High Broadband Absorption Research Articles

Robust Ultrablack Coating for Omnidirectional Broadband Light Absorption

AbstractDeveloping robust ultrahigh light absorption coatings has been a significant challenge, limited by the absorption‐adhesion tradeoff. Herein, a robust carbon‐based coating with omnidirectional broadband high absorption is designed and fabricated using a one‐step spray method. A novel rapidly cross‐linking resin is utilized as the binder to enhance adhesion. Beyond leveraging the intrinsic optical properties of carbon absorbents, the construction of a micro‐nano multi‐scale trapping structure is crucial for achieving high absorption efficiency in the coating. Innovatively, an inorganic matting agent is introduced to further diminish reflection by scattering incident light. The resulting ultrablack coating demonstrates good adhesion and an exceptionally high integral light absorption of 99.34% within the wavelength range of 1500–1800 nm, marking the highest reported value for binder‐incorporated spray coatings to date. This robust coating also exhibits outstanding thermal stability and resistance to vacuum thermal cycling and vibration. Furthermore, the application of the ultrablack coating via spraying is scalable and can be readily adapted to the surfaces or interiors of complex structural components made from diverse materials. The coating shows remarkable potential for solar energy harvesting and target stealth. This study presents a simple and efficient approach for developing robust ultrablack coatings suitable for widespread practical applications.

Accretion of SiO2/doped-Si cuboid for terahertz absorber and impedance matching

This paper presents an ultra-broadband polarization-insensitive terahertz absorber that consists of a doped Si substrate and a triple-layer of doped Si covered with a SiO2 anti-reflective coating. The finite element method is used to investigate the absorption of the absorber. The absorber exhibits high absorption rates of over 95 % between frequencies of 0.9 THz and 9.2 THz, with a center frequency of 5.05 THz and a relative bandwidth ratio of 164 %. Moreover, it exhibits outstanding wide-angle absorption properties, achieving over 90 % absorption at angles of incidence ranging from 0 to 55° and frequencies spanning from 1.1 to 10 THz. Furthermore, the underlying mechanisms behind broadband absorption and high absorption rates are studied by analyzing the electric field distribution and impedance matching theory. Additionally, this absorber showcases excellent fabrication tolerance. Therefore, the proposed terahertz absorber featuring doped silicon triple-layer stacked arrays has significant potential in applications such as sensing, stealth technology, and biomedicine.

Ultrafast active plasmonic switch based on the broadband high absorption of monolayer graphene with high modulation depth

Optical switches based on plasmonic nanostructures are of great interest due to their high speed performance. To improve the broadband switching performance, a plasmonic design based on metal-insulator-metal (MIM) structure and monolayer graphene (as an active layer) is proposed. In this scheme, the light absorption of the monolayer graphene and the optical bandwidth are increased due to magnetic dipole resonance and magnetic coupling effect. The numerical simulation results of the proposed structure reveal that high absorption is achieved at the wavelength of 1.55 ‌μm which is 67% and 93% for the monolayer graphene and the whole structure, respectively. This structure has a high absorption modulation depth which can be reached nearly 100% around the interband transition position in a wide wavelength range from 1 μm to 2.5 ‌‌‌‌‌μm. Also, regarding its short response time of 10 fs, this structure can be used as an ultrafast switch. In addition, the equivalent circuit model of the structure is derived from the transmission line model (TLM) that its results are in a very good agreement with the numerical simulation results.

Multifunctional hybrid plate lattice structure with high energy absorption and excellent sound absorption

Lattice structures are featured by their extraordinary mechanical performances in specific stiffness, specific strength, energy absorption, and sound absorption, etc. The recent trend of multifunctionality in engineering applications has raised new requirements for the integration of their mechanical and acoustic properties. In this paper, a multifunctional hybrid plate lattice structure denoted as SBHP is proposed by hybridizing the traditional body-centered cubic plate (BCCP) and simple cubic plate (SCP) lattice structures, and its acoustic and energy absorption properties are investigated by theoretical modeling, simulation analysis and experimental verification. The effects of hole diameters and plate thicknesses on the sound absorption performance are investigated by impedance matching and system damping state analysis. The results show that the average sound absorption coefficient of SBHP-1 is increased by 24% and 62%, and the normalized half-absorption bandwidth is enlarged by 45% and 89% than those of BCCP and SCP, respectively. Heterogeneous lattice structures constructed by using the synergistic mechanism of strong and weak coupling have a more outstanding broadband sound absorption effect. This work provides an effective approach for the design of multifunctional lightweight structures with excellent broadband sound absorption and high energy absorption.

