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Improvement of energy storage properties with the reduction of depolarization temperature in lead-free (1?–? <i>x</i> )Na <sub/>0.5</sub> Bi <sub/>0.5</sub> TiO <sub/>3</sub> - <i>x</i> AgTaO <sub/>3</sub> ceramics
摘要： The effects of electric field and temperature on structural, dielectric, and ferroelectric properties of (1 – x)(Na0.50Bi0.50TiO3)-xAgTaO3 (x = 0, 0.03, 0.05, and 0.10) ceramics prepared via the modified sol-gel method were investigated. Rietveld refinement of synchrotron radiation x-ray diffraction data (SRPXRD) confirmed the rhombohedral (R3c) phase in all the unpoled samples. After poling, the samples remained in the rhombohedral phase for x ≤ 0.03, whereas for x ≥ 0.05, it showed a mixed rhombohedral and tetragonal (P4bm) phase. The anti-phase octahedral tilt angle was found to increase from 8.49° to 9.50° (for x = 0) and from 7.60° to 7.85° (for x = 0.10) with poling due to the long-range ordering phenomenon in the lattice system. The temperature-dependent dielectric study showed that the depolarization temperature decreases with increasing composition. Unpoled x = 0.10 composition exhibited the wide thermal stability dielectric constant in the temperature range 120-450 °C with 1795 ± 15% (tan δ < 0.041). Polarization versus electric field measurement revealed that at room temperature, the presence of anti-ferroelectric ordering increases the energy storage efficiency from 2.6% (for x = 0) to 48.2% (for x = 0.10). With increasing temperature, it increased from 48.2% (30 °C) to 85.5% (140 °C) for x = 0.10 composition. Improvement in the energy storage efficiency was correlated with structural changes probed by temperature dependent SRPXRD measurements; it confirmed the increase in antiferroelectric ordering with increasing temperature. Dielectric and ferroelectric results indicate the usefulness of this material system in the field of wide thermal stability dielectric constant and high-temperature energy storage applications.
更新于2025-09-19 17:15:36
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Spirobifluorene-based oligopyridine derivatives as electron-transporting materials for green phosphorescent organic light-emitting diodes
摘要： The electron-transporting materials (ETMs), 2,7-bis(3,5-di(pyridin-3-yl)phenyl)-9,9'-spirobi[fluorene] (3-4PySF) and 2,7-bis(3,5-di(pyridin-4-yl)phenyl)-9,9'-spirobi[fluorene] (4-4PySF) were designed and synthesized by combining spirobifluorene moiety with di(pyridine-3-yl)phenyl and di(pyridine-4-yl)phenyl, respectively. The spirobifluorene moiety improves materials’ rigid twisted structure to ensure the morphological stability of amorphous film, and pyridine acts as electron acceptor to enhance electron-transporting ability of materials. The dependence of electron-transporting property on the position of substituted pyridine rings was studied. The melting point (Tm) of 4-4PySF is estimated to be 41 ℃ higher than that of 3-4PySF. And the higher current density in the electron only devices exhibited by 4-4PySF revealed the effect of nitrogen atom position on the charge-transporting properties. Green PhOLEDs based on bis(2-phenylpyridine)iridium(III)(2,2,6,6-tetramethylheptane-3,5-diketonate) (Ir(ppy)2tmd) as the emitter and 3-4PySF, 4-4PySF and 1,3,5-tris(N-phenylbenzimidazol-2-yl-benzene (TPBi) as ETMs were fabricated. Compared to the device based on the conventional ETM TPBi, the devices based on new ETMs exhibited a higher maximum external quantum efficiency (EQE) of 20.5% and a lower turn-on voltage (Von) of 2.6 V.
关键词： electron-transporting material,intermolecular interaction,oligopyridine,organic light-emitting diode,spirobifluorene
更新于2025-09-19 17:13:59
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Thermo mechanical analyses and characterizations of TiNiCu shape memory alloy structures developed by laser additive manufacturing
摘要： Three di?erent compositions of TiNiCu (Ti50Ni (50?x) Cux (x = 10, 20 and 30)) shape memory alloys (SMA) were developed using an intelligent manufacturing technique of laser additive manufacturing (LAM). Based on a numerical analysis the nature and amount of residual stress ?ow was predicted. By implementing ?nite element method (FEM) with Gaussian distributed volumetric heat source, the deposition process was simulated. The numerical and experimental analyses were at par with each other. The developed samples were subjected to several characterizations in order to determine the best among them. Scanning electron microscopy (SEM), atomic force microscopy (AFM), were used to study the surface morphology of the samples. The mechanical properties were studied using micro-hardness test and compression test. X-Ray di?raction (XRD) was deployed to investigate the crystalline nature of the samples. The phase transformation ability of the samples were determined by di?erential scanning calorimetry (DSC). The SEM revealed the deposition of all three samples to be homogeneous. The AFM results showed the grain size of TiNiCu10 to be 20.12 nm, the smallest among the samples. The micro-hardness and ultimate strength of TiNiCu10 was found to be 242 VHN and MPa respectively. XRD reveals the presence of three step transformation for TiNiCu20 sample. From the results, LAM process was considered as a successful methodology in developing TiNiCu bulk SMA structures. The properties of laser additive manufactured TiNiCu10 was found to be the best among the developed samples.
