and single layer graphene oxide (SGO) as control samples. The nanocomposite membranes show enhanced membrane density and glass transition temperature (Tg) due to the interaction of the polar group in GO/rGO with CTA chains. The GO (rGO) frustrates the polymer chain packing and decreases crystallinity of CTA membrane. The adding of rGO increases the water permeability by increasing its diffusivity due to the decreased crystallinity and additional channel from (r)GO, but decreases the salt permeability by decreasing its diffusivity due to membrane densification and the interactions of ions with GO/rGO. The water permeability and diffusivity of the nanocomposites increase when its water sorption decreases, which is against the trend of pure polymers, presumably due to the fact that water sorption is not a good reflection of the free volume in this heterogeneous membrane. Meanwhile, the GO/rGO blending slightly increases water sorption without changing the salt sorption because the newly-introduced polar groups in GO/rGO traps water and suppress its solvation capacity for salt. Both the water permeability and the water/salt selectivity increase with the reduction degree due to the decreased water transport resistance.

Besides the single crystals, ferroelectric materials are actually widely used in the forms of the polycrystals like ceramics. Multiaxial ferroelectrics with multiple equivalent polarization directions are preferable for such applications, because more equivalent ferroelectric axes allow random spontaneous polarization vectors to be oriented along the electric field to achieve a larger polarization after poling. Most of ceramic ferroelectrics like BaTiO3 have equivalent ferroelectric axes no more than three. We herein describe a molecular-ionic ferroelectric with 12 equivalent ferroelectric axes: tetraethylammonium perchlorate, whose number of axes is the most in the known ferroelectrics. Appearance of so many equivalent ferroelectric axes benefits from the plastic phase transition, because the plastic phase usually crystallizes in a highly symmetric cubic system. A perfect macroscopic ferroelectricity can be obtained on the polycrystalline film of this material. This finding opened an avenue constructing ...

The electrical performance of two dimensional transitional metal dichalcogenides (TMDs) is strongly influenced by the amount of structural defects inside. In this work, we provide an optical spectroscopic characterization approach to correlate the amount of structural defects and the electrical performance of WSe2 devices. Low temperature photoluminescence (PL) spectra of electron beam lithography (EBL) processed WSe2 presents a clear defect-induced PL emission due to excitons bound to defects, which would strongly degrade the electrical performance. By adopting an e-beam-free transfer-electrode technique, we are able to prepare backgated WSe2 device with limited amount of defects. A maximum hole-mobility of about 200 cm2/Vs was achieved due to reduced scattering sources, which is the highest reported value among its type. This work would not only provide a versatile and nondestructive method to monitor the defects in TMDs, but also a new route to approach the room temperature phonon-limited mobility in high performance TMDs devices., Comment: 22 pages, 10 figures, to appear in Nano Research

Semiconducting ferroelectricity is realized in hybrid perovskite-type compounds (cyclohexylammonium)2 PbBr4-4 x I4 x (x = 0-1). By adjusting the composition x, the bandgap is successfully tuned from previously reported 3.65 eV to as low as 2.74 eV, and the excellent ferroelectricity was kept intact. This finding may contribute to improving the photoelectronic and/or photovoltaic performance of hybrid perovskite-type compounds.

