Ceramic-Based Dielectric Materials for Energy Storage Capacitor Applications

Materials offering high energy density are currently desired to meet the increasing demand for energy storage applications, such as pulsed power devices, electric vehicles, high-frequency inverters, and so on. Particularly, ceramic-based dielectric materials have received significant attention for energy storage capacitor applications due to their outstanding properties of high power density, fast charge-discharge capabilities, and excellent temperature stability relative to batteries, electrochemical capacitors, and dielectric polymers. In this paper, we present fundamental concepts for energy storage in dielectrics, key parameters, and influence factors to enhance the energy storage performance, and we also summarize the recent progress of dielectrics, such as bulk ceramics (linear dielectrics, ferroelectrics, relaxor ferroelectrics, and anti-ferroelectrics), ceramic films, and multilayer ceramic capacitors. In addition, various strategies, such as chemical modification, grain refinement/microstructure, defect engineering, phase, local structure, domain evolution, layer thickness, stability, and electrical homogeneity, are focused on the structure-property relationship on the multiscale, which has been thoroughly addressed. Moreover, this review addresses the challenges and opportunities for future dielectric materials in energy storage capacitor applications. Overall, this review provides readers with a deeper understanding of the chemical composition, physical properties, and energy storage performance in this field of energy storage ceramic materials.

Single-Crystal Ferroelectric-Based (K,Na)NbO3 Microcuboid/CuO Nanodot Heterostructures with Enhanced Photo-Piezocatalytic Activity

Developing single-crystal-based heterostructured ferroelectrics with high-performance photo-piezocatalytic activity is highly desirable to utilize large piezopotentials and more reactive charges that can trigger the desired redox reactions. To that end, a single-crystal-based (K,Na)NbO3 (KNN) microcuboid/CuO nanodot heterostructure with enhanced photo-piezocataytic activity, prepared using a facile strategy that leveraged the synergy between heterojunction formation and an intense single-crystal-based piezoelectric effect, is reported herein. The catalytic rhodamine B degrading activity of KNN/CuO is investigated under light irradiation, ultrasonication, or co-excitation with both stimulations. Compared to polycrystalline KNN powders and bare KNN single-crystals, single-crystal-based KNN/CuO exhibits a higher piezocurrent density and an optimal energy band structure, resulting in 5.23 and 2.37 times higher piezocatalytic degradation activities, respectively. Furthermore, the maximum photo-piezocatalytic rate constant (≈0.093 min-1 ) of KNN/CuO under 25 min ultrasonication and light irradiation is superior to that of other KNN-based catalysts, and 1.6 and 48.6 times higher than individual piezocatalytic and photocatalytic reaction rate constants, respectively. The excellent photo-piezocatalytic activity is attributed to the enhanced charge-carrier separation and proper alignment of band structure to the required redox levels by the appropriate p-n heterojunction and high piezoelectric potential. This report provides useful insight into the relationships between heterojunctions, piezoelectric responses, and catalytic mechanisms for single-crystal-based heterostructured catalysts.

Giant Energy Density via Mechanically Tailored Relaxor Ferroelectric Behavior of PZT Thick Film

Relaxor ferroelectrics (RFEs) are being actively investigated for energy-storage applications due to their large electric-field-induced polarization with slim hysteresis and fast energy charging-discharging capability. Here, a novel nanograin engineering approach based upon high kinetic energy deposition is reported, for mechanically inducing the RFE behavior in a normal ferroelectric Pb(Zr0.52 Ti0.48 )O3 (PZT), which results in simultaneous enhancement in the dielectric breakdown strength (EDBS ) and polarization. Mechanically transformed relaxor thick films with 4 µm thickness exhibit an exceptional EDBS of 540 MV m-1 and reduced hysteresis with large unsaturated polarization (103.6 µC cm-2 ), resulting in a record high energy-storage density of 124.1 J cm-3 and a power density of 64.5 MW cm-3 . This fundamental advancement is correlated with the generalized nanostructure design that comprises nanocrystalline phases embedded within the amorphous matrix. Microstructure-tailored ferroelectric behavior overcomes the limitations imposed by traditional compositional design methods and provides a feasible pathway for realization of high-performance energy-storage materials.

