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Nonlinear optical materials, whose optical properties such as refractive index can be changed by light, are essential for advanced light functionalities such as all optical switching. In this chapter, the fundamentals of nonlinear optics have been described and the second- and third-order nonlinear optical materials based on both organic and inorganic molecules have been reviewed. In particular, the nonlinear optically active subwavelength scale architectures have been highlighted.

Lithium niobate LiNbO3 (LN) on insulator wafers (LNOI) representing a submicron-thick LN film bonded to a SiO2 layer deposited on a thick LN substrate have been manufactured recently by ion slicing. Today, LNOI is one of the most promising materials for fabrication of various integrated optical devices, including waveguides, electro-optical modulators, and wavelength convertors, due to their high drop in refractive index at the interface between the film and the SiO2 layer. Creation of the stable domain structures with submicron periods in LNOI will improve the properties of nonlinear optical devices. Periodically poled LN with periods below 300 nm can be used to implement an optical parametric oscillator in the backward configuration. We have studied experimentally the ways to create the stripe domains and periodical domain structures in LNOI with a dielectric layer under the film by local switching. The identified scenarios of the domain evolution were attributed to the ineffective screening of depolarization field. We have shown that stripe domains and periodic domain structures can be produced by scanning with a biased tip only at temperatures above 80 °C. Periodical stable domain structures with periods down to 300 nm have been created.

The rapid development of flexible micropower electronics has aided the opportunity for the broader application of flexible piezoelectric composites (PCs) but has also led to higher requirements for their power generation. Among them, 0-3 PCs with embedded zero-dimension piezoparticle fillers, although low cost and easy to prepare, suffer from suboptimal output performance because of inherent structural defects. In this work, the voltage output was increased from 3.4 to 12.7 V under a force of 7 N, through first-step regulation by aligning the KNbO3 (KN) particles in the polydimethylsiloxane (PDMS) matrix; then, a significantly enhanced current output (from 0.7 to 4.5 μA) through second-step regulation by introducing copper nanorods (Cu NRs) interspersed in the gaps between the KN chains. Consequently, the proposed PC exhibits much higher power density, 37.3 μW/cm2, than that of random KN/PDMS and thus shows good potential for high-performance, flexible piezoelectric energy harvesters.

The additive manufacturing of piezoelectric ceramic Lead Zirconate Titanate (PZT) through paste extrusion 3D printing was demonstrated. Different paste compositions with varied water weight content were studied to find a composition suitable for printing. The pastes were evaluated in terms of their viscosities, yield stresses, and stability when aged. Furthermore, the material properties of the ceramics produced through paste extrusion were characterized and compared with those of ceramics fabricated through a conventional die pressing method. Paste extruded PZT with achieved densities as high as 94.9% of the theoretical density after sintering, which nearly matched the 95% density attained by the pressed samples. Upon poling, the paste extruded PZT piezoelectric ceramics attained piezoelectric coefficients and dielectric constants that were close to the values of die pressed samples. As near full density PZT ceramics were successfully fabricated through paste extrusion, this work paves the way for piezoelectric ceramics with application-driven geometry designs for sensors, actuators, and energy harvesters.

This paper addresses a unimorph cantilevered piezoelectric nanogenerator having high ‎output power through vibrational energy harvesting that is simulated using finite element ‎method (FEM). The simulations are done for three types of perovskite piezoelectric ‎materials including PZT, PMN-PT and MAPbI3. The interdigitated electrodes were ‎exploited‏ ‏to obtain longitudinal vibration mode using d33 mode of piezoelectric layer during ‎the bending of nanogenerator structure. The presented structure consists of a piezoelectric ‎nanolayer with gold interdigitated electrodes on it, which is placed on a flexible PET ‎polymeric substrate. To encapsulate the piezoelectric layer, an SU-8 epoxy is placed over ‎the surface. The poling process is also simulated by applying high voltage through IDs to ‎piezoelectric layer. Generally, the electric potential distribution of the piezoelectric layer ‎must be performed by applying mechanical loadings. Then the output voltage, ‎power for free vibrations and base excitation (0.25-2g) of the nanogenerator at resonance ‎frequency are investigated. The resonance frequency of the PZT, PMN-PT, and MAPbI3 were ‎calculated to be 549 Hz, 560.5 Hz and 631 Hz, respectively. We found that PZT ‎piezoelectric materials yields maximum output voltage and electrical power values of 91.69 ‎V and 350 mW which shows better performance in vibrational energy harvesting ‎application. In comparison, the results of the simulation implied a good agreement with ‎other experimental studies. The unimorph piezoelectric energy harvester system generates ‎high voltage and output power in response to sub-kilohertz ambient vibration‎.‎‎

Multiferroic BiFeO3 materials have driven great interest due to their potential in solar-spectrum energy harvesting, optoelectronic and photodetection devices. Here we report effects of electric-field poling on electronic hybridization and domain structure, and their correlations with photovoltaic responses in the ITO/(Bi0.93Gd0.07)FeO3 ceramic/Au heterostructure under 405 nm and 532 nm irradiations. Photovoltaic conversion, photoresponsivity (R) and specific detectivity (D*) are sensitive to ceramic thickness, photon energy, light intensity and electric-field poling. The photoresponsivity and detectivity in the 1 kV/cm poled photovoltaic cell under low-intensity 405 nm irradiation can respectively reach ∼4.5 × 10−2 A/W and 2.5 × 1011 Jones, which are larger than ∼2.8 × 10−2 A/W and 1.56 × 1011 Jones in the unpoled cell. This study demonstrates fast response times of ∼1 × 10−3 s and ∼2 × 10-2 s respectively under 405 nm and 532 nm irradiations. The improved photoresponse was driven jointly by the p-n junction, the field-modulated Schottky barriers and the network of grain boundaries and domain walls.

