Properties of piezoelectric ceramic with textured structure for energy harvesting

Piezoelectric ceramics with microstructure texturing were fabricated and evaluated to investigate its feasibility to use in piezoelectric energy harvesting in response to external mechanical impact. Textured 0.945(Bi_0.5Na_0.5)TiO₃–0.55BaTiO₃ (BNTBT) ceramics were prepared by tape casting of slurries containing a template SrTiO₃ (STO). The orientation factor of more than 60% was obtained successfully when a plate-like SrTiO₃ was used as the templates using a tape casting process. The sections perpendicular to the sheet plane of BNTBT ceramics exhibited preferentially [0 0 1] oriented orientation. Under low stress-loading, the voltage and power value of STO-added BNTBT were slightly higher than those of the specimen without STO. Meanwhile, the STO-added specimens showed excellent power over the STO-free specimen when a high stress was applied. When low stress was applied to the specimens, the reduction of piezoelectric characteristics by the addition of STO in BNTBT may be prominent in that the mixture of ferroelectric BNTBT and the non-ferroelectric STO has less ferroelectric features compared with the pure ferroelectric BNTBT. In contrast, under high field and stress signal the textured microstructure along to 〈1 0 0〉 is a feature of the improved piezoelectric behavior.     

Prediction and characterization of drug release in a multi-drug release system

A new drug delivery system (DDS) was prepared by electrospinning and multi-layered coating methods. Lactobacillus was used as a target drug for release in the large intestine. Lactobacillus was incorporated into polyvinyl alcohol-based electrospun fibers. Alginate and chitosan were then used to coat these fibers to protect and deliver lactobacillus to the large intestine. The multi-layered coating procedure was carried out at various coating times to determine the optimal coating amount in human digestion conditions. The drug-release experiment was conducted using an in vitro model of human digestion processes. Chitosan and alginate were released by dissolving in acid and neutral conditions, respectively. Lactobacillus was then released in a large intestine model by the hydrogel swelling effects of PVA-based electrospun fibers. The drug-release behavior was predicted by calculated equations for optimized coating times. Eventually, the lactobacillus was effectively delivered to the target large intestine by chitosan and alginate coating and was released by PVA hydrogel swelling.     

Thermal conductivity of a graphene oxide–carbon nanotube hybrid/epoxy composite

Thermally conductive graphene oxide (GO)–multi-wall carbon nanotube (MWCNT)/epoxy composite materials were fabricated by epoxy wetting. The polar functionality on the GO surface allowed the permeation of the epoxy resin due to a secondary interaction between them, which allowed the fabrication of a composite containing a high concentration of this hybrid filler. The thermal transport properties of the composites were maximized at 50 wt.% of filler due to fixed pore volume fraction in filtrated GO cake. When the total amount of filler was fixed 50 wt.% while changing the amount of MWCNTs, a maximum thermal conductivity was obtained with the addition of about 0.36 wt.% of MWCNTs in the filler. Measured thermal conductivity was higher than the predicted value based on the by Maxwell–Garnett (M–G) approximation and decreased for MWCNT concentrations above 0.4%. The increased thermal conductivity was due to the formation of 3-D heat conduction paths by the addition of MWCNTs. Too high a MWCNT concentration led to increased phonon scattering, which in turn led to decreased thermal conductivity. The measured storage modulus was higher than that of the solvent mixed composite because of the insufficient interface between the large amount of filler and the epoxy.     

Effect of chemically reactive species on properties of ZnO nanowires exposed to oxygen and hydrogen plasma

We present a systematic study on the effect of oxygen and hydrogen plasma-generated reactive species on the properties of ZnO nanowires. Upon exposure to oxygen plasma, the electrical conductivity of an individual ZnO nanowire decreased with substantial changes in the surface chemistry, indicating a decrease in the number of donor-like defects and an increase in the number of electron-trapping species. In contrast, an individual ZnO nanowire exposed to hydrogen plasma showed a drastic increase in conductivity up to two orders of magnitude due to the incorporated hydrogen acting as a shallow donor inside the ZnO nanowires without a sputtering process.     

Ultrasonic Approach of Rayleigh Pitch-catch Contact Ultrasound Waves on CFRP Laminated Composites

CFRP （carbon fiber reinforced plastics） composite materials have wide applicability because of their inherent design flexibility and improved material properties. However, impacted composite structures have 50%-75% less strength than undamaged structures. In this work, a CFRP composite material was nondestructively characterized in order to ensure product quality and structural integrity of CFRP and one-sided pitch-catch technique was developed to measure impacted-damaged area by using an automated-data acquisition system in an immersion tank. A pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave under defect conditions in the composite.     