Improved Energy Storage Density and Efficiency of Nd and Mn Co-Doped Ba0.7Sr0.3TiO3 Ceramic Capacitors Via Defect Dipole Engineering

In this paper, we investigate the structural, microstructural, dielectric, and energy storage properties of Nd and Mn co-doped Ba0.7Sr0.3TiO3 [(Ba0.7Sr0.3)1-xNdxTi1-yMnyO3 (BSNTM) ceramics (x = 0, 0.005, and y = 0, 0.0025, 0.005, and 0.01)] via a defect dipole engineering method. The complex defect dipoles (MnTi"-VO∙∙)∙ and (MnTi"-VO∙∙) between acceptor ions and oxygen vacancies capture electrons, enhancing the breakdown electric field and energy storage performances. XRD, Raman, spectroscopy, XPS, and microscopic investigations of BSNTM ceramics revealed the formation of a tetragonal phase, oxygen vacancies, and a reduction in grain size with Mn dopant. The BSNTM ceramics with x = 0.005 and y = 0 exhibit a relative dielectric constant of 2058 and a loss tangent of 0.026 at 1 kHz. These values gradually decreased to 1876 and 0.019 for x = 0.005 and y = 0.01 due to the Mn2+ ions at the Ti4+- site, which facilitates the formation of oxygen vacancies, and prevents a decrease in Ti4+. In addition, the defect dipoles act as a driving force for depolarization to tailor the domain formation energy and domain wall energy, which provides a high difference between the maximum polarization of Pmax and remnant polarization of Pr (ΔP = 10.39 µC/cm2). Moreover, the complex defect dipoles with optimum oxygen vacancies in BSNTM ceramics can provide not only a high ΔP but also reduce grain size, which together improve the breakdown strength from 60.4 to 110.6 kV/cm, giving rise to a high energy storage density of 0.41 J/cm3 and high efficiency of 84.6% for x = 0.005 and y = 0.01. These findings demonstrate that defect dipole engineering is an effective method to enhance the energy storage performance of dielectrics for capacitor applications.

Intense Pulsed Light Thermal Treatment of Pb(Zr,Ti)O3 /Metglas Heterostructured Films Resulting in Extreme Magnetoelectric Coupling of over 20 V cm-1 Oe-1

Magnetoelectric (ME) film composites consisting of piezoelectric and magnetostrictive materials are promising candidates for application in magnetic field sensors, energy harvesters, and ME antennas. Conventionally, high-temperature annealing is required to crystallize piezoelectric films, restricting the use of heat-sensitive magnetostrictive substrates that enhance ME coupling. Herein, a synergetic approach is demonstrated for fabricating ME film composites that combines aerosol deposition and instantaneous thermal treatment based on intense pulsed light (IPL) radiation to form piezoelectric Pb(Zr,Ti)O3 (PZT) thick films on an amorphous Metglas substrate. IPL rapidly anneals PZT films within a few milliseconds without damaging the underlying Metglas. To optimize the IPL irradiation conditions, the temperature distribution inside the PZT/Metglas film is determined using transient photothermal computational simulation. The PZT/Metglas films are annealed using different IPL pulse durations to determine the structure-property relationship. IPL treatment results in an enhanced crystallinity of the PZT, thus improving the dielectric, piezoelectric, and ME properties of the composite films. An ultrahigh off-resonance ME coupling (≈20 V cm-1  Oe-1 ) is obtained for the PZT/Metglas film that is IPL annealed at a pulse width of 0.75 ms (an order of magnitude higher than that reported for other ME films), confirming the potential for next-generation, miniaturized, and high-performance ME devices.

