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The developed Eu2O3–BaTiO3/PVDF-HFP electrospun-nanofiber TENGs could be used not only as a self-powering device, but also as a sensor.

Sustainable organic materials have gained considerable attention as electrodes for zinc-ion batteries (ZIB) due to their high theoretical capacity, structural versatility, and environmental friendliness. However, issues of inferior capacities and poor rate performance owing to limited inherent electronic conductivity and severe dissolution still persist. Herein, sandwich-structured perylene diimide-ethylene diamine/graphene (PDI-EDA/EG) composites are judiciously designed and synthesized. The two-dimensional graphene host can interact with the PDI-EDA polymer through π–π stacking, endowing accelerated ion/electron transfer, abundant active sites, excellent structural integrity, and mitigated solubility of the hybrid electrodes. When evaluated as an anode in ZIB, the hybrid electrode delivers a high capacity (110.2 mAh g−1 at 0.1 A g−1), superior rate capability (88.9 mAh g−1 at 5 A g−1), and exceptional durability (93.4% capacity retained after 1000 cycles). The structure evolution of the hybrid electrode during the insertion/extraction cycle was investigated by ex-situ Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS), revealing the reversible Zn2+ storage at carbonyl sites. In addition, a prototype rocking-chair ZIB cell was constructed with a zinc pre-intercalated MnO2 cathode, displaying an ultrahigh energy density of 54.9 Wh kg−1 at a power density of 42.5 W kg−1 and excellent stability with negligible capacity decay after 1000 cycles.

Cell migration determines the complete development of mammalian tissue and other pathological phenomena. To investigate the effect of chemical stimuli on such behavior, cells are triggered to translate by the concentration gradient of different molecules on 2D substrates in vitro. But to date unfortunately the polymeric scaffolds for cell migration in 3D environment with chemical stimuli have not been proposed and developed yet. Herein, a novel 3D composite scaffold with an internal chemical boundary is fabricated by electrospinning and mask-assisted electrospray so that the deposition of PBG-N3 particles is confined at specific area initially. The chemical boundary is subsequently formed after selective surface modification of the particles via click reaction. Using a fluorescent alkyne, the boundary of modified regions is clearly observed by fluorescence microscope. This innovative bio-material has the potential to serve as a promising scaffold for investigating the effect of chemical stimuli on cell migration and growth in 3D environment and further on to the application in tissue engineering.

The design and construction of 3D architectures enabled by stimuli-responsive soft materials can yield novel functionalities for next generation soft-bodied actuating devices. Apart from additive manufacturing processes, origami inspired technology offers an alternative approach to fabricate 3D actuators from planar materials. Here we report a class of near-infrared (NIR) responsive 3D active origamis that deploy, actuate and transform between multistable structural equilibria. By exploiting the nonlinear coefficient of thermal expansion (CTE) of graphene oxide (GO), graphene oxide/ethylene cellulose (GO/EC) bilayers are readily fabricated to deliver precise origami structure control, and rapid low-temperature-triggered photothermal actuation. Complexity in 3D shapes is produced through heterogeneously patterning GO domains on 2D EC thin films, which allows us to customize 3D architectures that adapt to various robotic functions. The strategy also enables the construction of material systems possessing naturally inaccessible properties, such as remotely controlled mechanical metamaterials with auxetic behavior and bionic flowers with a rapid blooming rate. Harnessing deformability with multiple degrees of freedom (DOF) upon light irradiation, this work leads to breakthroughs in the design and implementation of shape-morphing functions with soft origamis. National Research Foundation (NRF) Accepted version This work was supported by the Competitive Research Program (NRF-CRP13-2014-02) and NRF Investigatorship (Award No. NRF-NRFI2016-05) under the National Research Foundation, Prime Minister’s Office, Singapore. D. Gao acknowledge the research scholarships awarded by Nanyang Technological University, Singapore.

