Perfect Light Absorbers Made of Tungsten-Ceramic Membranes

Abstract

Plasmonic materials are expanding their concept; in addition to noble metals that are good conductors even at optical frequencies and support surface plasmon polaritons at the interface, other metals and refractory materials are now being used as plasmonic materials. In terms of complex permittivity at optical frequencies, these new plasmonic materials are, though not ideal, quite good to support surface plasmons. Numerical investigations of the optical properties have been revealing new capabilities of the plasmonic materials. On the basis of the precise computations for electromagnetic waves in artificially designed nanostructures, in this article, we address membrane structures made of tungsten and silicon nitride that are a typical metal and ceramic, respectively, with high-temperature melting points. The membranes are applicable to low-power-consuming thermal emitters operating at and near the visible range. We numerically substantiate that the membranes serve as perfect light absorbers, in spite of the subwavelength thickness, that is, 200-250 nm thickness. Furthermore, we clarify that the underlying physical mechanism for the unconventional perfect absorption is ascribed to robust impedance matching at the interface between air and the membranes.

High-Sensitivity High-Throughput Detection of Nucleic Acid Targets on Metasurface Fluorescence Biosensors

“…Originally, metasurfaces have diverse potential and have exhibited various applications, stemming from their designs with large degree of freedom [ 14 , 15 , 16 ]. Most of metasurfaces intended to manipulate light waves for particular purposes such as focusing [ 17 , 18 , 19 , 20 , 21 , 22 , 23 ], polarization/phase control [ 24 , 25 , 26 , 27 , 28 , 29 ], perfect light absorption [ 30 , 31 , 32 , 33 , 34 , 35 ], and so on. The application of metasurfaces for FL enhancement has been tried in numerous studies; only a very small portion of the studies exceptionally reported prominent success in the very large FL-intensity enhancement more than 1000-fold to reference non-enhancing substrates [ 10 , 11 , 36 , 37 , 38 , 39 , 40 , 41 ].…”

Non-Empirical Large-Scale Search for Optical Metasurfaces

“…Designs for metasurfaces have been mostly human knowledge based and optimizations from building blocks known previously. For example, metalenses [ 1 , 2 , 3 , 4 , 5 , 6 ], holograms [ 7 , 8 , 9 ], light absorbers [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ], metagratings [ 17 , 18 , 19 ], luminescence-enhancing metasurfaces [ 20 , 21 , 22 , 23 , 24 , 25 , 26 ], and so on, were fabricated in such ways. The designs for metasurfaces with a particular function are generally elaborate and limited to the domain conceivable from human knowledge, though they are sometimes assisted by optimization algorithms.…”

Tungsten-based Ultrathin Absorber for Visible Regime

“…Broadband PLAs are also established with a topology of metal-dielectric-metal layers. Broadband Structures previously demonstrated had different variations of simpler structures such as nanopillars made up of different variations of cylinders 20 , disks (cylinders) 21 , 22 , arrangement of crosses and cylinders 23 , nanopyramids (cones) 24 – 26 , rods (in shape of square) 27 , spheres, tetrahedral structure 28 , and even random deposition of particles 29 . A simple structure of square and in the end cross is used as a design in this research.…”

“…Previous structures involving tungsten were made up in the shape of cones 25 , 26 , but the designs presented in this paper are 2D, as they are not varying in z-direction (height). The design presented in 22 is also 2D but it is not designed for visible regime and it gives less absorbance. Since tungsten does not support surface plasmons in optical range, high absorbance is ascribed to impedance matching of tungsten absorber with the free space.…”