This article reports a facile synthesis of radiolabeled PdCu@Au core-shell tripods for use in positron emission tomography (PET) and image-guided photothermal cancer treatment by directly incorporating radioactive (64)Cu atoms into the crystal lattice. The tripod had a unique morphology determined by the PdCu tripod that served as a template for the coating of Au shell, in addition to well-controlled specific activity and physical dimensions. The Au shell provided the nanostructure with strong absorption in the near-infrared region and effectively prevented the Cu and (64)Cu atoms in the core from oxidization and dissolution. When conjugated with D-Ala1-peptide T-amide (DAPTA), the core-shell tripods showed great enhancement in targeting the C-C chemokine receptor 5 (CCR5), a newly identified theranostic target up-regulated in triple negative breast cancer (TNBC). Specifically, the CCR5-targeted tripods with an arm length of about 45 nm showed 2- and 6-fold increase in tumor-to-blood and tumor-to-muscle uptake ratios, respectively, relative to their nontargeted counterpart in an orthotopic mouse 4T1 TNBC model at 24 h postinjection. The targeting specificity was further validated via a competitive receptor blocking study. We also demonstrated the use of these targeted, radioactive tripods for effective photothermal treatment in the 4T1 tumor model as guided by PET imaging. The efficacy of treatment was confirmed by the significant reduction in tumor metabolic activity revealed through the use of (18)F-fluorodeoxyglucose PET/CT imaging. Taken together, we believe that the (64)Cu-doped PdCu@Au tripods could serve as a multifunctional platform for both PET imaging and image-guided photothermal cancer therapy.

A novel positive-charged polyamine-based cyclophosphazene nanofiltration membrane (NF) was prepared via interfacial polymerization between branched polyethyleneimine (PEI) and hexachlorocyclotriphosphazene (HCCP). The composite membranes were characterized using ATR-FTIR, XPS, SEM, AFM, water contact angle, and zeta potential analysis. The membrane with optimal performance was prepared by interfacial reaction with 5 wt% PEI (Mn = 600 g/mol) in aqueous phase, 1 wt% HCCP in organic phase, 5 min dwell time, and 15 min curing time at 100 °C. The resultant membrane has a 97% rejection to MgCl2 and a water permeation of 55 L/m2 h when testing at 1.5 MPa and 25 °C with a 1000 ppm salt solution. The results for filtrating various dyes showed that the PEI/HCCP membrane could remove small organic compounds and contaminants. Antibacterial assay results indicated that the membrane had a nearly 100% bacterial inhibitate rate against both Gram-negative E. coli and Gram-positive S. aureus. In addition, all bacteria in a concentrated suspension (107 CFU/mL) could be completely eliminated within 20 min contacting with the PEI/HCCP membrane. Finally, a 140 h cross-flow testing indicates an excellent membrane performance stability.

Molecular piezoelectrics are attracting tremendous interest because of their easy processing, light weight, low acoustical impedance, and mechanical flexibility. However, reports of molecular piezoelectrics with a piezoelectric coefficient d33 comparable to piezoceramics such as barium titanate (BTO, 90–190 pC/N) have been scarce. Here, we present a uniaxial molecular ferroelectric, trimethylchloromethylammonium tribromocadmium(II) (TMCM-CdBr3), in which the halogen bonding might be a possible critical point for the stabilization of one-dimensional (1D) {CdBr3}− chain and further reservation of its ferroelectricity in such organic–inorganic hybrid crystalline systems. It has a large d33 of 139 pC/N, 1 order of magnitude higher than those of most classically uniaxial ferroelectrics such as LiNbO3 (6–16 pC/N) and Rochelle salt (∼7 pC/N), and comparable with those of multiaxial ferroelectrics such as BTO and trimethylbromomethylammonium tribromomanganese(II) (112 pC/N). Moreover, the simple single-crystal gr...

Inorganic perovskite ferroelectrics are widely used in nonvolatile memory elements, capacitors, and sensors because of their excellent ferroelectric and other properties. Organic ferroelectrics are desirable for their mechanical flexibility, low weight, environmentally friendly processing, and low processing temperatures. Although almost a century has passed since the first ferroelectric, Rochelle salt, was discovered, examples of highly desirable organic perovskite ferroelectrics are lacking. We found a family of metal-free organic perovskite ferroelectrics with the characteristic three-dimensional structure, among which MDABCO ( N -methyl- N9 -diazabicyclo[2.2.2]octonium)–ammonium triiodide has a spontaneous polarization of 22 microcoulombs per square centimeter [close to that of barium titanate (BTO)], a high phase transition temperature of 448 kelvins (above that of BTO), and eight possible polarization directions. These attributes make it attractive for use in flexible devices, soft robotics, biomedical devices, and other applications.

