Polarization Orientation Research Articles

Electron irradiation modified point defects of SiC nanoparticles with tunable high electromagnetic wave absorption

Silicon carbide nanoparticles (SiC nps) were modified by changing the injection amount using 1 MeV high-energy electron as radiation source. When the injection volume reaches 5ⅹ1013 cm−2, the irradiated particles produce defect structures sufficient to optimize the electromagnetic wave absorption performance. With the increase of beam amount, the value of g detected by electron paramagnetic resonance (EPR) energy spectrum moves towards the silicon suspension bond, and the macroscopic electromagnetic wave absorption peak gradually moves towards the low frequency, accompanied by the enhancement of absorption intensity and the increase of absorption bandwidth. When the injection volume reaches 3ⅹ1014 cm−2, the loss value of −62.79 dB is achieved at the optimal thickness of 2.56 mm, and the absorption frequency band covers the entire Ku band. SiC presents point defects, and carbon atoms leave the original lattice position due to electron irradiation, forming carbon vacancies, resulting in uneven charge distribution inside the material, resulting in dipoles of orientation polarization, which further affects the electromagnetic wave absorption performance. As the irradiation dosage increases, the defects become denser and purer. This leads to higher electromagnetic wave absorption intensity and a correspondingly lower optimal absorption frequency. Thus, the modification of SiC nps through irradiation achieves tunable absorbers.

Micromachined piezoelectric sensor with radial polarization for enhancing underwater acoustic measurement

This work presents an underwater acoustic sensor featuring a radial polarized piezoelectric diaphragm, which aims to work in d33 mode to enhance its performance. For the sake of accomplishing the in-plane polarization, interdigital electrodes based on semi-circular ring patterns are designed on both sides and aligned along the thickness direction of the diaphragm. Effects of electrode parameters on the polarization orientation are numerically analyzed by the conversion relationship between different coordinates. Using the Kirchhoff plate theory and Rayleigh-Ritz method, a mathematical model is developed to investigate the dynamic properties of the sensor. The results indicate that the output voltages increase with the increase of the electrode inner radius, width, and spacing but decrease with the increase of the diaphragm thickness and radius. Sensor prototypes are fabricated by the microelectromechanical system (MEMS) technology in a clean room and characterized by impedance spectrums. An underwater testing system is established to conduct the experimental verification, whose results are in good accord with those of mathematical modeling. The sensor output voltage has fine linearity with the underwater acoustic pressure and achieves a flat frequency response. Moreover, the sensor has a sensitivity of −172.7 dB (Ref. 1 V/μPa) superior to the reported devices in the same categories. This work provides significant guidance for modeling radial field piezoelectric diaphragms and designing more efficient piezoelectric microsensors, which have a fine application prospect in underwater acoustic measurement.

Controlling Charge Accumulation Properties at Organic Hetero Interfaces via Spontaneous Orientation Polarization

Controlling Charge Accumulation Properties at Organic Hetero Interfaces via Spontaneous Orientation Polarization

Enhancement on electro-response of gelatin hydrogels with grafted polar groups

ABSTRACT In this article, three grafted copolymers, namely gelatin-graft-polypyrrole copolymer (gelatin-g-PPy), gelatin-graft-polyaniline copolymer (gelatin-g-PANI), and gelatin-graft-monomethyl polyethylene glycol copolymer (gelatin-g-MPEG), were successfully synthesized by the introduction of polar groups onto the gelatin matrix. Their chemical compositions were primarily characterized through Fourier Transform Infrared spectroscopy (FT-IR) and Ultraviolet-Visible spectrum (UV-Vis) analyses. The grafted gelatin hydrogels were prepared by utilizing the three grafted gelatin copolymers under an applied electric field ranging from 0 ~ 0.8 kV/mm. The impact of the electric field on the hydrogels was assessed through scanning electron microscopy (SEM), thermogravimetric analysis (TGA), dielectric analysis (DA), and dynamic mechanical analysis (DMA). SEM analysis revealed that the grafted gelatin hydrogels exhibited an ordered microstructure and larger pores when subjected to an electric field. DA testing indicated that all grafted gelatin hydrogels displayed a higher dielectric constant compared to pure gelatin, suggesting an enhanced orientation polarization of the copolymers in response to the electric field. DMA experiments confirmed that, in comparison to pure gelatin hydrogel, all the grafted gelatin hydrogels demonstrated an increased storage modulus in the direction of the applied electric field. The storage modulus increment (ΔG′) and incremental ratio (ΔG′/G′0) of the grafted gelatin hydrogels reached their maximum values at specific grafting levels. These findings suggest that the grafted gelatin hydrogels have excellent electro-responsive property.

