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The large voltage loss (Vloss) mainly stems from the mismatch between the perovskite film and electron transport layer in CsPbI2Br-based all-inorganic perovskite solar cells (I-PSCs), which restricts the power conversion efficiency (PCE) of devices. To address this issue, potassium benzoate (BAP) is first introduced as a bifunctional passivation material to regulate the TiO2/CsPbI2Br interface, reduce the Vloss, and improve the photovoltaic performance of CsPbI2Br-based I-PSCs. Eventually, the champion PCE of CsPbI2Br-based I-PSCs without a hole transport layer modified by BAP (Target-PSCs) improves to 14.90% from the 12.14% of reference PSCs. The open-circuit voltage (Voc) increases to 1.27 V from the initial 1.14 V after BAP modification. A series of characterizations show that BAP modification can not only optimize the energy level alignment of I-PSCs but also passivize the surface defects caused by uncoordinated Cs+/Pb2+. Moreover, the Target-PSCs without encapsulation demonstrate better thermal stability, which can maintain 107.6% of the original PCE after annealing at 160 °C for 140 min in humid air. While the reference PSCs only maintain 76.5% of their initial PCE after annealing at the same process. This work provides a simple strategy to modify the buried interface and improve the performance of CsPbI2Br-based I-PSCs.

Due to the easy oxidation of Sn2+, which leads to form tin vacancy defects and poor perovskite film quality, caused by the rapid crystallization rate in tin-based perovskite solar cells (PSCs), their efficiency lags far behind that of lead-based PSCs. To improve the photovoltaic (PV) performance and stability of FA0.9PEA0.1SnI3-based PSCs (T-PSCs), a small amount of Pb(SCN)2is introduced into a perovskite precursor as an antioxidant, and acetaminophen (ACE) with various functional groups is used to modify a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/perovskite interface. The results show that the Pb(SCN)2additive and ACE interfacial modification can not only optimize energy level alignment in T-PSCs but also inhibit Sn2+oxidation to reduce the trap-state density, resulting in promoted carrier transport. The synergetic effect of the Pb(SCN)2antioxidant and ACE interfacial modification significantly reduces nonradiative recombination and improves the PV performance and stability of T-PSCs. Consequently, the unsealed T-PSCs with the Pb(SCN)2additive and ACE modification achieve a champion efficiency of 12.04% and maintain 99% of their initial PCE after being stored in N2for more than 2100 h, while reference T-PSCs demonstrate a champion PCE of 6.20% and retain only 72% of its initial PCE. Moreover, the modified T-PSCs without encapsulation demonstrate much better stability in humid air.

Serious open-circuit voltage (Voc) loss originating from nonradiative recombination and mismatch energy level at TiO2/perovskite buried interface dramatically limits the photovoltaic performance of all-inorganic CsPbIxBr3–x(x= 1, 2) perovskite solar cells (PSCs) fabricated through low-temperature methods. Here, an ionic liquid (IL) bridge is constructed by introducing 1-butyl-3-methylimidazolium acetate (BMIMAc) IL to treat the TiO2/perovskite buried interface, bilaterally passivate defects and modulate energy alignment. Therefore, the Vocof all-inorganic CsPbIBr2PSCs modified by BMIMAc (Target-1) significantly increases by 148 mV (from 1.213 to 1.361 V), resulting in the efficiency increasing to 10.30% from 7.87%. Unsealed Target-1 PSCs show outstanding long-term and thermal stability. During the accelerated degradation process (85 °C, RH: 50∼60%), the Target-1 PSCs achieve a champion PCE of 11.94% with a remarkable Vocof 1.403 V, while the control PSC yields a promising PCE of 10.18% with a Vocof 1.319 V. In particular, the Vocof 1.403 V is the highest Vocreported so far in carbon-electrode-based CsPbIBr2PSCs. Moreover, this strategy enables the modified all-inorganic CsPbI2Br PSCs to achieve a Vocof 1.295 V and a champion efficiency of 15.20%, which is close to the reported highest PCE of 15.48% for all-inorganic CsPbI2Br PSCs prepared by a low-temperature process. This study provides a simple BMIMAc IL bridge to assist bifacial defect passivation and elevate the photovoltaic performance of all-inorganic CsPbIxBr3–x(x= 1, 2) PSCs.

Rhenium disulfide (ReS2) is a promising piezoelectric catalyst due to its excellent electron transfer ability and abundant unsaturated sites. The 1T′ phase structure leads to the evolution of ReS2into a centrosymmetric spatial structure, which restricts its application in piezoelectric catalysis. Herein, we propose a controllable defect engineering strategy to trigger the piezoelectric response of ReS2. The introduction of vacancy defects disrupts the initial centrosymmetric structure, which breaks the piezoelectric polarization bond and generates piezoelectric properties. By using transmission electron microscopy, we characterized it at the atomic scale and determined that vacancy defects contribute to an excellent piezoelectric property through first-principles calculations. Notably, the piezoelectric coefficient of the catalyst with 40 s-etching (ReS2@C-40) is 23.07 pm/V, an order of magnitude greater than other transition metal dichalcogenides. It demonstrated the feasibility of optimizing piezoelectric properties by increasing the conformational asymmetry. Based on its remarkable piezoelectric activity, ReS2@C-40 exhibits highly efficient piezo-photocatalytic synergistic sterilization performance with 99.99% eradication of Escherichia coliand 96.67% of Staphylococcus aureuswithin 30 min. This pioneering research on the coupling effect of ReS2in piezoelectric catalysis and photocatalysis provides ideas for the development of piezo-photocatalysts and efficient water purification technologies.

Abstract

The construction of type-II or S-scheme heterojunctions can effectively accelerate the directional migration of charge carriers and inhibit the recombination of electron–hole pairs to improve the catalytic performance of the composite catalyst; therefore, the construction and formation mechanism of a heterojunction are worth further investigation. Herein, Cu2O@Cu4(SO4)(OH)6·H2O core–shell polyhedral heterojunctions were fabricated via in situ etching Cu2O with octahedral, cuboctahedral, and cubic shapes by sodium thiosulfate (Na2S2O3). Cu2O@Cu4(SO4)(OH)6·H2O polyhedral heterojunctions demonstrated obviously enhanced sterilization and degradation performance than the corresponding single Cu2O polyhedra and Cu4(SO4)(OH)6·H2O. When Cu2O with a different morphology contacts with Cu4(SO4)(OH)6·H2O, a built-in electric field is established at the interface due to the difference in Fermi level (Ef); meanwhile, the direction of band bending and the band alignment are determined. These lead to the different migration pathways of electrons and holes, and thereby, a type-II or S-scheme heterojunction is constructed. The results showed that octahedral o-Cu2O@Cu4(SO4)(OH)6·H2O is an S-scheme heterojunction; however, cuboctahedral co-Cu2O@Cu4(SO4)(OH)6·H2O and cubic c-Cu2O@Cu4(SO4)(OH)6·H2O are type-II heterojunctions. By means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), diffuse reflectance spectra (DRS), and Mott–Schottky analyses, the band alignments, Fermi levels, and band offsets (ΔECB, ΔEVB) of Cu2O@Cu4(SO4)(OH)6·H2O polyhedral heterojunctions were estimated; the results indicated that the catalytic ability of the composite catalyst is determined by the type of heterojunction and the sizes of band offsets. Cubic c-Cu2O@Cu4(SO4)(OH)6·H2O has the strongest driving force (namely, biggest band offsets) to accelerate charge migration and effectively separate charge carriers, so it exhibits the strongest catalytic bactericidal and degrading abilities.

