Angular-scattering characteristics of ferroelectric liquid-crystal electro-optical devices operating in the transient-scattering and the extended-scattering modes

The angular distribution of forward-scattered light in transient-scattering-mode (TSM) and extended-scattering-mode (ESM) ferroelectric liquid-crystal (FLC) devices was evaluated by use of circularly polarized incident light. For both modes the intensity and the distribution of forward-scattered light depended primarily on the FLC birefringence, spontaneous polarization, and the cell path length. In the FLC materials examined, the forward-scattering intensity under ESM drive conditions increased with longer FLC pitch lengths, whereas under TSM conditions stronger forward scattering was observed with increasing FLC spontaneous polarization. Although both TSM and ESM drive conditions displayed a similar angular distribution for forward-scattered light, the intensity of ESM scattering over a 0 degrees -6 degrees range was considerably smaller than that observed in earlier experiments with linearly polarized incident light.     

Electrical and optical modulation on ferroelectric properties of P(VDF-TrFE) thin film capacitors

Modulating the ferroelectric properties of P(VDF-TrFE) polymers both electrically and optically could open up new opportunities for their applications in non-volatile memories and sensors. Here by using the Nb:SrTiO₃ semiconductor as electrode compared with metal Au electrode, we report on the modulation of ferroelectric properties of P(VDF-TrFE) thin film capacitors both by electric field and UV light. A ferroelectric hysteresis loop shift together with the asymmetric switching behavior has been observed when using semiconducting electrode, which could be explained by the band alignment model based on interfacial charge screening. On the basis of band bending near the ferroelectric/semiconductor interface, we could further modulate the ferroelectric switching behaviors reversibly by UV light illumination. Our research provides a new route to engineer the ferroelectric properties of P(VDF-TrFE) polymer thin film capacitors, promising their applications in optoelectronic devices.     

Thin ferroelectric interferometer for spatial light modulations.

Thin ferroelectric interferometers (TFI's) for use as light-modulating devices were fabricated entirely with thin-film techniques on sapphire substrates. The ferroelectric layer in the TFI devices was a lead lanthanum zirconated titanate thin-film material, which can be formed from a chemical solution on highly reflective dielectric mirror surfaces. Light intensity modulation in both transmission and reflection modes was demonstrated with the fabricated devices. Experimental data and simulations show that TFI devices possess tremendous potential in spatial light modulators because of their fast-switching, low-driving voltage and readiness for integration with a variety of substrates, including silicon.     

Ferroelectric Tunnel Junctions: Modulations on the Potential Barrier

Recently, ferroelectric tunnel junctions (FTJs) have attracted considerable attention for potential applications in next-generation memories, owing to attractive advantages such as high-density of data storage, nondestructive readout, fast write/read access, and low energy consumption. Herein, recent progress regarding FTJ devices is reviewed with an emphasis on the modulation of the potential barrier. Electronic and ionic approaches that modulate the ferroelectric barriers themselves and/or induce extra barriers in electrodes or at ferroelectric/electrode interfaces are discussed with the enhancement of memory performance. Emerging physics, such as nanoscale ferroelectricity, resonant tunneling, and interfacial metallization, and the applications of FTJs in nonvolatile data storage, neuromorphic synapse emulation, and electromagnetic multistate memory are summarized. Finally, challenges and perspectives of FTJ devices are underlined.     

Short-Term Synaptic Plasticity Mimicked on Ionic/Electronic Hybrid Oxide Synaptic Transistor Gated by Nanogranular SiO_2 Films

An indium-zinc-oxide （IZO） based ionic/electronic hybrid synaptic transistor gated by field-configurable nanogranular SiO2 films was reported. The devices exhibited a high current ON/OFF ratio of above 107, a high electron mobility of ～14 cm2 V^-1 s^-1 and a low subthreshold swing of ～80 mV/decade. The gate bias would modulate the interplay between protons and electrons at the channel/dielectric interface. Due to the dynamic modulation of the transient protons flux within the nanogranular SiO2 films, the channel current would be modified dynamically. Short-term synaptic plasticities, such as short-term potentiation and short- term depression, were mimicked on the proposed IZO synaptic transistor. The results indicate that the synaptic transistor proposed here has potential applications in future neuromorphic devices.     

