Emerging half metal electrides in manganese oxyarsenide hydrides LaMnAsO1-xHx.

In the paper, we report that the hydrides LaMnAsO1-xHxcan serve as a switchable half-metal electride which combines the dual properties of half metals and electrides. Using density functional theory calculations, it is found that this hydride compounds exhibit a novel magnetic structure in which magnetic electrides arising from the excess electrons induced by the H dopants coexist with local-moment antiferromagnetism of the Mn spin lattice. While the reported sizable negative magnetoresistance and ferromagnetism are merely contributed by the spin polarization of excess electrons, this material mimics the behavior of a switchable half-metal electride because the completely spin polarization of excess electrons is easily achieved by controlling the concentration of conductive electrons or H dopants. These effects look very promising for continuing the rapid pace of spintronics application.

Hierarchical and Porous Structures of Carbon Nanotubes-Anchored MOF Derivatives Bridged by Carbon Nanocoils as Lightweight and Broadband Microwave Absorbers.

High-performance microwave absorption (MA) materials have attracted more and more attention because they can effectively prevent microwave radiation and interference from electronic devices. Herein, a new type of MA composite is constructed by introducing carbon nanotubes (CNTs)-anchored metal-organic framework derivatives (MOFDs) into a conductive carbon nanocoil (CNC) network, denoted as CNC/CNT-MOFD. The CNC/MOFD shows a wide effective absorption band of 6.7 GHz under a filling ratio of only 9% in wax-matrix. This is attributed to the hierarchical and porous structures of MOFD bridged by the uniformly dispersed conductive CNC network and the cross-polarization induced by the 3D spiral CNCs. Besides, the as-grown 1D CNTs improve space utilization, porosity, and polarization loss of the composites, resulting in the increase of imaginary permittivity, which further realizes impedance matching and energy attenuation. The Ni nanoparticles in layers of MOFD and at the tips of CNTs generate magnetic loss, promoting the low-frequency absorption ability. Resultantly, RCS values of the optimized composite in all tested theta (θ) ranges are less than -25 dB m2 at 9.5 GHz, effectively reducing the probability of the target detected by the radar.

Surface modification of helical carbon nanocoil (CNC) with N-doped and Co-anchored carbon layer for efficient microwave absorption.

Surface modification and composition control for nanomaterials are effective strategies for designing high-performance microwave absorbing materials (MWAMs). Herein, we have successfully fabricated Co-anchored and N-doped carbon layers on the surfaces of helical carbon nanocoils (CNCs) by wet chemical and pyrolysis methods, denoted as Co@N-Carbon/CNCs. It is found that pure CNCs show a very good microwave absorption performance under a filling ratio of only 6%, which is attributed to the uniformly dispersed conductive network and the cross polarization induced by the unique chiral and spiral morphology. The coating of N-doped carbon layers on CNCs further enriches polarization losses and the uniform anchoring of Co nanoparticles in these layers generates magnetic losses, which enhance the absorption ability and improve the low frequency performance. As compared with the pure CNCs-filling samples, the optimized Co@N-Carbon/CNCs-2.4 enhances the absorption capacity in the lower frequency range under the same thickness, and realizes the decreased thickness from 3.2 to 2.8 mm in the same X band, as well as the decreased thickness from 2.2 to 1.9 mm in the Ku band. Resultantly, a specific effective absorption wave value of 22 GHz g-1 mm-1 has been achieved, which enlightens the synthesis of ultrathin and light high-performance MWAMs.

Structural Engineering of Hierarchical Aerogels Comprised of Multi-dimensional Gradient Carbon Nanoarchitectures for Highly Efficient Microwave Absorption.

Recently, multilevel structural carbon aerogels are deemed as attractive candidates for microwave absorbing materials. Nevertheless, excessive stack and agglomeration for low-dimension carbon nanomaterials inducing impedance mismatch are significant challenges. Herein, the delicate "3D helix-2D sheet-1D fiber-0D dot" hierarchical aerogels have been successfully synthesized, for the first time, by sequential processes of hydrothermal self-assembly and in-situ chemical vapor deposition method. Particularly, the graphene sheets are uniformly intercalated by 3D helical carbon nanocoils, which give a feasible solution to the mentioned problem and endows the as-obtained aerogel with abundant porous structures and better dielectric properties. Moreover, by adjusting the content of 0D core-shell structured particles and the parameters for growth of the 1D carbon nanofibers, tunable electromagnetic properties and excellent impedance matching are achieved, which plays a vital role in the microwave absorption performance. As expected, the optimized aerogels harvest excellent performance, including broad effective bandwidth and strong reflection loss at low filling ratio and thin thickness. This work gives valuable guidance and inspiration for the design of hierarchical materials comprised of dimensional gradient structures, which holds great application potential for electromagnetic wave attenuation.

Highly Flexible, Stretchable, and Self-Powered Strain-Temperature Dual Sensor Based on Free-Standing PEDOT:PSS/Carbon Nanocoils-Poly(vinyl) Alcohol Films.

The wearable and self-powered sensors with multiple functions are urgently needed for energy saving devices, economical convenience, and artificial human skins. It is a meaningful idea to convert excess heat sources into power supplies for wearable sensors. In this report, we have fabricated a series of free-standing self-powered temperature-strain dual sensors based on poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS)/carbon nanocoils (CNCs)-poly(vinyl) alcohol composite films by a simple drop casting method. The Seebeck coefficients of the composite films were measured to be 19 µV/K. The sensor, with the addition of CNCs, showed a superior sensing performance to that without CNCs. PEDOT:PSS is used to provide a thermoelectric power to detect temperature changes and strain deformations. The minimum detect limit for the temperature difference was 0.3 K. Under a constant temperature gradient of 30 K, strains from 1 to 10% were detected without any external power supply. The films can be easily made into an array to detect the temperature of the fingers and motions of the wrist by attaching it to the human wrist directly. For the first time, due to the independent action of the thermoelectric material and strain sensing material, the thermoelectric voltage which is generated by a constant temperature difference is maintained under different strains. This kind of free-standing self-powered multifunctional sensors has great application prospects in the fields of healthcare and artificial intelligence in the future.