查看更多>>摘要：? 2022This paper proposes a dual-band tunable broadband metamaterials absorber, achieved absorption in 3-5 μm mid-wavelength infrared (MWIR) and 8-12 μm long-wavelength infrared (LWIR). The absorber is composed of periodic units, and each unit is composed of a bottom ideal electric conductor-dielectric layer-graphene layer-metal fractal cross resonator in which a graphene layer-metal fractal cross is embedded. The metal structure uses the multi-scale self-similar characteristics of fractal geometry to create multiple resonances for the same element structure. Numerical simulations were carried out using the finite element method (FEM). The optimization results show that the designed single-layer 3-Level graphene-metal fractal cross absorber produces broadband absorption of 2.86 μm (absorption >90%) in the LWIR region and an average absorption rate of 92.1%. By adding the bottom layer 3 × 3 graphene-metal fractal cross array structure, a resonant absorption peak is generated in the MWIR region, and the broadband absorption of 0.38 μm (absorption >80%), and it achieves broadband absorption of 2.48 μm (absorption >90%) in the LWIR region. For the double-layer graphene-metal structure, the resonance bandwidth and absorptivity of the absorber can be tuned by adjusting the Fermi energy of each layer of graphene. Due to its broadband, polarization insensitivity, high absorption, flexible tunable, and other characteristics, the proposed metamaterials absorber is beneficial for fabricating nano-optoelectronic devices and can be applied in thermal imaging and infrared detection.
查看更多>>摘要：? 2022 Elsevier B.V.Carbon dots (CDs), versatile nanomaterials with unique photophysical and structural properties, often have excitation-dependent fluorescence due to the presence of carboxylic groups on the surface of the nanostructure. The excitation-dependent fluorescence of CDs is valuable for bioimaging, but considered undesirable for applications where monochromatic emission is required. Here in this paper, we demonstrate a green, fast and simple way to control the excitation-dependent fluorescence of CDs by passivating carboxylic groups on the surface of CDs with zinc (II) ions through a microwave synthesis method. Conventional CDs without surface passivation had excitation-dependent fluorescence, whereas zinc(II) ion-passivated CDs had excitation-independent fluorescence. Also, the surface passivation of CDs led to an increase in the quantum yield of CDs. The present work provides an inexpensive and user-friendly way to develop carbon dots with controllable emission properties by incorporating a metal ion into carbon dots through simple microwave-assisted synthesis.
查看更多>>摘要：? 2022 Elsevier B.V.The tribology characteristics of diamond-like carbon (DLC) film are studied under different experiment temperatures. The outcomes reveal the average COF of DLC film will gradually decrease with the increase of temperature from 25 °C to 225 °C, but its wear rate will gradually increase. Especially at 225 °C, the DLC film is worn through in a very short time. The Raman characterizations imply that the low friction behavior of DLC film may be mainly caused by the synergistic effect of graphitized transfer layer and graphitized worn surface of DLC film as the temperature increases from 25 °C to 175 °C. Further analysis shows that the high wear of DLC film at high temperature may be mainly due to the reduction of wear resistance of worn DLC surface and the formation of soft oxide layer at friction interface.
查看更多>>摘要：? 2022 Elsevier B.V.In the present work, W-containing coatings were deposited on the surface of diamond microcrystals. The coatings formed as diamond reacted with a WO3 powder in the die of a hot press at elevated temperatures. The morphology and phase composition of the coatings were studied as functions of the treatment temperature and treatment time. The coated diamond crystals were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. After treatment of the mixture at 850 °C for 15 min, WO2 and W18O49 were found on the diamond surface. After treatment at 950 °C (15 min), tungsten was the dominant phase of the coating. Treatment at 1150 °C (15 min) led to the formation of the WC and W2C phases; no metallic tungsten was present in the coating obtained at this temperature. The reaction sequence describing the coating formation process was proposed. During the coating formation, the deposition selectivity with regard to the diamond facet was observed. The {100} facets of diamond were preferentially coated. The coating developed through the formation and coalescence of islands, which were of square shape on the {100} facets and of triangular shape on the {111} facets of diamond.