Absorptive metasurface inaccuracies made of micropore and microslit panels in multiple structures

Microperforated panels in forms of micropores/microslits (MPP/MSP) represent absorptive metasurfaces, which can achieve high absorption with single- or double-layer MSP/MPP absorbers. However, architectural acoustics practice usually requires broadband high absorption. Multiple metastructures in more than two layers become one of possible options. Multiple MPP/MSP metasurfaces arranged in layers inherently complicate the design process. This work applies a model-based Bayesian framework employing a potentially multilayered prediction model. The Bayesian framework involves two-levels of probabilistic inference to design a parsimonious number of layers as the higher level, quantitatively implementing Occam’s razor. Once the number of multilayers is selected, the MPP/MSP parameters are readily available within the Bayesian framework, so that the overall metastructure satisfies the design scheme. This work experimentally validates the designed prediction in comparison with the design scheme. However, manufacture inaccuracies may lead to unacceptable deviations. This work applies causation analysis based on a causal model to reveal causal uncertainties/inaccuracies. Using the causal model for causal inference, the Bayesian multilayer design can be satisfactorily validated. This paper discusses comparative investigations of metasurfaces made of micropores and microslits.

Bolometric IR photoresponse based on a 3D micro-nano integrated CNT architecture.

A new 3D micro-nano integrated M-shaped carbon nanotube (CNT) architecture was designed and fabricated. It is based on vertically aligned carbon nanotube arrays composed of low-density, mainly double-walled CNTs with simple lateral external contacts to the surroundings. Standard optical lithography techniques were used to locally tailor the width of the vertical block structure. The complete sensor system, based on a broadband blackbody absorber region and a high-resistance thermistor region, can be fabricated in a single chemical vapor deposition process step. The thermistor resistance is mainly determined by the high junction resistances of the adjacent aligned CNTs. This configuration also provides low lateral thermal conductivity and a high temperature coefficient of resistance (TCR). These properties are advantageous for new bolometric sensors with high voltage responsivity and broadband absorption from the infrared (IR) to the terahertz spectrum. Preliminary performance evaluations have shown current and voltage responsivities of 2 mA/W and 30 V/W, respectively, in response to IR (980 nm) absorption for a 20 × 20 μm2 device. The device exhibits an exceptionally fast response time of ≈0.15 ms, coupled with a TCR of -0.91 %/K. These attributes underscore its high operating speed and responsivity, respectively. In particular, the device maintains excellent thermal stability and reliable operation at elevated temperatures in excess of 200 °C, extending its potential utility in challenging environmental conditions. This design allows for further device miniaturization using optical lithography techniques. Its unique properties for mass production through large-scale integration techniques make it important for real-time broadband imaging systems.

Enhanced Photocharacteristics by Fermi Level Modulating in Sb2 Te3 /Bi2 Se3 Topological Insulator p-n Junction.

Topological insulators have recently received attention in optoelectronic devices because of their high mobility and broadband absorption resulting from their topological surface states. In particular, theoretical and experimental studies have emerged that can improve the spin generation efficiency in a topological insulator-based p-n junction structure called a TPNJ, drawing attention in optospintronics. Recently, research on implementing the TPNJ structure is conducted; however, studies on the device characteristics of the TPNJ structure are still insufficient. In this study, the TPNJ structure is effectively implemented without intermixing by controlling the annealing temperature, and the photocharacteristics appearing in the TPNJ structure are investigated using a cross-pattern that can compare the characteristics in a single device. Enhanced photo characteristics are observed for the TPNJ structure. An optical pump Terahertz probe and a physical property measurement system are used to confirm the cause of improved photoresponsivity. Consequently, the photocharacteristics are improved owing to the change in the absorption mechanism and surface transport channel caused by the Fermi level shift in the TPNJ structure.