The development of a new class of perovskite materials and enhancing its capability as an energy harvester that scavenges energy from various sources to power electronics systems has attracted significant attention. Herein, we report a cost-effective approach to synthesize a perovskite material, explore its properties, and further develop a high-performance flexible nanogenerator based on hybrid piezoelectric composite. The Aurivillius-based oxide, CaBi4Ti4O15 (CBTO) was fabricated via a mixed oxide reaction and crystallized in an orthorhombic symmetry at room temperature. The material properties were elucidated to act as a parallel plate capacitor that will further act as a base for the development of filter circuits. Aurivillus/PDMS composite films were used to fabricate a flexible Aurivillus-based piezoelectric nanogenerator (A-PENG) to act as a self-powered exercise counter and power the electronics. The A-PENG was systematically analyzed under different conditions such as weight percentage, before and after poling, and acceleration effects. In addition, device stability, and capacitor charging-discharging tests were performed. This study elucidated the formation of lead-free ceramic materials that were used to make a flexible composite film for the realization of a piezoelectric harvester acting as a sustainable energy source.

The creation of the stripe domain structures with submicron periods by local switching using a biased tip of a scanning probe microscope was studied on Z-cut of lithium niobate on insulator (LNOI)....

This work highlights improved photosensing performance in ITO/ ( Bi 0.93 Sm 0.07 ) FeO 3 /Au heterostructure through a prior electric field poling. Maximal responsivity (R) of 2.0 × 10 − 2 A / W and specific detectivity (D*) of 2.2 × 10 11 Jones were obtained under 405-nm irradiation. The mechanism behind the observed photosensing performance is linked to the combined effects of the polarization-induced electric field and built-in electric fields at the interfaces (i.e., p–n junction and Schottky barrier). The net internal electric field established in the device serves as the driving force for the separation and transport of the photo-generated electron–hole pairs. The reduced direct optical bandgap (Eg) of 2.13 eV, the well-defined ferroelectric polarization hysteresis loops, and the conduction pathways formed by the electric field-stimulated interconnection of domain walls and grain boundaries play significant roles in the remarkable photosensitivity of ( Bi 0.93 Sm 0.07 ) FeO 3 ceramics, thus providing insight into optimizing BiFeO3-based materials for near-UV photodetector.

The use of high κ dielectrics lowers the operating voltage in organic field-effect transistors (FETs). Polymer ferroelectrics open the path not just for high κ values but allow processing of the dielectric films via electrical poling. Poled ferroelectric dielectrics in p-type organic FETs was seen to improve carrier mobility and reduce leakage current when compared to unpoled devices using the same dielectric. For n-type FETs, solution-processed ZnO films provide a viable low-cost option. UV–ozone-treated ZnO films was seen to improve the FET performance due to the filling of oxygen vacancies. P-type FETs were fabricated using the ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) as the dielectric along with a donor–acceptor polymer based on diketopyrrolopyrrole (DPP-DTT) as the semiconductor layer. The DPP-DTT FETs yield carrier mobilities upwards of 0.4 cm2/Vs and high on/off ratios when the PVDF-TrFE layer is electrically poled. For n-type FETs, UV–ozone-treated sol–gel ZnO films on SiO2 yield carrier mobilities of 10−2 cm2/Vs. DPP-DTT-based p- and ZnO-based n-type FETs were used in a complementary voltage inverter circuit, showing promising characteristic gain. A basic inverter model was used to simulate the inverter characteristics, using parameters from the individual FET characteristics.

Multiferroic toxicity-free perovskite BiFeO3-based materials reveal potentials in photoelectrical conversion, energy harvesting and photodetector. This work highlights polarization-enhanced photovoltaic (PV) effects and mechanisms in B-site Ni-doped (Bi0.93Gd0.07)FeO3 ceramics with indium tin oxide (top electrode) and Au (bottom electrode) thin films. The enhanced PV effects are attributed to the reduced bandgap, polarization-modulated Schottky barrier, increased O 2p-Fe 3d orbital hybridization, and nucleation of domain walls to improve transportation of charge carriers. Improved PV parameters of responsivity (R) ∼1.71 × 10−2 A/W, detectivity (D*) ∼9.56 × 1011 Hz1/2/W (Jones), open-circuit voltage (Voc) ∼0.65 V, and short-circuit current density (Jsc) ∼80 μA/cm2 were obtained from the ITO/ (Bi0.93Gd0.07)(Fe0.97Ni0.03)O3/ Au heterostructure after 2 kV/cm poling under 405 nm irradiation at 103 W/m2 intensity. This work demonstrates that Ni-doped (Bi0.93Gd0.07)FeO3 ceramics can be potential candidates for self-powered UV photodetector.

Efficient charge separation, in particular bulk charge separation (BCS), is one of the most critical factors in determining the performance of photoelectrochemical (PEC) water-splitting. The BCS enhancement of CdS/BaTiO3 (CdS/BTO) nanowires (NWs) in photoelectrocatalysis has rarely been reported. This paper describes a remarkable PEC properties promotion of the CdS/BTO NWs, which is confirmed to be a result of the enhanced BCS efficiency induced by the ferroelectric polarization. The vertical arrays of BTO NWs endow fast transfer of carriers. Meanwhile, CdS is decorated uniformly on the surface of BTO NWs, which ensures a wide range of light absorption. After two negative polarizations, the CdS/BTO NWs have successfully obtained a remarkable photocurrent density, achieving 459.53 μA cm−2 at 1.2 V(vs.RHE), which is 2.86 times that of the unpolarized sample. However, after two positive polarizations, the photocurrent density dramatically decreases to 40.18 μA cm−2 at 1.2 V(vs.RHE), which is merely 0.25 times the original value. More importantly, the photocurrent density reaches up to a prominent value of −71.09 mA cm−2 at −0.8 V(vs.RHE) after two successive negative polarizations, which is a 40.87 mA cm−2 enhancement with respect to the sample without poling. Significantly, at −0.8 V(vs.RHE), the BCS efficiency of the CdS/BTO NWs is as high as 91.87% after two negative polarizations. The effects of ferroelectric polarization on the PEC performance of CdS/BTO NWs have been systematically studied. The results demonstrate that ferroelectric polarization, especially negative polarization, results in an internal electric field to tune band bending of CdS/BTO NWs, thus prominently enhancing the PEC performance.

