Maximizing Photoelectrochemical Performance in Metal-Oxide Hybrid Composites via Amorphous Exsolution-A New Exsolution Mechanism for Heterogeneous Catalysis.

Exsolution generates metal nanoparticles anchored within crystalline oxide supports, ensuring efficient exposure, uniform dispersion, and strong nanoparticle-perovskite interactions. Increased doping level in the perovskite is essential for further enhancing performance in renewable energy applications; however, this is constrained by limited surface exsolution, structural instability, and sluggish charge transfer. Here, hybrid composites are fabricated by vacuum-annealing a solution containing SrTiO3 photoanode and Co cocatalyst precursors for photoelectrochemical water-splitting. In situ transmission electron microscopy identifies uniform, high-density Co particles exsolving from amorphous SrTiO3 films, followed by film-crystallization at elevated temperatures. This unique process extracts entire Co dopants with complete structural stability, even at Co doping levels exceeding 30%, and upon air exposure, the Co particles embedded in the film oxidize to CoO, forming a Schottky junction at the interface. These conditions maximize photoelectrochemical activity and stability, surpassing those achieved by Co post-deposition and Co exsolution from crystalline oxides. Theoretical calculations demonstrate in the amorphous state, dopant─O bonds become weaker while Ti─O bonds remain strong, promoting selective exsolution. As expected from the calculations, nearly all of the 30% Fe dopants exsolve from SrTiO3 in an H2 environment, despite the strong Fe─O bond's low exsolution tendency. These analyses unravel the mechanisms driving the amorphous exsolution.

High Performance, Stable, and Flexible Piezoelectric Nanogenerator Based on GaN:Mg Nanowires Directly Grown on Tungsten Foil.

Rapid development of micro-electromechanical systems increases the need for flexible and durable piezoelectric nanogenerators (f-PNG) with high output power density. In this study, a high-performance, flexible, and highly stable f-PNG is prepared by directly growing the Mg-doped semi-insulating GaN nanowires (NWs) on a 30-µm-thick tungsten foil using vapor-liquid-solid growth mechanism. The direct growth of NWs on metal foil extends the overall lifetime of the f-PNG. The semi-insulating GaN NWs significantly enhance the piezoelectric performance of the f-PNG by reducing free electron density. Additionally, the direct integration of NWs on the tungsten foil improves the conductivity, resulting in current enhancement (2.5 mA) with an output power density of 13 mW cm-2 . The piezoelectric performance of the f-PNG is investigated under several bending angles, actuation frequencies, continuous vibrations, and airflow velocities. The maximum output voltage exhibited by the f-PNG is 20 V at a bending angle of 155°. The f-PNG is connected to the backside of an index finger to monitor finger bending behavior by changing the current density. Depending on its flexibility and sensitivity, the f-PNG can be used as a health-monitoring sensor to be mounted on joints (fingers, hands, elbows, and knees) to monitor their repeated bending and relaxation.

Enhanced stability of piezoelectric nanogenerator based on GaN/V2O5 core-shell nanowires with capacitive contact.

Enhanced stability of a piezoelectric nanogenerator (PNG) was demonstrated using c- and m-axis GaN/V2O5 core-shell nanowires (NWs) by analyzing the capacitive coupling of the PNG's output. The NW array grown on GaN thin film was embedded in polydimethylsiloxane (PDMS) matrix, following which the matrix was transferred to an indium (In)-coated PET substrate for achieving superior flexibility of the PNG. The stability of the PNG was enhanced by holding the NW PDMS composite with a PDMS polymer as a bonding material on the PET substrate. The inserted PDMS layer improved the lifetime of the PNG, however, because of the insulating nature of PDMS, the piezoelectric output of GaN NWs was coupled capacitively to In contact on PET substrate and it resulted in a slight degradation of piezoelectric output due to the voltage drop across the bottom capacitive contact. The maximum piezoelectric current was 64 nA and output voltage was 11.9 V from the PNG with c-axis NWs. While the PNG with direct bottom contact exhibited 57% output reduction after 72 000 operation cycles, the PNG with capacitive contact did not show any degradation in stability even after 150 000 cycles.

