Polarization Orientation Research Articles

Convenient dual-wavelength digital holography based on orthogonal polarization strategy with a Wollaston prism.

Dual-wavelength digital holography effectively expands the measurement range of digital holography, but it increases the complexity of optical system due to non-common-path of two wavelengths. Here, by using orthogonal polarization strategy, we present a dual-wavelength digital holography based on a Wollaston prism (DWDH-WP) to separate the reference beams of two wavelengths and realize the common-path of two wavelengths. A Wollaston prism is inset into the reference beam path of the off-axis digital holography system, so two orthogonal-polarized reference beams of two different wavelengths separated at different directions are generated. Then a dual-wavelength multiplexed interferogram with orthogonal interference fringes is captured by using a monochrome camera, in which both the polarization orientations and the interference fringe orientations of two wavelengths are orthogonal, so the spectral crosstalk of two wavelengths with arbitrary wavelength difference can be avoided. Compared with the existing DWDH method, the proposed DWDH-WP method can conveniently realize the common-path of the reference beams of two wavelengths, so it reveals obvious advantages in spectral separation, spectral crosstalk, system simplification, and adjustment flexibility. Both effectiveness and flexibility of the proposed DWDH-WP method are demonstrated by the phase measurement of the HeLa cell and vortex phase plate.

Generalized polarization and time-resolved fluorescence provide evidence for different populations of Laurdan in lipid vesicles

The solvatochromic dye Laurdan is widely used in sensing the lipid packing of both model and biological membranes. The fluorescence emission maximum shifts from about 440 nm (blue channel) in condensed membranes (So) to about 490 nm (green channel) in the liquid-crystalline phase (Lα). Although the fluorescence intensity based generalized polarization (GP) is widely used to characterize lipid membranes, the fluorescence lifetime of Laurdan, in the blue and the green channel, is less used for that purpose. Here we explore the correlation between GP and fluorescence lifetimes by spectroscopic measurements on the So and Lα phases of large unilamellar vesicles of DMPC and DPPC. A positive correlation between GP and the lifetimes is observed in each of the optical channels for the two lipid phases. Microfluorimetric determinations on giant unilamellar vesicles of DPPC and DOPC at room temperature are performed under linearly polarized two-photon excitation to disentangle possible subpopulations of Laurdan at a scale below the optical resolution. Fluorescence intensities, GP and fluorescence lifetimes depend on the angle between the orientation of the linear polarization of the excitation light and the local normal to the membrane of the optical cross-section. This angular variation depends on the lipid phase and the emission channel. GP and fluorescence intensities in the blue and green channel in So and in the blue channel in Lα exhibit a minimum near 90o. Surprisingly, the intensity in the green channel in Lα reaches a maximum near 90o. The fluorescence lifetimes in the two optical channels also reach a pronounced minimum near 90o in So and Lα, apart from the lifetime in the blue channel in Lα where the lifetime is short with minimal angular variation. To our knowledge, these experimental observations are the first to demonstrate the existence of a bent conformation of Laurdan in lipid membranes, as previously suggested by molecular dynamics calculations.

Simulating the Fluorescence of the Locally Excited State of DMABN in Solvents of Different Polarities.

4-(N,N-Dimethylamino)benzonitrile (DMABN) is a luminescent probe that can be used for tracking changes in the surrounding solvent due to the large change in polarity between its ground and excited states. An important characteristic of DMABN is that it exhibits dual fluorescence with two different emission energies that can be monitored, allowing for better characterization of the surrounding system. The first excited state is called the locally excited (LE) state and is characterized by the movement of charge over the conjugated ring structure. In nonpolar solvents and in the gas phase, the fluorescence of DMABN is entirely attributed to the transition from the near-planar LE state. In more polar environments, emission occurs from both the LE and a second excited state, corresponding to a twisted intramolecular charge-transfer (ICT) structure. For the sake of simplicity, this work considers transitions between only the ground and LE state. Molecular mechanical force field models of DMABN in its ground and LE states have been developed to investigate the sensitivity of the LE state to the polarity of the solvent. Both nonpolarizable and polarizable force fields were developed to simulate the molecule in a series of 10 different solvents of different polarities. The calculated Stokes shift of DMABN increases with increasing orientation polarizability of the surrounding solvent, which is the expected trend, as seen in experimental studies.

Simulating the Fluorescence of Di-8-ANEPPS in Solvents of Different Polarity.

Voltage-sensitive fluorescent probes, such as di-8-amino-naphthyl-ethylene-pyridinium-propyl-sulfonate (di-8-ANEPPS), are extremely useful for monitoring the membrane potential in biological and biophysical studies. However, because di-8-ANEPPS is very sensitive to its environment, it can be difficult to distinguish the degree to which a given external factor affects the observed fluorescence. Molecular dynamics simulations based on detailed atomic models make it possible to examine the particular characteristics of the system and predict the effects of the surroundings. Here, the sensitivity of the spectra of di-8-ANEPPS to solvent polarity is investigated by modeling the electronic transition between the ground and excited states using classical molecular mechanical force fields. The absorption and emission of di-8-ANEPPS were simulated in 12 solvents of increasing polarity using nonpolarizable and polarizable force fields. While the computational results and experimental data do not match perfectly, classical Lippert plots of both models show the expected increase of the Stokes shift of di-8-ANEPPS with the orientation polarizability of the surrounding solvent.

Enhanced tunneling electroresistance through interfacial charge-modulated barrier in α-In2Se3-based ferroelectric tunnel junction

The manipulation of tunneling resistance is critical for ferroelectric tunnel junction (FTJ) devices. In this work, we propose a mechanism to manipulate tunneling resistance through interfacial charge-modulated barrier in two-dimensional (2D) n-type semiconductor/ferroelectric FTJs. Driven by ferroelectric reversal, different effective tunneling barriers are realized by the depletion or accumulation of electrons near the n-type semiconductor surface in such devices. Thus, the tunneling resistance in FTJs undergoes significant changes for different polarization orientations, resulting in a giant tunneling electroresistance (TER) effect. To illustrate this idea, we construct 2D FTJs based on n-InSe/α-In2Se3 van der Waals (vdW) heterostructures. Based on the electronic transport calculations, it is found that TER ratio can reach 4.20 × 103% in the designed FTJs. The physical origin of the giant TER effect is verified through analysis of the effective potential energy of the n-InSe/α-In2Se3 vdW heterostructures and the real-space transmission eigenstates of the designed FTJs. This work contributes to the knowledge of carrier tunneling mechanisms at the interface of semiconductor/In2Se3 vdW heterostructures, and providing a significant insight into the TER effect of this FTJ systems, also presenting an alternative approach for the design of FTJ-based devices.

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.