Polyphenylene Oxide Film Sandwiched between SiO2 Layers for High-Temperature Dielectric Energy Storage

The commercial capacitor using dielectric biaxially oriented polypropylene (BOPP) can work effectively only at low temperatures (less than 105 °C). Polyphenylene oxide (PPO), with better heat resistance and a higher dielectric constant, is promising for capacitors operating at elevated temperatures, but its charge-discharge efficiency (η) degrades greatly under high fields at 125 °C. Here, SiO2 layers are magnetron sputtered on both sides of the PPO film, forming a composite material of SiO2/PPO/SiO2. Due to the wide bandgap and high Young's modulus of SiO2, the breakdown strength (Eb) of this composite material reaches 552 MV/m at 125 °C (PPO: 534 MV/m), and the discharged energy density (Ue) under Eb improves to 3.5 J/cm3 (PPO: 2.5 J/cm3), with a significantly enhanced η of 89% (PPO: 70%). Furthermore, SiO2/PPO/SiO2 can discharge a Ue of 0.45 J/cm3 with an η of 97% at 125 °C under 200 MV/m (working condition in hybrid electric vehicles) for 20,000 cycles, and this value is higher than the energy density (∼0.39 J/cm3 under 200 MV/m) of BOPP at room temperature. Interestingly, the metalized SiO2/PPO/SiO2 film exhibits valuable self-healing behavior. These results make PPO-based dielectrics promising for high-temperature capacitor applications.

Capacitance of Flexible Polymer/Graphene Microstructures with High Mechanical Strength

Carbon-modified fibrous structures with high biocompatibility have attracted much attention due to their low cost, sustainability, abundance, and excellent electrical properties. However, some carbon-based materials possess low specific capacitance and electrochemical performance, which pose significant challenges in developing electronic microdevices. In this study, we report a microfluidic-based technique of manufacturing alginate hollow microfibers incorporated by water dispersed modified graphene (bovine serum albumin-graphene). These architectures successfully exhibited enhanced conductivity ∼20 times higher than alginate hollow microfibers without any significant change in the inner dimension of the hollow region (220.0 ± 10.0 μm) compared with pure alginate hollow microfibers. In the presence of graphene, higher specific surface permeability, active ion adsorption sites, and shorter pathways were created. These continuous ion transport networks resulted in improved electrochemical performance. The desired electrochemical properties of the microfibers make alginate/graphene hollow fibers an excellent choice for further use in the development of flexible capacitors with the potential to be used in smart health electronics.

Demonstration of 10 nm Ferroelectric Al0.7Sc0.3N-Based Capacitors for Enabling Selector-Free Memory Array

In this work, 10 nm scandium-doped aluminum nitride (AlScN) capacitors are demonstrated for the construction of the selector-free memory array application. The 10 nm Al0.7Sc0.3N film deposited on an 8-inch silicon wafer with sputtering technology exhibits a large remnant polarization exceeding 100 µC/cm2 and a tight distribution of the coercive field, which is characterized by the positive-up-negative-down (PUND) method. As a result, the devices with lateral dimension of only 1.5 μm show a large memory window of over 250% and a low power consumption of ~40 pJ while maintaining a low disturbance rate of <2%. Additionally, the devices demonstrate stable multistate memory characteristics with a dedicated operation scheme. The back-end-of-line (BEOL)-compatible fabrication process, along with all these device performances, shows the potential of AlScN-based capacitors for the implementation of the high-density selector-free memory array.

Ultrathin Ambipolar Polyelectrolyte Capacitors Prepared via Layer-by-Layer Assembling

Miniaturized solid state capacitors leveraging migration of unipolar ions in a single polyelectrolyte layer sandwiched between metal electrodes, namely, polyelectrolyte capacitors (PECs), have been recently reported with areal capacitance up to 100-200 nF mm-2 . Nonetheless, application of PECs in consumer and industrial electronics has been hindered so far by their small operational frequency range, up to a few kHz, due to the resistive behavior (phase angle >-45°) of PECs in the range kHz-to-MHz. Here, it is reported on multilayer polyelectrolyte capacitors (mPECs) that leverage as dielectric an ambipolar nanometer-thick (down to 10 nm) stack of anionic and cationic polyelectrolytes assembled layer-by-layer between metal electrodes to eliminate the resistive behavior at frequencies from kHz to MHz. This significantly extends the operational range of mPECs over PECs. mPECs with areal capacitance as high as 25 nF mm-2 at 20 Hz and full capacitive behavior from 100 mHz to 10 MHz are demonstrated using different assembling conditions and anionic/cationic polyelectrolyte pairs. The mPECs reliably operate over time for >300 million cycles, at different biasing voltages up to 3 V, and temperatures up to 80 °C, showing a reversible capacitive behavior without significant hysteresis. Application of mPECs in flexible electronics, also operating at high frequency, is envisaged.

Effect of Sodium Phosphate Coating on Cu and Mg-Substituted P2-Na0.67Ni0.33Mn0.67O2 for Improving the Cycling Performance of Sodium-Ion Capacitors

Sodium-ion capacitors (SICs) bridge the performance gaps between batteries and supercapacitors by providing a high energy and power density in a single configuration. As battery-type active materials, sodium preintercalated layered metal oxides are desirable owing to their unique crystal structure, simple synthesis process, and high working voltage. However, their poor cyclic stability and low kinetics limit their application. Herein, we report increased rate capability and cycle stability achieved by introducing transition metal substitution and surface coating strategies. By substituting a portion of Ni and Mn with Cu and Mg (the sample name was denoted as NMCM), the P2-O2 transition which occurs at high voltages was alleviated. Additionally, a thin and uniform sodium phosphate coating layer suppressed surface side reactions occurring during charge-discharge processes, as observed through ex-situ X-ray photoelectron spectroscopy and ex-situ transmission electron microscopy. Compared to the pristine sample, the capacity improved by 48% at a high current density of 4 A g-1. After 100 cycles, the sodium-phosphate-coated sample (NMCM@P) retained about 90% of its capacity, whereas NMCM had a capacity retention of 63%. When evaluating the longer stability of SIC full cells, NMCM@P exhibited an outstanding stability of 71% after 5000 cycles. This was higher than that of NMCM, which retained only 17% of its initial capacity.

Nanoparticle-Polymer Surface Functionalizations for Capacitive Energy Storage: Experimental Comparison to First Principles Simulations

Dielectric capacitors present many advantages for large-scale energy storage, but they presently require higher energy density. We demonstrate novel high energy density polymer-nanoparticle composite capacitors utilizing thiol-ene click chemistry surface groups to bond the nanoparticles covalently to the polymer matrix. Interfacial effects in composites cannot be observed directly, and in our previous work, we examined the nanoparticle-polymer interface in silico. In this work, we experimentally examine the five surface functionalizations modeled previously, fabricating high energy density thin film capacitors to test our predictions. Results from this study, in conjunction with properties previously determined in silico, further improve the understanding of the role of surface functionalizations in composites prepared using click chemistry. The coating density of the surface functionalizations is shown to be a key factor in relating our computational results to experimental results. We show how using both coating density and our previous modeling in combination allows for prescreening of surface functionalizations for future composites, reducing experimental cost. We also demonstrate high energy density capacitors with ~20 J/cm3.