Solar hydrogen generation: feature introduction.

The expected depletion of fossil fuel reserves and its severe environmental impact have brought about the need for sustainable and clean energy resources. Solar hydrogen generation via photoelectrochemical (PEC) water splitting techniques, which combine sunlight, water, and semiconductor materials, are promising alternatives to conventional fossil fuels. Solar-hydrogen fuel produced using PEC methods are renewable, sustainable and environmentally friendly.

Type-II ZnO/ZnS core-shell nanowires: Earth-abundant photoanode for solar-driven photoelectrochemical water splitting.

A core-shell structure, formed in a nanostructured photoanode, is an effective strategy to achieve high solar-to-hydrogen conversion efficiency. In this study, we present a facile and simple synthesis of a unique vertically aligned ZnO/ZnS core-shell heterostructure nanowires (NWs) on a Si substrate. Well-aligned ZnO NWs were grown on Si (100) substrates on a low-temperature ZnO buffer layer by metal-organic chemical vapor deposition. The ZnO NWs were then coated with various thicknesses of ZnS shell layers using atomic layer deposition. The structural characterizations exhibit the well-developed ZnO/ZnS core-shell NWs heterostructure. The as-prepared ZnO/ZnS core-shell NWs was applied as photoanode for photoelectrochemical (PEC) water splitting. This unique ZnO/ZnS core-shell NWs photoanode shows photocurrent density of 1.21 mA cm-2, which is 8.5 times higher than bare ZnO NWs. The PEC performance and the applied-bias-photon-to-current conversion efficiency of ZnO/ZnS core-shell NWs photoanode are further improved with the optimized ZnS shell. The type-II band alignment of the heterostructure photoanode is the key factor for their excellent PEC performance. Importantly, this type of core-shell NWs heterostructure provides useful insights into novel electrode design and fabrication based on earth abundant materials for low-cost solar fuel generation.

Enhanced photoelectrochemical stability of GaN photoelectrodes by Al2O3 surface passivation layer.

Photoelectrochemical (PEC) water splitting is one of the most promising hydrogen production methods because of its high efficiency, renewable resources and harmless by-products. Gallium nitride (GaN) is suitable for PEC water splitting because it has excellent stability in electrolyte and band gap energy which straddles the redox potential of water (Vredox = 1.23 V). These characteristics allow this material to split water stably without external bias. However, the stability of GaN is still not sufficient for practical applications. In this study, we investigated the properties of GaN photoelectrodes with aluminum oxide (Al2O3) thin film as a protection layer for increasing stability. In a long-term stability test, Al2O3-coated GaN showed more stable photocurrent than that of bare GaN. The total hydrogen production amount was also improved in Al2O3-coated samples than bare GaN. These results indicate that the Al2O3 protection layer significantly enhances stability and hydrogen production.

Optically pumped GaN vertical cavity surface emitting laser with high index-contrast nanoporous distributed Bragg reflector.

Laser operation of a GaN vertical cavity surface emitting laser (VCSEL) is demonstrated under optical pumping with a nanoporous distributed Bragg reflector (DBR). High reflectivity, approaching 100%, is obtained due to the high index-contrast of the nanoporous DBR. The VCSEL system exhibits low threshold power density due to the formation of high Q-factor cavity, which shows the potential of nanoporous medium for optical devices.

Brachial-ankle pulse wave velocity and mean platelet volume as predictive values after percutaneous coronary intervention for long-term clinical outcomes in Korea: A comparable and additive study.

