A Transmission-Type Electrically Tunable Polarizer Based on Graphene Ribbons at Terahertz Wave Band

We theoretically and numerically demonstrate that a transmission-type electrically tunable polarizer can be realized by using graphene ribbons supported on a dielectric film with a graphene sheet behind. The polarization mechanism originates from the antenna plasmon resonance of graphene stripes. The results of full-wave numerical simulations reveal that transmittance of 0.70 for one polarization and 0.0073 for another polarization can be obtained at normal incidence. The transmission-type electrically tunable polarizer provides and facilitates a variety of applications, including filtering, detecting, and imaging.

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In_(0.18) Al_(0.82) N/AlN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional （quasi-2D） model, the current-voltage （l-V） characteristics of In0AsA10.82N/A1N/GaN heterostructure field-effect transistors （HFETs） with different gate lengths are simulated based on the measured capacitance-voltage （C-V） characteristics and I-V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas （2DEG） with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V.s for the prepared In0.38AI0.82N/A1N/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain-source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.

Ferroelectricity induced by the absorption of water molecules on double helix SnIP

We study the ferroelectricity in a one-dimensional(1D)system composed of a double helix SnIP with absorbing water molecules.Our ab initio calculations reveal two factors that are critical to the electrical polarization.The first one is the orientation of polarized water molecules staying in the R2 region of SnIP.The second one is the displacement of I atom which roots from subtle interaction with absorbed water molecules.A reasonable scenario of polarization flipping is proposed in this study.In the scenario,the water molecule is rolling-up with keeping the magnitude of its electrical dipole and changing its direction,meanwhile,the displacement of I atoms is also reversed.Highly tunable polarization can be achieved by applying strain,with 26.5%of polarization enhancement by applying tensile strain,with only 4%degradation is observed with 4%compressive strain.Finally,the direct band gap is also found to be correlated with strain.

The twisted two-dimensional ferroelectrics

Since the beginning of research on two-dimensional(2D)materials,a few numbers of 2D ferroelectric materials have been predicted or experimentally confirmed,but 2D ferroelectrics as necessary functional materials are greatly important in developing future electronic devices.Recent breakthroughs in 2D ferroelectric materials are impressive,and the physical and structural properties of twisted 2D ferroelectrics,a new type of ferroelectric structure by rotating alternating monolayers to form an angle with each other,have attracted widespread interest and discussion.Here,we review the latest research on twisted 2D ferroelectrics,including Bernal-stacked bilayer graphene/BN,bilayer boron nitride,and transition metal dichalcogenides.Finally,we prospect the development of twisted 2D ferroelectrics and discuss the challenges and future of 2D ferroelectric materials.

Review of ionospheric irregularities and ionospheric electrodynamic coupling in the middle latitude region

This paper briefly reviews ionospheric irregularities that occur in the E and F regions at mid-latitudes. Sporadic E(ES) is a common ionospheric irregularity phenomenon that is first noticed in the E layer. ES mainly appears during daytime in summer hemispheres, and is formed primarily from neutral wind shear in the mesosphere and lower thermosphere(MLT) region. Field-aligned irregularity(FAI) in the E region is also observed by Very High Frequency(VHF) radar in mid-latitude regions. FAI frequently occurs after sunset in summer hemispheres, and spectrum features of E region FAI echoes suggest that type-2 irregularity is dominant in the nighttime ionosphere. A close relationship between ES and E region FAI implies that ES may be a possible source of E region FAI in the nighttime ionosphere. Strong neutral wind shear, steep ES plasma density gradient, and a polarized electric field are the significant factors affecting the formation of E region FAI. At mid-latitudes, joint observational experiments including ionosonde, VHF radar, Global Positioning System(GPS) stations, and all-sky optical images have revealed strong connections across different scales of ionospheric irregularities in the nighttime F region, such as spread F(SF), medium-scale traveling ionospheric disturbances(MSTID), and F region FAI.Observations suggest that different scales of ionospheric irregularities are generally attributed to the Perkins instability and subsequently excited gradient drift instability. Nighttime MSTID can further evolve into small-scale structures through a nonlinear cascade process when a steep plasma density gradient exists at the bottom of the F region. In addition, the effect of ionospheric electrodynamic coupling processes, including ionospheric E-F coupling and inter-hemispheric coupling on the generation of ionospheric irregularities, becomes more prominent due to the significant dip angle and equipotentiality of magnetic field lines in the mid-latitude ionosphere. Polarized electric fields can map to different ionospheric regions and excite plasma instabilities which form ionospheric irregularities. Nevertheless,the mapping efficiency of a polarized electric field depends on the ionospheric background and spatial scale of the field.

