Biochar from Cyperus alternifolius Linn.: from a waste of phytoremediation processing to efficient depolluting agent

Phytoremediation is one of the most powerful and viable solutions for developing countries to clean the soil and water bodies from metallic pollutants. Cyperus alternifolius Linn. (CAL), a tropical wetland plant, has been widely researched for removing harmful contaminants due to its hyperaccumulation ability. However, the waste biomass of phytoremediation processing may risk secondary environmental pollution. Thus, the preparation and application of biochar from metal-contaminated plants can be considered a new approach. In a 60-day experiment, CAL plants were irrigated with different concentrations of Zn(II) (200, 700, 1200, 1700, and 2200 mg·L^-1), and then the plants were converted into biochar via the pyrolysis process. The characteristics of biochar including of surface composition and morphology, phase formation, and optical property were analyzed. The biochar enriched with Zn(II) at 1200 mg·L^-1 had a bandgap value of 3.17 eV and consisted of carbon microparticles intermingled with ZnO and SiO₂ nanoparticles. Furthermore, the adsorption and photocatalysis of the biochar were studied in the discolouration of methylene blue (MB), as a test reaction, with the maximum MB removal capacities of 55.2 mg·g^-1. Such results will serve as the basis for new research aiming at the potential for reusing metal-contaminated plants to produce efficient depolluting biochar.

Multimodal Encapsulation to Selectively Permeate Hydrogen and Engineer Channel Conduction for p-Type SnOx Thin-Film Transistor Applications

It has been challenging to synthesize p-type SnO_x (1 < x < 2) and engineer the electrical properties such as carrier density and mobility due to the narrow processing window and the localized oxygen 2p orbitals near the valence band. Herein, we report on the multifunctional encapsulation of p-SnO_x to limit the surface adsorption of oxygen and selectively permeate hydrogen into the p-SnO_x channel for thin-film transistor (TFT) applications. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements identified that ultrathin SiO₂ as a multifunctional encapsulation layer effectively suppressed the oxygen adsorption on the back channel surface of p-SnO_x and selectively diffused hydrogen across the entire thickness of the channel. Encapsulated p-SnO_x-based TFTs demonstrated much enhanced channel conductance modulation in response to the gate bias applied, featuring higher on-state current and lower off-state current (on/off ratio > 10³), field effect mobility of 3.41 cm²/(V s), and threshold voltages of ∼5-10 V. The fabricated devices show minimal deviations as small as ±6% in the TFT performance parameters, which demonstrates good reproducibility of the fabrication process. The relevance between the TFT performance and the effects of hydrogen permeation is discussed in regard to the intrinsic and extrinsic doping mechanisms. Density functional theory calculations reveal that hydrogen-related impurity complexes are in charge of the enhanced channel conductance with gate biases, which further supports the selective permeation of hydrogen through a thin SiO₂ encapsulation.

High-Performance Oxide-Based p-n Heterojunctions Integrating p-SnOx and n-InGaZnO

The fabrication of oxide-based p-n heterojunctions that exhibit high rectification performance has been difficult to realize using standard manufacturing techniques that feature mild vacuum requirements, low thermal budget processing, and scalability. Critical bottlenecks in the fabrication of these heterojunctions include the narrow processing window of p-type oxides and the charge-blocking performance across the metallurgical junction required for achieving low reverse current and hence high rectification behavior. The overarching goal of the present study is to demonstrate a simple processing route to fabricate oxide-based p-n heterojunctions that demonstrate high on/off rectification behavior, a low saturation current, and a small turn-on voltage. For this study, room-temperature sputter-deposited p-SnO_x and n-InGaZnO (IGZO) films were chosen. SnO_x is a promising p-type oxide material due to its monocationic system that limits complexities related to processing and properties, compared to other multicationic oxide materials. For the n-type oxide, IGZO is selected due to the knowledge that postprocessing annealing critically reduces the defect and trap densities in IGZO to ensure minimal interfacial recombination and high charge-blocking performance in the heterojunctions. The resulting oxide p-n heterojunction exhibits a high rectification ratio greater than 10³ at ±3 V, a low saturation current of ∼2 × 10^-10 A, and a small turn-on voltage of ∼0.5 V. In addition, the demonstrated oxide p-n heterojunctions exhibit excellent stability over time in air due to the p-SnO_x with completed reaction annealing in air and the reduced trap density in n-IGZO.

