Polarization Switching Research Articles

Tunable perfect meta-absorber with high sensitivity for refractive index sensing application

An infrared (IR) tunable perfect meta-absorber (TPM) is presented, which is configured of metal-insulator-metal (MIM) structure. The unit cell of the TPM device is composed of two opposite T-shaped and two rod-shaped Au resonators on the reflective mirror layer. The optimized feature size of TPM can achieve perfect absorption and the resonant wavelength can be tuned from blue-shift first and then red-shift by increasing the gap size between two T-shaped resonators continuously. The tuning process of red shift is linear. By changing the distance between two rod-shaped resonators, the TPM device exhibits red shift linearly. Moreover, TPM device shows polarization-dependent characteristic that the main absorption resonance can be attenuated from 100% to 0% by changing polarization angle from 0° to 90° of incident IR light. The resonance of TPM device has an excellent linear relationship with the ambient refractive index, and the sensitivity and maximum figure of merit (FOM) are calculated as 1249 nm/RIU and 21 RIU−1, respectively. These results prove that the design of the proposed TPM device is very suitable for the use of IR sensing, polarization switching, and refractive index sensing applications.

Effects of thickness and defect on ultrahigh electro strain of piezoelectric ceramics

Piezoelectric ceramics with high electro strain are widely used in actuators, sensors, and so on. Here, this work investigates the electro strain of representative piezoelectric materials, and analyzes the influence of electrode type on the electro strain of PZT41 with significant strain anomalies. It is found that the occurrence of abnormally significant strain is not affected by the electrode but caused by intrinsic defects. Therefore, the ceramic samples with and without defects tailoring in Na0.5Bi0.5TiO3 (NBT) based and PbZr0.52Ti0.48O3 (PZT) based systems were prepared by the solid-state reaction method, and the results show that abnormally ultrahigh electro strains occur in excessively thin samples with diploes due to defects tailoring. Through displacement configuration experiments and comprehensive analysis of polarization switching processes, it is found that the occurrence of asymmetric abnormal significant strains is caused by reversible bending deformation in excessively thin samples. This work provides new support for the emergence of ultrahigh electro strain in piezoelectric ceramics.

Polarity Switching and Josephson Junction Interfaces Investigated by Multislice Ptychography

Polarity Switching and Josephson Junction Interfaces Investigated by Multislice Ptychography

Electric Control of Magnetism in Multiferroic Rare-Earth-Substituted BiFeO_{3} with Ferrielectricity.

The multiferroic rare-earth-substituted BiFeO_{3} has emerged as a promising candidate to achieve ultralow-energy-dissipation logic or memory devices, but the fundamental details of the switching mechanism involving the electrical, structural, and magnetic degrees of freedom is not fully understood, in particular, in its single-phase form. Here, a first-principles-based computational scheme is used to study Nd-doped BiFeO_{3} as a model system. The structure that yields a reduced P-E hysteresis loop is found to be ferrielectric with modulated octahedral tiltings, and it is shown that both the in-plane and out-of-plane ferromagnetization can be controlled by an applied electric field. The switching behaviors can be well interpreted by a Landau-type model, in which the magnetoelectric coupling is indirect and mediated by octahedral tiltings. The effects of varied composition and temperature are further discussed, revealing important correlations between the polarization switching and the robustness of the control of magnetization.

Enhancement of ferroelectric properties of the Ga0.6Fe1.4O3 films by Zn,N co-doping