The paper studies the Electric Vehicle Routing problem with time-window (EVRPTW) in the field of logistics maintenance optimization. We use mixed integer linear programming techniques to model the EVRPTW considering various factors encountered in practice, including the battery's capacity limit, charge station selection, and battery's charging time determination, in order to improve the availability of electric vehicle in modern logistics system. Computational experiments are carried out to verify the feasibility of the proposed model and compare it with traditional routing model, which show that our model fits better for real-life applications and can yield better schedules that improve the utilization of electric vehicles.

Piezoelectric materials have been widely used in various applications, such as high-voltage sources, actuators, sensors, motors, fre-quency standard, vibration reducer, and so on. In the past decades, lead zirconate titanate (PZT) binary ferroelectric ceramics have dominated the commercial piezoelectric market due to their excellent properties near the morphotropic phase boundary (MPB), although they contain more than 60% toxic lead element. Here, we report a lead-free and one-composition molecular ferroelectric trimethylbromomethylammonium tribromomanganese (ΙΙ) (TMBM-MnBr3) with a large piezoelectric coefficient d33 of 112 pC/N along polar axis, comparable with those of typically one-composition piezoceramics such as BaTiO3 along polar axis [001] (~90 pC/N) and much greater than those of most known molecular ferroelectrics (almost below 40 pC/N). More significantly, the effec-tive local piezoelectric coefficient of TMBM-MnBr3 films is comparable to that of its bulk crystals. In terms of ferroelectric pe...

Recently, a plastic crystal of quinuclidinium perrhenate (${\mathrm{HQReO}}_{4}$) was reported to have the feasibility of controlling the crystallographic orientation in the grown crystal, but the corresponding temperature window is only about 22 K (345--367 K). Such a narrow window and uncertain ferroelectricity at room temperature would extremely limit its application potential. In this report, we prepared a large area high-quality polycrystalline thin film of ${\mathrm{HQReO}}_{4}$ and for the first time observed ferroelectricity in the temperature range from 298 to 367 K. Density functional theory calculations revealed the origin of room-temperature ferroelectricity is ascribed to the collaborative flipping of HQ (protonated quinuclidine) and ${\mathrm{ReO}}_{4}^{\ensuremath{-}}$, which is dynamically preferred in the presence of a $\mathrm{N}─\mathrm{H}\ensuremath{\cdots}\mathrm{O}$ hydrogen bond. A local piezoresponse force microscopy measurement was also employed to study the mechanisms of multiaxial polarization rotation and domain dynamics. By extending the ferroelectric temperature window to room temperature and the extraordinary thin-film processability, ${\mathrm{HQReO}}_{4}$ would certainly become a suitable candidate for next generation ferroelectric materials.

An outstanding advantage of inorganic ceramic ferroelectrics is their usability in the polycrystalline ceramic or thin film forms, which has dominated applications in the ferroelectric, dielectric, and piezoelectric fields. Although the history of ferroelectrics began with the molecular ferroelectric Rochelle salt in 1921, so far there have been very few molecular ferroelectrics, with lightweight, flexible, low-cost, and biocompatible superior properties compared to inorganic ceramic ferroelectrics, that can be applied in the polycrystalline form. Here, a multiaxial molecular ferroelectric, guanidinium perchlorate ([C(NH2 )3 ]ClO4 ), with a record-high phase transition temperature of 454 K is presented. It is the rectangular polarization-electric field (P-E) hysteresis loops recorded on the powder and thin film samples (with respective large Pr of 5.1 and 8.1 µC cm-2 ) that confirm the ferroelectricity of [C(NH2 )3 ]ClO4 in the polycrystalline states. Intriguingly, after poling, the piezoelectric coefficient (d33 ) of the powder sample shows a significant increase from 0 to 10 pC N-1 , comparable to that of LiNbO3 single crystal (8 pC N-1 ). This is the first time that such a phenomenon has been observed in molecular ferroelectrics, indicating the great potential of molecular ferroelectrics being used in the polycrystalline form like inorganic ferroelectrics, as well as being viable alternatives or supplements to conventional ceramic ferroelectrics.