Two-dimensional ferroelectric materials can generate a bulk photovoltaic effect, making them highly promising for self-powered photodetectors. However, their practical application is limited by a weak photoresponse due to a weak transition strength and wide band gap. In this study, we construct a van der Waals heterojunction using NbOI2, which has significant in-plane polarization, with a highly absorbing MoSe2layer. We observe ultrafast hole transfer from MoSe2to NbOI2within 0.4 ps and electron transfer in the opposite direction within 3.8 ps, facilitating efficient charge dissociation and extraction. Applying a direct current electric field poling modulates the ferroelectric domains in NbOI2, enhancing the bulk photovoltaic effect. This results in one of the highest responsivities for self-powered photodetectors (101.3 mA/W) at 0 V bias alongside excellent polarization sensitivity (∼7.58). This work advances the understanding of self-powering mechanisms via the bulk photovoltaic effect and proposes new strategies for future self-powered devices.

Neuromorphic computing has attracted great attention for its massive parallelism and high energy efficiency. As the fundamental components of neuromorphic computing systems, artificial neurons play a key role in information processing. However, the development of artificial neurons that can simultaneously incorporate low hardware overhead, high reliability, high speed, and low energy consumption remains a challenge. To address this challenge, we propose and demonstrate a piezoelectric neuron with a simple circuit structure, consisting of a piezoelectric cantilever, a parallel capacitor, and a series resistor. It operates through the synergy between the converse piezoelectric effect and the capacitive charging/discharging. Thanks to this efficient and robust mechanism, the piezoelectric neuron not only implements critical leaky integrate-and-fire functions (including leaky integration, threshold-driven spiking, all-or-nothing response, refractory period, strength-modulated firing frequency, and spatiotemporal integration), but also demonstrates small cycle-to-cycle and device-to-device variations (∼1.9% and ∼10.0%, respectively), high endurance (1010), high speed (integration/firing: ∼9.6/∼0.4 μs), and low energy consumption (∼13.4 nJ/spike). Furthermore, spiking neural networks based on piezoelectric neurons are constructed, showing capabilities to implement both supervised and unsupervised learning. This study therefore opens up a new way to develop high-performance artificial neurons by using piezoelectrics, which may facilitate the realization of advanced neuromorphic computing systems.

Flexoelectric and photo-flexoelectricity are scientifically intriguing and hold considerable potential for various applications such as soft strain sensing, photovoltaics, energy harvesting, etc.Among flexoelectric materials, freestanding ferroelectric thin films are believed to have huge flexoelectricity and tunability due to their excellent lattice regulatory freedom and sustainability to larger strain gradients. In this work, we demonstrated a freestanding BiFeO3(BFO) thin film-based soft strain sensor and explored their flexoelectric coefficient and flexoelectric photovoltaic effect under different strain gradients. Under different bending scales, the photocurrent of the thin film exhibits a step-like variation, indicating that the sensor can measure strain gradient with high sensitivity. These results show the potential application of freestanding ferroelectric films in flexible devices.

Effective tuning of nanoscale domain structures provides fundamental basis for controlling and engineering of various functionalities in ferroelectric materials. In this work, we demonstrate the precise patterning of nanoscopic domain structures in as-grown epitaxial PbTiO3(PTO) films by merely introducing an ultrathin pre-patterned doping layer (e.g., Fe-doped PTO). The doping layer can effectively reverse the interfacial built-in bias, consequent to a reversed initial polarization reorientation in the as-grown film, which makes it possible to transfer the nano-patterns in the doping layer into the domain structure of ferroelectric films. For instance, we have successfully fabricated large area ordered array of nanoscale cylindrical domains (downward polarization) embedded in the matrix domain with opposite polarization (upward polarization) in PTO film. These nanoscale cylinder domains also allow deterministic and reversible erasure and creation induced by biased tip scanning. The results provide an effective pathway for on-demand patterning of large area nanoscale domains in the as-grown films, which may find applications in a wide range of nanoelectronic devices.

BiFeO3–BaTiO3(BF–BT) dielectric ceramics are receiving more and more concern for advanced energy storage devices owing to their excellent ferroelectric properties and environmental sustainability. However, the energy density and efficiency are limited in spite of the large remanent polarization. Herein, we proposed a multiscale optimization strategy via a local compositional disorder with a Birich content and nanodomain engineering by introducing the Sr0.7Bi0.2Ca0.1TiO3(SBCT) into BF–BT ceramics. Interestingly, an extraordinary energy storage property (ESP) with a high reversible energy storage density (Wrec) of ∼3.79 J/cm3and an ultrahigh polarization discrepancy (ΔP) of ∼58.5 μC/cm2were obtained in the SBCT-modified BF–BT ceramics under 160 kV/cm. The boosted ESP should be attributed to the fact that the replacement of A/B-sites cations could transform the long-range ferroelectric order of the BF–BT system into polar nanoregions (PNRs) along with the refined grain size, decreased leakage current, and broadened energy band gap. Moreover, good frequency (1–103Hz) and temperature (25–125 °C) stabilities, high fatigue resistance (× 105), large power density (∼31.1 MW/cm3), and fast discharge time (∼97 ns) were also observed for the optimized ceramics. These results illustrate a potentially effective method for creating high ESP lead-free ceramics at a low electric field.

Realizing robust magnetoelectric (ME) coupling effect near room temperature is still a long-standing challenge for the application of multiferroic materials in next-generation low-power spintronic and memory devices. Here we report a systematic study on the magnetic, dielectric, and ME coupling properties of Y-type hexaferrite Ba0.5Sr1.5Co2Fe12–xAlxO22(x = 0.0, 0.5, 1.0) single crystals. The Al doping can induce the shifting of the alternating longitudinal conical (ALC)-proper screw (PS) magnetic phase transition temperature from 200 K for x = 0–365 K for x = 1.0. The most interesting feature is that the Ba0.5Sr1.5Co2Fe11AlO22single crystal displays a direct and converse ME coupling coefficient with αH∼3,100 ps/m and αE∼3,900 ps/m at 250 K, respectively, due to the Al-doped enhanced stability of ALC phase. Moreover, the exchange bias also verifies the strong coupling of electric and magnetic orders. These results provide a valuable insight on the modulation of ALC structure and the mechanism of ME effect in Y-type hexaferrites.