Enhanced Energy Storage Performance and Efficiency in Bi0.5(Na0.8K0.2)0.5TiO3-Bi0.2Sr0.7TiO3 Relaxor Ferroelectric Ceramics via Domain Engineering

Dielectric materials are highly desired for pulsed power capacitors due to their ultra-fast charge-discharge rate and excellent fatigue behavior. Nevertheless, the low energy storage density caused by the low breakdown strength has been the main challenge for practical applications. Herein, we report the electric energy storage properties of (1 - x) Bi_0.5(Na_0.8K_0.2)_0.5TiO₃-xBi_0.2Sr_0.7TiO₃ (BNKT-BST; x = 0.15-0.50) relaxor ferroelectric ceramics that are enhanced via a domain engineering method. A rhombohedral-tetragonal phase, the formation of highly dynamic PNRs, and a dense microstructure are confirmed from XRD, Raman vibrational spectra, and microscopic investigations. The relative dielectric permittivity (2664 at 1 kHz) and loss factor (0.058) were gradually improved with BST (x = 0.45). The incorporation of BST into BNKT can disturb the long-range ferroelectric order, lowering the dielectric maximum temperature T_m and inducing the formation of highly dynamic polar nano-regions. In addition, the T_m shifts toward a high temperature with frequency and a diffuse phase transition, indicating relaxor ferroelectric characteristics of BNKT-BST ceramics, which is confirmed by the modified Curie-Weiss law. The rhombohedral-tetragonal phase, fine grain size, and lowered T_m with relaxor properties synergistically contribute to a high P_max and low P_r, improving the breakdown strength with BST and resulting in a high recoverable energy density W_rec of 0.81 J/cm³ and a high energy efficiency η of 86.95% at 90 kV/cm for x = 0.45.

Magnetically Driven Powerless Lighting Device with Kirigami Structured Magneto-Mechanoluminescence Composite

The energy crisis and global shift toward sustainability drive the need for sustainable technologies that utilize often-wasted forms of energy. A multipurpose lighting device with a simplistic design that does not need electricity sources or conversions can be one such futuristic device. This study investigates the novel concept of a powerless lighting device driven by stray magnetic fields induced by power infrastructure for obstruction warning light systems. The device consists of mechanoluminescence (ML) composites of a Kirigami-shaped polydimethylsiloxane (PDMS) elastomer, ZnS:Cu particles, and a magneto-mechano-vibration (MMV) cantilever beam. Finite element analysis and luminescence characterization of the Kirigami structured ML composites are discussed, including the stress-strain distribution map and comparisons between different Kirigami structures based on stretchability and ML characteristic trade-offs. By coupling a Kirigami-structured ML material and an MMV cantilever structure, a device that can generate visible light as luminescence from a magnetic field can be created. Significant factors that contribute to luminescence generation and intensity are identified and optimized. Furthermore, the feasibility of the device is demonstrated by placing it in a practical environment. This further proves the functionality of the device in harvesting weak magnetic fields into luminescence or light, without complicated electrical energy conversion steps.

Perovskite Piezoelectric-Based Flexible Energy Harvesters for Self-Powered Implantable and Wearable IoT Devices

In the ongoing fourth industrial revolution, the internet of things (IoT) will play a crucial role in collecting and analyzing information related to human healthcare, public safety, environmental monitoring and home/industrial automation. Even though conventional batteries are widely used to operate IoT devices as a power source, these batteries have a drawback of limited capacity, which impedes broad commercialization of the IoT. In this regard, piezoelectric energy harvesting technology has attracted a great deal of attention because piezoelectric materials can convert electricity from mechanical and vibrational movements in the ambient environment. In particular, piezoelectric-based flexible energy harvesters can precisely harvest tiny mechanical movements of muscles and internal organs from the human body to produce electricity. These inherent properties of flexible piezoelectric harvesters make it possible to eliminate conventional batteries for lifetime extension of implantable and wearable IoTs. This paper describes the progress of piezoelectric perovskite material-based flexible energy harvesters for self-powered IoT devices for biomedical/wearable electronics over the last decade.