Charged domain walls (CDWs) have attracted considerable attention owing to their tunable properties related to high-density information storage and nanoelectronics devices. The excellent time endurance of conductivity is a pressing need, which is directly related to the domain stability and boundary conditions. In this study, we propose an effective method to promote the permanent formation of charged domain walls aimed with tip-induced electric fields. The permanent domain structures and CDWs are attributed to the robust stimulus with tip dimensions combined with effective screening conditions. This interesting conductivity near the domain walls is three orders of magnitude higher than the domain inner, and exhibits attractive anti-fatigue properties with the value of ∼60 pA for the duration of more than one month. In addition, the tunable mechanism of CDWs in LiNbO3 thin films is related to carrier gathering near the domain walls for the inclined boundary. These inclined head-to-head domain walls exhibit conductive features only along the negative direction, which can be modulated by the application of a sub-coercive voltage. The results demonstrate the stable manipulation of domain reversal and charged domain walls in LiNbO3 thin films, highlighting them as a critical component, especially for multiple-state logic circuits and potential ferroelectric diode applications in non-volatile memories and nanoelectronics devices.

With the aim of improving the photocatalytic activity for water splitting, novel core-shell-structured crystalline-BaTiO3/amorphous-BaTiO3-x/crystalline-CdS composite nanocubes are prepared by a facile two-step synthesis approach. Basic characterization techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy are carried out on the as-prepared composite nanocubes in order to confirm the quality of their crystal structure, morphology and chemical components correspondingly. UV-Vis-NIR measurements of the as-prepared composite nanocubes validate the presence of extended visible-light absorbance due to oxygen-deficient BaTiO3-x. Photoelectrochemical tests are carried out on the as-prepared nanocomposite films that are coated directly on indium tin oxide (ITO) glass substrates. The as-prepared composite nanocubes show a photocurrent density of 100 μA cm-2 without electric field poling, whereas they show about 200 μA cm-2 with an electric field poling of 18.8 kV cm-1. This study suggests that the photoelectrochemical performance is highest in our prepared BaTiO3/BaTiO3-x/CdS composite film compared to the pure BaTiO3, CdS and BaTiO3/BaTiO3-x films, and it may offer a new potential route for designing cost-effective, highly stable and efficient photocatalysts.

Ferroelectric (FE) materials are thought to be promising materials for self-powered ultraviolet (UV) photodetector applications because of their photovoltaic effects. However, FE-based photodetectors exhibited poor performance because of the weak photovoltaic effect of FE depolarization field (Edp) on the separation of photo-generated carriers. In this work, self-powered photodetectors based on both Edp and built-in electric field at the p-n junction (Ep-n) were designed to obtain enhanced device performance. A NiO/Pb0.95La0.05Zr0.54Ti0.46O3 (PLZT) heterojunction-based device is constructed to take advantage of energy level alignments that favor electron extraction. The device exhibits a tunable performance upon varying the polarization direction of PLZT. The NiO/PLZT heterojunction-based device with the PLZT layer in the poling down state shows a higher responsivity [R = (1.8 ± 0.12) × 10-4 A/W] and detectivity [D* = (3.69 ± 0.2) × 109 Jones], a faster response speed (τr = 0.34 ± 0.03 s, τd = 0.36 ± 0.02 s), and a lower dark current [Idark = (1.3 ± 0.19) × 10-12 A] under zero bias than the PLZT-based device because of the synergistic effects of Edp and Ep-n. Moreover, under weak-light illumination (0.1 mW/cm2), it exhibits even higher R [(6.3 ± 1.2) × 10-4 A/W] and D* [(1.29 ± 0.26) × 1010 Jones] values, which surpass those of most previously reported FE-based self-powered photodetectors. Our work emphasizes the role of the coupling effect between Ep-n and Edp in the photovoltaic process of NiO/PLZT heterojunction-based devices and provides an effective way to promote the self-powered UV photodetector applications.

Defect dipoles in acceptor-doped perovskite-based ferroelectric ceramics play an important role in piezoelectric properties. In this work, the acceptor, such as Fe2+ and Cu+, -doped (K0.5N0.5)NbO3 (KNN) ceramics are fabricated in reduced atmosphere by the conventional solid-state reaction method. By tailoring the strongly polarized defect dipoles through poling and aging processes, ultrahigh electro-strain and large signal piezoelectric d33* values can be achieved. The electro-strains of 0.41% and 0.50% with d33* ~820 pm/V and ~1000 pm/V are obtained in Fe2+-doped and Cu+-doped KNN samples, respectively, which are 4-fold and 5-fold larger than that of pure KNN. Of particular interest is that the electro-strain and d33* values are found to improve with increasing temperature up to 140°C, accompanied with low strain hysteresis of 10%-20%. A detailed mechanism considering the interaction between defect dipole polarization and spontaneous polarization after poling and aging processes is proposed to explain the observed phenomena, which provides a good paradigm for achieving high piezoelectric response by defect engineering in perovskite-based ferroelectric ceramics.

A comparative study of electromagnetic radiation (EMR) detection from Soft PZT (SP 5A) and Hard (SP 4) PZT under impact at high temperatures has been presented. EMR is detected by applying impact load on the samples at temperatures varying from 288 to 514 K. With increase in temperature, thermal energy increases imparting molecular vibrations which reduce the net effective polarization and this in turn results in the low amplitude of EMR signals. EMR voltage amplitude and EMR energy release rate show an overall decreasing pattern with increase in temperature. Experiments conducted on samples poled at different d.c. poling fields exhibit strong dependence of EMR signals on d.c. poling field. EMR voltage amplitude is found to increase with increase in the strength of d.c. poling field. This study pertaining to the effect of poling as well as high temperatures on the EMR signal variation will be an aid towards the development of wireless sensing technique.