While using ferroelectric polarization to tune the functional properties of 2D materials has been extensively studied recently, the effects of 2D materials on the ferroelectricity and piezoelectricity of ferroelectrics are much less explored. In this work, we report markedly enhanced ferroelectric and piezoelectric properties of graphene/Pb(Zr0.52Ti0.48)O3/SrRuO3(GR/PZT/SRO) capacitors. Compared with conventional metal-electroded ferroelectric capacitors, the GR/PZT/SRO capacitors exhibit more abrupt polarization switching, larger switchable polarization, lower leakage current, and smaller coercive voltage. Moreover, with graphene electrodes, the ferroelectric properties of PZT capacitors are much more stable against aging. The enhanced ferroelectric behaviors in GR/PZT/SRO capacitors can be attributed to an improved interface with fewer defects and inhibited growth of defective interfacial layer resulting from the graphene protection. Because of the atomic thickness and extraordinary mechanical flexibility of graphene, the piezoelectric response in PZT with graphene electrode is about four times larger than the one with an Au electrode. Our findings on the enhanced ferroelectric and piezoelectric properties of PZT with 2D electrodes advance the understanding of the 2D/PZT interface and provide solutions for developing high-performance ferroelectrics devices.

Recently, there is a surge of research interest in configurable ferroelectric conductive domain walls which have been considered as possible fundamental building blocks for future electronic devices. In this work, by using piezoresponse force microscopy and conductive atomic force microscopy, we demonstrated the controlled manipulation of various conductive domain walls in epitaxial BiFeO3thin films, e.g.neutral domain walls (NDW) and charged domain walls (CDWs). More interestingly, a specific type of nanoscale domains was also identified, which are surrounded by highly conductive circular CWDs. Similar nanoscale domains can also be controlled created and erasured by applying local field via conductive probe, which allow nondestructive current readout of different domain states with a large on/off resistance ratio up to 102. The results indicate the potential to design and develop high-density non-volatile ferroelectric memories by utilizing these programable conductive nanoscale domain walls.

In this study, an effective and simple approach for optimizing the performance of both cathode and anode interlayers in OSCs is demonstrated using 4-heptyl-4′-cyanobiphenyl (7CB) to dope a classic cathode (ZnO and SnO2) or an anode interlayer [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)]. Because of the enhanced light absorption, improved physical contact between a photoactive layer and an interlayer, and increased carrier recombination, all of the devices based on a 7CB-doped interlayer show increased short-circuit current density (Jsc), fill factor (FF), and power conversion efficiency (PCE) compared to the corresponding undoped interlayer, regardless it is the anode interlayer or the cathode interlayer, which is a rare phenomenon in the interlayer modification field.

When scaling the lateral size of a ferroelectric random access memory (FeRAM) device down to the nanometer range, the polarization switching-induced displacement current becomes small and challenging to detect, which greatly limits the storage density of FeRAM. Here, we report the observation of significantly enhanced injection currents, much larger than typical switching currents, induced by polarization switching in BiFeO3thin films via conductive atomic force microscopy. Interestingly, this injected current can be effectively modulated by applying mechanical force. As the loading force increases from ∼50 to ∼750 nN, the magnitude of the injected current increases and the critical voltage to trigger the current injection decreases. Notably, changing the loading force by an order of magnitude increases the peak current by 2–3 orders of magnitude. The mechanically boosted injected current could be useful for the development of high-density FeRAM devices. The mechanical modulation of the injected current may be attributed to the mechanical force-induced changes in the barrier height and interfacial layer width.

Sr0.7Bi0.2TiO3(SBT) is a promising pulse energy storage material due to minor hysteresis, but its low maximum polarization (Pmax) is bad for energy storage. K+–Bi3+defect pairs were introduced into the A-site of SBT to obtain Sr0.35Bi0.35K0.25TiO3(SBKT) with larger Pmax. Through first-principles calculations, we determined that the introduction of defect pairs destroys the paraelectric order phase and increases local polarization, resulting in more and larger polar nanoregion (PNR) formation. On this basis, doping NaNbO3(NN) in A- and B-sites of SBKT increases the cationic disorder and ferroelectric destabilization, further destroying the long-range order structure and forming more PNRs with smaller sizes. This enhances relaxation and decreases remnant polarization, and the broadened dielectric peak enables 0.85SBKT–0.15NN to meet the X7R specification. Furthermore, the decreased grain size and oxygen vacancy, increased thermal conductivity, and weakened local electric field (simulated by COMSOL) increase the dielectric breakdown strength (BDS). As a result, 0.95SBKT–0.05NN exhibits a high energy storage density (W) of 2.45 J/cm3with a high efficiency of 93.1%, a high pulsed discharge energy density of 2.1 J/cm3, and a high power density of 54.1 MW/cm3at 220 kV/cm. The energy storage properties show excellent stability of temperature (−55 to 150 °C), frequency (10–500 Hz), and cycling (105cycles). Notably, for the pulse charge–discharge properties, 0.95SBKT–0.05NN shows great fatigue resistance during 105cycles under 25 and 150 °C, accompanied by excellent thermal stability. Moreover, the BDS and Pmaxof 0.95SBKT–0.05NN sintered in O2further enhance. A higher Wof 2.92 J/cm3with a high efficiency of 89% at 250 kV/cm is achieved. Therefore, 0.95SBKT–0.05NN shows great application potential for pulse energy storage. In this work, we provide a novel strategy and systematic in-depth study for improving the energy storage properties of SBT.

The limitation of commercial single-crystal substrates and the lack of continuous strain tunability preclude the ability to take full advantage of strain engineering for further exploring novel properties and exhaustively studying fundamental physics in complex oxides. Here, we report an approach for imposing continuously tunable epitaxial strain in oxide heterostructures beyond substrate limitations by inserting an interface layer through tailoring of its gradual strain relaxation. Taking BiFeO3as a model system, we demonstrate the introduction of an ultrathin interface layer that allows the creation of desired strain states that can induce phase transition and stabilize a super-tetragonal phase as well as morphotropic phase boundaries, overcoming substrate limitations. Continuously tunable strain from tension to compression can be generated by precisely adjusting the interface layer thickness, enabling the achievement of continuous orthorhombic–rhombohedral-like–tetragonal-like phase transition. This proposed route could be extended to other oxide heterostructures, providing a platform for creating exotic phases and emergent phenomena.