Molten-Salt Processed Potassium Sodium Niobate Single-Crystal Microcuboids with Dislocation-Induced Nanodomain Structures and Relaxor Ferroelectric Behavior

We herein report a facile molten-salt synthetic strategy to prepare transparent and uniform Li, Ba-doped (K,Na)NbO₃ (KNN) single-crystal microcuboids (∼80 μm). By controlling the degree of supersaturation, different growth modes were found and the single-crystal microcuboids were synthesized via island-like oriented attachment of KNN particles onto the growing surface. The distinct relaxor ferroelectric (RFE) properties were achieved in the single-crystal microcuboids, which were different from the normal ferroelectric (FE) properties found in their KNN ceramic counterparts prepared through a solid-state reaction using the same initial precursors. The RFE properties were realized by dislocation-induced nanodomain formation during oriented attachment growth of single-crystal microcuboids, which is different from the current strategies to derive the nanodomains by the local compositional inhomogeneity or the application of an electric field. The dislocations served as nucleation sites for ferroelectric domain walls and block the growth of domains. The KNN single-crystal microcuboids exhibited a higher effective piezoelectric coefficient (∼459 pm/V) compared to that of the bulk KNN ceramic counterpart (∼90 pm/V) and showed the broad diffuse maxima in the temperature dependence dielectric permittivity. The high maximum polarization (69.6 μC/cm²) at a relatively low electric field (30 kV/cm) was beneficial for energy storage applications. Furthermore, the KNN-based transparent, flexible pressure sensor directly monitored the mechanical motion of human activity without any external electric power. This study provides insights and synthetic strategies of single-crystal RFE microcuboids for other different perovskites, in which nanodomain structures are primarily imposed by their chemical composition.

Magneto-Mechano-Electric (MME) Composite Devices for Energy Harvesting and Magnetic Field Sensing Applications

Magneto-mechano-electric (MME) composite devices have been used in energy harvesting and magnetic field sensing applications due to their advantages including their high-performance, simple structure, and stable properties. Recently developed MME devices can convert stray magnetic fields into electric signals, thus generating an output power of over 50 mW and detecting ultra-tiny magnetic fields below pT. These inherent outstanding properties of MME devices can enable the development of not only self-powered energy harvesters for internet of thing (IoT) systems but also ultra-sensitive magnetic field sensors for diagnosis of human bio-magnetism or others. This manuscript provides a brief overview of recently reported high-performance MME devices for energy harvesting and magnetic sensing applications.

Harvesting electrical energy using plasmon-enhanced light pressure in a platinum cut cone

We have designed a method of harvesting electrical energy using plasmon-enhanced light pressure. A device was fabricated as a cut cone structure that optimizes light collection so that the weak incident light pressure can be sufficiently enhanced inside the cut cone to generate electrical energy. An increase in the device's current output is a strong indication that the pressure of incident light has been enhanced by the surface plasmons on a platinum layer inside the cut cone. The electrical energy harvested in a few minutes by irradiating pulsed laser light on a single micro device was possible to illuminate a blue LED.

Multiscale surface modified magneto-mechano-triboelectric nanogenerator enabled by eco-friendly NaCl imprinting stamp for self-powered IoT applications

In this paper, we demonstrated a multiscale micro- and nano-structured magneto-mechano-triboelectric nanogenerator (MMTENG) enabled by a salt particle imprinting process to power an internet of thing (IoT) sensor. The fine salt particles were utilized to form a multiscale structure on a triboelectric polymer film by mechanical pressure via an eco-friendly, low-cost, and simple process, thereby reinforcing the contact triboelectrification and electrostatic induction. The surface modified MMTENG can generate an open-circuit peak-to-peak voltage of 851 V, a short-circuit current of 155 μA, and a maximum peak power of 10.3 mW under an AC magnetic field of 8 Oe. The energy device also presented output stability over 124 million operating cycles. Finally, the electricity of the surface enhanced MMTENG device was directly utilized to power an IoT temperature sensor with integration of an energy harvester, energy conversion circuit, and storage capacitor.