Impact of Intermittent Deposition on Spontaneous Orientation Polarization of Organic Amorphous Films Revealed by Rotary Kelvin Probe.

The control of the molecular orientation and resultant polarization is essential for improving the performance of organic optoelectronic devices. Conventionally, the substrate temperature and deposition rate are tuned to control the molecular orientation of vapor-deposited films. In this study, we proposed a novel method, referred to as "intermittent deposition", in which the polarization direction and magnitude are controlled by introducing intervals during physical vapor deposition. The rotary Kelvin probe measurement of the Alq3 and TPBi films clearly showed a time-dependent decrease in the surface potential owing to the surface relaxation of the molecular orientation immediately after deposition. Through a series of intermittent depositions, in which the deposition shutter is repeatedly opened and closed at certain intervals, a relaxed surface layer was built up, and we could control the polarization magnitude. For the Alq3 film, even the polarization direction was switched. The proposed new deposition method is applicable to general organic molecules, not limited to polar molecules, thereby potentially tuning the conduction properties of organic devices and fabricating novel devices.

Centrosomal Protein CEP135 Regulates the Migration and Angiogenesis of Endothelial Cells in a Microtubule-Dependent Manner.

Angiogenesis is the formation of blood vessels by sprouting from mature blood vessels and is regulated by multiple factors; however, the role of centrosome and centrosomal proteins (CEP) in angiogenesis needs further study. centrosomal protein 135 (CEP135) is an important centrosome-associated protein that can affect a variety of cellular processes, such as the cell cycle, but its effect on angiogenesis is still unknown. Tube formation and in vivo angiogenesis assays were performed to confirm the effects of CEP135 on endothelial cell (EC) angiogenesis in vitro and in mice. Cell counting kit-8 (CCK-8), 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), flow cytometry (FCM) and immunoblot assays were performed to confirm the effects of CEP135 on the proliferation and cell cycle of endothelial cells. Wound healing, transwell, and fluorescence staining were performed to confirm its effects on EC cell migration, polarization, and spindle orientation, and a tubulin turbidity assay was performed to confirm its effects on microtubule stabilization. We conducted a series of experiments to explore the potential role of CEP135 in angiogenesis. CEP135 siRNA obviously inhibits angiogenesis in vivo compared with the control. CEP135 could mediate cell proliferation and the cell cycle by mediating spindle orientation. Moreover, we showed that CEP135 is involved in the regulation of angiogenesis by affecting the migration of endothelial cells using wound closure and transwell assays. We further demonstrated that CEP135 promotes endothelial polarization and microtubule stability, thus affecting cell migration. CEP135 was involved in the polarization of centrosomes, which is important for the migration of human umbilical vein ECs (HUVECs). These findings indicated that CEP135 may promote the polarization of HUVECs and accelerate migration, which in turn promotes angiogenesis.