This study aimed to determine the association of the brachial-ankle pulse wave velocity (baPWV) and mean platelet volume (MPV) with the development of adverse outcomes after percutaneous coronary intervention (PCI). The baPWV and MPV were analyzed in 372 patients who underwent PCI, with the primary endpoint as cardiac death. The secondary endpoint was cardiovascular events (CVE): a composite of cardiac death, myocardial infarction (MI), target vessel revascularization (TVR), ischemic stroke, and stent thrombosis (ST). During the follow-up period (mean, 25.8 months), there were 21 cardiac deaths, 10 MIs including four events of ST, seven ischemic strokes, and 29 TVRs. The baPWV cut-off level was set at 1672 cm/s using the receiver operating characteristic curve; the sensitivity and specificity was 85.7 and 60.1%, respectively, to differentiate between the groups with and without cardiac death. The MPV cut-off level was set at 8.20 fL using the receiver operating characteristic curve; the sensitivity and specificity were 81 and 53.3%, respectively, to differentiate between the groups with and without cardiac death. Kaplan-Meier analysis revealed that the higher baPWV group (≥ 1672 cm/s) had a significantly higher cardiac death and CVE rate than the lower baPWV group (<1672 cm/s) (11.4 vs. 1.4%, log-rank: p < 0.0001; 25.3 vs. 7.5%, log-rank: p < 0.0001; respectively), and the higher MPV group (median, >8.20 fL,) had a significantly higher cardiac death and CVE rate than the lower MPV group (≤ 8.20 fL) (9.4 vs. 2.1%, log-rank: p = 0.0026; 23.8 vs. 6.8%, log-rank: p < 0.0001; respectively). Furthermore, the high baPWV and MPV groups were significantly associated with an increased risk of cardiac death. These results show that baPWV and MPV are predictive markers after PCI for cardiac death; they are also additively associated with a higher risk of cardiac death.

Self assembled growth of GaSb nano triangles on GaN/sapphire substrate.

Self-assembled GaSb nano structures were grown on GaN/sapphire. GaSb nano triangles as well as quantum dots were obtained under controlled growth conditions. Nano triangles were grown at 580 degrees C due to the growth rate anisotropy among the (1100) planes. The size of nano triangle was 87 nm in width, 5 nm in height, and the density was 5 x 10(8) cm(-2), when the growth time was 30 s. This is the first report on the self assembled growth of nano triangles within a highly strained material system.

Surface passivation of high density InGaN/GaN nanorods fabricated by reactive ion etching.

High density GaN nanorods containing InGaN quantum disks (QD's) were fabricated by inductively coupled plasma reactive ion etching (RIE) with self-assembled nano masks. Optical properties of the QD were severely degraded because of the damage on etched sidewalls during the RIE. However, after surface treatment with (NH4)2S, the QD showed improved photoluminescence. This result suggests that surface damage of GaN nanostructure during the dry etching can be passivated by sulfur atoms.

Improvement in crystal quality and optical properties of n-type GaN employing nano-scale SiO2 patterned n-type GaN substrate.

n-type GaN epitaxial layers were regrown on the patterned n-type GaN substrate (PNS) with different size of silicon dioxide (SiO2) nano dots to improve the crystal quality and optical properties. PNS with SiO2 nano dots promotes epitaxial lateral overgrowth (ELOG) for defect reduction and also acts as a light scattering point. Transmission electron microscopy (TEM) analysis suggested that PNS with SiO2 nano dots have superior crystalline properties. Hall measurements indicated that incrementing values in electron mobility were clear indication of reduction in threading dislocation and it was confirmed by TEM analysis. Photoluminescence (PL) intensity was enhanced by 2.0 times and 3.1 times for 1-step and 2-step PNS, respectively.

Epitaxial growth of 1D GaN-based heterostructures on various substrates for photonic and energy applications.

