Plasmonic enhanced ultra-thin solar cell: A combined approach using fractal and nano-antenna structure to maximize absorption

In this study, a combined structure is proposed to develop ultra-thin silicon solar cells. This integrated structure consists of silver fractal-like nano-particles and leaky wave nanoantennas. The nano-cuboid pattern embedded inside anti-reflective coating benefits from different optical modes, such as surface plasmons and cavity modes, which trap more light and amplify the electric field in the upper region of the absorber layer. On the bottom side, the hybrid plasmonic mode in the structure of the optical nanoantenna makes it possible to focus and direct the incoming light on the bottom of the absorber layer and increase the optical pathlengths in the ultra-thin film solar cell. The nanoantenna behavior and three-dimensional finite-difference time-domain analysis show that photon absorptions improve significantly at long wavelength lightwaves through this proposed combined structure. The short circuit current enhancement of the solar cell under 1 sun standard illumination is obtained by a factor of 1.94 and 1.80 for TM and TE polarization of incident light, respectively. Due to the acceptable results for different incident angles and polarizations, ultra-thin thickness, and nano-cuboids synthesis feasibility, our structure has the potential to be applied in the design of miniaturized photovoltaic devices

Controllable terahertz cross-shaped three-dimensional graphene intrinsically chiral metastructure and its biosensing application

Abstract In this research, a three-dimensional (3D) graphene intrinsically chiral metastructure in terahertz (THz) region was proposed and analyzed. The unit cell consists of bi-layer cross-shaped graphene ribbons in which the back layer is rotated compared to the front layer. Parameter retrieval method and Kramers–Kronig relations are used for theoretical analysis and derivation of the right-handed and left-handed electromagnetic effective refractive indices of the proposed structure. Based on our analysis, the proposed meta-structure has a tunable and controllable chiral response due to the tunability of graphene and circular dichroism (CD) was reached to 0.2. In order to evaluate the performance of the THz device in biosensor application, its characteristics in chiral biomolecule (collagen) sensing was analyzed. With an optimum design, our simulations show that the refractive index sensitivity value can be obtained as high as 0.96 THz per refractive index unit (THz/RIU) for the CD spectra. Proposed graphene chiral metastructure is promising enabler for controllable polarization-sensitive devices and systems such as tunable polarization filters, rotators, polarizers, biosensors, phase shifters, operating in the THz region

Concentric Nano Elliptical Apertures Array Tip for Intensity Enhancement in Scanning Near-Field Optical Microscopy for Imaging

The usage of electromagnetic computations to analyze the optical responses of microscopic devices, realizes this path to obtain the reliable results. Hence the main landscape of this scientific paper on the basis of computational assessments is the representation of a different array tip to ameliorate intensity of propagated and transmitted beams in near and far-fields, respectively to achieve the more excellent intensity compared with the used prior designs.  </p

Equivalent conductivity method: straightforward analytical solution for metasurface-based structures

We present an equivalent conductivity method for analyzing metasurface-based structures, which relies on the derivation of equivalent conductivity containing the properties such as the geometry, periodicity, and the surrounding materials. Using this approach, one can calculate the equivalent conductivity for a single metasurface layer and then consider it in further analysis of multilayer structures. Description of this method is made by considering an array of graphene nanodisks as a metasurface. The equivalent conductivity is achieved with the aid of the polarizability of a graphene nanodisk. This method is further applied to design graphene-based mid-infrared absorbers, and the results obtained by the equivalent conductivity method are confirmed by full-wave simulations