BiFeO3, a single-phase multiferroic material, possesses several polymorphs and exhibits a strong sensitivity to strain. Recently, emergent strain engineering in BiFeO3thin films has attracted intense interest, which can overcome the confines of traditional strain engineering introduced through the mismatch between the film and substrate. In this review, we discuss emerging non-traditional strain engineering approaches to create new ground states and manipulate novel functionalities in multiferroic BiFeO3thin films. Through fabricating freestanding thin films, inserting an interface layer or utilizing thermal expansion mismatch, continuously tunable strain can be imposed beyond substrate limitations. Nanostructured evolution and defect introduction are discussed as efficient routes to introduce strain, promising for the development of new nanodevices. Ultrafast optical excitation, growth conditions and chemical doping driven strain are summarized as well. We hope this review will arouse the readers’ interest in this fascinating field.

A capping layer is known to be critical for stabilizing the ferroelectric (FE) orthorhombic phase (o-phase) in a HfO2-based thin film. Here, vanadium oxide (VOx), a functional oxide exhibiting the insulator–metal transition, is used as a novel type of a capping layer for the Hf0.5Zr0.5O2(HZO) thin film. It is demonstrated that the VOxcapping layer (VCL) can enhance the FE properties of the HZO thin film comprehensively. Specifically, the HZO thin film with a VCL shows large remanent polarization (2Pr≈36.9 μC/cm2), relatively small coercive field (Ec≈1.09 MV/cm), high endurance (up to 109cycles), and long retention (>105seconds). The enhanced FE properties may be attributed to the VCL-induced stabilization of the FE o-phase and suppression of oxygen vacancies at the interface. Furthermore, the HZO thin film with a VCL exhibits a successive rightward shift of polarization-voltage (P-V) hysteresis loop as the temperature increases. This is well correlated with the insulator–metal transition in a VCL, which can modulate the interfacial built-in field and thus cause the P-Vloop shift. It is therefore demonstrated that a VCL not only enhances the FE properties of HZO thin films but also provides a temperature degree of freedom to modulate the FE properties, which may open up a new pathway to develop HfO2-based FE memories with high performance and novel functionalities.

Two-dimensional/one-dimensional (2D/1D) heterostructures have received much attention from researchers for their abundant catalytically active sites and low contact resistance due to formation of chemical bonds at the interface. The investigation of such heterostructures, however, is confined to lattice-matched materials, which severely limits the material candidates. Herein, we demonstrate a lattice-mismatched 2D/1D heterostructured electrocatalyst consisting of 2D ReS2nanosheets and 1D CoS2nanowires. We propose that the higher surface energy of the CoS2nanowire and the lattice mismatch between 1D and 2D units are crucial for the growth process of ReS2nanosheets. More importantly, the terminal S2–exposed on the surface of CoS2nanowires serves not only as the nucleus of ReS2nanosheets but also as a bridge to enhance electron transport efficiency. Thus, the ReS2/CoS2heterostructures show outstanding hydrogen evolution reaction performance. This work is of general interest for the design of complex multidimensional nano-heterostructures with outstanding functionalities.

Nanoscale phase mixtures in transition-metal oxides (TMOs) often render these materials susceptible to external stimuli (electric field, mechanical stress, etc.), which can lead to rich functional properties and device applications. Here, direct observation and multifield manipulation of a nanoscale mixture of brownmillerite SrFeO2.5(BM-SFO) and perovskite SrFeO3(PV-SFO) phases in SrFeOx(SFO) epitaxial thin films are reported. The mixed-phase SFO film in its pristine state exhibits a nanoscaffold structure consisting of PV-SFO nanodomains embedded in the BM-SFO matrix. This nanoscaffold structure produces gridlike patterns in the current and electrochemical strain maps, owing to the strikingly different electrical and electrochemical properties of BM-SFO and PV-SFO. Moreover, electric field control of reversible topotactic phase transformation between BM-SFO and PV-SFO is demonstrated by electric-field-induced reversible changes in surface height, conductance, and electrochemical strain response. In addition, it is also shown that the BM-SFO → PV-SFO phase transformation can be enabled by applying mechanical stress. This study therefore not only identifies a strong nanometric structure–property correlation in the mixed-phase SFO but also offers a new paradigm for the multifield control of topotactic phase transformation.

Flexible perovskite solar cells (F-PSCs) have been developing fast with the power conversion efficiency (PCE) exceeding 19%. However, aiming at the high-efficiency F-PSCs, to get a desired perovskite morphology before and after glass-supportive device transfer is still a challenge. Herein, we thoroughly investigated the effect of adhesive materials of substrates on the perovskite film and the solar cell performance and developed a nondestructive F-PSC transfer method by introducing a double-side tape/protective film/epoxy binder. This nondestructive transfer strategy leads to a uniform morphology of perovskites, even after transfer process, yielding an enhanced PCE up to 16.55%.

Achieving high power conversion efficiencies (PCEs) in ferroelectric photovoltaics (PVs) is a longstanding challenge. Although recently ferroelectric thick films, composite films, and bulk crystals have all been demonstrated to exhibit PCEs >1%, these systems still suffer from severe recombination because of the fundamentally low conductivities of ferroelectrics. Further improvement of PCEs may therefore rely on thickness reduction if the reduced recombination could overcompensate for the loss in light absorption. Here, a PCE of up to 2.49% (under 365-nm ultraviolet illumination) was demonstrated in a 12-nm Pb(Zr0.2Ti0.8)O3(PZT) ultrathin film. The strategy to realize such a high PCE consists of reducing the film thickness to be comparable with the depletion width, which can simultaneously suppress recombination and lower the series resistance. The basis of our strategy lies in the fact that the PV effect originates from the interfacial Schottky barriers, which is revealed by measuring and modeling the thickness-dependent PV characteristics. In addition, the Schottky barrier parameters (particularly the depletion width) are evaluated by investigating the thickness-dependent ferroelectric, dielectric and conduction properties. Our study therefore provides an effective strategy to obtain high-efficiency ferroelectric PVs and demonstrates the great potential of ferroelectrics for use in ultrathin-film PV devices. An approach to boost the power conversion efficiencies (PCEs) of ferroelectric photovoltaics (PVs) is proposed based on the Schottky barrier effect. This approach leverages the thinning of a ferroelectric film to somewhere close to the depletion width, which can simultaneously suppress the recombination and lower the series resistance. Using this approach, we achieve a PCE up to 2.49% (under 365-nm ultraviolet illumination) in the 12-nm Pb(Zr0.2Ti0.8)O3ultrathin films. Our study provides insightful guidance on how to design and tailor the ferroelectric films to achieve high PCEs, and also demonstrates the great potential of ferroelectrics for use in ultrathin-film PV devices. Eliminating stray electrical effects in ultra-thin films can help optimize an unconventional solar energy technology. Ferroelectric materials have internal dipoles that spontaneously move photogenerated charges toward external circuits, producing higher power outputs than predicted by theory. Zhen Fan from South China Normal University in Guangzhou and colleagues now report that the dimensions of ferroelectric thin films distinctly affect how efficiently they convert sunlight into electricity. Measurements of solar cells containing lead-zirconium-titanate ferroelectrics with different thicknesses revealed a jump in conversion efficiencies when the film reached a thickness of 12 nanometers. Further analysis showed that this thickness correlates with the solar cell’s ‘depletion width’, a zone formed when metal electrodes contact the film. The electric field in the depletion zone complements the pushing actions of the ferroelectric dipoles, lowering electrical losses compared to thicker ferroelectric films.

