Linear Polarization Response Research Articles

Wafer-Scale Patterning Integration of Chiral 3D Perovskite Single Crystals toward High-Performance Full-Stokes Polarimeter.

Chiral three-dimensional (3D) perovskites exhibit exceptional optoelectronic characteristics and inherent chiroptical activity, which may overcome the limitations of low-dimensional chiral optoelectronic devices and achieve superior performance. The integrated chip of high-performance arbitrary polarized light detection is one of the aims of chiral optoelectronic devices and may be achieved by chiral 3D perovskites. Herein, we first fabricate the wafer-scale integrated full-Stokes polarimeter by the synergy of unprecedented chiral 3D perovskites (R/S-PyEA)Pb2Br6 and one-step capillary-bridge assembly technology. Compared with the chiral low-dimensional perovskites, chiral 3D perovskites present smaller exciton binding energies of 57.3 meV and excellent circular dichroism (CD) absorption properties, yielding excellent circularly polarized light (CPL) photodetectors with an ultrahigh responsivity of 86.7 A W-1, an unprecedented detectivity exceeding 4.84 × 1013 Jones, a high anisotropy factor of 0.42, and high-fidelity CPL imaging with 256 pixels. Moreover, the anisotropic crystal structure also enables chiral 3D perovskites to have a large linear-polarization response with a polarized ratio of 1.52. The combination of linear-polarization and circular-polarization discrimination capabilities guarantees the achievement of a full-Stokes polarimeter. Our study provides new research insights for the large-scale patterning wafer integration of high-performance chiroptical devices.

Exploring low-temperature dynamics in triple perovskite ruthenates using nonlinear dielectric susceptibility measurements

We report the nonlinear dielectric properties of three triple-perovskite ruthenates: Ba3CoRu2O9, Ba3BiRu2O9, and Sr3CaRu2O9. These compounds exhibit notable correlations among their spin, charge, lattice, and polar degrees of freedom. Ba3CoRu2O9 displays a pronounced frequency-dependent relaxation in χ2,3 just above the magnetoelastic transition, occurring around 100 K, followed by an abrupt loss of polarization within the ordered phase. In Ba3BiRu2O9, we encounter the possibility of multiple coexisting relaxation behaviors, indicating a complex phase strongly influenced by the spin-gap opening at 175 K. Lastly, Sr3CaRu2O9 displays anomalies with strong dispersion effects close to its magnetic transitions, indicating a robust coupling between magnetic and dipolar orders in the system. These measurements highlight the significance of higher-order (hyper-)susceptibilities in providing profound insight into the dynamics of a system, offering information otherwise inaccessible through the linear polarization response alone.

Chiral 2D/Quasi‐2D Perovskite Heterojunction Nanowire Arrays for High‐Performance Full‐Stokes Polarization Detection

The realization of Stokes photodetectors accelerates the development of various modern optoelectronic applications. Chiral 2D perovskites with intrinsic chiral optical activity and superior carrier mobility are promising for next‐generation full‐Stokes polarization detection. So far, most of the chiral 2D metal‐halide perovskite‐based photodetectors suffer from limited discrimination of circularly polarized light due to the high exciton recombination rate in single‐phase perovskite, impeding the accurate measurement for Stokes parameters. Here, an on‐chip Stokes photodetector based on chiral 2D/quasi‐2D perovskite lateral heterojunction nanowire (NW) arrays with high polarization selectivity and photoresponsiveness is reported. The highly‐aligned heterojunction NW arrays not only build up a built‐in electric field for enhanced chiral discrimination, but also possess intrinsic anisotropy that enables outstanding linear polarization response. On this basis, the device exhibits reliable ability for polarization detection with a high anisotropy factor of 0.38, an outstanding polarized ratio of 1.5, and an excellent responsivity of 22.14 A W−1. These results will provide useful enlightenment for direct full‐Stokes polarization detection in optoelectronic integrated circuits.

Peculiar polarization response in chiral liquid crystal stacks for multispectral camouflage.