Binder-free printed PEDOT wearable sensors on everyday fabrics using oxidative chemical vapor deposition

Polymeric sensors on fabrics have vast potential toward the development of versatile applications, particularly when the ready-made wearable or fabric can be directly coated. However, traditional coating approaches, such as solution-based methods, have limitations in achieving uniform and thin films because of the poor surface wettability of fabrics. Herein, to realize a uniform poly(3,4-ethylenedioxythiophene) (PEDOT) layer on various everyday fabrics, we use oxidative chemical vapor deposition (oCVD). The oCVD technique is a unique method capable of forming patterned polymer films with controllable thicknesses while maintaining the inherent advantages of fabrics, such as exceptional mechanical stability and breathability. Utilizing the superior characteristics of oCVD PEDOT, we succeed in fabricating blood pressure– and respiratory rate–monitoring sensors by directly depositing and patterning PEDOT on commercially available disposable gloves and masks, respectively. Those results are expected to pave efficient and facile ways for skin-compatible and affordable sensors for personal health care monitoring.

Pseudo wastewater treatment by combining adsorption and phytoaccumulation on the Acrostichum aureum Linn. plant/activated carbon system

In this study, the pseudo wastewater containing Zn, Fe, Cu ions was clean-up by a combination of physical adsorption onto activated carbon medium and phytoaccumulation using Acrostichum aureum Linn. plants. The adsorption capability of the activated carbon for the Fe, Cu, and Zn ions was 3.05, 3.72, and 2.85 mg·g - 1, respectively, at the saturation. The phytoaccumulation performance was proved by analyzing the individual residual ash collected after pyrolysis up to 1000 °C of the leaf, stem, and root of the plants. Thermal analyses of thermogravimetry data showed that the weight of the residual ash of the phytoremediated leaf, stem, and root of the plants was 37.0, 19.0, and 65.7 wt.%, respectively. Energy-dispersive X - ray spectroscopy determined the amount of Fe element in the residual ash of phytoremediated root is 7.05 wt.%, while that of the initial root is 1.18 wt.%. Conclusively, it can be proved that combining physical and biological processes is feasible to treat wastewater containing metal ions.

Effects of membrane thickness on the performance of ionic polymer–metal composite actuators

In this study, we report the effects of Nafion thickness on the performance of ionic polymer–metal composite (IPMC) actuators. We analyzed the actuation properties of the IPMC actuators, such as displacement and tip force, under external voltage, as a function of their thickness. In order to understand the relationship between thickness and actuation properties, we developed a semi-quantitative model of voltage induced ionic diffusion and its contribution to bending of the Nafion cantilever. Furthermore, we investigated the mechanical properties of the Nafion membranes at sub-micro scale as well as bulk scale, using atomic force microscopy (AFM) and tensile test. The results of the two methods indicated opposite trends of elastic modulus and crystallinity as a function of thickness. We hypothesized that the hot-pressed Nafion was composed of three layers with different crystallinity. Our results suggest that for a high performance IPMC actuator, we need better control of the annealing temperature gradient.

We report the effects of Nafion thickness on the performance of ionic polymer–metal composite (IPMC) actuators.