Efficiency enhancement in organic solar cells with ferroelectric polymers

The recombination of electrons and holes in semiconducting polymer-fullerene blends has been identified as a main cause of energy loss in organic photovoltaic devices. Generally, an external bias voltage is required to efficiently separate the electrons and holes and thus prevent their recombination. Here we show that a large, permanent, internal electric field can be ensured by incorporating a ferroelectric polymer layer into the device, which eliminates the need for an external bias. The electric field, of the order of 50 V μm(-1), potentially induced by the ferroelectric layer is tens of times larger than that achievable by the use of electrodes with different work functions. We show that ferroelectric polymer layers enhanced the efficiency of several types of organic photovoltaic device from 1-2% without layers to 4-5% with layers. These enhanced efficiencies are 10-20% higher than those achieved by other methods, such as morphology and electrode work-function optimization. The devices show the unique characteristics of ferroelectric photovoltaic devices with switchable diode polarity and tunable efficiency.     

Non-volatile ferroelectric control of ferromagnetism in (Ga,Mn)As

Multiferroic structures that provide coupled ferroelectric and ferromagnetic responses are of significant interest as they may be used in novel memory devices and spintronic logic elements. One approach towards this goal is the use of composites that couple ferromagnetic and ferroelectric layers through magnetostrictive and piezoelectric strain transmitted across the interfaces. However, mechanical clamping of the films to the substrate limits their response. Structures where the magnetic response is modulated directly by the electric field of the poled ferroelectric would eliminate this constraint and provide a qualitatively higher level of integration, combining the emerging field of multiferroics with conventional semiconductor microelectronics. Here, we report the realization of such a device using (Ga,Mn)As, which is an archetypical diluted magnetic semiconductor with well-understood carrier-mediated ferromagnetism, and a polymer ferroelectric gate. Polarization reversal of the gate by a single voltage pulse results in a persistent modulation of the Curie temperature of the ferromagnetic semiconductor. The non-volatile gating of (Ga,Mn)As has been made possible by applying a low-temperature copolymer deposition technique that is distinct from pre-existing technologies for ferroelectric gates on magnetic oxides. This accomplishment opens a way to nanometre-scale modulation of magnetic semiconductor properties with rewritable ferroelectric domain patterns, operating at modest voltages and subnanosecond times.     

Mechanical Terahertz Modulation by Skin‐Like Ultrathin Stretchable Metasurface

The modulation of terahertz plays a key role in realizing the tunable terahertz devices. The concept of flexible and stretchable electronics provides the possibility to dynamically modulate the terahertz with mechanical strain rather than additional electrical components. Here, the mechanical modulation of the terahertz transmission with a freestanding, skin‐like, and highly stretchable metasurface is experimentally illustrated. The stretchable metasurface is fabricated by merely constructing an Al/PI mesh film consisting of serpentine‐like unit cells, with total thickness of only 7 µm. With the flexibility realized by the extremely small thickness, the metasurface can be stretched, bended, and twisted, which provides the possibility to modulate terahertz transmission properties by the mechanical deformation of the metasurface. The terahertz time domain spectroscopy results indicate that the stretchable metasurface shows the band‐stop frequency selective effect and the transmission of the terahertz wave can be modulated from 0.15 to 0.5 with applied external tensile strains up to 28%, while only 3.4% of the shift of the resonance frequency is observed. The mechanisms of the metasurface and the relation between the modulation effect and the structural mesh parameters are also discussed with the electromagnetic simulations and the LC equivalent circuit model.     

Responsivity optimization and stabilization in electro-optic field sensors

Electro-optic (EO) modulation devices, which utilize an external electric field to modulate a beam of optical radiation, are strongly affected by parasitic effects, which change the polarization state of the optical beam. As a result, very small changes in the birefringence or optical path length within the EO material can result in very large fluctuations of the amplitude and phase of the optical modulation signal. A method of actively analyzing the modulated beam is described and demonstrated, which eliminates these fluctuations and keeps the modulation device stably operating at its peak responsivity. Applications to electric field detection and measurements are discussed.     