Chiral liquid crystals are self-organized Bragg reflectors which respond to circularly polarized light. Manipulation of the chiral structure has aroused great research interest. The x-y plane two-dimensional patterning of chiral liquid crystals leads to reflective planar optics, and the z-axis modulation results in a variety of photonic bandgap controls. Here, the optical properties of even-number left- and right-handed chiral liquid crystal stacks are investigated, with emphasis on the linear polarization response. Under certain conditions, a linearly polarized incidence can result in a linearly polarized reflected light. More intriguingly, the linear polarization has different forms of response to thick and thin chiral liquid crystal sublayers and responds to the rotation of liquid crystal alignment. Based on the peculiar polarization response, a new type of wavelength-response camouflage and anti-counterfeiting is conceptually proposed, which can hide two different images simultaneously within a small spectral range. Our work paves the way for three-dimensional manipulation of chiral liquid crystals and enlightens novel applications.

Screening piezoelectricity in determination of flexoelectric coefficient at nanoscale

Piezoelectricity usually accompanies with flexoelectricity in polar materials which is the linear response of polarization to a strain gradient. Therefore, it is difficult to eliminate piezoelectric effect in determination of pure flexoelectric response. In this work, we propose an analytical method to characterize the flexoelectric coefficient quantitatively at nanoscale in piezoelectric materials by screening piezoelectricity. Our results show that the flexoelectricity reduces the nanopillar stiffness while the piezoelectricity enhances it. With precise design of the shape of the nanopillars and measurement of their stiffness difference, the flexoelectric coefficient can be obtained with the piezoelectric contribution eliminated completely. This approach avoids the measurement of electrical properties with dynamic load, which helps to reduce the challenge of flexoelectric characterization at nanoscale. Our work suggests an alternative strategy for quantitative characterization of flexoelectric properties and design of flexoelectric devices at nanoscale.

Application of generalized Bloch method: Strain engineering of low dimensional materials through inhomogeneous strains

Due to their special structural morphologies, low dimensional materials are in nanometer scale in zero, one or two dimensions. This feature offers them superior structural flexibility. This characteristic, together with their excellent electronic property response to mechanical deformation, makes strain engineering an important way to optimize the physical properties of materials. Because in low dimension, structural deformations are usually inhomogeneous, the standard electronic and phonon calculation methods formulated via translation under the periodic boundary conditions encounter fundamental difficulties. A fresh approach in this aspect is called for rapidly. In this paper, the essential idea of the generalized Bloch method is introduced, in the context of a tight-binding treatment of electrons. This special method makes use of the helical symmetry and rotational symmetry to deal with the two fundamental non-uniform structural deformations, i.e., torsion and bending. In this way, the atomistic simulation of the deformed structures can still be carried out through a relatively small repeating cell. Such treatment enables the realistic atomistic quantum mechanical simulations in a viable manner. In practice, this new method is implemented into the so-called density-functional tight-binding (DFTB) calculation, an approach widely used in the material computation today. We note that the utility of DFTB brings us several benefits. First of all, the self-consistent field improves the calculation accuracy to be compatible with first-principles calculations. Next, the capability to deal with spin freedoms of DFTB enables us to study the strain tunable properties of spin-polarized electronic states. We illustrate the application of the generalized Bloch method with several examples that can be categorized into “strain tunable electronic properties”, “spatial manipulation of dopants in semiconductor nanowires”, and “strain engineering of phonon properties”. We also have a vision that the generalized Bloch method shall have important application in more areas. Studies of twist bilayers of two-dimensional materials are one of the focuses of the current condensed matter physics research. However, due to the twist induced lattice mismatch, a twisted bilayer is often of a unit cell containing a huge number of atoms. This makes direct realistic atomistic simulations difficult. We indicate that the calculation can be simplified by using the generalized Bloch method where the helical symmetry and possible rotational symmetry of the twisted bilayer would be used. Exploring giant flexoelectricity is a growing area of materials science. Different from piezoelectricity, flexoelectricity is by definition the linear response of polarization to the strain gradient. Usually, in the actual experimental studies, the strain gradient of materials is generated by applying the bending deformation to the slab. This fact indicates that the generalized Bloch method can be used to simulate such systems. In today’s semiconductor technology, the design of flexible electronic devices is an important development field. The low dimensional materials are natural candidates of flexible systems. Obviously, the generalized Bloch method will also play an important role in this aspect. Our recent work has realized the phonon calculation for low-dimensional structures of helical and rotational symmetries based on the electronic structure calculation with the generalized Bloch method. This functionality will expand the application scope of the generalized Bloch method, making it possible to study the strain modulation of thermal properties in low-dimensional systems with inhomogeneous strain patterns.