GaN is an important III-V semiconductor for a variety of applications owing to its large direct band gap. GaN nanowires (NWs) have demonstrated significant potential as critical building blocks for nanoelectronics and nanophotonic devices, as well as integrated nanosystems. We present a comprehensive analysis of the vapor-liquid-solid (VLS) as a general synthesis technique for NWs on a variety of substrates, the morphological and structural characterization, and applications of GaN NWs in piezoelectric nanogenerators, light-emitting diodes, and solar-driven water splitting. We begin by summarizing the overall VLS growth process of GaN NWs, followed by the growth of NWs on several substrates. Subsequently, we review the various uses of GaN NWs in depth.

Technological Breakthroughs in Chip Fabrication, Transfer, and Color Conversion for High-Performance Micro-LED Displays.

The implementation of high-efficiency and high-resolution displays has been the focus of considerable research interest. Recently, micro light-emitting diodes (micro-LEDs), which are inorganic light-emitting diodes of size <100 µm2 , have emerged as a promising display technology owing to their superior features and advantages over other displays like liquid crystal displays and organic light-emitting diodes. Although many companies have introduced micro-LED displays since 2012, obstacles to mass production still exist. Three major challenges, i.e., low quantum efficiency, time-consuming transfer, and complex color conversion, have been overcome with technological breakthroughs to realize cost-effective micro-LED displays. In the review, methods for improving the degraded quantum efficiency of GaN-based micro-LEDs induced by the size effect are examined, including wet chemical treatment, passivation layer adoption, LED structure design, and growing LEDs in self-passivated structures. Novel transfer technologies, including pick-up transfer and self-assembly methods, for developing large-area micro-LED displays with high yield and reliability are discussed in depth. Quantum dots as color conversion materials for high color purity, and deposition methods such as electrohydrodynamic jet printing or contact printing on micro-LEDs are also addressed. This review presents current status and critical challenges of micro-LED technology and promising technical breakthroughs for commercialization of high-performance displays.

Effect of varying pore size of AAO films on refractive index and birefringence measured by prism coupling technique.

Anodic aluminum oxide (AAO) films with different pore sizes were prepared to modulate the effective refractive index and birefringence. To investigate the relationship between the refractive index and the pore size of the AAO film, optical constants were obtained using a prism coupler with various lasers. With experimental results, the dispersion curve of alumina itself without pores was extracted using a theoretical anisotropic model. We demonstrated that AAO films could offer a wide range of refractive index and birefringence values for optical device applications. Furthermore, index profiles as a function of the thickness of the AAO films were obtained by inverse Wentzel-Kramer-Brillouin approximation to examine the optical homogeneity.

Optical properties of porous anodic alumina membrane uniformly decorated with ultra-thin porous gold nanoparticles arrays.

In this paper, we directly develop a facile method to decorate a modified porous anodic alumina membrane (PAA) with an ultrathin porous film of gold nanoparticles with sub-gaps less than 25 nm and particle size less than 40 nm on the top surface and Au nanoparticles uniformly attached to the pore walls as well as the bottom of the pores, utilizing radio-frequency magnetron sputtering. The size as well as the interparticle distance of the gold nanostructures is adjusted by changing the structural properties of PAA membrane and the sputtering time. According to the measured reflection spectra, the saturation of interference color is significantly enhanced. As a result, the Au-coated PAA membrane exhibits a brilliant and tunable color. Field enhancement can be achieved in these structures through the excitation and constructive interference of surface plasmon waves. In addition, the role of localized surface plasmon and propagating surface plasmon was discussed. A four-layered model is presented to describe the reflectance data that show excellent agreement with the experimental data. The brilliant Au-coated PAA membrane is useful for decorative purposes and holds promise as an effective surface enhanced Raman scattering (SERS) substrate.

Fabrication of ordered Cr nanostructures by self agglomeration on porous anodic alumina membranes.

In this paper, we propose an efficient and effective method to fabricate highly ordered Cr nanoarrays with sub-gaps less than 15 nm and particle size less than 50 nm on the top surface of a modified porous anodic alumina membrane (PAA). In addition, the factors that influence the structural parameters of the fabricated nanostructures were studied. With the aid of SEM and AFM images, the amount of sputter-coated Cr was tailored to the given PAA surface morphology. The mechanism of formation of the Cr nanostructures was also discussed.

