The advent of negative index materials has spawned extensive research into metamaterials over the past decade. Metamaterials are attractive not only for their exotic electromagnetic properties, but also their promise for applications. A particular branch–the metamaterial perfect absorber (MPA)–has garnered interest due to the fact that it can achieve unity absorptivity of electromagnetic waves. Since its first experimental demonstration in 2008, the MPA has progressed significantly with designs shown across the electromagnetic spectrum, from microwave to optical. In this Progress Report we give an overview of the field and discuss a selection of examples and related applications. The ability of the MPA to exhibit extreme performance flexibility will be discussed and the theory underlying their operation and limitations will be established. Insight is given into what we can expect from this rapidly expanding field and future challenges will be addressed.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201200674

Metamaterial Electromagnetic Wave Absorbers

All-inorganic perovskites have high carrier mobility, long carrier diffusion length, excellent visible light absorption, and well overlapping with localized surface plasmon resonance (LSPR) of noble metal nanocrystals (NCs). The high-performance photodetectors can be constructed by means of the intrinsic outstanding photoelectric properties, especially plasma coupling. Here, for the first time, inorganic perovskite photodetectors are demonstrated with synergetic effect of preferred-orientation film and plasmonic with both high performance and solution process virtues, evidenced by 238% plasmonic enhancement factor and 106 on/off ratio. The CsPbBr3 and Au NC inks are assembled into high-quality films by centrifugal-casting and spin-coating, respectively, which lead to the low cost and solution-processed photodetectors. The remarkable near-field enhancement effect induced by the coupling between Au LSPR and CsPbBr3 photogenerated carriers is revealed by finite-difference time-domain simulations. The photodetector exhibits a light on/off ratio of more than 106 under 532 nm laser illumination of 4.65 mW cm−2. The photocurrent increases from 0.67 to 2.77 μA with centrifugal-casting. Moreover, the photocurrent rises from 245.6 to 831.1 μA with Au NCs plasma enhancement, leading to an enhancement factor of 238%, which is the most optimal report among the LSPR-enhanced photodetectors, to the best of our knowledge. The results of this study suggest that all-inorganic perovskites are promising semiconductors for high-performance solution-processed photodetectors, which can be further enhanced by Au plasmonic effect, and hence have huge potentials in optical communication, safety monitoring, and biological sensing.

Improving All‐Inorganic Perovskite Photodetectors by Preferred Orientation and Plasmonic Effect

In this paper, we report a successful realization and integration of a gold two-dimensional hole array (2DHA) structure with semiconductor InAs quantum dot (QD). We show experimentally that a properly designed 2DHA-QD photodetector can facilitate a strong plasmonic-QD interaction, leading to a 130% absolute enhancement of infrared photoresponse at the plasmonic resonance. Our study indicates two key mechanisms for the performance improvement. One is an optimized 2DHA design that permits an efficient coupling of light from the far-field to a localized plasmonic mode. The other is the close spatial matching of the QD layers to the wave function extent of the plasmonic mode. Furthermore, the processing of our 2DHA is amenable to large scale fabrication and, more importantly, does not degrade the noise current characteristics of the photodetector. We believe that this demonstration would bring the performance of QD-based infrared detectors to a level suitable for emerging surveillance and medical diagnostic applications.

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A Surface Plasmon Enhanced Infrared Photodetector Based on InAs Quantum Dots

Thermophotovoltaic emitters based on a two-dimensional grating/thin-film nanostructure

We propose a dual-band metamaterial perfect absorber with a metal–insulator–metal structure (MIM) for use in infrared (IR) stealth technology. We designed the MIM structure to have surface plasmon polariton (SPP) and magnetic polariton (MP) resonance peaks at 1.54 μm and 6.2 μm, respectively. One peak suppresses the scattering signals used by laser-guided missiles, and the other matches the atmospheric absorption band, thereby enabling the suppression of long-wavelength IR (LWIR) and mid-wavelength IR (MWIR) signals from objects as they propagate through the air. We analysed the spectral properties of the resonance peaks by comparing the wavelength of the MP peak calculated using the finite-difference time-domain method with that obtained by utilizing an inductor–capacitor circuit model. We evaluated the dependence of the performance of the dual-band metamaterial perfect absorber on the incident angle of light at the surface. The proposed absorber was able to reduce the scattering of 1.54 μm IR laser light by more than 90% and suppress the MWIR and LWIR signatures by more than 92%, as well as maintain MWIR and LWIR signal reduction rates greater than 90% across a wide temperature range from room temperature to 500 °C.

Selective dual-band metamaterial perfect absorber for infrared stealth technology.

The blackbody radiation spectrum is fundamental to any thermal emitter. However, by properly designing the emitter structure, a narrow bandwidth and high power infrared source can be achieved. This invention consists of a triple layer structure by sandwiching a dielectric SiO2 layer between two Ag metal films on the Si substrate. The top Ag layer is perforated by periodic holes. When the device was heated, the background thermal radiation was suppressed by the bottom Ag whose emissivity is very low. The thermal radiation generated in the SiO2 layer resonant between two metal films and the Ag∕SiO2 and the Ag/air surface plasmon polaritons are induced and converted to light radiation. Strong resonance at Ag∕SiO2 (1,0) degenerate modes results in the coherent light radiation at the wavelength associated with the dielectric constant of SiO2 and the lattice constant of the perforated hole array. The ratio of the full width at half maximum to the peak wavelength is 0.114. This narrow bandwidth and high power infrared light source can be used to explore the biological response of cells and plants.

High performance midinfrared narrow-band plasmonic thermal emitter

A manufacturing method of polysilicon thin films, which uses the heat absorption layer to provide heat source for the amorphous thin film to carry out crystal grain growth. Furthermore, this invention uses an insulating layer to isolate the heat absorption layer and the amorphous thin film. By using thermally-conductive layers arranged in an orderly manner as a cold source to control the location and the size of the crystal grain of the amorphous thin film, the amorphous thin film can be crystallized into a uniform polysilicon thin film, therefore, enabling a further steadily control on the electric property of the poly-Si thin film.

Manufacturing method of polysilicon thin films

Polysilicon films with regular-sized and large grains were fabricated by employing periodic metal (Cr-Al) pads as the heat sinks and with underlying silicon oxynitride (SiON) as the heat absorption layer. The poly-Si could grow to regular hexagonal grains after excimer laser annealing (ELA). The thin-film transistors (TFTs) fabricated by this method show uniform characteristics that are suitable for large-area applications. The TFT achieves a field-effect mobility of 270 cm2/Vmiddots and an on-off current ratio exceeding 108 . It is found that the TFT with the smaller channel width and length results in a better subthreshold swing because it contains fewer grain boundaries and, thus, fewer defects. After comparing the performance of TFTs using either double-metal Cr-Al or single-metal Al photonic-crystal pads, it is found that the Cr could efficiently impede the diffusion of Al into Si during ELA

Chao-Yu Meng

Papers

High performance midinfrared narrow-band plasmonic thermal emitter

Manufacturing method of polysilicon thin films

The Improvement of Polycrystalline Silicon TFTs Fabricated by Employing Periodic Metal Pads