With rapid advances in flexible electronics and communication devices, flexible dielectric capacitors exhibiting high permittivity, low loss, and large electric-field tunability over a wide frequency range have attracted increasing attention. Here, a large-scale Ba0.67Sr0.33TiO3(BST) dielectric thin film sandwiched between SrRuO3(SRO) bottom electrode and Pt top electrode is fabricated on a flexible mica substrate. The mica/SRO/BST/Pt capacitor exhibits a dielectric constant (εr′) of more than 1200, a loss tangent [tan(δ)] as low as 0.16, and a tunability of 67% at low frequencies around 10 kHz. Simultaneously, the capacitor can retain an εr′ of 540 and a tan(δ) of 0.07 at microwave frequencies, e.g., 18.6 GHz. Moreover, even when the capacitor is bent to a small radius of 5 mm or undergoes 12 000 bending cycles (at 5 mm radius), almost no deterioration in εr′, tan(δ), and tunability is observed. The excellent dielectricity and mechanical flexibility and durability endow the mica/SRO/BST/Pt capacitor with huge potential for flexible electronic and microwave applications.

Magnetic skyrmions are chiral quasiparticles that show promise for storage of information. At present, the achievable skyrmion density (ηSk) is generally low (10–20 μm–2) because of the lack of effective manipulation. Here, both the magnetic anisotropy (Keff) and interfacial Dzyaloshinskii–Moriya interaction (DMI) of [Pt/Co/Ta]nmultilayer films are elaborately modulated by changing the Co thickness (tCo) to study the ηSkdependence of intrinsic properties of the films systematically. The experimental and simulated results confirm that both the DMI and Keffhave significant modifications on ηSk, and their respective contributions vary with tCo. Only when the magnetic anisotropy transits from out-of-plane to in-plane at an appropriate tCorange (1.8–2.1 nm) does the Keffdecrease and the DMI increase with the tCo. Both the factors are favorable to the skyrmion formation and increase the density synergistically, toggling a maximal ηSkvalue of 45 μm–2. These findings provide a criterion for designing the high ηSkmagnetic film, which may advance the development of high-density skyrmion-based magnetic memorizers.

Precise manipulation of skyrmion nucleation in microscale or nanoscale areas of thin films is a critical issue in developing high-efficient skyrmionic memories and logic devices. Presently, the mainstream controlling strategies focus on the application of external stimuli to tailor the intrinsic attributes of charge, spin, and lattice. This work reports effective skyrmion manipulation by controllably modifying the lattice defect through ion implantation, which is potentially compatible with large-scale integrated circuit technology. By implanting an appropriate dose of nitrogen ions into a Pt/Co/Ta multilayer film, the defect density was effectively enhanced to induce an apparent modulation of magnetic anisotropy, consequently boosting the skyrmion nucleation. Furthermore, the local control of skyrmions in microscale areas of the macroscopic film was realized by combining the ion implantation with micromachining technology, demonstrating a potential application in both binary storage and multistate storage. These findings provide a new approach to advancing the functionalization and application of skyrmionic devices.

Recently, the ferroelectric photovoltaic (FePV) effect has attracted great interest due to its potential in developing optoelectronic devices such as solar cell and electric–optical sensors. It is important for actual applications to realize a controllable photovoltaic process in ferroelectric-based materials. In this work, we prepared well-ordered microarrays based on epitaxially tetragonal BiFeO3(T-BFO) films by the pulsed laser deposition technique. The polarization-dependent photocurrent image was directly observed by a conductive atomic force microscope under ultraviolet illumination. By choosing a suitable buffer electrode layer and controlling the ferroelectric polarization in the T-BFO layer, we realized the manipulation of the photovoltaic process. Moreover, based on the analysis of the band structure, we revealed the mechanism of manipulating the photovoltaic process and attributed it to the competition between two key factors, i.e., the internal electric field caused by energy band alignments at interfaces and the depolarization field induced by the ferroelectric polarization in T-BFO. This work is very meaningful for deeply understanding the photovoltaic process of BiFeO3-based devices at the microscale and provides us a feasible avenue for developing data storage or logic switching microdevices based on the FePV effect.

Negative differential resistance (NDR) has been extensively investigated for its wide device applications. However, a major barrier ahead is the low reliability. To address the reliability issues, we consider ferroelectrics and propose an alternative mechanism for realizing the NDR with deterministic current peak positions, in which the NDR results from the polarization switching-induced charge injection and subsequent charge trapping at the metal/ferroelectric interface. In this work, ferroelectric Au/BiFe0.6Ga0.4O3(BFGO)/Ca0.96Ce0.04MnO3(CCMO) nanocapacitors are prepared, and their ferroelectricity and NDR behaviors are studied concurrently. It is observed that the NDR current peaks are located at the vicinity of coercive voltages (Vc) of the ferroelectric nanocapacitors, thus evidencing the proposed mechanism. In addition, the NDR effect is reproducible and robust with good endurance and long retention time. This study therefore demonstrates a ferroelectric-based NDR device, which may facilitate the development of highly reliable NDR devices.

Ferroelectric nanocapacitors have attracted intensive research interest due to their novel functionalities and potential application in nanodevices. However, due to the lack of knowledge of domain evolution in isolated nanocapacitors, precise manipulation of topological domain switching in the nanocapacitor is still a challenge. Here, we report unique bubble and cylindrical domains in the well-ordered BiFeO3nanocapacitor array. The transformation of bubble, cylindrical and mono domains in isolated ferroelectric nanocapacitor has been demonstrated via scanning probe microscopy (SPM). The bubble domain can be erased to mono domain or written to cylindrical domain and mono domain by positive and negative voltage, respectively. Additionally, the domain evolution rules, which are mainly affected by the depolarization field, have been observed in the nanocapacitors with different domain structures. This work will be helpful in understanding the domain evolution in ferroelectric nanocapacitors and providing guidance on the manipulation of nanoscale topological domains.