Excellent Energy Storage Performance in Epoxy Resin Dielectric Polymer Films by a Facile Hot-Pressing Method

Epoxy resin (EP), as a kind of dielectric polymer, exhibits the advantages of low-curing shrinkage, high-insulating properties, and good thermal/chemical stability, which is widely used in electronic and electrical industry. However, the complicated preparation process of EP has limited their practical applications for energy storage. In this manuscript, bisphenol F epoxy resin (EPF) was successfully fabricated into polymer films with a thickness of 10~15 μm by a facile hot-pressing method. It was found that the curing degree of EPF was significantly affected by changing the ratio of EP monomer/curing agent, which led to the improvement in breakdown strength and energy storage performance. In particular, a high discharged energy density (U_d) of 6.5 J·cm^-3 and efficiency (η) of 86% under an electric field of 600 MV·m^-1 were obtained for the EPF film with an EP monomer/curing agent ratio of 1:1.5 by hot pressing at 130 °C, which indicates that the hot-pressing method could be facilely employed to produce high-quality EP films with excellent energy storage performance for pulse power capacitors.

Exploration of Breakdown Strength Decrease and Mitigation of Ultrathin Polypropylene

Polypropylene film is the most important organic dielectric in capacitor technology; however, applications such as power electronic devices require more miniaturized capacitors and thinner dielectric films. The commercial biaxially oriented polypropylene film is losing the advantage of its high breakdown strength as it becomes thinner. This work carefully studies the breakdown strength of the film between 1 and 5 microns. The breakdown strength drops rapidly and hardly ensures that the capacitor reaches a volumetric energy density of 2 J/cm³. Differential scanning calorimetry, X-ray, and SEM analyses showed that this phenomenon has nothing to do with the crystallographic orientation and crystallinity of the film but is closely related to the non-uniform fibers and many voids produced by overstretching the film. Measures must be taken to avoid their premature breakdown due to high local electric fields. An improvement below 5 microns will maintain a high energy density and the important application of polypropylene films in capacitors. Without destroying the physical properties of commercial films, this work employs the ALD oxide coating scheme to augment the dielectric strength of a BOPP in the thickness range below 5 μm, especially its high temperature performance. Therefore, the problem of the reduction in dielectric strength and energy density caused by BOPP thinning can be alleviated.

Mechanically Robust Poly(ionic liquid) Block Copolymers as Self-Assembling Gating Materials for Single-Walled Carbon-Nanotube-Based Thin-Film Transistors

The proliferation of high-performance thin-film electronics depends on the development of highly conductive solid-state polymeric materials. We report on the synthesis and properties investigation of well-defined cationic and anionic poly(ionic liquid) AB-C type block copolymers, where the AB block was formed by random copolymerization of highly conductive anionic or cationic monomers with poly(ethylene glycol) methyl ether methacrylate, while the C block was obtained by post-polymerization of 2-phenylethyl methacrylate. The resulting ionic block copolymers were found to self-assemble into a lamellar morphology, exhibiting high ionic conductivity (up to 3.6 × 10^-6 S cm^-1 at 25 °C) and sufficient electrochemical stability (up to 3.4 V vs Ag⁺/Ag at 25 °C) as well as enhanced viscoelastic (mechanical) performance (storage modulus up to 3.8 × 10⁵ Pa). The polymers were then tested as separators in two all-solid-state electrochemical devices: parallel plate metal-insulator-metal (MIM) capacitors and thin-film transistors (TFTs). The laboratory-scale truly solid-state MIM capacitors showed the start of electrical double-layer (EDL) formation at ∼10³ Hz and high areal capacitance (up to 17.2 μF cm^-2). For solid-state TFTs, low hysteresis was observed at 10 Hz due to the completion of EDL formation and the devices were found to have low threshold voltages of -0.3 and 1.1 V for p-type and n-type operations, respectively.

Experimental Formation and Mechanism Study for Super-High Dielectric Constant AlOx/TiOy Nanolaminates

Super-high dielectric constant (k) AlO_x/TiO_y nanolaminates (ATO NLs) are deposited by an atomic layer deposition technique for application in next-generation electronics. Individual multilayers with uniform thicknesses are formed for the ATO NLs. With an increase in AlO_x content in each ATO sublayer, the shape of the Raman spectrum has a tendency to approach that of a single AlO_x layer. The effects of ATO NL deposition conditions on the electrical properties of the metal/ATO NL/metal capacitors were investigated. A lower deposition temperature, thicker ATO NL, and lower TiO_y content in each ATO sublayer can lead to a lower leakage current and smaller loss tangent at 1 kHz for the capacitors. A higher deposition temperature, larger number of ATO interfaces, and higher TiO_y content in each ATO sublayer are important for obtaining higher k values for the ATO NLs. With an increase in resistance in the capacitors, the ATO NLs vary from semiconductors to insulators and their k values have a tendency to decrease. For most of the capacitors, the capacitances reduce with increments in absolute measurement voltage. There are semi-circular shapes for the impedance spectra of the capacitors. By fitting them with the equivalent circuit, it is observed that with the increase in absolute voltage, both parallel resistance and capacitance decrease. The variation in the capacitance is explained well by a novel double-Schottky electrode contact model. The formation of super-high k values for the semiconducting ATO NLs is possibly attributed to the accumulation of charges.

The Integration of Biopolymer-Based Materials for Energy Storage Applications: A Review

Biopolymers are an emerging class of novel materials with diverse applications and properties such as superior sustainability and tunability. Here, applications of biopolymers are described in the context of energy storage devices, namely lithium-based batteries, zinc-based batteries, and capacitors. Current demand for energy storage technologies calls for improved energy density, preserved performance overtime, and more sustainable end-of-life behavior. Lithium-based and zinc-based batteries often face anode corrosion from processes such as dendrite formation. Capacitors typically struggle with achieving functional energy density caused by an inability to efficiently charge and discharge. Both classes of energy storage need to be packaged with sustainable materials due to their potential leakages of toxic metals. In this review paper, recent progress in energy applications is described for biocompatible polymers such as silk, keratin, collagen, chitosan, cellulose, and agarose. Fabrication techniques are described for various components of the battery/capacitors including the electrode, electrolyte, and separators with biopolymers. Of these methods, incorporating the porosity found within various biopolymers is commonly used to maximize ion transport in the electrolyte and prevent dendrite formations in lithium-based, zinc-based batteries, and capacitors. Overall, integrating biopolymers in energy storage solutions poses a promising alternative that can theoretically match traditional energy sources while eliminating harmful consequences to the environment.

Preparation of Fluorescent Carbon Dots Composites and Their Potential Applications in Biomedicine and Drug Delivery-A Review

Carbon dots (CDs), a new member of carbon nanostructures, rely on surface modification and functionalization for their good fluorescence phosphorescence and excellent physical and chemical properties, including small size (<10 nm), high chemical stability, biocompatibility, non-toxicity, low cost, and easy synthesis. In the field of medical research on cancer (IARC), CDs, a new material with unique optical properties as a photosensitizer, are being applied to heating local apoptosis induction of cancer cells. In addition, imaging tools can also be combined with a drug to form the nanometer complex compound, the imaging guidance for multi-function dosage, so as to improve the efficiency of drug delivery, which also plays a big role in genetic diagnosis. This paper mainly includes three parts: The first part briefly introduces the synthesis and preparation of carbon dots, and summarizes the advantages and disadvantages of different preparation methods; The second part introduces the preparation methods of carbon dot composites. Finally, the application status of carbon dot composites in biomedicine, cancer theranostics, drug delivery, electrochemistry, and photocatalysis is summarized.