关键词： DSC,TiNiCu,SEM,XRD,Laser additive manufacturing,Shape memory alloy
更新于2025-09-16 10:30:52
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Hydrophilic to ultrahydrophobic transition of Al 7075 by affordable ns fiber laser and vacuum processing
摘要： A lot of research efforts have been invested in the fabrication of superhydrophobic surfaces in recent years due to many protentional applications in science and industry including anti-icing, self-cleaning and anti-corrosive surfaces. Laser as a non-polluting, precise and flexible tool can be applied to replicate surface microstructures of extremely water repellent lotus leave surface. In this study, a common nanosecond laser source is used to fabricate a super/ultrahydrophobic surfaces with different microstructure designs, contact angles above 170° and sliding angles below 5°. The freshly processed surface is hydrophilic and becomes hydrophobic and superhydrophobic in a certain time period, which could be dramatically reduced by storing samples in high vacuum. The transformation in wetting properties are analysed with respect to surface geometry and surface chemistry.
关键词： Surface functionalization,fiber laser,vacuum processing,ultrahydrophobicity
更新于2025-09-12 10:27:22
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Maskless Micro/Nanopatterning and Bipolar Electrical-Rectification of MoS2 Flakes Through Femtosecond Laser Direct Writing
摘要： MoS2 micro/nanostructures are desirable for tuning electronic properties, developing required functionality, and improving existing performance of multilayer MoS2 devices. This work presents a useful method to flexibly microprocess multilayer MoS2 flakes through femtosecond laser pulse direct writing, which can directly fabricate regular MoS2 nanoribbon arrays with ribbon widths of 179, 152, 116, 98, and 77 nm, and arbitrarily pattern MoS2 flakes to form micro/nanostructures such as single nanoribbon, labyrinth array, and cross structure. This method is mask-free and simple, and has high flexibility, strong controllability, and high precision. Moreover, numerous oxygen molecules are chemically and physically adsorbed on laser-processed MoS2, attributed to roughness defect-sites and edges of micro/nanostructures that contain numerous unsaturated edge-sites and highly active centres. In addition, electrical tests of the field effect transistor fabricated from prepared MoS2 nanoribbon arrays reveal new interesting features: output and transfer characteristics exhibit strong rectification (not going through zero and bipolar conduction) of drain?source current, which is supposedly attributed to the parallel structures with many edge-defects and p-type chemical doping of oxygen molecules on MoS2 nanoribbon arrays. This work demonstrates the ability of femtosecond laser pulses to directly induce micro/nanostructures, property changes, and new device-properties of two-dimension materials, which may future enable new applications at electronic devices based on MoS2 such as logic circuits, complementary circuits, chemical sensors, and p?n diodes.
关键词： micro/nanopatterning,MoS2 flakes,oxygen bonding,femtosecond laser direct writing,electrical rectification
更新于2025-09-12 10:27:22
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Ionically Modified Cellulose Nanocrystal Self-Assembled Films with a Mesoporous Twisted Superstructure: Polarizability and Application in Ion-Gated Transistors
摘要： Mesoporous structures made of cellulose nanocrystals (CNCs) and their self-assembly into films is of great interest not only due to their abundancy and sustainability but also due to their ease of chemical modification and nanoscale bio mimicry capabilities. However, their implementation in (opto)electronic devices requires further understanding on how these self-assembled twisted mesoporous superstructures respond to electrical stimulus. In this regard, this work focusses in the infiltration with three distinct alkali ions (Li+, Na+ and K+) to yield films with improved electrochemical response when compared to pristine ones, while preserving their photonic character. Electrochemical characterization shows capacitances of up to 2.5 μF cm-2 allowing for their integration as solid-state gate electrolytes in amorphous indium-gallium-zinc-oxide transistors, resulting in low operating voltages (< 2 V), On/Off ratios of up to 6 orders of magnitude and high saturation mobilities >10 cm2 V-1 s-1. Devices fabricated on Na+ and K+ infiltrated CNC films present the best characteristics, indicating pure capacitive charging of the semiconductor. The insights presented here contribute to applications in solid-state ionics in mesoporous structures or the combination of optically active electrolytes capable of providing unique functionalities in ion-gated transistors and circuitry.
关键词： Self-assembly,Mesoporous Structures,Cellulose Nanocrystals,Ion Gated Transistors,Photonics
更新于2025-09-12 10:27:22
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Retinal and Choroidal Perfusion Status in the Area of Laser Scars Assessed With Swept-Source Optical Coherence Tomography Angiography
摘要： To evaluate the perfusion status of the retina and choriocapillaris in the area of laser scars on swept-source optical coherence tomography angiography (OCTA) images of eyes previously treated with panretinal photocoagulation (PRP).