Multiferroic materials have attracted considerable interests due to their scientific and technological importance in advanced devices. Ga0.6Fe1.4O3 thin film exhibits ferrimagnetism above room temperature but suffers from large leakage current. To reduce the charge conduction and enhance the ferroelectric properties of Ga0.6Fe1.4O3 film, ion doping is a useful technique. In this study, we fabricated Ga0.6Fe1.4-xZnxO3/N films by substituting Zn2+ and N3- ions in Ga0.6Fe1.4O3 for Fe and O, respectively. The influence of Zn, N co-doping on the structure, leakage current, magnetic and ferroelectric properties of the films were investigated. The results indicated that the films exhibited the orthorhombic structure with the incorporation of Zn and N. All Ga0.6Fe1.4-xZnxO3/N films showed above room temperature ferrimagnetism, and the magnetization and transition temperature values decreased with Zn,N co-doping. The microscopic and macroscopic ferroelectric measurements have demonstrated the ferroelectric polarization switching of the films. The ferroelectric hysteresis loops of the Ga0.6Fe1.38Zn0.02O3/N film showed the remnant polarization of ∼0.46 μC/cm2 with the coercive field of ±2 V at room temperature. The leakage current significantly reduced from ∼3.27×10−1 A/cm2 for pure Ga0.6Fe1.4O3 film to ∼1.48×10−5 A/cm2 for Ga0.6Fe1.35Zn0.05O3/N film, by four orders of magnitude. This may be attributed to the incorporation of Zn2+ and N3-, providing charge compensation to valence fluctuations of Fe between Fe3+ and Fe2+. These results provide an effective method to improve the ferroelectricity of Ga0.6Fe1.4O3 film, and open a wide perspective for the potential application in magnetoelectric devices.

Ultrasensitive Paper-Based Photoelectrochemical Biosensor for Acetamiprid Detection Enabled by Spin-State Manipulation and Polarity-Switching.

Efficient carrier separation is vitally crucial to improving the detection sensitivity of photoelectrochemical (PEC) biosensors. Here, we developed a facile strategy to efficiently regulate the carrier separation efficiency of the photoactive matrix BiOI and In2S3 signal label functionalized paper chip by manipulation of electrons spin-state and rational design of electron transport pathways. The spin-dependent electronic structures of BiOI and In2S3 were regulated via enhanced electron-spin parallel alignment induced by an external magnetic field, markedly retarding carrier recombination and extending their lifetime. Simultaneously, with the progress of the target-induced catalytic hairpin assembly process, the transfer path of photogenerated carriers was changed, leading to a switch in photocurrent polarity from cathode to anode. This reversed electron transport pathway not only boosted the separation ability of photogenerated electrons but also eliminated false-positive and false-negative signals, thereby further improving the detection sensitivity. As a proof of concept, the well-designed magnetic field-stimulated paper-based PEC biosensor showed highly selectivity and sensitivity for acetamiprid assay with a wide linear range of 1 fM to 20 nM and an ultralow detection limit of 0.73 fM. This work develops a universal strategy for improving the sensitivity of biosensors and exhibits enormous potential in the fields of bioanalysis and clinical diagnosis.

Ferroelectric Stochasticity in 2D CuInP2S6 and Its Application for True Random Number Generator.

True random number generators (TRNGs), which create cryptographically secure random bitstreams, hold great promise in addressing security concerns regarding hardware, communication, and authentication in the Internet of Things (IoT) realm. Recently, TRNGs based on nanoscale materials have gained considerable attention for avoiding conventional and predictable hardware circuitry designs that can be vulnerable to machine learning (ML) attacks. In this article, a low-power and low-cost TRNG developed by exploiting stochastic ferroelectric polarization switching in 2D ferroelectric CuInP2S6 (CIPS)-based capacitive structures, is reported. The stochasticity arises from the probabilistic switching of independent electrical dipoles. The TRNG exhibits enhanced stochastic variability with near-ideal entropy, uniformity, uniqueness, Hamming distance, and independence from autocorrelation variations. Its unclonability is systematically examined using device-to-device variations. The generated cryptographic bitstreams pass the National Institute of Standards and Technology (NIST) randomness tests. This nanoscale CIPS-based TRNG is circuit-integrable and exhibits potential for hardware security in edge devices with advanced data encryption.

Robust Ferrimagnetism and Ferroelectricity in 2D ɛ-Fe2O3 Semiconductor with Ultrahigh Ordering Temperature.

