Spontaneous Polarization Field Research Articles

Enhancing photoelectrochemical properties of α-Fe2O3 using Zr-doped HfO2 ferroelectric nanoparticles

Hematite (α-Fe2O3) as a semiconductor photoanode for photoelectrochemical (PEC) water splitting is a promising candidate material. However, its PEC performance is limited by the slow charge transfer kinetics at the α-Fe2O3/electrolyte interface. Ferroelectric materials can be used as a tool for carrier separation in photoelectrochemical water splitting due to their spontaneous polarization electric field characteristics. Here, we deposited Hf0.5Zr0.5O2 (HZO) ferroelectric nanoparticles on the surface of α-Fe2O3 and use the spontaneous polarization field of ferroelectric HZO to promote the separation of photogenerated carriers, promote the charge transfer from α-Fe2O3 to the electrolyte, and enhance the PEC of hematite. After depositing the HZO nanoparticles, the photogenerated holes are efficiently extracted from α-Fe2O3 and then directed into the electrolyte to participate in water oxidation reaction at α-Fe2O3/HZO interfaces, which enhanced the charge separation efficiency by 58 % compared to that of pure α-Fe2O3. Consequently, the α-Fe2O3/HZO photoanode exhibits a 65 % boost in photocurrent density, reaching up to 0.28 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (VRHE) compared to that of pure α-Fe2O3. This study introduces a method to engineer the photoanode/ferroelectric interface, enhancing carrier separation and thereby optimizing PEC water splitting performance.

Physical reservoirs based on MoS2-HZO integrated ferroelectric field-effect transistors for reservoir computing systems.

Reservoir computing (RC), a variant of recurrent neural networks (RNNs), is well-known for its reduced energy consumption through exclusive focus on training the output weight and its superior performance in handling spatiotemporal information. Implementing these networks in hardware requires devices with superior fading memory behavior. Unlike filament-based two-terminal devices, those relying on ferroelectric switching demonstrate improved voltage reliability, while three-terminal transistors provide additional active control. HfO2-based ferroelectric materials such as Hf0.5Zr0.5O2 (HZO), have garnered attention for their scalability and seamless integration with CMOS technology. This study implements a RC hardware based on MoS2-HZO integrated device structure with enhanced spontaneous polarization field. By adjusting the oxygen vacancy concentration, the devices exhibit consistent responses to both identical and nonidentical voltages, making them suitable for diverse RC applications. The high accuracy of MNIST handwritten digits recognition highlights the rich reservoir states of the traditional RC architecture. Additionally, the impact of masks on RC implementation is assessed, showcasing the device's capability for spatiotemporal signal analysis. This development paves the way for implementing energy-efficient and high-performance computing solutions.

Dipole field in nitrogen-enriched carbon nitride with external forces to boost the artificial photosynthesis of hydrogen peroxide

Artificial photosynthesis is a promising strategy for efficient hydrogen peroxide production, but the poor directional charge transfer from bulk to active sites restricts the overall photocatalytic efficiency. To address this, a new process of dipole field-driven spontaneous polarization in nitrogen-rich triazole-based carbon nitride (C3N5) to harness photogenerated charge kinetics for hydrogen peroxide production is constructed. Here, C3N5 achieves a hydrogen peroxide photosynthesis rate of 3809.5 µmol g−1 h−1 and a 2e− transfer selectivity of 92% under simulated sunlight and ultrasonic forces. This high performance is attributed to the introduction of rich nitrogen active sites of the triazole ring in C3N5, which brings a dipole field. This dipole field induces a spontaneous polarization field to accelerate a rapid directional electron transfer process to nitrogen active sites and therefore induces Pauling-type adsorption of oxygen through an indirect 2e− transfer pathway to form hydrogen peroxide. This innovative concept using a dipole field to harness the migration and transport of photogenerated carriers provides a new route to improve photosynthesis efficiency via structural engineering.

Flexo-Pyrophotronic Effect Modulated Giant Near Infrared Photoresponse from VO2 -Based Heterojunction for Optical Communication.