Nanostructured CuO with a thin g-C3N4 layer as a highly efficient photocathode for solar water splitting.

A g-C3N4/CuO nanostructure featuring improved photoelectrochemical properties was successfully prepared using a facile and cost-effective method involving electrodeposition and thermal oxidation. The improved photoelectrochemical properties were mainly ascribed to the increased surface area and improved charge transportation of the g-C3N4/CuO photocathode. This photocathode can be used in novel strategies for resolving problems associated with low-efficiency CuO photocathodes.

GaN Nanowire Growth Promoted by In-Ga-Au Alloy Catalyst with Emphasis on Agglomeration Temperature and In Composition.

The crystallographic orientation control of GaN nanowires (NWs) has been widely investigated by varying the V-III ratio. Here, we report the tuning of crystallographic orientation of GaN NWs by varying the composition of indium (In) in gallium-gold (Ga-Au) alloy catalyst using metal-organic chemical vapor deposition (MOCVD). The c-plane GaN thin film and sapphire substrate are used as growth templates. We found that the substrates of same orientation have a negligible influence on the orientation of the GaN NWs. The catalyst composition and the dimensions of alloy droplets determine the morphology of the NWs. The density of the NWs was controlled by tuning the droplet size of the alloy catalysts. With the constant V/III ratio, the crystallographic orientation of the GaN NWs was tuned from m- to c-axis by increasing the In composition inside alloy catalyst.

Antinociceptive effect of intrathecal P7C3 via GABA in a rat model of inflammatory pain.

The recently identified molecule P7C3 has been highlighted in the field of pain research. We examined the effect of intrathecal P7C3 in tissue injury pain evoked by formalin injection and determined the role of the GABA system in the activity of P7C3 at the spinal level. Male Sprague-Dawley rats with intrathecal catheters implanted for experimental drug delivery were studied. The effects of intrathecal P7C3 and nicotinamide phosphoribosyltransferase (NAMPT) administered 10 min before the formalin injection were examined. Animals were pretreated with bicuculline, a GABA-A receptor antagonist; saclofen, a GABA-B receptor antagonist; L-allylglycine, a glutamic acid decarboxylase (GAD) blocker; and CHS 828, an NAMPT inhibitor; to observe involvement in the effects of P7C3. The effects of P7C3 alone and the mixture of P7C3 with GABA receptor antagonists on KCl-induced calcium transients were examined in rat dorsal root ganglion (DRG) neurons. The expression of GAD and the concentration of GABA in the spinal cord were evaluated. Intrathecal P7C3 and NAMPT produced an antinociceptive effect in the formalin test. Intrathecal bicuculline, saclofen, L-allylglycine, and CHS 828 reversed the antinociception of P7C3 in both phases. P7C3 decreased the KCl-induced calcium transients in DRG neurons. Both bicuculline and saclofen reversed the blocking effect of P7C3. The levels of GAD expression and GABA concentration decreased after formalin injection and were increased by P7C3. These results suggest that P7C3 increases GAD activity and then increases the GABA concentration in the spinal cord, which in turn may act on GABA receptors causing the antinociceptive effect against pain evoked by formalin injection.

Strong surface plasmon resonance of ordered gold nanorod array fabricated in porous anodic alumina template.

High-density, uniform-sized and vertically aligned gold nanorods were grown on aluminum substrate by DC electrodeposition into modified porous anodic alumina (PAA) template. Optical reflection measurements using s- and p-polarized light showed strong surface plasmon resonances (SPRs), for both Au/PAA composites and freestanding Au nanorod arrays. By changing the aspect ratio of the Au nanorods, the angle of incidence of the polarized light, and the dielectric environment, it was possible to vary the position and the intensity of the SPR reflection minima in a reproducible and predictable manner. We successfully measured higher order transverse SPR, which proves the formation of highly uniform Au nanorods.