To tackle the increasing electromagnetic pollution, broadband electromagnetic wave (EMW) absorption materials are urgently needed. Toward this goal, traditional strategies resort to the construction of multicomponent dielectric/magnetic hybrid materials, including ternary, quaternary, or even more complicated systems. However, they always suffer from many intrinsic drawbacks in practical applications. Herein, a theory‐directed strategy is presented to design plainified EMW absorption materials (binary hybrids) via amplified interface effects, which are based on well‐designed multilayer alternating core‐shell nanostructures by chemical vapor deposition (CVD). A defect‐engineered CVD graphene (DG) core composed of graphitic open edges and in‐plane defects is used as a lossy phase. Correspondingly, a CVD Si3N4 layer with nanometer thickness is used as an impedance matching shell. By optimizing the alternating numbers of DG/Si3N4 units, enhanced interface polarization and strong frequency dispersion behavior of permittivity (especially the real part, ε′) are obtained, which helps the plainified binary hybrids to reach an effective absorption bandwidth (EAB) of 8.0 GHz at a thickness of 2.7 mm. Moreover, these plainified hybrids show excellent thermal and pH stability. Even after 1000 °C oxidation, for example, an EAB of 7.44 GHz coupling with a minimum reflection coefficient of −77.3 dB is still achieved.
Modern electromagnetic (EM) absorbing materials (EAMs) are experiencing a revolution triggered by advanced information technology. Simultaneously, the diverse harsh EM application scenarios entail a more stringent appeal of practicability to EAMs, especially under high-temperature conditions. Therefore, exploring EAMs with both excellent absorbing performance and practicability at elevated temperatures is necessary. Herein, a novel 3D porous carbon foam/carbon nanotubes@Si3N4 (CF/CNTs@Si3N4) heterostructure was constructed by the chemical vapor infiltration process. The optimally grown 1D CNTs embedded in 3D CF/Si3N4 are utilized to provide abundant nanointerface coupling effects to compensate for the excessive increase in the conductive loss during rising temperature to realize a self-adjustment in response to high temperature. A high-efficiency EM absorption over a wide temperature range from 25 to 480 °C was achieved (with a ≥90% absorbing ratio covering the whole X-band). In addition, the Si3N4 coating can improve the thermal stability of the carbon matrix and maintain the tailored inner structure. Multiple investigations into other environmental adaptabilities also exhibited the application perspective of such a heterostructure. This work points out a new strategy for preparing designable, efficient, and high-temperature applicable EAMs, promoting the diverse development of electronic devices.
2D nanosheet is indispensable for the design and production of functional materials and devices. [1,2] Particularly, 2D layered materials, including graphene, phosphorene, and 2D bismuth selenide (Bi 2 Se 3 ), exhibit massive potential due to their unique electrical, optical, thermal, and mechanical properties. [3,4] Compared with classical graphene, phosphorene, 2D Bi 2 Se 3 , and other materials have shown more intriguing features and application prospects. [5][6][7][8] For example, single-and few-layer BP (2D BP) endow with a direct and tunable bandgap ranging from 0.3 eV (bulk) to 2.0 eV (monolayer), [9] which is favorable for making electric devices and photoelectric detectors. Bi and Se elements contained compounds are always selected as the electrode materials for supercapacitors and achieve satisfactory performance. [10][11][12] Khalafallah et al. designed the selenium-enriched reduced graphene oxide hybridized hetero-structured nickel bismuth selenide (RGO/Ni-Bi-Se) and bismuth selenide (RGO/Bi 2 Se 3 )based materials as positive and negative electrodes, respectively. The synthesized two electrode materials showed desirable performances (electrochemical behavior, pseudocapacitive properties, etc.). Furthermore, the established supercapacitor achieved admirable energy density with great capacity retention. [13] In addition, the layer 2D material has a considerable value of specific surface area and can be feasible for surface modification as catalysts. [14] The mainstream methodology to synthesize 2D thin nanosheets would be the exfoliation from the layered bulk form. [2] Due to the relatively weak van der Waals interlayer interaction of the materials, sometimes the exfoliation can be achieved via mechanical methods directly. [15] However, not all 2D materials can be easily exfoliated by the mechanical approach. The most prevalent and feasible way is the liquid exfoliation, where the layered bulk is immersed in suitable solutions. [16] In this case, chemical reactions intentionally introduce to facilitate the exfoliation process, such as oxidation reaction, intercalation, etc. Additional tools, including ultrasonic wave and electrochemical reaction, are also proposed to enhance liquid exfoliation. [2] Electrical explosion, characterized by ultrafast atomization and quenching rate (dT/dt ≈ 10 10 -10 12 K s -1 ) of the sample, is a unique approach for "onestep" synthesis of nanomaterials. Experiments are carried out with layered graphite and Bi 2 Se 3 under the action of electrical explosion in a confined reaction tube. High-speed photography and electrophysical diagnostics are applied to characterize dynamic processes. SEM and EDS are used to characterize surface micro-morphology of reaction products. The layered materials are first exfoliated to thin nanosheets/nanocrystals by shock waves and turbulent flow of the explosion. As the ionized explosion products (>10 000 K) contacts the sample, intense heat transfer happens, simultaneously atomizing the sample and quenching the plasmas. As a result, nanoparti...
The physical image of the confined electrical explosion in the source region is depicted. Metallic plasma/vapor dynamics and its fragmentation effect (on the confining structure) under μs-timescale are diagnosed via high-speed photography, electrophysical, and spectral measurements. When adding a 1-mm-thick Teflon tube outside the exploding wire, the growth of spatial heterogeneity by electro-thermal instability (ETI) is largely compressed and the deposited energy almost doubled from about 85 to 150 J. During the short period after breakdown, considerable energy depositing into the confined space, e.g., 100 J for 0.1 cm3, drives the fast inflation and burst of the 0.5 g confining tube to ~500 m/s (kinetic energy of ~62.5 J). Intense plasma jets eruption with supersonic speed >1.5 km/s and induced shock waves of 2-3 km/s are observed from cracks of the inflated tube. Besides, the erupted plasma jets gradually evolve Rayleigh-Taylor instability (RTI) and finally cause turbulent mixing with the ambient medium. This mechanism is very likely to explain the plasma cavity evolution in underwater explosion. Interestingly, although the confining effect of water is stronger than a Teflon tube, the latter has a better response to the high-rate impulse loading and absorbs more deposited energy by deformation, phase transition, and acceleration.
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