The flexoelectric phenomenon, which occurs when materials undergo mechanical deformation and cause strain gradients and a related spontaneous electric polarization field, can result in wide variety of energy- and cost-saving mechano-opto-electronics, such as night vision, communication, and security. However, accurate sensing of weak intensities under self-powered conditions with stable photocurrent and rapid temporal response remains essential despite the challenges related to having suitable band alignment and high junction quality. Taking use of the flexoelectric phenomena, it is shown that a centrosymmetric VO2 -based heterojunction exhibits a self-powered (i.e., 0V), infrared (λ = 940nm) photoresponse. Specifically, the device shows giant current modulation (103 %), good responsivity of >2.4mA W-1 , reasonable specific detectivity of ≈1010 Jones, and a fast response speed of 0.5ms, even at the nanoscale modulation. Through manipulation of the applied inhomogeneous force, the sensitivity of the infrared response is enhanced (> 640%). Ultrafast night optical communication like Morse code distress (SOS) signal sensing and high-performing obstacle sensors with potential impact alarms are created as proof-of-concept applications. These findings validate the potential of emerging mechanoelectrical coupling for a wide variety of novel applications, including mechanoptical switches, photovoltaics, sensors, and autonomous vehicles, which require tunable optoelectronic performance.

Effect of spontaneous polarization field on diffusion thermopower in AlGaN/GaN heterostructures

Polarization field on diffusion thermopower Sd, of a two-dimensional electron gas (2DEG) formed at a wurtzite AlGaN/GaN heterojunction is investigated. The investigations of macroscopic polarization effect on diffusion thermopower over the wide range of temperature and barrier fluctuations bring out the role of spontaneous and piezoelectric polarization fields present in the heterostructure. The induced 2DEG charge density formed at the interface of AlGaN/GaN heterojunction due to in-built spontaneous and piezoelectric fields are assumed to be scattered by acoustic phonons via deformation and piezoelectric couplings, background and remote impurities via Coulomb interaction, interface roughness and interface charges. We find, the dominant contribution is from interface roughness scattering mechanism and that from acoustic phonons via deformation potential is negligible. Theoretical investigations of Sd show that, the effect of the spontaneous polarization is to reduce the diffusion thermopower significantly at practically relevant temperatures.

Self-powered dual-wavelength polarization-sensitive photodetectors based on ZnO/BiFeO3 heterojunction

The ferroelectric-photovoltaic (FE-PV) devices have received growing attention for the FE polarization-induced internal electric field to facilitate the separation and transport of the photogenerated electron-hole (e-h) pairs in the FE semiconductors. However, the low photocurrent output of the FE-PV devices is still a key challenge for the application and development of these devices. Here, ZnO/BiFeO3 (BFO) heterojunction photodetectors (PDs) are designed to utilize the built-in electric field at the heterojunction interface of ZnO nanoparticles (NPs)/BFO and the spontaneous FE polarization field of BFO to promote the separation and transport of the photogenerated carriers. ZnO nanorod arrays (NRs) grown on ZnO NPs provide a directional transport channel for the photogenerated electrons. ZnO/BFO heterojunction devices demonstrate a self-powered photoresponse in the ultraviolet (UV) and visible (vis) dual-wavelength. The devices show a responsivity of 1.32 mA/W, response time (τrise/τdecay) of 12.6/44.9 ms at 420 nm light illumination. In addition, the polarization imaging function of ZnO/BFO PDs is explored by extending the polarization photocurrent mapping values of a single PD unit to a complex array of optical information image processing utilizing the polarization-sensitive properties of BFO without external bias.

Ferroelectric properties of Sr0.5Ba0.5Nb2O6 thin films grown on a Si(001) substrate by RF cathode sputtering

Using the RF cathode sputtering method, ferroelectric films of barium-strontium niobate Sr0.5Ba0.5Nb2O6 were synthesized on a semiconductor substrate. Their phase composition, crystal structure, nanostructure, dielectric, and ferroelectric characteristics were studied. The temperature ranges of phase transformations, the characteristic values of spontaneous polarization and coercive fields, the magnitude and nature of the change in the imaginary and real parts of the complex permittivity in the temperature range −190 ÷ 250 °C were established in the films. The reasons for the revealed regularities are discussed.

