查看更多>>摘要：Tin-assisted pure phase n-type ZrO2-doped ε-Ga2O3 films were synthesized by pulsed laser deposition (PLD) and deposited on (0001) epi-GaN/sapphire substrates. The characterization of n-type ZrO2-doped ε-Ga2O3 thin films and the electrical properties of SBD based on that film were investigated in details. From XRD, the pure Zr-doped ε-Ga2O3 without diffraction peaks of zirconia suggested the formation of ε-(ZrxGa1?x)2O3 solid solution. The surface morphology and chemical content of the ε-Ga2O3 thin film were studied by AFM and XPS. The electrical resistivity and related free carrier concentration at room temperature were measured to be 108 Ω·cm and 5.5 × 1015 cm?3, respectively, and mobility up to 10.3 cm2/V·s. The Schottky barrier diode possessed a rectification ratio up to 106~107, breakdown voltage of 392 V, and the interface states density from 2.4 × 1013 cm-2 eV-1 to 6.4 × 1014 cm-2 eV-1 with the trap energy level from 0.89 eV to 0.94 eV below the bottom of the conduction band.
查看更多>>摘要：The ever-increasing demand for portable smart devices through an extensive range of military, commercial, industrial, and consumer sectors has faced scientists with various challenges. Electromagnetic (EM) pollution is a critical issue threatening the general function of surrounding electronic systems and human well-being. The graphene family (GF) has been investigated thoroughly during the last decade to satisfy the need for light and cost-effective portable devices and address EM pollution and effective shielding devices from its adverse effects. GF has presented an incredible ability to attenuate the EM pollution and, therefore, be used as an alternative for the conventional metal-based electromagnetic interference (EMI) shielding materials. Due to the importance of this topic and the necessity of finding a practical solution for the real-life application of EMI shielding materials, we report the recent research progress and development status of using GFs as EMI shielding materials in a broad frequency range. This review surveys the shielding effectiveness of graphene as a two-dimensional (2D) structure (freestanding thin film and coating), skeleton, filler in polymers’ matrix, and three-dimensional (3D) structure (foam and aerogel). Moreover, the shielding mechanism of the materials is investigated comprehensively. This review will briefly discuss the importance of using graphene as an alternative to the conventional shielding material. In the following sections, the EMI shielding performance of graphene as 2D structure, skeleton, filler, and 3D structure is reviewed, and the influence of their conductivity, thickness, and composition on their shielding characteristics is investigated. Finally, the outlooks and conclusions of the recent research will be discussed.
查看更多>>摘要：The titanium dioxide (TiO2) with cubic shaped nanoparticles (CNPs) have been used to prepare TiO2/(Bi,Pb)2Sr2Ca2Cu3O10+θ (Bi-2223) composites. We fully characterized the structural and morphological properties of the synthesized composites using X-ray diffraction and scanning electron microscopy. The existence of the secondary superconducting phases increased by an increase in the TiO2 content according to the XRD results. In addition, the morphological studies exhibited that the best alignment and inter-connectivity of grains were explored in the composite with 0.2 wt% of TiO2-CNPs. It can be suggested that the existence of TiO2-CNPs between grains improve the connectivity and alignments in the synthesized compounds. Further, the superconducting transition temperature and critical current densities, along with the pinning force density were determined based on the electrical and magnetic measurements. The results demonstrated that by adding 0.2 wt% of TiO2-CNPs, superconducting features improved in the Bi-2223 superconductor. Consequently, the presence of the optimal amount of TiO2-CNPs as artificial pinning centers had improved the superconducting properties of the Bi-2223 superconductor. This work opens interesting avenues for the application of Bismuth Strontium Calcium Copper Oxide (BSCCO) superconductors in many fields such as tapes, wires, energy storages, and high-current applications.
查看更多>>摘要：Here, we report on the marine antifouling performance and electromagnetic wave absorption (EMWA) properties of multifunctional zinc-based acrylate resins (ARZn-x). Their controlled hydrolysis with varying contents of carboxylic acid groups and ZnO led to formation of new surfaces that contributed to excellent antibacterial activity (>90%) and reductions in algal adhesion (optimal: 92.5%). Marine field tests demonstrated ideal antifouling performance during immersion in seawater for 4 months, and the coatings inhibited the adhesion and growth of biofouling species in marine. Furthermore, the ARZn-x resin coatings exhibited remarkable EMWA performance, with an RLmin of ? 40.18 dB at 1.5 mm and 30.55 GHz, and full absorption of frequencies ranging from 18 to 40 GHz was achieved with thicknesses ranging from 1.0 to 5.5 mm. These resins provide new approaches to the development of multifunctional materials demonstrating marine antifouling performance and EMWA properties.
查看更多>>摘要：In this work, the synergistic effect of Re and W on the evolution of the topological close-packed phases (TCP) in Nickel-based superalloys were studied by means of Thermo-Calculation (TC), solidifying slowly, Differential Thermal Analysis (DTA), and solution-aging treatment. The specimens were analyzed by means of SEM-EDS, TEM-SADP, and EPMA. The calculated results indicated that the P phase precipitated prior to the μ phase with the temperature decrease, and both phases μ and P coexisted in a certain temperature range when the content of Re was higher ( Re: 5–7 wt%) and the content of W was lower ( W:4–6 wt%); Only phase μ precipitated from the alloy when Re content was less than 4 wt% and W content was higher than 7 wt%. The experimental results showed that the μ phases were slats-like and distributed in parallel in different orientations; and the μ/P intergrowth phases with coherent relationship were short rod-like. In addition, the gathered μ/P intergrowth phases around the big blocky-like γ' phases were found in alloys solidified slowly, which was prone to cause holes. Based on phase-transition temperature obtained by combining calculation and DTA, the solution-aging process of the alloys were determined. After solution-aging treatment, the long strip shape μ phases and short rod-like μ/P intergrowth phases distributed uniformly in the matrix, and the big blocky-like γ' phases and holes disappeared. The experimental results showed that the total amount of TCP phase decreased and the P phase gradually disappeared when the content of Re decreased and the content of W increased. The research results had a guiding role in optimizing the composition of alloys and predicting the safety performance of aerocraft during the flight cycle.