Core–shell nanostructured materials with synergetic effects have gained increasing attention for their widespread applications in electrochemical water-splitting field. However, for most electrocatalysts, the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) can only work efficiently in neutral solution or alkaline solution, which hinders their further applications using untreated natural waters with a wide pH range, such as seawater (pH ∼ 7.5–8.5). In this paper, we report the synthesis of core–shell MoS2@CoO bifunctional electrocatalysts. The MoS2@CoO-coated carbon cloth electrode demonstrates excellent electrocatalytic properties for both OER and HER with 325 and 173 mV at a current density of 10 mA cm–2and Tafel slopes of 129.9 and 83.0 mV dec–1in 1 M KOH solutions, respectively. Additionally, the electrode can also work efficiently in neutral solutions (1 M PBS, pH = 7), showing good OER and HER activities for potential electrocatalytic water splitting applications in untreated natural waters.

Exchange bias stems from the interaction between different magnetic phases, and therefore, it generally occurs in magnetic multilayers. Here, we present a large exchange bias in a single SrRuO3layer induced by helium ion irradiation. When the fluence increases, the induced defects not only suppress the magnetization and the Curie temperature but also drive a metal–insulator transition at a low temperature. In particular, a large exchange bias field up to ∼0.36 T can be created by the irradiation. This large exchange bias is related to the coexistence of different magnetic and structural phases that are introduced by embedded defects. Our work demonstrates that spintronic properties in complex oxides can be created and enhanced by applying ion irradiation.

Water disinfection is of great importance for human health and daily life. Photocatalysts with high efficiency, environmental protection, and narrow bandgaps are critical for practical water treatment. Here, a general approach is reported for the direct growth of pyramid-type MoS2(pyramid MoS2) on transparent glass by chemical vapor deposition (CVD). The pyramid MoS2exhibits a smaller bandgap and higher bactericidal activity than most TiO2-based photocatalysts. The adjustable-bandgap nature of two-dimensional (2-D) MoS2can harvest a wide spectrum of sunlight and provide more active sites with which to generate reactive oxygen species (ROS) for bacterial death in water. Furthermore, silver (Ag) with several nanometers thicknesses is thermally evaporated on the pyramid MoS2, which can greatly facilitate electron–hole pair separation to generate more ROS and has a certain bactericidal effect. With our established approach, under simulated visible light, more than 99.99% of Escherichia colican be successfully deactivated in 40 min, with an effective mass per unit of less than 0.7 mg L–1in a 0.9 wt % NaCl solution. Besides, for the first time, the generation of ROS is confirmed with in situ Raman spectroscopy on pyramid MoS2@Ag glass, and the related bactericidal mechanism is present as well.

Electrically driven magnetic switching (EDMS) is highly demanded for next-generation advanced memories or spintronic devices. The key challenge is to achieve repeatable and reversible EDMS at sufficiently small scale. In this work, we reported an experimental realization of room-temperature, electrically driven, reversible, and robust 120° magnetic state rotation in nanoscale multiferroic heterostructures consisting of a triangular Co nanomagnet array on tetragonal BiFeO3films, which can be directly monitored by magnetic force microscope (MFM) imaging. The observed reversible magnetic switching in an individual nanomagnet can be triggered by a small electric pulse within 10 V with an ultrashort time of ∼10 ns, which also demonstrates sufficient switching cycling and months-long retention lifetime. A mechanism based on synergic effects of interfacial strain and exchange coupling plus shape anisotropy was also proposed, which was also verified by micromagnetic simulations. Our results create an avenue to engineer the nanoscale EDMS for low-power-consumption, high-density, nonvolatile magnetoelectric memories and beyond.

Nanostructured molybdenum disulfide (MoS2) has been considered as one of the most promising catalysts in the hydrogen evolution reaction (HER), for its approximately intermediate hydrogen binding free energy to noble metals and much lower cost. The catalytically active sites of MoS2are along the edges, whereas thermodynamically MoS2favors the presence of a two-dimensional (2-D) basal plane and the catalytically active atoms only constitute a small portion of the material. The lack of catalytically active sites and low catalytic efficiency impede its massive application. To address the issue, we have activated the basal plane of monolayer 2H MoS2through an ultrathin alumina mask (UTAM)-assisted nanopore arrays patterning, creating a high edge density. The introduced catalytically active sites are identified by Cu electrochemical deposition, and the hydrogen generation properties are assessed in detail. We demonstrate a remarkably improved HER performance as well as the identical catalysis of the artificial edges and the pristine metallic edges of monolayer MoS2. Such a porous monolayer nanostructure can achieve a much higher edge atom ratio than the pristine monolayer MoS2flakes, which can lead to a much improved catalytic efficiency. This controllable edge engineering can also be extended to the basal plane modifications of other 2-D materials, for improving their edge-related properties.

We report a facile and cost-competitive nanopatterning route, using Ar ion beam etching through a monolayer polystyrene sphere (PS) array placed on a ferroelectric epitaxial thin film, to fabricate ordered ferroelectric nanodot arrays. Using this method, well-ordered BiFeO3epitaxial nanodots, with tunable sizes from ∼100 to ∼900 nm in diameter, have been successfully synthesized. Interestingly, a plethora of exotic nanodomain structures, e.g., stripe domains, vortex and antivortex domains, and single domains, are observed in these nanodots. Moreover, this novel technique has been extended to produce Pb(Zr,Ti)O3nanodots and multiferroic composite Co/BiFeO3nanodots. These observations enable the creation of exotic domain structures and provide a wide range of application potentials for future nanoelectronic devices.

Recent research progress in (K,Na)NbO3(KNN)-based lead-free piezoelectric ceramics has attracted increasing attention for their applications to microsystems or microelectromechanical systems (MEMS) in the form of thin films. This work demonstrates that high-quality KNN-based epitaxial films can be synthesized by a conventional sol–gel method, whose phase structure and domain characteristics have been investigated with emphasis on the temperature effect. A monoclinic MCstructure is observed at room temperature in KNN-based epitaxial films, which is close to but different from the orthorhombic phase in bulk counterparts. Piezoresponse force microscopy (PFM) at elevated temperatures reveals continuous changes of ferroelectric domains in KNN films during heating and cooling cycles between room temperature and 190 °C. A distinct change in domain morphology is observed upon heating to 110 °C, accompanied by a clear variation of dielectric permittivity suggesting a thermotropic phase transition, which is revealed to belong to a MC–MAphase transition on the basis of structural and PFM analysis on local ferroelectric and piezoelectric behaviors. Enhanced piezoelectric response at the thermotropic phase boundary is observed, which is attributed to active domains and/or nanodomains formed across the boundary. Domain engineering by utilizing the phase transition should be important and effective in KNN-based films not only for property enhancement but also for its textured ceramics.

