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Polymer composites receive attentions for protecting from electromagnetic (EM) pollution. However, their EM wave (EMW) attenuation mechanism primarily results from reflection rather than absorption. Herein, we prepared poly(vinylidene fluoride)/cobalt (Co)/MXene composite foams that exhibited applicable impedance matching, enhanced EMW absorption and high-performance thermal conduction properties. With CO2-assisted foaming, a uniform foam structure was integrated into the polymer composites, and meanwhile, the introduced MXenes were partially oxidized and transformed into TiO2 and amorphous carbon. The formed TiO2 not only provided extra heterogeneous interfaces and capacitor-like structures in favor of dielectric polarization but also reduced the excessive electrical conductivity of the pristine MXenes to favor impedance matching. Accordingly, the EMW absorbing performance of the composite foam was enhanced with a minimum reflection loss of −45.6 dB at 4 mm when the filler content was only 12 wt% (6 wt% MXene and 6 wt% Co). Additionally, the synergism between the foam structure and TiO2 nanocrystals resulted in improved thermal conductivity, ranging from 1.28 W/(m·K) to 1.36 W/(m·K), which were 2–6 times higher than that in the solid composite films. This study provided new insights into the simultaneously enhanced EMW absorption and dissipating heat ability in polymer composite foams with a low percolation threshold.

In addition to the demand of thin, lightweight, broadband and high-efficient characteristics, exploring microwave absorbents with superior resistance to oxidation and corrosion is urgently need for practical applications. Herein, carbon nanofibers embedded by α-Fe2O3, Fe or Fe3C nanocrystals are prepared through electrospinning technique followed by carbonization in different atmospheres. The one-dimensional structures can intertwine into three-dimensional conductive network, which is favored for energy dissipation. The Fe3C/N-doped carbon nanofibers show boosting microwave absorption properties compared to the bare carbon, α-Fe2O3/C and Fe/C nanofibers. The Fe3C/N-doped carbon nanofibers show an optimal reflection loss of −57.9 dB at 5.8 GHz with a thickness of 4.1 mm. Meanwhile, a reflection loss of −54.5 dB can be achieved at 17.8 GHz, when the absorber thickness is only 1.5 mm. The superior microwave absorption properties are attributed to the dipole polarization, interfacial polarization and ferromagnetic resonance, induced by the synergistic effect of Fe3C nanocrystals and carbon nanofibers. Moreover, acid-soaking and air-annealing treatments reveal that the Fe3C/N-doped carbon nanofibers show remarkable corrosion and oxidation resistance. This work suggests that encapsulating magnetic nanocrystals in dielectric carbon-based materials is an efficient strategy to construct high-efficient lightweight microwave absorbents with oxidation/corrosion resistance.

The impedance matching is a very important part to influence materials’ microwave absorption performance. However, a way to further discuss the impedance matching is still weak. We build a novel dielectric–magnetic impedance matching (DMIM) model to analyze the real part and imaginary part of materials’ impedance matching. To verify the practicality of the DMIM model, using MIL-100(Fe) as precursor, a series of FexNi1−x@C are synthesized via one-step pyrolysis by controlling the samples’ Fe–Ni ratio, changing their dielectric loss tangent and magnetic loss tangent and successfully regulating their impedance matching to optimize microwave absorption properties. In addition, the minimum reflection loss for MOF-derived Fe0.8Ni0.2@C can arrive at -71.3 dB at 10.3 GHz with a thickness of 3.1 mm, and the effective absorption bandwidth is 5.3 GHz. And combining with the RLGC equivalent circuit model to further indicate the FexNi1−x@C’s energy loss mechanism. The method of using DMIM model and RLGC model to discuss materials’ impedance matching and energy loss mechanism paves a new way to fabricate high-performance microwave materials with balanced electromagnetic distribution and further reveal the materials' microwave absorbing mechanism.

Ultrathin freestanding membranes with a pronounced metal–insulator transition (MIT) have huge potential for future flexible electronic applications as well as provide a unique aspect for the study of lattice–electron interplay. However, the reduction of the thickness to an ultrathin region (a few nm) is typically detrimental to the MIT in epitaxial films, and even catastrophic for their freestanding form. Here, we report an enhanced MIT in VO2-based freestanding membranes, with a lateral size up to millimeters and the VO2 thickness down to 5 nm. The VO2 membranes were detached by dissolving a Sr3Al2O6 sacrificial layer between the VO2 thin film and the c-Al2O3(0001) substrate, allowing the transfer onto arbitrary surfaces. Furthermore, the MIT in the VO2 membrane was greatly enhanced by inserting an intermediate Al2O3 buffer layer. In comparison with the best available ultrathin VO2 membranes, the enhancement of MIT is over 400% at a 5 nm VO2 thickness and more than 1 order of magnitude for VO2 above 10 nm. Our study widens the spectrum of functionality in ultrathin and large-scale membranes and enables the potential integration of MIT into flexible electronics and photonics. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version

A novel Sodium Carbonate (Na2CO3) promoted ultrasonic exfoliation (NPUE) method was proposed for the high efficiency preparation of high-quality two-dimensional (2D) Gallium Selenide (GaSe) nanosheets in isopropanol (IPA). It is found that Na2CO3 acting as an accelerant could enhance the exfoliation efficiency up to 40 times and increase the concentration for the dispersion of GaSe, which could quickly reach 1.2 mg mL−1 when the initial amount of GaSe and Na2CO3 is 30:30. A series of characterization show that bulk GaSe has been successfully exfoliated into single- to few-layer GaSe nanosheets.

High-quality neodymium oxychlorides nanocrystals with cubic shape were synthesized by a nonhydrolytic thermolysis route. The morphology and crystal structure of the neodymium oxychlorides nanocubes were characterized by transmission electron microscopy at the nanoscale. Transmission electron microscope (TEM) image shows that the neodymium oxychlorides nanocrystals are nearly monodispersed with cube-like shape. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns of numerous neodymium oxychlorides nanocubes suggest a pure crystal phase with tetragonal PbFCl matlockite structure. HRTEM image of individual neodymium oxychlorides nanocubes indicate that each nanocubes have a single-crystalline nature with high quality. Unlike the anti-ferromagnetism of the bulk, the neodymium oxychlorides nanocubes show clearly anomalous ferromagnetic characteristic at room temperature. This finding provides a new platform for the exploration of diluted magnetic semiconductors, rare earth-based nanomaterials and so on.