Electrostatic switch of magnetic core-shell in 0-3 type LSMO/PZT composite film

By dispersing La1-xSrxMnO3 (LSMO) granule into PbZrxTi1-xO3 (PZT) matrix, the 0-3 type LSMO/PZT composite film is synthesized through chemical solution method. The asymmetry of the top and bottom electrodes introduces novel electrostatic screening on LSMO/PZT interface. As electric polarization is switched between upward and downward orientations, the evolution of exchange bias, diode transport, and magnetoresistance is observed. The result implies the electrostatic switch of magnetic core-shell in the present film. In detail, as the spontaneous polarization is upward or downward in the PZT matrix, the ferromagnetic/antiferromagnetic or ferromagnetic/ferromagnetic core-shell structure is formed in LSMO granule, respectively. This work would develop a novel device for spintronics and metamaterial.

Self-screening of the polarized electric field in wurtzite gallium nitride along[0001]direction

The strong polarization effect of GaN-based materials is widely used in high-performance devices such as white-lightemitting diodes(white LEDs),high electron mobility transistors(HEMTs),and GaN polarization superjunctions.However,the current researches on the polarization mechanism of GaN-based materials are not sufficient.In this paper,we studied the influence of polarization on electric field and energy band characteristics of Ga-face GaN bulk materials by using a combination of theoretical analysis and semiconductor technology computer-aided design(TCAD) simulation.The selfscreening effect in Ga-face bulk GaN under ideal and non-ideal conditions is studied respectively.We believe that the formation of high-density two-dimensional electron gas(2 DEG) in GaN is the accumulation of screening charges.We also clarify the source and accumulation of the screening charges caused by the GaN self-screening effect in this paper and aim to guide the design and optimization of high-performance GaN-based devices.

The kinetic magnetoelectric effect in laterally boundary-confined ballistic two-dimensional hole gases

A theoretical investigation is presented on the characteristics of the kinetic magnetoelectric effect in laterally boundary-confined ballistic two-dimensional hole gases. It was shown that, though the momentum-dependent effective magnetic fields felt by charge carriers due to the spin-orbit interaction are in-plane orientated in such systems, both in-plane polarized and normal polarized nonequilibrium spin polarization densities could be electrically induced by the kinetic magnetoelectric effect, and the induced nonequilibrium spin polarizations exhibit some interesting characteristics. The characteristics we found indicate that there may be some possible relation between this effect and some recent experimental findings.

Distinct moiré textures of in-plane electric polarizations for distinguishing moiré origins in homobilayers

In binary compound 2D insulators/semiconductors such as hexagonal boron nitride(h BN), the different electron affinities of atoms can give rise to out-of-plane electric polarizations across inversion asymmetric van der Waals interface of near 0° interlayer twisting. Here we show that at a general stacking order where sliding breaks 2π/3-rotational symmetry, the interfacial charge redistribution also leads to an in-plane electric polarization, with a magnitude comparable to that of the out-of-plane ones.The effect is demonstrated in h BN bilayers, as well as in biased graphene bilayers with gate-controlled interlayer charge redistributions. In long wavelength moiré patterns, the in-plane electric polarizations determined by the local interlayer stacking registries constitute topologically nontrivial spatial textures. We show that these textures can be used to distinguish moirépatterns of different origins from twisting, biaxial-and uniaxial-heterostrain, where vector fields of electric polarizations feature Bloch-type merons, Néel-type merons, and anti-merons, respectively. Combinations of twisting and heterostrain can further be exploited for engineering various electric polarization textures including 1D quasiperiodic lattices.