查看更多>>摘要：? 2022Combining both defect and hydrogenation provides the possibility to create an unprecedented structure configuration using an optimally designed mechanical model. The effects of increasing the defect length, coverage of hydrogenation and also the effect of different locations of such defects (Stone-Wales (SW) and vacancy) in hybrid h-BN/Graphene/h-BN nanosheet on their mechanical properties have been studied. The result shows that hydrogenation can be regarded as a kind of pseudo-crack, and even the shape and structure of graphene heterojunction can be precisely controlled and cut. By creating the hydrogenation pseudo-crack in hybrid nanosheets, the carbon atoms in hydrogenated graphene are converted to sp3 hybridization, while the carbon atoms in un?hydrogenated regions are still sp2 hybridization. The hydrogenation pseudo-crack can also improve the stability and interfacial adhesion of the important region (interface region) of hybrid nanosheets, and transform the sp2 hybridization state into sp3 hybridization state, which can effectively hinder the transformation of six-membered rings in the structure. Only high stress can destroy the structure, so it shows obvious brittle fracture characteristics in the process of tension. Temperature and interface connection also have important influence on the mechanical properties of graphene heterostructure. Defects and hydrogenation pseudo-crack in heterostructures will cause local stress, hybridization state transition and “defect amplification effect”, which will further affect physical properties of materials. In addition, the hydrogenation pseudo-crack is more suitable for atom cutting than vacancy and SW defects, and can precisely control the fracture path of graphene heterostructure.
查看更多>>摘要：? 2022 Elsevier B.V.We deposited silicon- and nitrogen-doped diamond-like carbon (Si–N–DLC) films by radio frequency (RF) plasma-enhanced chemical vapor deposition using H2 and Ar as dilution gases. We investigated the influence of the H2 flow ratio [H?/(H? + Ar)] on the structure; chemical bonding; and mechanical, tribological, optical, and surface properties of the Si–N–DLC films. The optical bandgap increased from 1.88 eV to 2.06 eV with the H2 flow ratio, and it had a negative correlation with the sp2 C[dbnd]C bonding fraction in the films. When the H2 flow ratio increased from 0% to 100%, the critical load of the Si–N–DLC films increased by ~14% due to a reduction of ~26% in the internal stress of the films. As the H2 flow ratio increased, the friction coefficient and specific wear rate decreased by ~11% and ~35%, respectively, whereas the pure water contact angles of the film surfaces increased from 74.7° to 86.5°. The film surfaces had root mean square roughnesses (RMS) less than 0.2 nm. Therefore, the improvement in their tribological properties and the increase in their contact angles were probably due to the hydrogen termination of dangling bonds. The friction coefficient and wear rate of the Si–N–DLC film deposited at a H2 flow ratio of 0% (100%) changed little (increased) after annealing at 773 K.
查看更多>>摘要：? 2022 Elsevier B.V.This work reports a facile and scalable method for assembling a supercapacitor. Cost-effective solid-state supercapacitor contrived by combining waste biomass human hair derived activated carbon (HHCK) as an electrode and albumen (egg white gel polymer) in 1 M NaCl electrolyte (1 M NaCl-EWG). Human hair as an electrode precursor and egg white as a gel polymer precursor provide a sustainable approach for biomass-based material's cost-effective and eco-friendly utilization. Human hair derived interconnected three-dimensional hierarchal porous carbon of human hair possessed a high specific surface area of 1466 m2 g?1 along with the incorporation of ~23% heteroatoms into the carbon matrix. The solid-state supercapacitor (HE-SC) exhibits high specific capacitance of 491 F g?1 at 1 A g?1 within a wide electrochemical stable potential window of 1.5 V. HE-SC provided a high energy density of 38.4 W h kg?1 at 0.374 kW kg?1 power density, quick charge-discharge ability (time constant was 4.3 s), and high cyclic stability (86% capacitance retention with 95% coulombic efficiency after 6500 cycles). This current research provides a feasible and effective strategy for preparing low-cost and high-performance supercapacitors utilizing waste biomass.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, CVD graphene with a typical set of structural features (domains, folds and blisters) is used to see the relation between the effects of its nanostructuring by high-energy ion irradiation (Xe and Kr with energies 26–167 MeV) and the graphene structure. The pore size was found to depend on the domain size and the ion energy, and equal to 10–30 nm and 60–80 nm for domains of 1–3 μm and ~10 μm, respectively. The pore density was estimated as ~10% from the ion fluence. The maximum pore density, approximately equal to the ion dose, was found in the strained graphene blisters. The formation of more complex structural defects (presumably, ultrashort nanotubes covered with a graphene monolayer on the top) is also revealed after the ion irradiation in few-layer graphene. The top layer preservation after irradiation was justified by the molecular dynamics simulation and caused by lower energy losses (absence of the electrons knocked out of the previous layers). The possibility of forming vertical wells in ultrashort nanotubes, due to interlayer covalent bonds at the edges of some pores, is very attractive for applications. The use of CVD graphene provides ample opportunities for controlling the structure and properties of nanostructured materials.
