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Microwave dielectric properties of B and N co-doped SiC nanopowders prepared by combustion synthesis
摘要： B and N co-doped SiC nanopowders were prepared by combustion synthesis under a nitrogen atmosphere from the Si/C system, using α-Si3N4 powder and B powder as solid nitriding agent and dopant, respectively. The prepared particles had spherical morphology and narrow size distribution. XPS analysis demonstrated that B and N atoms successfully incorporated into SiC crystal and formed Si1-xBxC1-yNy solid solution. Results of dielectric properties showed that the real part ε′ and imaginary part ε″ of the complex permittivities of the samples decreased first, and then increased with increasing N content. The sample with 5% B and 15% N revealed the greatest values in ε′ and ε″ and better microwave absorption performance. The corresponding mechanism of the dielectric properties of SiC improved by co-doping was discussed in detail.
关键词： co-doping,SiC,dielectric property,microwave loss
更新于2025-09-23 15:21:21
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Thermodynamic stability, half-metallic and optical nature of graphene-like Mn <sub/>2</sub> Zr <i>Z</i> ( <i>Z</i> = Ge, Si): <i>Ab initio</i> study
摘要： Half-metallic, optical and thermodynamic phase diagrams of two-dimensional Mn2ZrZ (Z = Ge, Si) have been calculated by density functional theory (DFT) framework with full-potential linear augmented plane-wave (FP-LAPW) method. The spin-polarized electronic computations show that these layers have metallic behavior with a spin polarization less than 100%. It is observed that with increasing thickness of the layers, both the thermodynamic and energy stabilities increased, and the graphene-like layers of Mn2ZrGe with a thickness of 7.6955 ?A and Mn2ZrSi with a thickness of 7.551 ?A are completely stable thermodynamically. The optical responses of Mn2ZrZ (Z = Ge, Si) have anisotropy at infrared region versus the optical direction and have high metallic nature in this optical range. The plasmonic frequencies have occurred after the visible edge and the refraction index becomes lower than one after the ultra-violet edge.
关键词： optical property,half-metal,thermodynamic phase diagram,DFT,Graphene-like Mn2ZrZ (Z = Ge, Si)
更新于2025-09-23 15:21:21
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Reduction of Radius of Curvature in Thin-Sheet-Metal Bending by Ultrashort-Pulsed Laser Peen Forming
摘要： Ultrashort-pulsed laser peen forming is a method of thin-sheet-metal forming using laser-induced shock waves. The authors have applied the process to microsheet parts bending, which is accomplished by repeating line scanning. However, when a severe curvature is requested, nonnegligible reduction of sheet thickness is induced by laser ablation. In order to restrict the thickness reduction, the authors attempted to improve the bending efficiency, which would allow a reduction in the number of necessary pulses. Scanning velocity and scanning pitch were changed, while the total irradiated pulse number was constant. The obtained results showed that a scanning velocity higher than the conventional one is favorable for improving the bending efficiency. In addition, smaller scanning pitches were adopted to reduce the radius of curvature. The influence of the scanning pitch on the bending efficiency was much weaker than that of scanning velocity. From the results of the evaluation of efficiency and scanned surface asperity, a scanning velocity of 20 mm·s-1 was judged to be the best. The best scanning condition achieved a 40% smaller radius of curvature than the conventional one.
关键词： bending,bending efficiency,laser-induced shock wave,ultrashort-pulsed laser,incremental forming,scanning velocity,forming property,laser peen forming
更新于2025-09-23 15:21:01
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Acceptora??donora??acceptor type molecules for high performance organic photovoltaics a?? chemistry and mechanism
摘要： The study of organic photovoltaics (OPVs) has made great progress in the past decade, mainly attributed to the invention of new active layer materials. Among various types of active layer materials, molecules with A–D–A (acceptor–donor–acceptor) architecture have demonstrated much great success in recent years. Thus, in this review, we will focus on A–D–A molecules used in OPVs from the viewpoint of chemists. Notably, the chemical structure–property relationships of A–D–A molecules will be highlighted and the underlying reasons for their outstanding performance will be discussed. The device stability correlated to A–D–A molecules will also be commented on. Finally, an outlook and challenges for future OPV molecule design and device fabrication to achieve higher performance will be presented.