Electrical charge on ferroelectric nanocomposite membranes enhances SHED neural differentiation

Stem cells from human exfoliated deciduous teeth(SHED)uniquely exhibit high proliferative and neurogenic potential.Charged biomaterials have been demonstrated to promote neural differentiation of stem cells,but the dose-response effect of electrical stimuli from these materials on neural differentiation of SHED remains to be elucidated.Here,by utilizing different annealing temperatures prior to corona poling treatment,BaTiO_(3)/P(VDF-TrFE)ferroelectric nanocomposite membranes with varying charge polarization intensity(d_(33)≈0,4,12 and 19 pC N^(-1))were fabricated.Enhanced expression of neural markers,increased cell elongation and more prominent neurite outgrowths were observed with increasing surface charge of the nanocomposite membrane indicating a dose-response effect of surface electrical charge on SHED neural differentiation.Further investigations of the underlying molecular mechanisms revealed that intracellular calcium influx,focal adhesion formation,FAK-ERK mechanosensing pathway and neurogenic-related ErbB signaling pathway were implicated in the enhancement of SHED neural differentiation by surface electrical charge.Hence,this study confirms the dose-response effect of biomaterial surface charge on SHED neural differentiation and provides preliminary insights into the molecular mechanisms and signaling pathways involved.

Observation of room‐temperature out‐of‐plane switchable electric polarization in supported 3R‐MoS_(2) monolayers

Two‐dimensional(2D)ferroelectrics have attracted considerable attention due to their potential in the development of devices of miniaturization and multifunction.Although several van der Waals(vdW)‐layered materials show ferroelectricity,the experimental demonstrations of ferroelectric behavior in monolayers are very limited.Here we report the observation of room‐temperature out‐of‐plane switchable electric polarization in supported MoS_(2) monolayers exfoliated from 3R‐stacked bulk crystals under ambient conditions.Using in situ piezoelectric force microscopy and Kelvin probe force microscopy in a glovebox,we reveal that trapped water/ice molecules are responsible for this switchable electric polarization and this conclusion is strongly supported by theoretical simulations.It is worth noting that the water/ice trapping in the monolayers exfoliated from 2H‐stacked MoS_(2) crystals is not as much as that in 3R monolayers and,consequently,the out‐of‐plane electric polarization is missing there.Our findings indicate that monolayers with a trapped single layer of polar molecules might be emerging alternatives to 2D ferroelectrics.Furthermore,the stacking sequences may bring new properties and applications to 2D vdW materials not only when we stack them up but also when we thin them down.

Enhanced Fenton-like process over Cu/L(+)-ascorbic acid co-doping mesoporous silica for toxicity reduction of emerging contaminants

Effective removal of emerging contaminants(ECs)to minimize their impacts on human health and the natural environment is a global priority.For the removal of ECs in water,we fabricated a seaweed spherical microsphere catalyst with Cu cation-πstructures by in situ doping of Cu species and ascorbic acid in mesoporous silica(Cu-C-MSNs)via a hydrothermal method.The results indicate that bisphenol A(BPA)is substantially degraded within 5 min under natural conditions,with its biological toxicity considerably weakened.Moreover,industrial wastewater could also be effectively purified by Cu-C-MSNs/H_(2)O_(2) system.The presence of metal sites and the complexation of ECs via cation-πinteraction andπ-πstacking on the catalyst surface were directly responsible for the polarization distribution of electrons,thus activating H_(2)O_(2) and dissolved oxygen(DO).The removal of contaminants could be attributed primarily to 1)the activation of H_(2)O_(2) into ^(·)OH to attack the contaminants and 2)self-cleavage because of the transfer of electrons from the contaminants to the catalysts.This study provides an innovative solution for the effective treatment of ECs and has positive implications for easing global environmental crises.