Effects of NH4F and distilled water on structure of pores in TiO2 nanotube arrays

In this study, we report the influences of distilled water and ammonium fluoride (NH4F) on morphology of pores in honeycomb-like titanium dioxide (TiO2) nanotube arrays. We observed the structure and arrangement of pores in the TiO2 nanotube arrays based on scanning electron microscopy images and analyzed the spatial distribution of the pores using fast Fourier transform and Voronoi diagram. We studied the individual pore properties including pore diameter, wall thickness, and interpore distance and found that locally connected ordering defects decreased with increasing distilled water concentration. Furthermore, we found that the optimum conditions of well-ordered hexagonal pore arrangement were 2 and 10 vol% distilled water with 0.2 and 0.4 wt% NH4F, respectively. Throughout this study, we provide a better understanding about the roles of distilled water and NH4F in forming well-ordered nanoscale pore structure with less ordering defects in the honeycomb-like TiO2 nanotube arrays.

Synthesis and Application of Ferroelectric Poly(Vinylidene Fluoride-co-Trifluoroethylene) Films using Electrophoretic Deposition

In this study, we investigated the deposition kinetics of polyvinylidene fluoride copolymerized with trifluoroethylene (P(VDF-TrFE)) particles on stainless steel substrates during the electrophoretic deposition (EPD) process. The effect of applied voltage and deposition time on the structure and ferroelectric property of the P(VDF-TrFE) films was studied in detail. A method of repeated EPD and heat treatment above melting point were employed to fabricate crack-free P(VDF-TrFE) thick films. This method enabled us to fabricate P(VDF-TrFE) films with variable thicknesses. The morphology of the obtained films was investigated by scanning electron microscopy (SEM), and the formation of β-phase was confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. P(VDF-TrFE) films prepared with various thicknesses showed remnant polarization (P_r) of around 4 μC/cm². To demonstrate the applicability of our processing recipe to complex structures, we fabricated a spring-type energy harvester by depositing P(VDF-TrFE) films on stainless steel springs using EPD process. Our preliminary results show that an electrophoretic deposition can be applied to produce high-quality P(VDF-TrFE) films on planar as well as three-dimensional (3-D) substrates.

Visualization of ion transport in Nafion using electrochemical strain microscopy

The local strain change resulting from the proton redistribution and relaxation in Nafion could be visualized using electrochemical strain microscopy.

Effect of Ag nanoparticle concentration on the electrical and ferroelectric properties of Ag/P(VDF-TrFE) composite films

We investigated the effect of the Ag nanoparticles on the ferroelectric and piezoelectric properties of Ag/poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) composite films. We found that the remanent polarization and direct piezoelectric coefficient increased up to 12.14 μC/cm² and 20.23 pC/N when the Ag concentration increased up to 0.005 volume percent (v%) and decreased down to 9.38 μC/cm² and 13.45 pC/N when it increased up to 0.01 v%. Further increase in Ag concentration resulted in precipitation of Ag phase and significant leakage current that hindered any meaningful measurement of the ferroelectric and piezoelectric properties. 46% increase of the remanent polarization value and 27% increase of the direct piezoelectric coefficient were observed in the film with the 0.005 v% of the Ag nanoparticles added without significant changes to the crystalline structure confirmed by both X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) experiments. These enhancements of both the ferroelectric and piezoelectric properties are attributed to the increase in the effective electric field induced by the reduction in the effective volume of P(VDF-TrFE) that results in more aligned dipoles.

Fabrication of Highly Ordered and Well-Aligned PbTiO3/TiN Core-Shell Nanotube Arrays

Highly ordered and well-aligned PbTiO3/TiN core-shell nanotubes are fabricated via an anodic aluminum oxide templating route followed by TiN and TiO2 atomic layer deposition deposition and a subsequent PbO vapor reaction. PbTiO3/TiN nanotubes keep their original shape after the vapor phase reaction, and they display well-defined piezoresponse hysteresis curves with remnant piezoresponse of 38 pm V(-1) .