High-Speed and High-Power Ferroelectric Switching Current Measurement Instrument for Materials with Large Coercive Voltage and Remanent Polarization.

A high-speed and high-power current measurement instrument is described for measuring rapid switching of ferroelectric samples with large spontaneous polarization and coercive field. Instrument capabilities (±200 V, 200 mA, and 200 ns order response) are validated with a LiTaO3 single crystal whose switching kinetics are well known. The new instrument described here enables measurements that are not possible using existing commercial measurement systems, including the observation of ferroelectric switching in large coercive field and large spontaneous polarization Al0.7Sc0.3N thin films.

“Polymer-in-ceramic” PEO/2D heterojunction composite electrolytes for solid-state batteries

The ferroelectric spontaneous polarizability of the piezoelectric TBA+CNO− also has an enhanced effect on ion transport and electrode interface modification, and its ferroelectric spontaneous polarization field also helps to reduce the generation and growth of anode dendrites. The structural instability of LRAP electrolyte Li2.99Ba0.005OCl are maintained by forming a heterojunction structure with two-dimensional nanosheets TBA+CNO−, and the fast conduction channels of lithium ions (Li+) are established. Composite electrolytes possess Li+ conductivity σi > 10−4 S/cm at 25°C. The composite materials composed of “polymer-in-ceramic” with flexibility and mechanical strength are fabricated by the casting method. PEO-Li2.99Ba0.005OCl/TBA+CNO− shows good compatibility with lithium metal, forming a stable solid electrolyte interface. The plastic crystal electrolyte dripped on the cathode side avoids the direct contact between high-voltage cathode and electrolyte and protects PEO from being oxidized and decomposed. NCM811|Li batteries show 70.9 mAh•g−1 with capacity retention of 97.88% after 100 cycles.

Enhanced photocatalytic performance by polarizing ferroelectric KNbO3 for degradation of plastic wastes under mild conditions

Although photocatalysts can convert plastic wastes into energy fuels and show unique advantages in the treatment of plastic wastes, photocatalytic efficiency is still limited by the fast recombination of photoexcited charges. In this paper, potassium niobate (KNbO3) nanosheet with the ferroelectric property was synthesized and polarized under an external electric field. Polarization does not change the morphology and structure of KNbO3, but effectively enhances the spontaneous polarization field. This spontaneous polarization field exists through the whole material and can effectively improve the separation of photogenerated charges. The photocatalytic efficiency of polarized KNbO3 (P-KNbO3) for degradation of PE and PP improves by about 210 % and 140 %, compared with KNbO3. P-KNbO3 also shows excellent photocatalytic activity for the degradation of real-world waste plastic products (plastic bags, gloves, tubes and boxes). This study might provide insights into designing high-efficiency photocatalysts for plastic waste treatment by regulating and controlling the polarization of ferroelectric materials.

Depth profiled polarization effects in AlGaN quantum wells probed with interconnected cathodoluminescence spectroscopy and ion sputtering

Based on interconnected ion sputtering and cathodoluminescence spectroscopy, an optical spectroscopic strategy has been developed to profile depth-dependent polarization effects in an AlGaN multiple-quantum-well structure. Two emission bands at about 258 nm and 315 nm have been identified to originate from the quantum wells and Ga-rich domains, respectively, and their depth-dependent spectral characteristics reveal that the spontaneous polarization dominates the piezoelectric polarization in the quantum wells, and the emission wavelengths vary with respect to the etching depth due to interactions of the spontaneous polarization field with the piezoelectric polarization field and the surface charge induced electric field.

Ferroelectricity and Schottky Heterojunction Engineering in AgNbO3: A Simultaneous Way of Boosting Piezo-photocatalytic Activity.