Failure in an epoxy polymer composite material is prone to initiate by the coalescence of microcracks in its polymer matrix. As such, matrix toughening via addition of a second phase as rigid or/and rubber nano/micro-particles is one of the most popular approaches to improve the fracture toughness across multiple scales in a polymer composite, which dissipates fracture energy via deformation mechanisms and microcracks arrest. Few studies have focused on tailorable and variable toughening, so-called ‘active toughening’, mainly suggesting thermally induced strains which offer slow and irreversible toughening due to polymer’s poor thermal conductivity. The research presented in the current article has developed an instantaneous, reversible active toughening composite based upon contact-less introduction of a microscopic compressive extrinsic strain field via remote electromagnetic radiation. Quantification of the extrinsic strain evolving in the composite with the microwave energy has been conducted using in-situ real-time fibre optic sensing. A theoretical constitutive equation correlating the exposure energy to micro-strains has been developed, with its solution validating the experimental data and describing their underlying physics. The research has utilised functionalised dielectric ferroelectric nanomaterials, barium titanate (BaTiO3), as a second phase dispersed in an epoxy matrix, able to introduce microscopic electro-strains to their surrounding rigid epoxy subjected to an external electric field (microwaves, herein), as result of their domain walls dipole displacements. Epoxy Araldite LY1564, a diglycidyl ether of bisphenol A (DGEBA) associated with the curing agent Aradur 3487 were embedded with the BaTiO3 nanoparticles. The silane coupling agent for the nanoparticles’ surface functionalisation was 3-glycidoxypropyl trimethoxysilane (3-GPS). Hydrogen peroxide (H2O2, 30%) and acetic acid (C2H4O2, 99.9%) used as functionalisation aids, and the ethanol (C2H6O, 99.9%) used for BaTiO3 dispersion. Firstly, the crystal microstructure of the functionalised nanoparticles and the thermal and dielectric properties of the achieved epoxy composite materials have been characterised. It has been observed that the addition of the dielectric nanoparticles has a slight impact on the curing extent of the epoxy. Secondly, the surface-bonded fibre bragg grating (FBG) sensors have been employed to investigate the real-time variation of strain and temperature in the epoxy composites exposed to microwaves at 2.45 GHz and at different exposure energy. The strains developed due to the in-situ exposure at composite, adhesive and their holding fixture material were evaluated using the FBG. The domain wall induced extrinsic strains were distinguished from the thermally induced strains, and found that the increasing exposure energy has an instantaneously increasing effect on the development of compressive strains. Post-exposure Raman spectra showed no residual field in the composite indicating no remnant strain field examined under microwave powers < 1000 W, thus suggesting a reversible strain introduction mechanism, i.e. the composite retaining its nominal properties post exposure. The dielectric composite development and quantifications presented in this article proposes a novel active toughening technology for high-performance composite applications in numerous sectors.

Failure in an epoxy polymer composite material is prone to initiate by the coalescence of microcracks in its polymer matrix. As such, matrix toughening via addition of a second phase as rigid or/and rubber nano/micro-particles is one of the most popular approaches to improve the fracture toughness across multiple scales in a polymer composite, which dissipates fracture energy via deformation mechanisms and microcracks arrest. Few studies have focused on tailorable and variable toughening, so-called 'active toughening', mainly suggesting thermally induced strains which offer slow and irreversible toughening due to polymer's poor thermal conductivity. The research presented in the current article has developed an instantaneous, reversible extrinsic strain field via remote electromagnetic radiation. Quantification of the extrinsic strain evolving in the composite with the microwave energy has been conducted using in-situ real-time fibre optic sensing. A theoretical constitutive equation correlating the exposure energy to micro-strains has been developed, with its solution validating the experimental data and describing their underlying physics. The research has utilised functionalised dielectric ferroelectric nanomaterials, barium titanate (BaTiO

Core-shell nanofibers of PDMS ion gel /PVDF-HFP were successfully prepared by incorporating cross-linking agent during electrospinning. The electrospun nanofiber mats were used to fabricate pressure sensors to detect the static and dynamic pressures by harnessing the capacitance changes and triboelectric effects judiciously. The core-shell PDMS ion gel/PVDF-HFP nanofiber sensor functions as a capacitive pressure sensor, which offers high sensitivity of 0.43 kPa-1 in the low pressure ranges from 0.01 kPa to 1.5 kPa. The sensitivity, flexibility, and robustness of our capacitive pressure sensor allows it to be utilized as a wrist-based pulse wave detector for heart-rate monitoring. In addition, the core-shell PDMS ion gel/PVDF-HFP nanofiber mat made a good triboelectric based pressure sensor in the high pressure range with a linear pressure sensitivity 0.068 V∙kPa-1 from 100 kPa to 700 kPa, one of the best reported at present. The increase in inductive charges and the enhanced dielectric capacitance of the core-shell nanofiber layer compared to the pure PVDF-HFP nanofiber layer allows it to function in the triboelectric nanogenerator (TENG) with the maximum power density reaching 0.9 W/m2, which is sufficient to light up several hundred light emitting diodes (LEDs) instantaneously. NRF (Natl Research Foundation, S’pore) Published version

Smart sensing electronic devices with good transparency, high stretchability, and self-powered sensing characteristics are essential in wearable health monitoring systems. This paper innovatively proposes a stretchable nanocomposite nanogenerator with good transparency that can be conformally attached to the human body to harvest biomechanical energy and monitor physiological signals. The work reports an innovative device that uses sprayed silver nanowires as transparent electrodes and sandwiches a nanocomposite of piezoelectric BaTiO3 and polydimethylsiloxane as the sensing layer, which exhibits good transparency and mechanical transformability with stretchable, foldable, and twistable properties. The highly flexible nanogenerator affords a good input–output linearity under the vertical force and the sensing ability to detect lateral stretching deformation up to 60% strain under piezoelectric mechanisms. Furthermore, the proposed device can effectively harvest touch energies from the human body as a sing...