Spontaneous pattern of orthogonal ferroelectric domains in epitaxial KNN films

Lead-free piezoelectric (K, Na)NbO3 (KNN) is considered one of the promising candidates for the replacement of Pb(ZrxTi1−x)O3. Several studies underlined the issue of K and Na volatility with increasing deposition temperatures, leading to high leakage currents in thin films, which still represents a major drawback for applications. This paper shows how epitaxial growth with concomitant preferred orientation of KNN films on niobium-doped strontium titanate (Nb:STO) depends on growth temperature and substrate strain. A preferred out-of-plane polar (001) orientation of KNN is obtained at high temperatures (>600 °C), while (100) orientation is dominant for lower ones. The (001) orientation is forced out-of-plane due to the sizeable in-plane stress derived from a negative lattice mismatch of pseudo-cubic KNN with respect to the underlying cubic (001) Nb:STO substrate. Moreover, we show that K-Na deficiency and high leakage of epitaxial KNN films deposited at high temperatures are accompanied by the appearance of a pattern of orthogonal spontaneous ferroelectric domains aligned to the [100] and [010] directions of Nb:STO. This pattern, visible in secondary electron microscopy, piezoforce response microscopy, and conductive atomic force microscopy images, is uncorrelated to the surface morphology. Supported by reciprocal space mapping by x-ray diffraction, this phenomenon is interpreted as the result of strain relaxation via ferroelectric domain formation related to K-Na deficient films displaying a sizable and increasing compressive strain when grown on Nb:SrTiO3. Our findings suggest that strain engineering strategies in thin films could be used to stabilize specific configurations of piezo- and ferroelectric domains.

The Element of Physical Reality Hidden in the Letter of Malus to Lancret in 1800 can Solve the EPR Paradox (Malus Thermochromatic Loophole)

It is extremely difficult to discover an element of physical reality that might solve the “spooky action at a distance” formulated by Einstein-Podolsky-Rosen known as the EPR paradox. One very promising candidate was recently discovered in the letter of Malus addressed to Lancret in 1800. In this letter Malus (the discoverer of the polarization of light in 1808) modelled color as the composition of light and “caloric”. In the modern notation we can formulate the color and heat of polarized photons as the ratio of the ordinary and extraordinary wavefronts of that polarized photon in the Descartes’ model of colors caused by the rotation of spin-orbit of photons. Laser photons pass through the half waveplate where they get color and “heat content”, and then in the process of the spontaneous parametric down conversion, they create two entangled photons. In the pleochroic polarizers of Alice and Bob entangled colored photons modify individually their colors and their “heat content”. Pleochroism from Greek words πλÅLεω (pléon) and χρωμα (khrôma) means “more colors” and in the geological analysis describes dependence of color variation on the orientations of polarizer, analyzer, and the sample. This independent local color change in Alice and Bob polarizers can be mathematically described by the haversine and havercosine formulae. The havercosine describes the probability of a particle to stay on the same latitude. The haversine describes the probability of a particle to stay on the same longitude. In this model the “spooky action at a distance” is interpreted as the “local pleochroism” of entangled photons. This model can be further tested in the “Herschel-type” experiments where the polarized photons heat thermometers in the dependence of their “caloric” content. Bell four states mathematically describe the entanglement of two particles but without the physical interpretation based on the local pleochroism.

Hot‐Electron Driven Ultrafast Optical Polarization Conversion with Graphene‐Loaded Metasurface

AbstractThe switching speed of light polarization plays a crucial role in determining the upper‐limit bandwidth of applications like optical communications and laser microscopy. However, conventional polarization elements based on macroscopic anisotropic crystals like birefringent crystals and chalcogenide glasses are either static or restricted by the low switching time of about hundreds of picoseconds. Here, a femtosecond‐scale all‐optical polarization controlling method is proposed through engineering the excited hot electrons in a graphene‐loaded metasurface. Remarkably, a giant polarization orientation from left‐handed polarization (LCP) to right‐handed polarization (RCP) in the Poincaré sphere (≈80° rotation) is realized within only 200 fs in the mid‐infrared. With pumping, the dedicated polarization‐sensitive design allows the metasurface to exhibit a consistent resonance blueshift as the transient increase of the hot‐electron temperature in graphene for y‐polarized incidence. This polarization conversion approach features a giant modulation range and enables the reflected light to be dynamically and arbitrarily modulated into RCP, LCP, and linear states at femtosecond timescale. A few logic operations “AND”, “OR”, “NAND”, and “XOR” based on this method are also demonstrated by monitoring the normalized Stokes parameters. It is believed that this work may find practical application in next‐generation signal‐processing systems with large capacity.

Controlling Spontaneous Orientation Polarization in Organic Semiconductors─The Case of Phosphine Oxides.