Uncertainties and inaccuracies of micro-perforated and micro-slit panel absorbers in multiple layers

Multilayer micro-perforated/slit panels (MPP/MSP) are used to achieve broadband absorption in Architectural Acoustics. Both micro-perforated and micro-slit panels can achieve a high absorption coefficient, but the frequency bandwidth is usually narrow for single-layer panels. For this reason, the multilayer design is proposed to achieve a broadband high absorption coefficient. This work applies Bayesian inference to the design of multilayered micro-perforated/-slit panels for a given design scheme. A higher level of inference, Bayesian model selection, estimates the parsimonious number of layers needed to achieve the design scheme. The lower level of inference estimates MPP/MSP parameters once the structure of the multilayer design is chosen. Once the exact parameters and the model are given, the theoretical absorption coefficient is compared with the measurement results. The causal inference is further applied to analyze the possible reasons for the deviations between the model and the experimental data. Applying the Bayesian framework and causal inference minimizes the uncertainties and inaccuracies during the manufacture and leads to a satisfactory design.

From Micro-Perforates to Micro-Capillary Absorbers: Analysis of Their Broadband Absorption Performance through Modeling and Experiments

A challenging issue is currently the design of non-fibrous ultra-thin acoustic absorbers that are able to provide broadband performance in demanding environments. The objective of this study is to compare using simulations and measurements the broadband absorption performance of highly porous micro-capillary plates (MCPs) to that of micro-perforated panels (MPPs) under normal incidence while considering unbacked or backed configurations. MCPs are unusual materials used for sound absorption with micron-sized channels and a high perforation ratio. Impedance-based modeling and Kundt tube experiments show that MCPs with suitable channel diameters have a pure constant resistance that outperforms the acoustic efficiency of MPP absorbers. Unbacked MCPs exhibit a controllable amount of high absorption that can exceed 0.8 over more than five octaves starting from 80 Hz, thereby achieving a highly sub-wavelength absorber. MCPs still provide broadband high absorption when backed by a rigid cavity. Their bandwidth-to-thickness ratio increases toward its causal limit when the cavity depth decreases. A parallel MCP resonant absorber partly backed by closed and open cavities is proposed. Such MCP-based absorbers could serve as short anechoic terminations for the characterization of acoustic materials at low frequencies.

Design of a High-Performance Titanium Nitride Metastructure-Based Solar Absorber Using Quantum Computing-Assisted Optimization.

Metastructures of titanium nitride (TiN), a plasmonic refractory material, can potentially achieve high solar absorptance while operating at elevated temperatures, but the design has been driven by expert intuition. Here, we design a high-performance solar absorber based on TiN metastructures using quantum computing-assisted optimization. The optimization scheme includes machine learning, quantum annealing, and optical simulation in an iterative cycle. It designs an optimal structure with solar absorptance > 95% within 40 h, much faster than an exhaustive search. Analysis of electric field distributions demonstrates that combined effects of Fabry-Perot interferences and surface plasmonic resonances contribute to the broadband high absorption efficiency of the optimally designed metastructure. The designed absorber may exhibit great potential for solar energy harvesting applications, and the optimization scheme can be applied to the design of other complex functional materials.

Inverse Design of Broadband Absorption in the Visible with Plasmonic Multilayered Planar Structures

Plasmonic structures based on stacked layers of metal and dielectric materials excel as broadband absorbers because of the nonlinear relationship between the compound materials’ dispersion characteristics and the multilayered structure’s actual performance. In this work, radiation absorption along the plasmonic absorber is studied. Broadband absorptance spectra play an important role in applications such as photovoltaics, detectors, modulators, and emitters. We propose and analyze plasmonic stacked structures that exhibit high broadband absorption. For this purpose, an inverse design approach has been implemented using a conventional genetic algorithm as a global optimizer in conjunction with a pattern search as a local optimizer. The proposed strategy found structures with absorption covering the visible spectrum, maintaining its performance for high incident angles.