Vertically aligned P(VDF-TrFE) core-shell structures on flexible pillar arrays

PVDF and P(VDF-TrFE) nano- and micro- structures have been widely used due to their potential applications in several fields, including sensors, actuators, vital sign transducers, and energy harvesters. In this study, we developed vertically aligned P(VDF-TrFE) core-shell structures using high modulus polyurethane acrylate (PUA) pillars as the support structure to maintain the structural integrity. In addition, we were able to improve the piezoelectric effect by 1.85 times from 40 ± 2 to 74 ± 2 pm/V when compared to the thin film counterpart, which contributes to the more efficient current generation under a given stress, by making an effective use of the P(VDF-TrFE) thin top layer as well as the side walls. We attribute the enhancement of piezoelectric effects to the contributions from the shell component and the strain confinement effect, which was supported by our modeling results. We envision that these organic-based P(VDF-TrFE) core-shell structures will be used widely as 3D sensors and power generators because they are optimized for current generations by utilizing all surface areas, including the side walls of core-shell structures.

Selective current collecting design for spring-type energy harvesters

We designed and fabricated a high performance spring-type piezoelectric energy harvester that selectively collects current from the inner part of a spring shell.

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

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

Virus-directed design of a flexible BaTiO3 nanogenerator

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

Effects of an elastic mass on frequency response characteristics of an ultra-thin piezoelectric micro-acoustic actuator

This paper presents an optimized method to improve the sound quality of ultra-thin piezoelectric micro-acoustic actuators. To achieve flat and smooth frequency response characteristics of the piezoelectric acoustic actuators, we have proposed an elastic mass attached to the acoustic diaphragm. The effects of the elastic mass on frequency response characteristics of the piezoelectric acoustic actuator were investigated by finite element analysis simulation and laser scanning vibrometer measurement. Based on the modal and vibrational characteristics, it was found that the fabricated piezoelectric acoustic actuator has a significant dip of 1.32 kHz and peak of 2.24 kHz, which correspond respectively to the (1,3) and (3,1) resonant modes of the acoustic diaphragm. However, by attaching an elastic mass to the acoustic diaphragm with a shape similar to the (3,1) mode, the resonant frequencies corresponding to the (1,3) and (3,1) modes shifted to higher frequencies and the vibrational displacements at each mode were dramatically reduced by about 40%. As a result, the dip at (1,3) mode was greatly improved by 13 dB and total harmonic distortion was dramatically reduced from 80.83% to 8.71%. This paper shows that the optimized elastic mass can allow flat and smooth frequency response characteristics by improving the significant peak and dip.

Fabrication of vertically well-aligned P(VDF-TrFE) nanorod arrays

By combining the merits of traditional template-assisted methods for polymer nanostructure fabrication, we demonstrate an immersion crystallization process that combines features of polymer crystallization and template removal simultaneously. Well-aligned poly(vinylidene fluoride-trifluoroethylene) copolymer nanorod arrays are prepared for the first time via this simple and convenient new method.

Improvement of low-frequency characteristics of piezoelectric speakers based on acoustic diaphragms

The vibrational characteristics of 3 types of the acoustic diaphragms are investigated to enhance the output acoustic performance of the piezoelectric ceramic speaker in a low-frequency range. In other to achieve both a higher output sound pressure level and wider frequency range of the piezoelectric speaker, we have proposed a rubber/resin bi-layer acoustic diaphragm. The theoretical square-root dependence of the fundamental resonant frequency on the thickness and Young's modulus of the acoustic diaphragm was verified by finite-element analysis simulation and laser scanning vibrometer measurement. The simulated resonant frequencies for each diaphragm correspond well to the measured results. From the simulated and measured resonant frequency results, it is found that the fundamental resonant frequency of the piezoelectric ceramic speaker can be designed by adjusting the thickness ratio of the rubber/resin bi-layer acoustic diaphragm. Compared with a commercial piezoelectric speaker, the fabricated piezoelectric ceramic speaker with the rubber/resin bi-layer diaphragm has at least 10 dB higher sound pressures in the low-frequency range of less than 1 kHz.