In the recent years, an immense interest has been generated on developing suitable dielectric materials for high electric energy storage. Ferroelectric ceramic materials exhibit very high dielectric constant but they are brittle and possess low dielectric strength. On the other hand, polymer materials are flexible with high ease of processing at low processing temperatures, and possess high dielectric breakdown field. By combining these two materials, one can develop an improved material system with higher dielectric constant and higher breakdown field to realize the high energy storage density. Barium titanate (BaTiO3) is widely used in electronic devices such as multi layer ceramic capacitor and other electronic devices due to its superior dielectric characteristics. Structure distortion via doping has been used to modulate the physical properties of BaTiO3. In this work, single crystalline Nd-doped BaTiO3 hollow nanoparticles have been synthesized via a simple hydrothermal method. With unique hollow structured morphology, the nanoparticles not only exhibited excellent compatibility with poly (vinylidene fluoride) (PVDF), but showed significant enhancement of the dielectric properties of the nanocomposites. Design and optimization of the synthesis method have been achieved through a systematic study. The formation of hollow nanostructures is proposed to follow a Kirkendall induced hollowing mechanism which is governed by the differences in diffusion rates of dopant ions, water molecules and core ions during the synthesis reaction. The differences in the surface characteristics of ceramic fillers and polymer matrix in the nanocomposite system cause non-uniform dispersion in the polymer matrix which affects electrical properties. We studied the surface functionalization of BaTiO3 nanoparticles with dopamine using reflux method to strongly bind dopamine with hydrogen bonding on BaTiO3 nanoparticle surface and improve its compatibility with PVDF polymer matrix. FT-IR spectra were used to confirm the successful surface functionalization of BaTiO3 nanoparticles after immobilization with dopamine. SEM characterizations showed that the nanoparticles dispersed uniformly after the dopamine modification and void formation in the nanocomposite films has been lowered. Electrical properties of the resultant nanocomposite showed that the dielectric constant can be enhanced greatly with low dielectric loss There are several types of methods to prepare nanocomposites such us solution mixing, simple blending methods. Sample preparation method has a strong effect on the dispersion of nanoparticles into polymer matrices and phase separation which will in turn influence the electrical properties of the nanocomposite. Fillers are not easy to disperse homogeneously into fluorinated polymer matrix due to its chemical inertness. We developed novel in-situ synthesis methods to prepare core-shell structured ceramic-polymer nanocomposites in which the dielectric nanoparticle shell is attached well on to the insulating polymer core surface to prevent aggregation of nanoparticles. The core-shell structured ceramic-polymer nanocomposite was developed using two different types of cross-linking agents via in-situ synthesis method without any catalyst and initiators. We demonstrated that in-situ synthesis of nanocomposite using cross-linking agents not only enables highly uniform dispersion of the fillers to form core-shell structure nanocomposite but also improves electrical properties remarkably. DOCTOR OF PHILOSOPHY (MSE)

Accelerated curing of high performance fibre-reinforced polymer (FRP) composites via microwave heating or radiation, which can significantly reduce cure time and increase energy efficiency, has several major challenges (e.g. uneven depth of radiation penetration, reinforcing fibre shielding, uneven curing, introduction of hot spots etc). This article reviews the current scientific challenges with microwave curing of FRP composites considering the underlying physics of microwave radiation absorption in thermoset-matrix composites. The fundamental principles behind efficient accelerated curing of composites using microwave radiation heating are reviewed and presented, especially focusing on the relation between penetration depth, microwave frequency, dielectric properties and cure degree. Based on this review, major factors influencing microwave curing of thermoset-matrix composites are identified, and recommendations for efficient cure cycle design are provided.

Soft electronic systems are emerging that are heralded to bring revolution and a frontier for the interactions between human beings and machines. Interactive interfaces enable integrated bidirectional functionalities of sensing the external stimulus and providing interactive response to the users. Human body is considerably soft and stretchable; this characteristic puts forward the need for good mechanical conformabilities for the interfacing electronic devices. As a vital and indispensable component in electronic systems, soft and deformable conductor is of great importance to establish the enabling technologies. Significant progresses have been developed with new strategies and materials being exploited to improve the performance of elastic conductors. In this article, we review the latest advances in deformable conductors and their applications to enable soft electronic devices for human–machine interfaces. We first focus on the important characteristics of the deformable conductors in their stretchability, conductivity, and transparency. Representative soft electronic systems that are categorized into “receptive devices” and “responsive devices” are then reviewed. National Research Foundation (NRF) Published version This work was financially supported by the National Research Foundation Competitive Research Programme. Award No. NRFCRP- 13-2014-02, and the NRF Investigatorship (NRFI), Award No. NRF-NRFI2016-05.