Expanded linear polarization response and excellent energy-storage properties in (Bi0.5Na0.5)TiO3-KNbO3 relaxor antiferroelectrics with medium permittivity

Dielectric materials with both high recoverable energy-storage density Wrec and efficiency η have attracted a lot of attention in recent years. Permittivity plays a crucial role in simultaneously achieving high polarization strength and large applied electric fields for any kinds of dielectric materials, among which antiferroelectric ceramics exhibit giant potentials in energy storage. Adjustment of permittivity has seemed to be more in linear dielectrics, but much less cared about in polar dielectrics so far for high-power energy-storage applications. In this work, a novel lead-free solid solution of (1-x)(Bi0.5Na0.5)TiO3-xKNbO3 was reported to show excellent comprehensive energy-storage performances of Wrec of ~5.2 J/cm3, large η of ~88%, fast discharge rate of t0.9 < 200 ns and outstanding temperature and frequency stability at x = 0.16. The X-ray, Raman spectra and scanning electron microscopy and so on demonstrate that it was basically ascribed to the formation of relaxor antiferroelectric phases with temperature-stable dielectric response and expanded linear polarization response, as well as enhanced dielectric breakdown strength induced by sub-micron grains. Particularly, selection of an appropriately medium permittivity value of about one thousand enables the studied AFE composition bring its superiority into full play in energy-storage properties, as demonstrated by a comparison between Wrec values of most previously-reported lead-free ceramics and theoretically predicted ones for linear dielectrics. These findings achieved in current work would provide an important guidance for compositionally designing high-performance energy-storage dielectrics in terms of modifying dielectric properties and polarization responses, particularly for relaxor antiferroelectrics with linear-like characteristics.

Strain engineering of electronic, elastic, and piezoelectric responses in oxygen-decorated phosphorene

The electronic, elastic, and piezoelectric properties of semi-oxidized phosphorene subjected to uniaxial strains were studied using first-principles calculations based on the density functional theory. Both zigzag and armchair uniaxial loads caused significant changes in partial charges and band gaps as a semiconductor–metal transition occurs outside the metastable regions. The bridge structures exhibited great flexibility along the armchair direction resulting from the high buckling parameter in these structures. The calculations confirmed the linear response of polarization. The in plane and out of plane stress piezoelectric coefficients were comparable to 2D materials. The results demonstrated that both the uniaxial strain and the oxygen atom arrangement can be used to tune the anisotropic properties of phosphorene making the new derivatives ideal for flexible devices and energy conversion applications.

Thermoelectric transport coefficients in mono-layer MoS2 and WSe2: Role of substrate, interface phonons, plasmon, and dynamic screening

The thermoelectric transport coefficients of electrons in two recently emerged transition metal di-chalcogenides (TMD), MoS2 and WSe2, are calculated by solving Boltzmann transport equation using Rode's iterative technique in the diffusive transport regime and the coupled current (electrical and heat) equations. Scattering from remote phonons along with the hybridization of TMD plasmon with remote phonon modes and dynamic screening under linear polarization response are investigated in TMDs sitting on a dielectric environment. The transport coefficients are obtained for a varying range of temperature and doping density for three different types of substrates—SiO2, Al2O3, and HfO2. The Seebeck co-efficient for MoS2 and WSe2 is found to be higher than 3D semiconductors even with diffusive transport. The electronic thermal conductivity is found to be low, however, the thermoelectric figure of merit is limited by the high phonon thermal conductivity. It is found that judicious selection of a dielectric environment based on temperature of operation and carrier density is crucial to optimize the thermoelectric performance of TMD materials.

Rode's iterative calculation of surface optical phonon scattering limited electron mobility in N-polar GaN devices

N-polar GaN channel mobility is important for high frequency device applications. Here, we report theoretical calculations on the surface optical (SO) phonon scattering rate of two-dimensional electron gas (2DEG) in N-polar GaN quantum well channels with high-k dielectrics. Rode's iterative calculation is used to predict the scattering rate and mobility. Coupling of the GaN plasmon modes with the SO modes is taken into account and dynamic screening is employed under linear polarization response. The effect of SO phonons on 2DEG mobility was found to be small at >5 nm channel thickness. However, the SO mobility in 3 nm N-polar GaN channels with HfO2 and ZrO2 high-k dielectrics is low and limits the total mobility. The SO scattering for SiN dielectric on GaN was found to be negligible due to its high SO phonon energy. Using Al2O3, the SO phonon scattering does not affect mobility significantly only except the case when the channel is too thin with a low 2DEG density.