As an efficient and economical way of dealing with organic pollutants, piezo-photocatalysis has attracted great interest. In this work, we demonstrated that ferroelectricity and Schottky heterojunction engineering could significantly enhance the piezo-photocatalytic activity of AgNbO3. The poled 20 mol % K+ doped AgNbO3 disclosed its superior piezo-photocatalytic activity of 0.131 min-1 for 10 mg·L-1 RhB, which is 7.8 times of the pristine one under the condition of illumination only. The designed piezo-photocatalyst also exhibited good piezo-photocatalytic stability after four cycles. These merits are attributed to the built-in electric field associated with the large spontaneous polarization and low coercive field originated from the stable ferroelectric state after ferroelectricity engineering, plus with the electron trapper effect of the in situ precipitated metal Ag particles. Our work not only provides a promising piezo-photocatalyst for degrading organic contaminants but also paves a good way for developing high piezo-photocatalytic activity catalysts.

Analytical study of the ferroelectric properties of Fe-doped KNbO3 single crystal

We report herein the structural, dielectric, ferroelectric, and domain properties of an Fe-doped potassium niobate ([KNbO3] KNb1-xFexO3; x = 0.01 mol%) single crystal synthesized by a flux method. X-ray diffraction (XRD) results illustrate that the given sample adopts orthorhombic crystal symmetry with the space group Amm2. On submitting the sample to differential thermal analysis (DTA), two endothermic peaks were observed, the first at 224 °C and the second at 425 °C. Dielectric studies with respect to temperature from 30 to 500 °C showed that the Curie temperature (Tc) of the Fe-doped KNbO3 single crystal occurred at 435 °C. The measured dielectric loss of the crystal is in good agreement with other dielectric studies. The relationship between polarization and electric field (PE) shows that the spontaneous polarization (Ps) and coercive field (Vc) for the doped material are lower than those for an undoped KNbO3 single crystal, indicating a weakly ferroelectric nature of the sample. A trinocular microscope has been used to study the domain properties and revealed the formation of 60° and 90° domain walls. Furthermore, upon etching the single crystal with nitric acid (HNO3), etch pits and a twinning plane of the domains were formed. Finally, electric fields of 100, 500, and 1000 V/cm were applied to the Fe-doped KNbO3 single crystal surface, whereupon the nucleation and dissipation of new domains could be observed.

Highly Oriented Organic Ferroelectric Films with Single-Crystal-Level Properties from Restrained Crystallization

Crystallization is a key for ferroelectricity which is a collective behavior of microscopic electric dipoles. On the other hand, uncontrolled crystallization leads to uneven morphology and random crystal orientations, which undermines the application potential of ferroelectric thin films. In this work, we introduce a film fabrication method of low-temperature physical vapor deposition followed by restrained crystallization, with electrical properties monitored in real-time by in situ measurements. This method was adopted to fabricate films of 2-methylbenzimidazole (MBI), whose molecule crystals are proton-transfer type biaxial ferroelectrics and tend to grow into a hedgehog-shaped spherulites morphology. The in situ measurements confirm that the crystallization, corresponding to a clear transition of physical properties, occurs dominantly during post-deposition warming. This enables the fabrication of micron-thick films in disk-shaped morphology with one polarization axis aligned along the out-of-plane direction, while the measured spontaneous polarization and coercive field are comparable to the single-crystal values. These results mark an important advancement of film growth that is expected to benefit widely the fabrication of molecular materials films whose functional properties hinge on crystallization to achieve desirable morphology and crystallinity.

Simulation of Negative Capacitance Based on the Miller Model: Beyond the Limitation of the Landau Model

Here we demonstrate negative capacitance (NC) characteristics of a ferroelectric–dielectric (FE–DE) capacitor by means of a fully numerical, self-consistent simulation based on the Miller model (MM) and Poisson’s equation. Over the years, the Landau model (LM) has been widely used, which fits experimental data of spontaneous polarization versus electric field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}-{E}_{\mathrm {FE}}$ </tex-math></inline-formula> ) characteristics using a so-called “S-curve”; however, it cannot capture different transitions of polarization switching and can also fail to properly represent the material properties of certain FEs. To overcome such limitations of the LM, we have used the MM to simulate an FE–DE capacitor. Even though the MM seemingly fails to show steep switching characteristics due to the absence of the negative slope in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}-{E}_{\mathrm {FE}}$ </tex-math></inline-formula> curve unlike the LM, our simulation exhibits the NC characteristics of FE–DE capacitors with significant internal voltage amplification. Notably, we explore the effect of different transitions of polarization switching by varying the coercive field of FE within the MM, and exhibit that greater NC characteristics can be achieved with a FE having a more abrupt switching transition. We have also investigated the impact of other material parameters of FE, such as saturation and remnant polarization, on the NC characteristics of FE–DE capacitors. Our results provide comprehensive insight into the mechanism of FE-DE capacitors, suggesting sophisticated engineering of material and device parameters to seek desired performance of NC devices.