Evidence for distortion-induced local electric polarization in α-RuCl_(3)

The spin-orbit assisted Mott insulator α-RuCl_(3) is a prime candidate for material realization of the Kitaev quantum spin liquid.While little attention has been paid to charge degrees of freedom,charge effects,such as electric polarization,may arise in this system.Here,we report distortion-induced local electric polarization in α-RuCl_(3) as evidenced by single-crystal X-ray diffraction,second harmonic generation(SHG)and dielectric measurements.The SHG signal appears at room temperature and develops substantially in the Kitaev paramagnetic state when short-range spin correlations come into play.Despite sizable pyroelectric currents in the Kitaev paramagnetic state,the absence of hysteresis in the polarization-electric field(P-E)points to the shortrange nature of electric polarization.This localized electric polarization is likely the result of distortion-induced charge dimerization,achieved through virtual hopping-induced charge redistribution.In addition,the electric polarization is boosted by short-range spin correlations via spin-phonon coupling in the Kitaev paramagnetic state.Our results emphasize the importance of charge degrees of freedom in α-RuCl_(3),which establish a novel platform to investigate charge effects in Kitaev materials.

Evaluation of the differential capacitance for ferroelectric materials using either charge-based or energy-based expressions

Differential capacitance is derived based upon energy,charge or current considerations,and determined when it may go negative or positive.These alternative views of differential capacitances are analyzed,and the relationships between them are shown.Because of recent interest in obtaining negative capacitance for reducing the subthreshold voltage swing in field effect type of devices,using ferroelectric materials characterized by permittivity,these concepts are now of paramount interest to the research community.For completeness,differential capacitance is related to the static capacitance,and conditions when the differential capacitance may go negative in relation to the static capacitance are shown.

Dielectric and ferroelectric properties of CoCr_(2)O_(4)nanoceramics

CoCr_(2)O_(4)nanoceramics are prepared by sol-gel auto combustion method.Synchrotron X-ray diffraction analysis affirms the singlephasepristine cubic structure with space group Fd3m.Debye-Scherrer method estimates the crystallite size of main intense peak tobe~27:15 nm.Prominent bands obtained in infrared spectra at 448 and 599 cm^(-1)are due to metal-oxygen stretching bond presentat tetrahedral and octahedral sites.Dielectric parameters decrease as frequency increases from 103 to 106 Hz that can be interpretedby Maxwell-Wagner-type interfacial polarization.Complex impedance spectra(Nyquist plot)reveal arc like behavior,which ismainly due to intergrain(grain boundary)resistance that also exhibits conducting nature of the nanoceramics.Weak ferroelectricityis mainly associated with the partial reversal of the polarization.Leakage current behavior follows the Ohmic and Child square law.Electron conduction process was interpreted by space-charge limited current(SCLC)mechanism.Leakage current behaviorobserved in cobalt chromite nanoceramics is mainly attributed to the oxygen vacancies.

SH Waves in(1-x)Pb(Mg_(1/3)Nb_(2/3))O_(3-x)PbTiO_3 Piezoelectric Layered Structures Loaded with Viscous Liquid

The velocity dispersion and attenuation of shear horizontal（SH） waves in a layered piezoelectric structure loaded with viscous liquid is studied,where the（1- x）Pb（Mg（1/3）Nb（2/3））O（3-x）PbTiO3[PMN-xPT]single crystal is chosen as the piezoelectric layer.The PMN-xPT is being polarized along[011]c and[001]c so that the macroscopic symmetries are mm 2 and 4 mm,respectively.For the nonconductive liquid,the electrically open and shorted conditions at the interface between the liquid and the piezoelectric layer are considered.The phase velocity equations are derived analytically.The effects of the electrically boundary condition,the viscous coefficient and mass density of liquid as well as the thickness of the PMN-xPT layer on the phase velocity and attenuation are graphically illustrated.The results show that the phase velocity for the[011]c polarized PMN-0.29 PT is much smaller than that for the[001]c polarized PMN-0.33 PT,and the effects of viscous coefficient and piezoelectric layer thickness on the phase velocity for the[011]c case are stronger than that for the[001]c case.In addition,the electrical boundary conditions have an obvious influence on the propagation behaviors.These results can be useful for the designs and applications of acoustic wave devices and liquid biosensors.