2D single-phase multiferroic materials with the coexistence of electric and spin polarization offer a tantalizing potential for high-density multilevel data storage. One of the current limitations for application is the scarcity of the materials, especially those combine ferromagnetism and ferroelectricity at high temperatures. Here, robust ferrimagnetism and ferroelectricity in 2D ɛ-Fe2O3 samples with both single-crystalline and polycrystalline form are demonstrated. Interestingly, the polycrystalline nanosheets also exhibit easily switchable ferroelectric polarizations comparable to that of single crystals. The existence of grain boundary does not hinder the switching and retention of ferroelectric polarization. Furthermore, the ɛ-Fe2O3 nanosheets show ferrimagnetic and ferroelectric Curie temperatures up to 800K, which reaches record highs in 2D single-phase multiferroic materials. This work provides important progress in the exploration of 2D high-temperature single-phase multiferroics for potentially compact high-temperature information nanodevices.

Fast polarization switching of undulator radiation up to kilohertz with magnetic field modulation

The fast polarization switching of undulator radiation has attracted more and more attention in recent years. In this paper, a new method is proposed for fast polarization switching of undulator radiation by using magnetic field modulation generated from low-current electromagnetic coils. The key point is that we propose to use the coils with a period length of an integral multiple of the undulator period, which can significantly reduce the required coil field. Through fast switching the power of coils, the radiation spectra of two undulators can be rapidly shifted into and out of the bandpass of a monochromator, enabling fast polarization switching for the user beamline. Based on this advantage, this method has strong potential to be implemented in a storage ring and a high switching frequency up to kilohertz can be expected. Published by the American Physical Society 2024

Versatile platform for electrically reconfigurable THz devices based on silicon Schottky-metasurfaces

We propose a versatile platform to design tunable metasurface devices based on Au/n-Si Schottky diodes embedded in a split-ring resonator (SRR) devised on a Si-on-insulator (SOI) wafer. The horizontally formed diodes are connected in the SRR radial direction, reducing the overall junction capacitance of the metasurface array compared to its counterparts with vertically formed Schottky junctions. This reduction in the junction capacitance has an essential role in the switching speed of the metasurface between the On and Off states. By carefully varying the externally applied bias voltage to the Schottky diodes, one can manipulate the incident THz signal at the metasurface resonance frequencies by converting its resonance mode by switching states. We use the forenamed platform to design three fundamental THz devices: a modulator, a polarization switch, and a polarizing beam splitter. A reverse bias of V R =5V excites two LC resonances at 0.3 THz and 0.89 THz in the modulator, which fade away by switching the gate voltage to V F =0.49V, exciting a dipole resonance in the metasurface at 0.75 THz. The numerical results show that this THz modulator enjoys modulation depths of ≥92% at the LC resonances and a phase modulation of ∼1.16rad at 0.86 THz. An identical electric bias change of the Schottky diodes in the polarization switch alters the resonators from anisotropic to isotropic, changing the output wave polarization from circular with nearly 99% of the circular polarization percentage to linear or quasi-linear at four frequencies simultaneously. Additionally, the proposed THz polarization splitter can deflect the cross-polarized transmitted component from the normally outgoing co-polarized one with an angle of 70° at 0.56 THz. The splitting ratio is switched from 1:1 in reverse bias to 14:1 in forward bias by changing the bias to forward bias. We expect that the proposed designs in the THz frequency domain, benefiting from the several hundred GHz switching speed of the Schottky diodes array, will be beneficial in applications such as analysis of the complex organic structures or polarization modulation and polarization-dependent multiplexing/demultiplexing in wireless communication systems.

Ultra-fast polarity switching GC-IMS for the analysis of volatiles in biogas

The Renewable Energy Act 2023 (§39i) requires reducing corn silage in biogas plants from 40 % to 30 % in 2026. Since corn silage yields the highest biogas per weight unit of all biogas feedstocks, this poses new challenges for biogas plant operators. However, alternative biogas feedstocks not harvested directly from the field may contain siloxanes due to the use of care products and disinfectants. The conversion of siloxanes into silicon dioxide during the combustion process seriously threatens the lifetime and efficiency of the used gas engine, even in very low concentrations. Consequently, we present a highly sensitive measurement system for monitoring biogas. Detection limits down to 0.037 mg/m³ for the tested siloxanes have been reached. Furthermore, ketones can be detected down to 0.002 mg/m³, alcohols down to 0.001 mg/m³. The device combines an ultra-fast polarity switching ion mobility spectrometer with a switching time of 12 ms and a resolving power of RP = 70, a gas chromatographic pre-separation, and a non-dispersive infrared sensor for methane. In this context, we analyzed the biogas composition for volatile substances and siloxanes, whereby we only found the volatile substances. For demonstration, biogas was analyzed at three different stages during the gas purification process.