A large-sized zero-valent iron plate (LSZVIP) with excellent reaction efficiency and cycle performance for heavy-metal ion removal from wastewater is desirable. However, it has yet to be achieved due to its relatively low specific surface area and non-crystal oxide shells produced during treatment, preventing its core electrons from transporting to the shell surface for heavy-metal ion reduction. Therefore, we proposed a novel mechanism to address the challenges in this paper by earthing the iron plate and stirring the treated solution to trigger an insulator-to-metal transition in the non-crystal oxides shell, thereby removing the barrier to electron transport in the oxide shells. Furthermore, earthing of the iron plate allows electrons from the earth to participate in hexavalent chromium (Cr(VI)) reduction, thereby eliminating the production of oxide shells during the reduction. With the stirring and earthing strategy, an acceptable Cr(VI)-reduction performance is obtained over the decimeter-sized zero-valent iron plate (DSZVIP). The residence time of earthing DSZVIP in the 1st cycle is 25 min and 80 min in the 10th cycle by stirring at 350 rotations per minutes (rpm) to achieve 100% Cr(VI)-reduction. This study provides a novel and applicable method for treating heavy-metal wastewater on a large scale.

Ferroelectric resistive switching (RS), manifested as a switchable ferroelectric diode effect, was observed in well-ordered and high-density nanocapacitor arrays based on continuous BiFeO3(BFO) ultrathin films and isolated Pt nanonelectrodes. The thickness of BFO films and the lateral dimension of Pt electrodes were aggressively scaled down to <10 nm and ∼60 nm, respectively, representing an ultrahigh ferroelectric memory density of ∼100 Gbit/inch2. Moreover, the RS behavior in those nanocapacitors showed a large ON/OFF ratio (above 103) and a long retention time of over 6,000 s. Our results not only demonstrate for the first time that the switchable ferroelectric diode effect could be realized in BFO films down to <10 nm in thickness, but also suggest the great potentials of those nanocapacitors for applications in high-density data storage.

High quality zirconium oxide (ZrO2) high-kdielectrics have been fabricated by chemical solution processes. The ZrO2thin films annealed at various temperatures were studied from microstructure properties to electric properties in detail. The dielectric film annealed at 700 °C features a smooth surface, low leakage current density (1.89 × 10–6A/cm2@ −3 MV/cm) and high dielectric constant (20). Organic thin film transistors (OTFTs) based on ZrO2with different surface modifications were characterized to investigate the interfacial effects between the high-kdielectric and organic semiconductors. The OTFTs with poly(α-methylstyrene) (PαMS) coated ZrO2show much higher carrier mobility and on/off ratio than those with bare-ZrO2or with hexamethyldisilazane-treated ZrO2. The ZrO2/PαMS layers offer a low surface energy to grow large crystals and benefit the charge transport in organic semiconductors, whereas the dielectric surface roughness and dipole scattering are less important. The resulting OTFTs show high current on/off ratio (1.2 × 105), low threshold voltage (−0.38 V), and low SS (0.26 V/dec). Our work has deepened the understanding on the complex interfacial effects between high-kdielectric and organic semiconductor. Finally, we demonstrate low temperature fabrication of ZrO2-OTFTs on a flexible substrate, demonstrating solution processable high-kZrO2dielectric films offer great potentials for low-cost organic electronic devices, especially for low voltage organic electronic devices.

Tin-based perovskite solar cells (T-PSCs) have become the star photovoltaic products in recent years due to their low environmental toxicity and superior photovoltaic performance. However, the easy oxidation of Sn2+and the energy level mismatch between the perovskite film and charge transport layer limit its efficiency. In order to regulate the microstructure and photoelectric properties of tin-based perovskite films to enhance the efficiency and stability of T-PSCs, guanidinium bromide (GABr) and organic Lewis-based additive methylamine cyanate (MAOCN) are introduced into the FA0.9PEA0.1SnI3-based perovskite precursor. A series of characterizations show that the interactions between additive molecules and perovskite mutually reconcile to improve the photovoltaic performance of T-PSCs. The introduction of GABr can adjust the band gap of the perovskite film and energy level alignment of T-PSCs. They significantly increase the open-circuit voltage (Voc). The MAOCN material can form hydrogen bonds with SnI2in the precursor, which can inhibit the oxidation of Sn2+and significantly improve the short-circuit current density (Jsc). The synergistic modulation of the dual additives reduces the trap-state density and improves photovoltaic performance, resulting in an increased champion efficiency of 9.34 for 5.22% of the control PSCs. The unencapsulated T-PSCs with GABr and MAOCN dual additives prepared in the optimized process can retain more than 110% of their initial efficiency after aging for 1750 h in a nitrogen glovebox, but the control PSCs maintain only 50% of their initial efficiency kept in the same conditions. This work provides a new perspective to further improve the efficiency and stability of T-PSCs.

Piezoelectricity in 2D transition metal dichalcogenides (TMDs) has gathered significant interest due to their massive exposure of unsaturated edge sites and high piezoelectric modulus. Nevertheless, the piezoelectricity in 1T' phase TMDs is inhibited by its center symmetry of space group. Herein, to break the shackles of piezoelectric polarization, we synthesize a piezoelectric material composed of an atomic molybdenum array bound to distorted 1T' ReS2(MDR). The phase transition from 1T' to distorted 1T' (D-1T') removes the special Peierl's distortion of ReS2, breaking its center symmetry and allowing for piezoelectric generation. Remarkably, MDR exhibits a large piezoelectric coefficient (d33) value of 15.45pm/V, which is an order of magnitude higher than those reported in other TMDs. Combining with excellent piezocatalytic activity, a 0D/3D di-piezoelectric porous electret featuring an enhanced quantum confinement piezoelectric effect based on the MDR quantum dots (QDs) and inverse opal g-C3N4(IOCN) is demonstrated for high-efficiency piezoelectric catalysis.

Ferroelectrics with negative capacitance effects can amplify the gate voltage in field-effect transistors to achieve low power operation beyond the limits of Boltzmann’s Tyranny. The reduction of power consumption depends on the capacitance matching between the ferroelectric layer and gate dielectrics, which can be well controlled by adjusting the negative capacitance effect in ferroelectrics. However, it is a great challenge to experimentally tune the negative capacitance effect. Here, the observation of the tunable negative capacitance effect in ferroelectric KNbO3through strain engineering is demonstrated. The magnitude of the voltage reduction and negative slope in polarization-electric field (P–E) curves as the symbol of negative capacitance effects can be controlled by imposing various epitaxial strains. The adjustment of the negative curvature region in the polarization-energy landscape under different strain states is responsible for the tunable negative capacitance. Our work paves the way for fabricating low-power devices and further reducing energy consumption in electronics.