Enhancement of Energy-Harvesting Performance of Magneto-Mechano-Electric Generators through Optimization of the Interfacial Layer

Among various energy harvester paradigms, the simple cantilever-structured magneto-mechano-electric (MME) energy generator comprises a piezoelectric material laminated on a magnetostrictive metal plate and permanent magnets as proof mass, exhibiting excellent magnetic energy-harvesting performance. The current challenge in using MME energy harvesters is the mechano-electric coupling at the interface between the piezoelectric material and magnetostrictive metal layer, which depends significantly on the mechanical properties of the interfacial adhesive layer. In this study, the effects of four types of adhesive interfacial layers on the output power and environmental and fatigue resistances of MME harvesters are systematically investigated. An optimized MME energy generator with an adhesive interfacial layer of 18.8 μm thickness and elastic modulus of 3.1 GPa achieves colossal enhancement (∼300%) with a maximum output power density of 0.92 mW/cm², while a 10 Oe (=10 G = 1 mT in air; 60 Hz) magnetic field is applied. In addition, the generator exhibits a robust endurance of continuous 10⁸ fatigue cycles and excellent temperature stability in the range of -30 to 70 °C. The presented MME generator, which harvests stray magnetic energy reliably, is promising as a low-cost and efficient autonomous power source for Internet of Things devices, wireless sensor networks, and so on.

A Comparison Study of Fatigue Behavior of Hard and Soft Piezoelectric Single Crystal Macro-Fiber Composites for Vibration Energy Harvesting

Designing a piezoelectric energy harvester (PEH) with high power density and high fatigue resistance is essential for the successful replacement of the currently using batteries in structural health monitoring (SHM) systems. Among the various designs, the PEH comprising of a cantilever structure as a passive layer and piezoelectric single crystal-based fiber composites (SFC) as an active layer showed excellent performance due to its high electromechanical properties and dynamic flexibilities that are suitable for low frequency vibrations. In the present study, an effort was made to investigate the reliable performance of hard and soft SFC based PEHs. The base acceleration of both PEHs is held at 7 m/s² and the frequency of excitation is tuned to their resonant frequency (f_r) and then the output power (P_rms) is monitored for 10⁷ fatigue cycles. The effect of fatigue cycles on the output voltage, vibration displacement, dielectric, and ferroelectric properties of PEHs was analyzed. It was noticed that fatigue-induced performance degradation is more prominent in soft SFC-based PEH (SS-PEH) than in hard SFC-based PEH (HS-PEH). The HS-PEH showed a slight degradation in the output power due to a shift in f_r, however, no degradation in the maximum power was noticed, in fact, dielectric and ferroelectric properties were improved even after 10⁷ vibration cycles. In this context, the present study provides a pathway to consider the fatigue life of piezoelectric material for the designing of PEH to be used at resonant conditions for long-term operation.

Enhancement of Magnetoelectric Conversion Achieved by Optimization of Interfacial Adhesion Layer in Laminate Composites

We report the effect of epoxy adhesion layers with different mechanical or physical property on a magnetoelectric (ME) composite laminate composed of FeBSi alloy (Metglas)/single-crystal Pb(Mg_1/3Nb_2/3)O₃-Pb(Zr,Ti)O₃/Metglas to achieve an improved ME conversion performance. Through theoretical simulation, it was revealed that the Young's modulus and the thickness of interfacial adhesives were major parameters that influence the conversion efficiency in ME composites. In the experimental evaluation, we utilized three epoxy materials with a distinct Young's modulus and adjusted the average thickness of the adhesion layers to optimize the ME conversion. The experimental results show that a thin epoxy layer with a high Young's modulus provided the best performance in the inorganic-based ME conversion process. By tailoring the interfacial adhesion property, the ME laminate generated a high conversion coefficient of 328.8 V/(cm Oe), with a mechanical quality factor of 132.0 at the resonance mode. Moreover, we demonstrated a highly sensitive alternating current magnetic field sensor that had a detection resolution below 10 pT. The optimization of the epoxy layers in the ME laminate composite provided significant enhancement of the ME response in a simple manner.