Defects and oxygen impurities in ferroelectric wurtzite Al1−xScxN alloys

III-nitrides and related alloys are widely used for optoelectronics and as acoustic resonators. Ferroelectric wurtzite nitrides are of particular interest because of their potential for direct integration with Si and wide bandgap semiconductors and unique polarization switching characteristics; such interest has taken off since the first report of ferroelectric Al1−xScxN alloys. However, the coercive fields needed to switch polarization are on the order of MV/cm, which are 1–2 orders of magnitude larger than oxide perovskite ferroelectrics. Atomic-scale point defects are known to impact the dielectric properties, including breakdown fields and leakage currents, as well as ferroelectric switching. However, very little is known about the native defects and impurities in Al1−xScxN and their effect on the dielectric and ferroelectric properties. In this study, we use first-principles calculations to determine the formation energetics of native defects and unintentional oxygen incorporation and their effects on the polarization switching barriers in Al1−xScxN alloys. We find that nitrogen vacancies are the dominant native defects, and unintentional oxygen incorporation on the nitrogen site is present in high concentrations. They introduce multiple mid-gap states that can lead to premature dielectric breakdown and increased temperature-activated leakage currents in ferroelectrics. We also find that nitrogen vacancy and substitutional oxygen reduce the switching barrier in Al1−xScxN at low Sc compositions. The effect is minimal or even negative (increases barrier) at higher Sc compositions. Unintentional defects are generally considered to adversely affect ferroelectric properties, but our findings reveal that controlled introduction of point defects by tuning synthesis conditions can instead benefit polarization switching in ferroelectric Al1−xScxN at certain compositions.

High-Performance Piezoelectric Two-Dimensional Covalent Organic Frameworks.

Organic piezoelectric nanogenerators (PENGs) are attractive in harvesting mechanical energy for various self-powering systems. However, their practical applications are severely restricted by their low output open circuit voltage. To address this issue, herein, we prepared two two-dimensional (2D) covalent organic frameworks (COFs, CityU-13 and CityU-14), functionalized with fluorinated alkyl chains for PENGs. The piezoelectricity of both COFs was evidenced by switchable polarization, characteristic butterfly amplitude loops, phase hysteresis loops, conspicuous surface potentials and high piezoelectric coefficient value (d33). The PENGs fabricated with COFs displayed highest output open circuit voltages (60 V for CityU-13 and 50 V for CityU-14) and delivered satisfactory short circuit current with an excellent stability of over 600 seconds. The superior open circuit voltages of CityU-13 and CityU-14 rank in top 1 and 2 among all reported organic materials-based PENGs.

High‐performance Piezoelectric Two‐dimensional Covalent Organic Frameworks

Organic piezoelectric nanogenerators (PENGs) are attractive in harvesting mechanical energy for various self‐powering systems. However, their practical applications are severely restricted by their low output open circuit voltage. To address this issue, herein, we prepared two two‐dimensional (2D) covalent organic frameworks (COFs, CityU‐13 and CityU‐14), functionalized with fluorinated alkyl chains for PENGs. The piezoelectricity of both COFs was evidenced by switchable polarization, characteristic butterfly amplitude loops, phase hysteresis loops, conspicuous surface potentials and high piezoelectric coefficient value (d33). The PENGs fabricated with COFs displayed highest output open circuit voltages (60 V for CityU‐13 and 50 V for CityU‐14) and delivered satisfactory short circuit current with an excellent stability of over 600 seconds. The superior open circuit voltages of CityU‐13 and CityU‐14 rank in top 1 and 2 among all reported organic materials‐based PENGs.