Upon film growth by physical vapor deposition, the preferential orientation of polar organic molecules can result in a nonzero permanent dipole moment (PDM) alignment, causing a macroscopic film polarization. This effect, known as spontaneous orientation polarization (SOP), was studied in the case of different phosphine oxides (POs). We investigate the control of SOP by molecular design and film-growth conditions. Our results show that using less polar POs with just one phosphor-oxygen bond yields an exceptionally high degree of SOP with the so-called giant surface potential (slope), reaching more than 150 mV nm-1 in a neat bis-4-(N-carbazol(yl)phenyl)phenyl phosphine oxide (BCPO) film grown at room temperature. Additionally, by altering the evaporation rate and substrate temperature, we are able to control the SOP magnitude over a broad range from 0 to almost 300 mV nm-1. Diluting BCPO in a nonpolar host enhances the PDM alignment only marginally, but combining temperature control with dipolar doping can result in highly aligned molecules with more than 80% of their PDMs standing upright on the substrate on average.

Low-dimensional lead chromate-based hybrid system for capacitance and polarization performances: a flexible device for pressure-induced voltage generator

AbstractOrganic molecule–functionalized lead chromate nanoparticle was synthesized using a complexation strategy route. The structural characterization revealed the single-phase lead chromate system belongs to monazite-type monoclinic structure with the space group of P21/n. The unit cell consists of an alternating chain of polyhedra (PbO9) and tetrahedra (CrO4) units, connected via edge and corner-sharing arrangement. A flexible device of lead chromate was fabricated and investigated dielectric capacitance, electrical impedance, conductivity, and field dependent polarization performances under different frequency and temperature environments. The device displayed a maximum dielectric constant (εʹ) value ~ 2400 at 120°C under 100 Hz frequency condition. High dielectric constant value is originated from the orientation polarization of CrO4 unit and space charge contribution in the system. AC conductivity of the device suggested the polaronic charge carriers control the overall conduction process via localized hopping mechanism. A fatigue-free polarization behavior was observed in the device under the applied field of 4.0 kV/mm, for 103 cycles and retained the polarization value ~ 0.26 μC/cm2 over the switching cycles. Lead chromate–based device also showed pressure-induced voltage generation under different pressure conditions and could have the potential application as a voltage generator.

Ferroelectric Layer‐Assisted Asymmetric Heterojunction Boosts Power Output in Silicon Hydrovoltaic Device

AbstractHydrovoltaic devices (HDs) that convert ubiquitous environmental energy via water evaporation serves as a prospective technology for renewable power schemes. However, it remains a grand challenge to perform controllable and stable modulation of hydrovoltaic power generation for multi‐scenario practical applications. Here, a ferroelectric‐field assisted silicon HD is proposed, which sandwiches an ultrathin polarizable polymer between nanostructured silicon and the top electrode, constituting an asymmetric heterojunction designed to clinch well‐regulated and robust electrical signal output. Tunable modulation of the internal electric field at the silicon/top electrode interface can be realized by facilely aligning the polarization orientation of the ferroelectric domains, thus dominating the silicon energy band bending and controlling the ultimate electrical signal. Upon effective forward polarization, the interfacial dipoles can build a stronger asymmetric electric field, which allows an efficient sweep of the charges out of the heterojunction. Accordingly, the resulting device clinches to yield a considerably modulated voltage of 1.04 V, nearly three‐fold modulation over the reverse polarization one. As prospective applications, multifunctional sensing platforms including the self‐sufficient environmental temperature detector, intelligent water‐level alarm system, and automatic‐manual dual‐mode irrigation control system are demonstrated. This work exhibits the unique characteristics of ferroelectric HDs with tunable electrical performance.