Near-perfect wide-band absorbers based onone-dimensional photonic crystal structures in1-20 THz frequencies.

This paper investigates the absorption behavior of one-dimensional (1D) photonic crystal (PhC) structures in the 1-20THz region. The structures are analyzed by the transfer matrix method to achieve accurate results quickly with ordinary simulation facilities. The simulation results indicate a strong dependence of the absorber performance on the thickness and material of the PhC layers, as well as the frequency and angle of incident light. The combination of silica and titanium (Ti) materials as dielectric and metal layers presents a great choice for broadband high-absorption applications so that this structure can absorb, on average, more than 80% of the normal incident radiation in the studied frequency range. Additionally, this absorber has the lowest dependence on incident light with the angle varying from 0° to 80° compared to identical absorbers with silver, aluminum, gold, chromium, nickel, and tungsten metals. The excellent absorption feature of the Ti-based absorber compared to the other absorbers is attributed to the lower permittivity of Ti (in both real and imaginary parts) in comparison with the other metals. In addition to owning simple and fabrication-friendly structures, 1D PhCs can pave the way to achieve various absorption spectra proportional to the needs of photonics, communications, and aerospace applications.

Comparison of random upright pyramids and inverted pyramid photonic crystals in thin crystalline silicon solar cells: An optical and morphological study

The potential of enabling a wide range of applications with lightweight, flexible, thin silicon photovoltaic (PV) devices has led to research interest in various light-trapping technologies for thin silicon absorbers. Herein, using both experiments and photonic modelling, we present a detailed comparison between random pyramid texturing and inverted pyramid photonic crystal patterning in thin silicon vis-à-vis light trapping. In particular, we investigate the potential of uniform single-dimension periodic structures in contrast to conventional multi-dimensional random structures for high broadband absorption efficiency in ultra-thin silicon. We find that inverted pyramid photonic crystals cause a large increase in optical path length especially for long wavelength photons due to strong wave interference producing exceptionally high absorption and so does random pyramids though with slightly lower absorption than that of photonic crystals. On the other hand, the random pyramids, fabricated via a one-step etching process with feature sizes ranging from sub-micron to 4 µm, have higher absorption at short wavelengths due to their multi-dimensional size distribution. Overall, we find that random textured pyramids appropriately fabricated can yield a comparable ideal photocurrent density to that by photonic crystals for 10 µm thick silicon.

Broadband long-wave infrared high-absorption of active materials through hybrid plasmonic resonance modes

Broadband high absorption of long-wavelength infrared light for rough submicron active material films is quite challenging to achieve. Unlike conventional infrared detection units, with over three-layer complex structures, a three-layer metamaterial with mercury cadmium telluride (MCT) film sandwiched between an Au cuboid array and Au mirror is studied through theory and simulations. The results show that propagated/localized surface plasmon resonance simultaneously contribute to broadband absorption under the TM wave of the absorber, while the Fabry–Perot (FP) cavity resonance causes absorption of the TE wave. As surface plasmon resonance concentrates most of the TM wave on the MCT film, 74% of the incident light energy is absorbed by the submicron thickness MCT film within the 8–12 μm waveband, which is approximately 10 times than that of the rough same thickness MCT film. In addition, by replacing the Au mirror with Au grating, the FP cavity along the y-axis direction was destroyed, and the absorber exhibited excellent polarization-sensitive and incident angle-insensitive properties. For the corresponding conceived metamaterial photodetector, as carrier transit time across the gap between Au cuboid is much less than that of other paths, the Au cuboids simultaneously act as microelectrodes to collect photocarriers generated in the gap. Thus the light absorption and photocarrier collection efficiency are hopefully improved simultaneously. Finally, the density of the Au cuboids is increased by adding the same arranged cuboids perpendicular to the original direction on the top surface or by replacing the cuboids with crisscross, which results in broadband polarization-insensitive high absorption by the absorber.