Tailoring ferroelectricity in P(VDF/TrFE) thin films: Unveiling the hidden role of cooling rate

P(VDF/TrFE), a versatile ferroelectric polymer, holds immense promise for diverse applications, but optimizing its ferroelectric properties has been a major bottleneck. We present a groundbreaking approach, demonstrating a remarkable 48 % enhancement in polarization through a precise control of the cooling rate after annealing. Slow cooling at 0.5 °C/min significantly enhances the β-phase crystallinity, the ferroelectrically active phase, as evidenced by X-ray diffraction. This improved crystallinity directly contributes to the observed polarization enhancement. Dielectric analysis reveals a strong link between cooling rate and molecular alignment, with slower cooling leading to a higher dielectric constant, indicative of superior chain order. This improved order facilitates more efficient polarization switching, further contributing to the enhanced ferroelectricity. Our study unveils the often-overlooked impact of cooling rate on the ferroelectric properties of P(VDF/TrFE) thin films. By manipulating the cooling speed after annealing, we can effectively tailor the material's ferroelectricity, opening new avenues for optimizing device performance and expanding its application potential.

MEMS reconfigurable terahertz meta-absorber with polarization-dependent and sensing characteristics

This study presents and demonstrates a design of a micro-electro-mechanical system (MEMS) reconfigurable terahertz (THz) metamaterial absorber (TMA) that shows tunable free spectra range with a maximum value as 166 GHz in transverse magnetic mode and switchable resonance from 1.24 THz to 1.53 THz. The unit structure of TMA consists of two movable rectangular resonators aside and an x-shaped resonator at the center comprising two c-shaped resonators connected upside down. The material configuration of TMA is typical of the metal–insulator-metal sandwich configuration. That is a bottom Au layer preventing the penetration of the THz wave, a dielectric SiO2 layer to accommodate and absorb the incident wave, and a patterned Au structure array to select the resonant frequency. The electromagnetic response of TMA could be flexibly modulated when the structure is reconfigured by changing the gaps between x-shaped resonators and rectangular resonators based on the MEMS platform. Meanwhile, owing to the asymmetry of resonant structure, the electromagnetic response of TMA could be tuned from single-, dual-, triple- quad-resonances by varying the polarization state of incidence. Furthermore, the sensitivity of TMA is explored and demonstrated with remarkable linearity under a variation of the surrounding environment refractive index from 1.0 to 2.0. The feasibility of TMA is validated as the experimental absorption spectra are well meet the simulation results. The above results indicate the proposed TMA possesses great potential applications in multiple resonance switches, polarization switches, and highly efficient environmental sensors.

Fully Optical Control of Polarization Current Direction in a Cyanide‐Bridged Trinuclear Complex

As a remote and non‐contact stimulus, light offers the potential for manipulating the polarization of ferroelectric materials without physical contact. However, in current research, the non‐contact write‐read (erase) process lacks direct observation through the stable current as output signal. To address this limitation, we investigated the photoinduced polarization switching capabilities of the cyanide‐bridged compound [Fe2Co] using visible light, leading to the achievement of rewritable polarization. By subjecting [Fe2Co] crystals to alternating irradiation with 785 nm and 532 nm light, the polarization changes exhibited a distinct square wave pattern, confirming the reliability of the writing and erasing processes. Initialization involved exposing specific crystal units to 532 nm light for storing "1" or "0" information, while reading was accomplished by scanning the units with 785 nm light, resulting in brief current pulses for "1" states and no current signal for "0" states. This research unveils new possibilities for optical storage systems, paving the way for efficient and rewritable data storage and retrieval technologies, such as the next‐generation memories.

Enhanced Performance of Self-Powered Ga2O3/ZnO:V Heterojunction Solar-Blind Ultraviolet Photodetectors by Coupling Ferroelectricity and Piezoelectricity.

Ferroelectric materials have aroused increasing interest in the field of self-powered ultraviolet (UV) photodetectors (PDs) for their switchable spontaneous polarization. However, the utilization of ferroelectric materials to modulate the built-in electric field and energy band at the junction interface has rarely been investigated. Herein, we design and fabricate self-powered solar-blind UV PDs based on a Ga2O3/ZnO:V heterojunction. The performance of the Ga2O3/ZnO:V PD is significantly enhanced through the reasonable coupling of ferroelectricity and piezoelectricity within the ZnO:V film. The device at 260 nm exhibits excellent photoelectric properties with high peak responsivity of 64.5 mA/W, a specific detectivity of 3.8 × 1010 Jones, and a rise/decay time of 1.9/45.2 μs, together with reproducibility and stability. Systematical energy band diagram analysis reveals that the excellent performance of Ga2O3/ZnO:V PD can be attributed to the driving forces arising from the addition of the depolarization field and piezoelectric field, which increases the intensity of built-in electric field and promotes the separation and transport of photogenerated carriers at the heterojunction interface. The findings of our research provide a novel avenue and valuable guidance for the design of high-performance self-powered photodetectors.