Interfacial Engineered Vanadium Oxide Nanoheterostructures Synchronizing High-Energy and Long-Term Potassium-Ion Storage

Potassium ion hybrid capacitors (KICs) have drawn tremendous attention for large-scale energy storage applications because of their high energy and power densities and the abundance of potassium sources. However, achieving KICs with high capacity and long lifespan remains challenging because the large size of potassium ions causes sluggish kinetics and fast structural pulverization of electrodes. Here, we report a composite anode of VO2-V2O5 nanoheterostructures captured by a 3D N-doped carbon network (VO2-V2O5/NC) that exhibits a reversible capacity of 252 mAh g-1 at 1 A g-1 over 1600 cycles and a rate performance with 108 mAh g-1 at 10 A g-1. Quantitative kinetics analyses demonstrate that such great rate capability and cyclability are enabled by the capacitive-dominated potassium storage mechanism in the interfacial engineered VO2-V2O5 nanoheterostructures. The further fabricated full KIC cell consisting of a VO2-V2O5/NC anode and an active carbon cathode delivers a high operating voltage window of 4.0 V and energy and power densities up to 154 Wh kg-1 and 10 000 W kg-1, respectively, surpassing most state-of-the-art KICs.

Design and Micro-Nano Fabrication of a GaAs-Based On-Chip Miniaturized Bandpass Filter with Intertwined Inductors and Circinate Capacitor Using Integrated Passive Device Technology

In this study, we propose a miniaturized bandpass filter (BPF) developed by combining an approximate circular (36-gon) winding inductor, a circinate capacitor, and five air-bridge structures fabricated on a gallium arsenide (GaAs) substrate using an integrated passive device (IPD) technology. We introduced air-bridge structures into the outer metal wire to improve the capacitance per unit volume while utilizing a miniaturized chip with dimensions 1538 μm × 800 μm (0.029 λ₀ × 0.015 λ₀) for the BPF. The pattern was designed and optimized by simulating different dimensional parameters, and the group delay and current density are presented. The equivalent circuit was modeled to analysis various parasitic effect. Additionally, we described the GaAs-based micro-nano scale fabrication process to elucidate the proposed IPD technology and the physical structure of the BPF. Measurements were conducted with a center frequency of 1.53 GHz (insertion loss of 0.53 dB) and a 3-dB fractional bandwidth (FBW) of 70.59%. The transmission zero was located at 4.16 GHz with restraint of 35.86 dB. Owing to the benefits from its miniaturized chip size and high performance, the proposed GaAs-based IPD BPF was verified as an excellent device for various S-band applications, such as satellite communication, keyless vehicle locks, wireless headphones, and radar.

Ionic Liquid-Based Gels for Applications in Electrochemical Energy Storage and Conversion Devices: A Review of Recent Progress and Future Prospects

Ionic liquids (ILs) are molten salts that are entirely composed of ions and have melting temperatures below 100 °C. When immobilized in polymeric matrices by sol-gel or chemical polymerization, they generate gels known as ion gels, ionogels, ionic gels, and so on, which may be used for a variety of electrochemical applications. One of the most significant research domains for IL-based gels is the energy industry, notably for energy storage and conversion devices, due to rising demand for clean, sustainable, and greener energy. Due to characteristics such as nonvolatility, high thermal stability, and strong ionic conductivity, IL-based gels appear to meet the stringent demands/criteria of these diverse application domains. This article focuses on the synthesis pathways of IL-based gel polymer electrolytes/organic gel electrolytes and their applications in batteries (Li-ion and beyond), fuel cells, and supercapacitors. Furthermore, the limitations and future possibilities of IL-based gels in the aforementioned application domains are discussed to support the speedy evolution of these materials in the appropriate applicable sectors.

Soft Elastomeric Capacitor for Angular Rotation Sensing in Steel Components

The authors have previously proposed corrugated soft elastomeric capacitors (cSEC) to create ultra compliant scalable strain gauges. The cSEC technology has been successfully demonstrated in engineering and biomechanical applications for in-plane strain measurements. This study extends work on the cSEC to evaluate its performance at measuring angular rotation when installed folded at the junction of two plates. The objective is to characterize the sensor’s electromechanical behavior anticipating applications to the monitoring of welded connections in steel components. To do so, an electromechanical model that maps the cSEC signal to bending strain induced by angular rotation is derived and adjusted using a validated finite element model. Given the difficulty in mapping strain measurements to rotation, an algorithm termed angular rotation index (ARI) is formulated to link measurements to angular rotation directly. Experimental work is conducted on a hollow structural section (HSS) steel specimen equipped with cSECs subjected to compression to generate angular rotations at the corners within the cross-section. Results confirm that the cSEC is capable of tracking angular rotation-induced bending strain linearly, however with accuracy levels significantly lower than found over flat configurations. Nevertheless, measurements were mapped to angular rotations using the ARI, and it was found that the ARI mapped linearly to the angle of rotation, with an accuracy of 0.416∘.

Self-Powered Potentiometric Sensors with Memory

Potentiometric sensors induce a spontaneous voltage that indicates ion activity in real time. We present here an advanced self-powered potentiometric sensor with memory. Specifically, the approach allows for one to record a deviation from the analyte's original concentration or determine whether the analyte concentration has surpassed a threshold in a predefined time interval. The sensor achieves this by harvesting energy in a capacitor and preserving it with the help of a diode. While the analyte concentration is allowed to return to an original value following a perturbation over time, this may not influence the sensor readout. To achieve the diode function, the sensor utilizes an additional pair of driving electrodes to move the potentiometric signal to a sufficiently high base voltage that is required for operating the diode placed in series with the capacitor and between the sensing probes. A single voltage measurement across the capacitor at the end of a chosen time interval is sufficient to reveal any altered ion activity occurring during that period. We demonstrate the applicability of the sensor to identify incurred pH changes in a river water sample during an interval of 2 h. This approach is promising for achieving deployable sensors to monitor ion activity relative to a defined threshold during a time interval with minimal electronic components in a self-powered design.

A Resonantly Driven, Electroluminescent Metal Oxide Semiconductor Capacitor with High Power Efficiency

Electroluminescence can be generated from a wide variety of emissive materials using a simple, generic device structure. In such a device, emissive materials are deposited by various means on a metal oxide semiconductor capacitor structure across which alternating current voltage is applied. However, these devices suffer from low external efficiencies and require the application of high voltages, thus hindering their practical usage and raising questions about the possible efficiencies that can be achieved using alternating current driving schemes in which injection of bipolar charges does not occur simultaneously. We show that appropriately chosen reactive electrical components can be leveraged to generate passive voltage gain across the device, allowing operation at input voltages below 1 V for devices across a range of gate oxide thicknesses. Furthermore, high power efficiencies are observed when using thermally activated delayed fluorescence emitters deposited by a single thermal evaporation step, suggesting that the efficiency of a light-emitting device with simplified structure can be high.