Textiles that are capable of harvesting biomechanical energy via triboelectric effects are of interest for self-powered wearable electronics. Fabrication of conformable and durable textiles with high triboelectric outputs remains challenging. Here we propose a washable skin-touch-actuated textile-based triboelectric nanogenerator for harvesting mechanical energy from both voluntary and involuntary body motions. Black phosphorus encapsulated with hydrophobic cellulose oleoyl ester nanoparticles serves as a synergetic electron-trapping coating, rendering a textile nanogenerator with long-term reliability and high triboelectricity regardless of various extreme deformations, severe washing, and extended environmental exposure. Considerably high output (~250–880 V, ~0.48–1.1 µA cm−2) can be attained upon touching by hand with a small force (~5 N) and low frequency (~4 Hz), which can power light-emitting diodes and a digital watch. This conformable all-textile-nanogenerator is incorporable onto cloths/skin to capture the low output of 60 V from subtle involuntary friction with skin, well suited for users’ motion or daily operations., Incorporation of triboelectric nanogenerators into textiles is attractive for self-powered wearable electronics. Here the authors employ black phosphorus with a hydrophobic coating in a durable, washable, and air permeable textile-based device that converts biomechanical motion into electricity.

Solar-blind photodetectors based on Zn2GeO4 (ZGO) nanowires (NWs) with high transparency and good flexibility were successfully fabricated on a polyethylene terephthalate (PET) substrate using a facile all solution-processible method. The electrodes and functional channels are constructed with silver NWs (Ag NWs) and ZGO NWs, respectively, using a spray coating method. The spray-coated all-NW device exhibited high transparency, good mechanical bending stability, high photoresponse, and short cutoff wavelength. The Schottky barrier between the Ag–ZGO NWs together with the junction barrier between interconnecting ZGO NWs contributed to a high photoresponse and improved switching time in the devices. We propose that the unique energy band structure of the ZGO NW networks provides an additional mechanism to further reduce the cutoff wavelength in solar-blind photodetectors.

Electronics with multifunctionalities such as transparency, portability, and flexibility are anticipated for future circuitry development. Flexible memory is one of the indispensable elements in a hybrid electronic integrated circuit as the information storage device. Herein, we demonstrate a transparent, flexible, and transferable hexagonal boron nitride (hBN)-based resistive switching memory with indium tin oxide (ITO) and graphene electrodes on soft polydimethylsiloxane (PDMS) substrate. The ITO/hBN/graphene/PDMS memory device not only exhibits excellent performance in terms of optical transmittance (∼85% in the visible wavelength), ON/OFF ratio (∼480), retention time (∼5 × 104 s) but also shows robust flexibility under bending conditions and stable operation on arbitrary substrates. More importantly, direct observation of indium filaments in an ITO/hBN/graphene device is found via ex situ transmission electron microscopy, which provides critical insight on the complex resistive switching mechanisms.

Many organisms and animals have sensing abilities that are different from those of human beings; for example, snakes have strong smell-, vibration-, touch- and heat-sensing abilities. A nature-mimicking sensing platform capable of sensing multiple stimuli, such as strain, pressure, temperature and other uncorrelated conditions, is highly desirable to broaden the applications of sensors. Here, we construct a semitransparent intelligent skin-like sensing platform based on polyaniline (PANI) nanowire arrays that can act as a bionic component by simultaneously sensing tactile stimuli and detecting colorless, odorless gas. Our multifunctional bionic sensing strategy is remarkably adaptive for versatile applications. The strain-sensing performance is superior to that of most conducting polymer-based sensors reported so far and is comparable to or even better than traditional metal and carbon nanowire/nanotube-based strain sensors. The highest gauge factor demonstrated is 149, making our system a remarkable candidate for strain-sensing applications. The sensor can accurately detect a wide range of human motions. We also demonstrate the simultaneous controlled olfaction ability for the detection of methane with high sensitivity and a fast response time. These results enable the realization of multifunctional and uncorrelated sensing capabilities, which will afford a wide range of applications to augment robotics, treatment, simulated skin, health monitoring and bionic systems. A wearable sensor can track full-range human motion and sniff out toxic gases using polymer nanowires with features similar to snakeskin. The device, which was developed by Pooi See Lee and co-workers at Nanyang Technological University, is based on polyaniline, a conducting polymer with natural flexibility and chemical sensitivity. Polyaniline often becomes unworkably rigid when deposited as a thin film, but the Singapore-based team avoided this issue by growing a vertical forest of polymer nanowires on a thin silicone support. Scanning electron microscopy revealed that when stretched, the nanowires formed scale-like islands and cracks that alter the resistance of the thin film. The researchers demonstrated that these electrical changes were sensitive enough to use for forehead sensors of breathing and eye movement and as a ‘smelling skin’ for detecting methane–an odorless and explosive gas. A semitransparent intelligent skin-like sensor platform based on polyaniline nanowire arrays was constructed, which can act as bionic component by simultaneously sensing tactile stimuli and detecting colorless odorless gas. The highest gauge factor demonstrated is 149, making it a remarkable candidate in strain sensing applications. Simultaneously, we demonstrate the controlled olfaction ability of the sensor with the detection of methane with high sensitivity and fast response time. These results enable the realization of multifunctional and uncorrelated sensing capabilities that will have wide range applications to augment robotics, treatment, simulate skin, health and bionic system.