Boosting the Recoverable Energy Density of Lead-Free Ferroelectric Ceramic Thick Films through Artificially Induced Quasi-Relaxor Behavior

Dielectric ceramic film capacitors, which store energy in the form of electric polarization, are promising for miniature pulsed power electronic device applications. For a superior energy storage performance of the capacitors, large recoverable energy density, along with high efficiency, high power density, fast charge/discharge rate, and good thermal/fatigue stability, is desired. Herein, we present highly dense lead-free 0.942[Na_0.535K_0.480NbO₃]-0.058LiNbO₃ (KNNLN) ferroelectric ceramic thick films (∼5 μm) demonstrating remarkable energy storage performance. The nanocrystalline KNNLN thick film fabricated by aerosol deposition (AD) process and annealed at 600 °C displayed a quasi-relaxor ferroelectric behavior, which is in contrast to the typical ferroelectric nature of the KNNLN ceramic in its bulk form. The AD film exhibited a large recoverable energy density of 23.4 J/cm³, with an efficiency of over 70% under the electric field of 1400 kV/cm. Besides, an ultrahigh power density of 38.8 MW/cm³ together with a fast discharge speed of 0.45 μs, good fatigue endurance (up to 10⁶ cycles), and thermal stability in a wide temperature range of 20-160 °C was also observed. Using the AD process, we could make a highly dense microstructure of the film containing nano-sized grains, which gave rise to the quasi-relaxor ferroelectric characteristics and the remarkable energy storage properties.

Enhanced Self-Biased Magnetoelectric Coupling in Laser-Annealed Pb(Zr,Ti)O3 Thick Film Deposited on Ni Foil

Enhanced and self-biased magnetoelectric (ME) coupling is demonstrated in a laminate heterostructure comprising 4 μm-thick Pb(Zr,Ti)O₃ (PZT) film deposited on 50 μm-thick flexible nickel (Ni) foil. A unique fabrication approach, combining room temperature deposition of PZT film by granule spray in vacuum (GSV) process and localized thermal treatment of the film by laser radiation, is utilized. This approach addresses the challenges in integrating ceramic films on metal substrates, which is often limited by the interfacial chemical reactions occurring at high processing temperatures. Laser-induced crystallinity improvement in the PZT thick film led to enhanced dielectric, ferroelectric, and magnetoelectric properties of the PZT/Ni composite. A high self-biased ME response on the order of 3.15 V/cm·Oe was obtained from the laser-annealed PZT/Ni film heterostructure. This value corresponds to a ∼2000% increment from the ME response (0.16 V/cm·Oe) measured from the as-deposited PZT/Ni sample. This result is also one of the highest reported values among similar ME composite systems. The tunability of self-biased ME coupling in PZT/Ni composite has been found to be related to the demagnetization field in Ni, strain mismatch between PZT and Ni, and flexural moment of the laminate structure. The phase-field model provides quantitative insight into these factors and illustrates their contributions toward the observed self-biased ME response. The results present a viable pathway toward designing and integrating ME components for a new generation of miniaturized tunable electronic devices.

Laser Irradiation of Metal Oxide Films and Nanostructures: Applications and Advances

Recent technological advances in developing a diverse range of lasers have opened new avenues in material processing. Laser processing of materials involves their exposure to rapid and localized energy, which creates conditions of electronic and thermodynamic nonequilibrium. The laser-induced heat can be localized in space and time, enabling excellent control over the manipulation of materials. Metal oxides are of significant interest for applications ranging from microelectronics to medicine. Numerous studies have investigated the synthesis, manipulation, and patterning of metal oxide films and nanostructures. Besides providing a brief overview on the principles governing the laser-material interactions, here, the ongoing efforts in laser irradiation of metal oxide films and nanostructures for a variety of applications are reviewed. Latest advances in laser-assisted processing of metal oxides are summarized.