Control of electric properties of silicene heterostructure by reversal of ferroelectric polarization

Silicene is a kind of two-dimensional material composed of a honeycomb arrangement of silicon atoms. Compared with the structure of graphene, the buckled structure of silicene weakens the &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}$\pi—\pi$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; overlaps and turns the hybrid orbitals from &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$\rm sp^2$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; to &lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}$\rm sp^3$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, which enhances the spin-orbit coupling strength but still preserves the Dirac cone near &lt;i&gt;K&lt;/i&gt; or &lt;i&gt;K&lt;/i&gt;&lt;i&gt;'&lt;/i&gt;. Owing to its buckled structure, silicene is susceptible to external parameters like electric field and substrate, which draws lots of attention both experimentally and theoretically. Recent progress of ferroelectricity in two-dimensional (2D) van der Waals materials found that the spontaneous ferroelectric polarization can be preserved even above room temperature, which inspires us to investigate how to tune the electric properties of silicene through the spontaneous polarization field of 2D ferroelectric substrate. &lt;inline-formula&gt;&lt;tex-math id="M8"&gt;\begin{document}${\rm In_{2}}X_3$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M8.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M8.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; (&lt;i&gt;X&lt;/i&gt; = Se,S,Te) Family recently were found to have single ferroelectric monolayers with reversible spontaneous electric polarization in both out-of-plane and in-plane orientations, and the lattice mismatch between silicene and &lt;inline-formula&gt;&lt;tex-math id="M9"&gt;\begin{document}$\rm In_{2}S_3$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M9.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M9.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;is negligible. Therefore, we investigate the stacking and electric properties of silicene and monolayer &lt;inline-formula&gt;&lt;tex-math id="M10"&gt;\begin{document}$\rm In_{2}S_3$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M10.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M10.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; heterostructure by the first-principles calculations. The spontaneous polarization field of &lt;inline-formula&gt;&lt;tex-math id="M11"&gt;\begin{document}$\rm In_{2}S_3$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M11.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M11.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is calculated to be 1.26 &lt;inline-formula&gt;&lt;tex-math id="M12"&gt;\begin{document}$\rm μC {\cdot} cm^{-2}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M12.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M12.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, comparable to the experimental results of &lt;inline-formula&gt;&lt;tex-math id="M13"&gt;\begin{document}$\rm In_{2}Se_3$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M13.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M13.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. We compare the different stacking order between silicene and &lt;inline-formula&gt;&lt;tex-math id="M14"&gt;\begin{document}$\rm In_{2}S_3$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M14.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M14.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. The calculated results shown that the &lt;i&gt;AB&lt;/i&gt; stacking is the ground state stacking order, and the reversal of the ferroelectric polarization could tune the band structure of heterostructure. When the polarization direction of &lt;inline-formula&gt;&lt;tex-math id="M15"&gt;\begin{document}$\rm In_{2}S_3$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M15.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M15.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is upward, the layer distance between silicene and &lt;inline-formula&gt;&lt;tex-math id="M16"&gt;\begin{document}$\rm In_{2}S_3$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M16.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M16.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is 3.93 Å, the polarization field and substrate interaction together break the&lt;i&gt; AB&lt;/i&gt; sublattice symmetry and induce a 1.8 meV band gap near the Dirac point of &lt;i&gt;K&lt;/i&gt; and &lt;i&gt;K'&lt;/i&gt;, while the Berry curvature around &lt;i&gt;K &lt;/i&gt;and &lt;i&gt;K' &lt;/i&gt;have opposite signs, corresponding to valley Hall effect. When the polarization is downward, the layer distance decreases to 3.62 Å and the band gap around &lt;i&gt;K&lt;/i&gt; and&lt;i&gt; K'&lt;/i&gt; both increase to 30.8 meV. At the same time a 0.04&lt;i&gt;e&lt;/i&gt; charge transfer makes some bands move across the Fermi energy, corresponding to metal state. Our results pave the way for studying the ferroelectric tuning silicene heterostructures and their potential applications in information industry.