Liquid-crystal luminaire consisting of an optical shutter and a metal halide lamp

We made a liquid-crystal (LC) luminaire for the first time to our knowledge by combining a metal halide lamp and an optical shutter composed of a compound of a very high nematic-isotropic point (172 degrees C) LC and a polymer (CLCP). The shutter can modulate high-power light independently of the state of polarization because the CLCP film becomes transparent or opalescent when either sufficiently high or no voltage is applied to it. To solve the problem, which is peculiar to CLCP films, that the color temperature of light modulated by the film changes with the film's transmittance, a pulse-width modulation method that varies the time ratio of the on and off states of the shutter was developed. The performance characteristics of the luminaire were as follows: illuminance range, 192 to 10,400 lx at a distance of 5 m from the luminaire; rise and decay times, 1.4 and 1.5 ms; color temperature, 4060-5600 K; operation room temperature, ~150 degrees C; stable operation time, more than 2000 h. Experimental results show the feasibility of applications of this luminaire in various fields, including television, movie, and stage lighting.     

铁电材料的核辐射效应

大量研究结果和实验数据显示,铁电材料与器件具有极强的抗辐射能力,在军事和空间领域具有广阔的应用前景,因此铁电材料及其器件的抗辐射能力与机理研究日益受到关注.首先综述了国内外关于铁电材料的核辐射效应研究最新进展,在此基础上对其核辐射效应微观机理进行了分析和讨论,指出了铁电材料在抗辐射领域的发展趋势和研究方向.     

Enhanced second-harmonic generation in an electro-optic controlled periodically poled ferroelectric crystal

We present a novel design of enhanced second-harmonic generation in a periodically poled ferroelectric crystal. It profits from enhanced light intensity and slowed group velocity, which occur near photonic band edges through electro-optic modulation. The designed structure, with 108 periods and a length of 322 microm, can generate a second-harmonic beam whose conversion efficiency is 2 orders of magnitude larger than the one produced by an equivalent length of quasi-phase-matching bulk medium. This result might be beneficial to the development of optics integration and compact devices.     

Metal slits and liquid crystals at microwave frequencies

While the use of liquid crystals (LCs) over the visible region is ubiquitous in flat-screen displays, there has been little by the way of applications at other wavelengths. Specifically, notwithstanding the continuing permittivity anisotropy to be found at longer wavelengths, there has been virtually no development in the microwave domain. This is largely due to the fact that scaling up the micrometer-thick LC layers used for visible radiation to millimetre dimensions is seen as impractical. In this study, it is shown how, using thin slits in metal structures, a completely new generation of LC devices for use at microwaves may be realized. Such structures include slatted metal Fabry-Perot resonators, beam-steering devices, thin flexible voltage tunable filters and even cascade structures with strongly enhanced and reshaped microwave fields.     

Light scattering from ferroelectric domains in LiTaO3

When a He-Ne 0.633 μm laser light passes through an as-grown LiTaO₃ single crystal, the Tyndall phenomenon is observed along the beam path. The scattered light intensity distribution was measured in the plane perpendicular to the incident beam. Results were discussed from the viewpoint of very small ferroelectric domains using light scattering theory. It was concluded that light scattering centers in LiTaO₃ are ferroelectric multi-domains of size in order of one wavelength.     

Thermal modulation for multidimensional liquid chromatography separations using low-thermal-mass liquid chromatography (LC)

We report on a proof-of-principle experiment with a novel thermal modulation device with potential use in two-dimensional liquid chromatography (LC × LC) systems. It is based on the thermal desorption concept used in two-dimensional gas chromatography (GC × GC) systems. Preconcentration of neutral analytes eluting from the first dimension column is performed in a capillary "trap" column packed with highly retentive porous graphitic carbon particles, placed in an aluminum low-thermal-mass LC heating sleeve. Remobilization of the trapped analytes is achieved by rapidly heating the trap column, by applying temperature ramps up to +1200 °C/min. Compared to the nonmodulated signal, the presented thermal modulator yielded narrow peaks, and a concentration enhancement factor up to 18 was achieved. With a thermally modulated LC separation of an epoxy resin, it is shown that when the thermal modulation is applied periodically, the trapped and concentrated molecules can be released periodically and that the modulating interface can both serve as a preconcentration device and as an injector for the second dimension column of an LC × LC setup. Because of the thermal modulation, a high-molecular-weight epoxy resin could be adequately separated and the different fractions were identified with a GPC analysis, as well as an offline second dimension LC analysis.     