Spontaneous orientation polarization of flavonoids

Spontaneous orientation polarization (SOP) is macroscopic electric polarization that is attributed to a constant orientational degree of dipole moments of polar molecules on average. The phenomenon has been found in small molecules like H2O at low temperatures and π-conjugated molecules employed in organic light-emitting diodes. In this study, we demonstrate that a thin film of baicalein, a flavonoid compound found in natural products, exhibits SOP and resultant giant surface potential (GSP) exceeding 5500 mV at a film thickness of 100 nm. Vacuum-deposition of baicalein under high vacuum results in smooth and amorphous films, which enables the generation of GSP with a slope of 57 mV/nm in air, a value comparable to the representative of an organic semiconductor showing GSP, tris(8-hydroxyquinoline)aluminum(III) (Alq3). We also found the superior photostability of a baicalein film compared to an Alq3 film. These findings highlight the potential of baicalein in new applications to organic electronics.

Cu, Ni and Ag ions assisted preparation of nonpolar preferential oriented ZnO films with controlled morphology and optical properties

ZnO nanodevices have been widely used in practice, but one-dimensional ZnO grown in a polar preferred orientation is still partially localized. In this work, copper nitrate, nickel nitrate and silver nitrate were assisted with zinc acetate and hexamethylenetetetramine for the synthesis of ZnO films by conventional chemical bath deposition method. All samples were characterised by X-ray diffraction, field emission scanning electron microscopy, atomic force microscopy, photoluminescence, and UV–visible spectrophotometer. The results show that non-polar (110), (100) and coexisting preferred orientation ZnO films were controllably prepared by controlling the type and concentration of nitrate. On this basis, the growth process and mechanism of ZnO films with different nonpolar preferred orientations were characterized. It was also found that the ZnO films with 5 % Cu(NO3)2·3 H2O had the minimum surface roughness. The PL spectra confirmed the type and number of defects were also related to the preferred orientations. In addition, the non-polar (110) preferred orientation ZnO films had the highest optical transmittance of 82.26 %. This work enriches the method of preparing ZnO films with various nonpolar preferred orientations and provides new ideas for the design of ZnO-based transparent nanodevices.

Ultrafast helicity-dependent photocurrents in Weyl Magnet Mn3Sn

Mn3Sn is a material that has attracted a lot of attention lately for its topologically non-trivial band structure, which leads to very promising spintronic properties. In this work we experimentally demonstrate that an epitaxially grown thin film of Mn3Sn acts as a source of THz radiation at room temperature when irradiated by a femtosecond laser pulse. By combining various experimental measurements as a function of pump polarisation, magnetic field, and sample orientation we are able to explain the origin of the THz emission with the photocurrents generated via the photon drag effect. A thorough symmetry analysis combined with electronic band structure calculations using density-functional theory (DFT) are used to support our conclusions and provide a guide towards the important features that lead to photocurrent generation, which is useful for designing ultra-fast current pulses emitters.

Large bi-axial tensile strain effect in epitaxial BiFeO3 film grown on single crystal PrScO3

A BiFeO3 film is grown epitaxially on a PrScO3 single crystal substrate which imparts ~ 1.45% of biaxial tensile strain to BiFeO3 resulting from lattice misfit. The biaxial tensile strain effect on BiFeO3 is investigated in terms of crystal structure, Poisson ratio, and ferroelectric domain structure. Lattice resolution scanning transmission electron microscopy, precession electron diffraction, and X-ray diffraction results clearly show that in-plane interplanar distance of BiFeO3 is the same as that of PrScO3 with no sign of misfit dislocations, indicating that the biaxial tensile strain caused by lattice mismatch between BiFeO3 and PrScO3 are stored as elastic energy within BiFeO3 film. Nano-beam electron diffraction patterns compared with structure factor calculation found that the BiFeO3 maintains rhombohedral symmetry, i.e., space group of R3c. The pattern analysis also revealed two crystallographically distinguishable domains. Their relations with ferroelectric domain structures in terms of size and spontaneous polarization orientations within the domains are further understood using four-dimensional scanning transmission electron microscopy technique.

Effect of ZnCl2 assisted chemical bath deposition on preferred orientations and optical properties of ZnO films.