Stacking induced nonvolatile tuning of band gap in bilayer [formula omitted

Using density functional theory calculations, we investigate the structural and electronic properties of bilayer α phase In2Se3 corresponding to different stacking orders. We found that for bilayer the interlayer antiferroelectric tail-to-tail aligned is more stable than ferroelectric aligned. The band gap varies significantly from 0.158 eV in ferroelectric bilayer to 1.278 eV in antiferroelectric one, which is due to the spontaneous polarization field induced energy shift in the ferroelectric bilayer. Transition form antiferroelectric to ferroelectric bilayer could be realized by a proper external electric field, which corresponding to the nonvolatile tuning of band gap desired in new-generation memory devices.

The role of spontaneous and piezoelectric polarization fields on the spectral and power characteristics of InxGa1-xN/GaN superluminescent light emitting diodes

The role of spontaneous and piezoelectric polarization fields on the spectral and power characteristics of InxGa1-xN/GaN superluminescent light emitting diodes

Effect of ferroelectric polarization field on different carrier migration in photoanode

Spontaneous polarization field in ferroelectric can improve the oxidation kinetics and photocurrent of a photoanode in photoelectrochemical water splitting. But the impact of ferroelectric polarization field on the migration of different charge carriers which have different mobility and diffusion length is still unknown. In this work, we synthesized tetragonal BaTiO3 nanoparticles by solvothermal method successfully and fabricated the hybrid photoanode composed by monoclinic WO3 and BaTiO3 for solar water oxidation. Density functional theory calculations showed that the mobility of electron was faster than that of the hole in WO3, and had a longer diffusion length. We demonstrated that the polarization field of ferroelectric had a greatly impact upon holes migration compared with electrons, thus the thin hybrid photoanode after poling by bias presented a significant improvement of photocurrent (210.5%) under the back-side illumination, and a remarkable augment of charge separation efficiency (94%) and oxidation kinetics (69%) at 1.23 V. Our work provided a deeper understanding of how ferroelectric polarization field affected the photoelectrochemical water oxidation and a general pathway towards enhancing minority carrier collection in photoanode.

Controllable, Self-Powered, and High-Performance Short-Wavelength Infrared Photodetector Driven by Coupled Flexoelectricity and Strain Effect.

Mechanical deformation-induced strain gradients and coupled spontaneous electric polarization field in centrosymmetric materials, known as the flexoelectric effect, can generate ubiquitous mechanoelectrical functionalities, like the flexo-photovoltaic effect. Concurrently, nano/micrometer-scale inhomogeneous strain reengineers the electronic arrangements and in turn, could alter the fundamental limits of optoelectronic performance. Here, the flexoelectric effect-driven self-powered giant short-wavelength infrared (λ≤ 1800nm) photoresponse from centrosymmetric bulk silicon, indeed far beyond the fundamental bandgap (λ= 1100nm) is demonstrated. Particularly, large on/off ratio (≈105 ), extremely high sensitivity (2.5 × 108 %), good responsivity of 96mA W-1 , decent specific detectivity of ≈1.54 × 1014 Jones, and a rapid response speed of ≈100 µs, even at nanoscale (<30nm), are measured at λ= 1620nm. The infrared response sensitivity is tuned in a wide range (up to 1.4 × 108 %) by controlling the applied pointed force from 1 to 10 µN. These results confirm that emerging mechanoelectrical coupling not only sheds to achieve tunable optoelectronic performance beyond the fundamental limit, but also offers innovative numerous applications like mechanoptical switch, photovoltaic, sensors, and self-driving vehicles.