Iron Cycle Tuned by Outer-Membrane Cytochromes of Dissimilatory Metal-Reducing Bacteria: Interfacial Dynamics and Mechanisms In Vitro

The biogeochemical cycle of iron is of great importance to living organisms on Earth, and dissimilatory metal-reducing bacteria (DMRB) with the capability of reducing hematite (α-Fe2O3) by outer-membrane (OM) cytochromes play a great role in the iron cycle. However, the dynamic binding of cytochromes to α-Fe2O3 at the molecular level and the resulting impact on the photon-to-electron conversion of α-Fe2O3 for the iron cycle are not fully understood. To address these issues, two-dimensional IR correlation analysis coupled with molecular dynamics (MD) simulations was conducted for an OmcA-Fe2O3 system as OmcA bonds stronger with hematite in a typical DMRB,Shewanella. The photoelectric response of α-Fe2O3 with the OmcA coating was evaluated at three different potentials. Specifically, the binding groups from OmcA to α-Fe2O3 were in the sequence of carboxyl groups, amide II, and amide I. Further MD analysis reveals that both electrostatic interactions and hydrogen bonds played essential roles in the binding process, leading to the structural changes of OmcA to facilitate iron reduction. Moreover, the OmcA coating could store the photogenerated electrons from α-Fe2O3 like a capacitor and utilize the stored electrons for α-Fe2O3 reduction in dark and anoxic environments, further driving the biogeochemical cycle of iron. These investigations give the dynamic information on the OM protein/hematite interaction and provide fundamental insights into the biogeochemical cycle of iron by taking the photon-induced redox chemistry of iron oxide into consideration.

Mesoporous Carbon: A Versatile Material for Scientific Applications

Mesoporous carbon is a promising material having multiple applications. It can act as a catalytic support and can be used in energy storage devices. Moreover, mesoporous carbon controls body’s oral drug delivery system and adsorb poisonous metal from water and various other molecules from an aqueous solution. The accuracy and improved activity of the carbon materials depend on some parameters. The recent breakthrough in the synthesis of mesoporous carbon, with high surface area, large pore-volume, and good thermostability, improves its activity manifold in performing functions. Considering the promising application of mesoporous carbon, it should be broadly illustrated in the literature. This review summarizes the potential application of mesoporous carbon in many scientific disciplines. Moreover, the outlook for further improvement of mesoporous carbon has been demonstrated in detail. Hopefully, it would act as a reference guidebook for researchers about the putative application of mesoporous carbon in multidimensional fields.

Low-Temperature Synthesis of Titanium Oxynitride Nanoparticles

The synthesis of transition metal oxynitrides is complicated by extreme reaction conditions such as high temperatures and/or high pressures. Here, we show an unprecedented solution-based synthesis of narrowly dispersed titanium oxynitride nanoparticles of cubic shape and average size of 65 nm. Their synthesis is performed by using titanium tetrafluoride and lithium nitride as precursors alongside trioctylphosphine oxide (TOPO) and cetrimonium bromide (CTAB) as stabilizers at temperatures as low as 250 °C. The obtained nanoparticles are characterized in terms of their shape and optical properties, as well as their crystalline rock-salt structure, as confirmed by XRD and HRTEM analysis. We also determine the composition and nitrogen content of the synthesized particles using XPS and EELS. Finally, we investigate the applicability of our titanium oxynitride nanoparticles by compounding them into carbon fiber electrodes to showcase their applicability in energy storage devices. Electrodes with titanium oxynitride nanoparticles exhibit increased capacity compared to the pure carbon material.

Effect of Buffer Layer Capacitance on the Electrical Characteristics of Ferroelectric Polymer Capacitors and Field Effect Transistors

We demonstrated the effect of a buffer layer on the electrical characteristics of ferroelectric polymer capacitors and field-effect transistors. Various polymer materials with a dielectric constant between 2 and 42 were used to form buffer layers with a similar thicknesses, but with different capacitances. In order to evaluate the characteristics of the ferroelectrics with a buffer layer, the polarization–voltage characteristics of the capacitor, the transfer characteristics, and the retention characteristics of the transistors were investigated. As the capacitance of the buffer layer increased, high remnant polarization (P_r), high hysteresis, and long retention times were observed. Exceptionally, when poly(methylmethacrylate) and rigid poly(aryl ether) (poly(9,9-bis(4-hydroxyphenyl)fluorene-co-decafluorobiphenyl)) were used as the buffer layer, P_r had a value close to 0 in the dynamic measurement polarization–voltage (P–V) characteristic, but the quasi-static measurement transfer characteristic and the static measurement retention characteristic showed relatively high hysteresis and long retention times. Our study provides a scientific and technical basis for the design of ferroelectric memory and neuromorphic devices.

Modeling Capacitive Low-Power Voltage Transformer Behavior over Temperature and Frequency

The use of capacitive dividers (CDs) in medium-voltage (MV) networks started as simple voltage detectors and as rough voltage measurement instruments for protective purposes. Now, with the spread of intelligent electronic devices and renewable energy sources at the distribution level, capacitive dividers are designed and installed to perform accurate voltage measurements. Such a requirement is mandatory when the power quality has to be assessed. Therefore, CDs are currently being used either for power frequency or for high-frequency (supraharmonic- or partial-discharge-level) measurements. In this paper, typical off-the-shelf CDs are studied and modeled to understand how they behave in a wide range of frequencies and when the temperature varies. To this purpose, specific setups and tests have been developed and performed. From the results, it is clear that with proper modeling of CDs, it is possible to exploit them for measuring phenomena in a wide range of frequencies, including the effects due to temperature variations and self-resonances.

Raman Spectroscopy Imaging of Exceptional Electronic Properties in Epitaxial Graphene Grown on SiC

Graphene distinctive electronic and optical properties have sparked intense interest throughout the scientific community bringing innovation and progress to many sectors of academia and industry. Graphene manufacturing has rapidly evolved since its discovery in 2004. The diverse growth methods of graphene have many comparative advantages in terms of size, shape, quality and cost. Specifically, epitaxial graphene is thermally grown on a silicon carbide (SiC) substrate. This type of graphene is unique due to its coexistence with the SiC underneath which makes the process of transferring graphene layers for devices manufacturing simple and robust. Raman analysis is a sensitive technique extensively used to explore nanocarbon material properties. Indeed, this method has been widely used in graphene studies in fundamental research and application fields. We review the principal Raman scattering processes in SiC substrate and demonstrate epitaxial graphene growth. We have identified the Raman bands signature of graphene for different layers number. The method could be readily adopted to characterize structural and exceptional electrical properties for various epitaxial graphene systems. Particularly, the variation of the charge carrier concentration in epitaxial graphene of different shapes and layers number have been precisely imaged. By comparing the intensity ratio of 2D line and G line-"I2D/IG"-the density of charge across the graphene layers could be monitored. The obtained results were compared to previous electrical measurements. The substrate longitudinal optical phonon coupling "LOOPC" modes have also been examined for several epitaxial graphene layers. The LOOPC of the SiC substrate shows a precise map of the density of charge in epitaxial graphene systems for different graphene layers number. Correlations between the density of charge and particular graphene layer shape such as bubbles have been determined. All experimental probes show a high degree of consistency and efficiency. Our combined studies have revealed novel capacitor effect in diverse epitaxial graphene system. The SiC substrate self-compensates the graphene layer charge without any external doping. We have observed a new density of charge at the graphene-substrate interface. The located capacitor effects at epitaxial graphene-substrate interfaces give rise to an unexpected mini gap in graphene band structure.

Self-Powered Potentiometric Sensor Transduction to a Capacitive Electronic Component for Later Readout

Potentiometric sensors operate as galvanic cells where the voltage is spontaneously generated as a function of the sample composition. We show here that energy can be harvested, stored during the sensing process without external power, and physically isolated from the sensor circuit for later readout. This is accomplished by placing an electronic capacitor as a portable transduction component between the indicator and the reference electrode at the point where one would ordinarily connect the high-input-impedance voltmeter. The voltage across this isolated capacitor indicates the originally measured ion activity and can be read out conveniently, for example, using a simple handheld multimeter. The capacitor is shown to maintain the transferred charge for hours after its complete disconnection from the sensor. The concept is demonstrated to detect the physiological concentrations of K⁺ in artificial sweat samples. The methodology provides a readout principle that could become very useful in portable form factors and opens possibilities for potentiometric detection in point-of-care applications and inexpensive sensing devices where an external power source is not desired.