Design and validation of microperforated panel absorbers using Occam's razor and causal inference

Microperforated panel absorbers in forms of micro-poles /-slits (MPP/MSP) can achieve high absorption. However, noise control practice usually requires broadband high absorption. Single- or double-layer MSP/MPP absorbers often cannot meet practical requirements. Multilayers become a natural option. Multiple layers of MSP/MPP absorbers inherently complicates the design process upon a given design scheme. This work applies a Bayesian framework using a potentially multilayered prediction model. The Bayesian design involves two-levels of probabilistic inference to design a parsimonious number of layers using the model-selection solution, a quantitative implementation of Occam's razor, while the parameter estimation is used to estimate MPP/MSP parameters given the selected number of multilayers. This probabilistic design process rapidly hones in on the MPP/MSP parameters of each individual layer so that the overall composite meets the design goal. When experimentally validating the designed prediction upon the design scheme, manufacture inaccuracies may lead to deviations. In analyzing reasons of the deviations, this work further applies causal inference to analyze the cause-effect relationship. To this end a causal model has also been established. Using both parametric prediction model for the absorption performance and the causal model for causal inference of the deviation causes, the Bayesian multilayer design can be satisfactorily validated.

Applications of Fluorescent Carbon Dots as Photocatalysts: A Review

Carbon dots (CDs) have attracted considerable interest from the scientific community due to their exceptional properties, such as high photoluminescence, broadband absorption, low toxicity, water solubility and (photo)chemical stability. As a result, they have been applied in several fields, such as sensing, bioimaging, artificial lighting and catalysis. In particular, CDs may act as sole photocatalysts or as part of photocatalytic nanocomposites. This study aims to provide a comprehensive review on the use of CDs as sole photocatalysts in the areas of hydrogen production via water splitting, photodegradation of organic pollutants and photoreduction and metal removal from wastewaters. Furthermore, key limitations preventing a wider use of CDs as photocatalysts are pointed out. It is our hope that this review will serve as a basis on which researchers may find useful information to develop sustainable methodologies for the synthesis and use of photocatalytic CDs.

Multi-chamber micro-perforated panel absorbers optimised for high amplitude broadband absorption using a two-point impedance method

An optimised, multi-chamber, micro-perforated panel absorber (MC-MPPA) with micro-perforated adjoining panels is presented in this paper. An MPPA is a clean and efficient noise absorber with a simple structure making it an increasingly popular choice over porous material-based solutions. For the basic configuration, the bandwidth is typically limited by the perforation size and the frequency range by the backing cavity depth. In order to improve these parameters, innovative variations of the MPPA have been proposed in the literature, but the development of a solution which delivers both a broadband frequency response at low frequencies, with a shallow cavity has yet to appear. This paper proposes such a technological breakthrough by employing a graph-theory-based method to the MPPA problem. By using the two-point impedance method (TpIM) based on graph theory, a model for multi-chamber MPPAs which are coupled with each other in two dimensions through perforated side panels can be developed, an onerous task for standard equivalent circuit analysis due to the generation of non-planar circuits. The resulting model lends itself to optimisation and thus allows the differing geometric parameters of a tessellated network of chambers to be combined to maximise the sound absorption in a frequency range for a particular depth. An overall absorption coefficient of 0.83 can be achieved experimentally in the frequency range of 660 Hz to 2 kHz with an MC-MPPA of only 22 mm thick. In addition, when the air cavity depth is slightly increased to 50 mm, an overall absorption coefficient of greater than 0.82 can be achieved in the 281 Hz to 1 kHz frequency range. Experimentally, an absorption coefficient of approximately 0.82 is achieved at 340 Hz at an air cavity depth of 50 mm, which is a depth-to-wavelength ratio of 20, making the MC-MPPA a deeply subwavelength absorber. Results have been verified theoretically, numerically and experimentally.