Biomineralized N-doped CNT/TiO2 core/shell nanowires for visible light photocatalysis

We report an efficient and environmentally benign biomimetic mineralization of TiO(2) at the graphitic carbon surface, which successfully created an ideal TiO(2)/carbon hybrid structure without any harsh surface treatment or interfacial adhesive layer. The N-doped sites at carbon nanotubes (CNTs) successfully nucleated the high-yield biomimetic deposition of a uniformly thick TiO(2) nanoshell in neutral pH aqueous media at ambient pressure and temperature and generated N-doped CNT (NCNT)/TiO(2) core/shell nanowires. Unlike previously known organic biomineralization templates, such as proteins or peptides, the electroconductive and high-temperature-stable NCNT backbone enabled high-temperature thermal treatment and corresponding crystal structure transformation of TiO(2) nanoshells into the anatase or rutile phase for optimized material properties. The direct contact of the NCNT surface and TiO(2) nanoshell without any adhesive interlayer introduced a new carbon energy level in the TiO(2) band gap and thereby effectively lowered the band gap energy. Consequently, the created core/shell nanowires showed a greatly enhanced visible light photocatalysis. Other interesting synergistic properties such as stimuli-responsive wettabilites were also demonstrated.

Quantitative measurement of in-plane cantilever torsion for calibrating lateral piezoresponse force microscopy

A simple quantitative measurement procedure of in-plane cantilever torsion for calibrating lateral piezoresponse force microscopy is presented. This technique enables one to determine the corresponding lateral inverse optical lever sensitivity (LIOLS) of the cantilever on the given sample. Piezoelectric coefficient, d(31) of BaTiO(3) single crystal (-81.62 ± 40.22 pm/V) which was calculated using the estimated LIOLS was in good agreement with the reported value in literature.

Characterization of Retention Phenomena of Micron-Size Electrical Domains in Pzt Thin Films

The retention phenomena of purposely aligned micron-size domains (defined as “bits”) in Pb(Zr,Ti)O3 thin films were characterized by atomic force microscopy (AFM) combined with a lock-in amplifier. It is found that the retention loss occurs by “region by region” showing local variation of the rate of the loss. Furthermore, the total retention loss can be successfully described by an extended exponential decay, which implies a narrow distribution of the relaxation times of the domains. This probably comes from the fact that the micron-size bits consist a few hundreds of domains. Along with the characterization, the effects of the bit size and the poling time per unit area on the retention characteristics were investigated. Based on our observations, it is concluded that the retention time is proportional to both the poling time per unit area and the bit size. This trend is successfully explained by a kinetic model developed by our group.

Quantitative measurements of absolute dielectrophoretic forces using optical tweezers

Optical tweezers were used for quantitative measurement of the absolute dielectrophoresis (DEP) forces acting on polystyrene microparticles. The electrodes and tweezers were configured to create one-dimensional DEP forces acting perpendicular to the tweezers' beam. The influences of various external factors, such as applied voltage frequency, conductivity of the medium, and particle size on the measurement were estimated. By accounting for these factors, actual measurements were in close agreement with theoretical predictions. Our results show that the optical tweezers may serve as a unique tool for the measurement of DEP forces in various applications.