Monolayer Quantum-Dot Based Light-Sensor by a Photo-Electrochemical Mechanism

Monolayer nanocrystal-based light sensors with cadmium-selenium thin film electrodes have been investigated using electrochemical cyclic voltammetry tests. An indium tin oxide electrode system, with a monolayer of homogeneously deposited cadmium-selenium quantum dots was proven to work as a photo-sensor via an electrochemical cell mechanism; it was possible to tune current densities under light illumination. Electrochemical tests on a quantum dot capacitor, using different sized (red, yellow and green) cadmium-selenium quantum dots on indium tin oxide substrates, showed typical capacitive behavior of cyclic voltammetry curves in 2M H2SO4 aqueous solutions. This arrangement provides a beneficial effect in, both, charge separation and light sensory characteristics. Importantly, the photocurrent density depended on quantum yield rendering tunable photo-sensing properties.

Fabrication of QFN-Packaged Miniaturized GaAs-Based Bandpass Filter with Intertwined Inductors and Dendritic Capacitor

This article presents a compact quad flat no-lead (QFN)-packaged second-order bandpass filter (BPF) with intertwined inductors, a dendritic capacitor, and four air-bridge structures, which was fabricated on a gallium arsenide (GaAs) substrate by integrated passive device (IPD) technology. Air-bridge structures were introduced into an approximate octagonal outer metal track to provide a miniaturized chip size of 0.021 × 0.021 λ₀ (0.8 × 0.8 mm²) for the BPF. The QFN-packaged GaAs-based bandpass filter was used to protect the device from moisture and achieve good thermal and electrical performances. An equivalent circuit was modeled to analyze the BPF. A description of the manufacturing process is presented to elucidate the physical structure of the IPD-based BPF. Measurements were performed on the proposed single band BPF using a center frequency of 2.21 GHz (return loss of 26.45 dB) and a 3-dB fractional bandwidth (FBW) of 71.94% (insertion loss of 0.38 dB). The transmission zero is located at the 6.38 GHz with a restraint of 30.55 dB. The manufactured IPD-based BPF can play an excellent role in various S-band applications, such as a repeater, satellite communication, and radar, owing to its miniaturized chip size and high performance.

Enhanced Dielectric Permittivity of Optimized Surface Modified of Barium Titanate Nanocomposites

High permittivity polymer-ceramic nanocomposite dielectric films take advantage of the ease of flexibility in processing of polymers and the functionality of electroactive ceramic fillers. Hence, films like these may be applied to embedded energy storage devices for printed circuit electrical boards. However, the incompatibility of the hydrophilic ceramic filler and hydrophobic epoxy limit the filler concentration and therefore, dielectric permittivity of these materials. Traditionally, surfactants and core-shell processing of ceramic fillers are used to achieve electrostatic and steric stabilization for adequate ceramic particle distribution but, questions regarding these processes still remain. The purpose of this work is to understand the role of surfactant concentration ceramic particle surface morphology, and composite dielectric permittivity and conductivity. A comprehensive study of barium titanate-based epoxy nanocomposites was performed. Ethanol and 3-glycidyloxypropyltrimethoxysilan surface treatments were performed, where the best reduction in particle agglomeration, highest value of permittivity and the lowest value of loss were observed. The results demonstrate that optimization of coupling agent may lead to superior permittivity values and diminished losses that are ~2-3 times that of composites with non-optimized and traditional surfactant treatments.

Gram-Scale Synthesis of Bimetallic ZIFs and Their Thermal Conversion to Nanoporous Carbon Materials

The hybrid metal-organic frameworks (MOFs) with different Zn²⁺/Co²⁺ ratios are synthesized at room temperature with deionized water as the solvent. This use of deionized water can increase the yield of hybrid MOFs (up to 65–70%). After the pyrolysis, the obtained nanoporous carbons (NPCs) show a decrease in the surface area, in which the highest surface area is 655 m² g⁻¹. The as-prepared NPCs are subjected to activation with KOH in order to increase their surface area and convert cobalt nanoparticles (Co NPs) to Co oxides. These activated carbons are applied to electrical double-layer capacitors (EDLCs) and pseudocapacitors due to the presence of CoO and Co₃O₄ nanoparticles in the carbon framework, leading to significantly enhanced specific capacitance as compared to that of pristine NPCs. This synthetic method can be utilized in future research to enhance pseudocapacitance further while maintaining the maximum surface area of the carbon materials.

Fast Energy Storage in Two-Dimensional MoO2 Enabled by Uniform Oriented Tunnels

While pseudocapacitive electrodes have potential to store more energy than electrical double-layer capacitive electrodes, their rate capability is often limited by the sluggish kinetics of the Faradaic reactions or poor electronic and ionic conductivity. Unlike most transition-metal oxides, MoO₂ is a very promising material for fast energy storage, attributed to its unusually high electronic and ionic conductivity; the one-dimensional tunnel is ideally suited for fast ionic transport. Here we report our findings in preparation and characterization of ultrathin MoO₂ sheets with oriented tunnels as a pseudocapacitive electrode for fast charge storage/release. A composite electrode consisting of MoO₂ and 5 wt % GO demonstrates a capacity of 1097 C g^-1 at 2 mV s^-1 and 390 C g^-1 at 1000 mV s^-1 while maintaining ∼80% of the initial capacity after 10,000 cycles at 50 mV s^-1, due to minimal change in structural features of the MoO₂ during charge/discharge, except a small volume change (∼14%), as revealed from operando Raman spectroscopy, X-ray analyses, and density functional theory calculations. Further, the volume change during cycling is highly reversible, implying high structural stability and long cycling life.

Investigation of Acoustic Injection on the MPU6050 Accelerometer

Acoustic injection is one of the most dangerous ways of causing micro-electro–mechanical systems (MEMS) failures. In this paper, the failure mechanism of acoustic injection on the microprocessor unit 6050 (MPU6050) accelerometer is investigated by both experiment and simulation. A testing system was built to analyze the performance of the MPU6050 accelerometer under acoustic injection. A MEMS disassembly method was adopted and a MATLAB program was developed to establish the geometric model of MPU6050. Subsequently, a finite element model of MPU6050 was established. Then, the acoustic impacts on the sensor layer of MPU6050 were studied by acoustic–solid coupling simulations. The effects of sound frequencies, pressures and directions were analyzed. Simulation results are well agreed with the experiments which indicate that MPU6050 is most likely to fail under the sounds of 11,566 Hz. The failure mechanism of MPU6050 under acoustic injection is the relative shift of the capacitor flats caused by acoustic–solid resonance that make the sensor detect false signal and output error data. The stress is focused on the center linkage. MPU6050 can be reliable when the sound pressure is lower than 100 dB.