关键词： chemical structure–property relationships,device stability,organic photovoltaics,acceptor–donor–acceptor,molecule design
更新于2025-09-23 15:21:01
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Structure-Property Study of Homoleptic Zinc(II) Complexes of Di(arylethynyl) Azadipyrromethene as Non-Fullerene Acceptors for Organic Photovoltaics: Effect of Aryl Group
摘要： Azadipyrromethene-based zinc(II) complexes were demonstrated to be promising molecular organic semiconductors for electronic applications due to their easy preparation, tunable structures and high electron affinity. The first successful such complex incorporated phenylethynyl groups at the pyrrolic positions, which red-shifted the absorption spectra of zinc(II) bis(tetraphenyl azadipyrromethene) and improved morphology in blends with poly(3-hexylthiophene) (P3HT). We recently discovered that replacing the phenyl group in the pyrrolic positions with the larger 1-naphthyl group [Zn(L2)2] increases crystallinity and improves the organic photovoltaic (OPV) performance. In this work, two more aryl groups were explored to further investigate the relationship between the aryl groups in the pyrrolic position and electronic properties: naphthyl with a different anchoring site, 2-naphthyl [Zn(L3)2], and a larger aryl group, 9-phenanthrenyl [Zn(L4)2]. The larger aryl group slightly improved absorptivity and red-shifted the absorption spectra and lead to different packing modes in crystals with most intermolecular π-π stacking interactions being of T-shaped type involving the pyrrolic aryl group of one complex. Of the series, 1-naphthyl gave the highest crystallinity. The OPV power conversion efficiency (PCE) of Zn(L3)2 and Zn(L4)2 when blended with P3HT was 3.7% and 3.4%, respectively, both lower than that of Zn(L2)2, PCE of 5.5% due to higher trap-assisted recombination and less favorable morphology. Charge carrier mobility in these complexes was also relatively low, also limiting performance. Single-point energy calculations point to low overlap integrals as a cause for the low mobility. The aryl group anchoring position and size therefore have a large effect on properties in these systems, but do not appear to significantly enhance intermolecular interactions.
关键词： Azadipyrromethene,zinc(II) complexes,non-fullerene acceptors,structure-property study,organic photovoltaics
更新于2025-09-23 15:21:01
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Synthesis and electrochromic properties of electrochromic polymers based on propylenedioxythiophene, diketopyrrolopyrrole and benzodithiophene units
摘要： Two novel soluble polymers, PD-1 and PD-2, were synthesized based on three kinds of monomers, including propylenedioxythiophene (ProDOT), diketopyrrolopyrrole (DPP) and benzodithiophene (BDT), via Stille coupling reaction with the feed ratios (ProDOT:BDT:DPP) of 3:4:1, and 1:2:1, respectively. Wherein, propylenedioxythiophene (ProDOT) and benzodithiophene (BDT) exist as the donor unit, and diketopyrrolopyrrole (DPP) as the acceptor units. Both of the two copolymers were characterized via 1H NMR, FT-IR spectra, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), spectroelectrochemistry, switching kinetics, colorimetry and thermogravimetric analysis. Electrochemical studies demonstrate that both copolymers have the ability of rapid doping and dedoping and excellent stability. PD-1 displays a brown color in the neutral state, and a light green color in the oxidized state, while PD-2 exhibits gray green color in the neutral state and a transparent light green color in the oxidized state. As the content of the DPP remains constant, the changes in the content of the ProDOT unit can effectively control the color changes of the copolymers without apparent changes in bandgap (Eg) values, and subsequently lead to the fine tune of the other properties of the copolymers, such as optical contrast, response time and coloring efficiency. The Eg values of PD-1 and PD-2 are 1.55 eV and 1.52 eV, respectively. The optical contrasts are 42.36% (1600 nm) for PD-1 and 67.74% (at 1620 nm) for PD-2, both are ideal candidate materials for the fabrication of near infrared devices. They also have moderate optical contrast in the visible region, with fast response time and high coloring efficiency.