Reversible electrochemical mirror (REM) device can be electrochemically tuned to exhibit dual transmittance and reflectance modulations in a single device. Conventional REM devices reversibly switched between transparent and mirror states. However, it is of great challenge to maintain the mirror state of the REM devices due to the diffusion of anions into the metallic film at the open-circuit state. In this work, we report a Cu-based REM device which offers reversible switching between transparent, blue and mirror states with judicious selection of electrolyte and controllable electrodeposition. The blue state can be obtained through the formation of copper (I) chloride, CuCl, when copper (II) chloride CuCl2 undergoes electrochemical reduction. The polymer host, PVA (poly(vinyl alcohol)) plays an important role in reducing the surface roughness of the electrodeposited mirror film, improving film uniformity and sustaining the mirror state of the device during the voltage-off state. NRF (Natl Research Foundation, S’pore) Accepted version

It is of great challenge to develop a transparent solid state electrochromic device which is foldable at the device level. Such devices require delicate designs of every component to meet the stringent requirements for transparency, foldability, and deformation stability. Meanwhile, nanocellulose, a ubiquitous natural resource, is attracting escalating attention recently for foldable electronics due to its extreme flexibility, excellent mechanical strength, and outstanding transparency. In this article, transparent conductive nanopaper delivering the state‐of‐the‐art electro‐optical performance is achieved with a versatile nanopaper transfer method that facilitates junction fusing for high‐quality electrodes. The highly compliant nanopaper electrode with excellent electrode quality, foldability, and mechanical robustness suits well for the solid state electrochromic device that maintains good performance through repeated folding, which is impossible for conventional flexible electrodes. A concept of camouflage wearables is demonstrated using gloves with embedded electrochromics. The discussed strategies here for foldable electrochromics serve as a platform technology for futuristic deformable electronics. NRF (Natl Research Foundation, S’pore) Accepted version

Huge challenges remain regarding the facile fabrication of neat metallic nanowires mesh for high-quality transparent conductors (TCs). Here, a scalable metallic nanowires bundle micromesh is achieved readily by a spray-assisted self-assembly process, resulting in a conducting mesh with controllable ring size (4-45 µm) that can be easily realized on optional polymer substrates, rendering it transferable to various deformable and transparent substrates. The resultant conductors with the embedded nanowires bundle micromesh deliver superior and customizable optoelectronic performances, and can sustain various mechanical deformations, environmental exposure, and severe washing, exhibiting feasibility for large-scale manufacturing. The silver nanowires bundle micromesh with explicit conductive paths is embedded into an ethyl cellulose (EC) transparent substrate to achieve superior optoelectronic properties endowed by a low amount of incorporated nanowires, which leads to reduced extinction cross-section as verified by optical simulation. A representative EC conductor with a low sheet resistance of 25 Ω □-1 , ultrahigh transmittance of 97%, and low haze of 2.6% is attained, with extreme deformability (internal bending radius of 5 µm) and waterproofing properties, opening up new possibilities for low-cost and scalable TCs to replace indium-tin oxide (ITO) for future flexible electronics, as demonstrated in a capacitive touch panel in this work. National Research Foundation (NRF) This work was financially supported by the Competitive Research Program (Award No. NRF-CRP13-2014-02), National Research Foundation, Prime Minister’s Office, Singapore. The authors acknowledge Xiaoliang Chen and Jing-Hao Ciou for their assistance in some measurements.

Few-layered phosphorene is exfoliated through a liquid phase exfoliation in ethanol, acting as an additive to mix with tempo-oxidized cellulose nanofibrils (CNF), forming a transparent, flexible nanogenerator paper. The gas barrier property of CNF protects phosphorene against oxidation in ambient condition. The phosphorene in the hybrid paper is stable over six months even with exposure to ambient condition (23 °C, 70% RH) in air. The hybrid paper is used as an active layer to construct a triboelectric energy nanogenerator (TENG). This hybrid paper shows an open-circuit voltage of 5.2 V with a current density of 1.8 µA cm−2, which is five and nine times higher than that of the pure CNF paper device, respectively. This work reveals the role of phosphorene in acting as a charge carrier in the hybrid paper and demonstrates a new way to attain stable functional phosphorene hybrids in ambient condition. The resultant phosphorene hybrid paper could be used as a building block for TENG with enhanced output performance.