We report a successful realization of a self-actuating and self-sensing piezoelectric diaphragm resonator for sensing applications with high signal to background ratio (SBR). A fully differential electrode topology is designed for actuation of the diaphragm in the first flexural mode, and for simultaneously sensing the resulting vibrational response. The electrical (sense) outputs from the resonator (of radius $1000~\mu \text{m}$ and thickness $25~\mu \text{m}$ ) in two different experimental arrangements — partial differential and fully differential — are compared with the mechanical vibration response obtained from a laser Doppler vibrometer. The effect of poling on electrical crosstalk for the fully differential operation is investigated. The resonator suffers from electrical crosstalk even in fully differential operation when characterized without poling the PZT thin film. The sense output from the resonator after poling, when actuated using a differential electrical input of 0.5 Vpp, is measured both in-air and in liquids of different densities. In the self-sensing mode, the peak output from the device at the first flexural mode resonance is 2-3 mV in different density liquids and ~9 mV in air. The resonator is also characterized as a resonant sensor for liquid density measurements. The sensitivity of the device is found to be 11.9 Hz/(kg/m3). The corresponding sensitivity in parts per million is calculated to be ~454 ppm/(kg/m3) with the resonance frequency in DI water (26.3 kHz) as the reference. [2020-0137]

We present an EO Q-switched Tm:YAP laser constructed with a periodically poled Mg-doped congruent lithium niobate (PPMgCLN) Bragg modulator. A 2-mm-thick PPMgCLN modulator was adopted, and the internal stress generated in the electric poling process was released by annealing. The peak stress-induced refractive index variance for e-wave was deduced to be 2.29 × 10-5 at 1064 nm. When the absorbed pump power and repetition rate were 13.4 W and 1 kHz, respectively, the laser had a Q-switched pulse energy of 2 mJ, a pulse duration of 60 ns, and a peak power of 33.3 kW. By varying the reflection of the output coupler, output wavelengths of between approximately 1985 and approximately 1940 nm can be selected, making this laser a potential tool for pumping mid-IR sources and biomedical applications.

A watt-level continuous wave (CW) orange-red laser with wavelength tunable properties is experimentally implemented based on sum-frequency generation (SFG) in a composite cavity. The cavity is composed of an 880 nm laser diode (LD) side-pumped Nd: GdVO4 p-polarized 1062.9 nm cavity and a single-resonant optical parametric oscillator (SRO) of signal light using a magnesium oxide-doped periodically-poled LiNbO3 (MgO: PPLN) crystal with a poling period of 29.1 μm. In the overlap region of the two cavities, orange-red laser is generated by using a type-II critical phase-matched potassium titanyl phosphate crystal (KTP) crystal. In the temperature tuning range of the MgO: PPLN crystal (from 30 °C to 200 °C), the CW orange-red laser beams are generated in a tunable waveband from 612.24 nm to 620.72 nm (Δλ = 8.48 nm), corresponding to the mid-infrared idler light is also obtained with tunable wavelength from 4027.5 nm to 3708.2 nm (Δλ = 319.3 nm). At the lowest tuning temperature of 30 °C, the maximum CW output power of the orange-red laser at 612.24 nm and the idler light at 4027.5 nm are obtained, which are 1.145 W and 2.83 W, respectively.

Using the experimental setup for poling film samples with capability of continuous monitoring of generation signal of second harmonic, the conditions of effective orientation of chromophore molecules based on polyfluoro-substituted triaryl pyrazoline and dicyan-substituted isophoron in micron films of polycarbonate are determined. The second harmonic is excited with the pulse Nd:YAG laser with 1064 nm when chromophore molecules are oriented in the field of corona discharge. The dependences of signal level of the second harmonic on the potential at field mesh and on the potential at needle electrode are measured.

In order to develop ferroelectric photovoltaic devices with high power conversion efficiency, ferroelectric materials must have simultaneously large remnant polarization and narrow band gap so as to efficiently separate photo-generated carriers and absorb more sunlight. Based on this idea, in this report, we introduce Fe3+ into Pb0·93La0·07(Zr0·6Ti0.4)0.9825O3 ferroelectric thin film to increase the remnant polarization and decrease the band gap of the thin film. In doing so, we prepare Fe3+ doping Pb0·93La0·07(Zr0·6Ti0.4)0.9825O3 thin-film based photovoltaic devices. The experimental results indicate that with increasing the Fe3+ amount, the remnant polarization of the film first improves to the maximum value of 50 μC/cm2 at the 4.8 mol% Fe3+ content and then reduces gradually, while the band gap continuously decreases. In addition, at a negative poling voltage, the device exhibits larger short-circuit current and open-circuit voltage in comparison with those obtained at the positive poling voltage, which is attributed to the depolarization electric field originating from the remnant polarization of ferroelectric thin films in the same direction as the built-in electric field caused by the Schottky barrier. In this report, the most superior photovoltaic performances with the open-circuit voltage of as large as −0.55 V and short-circuit current of as high as 0.4 μA/cm2 are obtained in the device with 4.8 mol% Fe3+ amount and at −5 V poling voltage. This is on account of the improved sunlight absorbing properties and photo-generated carriers separation ability of the device. This work provides a novel idea for designing and preparing ferroelectric photovoltaic devices with high power conversion efficiency.

In this work, the commercial BaTiO3 crystal was cut into the same wafers along (101) crystal plane. These wafers were poled under various poling fields to study the effect of electric poling on the pyroelectric catalysis performance during the process of dye decomposition. Under 140 cold-hot (28 - 60 °C) cycles, the dye decomposition ratio using the unpoled BaTiO3 catalyst is close to 0, whereas it reaches ~ 56% using the BaTiO3 poled under a poling field of ~5.00 kV/mm. The poling treatment shows a great influence on the pyroelectric catalysis since it directly affects the number of charges generated on the surface of BaTiO3 crystal under the external temperature variation excitation. The generation of these middle product hydroxyl radicals further proves the reaction mechanism of the pyroelectric catalysis. The good catalysis and recyclability performance suggests the poled BaTiO3 pyroelectric crystal is an potential material in dye wastewater remediation through utilizing room-temperature thermal energy.

A hybrid, microstructured optical fiber (MOF) comprised of a silica glass, endlessly single mode optical fiber infiltrated with 2-methyl, 4-nitroaniline (MNA) is subjected to electric field poling for enhancing non-linear wavelength conversion properties. Different poling conditions (temperature, and electric field) are applied, resulting in significant changes manifested in the transmittance and second harmonic generation (SHG) behavior of this hybrid optical fiber. The origins of material and guidance changes induced by the electric poling are investigated by scanning electron microscopy, backscattered SHG microscopy and modal imaging as a function of the polarization state of a 1064 nm, pulsed laser pump. Results show that the improved crystallinity, induced by the poling of the MNA material infiltrated into the MOF capillaries surrounding the optical fiber core, play a dominant role in both SHG efficiency and the transmission performance of these hybrid optical fibers, opening new prospects in the development of in-fiber light switching and wavelength conversion devices.