Flash-Induced Self-Limited Plasmonic Welding of Silver Nanowire Network for Transparent Flexible Energy Harvester

The outstanding performance (sheet resistance of 5 Ω sq^-1 at transmittance of 90%) and strongly adhesive (30.7 J m^-2 ) silver nanowires (AgNWs) are fabricated using flash-induced plasmonic welding (FPW) based on theoretical research of photothermal interactions. The FPW-processed AgNWs are utilized as electrodes of a transparent flexible energy harvester, and this device exhibits excellent transmittance and high electric output performance. The FPW methodology provides a high-tech solution for transparent flexible electronics.

Flexible piezoelectric thin-film energy harvesters and nanosensors for biomedical applications

The use of inorganic-based flexible piezoelectric thin films for biomedical applications has been actively reported due to their advantages of highly piezoelectric, pliable, slim, lightweight, and biocompatible properties. The piezoelectric thin films on plastic substrates can convert ambient mechanical energy into electric signals, even responding to tiny movements on corrugated surfaces of internal organs and nanoscale biomechanical vibrations caused by acoustic waves. These inherent properties of flexible piezoelectric thin films enable to develop not only self-powered energy harvesters for eliminating batteries of bio-implantable medical devices but also sensitive nanosensors for in vivo diagnosis/therapy systems. This paper provides recent progresses of flexible piezoelectric thin-film harvesters and nanosensors for use in biomedical fields. First, developments of flexible piezoelectric energy-harvesting devices by using high-quality perovskite thin film and innovative flexible fabrication processes are addressed. Second, their biomedical applications are investigated, including self-powered cardiac pacemaker, acoustic nanosensor for biomimetic artificial hair cells, in vivo energy harvester driven by organ movements, and mechanical sensor for detecting nanoscale cellular deflections. At the end, future perspective of a self-powered flexible biomedical system is also briefly discussed with relation to the latest advancements of flexible electronics.

Topographically-designed triboelectric nanogenerator via block copolymer self-assembly

Herein, we report a facile and robust route to nanoscale tunable triboelectric energy harvesters realized by the formation of highly functional and controllable nanostructures via block copolymer (BCP) self-assembly. Our strategy is based on the incorporation of various silica nanostructures derived from the self-assembly of BCPs to enhance the characteristics of triboelectric nanogenerators (TENGs) by modulating the contact-surface area and the frictional force. Our simulation data also confirm that the nanoarchitectured morphologies are effective for triboelectric generation.

Self-powered cardiac pacemaker enabled by flexible single crystalline PMN-PT piezoelectric energy harvester

A flexible single-crystalline PMN-PT piezoelectric energy harvester is demonstrated to achieve a self-powered artificial cardiac pacemaker. The energy-harvesting device generates a short-circuit current of 0.223 mA and an open-circuit voltage of 8.2 V, which are enough not only to meet the standard for charging commercial batteries but also for stimulating the heart without an external power source.

Highly-efficient, flexible piezoelectric PZT thin film nanogenerator on plastic substrates

A highly-efficient, flexible piezoelectric PZT thin film nanogenerator is demonstrated using a laser lift-off (LLO) process. The PZT thin film nanogenerator harvests the highest output performance of ∼200 V and ∼150 μA·cm(-2) from regular bending motions. Furthermore, power sources generated from a PZT thin film nanogenerator, driven by slight human finger bending motions, successfully operate over 100 LEDs.