Molecular simulation study on adhesions and deformations for Polymethyl Methacrylate (PMMA) resist in nanoimprint lithography

The NIL (nanoimprint lithography) process is explored through numerical simulation, utilizing MD (molecular dynamics), with a focus on the resin deformations and the adhesion between the resin material and the tool. For the force-field of the Polymethyl Methacrylate (PMMA), used for the resin material, a united atom model is employed. For temperature control in the MD simulation, the recursive multiple chains of the Nosé-Poincaré thermostat is applied. The deformation and adhesion in the NIL process are explored from the mechanics viewpoint based on the present MD results. In particular, the adhesion behavior of a self-assembly monolayer (SAM) in the stamp-releasing stage is discussed in connection with the monolayer thickness.     

Extraction behaviors of caffeine and chlorophylls in supercritical decaffeination of green tea leaves

The decaffeination of green tea using supercritical carbon dioxide (SC-CO₂) was optimized by response surface methodology (RSM) for the maximal removal of caffeine, and the coextration of chlorophylls was also monitored during decaffeination. The experimental conditions for the SC-CO₂ extraction of caffeine were set up according to the Box-Behnken design of RSM. The relationships between the extraction yield of caffeine and various parameters used for the SC-CO₂ extraction such as pressure, temperature and concentration of ethanol were studied at a fixed CO₂ flow rate. The extraction yields of caffeine and total chlorophyll were significantly influenced by extraction pressure, temperature and concentration of cosolvent, and their extraction yields behaved almost in parallel at different extraction conditions that were obtained by varying pressure, temperature and ethanol cosolvent concentration. At the optimal decaffeination conditions such as 3.0 g of 95% (v/v) ethanol cosolvent per 100 g of CO₂, 23 MPa, 63 °C and an extraction duration of 120 min for 10 g of green tea leaves, the extraction yields for caffeine and catechins were 96.60% (w/w) and 40.61% (w/w), respectively, and the substantial coextraction of total chlorophyll (43.09% of the total amount) was also observed during the decaffeination process.     

Residual stress behaviors induced by laser peening along the edge of curved models

Laser peening (LP) induces high-magnitude compressive residual stresses in a small region of a component. The compressive residual stresses cause plastic deformation that is resistant to fatigue fracture. Fatigue cracks are generally nucleated at critical areas, and LP is applied for those regions so as to delay the crack initiation. Many critical regions are located on the edge of the curved portion of structures because of stress concentration effects. Several investigations that are available for straight components may not give meaningful guidelines for peening curved components. Therefore, in this paper, we investigate residual stress behaviors induced by LP along the edge of curved models. Three curved models that have different curvatures are investigated for peening performance. Two types of peening configurations, which are simultaneous corner shot and sequential corner shots, are considered in order to obtain compressive residual stresses along an edge. LP simulations of multiple shots are performed to identify overlapping effects on the edge portion of a curved model. In addition, the uncertainty calculation of residual stress induced by LP considering laser pulse duration is performed.     

Corrugated structure through a spin-coating process for enhanced light extraction from organic light-emitting diodes

We have demonstrated a simple fabrication method for an out-coupling structure to enhance light extraction from organic light-emitting diodes (OLEDs). Spin-coating of SiO₂ and TiO_x sol mixture solution develops corrugated film. The structural evolution of the corrugation was explained by the localization of surface tension during the solvent evaporation. The structural parameters of the corrugated structure were characterized by varying the spin-coating speed and the mixing ratio of the solution. Compared to conventional devices, OLEDs with a corrugated structure at the backside of the glass substrate showed increased external quantum efficiency without change in the electroluminescence spectrum. The light extraction enhancement is attributed to the decreased incidence angle at the interface of glass substrate and air.     

Oxygen Ion Drift‐Induced Complementary Resistive Switching in Homo TiOx/TiOy/TiOx and Hetero TiOx/TiON/TiOx Triple Multilayer Frameworks

Developing a means by which to compete with commonly used Si‐based memory devices represents an important challenge for the realization of future three‐dimensionally stacked crossbar‐array memory devices with multifunctionality. Therefore, oxide‐based resistance switching memory (ReRAM), with its associated phenomena of oxygen ion drifts under a bias, is becoming increasingly important for use in nanoscalable crossbar arrays with an ideal memory cell size due to its simple metal–insulator–metal structure and low switching current of 10–100 μA. However, in a crossbar array geometry, one single memory element defined by the cross‐point of word and bit lines is highly susceptible to unintended leakage current due to parasitic paths around neighboring cells when no selective devices such as diodes or transistors are used. Therefore, the effective complementary resistive switching (CRS) features in all Ti‐oxide‐based triple layered homo Pt/TiO_x/TiO_y/TiO_x/Pt and hetero Pt/TiO_x/TiON/TiO_x/Pt geometries as alternative resistive switching matrices are reported. The possible resistive switching nature of the novel triple matrices is also discussed together with their electrical and structural properties. The ability to eliminate both an external resistor for efficient CRS operation and a metallic Pt middle electrode for further cost‐effective scalability will accelerate progress toward the realization of cross‐bar ReRAM in this framework.