Interfacial ‘dead’ layers between metals and ferroelectric thin films generally induce detrimental effects in nanocapacitors, yet their peculiar properties can prove advantageous in other electronic devices. Here, we show that dead layers with low Li concentration located at the surface of LiNbO3 ferroelectric materials can function as unipolar selectors. LiNbO3 mesa cells were etched from a single-crystal LiNbO3 substrate, and Pt metal contacts were deposited on their sides. Poling induced non-volatile switching of ferroelectric domains in the cell, and volatile switching in the domains in the interfacial (dead) layers, with the domain walls created within the substrate being electrically conductive. These features were also confirmed using single-crystal LiNbO3 thin films bonded to SiO2/Si wafers. The fabricated nanoscale mesa-structured memory cell with an embedded interfacial-layer selector shows a high on-to-off ratio (>106) and high switching endurance (~1010 cycles), showing potential for the fabrication of crossbar arrays of ferroelectric domain wall memories. An integrated one selector–one resistor device is realized using the volatile and non-volatile switching properties of ferroelectric domains created, respectively, at the interface and in the bulk of mesa-like LiNbO3 domain wall memory cells.

Defect density is one of the most significant characteristics of perovskite single crystals (PSCs) that determines their optical and electrical properties, but few strategies are available to tune this property. Here, we demonstrate that voltage regulation is an efficient method to tune defect density, as well as the optical and electrical properties of PSCs. A three-step carrier transport model of MAPbBr3 PSCs is proposed to explore the defect regulation mechanism and carrier transport dynamics via an applied bias. Dynamic and steady-state photoluminescence measurements subsequently show that the surface defect density, average carrier lifetime, and photoluminescence intensity can be efficiently tuned by the applied bias. In particular, when the regulation voltage is 20 V (electrical poling intensity is 0.167 V μm−1), the surface defect density of MAPbBr3 PSCs is reduced by 24.27%, the carrier lifetime is prolonged by 32.04%, and the PL intensity is increased by 112.96%. Furthermore, a voltage-regulated MAPbBr3 PSC memristor device shows an adjustable multiresistance, weak ion migration effect and greatly enhanced device stability. Voltage regulation is a promising engineering technique for developing advanced perovskite optoelectronic devices., Perovskite devices: Digital memories thrive by tuning out defects Innovative materials gaining favor as replacements for silicon solar cells can also be transformed into memory logic circuits using a new fabrication procedure. Lead halide perovskites can be turned into optoelectronic devices through low-cost solution depositions, but these approaches often leave numerous charge-trapping defects in the perovskite. Weili Yu from China’s Changchun Institute of Optics and colleagues have now developed a technique for modifying the defect population of perovskite crystals without requiring chemical additives. The team used probes to apply an electric field to the surface of a perovskite sample for helping move injected charges into defect sites with a high degree of control, which further modulated the optical and electrical properties of perovskite sample. Optimized defect populations enabled the perovskite to act as memristor device, capable of activating multiple resistance states.

Composite-type piezoelectric nanogenerator (PENG) can potentially provide power to the flexible electronics devices by harvesting the mechanical energy. The electricity output of the PENG is not entirely excavated until now because the polarization dipoles are not sufficiently aligned during the high-voltage poling process. In this study, some Ag particles are attached on the (K0.4425Na0.52Li0.0375) (Nb0.86Ta0.06Sb0.08)O3 (KNN) piezoelectric particles and then they are mixed with multi-walled carbon nanotubes and polydimethylsiloxane to fabricate the PENG device. The Ag particles can reduce the optimal poling electric field from 10 kV/mm down to 5 kV/mm. The PENG device with Ag particles poled at 5 kV/mm can generate the highest open-circuit voltage of 282 V, short-circuit voltage of 32.2 μA, and maximum instantaneous power of 3.5 mW under the external mechanical stress of 10 kPa without time-dependent degradation (only 27.9 V and 2.6 μA for the pure KNN-based PENG poled at 10 kV/mm). These are much better than previously reported composite-type PENG. The electrical energy generated from the PENG (20 mm × 40 mm) can light up 40 white light emitting diodes instantaneously without any storage unit during the stomping stage. Keywords: Composite-type piezoelectric energy harvester, Lead-free piezoelectric materials, Ultrahigh electrical output, Low poling electric field

A periodically-poled LiNbO3 (PPLN) crystal features space-dependent second-order nonlinear coefficients, which is one of the most important materials to effectively control nonlinear optical interactions through quasi-phase matching (QPM). By using electric-field poling method, 1D and 2D PPLN crystals have been successfully fabricated for laser frequency conversion, quantum light sources, nonlinear beam shaping and nonlinear optical imaging. Recently, femtosecond laser engineering technique is utilized to prepare 3D domain structures inside LiNbO3 crystal, which provides a promising platform to control nonlinear interacting waves in 3D configuration. After 40 years of developments, PPLN crystals still have exciting prospects in fundamental researches and practical applications for integrated photonic chip, quantum information processing, and so on.

A diffractive optical element (DOE) covering visible to middle-infrared regions is imprinted in chalcohalide glass by microthermal poling under ultralow voltages (~125 V). The effect of the poling voltage on the surface profiling, optical diffraction, optical transmittance, and anode-side structural rearrangement is investigated. Deformation of the surface profiling and diffraction order increase with increasing poling voltage, showing a saturation voltage of 125 V and a decrease in the transmittance within 10%. In addition to the normal vertical migration of silver ions, an obvious and unexpected transverse migration of silver ions and mutual structural transformation occur between homopolar bonds Ge–Ge (Ga–Ga) and S–S and the heteropolar bond Ge–S (Ga–S), which are key to forming the surface profiling and subsurface structures. Formation of the DOE mainly depends on the periodic subsurface microstructure rather than surface profiling. Thus, simple and inexpensive processes can fabricate broadband wavelength-based DOEs for military, medical and biological applications.

Ferroelectric domain structure in BaTiO3 ceramics was studied with nanoscale spatial resolution before and after poling by application of the uniform electric field. Complimentary vector piezorespo...

We present resistive switching characteristics of methylammonium lead iodide (CH3NH3PbI3) films through a noncontact electrical poling process toward memristive applications. The noncontact nature ...

