In this paper, an incident angle- and polarization-insensitive metamaterial absorber is proposed for X-band applications. A unit cell of the proposed absorber has a square patch at the centre and four circular sectors are rotated around the square patch. The vertically and horizontally symmetric structure of the unit cell enables polarization-insensitivity. The circular sector of the unit cell enables an angle-insensitivity. The performances of the proposed absorber are demonstrated with a full-wave simulation and measurements. The angular sensitivity is studied at different inner angles of the circular sector. When the inner angle of the circular sector is 90°, the simulated absorptivity is higher than 90%, and the frequency variation is less than 0.96% for incident angles up to 70°. The measured absorptivity at 10.44 GHz is close to 100% for all the polarization angles under normal incidence. When the incident angles are varied from 0°– 60°, the measured absorptivity is maintained above 90% for both the transverse electric (TE) and the transverse magnetic (TM) modes.

In this paper, a novel flexible tunable metasurface absorber is proposed for large-scale remote ethanol sensor applications. The proposed metasurface absorber consists of periodic split-ring-cross resonators (SRCRs) and microfluidic channels. The SRCR patterns are inkjet-printed on paper using silver nanoparticle inks. The microfluidic channels are laser-etched on polydimethylsiloxane (PDMS) material. The proposed absorber can detect changes in the effective permittivity for different liquids. Therefore, the absorber can be used for a remote chemical sensor by detecting changes in the resonant frequencies. The performance of the proposed absorber is demonstrated with full-wave simulation and measurement results. The experimental results show the resonant frequency increases from 8.9 GHz to 10.04 GHz when the concentration of ethanol is changed from 0% to 100%. In addition, the proposed absorber shows linear frequency shift from 20% to 80% of the different concentrations of ethanol.

A three-dimensional (3D) bimodal-porous silver nanowire (AgNW) nanostructure with superior electrical properties is fabricated by freeze drying of AgNW aqueous dispersion with macrosized ice spheres for bimodal-porous structure. The ice sphere dispersed AgNW solution yields a 3D AgNW network at the surface of ice sphere and formation of macropores by removal of ice sphere during freeze-drying process. The resulting nanostructures exhibit excellent electrical properties due to their low electrical percolation threshold by the formation of macropores, which results in an efficient and dense 3D AgNW network with a small amount of AgNWs. The highly conductive and stretchable AgNW/poly(dimethylsiloxane) (PDMS) nanocomposites are made by impregnating the 3D porous conductive network with highly stretchable poly(dimethylsiloxane) (PDMS) matrix. The AgNW/PDMS nanocomposites exhibit a high conductivity of 42 S/cm with addition of relatively small amount of 2 wt %. The high conductivity is retained when stretched up to 120% elongation even after 100 stretching-releasing cycles. Due to high electrical conductivity and superior stretchability of AgNW/PDMS nanocomposites, these are expected to be used in stretchable electronic devices.

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A frequency-tunable metamaterial absorber is designed with the unit cell consisting of a varactor-loaded fishnet-like resonator. This geometry allows all cathode and anode pads of the unit cells to be connected to their counterparts. Hence, only the ends of the periodic structure need to be biased, reducing the complexity of the bias network. The absorber was modeled using a full-wave simulation tool and verified experimentally with a 20×20 unit-cell prototype. Using free-space measurements, the absorber shows >90% absorption ratio from 3.96 to 5.29 GHz with a frequency tuning ratio of 28.7%, when the reverse voltage varied from 0 to 19 V.

Highly dispersive molybdenum disulfide nanoflakes (MoS2 NFs), without any phase transition during the exfoliation process, are desirable for full utilization of their semiconductor properties in practical applications. Here, we demonstrate an innovate approach for fabricating MoS2 NFs by using hydrazine-assisted ball milling via the synergetic effect of chemical intercalation and mechanical exfoliation. The NFs obtained have a lateral size of 600–800 nm, a thickness less than 3 nm, and high crystallinity in the 2H semiconducting phase. They form a stable dispersion in various solvents, which will be helpful for many applications, due to the oxygen functional group. To investigate production of a two-dimensional (2D) photodetector, 2D semiconducting MoS2, MoS2–p-Si vertical devices were fabricated, and their optical properties were characterized. The photodiode exhibited consistent responses with excellent photo-switching characteristics with wavelengths of 850, 530, and 400 nm.

In this paper, we propose an angle- and polarization-insensitive metamaterial absorber. We design a metamaterial unit cell that is based on a split ring cross resonator (SRCR). We observe that the absorption frequency and absorption ratio are insensitive to incident angles when a via array surrounds the SRR. We demonstrate the effect of the via array using full-wave simulations by comparing the absorptivity of the SRCR with and without the via array. Because of the symmetric geometry, we also realize polarization insensitivity. We build the proposed absorber on a printed-circuit-board with 30 × 30 unit cells, and we demonstrate its performance experimentally in free space. Under normal incidence, the fabricated absorber shows 99.6% absorptivity at 11.3 GHz for all polarization angles, while for oblique incidence, the fabricated absorber maintains an absorptivity higher than 90% for incident angles up to 70° and 60° for transverse magnetic (TM) and transverse electric (TE) modes, respectively.

Photocatalytic water splitting is the most environmentally friendly method to generate energy. Despite intense research in this area, rapid charge-carrier recombination and limited light absorption of semiconductor-based photocatalysts remain key challenges. Herein, protonated g-C 3 N 4 /Ti 3 C 2 T x MXene hollow spheres, fabricated by electrostatic layer-by layer assembly and a sacrificial template, were used for effective photocatalytic hydrogen (H 2 ) evolution. The constructed three-dimensional (3D) hollow spheres exhibited enhanced light absorption, a two-dimensional (2D) heterostructure to shorten the electron migration distance, a Schottky junction to facilitate separation and transfer of charge carriers, and high specific surface area for efficient H 2 adsorption. The optimal formulation had an H 2 production rate of 982.8 μmol g −1 h −1 , which is more than 3.5-fold higher than the H 2 production rate of pure protonated g-C 3 N 4 and 1.22-fold higher than the H 2 production rate of protonated g-C 3 N 4 /Ti 3 C 2 T x , which lacks the hollow structure. This unique 3D heterojunction structure made from 2D materials improved photocatalytic H 2 production performance and can be readily extended to other reactions. KEYWORDS: Ti 3 C 2 T x MXene, g-C 3 N 4 , photocatalytic water splitting, hydrogen evolution reaction, 3D architecture