关键词： Electrochromic property,Diketopyrrolopyrrole,Propylenedioxythiophene,Benzodithiophene,Soluble copolymer
更新于2025-09-23 15:21:01
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Temperature and hydrostatic pressure effects on the electronic structure, optical properties of spherical segment quantum dot/wetting layer and group velocity of light
摘要： To investigate hydrostatic pressure and temperature effects on electron energy levels of an InAs spherical segment quantum dot with wetting layer embedded in GaAs barrier, we use the finite element method to solve the Schr?dinger equation in the effective mass approximation. Results show that the ground, the first and the second excited state energies decrease (increase) as the hydrostatic pressure (temperature) increases for the constant temperature (pressure). Moreover, given the optical properties of the system interacting with two laser fields, red (blue) shifts are observed in the linear and nonlinear absorptions and dispersions for the probe pulse as the hydrostatic pressure (temperature) increases. Furthermore, as the hydrostatic pressure increases, the maximum of the group velocity of light inside the slow light frequency range increases and the slow light frequency range shifts to the lower probe frequencies.
关键词： temperature,group velocity of light,hydrostatic pressure,optical property,quantum dot/wetting layer
更新于2025-09-23 15:21:01
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<i>(Invited)</i> Fluid Spectroscopy with Piezoelectric Ultrasound MEMS Transducers
摘要： In this work, Piezoelectric Micromachined Ultrasound Transducers (PMUTs) are explored as a potential MEMS solution for fluid property monitoring. PZT based PMUTs fabricated with three different diameters—1000 μm, 500 μm, 250 μm—showing in-air resonant frequencies between 100 kHz to 2 MHz are tested in water-glycerol mixtures with glycerol concentrations varying between 0% to 80% in both static and dynamic conditions. Spectral shifts of fluid environment are PMUT vibrations with changing quantitatively related to the density and viscosity of the fluid. The density sensitivity of the PMUTs is found to increase from 27 Hz/kg.m-3 for 1000 μm to 365 Hz/kg.m-3 for 250 μm, which is in close agreement with theoretical expectations. Similarly, viscosity sensing is also explored using PMUT arrays. A through-the-fluid ultrasound transmission architecture is proposed for a potential fluid property sensor that can fill the gap of miniature sensors for sensing physical properties of various fluids.
关键词： fluid property monitoring,viscosity,density,Piezoelectric Micromachined Ultrasound Transducers,PMUTs
更新于2025-09-23 15:21:01
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Electronic structure and transport properties of graphene/h-BN controlled by boundary potential and magnetic field
摘要： We study the band structure of the lattice-matched graphene/h-BN bilayer system in the most stable configuration. An effective way to individually manipulate the edge state by the boundary potentials is proposed. It is shown that the boundary potential can not only shift and deform the edge bands, but also modify the energy gap. We also explore the transport properties of graphene/h-BN under a magnetic field. The boundary potential can change the distribution of the edge states, resulting in an interesting evolution of the quantized conductance.
关键词： energy gap,transport property,Lattice-matched graphene/h-BN,boundary potential
更新于2025-09-23 15:21:01
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Porosity and joint property of laser-MIG hybrid welding joints for 304 stainless steel
摘要： Laser-metal inert gas (MIG) hybrid butt welding was carried out on 5 mm-thick 304 stainless steel to study the influence of parameters on porosity defect, weld formation, and property of the joints. Research reveals that laser-MIG hybrid welding of 304 stainless steel has porosity sensitivity. The effects of welding speed and laser power on porosity and formation of welds were analyzed. Results show that increasing of laser power and decreasing of welding speed are conducive to improve the formation of welds and reduce porosity. Improving the welding speed on the premise of ensuring proper weld formation is of considerable significance, which is recommended to be 1.8 m/min. Based on the fixed welding speed, parameter of laser power optimization is carried out. Results show that tensile strength and elongation of the welded joints reach at least 98.1% and 75.8% of the base metal when laser powers are 4.3 and 5.0 kW. Compared with real-time monitoring and the numerical simulation method, this kind of results-oriented optimization parameter method has engineering guiding significance.
关键词： property,welding parameter,weld formation,304 stainless steel,porosity,laser-MIG hybrid weld
更新于2025-09-23 15:21:01