Pure phase polycrystalline BiFeO₃ film was deposited onto FTO substrate by RF magnetron sputtering method. SEM result shows that BiFeO₃ film has the obvious porosity and large clusters which lead to the poor ferroelectric and photovoltaic properties in FTO/BiFeO₃/Ag device. However, these properties are improved in p-i-n structured FTO/TiO₂/BiFeO₃/HTM/Ag device by incorporating the electron and hole transport materials. The hysteresis loop measurement demonstrates the excellent ferroelectric property with large remnant polarization (2Pr = 180 μC/cm²) and low leakage current. The J-V curve shows the short-circuit current density is dozens of times larger than that of FTO/BiFeO₃/Ag device. Moreover, the photovoltaic output depends on the poling field where the positive poling improves the short-circuit current density to -85 μA/cm₂ and the negative poling reduces both the photocurrent and photovoltage. It is believed that the ferroelectric polarization plays a dominant role in the photovoltaic effect.

The ferroelectric photovoltaic (FPV) effect obtained in inorganic perovskite ferroelectric materials has received much attention because of its large potential in preparing FPV devices with superior stability, high open-circuit voltage (Voc) and large short-circuit current density (Jsc). In order to obtain suitable thickness for the ferroelectric thin film as light absorption layer, in which, the sunlight can be fully absorbed and the photo-generated electrons and holes are recombined as few as possible, we prepare Pb0.93La0.07(Zr0.6Ti0.4)0.9825O3 (PLZT) ferroelectric thin films with different layer numbers by the sol-gel method and based on these thin films, obtain FPV devices with FTO/PLZT/Au structure. By measuring photovoltaic properties, it is found that the device with 4 layer-PLZT thin film (~300 nm thickness) exhibits the largest Voc and Jsc and the photovoltaic effect obviously depends on the value and direction of the poling electric field. When the device is applied a negative poling electric field, both the Voc and Jsc are significantly higher than those of the device applied the positive poling electric field, due to the depolarization field resulting from the remnant polarization in the same direction with the built-in electric field induced by the Schottky barrier, and the higher the negative poling electric field, the larger the Voc and Jsc. At a -333 kV/cm poling electric field, the FPV device exhibits the most superior photovoltaic properties with a Voc of as high as 0.73 V and Jsc of as large as 2.11 μA/cm2. This work opens a new way for developing ferroelectric photovoltaic devices with good properties.

The development of high dielectric materials with high energy densities is a crucial research domain in the modern microelectronics and power systems. The objective of this work was to develop the highly ordered crystal orientations and large ferroelectric crystalline β/γ-phases in the biaxially oriented poly(vinylidene fluoride) (BOPVDF). Importantly, a high discharged energy density and high dielectric constant was achieved by using a high-electric-induced technique. A suitable poling electric field was applied to the BOPVDF films in order to enhance the breakdown strength. Remarkably, the BOPVDF film poled at the electric field of 113 MV m−1 achieved an unprecedented discharged energy density of 25.4 J cm−3 at an ultra-high electric field of 550 MV m−1, which is by far the highest value ever achieved in flexible polymer-based capacitor films. Comparatively, the unpoled BOPVDF and commercial biaxially oriented polypropylene (BOPP) exhibited only a discharged energy density of 7.9 J cm−3 and 1.2 J cm−3, respectively. This systematic study provides a new design paradigm to exploit PVDF-based dielectric polymers for capacitor applications.

The demand for wearable devices has generated intense interest from both industrial scientists and academic researchers. Wearable technology devices must be small, lightweight, and flexible. We propose wearable devices incorporating ferroelectric Bi0.5Na0.5TiO3 nanoparticles (BNT NPs) for motion monitoring and energy harvesting. BNT NPs were prepared using an inexpensive approach, and their fundamental material properties were evaluated by X-ray diffraction analyses, Raman spectroscopy, and scanning electron microscopy. The dielectric, ferroelectric, and piezoelectric properties of our BNT system were characterized: it exhibited a dielectric constant/loss of 325/0.039 at 1 kHz with a depolarization temperature of ∼205 °C. A maximum ferroelectric remnant polarization (Pr) of 34 μC cm−2 at 1 Hz was obtained with a piezoelectric coefficient of 79 pC N−1. Polycaprolactone was used as a matrix to fabricate flexible composite films (PBNT CFs) containing different amounts of BNT NPs. Optimized composites containing 50% BNT based piezoelectric nanogenerators (CPNGs) generated a maximum electrical response of 22 V and 140 nA, and an instantaneous power density of 3.95 mW m−2 in response to an applied mechanical force of 6 N @ 1 m s−2. The PBNT CPNGs were used to charge capacitors and were analyzed in terms of stability, poling, and acceleration-dependent energy harvesting performance. Motion monitoring and energy harvesting in a wearable device were demonstrated while walking, with a heel strike motion yielding 40 V and 220 nA.

More than one century ago, piezoelectricity and ferroelectricity were discovered using Rochelle salt crystals. Today, modern societies are invited to switch to a resilient and circular economic model. In this context, this work proposes a method to manufacture piezoelectric devices made from agro-resources such as tartaric acid and polylactide, thereby significantly reducing the energy budget without requiring any sophisticated equipment. These piezoelectric devices are manufactured by liquid-phase epitaxy-grown Rochelle salt (RS) crystals in a 3D-printed poly(Lactic acid) (PLA) matrix, which is an artificial squared mesh which mimics anatomy of natural wood. This composite material can easily be produced in any fablab with renewable materials and at low processing temperatures, which reduces the total energy consumed. Manufactured biodegradable samples are fully recyclable and have good piezoelectric properties without any poling step. The measured piezoelectric coefficients of manufactured samples are higher than many piezoelectric polymers such as PVDF-TrFE.