The controllable manipulation of polar topological structures (e.g.skyrmion bubble) in ferroelectric materials have been considered as a cornerstone for future programmable nano-electronics. Here, we present the effective creation and erasure of polar bubble states PbTiO3(PTO) multilayers trigged by mechanical stress and light illumination, respectively. It was found that applying atomic force microscope (AFM) tip force can induced formation of nanoscale bubble domains from the initial monodomain state. Moreover, the created bubble domain can be eliminated by exposure to ultraviolet or infrared light illumination. The above results can be understood by modulation of depolarization screening charges and bias fields, as reflected by scanning Kelvin potential microscopic (SKPM) observations, whereby the flexoelectric effect from the tip force tends to remove the screening charges on top surface and modulate the bias field that favors the formation of bubble state while light illumination tends to recover the screen charges and favor the monodomain state. The results provide a good example for multi-field manipulation of polar topologies, which might create a new avenue towards the immerging new concept electronic devices.

Magnetic skyrmions are topologically protected swirling spin textures with great potential for future spintronic applications. The ability to induce skyrmion motion using mechanical strain not only stimulates the exploration of exotic physics but also affords the opportunity to develop energy-efficient spintronic devices. However, the experimental realization of strain-driven skyrmion motion remains a formidable challenge. Herein, we demonstrate that the inhomogeneous uniaxial compressive strain can induce the movement of isolated skyrmions from regions of high strain to regions of low strain at room temperature, which was directly observed using an in situLorentz transmission electron microscope with a specially designed nanoindentation holder. We discover that the uniaxial compressive strain can transform skyrmions into a single domain with in-plane magnetization, resulting in the coexistence of skyrmions with a single domain along the direction of the strain gradient. Through comprehensive micromagnetic simulations, we reveal that the repulsive interactions between skyrmions and the single domain serve as the driving force behind the skyrmion motion. The precise control of skyrmion motion through strain provides exciting opportunities for designing advanced spintronic devices that leverage the intricate interplay between strain and magnetism.

Tin-based perovskite solar cells (TPSCs) have become one of the most prospective photovoltaic materials due to their remarkable optoelectronic properties and relatively low toxicity. Nevertheless, the rapid crystallization of perovskites and the easy oxidization of Sn2+to Sn4+make it challenging to fabricate efficient TPSCs. In this work, a piperazine iodide (PI) material with −NH– and −NH2+– bifunctional groups is synthesized and introduced into the PEA0.1FA0.9SnI3-based precursor solution to tune the microstructure, charge transport, and stability of TPSCs. Compared with piperazine (PZ) containing only the −NH– group, the PI additive displays better effects on regulating the microstructure and crystallization, inhibiting Sn2+oxidation and reducing trap states, resulting in an optimal efficiency of 10.33%. This is substantially better than that of the reference device (6.42%). Benefiting from the fact that PI containing −NH– and −NH2+– groups can passivate both positively charged defects and negatively charged halogen defects, unencapsulated TPSCs modified with the PI material can maintain about 90% of their original efficiency after being kept in a N2atmosphere for 1000 h, much higher than the value of 47% in reference TPSCs without additives. This work provides a practical method to prepare efficient and stable pure TPSCs.

Multiferroic magnetoelectric (ME) composites exhibit sizable ME coupling at room temperature, promising applications in a wide range of novel devices. For high density integrated devices, it is indispensable to achieve a well-ordered nanostructured array with reasonable ME coupling. For this purpose, we explored the well-ordered array of isolated epitaxial BiFeO3/CoFe2O4/SrRuO3heterostructured nanodots fabricated by nanoporous anodic alumina (AAO) template method. The arrayed heterostructured nanodots demonstrate well-established epitaxial structures and coexistence of piezoelectric and ferromagnetic properties, as revealed by transmission electron microscopy (TEM) and peizoeresponse/magnetic force microscopy (PFM/MFM). It was found that the heterostructured nanodots yield apparent ME coupling, likely due to the effective transfer of interface couplings along with the substantial release of substrate clamping. A noticeable change in piezoelectric response of the nanodots can be triggered by magnetic field, indicating a substantial enhancement of ME coupling. Moreover, an electric field induced magnetization switching in these nanodots can be observed, showing a large reverse ME effect. These results offer good opportunities of the nanodots for applications in high-density ME devices, e.g., high density recording (>100 Gbit/in.2) or logic devices.

Ferroelectric tunnel junction (FTJ) has attracted considerable attention for its potential applications in nonvolatile memory and neuromorphic computing. However, the experimental exploration of FTJs with high ON/OFF ratios is a challenging task due to the vast search space comprising of ferroelectric and electrode materials, fabrication methods and conditions and so on. Here, machine learning (ML) is demonstrated to be an effective tool to guide the experimental search of FTJs with high ON/OFF ratios. A dataset consisting of 152 FTJ samples with nine features and one target attribute (i.e., ON/OFF ratio) is established for ML modeling. Among various ML models, the gradient boosting classification model achieves the highest prediction accuracy. Combining the feature importance analysis based on this model with the association rule mining, it is extracted that the utilizations of {graphene/graphite (Gra) (top), LaNiO3(LNO) (bottom)} and {Gra (top), Ca0.96Ce0.04MnO3(CCMO) (bottom)} electrode pairs are likely to result in high ON/OFF ratios in FTJs. Moreover, two previously unexplored FTJs: Gra/BaTiO3(BTO)/LNO and Gra/BTO/CCMO, are predicted to achieve ON/OFF ratios higher than 1000. Guided by the ML predictions, the Gra/BTO/LNO and Gra/BTO/CCMO FTJs are experimentally fabricated, which unsurprisingly exhibit ≥1000 ON/OFF ratios (∼8540 and ∼7890, respectively). This study demonstrates a new paradigm of developing high-performance FTJs by using ML.

High-efficiency hybrid solar cells (HSCs) based on electrospun titanium dioxide (TiO2) nanofibers plus poly(3-hexylthiophene) (P3HT) are fabricated by means of both the pretreatment using tetrahydrofuran (THF) vapor and the surface modification using n-type antimony chalcogenide (Sb2S3) on the TiO2nanofibrous networks. It is revealed that the THF pretreatment not only reinforces the interfacial physical contact but also suppresses the interfacial recombination. The Sb2S3modification improves the light absorption and charge transfer. Given that the active layer of the HSCs is as thin as 300 nm, it is demonstrated that the power conversion efficiency (PCE) is enhanced over 175%, exhibiting a PCE of 2.32%.