查看更多>>摘要：In this study, the effects of sub-Tg isothermal annealing on the microstructure, mechanical and serrated flow behaviors of Ti33Zr30Cu9Ni5.5Be22.5 bulk metallic glass (BMG) were investigated. The change in free volume content of the BMG was characterized according to the structural relaxation enthalpy δHr and the onset structural relaxation temperature Tr, with the results indicating a monotonic decreasing trend of the free volume content with the extension in annealing time. A number of nanocrystals with a size of approximately 4 nm were precipitated on the glassy matrix when the annealing time was extended to 1.0 h, and then the size of these nanocrystals increased with further prolongation of the annealing time. Meanwhile, the room-temperature compressive plasticity of the Ti33Zr30Cu9Ni5.5Be22.5 BMG greatly improved from 1.4% to 4.2%, and the high strength was retained after annealing for 1.0 h, which can be largely attributed to the formation of the nanocrystals with the size of about 4 nm. With the extension of the annealing time, however, the further growth of the nanocrystals resulted in the degeneration of the compressive strength and the plasticity. The serrated rheology analysis revealed that the distribution histogram of the stress drop for the 1.0 h-annealed specimen represented a well characteristic of power-law distribution, whereas the 4.0 h-annealed showed a chaotic dynamics of jerk flow. Furthermore, the 1.0 h-annealed specimen possessed the lower average stress drop (12 MPa), formation energy per unit shear band (254.9 J/m2) and average shear band velocity (1.21 × 10?5 m s?1).
查看更多>>摘要：Orientation relationship at the Al/graphene interface was investigated through first-principles calculations and high-resolution transmission electron microscope (HRTEM). Calculations revealed the preferred orientation of Al(211)/graphene(0001) for the first time. Interface energy of Al(211)/graphene(0001) was much lower than that of published Al(111)/graphene(0001), Al(110)/graphene(0001) and Al(100)/graphene(0001), which was confirmed by HRTEM observation on the orientation of graphene(0001)//Al(21?1). Further calculations revealed that interplanar spacing of Al slabs increased in Al(211)/graphene(0001) and calculation angle between graphene and Al slabs was in excellent agreement with HRTEM investigations. The findings of most stable Al(211)/graphene(0001) interface threw new lights for researches on Al/graphene interface.
查看更多>>摘要：Lithium-ion batteries (LIBs) contain a variety of toxic inorganic and organic compounds, and the spent cathode materials are high quality resources of Ni, Co, Mn, and Li elements. In this case, how to efficiently deal with spent materials has become an urgent problem. In this work, the regeneration of spent ternary materials via molten salt solid-liquid method and traditional solid-solid method are studied comparatively. Ordered and uniform crystals in MS-NCM are successfully grown in liquid medium of molten salts. The regenerated TS-NCM by traditional sintering method still presents inhomogeneous larger and smaller crystals. Moreover, only regeneration by molten salt method effectively removes F-contained impurity on the surface of spent materials, and the Ni3+ and Mn3+ on the crystal surface of MS-NCM are close to the values in commercial sample (Com-NCM). After 100 cycles at 0.2 C rate, MS-NCM and TS-NCM respectively deliver 149.1 mA h g?1 and 123.2 mA h g?1, maintaining 98.1% and 84.4% of their initial capacity. MS-NCM presenting better electrochemical performance than TS-NCM is attributed to the efficient regeneration of the spent cathode material in liquid medium of molten salts.
查看更多>>摘要：The polymerization of graphitic carbon nitride (g-C3N4) into large single crystals has been particularly challenging. This study presents a quick and simple method to grow high quality two-dimensional graphitic carbon nitride nanosheets with a large domain size (up to 40 μm) on copper (Cu) foils. The chemical vapor deposition (CVD) method was used with melamine (C?H?N?) as the source. Electron backscatter diffraction (EBSD) revealed that graphitic carbon nitride prefers a Cu(111) surface to a Cu(211) surface, which is consistent with the theoretical calculations. Moreover, it was demonstrated that the carrier gas is critical for the growth of graphitic carbon nitride. The use of noble Ar gas is recommended because it has a weaker etching effect compared to that of the more commonly used hydrogen (H2) gas. Furthermore, CVD-grown high-quality graphitic carbon nitride films can be easily transferred onto other substrates for various applications, such as photodetectors or metal-free photocatalysts.
查看更多>>摘要：In this work, the influence of temperature on the optical constants of zinc oxide (ZnO) and aluminum-doped zinc oxide (AZO) thin layers is presented. Thin layers of ZnO and AZO were deposited on silicon using the atomic layer deposition (ALD) method. Optical constants were determined based on ellipsometric measurements in spectral range of 193–1690 nm at temperatures varying from 25° to 300°C. From thermal ellipsometric results, the thermo-optical coefficient (TOC) and thermal expansion coefficient (TEC) have been determined. We have shown that after two cycles of heating and cooling, the thermo-optic processes are reversible. Additionally, complementary studies: XRD, EDS, SEM have been presented. The relationships between the structure of presented films and their optical properties have been discussed. We have shown that the doping of Al to the ZnO matrix changes the sign of the thermo-optical coefficient from negative to positive. The results have been explained based on Prod-Homme theory.
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Elsevier