This work presents a new process to print piezoelectric polymer-based sensors through additive manufacturing via three-dimensional (3D) printing technology. 3D printing has become an efficient method to fabricate devices with complex geometric structures and embedded functionalities. The motivation of this research was to explore a path towards fully 3D printed multifunctional thin and flexible sensing devices. The 3D printed methods used were Fused Deposition Modelling and Direct Ink Writing. A fully 3D printed sensor consisting of a (2.54 cm × 2.54 cm) poly(vinylidene fluoride) (PVdF) film with thickness in the range of ∼250 μm to 350 μm was sandwiched between two fast-drying silver paint printed electrodes with thickness ranging from ∼10 μm to 50 μm. The arithmetic average roughness, Ra, of typical printed PVdF profiles with and without printed silver electrodes was ∼12.9 μm and ∼7.3 μm, respectively. Silver electrodes were printed to facilitate contact poling and to collect charges generated due to piezoelectricity. The average piezoelectric activity of printed unpoled films was 7.13 pC/N. The polarization in the printed PVdF films was realized by conventional contact poling at elevated temperatures (100, 110, 120 and 130 °C, respectively) with step increased electric fields, which were varied from 0.4 MV/m to 14 MV/m at 1 MV/m increments. To perform contact poling, PVdF films were immersed in mineral oil and a controlled voltage was applied to electrodes on one side while electrodes on the opposite side were grounded. The extrusion process during 3D printing and the subsequent contact poling process enabled the phase transition from the thermally stable α-phase to the piezoelectric active β-phase and the rearranging of the dipole alignments. The efficiency of poling was evaluated through measurement of the average value of the charge generated by six poled PVdF films in response to mechanical input increasing from 0.29 N to 1.91 N with ∼0.27 N increments. The highest average piezoelectric activity obtained was 59.2 pC/N, and a single device of 96.44 pC/N, at step increased poling voltages up to 3.5 kV under a fixed temperature 120 °C. The results demonstrate that by increasing the poling voltages and time, a higher piezoelectric activity (about 8 times compared to unpoled films) was achieved, indicating improvement of the β-phase content. This study provides a new method for continuous and direct printing of piezoelectric devices from PVdF polymeric filament. This technology opens a new path towards fully 3D printed free-form structured functional materials for sensing applications.

In ultrasonic transducers, there is a problem that the couplant to match the acoustic impedance and the backing material to absorb unnecessary vibration have low durability at high temperature. We have developed an ultrasonic transducer that does not require a couplant or backing material by using a sol-gel composite method. Although the Curie temperature of PT is around 490°C, when the poling voltage and the polarity of the applied electric field during measurement are matched, high temperature durability is achieved and clear ultrasonic waveforms can be measured even at 600°C. The polarity of the poling voltage and the applied electric field during measurement was matched.

Potassium titanyl phosphate (KTP) is a nonlinear optical material with applications in high-power frequency conversion or quasi-phase matching in submicron period domain grids. A prerequisite for these applications is a precise control and understanding of the poling mechanisms to enable the fabrication of high-grade domain grids. In contrast to the widely used material lithium niobate, the domain growth in KTP is less studied, because many standard methods, such as selective etching or polarization microscopy, provides less insight or are not applicable on non-polar surfaces, respectively. In this work, we present results of confocal Raman-spectroscopy of the ferroelectric domain structure in KTP. This analytical method allows for the visualization of domain grids of the non-polar KTP y-face and therefore more insight into the domain-growth and -structure in KTP, which can be used for improved domain fabrication.

Small organic molecules with a π-conjugated system that consists of only a few double or triple bonds can have significantly smaller optical excitation energies when equipped with donor and acceptor groups, which raises the quantum limits to the molecular polarizabilities. As a consequence, third-order nonlinear optical polarizabilities become orders of magnitude larger than those of molecules of similar size without donor-acceptor substitution. This enables strong third-order nonlinear optical effects (as high as 1000 times those of silica glass) in dense, amorphous monolithic assemblies. These properties, accompanied by the possibility of deposition from the vapor phase and of electric-field poling at higher temperatures, make the resulting materials competitive towards adding an active nonlinear optical or electro-optic functionality to state-of-the-art integrated photonics platforms.

We experimentally measure percent-level optical-to-multi-cycle terahertz conversion efficiencies by injecting a home-made wavelength- and duration-tunable two-line laser into periodically poled lithium niobate. We study the efficiency vs. the input laser peak fluence, pulse duration, crystal length and poling period at cryogenic temperature. Our work is a significant step towards high energy terahertz pulses for linear electron acceleration.

Hybrid organic electro-optic (OEO) devices consist of a layer of ordered organic chromophores confined between layers of metals or semiconductors, enabling optical fields to be tightly confined within the OEO material. The combination of tight confinement with the high electro-optic (EO) performance of state-of-the art OEO materials enables exceptional electro-optic switching performance in silicon-organic hybrid (SOH) and plasmonic-organic hybrid (POH) device architectures. Recent records in POH devices include bandwidths < 500 GHz and energy efficiency < 100 aJ/bit. However, optimization of device performance requires both understanding and improving the degree to which chromophores can be acentrically ordered near a metal or semiconductor interface. Applying bulk and/or isotropic models of OEO materials to nanophotonic device architectures often lead to overly optimistic translation of materials performance to device performance. Prior work has identified influences of high centrosymmetric order (birefringence), altered relations between acentric and centrosymmetric order (dimensionality), and surface electrostatics on chromophore ordering. We combine these models into a representation that can be used to understand the influences of these phenomena on device performance, how some prior OEO materials exhibited unusually high performance under confinement, how ordering close to surfaces may be improved, and implications for future electro-optic device design.

The charge carrier mobility in organic field-effect transistors (FETs) may be enhanced by a few orders of magnitude by an appropriate choice of the dielectric layer. Polymer ferroelectric dielectrics with their high dielectric constants are attractive for low-operating voltage FETs. However, due to the dynamic coupling of the charge carriers to the electronic polarization at the semiconductor-dielectric interface, polymer ferroelectric based organic FETs may result in low carrier mobilities. Selective electrical poling of the ferroelectric dielectric, poly(vinylidene fluoride trifluorethylene) (PVDF-TrFE), is seen to greatly improve the performance of small molecule and donor-acceptor copolymer based FETs [1]. A combination of vertical and lateral poling of the PVDF-TrFE layer, which reduces the gate leakage current as well as mitigates polarization fluctuation driven transport, yields carrier mobilities upwards of 1 cm2/Vs in TIPS-pentacene and 0.5 cm2/Vs in diketopyrrolopyrrole based FETs under ambient conditions [2]. Other strategies for improving the performance of FETs involve dissolving the ferroelectric polymer in high dipole moment solvents and adding thin polymer buffer layers. The incorporation of magnetic nanoparticles in non-ferroelectric dielectrics is yet another approach for enhancing the dielectric constant. Ferrite nanoparticles with biomimetic peptide nanostructures as gate dielectrics have ramifications in low-operating voltage organic FETs [3]. This work was supported by National Science Foundation under Grant No. ECCS-1707588 [1] Laudari et al. Adv. Mater. Interfaces 6, 1801787 (2019). [2] Laudari et al. ACS Appl. Mater. Interfaces 12, 26757 (2020). [3] Khanra et al. ACS Appl. Nano Mater 1, 1175 (2018).