AC frequency characteristics of coplanar impedance sensors as design parameters

Glass-based microchannel chips were fabricated using photolithographic technology, and Pt thin-film microelectrodes, as coplanar impedance sensors, were integrated on them. Longitudinal design parameters, such as interelectrode spacing and electrode width, of coplanar impedance sensors were changed to determine AC frequency characteristics as design parameters. Through developing total impedance equations and modeling equivalent circuits, the dominant components in each frequency region were illustrated for coplanar impedance sensors and the measured results were compared with fitted values. As the ionic concentration increased, the value of the frequency-independent region decreased and cut-off frequencies increased. As the interelectrode spacing increased, cut-off frequencies decreased and total impedance increased. However, the width of each frequency-independent region was similar. As the electrode area increased, f(low) decreased but f(high) was fixed. We think that the decrease in R(Sol) dominated over the influence of other components, which resulted in heightening f(low) and f(high). The interelectrode spacing is a more significant parameter than the electrode area in the frequency characteristics of coplanar sensors. The deviation of experimentally obtained results from theoretically predicted values may result from the fringing effect of coplanar electrode structure and parasitic capacitance due to dielectric substrates. We suggest the guidelines of dominant components for sensing as design parameters.

Attenuated phase-shifting masks of chromium aluminum oxide

Chromium aluminum oxide was chosen as a new candidate for use as an attenuated phase-shifting mask (Att-PSM) material. The compositions of films were correlated with optical properties. With the measured and the fitted data, we simulated the transmittance and the phase shift using the matrix method. Consequently, we acquired optimum parameters for Att-PSM's, such as Al/Cr = 1.9-2.5 and d = 120 nm at a 193-nm wavelength, Al/Cr = 1.0-1.7 and d = 128 nm at a 248-nm wavelength, and Al/Cr = 0-0.1 and d = 170 nm at a 365-nm wavelength. This simulation was verified by transmittance measurement.

Simulation and fabrication of attenuated phase-shifting masks: CrF(x)

To acquire the required resolution for 248- and 193-nm lithography, a study of attenuated phase-shifting mask (Att-PSM) technology is in progress. We performed a simulation study using a matrix method to calculate relative transmittance and the amount of phase shift of light through the PSM. However, we found that the average film composition changed with deposition time. Accordingly, optical constants were found to be a strong function of film thickness. Therefore we rearranged the relationship between deposition parameters (e.g., deposition time or gas flow rate ratio) and optical constants (e.g., refractive index and extinction coefficient) to extract the empirical formula for the optical constants with respect to film composition. To verify our simulation study, we fabricated a phase shifter based on our simulation result, which was found to have a transmittance of 8.3% and a phase shift of 179.5 degrees . Consequently, we obtained a reliable optimum condition for the deep-ultraviolet Att-PSM.

Titanium oxide film for the bottom antireflective layer in deep ultraviolet lithography

Titanium oxide thin film, fabricated with tetraisopropyltitanate and oxygen by electron cyclotron resonance-plasma-enhanced chemical vapor deposition, is investigated as a potential candidate for the antireflective layer in KrF excimer laser (248-nm) lithography. The oxygen flow-rate dependence of the optical properties such as the refractive index (n) and the extinction coefficient (k) of the film at the 248-nm wavelength has been characterized, and the films with the expected combinations of n and k values for the antireflective layer have been deposited. Simulation results indicate that reflectance values of less than 4% and as low as 1.2% can be reached at the interface between the photoresist and the film postulating the structures of the photoresist/300-A TiO(x) film/c-Si substrate and the W-Si substrate, respectively, by selected proper combinations of n and k values. Moreover the reflectance can be further reduced to almost zero by changing the film thickness. Thus it is found that titanium oxide thin films can be used as the bottom antireflective layer in KrF excimer laser lithography.

Phenyl-substituted prostaglandins: potent and selective antiglaucoma agents

A series of phenyl-substituted analogues of prostaglandin F2 alpha (PGF2 alpha) were prepared and evaluated for ocular hypotensive effect and side effects in different animal models. In addition, the activity of the analogues on FP receptors was studied in vitro. The results were compared with those of PGF2 alpha and its isopropyl ester. The phenyl-substituted PGF2 alpha analogues exhibited good intraocular pressure reducing effect, were more selective, and exhibited a much higher therapeutic index in the eye than PGF2 alpha or its isopropyl ester. The analogues exhibited high activity on FP receptors in a stereoselective manner for the 15 alpha-hydroxyl group.