Virus-directed design of a flexible BaTiO3 nanogenerator

Biotemplated synthesis of functional nanomaterials has received increasing attention for applications in energy, catalysis, bioimaging, and other technologies. This approach is justified by the unique abilities of biological systems to guide sophisticated assembly and organization of molecules and materials into distinctive nanoscale morphologies that exhibit physicochemical properties highly desirable for specific purposes. Here, we present a high-performance, flexible nanogenerator using anisotropic BaTiO3 (BTO) nanocrystals synthesized on an M13 viral template through the genetically programmed self-assembly of metal ion precursors. The filamentous viral template realizes the formation of a highly entangled, well-dispersed network of anisotropic BTO nanostructures with high crystallinity and piezoelectricity. Even without the use of additional structural stabilizers, our virus-enabled flexible nanogenerator exhibits a high electrical output up to ∼300 nA and ∼6 V, indicating the importance of nanoscale structures for device performances. This study shows the biotemplating approach as a facile method to design and fabricate nanoscale materials particularly suitable for flexible energy harvesting applications.

Multicomponent nanopatterns by directed block copolymer self-assembly

Complex nanopatterns integrating diverse nanocomponents are crucial requirements for advanced photonics and electronics. Currently, such multicomponent nanopatterns are principally created by colloidal nanoparticle assembly, where large-area processing of highly ordered nanostructures raises significant challenge. We present multicomponent nanopatterns enabled by block copolymer (BCP) self-assembly, which offers device oriented sub-10-nm scale nanopatterns with arbitrary large-area scalability. In this approach, BCP nanopatterns direct the nanoscale lateral ordering of the overlaid second level BCP nanopatterns to create the superimposed multicomponent nanopatterns incorporating nanowires and nanodots. This approach introduces diverse chemical composition of metallic elements including Au, Pt, Fe, Pd, and Co into sub-10-nm scale nanopatterns. As immediate applications of multicomponent nanopatterns, we demonstrate multilevel charge-trap memory device with Pt-Au binary nanodot pattern and synergistic plasmonic properties of Au nanowire-Pt nanodot pattern.

In vivo silicon-based flexible radio frequency integrated circuits monolithically encapsulated with biocompatible liquid crystal polymers

Biointegrated electronics have been investigated for various healthcare applications which can introduce biomedical systems into the human body. Silicon-based semiconductors perform significant roles of nerve stimulation, signal analysis, and wireless communication in implantable electronics. However, the current large-scale integration (LSI) chips have limitations in in vivo devices due to their rigid and bulky properties. This paper describes in vivo ultrathin silicon-based liquid crystal polymer (LCP) monolithically encapsulated flexible radio frequency integrated circuits (RFICs) for medical wireless communication. The mechanical stability of the LCP encapsulation is supported by finite element analysis simulation. In vivo electrical reliability and bioaffinity of the LCP monoencapsulated RFIC devices are confirmed in rats. In vitro accelerated soak tests are performed with Arrhenius method to estimate the lifetime of LCP monoencapsulated RFICs in a live body. The work could provide an approach to flexible LSI in biointegrated electronics such as an artificial retina and wireless body sensor networks.

Piezoelectric BaTiO₃ thin film nanogenerator on plastic substrates

The piezoelectric generation of perovskite BaTiO3 thin films on a flexible substrate has been applied to convert mechanical energy to electrical energy for the first time. Ferroelectric BaTiO3 thin films were deposited by radio frequency magnetron sputtering on a Pt/Ti/SiO2/(100) Si substrate and poled under an electric field of 100 kV/cm. The metal-insulator (BaTiO3)-metal-structured ribbons were successfully transferred onto a flexible substrate and connected by interdigitated electrodes. When periodically deformed by a bending stage, a flexible BaTiO3 nanogenerator can generate an output voltage of up to 1.0 V. The fabricated nanogenerator produced an output current density of 0.19 μA/cm(2) and a power density of ∼7 mW/cm(3). The results show that a nanogenerator can be used to power flexible displays by means of mechanical agitations for future touchable display technologies.

Novel fluorophores: efficient synthesis and photophysical study

[structure: see text] We have synthesized novel fluorophores by using Sonogashira reactions of 1,4-bis(dibromovinyl)benzene and 2,5-bis(dibromovinyl)thiophene with various aromatic bromides. The emission maxima of these fluorophores vary from the indigo blue to the reddish-orange region, depending on the structures of aromatic nuclei and peripheral moieties.