Stabilization of the orthorhombic phase of HfO2 with La allows very high polarization and endurance. However, these properties have not been confirmed yet in films having thickness of less than 10 nm. We have grown (111)-oriented La (2 at%) doped epitaxial HfO2 films on SrTiO3(001) and Si(001) substrates, and we report on the thickness dependence of their ferroelectric properties. Films of less than 7 nm have a high remanent polarization of about 30 µC cm-2 , show slight wakeup, endurance of at least 1010 cycles and retention of more than 10 years, both latest properties measured at the same poling voltage. La-doped HfO2 films even as thin as 4.5 nm also show robust ferroelectric properties., Financial support from the Spanish Ministry of Science and Innovation, through the Severo Ochoa FUNFUTURE (CEX2019- 000917-S), MAT2017-85232-R (AEI/FEDER, EU), PID2020- 112548RB-I00 (AEI/FEDER, EU), and PID2019-107727RB-I00 (AEI/FEDER, EU) projects, from CSIC through the i-LINK (LINKA20338) program, and from Generalitat de Catalunya (2017 SGR 1377) is acknowledged. Project supported by a 2020 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. IF acknowledges Ramón y Cajal contract RYC-2017- 22531. TS is financially supported by China Scholarship Council (CSC), grant No. 201807000104. TS work has been done as a part of his Ph.D. program in Materials Science at Universitat Autònoma de Barcelona. RB and GSG acknowledge the financial support from the European Commission through the project TIPS (No. H2020-ICT-02-2014-1-644453), from the French national research agency (ANR) through the projects DIAMWAFEL (No. ANR-15-CE08-0034), and MITO (No. ANR-17- CE05-0018), and from CNRS through the MITI interdisciplinary programs (project NOTE). They are also grateful to the joint laboratory INL-RIBER, P. Regreny, C. Botella and J. B. Goure for the MBE technical support on the Nanolyon technological platform.

Piezoelectric nanogenerators (PENGs), as a promising solution to harvest mechanical energy from ambient environment, have attracted much attention over the past decade. Here, the core-shell structured BaTiO3@Carbon (BT@C) nanoparticles (NPs) were synthesized by a simple surface-modifying method and then used to fabricate the efficient PENGs with poly[(vinylidene fluoride)-co-trifluoroethylene] (P(VDF-TrFE)). The carbon shell with the uniform thickness of 10-15 nm can increase the content of the polar β phase in P(VDF-TrFE) and significantly enhance the interfacial polarization between BT NPs and the polymer matrix during the poling process. Out of all compositions, the 15 wt % BT@C/P(VDF-TrFE) PENG exhibited the optimal piezoelectric performance with an output voltage of ∼17 V and a maximum power of 14.3 μW under bending-releasing mode. More importantly, the PENG can also efficiently harvest other types of mechanical energy from human activities and exhibits stable output after 1500 bending-releasing cycles. When the PENG was bent and beat by bicycle spokes, a peak voltage of 16 V was generated, which can light up 12 white LEDs directly and charge the commercial capacitors. Our research provides a new strategy to fabricate flexible and efficient PENGs from a nanoscale viewpoint; it can be hopefully applied in energy-harvesting systems and wearable electric sensors.

The local ferroelectric domain structure of interconnected PVDF nano-dots with applied DC voltages of ± 10 V to ± 100 V is evaluated using various Piezo force microscopy (PFM) methods such as conventional PFM and Dynamic contact electrostatic force microscopy (DC-EFM). The self-assembled PVDF nano-dots are fabricated by using a spin coater method with 2 wt% of PVDF-DMSO solution. The polar gamma phase is found to be induced by the microstructural confinement of PVDF monomers and also reveals a strong ferroelectric nature after poling at different DC bias voltages. Poling with altered directions of the voltages renders a 180° phase reversal of PVDF domains. The local domain study depicts that each nano-dot is functioning as a single domain and switches as a whole. The single nano-dot switching signifies the potential of using the nano-dots for organic ferroelectric memory devices.

Multiferroic materials exhibit both ferroelectricity and ferromagnetism, and their magnetoelectric effects can be modulated by both magnetic and electric fields. Thus, they exhibit great potential in next-generation data memory devices. In this study, we implemented an eight-state memory prototype based on room-temperature single-phase multiferroic Sr 3 Co 2 Fe 24 O 41 . Data were imported by a poling procedure with electric and magnetic fields and derived visa electric polarization, P m , or the magnetoelectric coefficient, α m . This memory prototype possesses the advantages of a single structure, being easy to integrate, having a high storage capacity and a high stability. In this research, we enriched the magnetoelectric coupling performance of multiferroic materials, which demonstrates their possibilities for applications in the memory field.

Above-bandgap photovoltages in lead-free perovskite BiFeO 3 have been substantially studied for energy harvesting and photocatalytic applications. However, most reported photocurrents and conversion efficiencies are still too small due to wide bandgaps. Remarkably large and durable field-modulated external quantum efficiency (EQE) ∼11% and power conversion efficiency (PCE) ∼1% have been achieved under 405 nm irradiation in polycrystalline Nd-doped BiFeO 3 (BNFO) ceramic with a bandgap E g ∼2.12-2.24 eV. The photovoltaic voltage and current density can reach ∼0.9 V and ∼8.0 A/m 2 after poling ( E =1 kV/cm) at irradiation intensity 10 3 W/m 2 . The p-n-junction layer between indium tin oxide (ITO) thin film and BNFO ceramic is the primary mechanism for the field-modulated photovoltaic responses in conjunction with the polarization-induced Schottky-barrier modulation. The field-induced domain nucleation within the grains and nanodomains play important roles for the enhanced photocurrent and conversion efficiencies.