Using zinc chloride as an additive assisted with conventional solutions of zinc acetate dihydrate and hexamethylenetetramine, the synthesis of ZnO films by chemical bath deposition was investigated and characterized by x-ray diffraction, field emission scanning electron microscopy, atomic force microscope, photoluminescence (PL) and UV-Vis spectrophotometry. ZnO films with (0002), (101̄2), (112̄2), (112̄0), and (101̄0) preferential growth orientation were prepared by changing the concentration of the introduced zinc chloride. The results of UV-Vis spectrophotometry show that the ZnO films with different preferential growth orientations have optical transmittance of more than 80% in the visible light region. Results from PL show that compared to the typical polar (0002) preferential growth orientation of ZnO, other films with different preferential growth orientations have different visible emissions. It was also confirmed that the concentration of Cl- can affect the defects and preferred orientations of ZnO films. This work enriches the fabrication of ZnO films with different preferential growth orientations and also provides new ideas for the fabrication of ZnO-based transparent nanodevices.

Active correction of window Faraday effects for ITER laser diagnostics

Measurement of the change in polarization of a laser beam traversing a magnetized plasma is a standard diagnostic technique for extracting key plasma parameters, including density and current profile. Depending on the polarization orientation of the incident laser beam relative to theplasma magnetic field, the polarization change is denoted as either Faraday rotation or Cotton-Mouton effect. On ITER three laser diagnostics will make use of this effect to make their measurements. Unfortunately, this effect is also evident when the laser beam passes through the vacuum window. The large magnetic field and finite verdet constant of the window material mean that on ITER this effect — in particular faraday rotation — is non-negligible, and needs to be disentangled from the desired measurement parameter. The Toroidal Interferometer-Polarimeter (TIP) and Density Interferometer-Polarimeter (DIP), in particular, are affected. Both diagnostics use lasers in the 5–10 μm range, and will use zinc-selenide (ZnSe) as the vacuum window material. In order to compensate for the unwanted window distortion a sensor is being developed to monitor the magnetic field perpendicular to the window and activelycorrectfor the faraday rotation in real time. The sensor consists of an inductive coil closely fitted just in front of the window disc. It comprises several turns of fine wire in center-tap configuration. Both the raw voltage signal, as well as the integrated signal, will be monitored to estimate the magnetic field through the window disk. The system is designed to measure fields up to B <1 T with an accuracy of 0.01 T, at frequencies of D.C. to 1 kHz. The backend electronics will leverage off similar technology developed for other ITER magnetics systems. Using the real-time magnetic field information, in conjunction with published and/or measured data on the verdet constant of the ZnSe window material, in-house developed software will estimate the faraday rotation induced by passing through the window.An initial prototype of the sensor has been fabricated and results from preliminary characterization trials of the system are presented. Detailed testing is planned for the future using the DIP system prototype currently under development.

Microscopic insight into domain configuration in orthorhombic K0.52Na0.48NbO3 single crystals driven by electric-field

Domain switching not only exhibits a great effect on piezoelectric performance, but also serves as foundation of some ferroelectric applications, such as ferroelectric nonvolatile memories and nonlinear optical devices. Therefore, a thorough understanding in the process and mechanism of domain switching is of vital significance. In this paper, we observed the process of domain switching under electric field by controlling poling conditions. The domain structures, polarization orientation, and piezoelectric performance of K0.52Na0.48NbO3 single crystals poled at different temperatures and electric fields were investigated. We found that the polarization-rotation in poling process of the crystals occurs in steps and along a specific conversion path: [1¯01] - [011] - [1¯10]. Furthermore, poling under specific conditions can construct specific domains, which can be used in optical-function devices and may significantly promote the design of new generation ferroelectric memory devices.

A polar transition of spontaneous orientation polarization in organic amorphous thin films

Certain organic molecules autonomously form dipole orientation during a thin-film formation, leading to spontaneous orientational polarization (SOP) even in an amorphous film. Although the polarity of SOP can be controllable by molecular design itself, we demonstrate that a guest–host system also provides a unique tool for controlling SOP. Here, we report that the transition of SOP polarity occurs depending on the concentration of a polar guest molecule in a non-polar matrix. While a 2,8-bis(diphenylphosphoryl)dibenzo-[b,d]thiophene (PPT) film shows negative SOP in the neat film, the polarity could be changed to positive with a concentration increase of the non-polar molecule.