Nonlinear optical properties and broadband ultrafast photonics application of 2D-zirconium tritelluride (ZrTe3)

Two-dimensional (2D) transition metal chalcogenides (TMCs) have lately attracted broad interest in advanced photonics field due to their tunable bandgap, high broadband absorption, and excellent nonlinear optical (NLO) performances. Among other TMCs, group-IV transition metal trichalcogenides (TMTs) are rarely investigated for the NLO applications. Zirconium tritelluride (ZrTe3) is a kind of group-IV TMTs that shows metallic behavior among TMTs materials. While several electrical properties of ZrTe3 have been studied recently, the research community is longing to explore NLO features of ZrTe3. Herein, by using open aperture Z-scan method, the NLO properties of ZrTe3-nanosheets are investigated. The admirable NLO characteristics of ZrTe3 are realized from the obtained highest nonlinear absorption coefficient value of −82.1 × 103 in 1 µm and −13.05 × 103 cm/GW in 1.5 µm. Moreover, broadband fiber optics ZrTe3-based saturable absorbers (SAs) are prepared for the first time by depositing 2D-ZrTe3 nanosheets on a side-polished fiber. Following integration of these ZrTe3-SAs into three distinct rare earth-doped fiber laser cavities, stable mode-locking pulses with pulse widths of 323 ps (1 µm), 751 fs (1.5 µm), and 1.2 ps (2 µm) are obtained, respectively. These findings indicate that the ZrTe3 can facilitate the exploration of 2D materials in nonlinear optics and ultrafast photonics applications.

High broadband light absorption in ultrathin MoS2 homojunction solar cells.

Transition metal dichalcogenides (TMDCs) have been proposed as light absorber materials for ultrathin solar cells. These materials are characterized by their strong light-matter interaction and the possibility to be assembled into devices at room temperature. Here, we model the optical absorptance of an ultrathin MoS2 absorber embedded in different designs of a 1D optical cavity. We find that up to 87% of the photons contained in the 300-700 nm range of the AM1.5G spectrum can be absorbed employing MoS2 absorbers as thin as 10 nm sandwiched between a h-BN top layer and an optically thick Ag reflector. An h-BN/MoS2/h-BN/Ag cavity produces 0.89 average absorptance for a 57-nm-thick MoS2 slab and it also maximizes the absorption of extremely thin absorbers, between 1 and 9 nm. We also model a possible large-scale device on a glass substrate combined with indium-tin oxide (ITO) whose absorptance is comparable to the other presented structures. The high broadband absorption in these light-trapping structures is caused by the amplification of the zeroth Fabry-Perot interference mode. This study demonstrates that light absorption in ultrathin solar cells based on nanometric TMDC absorbers can compete with conventional photovoltaic technology and provides different simple optical designs to choose from depending on the electronic characteristics of the TMDC junction.

Design of broadband high efficiency absorption antenna based on metamaterial nano-ring array

Compared with the traditional solar cells, the nano-optical antenna breaks through the band-gap limitation of semiconductor materials, and provides a new scheme for solar energy collection. In order to solve the problems of complex structure, low efficiency and narrow bandwidth of nano-optical antenna, a novel nano-ring-cylinder based on metamaterials is proposed in this paper. The antenna has an average absorption efficiency of 96.93% in the wide-band absorption range of visible and near-infrared light. First of all, the basic design theory of the antenna was given based on the surface plasma theory. Then, the antenna structure design scheme was determined, the overall structure consists of two layers of metal and an insulating layer formed by Al2O3. Finally, on the basis of the established antenna model, the absorption characteristics were analyzed by simulation. The analysis result shows that the super-absorption ability of the antenna is independent of the polarization of the incident light, and the average absorption ability can be maintained at about 91% when the incident angle is ±60°. The absorption capability of the antenna is mainly due to the synergistic effect of Fabry-Perot resonance and localized surface plasmon resonance enhancement. The conclusion can provide a theoretical guidance for the structural design of nano-optical antenna.