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We report the complex dielectric function ε = ε 1 + iε 2 of MoS 2 /WS 2 and WS 2 /MoS 2 heterostructures and their constituent monolayers MoS 2 and WS 2 for an energy range from 1.5 to 6.0 eV and temperatures from 39 to 300 K. Comparisons between the optical properties of the heterostructures and their monolayers were conducted. Critical-point (CP) energies of the heterostructures were traced back to their origins in the monolayers. Low-temperature measurements confirmed the existence of only three excitonic CPs from 1.5 to 2.5 eV due to the overlap of trion B - of the MoS 2 monolayer and exciton A 0 of the WS 2 monolayer. Due to the dielectric screening effect, most CPs exhibit red shifts in the heterostructures compared to their monolayer counterparts.

A simple design of a broadband multifunctional polarization converter using an anisotropic metasurface for X-band application is proposed. The proposed polarization converter consists of a periodic array of the two-corner-cut square patch resonators based on the FR-4 substrate that achieves both cross-polarization and linear-to-circular polarization conversions. The simulated results show that the polarization converter displays the linear cross-polarization conversion in the frequency range from 8 to 12 GHz with the polarization conversion efficiency above 90%. The efficiency is kept higher than 80% with wide incident angle up to 45°. Moreover, the proposed design achieves the linear-to-circular polarization conversion at two frequency bands of 7.42-7.6 GHz and 13-13.56 GHz. A prototype of the proposed polarization converter is fabricated and measured, showing a good agreement between the measured and simulated results. The proposed polarization converter exhibits excellent performances such as simple structure, multifunctional property, and large cost-efficient bandwidth and wide incident angle insensitivity in the linear cross polarization conversion, which can be useful for X-band applications. Furthermore, this structure can be extended to design broadband polarization converters in other frequency bands.

We present a numerical study of thermo-tunable broadband-negative-permeability metamaterial based on second-order hybridization operating at the THz regime. The conventional metal is replaced by InSb, in which the temperature-dependent conductivity plays a key role in tuning the separation of second-order-hybridization magnetic-resonance modes. It is demonstrated that the hybridization in a simple disk-pair dimer can be tuned by temperature, leading to a significant broadening of the negative-permeability at THz frequencies. By increasing the temperature of the InSb patterns in the structure from 300 to 450 K, the fractional bandwidth (FBW) of the negative permeability curve varies from 4.4% to 12.9%. The thermally-increased carrier-density of InSb reduces the kinetic inductance, the main mechanism of the enhanced magnetic-resonance and the stronger activated-hybridization. Moreover, optimization for the bandwidth of negative permeability is also carried out by changing the geometrical parameters to have a FBW of 20.9%. The equivalent LC-circuit model and standard retrieval method are performed to elaborate our proposed idea. Our results would pave the way for the implementations of diversified semiconductors in tunable broadband-negative-permeability and broadband-negative-refractive-index metamaterials at THz frequencies., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this paper, a broadband metamaterial microwave absorber is designed, simulated and measured. Differently from the traditional method which is only based on unit cell boundary conditions, we carried out full-wave finite integration simulations using full-sized configurations. Starting from an elementary unit cell structure, four kinds of coding metamaterial blocks, 2 × 2, 3 × 3, 4 × 4 and 6 × 6 blocks were optimized and then used as building blocks (meta-block) for the construction of numerous 12 × 12 topologies with a realistic size scale. We found the broadband absorption response in the frequency range 16 GHz to 33 GHz, in good agreement with the equivalent medium theory prediction and experimental observation. Considering various applications of metamaterials or metamaterial absorbers in the electromagnetic wave processing, including the radars or satellite communications, requires the frequency in the range up to 40 GHz. Our study could be useful to guide experimental work. Furthermore, compared to the straightforward approach that represents the metamaterials configurations as 12 × 12 matrices of random binary bits (0 and 1), our new approach achieves significant gains in the broadband absorption. Our method also may be applied to the full-sized structures with arbitrary dimensions, and thus provide a useful tool in the design of metamaterials with specific desired frequency ranges.