A Soft Polydimethylsiloxane Liquid Metal Interdigitated Capacitor Sensor and Its Integration in a Flexible Hybrid System for On-Body Respiratory Sensing

We report on the dual mechanical and proximity sensing effect of soft-matter interdigitated (IDE) capacitor sensors, together with its modelling using finite element (FE) simulation to elucidate the sensing mechanism. The IDE capacitor is based on liquid-phase GaInSn alloy (Galinstan) embedded in a polydimethylsiloxane (PDMS) microfludics channel. The use of liquid-metal as a material for soft sensors allows theoretically infinite deformation without breaking electrical connections. The capacitance sensing is a result of E-field line disturbances from electrode deformation (mechanical effect), as well as floating electrodes in the form of human skin (proximity effect). Using the proximity effect, we show that spatial detection as large as 28 cm can be achieved. As a demonstration of a hybrid electronic system, we show that by integrating the IDE capacitors with a capacitance sensing chip, respiration rate due to a human's chest motion can be captured, showing potential in its implementation for wearable health-monitoring.

Fully Bioabsorbable Capacitor as an Energy Storage Unit for Implantable Medical Electronics

Implantable medical electronic devices are usually powered by batteries or capacitors, which have to be removed from the body after completing their function due to their non-biodegradable property. Here, a fully bioabsorbable capacitor (BC) is developed for life-time implantation. The BC has a symmetrical layer-by-layer structure, including polylactic acid (PLA) supporting substrate, PLA nanopillar arrays, self-assembled zinc oxide nanoporous layer, and polyvinyl alcohol/phosphate buffer solution (PVA/PBS) hydrogel. The as-fabricated BC can not only work normally in air but also in a liquid environment, including PBS and the animal body. Long-term normal work time is achieved to 30 days in PBS and 50 days in Sprague-Dawley (SD) rats. The work time of BC in the liquid environment is tunable from days to weeks by adopting different encapsulations along BC edges. Capacitance retention of 70% is achieved after 3000 cycles. Three BCs in series can light up 15 green light-emitting diodes (LEDs) in vivo. Additionally, after completing its mission, the BC can be fully degraded in vivo and reabsorbed by a SD rat. Considering its performance, the developed BC has a great potential as a fully bioabsorbable power source for transient electronics and implantable medical devices.

6/2019)

Transient electronics provide an effective technology to develop bioabsorbable implantable medical devices (IMDs). In article number 1801625, Yubo Fan, Zhong Lin Wang, Zhou Li, and co‐workers design a new fully bioabsorbable capacitor as an energy storage unit for IMDs. This capacitor achieves good working performance and full biodegradability in animals.

Laterally Movable Triple Electrodes Actuator toward Low Voltage and Fast Response RF-MEMS Switches

A novel actuator toward a low voltage actuation and fast response in RF-MEMS (radio frequency micro-electro-mechanical systems) switches is reported in this paper. The switch is comprised of laterally movable triple electrodes, which are bistable by electrostatic forces applied for not only the on-state, but also the off-state. The bistable triple electrodes enable the implementation of capacitive series and shunt type switches on a single switch, which leads to high isolation in spite of the small gap between the electrodes on the series switch. These features of the actuator are effective for a low voltage and fast response actuation in both the on- and off-state. The structure was designed in RF from a mechanical point of view. The laterally movable electrodes were achieved using a simple, low-cost two-mask process with 2.0 µm thick sputtered aluminum. The characteristics of switching response time and actuation voltage were 5.0 µs and 9.0 V, respectively.

Morphotropic Phase Boundary of Hf1- xZr xO2 Thin Films for Dynamic Random Access Memories

The utilization of the morphotropic phase boundary (MPB) between the newly found ferroelectric orthorhombic phase and the tetragonal phase in an HfO₂-ZrO₂ solid solution is suggested for a high-capacitance dielectric capacitor. Being different from other high- k dielectrics, where the k value decreases with decreasing film thickness, these films (Hf/Zr ratio = 6:4, 5:5, 3:7) showed increasing k values with decreasing film thicknesses in the ∼5-20 nm range. Among them, Hf_0.5Zr_0.5O₂ and Hf_0.3Zr_0.7O₂ films showed 47 and 43 peak k values at 6.5 and 9.2 nm thicknesses, respectively, suggesting the involvement of the MPB phenomenon. For the systematic understanding of this peculiar phenomenon, the phase evolution of the HfO₂-ZrO₂ solid solution is presented based on experimental observations. The detailed electrical tests of the films with different compositions and thicknesses demonstrated that the characteristic feature of this material system is consistent with the involvement of the MPB depending on the composition and thickness. Through the optimization of the annealing process for crystallization, a 0.62 nm minimum equivalent oxide thickness was reported for the 6.5 nm thick Hf_0.5Zr_0.5O₂ film, which is highly promising for the future dynamic random access memories. This work provided a breakthrough method for overcoming the fundamental limitation of a decreasing k value with a decreasing film thickness of other high- k dielectrics.

Effect of Growth Temperature during the Atomic Layer Deposition of the SrTiO3 Seed Layer on the Properties of RuO2/SrTiO3/Ru Capacitors for Dynamic Random Access Memory Applications

The atomic layer deposition process of SrTiO₃ (STO) films at 230 °C was studied with Sr(ⁱPr₃Cp)₂ and Ti(CpMe₅)(OMe)₃ (Pr, Cp, and Me are propyl, cyclopentadienyl, and methyl groups, respectively) on Ru substrates. The growth behavior and properties of STO films grown at 230 °C were compared with those deposited at 370 °C. With the limited over-reaction of the Sr precursor during the initial growth stage at a lower temperature, the cation composition was more controllable, and the surface morphology after crystallization annealing at 650 °C had more uniform grains with fewer defects. Here, the excess reaction of the Sr precursor means the chemical-vapor-deposition-like growth of the SrO component mediated through the thermal decomposition of the adsorbed Sr precursor molecules. It was by the reaction of the Sr precursor with the oxygen supplied from the partly oxidized Ru substrate. The second STO was grown at 370 °C (main layer) on the annealed first STO layer (crystallized seed layer) to lead to the in situ crystallization of the main layer. Due to the improved microstructure of STO films induced by the seed layer deposited at 230 °C, the bulk dielectric constant of 167 was obtained for the main layer, which was higher than the value of 101 where the seed layer was deposited at 370 °C, even though the crystallization annealing condition of the seed layer and the deposition condition of the main layer were consistent. The seed layer grown at 230 °C, however, had a lower dielectric constant of only ∼49, whereas the high-temperature seed layer had a dielectric constant of ∼106. Therefore, the low-temperature seed layer posed a severe limitation in acquiring an advanced capacitor property with the involvement of a low-dielectric interfacial layer.

A Novel Method for the Micro-Clearance Measurement of a Precision Spherical Joint Based on a Spherical Differential Capacitive Sensor

A spherical joint is a commonly used mechanical hinge with the advantages of compact structure and good flexibility, and it becomes a key component in many types of equipment, such as parallel mechanisms, industrial robots, and automobiles. Real-time detection of a precision spherical joint clearance is of great significance in analyzing the motion errors of mechanical systems and improving the transmission accuracy. This paper presents a novel method for the micro-clearance measurement with a spherical differential capacitive sensor (SDCS). First, the structure and layout of the spherical capacitive plates were designed according to the measuring principle of capacitive sensors with spacing variation. Then, the mathematical model for the spatial eccentric displacements of the ball and the differential capacitance was established. In addition, equipotential guard rings were used to attenuate the fringe effect on the measurement accuracy. Finally, a simulation with Ansoft Maxwell software was carried out to calculate the capacitance values of the spherical capacitors at different eccentric displacements. Simulation results indicated that the proposed method based on SDCS was feasible and effective for the micro-clearance measurement of the precision spherical joints with small eccentricity.