The process of molecular recognition is the assembly of two or more molecules through weak interactions. Information in the process of molecular recognition can be transmitted to us via physical signals, which may find applications in sensing and switching. The conventional signals are mainly limited to light signal. Here, we describe the recognition of diols with Cu(1,10-phenlothroline)2SeO4 and the transduction of discrete recognition events into dielectric and/or ferroelectric signals. We observe that systems of Cu(1,10-phenlothroline)2SeO4·(diol) exhibit significant dielectric and/or ferroelectric dependence on different diol molecules. The compounds including ethane-1,2-diol or propane-1,2-diol just show small temperature-dependent dielectric anomalies and no reversible polarization, while the compound including ethane-1,3-diol shows giant temperature-dependent dielectric anomalies as well as ferroelectric reversible spontaneous polarization. This finding shows that dielectricity and/or ferroelectricity has the potential to be used for signalling molecular recognition., Molecular recognition is an important biological process where guest and host molecules interact through non-covalent bonding. Ye et al. show that this can be sensed by the dielectric and ferroelectric signals of the final complexes in a series of metal-coordination compounds with different diol molecules.

Finding a more flexible mechanical sensor Piezoelectric materials allow conversion between electricity and mechanical stresses. The most efficient piezoelectric materials are ceramics such as BaTiO 3 or PbZrO 3 , which are also extremely stiff. You et al. identified an organic perovskite structured piezoelectric material that is far more pliable yet has a piezoelectric response similar to that of traditional ceramics. This material may be a better option to use as a mechanical sensor for flexible devices, soft robotics, biomedical devices, and other micromechanical applications that benefit from a less stiff piezoelectric material. Science , this issue p. 306

Defect-induced trap states are essential in determining the performance of semiconductor photodetectors. The de-trap time of carriers from a deep trap can be prolonged by several orders of magnitude as compared to shallow traps, resulting in additional decay/response time of the device. Here, it is demonstrated that the trap states in 2D ReS2 can be efficiently modulated by defect engineering through molecule decoration. The deep traps that greatly prolong the response time can be mostly filled by protoporphyrin molecules. At the same time, carrier recombination and shallow traps in-turn play dominant roles in determining the decay time of the device, which can be several orders of magnitude faster than the as-prepared device. Moreover, the specific detectivity of the device is enhanced (as high as ≈1.89 × 1013 Jones) due to the significant reduction of the dark current through charge transfer between ReS2 and molecules. Defect engineering of trap states therefore provides a solution to achieve photodetectors with both high responsivity and fast response.

Two-dimensional (2D) molybdenum disulfide (MoS2) is considered as a promising candidate for electronic and optoelectronic devices. However, structural defects in MoS2 are widely reported and can greatly degrade its electrical and optical properties. In this work, we investigate the structural defects in MoS2 by low temperature photoluminescence (PL) spectroscopy and study their effects on the electrical performance, i.e. carrier mobility. We also adopt the mild oxygen plasma treatment to repair the structural defects and found that the carrier mobility of monolayer MoS2 can be greatly improved. This work would therefore offer a practical route to improve the performance of 2D dichalcogenide-based electrical and optoelectronic devices.