Realizing energy harvesting from water flow using triboelectric generators (TEGs) based on our daily wearable fabric or textile has practical significance. Challenges remain on methods to fabricate conformable TEGs that can be easily incorporated into waterproof textile, or directly harvest energy from water using hydrophobic textile. Herein, a wearable all-fabric-based TEG for water energy harvesting, with additional self-cleaning and antifouling properties is reported for the first time. Hydrophobic cellulose oleoyl ester nanoparticles (HCOENPs) are prepared from microcrystalline cellulose, as a low-cost and nontoxic coating material to achieve superhydrophobic coating on fabrics, including cotton, silk, flax, polyethylene terephthalate (PET), polyamide (nylon), and polyurethane. The resultant PET fabric-based water-TEG can generate an instantaneous output power density of 0.14 W m−2 at a load resistance of 100 MΩ. An all-fabric-based dual-mode TEG is further realized to harvest both the electrostatic energy and mechanical energy of water, achieving the maximum instantaneous output power density of 0.30 W m−2. The HCOENPs-coated fabric provides excellent breathability, washability, and environmentally friendly fabric-based TEGs, making it a promising wearable self-powered system.

Decreasing the active layer thickness has been recently reported as an alternative way to achieve fully depleted oxide thin-film transistors for the realization of low-voltage operations. However, the correlation between the active layer thickness and device resistivity to environmental changes is still unclear, which is important for the optimized design of oxide thin-film transistors. In this work, the ambient gas stability of IGZO thin-film transistors is found to be strongly correlated to the IGZO thickness. The TFT with the thinnest IGZO layer shows the highest intrinsic electron mobility in a vacuum, which is greatly reduced after exposure to O2/air. The device with a thick IGZO layer shows similar electron mobility in O2/air, whereas the mobility variation measured in the vacuum is absent. The thickness dependent ambient gas stability is attributed to a high-mobility region in the IGZO surface vicinity with less sputtering-induced damage, which will become electron depleted in O2/air due to the electron transfer to adsorbed gas molecules. The O2 adsorption and deduced IGZO surface band bending is demonstrated by the ambient-pressure x-ray photoemission spectroscopy results.

A flexible superamphiphobic SiO2/poly (vinylidene difluoride-co-trifluoroethylene) (PVDF-TrFE) film is designed to harvest the electrostatic energy from water. The working mechanism of the water-triboelectric nanogenerator is based on the triboelectricity generated from the contact electrification between water and the superamphiphobic SiO2/P(VDF-TrFE) film. The maximum power density for harvesting water can be brought up to 62.5 mW m−2, which is able to charge a capacitor and sufficient to light up light emitting diodes. NRF (Natl Research Foundation, S’pore)

In this work, monodisperse polydopamine (PDA) spheres with tunable diameters have been synthesized through a facile and low cost method using a deionized water and alcohol mixed solvent. The PDA spheres possess surface functional groups (-OH, -NH(2)), exhibiting an extraordinary versatile active nature. It is demonstrated that the PDA spheres could serve as an active template for the convenient synthesis of various nanostructures, e.g., MnO(2) hollow spheres or PDA/Fe(3)O(4) and PDA/Ag core/shell nanostructures. No surface modification or special treatment is required for the synthesis of these nanostructures, which makes the fabrication process simple and very convenient. The novel application of PDA/Fe(3)O(4) spheres as fillers in nanocomposites for high-performance capacitors is demonstrated, indicating a promising practicality. The PDA spheres provide a new general platform not only for the facile assembly of nanostructures but also a green synthetic template for practical applications.

Fluoropolymers are of prime interest as solution processable materials for electronic applications such as embedded capacitors, multilayer capacitors, and high-energy-density capacitors. Herein, for the first time, we investigated an environmentally friendly green aqueous modification of fluoropolymers, poly(vinylidene fluoride) (PVDF) for energy storage applications. The PVDF polymer was modified in aqueous medium by using bioinspired protein dopamine without any harmful toxic chemicals. Dopamine functionalization onto pre-irradiated PVDF polymer powder was carried out using a simple reflux method to strongly bind dopamine onto the PVDF surface. The resulting dopamine modified PVDF films exhibited excellent dielectric properties, when compared with the pristine PVDF polymer. The dielectric constant can be enhanced up to 32 with fairly low dielectric loss as compared to pristine PVDF. Furthermore, the modified films were found to have good flexibility; they could be curled as easily as pristine PVDF films. Since this method avoids the use of toxic chemicals, it may allow the application of modified PVDF not only for energy storage applications but also for other applications such as in biocompatible materials.