A High-Frequency-Compatible Miniaturized Bandpass Filter with Air-Bridge Structures Using GaAs-Based Integrated Passive Device Technology

This paper reports on the use of gallium arsenide-based integrated passive device technology for the implementation of a miniaturized bandpass filter that incorporates an intertwined circle-shaped spiral inductor and an integrated center-located capacitor. Air-bridge structures were introduced to the outer inductor and inner capacitor for the purpose of space-saving, thereby yielding a filter with an overall chip area of 1178 μm × 970 μm. Thus, not only is the chip area minimized, but the magnitude of return loss is also improved as a result of selective variation of bridge capacitance. The proposed device possesses a single passband with a central frequency of 1.71 GHz (return loss: 32.1 dB), and a wide fractional bandwidth (FBW) of 66.63% (insertion loss: 0.50 dB). One transmission zero with an amplitude of 43.42 dB was obtained on the right side of the passband at 4.48 GHz. Owing to its miniaturized chip size, wide FBW, good out-band suppression, and ability to yield high-quality signals, the fabricated bandpass filter can be implemented in various L-band applications such as mobile services, satellite navigation, telecommunications, and aircraft surveillance.

A Highly Sensitive Capacitive-type Strain Sensor Using Wrinkled Ultrathin Gold Films

Soft strain sensors are needed for a variety of applications including human motion and health monitoring, soft robotics, and human/machine interactions. Capacitive-type strain sensors are excellent candidates for practical applications due to their great linearity and low hysteresis; however, a big limitation of this sensor is its inherent property of low sensitivity when it comes to detecting various levels of applied strain. This limitation is due to the structural properties of the parallel plate capacitor structure during applied stretching operations. According to this model, at best the maximum gauge factor (sensitivity) that can be achieved is 1. Here, we report the highest gauge factor ever achieved in capacitive-type strain sensors utilizing an ultrathin wrinkled gold film electrode. Our strain sensor achieved a gauge factor slightly above 3 and exhibited high linearity with negligible hysteresis over a maximum applied strain of 140%. We further demonstrated this highly sensitive strain sensor in a wearable application. This work opens up the possibility of engineering even higher sensitivity in capacitive-type strain sensors for practical and reliable wearable applications.

Toward an Improved Understanding of the Role of Dielectrics in Capacitors

A new fundamental principle of the theory of dielectrics in capacitors is demonstrated. That is, dielectric material in any geometry that reduces the field generated by charges on capacitor electrodes is effective in increasing capacitance. Specifically, it is shown that super dielectric material on the outer surfaces of the electrodes of a parallel plate capacitor increases dielectric constant, as well as energy and power densities, by orders of magnitude. The implicit assumption in all current capacitor theory, that the “capacitor” is only that region occupied by the electrodes and the space between them, is shown to be incorrect.

Effect of Growth Temperature on the Structural and Electrical Properties of ZrO₂ Films Fabricated by Atomic Layer Deposition Using a CpZr[N(CH₃)₂]₃/C₇H₈ Cocktail Precursor

The effect of growth temperature on the atomic layer deposition of zirconium oxide (ZrO₂) dielectric thin films that were fabricated using a CpZr[N(CH₃)₂]₃/C₇H₈ cocktail precursor with ozone was investigated. The chemical, structural, and electrical properties of ZrO₂ films grown at temperatures from 250 to 350 °C were characterized. Stoichiometric ZrO₂ films formed at 250–350 °C with an atomic ratio of O to Zr of 1.8–1.9 and a low content of carbon impurities. The film formed at 300 °C was predominantly the tetragonal crystalline phase, whereas that formed at 350 °C was a mixture of tetragonal and monoclinic phases. Electrical properties, such as capacitance, leakage current, and voltage linearity of TiN/ZrO₂/TiN capacitors fabricated using the thin ZrO₂ films grown at different temperatures were compared capacitor applications. The ZrO₂ film grown at 300 °C exhibited low impurity content, predominantly tetragonal crystalline structure, a high dielectric permittivity of 38.3, a low leakage current of below 10⁻⁷ A/cm² at 2 V, and low-voltage linearity.

Monomer Derived Poly(Furfuryl)/BaTiO3 0-3 Nanocomposite Capacitors: Maximization of the Effective Permittivity Through Control at the Interface

Frequency stable, high permittivity nanocomposite capacitors produced under mild processing conditions offer an attractive replacement to MLCCs derived from conventional ceramic firing. Here, 0-3 nanocomposites were prepared using gel-collection derived barium titanate nanocrystals, suspended in a poly(furfuryl alcohol) matrix, resulting in a stable, high effective permittivity, low loss dielectric. The nanocrystals are produced at 60 °C, emerging as fully crystallized cubic BTO, 8 nm, paraelectric with a highly functional surface that enables both suspension and chemical reaction in organic solvents. The nanocrystals were suspended in furfuryl alcohol inside a uniquely prepared mold, in which volume fraction of nanocrystal filler (ν_f) could be varied. Polymerization of the matrix in situ at 70-90 °C resulted in a nanocomposite with a higher than anticipated effective permittivity (up to 50, with ν_f only 0.41, 0.5-2000 kHz), exceptional stability as a function of frequency, and very favorable dissipation factors (tan δ < 0.01, ν_f < 0.41; tan δ < 0.05, ν_f < 0.5). The increased permittivity is attributed to the covalent attachment of the poly(furfuryl alcohol) matrix to the surface of the nanocrystals, homogenizing the particle-matrix interface, limiting undercoordinated surface sites and reducing void space. XPS and FTIR confirmed strong interfacial interaction between matrix and nanocrystal surface. Effective medium approximations were used to compare this with similar nanocomposite systems. It was found that the high effective permittivity could not be attributed to the combination of two components alone, rather the creation of a hybrid nanocomposite possessing its own dielectric behavior. A nondispersive medium was selected to focus on the frequency dependent permittivity of the 8 nm barium titanate nanocrystals. Experimental corroboration with known theory is evident until a specific volume fraction (ν_f ≈ 0.3) where, due to a sharp increase in the effective permittivity, approximations fail to adequately describe the nanocomposite medium.

Cl-Assisted Large Scale Synthesis of Cm-Scale Buckypapers of Fe₃C-Filled Carbon Nanotubes with Pseudo-Capacitor Properties: The Key Role of SBA-16 Catalyst Support as Synthesis Promoter

We show a novel chemical vapour deposition (CVD) approach, in which the large-scale fabrication of ferromagnetically-filled cm-scale buckypapers is achieved through the deposition of a mesoporous supported catalyst (SBA-16) on a silicon substrate. We demonstrate that SBA-16 has the crucial role of promoting the growth of carbon nanotubes (CNTs) on a horizontal plane with random orientation rather than in a vertical direction, therefore allowing a facile fabrication of cm-scale CNTs buckypapers free from the onion-crust by-product observed on the buckypaper-surface in previous reports. The morphology and composition of the obtained CNTs-buckypapers are analyzed in detail by scanning electron microscopy (SEM), Energy Dispersive X-ray (EDX), transmission electron microscopy (TEM), high resolution TEM (HRTEM), and thermogravimetric analysis (TGA), while structural analysis is performed by Rietveld Refinement of XRD data. The room temperature magnetic properties of the produced buckypapers are also investigated and reveal the presence of a high coercivity of 650 Oe. Additionally, the electrochemical performances of these buckypapers are demonstrated and reveal a behavior that is compatible with that of a pseudo-capacitor (resistive-capacitor) with better performances than those presented in other previously studied layered-buckypapers of Fe-filled CNTs, obtained by pyrolysis of dichlorobenzene-ferrocene mixtures. These measurements indicate that these materials show promise for applications in energy storage systems as flexible electrodes.