Ferroelectrics have been attracting increasing attention as good candidates for multifunctional materials because of their fascinating properties. However, their large bandgap has been a roadblock limiting their application in optoelectronics and photovoltaics, among other applications. Hybrid ferroelectrics have the potential to combine the advantages of both molecular materials and ferroelectrics. In this context, we designed a hybrid ferroelectric: (2-(ammoniomethyl)pyridinium)SbI5. It shows an above-room-temperature Curie temperature (Tc=360 K), a large spontaneous polarization (Ps=4 μC cm−2) and a small bandgap (2.03 eV) that is much smaller than the recently reported 2.7–3.65 eV for the lead-halide perovskite ferroelectrics. The implementation of ferroelectricity in hybrid semiconducting materials may be a feasible way to realize high-performance ferroelectric optoelectronic and photovoltaic devices. Replacing lead-based perovskite crystals with hybrid organic–inorganic materials may generate safer, more efficient solar cell devices. Lead halide perovskites can convert over 20% of incoming light to electricity and are inexpensive to produce, but have troubling moisture instability and toxicity issues. Ren-Gen Xiong from China's Southeast University and colleagues investigated alternatives based on semiconducting ferroelectrics that offer polarization-based manipulation of photogenerated electrons. Because all-inorganic ferroelectrics typically have poor light sensitivity due to their large bandgaps, the researchers synthesized a new compound that fuses antimony and iodine atoms with organonitrogen rings. These large, dark-red crystals show room-temperature ferroelectricity that can be manipulated at nanoscale dimensions using force microscopy. Furthermore, tweaking the antimony–iodine framework with the organic component lowered the bandgap to levels even below those of lead halides. A semiconducting molecular ferroelectric (2-(ammoniomethyl)pyridinium)SbI5 was designed. It shows an above-room-temperature Curie temperature (Tc=360 K), a large spontaneous polarization (Ps=4 μC cm−2) and small bandgap (2.03 eV) that are comparable to those of the well-known semiconducting ferroelectrics BiFeO3 (Eg=2.7 eV) and SbSI (Eg=2.0 eV). The implementation of ferroelectricity into hybrid semiconducting materials will move the applications of hybrid semiconducting molecular ferroelectrics in optoelectronic and photovoltaics devices forward.

Graphene-based photodetectors have recently received much attention for their potential to detect weak signals and their short response time, both of which are crucial in applications such as optical positioning, remote sensing, and biomedical imaging. However, existing devices for detecting weak signals are limited by the current photogating mechanism, so the price for achieving ultrahigh sensitivity is to sacrifice response time. In this work, we bridge the gap between ultrafast response and ultrahigh sensitivity by employing a graphene/SiO2/lightly doped Si architecture with an interfacial gating mechanism. Our device is capable of detecting a signal of

Light absorption plays a key role in photovoltaic devices, especially in thin-film CdTe-based solar cells. Here we study the enhancement of optical absorption in a ultrathin CdTe layer by embedding it into optical magnetic metamaterials. In a periodic metal-CdS-CdTe-metal sandwiched structure, the absorption of transverse magnetic polarized light has been significantly enhanced. The maximum enhancement is around 3 times, which is attributed to the strong local field enhancement in the CdTe thin film. Importantly, due to the coexistence of large electric resonance and magnetic resonance in magnetic metamaterials, the enhancement of light absorption has been obtained in a broadband from 400 nm to 800 nm, which is almost 1.5 times of that of the conventional CdTe-based photovoltaic device and covers the strongest part of the solar spectrum. Moreover, such absorption enhancement is also valid for a wide range of incident angles. We believe that our finding can lead to a variety of important applications in ultrathin CdTe-based solar cell technology.

Here we demonstrate the control of magnetic dipole spontaneous emission at yellow light by polarization-independent hexagonally arrayed nanorods magnetic metamaterials. By embedding a magnetic dipole into a polarization-independent magnetic metamaterial consisting of hexagonal arrays of paired silver nanorods, the radiative emission enhancement and the Purcell factor around 590 nm have been dramatically increased 44 times for a significant general far-field emission enhancement and 57 times for a maximum general magnetic dipole near-field emission enhancement, respectively. Moreover, the polarization-independent enhancements are found to be a robust variation of the dipole’s positions and structure geometries, showing nice fabrication tolerance for practical applications.