关键词： diabetic retinopathy,OCT angiography,laser photocoagulation,choriocapillaris
更新于2025-09-11 14:15:04
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Synthesis of Silica Microspheres—Inspired by the Formation of Ice Crystals—With High Homogeneous Particle Sizes and Their Applications in Photonic Crystals
摘要： Silica microspheres (SMs) must possess the performances of desirable monodispersity, narrow particle size distribution, and high sphericity for preparing photonic crystals (PCs) and other materials such as microspheres reference material, etc. We have adopted the techniques of increasing reactant concentration and raising the temperature to improve the synthesis rate of SMs, gaining inspiration from the formation mechanism of ice crystals. SMs with uniform particle sizes (polydispersity index less than 0.05) and good spherical features were fabricated through homogeneous nucleation. The mathematical relationship between particle sizes of SMs and reactant concentrations is further fitted. High accuracy of the regression equation is verified by an F-test and verification experiment. Highly ordered PCs (the stacking fault is about 1.5%, and the point defect is about 10?3) with dense stacked opal structures have been obtained by self-assembly of SMs. In addition, highly ordered PCs (the stacking fault is about 3%, and the point defect is about 10?3) with non-dense packed opal structure and inverse opal structure were successfully prepared. PCs of inverse opal structure were used to examine their response characteristics to identify ethanol, exhibiting good performance. Our research may provide significant inspiration for the development of other sorts of microspheres.
关键词： photonic crystals,silica microspheres,homogeneous nucleation,self-assembly
更新于2025-09-09 09:28:46
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Growth of 1T’ MoTe <sub/>2</sub> by Thermally-Assisted Conversion of Electrodeposited Tellurium Films
摘要： Molybdenum ditelluride (MoTe2) is a transition metal dichalcogenide (TMD) which has two phases stable under ambient conditions, a semiconducting (2H) and semimetallic (1T’) phase. Despite a host of interesting properties and potential applications, MoTe2 is one of the less-studied TMDs, perhaps due its relatively-low abundance in nature or challenges associated with its synthesis, such as the toxicity of most precursors. In this report, we describe the fabrication of thin films of phase-pure 1T’ MoTe2 using pre-deposited molybdenum and electrodeposited tellurium layers, at the relatively low temperature of 450?C. This method allows control over film geometry and over the tellurium concentration during the conversion. The MoTe2 films are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy and electron microscopies. When applied as a catalyst for the hydrogen evolution reaction, the films display promising initial results. The MoTe2 films have a Tafel slope of below 70 mV dec-1 and compare favorably with other MoTe2 catalysts reported in the literature, especially considering the inherently-scalable fabrication method. The variation in electrocatalytic behavior with thickness and morphology of the films is also investigated.
关键词： 1T’ phase,thin-film,hydrogen evolution reaction,Raman spectroscopy,MoTe2,electrocatalysis
更新于2025-09-09 09:28:46
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Redox-Mediated Shape-transformation of Fe3O4 Nanoflake to Chemically Stable Au-Fe2O3 Composite Nanorod for High-Performance Asymmetric Solid-State Supercapacitor Device
摘要： Development of a stable and highly active metal oxide based electrochemical supercapacitor is a major challenge. Herein, we report Au-Fe2O3 nanocomposite having tiny amount of gold (3 atomic % Au) by employing a simple redox-mediated synthetic methodology using modified hydrothermal system. Structural and morphological studies of the synthesized Au-Fe2O3 nanocomposite have been performed both experimentally (XRD, IR, Raman, XPS, TEM and FESEM analyses) and theoretically (WIEN2K). A probable dissolution-nucleation-recrystallization growth mechanism has been suggested to explain the morphological transformation from Fe3O4 nanoflake to Au-Fe2O3nanorod. We have observed the superior chemical stability of Au-Fe2O3 nanocomposite in acidic medium due to composite formation. The electrochemical measurement of the synthesized Au-Fe2O3 nanocomposite exhibits specific capacitance of ~570 F g-1 at the current density of 1 A g-1 in 0.5 M H2SO4 electrolyte. The result is superior compared to the mother component i.e., Fe2O3 (138 F g-1) under identical condition. It is credited to its higher specific surface area and composite effect. Theoretically, decrease in band gap associated with increase in conductivity support the superiority of Au-Fe2O3 nanocomposite compared to the mother compound i.e., Fe2O3. In addition, electrochemical kinetic analysis showed that the charge-storage mechanism is mostly from a dominant capacitive process (78 % at 1.5 mV s-1). Solid-state asymmetric supercapacitor device has been fabricated using synthesized Au-Fe2O3 composite nanorod as positive and activated carbon as negative electrodes. The asymmetric solid-state device exhibits maximum energy density of 34.2 Wh kg-1 and power density of 2.73 kW kg-1 at current densities 1 A g-1 and 10 A g-1, respectively. Thus, the synthesized nanocomposite shows excellent activity as a supercapacitor with long term durability (91% capacitance retention) up to 5000 cycles even in acidic medium.
关键词： Shape-transformation,Redox mediated synthesis,Chemical stability,High power density/energy density,Au-Fe2O3 composite nanorod,Asymmetric supercapacitor
更新于2025-09-09 09:28:46