查看更多>>摘要：? 2022A simple structure graphene metasurface composed of a continuous graphene strip and a truncated graphene strip is designed and investigated for sensing and slow light applications in terahertz. The results reveal that plasmonic-induced transparency (PIT) can be produced in our designed graphene metasurface with the destructive interference between bright and dark modes. Transmission, reflectivity, and absorbance spectra of optical response effectively tuned by the Fermi level, and numerical results are consistent with theoretical results of developed coupled mode theory (CMT). In addition, PIT window is also tuned by the polarization angle of the linearly polarized plane light. Intriguingly, owing to the surface plasmon has field enhancement and strong dispersion, our proposed graphene metasurface exhibit potential optical applications, such as the sensing and the slow light. The sensitivity and Figure of merit (FOM) for sensing characteristics reach up to 0.7928 THz/RIU and 8.12, respectively. The largest group index is of 511 for slow light effect. Therefore, our proposed graphene-based metasurface may be expected to make an important contribution in micro-nano optical sensing and slow light devices.
查看更多>>摘要：? 2022A novel multilayer polymeric epoxy coating consisting of 3-(2-aminoethylamino) propyl dimethoxy methylsilane (AEAPS), Mo2C and graphene oxide (GO) was synthesized. The graphene oxide wrapped molybdenum carbide was examined by SEM/EDX, TEM, and XRD. The protective performance of epoxy-GO/AEAPS-Mo2C coating on mild steel was evaluated in 3.5% NaCl solution by EIS, polarization, and SECM studies. The optimum percentage of graphene oxide embedded Mo2C nanoparticles in the epoxy matrix was found to be 2.0 wt% in which the coating has the least aggregation and higher coating resistance. The EIS measurements showed an enhanced coating resistance of EP-GO/AEAPS-Mo2C nanocomposite (7301.75 kΩ·cm2) after 360 h of immersion compared to plain epoxy (1.05 kΩ·cm2) coatings. Moreover, it was also found that the coating resistance of EP-GO/AEAPS-Mo2C was 49.93% higher than that of pure matrix after 1 h immersion. SECM measurements confirmed that the least dissipation of ferrous ions was observed at the crack of the EP-GO/AEAPS-Mo2C nanocomposite coated steel specimen (1.4 I/nA) due to the improved resistance for anodic dissipation of the coated substrate. FE-SEM/EDX examined that Mo was reinforced in the degradation products which formed an excellent passive layer at the coating/steel interface. The results showed that the newly developed EP-GO/AEAPS-Mo2C nanocomposite coating possessed superior corrosion protection and enhanced hydrophobic behaviors (WCA: 152°). The investigated coatings showed profound mechanical properties. The hardness value was found to be 1290 MPa for EP-GO/AEAPS-Mo2C nanocomposite while the value of the pure epoxy coated specimen was 275 MPa. The inclusion of graphene oxide wrapped molybdenum carbide in the epoxy matrix displayed superior mechanical properties in term of adhesion strength and hardness.
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