Turn a Highly-Reflective Metal Into an Omnidirectional Broadband Absorber by Coating a Purely-Dielectric Thin Layer of Grating

Abstract

Abstract-We show that a metal can be turned into a broadband and omnidirectional absorber by coating a purely-dielectric thin layer of grating. An optimal design for such an absorber is proposed by putting a dielectric slot waveguide grating (SWG) on the metallic substrate. The SWG consists of two germanium nanowires (Ge NWs) separated by a sub-100 nm slot in each period. Average absorption reaches 90% when the incident angle varies between 0 • and 80 • over a broad wavelength range from 300 nm to 1400 nm. Multiple optical mechanisms/effects, namely, diffraction, waveguiding in the high-index Ge NWs and low-index air slot, Fabry-Perot resonances as well as surface plasmon polaritons (SPPs), are identified to govern the absorption characteristics of the present absorber. The designed absorber with such a dielectric grating is easier to fabricate as compared with other absorbers with metallic nanostructures, and has potential applications in, e.g., solar cells and photodetectors.

Approximate Model for Universal Broadband Antireflection Nano-Structure

“…This treatment results in a formation of conical protrusions on a surface. Analogues results are reported in [7,8]. There exist also the antireflection coating made of artificial materials with adjustable properties represented by films with embedded and chaotically distributed nano-particles [9][10][11] which can be obtained, for example, by sol-gel technique.…”

“…In the case δ = 0, the dependence λ max (∆, n m ) should exactly follow the behavior of function λ max (a, n m ) and satisfy Eqs. (7), (8). Thus, according to above statements, we can set…”

“…In order to verify extrapolation abilities of the model, let us consider the antireflection of some abstract medium with high refractive index n m = 4 which did not appear in calculations in derivation of relations (7)- (11). According to formulas (7), (8), the radius of nano-cavities being a = 25nm, the transmission maximum occurs at the wavelength λ app max = 519 nm. Now we can use these parameters for numerical calculation and compare λ app max and λ num max .…”

“…(7), (8), (11) have good accuracy-simplicity ratio and, correspondingly, can be used for determination of nano-layer parameters that are necessary for antireflection of any a priori specified medium.…”

Reduction of PCB PDN Impedance and Radiated Emissions Using a Hybrid Technique With Absorbing Materials and Decoupling Capacitors

“…Absorbing materials have been widely used. Some of the areas include the defense industry, in traditional microwave component designs, and in conventional EMC/EMI test and control environments [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Recently, novel applications of microwave absorbing materials in computer system designs have been investigated [34][35][36][37][38][39][40].…”