Mixing rules and morphology dependence of the scatterer

We use the discrete dipole algorithm (DDA) to calculate the light-scattering properties from arbitrarily shaped, heterogeneous agglomerated debris particles to study the performance of effective medium approximations. The homogenization of the material properties of the particle has little effect on the orientation-averaged intensity phase function. However, there are some differences in the polarization response. While the structure of the linear-polarization response is not significantly different between the homogeneous and heterogeneous cases, the amplitude of the polarization tends to show a dependence on particle heterogeneity. The Bruggeman mixing rule tends to reproduce the heterogeneous results marginally better than using the average of two distributions of the individual homogeneous components. In addition to the irregularly shaped particles, we also calculated scattering properties of equivalent-volume, homogeneous spheres. As expected, the errors due to assuming homogeneous particles are overwhelmed by those introduced by assuming the irregularly shaped particle may be replaced by an equivalent spherical particle.

Temperature-stable high-energy-density capacitors using complex perovskite thin films

Chemical-solution-derived thin film synthesis and dielectric characterizations of (1 - x)BaTiO(3-x)Bi(Mg,Ti) O(3) complex perovskites with compositions x <0.15 have been explored for temperature-stable high-energy-density capacitor applications. Solution chemistry has been optimized to synthesize and stabilize the precursor solution. Solution-derived (1 - x)BaTiO(3-x)Bi(Mg,Ti)O(3) thin film samples in thicknesses ranging from 250 to 500 nm were fabricated by repeated spinning and subsequent crystallization processes. These thin films showed nearly linear polarization response with high relative dielectric permittivity exceeding 900, which is beneficial for high-capacitance-density and high-energy-density capacitors. Average dielectric breakdown strengths of the dense films were as high as 2.08 MV/cm. The BaTiO(3)-Bi(Mg,Ti) O3 samples showed very low leakage current densities of the order of 10-8 A/cm(2) even at temperatures of 200°C. Based on the structural stability at high temperatures of the pseudocubic perovskite, the high dielectric permittivity and the typical P-E behaviors of the BaTiO(3)-Bi(Mg,Ti)O(3) thin films were also maintained at such high temperatures. Resulting energy density of the 500-nm-thick 0.88BaTiO(3)-0.12Bi(Mg,Ti) O(3) thin film was as high as 37 J/cm(3) at 1.9 MV/cm. The high energy density and excellent temperature stability of the Ba- TiO(3)-Bi(Mg,Ti)O(3) complex perovskite show promise for use in high-temperature pulse power capacitor applications.

Towards a Bulk Theory of Flexoelectricity

Flexoelectricity is the linear response of polarization to a strain gradient. Here we address the simplest class of dielectrics, namely, elemental cubic crystals, and we prove that therein there is no extrinsic (i.e., surface) contribution to flexoelectricity in the thermodynamic limit. The flexoelectric tensor is expressed as a bulk response of the solid, manifestly independent of surface configurations. Furthermore, we prove that the flexoelectric responses induced by a long-wavelength phonon and by a uniform strain gradient are identical.

A New Way of Introducing Linear Polarization Response

A New Way of Introducing Linear Polarization Response

Pyroelectric, piezoelectric, flexoelectric, and thermal polarization effects in ionic crystals

An analysis has been made of the linear response of polarization to a uniform change in temperature, in its gradient (thermal polarization effect), in macroscopic deformation and in its gradient (flexoelectric effect). It has been shown how the use of some definitions of polarization widespread in the literature can lead to essentially incorrect results in the analysis of piezo- and flexoelectric effects in the field of elastic deformations of an acoustic wave. It has also been shown that in calculating the above responses in the case of a spatially uniform disturbance in a sample of finite size two classes of contributions arise: 1) contributions depending on the microscopic properties of the lattice, and 2) contributions depending only on changes in the distortion tensor accompanying the response, and on multipole moments of the charge distribution of the whole unperturbed crystal. In this connection it was established that the former contributions are bulk effects while the latter ones are surface or false contributions (which are not manifested in the generally accepted experimental arrangements for measurements). The special features of the manifestation of the flexoelectric and thermal polarization effects are discussed in detail.