Photocurrent polarity switching photoelectrochemical aptasensor for oxytetracycline based on BiOBr/Ag2S/PDA//CuO: CuO-induced II-type to dual Z-scheme system

BackgroundAs a broad-spectrum tetracycline antibiotic, Oxytetracycline (OTC) was widely used in a variety of applications. But, the overuse of OTC had led to the detection of it in food, water and soil, which could present significance risk to human health and cause damage to ecosystem. It was of great significance to develop sensitive detection methods for OTC.Herein, an environmentally friendly photoelectrochemical (PEC) aptasensor was constructed for the sensitive detection of OTC based on CuO-induced BiOBr/Ag2S/PDA (Polydopamine) photocurrent polarity reversal. ResultsBiOBr/Ag2S/PDA composites modified electrode not only produced stable initial anodic photocurrent but also provided attachment sites for the aptamer S1 of OTC by the strong adhesion of PDA. On the other hand, CuO loaded OTC aptamer S2 (Cu–S2) was got through Cu–S bonds. After the target OTC was identified on the electrode surface, CuO was introduced to the surface of ITO/BiOBr/Ag2S/PDA through the specific binding of OTC to S2. This identification process formed dual Z-type heterojunctions and resulted in a remarkable reversal of photocurrent polarity from anodic to cathodic. Under optimization conditions, the PEC aptasensor showed a wide linear range (50 fM ∼ 100 nM), low detection limit (1.9 fM), excellent selectivity, stability and reproducibility for the detection of OTC. Moreover, it was successfully used for the analysis of OTC in real samples of tap water, milk and honey, and had the potential for practical application. SignificanceThis work developed an environmentally friendly photocurrent-polarity-switching PEC aptasensor with excellent selectivity, reproducibility, stability, low LOD and wide linear range for OTC detection. This sensitive system, which was including BiOBr, Ag2S, PDA and CuO were low toxicity, not only reduced the risk of traditional toxic semiconductors to operators and the environment, but can also be used for the detection of real samples, broadening the wider range of applications for BiOBr, Ag2S, PDA and CuO.

Ultrahigh Bipolar Photoresponse in a Self-Powered Ultraviolet Photodetector Based on GaN and In/Sn-Doped Ga2O3 Nanowires pn junction.

Self-powered ultraviolet photodetectors with bipolar photoresponse have great potential in the fields of ultraviolet optical communication, all-optical controlled artificial synapses, high-resolution ultraviolet imaging equipment, and multiband photoelectric detection. However, the current low optoelectronic performance limits the development of such polar switching devices. Here, we construct a self-powered ultraviolet photodetector based on GaN and In/Sn-doped Ga2O3 (IGTO) nanowires (NWs) pn junction structure. This unique nanowire/thin film structure allows GaN and IGTO to dominate the absorption of light at different wavelengths, resulting in a highly bipolar photoresponse. The device has a responsivity of 2.04 A/W and a normalized detectivity of 7.18 × 1013 Jones at 254 nm and a responsivity of -2.09 A/W and a normalized detectivity of -7 × 1013 Jones at 365 nm, both at zero bias. In addition, it has an extremely high Ilight/Idark ratio of 1.05 × 105 and ultrafast response times of 2.4/1.9 ms (at 254 nm) and 5.7/5.2 ms (at 365 nm). These excellent properties are attributed to the high specific surface area of the one-dimensional nanowire structure and the abundant voids generated by the nanowire network to enhance the absorption of light, and the p-n junction structure enables the rapid separation and transfer of photogenerated electron-hole pairs. Our findings provide a feasible strategy for high-performance wavelength-controlled polarity switching devices.