Effect of Transition Metal Cations on Stability Enhancement for Molybdate-Based Hybrid Supercapacitor

The race for better electrochemical energy storage systems has prompted examination of the stability in the molybdate framework (MMoO₄; M = Mn, Co, or Ni) based on a range of transition metal cations from both computational and experimental approaches. Molybdate materials synthesized with controlled nanoscale morphologies (such as nanorods, agglomerated nanostructures, and nanoneedles for Mn, Co, and Ni elements, respectively) have been used as a cathode in hybrid energy storage systems. The computational and experimental data confirms that the MnMoO₄ crystallized in β-form with α-MnMoO₄ type whereas Co and Ni cations crystallized in α-form with α-CoMoO₄ type structure. Among the various transition metal cations studied, hybrid device comprising NiMoO₄ vs activated carbon exhibited excellent electrochemical performance having the specific capacitance 82 F g^-1 at a current density of 0.1 A g^-1 but the cycling stability needed to be significantly improved. The specific capacitance of the NiMoO₄ electrode material is shown to be directly related to the surface area of the electrode/electrolyte interface, but the CoMoO₄ and MnMoO₄ favored a bulk formation that could be suitable for structural stability. The useful insights from the electronic structure analysis and effective mass have been provided to demonstrate the role of cations in the molybdate structure and its influence in electrochemical energy storage. With improved cycling stability, NiMoO₄ can be suitable for renewable energy storage. Overall, this study will enable the development of next generation molybdate materials with multiple cation substitution resulting in better cycling stability and higher specific capacitance.

In Situ Expanding Pores of Dodecahedron-like Carbon Frameworks Derived from MOFs for Enhanced Capacitive Deionization

The pores of dodecahedron-like carbon frameworks derived from metal-organic frameworks (MOFs) were in situ expanded via a surfactant-template strategy, which were originally demonstrated to enhance capacitive deionization (CDI). The dodecahedron-like carbon frameworks were obtained through carbonization of zeolitic imidazolate framework-8 (ZIF-8) using the cetyltrimethylammonium bromide as a supramolecular template. It is found that the dodecahedron-like carbon frameworks derived from ZIF-8 possess efficiently expanded pores while retaining the original morphology and high nitrogen contents. Compared to those of the normal ZIF-8-derived carbon, the obtained materials exhibit a hierarchically porous structure with a higher specific surface area and an improved pore volume. Electrochemical studies of the obtained electrode demonstrate that this material has a high specific capacitance and lower inner resistance. More importantly, the obtained material shows a higher salt adsorption capacity (20.05 mg/g) than the normal ZIF-8-derived carbon (13.01 mg/g). Furthermore, the obtained electrode presents a rapid salt removal rate and excellent cycling stability. The significantly enhanced deionization behavior of the obtained materials is due to the combination effect of its large accessible surface area, large pore volume, and rich nitrogen doping. The results reveal that in situ expanding pores of carbon frameworks derived from MOFs is an ideal way for constructing electrode materials with enhanced CDI performance. The present work may pave a path for the design and development of highly efficient MOF-derived electrode materials.

Fully inkjet-printed microwave passive electronics

Fully inkjet-printed three-dimensional (3D) objects with integrated metal provide exciting possibilities for on-demand fabrication of radio frequency electronics such as inductors, capacitors, and filters. To date, there have been several reports of printed radio frequency components metallized via the use of plating solutions, sputtering, and low-conductivity pastes. These metallization techniques require rather complex fabrication, and do not provide an easily integrated or versatile process. This work utilizes a novel silver ink cured with a low-cost infrared lamp at only 80 °C, and achieves a high conductivity of 1×10⁷ S m^-1. By inkjet printing the infrared-cured silver together with a commercial 3D inkjet ultraviolet-cured acrylic dielectric, a multilayer process is demonstrated. By using a smoothing technique, both the conductive ink and dielectric provide surface roughness values of <500 nm. A radio frequency inductor and capacitor exhibit state-of-the-art quality factors of 8 and 20, respectively, and match well with electromagnetic simulations. These components are implemented in a lumped element radio frequency filter with an impressive insertion loss of 0.8 dB at 1 GHz, proving the utility of the process for sensitive radio frequency applications.

Creating 3D Hierarchical Carbon Architectures with Micro-, Meso-, and Macropores via a Simple Self-Blowing Strategy for a Flow-through Deionization Capacitor

In this work, 3D hierarchical carbon architectures (3DHCAs) with micro-, meso-, and macropores were prepared via a simple self-blowing strategy as highly efficient electrodes for a flow-through deionization capacitor (FTDC). The obtained 3DHCAs have a hierarchically porous structure, large accessible specific surface area (2061 m(2) g(-1)), and good wettability. The electrochemical tests show that the 3DHCA electrode has a high specific capacitance and good electric conductivity. The deionization experiments demonstrate that the 3DHCA electrodes possess a high deionization capacity of 17.83 mg g(-1) in a 500 mg L(-1) NaCl solution at 1.2 V. Moreover, the 3DHCA electrodes present a fast deionization rate in 100-500 mg L(-1) NaCl solutions at 0.8-1.4 V. The 3DHCA electrodes also present a good regeneration behavior in the reiterative regeneration test. These above factors render the 3DHCAs a promising FTDC electrode material.

Thermally Reduced Graphene Oxide Electrochemically Activated by Bis-Spiro Quaternary Alkyl Ammonium for Capacitors

Thermally reduced graphene oxide (RGO) electrochemically activated by a quaternary alkyl ammonium-based organic electrolytes/activated carbon (AC) electrode asymmetric capacitor is proposed. The electrochemical activation process includes adsorption of anions into the pores of AC in the positive electrode and the interlayer intercalation of cations into RGO in the negative electrode under high potential (4.0 V). The EA process of RGO by quaternary alkyl ammonium was investigated by X-ray diffraction and electrochemical measurements, and the effects of cation size and structure were extensively evaluated. Intercalation by quaternary alkyl ammonium demonstrates a small degree of expansion of the whole crystal lattice (d002) and a large degree of expansion of the partial crystal lattice (d002) of RGO. RGO electrochemically activated by bis-spiro quaternary alkyl ammonium in propylene carbonate/AC asymmetric capacitor exhibits good activated efficiency, high specific capacity, and stable cyclability.

Biomass-Based Mechanically Strong and Electrically Conductive Polymer Aerogels and Their Application for Supercapacitors

A novel biomass-based mechanically strong and electrically conductive polymer aerogel was fabricated from aniline and biodegradable pectin. The strong hydrogen bonding interactions between polyaniline (PANI) and pectin resulted in a defined structure and enhanced properties of the aerogel. All the resultant aerogels exhibited self-surppoted 3D nanoporous network structures with high surface areas (207-331m(2)/g) and hierarchical pores. The results from electrical conductivity measurements and compressive tests revealed that these aerogels also had favorable conductivities (0.002-0.1 S/m) and good compressive modulus (1.2-1.4 MPa). The aerogel further used as electrode for supercapacitors showed enhanced capacitive performance (184 F/g at 0.5 A/g). Over 74% of the initial capacitance was maintained after repeating 1000 cycles of the cylic voltammetry test, while the capacitance retention of PANI was only 57%. The improved electrochemical performance may be attributed to the combinative properties of good electrical conductivity, BET surface areas, and stable nanoporous structure of the aerogel. Thus, this aerogel shows great potential as electrode materials for supercapacitors.