We report the graft copolymerization synthesis of novel high dielectric constant HEMA (2-hydroxyethylmethacrylate)-graft-poly(vinylidene fluoride) (PVDF) copolymers for potential applications in high energy density capacitors. In the present study the graft copolymerization reaction was introduced by irradiation (electron beam) treatment of the PVDF polymer powder. The chemical changes in the PVDF polymers after HEMA grafting were monitored and the results were evaluated by FTIR, DSC, TGA and contact angle measurement. An analysis is presented on the effectiveness of this approach as a function of electron beam operating variables including radiation dose, reaction time, reaction temperature, monomer concentration and effect of solvent. The PHEMA-g-PVDF copolymers demonstrate improved dielectric properties such as high dielectric constant, lower leakage and low dielectric loss as compared to pristine PVDF. Correlation of dielectric properties with the graft copolymerization reaction mechanism was discussed. Accepted version

The dependence of oxygen vacancy suppression on dopant species in amorphous indium oxide (a-InOx) thin film transistors (TFTs) is reported. In a-InOx TFTs incorporating equivalent atom densities of Si- and W-dopants, absorption of oxygen in the host a-InOx matrix was found to depend on difference of Gibbs free energy of the dopants for oxidation. For fully oxidized films, the extracted channel conductivity was higher in the a-InOx TFTs containing dopants of small ionic radius. This can be explained by a reduction in the ionic scattering cross sectional area caused by charge screening effects.

The stable operation of transistors under a positive bias stress (PBS) is achieved using Hf incorporated into InOx-based thin films processed at relatively low temperatures (150 to 250 °C). The mobilities of the Hf-InOx thin-film transistors (TFTs) are higher than 8 cm2/Vs. The TFTs not only have negligible degradation in the mobility and a small shift in the threshold voltage under PBS for 60 h, but they are also thermally stable at 85 °C in air, without the need for a passivation layer. The Hf-InOx TFT can be stable even annealed at 150 °C for positive bias temperature stability (PBTS). A higher stability is achieved by annealing the TFTs at 250 °C, originating from a reduction in the trap density at the Hf-InOx/gate insulator interface. The knowledge obtained here will aid in the realization of stable TFTs processed at low temperatures.

To avoid the problem of air sensitive and wet-etched Zn and/or Ga contained amorphous oxide transistors, we propose an alternative amorphous semiconductor of indium silicon tungsten oxide as the channel material for thin film transistors. In this study, we employ the material to reveal the relation between the active thin film and the transistor performance with aid of x-ray reflectivity study. By adjusting the pre-annealing temperature, we find that the film densification and interface flatness between the film and gate insulator are crucial for achieving controllable high-performance transistors. The material and findings in the study are believed helpful for realizing controllable high-performance stable transistors.

Oxide thin film transistor employing copper source/drain electrodes shows a small turn on voltage and reduced hysteresis. Cross-sectional high-resolution transmission electron microscopy image confirmed the formation of ∼4 nm CuOx related interlayer. The lower bond-dissociation energy of Cu-O compared to Si-O and In-O suggests that the interlayer was formed by adsorbing oxygen molecules from surrounding environment instead of getting oxygen atoms from the semiconductor film. The formation of CuOx interlayer acting as an acceptor could suppress the carrier concentration in the transistor channel, which would be utilized to control the turn on voltage shifts in oxide thin film transistors.

Thin-film transistors (TFTs) with a high stability and a high field-effect mobility have been achieved using W-doped indium oxide semiconductors in a low-temperature process (∼150 °C). By incorporating WO3 into indium oxide, TFTs that were highly stable under a negative bias stress were reproducibly achieved without high-temperature annealing, and the degradation of the field-effect mobility was not pronounced. This may be due to the efficient suppression of the excess oxygen vacancies in the film by the high dissociation energy of the bond between oxygen and W atoms and to the different charge states of W ions.

Incorporating SiO2 into amorphous In2O3-based thin films is found to suppress the formation of unstable oxygen vacancies. The SiO2 incorporated thin film transistors exhibited reliable device characteristics after being annealed at 250 °C. Increasing the SiO2 content of the sputtering target decreased the sensitivity of the subthreshold swing and turn-on voltage of the device to the sputtering conditions used to deposit the amorphous oxide, making them more stable against electrical and thermal stresses. The increased activation energy of the charge carriers in the current off region indicated a smaller density of states at the conduction-band tail, supporting stable transistor operations.

PVDF-g-HEMA [poly(vinylidene fluoride)-graft-poly(2-hydroxyethylmethacrylate)]/Barium Titanate (BaTiO3) nanocomposites were prepared successfully via an in situ synthesis method without any catalyst or initiator. The in situ synthesis approach enables the formation of oxide nanoparticles in the presence of the grafted polymer with a hydroxyl functionalization group for direct coupling with oxide nanofillers. This elegant in situ nanoparticle synthesis method provides a facile, cost-effective and void-free dispersion of the nanoparticles in the matrix. The dielectric nanoparticle (BaTiO3) is well-attached onto the insulating polymer (PVDF) surface due to the surface anchoring linkage through hydrogen bonding between the two components, leading to the reduced aggregation in the resultant nanocomposites. The novel PVDF-g-HEMA/BaTiO3 nanocomposites are investigated as high energy density capacitor materials, achieving highest dielectric constant reaching up to 333, and a dielectric loss of 0.73 at 30 wt% BaTiO3 at 1 kHz.