Effect of interfaces on the magnetoelectric properties of Co/PZT/Co heterostructures

We have studied Co (film)/PZT (substrate)/Co (film) heterostructures with plane-parallel interfaces, produced by direct growth of cobalt films 0.5 to 3.5 μm thick on PZT surfaces smoothed to a subnanometer level (where PZT stands for a ceramic PbZr_0.45Ti_0.55O₃ lead zirconate titanate ferroelectric substrate). The results demonstrate that they possess magnetoelectric properties comparable in magnitude to those characteristic of known structures but, in contrast to these latter, allow one to dispense with the condition that the volume fractions of the ferromagnetic and ferroelectric components be roughly equal. The interface is shown to play a key role in determining the magnetoelectric response of the heterostructures: above 9 mV/(cm Oe) (11.7 mV/A) in a magnetic field of 50 Oe (3980 A/m) at a frequency of 100 Hz and room temperature. The heterostructures are potentially attractive for use as nonvolatile sensors in household devices.     

Optical properties of conductive silver-nanowire films with different nanowire lengths

Transparent electrodes made of silver nanowires (Ag NWs) exhibit a higher flexibility than conventional indium tin oxide electrodes.For this reason,Ag NWs may find applications in future flexible electronic and optoelectronic devices.However,different optoelectronic devices have different specific requirements for Ag NWs.For example,the optical transmittance haze is an important but rarely studied aspect of Ag NW films.In this study,the optical transmittance and optical scattering of long (5-50 μm,L-NWs) and short (1-20 μm,S-NWs) Ag NW films were investigated.The L-NWs exhibited better optical transmission than the S-NWs,whereas the S-NWs exhibited better light-scattering properties than the L-NWs.Our results indicate that the L-NWs are suitable for touch-screen displays,whereas the S-NWs are better suited as transparent conductive films for solar cells.We analyzed the scattering ratio of forward-scattered light to backscattered light for both the L-NWs and S-NWs and discovered that the mesh size affected the scattering ratio.For longer wavelengths,a larger mesh yielded a higher backscattering ratio,whereas a smaller mesh yielded a lower backscattering ratio.We formulated an equation for calculating the reflection haze using the total reflection (Ag NWs/glass),R and the reflection of glass,R0.The reflection haze of the S-NWs and L-NWs exhibited different trends in the visible-near-infrared region.An omnidirectional scattering model for the Ag NWs was used to evaluate the Ag NW scattering properties.The results of this study have great significance for the evaluation of the performance of Ag NWs in optoelectronic devices.     

Liquid-crystal panel with microdots on an electrode used to modulate optical phase profiles

The optical characteristics of a liquid-crystal (LC) panel with microdots on an electrode are investigated. Although 3 mum is larger than 1 molecule of LC material, microdots with a 3 microm diameter are sufficiently small to produce a smooth index profile. We use an electrode patterned in a new way to modulate the index profile of the LC panel, which allows us to modulate the optical phase of the passing light.     

Novel nonvolatile memory with multibit storage based on a ZnO nanowire transistor

We demonstrate a room temperature processed ferroelectric (FE) nonvolatile memory based on a ZnO nanowire (NW) FET where the NW channel is coated with FE nanoparticles. A single device exhibits excellent memory characteristics with the large modulation in channel conductance between ON and OFF states exceeding 10(4), a long retention time of over 4 × 10(4) s, and multibit memory storage ability. Our findings provide a viable way to create new functional high-density nonvolatile memory devices compatible with simple processing techniques at low temperature for flexible devices made on plastic substrates.     

Individually addressable epitaxial ferroelectric nanocapacitor arrays with near Tb inch-2 density

Ferroelectric materials have emerged in recent years as an alternative to magnetic and dielectric materials for nonvolatile data-storage applications. Lithography is widely used to reduce the size of data-storage elements in ultrahigh-density memory devices. However, ferroelectric materials tend to be oxides with complex structures that are easily damaged by existing lithographic techniques, so an alternative approach is needed to fabricate ultrahigh-density ferroelectric memories. Here we report a high-temperature deposition process that can fabricate arrays of individually addressable metal/ferroelectric/metal nanocapacitors with a density of 176 Gb inch(-2). The use of an ultrathin anodic alumina membrane as a lift-off mask makes it possible to deposit the memory elements at temperatures as high as 650 degrees C, which results in excellent ferroelectric properties.