Boron nitride nanotubes (BNNTs) are excellent nanofillers to enhance the mechanical and thermal properties of polymer nanocomposites. Despite the rapid progress in the effective syntheses of BNNTs, the ease of processability and solubility are major roadblocks for their widespread applications. The present work reports for the first time: a facile and environment-friendly green approach for aqueous bioinspired functionalization of boron nitride nanotubes through the use of dopamine, a synthetic mimic of mussel adhesive proteins. This approach is based on the affinity of the amino group of dopamine molecules for the boron atoms in BNNTs and π–π interactions as well as van der Waals interactions between the BNNTs network and dopamine molecules. Functionalization of the boron nitride nanotubes was evidently found to be associated with the existing π–π bonding and van der Waals interactions at the BNNT surfaces, involving the aromatic core structures of the dopamine molecules based on various characterizations. The resultant functionalized BNNTs are highly dispersible in water and a number of solvents. Polymer nanocomposites were prepared using pristine and dopamine functionalized BNNTs as reinforcement in a poly(vinyl difluoroethylene) matrix and tested for the thermal and mechanical properties. The functionalized BNNT reinforced polymer nanocomposites exhibit superior properties as compared to nanocomposites based on pristine BNNTs. This comprehensive study indicates that dopamine functionalized BNNTs are promising materials for various applications and are expected to form the basis of a new class of chemically reactive nanostructures.

Conducting nanowires are of particular interest in energy-related research on devices such as supercapacitors, batteries, water splitting electrodes and solar cells. Their direct electrode/current collector contact and highly conductive 1D structure enable conducting nanowires to provide ultrafast charge transportation. In this paper, we report the facile synthesis of nickel cobalt layered double hydroxides (LDHs) on conducting Zn(2)SnO(4) (ZTO) and the application of this material to a supercapacitor. This study also presents the first report of an enhancement of the active faradic reaction sites (electroactive sites) resulting from the heterostructure. This novel material demonstrates outstanding electrochemical performance with a high specific capacitance of 1805 F g(-1) at 0.5 A g(-1), and an excellent rate performance of 1275 F g(-1) can be achieved at 100 A g(-1). Furthermore, an asymmetric supercapacitor was successfully fabricated using active carbon as a negative electrode. This asymmetric device exhibits a high energy density of 23.7 W h kg(-1) at a power density of 284.2 W kg(-1). Meanwhile, a high power density of 5817.2 W kg(-1) can be achieved at an energy density of 9.7 W h kg(-1). More importantly, this device exhibits long-term cycling stability, with 92.7% capacity retention after 5000 cycles.

In this work, large-scale single crystalline Nd-doped BaTiO3 hollow nanoparticles have been synthesized via a simple hydrothermal method without the assistance of a surfactant or high temperature sintering. With unique hollow structures, the nanoparticles not only exhibit excellent compatibility with poly(vinylidene fluoride) (PVDF), but significantly enhanced the dielectric properties of the nanocomposites. We demonstrated that the dielectric constant of the nanocomposite reached up to 480.3 with dielectric loss of 0.6 at 102 Hz. Design and optimization of the synthesis method have been achieved through a systematic study of the effect of reaction conditions on the size and morphology evolution of the hollow nanoparticles. The formation of hollow nanostructures is proposed to follow a Kirkendall induced hollowing mechanism which is governed by the differences in diffusion rates of dopant ions, water molecules and core ions during the synthesis reaction.

Electroactive materials are of great interest for high performance capacitive behavior due to their relaxed ferroelectric properties. In this work, we studied the dielectric properties of poly(vinylidene fluoride) (PVDF) grafted with polystyrene (PS) by electron beam radiation induced free radical graft copolymerization reaction in solution. The dielectric constant of polystyrene grafted PVDF copolymers reaches about 90 at 100 Hz at room temperature representing more than seven times increment compared with the pristine PVDF matrix. The dielectric loss of 0.005 at 1 KHz can be achieved. Correlation of the dielectric properties with the graft copolymerization reaction mechanism was discussed. This route represents one of the most effective techniques to synthesize potential graft copolymers with desirable dielectric properties in a wide frequency range for energy storage applications.

Surface functionalization of BaTiO3 nanoparticles with dopamine was carried out using a reflux method to strongly bind dopamine on the BaTiO3 nanoparticle surface and improve its compatibility with the polyvinylidene fluoride (PVDF) polymer matrix. Fourier transform infrared spectra confirm the successful surface functionalization of BaTiO3 nanoparticles after immobilization with dopamine. Electrical properties of the resultant nanocomposite show that the dielectric constant can be enhanced up to 56.8 with low dielectric loss.